Time-resolved energy transfer from single chloride-terminated nanocrystals to graphene

Energy Technology Data Exchange (ETDEWEB)

Ajayi, O. A., E-mail: oaa2114@columbia.edu, E-mail: cww2104@columbia.edu; Wong, C. W., E-mail: oaa2114@columbia.edu, E-mail: cww2104@columbia.edu [Optical Nanostructures Laboratory, Center for Integrated Science and Engineering, Solid-State Science and Engineering, Columbia University, New York, New York 10027 (United States); Department of Mechanical Engineering, Columbia University, New York, New York 10027 (United States); Anderson, N. C.; Wolcott, A.; Owen, J. S. [Department of Chemistry, Columbia University, New York, New York 10027 (United States); Cotlet, M. [Brookhaven National Laboratory, Upton, New York, New York 11973 (United States); Petrone, N.; Hone, J. [Department of Mechanical Engineering, Columbia University, New York, New York 10027 (United States); Gu, T.; Gesuele, F. [Optical Nanostructures Laboratory, Center for Integrated Science and Engineering, Solid-State Science and Engineering, Columbia University, New York, New York 10027 (United States)

2014-04-28

We examine the time-resolved resonance energy transfer of excitons from single n-butyl amine-bound, chloride-terminated nanocrystals to two-dimensional graphene through time-correlated single photon counting. The radiative biexponential lifetime kinetics and blinking statistics of the individual surface-modified nanocrystal elucidate the non-radiative decay channels. Blinking modification as well as a 4× reduction in spontaneous emission were observed with the short chloride and n-butylamine ligands, probing the energy transfer pathways for the development of graphene-nanocrystal nanophotonic devices.

Uncovering the intrinsic size dependence of hydriding phase transformations in nanocrystals.

Science.gov (United States)

Bardhan, Rizia; Hedges, Lester O; Pint, Cary L; Javey, Ali; Whitelam, Stephen; Urban, Jeffrey J

2013-10-01

A quantitative understanding of nanocrystal phase transformations would enable more efficient energy conversion and catalysis, but has been hindered by difficulties in directly monitoring well-characterized nanoscale systems in reactive environments. We present a new in situ luminescence-based probe enabling direct quantification of nanocrystal phase transformations, applied here to the hydriding transformation of palladium nanocrystals. Our approach reveals the intrinsic kinetics and thermodynamics of nanocrystal phase transformations, eliminating complications of substrate strain, ligand effects and external signal transducers. Clear size-dependent trends emerge in nanocrystals long accepted to be bulk-like in behaviour. Statistical mechanical simulations show these trends to be a consequence of nanoconfinement of a thermally driven, first-order phase transition: near the phase boundary, critical nuclei of the new phase are comparable in size to the nanocrystal itself. Transformation rates are then unavoidably governed by nanocrystal dimensions. Our results provide a general framework for understanding how nanoconfinement fundamentally impacts broad classes of thermally driven solid-state phase transformations relevant to hydrogen storage, catalysis, batteries and fuel cells.

Probing surface states in PbS nanocrystal films using pentacene field effect transistors: controlling carrier concentration and charge transport in pentacene.

Science.gov (United States)

Park, Byoungnam; Whitham, Kevin; Bian, Kaifu; Lim, Yee-Fun; Hanrath, Tobias

2014-12-21

We used a bilayer field effect transistor (FET) consisting of a thin PbS nanocrystals (NCs) film interfaced with vacuum-deposited pentacene to probe trap states in NCs. We interpret the observed threshold voltage shift in context of charge carrier trapping by PbS NCs and relate the magnitude of the threshold voltage shift to the number of trapped carriers. We explored a series of NC surface ligands to modify the interface between PbS NCs and pentacene and demonstrate the impact of interface chemistry on charge carrier density and the FET mobility in a pentacene FET.

Evidence of localized amorphous silicon clustering from Raman depth-probing of silicon nanocrystals in fused silica

International Nuclear Information System (INIS)

Barba, D; Martin, F; Ross, G G

2008-01-01

Silicon nanocrystals (Si-nc) and amorphous silicon (α-Si) produced by silicon implantation in fused silica have been studied by micro-Raman spectroscopy. Information regarding the Raman signature of the α-Si phonon excitation was extracted from Raman depth-probing measurements using the phenomenological phonon confinement model. The spectral deconvolution of the Raman measurements recorded at different laser focusing depths takes into account both the Si-nc size variation and the Si-nc spatial distribution within the sample. The phonon peak associated with α-Si around 470 cm -1 is greatest for in-sample laser focusing, indicating that the formation of amorphous silicon is more important in the region containing a high concentration of silicon excess, where large Si-nc are located. As also observed for Si-nc systems prepared by SiO x layer deposition, this result demonstrates the presence of α-Si in high excess Si implanted Si-nc systems

Synthesis, characterization and spectral temperature-dependence of thioglycerol-CdSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Ben Brahim, Nassim, E-mail: nassim.benbrahim.fsm@gmail.com [Laboratoire des Interfaces et Matériaux Avancés, Faculté des Sciences de Monastir, Boulevard de l’Environnement, 5019 Monastir (Tunisia); Poggi, Mélanie [Laboratoire de Physique de la Matière Condensée, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France); Haj Mohamed, Naim Bel; Ben Chaâbane, Rafik; Haouari, Mohamed [Laboratoire des Interfaces et Matériaux Avancés, Faculté des Sciences de Monastir, Boulevard de l’Environnement, 5019 Monastir (Tunisia); Negrerie, Michel, E-mail: michel.negrerie@polytechnique.fr [Laboratoire d' Optique et Biosciences, INSERM, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau (France); Ben Ouada, Hafedh [Laboratoire des Interfaces et Matériaux Avancés, Faculté des Sciences de Monastir, Boulevard de l’Environnement, 5019 Monastir (Tunisia)

2016-09-15

Water-soluble CdSe quantum dots (QDs) have been synthesized with thioglycerol as a stabilizer through a novel hydrothermal route. The obtained thioglycerol capped CdSe (TG-CdSe) nanocrystals were characterized regarding their morphology and structural, thermal and optical properties. The resulting nanocrystals were synthesized in the cubic structure with a near spherical shape, as confirmed by X-ray diffraction and transmission electron microscopy. Combining transmission electron microscopy imaging and calculations using UV–visible absorption spectrum and X-ray diffraction pattern, the diameter of the synthesized nanocrystals was estimated to 2.26 nm. As confirmed by its Fourier transform IR spectrum, thioglycerol was successfully liganded on the surface of the resulting nanocrystals. Band structure parameters of the TG-CdSe nanoparticles were determined and quantum confinement effect was evidenced by optical absorption, fluorescence and Raman measurements. The thermal properties of the TG-CdSe were explored by thermal gravimetric analysis and differential scanning calorimetry. The temperature dependence of both the absorption and fluorescence spectra in the physiological range makes the TG-CdSe nanocrystals sensitive temperature markers, a property that must be taken into account when developing any probing applications, especially for cellular imaging.

Volumetric flame synthesis of well-defined molybdenum oxide nanocrystals.

Science.gov (United States)

Merchan-Merchan, Wilson; Saveliev, Alexei V; Desai, Milind

2009-11-25

Well-defined faceted inorganic Mo oxide nanocrystals are synthesized in the gas phase using a solid-fed-precursor flame synthesis method. The solid crystals have rectangular cross-section with characteristic size of 10-20 nm and with lengths ranging from 50 nm to a few hundred nanometres. A 1 mm diameter high purity Mo probe introduced in the oxygen-rich part of the flame serves as the material source. A combination of the strong temperature gradient and varying chemical species concentrations within the flame volume provides the ideal conditions for the rapid and direct formation of these unique nanocrystals. Oxidation and evaporation of MoO3 in the oxygen-rich zone are followed by reduction to MoO2 in the lower temperature, more fuel-rich zone. The MoO3 vapours formed are pushed in the direction of the gas flow and transformed into mature well-defined convex polyhedron nanocrystals bounded with six faces resembling rectangular parallelepipeds.

Synthesis and Doping of Silicon Nanocrystals for Versatile Nanocrystal Inks

Science.gov (United States)

Kramer, Nicolaas Johannes

The impact of nanotechnology on our society is getting larger every year. Electronics are becoming smaller and more powerful, the "Internet of Things" is all around us, and data generation is increasing exponentially. None of this would have been possible without the developments in nanotechnology. Crystalline semiconductor nanoparticles (nanocrystals) are one of the latest developments in the field of nanotechnology. This thesis addresses three important challenges for the transition of silicon nanocrystals from the lab bench to the marketplace: A better understanding of the nanocrystal synthesis was obtained, the electronic properties of the nanocrystals were characterized and tuned, and novel silicon nanocrystal inks were formed and applied using simple coating technologies. Plasma synthesis of nanocrystals has numerous advantages over traditional solution-based synthesis methods. While the formation of nanoparticles in low pressure nonthermal plasmas is well known, the heating mechanism leading to their crystallization is poorly understood. A combination of comprehensive plasma characterization with a nanoparticle heating model presented here reveals the underlying plasma physics leading to crystallization. The model predicts that the nanoparticles reach temperatures as high as 900 K in the plasma as a result of heating reactions on the nanoparticle surface. These temperatures are well above the gas temperature and sufficient for complete nanoparticle crystallization. Moving the field of plasma nanoparticle synthesis to atmospheric pressures is important for lowering its cost and making the process attractive for industrial applications. The heating and charging model for silicon nanoparticles was adapted in Chapter 3 to study plasmas maintained over a wide range of pressures (10 -- 105 Pa). The model considers three collisionality regimes and determines the dominant contribution of each regime under various plasma conditions. Strong nanoparticle cooling at

X-ray and photoelectron spectroscopy of the structure, reactivity, and electronic structure of semiconductor nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Hamad, Kimberly Sue [Univ. of California, Berkeley, CA (United States)

2000-01-01

Semiconductor nanocrystals are a system which has been the focus of interest due to their size dependent properties and their possible use in technological applications. Many chemical and physical properties vary systematically with the size of the nanocrystal and thus their study enables the investigation of scaling laws. Due to the increasing surface to volume ratio as size is decreased, the surfaces of nanocrystals are expected to have a large influence on their electronic, thermodynamic, and chemical behavior. In spite of their importance, nanocrystal surfaces are still relatively uncharacterized in terms of their structure, electronic properties, bonding, and reactivity. Investigation of nanocrystal surfaces is currently limited by what techniques to use, and which methods are suitable for nanocrystals is still being determined. This work presents experiments using x-ray and electronic spectroscopies to explore the structure, reactivity, and electronic properties of semiconductor (CdSe, InAs) nanocrystals and how they vary with size. Specifically, x-ray absorption near edge spectroscopy (XANES) in conjunction with multiple scattering simulations affords information about the structural disorder present at the surface of the nanocrystal. X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) probe the electronic structure in terms of hole screening, and also give information about band lineups when the nanocrystal is placed in electric contact with a substrate. XPS of the core levels of the nanocrystal as a function of photo-oxidation time yields kinetic data on the oxidation reaction occurring at the surface of the nanocrystal.

The Role of Shape on Electronic Structure and Charge Transport in Faceted PbSe Nanocrystals

KAUST Repository

Kaushik, Ananth P.

2014-03-25

We have determined the effect of shape on the charge transport characteristics of nanocrystals. Our study looked at the explicit determination of the electronic properties of faceted nanocrystals that essentially probe the limit of current computational reach, i.e., nanocrystals from 1.53 to 2.1 nm in diameter. These nanocrystals, which resemble PbSe systems, are either bare or covered in short ligands. They also differ in shape, octahedral vs cube-octahedral, and in superlattice symmetry (fcc vs bcc). We have provided insights on electron and hole coupling along different facets and overall charge mobility in bcc and fcc superlattices. We have determined that the relative areas of (100) to (111) facets, and facet atom types are important factors governing the optimization of charge transport. The calculated electronic density of states shows no role of -SCH3 - ligands on states near the band gap. Electron coupling between nanocrystals is significantly higher than that of hole coupling; thiol ligands lower the ratio between electron and hole couplings. Stronger coupling exists between smaller nanocrystals. © 2014 American Chemical Society.

Brilliant molecular nanocrystals emerging from sol-gel thin films: towards a new generation of fluorescent biochips

International Nuclear Information System (INIS)

Dubuisson, E; Monnier, V; Sanz-Menez, N; Ibanez, A; Boury, B; Usson, Y; Pansu, R B

2009-01-01

To develop highly sensitive biosensors, we made directly available to biological aqueous solutions organic nanocrystals previously grown in the pores of sol-gel films. Through the controlled dissolution of the sol-gel surface, we obtained emerging nanocrystals that remained strongly anchored to the sol-gel coating for good mechanical stability of the final sensing device. We demonstrated that in the presence of a solution of DNA functionalized with a molecular probe, the nanocrystal fluorescence is strongly quenched by Foerster resonance energy transfer thus opening the way towards very sensitive fluorescent biosensors through biomolecules grafted onto fluorescent nanocrystals. Finally, this controlled dissolution, involving weak concentrated NaOH solution, is a generic process that can be used for the thinning of any kind of sol-gel layer.

Seeded Growth Route to Noble Calcium Carbonate Nanocrystal.

Directory of Open Access Journals (Sweden)

Aminul Islam

Full Text Available A solution-phase route has been considered as the most promising route to synthesize noble nanostructures. A majority of their synthesis approaches of calcium carbonate (CaCO3 are based on either using fungi or the CO2 bubbling methods. Here, we approached the preparation of nano-precipitated calcium carbonate single crystal from salmacis sphaeroides in the presence of zwitterionic or cationic biosurfactants without external source of CO2. The calcium carbonate crystals were rhombohedron structure and regularly shaped with side dimension ranging from 33-41 nm. The high degree of morphological control of CaCO3 nanocrystals suggested that surfactants are capable of strongly interacting with the CaCO3 surface and control the nucleation and growth direction of calcium carbonate nanocrystals. Finally, the mechanism of formation of nanocrystals in light of proposed routes was also discussed.

Large-scale, rapid synthesis and application in surface-enhanced Raman spectroscopy of sub-micrometer polyhedral gold nanocrystals

International Nuclear Information System (INIS)

Guo Shaojun; Wang Yuling; Wang Erkang

2007-01-01

Macromolecule-protected sub-micrometer polyhedral gold nanocrystals have been facilely prepared by heating an aqueous solution containing poly (N-vinyl-2-pyrrolidone) (PVP) and HAuCl 4 without adding other reducing agents. Scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), ultraviolet-visible-near-infrared spectroscopy (UV-vis-NIR), and x-ray diffraction (XRD) were employed to characterize the obtained polyhedral gold nanocrystals. It is found that the 10:1 molar ratio of PVP to gold is a key factor for obtaining quasi-monodisperse polyhedral gold nanocrystals. Furthermore, the application of polyhedral gold nanocrystals in surface-enhanced Raman scattering (SERS) was investigated by using 4-aminothiophenol (4-ATP) as a probe molecule. The results indicated that the sub-micrometer polyhedral gold nanocrystals modified on the ITO substrate exhibited higher SERS activity compared to the traditional gold nanoparticle modified film. The enhancement factor (EF) on polyhedral gold nanocrystals was about six times larger than that obtained on aggregated gold nanoparticles (∼25 nm)

Soluble Supercapacitors: Large and Reversible Charge Storage in Colloidal Iron-Doped ZnO Nanocrystals.

Science.gov (United States)

Brozek, Carl K; Zhou, Dongming; Liu, Hongbin; Li, Xiaosong; Kittilstved, Kevin R; Gamelin, Daniel R

2018-05-09

Colloidal ZnO semiconductor nanocrystals have previously been shown to accumulate multiple delocalized conduction-band electrons under chemical, electrochemical, or photochemical reducing conditions, leading to emergent semimetallic characteristics such as quantum plasmon resonances and raising prospects for application in multielectron redox transformations. Here, we demonstrate a dramatic enhancement in the capacitance of colloidal ZnO nanocrystals through aliovalent Fe 3+ -doping. Very high areal and volumetric capacitances (33 μF cm -2 , 233 F cm -3 ) are achieved in Zn 0.99 Fe 0.01 O nanocrystals that rival those of the best supercapacitors used in commercial energy-storage devices. The redox properties of these nanocrystals are probed by potentiometric titration and optical spectroscopy. These data indicate an equilibrium between electron localization by Fe 3+ dopants and electron delocalization within the ZnO conduction band, allowing facile reversible charge storage and removal. As "soluble supercapacitors", colloidal iron-doped ZnO nanocrystals constitute a promising class of solution-processable electronic materials with large charge-storage capacity attractive for future energy-storage applications.

Nanocrystal quantum dots

CERN Document Server

Klimov, Victor I

2010-01-01

""Soft"" Chemical Synthesis and Manipulation of Semiconductor Nanocrystals, J.A. Hollingsworth and V.I. Klimov Electronic Structure in Semiconductor Nanocrystals: Optical Experiment, D.J. NorrisFine Structure and Polarization Properties of Band-Edge Excitons in Semiconductor Nanocrystals, A.L. EfrosIntraband Spectroscopy and Dynamics of Colloidal Semiconductor Quantum Dots, P. Guyot-Sionnest, M. Shim, and C. WangMultiexciton Phenomena in Semiconductor Nanocrystals, V.I. KlimovOptical Dynamics in Single Semiconductor Quantum Do

Quenching of photoluminescence of colloidal ZnO nanocrystals by nitronyl nitroxide radicals

Energy Technology Data Exchange (ETDEWEB)

Stroyuk, Oleksandr L., E-mail: stroyuk@inphyschem-nas.kiev.ua [L.V. Pysarzhevsky Institute of Physical Chemistry of National Academy of Sciences of Ukraine, 31 Nauky avenue, 03028 Kyiv (Ukraine); Yakovenko, Anastasiya V.; Raevskaya, Oleksandra E. [L.V. Pysarzhevsky Institute of Physical Chemistry of National Academy of Sciences of Ukraine, 31 Nauky avenue, 03028 Kyiv (Ukraine); Plyusnin, Victor F. [Institute of Chemical Kinetics and Combustion of Siberian Branch of Russian Academy of Sciences, Novosibirsk (Russian Federation)

2014-11-15

Quenching of the photoluminescence of colloidal zinc oxide nanocrystals by a series of stable nitronyl nitroxide radicals was studied by means of stationary and time-resolved luminescence spectroscopy. Among the studied radicals the most efficient quenchers of the ZnO luminescence are the carboxyl-substituted species. The meta-substituted radical was found to be a more active quencher, than para-substituted one due to a closer proximity of the radical center to the nanocrystals surface. The PL quenching has a complex dynamic/static character. The dynamic quenching arises from photocatalytic radical reduction by ZnO conduction band electrons, while the static quenching is caused by adsorption of the photoreduction products on the nanocrystal surface. The non-substituted and OH-substituted radicals are inferior to the products of their photoreduction in capability of adsorption of the ZnO surface, and the quenching is dominated by interactions between the nanocrystals and photoreduced hydroxylamines. In case of COOH-substituted radicals, however, the radicals compete with the photoreduction products for the surface sites of ZnO nanocrystals resulting in a dynamic character of photoluminescence quenching.

Synthesis and characterization of KTiOPO4 nanocrystals and their PMMA nanocomposites

International Nuclear Information System (INIS)

Galceran, M; Pujol, M C; Carvajal, J J; Diaz, F; Aguilo, M; Tkaczyk, S; Kityk, I V

2009-01-01

KTiOPO 4 (KTP) nanocrystals have been synthesized by the modified Pechini method using ethylenediaminetetraacetic acid (EDTA) and ethylene glycol (EG) as chelating and sterification agents, respectively. Orthorhombic KTP has been obtained by calcination at 1073 K for several hours. Differential thermal and thermogravimetric (DTA-TG) analyses have been used to study the optimized heat treatment used on the precursor powder to obtain KTP nanocrystals. X-ray powder diffraction (XRD) studies on the thermally treated precursor powders indicated that nanocrystals began to crystallize at 923 K. Nanocrystals with a size dispersion distribution that fit to a lognormal function centered at 25 nm were observed by electronic microscopy. KTP nanocomposites were prepared by embedding nanocrystals in poly(methyl methacrylate) (PMMA). The photoinduced second-order susceptibility parameter and the piezo-optical coefficient were measured for the KTP nanocomposites. The optimal conditions for the generation of the frequency-doubled second harmonic generation were recorded at 391 K, and at a fundamental laser wavelength of 1064 nm and under additional treatment by polarized UV light, provided the maximum value obtained of 3.23 pm V -1 . The piezo-optical coefficients were recorded at room temperature under photoinduced treatment by a UV laser beam; the maximum value achieved was 0.673 x 10 -14 m 2 N -1 at a pump-probe delaying time of 160 s.

Electronic Structure of Hydrogenated and Surface-Modified GaAs Nanocrystals: Ab Initio Calculations

Directory of Open Access Journals (Sweden)

Hamsa Naji Nasir

2012-01-01

Full Text Available Two methods are used to simulate electronic structure of gallium arsenide nanocrystals. The cluster full geometrical optimization procedure which is suitable for small nanocrystals and large unit cell that simulates specific parts of larger nanocrystals preferably core part as in the present work. Because of symmetry consideration, large unit cells can reach sizes that are beyond the capabilities of first method. The two methods use ab initio Hartree-Fock and density functional theory, respectively. The results show that both energy gap and lattice constant decrease in their value as the nanocrystals grow in size. The inclusion of surface part in the first method makes valence band width wider than in large unit cell method that simulates the core part only. This is attributed to the broken symmetry and surface passivating atoms that split surface degenerate states and adds new levels inside and around the valence band. Bond length and tetrahedral angle result from full geometrical optimization indicate good convergence to the ideal zincblende structure at the centre of hydrogenated nanocrystal. This convergence supports large unit cell methodology. Existence of oxygen atoms at nanocrystal surface melts down density of states and reduces energy gap.

Nonlinear optical effect and excited electron dynamics of semiconductor nanocrystals; Handotai nano kessh no hisenkei kogaku koka to reiki denshi dynamics

Energy Technology Data Exchange (ETDEWEB)

Goto, T. [Tohoku University, Sendai (Japan)

1996-08-20

Investigations were given on nanocrystals of CuCl and CdTe with regard to their nonlinear optical mechanism. The experiment used a femto-second pump probe spectroscope. The experiment on CuCl nanocrystals revealed the following facts: in the case where one photon is absorbed into one nanocrystal, cascade mitigation occurs to the pair of electrons and holes, and exciters; and in the case where two photons are absorbed into one nanocrystal, exciter molecules are made via the pair of electrons and holes and the exciters. Thus, it was found that the optical nonlinearity occurs when more than two photons are absorbed into one nanocrystal, and inter-exciter interactions and formation of the exciter molecules are the physical causes thereof. The experiment on CdTe nanocrystals indicated that electrons and holes produced by laser beam are distributed instantaneously between the size-quantized discrete levels, and that temperature in the electron system drops with lapse of time. 9 refs., 6 figs.

Nanocrystals Technology for Pharmaceutical Science.

Science.gov (United States)

Cheng, Zhongyao; Lian, Yumei; Kamal, Zul; Ma, Xin; Chen, Jianjun; Zhou, Xinbo; Su, Jing; Qiu, Mingfeng

2018-05-17

Nanocrystals technology is a promising method for improving the dissolution rate and enhancing the bioavailability of poorly soluble drugs. In recent years, it has been developing rapidly and applied to drug research and engineering. Nanocrystal drugs can be formulated into various dosage forms. This review mainly focused on the nanocrystals technology and its application in pharmaceutical science. Firstly, different preparation methods of nanocrystal technology and the characterization of nanocrystal drugs are briefly described. Secondly, the application of nanocrystals technology in pharmaceutical science is mainly discussed followed by the introduction of sustained release formulations. Then, the scaling up process, marketed nanocrystal drug products and regulatory aspects about nanodrugs are summarized. Finally, the specific challenges and opportunities of nanocrystals technology for pharmaceutical science are summarized and discussed. This review will provide a comprehensive guide for scientists and engineers in the field of pharmaceutical science and biochemical engineering. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Exploring exciton relaxation and multiexciton generation in PbSe nanocrystals using hyperspectral near-IR probing.

Science.gov (United States)

Gdor, Itay; Sachs, Hanan; Roitblat, Avishy; Strasfeld, David B; Bawendi, Moungi G; Ruhman, Sanford

2012-04-24

Hyperspectral femtosecond transient absorption spectroscopy is employed to record exciton relaxation and recombination in colloidal lead selenide (PbSe) nanocrystals in unprecedented detail. Results obtained with different pump wavelengths and fluences are scrutinized with regard to three issues: (1) early subpicosecond spectral features due to "hot" excitons are analyzed in terms of suggested underlying mechanisms; (2) global kinetic analysis facilitates separation of the transient difference spectra into single, double, and triple exciton state contributions, from which individual band assignments can be tested; and (3) the transient spectra are screened for signatures of multiexciton generation (MEG) by comparing experiments with excitation pulses both below and well above the theoretical threshold for multiplication. For the latter, a recently devised ultrafast pump-probe spectroscopic approach is employed. Scaling sample concentrations and pump pulse intensities inversely with the extinction coefficient at each excitation wavelength overcomes ambiguities due to direct multiphoton excitation, uncertainties of absolute absorption cross sections, and low signal levels. As observed in a recent application of this method to InAs core/shell/shell nanodots, no sign of MEG was detected in this sample up to photon energy 3.7 times the band gap. Accordingly, numerous reports of efficient MEG in other samples of PbSe suggest that the efficiency of this process varies from sample to sample and depends on factors yet to be determined.

Lanthanide-doped Na xScF 3+ x nanocrystals: Crystal structure evolution and multicolor tuning

KAUST Repository

Teng, Xue

2012-05-23

Rare-earth-based nanomaterials have recently drawn considerable attention because of their unique energy upconversion (UC) capabilities. However, studies of Sc 3+-based nanomaterials are still absent. Herein we report the synthesis and fine control of Na xScF 3+x nanocrystals by tuning of the ratio of oleic acid (OA, polar surfactant) to 1-octadecene (OD, nonpolar solvent). When the OA:OD ratio was increased from low (3:17) to high (3:7), the nanocrystals changed from pure monoclinic phase (Na 3ScF 6) to pure hexagonal phase (NaScF 4) via a transition stage at an intermediate OA:OD ratio (3:9) where a mixture of nanocrystals in monoclinic and hexagonal phases was obtained and the coexistence of the two phases inside individual nanocrystals was also observed. More significantly, because of the small radius of Sc 3+, Na xScF 3+x:Yb/Er nanocrystals show different UC emission from that of NaYF 4:Yb/Er nanocrystals, which broadens the applications of rare-earth-based nanomaterials ranging from optical communications to disease diagnosis. © 2012 American Chemical Society.

One dimensional CuO nanocrystals synthesis by electrical explosion: A study on structural, optical and electronic properties

Energy Technology Data Exchange (ETDEWEB)

Krishnan, Shutesh, E-mail: shutesh.k@onsemi.com [Department of Mechanical Engineering University of Malaya, 50603 Kuala Lumpur (Malaysia); ON Semiconductor Package Innovation and Development Center, 70450 Seremban (Malaysia); Haseeb, A.S.M.A.; Johan, Mohd Rafie [Department of Mechanical Engineering University of Malaya, 50603 Kuala Lumpur (Malaysia)

2014-02-15

Highlights: • One-dimensional CuO nanoflakes were synthesized by novel wire explosion technique. • A physical synthesis method capable of producing high aspect ratio (1:16) nanocrystals. • Most energy efficient and eco-friendly synthesis of low-dimensional transition metal oxide nanocrystals. -- Abstract: One-dimensional (1D) copper oxide (CuO) nanocrystals were synthesized using a novel wire explosion in de-ionized (DI) water without any chemical additives. Highly crystalline 1D CuO nanocrystals with 1:16 aspect ratio were successfully synthesized using this technique. The chemical nature and physical structure of the nanocrystals were controlled by simply modulating the exploding medium temperature. The results showed that nanocrystals produced at explosion temperatures 65 °C and 95 °C are pure CuO with optical band-gap energy of 2.38 eV. High Resolution Transmission Electron Microscope analysis (HRTEM) indicates that the CuO nanocrystals are with growth in [1{sup ¯}11] and [1 1 1] directions. The epitaxial crystal growth kinetics of the 1D nanostructure by aggregation was discussed. The incorporation of microstructural features like edge dislocations and porosity in the growth mechanism was examined. X-ray photoelectron spectroscopy (XPS) characterization indicates the formation of high purity CuO nanocrystals with valence state +2. This study provides an energy efficient and eco-friendly synthesis method of 1D transition metal oxide nanocrystals for electronic applications.

One dimensional CuO nanocrystals synthesis by electrical explosion: A study on structural, optical and electronic properties

International Nuclear Information System (INIS)

Krishnan, Shutesh; Haseeb, A.S.M.A.; Johan, Mohd Rafie

2014-01-01

Highlights: • One-dimensional CuO nanoflakes were synthesized by novel wire explosion technique. • A physical synthesis method capable of producing high aspect ratio (1:16) nanocrystals. • Most energy efficient and eco-friendly synthesis of low-dimensional transition metal oxide nanocrystals. -- Abstract: One-dimensional (1D) copper oxide (CuO) nanocrystals were synthesized using a novel wire explosion in de-ionized (DI) water without any chemical additives. Highly crystalline 1D CuO nanocrystals with 1:16 aspect ratio were successfully synthesized using this technique. The chemical nature and physical structure of the nanocrystals were controlled by simply modulating the exploding medium temperature. The results showed that nanocrystals produced at explosion temperatures 65 °C and 95 °C are pure CuO with optical band-gap energy of 2.38 eV. High Resolution Transmission Electron Microscope analysis (HRTEM) indicates that the CuO nanocrystals are with growth in [1 ¯ 11] and [1 1 1] directions. The epitaxial crystal growth kinetics of the 1D nanostructure by aggregation was discussed. The incorporation of microstructural features like edge dislocations and porosity in the growth mechanism was examined. X-ray photoelectron spectroscopy (XPS) characterization indicates the formation of high purity CuO nanocrystals with valence state +2. This study provides an energy efficient and eco-friendly synthesis method of 1D transition metal oxide nanocrystals for electronic applications

Optimizing colloidal nanocrystals for applications

International Nuclear Information System (INIS)

Sytnyk, M.

2015-01-01

In the scientific literature colloidal nanocrystals are presented as promising materials for multiple applications, in areas covering optoelectronics, photovoltaics, spintronics, catalysis, and bio-medicine. On the marked are, however, only a very limited number of examples found, indeed implementing colloidal nanocrystals. Thus the scope of this thesis was to modify nanocrystals and to tune their properties to fulfill specific demands. While some modifications could be achieved by post synthetic treatments, one key problem of colloidal nanocrystals, hampering there widespread application is the toxicity of their constituents. To develop nanocrystals from non-toxic materials has been a major goal of this thesis as well. Roughly, the results in this thesis could be subdivided into three parts: (i) the development of ion exchange methods to tailor the properties of metallic and metal-oxide based nanocrystal heterostructures, (ii), the synthesis of semiconductor nanocrystals from non-toxic materials, and (iii) the characterization of the nanocrystals by measurements of their morphology, chemical composition, magnetic-, optical-, and electronic properties. In detail, the thesis is subdivided into an introductory chapter, 4 chapters reporting on scientific results, a chapter reporting the used methods, and the conclusions. The 4 chapters devoted to the scientific results correspond to manuscripts, which are either currently in preparation, or have been published in highly ranked scientific journals such as NanoLetters (chapter 2), ACS Nano (chapter 4), or JACS (chapter 5). Thus, these chapters provide also an extra introduction and conclusion section, as well as separate reference lists. Chapter 2 describes a cation exchange process which is used to tune and improve the magnetic properties of different iron-oxide based colloidal nanocrystal-heterostructures. The superparamagnetic blocking temperature, magnetic remanence, and coercivity is tuned by replacing Fe2+ by Co2

Anode property of carbon coated LiFePO4 nanocrystals

Science.gov (United States)

Ni, Jiangfeng; Jiang, Jiaxing; Savilov, S. V.; Aldoshin, S. M.

2016-10-01

Nanostructured LiFePO4 is appealing cathode material for rechargeable lithium batteries. Herein, however, we report the intriguing anode properties of carbon coated LiFePO4 nanocrystals. In the potential range of 0-3.0 V, the LiFePO4 nanocrystal electrodes afford high reversible capacity of 373 mAhg-1 at a current rate of 0.05 Ag-1 and retains 239 mAhg-1 at a much higher rate of 1.25 Ag-1. In addition, it is capable of sustaining 1000 cycles at 1.25 Ag-1 without any capacity fading. Such superior properties indicate that nanostructured LiFePO4 could also be promising anode for rechargeable battery applications.

Fluorescent cellulose nanocrystals via supramolecular assembly of terpyridine-modified cellulose nanocrystals and terpyridine-modified perylene

International Nuclear Information System (INIS)

Hassan, Mohammad L.; Moorefield, Charles M.; Elbatal, Hany S.; Newkome, George R.; Modarelli, David A.; Romano, Natalie C.

2012-01-01

Highlights: ► Surfaces of cellulose nanocrystals were modified with terpyridine ligands. ► Fluorescent nanocrystals could be obtained via self-assembly of terpyridine-modified perylene dye onto the terpyridine-modified cellulose nanocrystals. ► Further self-assembly of azide-functionalized terpyridine onto the fluorescent cellulose nanocrystals was possible to obtain nanocellulosic material with expected use in bioimaging. - Abstract: Due to their natural origin, biocompatibility, and non-toxicity, cellulose nanocrystals are promising candidates for applications in nanomedicine. Highly fluorescent nanocellulosic material was prepared via surface modification of cellulose nanocrystals with 2,2′:6′,2″-terpyridine side chains followed by supramolecular assembly of terpyridine-modified perylene dye onto the terpyridine-modified cellulose nanocrystals (CTP) via Ru III /Ru II reduction. The prepared terpyridine-modified cellulose-Ru II -terpyridine-modified perylene (CTP-Ru II -PeryTP) fluorescent nanocrystals were characterized using cross-polarized/magic angle spin 13 C nuclear magnetic resonance (CP/MAS 13 C NMR), Fourier transform infrared (FTIR), UV–visible, and fluorescence spectroscopy. In addition, further self-assembly of terpyridine units with azide functional groups onto CTP-Ru II -PeryTP was possible via repeating the Ru III /Ru II reduction protocol to prepare supramolecular fluorescent nanocrystals with azide functionality (CTP-Ru II -PeryTP-Ru II -AZTP). The prepared derivative may have potential application in bio-imaging since the terminal azide groups can be easily reacted with antigens via “Click” chemistry reaction.

Photoemission studies of semiconductor nanocrystals

International Nuclear Information System (INIS)

Hamad, K.S.; Roth, R.; Alivisatos, A.P.

1997-01-01

Semiconductor nanocrystals have been the focus of much attention in the last ten years due predominantly to their size dependent optical properties. Namely, the band gap of nanocrystals exhibits a shift to higher energy with decreasing size due to quantum confinement effects. Research in this field has employed primarily optical techniques to study nanocrystals, and in this respect this system has been investigated extensively. In addition, one is able to synthesize monodisperse, crystalline particles of CdS, CdSe, Si, InP, InAs, as well as CdS/HgS/CdS and CdSe/CdS composites. However, optical spectroscopies have proven ambiguous in determining the degree to which electronic excitations are interior or surface admixtures or giving a complete picture of the density of states. Photoemission is a useful technique for understanding the electronic structure of nanocrystals and the effects of quantum confinement, chemical environments of the nanocrystals, and surface coverages. Of particular interest to the authors is the surface composition and structure of these particles, for they have found that much of the behavior of nanocrystals is governed by their surface. Previously, the authors had performed x-ray photoelectron spectroscopy (XPS) on CdSe nanocrystals. XPS has proven to be a powerful tool in that it allows one to determine the composition of the nanocrystal surface

Ferromagnetism in Fe-doped ZnO Nanocrystals: Experimental and Theoretical investigations

OpenAIRE

Karmakar, Debjani; Mandal, S. K.; Kadam, R. M.; Paulose, P. L.; Rajarajan, A. K.; Nath, T. K.; Das, A. K.; Dasgupta, I.; Das, G. P.

2007-01-01

Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature > 450 K with a low-temperature transition from ferromagnetic to spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like EPR and Mossbauer indicate the presence of Fe in both v...

Nanocrystal Solar Cells

Energy Technology Data Exchange (ETDEWEB)

Gur, Ilan [Univ. of California, Berkeley, CA (United States)

2006-01-01

This dissertation presents the results of a research agenda aimed at improving integration and stability in nanocrystal-based solar cells through advances in active materials and device architectures. The introduction of 3-dimensional nanocrystals illustrates the potential for improving transport and percolation in hybrid solar cells and enables novel fabrication methods for optimizing integration in these systems. Fabricating cells by sequential deposition allows for solution-based assembly of hybrid composites with controlled and well-characterized dispersion and electrode contact. Hyperbranched nanocrystals emerge as a nearly ideal building block for hybrid cells, allowing the controlled morphologies targeted by templated approaches to be achieved in an easily fabricated solution-cast device. In addition to offering practical benefits to device processing, these approaches offer fundamental insight into the operation of hybrid solar cells, shedding light on key phenomena such as the roles of electrode-contact and percolation behavior in these cells. Finally, all-inorganic nanocrystal solar cells are presented as a wholly new cell concept, illustrating that donor-acceptor charge transfer and directed carrier diffusion can be utilized in a system with no organic components, and that nanocrystals may act as building blocks for efficient, stable, and low-cost thin-film solar cells.

Sorting fluorescent nanocrystals with DNA

Energy Technology Data Exchange (ETDEWEB)

Gerion, Daniele; Parak, Wolfgang J.; Williams, Shara C.; Zanchet, Daniela; Micheel, Christine M.; Alivisatos, A. Paul

2001-12-10

Semiconductor nanocrystals with narrow and tunable fluorescence are covalently linked to oligonucleotides. These biocompounds retain the properties of both nanocrystals and DNA. Therefore, different sequences of DNA can be coded with nanocrystals and still preserve their ability to hybridize to their complements. We report the case where four different sequences of DNA are linked to four nanocrystal samples having different colors of emission in the range of 530-640 nm. When the DNA-nanocrystal conjugates are mixed together, it is possible to sort each type of nanoparticle using hybridization on a defined micrometer -size surface containing the complementary oligonucleotide. Detection of sorting requires only a single excitation source and an epifluorescence microscope. The possibility of directing fluorescent nanocrystals towards specific biological targets and detecting them, combined with their superior photo-stability compared to organic dyes, opens the way to improved biolabeling experiments, such as gene mapping on a nanometer scale or multicolor microarray analysis.

Synthesis and Manipulation of Semiconductor Nanocrystals inMicrofluidic Reactors

Energy Technology Data Exchange (ETDEWEB)

Chan, Emory Ming-Yue [Univ. of California, Berkeley, CA (United States)

2006-01-01

Microfluidic reactors are investigated as a mechanism tocontrol the growth of semiconductor nanocrystals and characterize thestructural evolution of colloidal quantum dots. Due to their shortdiffusion lengths, low thermal masses, and predictable fluid dynamics,microfluidic devices can be used to quickly and reproducibly alterreaction conditions such as concentration, temperature, and reactiontime, while allowing for rapid reagent mixing and productcharacterization. These features are particularly useful for colloidalnanocrystal reactions, which scale poorly and are difficult to controland characterize in bulk fluids. To demonstrate the capabilities ofnanoparticle microreactors, a size series of spherical CdSe nanocrystalswas synthesized at high temperature in a continuous-flow, microfabricatedglass reactor. Nanocrystal diameters are reproducibly controlled bysystematically altering reaction parameters such as the temperature,concentration, and reaction time. Microreactors with finer control overtemperature and reagent mixing were designed to synthesize nanoparticlesof different shapes, such as rods, tetrapods, and hollow shells. The twomajor challenges observed with continuous flow reactors are thedeposition of particles on channel walls and the broad distribution ofresidence times that result from laminar flow. To alleviate theseproblems, I designed and fabricated liquid-liquid segmented flowmicroreactors in which the reaction precursors are encapsulated inflowing droplets suspended in an immiscible carrier fluid. The synthesisof CdSe nanocrystals in such microreactors exhibited reduced depositionand residence time distributions while enabling the rapid screening aseries of samples isolated in nL droplets. Microfluidic reactors werealso designed to modify the composition of existing nanocrystals andcharacterize the kinetics of such reactions. The millisecond kinetics ofthe CdSe-to-Ag₂Se nanocrystal cation exchange reaction are measured insitu with micro

Hybrid nanocrystal/polymer solar cells based on tetrapod-shaped CdSexTe1-x nanocrystals

International Nuclear Information System (INIS)

Zhou Yi; Li Yunchao; Zhong Haizheng; Hou Jianhui; Ding Yuqin; Yang Chunhe; Li Yongfang

2006-01-01

A series of ternary tetrapodal nanocrystals of CdSe x Te 1-x with x = 0 (CdTe), 0.23, 0.53, 0.78, 1 (CdSe) were synthesized and used to fabricate hybrid nanocrystal/polymer solar cells. Herein, the nanocrystals acted as electron acceptors, and poly(2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) was used as an electron donor. It was found that the open circuit voltage (V oc ), short-circuit current (J sc ) and power conversion efficiency (η) of the devices all increased with increasing Se content in the CdSe x Te 1-x nanocrystals under identical experimental conditions. The solar cell based on the blend of tetrapodal CdSe nanocrystals and MEH-PPV (9:1 w/w) showed the highest power conversion efficiency of 1.13% under AM 1.5, 80 mW cm -2 , and the maximum incident photon to converted current efficiency (IPCE) of the device reached 47% at 510 nm. The influence of nanocrystal composition on the photovoltaic properties of the hybrid solar cells was explained by the difference of the band level positions between MEH-PPV and the nanocrystals

Biomolecular Assembly of Gold Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Micheel, Christine Marya [Univ. of California, Berkeley, CA (United States)

2005-05-20

Over the past ten years, methods have been developed to construct discrete nanostructures using nanocrystals and biomolecules. While these frequently consist of gold nanocrystals and DNA, semiconductor nanocrystals as well as antibodies and enzymes have also been used. One example of discrete nanostructures is dimers of gold nanocrystals linked together with complementary DNA. This type of nanostructure is also known as a nanocrystal molecule. Discrete nanostructures of this kind have a number of potential applications, from highly parallel self-assembly of electronics components and rapid read-out of DNA computations to biological imaging and a variety of bioassays. My research focused in three main areas. The first area, the refinement of electrophoresis as a purification and characterization method, included application of agarose gel electrophoresis to the purification of discrete gold nanocrystal/DNA conjugates and nanocrystal molecules, as well as development of a more detailed understanding of the hydrodynamic behavior of these materials in gels. The second area, the development of methods for quantitative analysis of transmission electron microscope data, used computer programs written to find pair correlations as well as higher order correlations. With these programs, it is possible to reliably locate and measure nanocrystal molecules in TEM images. The final area of research explored the use of DNA ligase in the formation of nanocrystal molecules. Synthesis of dimers of gold particles linked with a single strand of DNA possible through the use of DNA ligase opens the possibility for amplification of nanostructures in a manner similar to polymerase chain reaction. These three areas are discussed in the context of the work in the Alivisatos group, as well as the field as a whole.

Annealing effects on the photoresponse properties of CdSe nanocrystal thin films

International Nuclear Information System (INIS)

Lou Shiyun; Zhou Changhua; Wang Hongzhe; Shen Huaibin; Cheng Gang; Du Zuliang; Zhou, Shaomin; Li Linsong

2011-01-01

Highlights: → The as-prepared CdSe nanocrystal films were treated at 500 deg. C for 3 h under continuous N 2 . → Annealing process removed the organic capping completely and eliminated oxide on the CdSe surface. → Thermal annealing resulted the increase of the crystallite sizes and necking the NCs. → The photoresponse speed of the CdSe nanocrystal films was improved. - Abstract: The photoresponse properties of the as-prepared and annealed close-packed CdSe nanocrystal (NC) films were investigated under laser illumination by Kelvin probe force microscopy. The annealing process improved the photoresponse speed of the CdSe NC films. The work function of the annealed CdSe NC films changed more rapidly than that of the non-annealed film in air at room temperature. Combined with X-ray photoelectron spectroscopy measurements and thermogravimetric analysis, the observed phenomena can be interpreted that annealing process removed the organic capping agents completely and eliminated oxide on the CdSe surface, which formed the tunnel barrier between NCs in the CdSe NC films. Consequently, it improved the separation rate of photoelectric charges and thus provided high speed photoresponse.

Nanocrystal conversion chemistry: A unified and materials-general strategy for the template-based synthesis of nanocrystalline solids

International Nuclear Information System (INIS)

Vasquez, Yolanda; Henkes, Amanda E.; Chris Bauer, J.; Schaak, Raymond E.

2008-01-01

The concept of nanocrystal conversion chemistry, which involves the use of pre-formed nanoparticles as templates for chemical transformation into derivative solids, has emerged as a powerful approach for designing the synthesis of complex nanocrystalline solids. The general strategy exploits established synthetic capabilities in simple nanocrystal systems and uses these nanocrystals as templates that help to define the composition, crystal structure, and morphology of product nanocrystals. This article highlights key examples of 'conversion chemistry' approaches to the synthesis of nanocrystalline solids using a variety of techniques, including galvanic replacement, diffusion, oxidation, and ion exchange. The discussion is organized according to classes of solids, highlighting the diverse target systems that are accessible using similar chemical concepts: metals, oxides, chalcogenides, phosphides, alloys, intermetallic compounds, sulfides, and nitrides. - Graphical abstract: Nanocrystal conversion chemistry uses pre-formed nanoparticles as templates for chemical transformation into derivative solids, helping to define the composition, crystal structure, and morphology of product nanocrystals that have more complex features than their precursor templates. This article highlights the application of this concept to diverse classes of solids, including metals, oxides, chalcogenides, phosphides, alloys, intermetallics, sulfides, and nitrides

Optical luminescence from alkyl-passivated Si nanocrystals under vacuum ultraviolet excitation: Origin and temperature dependence of the blue and orange emissions

OpenAIRE

Chao, Y; Houlton, A; Horrocks, BR; Hunt, MRC; Poolton, NRJ; Yang, J; Šiller, L

2006-01-01

The origin and stability of luminescence are critical issues for Si nanocrystals which are intended for use as biological probes. The optical luminescence of alkyl-monolayer-passivated silicon nanocrystals was studied under excitation with vacuum ultraviolet photons (5.1–23 eV). Blue and orange emission bands were observed simultaneously, but the blue band only appeared at low temperatures (8.7 eV). At 8 K, the peak wavelengths of the emission bands were 430±2 nm (blue) and 600±2 nm (orange)....

Thorium/uranium mixed oxide nano-crystals: Synthesis, structural characterization and magnetic properties

International Nuclear Information System (INIS)

Hudry, Damien; Griveau, Jean-Christophe; Apostolidis, Christos; Colineau, Eric; Rasmussen, Gert; Walter, Olaf; Wang, Di; Venkata Sai Kiran Chakravadhaluna; Courtois, Eglantine; Kubel, Christian

2014-01-01

One of the primary aims of the actinide community within nano-science is to develop a good understanding similar to what is currently the case for stable elements. As a consequence, efficient, reliable and versatile synthesis techniques dedicated to the formation of new actinide-based nano-objects (e.g., nano-crystals) are necessary. Hence, a 'library' dedicated to the preparation of various actinide based nano-scale building blocks is currently being developed. Nano-scale building blocks with tunable sizes, shapes and compositions are of prime importance. So far, the non-aqueous synthesis method in highly coordinating organic media is the only approach which has demonstrated the capability to provide size and shape control of actinide-based nano-crystals (both for thorium and uranium, and recently extended to neptunium and plutonium). In this paper, we demonstrate that the non-aqueous approach is also well adapted to control the chemical composition of the nano-crystals obtained when mixing two different actinides. Indeed, the controlled hot co-injection of thorium acetylacetonate and uranyl acetate (together with additional capping agents) into benzyl ether can be used to synthesize thorium/uranium mixed oxide nano-crystals covering the full compositional spectrum. Additionally, we found that both size and shape are modified as a function of the thorium/uranium ratio. Finally, the magnetic properties of the different thorium/uranium mixed oxide nano-crystals were investigated. Contrary to several reports, we did not observe any ferromagnetic behavior. As a consequence, ferromagnetism cannot be described as a universal feature of nano-crystals of non-magnetic oxides as recently claimed in the literature. (authors)

One pot synthesis, growth mechanism and optical properties of Zn{sub 1-x}Cd{sub x}Se graded core/shell and alloy nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Sonawane, Kiran G. [Department of Physics, University of Pune, Pune 411 007 (India); Patil, K.R. [Centre for Materials Characterization, National Chemical Laboratory, Pune 411 008 (India); Mahamuni, Shailaja, E-mail: shailajamahamuni@yahoo.co.in [Department of Physics, University of Pune, Pune 411 007 (India)

2013-03-15

Comparatively higher photoluminescence yield along with robustness of core/shell semiconductor nanocrystals make them attractive candidates for studying intricate quantum size effects. Here, we report, one pot synthesis of Zn{sub 1-x}Cd{sub x}Se graded core/shell structures by exploiting change in the reactivity of precursors. Optical and structural measurements indicate formation of graded structure. Growth mechanism probed by inductively coupled plasma atomic emission spectroscopy shows formation of graded core/shell structure, with CdSe rich core and ZnSe rich shell. Annealing these nanocrystals, in chemical bath, leads to diffusion of Cd from core to shell region. Formation of Zn{sub 1-x}Cd{sub x}Se alloy is also observed in X-ray photoelectron spectroscopic measurements, confirming the diffusion of Cd from core to shell region. Substantially high photoluminescence quantum efficiency of 60% with narrow line width of about 27 nm, was observed and is attributable to the reduced strain due to graded core/shell structure. - Highlights: Black-Right-Pointing-Pointer Graded CdSe/ZnSe core-shell nanocrystals are synthesized exploiting reactivity of precursors. Black-Right-Pointing-Pointer Growth mechanism is probed using ICP-AES spectroscopy. Black-Right-Pointing-Pointer Reduced strain leads to luminescence efficiency as high as 60%. Black-Right-Pointing-Pointer Alloy formation by annealing in chemical bath is probed using XPS.

Effect of argon implantation on solid-state dewetting: control of size and surface density of silicon nanocrystals.

Science.gov (United States)

Almadori, Y; Borowik, Ł; Chevalier, N; Barbé, J-C

2017-01-27

Thermally induced solid-state dewetting of ultra-thin films on insulators is a process of prime interest, since it is capable of easily forming nanocrystals. If no particular treatment is performed to the film prior to the solid-state dewetting, it is already known that the size, the shape and the density of nanocrystals is governed by the initial film thickness. In this paper, we report a novel approach to control the size and the surface density of silicon nanocrystals based on an argon-implantation preliminary surface treatment. Using 7.5 nm thin layers of silicon, we show that increasing the implantation dose tends to form smaller silicon nanocrystals with diameter and height lower than 50 nm and 30 nm, respectively. Concomitantly, the surface density is increased by a factor greater than 20, going from 5 μm -2 to values over 100 μm -2 .

Phase transitions and doping in semiconductor nanocrystals

Science.gov (United States)

Sahu, Ayaskanta

Colloidal semiconductor nanocrystals are a promising technological material because their size-dependent optical and electronic properties can be exploited for a diverse range of applications such as light-emitting diodes, bio-labels, transistors, and solar cells. For many of these applications, electrical current needs to be transported through the devices. However, while their solution processability makes these colloidal nanocrystals attractive candidates for device applications, the bulky surfactants that render these nanocrystals dispersible in common solvents block electrical current. Thus, in order to realize the full potential of colloidal semiconductor nanocrystals in the next-generation of solid-state devices, methods must be devised to make conductive films from these nanocrystals. One way to achieve this would be to add minute amounts of foreign impurity atoms (dopants) to increase their conductivity. Electronic doping in nanocrystals is still very much in its infancy with limited understanding of the underlying mechanisms that govern the doping process. This thesis introduces an innovative synthesis of doped nanocrystals and aims at expanding the fundamental understanding of charge transport in these doped nanocrystal films. The list of semiconductor nanocrystals that can be doped is large, and if one combines that with available dopants, an even larger set of materials with interesting properties and applications can be generated. In addition to doping, another promising route to increase conductivity in nanocrystal films is to use nanocrystals with high ionic conductivities. This thesis also examines this possibility by studying new phases of mixed ionic and electronic conductors at the nanoscale. Such a versatile approach may open new pathways for interesting fundamental research, and also lay the foundation for the creation of novel materials with important applications. In addition to their size-dependence, the intentional incorporation of

Fabrication of a novel nano-probe slide for near-field optical microscopy

International Nuclear Information System (INIS)

Yim, Sang-Youp; Jeang, Eun-Hee; Lee, Jae-Hoon; Park, Seung-Han; Cho, Kyu-Man

2004-01-01

A novel probe structure, which can act as a planar nano-probe slide for near-field microscopy, was proposed and fabricated. Sub-wavelength apertures on a Si substrate are successfully produced by means of standard photolithography techniques with properly selected masks. In particular, the anisotropic etching characteristics of Si substrate and the hardness of the Si 3 N 4 film are utilized. Probe-to-probe scanning of the fabricated near-field nano-probe slide shows sub-wavelength confinement of light and comparable throughput to the conventional optical fiber probe. We also show that the nano-probe slide can serve as a supporting base and a sub-wavelength aperture to obtain the near-field photoluminescence spectra of a limited number of CdSe nanocrystals.

PTFE-based microreactor system for the continuous synthesis of full-visible-spectrum emitting cesium lead halide perovskite nanocrystals

Directory of Open Access Journals (Sweden)

Chengxi Zhang

2017-11-01

Full Text Available Colloidal perovskite nanocrystals comprised of all inorganic cesium lead halide (CsPbX3, X = Cl, Br, I or a mixture thereof have potential as optical gain materials due to their high luminescence efficiency. In this work, cesium lead halide nanocrystals are continuously synthesized via a microreactor system consisting of poly(tetrafluoroethylene (PTFE capillaries. The synthesized nanocrystals possess excellent optical properties, including a full width at half maximum of 19–35 nm, high fluorescence quantum yield of 47.8–90.55%, and photoluminescence emission in the range of 450–700 nm. For the same precursor concentrations, the photoluminescence emission peak generally increases with increasing reaction temperature, revealing a controllable temperature effect on the photoluminescence characteristics of the synthesized nanocrystals. For quantum dots synthesized with a Br/I ratio of 1:3, a slight blue shift was observed for reaction temperatures greater than 100 °C. This PTFE-based microreactor system provides the unique capability of continuously synthesizing high-quality perovskite nanocrystals that emit over the full visible spectrum with applications ranging from displays and optoelectronic devices.

Intracellular delivery of peptide nucleic acid and organic molecules using zeolite-L nanocrystals.

Science.gov (United States)

Bertucci, Alessandro; Lülf, Henning; Septiadi, Dedy; Manicardi, Alex; Corradini, Roberto; De Cola, Luisa

2014-11-01

The design and synthesis of smart nanomaterials can provide interesting potential applications for biomedical purposes from bioimaging to drug delivery. Manufacturing multifunctional systems in a way to carry bioactive molecules, like peptide nucleic acids able to recognize specific targets in living cells, represents an achievement towards the development of highly selective tools for both diagnosis and therapeutics. This work describes a very first example of the use of zeolite nanocrystals as multifunctional nanocarriers to deliver simultaneously PNA and organic molecules into living cells. Zeolite-L nanocrystals are functionalized by covalently attaching the PNA probes onto the surface, while the channel system is filled with fluorescent guest molecules. The cellular uptake of the PNA/Zeolite-L hybrid material is then significantly increased by coating the whole system with a thin layer of biodegradable poly-L-lysine. The delivery of DAPI as a model drug molecule, inserted into the zeolite pores, is also demonstrated to occur in the cells, proving the multifunctional ability of the system. Using this zeolite nanosystem carrying PNA probes designed to target specific RNA sequences of interest in living cells could open new possibilities for theranostic and gene therapy applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Measuring the Valence of Nanocrystal Surfaces

Energy Technology Data Exchange (ETDEWEB)

Owen, Jonathan Scharle [Columbia Univ., New York, NY (United States)

2016-11-30

The goal of this project is to understand and control the interplay between nanocrystal stoichiometry, surface ligand binding and exchange, and the optoelectronic properties of semiconductor nanocrystals in solution and in thin solid films. We pursued three research directions with this goal in mind: 1) We characterized nanocrystal stoichiometry and its influence on the binding of L-type and X-type ligands, including the thermodynamics of binding and the kinetics of ligand exchange. 2) We developed a quantitative understanding of the relationship between surface ligand passivation and photoluminescence quantum yield. 3) We developed methods to replace the organic ligands on the nanocrystal with halide ligands and controllably deposit these nanocrystals into thin films, where electrical measurements were used to investigate the electrical transport and internanocrystal electronic coupling.

Composite material including nanocrystals and methods of making

Science.gov (United States)

Bawendi, Moungi G.; Sundar, Vikram C.

2010-04-06

Temperature-sensing compositions can include an inorganic material, such as a semiconductor nanocrystal. The nanocrystal can be a dependable and accurate indicator of temperature. The intensity of emission of the nanocrystal varies with temperature and can be highly sensitive to surface temperature. The nanocrystals can be processed with a binder to form a matrix, which can be varied by altering the chemical nature of the surface of the nanocrystal. A nanocrystal with a compatibilizing outer layer can be incorporated into a coating formulation and retain its temperature sensitive emissive properties.

Nanocrystal/sol-gel nanocomposites

Science.gov (United States)

Petruska, Melissa A [Los Alamos, NM; Klimov, Victor L [Los Alamos, NM

2007-06-05

The present invention is directed to solid composites including colloidal nanocrystals within a sol-gel host or matrix and to processes of forming such solid composites. The present invention is further directed to alcohol soluble colloidal nanocrystals useful in formation of sol-gel based solid composites.

Z-Contrast STEM Imaging and EELS of CdSe Nanocrystals: Towards the Analysis of Individual Nanocrystal Surfaces

International Nuclear Information System (INIS)

Erwin, M.; Kadavanich, A.V.; Kippeny, T.; Pennycook, S.J.; Rosenthal, S.J.

1999-01-01

We have applied Atomic Number Contract Scanning Transmission Electron Microscopy (Z-Contrast STEM) and STEM/EELS (Electron Energy Loss Spectroscopy) towards the study of colloidal CdSe semiconductor nanocrystals embedded in MEH-PPV polymer films. Unlike the case of conventional phase-contrast High Resolution TEM, Z-Contrast images are direct projections of the atomic structure. Hence they can be interpreted without the need for sophisticated image simulation and the image intensity is a direct measure of the thickness of a nanocrystal. Our thickness measurements are in agreement with the predicted faceted shape of these nanocrystals. Our unique 1.3A resolution STEM has successfully resolve3d the sublattice structure of these CdSe nanocrystals. In [010] projection (the polar axis in the image plane) we can distinguish Se atom columns from Cd columns. Consequently we can study the effects of lattice polarity on the nanocrystal morphology. Furthermore, since the STEM technique does not rely on diffraction, it is superbly suited to the study of non-periodic detail, such as the surface structure of the nanocrystals. EELS measurements on individual nanocrystals indicate a significant amount (equivalet to 0.5-1 surface monolayers) of oxygen on the nanocrystals, despite processing in an inert atmosphere. Spatially resolved measurements at 7A resolution suggest a surface oxide layer. However, the uncertainty in the measurement precludes definitive assignment at this time. The source of the oxygen is under investigation as well

Nanocrystal thin film fabrication methods and apparatus

Science.gov (United States)

Kagan, Cherie R.; Kim, David K.; Choi, Ji-Hyuk; Lai, Yuming

2018-01-09

Nanocrystal thin film devices and methods for fabricating nanocrystal thin film devices are disclosed. The nanocrystal thin films are diffused with a dopant such as Indium, Potassium, Tin, etc. to reduce surface states. The thin film devices may be exposed to air during a portion of the fabrication. This enables fabrication of nanocrystal-based devices using a wider range of techniques such as photolithography and photolithographic patterning in an air environment.

Automated microfluidic platform for systematic studies of colloidal perovskite nanocrystals: towards continuous nano-manufacturing.

Science.gov (United States)

Epps, Robert W; Felton, Kobi C; Coley, Connor W; Abolhasani, Milad

2017-11-21

Colloidal organic/inorganic metal-halide perovskite nanocrystals have recently emerged as a potential low-cost replacement for the semiconductor materials in commercial photovoltaics and light emitting diodes. However, unlike III-V and IV-VI semiconductor nanocrystals, studies of colloidal perovskite nanocrystals have yet to develop a fundamental and comprehensive understanding of nucleation and growth kinetics. Here, we introduce a modular and automated microfluidic platform for the systematic studies of room-temperature synthesized cesium-lead halide perovskite nanocrystals. With abundant data collection across the entirety of four orders of magnitude reaction time span, we comprehensively characterize nanocrystal growth within a modular microfluidic reactor. The developed high-throughput screening platform features a custom-designed three-port flow cell with translational capability for in situ spectral characterization of the in-flow synthesized perovskite nanocrystals along a tubular microreactor with an adjustable length, ranging from 3 cm to 196 cm. The translational flow cell allows for sampling of twenty unique residence times at a single equilibrated flow rate. The developed technique requires an average total liquid consumption of 20 μL per spectra and as little as 2 μL at the time of sampling. It may continuously sample up to 30 000 unique spectra per day in both single and multi-phase flow formats. Using the developed plug-and-play microfluidic platform, we study the growth of cesium lead trihalide perovskite nanocrystals through in situ monitoring of their absorption and emission band-gaps at residence times ranging from 100 ms to 17 min. The automated microfluidic platform enables a systematic study of the effect of mixing enhancement on the quality of the synthesized nanocrystals through a direct comparison between single- and multi-phase flow systems at similar reaction time scales. The improved mixing characteristics of the multi-phase flow

Electronic displays using optically pumped luminescent semiconductor nanocrystals

Science.gov (United States)

Weiss, Shimon [Pinole, CA; Schlamp, Michael C [Plainsboro, NJ; Alivisatos, A Paul [Oakland, CA

2011-09-27

A multicolor electronic display is based on an array of luminescent semiconductor nanocrystals. Nanocrystals which emit light of different colors are grouped into pixels. The nanocrystals are optically pumped to produce a multicolor display. Different sized nanocrystals are used to produce the different colors. A variety of pixel addressing systems can be used.

Charge transport in metal oxide nanocrystal-based materials

Science.gov (United States)

Runnerstrom, Evan Lars

There is probably no class of materials more varied, more widely used, or more ubiquitous than metal oxides. Depending on their composition, metal oxides can exhibit almost any number of properties. Of particular interest are the ways in which charge is transported in metal oxides: devices such as displays, touch screens, and smart windows rely on the ability of certain metal oxides to conduct electricity while maintaining visible transparency. Smart windows, fuel cells, and other electrochemical devices additionally rely on efficient transport of ionic charge in and around metal oxides. Colloidal synthesis has enabled metal oxide nanocrystals to emerge as a relatively new but highly tunable class of materials. Certain metal oxide nanocrystals, particularly highly doped metal oxides, have been enjoying rapid development in the last decade. As in myriad other materials systems, structure dictates the properties of metal oxide nanocrystals, but a full understanding of how nanocrystal synthesis, the processing of nanocrystal-based materials, and the structure of nanocrystals relate to the resulting properties of nanocrystal-based materials is still nascent. Gaining a fundamental understanding of and control over these structure-property relationships is crucial to developing a holistic understanding of metal oxide nanocrystals. The unique ability to tune metal oxide nanocrystals by changing composition through the introduction of dopants or by changing size and shape affords a way to study the interplay between structure, processing, and properties. This overall goal of this work is to chemically synthesize colloidal metal oxide nanocrystals, process them into useful materials, characterize charge transport in materials based on colloidal metal oxide nanocrystals, and develop ways to manipulate charge transport. In particular, this dissertation characterizes how the charge transport properties of metal oxide nanocrystal-based materials depend on their processing and

Bright trions in direct-bandgap silicon nanocrystals revealed bylow-temperature single-nanocrystal spectroscopy

Czech Academy of Sciences Publication Activity Database

Kůsová, Kateřina; Pelant, Ivan; Valenta, J.

2015-01-01

Roč. 4, Oct (2015), e336 ISSN 2047-7538 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA ČR GPP204/12/P235 Institutional support: RVO:68378271 Keywords : silicon nanocrystals * single-nanocrystal spectroscopy * luminescing trions Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 13.600, year: 2015

Development Considerations for Nanocrystal Drug Products.

Science.gov (United States)

Chen, Mei-Ling; John, Mathew; Lee, Sau L; Tyner, Katherine M

2017-05-01

Nanocrystal technology has emerged as a valuable tool for facilitating the delivery of poorly water-soluble active pharmaceutical ingredients (APIs) and enhancing API bioavailability. To date, the US Food and Drug Administration (FDA) has received over 80 applications for drug products containing nanocrystals. These products can be delivered by different routes of administration and are used in a variety of therapeutic areas. To aid in identifying key developmental considerations for these products, a retrospective analysis was performed on the submissions received by the FDA to date. Over 60% of the submissions were for the oral route of administration. Based on the Biopharmaceutics Classification System (BCS), most nanocrystal drugs submitted to the FDA are class II compounds that possess low aqueous solubility and high intestinal permeability. Impact of food on drug bioavailability was reduced for most nanocrystal formulations as compared with their micronized counterparts. For all routes of administration, dose proportionality was observed for some, but not all, nanocrystal products. Particular emphasis in the development of nanocrystal products was placed on the in-process tests and controls at critical manufacturing steps (such as milling process), mitigation and control of process-related impurities, and the stability of APIs or polymorphic form (s) during manufacturing and upon storage. This emphasis resulted in identifying challenges to the development of these products including accurate determination of particle size (distribution) of drug substance and/or nanocrystal colloidal dispersion, identification of polymorphic form (s), and establishment of drug substance/product specifications.

Hydrothermal synthesis of tungsten doped tin dioxide nanocrystals

Science.gov (United States)

Zhou, Cailong; Li, Yufeng; Chen, Yiwen; Lin, Jing

2018-01-01

Tungsten doped tin dioxide (WTO) nanocrystals were synthesized through a one-step hydrothermal method. The structure, composition and morphology of WTO nanocrystals were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, UV-vis diffuse reflectance spectra, zeta potential analysis and high-resolution transmission electron microscopy. Results show that the as-prepared WTO nanocrystals were rutile-type structure with the size near 13 nm. Compared with the undoped tin dioxide nanocrystals, the WTO nanocrystals possessed better dispersity in ethanol phase and formed transparent sol.

Proving the capabilities of the phased-array probe/ALOK inspection technique

International Nuclear Information System (INIS)

Bohn, H.; Kroening, M.; Rathgeb, W.; Gebhardt, W.; Kappes, W.; Barbian, O.A.

1987-01-01

The capability of the ALOK phased-probe-array inspection technique results from the simplicity of the testing system structure, the reflector detection and identification by means of transit time curves, and the analytical capacity of the system. Testing times are shortened, with the test results meeting the current standards, and further possibilities being given: Areas that could so far only be inspected with difficulty of not at all, can be examined, thanks to the compact equipment and without having to modify the system, very informative analysis measurements for interpreting indications can be made. Furthermore, it may be expected from the testing practice that descriptions of indications will become more reliable and reproducible, due to transit time curve identification. In addition to conventional criteria for reflector evaluation, the potential of transit time curve identification, and flaw boundary imaging of the reconstruction image can be utilized. (orig.)

Conformational Control of Energy Transfer: A Mechanism for Biocompatible Nanocrystal-Based Sensors

OpenAIRE

Kay, Euan R.; Lee, Jungmin; Nocera, Daniel; Bawendi, Moungi G.

2012-01-01

Fold-up fluorophore: A new paradigm for designing self-referencing fluorescent nanosensors is demonstrated by interfacing a pH-triggered molecular conformational switch with quantum dots. Analytedependent, large-amplitude conformational motion controls the distance between the nanocrystal energy donor and an organic FRET acceptor. The result is a fluorescence signal capable of reporting pH values from individual endosomes in living cells.

Facile synthesis of water-soluble curcumin nanocrystals

Directory of Open Access Journals (Sweden)

Marković Zoran M.

2015-01-01

Full Text Available In this paper, facile synthesis of water soluble curcumin nanocrystals is reported. Solvent exchange method was applied to synthesize curcumin nanocrystals. Different techniques were used to characterize the structural and photophysical properties of curcumin nanocrystals. We found that nanocurcumin prepared by this method had good chemical and physical stability, could be stored in the powder form at room temperature, and was freely dispersible in water. It was established that the size of curcumin nanocrystals was varied in the range of 20-500 nm. Fourier transform infrared spectroscopy and UV-Vis analyses showed the presence of tetrahydrofuran inside the curcumin nanocrystals. Also, it was found that nanocurcumin emitted photoluminescencewith yellow-green colour. [Projekat Ministarstva nauke Republike Srbije, br. 172003

Direct femtosecond observation of charge carrier recombination in ternary semiconductor nanocrystals: The effect of composition and shelling

KAUST Repository

Bose, Riya

2015-02-12

Heavy-metal free ternary semiconductor nanocrystals are emerging as key materials in photoactive applications. However, the relative abundance of intra-bandgap defect states and lack of understanding of their origins within this class of nanocrystals are major factors limiting their applicability. To remove these undesirable defect states which considerably shorten the lifetimes of photogenerated excited carriers, a detailed understanding about their origin and nature is required. In this report, we monitor the ultrafast charge carrier dynamics of CuInS2 (CIS), CuInSSe (CISSe), and CuInSe2 (CISe) nanocrystals, before and after ZnS shelling, using state-of-the-art time-resolved laser spectroscopy with broadband capabilities. The experimental results demonstrate the presence of both electron and hole trapping intra-bandgap states in the nanocrystals which can be removed significantly by ZnS shelling, and the carrier dynamics is slowed down. Another important observation remains the reduction of carrier lifetime in the presence of Se, and the shelling strategy is observed to be less effective at suppressing trap states. This study provides quantitative physical insights into the role of anion composition and shelling on the charge carrier dynamics in ternary CIS, CISSe, and CISe nanocrystals which are essential to improve their applicability for photovoltaics and optoelectronics.

Luminescence in colloidal Mn2+-doped semiconductor nanocrystals

International Nuclear Information System (INIS)

Beaulac, Remi; Archer, Paul I.; Gamelin, Daniel R.

2008-01-01

Recent advances in nanocrystal doping chemistries have substantially broadened the variety of photophysical properties that can be observed in colloidal Mn 2+ -doped semiconductor nanocrystals. A brief overview is provided, focusing on Mn 2+ -doped II-VI semiconductor nanocrystals prepared by direct chemical synthesis and capped with coordinating surface ligands. These Mn 2+ -doped semiconductor nanocrystals are organized into three major groups according to the location of various Mn 2+ -related excited states relative to the energy gap of the host semiconductor nanocrystals. The positioning of these excited states gives rise to three distinct relaxation scenarios following photoexcitation. A brief outlook on future research directions is provided. - Graphical abstract: Mn 2+ -doped semiconductor nanocrystals are organized into three major groups according to the location of various Mn 2+ -related excited states relative to the energy gap of the host semiconductor nanocrystals. The positioning of these excited states gives rise to three distinct relaxation scenarios following photoexcitation

Method of synthesizing pyrite nanocrystals

Science.gov (United States)

Wadia, Cyrus; Wu, Yue

2013-04-23

A method of synthesizing pyrite nanocrystals is disclosed which in one embodiment includes forming a solution of iron (III) diethyl dithiophosphate and tetra-alkyl-ammonium halide in water. The solution is heated under pressure. Pyrite nanocrystal particles are then recovered from the solution.

Charge transport in a CoPt3 nanocrystal microwire

International Nuclear Information System (INIS)

Beecher, P.; De Marzi, G.; Quinn, A.J.; Redmond, G.; Shevchenko, E.V.; Weller, H.

2004-01-01

The electrical characteristics of single CoPt 3 nanocrystal microwires formed by magnetic field-directed growth from colloidal solutions are presented. The wires comprise disordered assemblies of discrete nanocrystals, separated from each other by protective organic ligand shells. Electrical data indicate that the activated charge transport properties of the wires are determined by the nanocrystal charging energy, governed by the size and capacitance of the individual nanocrystals. Focused ion beam-assisted deposition of Pt metal at the wire-electrode junctions is employed to optimize the wire-electrode contacts, whilst maintaining the nanocrystal-dominated transport characteristics of these one-dimensional nanocrystal structures

Plasmonic light-sensitive skins of nanocrystal monolayers

Science.gov (United States)

Akhavan, Shahab; Gungor, Kivanc; Mutlugun, Evren; Demir, Hilmi Volkan

2013-04-01

We report plasmonically coupled light-sensitive skins of nanocrystal monolayers that exhibit sensitivity enhancement and spectral range extension with plasmonic nanostructures embedded in their photosensitive nanocrystal platforms. The deposited plasmonic silver nanoparticles of the device increase the optical absorption of a CdTe nanocrystal monolayer incorporated in the device. Controlled separation of these metallic nanoparticles in the vicinity of semiconductor nanocrystals enables optimization of the photovoltage buildup in the proposed nanostructure platform. The enhancement factor was found to depend on the excitation wavelength. We observed broadband sensitivity improvement (across 400-650 nm), with a 2.6-fold enhancement factor around the localized plasmon resonance peak. The simulation results were found to agree well with the experimental data. Such plasmonically enhanced nanocrystal skins hold great promise for large-area UV/visible sensing applications.

Binding SnO2 nanocrystals in nitrogen-doped graphene sheets as anode materials for lithium-ion batteries.

Science.gov (United States)

Zhou, Xiaosi; Wan, Li-Jun; Guo, Yu-Guo

2013-04-18

Hybrid anode materials for Li-ion batteries are fabricated by binding SnO2 nanocrystals (NCs) in nitrogen-doped reduced graphene oxide (N-RGO) sheets by means of an in situ hydrazine monohydrate vapor reduction method. The SnO2NCs in the obtained SnO2NC@N-RGO hybrid material exhibit exceptionally high specific capacity and high rate capability. Bonds formed between graphene and SnO2 nanocrystals limit the aggregation of in situ formed Sn nanoparticles, leading to a stable hybrid anode material with long cycle life. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superimposed noninterfering probes to extend the capabilities of phase Doppler anemometry.

Science.gov (United States)

Onofri, Fabrice; Lenoble, Anne; Radev, Stefan

2002-06-20

We propose using multiple superimposed noninterfering probes (SNIPs) of the same wavelength but different beam angles to extend the capabilities of phase Doppler anemometry. When a particle is moving in a SNIP the Doppler signals that are produced exhibit multiple Doppler frequencies and phase shifts. The resolution of the measurements of particle size (i.e., by fringe spacing and Doppler frequency) increases with beam angle. Then, with the solution proposed, even with only two detectors several measurements of size can be obtained for the same particle with increasing resolution if we consider higher frequencies in the signal. Several optical solutions to produce SNIPs as well as a signal-processing algorithm to treat the multiple-frequency Doppler signals are proposed. Experimental validations of the sizing of spherical and cylindrical particles demonstrate the applicability of this technique for particle measurement. We believe that this new technique can be of great interest when high resolution of size, velocity, and even refractive index is required.

Applying analytical ultracentrifugation to nanocrystal suspensions

Energy Technology Data Exchange (ETDEWEB)

Jamison, Jennifer A; Krueger, Karl M; Mayo, J T; Yavuz, Cafer T; Redden, Jacina J; Colvin, Vicki L, E-mail: colvin@rice.ed [Department of Chemistry, Rice University, 6100 Main Street, MS-60, Houston, TX 77005 (United States)

2009-09-02

While applied frequently in physical biochemistry to the study of protein complexes, the quantitative use of analytical ultracentrifugation (AUC) for nanocrystal analysis is relatively rare. Its application in nanoscience is potentially very powerful as it provides a measure of nanocrystal density, size and structure directly in the solution phase. Towards that end, this paper examines the best practices for applying data collection and analysis methods for AUC, geared towards the study of biomolecules, to the unique problems of nanoparticle analysis. Using uniform nanocrystals of cadmium selenide, we compared several schemes for analyzing raw sedimentation data. Comparable values of the mean sedimentation coefficients (s-value) were found using several popular analytical approaches; however, the distribution in sample s-values is best captured using the van Holde-Weischt algorithm. Measured s-values could be reproducibly collected if sample temperature and concentration were controlled; under these circumstances, the variability for average sedimentation values was typically 5%. The full shape of the distribution in s-values, however, is not easily subjected to quantitative interpretation. Moreover, the selection of the appropriate sedimentation speed is crucial for AUC of nanocrystals as the density of inorganic nanocrystals is much larger than that of solvents. Quantitative analysis of sedimentation properties will allow for better agreement between experimental and theoretical models of nanocrystal solution behavior, as well as providing deeper insight into the hydrodynamic size and solution properties of nanomaterials.

Symmetry breaking during seeded growth of nanocrystals.

Science.gov (United States)

Xia, Xiaohu; Xia, Younan

2012-11-14

Currently, most of the reported noble-metal nanocrystals are limited to a high level of symmetry, as constrained by the inherent, face-centered cubic (fcc) lattice of these metals. In this paper, we report, for the first time, a facile and versatile approach (backed up by a clear mechanistic understanding) for breaking the symmetry of an fcc lattice and thus obtaining nanocrystals with highly unsymmetrical shapes. The key strategy is to induce and direct the growth of nanocrystal seeds into unsymmetrical modes by manipulating the reduction kinetics. With silver as an example, we demonstrated that the diversity of possible shapes taken by noble-metal nanocrystals could be greatly expanded by incorporating a series of new shapes drastically deviated from the fcc lattice. This work provides a new method to investigate shape-controlled synthesis of metal nanocrystal.

Engineering Plasmonic Nanocrystal Coupling through Template-Assisted Self-Assembly

Science.gov (United States)

Greybush, Nicholas J.

The construction of materials from nanocrystal building blocks represents a powerful new paradigm for materials design. Just as nature's materials orchestrate intricate combinations of atoms from the library of the periodic table, nanocrystal "metamaterials" integrate individual nanocrystals into larger architectures with emergent collective properties. The individual nanocrystal "meta-atoms" that make up these materials are themselves each a nanoscale atomic system with tailorable size, shape, and elemental composition, enabling the creation of hierarchical materials with predesigned structure at multiple length scales. However, an improved fundamental understanding of the interactions among individual nanocrystals is needed in order to translate this structural control into enhanced functionality. The ability to form precise arrangements of nanocrystals and measure their collective properties is therefore essential for the continued development of nanocrystal metamaterials. In this dissertation, we utilize template-assisted self-assembly and spatially-resolved spectroscopy to form and characterize individual nanocrystal oligomers. At the intersection of "top-down" and "bottom-up" nanoscale patterning schemes, template-assisted self-assembly combines the design freedom of lithography with the chemical control of colloidal synthesis to achieve unique nanocrystal configurations. Here, we employ shape-selective templates to assemble new plasmonic structures, including heterodimers of Au nanorods and upconversion phosphors, a series of hexagonally-packed Au nanocrystal oligomers, and triangular formations of Au nanorods. Through experimental analysis and numerical simulation, we elucidate the means through which inter-nanocrystal coupling imparts collective optical properties to the plasmonic assemblies. Our self-assembly and measurement strategy offers a versatile platform for exploring optical interactions in a wide range of material systems and application areas.

"Nanocrystal bilayer for tandem catalysis"

Energy Technology Data Exchange (ETDEWEB)

Yamada, Yusuke; Tsung, Chia Kuang; Huang, Wenyu; Huo, Ziyang; E.Habas, Susan E; Soejima, Tetsuro; Aliaga, Cesar E; Samorjai, Gabor A; Yang, Peidong

2011-01-24

Supported catalysts are widely used in industry and can be optimized by tuning the composition and interface of the metal nanoparticles and oxide supports. Rational design of metal-metal oxide interfaces in nanostructured catalysts is critical to achieve better reaction activities and selectivities. We introduce here a new class of nanocrystal tandem catalysts that have multiple metal-metal oxide interfaces for the catalysis of sequential reactions. We utilized a nanocrystal bilayer structure formed by assembling platinum and cerium oxide nanocube monolayers of less than 10 nm on a silica substrate. The two distinct metal-metal oxide interfaces, CeO2-Pt and Pt-SiO2, can be used to catalyse two distinct sequential reactions. The CeO2-Pt interface catalysed methanol decomposition to produce CO and H2, which were subsequently used for ethylene hydroformylation catalysed by the nearby Pt-SiO2 interface. Consequently, propanal was produced selectively from methanol and ethylene on the nanocrystal bilayer tandem catalyst. This new concept of nanocrystal tandem catalysis represents a powerful approach towards designing high-performance, multifunctional nanostructured catalysts

Highly aqueous soluble CaF2:Ce/Tb nanocrystals: effect of surface functionalization on structural, optical band gap, and photoluminescence properties.

Science.gov (United States)

Ansari, Anees A; Parchur, Abdul K; Kumar, Brijesh; Rai, S B

2016-12-01

The design of nanostructured materials with highly stable water-dispersion and luminescence efficiency is an important concern in nanotechnology and nanomedicine. In this paper, we described the synthesis and distinct surface modification on the morphological structure and optical (optical absorption, band gap energy, excitation, emission, decay time, etc.) properties of highly crystalline water-dispersible CaF 2 :Ce/Tb nanocrystals (core-nanocrystals). The epitaxial growth of inert CaF 2 and silica shell, respectively, on their surface forming as CaF 2 :Ce/Tb@CaF 2 (core/shell) and CaF 2 :Ce/Tb@CaF 2 @SiO 2 (core/shell/SiO 2 ) nanoarchitecture. X-ray diffraction and transmission electron microscope image shows that the nanocrystals were in irregular spherical phase, highly crystalline (~20 nm) with narrow size distribution. The core/shell nanocrystals confirm that the surface coating is responsible in the change of symmetrical nanostructure, which was determined from the band gap energy and luminescent properties. It was found that an inert inorganic shell formation effectively enhances the luminescence efficiency and silica shell makes the nanocrystals highly water-dispersible. In addition, Ce 3+ /Tb 3+ -co-doped CaF 2 nanocrystals show efficient energy transfer from Ce 3+ to Tb 3+ ion and strong green luminescence of Tb 3+ ion at 541 nm( 5 D 4 → 7 F 5 ). Luminescence decay curves of core and core/shell nanocrystals were fitted using mono and biexponential equations, and R 2 regression coefficient criteria were used to discriminate the goodness of the fitted model. The lifetime values for the core/shell nanocrystals are higher than core-nanocrystals. Considering the high stable water-dispersion and intensive luminescence emission in the visible region, these luminescent core/shell nanocrystals could be potential candidates for luminescent bio-imaging, optical bio-probe, displays, staining, and multianalyte optical sensing. A newly designed CaF 2 :Ce

Isolating and moving single atoms using silicon nanocrystals

Science.gov (United States)

Carroll, Malcolm S.

2010-09-07

A method is disclosed for isolating single atoms of an atomic species of interest by locating the atoms within silicon nanocrystals. This can be done by implanting, on the average, a single atom of the atomic species of interest into each nanocrystal, and then measuring an electrical charge distribution on the nanocrystals with scanning capacitance microscopy (SCM) or electrostatic force microscopy (EFM) to identify and select those nanocrystals having exactly one atom of the atomic species of interest therein. The nanocrystals with the single atom of the atomic species of interest therein can be sorted and moved using an atomic force microscope (AFM) tip. The method is useful for forming nanoscale electronic and optical devices including quantum computers and single-photon light sources.

Synthesis of Silicon Nanocrystals in Microplasma Reactor

Science.gov (United States)

Nozaki, Tomohiro; Sasaki, Kenji; Ogino, Tomohisa; Asahi, Daisuke; Okazaki, Ken

Nanocrystalline silicon particles with a grain size of at least less than 10 nm are widely recognized as one of the key materials in optoelectronic devices, electrodes of lithium battery, bio-medical labels. There is also important character that silicon is safe material to the environment and easily gets involved in existing silicon technologies. To date, several synthesis methods such as sputtering, laser ablation, and plasma enhanced chemical vapor deposition (PECVD) based on low-pressure silane chemistry (SiH4) have been developed for precise control of size and density distributions of silicon nanocrystals. We explore the possibility of microplasma technologies for the efficient production of mono-dispersed nanocrystalline silicon particles in a micrometer-scale, continuous-flow plasma reactor operated at atmospheric pressure. Mixtures of argon, hydrogen, and silicon tetrachloride were activated using very high frequency (VHF = 144 MHz) power source in a capillary glass tube with a volume of less than 1 μ-liter. Fundamental plasma parameters of VHF capacitively coupled microplasma were characterized by optical emission spectroscopy, showing electron density of approximately 1015 cm-3 and rotational temperature of 1500 K, respectively. Such high-density non-thermal reactive plasma has a capability of decomposing silicon tetrachloride into atomic silicon to produce supersaturated atomic silicon vapor, followed by gas phase nucleation via three-body collision. The particle synthesis in high-density plasma media is beneficial for promoting nucleation process. In addition, further growth of silicon nuclei was able to be favorably terminated in a short-residence time reactor. Micro Raman scattering spectrum showed that as-deposited particles were mostly amorphous silicon with small fraction of silicon nanocrystals. Transmission electron micrograph confirmed individual silicon nanocrystals of 3-15 nm size. Although those particles were not mono-dispersed, they were

Interfacial interactions between calcined hydroxyapatite nanocrystals and substrates.

Science.gov (United States)

Okada, Masahiro; Furukawa, Keiko; Serizawa, Takeshi; Yanagisawa, Yoshihiko; Tanaka, Hidekazu; Kawai, Tomoji; Furuzono, Tsutomu

2009-06-02

Interfacial interactions between calcined hydroxyapatite (HAp) nanocrystals and surface-modified substrates were investigated by measuring adsorption behavior and adhesion strength with a quartz crystal microbalance (QCM) and a contact-mode atomic force microscope (AFM), respectively. The goal was to develop better control of HAp-nanocrystal coatings on biomedical materials. HAp nanocrystals with rodlike or spherical morphology were prepared by a wet chemical process followed by calcination at 800 degrees C with an antisintering agent to prevent the formation of sintered polycrystals. The substrate surface was modified by chemical reaction with a low-molecular-weight compound, or graft polymerization with a functional monomer. QCM measurement showed that the rodlike HAp nanocrystals adsorbed preferentially onto anionic COOH-modified substrates compared to cationic NH2- or hydrophobic CH3-modified substrates. On the other hand, the spherical nanocrystals adsorbed onto NH2- and COOH-modified substrates, which indicates that the surface properties of the HAp nanocrystals determined their adsorption behavior. The adhesion strength, which was estimated from the force required to move the nanocrystal in contact-mode AFM, on a COOH-grafted substrate prepared by graft polymerization was almost 9 times larger than that on a COOH-modified substrate prepared by chemical reaction with a low-molecular-weight compound, indicating that the long-chain polymer grafted on the substrate mitigated the surface roughness mismatch between the nanocrystal and the substrate. The adhesion strength of the nanocrystal bonded covalently by the coupling reaction to a Si(OCH3)-grafted substrate prepared by graft polymerization was approximately 1.5 times larger than that when adsorbed on the COOH-grafted substrate.

Spectroscopic characterization of ligands on the surface of water dispersible NaGdF4:Ln3+ nanocrystals

International Nuclear Information System (INIS)

Cichos, J.; Karbowiak, M.

2012-01-01

For electronic or biomedical applications it is desirable to have ligand-free water-dispersible nanocrystals (NCs). The commonly used FTIR spectroscopy often provides a direct evidence for molecules on the surface. In some cases, however, the strong bands of solvent molecules may obscure the peaks of surface bounded ligands. We show that in this regard the emission spectroscopy may be used as a more reliable probing tool. The relevant information can be obtained from emission and excitation spectra, emission decay times as well as from analysis of relative efficiency of excitation energy transfer from Gd 3+ to Eu 3+ ions. Using these methods we tested samples obtained by various synthetic routes and indicated that only nitrosonium tetrafluoroborate (NOBF 4 ) removes successfully the organic ligands from the nanocrystals surface, yielding organic ligand-free NCs dispersible in aqueous solutions. The conclusions drawn from emission spectroscopy are useful for interpretation of results of FTIR, Raman and NMR studies. The detailed assignment of FTIR peaks for oleate-capped and oleate-free NCs is also provided. Finally, we point to the risk of drawing erroneous conclusions about colloidal stability of nanocrystals if refractive indexes of NCs and medium are similar.

Spectroscopic characterization of ligands on the surface of water dispersible NaGdF4:Ln3+ nanocrystals

Science.gov (United States)

Cichos, J.; Karbowiak, M.

2012-05-01

For electronic or biomedical applications it is desirable to have ligand-free water-dispersible nanocrystals (NCs). The commonly used FTIR spectroscopy often provides a direct evidence for molecules on the surface. In some cases, however, the strong bands of solvent molecules may obscure the peaks of surface bounded ligands. We show that in this regard the emission spectroscopy may be used as a more reliable probing tool. The relevant information can be obtained from emission and excitation spectra, emission decay times as well as from analysis of relative efficiency of excitation energy transfer from Gd3+ to Eu3+ ions. Using these methods we tested samples obtained by various synthetic routes and indicated that only nitrosonium tetrafluoroborate (NOBF4) removes successfully the organic ligands from the nanocrystals surface, yielding organic ligand-free NCs dispersible in aqueous solutions. The conclusions drawn from emission spectroscopy are useful for interpretation of results of FTIR, Raman and NMR studies. The detailed assignment of FTIR peaks for oleate-capped and oleate-free NCs is also provided. Finally, we point to the risk of drawing erroneous conclusions about colloidal stability of nanocrystals if refractive indexes of NCs and medium are similar.

Atomistic tight-binding computations of the structural and optical properties of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals

Science.gov (United States)

Sukkabot, Worasak

2018-05-01

A study of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals is carried out using atomistic tight-binding theory and the configuration interaction method to provide information for applications in bioimaging, biolabeling, display devices and near-infrared electronic instruments. The calculations yield the dependences of the internal and external passivated shells on the natural behaviours of CdTe/CdX (X=S and Se)/ZnS core/shell/shell nanocrystals. The reduction of the optical band gaps is observed with increasing numbers of monolayers in the external ZnS shell due to quantum confinement. Interestingly, the optical band gaps of CdTe/CdS/ZnS core/shell/shell nanocrystals are greater than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. In the presence of an external ZnS-coated shell, electron-hole wave function overlaps, oscillation strengths, ground-state exchange energies and Stokes shift are improved, whereas ground-state coulomb energies and fine-structure splitting are reduced. The oscillation strengths, Stokes shift and fine-structure splitting are reduced with the increase in external ZnS shell thickness. The oscillation strengths, Stokes shift and fine-structure splitting of CdTe/CdS/ZnS core/shell/shell nanocrystals are larger than those of CdTe/CdSe/ZnS core/shell/shell nanocrystals. Reduction of the atomistic electron-hole interactions is observed with increasing external ZnS shell size. The strong electron-hole interactions are more probed in CdTe/CdS/ZnS core/shell/shell nanocrystals than in CdTe/CdSe/ZnS core/shell/shell nanocrystals.

Photoluminescence behaviors of single CdSe/ZnS/TOPO nanocrystals: Adsorption effects of water molecules onto nanocrystal surfaces

International Nuclear Information System (INIS)

Oda, Masaru; Hasegawa, Atsushi; Iwami, Noriya; Nishiura, Ken; Ando, Naohisa; Nishiyama, Akira; Horiuchi, Hiromi; Tani, Toshiro

2007-01-01

We report here the distinctive modifications of photoluminescence (PL) behaviors in single CdSe/ZnS/TOPO nanocrystals depending on their environments. Long-time traces of PL intensity from single nanocrystals have been obtained in both vacuum and a wet nitrogen atmosphere. While all of the nanocrystals in both environments exhibit PL blinking behaviors, i.e. on-off intermittency of PL intensity, as usual, some of the nanocrystals in the wet nitrogen atmosphere show significant increase in duration time of on-events. As for the duration time of blinking off-events, it is for the moment associated with the occasional events of carrier capturing at trap sites on or near the nanocrystal surfaces. We propose a model in which adsorbed water molecules at the trap sites on the nanocrystal surfaces transform them under light irradiation, which eventually decreases the occurrence of the trapping events due to their inactivation. It in turn increases the PL on-times. In addition to the drastic modification of the blinking profile, we also found that in the PL time traces some kinds of undulated behaviors, i.e. continuous and rather low frequency fluctuation of PL intensity, appear during each on-event in vacuum while they disappear totally in the wet nitrogen atmosphere. These results are also described on the basis of the inactivation model of the trap sites introduced above

Hollow nanocrystals and method of making

Science.gov (United States)

Alivisatos, A Paul [Oakland, CA; Yin, Yadong [Moreno Valley, CA; Erdonmez, Can Kerem [Berkeley, CA

2011-07-05

Described herein are hollow nanocrystals having various shapes that can be produced by a simple chemical process. The hollow nanocrystals described herein may have a shell as thin as 0.5 nm and outside diameters that can be controlled by the process of making.

Cellulose nanocrystal: electronically conducting polymer nanocomposites for supercapacitors

OpenAIRE

Liew, Soon Yee

2012-01-01

This thesis describes the use of cellulose nanocrystals for the fabrication of porous nanocomposites with electronic conducting polymers for electrochemical supercapacitor applications. The exceptional strength and negatively charged surface functionalities on cellulose nanocrystals are utilised in these nanocomposites. The negatively charged surface functionalities on cellulose nanocrystals allow their simultaneous incorporation into electropolymerised, positively charged conducting polymer ...

Surface structure of alpha-Fe sub 2 O sub 3 nanocrystal observed by O K-edge X-ray absorption spectroscopy

CERN Document Server

Zhang, J; Ibrahim, K; Abbas, M I; Ju, X

2003-01-01

X-ray absorption near edge structure (XANES) spectra is used as a probe of surface structure of alpha-Fe sub 2 O sub 3 nanocrystal, prepared by sol-gel method. We present O K-edge XANES of alpha-Fe sub 2 O sub 3 in nanocrystal and bulk by total electron yield at the photoemission station of Beijing Synchrotron Radiation Facility. The spectrum of alpha-Fe sub 2 O sub 3 shows a splitting of the pre-edge structure, which is interpreted as two subsets of Fe 3d t sub 2 sub g and e sub g orbitals in oxygen octahedral (O sub h) crystal field, and is also sensitive to long-range order effects. However, no distinguishable splitting of the pre-edge peak of nanocrystal alpha-Fe sub 2 O sub 3 is observed. This suggests that there exists the distorted octahedral coordination around Fe sites and also the long-range disorder due to the surface as compared with bulk alpha-Fe sub 2 O sub 3.

Doping effect in Si nanocrystals

Science.gov (United States)

Li, Dongke; Xu, Jun; Zhang, Pei; Jiang, Yicheng; Chen, Kunji

2018-06-01

Intentional doping in semiconductors is a fundamental issue since it can control the conduction type and ability as well as modify the optical and electronic properties. To realize effective doping is the basis for developing semiconductor devices. However, by reducing the size of a semiconductor, like Si, to the nanometer scale, the doping effects become complicated due to the coupling between the quantum confinement effect and the surfaces and/or interfaces effect. In particular, by introducing phosphorus or boron impurities as dopants into material containing Si nanocrystals with a dot size of less than 10 nm, it exhibits different behaviors and influences on the physical properties from its bulk counterpart. Understanding the doping effects in Si nanocrystals is currently a challenge in order to further improve the performance of the next generation of nano-electronic and photonic devices. In this review, we present an overview of the latest theoretical studies and experimental results on dopant distributions and their effects on the electronic and optical properties of Si nanocrystals. In particular, the advanced characterization techniques on dopant distribution, the carrier transport process as well as the linear and nonlinear optical properties of doped Si nanocrystals, are systematically summarized.

Structure and transformation of tactoids in cellulose nanocrystal suspensions

Science.gov (United States)

Wang, Pei-Xi; Hamad, Wadood Y.; MacLachlan, Mark J.

2016-05-01

Cellulose nanocrystals obtained from natural sources are of great interest for many applications. In water, cellulose nanocrystals form a liquid crystalline phase whose hierarchical structure is retained in solid films after drying. Although tactoids, one of the most primitive components of liquid crystals, are thought to have a significant role in the evolution of this phase, they have evaded structural study of their internal organization. Here we report the capture of cellulose nanocrystal tactoids in a polymer matrix. This method allows us to visualize, for the first time, the arrangement of cellulose nanocrystals within individual tactoids by electron microscopy. Furthermore, we can follow the structural evolution of the liquid crystalline phase from tactoids to iridescent-layered films. Our insights into the early nucleation events of cellulose nanocrystals give important information about the growth of cholesteric liquid crystalline phases, especially for cellulose nanocrystals, and are crucial for preparing photonics-quality films.

Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus.

Science.gov (United States)

Kramer, Nicolaas J; Schramke, Katelyn S; Kortshagen, Uwe R

2015-08-12

Degenerately doped silicon nanocrystals are appealing plasmonic materials due to silicon's low cost and low toxicity. While surface plasmonic resonances of boron-doped and phosphorus-doped silicon nanocrystals were recently observed, there currently is poor understanding of the effect of surface conditions on their plasmonic behavior. Here, we demonstrate that phosphorus-doped silicon nanocrystals exhibit a plasmon resonance immediately after their synthesis but may lose their plasmonic response with oxidation. In contrast, boron-doped nanocrystals initially do not exhibit plasmonic response but become plasmonically active through postsynthesis oxidation or annealing. We interpret these results in terms of substitutional doping being the dominant doping mechanism for phosphorus-doped silicon nanocrystals, with oxidation-induced defects trapping free electrons. The behavior of boron-doped silicon nanocrystals is more consistent with a strong contribution of surface doping. Importantly, boron-doped silicon nanocrystals exhibit air-stable plasmonic behavior over periods of more than a year.

Synthesis and preservation of graphene-supported uranium dioxide nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Ma, Hanyu [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States); Wang, Haitao [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States); Department of Civil, Environmental, and Construction Engineering, Texas Tech University, 911 Boston Ave., Lubbock, TX 79409 (United States); Burns, Peter C. [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States); Department of Chemistry and Biochemistry, University of Notre Dame, 251 Nieuwland Science Hall, Notre Dame, IN 46556 (United States); McNamara, Bruce K.; Buck, Edgar C. [Nuclear Chemistry & Engineering Group, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, WA 99352 (United States); Na, Chongzheng, E-mail: chongzheng.na@gmail.com [Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, 156 Fitzpatrick Hall, Notre Dame, IN 46556 (United States); Department of Civil, Environmental, and Construction Engineering, Texas Tech University, 911 Boston Ave., Lubbock, TX 79409 (United States)

2016-07-15

Graphene-supported uranium dioxide (UO{sub 2}) nanocrystals are potentially important fuel materials. Here, we investigate the possibility of synthesizing graphene-supported UO{sub 2} nanocrystals in polar ethylene glycol compounds by the polyol reduction of uranyl acetylacetone under boiling reflux, thereby enabling the use of an inexpensive graphene precursor graphene oxide into a one-pot process. We show that triethylene glycol is the most suitable solvent with an appropriate reduction potential for producing nanometer-sized UO{sub 2} crystals compared to monoethylene glycol, diethylene glycol, and polyethylene glycol. Graphene-supported UO{sub 2} nanocrystals synthesized with triethylene glycol show evidence of heteroepitaxy, which can be beneficial for facilitating heat transfer in nuclear fuel particles. Furthermore, we show that graphene-supported UO{sub 2} nanocrystals synthesized by polyol reduction can be readily stored in alcohols, impeding oxidation from the prevalent oxygen in air. Together, these methods provide a facile approach for preparing and storing graphene-supported UO{sub 2} nanocrystals for further investigation and development under ambient conditions. - Highlights: • UO{sub 2} nanocrystals are synthesized using polyol reduction method. • Triethylene glycol is the best reducing agent for nano-sized UO{sub 2} crystals. • UO{sub 2} nanocrystals grow on graphene through heteroepitaxy. • Graphene-supported UO{sub 2} nanocrystals can be stored in alcohols to prevent oxidation.

Structural and thermal characterization of polyvinylalcohol grafted SiC nanocrystals

DEFF Research Database (Denmark)

Saini, Isha; Sharma, Annu; Dhiman, Rajnish

2017-01-01

introduced in the characteristic TO and LO mode of vibration of SiC nanocrystals after grafting procedure.XRD analysis confirmed that the grafting procedure did not alter the crystalline geometry of SiC nanocrystals. TEM and SEM images further support the FTIR and Raman spectroscopic results and confirm...... of semiconducting SiC nanocrystals using a novel method. FTIR spectroscopy reveals the introduction of new peaks corresponding to various functional groups of PVA alongwith the presence of characteristic Si-C vibrational peak in the spectra of grafted SiC nanocrystals. Raman spectra depict the presence of changes...... the presence of PVA layer around SiC nanocrystals. Thermal degradation behavior of PVA-g-SiC nanocrystals has been studied using TGA analysis....

Self-aggregation of magnetic semiconductor EuS nanocrystals

International Nuclear Information System (INIS)

Tanaka, Atsushi; Hasegawa, Yasuchika; Kamikubo, Hironari; Kataoka, Mikio; Kawai, Tsuyoshi

2009-01-01

Controlled formation of aggregates having organized structure of cube-shaped EuS nanocrystals is reported. The EuS aggregates in liquid media (methanol) were obtained by means of van der Waals interaction between EuS nanocrystals. The packing structure of the EuS aggregates is characterized with transmission electron microscopy (TEM) and small angle X-ray scattering measurements (SAXS). TEM image indicates the EuS nanocrystals form self-aggregated 2D orthogonal lattice structure. The diffraction peak of (111) of SAXS profile shows that the cube-shaped EuS form 3D cubic superlattice. We successfully demonstrated that the aggregates of cube-shaped EuS nanocrystals formed cubic stacking structure.

Microscopic and macroscopic characterization of the charging effects in SiC/Si nanocrystals/SiC sandwiched structures

International Nuclear Information System (INIS)

Xu, Jie; Xu, Jun; Wang, Yuefei; Cao, Yunqing; Li, Wei; Yu, Linwei; Chen, Kunji

2014-01-01

Microscopic charge injection into the SiC/Si nanocrystals/SiC sandwiched structures through a biased conductive AFM tip is subsequently characterized by both electrostatic force microscopy and Kelvin probe force microscopy (KPFM). The charge injection and retention characteristics are found to be affected by not only the band offset at the Si nanocrystals/SiC interface but also the doping type of the Si substrate. On the other hand, capacitance–voltage (C–V) measurements investigate the macroscopic charging effect of the sandwiched structures with a thicker SiC capping layer, where the charges are injected from the Si substrates. The calculated macroscopic charging density is 3–4 times that of the microscopic one, and the possible reason is the underestimation of the microscopic charging density caused by the averaging effect and detection delay in the KPFM measurements. (paper)

Structure/Processing Relationships of Highly Ordered Lead Salt Nanocrystal Superlattices

KAUST Repository

Hanrath, Tobias; Choi, Joshua J.; Smilgies, Detlef-M.

2009-01-01

We investigated the influence of processing conditions, nanocrystal/substrate interactions and solvent evaporation rate on the ordering of strongly interacting nanocrystals by synergistically combining electron microscopy and synchrotron-based small-angle X-ray scattering analysis. Spin-cast PbSe nanocrystal films exhibited submicrometer-sized supracrystals with face-centered cubic symmetry and (001)s planes aligned parallel to the substrate. The ordering of drop-cast lead salt nanocrystal films was sensitive to the nature of the substrate and solvent evaporation dynamics. Nanocrystal films drop-cast on rough indium tin oxide substrates were polycrystalline with small grain size and low degree of orientation with respect to the substrate, whereas films drop-cast on flat Si substrates formed highly ordered face-centered cubic supracrystals with close-packed (111)s planes parallel to the substrate. The spatial coherence of nanocrystal films drop-cast in the presence of saturated solvent vapor was significantly improved compared to films drop-cast in a dry environment. Solvent vapor annealing was demonstrated as a postdeposition technique to modify the ordering of nanocrystals in the thin film. Octane vapor significantly improved the long-range order and degree of orientation of initially disordered or polycrystalline nanocrystal assemblies. Exposure to 1,2-ethanedithiol vapor caused partial displacement of surface bound oleic acid ligands and drastically degraded the degree of order in the nanocrystal assembly. © 2009 American Chemical Society.

Structure/Processing Relationships of Highly Ordered Lead Salt Nanocrystal Superlattices

KAUST Repository

Hanrath, Tobias

2009-10-27

We investigated the influence of processing conditions, nanocrystal/substrate interactions and solvent evaporation rate on the ordering of strongly interacting nanocrystals by synergistically combining electron microscopy and synchrotron-based small-angle X-ray scattering analysis. Spin-cast PbSe nanocrystal films exhibited submicrometer-sized supracrystals with face-centered cubic symmetry and (001)s planes aligned parallel to the substrate. The ordering of drop-cast lead salt nanocrystal films was sensitive to the nature of the substrate and solvent evaporation dynamics. Nanocrystal films drop-cast on rough indium tin oxide substrates were polycrystalline with small grain size and low degree of orientation with respect to the substrate, whereas films drop-cast on flat Si substrates formed highly ordered face-centered cubic supracrystals with close-packed (111)s planes parallel to the substrate. The spatial coherence of nanocrystal films drop-cast in the presence of saturated solvent vapor was significantly improved compared to films drop-cast in a dry environment. Solvent vapor annealing was demonstrated as a postdeposition technique to modify the ordering of nanocrystals in the thin film. Octane vapor significantly improved the long-range order and degree of orientation of initially disordered or polycrystalline nanocrystal assemblies. Exposure to 1,2-ethanedithiol vapor caused partial displacement of surface bound oleic acid ligands and drastically degraded the degree of order in the nanocrystal assembly. © 2009 American Chemical Society.

Synthesis and Characterization of Colloidal Metal and Photovoltaic Semiconductor Nanocrystals

KAUST Repository

Abulikemu, Mutalifu

2014-11-05

Metal and semiconducting nanocrystals have received a great deal of attention from fundamental scientists and application-oriented researchers due to their physical and chemical properties, which differ from those of bulk materials. Nanocrystals are essential building blocks in the development of nanostructured devices for energy conversion. Colloidal metals and metal chalcogenides have been developed for use as nanocrystal inks to produce efficient solar cells with lower costs. All high-performing photovoltaic nanocrystals contain toxic elements, such as Pb, or scarce elements, such as In; thus, the production of solution-processable nanocrystals from earth-abundant materials using environmentally benign synthesis and processing methods has become a major challenge for the inorganic semiconductor-based solar field. This dissertation, divided into two parts, addresses several aspects of these emerging challenges. The first portion of the thesis describes the synthesis and characterization of nanocrystals of antimony sulfide, which is composed of non-scarce and non-toxic elements, and examines their performance in photovoltaic devices. The effect of various synthetic parameters on the final morphology is explored. The structural, optical and morphological properties of the nanocrystals were investigated, and Sb2S3 nanocrystal-based solid-state semiconductor-sensitized solar cells were fabricated using different deposition processes. We achieved promising power conversion efficiencies of 1.48%. The second part of the thesis demonstrates a novel method for the in situ synthesis and patterning of nanocrystals via reactive inkjet printing. The use of low-cost manufacturing approaches for the synthesis of nanocrystals is critical for many applications, including photonics and electronics. In this work, a simple, low-cost method for the synthesis of nanocrystals with minimum size variation and waste using reactive inkjet printing is introduced. As a proof of concept, the

Formation of noble metal nanocrystals in the presence of biomolecules

Science.gov (United States)

Burt, Justin Lockheart

One of the most promising, yet least studied routes for producing biocompatible nanostructures involves synthesis in the presence of biomolecules. I hypothesized that globular proteins could provide a suitable framework to regulate the formation of noble metal nanocrystals. As proof of concept, I designed two novel synthesis protocols utilizing bovine serum albumin (BSA) protein to regulate the formation of gold nanocrystals. In the first case, the standard protocol for polyol reduction was modified by replacing ethylene glycol with glycerin, replacing synthetic polymers with BSA as protecting agent, and decreasing the reaction temperature. In the second case, the Brust-Schiffrin two-phase reduction was modified by replacing alkylthiols with BSA as protecting agent, which facilitated a strictly aqueous phase synthesis. Due to superior product yield and rapid reduction at room temperature, the aqueous protocol became the foundation for subsequent studies. I extended this approach to produce well-dispersed ˜2nm silver, gold, and platinum nanocrystals. Having demonstrated the feasibility of BSA-functionalized nanocrystals, some potential uses were explored. BSA-functionalized silver nanocrystals were employed in a broader study on the interaction of silver nanocrystals with HIV. BSA-functionalized gold nanocrystals were utilized for in vivo dosage of a contrast enhancing agent to bacteria. BSA-functionalized platinum nanocrystals were studied as hydrogenation catalysts. Since many intriguing uses for protein-functionalized nanocrystals involve incorporation into biosystems, I sought to enhance biocompatibility by using ascorbic acid as reducing agent. Initial experiments revealed elongated and branched nanocrystals. Such structures were not observed in previous synthesis protocols with BSA, so I hypothesized ascorbic acid was driving their formation. To test my assertion, I reduced ionic gold in an aqueous solution of ascorbic acid, thereby discovering a new method

Semiconductor nanocrystals formed in SiO2 by ion implantation

International Nuclear Information System (INIS)

Zhu, J.G.; White, C.W.; Budai, J.D.; Withrow, S.P.; Chen, Y.

1994-11-01

Nanocrystals of group IV (Si, Ge and SiGe), III-V (GaAs), and II-VI (CdSe) semiconductor materials have been fabricated inside SiO 2 by ion implantation and subsequent thermal annealing. The microstructure of these nanocrystalline semiconductor materials has been studied by transmission electron microscopy (TEM). The nanocrystals form in near-spherical shape with random crystal orientations in amorphous SiO 2 . Extensive studies on the nanocrystal size distributions have been carried out for the Ge nanocrystals by changing the implantation doses and the annealing temperatures. Remarkable roughening of the nanocrystals occurs when the annealing temperature is raised over the melting temperature of the implanted semiconductor material. Strong red photoluminescence peaked around 1.67 eV has been achieved in samples with Si nanocrystals in SiO 2

Simultaneous control of nanocrystal size and nanocrystal ...

Indian Academy of Sciences (India)

applications such as a photo-sensor [11]. Thus, it is desirable to have, not only a control on the size of the nanocrystals, but also an independent tunability of the ... 1-thioglycerol) in 25 ml methanol under inert atmosphere. 10 ml of 0.2 M sodium sulfide solution is then added to the reaction mixture dropwise and the reaction.

Cellulose nanocrystals with tunable surface charge for nanomedicine

Science.gov (United States)

Hosseinidoust, Zeinab; Alam, Md Nur; Sim, Goeun; Tufenkji, Nathalie; van de Ven, Theo G. M.

2015-10-01

Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For applications in imaging and drug delivery, surface charge is one of the most important factors affecting the performance of nanocarriers. However, current methods of preparation offer little flexibility for controlling the surface charge of cellulose nanocrystals, leading to compromised colloidal stability under physiological conditions. We report a synthesis method that results in nanocrystals with remarkably high carboxyl content (6.6 mmol g-1) and offers continuous control over surface charge without any adjustment to the reaction conditions. Six fractions of nanocrystals with various surface carboxyl contents were synthesized from a single sample of softwood pulp with carboxyl contents varying from 6.6 to 1.7 mmol g-1 and were fully characterized. The proposed method resulted in highly stable colloidal nanocrystals that did not aggregate when exposed to high salt concentrations or serum-containing media. Interactions of these fractions with four different tissue cell lines were investigated over a wide range of concentrations (50-300 μg mL-1). Darkfield hyperspectral imaging and confocal microscopy confirmed the uptake of nanocrystals by selected cell lines without any evidence of membrane damage or change in cell density; however a charge-dependent decrease in mitochondrial activity was observed for charge contents higher than 3.9 mmol g-1. A high surface carboxyl content allowed for facile conjugation of fluorophores to the nanocrystals without compromising colloidal stability. The cellular uptake of fluoresceinamine-conjugated nanocrystals exhibited a time-dose dependent relationship and increased significantly with doubling of the surface charge.Crystalline nanoparticles of cellulose exhibit attractive properties as nanoscale carriers for bioactive molecules in nanobiotechnology and nanomedicine. For

Microscopic theory of cation exchange in CdSe nanocrystals.

Science.gov (United States)

Ott, Florian D; Spiegel, Leo L; Norris, David J; Erwin, Steven C

2014-10-10

Although poorly understood, cation-exchange reactions are increasingly used to dope or transform colloidal semiconductor nanocrystals (quantum dots). We use density-functional theory and kinetic Monte Carlo simulations to develop a microscopic theory that explains structural, optical, and electronic changes observed experimentally in Ag-cation-exchanged CdSe nanocrystals. We find that Coulomb interactions, both between ionized impurities and with the polarized nanocrystal surface, play a key role in cation exchange. Our theory also resolves several experimental puzzles related to photoluminescence and electrical behavior in CdSe nanocrystals doped with Ag.

Aqueous synthesis and characterization of bovine hemoglobin-conjugated cadmium sulfide nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Yang, Guangrui [Institute of Environmental and Municipal Engineering, North China University of Water Conservancy and Electric Power, Zhengzhou 450011 (China); Qin, Dezhi, E-mail: dezhiqin@163.com [College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan 467000 (China); Du, Xian; Zhang, Li; Zhao, Ganqing; Zhang, Qiuxia; Wu, Jiulin [College of Chemistry and Chemical Engineering, Pingdingshan University, Pingdingshan 467000 (China)

2014-08-01

Highlights: • CdS nanocrystals were synthesized by biomimetic method in bovine hemoglobin (BHb) solution. • The study of the interaction between Cd{sup 2+}/CdS and BHb. • The optical properties of BHb-conjugated CdS nanocrystals. • The synthesis process of BHb-conjugated CdS nanocrystals is facile, effective and environment friendly. • The change of secondary structure of BHb after binding to CdS nanocrystals. - Abstract: Cadmium sulfide (CdS) nanocrystals with average diameter about 5.5 nm were synthesized in aqueous solution of bovine hemoglobin (BHb) via simple biomimetic method. Powder X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED) characterizations were used to determine the structure and morphology of CdS nanocrystals. It was revealed that amount of BHb, chelating of Cd{sup 2+} to BHb and reaction temperature were key factors in controlling shape and dispersion of CdS nanocrystals. The binding sites of BHb to CdS nanocrystals and the change of secondary structure of protein have been identified by Fourier transform infrared (FT-IR) and circular dichroism (CD) spectroscopy. It was found that conjugating of BHb with Cd{sup 2+} and CdS could protect nanocrystals from agglomerating. Moreover, the thermostability of BHb enhanced after conjugating with CdS nanocrystals. The interaction mechanism of BHb with Cd{sup 2+}/CdS was also proposed. The quantum-confined effect of CdS nanocrystals was confirmed by ultraviolet–visible (UV–vis) spectrum. The nanocrystals exhibited a well-defined photoluminescence (PL) emission feature at about 510 nm with narrow full width at half maximum (FWHM)

Silicon nanocrystal films for electronic applications

Energy Technology Data Exchange (ETDEWEB)

Lechner, Robert W.

2009-02-06

Whether nanoparticles of silicon are really suited for such applications, whether layers fabricated from this exhibit semiconducting properties, whether they can be doped, and whether for instance via the doping the conductivity can be tuned, was studied in the present thesis. Starting material for this were on the one hand spherical silicon nanocrystals with a sharp size distribution and mean diameters in the range from 4-50 nm. Furthermore silicon particle were available, which are with 50-500 nm distinctly larger and exhibit a broad distribution of the mean size and a polycrystalline fine structure with strongly bifurcated external morphology. The small conductivities and tje low mobility values of the charge carriers in the layers of silicon nanocrystals suggest to apply suited thermal after-treatment procedures. So was found that the aluminium-induced layer exchange (ALILE) also can be transferred to the porous layers of nanocrystals. With the deuteron passivation a method was available to change the charge-carrier concentration in the polycrystalline layers. Additionally to ALILE laser crystallization as alternative after-treatment procedure of the nanocrystal layers was studied.

Micromagnetic study of single-domain FePt nanocrystals overcoated with silica

International Nuclear Information System (INIS)

Hyun, Changbae; Lee, Doh C; Korgel, Brian A; Lozanne, Alex de

2007-01-01

Chemically-synthesized FePt nanocrystals must be annealed at a high temperature (>550 deg. C) to induce the hard ferromagnetic L 1 0 phase. Unfortunately, the organic stabilizer covering these nanocrystals degrades at these temperatures and the nanocrystals sinter, resulting in the loss of control over nanocrystal size and separation in the film. We have developed a silica overcoating strategy to prevent nanocrystal sintering. In this study, 6 nm diameter FePt nanocrystals were coated with 17 nm thick shells of silica using an inverse micelle process. Magnetization measurements of the annealed FePt-SiO 2 nanocrystals indicate ferromagnetism with a high coercivity at room temperature. Magnetic force microscopy (MFM) results show that the film composed of nanocrystals behaves as a dipole after magnetization by an 8 T external field. The individual nanocrystals are modelled as single-domain particles with random crystallographic orientations. We propose that the interparticle magnetic dipole interaction is weaker than the magnetocrystalline energy in the remanent state, leading to an unusual material with no magnetic anisotropy and no domains. Films of these nanoparticles are promising candidates for magnetic media with a data storage density of ∼Tb/in 2

TiO2 Nanoparticles as a Soft X-ray Molecular Probe

Energy Technology Data Exchange (ETDEWEB)

Larabell, Carolyn; Ashcroft, Jared M.; Gu, Weiwei; Zhang, Tierui; Hughes, Steven M.; Hartman, Keith B.; Hofmann, Cristina; Kanaras, Antonios G.; Kilcoyne, David A.; Le Gros, Mark; Yin, Yadong; Alivisatos, A. Paul; Larabell, Carolyn A.

2007-06-30

With the emergence of soft x-ray techniques for imaging cells, there is a pressing need to develop protein localization probes that can be unambiguously identified within the region of x-ray spectrum used for imaging. TiO2 nanocrystal colloids, which have a strong absorption cross-section within the "water-window" region of x-rays, areideally suited as soft x-ray microscopy probes. To demonstrate their efficacy, TiO2-streptavidin nanoconjugates were prepared and subsequently labeled microtubules polymerized from biotinylated tubulin. The microtubules were imaged using scanning transmission x-ray microscopy (STXM), and the TiO2 nanoparticle tags were specifically identified using x-ray absorption near edge spectroscopy (XANES). These experiments demonstrate that TiO2 nanoparticles are potential probes for protein localization analyses using soft x-ray microscopy.

L-serine capped ZnS:Mn nanocrystals for plant cell biological studies and as a growth enhancing agent for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae)

Science.gov (United States)

Augustine, M. Sajimol; Mathew, Lizzy; Alex, Roselin; Deepa, G. D.; Jayalekshmi, S.

2014-01-01

In the present work, the prospects of ZnS:Mn nanocrystals capped with L- serine, a bio-compatible amino acid, synthesized by wet chemical route, as efficient fluorescent probes for plant cell biological studies have been investigated. The present synthesis route using bio-compatible material is a low cost and easy to control method. The colloidal stability of the capped nano crystals is very good as they remain stable without settling down for long time. It is observed that L- serine significantly modifies the structural and optical characteristics of the ZnS:Mn nanocrystals and hence is suitable as a bio-compatible capping agent. The structural properties of L- serine capped nanocrystals were investigated by XRD technique. The size of the L- serine capped ZnS:Mn nanocrystals is found to be around 2 nm . The optical characterization of the nanocrystals was carried out on the basis of photoluminescence (PL) spectroscopic studies. The intense photoluminescence emission observed around 597nm for L-serine capped ZnS:Mn offers high prospects of applications in bio-imaging fields. The unique optical properties of nanoparticles make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations. In the present study, L-serine capped ZnS:Mn nanocrystals were used as a staining dye in fluorescent microscope for observing cell division, cell structure etc. These nanocrystals were also incorporated into the culture media along with the normal auxin- cytokinin hormone combinations in Murashige and Skoog (MS) medium for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae), an Ayurvedic medicine. The results suggest that L-serine capped ZnS:Mn nanocrystals can act as efficient enhancers towards quick callusing and shoot proliferation.

L-serine capped ZnS:Mn nanocrystals for plant cell biological studies and as a growth enhancing agent for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae)

International Nuclear Information System (INIS)

Augustine, M. Sajimol; Mathew, Lizzy; Alex, Roselin; Deepa, G. D.; Jayalekshmi, S.

2014-01-01

In the present work, the prospects of ZnS:Mn nanocrystals capped with L- serine, a bio-compatible amino acid, synthesized by wet chemical route, as efficient fluorescent probes for plant cell biological studies have been investigated. The present synthesis route using bio-compatible material is a low cost and easy to control method. The colloidal stability of the capped nano crystals is very good as they remain stable without settling down for long time. It is observed that L- serine significantly modifies the structural and optical characteristics of the ZnS:Mn nanocrystals and hence is suitable as a bio-compatible capping agent. The structural properties of L- serine capped nanocrystals were investigated by XRD technique. The size of the L- serine capped ZnS:Mn nanocrystals is found to be around 2 nm . The optical characterization of the nanocrystals was carried out on the basis of photoluminescence (PL) spectroscopic studies. The intense photoluminescence emission observed around 597nm for L-serine capped ZnS:Mn offers high prospects of applications in bio-imaging fields. The unique optical properties of nanoparticles make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations. In the present study, L-serine capped ZnS:Mn nanocrystals were used as a staining dye in fluorescent microscope for observing cell division, cell structure etc. These nanocrystals were also incorporated into the culture media along with the normal auxin- cytokinin hormone combinations in Murashige and Skoog (MS) medium for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae), an Ayurvedic medicine. The results suggest that L-serine capped ZnS:Mn nanocrystals can act as efficient enhancers towards quick callusing and shoot proliferation

L-serine capped ZnS:Mn nanocrystals for plant cell biological studies and as a growth enhancing agent for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae)

Energy Technology Data Exchange (ETDEWEB)

Augustine, M. Sajimol, E-mail: sajimollazar@gmail.com [Department of Physics, St.Teresa' s College , Kochi-11, Kerala (India); Mathew, Lizzy [Department of Botany, St.Teresa' s College , Kochi-11, Kerala (India); Alex, Roselin [Department of Biotechnology, Cochin University of Science and Technology, Kochi-22 (India); Deepa, G. D. [NCAAH, Cochin University of Science and Technology,Kochi-22, Kerala (India); Jayalekshmi, S., E-mail: jayalekshmi@cusat.ac.in [Department of Physics, Cochin University of Science and Technology, Kochi-22 (India)

2014-01-28

In the present work, the prospects of ZnS:Mn nanocrystals capped with L- serine, a bio-compatible amino acid, synthesized by wet chemical route, as efficient fluorescent probes for plant cell biological studies have been investigated. The present synthesis route using bio-compatible material is a low cost and easy to control method. The colloidal stability of the capped nano crystals is very good as they remain stable without settling down for long time. It is observed that L- serine significantly modifies the structural and optical characteristics of the ZnS:Mn nanocrystals and hence is suitable as a bio-compatible capping agent. The structural properties of L- serine capped nanocrystals were investigated by XRD technique. The size of the L- serine capped ZnS:Mn nanocrystals is found to be around 2 nm . The optical characterization of the nanocrystals was carried out on the basis of photoluminescence (PL) spectroscopic studies. The intense photoluminescence emission observed around 597nm for L-serine capped ZnS:Mn offers high prospects of applications in bio-imaging fields. The unique optical properties of nanoparticles make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations. In the present study, L-serine capped ZnS:Mn nanocrystals were used as a staining dye in fluorescent microscope for observing cell division, cell structure etc. These nanocrystals were also incorporated into the culture media along with the normal auxin- cytokinin hormone combinations in Murashige and Skoog (MS) medium for micropropagation of Bacopa monnieri Linn. (Brahmi:Scrophulariaceae), an Ayurvedic medicine. The results suggest that L-serine capped ZnS:Mn nanocrystals can act as efficient enhancers towards quick callusing and shoot proliferation.

Biomimetic synthesis of noble metal nanocrystals

Science.gov (United States)

Chiu, Chin-Yi

At the nanometer scale, the physical and chemical properties of materials heavily depend on their sizes and shapes. This fact has triggered considerable efforts in developing controllable nanomaterial synthesis. The controlled growth of colloidal nanocrystal is a kinetic process, in which high-energy facets grow faster and then vanish, leading to a nanocrystal enclosed by low-energy facets. Identifying a surfactant that can selectively bind to a particular crystal facet and thus lower its surface energy, is critical and challenging in shape controlled synthesis of nanocrystals. Biomolecules exhibiting exquisite molecular recognition properties can be exploited to precisely engineer nanostructured materials. In the first part of my thesis, we employed the phage display technique to select a specific multifunctional peptide sequence which can bind on Pd surface and mediate Pd crystal nucleation and growth, achieving size controlled synthesis of Pd nanocrystals in aqueous solution. We further demonstrated a rational biomimetic approach to the predictable synthesis of nanocrystals enclosed by a particular facet in the case of Pt. Specifically, Pt {100} and Pt {111} facet-specific peptides were identified and used to synthesize Pt nanocubes and Pt nano-tetrahedrons, respectively. The mechanistic studies of Pt {111} facet-specific peptide had led us to study the facet-selective adsorption of aromatic molecules on noble metal surfaces. The discoveries had achieved the development of design strategies to select facet-selective molecules which can synthesize nanocrystals with expected shapes in both Pt and Pd system. At last, we exploited Pt facet-specific peptides and controlled the molecular interaction to produce one- and three- dimensional nanostructures composed of anisotropic nanoparticles in synthetic conditions without supramolecular pre-organization, demonstrating the full potential of biomolecules in mediating material formation process. My research on biomimetic

Charge transfer between acenes and PbS nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Dissanayake, D M N M [Solid State Electronics Laboratory, University of Michigan, Ann Arbor, MI 48109-2122 (United States); Hatton, R A [Department of Chemistry, University of Warwick, Coventry CV4 7AL (United Kingdom); Lutz, T [Departments of Chemistry and Physics, Imperial College, London SW7 2AY (United Kingdom); Curry, R J; Silva, S R P [Advanced Technology Institute, University of Surrey, Guildford GU2 7XH (United Kingdom)], E-mail: ndissa@umich.edu

2009-05-13

Organic-inorganic hybrid heterojunctions have potential as the basis for future photovoltaic devices. Herein, we report the results of investigations exploring the possibility of using pentacene and tetracene as photoelectron donors in conjunction with PbS nanocrystals (PbS-NCs). Photoinduced charge transfer was probed using external quantum efficiency measurements on acene:PbS-NC hybrid photovoltaic devices in conjunction with photoluminescence studies of the corresponding bilayer films. It is shown that photoelectron transfer from pentacene to the PbS-NCs is inefficient as compared to that between tetracene and PbS-NCs. The latter case can be rationalized in terms of the energy level alignment at the heterojunction assuming a common vacuum level. However, in the case of pentacene:PbS-NC junctions an interfacial energy level shift must be considered in order to explain the observations.

Size- and shape-dependent surface thermodynamic properties of nanocrystals

Science.gov (United States)

Fu, Qingshan; Xue, Yongqiang; Cui, Zixiang

2018-05-01

As the fundamental properties, the surface thermodynamic properties of nanocrystals play a key role in the physical and chemical changes. However, it remains ambiguous about the quantitative influence regularities of size and shape on the surface thermodynamic properties of nanocrystals. Thus by introducing interface variables into the Gibbs energy and combining Young-Laplace equation, relations between the surface thermodynamic properties (surface Gibbs energy, surface enthalpy, surface entropy, surface energy and surface heat capacity), respectively, and size of nanocrystals with different shapes were derived. Theoretical estimations of the orders of the surface thermodynamic properties of nanocrystals agree with available experimental values. Calculated results of the surface thermodynamic properties of Au, Bi and Al nanocrystals suggest that when r > 10 nm, the surface thermodynamic properties linearly vary with the reciprocal of particle size, and when r < 10 nm, the effect of particle size on the surface thermodynamic properties becomes greater and deviates from linear variation. For nanocrystals with identical equivalent diameter, the more the shape deviates from sphere, the larger the surface thermodynamic properties (absolute value) are.

Cellulose nanocrystals from acacia bark-Influence of solvent extraction.

Science.gov (United States)

Taflick, Ticiane; Schwendler, Luana A; Rosa, Simone M L; Bica, Clara I D; Nachtigall, Sônia M B

2017-08-01

The isolation of cellulose nanocrystals from different lignocellulosic materials has shown increased interest in academic and technological research. These materials have excellent mechanical properties and can be used as nanofillers for polymer composites as well as transparent films for various applications. In this work, cellulose isolation was performed following an environmental friendly procedure without chlorine. Cellulose nanocrystals were isolated from the exhausted acacia bark (after the industrial process of extracting tannin) with the objective of evaluating the effect of the solvent extraction steps on the characteristics of cellulose and cellulose nanocrystals. It was also assessed the effect of acid hydrolysis time on the thermal stability, morphology and size of the nanocrystals, through TGA, TEM and light scattering analyses. It was concluded that the extraction step with solvents was important in the isolation of cellulose, but irrelevant in the isolation of cellulose nanocrystals. Light scattering experiments indicated that 30min of hydrolysis was long enough for the isolation of cellulose nanocrystals. Copyright © 2017 Elsevier B.V. All rights reserved.

Depleted Nanocrystal-Oxide Heterojunctions for High-Sensitivity Infrared Detection

Science.gov (United States)

2015-08-28

Approved for Public Release; Distribution Unlimited Final Report: 4.3 Electronic Sensing - Depleted Nanocrystal- Oxide Heterojunctions for High...reviewed journals: Final Report: 4.3 Electronic Sensing - Depleted Nanocrystal- Oxide Heterojunctions for High-Sensitivity Infrared Detection Report Title...PERCENT_SUPPORTEDNAME FTE Equivalent: Total Number: 1 1 Final Progress Report Project title: Depleted Nanocrystal- Oxide Heterojunctions for High

Nanocrystals for enhancement of oral bioavailability of poorly water-soluble drugs

Directory of Open Access Journals (Sweden)

Varaporn Buraphacheep Junyaprasert

2015-02-01

Full Text Available Nanocrystals, a carrier-free colloidal delivery system in nano-sized range, is an interesting approach for poorly soluble drugs. Nanocrystals provide special features including enhancement of saturation solubility, dissolution velocity and adhesiveness to surface/cell membranes. Several strategies are applied for nanocrystals production including precipitation, milling, high pressure homogenization and combination methods such as NanoEdge™, SmartCrystal and Precipitation-lyophilization-homogenization (PLH technology. For oral administration, many publications reported useful advantages of nanocrystals to improve in vivo performances i.e. pharmacokinetics, pharmacodynamics, safety and targeted delivery which were discussed in this review. Additionally, transformation of nanocrystals to final formulations and future trends of nanocrystals were also described.

Synthesis of compositionally controllable Cu{sub 2}(Sn{sub 1−x}Ge{sub x})S{sub 3} nanocrystals with tunable band gaps

Energy Technology Data Exchange (ETDEWEB)

Liang, Qingshuang, E-mail: lqs671@163.com [Jilin University, State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry (China)

2016-06-15

In this work, we show that compositionally controlled Cu{sub 2}(Sn{sub 1–x}Ge{sub x})S{sub 3} nanocrystals can be successfully synthesized by the hot-injection method through careful tuning the Ge/(Sn+Ge) precursor ratio. The band gaps of the resultant nanocrystals are demonstrated to be linearly tuned from 1.45 to 2.33 eV by adjusting the composition parameter x of the Ge/(Sn+Ge) ratio from 0.0 to 1.0. The crystalline structures of the resultant NCs have been studied by the X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), select area electron diffraction (SAED), and Raman spectroscopy. A ligand exchange procedure is further performed to replace the native ligands on the surface of the NCs with sulfur ions. The photoresponsive behavior indicates the potential use of as-prepared Cu{sub 2}(Sn{sub 1–x}Ge{sub x})S{sub 3} nanocrystals in solar energy conversion systems. The synthesis of compositionally controlled Cu{sub 2}(Sn{sub 1–x}Ge{sub x})S{sub 3} nanocrystals reported herein provides a way for probing the effect of Ge inclusion in the Cu-Sn-S system thin films.

Processing of ZnO nanocrystals by solochemical technique

International Nuclear Information System (INIS)

Gusatti, M.; Speckhahn, R.; Silva, L.A.; Rosario, J.A.; Lima, R.B.; Kuhnen, N.C.; Riella, H.G.; Campos, C.E.M.

2009-01-01

In the present work, we report the synthesis of high quality ZnO nanocrystals by solochemical technique. This synthetic strategy has been shown to have advantages over other methods of producing nanostructures in terms of low cost, efficiency, simplicity and uniformity of crystal structure. Zinc chloride solution at room temperature was mixed with sodium hydroxide solution at 50°C to produce ZnO nanocrystals. Transmission electronic microscopy (TEM) and X-ray powder diffraction (XRD) were used to characterize the ZnO nanocrystals obtained. The structure of ZnO was refined by the Rietveld Method from X-ray diffraction data. These methods showed that the product consisted of pure ZnO nanocrystals and has, predominantly, a rod-like morphology. (author)

Energy Transfer between Conjugated Colloidal Ga2O3 and CdSe/CdS Core/Shell Nanocrystals for White Light Emitting Applications

Directory of Open Access Journals (Sweden)

Paul C. Stanish

2016-02-01

Full Text Available Developing solid state materials capable of generating homogeneous white light in an energy efficient and resource-sustainable way is central to the design of new and improved devices for various lighting applications. Most currently-used phosphors depend on strategically important rare earth elements, and rely on a multicomponent approach, which produces sub-optimal quality white light. Here, we report the design and preparation of a colloidal white-light emitting nanocrystal conjugate. This conjugate is obtained by linking colloidal Ga2O3 and II–VI nanocrystals in the solution phase with a short bifunctional organic molecule (thioglycolic acid. The two types of nanocrystals are electronically coupled by Förster resonance energy transfer owing to the short separation between Ga2O3 (energy donor and core/shell CdSe/CdS (energy acceptor nanocrystals, and the spectral overlap between the photoluminescence of the donor and the absorption of the acceptor. Using steady state and time-resolved photoluminescence spectroscopies, we quantified the contribution of the energy transfer to the photoluminescence spectral power distribution and the corresponding chromaticity of this nanocrystal conjugate. Quantitative understanding of this new system allows for tuning of the emission color and the design of quasi-single white light emitting inorganic phosphors without the use of rare-earth elements.

Energy Transfer between Conjugated Colloidal Ga2O3 and CdSe/CdS Core/Shell Nanocrystals for White Light Emitting Applications

Science.gov (United States)

Stanish, Paul C.; Radovanovic, Pavle V.

2016-01-01

Developing solid state materials capable of generating homogeneous white light in an energy efficient and resource-sustainable way is central to the design of new and improved devices for various lighting applications. Most currently-used phosphors depend on strategically important rare earth elements, and rely on a multicomponent approach, which produces sub-optimal quality white light. Here, we report the design and preparation of a colloidal white-light emitting nanocrystal conjugate. This conjugate is obtained by linking colloidal Ga2O3 and II–VI nanocrystals in the solution phase with a short bifunctional organic molecule (thioglycolic acid). The two types of nanocrystals are electronically coupled by Förster resonance energy transfer owing to the short separation between Ga2O3 (energy donor) and core/shell CdSe/CdS (energy acceptor) nanocrystals, and the spectral overlap between the photoluminescence of the donor and the absorption of the acceptor. Using steady state and time-resolved photoluminescence spectroscopies, we quantified the contribution of the energy transfer to the photoluminescence spectral power distribution and the corresponding chromaticity of this nanocrystal conjugate. Quantitative understanding of this new system allows for tuning of the emission color and the design of quasi-single white light emitting inorganic phosphors without the use of rare-earth elements. PMID:28344289

Strained interface defects in silicon nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Lee, Benjamin G.; Stradins, Paul [National Center for Photovoltaics, National Renewable Energy Laboratory, Golden, CO (United States); Hiller, Daniel; Zacharias, Margit [IMTEK - Faculty of Engineering, Albert-Ludwigs-University Freiburg (Germany); Luo, Jun-Wei; Beard, Matthew C. [Chemical and Materials Science, National Renewable Energy Laboratory, Golden, CO (United States); Semonin, Octavi E. [Chemical and Materials Science, National Renewable Energy Laboratory, Golden, CO (United States); Department of Physics, University of Colorado, Boulder, CO (United States)

2012-08-07

The surface of silicon nanocrystals embedded in an oxide matrix can contain numerous interface defects. These defects strongly affect the nanocrystals' photoluminescence efficiency and optical absorption. Dangling-bond defects are nearly eliminated by H{sub 2} passivation, thus decreasing absorption below the quantum-confined bandgap and enhancing PL efficiency by an order of magnitude. However, there remain numerous other defects seen in absorption by photothermal deflection spectroscopy; these defects cause non-radiative recombination that limits the PL efficiency to <15%. Using atomistic pseudopotential simulations, we attribute these defects to two specific types of distorted bonds: Si-Si and bridging Si-O-Si bonds between two Si atoms at the nanocrystal surface. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Modeling and simulation of floating gate nanocrystal FET devices and circuits

Science.gov (United States)

Hasaneen, El-Sayed A. M.

The nonvolatile memory market has been growing very fast during the last decade, especially for mobile communication systems. The Semiconductor Industry Association International Technology Roadmap for Semiconductors states that the difficult challenge for nonvolatile semiconductor memories is to achieve reliable, low power, low voltage performance and high-speed write/erase. This can be achieved by aggressive scaling of the nonvolatile memory cells. Unfortunately, scaling down of conventional nonvolatile memory will further degrade the retention time due to the charge loss between the floating gate and drain/source contacts and substrate which makes conventional nonvolatile memory unattractive. Using nanocrystals as charge storage sites reduces dramatically the charge leakage through oxide defects and drain/source contacts. Floating gate nanocrystal nonvolatile memory, FG-NCNVM, is a candidate for future memory because it is advantageous in terms of high-speed write/erase, small size, good scalability, low-voltage, low-power applications, and the capability to store multiple bits per cell. Many studies regarding FG-NCNVMs have been published. Most of them have dealt with fabrication improvements of the devices and device characterizations. Due to the promising FG-NCNVM applications in integrated circuits, there is a need for circuit a simulation model to simulate the electrical characteristics of the floating gate devices. In this thesis, a FG-NCNVM circuit simulation model has been proposed. It is based on the SPICE BSIM simulation model. This model simulates the cell behavior during normal operation. Model validation results have been presented. The SPICE model shows good agreement with experimental results. Current-voltage characteristics, transconductance and unity gain frequency (fT) have been studied showing the effect of the threshold voltage shift (DeltaVth) due to nanocrystal charge on the device characteristics. The threshold voltage shift due to

Mechanical, barrier and morphological properties of starch nanocrystals-reinforced pea starch films.

Science.gov (United States)

Li, Xiaojing; Qiu, Chao; Ji, Na; Sun, Cuixia; Xiong, Liu; Sun, Qingjie

2015-05-05

To characterize the pea starch films reinforced with waxy maize starch nanocrystals, the mechanical, water vapor barrier and morphological properties of the composite films were investigated. The addition of starch nanocrystals increased the tensile strength of the composite films, and the value of tensile strength of the composite films was highest when starch nanocrystals content was 5% (w/w). The moisture content (%), water vapor permeability, and water-vapor transmission rate of the composite films significantly decreased as starch nanocrystals content increased. When their starch nanocrystals content was 1-5%, the starch nanocrystals dispersed homogeneously in the composite films, resulting in a relatively smooth and compact film surface and better thermal stability. However, when starch nanocrystals content was more than 7%, the starch nanocrystals began to aggregate, which resulted in the surface of the composite films developing a longitudinal fibrous structure. Copyright © 2014 Elsevier Ltd. All rights reserved.

Inhibition of palm oil oxidation by zeolite nanocrystals.

Science.gov (United States)

Tan, Kok-Hou; Awala, Hussein; Mukti, Rino R; Wong, Ka-Lun; Rigaud, Baptiste; Ling, Tau Chuan; Aleksandrov, Hristiyan A; Koleva, Iskra Z; Vayssilov, Georgi N; Mintova, Svetlana; Ng, Eng-Poh

2015-05-13

The efficiency of zeolite X nanocrystals (FAU-type framework structure) containing different extra-framework cations (Li(+), Na(+), K(+), and Ca(2+)) in slowing the thermal oxidation of palm oil is reported. The oxidation study of palm oil is conducted in the presence of zeolite nanocrystals (0.5 wt %) at 150 °C. Several characterization techniques such as visual analysis, colorimetry, rheometry, total acid number (TAN), FT-IR spectroscopy, (1)H NMR spectroscopy, and Karl Fischer analyses are applied to follow the oxidative evolution of the oil. It was found that zeolite nanocrystals decelerate the oxidation of palm oil through stabilization of hydroperoxides, which are the primary oxidation product, and concurrently via adsorption of the secondary oxidation products (alcohols, aldehydes, ketones, carboxylic acids, and esters). In addition to the experimental results, periodic density functional theory (DFT) calculations are performed to elucidate further the oxidation process of the palm oil in the presence of zeolite nanocrystals. The DFT calculations show that the metal complexes formed with peroxides are more stable than the complexes with alkenes with the same ions. The peroxides captured in the zeolite X nanocrystals consequently decelerate further oxidation toward formation of acids. Unlike the monovalent alkali metal cations in the zeolite X nanocrystals (K(+), Na(+), and Li(+)), Ca(2+) reduced the acidity of the oil by neutralizing the acidic carboxylate compounds to COO(-)(Ca(2+))1/2 species.

Magneto-optical transitions in multilayer semiconductor nanocrystals

CERN Document Server

Climente, J; Jaskolski, W; Aliaga, J I

2003-01-01

Absorption spectra of chemically synthesized uniform and multilayer semiconductor nanocrystals in a magnetic field are investigated theoretically. The nanocrystals are modelled by spherical barrier/well potentials. The electron states are calculated within the effective mass model. A four-band k centre dot p Hamiltonian, accounting for the valence subband mixing, is used to obtain the hole states. The magneto-optical transition spectrum depends strongly on the size and composition of the nanocrystals. In the case of small uniform quantum dots, only the linear Zeeman splitting of the electron and hole energy levels is observed even for very strong magnetic fields. In larger nanocrystals, the quadratic magnetic interaction turns out to be important and the transition spectrum becomes complicated. The most complicated influence of the magnetic field is found in quantum dot-quantum well systems in which the lowest electron and hole states are localized in a thin spherical layer. It is shown that transitions that ...

Hafnium carbide nanocrystal chains for field emitters

International Nuclear Information System (INIS)

Tian, Song; Li, Hejun; Zhang, Yulei; Ren, Jincui; Qiang, Xinfa; Zhang, Shouyang

2014-01-01

A hafnium carbide (HfC) nanostructure, i.e., HfC nanocrystal chain, was synthesized by a chemical vapor deposition (CVD) method. X-ray diffractometer, field-emission scanning electron microscope, transmission electron microscope, and energy-dispersive X-ray spectrometer were employed to characterize the product. The synthesized one-dimensional (1D) nanostructures with many faceted octahedral nanocrystals possess diameters of tens of nanometers to 500 nm and lengths of a few microns. The chain-like structures possess a single crystalline structure and preferential growth direction along the [1 0 0] crystal orientation. The growth of the chains occurred through the vapor–liquid–solid process along with a negative-feedback mechanism. The field emission (FE) properties of the HfC nanocrystal chains as the cold cathode emitters were examined. The HfC nanocrystal chains display good FE properties with a low turn-on field of about 3.9 V μm −1 and a high field enhancement factor of 2157, implying potential applications in vacuum microelectronics.

Organization of silicon nanocrystals by localized electrochemical etching

International Nuclear Information System (INIS)

Ayari-Kanoun, Asma; Drouin, Dominique; Beauvais, Jacques; Lysenko, Vladimir; Nychyporuk, Tetyana; Souifi, Abdelkader

2009-01-01

An approach to form a monolayer of organized silicon nanocrystals on a monocrystalline Si wafer is reported. Ordered arrays of nanoholes in a silicon nitride layer were obtained by combining electron beam lithography and plasma etching. Then, a short electrochemical etching current pulse led to formation of a single Si nanocrystal per each nanohole. As a result, high quality silicon nanocrystal arrays were formed with well controlled and reproducible morphologies. In future, this approach can be used to fabricate single electron devices.

Near-infrared light emitting device using semiconductor nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Supran, Geoffrey J.S.; Song, Katherine W.; Hwang, Gyuweon; Correa, Raoul Emile; Shirasaki, Yasuhiro; Bawendi, Moungi G.; Bulovic, Vladimir; Scherer, Jennifer

2018-04-03

A near-infrared light emitting device can include semiconductor nanocrystals that emit at wavelengths beyond 1 .mu.m. The semiconductor nanocrystals can include a core and an overcoating on a surface of the core.

Patterning nanocrystals using DNA

Energy Technology Data Exchange (ETDEWEB)

Williams, Shara Carol [Univ. of California, Berkeley, CA (United States)

2003-01-01

One of the goals of nanotechnology is to enable programmed self-assembly of patterns made of various materials with nanometer-sized control. This dissertation describes the results of experiments templating arrangements of gold and semiconductor nanocrystals using 2'-deoxyribonucleic acid (DNA). Previously, simple DNA-templated linear arrangements of two and three nanocrystals structures have been made.[1] Here, we have sought to assemble larger and more complex nanostructures. Gold-DNA conjugates with 50 to 100 bases self-assembled into planned arrangements using strands of DNA containing complementary base sequences. We used two methods to increase the complexity of the arrangements: using branched synthetic doublers within the DNA covalent backbone to create discrete nanocrystal groupings, and incorporating the nanocrystals into a previously developed DNA lattice structure [2][3] that self-assembles from tiles made of DNA double-crossover molecules to create ordered nanoparticle arrays. In the first project, the introduction of a covalently-branched synthetic doubler reagent into the backbone of DNA strands created a branched DNA ''trimer.'' This DNA trimer templated various structures that contained groupings of three and four gold nanoparticles, giving promising, but inconclusive transmission electron microscopy (TEM) results. Due to the presence of a variety of possible structures in the reaction mixtures, and due to the difficulty of isolating the desired structures, the TEM and gel electrophoresis results for larger structures having four particles, and for structures containing both 5 and 10 nm gold nanoparticles were inconclusive. Better results may come from using optical detection methods, or from improved sample preparation. In the second project, we worked toward making two-dimensional ordered arrays of nanocrystals. We replicated and improved upon previous results for making DNA lattices, increasing the size of the lattices

Synthesis, spectroscopy and simulation of doped nanocrystals

NARCIS (Netherlands)

Suyver, Jan Frederik

2003-01-01

This thesis deals with the properties of semiconductor nanocrystals (ZnS or ZnSe) in the size range (diameter) of 2 nm to 10 nm. The nanocrystals under investigation are doped with the transition metal ions manganese or copper. The goal is to study photoluminescence and electroluminescence from

Sensing the facet orientation in silver nano-plates using scanning Kelvin probe microscopy in air

Energy Technology Data Exchange (ETDEWEB)

Abdellatif, M.H. [Department of Nanostructures, Istituto Italiano di Tecnologia, via Morego 30, I-16163 Genova (Italy); Physics Department, National Research Center, Elbehoos st., 12622, Dokki, Giza (Egypt); Salerno, M., E-mail: marco.salerno@iit.it [Department of Nanophysics, Istituto Italiano di Tecnologia, via Morego 30, I-16163 Genova (Italy); Polovitsyn, Anatolii [Department of Nanochemistry, Istituto Italiano di Tecnologia, via Morego 30, I-16163 Genova (Italy); Dipartimentodi Fisica, Università di Genova, via Dodecaneso 33, I-16146 Genova (Italy); Marras, Sergio [Department of Nanochemistry, Istituto Italiano di Tecnologia, via Morego 30, I-16163 Genova (Italy); De Angelis, Francesco [Department of Nanostructures, Istituto Italiano di Tecnologia, via Morego 30, I-16163 Genova (Italy)

2017-05-01

Highlights: • The surface potential of drop cast nanocrystals was measured by SKPM in ambient air. • The nanocrystal facet work function was derived by theory. • By comparing theory and experiment we distinguished the nanocrystal facets. • Nanocrystal facet control is of practical interest for optoelectronic devices. - Abstract: The work function of nano-materials is important for a full characterization of their electronic properties. Because the band alignment, band bending and electronic noise are very sensitive to work function fluctuations, the dependence of the work function of nano-scale crystals on facet orientation can be a critical issue in optimizing optoelectronic devices based on these materials. We used scanning Kelvin probe microscopy to assess the local work function on samples of silver nano-plates at sub-micrometric spatial resolution. With the appropriate choice of the substrate and based on statistical analysis, it was possible to distinguish the surface potential of the different facets of silver nano-plates even if the measurements were done in ambient conditions without the use of vacuum. A phenomenological model was used to calculate the differences of facet work function of the silver nano-plates and the corresponding shift in Fermi level. This theoretical prediction and the experimentally observed difference in surface potential on the silver nano-plates were in good agreement. Our results show the possibility to sense the nano-crystal facets by appropriate choice of the substrate in ambient conditions.

Sensing the facet orientation in silver nano-plates using scanning Kelvin probe microscopy in air

International Nuclear Information System (INIS)

Abdellatif, M.H.; Salerno, M.; Polovitsyn, Anatolii; Marras, Sergio; De Angelis, Francesco

2017-01-01

Highlights: • The surface potential of drop cast nanocrystals was measured by SKPM in ambient air. • The nanocrystal facet work function was derived by theory. • By comparing theory and experiment we distinguished the nanocrystal facets. • Nanocrystal facet control is of practical interest for optoelectronic devices. - Abstract: The work function of nano-materials is important for a full characterization of their electronic properties. Because the band alignment, band bending and electronic noise are very sensitive to work function fluctuations, the dependence of the work function of nano-scale crystals on facet orientation can be a critical issue in optimizing optoelectronic devices based on these materials. We used scanning Kelvin probe microscopy to assess the local work function on samples of silver nano-plates at sub-micrometric spatial resolution. With the appropriate choice of the substrate and based on statistical analysis, it was possible to distinguish the surface potential of the different facets of silver nano-plates even if the measurements were done in ambient conditions without the use of vacuum. A phenomenological model was used to calculate the differences of facet work function of the silver nano-plates and the corresponding shift in Fermi level. This theoretical prediction and the experimentally observed difference in surface potential on the silver nano-plates were in good agreement. Our results show the possibility to sense the nano-crystal facets by appropriate choice of the substrate in ambient conditions.

High index surfaces of Au-nanocrystals supported on one-dimensional MoO3-nanorod as a bi-functional electrocatalyst for ethanol oxidation and oxygen reduction

International Nuclear Information System (INIS)

Karuppasamy, L.; Chen, C.Y.; Anandan, S.; Wu, J.J.

2017-01-01

Highlights: •Synthesis of a new class of Au nanocrystals enclosed with high index surface supported on MoO 3 nanorods by ultrasonic probe method. •The role of supporting materials reduces the loading of Au and acts as a co-catalyst. •The as prepared electrocatalyst exhibits enhanced catalytic activity and stability towards both EOR and ORR. -- Abstract: The design of highly active electrocatalyst for ethanol electrooxidation (EOR) and oxygen reduction reaction (ORR) is of great significance for the improvement of efficient direct ethanol fuel cells (DEFCs). Therefore, creating high index facets nanocrystals with abundant catalytic active sites of stepped atoms is an effective way to enhance the electrocatalytic performance. In this article, we prepared the high index surface structures of Au nanocrystals supported on one-dimensional (1-D) MoO 3 nanorods by using two steps ultrasonic probe irradiation method. The size and physical properties of as electrocatalysts were studied by using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and x-ray diffraction (XRD) instrumentation. Besides, the catalytic activity of as Au-MoO 3 electrocatalyst was determined by using cyclic voltammetry (CV), chronoamperometric (CA), electrochemical impedance spectroscopy (EIS), CO-stripping, and linear sweep voltammetry-rotating disk electrode (LSV-RDE). As a consequence, the Au-MoO 3 nanocomposites has been considered as an effective electrocatalyst for both ethanol oxidation and oxygen reduction reaction.

Flexible and low-voltage integrated circuits constructed from high-performance nanocrystal transistors.

Science.gov (United States)

Kim, David K; Lai, Yuming; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

2012-01-01

Colloidal semiconductor nanocrystals are emerging as a new class of solution-processable materials for low-cost, flexible, thin-film electronics. Although these colloidal inks have been shown to form single, thin-film field-effect transistors with impressive characteristics, the use of multiple high-performance nanocrystal field-effect transistors in large-area integrated circuits has not been shown. This is needed to understand and demonstrate the applicability of these discrete nanocrystal field-effect transistors for advanced electronic technologies. Here we report solution-deposited nanocrystal integrated circuits, showing nanocrystal integrated circuit inverters, amplifiers and ring oscillators, constructed from high-performance, low-voltage, low-hysteresis CdSe nanocrystal field-effect transistors with electron mobilities of up to 22 cm(2) V(-1) s(-1), current modulation >10(6) and subthreshold swing of 0.28 V dec(-1). We fabricated the nanocrystal field-effect transistors and nanocrystal integrated circuits from colloidal inks on flexible plastic substrates and scaled the devices to operate at low voltages. We demonstrate that colloidal nanocrystal field-effect transistors can be used as building blocks to construct complex integrated circuits, promising a viable material for low-cost, flexible, large-area electronics.

Formation of colloidal semiconductor nanocrystals. The aspect of nucleation

Energy Technology Data Exchange (ETDEWEB)

Kudera, S.

2007-08-17

The present work describes different techniques to control some major parameters of colloidal nanocrystals. The individual techniques rely on the manipulation of the nucleation event. The sensitive control of the nanocrystals' size and shape is discussed. Furthermore the formation of hybrid nanocrystals composed of different materials is presented. The synthesis technique for the production of the different samples involves organic solvents and surfactants and reactions at elevated temperatures. The presence of magic size clusters offers a possibility to control the size of the nanocrystals even at very small dimensions. The clusters produced comprise ca. 100 atoms. In the case of CdSe, nanocrystals of this size emit a blue fluorescence and therefore extend the routinely accessible spectrum for this material over the whole visible range. Samples fluorescing in the spectral range from green to red are produced with standard recipes. In this work a reaction scheme for magic size clusters is presented and a theoretical model to explain the particular behaviour of their growth dynamics is discussed. The samples are investigated by optical spectroscopy, transmission electron microscopy, X-ray diffraction and elemental analysis. A method to form branched nanocrystals is discussed. The branching point is analysed by high resolution transmission electron microscopy and proves for the occurrence of a multiple twinned structure are strengthened by simulation of the observed patterns. Two different techniques to generate nanocrystals of this type are presented. The first relies on a seeded growth approach in which the nucleation of the second material is allowed only on de ned sites of the seeds. The second technique uses the tips of pre-formed nano-dumbbells as sacrificial domains. The material on the tips is replaced by gold. Hybrid materials are formed by a seeded-growth mechanism. Pre-formed nanocrystals provide the nucleation sites for the second material. (orig.)

Formation of colloidal semiconductor nanocrystals. The aspect of nucleation

Energy Technology Data Exchange (ETDEWEB)

Kudera, S

2007-08-17

The present work describes different techniques to control some major parameters of colloidal nanocrystals. The individual techniques rely on the manipulation of the nucleation event. The sensitive control of the nanocrystals' size and shape is discussed. Furthermore the formation of hybrid nanocrystals composed of different materials is presented. The synthesis technique for the production of the different samples involves organic solvents and surfactants and reactions at elevated temperatures. The presence of magic size clusters offers a possibility to control the size of the nanocrystals even at very small dimensions. The clusters produced comprise ca. 100 atoms. In the case of CdSe, nanocrystals of this size emit a blue fluorescence and therefore extend the routinely accessible spectrum for this material over the whole visible range. Samples fluorescing in the spectral range from green to red are produced with standard recipes. In this work a reaction scheme for magic size clusters is presented and a theoretical model to explain the particular behaviour of their growth dynamics is discussed. The samples are investigated by optical spectroscopy, transmission electron microscopy, X-ray diffraction and elemental analysis. A method to form branched nanocrystals is discussed. The branching point is analysed by high resolution transmission electron microscopy and proves for the occurrence of a multiple twinned structure are strengthened by simulation of the observed patterns. Two different techniques to generate nanocrystals of this type are presented. The first relies on a seeded growth approach in which the nucleation of the second material is allowed only on de ned sites of the seeds. The second technique uses the tips of pre-formed nano-dumbbells as sacrificial domains. The material on the tips is replaced by gold. Hybrid materials are formed by a seeded-growth mechanism. Pre-formed nanocrystals provide the nucleation sites for the second material. (orig.)

Hybrid Light-Emitting Diode Enhanced With Emissive Nanocrystals

DEFF Research Database (Denmark)

Kopylov, Oleksii

This thesis investigates a new type of white light emitting hybrid diode, composed of a light emitting GaN/InGaN LED and a layer of semiconductor nanocrystals for color conversion. Unlike standard white LEDs, the device is configured to achieve high color conversion efficiency via non-radiative e......This thesis investigates a new type of white light emitting hybrid diode, composed of a light emitting GaN/InGaN LED and a layer of semiconductor nanocrystals for color conversion. Unlike standard white LEDs, the device is configured to achieve high color conversion efficiency via non...... of the hybrid diode fabrication including process techniques for GaN LED and incorporation of the nanocrystals are presented with the emphasis on the differences with standard LED processing. Results and analysis of optical and electrical characterization including photoluminescence (PL), micro-PL, time......-resolved PL and electroluminescence (EL) together with current-voltage characteristics are presented to evaluate the device performance. A clear evidence of non-radiative energy transfer was seen in the carrier dynamics of both the LED and the nanocrystals when the quantum well – nanocrystals separation...

Octacosanol educes physico-chemical attributes, release and bioavailability as modified nanocrystals.

Science.gov (United States)

Sen Gupta, Surashree; Ghosh, Mahua

2017-10-01

Octacosanol is a lesser known nutraceutical with the potential for treatment of several inflammatory diseases, high cholesterol, Parkinson's symptoms and tumour growth along with the capacity to improve athletic performance. But its lipophilicity and large structure inhibits extended solubility in water resulting in poor absorption and a low bioavailability. In the present work, sodium salt of octacosyl sulfate was synthesized. It displayed improved water solubility. Its nanocrystals, synthesized by means of nanoprecipitation technique, enhanced diffusion velocity, antioxidant capacity, shelf-life, penetrability and bioavailability. Particle size of the nanocrystals ranged between 197 and 220nm. Both modified octacosanol and its nanocrystals displayed maximum lipid peroxidation activities at a concentration 1000ppm, but nanocrystals demonstrated higher prevention. From freeze-thaw cycles it was evident that normal octacosanol crystals were far more prone to temperature variations than the nanocrystals. A pronounced increase in release/diffusion rate and bioavailability was observed for the nanocrystals of the modified octacosanol. In vitro release kinetics, bioavailability and bioequivalence were studied. Relative bioavailability for gastric passage and pancreatic passage of nanocrystals was 2.58 times and 1.81 times that of normal crystals respectively. Furthermore the nanocrystals displayed a superior in vitro release rate, while following a non-Fickian mode. Copyright © 2017 Elsevier B.V. All rights reserved.

Identification of nasopharyngeal carcinoma from photoluminescence spectra of 3C-SiC nanocrystals

Science.gov (United States)

Wang, Li-Fen; Guo, Jun-Hong; Huang, Zhi-Chun; Gu, Jian-Sen; Feng, Li-Ren; Liu, Li-Zhe

2017-09-01

The identification of intracellular pH (pHi) during carcinogenesis progression plays a crucial role in the studies of biochemistry, cytology, and clinical medicine. In this work, 3C-SiC nanocrystals (NCs), which can effectively monitor the pH environment by using the linear relation between photoluminescence intensity and surface OH- and H+ concentration, are adapted as fluorescent probes for monitoring carcinogenesis progression of nasopharyngeal carcinoma. Our results demonstrated that 3C-SiC NCs are compatible with living cells and have low cytotoxicity. The pHi measurements in different carcinogenesis environments indicate the validity and sensitivity of this technology in identifying nasopharyngeal carcinoma in application.

Self organized formation of Ge nanocrystals in multilayers

OpenAIRE

Zschintzsch-Dias, Manuel

2012-01-01

The aim of this work is to create a process which allows the tailored growth of Ge nanocrystals for use in photovoltic applications. The multilayer systems used here provide a reliable method to control the Ge nanocrystal size after phase separation. In this thesis, the deposition of GeOx/SiO2 and Ge:SiOx~ 2/SiO2 multilayers via reactive dc magnetron sputtering and the self-ordered Ge nanocrystal formation within the GeOx and Ge:SiOx~ 2 sublayers during subsequent annealing is investigated...

Photoluminescence from Si nanocrystals in silica: The effect of hydrogen

International Nuclear Information System (INIS)

Cheylan, S.; Elliman, R.G.

2001-01-01

The effect of H passivation on the PL emission of Si nanocrystals produced in silica by ion-implantion and annealing is shown to depend on the implant fluence. At low fluences, where the nanocrystals are small, passivation causes an enhancement of the emission intensity that is uniform over the full spectral range and therefore appears to be independent of nanocrystal size. For higher fluences, where the average size and size distribution of the nanocrystals are larger, the enhancement occurs preferentially at longer wavelengths, giving rise to a red-shift in the emission spectra. Both the enhancement and the red-shift increase monotonically with increasing fluence. These data are shown to be consistent with a model in which the probability to contain a non-radiative defect increases with nanocrystal size

Multicolour synthesis in lanthanide-doped nanocrystals through cation exchange in water

KAUST Repository

Han, Sanyang

2016-10-04

Meeting the high demand for lanthanide-doped luminescent nanocrystals across a broad range of fields hinges upon the development of a robust synthetic protocol that provides rapid, just-in-time nanocrystal preparation. However, to date, almost all lanthanide-doped luminescent nanomaterials have relied on direct synthesis requiring stringent controls over crystal nucleation and growth at elevated temperatures. Here we demonstrate the use of a cation exchange strategy for expeditiously accessing large classes of such nanocrystals. By combining the process of cation exchange with energy migration, the luminescence properties of the nanocrystals can be easily tuned while preserving the size, morphology and crystal phase of the initial nanocrystal template. This post-synthesis strategy enables us to achieve upconversion luminescence in Ce3+ and Mn2+-activated hexagonal-phased nanocrystals, opening a gateway towards applications ranging from chemical sensing to anti-counterfeiting.

Light Scattering Spectroscopies of Semiconductor Nanocrystals (Quantum Dots)

International Nuclear Information System (INIS)

Yu, Peter Y; Gardner, Grat; Nozaki, Shinji; Berbezier, Isabelle

2006-01-01

We review the study of nanocrystals or quantum dots using inelastic light scattering spectroscopies. In particular recent calculations of the phonon density of states and low frequency Raman spectra in Ge nanocrystals are presented for comparison with experimental results

Chemistry of the Colloidal Group II-VI Nanocrystal Synthesis

International Nuclear Information System (INIS)

Liu, Haitao

2007-01-01

In the last two decades, the field of nanoscience and nanotechnology has witnessed tremendous advancement in the synthesis and application of group II-VI colloidal nanocrystals. The synthesis based on high temperature decomposition of organometallic precursors has become one of the most successful methods of making group II-VI colloidal nanocrystals. This method is first demonstrated by Bawendi and coworkers in 1993 to prepare cadmium chalcogenide colloidal quantum dots and later extended by others to prepare other group II-VI quantum dots as well as anisotropic shaped colloidal nanocrystals, such as nanorod and tetrapod. This dissertation focuses on the chemistry of this type of nanocrystal synthesis. The synthesis of group II-VI nanocrystals was studied by characterizing the molecular structures of the precursors and products and following their time evolution in the synthesis. Based on these results, a mechanism was proposed to account for the 2 reaction between the precursors that presumably produces monomer for the growth of nanocrystals. Theoretical study based on density functional theory calculations revealed the detailed free energy landscape of the precursor decomposition and monomer formation pathway. Based on the proposed reaction mechanism, a new synthetic method was designed that uses water as a novel reagent to control the diameter and the aspect ratio of CdSe and CdS nanorods

Aqueous dispersion of monodisperse magnetic iron oxide nanocrystals through phase transfer

International Nuclear Information System (INIS)

Yu, William W; Chang, Emmanuel; Sayes, Christie M; Drezek, Rebekah; Colvin, Vicki L

2006-01-01

A facile method was developed for completely transferring high quality monodisperse iron oxide nanocrystals from organic solvents to water. The as-prepared aqueous dispersions of iron oxide nanocrystals were extremely stable and could be functionalized for bioconjugation with biomolecules. These iron oxide nanocrystals showed negligible cytotoxicity to human breast cancer cells (SK-BR-3) and human dermal fibroblast cells. This method is general and versatile for many organic solvent-synthesized nanoparticles, including fluorescent semiconductor nanocrystals

Preparation of NiFe binary alloy nanocrystals for nonvolatile memory applications

Institute of Scientific and Technical Information of China (English)

无

2010-01-01

In this work,an idea which applies binary alloy nanocrystal floating gate to nonvolatile memory application was introduced.The relationship between binary alloy’s work function and its composition was discussed theoretically.A nanocrystal floating gate structure with NiFe nanocrystals embedded in SiO2 dielectric layers was fabricated by magnetron sputtering.The micro-structure and composition deviation of the prepared NiFe nanocrystals were also investigated by TEM and EDS.

Ultrahigh intercalation pseudocapacitance of mesoporous orthorhombic niobium pentoxide from a novel cellulose nanocrystal template

International Nuclear Information System (INIS)

Kong, Lingping; Zhang, Chuangfang; Wang, Jitong; Long, Donghui; Qiao, Wenming; Ling, Licheng

2015-01-01

A facile biotemplating method has been developed to prepare mesoporous orthorhombic nobium pentoxide (T-Nb 2 O 5 ) films with ultrahigh lithium ion (Li + ) intercalation pseudocapacitance. Nanorod-like cellulose nanocrystals (CNs) with 5–10 nm in width and 100–300 nm in length are produced by the hydrolysis of cotton, which can serve as a novel soft templating agent enabling the straightforward synthesis of mesoporous T-Nb 2 O 5 films. By varying the niobic-to-template ratio, it is possible to tune the surface area and crystallite dimension of the Nb 2 O 5 films. The obtained T-Nb 2 O 5 films show typical capacitive-dominated behaviour in the sweep rate range of 1–20 mV s −1 . It delivers an initial intercalation capacity of 644 C g −1 at a current density of 0.625 A g −1 , corresponding to x = 1.83 for Li x Nb 2 O 5 , and can still keep relatively stable capacity of 560 C g −1 after 300 cycles. Moreover, its excellent high-rate capability (450 C g −1 at 12.5 A g −1 ) and wider temperature adaptability present here suggests the promising of T-Nb 2 O 5 as high-energy pseudocapacitor electrode with superior intercalation capacitive behaviour. - Graphical abstract: We developed a facile and sustainable method to prepare T-Nb 2 O 5 nanocrystals using novel nanorod-like cellulose nanocrystals (CNs) as soft templates. The T-Nb 2 O 5 nanocrystals exhibited unprecedented Li + intercalation pseudocapacitance, excellent cycle performance and good high-and-low temperature tolerance performance.

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

Science.gov (United States)

Scarfiello, Riccardo; Nobile, Concetta; Cozzoli, P. Davide

2016-12-01

Colloidal inorganic nanocrystals, free-standing crystalline nanostructures generated and processed in solution phase, represent an important class of advanced nanoscale materials owing to the flexibility with which their physical-chemical properties can be controlled through synthetic tailoring of their compositional, structural and geometric features and the versatility with which they can be integrated in technological fields as diverse as optoelectronics, energy storage/ conversion/production, catalysis and biomedicine. In recent years, building upon mechanistic knowledge acquired on the thermodynamic and kinetic processes that underlie nanocrystal evolution in liquid media, synthetic nanochemistry research has made impressive advances, opening new possibilities for the design, creation and mastering of increasingly complex “colloidal molecules”, in which nanocrystal modules of different materials are clustered together via solid-state bonding interfaces into free-standing, easily processable multifunctional nanocomposite systems. This Review will provide a glimpse into this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of all-inorganic heterostructured nanocrystals (HNCs) in asymmetric non-onionlike geometries, inorganic analogues of polyfunctional organic molecules, in which distinct nanoscale crystalline modules are interconnected in hetero-dimer, hetero-oligomer and anisotropic multidomain architectures via epitaxial heterointerfaces of limited extension. The focus will be on modular HNCs entailing at least one magnetic material component combined with semiconductors and/or metals, which hold potential for generating enhanced or unconventional magnetic properties, while offering diversified or even new chemical-physical properties and functional capabilities. The available toolkit of synthetic strategies, all based on the manipulation of seeded-growth techniques, will be described

Colloidal Magnetic Heterostructured Nanocrystals with Asymmetric Topologies: Seeded-Growth Synthetic Routes and Formation Mechanisms

Directory of Open Access Journals (Sweden)

Riccardo Scarfiello

2016-12-01

Full Text Available Colloidal inorganic nanocrystals, free-standing crystalline nanostructures generated and processed in solution phase, represent an important class of advanced nanoscale materials owing to the flexibility with which their physical–chemical properties can be controlled through synthetic tailoring of their compositional, structural and geometric features and the versatility with which they can be integrated in technological fields as diverse as optoelectronics, energy storage/ conversion/production, catalysis and biomedicine. In recent years, building upon mechanistic knowledge acquired on the thermodynamic and kinetic processes that underlie nanocrystal evolution in liquid media, synthetic nanochemistry research has made impressive advances, opening new possibilities for the design, creation and mastering of increasingly complex colloidal molecules, in which nanocrystal modules of different materials are clustered together via solid-state bonding interfaces into free-standing, easily processable multifunctional nanocomposite systems. This Review will provide a glimpse into this fast-growing research field by illustrating progress achieved in the wet-chemical development of last-generation breeds of all-inorganic heterostructured nanocrystals (HNCs in asymmetric non-onionlike geometries, inorganic analogues of polyfunctional organic molecules, in which distinct nanoscale crystalline modules are interconnected in hetero-dimer, hetero-oligomer and anisotropic multidomain architectures via epitaxial heterointerfaces of limited extension. The focus will be on modular HNCs entailing at least one magnetic material component combined with semiconductors and/or metals, which hold potential for generating enhanced or unconventional magnetic properties, while offering diversified or even new chemical-physical properties and functional capabilities. The available toolkit of synthetic strategies, all based on the manipulation of seeded-growth techniques

The structure and morphology of semiconductor nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Kadavanich, Andreas V. [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

1997-11-01

Colloidal semiconductor nanocrystals were studied using High Resolution Transmission Electron Microscopy (HRTEM). Organically capped nanocrystals were found to have faceted shapes consistent with Wulff polyhedra after the effects of capping ligands on surface energies were taken into account. The basic shape thus derived for wurtzite (WZ) structure CdSe nanocrystals capped by tri-octyl phosphine oxide (TOPO) was a truncated hexagonal prism, elongated alone the <001> axis with (100) and (002) facets. This structure has C{sub 3v} point group symmetry. The main defect in this structure is a stacking fault (a single layer of zinc blende type stacking), which does not significantly affect the shape (does not alter the point group).

Surface and Core Electronic Structure of Oxidized Silicon Nanocrystals

Directory of Open Access Journals (Sweden)

Noor A. Nama

2010-01-01

Full Text Available Ab initio restricted Hartree-Fock method within the framework of large unit cell formalism is used to simulate silicon nanocrystals between 216 and 1000 atoms (1.6–2.65 nm in diameter that include Bravais and primitive cell multiples. The investigated properties include core and oxidized surface properties. Results revealed that electronic properties converge to some limit as the size of the nanocrystal increases. Increasing the size of the core of a nanocrystal resulted in an increase of the energy gap, valence band width, and cohesive energy. The lattice constant of the core and oxidized surface parts shows a decreasing trend as the nanocrystal increases in a size that converges to 5.28 Ǻ in a good agreement with the experiment. Surface and core convergence to the same lattice constant reflects good adherence of oxide layer at the surface. The core density of states shows highly degenerate states that split at the oxygenated (001-(1×1 surface due to symmetry breaking. The nanocrystal surface shows smaller gap and higher valence and conduction bands when compared to the core part, due to oxygen surface atoms and reduced structural symmetry. The smaller surface energy gap shows that energy gap of the nanocrystal is controlled by the surface part. Unlike the core part, the surface part shows a descending energy gap that proves its obedience to quantum confinement effects. Nanocrystal geometry proved to have some influence on all electronic properties including the energy gap.

Four-probe measurements with a three-probe scanning tunneling microscope

International Nuclear Information System (INIS)

Salomons, Mark; Martins, Bruno V. C.; Zikovsky, Janik; Wolkow, Robert A.

2014-01-01

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe

Four-probe measurements with a three-probe scanning tunneling microscope

Energy Technology Data Exchange (ETDEWEB)

Salomons, Mark [National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta T6G 2M9 (Canada); Martins, Bruno V. C.; Zikovsky, Janik; Wolkow, Robert A., E-mail: rwolkow@ualberta.ca [National Institute for Nanotechnology, National Research Council of Canada, Edmonton, Alberta T6G 2M9 (Canada); Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1 (Canada)

2014-04-15

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.

Four-probe measurements with a three-probe scanning tunneling microscope.

Science.gov (United States)

Salomons, Mark; Martins, Bruno V C; Zikovsky, Janik; Wolkow, Robert A

2014-04-01

We present an ultrahigh vacuum (UHV) three-probe scanning tunneling microscope in which each probe is capable of atomic resolution. A UHV JEOL scanning electron microscope aids in the placement of the probes on the sample. The machine also has a field ion microscope to clean, atomically image, and shape the probe tips. The machine uses bare conductive samples and tips with a homebuilt set of pliers for heating and loading. Automated feedback controlled tip-surface contacts allow for electrical stability and reproducibility while also greatly reducing tip and surface damage due to contact formation. The ability to register inter-tip position by imaging of a single surface feature by multiple tips is demonstrated. Four-probe material characterization is achieved by deploying two tips as fixed current probes and the third tip as a movable voltage probe.

Structure Map for Embedded Binary Alloy Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Yuan, C.W.; Shin, S.J.; Liao, C.Y.; Guzman, J.; Stone, P.R.; Watanabe, M.; Ager III, J.W.; Haller, E.E.; Chrzan, D.C.

2008-09-20

The equilibrium structure of embedded nanocrystals formed from strongly segregating binary-alloys is considered within a simple thermodynamic model. The model identifies two dimensionlessinterface energies that dictate the structure, and allows prediction of the stable structure for anychoice of these parameters. The resulting structure map includes three distinct nanocrystal mor-phologies: core/shell, lobe/lobe, and completely separated spheres.

Stability studies of CdSe nanocrystals in an aqueous environment

DEFF Research Database (Denmark)

Xi, Lifei; Lek, Jun Yan; Liang, Yen Nan

2011-01-01

In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH − ) while photo......-generated holes oxidize CdSe to Cd2 + and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH = 10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments...

State of the art of nanocrystals technology for delivery of poorly soluble drugs

Energy Technology Data Exchange (ETDEWEB)

Zhou, Yuqi; Du, Juan; Wang, Lulu; Wang, Yancai, E-mail: wangyancai1999@163.com [Qilu University of Technology, School of Chemistry and Pharmaceutical Engineering (China)

2016-09-15

Formulation of nanocrystals is a distinctive approach which can effectively improve the delivery of poorly water-soluble drugs, thus enticing the development of the nanocrystals technology. The characteristics of nanocrystals resulted in an exceptional drug delivery conductance, including saturation solubility, dissolution velocity, adhesiveness, and affinity. Nanocrystals were treated as versatile pharmaceuticals that could be delivered through almost all routes of administration. In the current review, oral, pulmonary, and intravenous routes of administration were presented. Also, the targeting of drug nanocrystals, as well as issues of efficacy and safety, were also discussed. Several methods were applied for nanocrystals production including top-down production strategy (media milling, high-pressure homogenization), bottom-up production strategy (antisolvent precipitation, supercritical fluid process, and precipitation by removal of solvent), and the combination approaches. Moreover, this review also described the evaluation and characterization of the drug nanocrystals and summarized the current commercial pharmaceutical products utilizing nanocrystals technology.

Protein Adsorption and Antibacterial Behavior for Hydroxyapatite Nanocrystals Prepared by Hydrothermal Method

OpenAIRE

笠原, 英充; 小形, 信男; 荻原, 隆

2005-01-01

Homogeneous hydroxyapatite nanocrystals which have aspect ratio with more than four were synthesized by hydrothermal method. X-ray fluorescence analysis revealed that the Ca/P ratio of hydroxyapatite nanocrystals was maintaining start composition. The protein adsorption properties and bacteria-resistant of hydroxyapatite nanocrystals were investigated. The protein adsorption properties of hydroxyapatite nanocrystals were improvement after the hydrothermal treatment. Bacteria-resistant behavio...

Facile fabrication and electrochemical behaviors of Mn:ZnS nanocrystals

International Nuclear Information System (INIS)

Xie, Ruishi; Li, Yuanli; Liu, Haifeng; Guo, Baogang

2016-01-01

Here, we demonstrate the rational design and synthesis of Mn:ZnS nanocrystals with adjustable doping concentrations utilizing a facile, cost effective, and environmentally benign chemical protocol. These nanostructures were investigated as electrode materials for lithium-ion batteries. Compared with pristine ZnS nanocrystals, the Mn:ZnS nanocrystals exhibit significantly improved electrochemical performances in terms of specific capacity and cycling performance. The Mn:ZnS nanocrystal sample with doping concentration of 1 at% displays second discharge capacity of 789.9 mA h g"−"1 at a current density of 24 mA g"−"1, about 2.39 times higher than that of the pure ZnS nanocrystal. Furthermore, the Mn:ZnS nanocrystal electrodes represent much better capacity retention than that of the undoped one. The greatly improved electrochemical performances of the Mn:ZnS nanocrystal samples could be attributed to the following factors. The large specific surface area can significantly enhance structural integrity by acting as mechanical buffer, effectively alleviating the volume changes generated during the lithiation/delithiation process. The incorporation of Mn into the lattice of ZnS improves charge transfer kinetics and results in a faster Li"+ diffusion rate during the charge–discharge process. It is of great significance to incorporate guest metal ions into nanostructured materials to display especial electrochemical characteristics triggering an effective approach to improve the electrochemical properties.

Facile fabrication and electrochemical behaviors of Mn:ZnS nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Xie, Ruishi [Analytical and Testing Center, Southwest University of Science and Technology, Mianyang, 621010 (China); Li, Yuanli, E-mail: yuanlyl@foxmail.com [Department of Materials, Southwest University of Science and Technology, Mianyang, 621010 (China); Liu, Haifeng; Guo, Baogang [Analytical and Testing Center, Southwest University of Science and Technology, Mianyang, 621010 (China)

2016-07-05

Here, we demonstrate the rational design and synthesis of Mn:ZnS nanocrystals with adjustable doping concentrations utilizing a facile, cost effective, and environmentally benign chemical protocol. These nanostructures were investigated as electrode materials for lithium-ion batteries. Compared with pristine ZnS nanocrystals, the Mn:ZnS nanocrystals exhibit significantly improved electrochemical performances in terms of specific capacity and cycling performance. The Mn:ZnS nanocrystal sample with doping concentration of 1 at% displays second discharge capacity of 789.9 mA h g{sup −1} at a current density of 24 mA g{sup −1}, about 2.39 times higher than that of the pure ZnS nanocrystal. Furthermore, the Mn:ZnS nanocrystal electrodes represent much better capacity retention than that of the undoped one. The greatly improved electrochemical performances of the Mn:ZnS nanocrystal samples could be attributed to the following factors. The large specific surface area can significantly enhance structural integrity by acting as mechanical buffer, effectively alleviating the volume changes generated during the lithiation/delithiation process. The incorporation of Mn into the lattice of ZnS improves charge transfer kinetics and results in a faster Li{sup +} diffusion rate during the charge–discharge process. It is of great significance to incorporate guest metal ions into nanostructured materials to display especial electrochemical characteristics triggering an effective approach to improve the electrochemical properties.

Formic acid-assisted synthesis of palladium nanocrystals and their electrocatalytic properties.

Science.gov (United States)

Wang, Qinchao; Wang, Yiqian; Guo, Peizhi; Li, Qun; Ding, Ruixue; Wang, Baoyan; Li, Hongliang; Liu, Jingquan; Zhao, X S

2014-01-14

Palladium (Pd) nanocrystals have been synthesized by using formic acid as the reducing agent at room temperature. When the concentration of formic acid was increased continuously, the size of Pd nanocrystals first decreased to a minimum and then increased slightly again. The products have been investigated by a series of techniques, including X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), UV-vis absorption, and electrochemical measurements. The formation of Pd nanocrystals is proposed to be closely related to the dynamical imbalance of the growth and dissolution rate of Pd nanocrystals associated with the adsorption of formate ions onto the surface of the intermediates. It is found that small Pd nanocrystals showed blue-shifted adsorption peaks compared with large ones. Pd nanocrystals with the smallest size display the highest electrocatalytic activity for the electrooxidation of formic acid and ethanol on the basis of cyclic voltammetry and chronoamperometric data. It is suggested that both the electrochemical active surface area and the small size effect are the key roles in determining the electrocatalytic performances of Pd nanocrystals. A "dissolution-deposition-aggregation" process is proposed to explain the variation of the electrocatalytic activity during the electrocatalysis according to the HRTEM characterization.

Controlled synthesis of thorium and uranium oxide nano-crystals

International Nuclear Information System (INIS)

Hudry, Damien; Apostolidis, Christos; Walter, Olaf; Gouder, Thomas; Courtois, Eglantine; Kubel, Christian; Meyer, Daniel

2013-01-01

Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well-defined actinide-based nano-crystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non-aqueous surfactant-assisted synthesis of thorium and uranium oxide nano-crystals. The final characteristics of thorium and uranium oxide nano-crystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nano-crystals with different sizes (4.5 and 10.7 nm) as well as branched nano-crystals (overall size ca. 5 nm), nano-dots (ca. 4 nm) and nano-rods (with ultra-small diameters of 1 nm) of thorium oxide were synthesised. (authors)

Performance Parameters and Characterizations of Nanocrystals: A Brief Review

Directory of Open Access Journals (Sweden)

Manasi M. Chogale

2016-08-01

Full Text Available Poor bioavailability of drugs associated with their poor solubility limits the clinical effectiveness of almost 40% of the newly discovered drug moieties. Low solubility, coupled with a high log p value, high melting point and high dose necessitates exploration of alternative formulation strategies for such drugs. One such novel approach is formulation of the drugs as “Nanocrystals”. Nanocrystals are primarily comprised of drug and surfactants/stabilizers and are manufactured by “top-down” or “bottom-up” methods. Nanocrystals aid the clinical efficacy of drugs by various means such as enhancement of bioavailability, lowering of dose requirement, and facilitating sustained release of the drug. This effect is dependent on the various characteristics of nanocrystals (particle size, saturation solubility, dissolution velocity, which have an impact on the improved performance of the nanocrystals. Various sophisticated techniques have been developed to evaluate these characteristics. This article describes in detail the various characterization techniques along with a brief review of the significance of the various parameters on the performance of nanocrystals.

Potentiometric Titrations for Measuring the Capacitance of Colloidal Photodoped ZnO Nanocrystals.

Science.gov (United States)

Brozek, Carl K; Hartstein, Kimberly H; Gamelin, Daniel R

2016-08-24

Colloidal semiconductor nanocrystals offer a unique opportunity to bridge molecular and bulk semiconductor redox phenomena. Here, potentiometric titration is demonstrated as a method for quantifying the Fermi levels and charging potentials of free-standing colloidal n-type ZnO nanocrystals possessing between 0 and 20 conduction-band electrons per nanocrystal, corresponding to carrier densities between 0 and 1.2 × 10(20) cm(-3). Potentiometric titration of colloidal semiconductor nanocrystals has not been described previously, and little precedent exists for analogous potentiometric titration of any soluble reductants involving so many electrons. Linear changes in Fermi level vs charge-carrier density are observed for each ensemble of nanocrystals, with slopes that depend on the nanocrystal size. Analysis indicates that the ensemble nanocrystal capacitance is governed by classical surface electrical double layers, showing no evidence of quantum contributions. Systematic shifts in the Fermi level are also observed with specific changes in the identity of the charge-compensating countercation. As a simple and contactless alternative to more common thin-film-based voltammetric techniques, potentiometric titration offers a powerful new approach for quantifying the redox properties of colloidal semiconductor nanocrystals.

Stabilizing Agents for Drug Nanocrystals: Effect on Bioavailability

Directory of Open Access Journals (Sweden)

Annika Tuomela

2016-05-01

Full Text Available Drug nanocrystals are a versatile option for drug delivery purposes, and while the number of poorly soluble drug materials is all the time increasing, more research in this area is performed. Drug nanocrystals have a simple structure—a solid drug core is surrounded by a layer of stabilizing agent. However, despite the considerably simple structure, the selection of an appropriate stabilizer for a certain drug can be challenging. Mostly, the stabilizer selection is based purely on the requirement of physical stability, e.g., maintaining the nanosized particle size as long as possible after the formation of drug nanocrystals. However, it is also worth taking into account that stabilizer can affect the bioavailability in the final formulation via interactions with cells and cell layers. In addition, formation of nanocrystals is only one process step, and for the final formulation, more excipients are often added to the composition. The role of the stabilizers in the final formulation can be more than only stabilizing the nanocrystal particle size. A good example is the stabilizer’s role as cryoprotectant during freeze drying. In this review, the stabilizing effect, role of stabilizers in final nanocrystalline formulations, challenges in reaching in vitro–in vivo correlation with nanocrystalline products, and stabilizers’ effect on higher bioavailability are discussed.

Sulfur nanocrystals anchored graphene composite with highly improved electrochemical performance for lithium-sulfur batteries

Science.gov (United States)

Zhang, Jun; Dong, Zimin; Wang, Xiuli; Zhao, Xuyang; Tu, Jiangping; Su, Qingmei; Du, Gaohui

2014-12-01

Two kinds of graphene-sulfur composites with 50 wt% of sulfur are prepared using hydrothermal method and thermal mixing, respectively. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray Spectra mapping show that sulfur nanocrystals with size of ∼5 nm dispersed on graphene sheets homogeneously for the sample prepared by hydrothermal method (NanoS@G). While for the thermal mixed graphene-sulfur composite (S-G mixture), sulfur shows larger and uneven size (50-200 nm). X-ray Photoelectron Spectra (XPS) reveals the strong chemical bonding between the sulfur nanocrystals and graphene. Comparing with the S-G mixture, the NanoS@G composite shows highly improved electrochemical performance as cathode for lithium-sulfur (Li-S) battery. The NanoS@G composite delivers an initial capacity of 1400 mAh g-1 with the sulfur utilization of 83.7% at a current density of 335 mA g-1. The capacity keeps above 720 mAh g-1 over 100 cycles. The strong adherence of the sulfur nanocrystals on graphene immobilizes sulfur and polysulfides species and suppressed the "shuttle effect", resulting higher coulombic efficiency and better capacity retention. Electrochemical impedance also suggests that the strong bonding enabled rapid electronic/ionic transport and improved electrochemical kinetics, therefore good rate capability is obtained. These results demonstrate that the NanoS@G composite is a very promising candidate for high-performance Li-S batteries.

Colloidal nanocrystals in epitactical semiconductor structures; Kolloidale Nanokristalle in epitaktischen Halbleiterstrukturen

Energy Technology Data Exchange (ETDEWEB)

Arens, C.

2007-10-15

in this thesis for the first time a new method for the fabrication of semiconductor quantum-dot structures was successfully applied. thereby colloidal CdSe nanocrystals have been imbedded by means of molecular-beam epitaxy into an epitactical ZnSe crystal matrix. The properties of the epitactically overgrown nanocrystals are elaborated in this thesis. The distribution of the nanocrystals on ZnSe surfaces dependes on the stressed state of the ZnSe layer. Nanocrystals on stressed ZnSe grow in agglomerates on its surface. Individual nanocrystals however can only be deposited on relaxed ZnSe. In-situ studies by means of reflection of high-energetically diffracted electrons show in both cases that under stoichiometrical conditions the ZnSe covering layer grows two-dimensionally. It is epitactic what is proved by means of highly resolving X-ray diffraction and transmission electron microscopy. The nanocrystals are after the overgrowth with ZnSe optically activ.

Colloidal infrared reflective and transparent conductive aluminum-doped zinc oxide nanocrystals

Science.gov (United States)

Buonsanti, Raffaella; Milliron, Delia J

2015-02-24

The present invention provides a method of preparing aluminum-doped zinc oxide (AZO) nanocrystals. In an exemplary embodiment, the method includes (1) injecting a precursor mixture of a zinc precursor, an aluminum precursor, an amine, and a fatty acid in a solution of a vicinal diol in a non-coordinating solvent, thereby resulting in a reaction mixture, (2) precipitating the nanocrystals from the reaction mixture, thereby resulting in a final precipitate, and (3) dissolving the final precipitate in an apolar solvent. The present invention also provides a dispersion. In an exemplary embodiment, the dispersion includes (1) nanocrystals that are well separated from each other, where the nanocrystals are coated with surfactants and (2) an apolar solvent where the nanocrystals are suspended in the apolar solvent. The present invention also provides a film. In an exemplary embodiment, the film includes (1) a substrate and (2) nanocrystals that are evenly distributed on the substrate.

Crystallization and Growth of Colloidal Nanocrystals

CERN Document Server

Leite, Edson Roberto

2012-01-01

Since the size, shape, and microstructure of nanocrystalline materials strongly impact physical and chemical properties, the development of new synthetic routes to  nanocrystals with controlled composition and morphology is a key objective of the nanomaterials community. This objective is dependent on control of the nucleation and growth mechanisms that occur during the synthetic process, which in turn requires a fundamental understanding of both classical nucleation and growth and non-classical growth processes in nanostructured materials.  Recently, a novel growth process called Oriented Attachment (OA) was identified which appears to be a fundamental mechanism during the development of nanoscale  materials. OA is a special case of aggregation that provides an important route by which nanocrystals grow, defects are formed, and unique—often symmetry-defying—crystal morphologies can be produced. This growth mechanism involves reversible self-assembly of primary nanocrystals followed by reorientati...

Increased electronic coupling in silicon nanocrystal networks doped with F4-TCNQ.

Science.gov (United States)

Carvalho, Alexandra; Oberg, Sven; Rayson, Mark J; Briddon, Patrick R

2013-02-01

The modification of the electronic structure of silicon nanocrystals using an organic dopant, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), is investigated using first-principles calculations. It is shown that physisorbed F4-TCNQ molecules have the effect of oxidizing the nanocrystal, attracting the charge density towards the F4-TCNQ-nanocrystal interface, and decreasing the excitation energy of the system. In periodic F4-TCNQ/nanocrystal superlattices, F4-TCNQ is suggested to enhance exciton separation, and in the presence of free holes, to serve as a bridge for electron/hole transfer between adjacent nanocrystals.

Insights into the microstructural and physical properties of colloidal Fe:ZnSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Xie, Ruishi, E-mail: rxie@foxmail.com [Analytical and Testing Center, Southwest University of Science and Technology, Mianyang 621010 (China); Li, Yuanli [Department of Materials, Southwest University of Science and Technology, Mianyang 621010 (China); Jiang, Linhai; Zhang, Xingquan [Analytical and Testing Center, Southwest University of Science and Technology, Mianyang 621010 (China)

2014-10-30

Highlights: • We present a facile and environmentally friendly protocol to fabricate Fe:ZnSe nanocrystals. • The microstructural and physical properties of Fe:ZnSe nanocrystals were systematically investigated. • The current synthesis is dramatically simple and highly reproducible, it will facilitate the commercial scale synthesis of highly luminescent water-soluble nanocrystals with surface functionality in the near future. - Abstract: Here, we present a facile and environmentally friendly synthetic protocol to fabricate highly luminescent and water-soluble Fe:ZnSe nanocrystals in aqueous solution at low temperature. The microstructure and various physical properties (e.g., crystal structure, interplanar spacing, lattice parameter, crystalline size, lattice microstrain, intrinsic stress, X-ray density, specific surface area, dislocation density, porosity, agglomeration number) of the Fe:ZnSe nanocrystals were systematically investigated using X-ray diffraction. The particle size and morphology of the Fe:ZnSe nanocrystals were determined by transmission electron microscopy. The optical properties (e.g., absorption and photoluminescence) of the fabricated nanocrystals were explored using ultraviolet–visible absorption and photoluminescence spectroscopies, respectively. The surface functionalization of the Fe:ZnSe nanocrystals by mercaptoacetic acid ligand was evidenced by Fourier transform infrared spectroscopy. To confirm the elementary composition of the obtained nanocrystals, Energy dispersive X-ray spectroscopy was performed. To further shed light upon elemental distribution of the resulting nanocrystals, elemental mapping measurements were conducted. Moreover, the underlying mechanisms were also elucidated. As a consequence, the current investigation not only provides a deep insight into exploring the physical properties of doped nanocrystals, but also demonstrates a useful synthetic strategy for producing water-soluble and highly fluorescent doped

Facile template-directed synthesis of carbon-coated SnO2 nanotubes with enhanced Li-storage capabilities

International Nuclear Information System (INIS)

Zhu, Xiaoshu; Zhu, Jingyi; Yao, Yinan; Zhou, Yiming; Tang, Yawen; Wu, Ping

2015-01-01

Herein, a novel type of carbon-coated SnO 2 nanotubes has been designed and synthesized through a facile two-step hydrothermal approach by using ZnO nanorods as templates. During the synthetic route, SnO 2 nanocrystals and carbon layer have been uniformly deposited on the rod-like templates in sequence, meanwhile ZnO nanorods could be in situ dissolved owing to the generated alkaline and acidic environments during hydrothermal coating of SnO 2 nanocrystals and hydrothermal carbonization of glucose, respectively. When utilized as an anode material in lithium-ion batteries, the carbon-coated SnO 2 nanotubes manifests markedly enhanced Li-storage capabilities in terms of specific capacity and cycling stability in comparison with bare SnO 2 nanocrystals. - Graphical abstract: Display Omitted - Highlights: • C-coated SnO 2 nanotubes prepared via facile ZnO-nanorod-templated hydrothermal route. • Unique morphological and structural features toward lithium storage. • Enhanced Li-storage performance in terms of specific capacity and cycling stability

Stability studies of CdSe nanocrystals in an aqueous environment

Energy Technology Data Exchange (ETDEWEB)

Xi Lifei; Lek, Jun Yan; Liang, Yen Nan; Zhou Wenwen; Yan Qingyu; Hu Xiao; Chiang, Freddy Boey Yin; Lam, Yeng Ming [School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, 639798 (Singapore); Boothroyd, Chris, E-mail: ymlam@ntu.edu.sg [Center for Electron Nanoscopy, Technical University of Denmark, DK-2800 Kongens Lyngby (Denmark)

2011-07-08

In this paper, CdSe nanocrystal dissolution in an aqueous solution was studied. It was found that light is a key factor affecting the dissolution of nanocrystals. In the presence of light, the electrons generated from CdSe nanocrystals reduce water to hydrogen and hydroxide ions (OH{sup -}) while photo-generated holes oxidize CdSe to Cd{sup 2+} and elemental Se. The dissolution was accelerated in an acidic medium while moderate alkalinity (pH = 10.3) can slow down the dissolution possibly due to precipitation of nanocrystals. This study has strong implications for the use of these crystals in aqueous environments (bioimaging and dye-sensitized solar cells).

Hydroxyapatite nanocrystals: Simple preparation, characterization and formation mechanism

International Nuclear Information System (INIS)

Mohandes, Fatemeh; Salavati-Niasari, Masoud; Fathi, Mohammadhossein; Fereshteh, Zeinab

2014-01-01

Crystalline hydroxyapatite (HAP) nanoparticles and nanorods have been successfully synthesized via a simple precipitation method. To control the shape and particle size of HAP nanocrystals, coordination ligands derived from 2-hydroxy-1-naphthaldehyde were first prepared, characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ( 1 H-NMR) spectroscopies, and finally applied in the synthesis process of HAP. On the other hand, the HAP nanocrystals were also characterized by several techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to the FE-SEM and TEM micrographs, it was found that the morphology and crystallinity of the HAP powders depended on the coordination mode of the ligands. - Highlights: • HAP nanobundles and nanoparticles have been prepared by a precipitation method. • Morphologies of HAP nanocrystals were controlled by different coordination ligands. • The formation mechanism of hydroxyapatite nanocrystals was also considered

Hydroxyapatite nanocrystals: Simple preparation, characterization and formation mechanism

Energy Technology Data Exchange (ETDEWEB)

Mohandes, Fatemeh [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P. O. Box. 87317-51167, Islamic Republic of Iran (Iran, Islamic Republic of); Salavati-Niasari, Masoud, E-mail: salavati@kashanu.ac.ir [Department of Inorganic Chemistry, Faculty of Chemistry, University of Kashan, Kashan, P. O. Box. 87317-51167, Islamic Republic of Iran (Iran, Islamic Republic of); Institute of Nano Science and Nano Technology, University of Kashan, Kashan, P. O. Box 87317-51167, Islamic Republic of Iran (Iran, Islamic Republic of); Fathi, Mohammadhossein [Biomaterials Research Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Islamic Republic of Iran (Iran, Islamic Republic of); Dental Materials Research Center, Isfahan University of Medical Sciences, Isfahan, Islamic Republic of Iran (Iran, Islamic Republic of); Fereshteh, Zeinab [Biomaterials Research Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Islamic Republic of Iran (Iran, Islamic Republic of)

2014-12-01

Crystalline hydroxyapatite (HAP) nanoparticles and nanorods have been successfully synthesized via a simple precipitation method. To control the shape and particle size of HAP nanocrystals, coordination ligands derived from 2-hydroxy-1-naphthaldehyde were first prepared, characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ({sup 1}H-NMR) spectroscopies, and finally applied in the synthesis process of HAP. On the other hand, the HAP nanocrystals were also characterized by several techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to the FE-SEM and TEM micrographs, it was found that the morphology and crystallinity of the HAP powders depended on the coordination mode of the ligands. - Highlights: • HAP nanobundles and nanoparticles have been prepared by a precipitation method. • Morphologies of HAP nanocrystals were controlled by different coordination ligands. • The formation mechanism of hydroxyapatite nanocrystals was also considered.

Visualization of nanocrystal breathing modes at extreme strains

Science.gov (United States)

Szilagyi, Erzsi; Wittenberg, Joshua S.; Miller, Timothy A.; Lutker, Katie; Quirin, Florian; Lemke, Henrik; Zhu, Diling; Chollet, Matthieu; Robinson, Joseph; Wen, Haidan; Sokolowski-Tinten, Klaus; Lindenberg, Aaron M.

2015-03-01

Nanoscale dimensions in materials lead to unique electronic and structural properties with applications ranging from site-specific drug delivery to anodes for lithium-ion batteries. These functional properties often involve large-amplitude strains and structural modifications, and thus require an understanding of the dynamics of these processes. Here we use femtosecond X-ray scattering techniques to visualize, in real time and with atomic-scale resolution, light-induced anisotropic strains in nanocrystal spheres and rods. Strains at the percent level are observed in CdS and CdSe samples, associated with a rapid expansion followed by contraction along the nanosphere or nanorod radial direction driven by a transient carrier-induced stress. These morphological changes occur simultaneously with the first steps in the melting transition on hundreds of femtosecond timescales. This work represents the first direct real-time probe of the dynamics of these large-amplitude strains and shape changes in few-nanometre-scale particles.

Solvothermal synthesis and characterization of CZTS nanocrystals

Science.gov (United States)

Dumasiya, Ajay; Shah, N. M.

2017-05-01

Cu2ZnSnS4 (CZTS) is a promising thin film absorber material for low cost solar cell applications. CZTS nanoparticle ink synthesized using solvothermal route is an attractive option to deposit absorber layer using screen printing or spin coating method in CZTS thin film solar cell. In this study we have synthesized CZTS nanocrystals using solvothermal method from aqueous solution of Copper nitrate [Cu(NO3)2], Zinc nitrate [Zn(NO3)2], tin chloride [SnCl4] and thiourea with varying concentration of Cu(NO3)2 (viz 0.82 mmol,1.4 mmol, 1.7 mmol) keeping concentrations of rest of solutions constant. As synthesized CZTS nanocrystals are characterized using Energy Dispersive Analysis of X-rays (EDAX) to verify stoichiometry of elements. Analysis of EDAX data suggests that CZTS nanocrystals having Copper nitrate [Cu (NO3)2] concentration of 1.4 m mole is near stoichiometric. X-ray diffraction analysis study of CZTS nanocrystals having Copper nitrate [Cu (NO3)2] concentration of 1.4 m mole reveals the preferred orientation of the grains in (112), (220) and (312) direction confirming Kesterite structure of CZTS.

Photoluminescence of nanocrystals embedded in oxide matrices

International Nuclear Information System (INIS)

Estrada, C.; Gonzalez, J.A.; Kunold, A.; Reyes-Esqueda, J.A.; Pereyra, P.

2006-12-01

We used the theory of finite periodic systems to explain the photoluminescence spectra dependence on the average diameter of nanocrystals embedded in oxide matrices. Because of the broad matrix band gap, the photoluminescence response is basically determined by isolated nanocrystals and sequences of a few of them. With this model we were able to reproduce the shape and displacement of the experimentally observed photoluminescence spectra. (author)

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

International Nuclear Information System (INIS)

Shirazi, Roza; Kovacs, Andras; Dan Corell, Dennis; Gritti, Claudia; Thorseth, Anders; Dam-Hansen, Carsten; Michael Petersen, Paul; Kardynal, Beata

2014-01-01

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude compared to the quantum efficiency of the small nanocrystals. By correlating this result with the time-resolved photoluminescence we find that the reduced photoluminescence efficiency is caused by a fast growing fraction of non-emissive nanocrystals while the quality of the nanocrystals that emit light is similar for all samples. Transmission electron microscopy reveals the polycrystalline nature of many of the large nanocrystals, pointing to the grain boundaries as one possible site for the photoluminescence quenching defects. -- Highlights: • We investigate drop of quantum efficiency of InP/ZnS nanocrystals emitting at longer wavelengths. • We correlate quantum efficiency measurements with time-resolved carrier dynamics. • We find that only a small fraction of larger nanocrystals is optically active

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Shirazi, Roza, E-mail: rozas@fotonik.dtu.dk [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); Kovacs, Andras [Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons, Peter Grunberg Institute, Forschungszentrum Julich, 52425 Julich (Germany); Dan Corell, Dennis [Department of Photonics Engineering, Technical University of Denmark, Riso, Frederiksborgvej 399, 4000 Roskilde (Denmark); Gritti, Claudia [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); Thorseth, Anders; Dam-Hansen, Carsten; Michael Petersen, Paul [Department of Photonics Engineering, Technical University of Denmark, Riso, Frederiksborgvej 399, 4000 Roskilde (Denmark); Kardynal, Beata [Department of Photonics Engineering, Technical University of Denmark, Oersted Plads 343, 2800 Kgs Lyngby (Denmark); PGI-9, Forschungszentrum Julich, JARA FIT, 52425 Julich (Germany)

2014-01-15

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude compared to the quantum efficiency of the small nanocrystals. By correlating this result with the time-resolved photoluminescence we find that the reduced photoluminescence efficiency is caused by a fast growing fraction of non-emissive nanocrystals while the quality of the nanocrystals that emit light is similar for all samples. Transmission electron microscopy reveals the polycrystalline nature of many of the large nanocrystals, pointing to the grain boundaries as one possible site for the photoluminescence quenching defects. -- Highlights: • We investigate drop of quantum efficiency of InP/ZnS nanocrystals emitting at longer wavelengths. • We correlate quantum efficiency measurements with time-resolved carrier dynamics. • We find that only a small fraction of larger nanocrystals is optically active.

Surface treatment of nanocrystal quantum dots after film deposition

Science.gov (United States)

Sykora, Milan; Koposov, Alexey; Fuke, Nobuhiro

2015-02-03

Provided are methods of surface treatment of nanocrystal quantum dots after film deposition so as to exchange the native ligands of the quantum dots for exchange ligands that result in improvement in charge extraction from the nanocrystals.

High-purity Cu nanocrystal synthesis by a dynamic decomposition method

OpenAIRE

Jian, Xian; Cao, Yu; Chen, Guozhang; Wang, Chao; Tang, Hui; Yin, Liangjun; Luan, Chunhong; Liang, Yinglin; Jiang, Jing; Wu, Sixin; Zeng, Qing; Wang, Fei; Zhang, Chengui

2014-01-01

Cu nanocrystals are applied extensively in several fields, particularly in the microelectron, sensor, and catalysis. The catalytic behavior of Cu nanocrystals depends mainly on the structure and particle size. In this work, formation of high-purity Cu nanocrystals is studied using a common chemical vapor deposition precursor of cupric tartrate. This process is investigated through a combined experimental and computational approach. The decomposition kinetics is researched via differential sca...

Synthesis and spectroscopic properties of silica-dye-semiconductor nanocrystal hybrid particles.

Science.gov (United States)

Ren, Ting; Erker, Wolfgang; Basché, Thomas; Schärtl, Wolfgang

2010-12-07

We prepared silica-dye-nanocrystal hybrid particles and studied the energy transfer from semiconductor nanocrystals (= donor) to organic dye molecules (= acceptor). Multishell CdSe/CdS/ZnS semiconductor nanocrystals were adsorbed onto monodisperse Stöber silica particles with an outer silica shell of thickness 2-23 nm containing organic dye molecules (Texas Red). The thickness of this dye layer has a strong effect on the energy transfer efficiency, which is explained by the increase in the number of dye molecules homogeneously distributed within the silica shell, in combination with an enhanced surface adsorption of nanocrystals with increasing dye amount. Our conclusions were underlined by comparison of the experimental results with numerically calculated FRET efficiencies and by control experiments confirming attractive interaction between the nanocrystals and Texas Red freely dissolved in solution.

Ultrahigh intercalation pseudocapacitance of mesoporous orthorhombic niobium pentoxide from a novel cellulose nanocrystal template

Energy Technology Data Exchange (ETDEWEB)

Kong, Lingping; Zhang, Chuangfang; Wang, Jitong; Long, Donghui, E-mail: longdh@mail.ecust.edu.cn; Qiao, Wenming; Ling, Licheng

2015-01-15

A facile biotemplating method has been developed to prepare mesoporous orthorhombic nobium pentoxide (T-Nb{sub 2}O{sub 5}) films with ultrahigh lithium ion (Li{sup +}) intercalation pseudocapacitance. Nanorod-like cellulose nanocrystals (CNs) with 5–10 nm in width and 100–300 nm in length are produced by the hydrolysis of cotton, which can serve as a novel soft templating agent enabling the straightforward synthesis of mesoporous T-Nb{sub 2}O{sub 5} films. By varying the niobic-to-template ratio, it is possible to tune the surface area and crystallite dimension of the Nb{sub 2}O{sub 5} films. The obtained T-Nb{sub 2}O{sub 5} films show typical capacitive-dominated behaviour in the sweep rate range of 1–20 mV s{sup −1}. It delivers an initial intercalation capacity of 644 C g{sup −1} at a current density of 0.625 A g{sup −1}, corresponding to x = 1.83 for Li{sub x}Nb{sub 2}O{sub 5}, and can still keep relatively stable capacity of 560 C g{sup −1} after 300 cycles. Moreover, its excellent high-rate capability (450 C g{sup −1} at 12.5 A g{sup −1}) and wider temperature adaptability present here suggests the promising of T-Nb{sub 2}O{sub 5} as high-energy pseudocapacitor electrode with superior intercalation capacitive behaviour. - Graphical abstract: We developed a facile and sustainable method to prepare T-Nb{sub 2}O{sub 5} nanocrystals using novel nanorod-like cellulose nanocrystals (CNs) as soft templates. The T-Nb{sub 2}O{sub 5} nanocrystals exhibited unprecedented Li{sup +} intercalation pseudocapacitance, excellent cycle performance and good high-and-low temperature tolerance performance.

Engineering Gold Nanorod-Based Plasmonic Nanocrystals for Optical Applications

KAUST Repository

Huang, Jianfeng

2015-09-01

Plasmonic nanocrystals have a unique ability to support localized surface plasmon resonances and exhibit rich and intriguing optical properties. Engineering plasmonic nanocrystals can maximize their potentials for specific applications. In this dissertation, we developed three unprecedented Au nanorod-based plasmonic nanocrystals through rational design of the crystal shape and/or composition, and successfully demonstrated their applications in light condensation, photothermal conversion, and surface-enhanced Raman spectroscopy (SERS). The “Au nanorod-Au nanosphere dimer” nanocrystal was synthesized via the ligand-induced asymmetric growth of a Au nanosphere on a Au nanorod. This dimeric nanostructure features an extraordinary broadband optical absorption in the range of 400‒1400nm, and it proved to be an ideal black-body material for light condensation and an efficient solar-light harvester for photothermal conversion. The “Au nanorod (core) @ AuAg alloy (shell)” nanocrystal was built through the epitaxial growth of homogeneously alloyed AuAg shells on Au nanorods by precisely controlled synthesis. The resulting core-shell structured, bimetallic nanorods integrate the merits of the AuAg alloy with the advantages of anisotropic nanorods, exhibiting strong, stable and tunable surface plasmon resonances that are essential for SERS applications in a corrosive environment. The “high-index faceted Au nanorod (core) @ AuPd alloy (shell)” nanocrystal was produced via site-specific epitaxial growth of AuPd alloyed horns at the ends of Au nanorods. The AuPd alloyed horns are bound with high-index side facets, while the Au nanorod concentrates an intensive electric field at each end. This unique configuration unites highly active catalytic sites with strong SERS sites into a single entity and was demonstrated to be ideal for in situ monitoring of Pd-catalyzed reactions by SERS. The synthetic strategies developed here are promising towards the fabrication of

Protein unfolding versus β-sheet separation in spider silk nanocrystals

International Nuclear Information System (INIS)

Alam, Parvez

2014-01-01

In this communication a mechanism for spider silk strain hardening is proposed. Shear failure of β-sheet nanocrystals is the first failure mode that gives rise to the creation of smaller nanocrystals, which are of higher strength and stiffness. β-sheet unfolding requires more energy than nanocrystal separation in a shear mode of failure. As a result, unfolding occurs after the nanocrystals separate in shear. β-sheet unfolding yields a secondary strain hardening effect once the β-sheet conformation is geometrically stable and acts like a unidirectional fibre in a fibre reinforced composite. The mechanism suggested herein is based on molecular dynamics calculations of residual inter-β-sheet separation strengths against residual intra-β-sheet unfolding strengths. (paper)

Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

Energy Technology Data Exchange (ETDEWEB)

Sachleben, Joseph Robert [Lawrence Berkeley Lab., CA (United States); California Univ., Berkeley, CA (United States). Dept. of Chemistry

1993-09-01

Semiconductor nanocrystals, small biomolecules, and ¹³C enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution ¹H and ¹³C liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 Å. Internal motion is estimated to be slow with a correlation time > 10^-8 s^-1. The surface thiophenol ligands react to form a dithiophenol when the nanocrystals were subjected to O₂ and ultraviolet. A method for measuring ¹⁴N-¹H J-couplings is demonstrated on pyridine and the peptide oxytocin; selective 2D T₁ and T₂ experiments are presented for measuring relaxation times in crowded spectra with overlapping peaks in 1D, but relaxation effects interfere. Possibility of carbon-carbon cross relaxation in ¹³C enriched solids is demonstrated by experiments on zinc acetate and L-alanine.

Shaping metal nanocrystals through epitaxial seeded growth

Energy Technology Data Exchange (ETDEWEB)

Habas, Susan E.; Lee, Hyunjoo; Radmilovic, Velimir; Somorjai,Gabor A.; Yang, Peidong

2008-02-17

Morphological control of nanocrystals has becomeincreasingly important, as many of their physical and chemical propertiesare highly shape-dependent. Nanocrystal shape control for both single andmultiple material systems, however, remains fairly empirical andchallenging. New methods need to be explored for the rational syntheticdesign of heterostructures with controlled morphology. Overgrowth of adifferent material on well-faceted seeds, for example, allows for the useof the defined seed morphology to control nucleation and growth of thesecondary structure. Here, we have used highly faceted cubic Pt seeds todirect the epitaxial overgrowth of a secondary metal. We demonstrate thisconcept with lattice matched Pd to produce conformal shape-controlledcore-shell particles, and then extend it to lattice mismatched Au to giveanisotropic growth. Seeding with faceted nanocrystals may havesignificant potential towards the development of shape-controlledheterostructures with defined interfaces.

Investigation of the photoluminescence properties of thermochemically synthesized CdS nanocrystals

Directory of Open Access Journals (Sweden)

M. Molaei

2011-03-01

Full Text Available In this work we have synthesized CdS nanocrystals with thermochemical method. CdSO4 and Na2S2O3 were used as the precursors and thioglycolic acid (TGA was used as capping agent molecule. The structure and optical property of the nanocrystals were characterized by means of XRD, TEM, UV-visible optical spectroscopy and photoluminescence (PL. X-ray diffraction (XRD and TEM analyses demonstrated hexagonal phase CdS nanocrystals with an average size around 2 nm. Synthesized nanocrystals exhibited band gap of about 3.2 eV and showed a broad band emission from 400-750 nm centered at 504 nm with a (0.27, 0.39 CIE coordinate. This emission can be attributed to recombination of an electron in conduction band with a hole trapped in Cd vacancies near to the valance band of CdS. The best attained photoluminescence quantum yield of the nanocrystals was about 12%, this amount is about 20 times higher than that for thioglycerol (TG capped CdS nanocrystals.

Fine-tuning the Wall Thickness of Ordered Mesoporous Graphene by Exploiting Ligand Exchange of Colloidal Nanocrystals

Science.gov (United States)

Han, Dandan; Yan, Yancui; Wei, Jishi; Wang, Biwei; Li, Tongtao; Guo, Guannan; Yang, Dong; Xie, Songhai; Dong, Angang

2017-12-01

Because of their unique physical properties, three-dimensional (3D) graphene has attracted enormous attention over the past years. However, it is still a challenge to precisely control the layer thickness of 3D graphene. Here, we report a novel strategy to rationally adjust the wall thickness of ordered mesoporous graphene (OMG). By taking advantage of ligand exchange capability of colloidal Fe3O4 nanocrystals, we are able to fine-tune the wall thickness of OMG from 2 to 6 layers of graphene by tailoring the hydrocarbon ligands attached to the nanocrystal surface. When evaluated as electrocatalyst for oxygen reduction reaction upon S and N doping, the 4-layer OMG is found to show better catalytic performance compared with its 2- and 6-layer counterparts, which we attribute to the enhanced exposure of active sites resulting from its ultrathin wall thickness and high surface area.

The aggregation and characteristics of radiation-induced defects in lithium fluoride nanocrystals

Science.gov (United States)

Voitovich, A. P.; Kalinov, V. S.; Korzhik, M. V.; Martynovich, E. F.; Runets, L. P.; Stupak, A. P.

2013-02-01

It has been established that diffusion activation energies for anion vacancies and centres ? in lithium fluoride nanocrystals are higher than those in bulk crystals. In nanocrystals, ? centres migrating in the range of the temperature close to room temperature is not observed and these centres remain stable. The ratio of centres ? and F 2 concentrations in nanocrystals is higher than in bulk crystals. A new type of colour centres, which is absent in bulk crystals, is discovered in nanocrystals.

Second- and third-harmonic generation as a local probe for nanocrystal-doped polymer materials with a suppressed optical breakdown threshold

Science.gov (United States)

Konorov, S. O.; Fedotov, A. B.; Ivanov, A. A.; Alfimov, M. V.; Zabotnov, S. V.; Naumov, A. N.; Sidorov-Biryukov, D. A.; Podshivalov, A. A.; Petrov, A. N.; Fornarini, L.; Carpanese, M.; Ferrante, G.; Fantoni, R.; Zheltikov, A. M.

2003-09-01

Second- and third-harmonic generation processes are shown to allow the detection of absorptive agglomerates of nanocrystals in transparent materials and the visualization of optical breakdown in nanocomposite materials. Correlations between laser-induced breakdown and the behavior of the second- and third-harmonic signals produced in SiC/PMMA nanocomposite films are studied. The potential of second- and third-harmonic generation for the on-line visualization of laser breakdown in nanocomposite polymer materials is revealed, with the ablative material removal being monitored by the decay of the second- and third-harmonic signals. The second and third harmonics generated around the optical breakdown threshold by 75-fs pulses of 1.25-μm Cr:forsterite laser radiation are respectively more than two and four orders of magnitude more intense than the second and third harmonics produced under identical conditions by 40-ps pulses of a Nd:YAG laser. The breakdown threshold for PMMA films doped with 10-20-nm SiC nanocrystals forming absorptive agglomerates are demonstrated to be more than an order of magnitude lower than the breakdown threshold for crystalline SiC and about an order of magnitude lower than that for nondoped PMMA films.

Semiconductor Nanocrystals for Biological Imaging

Energy Technology Data Exchange (ETDEWEB)

Fu, Aihua; Gu, Weiwei; Larabell, Carolyn; Alivisatos, A. Paul

2005-06-28

Conventional organic fluorophores suffer from poor photo stability, narrow absorption spectra and broad emission feature. Semiconductor nanocrystals, on the other hand, are highly photo-stable with broad absorption spectra and narrow size-tunable emission spectra. Recent advances in the synthesis of these materials have resulted in bright, sensitive, extremely photo-stable and biocompatible semiconductor fluorophores. Commercial availability facilitates their application in a variety of unprecedented biological experiments, including multiplexed cellular imaging, long-term in vitro and in vivo labeling, deep tissue structure mapping and single particle investigation of dynamic cellular processes. Semiconductor nanocrystals are one of the first examples of nanotechnology enabling a new class of biomedical applications.

Controlled synthesis of novel octapod platinum nanocrystals under microwave irradiation

International Nuclear Information System (INIS)

Dai, Lei; Chi, Quan; Zhao, Yanxi; Liu, Hanfan; Zhou, Zhongqiang; Li, Jinlin; Huang, Tao

2014-01-01

Graphical abstract: Under microwave irradiation, novel octapod Pt nanocrystals were synthesized by reducing H 2 PtCl 6 in TEG with PVP as a stabilizer. The as-prepared Pt nanocrystals displayed a unique octapod nanostructure with five little mastoids in each concave center. The use of KI was crucial to the formation of novel Pt octapods. Novel Octapod Platinum Nanocrystals. - Highlights: • A novel octapod Pt nanocrystals different from the common octapod were obtained. • The use of KI was crucial to the formation of the novel Pt octapods. • Microwave was readily employed in controlled synthesis of the novel Pt octapods. - Abstract: Microwave was employed in the shape-controlled synthesis of Pt nanoparticles. Novel octapod Pt nanocrystals enclosed with (1 1 1) facets were readily synthesized with H 2 PtCl 6 as a precursor, tetraethylene glycol (TEG) as both a solvent and a reducing agent, polyvinylpyrrolidone (PVP) as a stabilizer in the presence of an appropriate amount of KI under microwave irradiation for 140 s. The as-prepared Pt nanocrystals displayed a unique octapod nanostructure with five little mastoids in each concave center and exhibited higher electrocatalytic activity than commercial Pt black in the electro-oxidations of methanol and formic acid. The results demonstrated that the use of KI was crucial to the formation of Pt octapods. KI determined the formation of the novel octapod Pt nanocrystals by tuning up the reduction kinetics and adsorbing on the surfaces of growing Pt nanoparticles. The optimum molar ratio of H 2 PtCl 6 /KI/PVP was 1/30/45

Photoresponse of hybrids made of carbon nanotubes and CdTe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Zebli, Bernd; Vieyra, Hugo A.; Kotthaus, Joerg P. [Department fuer Physik and Center for NanoScience (CeNS), Ludwig-Maximilians-Universitaet Muenchen, Geschwister-Scholl-Platz 1, 80539 Munich (Germany); Carmeli, Itai [Department of Chemistry and Biochemistry, Tel-Aviv University, Tel-Aviv 69978 (Israel); Hartschuh, Achim [Department fuer Chemie, Physikalische Chemie, Butenandtstr. 5-13 E, 81377 Munich (Germany); Holleitner, Alexander W. [Walter-Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 3, 85748 Garching (Germany)

2008-07-01

We observe that the photoresponse of single-walled carbon nanotubes can be adjusted by the absorption characteristics of colloidal CdTe nanocrystals, which are bound to the side-walls of the carbon nanotubes via molecular recognition. To this end, the hybrid systems are characterized using charge transport measurements under resonant optical excitation of the carbon nanotubes and nanocrystals, respectively. We investigate the photoresponse of both ensembles of hybrid systems and single carbon-nanotube-nanocrystal-hybrids. The data suggest a bolometrically induced increase of the current in the carbon nanotubes, which is due to photon absorption in the nanocrystals.

Characterization of Ge-nanocrystal films with photoelectron spectroscopy

International Nuclear Information System (INIS)

Bostedt, C.; Buuren, T. van; Willey, T.M.; Nelson, A.J.; Franco, N.; Moeller, T.; Terminello, L.J.

2003-01-01

The Ge 3d core-levels of germanium nanocrystal films have been investigated by means of photoelectron spectroscopy. The experiments indicate bulk-like coordinated atoms in the nanocrystals and suggest structured disorder on the nanoparticle surface. The results underline the importance of the surface on the overall electronic structure of this class of nanostructured materials

Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

DEFF Research Database (Denmark)

Walzer, K.; Marx, E.; Greenham, N.C.

2003-01-01

We present scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) measurements of CdSe nanocrystals covalently attached to doped GaAs substrates using monolayers of 1,6-hexanedithiol. STM measurements showed the formation of stable, densely packed, homogeneous monolayers...... of nanocrystals. STS measurements showed rectifying behaviour, with high currents at the opposite sample bias to that previously observed for CdSe nanocrystals adsorbed on Si substrates. We explain the rectifying behaviour by considering the interaction between the electronic states of the nanocrystals...

Melting Behavior of Organic Nanocrystals Grown in Sol-gel Matrices

International Nuclear Information System (INIS)

Sanz, N.; Boudet, A.; Ibanez, A.

2002-01-01

We have characterized the thermal stability of organic nanocrystals grown in the pores of sol-gel matrices. The structure has been measured with transmission electron microscopy (TEM) analysis. Depending on the nature of organic molecules and sol-gel matrices, we have modified the dye-matrix interactions and the interfacial structure between nanocrystals and gel-glasses. When the dye-matrix interactions are weak (Van der Waals' bonds), the corresponding interfacial structure observed by TEM is sharp and the nanocrystals melt below the bulk melting point. On the other hand, when the dye-matrix interactions are strong (hydrogen bonds), the interfacial structure is fuzzy and a great superheating of organic nanocrystals is observed in comparison to the bulk melting point of the dye

Biodegradation behaviors of cellulose nanocrystals -PVA nanocomposites

Directory of Open Access Journals (Sweden)

Mahdi Rohani

2014-11-01

Full Text Available In this research, biodegradation behaviors of cellulose nanocrystals-poly vinyl alcohol nanocomposites were investigated. Nanocomposite films with different filler loading levels (3, 6, 9 and 12% by wt were developed by solvent casting method. The effect of cellulose nanocrystals on the biodegradation behaviors of nanocomposite films was studied. Water absorption and water solubility tests were performed by immersing specimens into distilled water. The characteristic parameter of diffusion coefficient and maximum moisture content were determined from the obtained water absorption curves. The water absorption behavior of the nanocomposites was found to follow a Fickian behavior. The maximum water absorption and diffusion coefficients were decreased by increasing the cellulose nanocrystals contents, however the water solubility decrease. The biodegradability of the films was investigated by immersing specimens into cellulase enzymatic solution as well as by burial in soil. The results showed that adding cellulose nanocrystals increase the weight loss of specimens in enzymatic solution but decrease it in soil media. The limited biodegradability of specimens in soil media attributed to development of strong interactions with solid substrates that inhibit the accessibility of functional groups. Specimens with the low degree of hydrolysis underwent extensive biodegradation in both enzymatic and soil media, whilst specimens with the high degree of hydrolysis showed recalcitrance to biodegradation under those conditions.

Pulsed ion-beam induced nucleation and growth of Ge nanocrystals on SiO2

International Nuclear Information System (INIS)

Stepina, N. P.; Dvurechenskii, A. V.; Armbrister, V. A.; Kesler, V. G.; Novikov, P. L.; Gutakovskii, A. K.; Kirienko, V. V.; Smagina, Zh. V.; Groetzschel, R.

2007-01-01

Pulsed low-energy (200 eV) ion-beam induced nucleation during Ge deposition on thin SiO 2 film was used to form dense homogeneous arrays of Ge nanocrystals. The ion-beam action is shown to stimulate the nucleation of Ge nanocrystals when being applied after thin Ge layer deposition. Temperature and flux variation was used to optimize the nanocrystal size and array density required for memory device. Kinetic Monte Carlo simulation shows that ion impacts open an additional channel of atom displacement from a nanocrystal onto SiO 2 surface. This results both in a decrease in the average nanocrystal size and in an increase in nanocrystal density

Microfluidic Fabrication of Hydrocortisone Nanocrystals Coated with Polymeric Stabilisers

Directory of Open Access Journals (Sweden)

David F. Odetade

2016-12-01

Full Text Available Hydrocortisone (HC nanocrystals intended for parenteral administration of HC were produced by anti-solvent crystallisation within coaxial assemblies of pulled borosilicate glass capillaries using either co-current flow of aqueous and organic phases or counter-current flow focusing. The organic phase was composed of 7 mg/mL of HC in a 60:40 (v/v mixture of ethanol and water and the anti-solvent was milli-Q water. The microfluidic mixers were fabricated with an orifice diameter of the inner capillary ranging from 50 µm to 400 µm and operated at the aqueous to organic phase flow rate ratio ranging from 5 to 25. The size of the nanocrystals decreased with increasing aqueous to organic flow rate ratio. The counter-current flow microfluidic mixers provided smaller nanocrystals than the co-current flow devices under the same conditions and for the same geometry, due to smaller diameter of the organic phase stream in the mixing zone. The Z-average particle size of the drug nanocrystals increased from 210–280 nm to 320–400 nm after coating the nanocrystals with 0.2 wt % aqueous solution of hydroxypropyl methylcellulose (HPMC in a stirred vial. The differential scanning calorimetry (DSC and X-ray powder diffraction (XRPD analyses carried out on the dried nanocrystals stabilized with HPMC, polyvinyl pyrrolidone (PVP, and sodium lauryl sulfate (SLS were investigated and reported. The degree of crystallinity for the processed sample was lowest for the sample stabilised with HPMC and the highest for the raw HC powder.

High-purity Cu nanocrystal synthesis by a dynamic decomposition method

Science.gov (United States)

Jian, Xian; Cao, Yu; Chen, Guozhang; Wang, Chao; Tang, Hui; Yin, Liangjun; Luan, Chunhong; Liang, Yinglin; Jiang, Jing; Wu, Sixin; Zeng, Qing; Wang, Fei; Zhang, Chengui

2014-12-01

Cu nanocrystals are applied extensively in several fields, particularly in the microelectron, sensor, and catalysis. The catalytic behavior of Cu nanocrystals depends mainly on the structure and particle size. In this work, formation of high-purity Cu nanocrystals is studied using a common chemical vapor deposition precursor of cupric tartrate. This process is investigated through a combined experimental and computational approach. The decomposition kinetics is researched via differential scanning calorimetry and thermogravimetric analysis using Flynn-Wall-Ozawa, Kissinger, and Starink methods. The growth was found to be influenced by the factors of reaction temperature, protective gas, and time. And microstructural and thermal characterizations were performed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and differential scanning calorimetry. Decomposition of cupric tartrate at different temperatures was simulated by density functional theory calculations under the generalized gradient approximation. High crystalline Cu nanocrystals without floccules were obtained from thermal decomposition of cupric tartrate at 271°C for 8 h under Ar. This general approach paves a way to controllable synthesis of Cu nanocrystals with high purity.

Extraordinary Interfacial Stitching between Single All-Inorganic Perovskite Nanocrystals

NARCIS (Netherlands)

Gomez, Leyre; Lin, Junhao; De Weerd, Chris; Poirier, Lucas; Boehme, Simon C.; Von Hauff, Elizabeth; Fujiwara, Yasufumi; Suenaga, Kazutomo; Gregorkiewicz, Tom

2018-01-01

All-inorganic cesium lead halide perovskite nanocrystals are extensively studied because of their outstanding optoelectronic properties. Being of a cubic shape and typically featuring a narrow size distribution, CsPbX3 (X = Cl, Br, and I) nanocrystals are the ideal starting material for the

PPLA-cellulose nanocrystals nanocomposite prepared by in situ polymerization

International Nuclear Information System (INIS)

Paula, Everton L. de; Pereirea, Fabiano V.; Mano, Valdir

2011-01-01

This work reports the preparation and and characterization of a PLLA-cellulose nanocrystals nanocomposite obtained by in situ polymerization. The nanocomposite was prepared by ring opening polymerization of the lactide dimer in the presence of cellulose nanocrystals (CNCs) and the as-obtained materials was characterized using FTIR, DSC, XRD and TGA measurements. The incorporation of cellulose nanocrystals in PLLA using this method improved the thermal stability and increased the crystallinity of PLLA. These results indicate that the incorporation of CNCs by in situ polymerization improve thermal properties and has potential to improve also mechanical properties of this biodegradable polymer. (author)

Effects of small-angle mistilts on dopant visibility in ADF-STEM imaging of nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Held, Jacob T.; Duncan, Samuel; Mkhoyan, K. Andre, E-mail: mkhoyan@umn.edu

2017-06-15

Highlights: • ADF-STEM is powerful technique for 3D location of substitutionally doped atoms. • The effects of specimen mistilt on ADF-STEM imaging of doped atoms are evaluated. • Visibility changes over 0–30 mrad mistilts are large enough to preclude 3D dopant location. • Dopant visibility is a strong function of specimen mistilt and cannot be ignored. - Abstract: Quantitative ADF-STEM imaging paired with image simulations has proven to be a powerful technique for determining the three dimensional location of substitutionally doped atoms in thin films. Expansion of this technique to lightly-doped nanocrystals requires an understanding of the influence of specimen mistilt on dopant visibility due to the difficulty of accurate orientation determination in such systems as well as crystal movement under the beam. In this study, the effects of specimen mistilt on ADF-STEM imaging are evaluated using germanium-doped silicon nanocrystals as model systems. It is shown that dopant visibility is a strong function of specimen mistilt, and the accuracy of specimen orientation is an important factor in the analysis of three-dimensional dopant location, but the sensitivity to mistilt can be weakened by increasing the STEM probe convergence angle and optimizing ADF detector inner angle.

Synthesis of highly faceted multiply twinned gold nanocrystals stabilized by polyoxometalates

International Nuclear Information System (INIS)

Yuan Junhua; Chen Yuanxian; Han Dongxue; Zhang Yuanjian; Shen Yanfei; Wang Zhijuan; Niu Li

2006-01-01

A novel and facile chemical synthesis of highly faceted multiply twinned gold nanocrystals is reported. The gold nanocrystals are hexagonal in transmission electron microscopy and icosahedral in scanning electron microscopy. Phosphotungstic acid (PTA), which was previously reduced, serves as a reductant and stabilizer for the synthesis of gold nanocrystals. The PTA-gold nanocomposites are quite stable in aqueous solutions, and electrochemically active towards the hydrogen evolution reaction

Inorganic nanocrystals as contrast agents in MRI:synthesis, coating and introducing multifunctionality

Science.gov (United States)

Sanchez-Gaytan, Brenda L.; Mieszawska, Aneta J.; Fayad, Zahi A.

2013-01-01

Inorganic nanocrystals have myriad applications in medicine, which includes their use as drug or gene delivery complexes, therapeutic hyperthermia agents, in diagnostic systems and as contrast agents in a wide range of medical imaging techniques. For MRI, nanocrystals can produce contrast themselves, of which iron oxides have been most extensively explored, or be given a coating that generates MR contrast, for example gold nanoparticles coated with gadolinium chelates. These MR-active nanocrystals can be used in imaging of the vasculature, liver and other organs, as well as molecular imaging, cell tracking and theranostics. Due to these exciting applications, synthesizing and rendering these nanocrystals water-soluble and biocompatible is therefore highly desirable. We will discuss aqueous phase and organic phase methods for synthesizing inorganic nanocrystals such as gold, iron oxides and quantum dots. The pros and cons of the various methods will be highlighted. We explore various methods for making nanocrystals biocompatible, i.e. directly synthesizing nanocrystals coated with biocompatible coatings, ligand substitution, amphiphile coating and embedding in carrier matrices that can be made biocompatible. Various examples will be highlighted and their applications explained. These examples signify that synthesizing biocompatible nanocrystals with controlled properties has been achieved by numerous research groups and can be applied for a wide range of applications. Therefore we expect to see reports of preclinical applications of ever more complex MRI-active nanoparticles and their wider exploitation, as well as in novel clinical settings. PMID:23303729

Enriching Silver Nanocrystals with a Second Noble Metal.

Science.gov (United States)

Wu, Yiren; Sun, Xiaojun; Yang, Yin; Li, Jumei; Zhang, Yun; Qin, Dong

2017-07-18

Noble-metal nanocrystals have received considerable interests owing to their fascinating properties and promising applications in areas including plasmonics, catalysis, sensing, imaging, and medicine. As demonstrated by ample examples, the performance of nanocrystals in these and related applications can be augmented by switching from monometallic to bimetallic systems. The inclusion of a second metal can enhance the properties and greatly expand the application landscape by bringing in new capabilities. Seeded growth offers a powerful route to bimetallic nanocrystals. This approach is built upon the concept that preformed nanocrystals with uniform, well-controlled size, shape, and structure can serve as seeds to template and direct the deposition of metal atoms. Seeded growth is, however, limited by galvanic replacement when the deposited metal is less reactive than the seed. The involvement of galvanic replacement not only makes it difficult to control the outcome of seeded growth but also causes degradation to some properties. We have successfully addressed this issue by reducing the salt precursor(s) into atoms with essentially no galvanic replacement. In the absence of self-nucleation, the atoms are preferentially deposited onto the seeds to generate bimetallic nanocrystals with controlled structures. In this Account, we use Ag nanocubes as an example to demonstrate the fabrication of Ag@M and Ag@Ag-M (M = Au, Pd, or Pt) nanocubes with a core-frame or core-shell structure by controlling the deposition of M atoms. A typical synthesis involves the titration of M n+ (a precursor to M) ions into an aqueous suspension containing Ag nanocubes, ascorbic acid, and poly(vinylpyrrolidone) under ambient conditions. In one approach, aqueous sodium hydroxide is introduced to increase the initial pH of the reaction system. At pH = 11.9, ascorbic acid is dominated by ascorbate monoanion, a much stronger reductant, to suppress the galvanic replacement between M n+ and Ag. In

Assembling a Lasing Hybrid Material With Supramolecular Polymers and Nanocrystals

National Research Council Canada - National Science Library

Li, Leiming

2003-01-01

.... In the system containing ZnO nanocrystals as the inorganic component, both phases are oriented in the hybrid material forming an ultraviolet lasing medium with a lower threshold relative to pure ZnO nanocrystals.

Light emission from silicon with tin-containing nanocrystals

Directory of Open Access Journals (Sweden)

Søren Roesgaard

2015-07-01

Full Text Available Tin-containing nanocrystals, embedded in silicon, have been fabricated by growing an epitaxial layer of Si1−x−ySnxCy, where x = 1.6 % and y = 0.04 % on a silicon substrate, followed by annealing at various temperatures ranging from 650 ∘C to 900 ∘C. The nanocrystal density and average diameters are determined by scanning transmission-electron microscopy to ≈1017 cm−3 and ≈5 nm, respectively. Photoluminescence spectroscopy demonstrates that the light emission is very pronounced for samples annealed at 725 ∘C, and Rutherford back-scattering spectrometry shows that the nanocrystals are predominantly in the diamond-structured phase at this particular annealing temperature. The origin of the light emission is discussed.

Group IV nanocrystals with ion-exchangeable surface ligands and methods of making the same

Science.gov (United States)

Wheeler, Lance M.; Nichols, Asa W.; Chernomordik, Boris D.; Anderson, Nicholas C.; Beard, Matthew C.; Neale, Nathan R.

2018-01-09

Methods are described that include reacting a starting nanocrystal that includes a starting nanocrystal core and a covalently bound surface species to create an ion-exchangeable (IE) nanocrystal that includes a surface charge and a first ion-exchangeable (IE) surface ligand ionically bound to the surface charge, where the starting nanocrystal core includes a group IV element.

X-Ray Emission Spectrometer Design with Single-Shot Pump-Probe and Resonant Excitation Capabilities

Energy Technology Data Exchange (ETDEWEB)

Spoth, Katherine; /SUNY, Buffalo /SLAC

2012-08-28

Core-level spectroscopy in the soft X-ray regime is a powerful tool for the study of chemical bonding processes. The ultrafast, ultrabright X-ray pulses generated by the Linac Coherent Light Source (LCLS) allow these reactions to be studied in greater detail than ever before. In this study, we investigated a conceptual design of a spectrometer for the LCLS with imaging in the non-dispersive direction. This would allow single-shot collection of X-ray emission spectroscopy (XES) measurements with varying laser pump X-ray probe delay or a variation of incoming X-ray energy over the illuminated area of the sample. Ray-tracing simulations were used to demonstrate how the components of the spectrometer affect its performance, allowing a determination of the optimal final design. These simulations showed that the spectrometer's non-dispersive focusing is extremely sensitive to the size of the sample footprint; the spectrometer is not able to image a footprint width larger than one millimeter with the required resolution. This is compatible with a single shot scheme that maps out the laser pump X-ray probe delay in the non-dispersive direction as well as resonant XES applications at normal incidence. However, the current capabilities of the Soft X-Ray (SXR) beamline at the LCLS do not produce the required energy range in a small enough sample footprint, hindering the single shot resonant XES application at SXR for chemical dynamics studies at surfaces. If an upgraded or future beamline at LCLS is developed with lower monochromator energy dispersion the width can be made small enough at the required energy range to be imaged by this spectrometer design.

Synthesis of silicon nanocrystals in silane plasmas for nanoelectronics and large area electronic devices

International Nuclear Information System (INIS)

Roca i Cabarrocas, P; Nguyen-Tran, Th; Djeridane, Y; Abramov, A; Johnson, E; Patriarche, G

2007-01-01

The synthesis of silicon nanocrystals in standard radio-frequency glow discharge systems is studied with respect to two main objectives: (i) the production of devices based on quantum size effects associated with the small dimensions of silicon nanocrystals and (ii) the synthesis of polymorphous and polycrystalline silicon films in which silicon nanocrystals are the elementary building blocks. In particular we discuss results on the mechanisms of nanocrystal formation and their transport towards the substrate. We found that silicon nanocrystals can contribute to a significant fraction of deposition (50-70%) and that they can be positively charged. This has a strong influence on their deposition because positively charged nanocrystals will be accelerated towards the substrate with energy of the order of the plasma potential. However, the important parameter with respect to the deposition of charged nanocrystals is not the accelerating voltage but the energy per atom and thus a doubling of the diameter will result in a decrease in the energy per atom by a factor of 8. To leverage this geometrical advantage we propose the use of more electronegative gases, which may have a strong effect on the size and charge distribution of the nanocrystals. This is illustrated in the case of deposition from silicon tetrafluoride plasmas in which we observe low-frequency plasma fluctuations, associated with successive generations of nanocrystals. The contribution of larger nanocrystals to deposition results in a lower energy per deposited atom and thus polycrystalline films

A dual-colored bio-marker made of doped ZnO nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Wu, Y L; Zeng, X T [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, 638075 (Singapore); Fu, S; Kwek, L C [National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, 637616 (Singapore); Tok, A I Y; Boey, F C Y [School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore); Lim, C S [School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 (Singapore)

2008-08-27

Bio-compatible ZnO nanocrystals doped with Co, Cu and Ni cations, surface capped with two types of aminosilanes and titania are synthesized by a soft chemical process. Due to the small particle size (2-5 nm), surface functional groups and the high photoluminescence emissions at the UV and blue-violet wavelength ranges, bio-imaging on human osteosarcoma (Mg-63) cells and histiocytic lymphoma U-937 monocyte cells showed blue emission at the nucleus and bright turquoise emission at the cytoplasm simultaneously. This is the first report on dual-color bio-images labeled by one semiconductor nanocrystal colloidal solution. Bright green emission was detected on mung bean seedlings labeled by all the synthesized ZnO nanocrystals. Cytotoxicity tests showed that the aminosilanes capped nanoparticles are non-toxic. Quantum yields of the nanocrystals varied from 79% to 95%. The results showed the potential of the pure ZnO and Co-doped ZnO nanocrystals for live imaging of both human cells and plant systems.

Synthesis and Characterization of Colloidal Metal and Photovoltaic Semiconductor Nanocrystals

KAUST Repository

Abulikemu, Mutalifu

2014-01-01

-performing photovoltaic nanocrystals contain toxic elements, such as Pb, or scarce elements, such as In; thus, the production of solution-processable nanocrystals from earth-abundant materials using environmentally benign synthesis and processing methods has become a

Size-tunable phosphorescence in colloidal metastable gamma-Ga2O3 nanocrystals.

Science.gov (United States)

Wang, Ting; Farvid, Shokouh S; Abulikemu, Mutalifu; Radovanovic, Pavle V

2010-07-14

We report a colloidal synthesis of gallium oxide (Ga(2)O(3)) nanocrystals having metastable cubic crystal structure (gamma phase) and uniform size distribution. Using the synthesized nanocrystal size series we demonstrate for the first time a size-tunable photoluminescence in Ga(2)O(3) from ultraviolet to blue, with the emission shifting to lower energies with increasing nanocrystal size. The observed photoluminescence is dominated by defect-based donor-acceptor pair recombination and has a lifetime of several milliseconds. Importantly, the decay of this phosphorescence is also size dependent. The phosphorescence energy and the decay rate increase with decreasing nanocrystal size, owing to a reduced donor-acceptor separation. These results allow for a rational and predictable tuning of the optical properties of this technologically important material and demonstrate the possibility of manipulating the localized defect interactions via nanocrystal size. Furthermore, the same defect states, particularly donors, are also implicated in electrical conductivity rendering monodispersed Ga(2)O(3) nanocrystals a promising material for multifunctional optoelectronic structures and devices.

Cloning nanocrystal morphology with soft templates

Science.gov (United States)

Thapa, Dev Kumar; Pandey, Anshu

2016-08-01

In most template directed preparative methods, while the template decides the nanostructure morphology, the structure of the template itself is a non-general outcome of its peculiar chemistry. Here we demonstrate a template mediated synthesis that overcomes this deficiency. This synthesis involves overgrowth of silica template onto a sacrificial nanocrystal. Such templates are used to copy the morphologies of gold nanorods. After template overgrowth, gold is removed and silver is regrown in the template cavity to produce a single crystal silver nanorod. This technique allows for duplicating existing nanocrystals, while also providing a quantifiable breakdown of the structure - shape interdependence.

Capping Ligand Vortices as "Atomic Orbitals" in Nanocrystal Self-Assembly.

Science.gov (United States)

Waltmann, Curt; Horst, Nathan; Travesset, Alex

2017-11-28

We present a detailed analysis of the interaction between two nanocrystals capped with ligands consisting of hydrocarbon chains by united atom molecular dynamics simulations. We show that the bonding of two nanocrystals is characterized by ligand textures in the form of vortices. These results are generalized to nanocrystals of different types (differing core and ligand sizes) where the structure of the vortices depends on the softness asymmetry. We provide rigorous calculations for the binding free energy, show that these energies are independent of the chemical composition of the cores, and derive analytical formulas for the equilibrium separation. We discuss the implications of our results for the self-assembly of single-component and binary nanoparticle superlattices. Overall, our results show that the structure of the ligands completely determines the bonding of nanocrystals, fully supporting the predictions of the recently proposed Orbifold topological model.

Nonvolatile memory effect of tungsten nanocrystals under oxygen plasma treatments

International Nuclear Information System (INIS)

Chen, Shih-Cheng; Chang, Ting-Chang; Chen, Wei-Ren; Lo, Yuan-Chun; Wu, Kai-Ting; Sze, S.M.; Chen, Jason; Liao, I.H.; Yeh, Fon-Shan

2010-01-01

In this work, an oxygen plasma treatment was used to improve the memory effect of nonvolatile W nanocrystal memory, including memory window, retention and endurance. To investigate the role of the oxygen plasma treatment in charge storage characteristics, the X-ray photon-emission spectra (XPS) were performed to analyze the variation of chemical composition for W nanocrystal embedded oxide both with and without the oxygen plasma treatment. In addition, the transmission electron microscopy (TEM) analyses were also used to identify the microstructure in the thin film and the size and density of W nanocrystals. The device with the oxygen plasma treatment shows a significant improvement of charge storage effect, because the oxygen plasma treatment enhanced the quality of silicon oxide surrounding the W nanocrystals. Therefore, the data retention and endurance characteristics were also improved by the passivation.

Fundamental absorption edge of NiO nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Sokolov, V.I., E-mail: visokolov@imp.uran.ru [Institute of Metal Physics, Ural Branch of RAS, S. Kovalevskaya Street 18, 620990 Yekaterinburg (Russian Federation); Druzhinin, A.V. [Institute of Metal Physics, Ural Branch of RAS, S. Kovalevskaya Street 18, 620990 Yekaterinburg (Russian Federation); Kim, G.A. [Institute of Organic Synthesis Ural Branch of RAS, S. Kovalevskaya Street 20, 620990 Yekaterinburg (Russian Federation); Gruzdev, N.B.; Yermakov, A.Ye.; Uimin, M.A.; Byzov, I.V.; Shchegoleva, N.N.; Vykhodets, V.B.; Kurennykh, T.E. [Institute of Metal Physics, Ural Branch of RAS, S. Kovalevskaya Street 18, 620990 Yekaterinburg (Russian Federation)

2013-12-01

NiO nanocrystals with the average size of 5, 10 and 25 nm were synthesized by gas-condensation method. The well-defined increase of the optical density D near the fundamental absorption edge of NiO nanocrystals in the range of 3.5–4.0 eV observed after the annealing in air is caused by the oxygen content growth. It is the direct experimental evidence of the fact that p—d charge transfer transitions form the fundamental absorption edge.

Fundamental absorption edge of NiO nanocrystals

International Nuclear Information System (INIS)

Sokolov, V.I.; Druzhinin, A.V.; Kim, G.A.; Gruzdev, N.B.; Yermakov, A.Ye.; Uimin, M.A.; Byzov, I.V.; Shchegoleva, N.N.; Vykhodets, V.B.; Kurennykh, T.E.

2013-01-01

NiO nanocrystals with the average size of 5, 10 and 25 nm were synthesized by gas-condensation method. The well-defined increase of the optical density D near the fundamental absorption edge of NiO nanocrystals in the range of 3.5–4.0 eV observed after the annealing in air is caused by the oxygen content growth. It is the direct experimental evidence of the fact that p—d charge transfer transitions form the fundamental absorption edge

Superheating and supercooling of Ge nanocrystals embedded in SiO2

International Nuclear Information System (INIS)

Xu, Q; Sharp, I D; Yuan, C W; Yi, D O; Liao, C Y; Glaeser, A M; Minor, A M; Beeman, J W; Ridgway, M C; Kluth, P; Iii, J W Ager; Chrzan, D C; Haller, E E

2007-01-01

Free-standing nanocrystals exhibit a size-dependant thermodynamic melting point reduction relative to the bulk melting point that is governed by the surface free energy. The presence of an encapsulating matrix, however, alters the interface free energy of nanocrystals and their thermodynamic melting point can either increase or decrease relative to bulk. Furthermore, kinetic contributions can significantly alter the melting behaviours of embedded nanoscale materials. To study the effect of an encapsulating matrix on the melting behaviour of nanocrystals, we performed in situ electron diffraction measurements on Ge nanocrystals embedded in a silicon dioxide matrix. Ge nanocrystals were formed by multi-energy ion implantation into a 500 nm thick silica thin film on a silicon substrate followed by thermal annealing at 900 deg. C for 1 h. We present results demonstrating that Ge nanocrystals embedded in SiO 2 exhibit a 470 K melting/solidification hysteresis that is approximately symmetric about the bulk melting point. This unique behaviour, which is thought to be impossible for bulk materials, is well described using a classical thermodynamic model that predicts both kinetic supercooling and kinetic superheating. The presence of the silica matrix suppresses surface pre-melting of nanocrystals. Therefore, heterogeneous nucleation of both the liquid phase and the solid phase are required during the heating and cooling cycle. The magnitude of melting hysteresis is governed primarily by the value of the liquid Ge/solid Ge interface free energy, whereas the relative values of the solid Ge/matrix and liquid Ge/matrix interface free energies govern the position of the hysteresis loop in absolute temperature

Surface states in the photoionization of high-quality CdSe core/shell nanocrystals.

Science.gov (United States)

Li, Shu; Steigerwald, Michael L; Brus, Louis E

2009-05-26

We use electric force microscopy (EFM) to study single nanocrystal photoionization in two classes of high-quality nanocrystals whose exciton luminescence quantum yields approach unity in solution. The CdSe/CdS/ZnS core/shell nanocrystals do not photoionize, while the CdSe/CdS nanocrystals do show substantial photoionization. This verifies the theoretical prediction that the ZnS shell confines the excited electron within the nanocrystal. Despite the high luminescence quantum yield, photoionization varies substantially among the CdSe/CdS nanocrystals. We have studied the nanocrystal photoionization with both UV (396 nm) and green (532 nm) light, and we have found that the magnitude of the charge due to photoionization per absorbed photon is greater for UV excitation than for green excitation. A fraction of the photoionization occurs directly via a "hot electron" process, using trap states that are either on the particle surface, within the ligand sphere, or within the silicon oxide layer. This must occur without relaxation to the thermalized, lowest-energy, emitting exciton. We discuss the occurrence of hot carrier processes that are common to photoionization, luminescence blinking, and the fast transient optical absorption that is associated with multiple exciton generation MEG studies.

Adsorption of vitamin E on mesoporous titania nanocrystals

International Nuclear Information System (INIS)

Shih, C.J.; Lin, C.T.; Wu, S.M.

2010-01-01

Tri-block nonionic surfactant and titanium chloride were used as starting materials for the synthesis of mesoporous titania nanocrystallite powders. The main objective of the present study was to examine the synthesis of mesoporous titania nanocrystals and the adsorption of vitamin E on those nanocrystals using X-ray diffraction (XRD), transmission electron microscopy, and nitrogen adsorption and desorption isotherms. When the calcination temperature was increased to 300 o C, the reflection peaks in the XRD pattern indicated the presence of an anatase phase. The crystallinity of the nanocrystallites increased from 80% to 98.6% with increasing calcination temperature from 465 o C to 500 o C. The N 2 adsorption data and XRD data taken after vitamin E adsorption revealed that the vitamin E molecules were adsorbed in the mesopores of the titania nanocrystals.

Memory characteristics of an MOS capacitor structure with double-layer semiconductor and metal heterogeneous nanocrystals

International Nuclear Information System (INIS)

Ni Henan; Wu Liangcai; Song Zhitang; Hui Chun

2009-01-01

An MOS (metal oxide semiconductor) capacitor structure with double-layer heterogeneous nanocrystals consisting of semiconductor and metal embedded in a gate oxide for nonvolatile memory applications has been fabricated and characterized. By combining vacuum electron-beam co-evaporated Si nanocrystals and self-assembled Ni nanocrystals in a SiO 2 matrix, an MOS capacitor with double-layer heterogeneous nanocrystals can have larger charge storage capacity and improved retention characteristics compared to one with single-layer nanocrystals. The upper metal nanocrystals as an additional charge trap layer enable the direct tunneling mechanism to enhance the flat voltage shift and prolong the retention time. (semiconductor devices)

Structural phase transitions in niobium oxide nanocrystals

Science.gov (United States)

Yuvakkumar, R.; Hong, Sun Ig

2015-09-01

Niobium oxide nanocrystals were successfully synthesized employing the green synthesis method. Phase formation, microstructure and compositional properties of 1, 4 and 7 days incubation treated samples after calcinations at 450 °C were examined using X-ray diffraction, Raman, photoluminescence (PL), infrared, X-ray photoelectron spectra and transmission electron microscopic characterizations. It was observed that phase formation of Nb2O5 nanocrystals was dependent upon the incubation period required to form stable metal oxides. The characteristic results clearly revealed that with increasing incubation and aging, the transformation of cubic, orthorhombic and monoclinic phases were observed. The uniform heating at room temperature (32 °C) and the ligation of niobium atoms due to higher phenolic constituents of utilized rambutan during aging processing plays a vital role in structural phase transitions in niobium oxide nanocrystals. The defects over a period of incubation and the intensities of the PL spectra changing over a period of aging were related to the amount of the defects induced by the phase transition.

Surface structures for enhancement of quantum yield in broad spectrum emission nanocrystals

Science.gov (United States)

Schreuder, Michael A.; McBride, James R.; Rosenthal, Sandra J.

2014-07-22

Disclosed are inorganic nanoparticles comprising a body comprising cadmium and/or zinc crystallized with selenium, sulfur, and/or tellurium; a multiplicity of phosphonic acid ligands comprising at least about 20% of the total surface ligand coverage; wherein the nanocrystal is capable of absorbing energy from a first electromagnetic region and capable of emitting light in a second electromagnetic region, wherein the maximum absorbance wavelength of the first electromagnetic region is different from the maximum emission wavelength of the second electromagnetic region, thereby providing a Stokes shift of at least about 20 nm, wherein the second electromagnetic region comprises an at least about 100 nm wide band of wavelengths, and wherein the nanoparticle exhibits has a quantum yield of at least about 10%. This abstract is intended as a scanning tool for purposes of searching in the particular art and is not intended to be limiting of the present invention.

Synthesis and characterization of some metal oxide nanocrystals by microwave irradiation

Energy Technology Data Exchange (ETDEWEB)

Rashad, M.; Gaber, A.; Abdelrahim, M. A.; Abdel-Baset, A. M. [Physics Department, Faculty of Science, Assiut University, 71516 Assiut (Egypt); Moharram, A. H. [Physics Dept., College of Science and Arts, King Abdulaziz Univ., Rabigh 21911 (Saudi Arabia)

2013-12-16

Copper oxide and cobalt oxide (CuO, Co3O4) nanocrystals (NCs) have been successfully prepared in a short time using microwave irradiation. The resulted powders of nanocrystals (NCs) were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Thermogravimetric analysis (TGA) measurements are also studied. Fourier-transform infrared (FT-IR) and UV–visible absorption spectroscopy of both kind of nanoparticels are illustrated. Optical absorption analysis indicated the direct band gap for both kinds of nanocrystals.

From Artificial Atoms to Nanocrystal Molecules: Preparation and Properties of More Complex Nanostructures

Energy Technology Data Exchange (ETDEWEB)

Choi, Charina L; Alivisatos, A Paul

2009-10-20

Quantum dots, which have found widespread use in fields such as biomedicine, photovoltaics, and electronics, are often called artificial atoms due to their size-dependent physical properties. Here this analogy is extended to consider artificial nanocrystal molecules, formed from well-defined groupings of plasmonically or electronically coupled single nanocrystals. Just as a hydrogen molecule has properties distinct from two uncoupled hydrogen atoms, a key feature of nanocrystal molecules is that they exhibit properties altered from those of the component nanoparticles due to coupling. The nature of the coupling between nanocrystal atoms and its response to vibrations and deformations of the nanocrystal molecule bonds are of particular interest. We discuss synthetic approaches, predicted and observed physical properties, and prospects and challenges toward this new class of materials.

Size limit on the phosphorous doped silicon nanocrystals for dopant activation

Energy Technology Data Exchange (ETDEWEB)

Yang, P., E-mail: pengyuan.yang@surrey.ac.uk [Surrey Ion Beam Centre, Advanced Technology Institute, University of Surrey, Guildford GU2 5XH (United Kingdom); Gwilliam, R.M. [Surrey Ion Beam Centre, Advanced Technology Institute, University of Surrey, Guildford GU2 5XH (United Kingdom); Crowe, I.F.; Papachristodoulou, N.; Halsall, M.P. [Photon Science Institute, School of Electrical and Electronic Engineering, Alan Turing Building, University of Manchester, Manchester M13 9PL (United Kingdom); Hylton, N.P. [Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Hulko, O.; Knights, A.P. [Department of Engineering Physics and the Centre for Emerging Device Technologies, McMaster University, 1280 Main Street West, Hamilton L8S 4L7, Ontario (Canada); Shah, M.; Kenyon, A.J. [Department of Electronic and Electrical Engineering, University College London, London WC1E 7JE (United Kingdom)

2013-07-15

We studied the photoluminescence spectra of silicon nanocrystals doped with and without phosphorus as a function of isothermal annealing time. Silicon nanocrystals were prepared by the implantation of 80 keV Si{sup +} into a 500 nm SiO{sub 2} film to an areal density of 8 × 10{sup 16} at/cm{sup 2}. Half of the samples were co-implanted with P{sup +} at 80 keV to 5 × 10{sup 15} at/cm{sup 2}. The photoluminescence of the annealed samples were photo-excited at wavelength of 405 nm. For short anneal times, when the nanocrystal size distribution has a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts to the red. Our results indicate the donor electron generation depends strongly on the nanocrystal size. We also found a critical limit above which it allows dopant activation.

Growth kinetics of tin oxide nanocrystals in colloidal suspensions under hydrothermal conditions

International Nuclear Information System (INIS)

Lee, Eduardo J.H.; Ribeiro, Caue; Longo, Elson; Leite, Edson R.

2006-01-01

Colloidal suspensions of tin oxide nanocrystals were synthesized at room temperature by the hydrolysis reaction of tin chloride (II), in an ethanolic solution. The coarsening kinetics of such nanocrystals was studied by submitting the as-prepared suspensions to hydrothermal treatments at temperatures of 100, 150 and 200 deg. C for periods between 60 and 12,000 min. Transmission electron microscopy (TEM) was used to characterize the samples (i.e. distribution of nanocrystal size, average particle radius and morphology). The results show that the usual Ostwald ripening coarsening mechanism does not fit well the experimental data, which is an indicative that this process is not significant for SnO 2 nanocrystals, in the studied experimental conditions. The morphology evolution of the nanocrystals upon hydrothermal treatment indicates that growth by oriented attachment (OA) should be significant. A kinetic model that describes OA growth is successfully applied to fit the data

Fabrication of multilayered Ge nanocrystals embedded in SiOxGeNy films

International Nuclear Information System (INIS)

Gao Fei; Green, Martin A.; Conibeer, Gavin; Cho, Eun-Chel; Huang Yidan; Perez-Wurfl, Ivan; Flynn, Chris

2008-01-01

Multilayered Ge nanocrystals embedded in SiO x GeN y films have been fabricated on Si substrate by a (Ge + SiO 2 )/SiO x GeN y superlattice approach, using a rf magnetron sputtering technique with a Ge + SiO 2 composite target and subsequent thermal annealing in N 2 ambient at 750 deg. C for 30 min. X-ray diffraction (XRD) measurement indicated the formation of Ge nanocrystals with an average size estimated to be 5.4 nm. Raman scattering spectra showed a peak of the Ge-Ge vibrational mode downward shifted to 299.4 cm -1 , which was caused by quantum confinement of phonons in the Ge nanocrystals. Transmission electron microscopy (TEM) revealed that Ge nanocrystals were confined in (Ge + SiO 2 ) layers. This superlattice approach significantly improved both the size uniformity of Ge nanocrystals and their uniformity of spacing on the 'Z' growth direction

MEGACELL: A nanocrystal model construction software for HRTEM multislice simulation

International Nuclear Information System (INIS)

Stroppa, Daniel G.; Righetto, Ricardo D.; Montoro, Luciano A.; Ramirez, Antonio J.

2011-01-01

Image simulation has an invaluable importance for the accurate analysis of High Resolution Transmission Electron Microscope (HRTEM) results, especially due to its non-linear image formation mechanism. Because the as-obtained images cannot be interpreted in a straightforward fashion, the retrieval of both qualitative and quantitative information from HRTEM micrographs requires an iterative process including the simulation of a nanocrystal model and its comparison with experimental images. However most of the available image simulation software requires atom-by-atom coordinates as input for the calculations, which can be prohibitive for large finite crystals and/or low-symmetry systems and zone axis orientations. This paper presents an open source citation-ware tool named MEGACELL, which was developed to assist on the construction of nanocrystals models. It allows the user to build nanocrystals with virtually any convex polyhedral geometry and to retrieve its atomic positions either as a plain text file or as an output compatible with EMS (Electron Microscopy Software) input protocol. In addition to the description of this tool features, some construction examples and its application for scientific studies are presented. These studies show MEGACELL as a handy tool, which allows an easier construction of complex nanocrystal models and improves the quantitative information extraction from HRTEM images. -- Highlights: → A software to support the HRTEM image simulation of nanocrystals in actual size. → MEGACELL allows the construction of complex nanocrystals models for multislice image simulation. → Some examples of improved nanocrystalline system characterization are presented, including the analysis of 3D morphology and growth behavior.

Unravelling the surface chemistry of metal oxide nanocrystals, the role of acids and bases.

Science.gov (United States)

De Roo, Jonathan; Van den Broeck, Freya; De Keukeleere, Katrien; Martins, José C; Van Driessche, Isabel; Hens, Zeger

2014-07-09

We synthesized HfO2 nanocrystals from HfCl4 using a surfactant-free solvothermal process in benzyl alcohol and found that the resulting nanocrystals could be transferred to nonpolar media using a mixture of carboxylic acids and amines. Using solution (1)H NMR, FTIR, and elemental analysis, we studied the details of the transfer reaction and the surface chemistry of the resulting sterically stabilized nanocrystals. As-synthesized nanocrystals are charge-stabilized by protons, with chloride acting as the counterion. Treatment with only carboxylic acids does not lead to any binding of ligands to the HfO2 surface. On the other hand, we find that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride. This results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands. Moreover, titrations with deuterated carboxylic acid show that the charge on the carboxylate ligands is balanced by coadsorbed protons. Hence, opposite from the X-type/nonstoichiometric nanocrystals picture prevailing in literature, one should look at HfO2/carboxylate nanocrystals as systems where carboxylic acids are dissociatively adsorbed to bind to the nanocrystals. Similar results were obtained with ZrO2 NCs. Since proton accommodation on the surface is most likely due to the high Brønsted basicity of oxygen, our model could be a more general picture for the surface chemistry of metal oxide nanocrystals with important consequences on the chemistry of ligand exchange reactions.

Infrared emitting and photoconducting colloidal silver chalcogenide nanocrystal quantum dots from a silylamide-promoted synthesis.

Science.gov (United States)

Yarema, Maksym; Pichler, Stefan; Sytnyk, Mykhailo; Seyrkammer, Robert; Lechner, Rainer T; Fritz-Popovski, Gerhard; Jarzab, Dorota; Szendrei, Krisztina; Resel, Roland; Korovyanko, Oleksandra; Loi, Maria Antonietta; Paris, Oskar; Hesser, Günter; Heiss, Wolfgang

2011-05-24

Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region, making these materials promising as environmentally benign alternatives to established infrared active nanocrystals containing toxic metals such as Hg, Cd, and Pb. We present Ag(2)Se nanocrystals in detail, giving size-tunable luminescence with quantum yields above 1.7%. The luminescence, with a decay time on the order of 130 ns, was shown to improve due to the growth of a monolayer thick ZnSe shell. Photoconductivity with a quantum efficiency of 27% was achieved by blending the Ag(2)Se nanocrystals with a soluble fullerene derivative. The co-injection of lithium silylamide was found to be crucial to the synthesis of Ag chalcogenide nanocrystals, which drastically increased their nucleation rate even at relatively low growth temperatures. Because the same observation was made for the nucleation of Cd chalcogenide nanocrystals, we conclude that the addition of lithium silylamide might generally promote wet-chemical synthesis of metal chalcogenide nanocrystals, including in as-yet unexplored materials.

Synthesis and characterization of MgO nanocrystals for biosensing applications

Energy Technology Data Exchange (ETDEWEB)

Li, Hongji [Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry & Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Li, Mingji, E-mail: limingji@163.com [Tianjin Key Laboratory of Film Electronic and Communication Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300384 (China); Qiu, Guojun [Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion, School of Chemistry & Chemical Engineering, Tianjin University of Technology, Tianjin 300384 (China); Li, Cuiping; Qu, Changqing; Yang, Baohe [Tianjin Key Laboratory of Film Electronic and Communication Devices, School of Electronics Information Engineering, Tianjin University of Technology, Tianjin 300384 (China)

2015-05-25

Highlights: • MgO nanocrystals were prepared using DC arc plasma jet CVD method. • The growth time does not exceed 10 min in process of the synthesis. • The samples were found to consist of cubic MgO nanobelts and nanosheets. • Nanocrystals contain contacts, rough edges, vacancies, and doping defects. • The samples exhibited excellent electrochemical biosensing properties. - Abstract: MgO nanocrystals were prepared using a simple direct current arc plasma jet chemical vapor deposition method. Magnesium nitrate was used as source material and Mo film was used as a substrate and catalyst. The high-temperature plasma produced ensured rapid synthesis of the MgO nanocrystals. The as-prepared nanocrystals were characterized by field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, energy-dispersive spectroscopy, Fourier transform infrared spectrometry, ultraviolet–visible spectrophotometry, and photoluminescence measurements. The as-synthesized samples were found to consist of cubic MgO nanobelts and nanosheets with large surface areas and low coordination oxide ions, and contained numerous contacts, rough edges, vacancies, and doping defects. The nanostructures exhibited excellent electrochemical sensing properties with high-sensing sensitivity toward ascorbic acid. Their high electrocatalytic activity was attributed to the effect of defects and the surface electron transfer ability of the one-dimensional MgO nanobelts.

Adsorption of vitamin E on mesoporous titania nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Shih, C.J., E-mail: cjshih@kmu.edu.tw [Department of Fragrance and Cosmetic Science, Kaohsiung Medical University, Kaohsiung 807, Taiwan (China); Lin, C.T.; Wu, S.M. [School of Pharmacy, College of Pharmacy, Kaohsiung Medical University, Kaohsiung 807, Taiwan (China)

2010-07-15

Tri-block nonionic surfactant and titanium chloride were used as starting materials for the synthesis of mesoporous titania nanocrystallite powders. The main objective of the present study was to examine the synthesis of mesoporous titania nanocrystals and the adsorption of vitamin E on those nanocrystals using X-ray diffraction (XRD), transmission electron microscopy, and nitrogen adsorption and desorption isotherms. When the calcination temperature was increased to 300 {sup o}C, the reflection peaks in the XRD pattern indicated the presence of an anatase phase. The crystallinity of the nanocrystallites increased from 80% to 98.6% with increasing calcination temperature from 465 {sup o}C to 500 {sup o}C. The N{sub 2} adsorption data and XRD data taken after vitamin E adsorption revealed that the vitamin E molecules were adsorbed in the mesopores of the titania nanocrystals.

Blue-green luminescent CdZnSeS nanocrystals synthesized with activated alkyl thiol

International Nuclear Information System (INIS)

Xia Xing; Liu Zuli; Du Guihuan; Li Yuebin; Ma Ming; Yao Kailun

2012-01-01

Semiconductor nanocrystals with blue-green luminescence are potentially useful in various applications, but the preparation has not been easy compared to regular semiconductor nanocrystals with emission in the orange-red range. In this research alloyed CdZnSeS nanocrystals with luminescence covering the wavelength range from 430 to 560 nm are obtained by a one-step method with the assistance of alkyl thiol compound 1-dodecanethiol, which serves both as the sulfur source and surface ligand. The luminescence of CdZnSeS nanocrystals can be tuned from blue to green by altering the Cd:Zn molar ratio. Besides, the amount of 1-dodecanethiol in the reaction mixture can influence the emission wavelength by restricting the growth of nanocrystals. The dual control of both particle composition and size has enabled the tuning of luminescence to cover the blue-green spectral window. This research presents a convenient method to synthesize nanocrystals with tunable blue-green emission; these materials can be useful in advanced technologies such as photovoltaics, lighting and display. - Highlights: → Obtained blue-green luminescent nanocrystals by a one-step process. → Alkyl thiol used as a sulfur source and a surface stabilizer to control particle size. → Luminescence color of NCs could be easily tuned by changing their composition and particle size simultaneously.

Preparation, characterization and catalytic effects of copper oxalate nanocrystals

International Nuclear Information System (INIS)

Singh, Gurdip; Kapoor, Inder Pal Singh; Dubey, Reena; Srivastava, Pratibha

2012-01-01

Graphical abstract: Prepared copper oxalate nanocrystals were characterized by FE-SEM and bright field TEM micrographs. Its catalytic activity was evaluated on the thermal decomposition of ammonium perchlorate using TG and TG-DSC techniques. Highlights: ► Preparation of nanocrystals (∼9.0 nm) of copper oxalate using Cu(NO 3 ) 2 ·2H 2 O, oxalic acid and acetone under thermal conditions. ► Method is simple and novel. ► Characterization using XRD, SEM, TEM, HRTEM and ED pattern. ► Catalytic activity of copper oxalate nanocrystals on AP thermal decomposition using thermal techniques (TG, TG-DSC and ignition delay). ► Kinetics of thermal decomposition of AP + CONs using isoconversional and model fitting kinetic approaches. - Abstract: Recent work has described the preparation and characterization of copper oxalate nanocrystals (CONs). It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and electron diffraction pattern (ED). The catalytic activity of CONs on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellants (CSPs) has been done by thermogravimetry (TG), differential scanning calorimetry (DSC) and ignition delay measurements. Burning rate of CSPs was also found to be enhanced in presence of copper oxalate nanocrystals. Kinetics of thermal decomposition of AP with and without CONs has also been investigated. The model free (isoconversional) and model-fitting kinetic approaches have been applied to data for isothermal TG decomposition.

In situ microscopy of the self-assembly of branched nanocrystals in solution

Science.gov (United States)

Sutter, Eli; Sutter, Peter; Tkachenko, Alexei V.; Krahne, Roman; de Graaf, Joost; Arciniegas, Milena; Manna, Liberato

2016-04-01

Solution-phase self-assembly of nanocrystals into mesoscale structures is a promising strategy for constructing functional materials from nanoscale components. Liquid environments are key to self-assembly since they allow suspended nanocrystals to diffuse and interact freely, but they also complicate experiments. Real-time observations with single-particle resolution could have transformative impact on our understanding of nanocrystal self-assembly. Here we use real-time in situ imaging by liquid-cell electron microscopy to elucidate the nucleation and growth mechanism and properties of linear chains of octapod-shaped nanocrystals in their native solution environment. Statistical mechanics modelling based on these observations and using the measured chain-length distribution clarifies the relative importance of dipolar and entropic forces in the assembly process and gives direct access to the interparticle interaction. Our results suggest that monomer-resolved in situ imaging combined with modelling can provide unprecedented quantitative insight into the microscopic processes and interactions that govern nanocrystal self-assembly in solution.

Highly stable colloidal TiO2 nanocrystals with strong violet-blue emission

International Nuclear Information System (INIS)

Ghamsari, Morteza Sasani; Gaeeni, Mohammad Reza; Han, Wooje; Park, Hyung-Ho

2016-01-01

Improved sol–gel method has been applied to prepare highly stable colloidal TiO 2 nanocrystals. The synthesized titania nanocrystals exhibit strong emission in the violet-blue wavelength region. Very long evolution time was obtained by preventing the sol to gel conversion with reflux process. FTIR, XRD, UV–vis absorption, photoluminescence and high resolution transmission electron microscope (HRTEM) were used to study the optical properties, crystalline phase, morphology, shape and size of prepared TiO 2 colloidal nanocrystals. HRTEM showed that the diameter of TiO 2 colloidal nanocrystals is about 5 nm. Although the PL spectra show similar spectral features upon excitation wavelengths at 280, 300 and 350 nm, but their emission intensities are significantly different from each other. Photoluminescence quantum yield for TiO 2 colloidal nanocrystals is estimated to be 49% with 280 nm excitation wavelength which is in agreement and better than reported before. Obtained results confirm that the prepared colloidal TiO 2 sample has enough potential for optoelectronics applications.

Lead Halide Perovskite Nanocrystals in the Research Spotlight: Stability and Defect Tolerance

Science.gov (United States)

2017-01-01

This Perspective outlines basic structural and optical properties of lead halide perovskite colloidal nanocrystals, highlighting differences and similarities between them and conventional II–VI and III–V semiconductor quantum dots. A detailed insight into two important issues inherent to lead halide perovskite nanocrystals then follows, namely, the advantages of defect tolerance and the necessity to improve their stability in environmental conditions. The defect tolerance of lead halide perovskites offers an impetus to search for similar attributes in other related heavy metal-free compounds. We discuss the origins of the significantly blue-shifted emission from CsPbBr3 nanocrystals and the synthetic strategies toward fabrication of stable perovskite nanocrystal materials with emission in the red and infrared parts of the optical spectrum, which are related to fabrication of mixed cation compounds guided by Goldschmidt tolerance factor considerations. We conclude with the view on perspectives of use of the colloidal perovskite nanocrystals for applications in backlighting of liquid-crystal TV displays. PMID:28920080

Pseudo-direct bandgap transitions in silicon nanocrystals: effects on optoelectronics and thermoelectrics

Science.gov (United States)

Singh, Vivek; Yu, Yixuan; Sun, Qi-C.; Korgel, Brian; Nagpal, Prashant

2014-11-01

While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in nanoscaled silicon semiconductors. Therefore, these results can have important implications for the design of optoelectronics and thermoelectric devices based on nanostructured silicon.While silicon nanostructures are extensively used in electronics, the indirect bandgap of silicon poses challenges for optoelectronic applications like photovoltaics and light emitting diodes (LEDs). Here, we show that size-dependent pseudo-direct bandgap transitions in silicon nanocrystals dominate the interactions between (photoexcited) charge carriers and phonons, and hence the optoelectronic properties of silicon nanocrystals. Direct measurements of the electronic density of states (DOS) for different sized silicon nanocrystals reveal that these pseudo-direct transitions, likely arising from the nanocrystal surface, can couple with the quantum-confined silicon states. Moreover, we demonstrate that since these transitions determine the interactions of charge carriers with phonons, they change the light emission, absorption, charge carrier diffusion and phonon drag (Seebeck coefficient) in

A radiation-tolerant, low-power non-volatile memory based on silicon nanocrystal quantum dots

OpenAIRE

Bell, L. D.; Boer, E.; Ostraat, M.; Brongersma, M. L.; Flagan, R. C.; Atwater, H. A.; De Blauwe, J.; Green, M. L.

2001-01-01

Nanocrystal nonvolatile floating-gate memories are a good candidate for space applications - initial results suggest they are fast, more reliable and consume less power than conventional floating gate memories. In the nanocrystal based NVM device, charge is not stored on a continuous polysilicon layer (so-called floating gate), but instead on a layer of discrete nanocrystals. Charge injection and storage in dense arrays of silicon nanocrystals in SiO_2 is a critical aspect of the performance ...

Study of the photodissociation of a CdSe nanocrystal beam by means of photoluminescence and Raman scattering

CERN Document Server

Orii, T; Onari, S; Kaito, S I; Arai, T

1997-01-01

We developed an apparatus that enables us to perform optical measurements of nanocrystals suspended in vacuum. CdSe nanocrystals were produced by a gas evaporation method, and nanocrystal beams were then formed using an inert-gas flow with differential pumping. We measured photoluminescence spectra of the nanocrystal beams with excitations of various photon energies and powers. For a low excitation power, edge emission of the CdSe nanocrystal beam was observed. With increase of the laser power, Raman lines of Se dimers emitted due to the photodissociation of CdSe nanocrystals were observed. It was found that the thresholds of the excitation laser fluence for the photodissociation of CdSe nanocrystals were much smaller than the thresholds of laser fluence for the laser-induced emission of Se atoms from bulk CdSe. The electronic process is dominant in the photodissociation of CdSe nanocrystals whose surfaces are completely free. We suggest that the effective supply of carriers confined in nanocrystals to the su...

Discrete Charge Storage Nonvolatile Memory Based on Si Nanocrystals with Nitridation Treatment

International Nuclear Information System (INIS)

Xian-Gao, Zhang; Kun-Ji, Chen; Zhong-Hui, Fang; Xin-Ye, Qian; Guang-Yuan, Liu; Xiao-Fan, Jiang; Zhong-Yuan, Ma; Jun, Xu; Xin-Fan, Huang; Jian-Xin, Ji; Fei, He; Kuang-Bao, Song; Jun, Zhang; Hui, Wan; Rong-Hua, Wang

2010-01-01

A nonvolatile memory device with nitrided Si nanocrystals embedded in a Boating gate was fabricated. The uniform Si nanocrystals with high density (3 × 10 11 cm −2 ) were deposited on ultra-thin tunnel oxide layer (∼ 3 nm) and followed by a nitridation treatment in ammonia to form a thin silicon nitride layer on the surface of nanocrystals. A memory window of 2.4 V was obtained and it would be larger than 1.3 V after ten years from the extrapolated retention data. The results can be explained by the nitrogen passivation of the surface traps of Si nanocrystals, which slows the charge loss rate. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Accurate Extraction of Charge Carrier Mobility in 4-Probe Field-Effect Transistors

KAUST Repository

Choi, Hyun Ho; Rodionov, Yaroslav I.; Paterson, Alexandra F.; Panidi, Julianna; Saranin, Danila; Kharlamov, Nikolai; Didenko, Sergei I.; Anthopoulos, Thomas D.; Cho, Kilwon; Podzorov, Vitaly

2018-01-01

Charge carrier mobility is an important characteristic of organic field-effect transistors (OFETs) and other semiconductor devices. However, accurate mobility determination in FETs is frequently compromised by issues related to Schottky-barrier contact resistance, that can be efficiently addressed by measurements in 4-probe/Hall-bar contact geometry. Here, it is shown that this technique, widely used in materials science, can still lead to significant mobility overestimation due to longitudinal channel shunting caused by voltage probes in 4-probe structures. This effect is investigated numerically and experimentally in specially designed multiterminal OFETs based on optimized novel organic-semiconductor blends and bulk single crystals. Numerical simulations reveal that 4-probe FETs with long but narrow channels and wide voltage probes are especially prone to channel shunting, that can lead to mobilities overestimated by as much as 350%. In addition, the first Hall effect measurements in blended OFETs are reported and how Hall mobility can be affected by channel shunting is shown. As a solution to this problem, a numerical correction factor is introduced that can be used to obtain much more accurate experimental mobilities. This methodology is relevant to characterization of a variety of materials, including organic semiconductors, inorganic oxides, monolayer materials, as well as carbon nanotube and semiconductor nanocrystal arrays.

Accurate Extraction of Charge Carrier Mobility in 4-Probe Field-Effect Transistors

KAUST Repository

Choi, Hyun Ho

2018-04-30

Charge carrier mobility is an important characteristic of organic field-effect transistors (OFETs) and other semiconductor devices. However, accurate mobility determination in FETs is frequently compromised by issues related to Schottky-barrier contact resistance, that can be efficiently addressed by measurements in 4-probe/Hall-bar contact geometry. Here, it is shown that this technique, widely used in materials science, can still lead to significant mobility overestimation due to longitudinal channel shunting caused by voltage probes in 4-probe structures. This effect is investigated numerically and experimentally in specially designed multiterminal OFETs based on optimized novel organic-semiconductor blends and bulk single crystals. Numerical simulations reveal that 4-probe FETs with long but narrow channels and wide voltage probes are especially prone to channel shunting, that can lead to mobilities overestimated by as much as 350%. In addition, the first Hall effect measurements in blended OFETs are reported and how Hall mobility can be affected by channel shunting is shown. As a solution to this problem, a numerical correction factor is introduced that can be used to obtain much more accurate experimental mobilities. This methodology is relevant to characterization of a variety of materials, including organic semiconductors, inorganic oxides, monolayer materials, as well as carbon nanotube and semiconductor nanocrystal arrays.

Influence of multi-hit capability on quantitative measurement of NiPtSi thin film with laser-assisted atom probe tomography

International Nuclear Information System (INIS)

Kinno, T.; Akutsu, H.; Tomita, M.; Kawanaka, S.; Sonehara, T.; Hokazono, A.; Renaud, L.; Martin, I.; Benbalagh, R.; Sallé, B.; Takeno, S.

2012-01-01

Highlights: ► Laser-assisted atom probe tomography was applied to NiPtSi films on Si substrates. ► Comparison of depth profiles of single-hit events and those of multi-hit events. ► ∼80% of Pt atoms were detected in multi-hit events. ► Multiple-ion detection is important for Laser-assisted atom probe tomography. - Abstract: Laser-assisted atom probe tomography (LA-APT) was applied to NiPtSi (0, 30, and 50% Pt contents) thin films on Si substrates. Consistent results with those of high-resolution Rutherford backscattering spectrometry (HR-RBS) were obtained. Based on the obtained data sets, the composition profiles from only the signals of single-hit events, meaning detection of one ion by one laser pulse, were compiled. The profiles from only the signals of multi-hit events, meaning detection of multiple ions by one laser pulse, were also compiled. There were large discrepancies with respect to Ni and Pt concentrations among the compiled profiles and the original profiles including the signals of both types of detection events. Additionally, the profiles compiled from single-hit events showed that Si concentration in NiPtSi layer became smaller toward the surface, differing from the original profiles and the multi-hit profiles. These results suggest that capability of simultaneous multiple-ion detection is important for appropriate LA-APT analyses.

Conjugation of hydroxyapatite nanocrystals with human immunoglobulin G for nanomedical applications.

Science.gov (United States)

Iafisco, Michele; Varoni, Elena; Di Foggia, Michele; Pietronave, Stefano; Fini, Milena; Roveri, Norberto; Rimondini, Lia; Prat, Maria

2012-02-01

Inorganic nanosized drug carriers are a promising field in nanomedicine applied to cancer. Their conjugation with antibodies combines the properties of the nanoparticles themselves with the specific and selective recognition ability of the antibodies to antigens. Biomimetic carbonate-hydroxyapatite (HA) nanoparticles were synthesized and fully characterized; human IgGs, used as model antibodies, were coupled to these nanocrystals. The maximum loading amount, the interaction modelling, the preferential orientation and the secondary structure modifications were evaluated using theoretical models (Langmuir, Freundlich and Langmuir-Freundlich) spectroscopic (UV-Vis, Raman), calorimetric (TGA), and immunochemical techniques (ELISA, Western Blot). HA nanoparticles of about 30 nm adsorbed human IgGs, in a dose-dependent, saturable and stable manner with micromolar affinity and adsorption capability around 2.3 mg/m(2). Adsorption isotherm could be described by Langmuir-Freundlich model, and was due to both energetically homogeneous and heterogeneous binding sites on HA surface, mainly of electrostatic nature. Binding did not induce secondary structure modification of IgGs. A preferential IgG end-on orientation with the involvement of IgG Fc moiety in the adsorption seems most probable due to the steric hindrance of their Fab domains. Biomimetic HA nanocrystals are suitable substrates to produce nanoparticles which can be functionalized with antibodies for efficient targeted drug delivery to tumours. Copyright © 2011 Elsevier B.V. All rights reserved.

Dermal miconazole nitrate nanocrystals - formulation development, increased antifungal efficacy & skin penetration.

Science.gov (United States)

Pyo, Sung Min; Hespeler, David; Keck, Cornelia M; Müller, Rainer H

2017-10-05

Miconazole nitrate nanosuspension was developed to increase its antifungal activity and dermal penetration. In addition, the nanosuspension was combined with the synergistic additive chlorhexidine digluconate. The production was performed by wet bead milling and both production and formulation parameters were optimized. A stabilizer screening revealed poloxamer 407 and Tween 80 both at 0.15% as the most effective stabilizers for miconazole nanosuspensions at 1.0%. The nanocrystals were incorporated into a hydroxypropyl cellulose gel base. Short-term stability (3months) of the nanocrystal bulk population could be shown at room temperature and fridge. Besides the stable bulk nanocrystals, some longitudinal crystal growth to needle like crystals occurred. The addition of ionic compounds as the chlorhexidine digluconate often destabilizes suspensions. Surprisingly here, the addition minimized the crystal growth. An underlying mechanism is proposed. An inhibition zone assay was performed using Candida albicans (ATCC ® 10231™). When comparing the nanocrystals in suspension and in gel to μm-sized miconazole nitrate formulations and two market products, the increase in inhibition zone diameter for the nanosuspension formulations was most pronounced in the chlorhexidine digluconate free formulations. These nanocrystal formulations were closely or similarly effective as the microsuspensions and the market products containing the synergistic chlorhexidine digluconate, showing the potential of the nanosuspension formulation. Nanosuspension performance was even further increased when chlorhexidine digluconate was added. Ex-vivo skin penetration studies on porcine ears revealed distinctly less remaining miconazole nitrate on the skin surface for nanocrystals (e.g., 76-86%) compared to market products (e.g. 94%). Also, penetration was increased e.g. in skin depth of 5-10μm from <1.0/1.7% to e.g. 3.3-6.2% for nanocrystals. Copyright © 2017 Elsevier B.V. All rights reserved.

NanoCrySP technology for generation of drug nanocrystals: translational aspects and business potential.

Science.gov (United States)

Shete, Ganesh; Bansal, Arvind Kumar

2016-08-01

Drug nanocrystals have rapidly evolved into a mature drug delivery strategy in the last decade, with almost 16 products currently on the market. Several "top-down" technologies are available in the market for generation of nanocrystals. Despite several advantages, very few bottom-up technologies have been explored for commercial purpose. This short communication highlights a novel, bottom-up, spray drying based technology-NanoCrySP-to generate drug nanocrystals. Nanocrystals are generated in the presence of non-polymeric excipients that act as crystallization inducer for the drug. Excipients encourage crystallization of drug by plasticization, primary heterogeneous nucleation, and imparting physical barrier to crystal growth. Nanocrystals have shown significant improvement in dissolution and thereby oral bioavailability. NanoCrySP technology is protected through patents in India, the USA, and the European Union. NanoCrySP can be utilized for (i) pharmaceutical development of new chemical entities, (ii) differentiated products of existing molecules, and (iii) generic drug products. The aggregation of drug nanocrystals generated using NanoCrySP poses significant challenges in the nanocrystal-based product development. Addition of stabilizers either during spray drying or during dissolution has shown beneficial effects.

Hot-injection synthesis of Ni-ZnO hybrid nanocrystals with tunable magnetic properties and enhanced photocatalytic activity

Energy Technology Data Exchange (ETDEWEB)

Zeng, Deqian; Qiu, Yulong; Chen, Yuanzhi, E-mail: yuanzhi@xmu.edu.cn; Zhang, Qinfu; Liu, Xiang; Peng, Dong-Liang, E-mail: dlpeng@xmu.edu.cn [Xiamen University, Department of Materials Science and Engineering, Fujian Provincial Key Laboratory of Materials Genome, Collaborative Innovation Center of Chemistry for Energy Materials, College of Materials (China)

2017-04-15

Magnetic metal-semiconductor hybrid nanocrystals containing ferromagnetic Ni and semiconductor ZnO have been prepared via a hot-injection route. The Ni-ZnO hybrid nanocrystals have a flower-like morphology that consists of Ni inner cores and ZnO petal shells. In spite of their large lattice mismatch, ZnO nanocrystals can still grow on faceted Ni nanocrystals to form stable interfaces. The composition of Ni-ZnO hybrid nanocrystals is readily controlled, and the average size of Ni core is tunable from 25 to 50 nm. Room temperature ferromagnetic properties are observed in these hybrid nanocrystals, and tunable magnetic properties also can be achieved by varying the size of Ni core. The as-prepared Ni-ZnO hybrid nanocrystals exhibit enhanced photocatalytic performance under ultraviolet light illumination as compared to pure ZnO nanocrystals. Furthermore, the superior reusability of hybrid nanocrystals for photocatalytic application is achieved by virtue of their magnetic properties. The facile and efficient seed-mediate strategy is particularly attractive to construct hybrid magnetic-semiconducting heterostructures. The as-obtained Ni-ZnO hybrid nanocrystals offer great potential for various applications due to their combined magnetic and semiconducting properties and low-cost earth-abundant availability.

InAs nanocrystals on SiO2/Si by molecular beam epitaxy for memory applications

International Nuclear Information System (INIS)

Hocevar, Moiera; Regreny, Philippe; Descamps, Armel; Albertini, David; Saint-Girons, Guillaume; Souifi, Abdelkader; Gendry, Michel; Patriarche, Gilles

2007-01-01

We studied a memory structure based on InAs nanocrystals grown by molecular beam epitaxy directly on thermal SiO 2 on silicon. Both nanocrystal diameter and density can be controlled by growth parameters. Transmission electron microscopy analysis shows high crystallinity and low size dispersion. In an electrical test structure with a 3.5 nm tunnel oxide, we observed that 80% of the initial injected electrons remain stored in the InAs nanocrystals after 3 months and that the retention time for electrons in InAs nanocrystals is four orders of magnitude higher than in silicon nanocrystals

Doped and codoped silicon nanocrystals: The role of surfaces and interfaces

Science.gov (United States)

Marri, Ivan; Degoli, Elena; Ossicini, Stefano

2017-12-01

Si nanocrystals have been extensively studied because of their novel properties and their potential applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. These new properties are achieved through the combination of the quantum confinement of carriers and the strong influence of surface chemistry. As in the case of bulk Si the tuning of the electronic, optical and transport properties is related to the possibility of doping, in a controlled way, the nanocrystals. This is a big challenge since several studies have revealed that doping in Si nanocrystals differs from the one of the bulk. Theory and experiments have underlined that doping and codoping are influenced by a large number of parameters such as size, shape, passivation and chemical environment of the silicon nanocrystals. However, the connection between these parameters and dopant localization as well as the occurrence of self-purification effects are still not clear. In this review we summarize the latest progress in this fascinating research field considering free-standing and matrix-embedded Si nanocrystals both from the theoretical and experimental point of view, with special attention given to the results obtained by ab-initio calculations and to size-, surface- and interface-induced effects.

Magnesium ferrite nanocrystal clusters for magnetorheological fluid with enhanced sedimentation stability

Science.gov (United States)

Wang, Guangshuo; Ma, Yingying; Li, Meixia; Cui, Guohua; Che, Hongwei; Mu, Jingbo; Zhang, Xiaoliang; Tong, Yu; Dong, Xufeng

2017-01-01

In this study, magnesium ferrite (MgFe2O4) nanocrystal clusters were synthesized using an ascorbic acid-assistant solvothermal method and evaluated as a candidate for magnetorheological (MR) fluid. The morphology, microstructure and magnetic properties of the MgFe2O4 nanocrystal clusters were investigated in detail by field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), thermogravimetric analyzer (TGA), X-ray diffraction (XRD) and superconducting quantum interference device (SQUID). The MgFe2O4 nanocrystal clusters were suspended in silicone oil to prepare MR fluid and the MR properties were tested using a Physica MCR301 rheometer fitted with a magneto-rheological module. The prepared MR fluid showed typical Bingham plastic behavior, changing from a liquid-like to a solid-like structure under an external magnetic field. Compared with the conventional carbonyl iron particles, MgFe2O4 nanocrystal clusters-based MR fluid demonstrated enhanced sedimentation stability due to the reduced mismatch in density between the particles and the carrier medium. In summary, the as-prepared MgFe2O4 nanocrystal clusters are regarded as a promising candidate for MR fluid with enhanced sedimentation stability.

Low temperature synthesis of carbon encapsulated Fe7S8 nanocrystals as high performance anode for lithium-ion batteries

International Nuclear Information System (INIS)

Liu, Boyang; Zhang, Fuhua; Wu, Qianlin; Wang, Junhua; Li, Wenge; Dong, Lihua; Yin, Yansheng

2015-01-01

A novel method is developed for low temperature synthesis of carbon encapsulated spherical Fe 7 S 8 nanocrystals with core–shell structure (Fe 7 S 8 @C) by the reaction of ferrocene with ammonium persulphate. The phase structure, morphology, specific surface area and composition of the nanocomposite are systematically characterized. It is found that the Fe 7 S 8 nanocrystals with a weight percent of 33.5% have a median size of 25.2 nm. The Fe 7 S 8 @C electrodes retain a reversible capacity of 815 and 539 mAh g −1 after 50 cycles at a current density of 200 and 2284 mA g −1 , respectively. The high capacity, good cycling behavior and rate capability of Fe 7 S 8 @C electrodes are attributed to the good protection and electrical conductivity of carbon shell. - Highlights: • Large scale and low temperature synthesis of Fe 7 S 8 @C with core–shell structure. • The Fe 7 S 8 @C electrodes retain a capacity of 815 mAh g −1 after 50 cycles at 200 mA g −1 . • The Fe 7 S 8 @C electrodes show good cycling behavior and rate capability

Inorganic Nanocrystals Functionalized Mesoporous Silica Nanoparticles: Fabrication and Enhanced Bio-applications

Directory of Open Access Journals (Sweden)

Tiancong Zhao

2017-12-01

Full Text Available Mesoporous SiO2 nanoparticles (MSNs are one of the most promising materials for bio-related applications due to advantages such as good biocompatibility, tunable mesopores, and large pore volume. However, unlike the inorganic nanocrystals with abundant physical properties, MSNs alone lack functional features. Thus, they are not sufficiently suitable for bio-applications that require special functions. Consequently, MSNs are often functionalized by incorporating inorganic nanocrystals, which provide a wide range of intriguing properties. This review focuses on inorganic nanocrystals functionalized MSNs, both their fabrication and bio-applications. Some of the most utilized methods for coating mesoporous silica (mSiO2 on nanoparticles were summarized. Magnetic, fluorescence and photothermal inorganic nanocrystals functionalized MSNs were taken as examples to demonstrate the bio-applications. Furthermore, asymmetry of MSNs and their effects on functions were also highlighted.

Extraction and characterisation of cellulose nanocrystals from pineapple peel

Directory of Open Access Journals (Sweden)

Ana Raquel Madureira

2018-04-01

Full Text Available The potential of pineapple peel as a source of cellulose nanocrystals was evaluated. Peels skin from fresh-cut fruit was used as raw material. These residues were purified to remove pigments, lipids and hemicellulose, and a bleaching process for delignification was carried out for 4-6 h. All resulting products were characterised for their lignin, hemicellulose, cellulose and ash contents using standard techniques. Dry matter at the end was low (ca. 50% compared with the raw material (ca. 90%. The process applied resulted in ca. 20% (m/m of purified cellulose (ca. 80% purity, with ineligible levels of lignin and hemicellulose present, especially when using 6h of bleaching. The purified cellulose was subject to acid hydrolysis for nanocrystal extraction with two testing times, 30 and 60 minutes. These cellulose nanocrystals had small sizes (< 1000 nm, with high variability and negative zeta potential values. The time of extraction did not affect the nanocrystals’ chemical and physical properties. The use of 6 h of bleaching treatment during purification was shown to be more effective than 4 h. Pineapple peel was demonstrated to be a good source of cellulose for the production of cellulose nanocrystals.

Tunable plasmonic lattices of silver nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Tao, Andrea; Sinsermsuksakul, Prasert; Yang, Peidong

2008-02-18

Silver nanocrystals are ideal building blocks for plasmonicmaterials that exhibit a wide range of unique and potentially usefuloptical phenomena. Individual nanocrystals display distinct opticalscattering spectra and can be assembled into hierarchical structures thatcouple strongly to external electromagnetic fields. This coupling, whichis mediated by surface plasmons, depends on their shape and arrangement.Here we demonstrate the bottom-up assembly of polyhedral silvernanocrystals into macroscopic two-dimensional superlattices using theLangmuir-Blodgett technique. Our ability to control interparticlespacing, density, and packing symmetry allows for tunability of theoptical response over the entire visible range. This assembly strategyoffers a new, practical approach to making novel plasmonic materials forapplication in spectroscopic sensors, sub-wavelength optics, andintegrated devices that utilize field enhancement effects.

Novel silica stabilization method for the analysis of fine nanocrystals using coherent X-ray diffraction imaging

Energy Technology Data Exchange (ETDEWEB)

Monteforte, Marianne; Estandarte, Ana K.; Chen, Bo; Harder, Ross; Huang, Michael H.; Robinson, Ian K.

2016-06-23

High-energy X-ray Bragg coherent diffraction imaging (BCDI) is a well established synchrotron-based technique used to quantitatively reconstruct the three-dimensional morphology and strain distribution in nanocrystals. The BCDI technique has become a powerful analytical tool for quantitative investigations of nanocrystals, nanotubes, nanorods and more recently biological systems. BCDI has however typically failed for fine nanocrystals in sub-100?nm size regimes ? a size routinely achievable by chemical synthesis ? despite the spatial resolution of the BCDI technique being 20?30?nm. The limitations of this technique arise from the movement of nanocrystals under illumination by the highly coherent beam, which prevents full diffraction data sets from being acquired. A solution is provided here to overcome this problem and extend the size limit of the BCDI technique, through the design of a novel stabilization method by embedding the fine nanocrystals into a silica matrix. Chemically synthesized FePt nanocrystals of maximum dimension 20?nm and AuPd nanocrystals in the size range 60?65?nm were investigated with BCDI measurement at beamline 34-ID-C of the APS, Argonne National Laboratory. Novel experimental methodologies to elucidate the presence of strain in fine nanocrystals are a necessary pre-requisite in order to better understand strain profiles in engineered nanocrystals for novel device development.

Building Structural Complexity in Semiconductor Nanocrystals through Chemical Transformations

Energy Technology Data Exchange (ETDEWEB)

Sadtler, Bryce F [Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2009-05-01

Methods are presented for synthesizing nanocrystal heterostructures comprised of two semiconductor materials epitaxially attached within individual nanostructures. The chemical transformation of cation exchange, where the cations within the lattice of an ionic nanocrystal are replaced with a different metal ion species, is used to alter the chemical composition at specific regions ofa nanocrystal. Partial cation exchange was performed in cadmium sulfide (CdS) nanorods of well-defined size and shape to examine the spatial organization of materials within the resulting nanocrystal heterostructures. The selectivity for cation exchange to take place at different facets of the nanocrystal plays an important role in determining the resulting morphology of the binary heterostructure. The exchange of copper (I) (Cu⁺) cations in CdS nanorods occurs preferentially at the ends of the nanorods. Theoretical modeling of epitaxial attachments between different facets of CdS and Cu₂S indicate that the selectivity for cation exchange at the ends of the nanorods is a result of the low formation energy of the interfaces produced. During silver (I) (Ag⁺) cation exchange in CdS nanorods, non-selective nucleation of silver sulfide (Ag₂S), followed by partial phase segregation leads to significant changes in the spatial arrangement of CdS and Ag₂S regions at the exchange reaction proceeds through the nanocrystal. A well-ordered striped pattern of alternating CdS and Ag₂S segments is found at intermediate fractions of exchange. The forces mediating this spontaneous process are a combination of Ostwald ripening to reduce the interfacial area along with a strain-induced repulsive interaction between Ag₂S segments. To elucidate why Cu⁺ and Ag⁺ cation exchange with CdS nanorods produce different morphologies, models for epitaxial attachments between various facets of CdS with Cu₂S or

Facile synthesis of ultrafine Co3O4 nanocrystals embedded carbon matrices with specific skeletal structures as efficient non-enzymatic glucose sensors

International Nuclear Information System (INIS)

Li, Mian; Han, Ce; Zhang, Yufan; Bo, Xiangjie; Guo, Liping

2015-01-01

Highlights: • Novel hyperfine Co 3 O 4 nanocrystals decorated porous carbon matrixes. • Facile synthesis without use of any harmful dispersing reagents or surfactants. • High dispersion degree of Co 3 O 4 nanocrystals and excellent e − transport rates. • A large current sensitivity of 955.9 μA cm −2 mM −1 toward glucose. • Excellent anti-interference and stability for glucose detection. - Abstract: A facile, effective, and environmentally friendly method has been adopted for the first time to prepare tiny Co 3 O 4 nanocrystals embedded carbon matrices without using surfactants, harmful organic reagents or extreme conditions. Structural characterizations reveal that the size-controlled Co 3 O 4 nanocrystals are uniformly dispersed on carbon matrices. Electrochemical measurements reveal that Co 3 O 4 -ordered mesoporous carbon (OMC) can more efficiently catalyze glucose oxidation and acquire better detection parameters compared with those for the Co 3 O 4 -macroporous carbon, Co 3 O 4 -reduced graphene oxide, and free Co 3 O 4 nanoparticles (NPs) (such as: the large sensitivity (2597.5 μA cm −2 mM −1 between 0 and 0.8 mM and 955.9 μA cm −2 mM −1 between 0.9 and 7.0 mM), fast response time, wide linear range, good stability, and surpassingly selective capability to electroactive molecules or Cl − ). Such excellent performances are attributed to the synergistic effect of the following three factors: (1) the high catalytic sites provided by the uniformly dispersed and size-controlled Co 3 O 4 nanocrystals embedded on OMC; (2) the excellent reactant transport efficiency caused by the abundant mesoporous structures of OMC matrix: (3) the improved electron transport in high electron transfer rate (confinement of the Co 3 O 4 NPs in nanoscale spaces ensured intimate contact between Co 3 O 4 nanocrystals and the conducting OMC matrix). The superior catalytic activity and selectivity make Co 3 O 4 -OMC very promising for application in direct

Acceptors in ZnO nanocrystals: A reinterpretation

Science.gov (United States)

Gehlhoff, W.; Hoffmann, A.

2012-12-01

In a recent article, Teklemichael et al. reported on the identification of an uncompensated acceptor in ZnO nanocrystals using infrared spectroscopy and electron paramagnetic resonance (EPR) in the dark and under illumination. Most of their conclusions, interpretations, and suggestions turned out to be erroneous. The observed EPR signals were interpreted to originate from axial and nonaxial VZn-H defects. We show that the given interpretation of the EPR results is based on misinterpretations of EPR spectra arising from defects in nanocrystals. The explanation of the infrared absorption lines is in conflict with recent results of valence band ordering and valence band splitting.

Confocal microscopy and spectroscopy of nanocrystals on a high-Q microsphere resonator

International Nuclear Information System (INIS)

Goetzinger, S; Menezes, L de S; Benson, O; Talapin, D V; Gaponik, N; Weller, H; Rogach, A L; Sandoghdar, V

2004-01-01

We report on experiments where we used a home-made confocal microscope to excite single nanocrystals on a high-Q microsphere resonator. In that way spectra of an individual quantum emitter could be recorded. The Q factor of the microspheres coated with nanocrystals was still up to 10 9 . We also demonstrate the use of a prism coupler as a well-defined output port to collect the fluorescence of an ensemble of nanocrystals coupled to whispering-gallery modes

Predicting Nanocrystal Shape through Consideration of Surface-Ligand Interactions

KAUST Repository

Bealing, Clive R.

2012-03-27

Density functional calculations for the binding energy of oleic acid-based ligands on Pb-rich {100} and {111} facets of PbSe nanocrystals determine the surface energies as a function of ligand coverage. Oleic acid is expected to bind to the nanocrystal surface in the form of lead oleate. The Wulff construction predicts the thermodynamic equilibrium shape of the PbSe nanocrystals. The equilibrium shape is a function of the ligand surface coverage, which can be controlled by changing the concentration of oleic acid during synthesis. The different binding energy of the ligand on the {100} and {111} facets results in different equilibrium ligand coverages on the facets, and a transition in the equilibrium shape from octahedral to cubic is predicted when increasing the ligand concentration during synthesis. © 2012 American Chemical Society.

Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Wu, Yimin A; Kirkland, Angus I; Schaeffel, Franziska; Porfyrakis, Kyriakos; Young, Neil P; Briggs, G Andrew D; Warner, Jamie H, E-mail: Jamie.warner@materials.ox.ac.uk [Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH (United Kingdom)

2011-05-13

We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-sized dimensions. This generic approach of using BN sheets as supports is shown by depositing Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moire patterns of interference between the beams diffracted by the nanocrystals and the BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes. Double diffraction is observed and has been analyzed.

Utilizing boron nitride sheets as thin supports for high resolution imaging of nanocrystals

International Nuclear Information System (INIS)

Wu, Yimin A; Kirkland, Angus I; Schaeffel, Franziska; Porfyrakis, Kyriakos; Young, Neil P; Briggs, G Andrew D; Warner, Jamie H

2011-01-01

We demonstrate the use of thin BN sheets as supports for imaging nanocrystals using low voltage (80 kV) aberration-corrected high resolution transmission electron microscopy. This provides an alternative to the previously utilized 2D crystal supports of graphene and graphene oxide. A simple chemical exfoliation method is applied to get few layer boron nitride (BN) sheets with micrometer-sized dimensions. This generic approach of using BN sheets as supports is shown by depositing Mn doped ZnSe nanocrystals directly onto the BN sheets and resolving the atomic structure from both the ZnSe nanocrystals and the BN support. Phase contrast images reveal moire patterns of interference between the beams diffracted by the nanocrystals and the BN substrate that are used to determine the relative orientation of the nanocrystals with respect to the BN sheets and interference lattice planes. Double diffraction is observed and has been analyzed.

Nonvolatile memory characteristics influenced by the different crystallization of Ni-Si and Ni-N nanocrystals

International Nuclear Information System (INIS)

Chen, W.-R.; Yeh, J.-L.; Chang, C.-Y.; Chang, T.-C.; Chen, S.-C.

2008-01-01

The formation of Ni-Si and Ni-N nanocrystals by sputtering a Ni 0.3 Si 0.7 target in argon and nitrogen environment were proposed in this paper. A transmission electron microscope analysis shows the nanocrystals embedded in the nitride layer. X-ray photoelectron spectroscopy and x-ray diffraction also offer the chemical material analysis of nanocrystals with surrounding dielectric and the crystallization of nanocrystals for different thermal annealing treatments. Nonvolatile Ni-Si nanocrystal memories reveal superior electrical characteristics for charge storage capacity and reliability due to the improvement of thermal annealing treatment. In addition, we used energy band diagrams to explain the significance of surrounding dielectric for reliability

Synthesis of Semiconductor Nanocrystals, Focusing on Nontoxic and Earth-Abundant Materials

NARCIS (Netherlands)

Reiss, Peter; Carrière, Marie; Lincheneau, Christophe; Vaure, Louis; Tamang, Sudarsan

2016-01-01

We review the synthesis of semiconductor nanocrystals/colloidal quantum dots in organic solvents with special emphasis on earth-abundant and toxic heavy metal free compounds. Following the Introduction, section 2 defines the terms related to the toxicity of nanocrystals and gives a comprehensive

High Temperature AL-Nanocrystal Alloy Synthesis

National Research Council Canada - National Science Library

Perepezko, J

2001-01-01

Aluminum-rich metallic glasses containing transition metals and rare earth elements have been found to yield finely mixed microstructures of Al nanocrystals embedded in an amorphous matrix and exhibit...

Nonthermal plasma synthesis of size-controlled, monodisperse, freestanding germanium nanocrystals

International Nuclear Information System (INIS)

Gresback, Ryan; Holman, Zachary; Kortshagen, Uwe

2007-01-01

Germanium nanocrystals may be of interest for a variety of electronic and optoelectronic applications including photovoltaics, primarily due to the tunability of their band gap from the infrared into the visible range of the spectrum. This letter discusses the synthesis of monodisperse germanium nanocrystals via a nonthermal plasma approach which allows for precise control of the nanocrystal size. Germanium crystals are synthesized from germanium tetrachloride and hydrogen entrained in an argon background gas. The crystal size can be varied between 4 and 50 nm by changing the residence times of crystals in the plasma between ∼30 and 440 ms. Adjusting the plasma power enables one to synthesize fully amorphous or fully crystalline particles with otherwise similar properties

Ion beam assisted synthesis of nano-crystals in glasses (silver and lead chalcogenides)

International Nuclear Information System (INIS)

Espiau de Lamaestre, R.

2005-04-01

This work deals with the interest in ion beams for controlling nano-crystals synthesis in glasses. We show two different ways to reach this aim, insisting on importance of redox phenomena induced by the penetration and implantation of ions in glasses. We first show that we can use the great energy density deposited by the ions to tailor reducing conditions, favorable to metallic nano-crystal precipitation. In particular, we show that microscopic mechanism of radiation induced silver precipitation in glasses are analogous to the ones of classical photography. Ion beams can also be used to overcome supersaturation of elements in a given matrix. In this work, we synthesized lead chalcogenide nano-crystals (PbS, PbSe, PbTe) whose optical properties are interesting for telecommunication applications. We demonstrate the influence of complex chalcogenide chemistry in oxide glasses, and its relationship with the observed loss of growth control when nano-crystals are synthesized by sequential implantation of Pb and S in pure silica. As a consequence of this understanding, we demonstrate a novel and controlled synthesis of PbS nano-crystals, consisting in implanting sulfur into a Pb-containing glass, before annealing. Choice of glass composition provides a better control of precipitation physico-chemistry, whereas the use of implantation allows high nano-crystal volume fractions to be reached. Our study of IR emission properties of these nano-crystals shows a very high excitation cross section, and evidence for a 'dark exciton' emitting level. (author)

Facile Synthesis of Colloidal CuO Nanocrystals for Light-Harvesting Applications

KAUST Repository

Lim, Yee-Fun; Choi, Joshua J.; Hanrath, Tobias

2012-01-01

CuO is an earth-abundant, nontoxic, and low band-gap material; hence it is an attractive candidate for application in solar cells. In this paper, a synthesis of CuO nanocrystals by a facile alcohothermal route is reported. The nanocrystals are dispersible in a solvent mixture of methanol and chloroform, thus enabling the processing of CuO by solution. A bilayer solar cell comprising of CuO nanocrystals and phenyl-C61-butyric acid methyl ester (PCBM) achieved a power conversion efficiency of 0.04%, indicating the potential of this material for light-harvesting applications.

Characterization of memory and measurement history in photoconductivity of nanocrystal arrays

Science.gov (United States)

Fairfield, Jessamyn A.; Dadosh, Tali; Drndic, Marija

2010-10-01

Photoconductivity in nanocrystal films has been previously characterized, but memory effects have received little attention despite their importance for device applications. We show that the magnitude and temperature dependence of the photocurrent in CdSe/ZnS core-shell nanocrystal arrays depends on the illumination and electric field history. Changes in photoconductivity occur on a few-hour timescale, and subband gap illumination of nanocrystals prior to measurements modifies the photocurrent more than band gap illumination. The observed effects can be explained by charge traps within the band gap that are filled or emptied, which may alter nonradiative recombination processes and affect photocurrent.

Colloidal Fe-doped ZnO nanocrystals: Facile low temperature synthesis, characterization and properties

Energy Technology Data Exchange (ETDEWEB)

Singhal, A. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)], E-mail: ansing@barc.gov.in; Achary, S.N.; Tyagi, A.K. [Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085 (India); Manna, P.K.; Yusuf, S.M. [Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085 (India)

2008-09-25

Colloidal Fe-doped ZnO nanocrystals, Zn{sub 1-x}Fe{sub x}O (x = 0.00, 0.05, 0.07 and 0.1) have been prepared by thermal decomposition of metal precursors at 200 deg. C with hexadecylamine (HDA) as solvent and surfactant. The nanocrystals so prepared can be easily dispersed in non-polar solvents like chloroform and toluene. The nanocrystals have been structurally characterized using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). Magnetization measurements on a representative sample, Zn{sub 0.95}Fe{sub 0.05}O using a vibrating sample magnetometer (VSM) reveal that the nanocrystals exhibit a weak ferromagnetic behavior at 300 K. This observation is further confirmed by the electron paramagnetic resonance spectrum of Zn{sub 0.95}Fe{sub 0.05}O nanocrystals, which shows a distinct ferromagnetic resonance signal at room temperature.

Synthesis of highly luminescent Mn:ZnSe/ZnS nanocrystals in aqueous media

International Nuclear Information System (INIS)

Fang Zheng; Wu Ping; Zhong Xinhua; Yang Yongji

2010-01-01

High-quality water-dispersible Mn 2+ -doped ZnSe core/ZnS shell (Mn:ZnSe/ZnS) nanocrystals have been synthesized directly in aqueous media. Overcoating a high bandgap ZnS shell around the Mn:ZnSe cores can bring forward an efficient energy transfer from the ZnSe host nanocrystals to the dopant Mn. The quantum yields of the dopant Mn photoluminescence in the as-prepared water-soluble Mn:ZnSe/ZnS core/shell nanocrystals can be up to 35 ± 5%. The optical features and structure of the obtained Mn:ZnSe/ZnS core/shell nanocrystals have been characterized by UV-vis, PL spectroscopy, TEM, XRD and ICP elementary analysis. The influences of various experimental variables, including the Mn concentration, the Se/Zn molar ratio as well as the kind and amount of capping ligand used in the core production and shell deposition process, on the luminescent properties of the obtained Mn:ZnSe/ZnS nanocrystals have been systematically investigated.

Improved oral bioavailability for lutein by nanocrystal technology: formulation development, in vitro and in vivo evaluation.

Science.gov (United States)

Chang, Daoxiao; Ma, Yanni; Cao, Guoyu; Wang, Jianhuan; Zhang, Xia; Feng, Jun; Wang, Wenping

2018-08-01

Lutein is a kind of natural carotenoids possessing many pharmacological effects. The application of lutein was limited mainly due to its low oral bioavailability caused by poor aqueous solubility. Nanocrystal formulation of lutein was developed to improve the oral bioavailability in this study. The nanosuspension was prepared by the anti-solvent precipitation-ultrasonication method and optimized by Box-Behnken design, followed by freeze-drying to obtain lutein nanocrystals. The nanocrystals were characterized on their physical properties, in vitro dissolution and in vivo absorption performance. Lutein nanocrystals showed as tiny spheres with an average particle size of 110.7 nm. The result of diffractograms indicated that the percent crystallinity of lutein was 89.4% in coarse powder and then declined in nanocrystal formulation. The saturated solubility of lutein in water increased from 7.3 μg/ml for coarse powder up to 215.7 μg/ml for lutein nanocrystals. The dissolution rate of lutein nanocrystals was significantly higher than that of coarse powder or the physical mixture. The C max and AUC 0-24 h of lutein nanocrystals after oral administration in rats was 3.24 and 2.28 times higher than those of lutein suspension, respectively. These results indicated that the nanocrystal formulation could significantly enhance the dissolution and absorption of lutein and might be a promising approach for improving its oral bioavailability.

Recent Developments in Shape-Controlled Synthesis of Silver Nanocrystals.

Science.gov (United States)

Xia, Xiaohu; Zeng, Jie; Zhang, Qiang; Moran, Christine H; Xia, Younan

2012-01-01

This feature article introduces our recent work on understanding the roles played by citrate and poly(vinyl pyrrolidone) (PVP) as capping agents in seed-mediated syntheses of Ag nanocrystals with controlled shapes. We have demonstrated that citrate and PVP selectively bind to Ag(111) and Ag(100) surfaces, respectively, and thus favor the formation of Ag nanocrystals enclosed preferentially by {111} or {100} facets. In addition, we have quantified the coverage density of PVP adsorbed on the surface of Ag nanocubes. Based on the mechanistic understanding, a series of Ag nanocrystals with controlled shapes and sizes have been successfully synthesized by using different combinations of seeds and capping agents: single-crystal spherical/cubic seeds with citrate for cuboctahedrons and octahedrons or with PVP for cubes and bars; and plate-like seeds with citrate for enlarged thin plates or with PVP for thickened plates.

Rapid synthesis of triangular CdS nanocrystals without any trap emission

International Nuclear Information System (INIS)

Poulose, Aby Cheruvathoor; Veeranarayanan, Srivani; Yoshida, Yasuhiko; Maekawa, Toru; Sakthi Kumar, D.

2012-01-01

Nanocrystals (NCs) with anisotropic dimensions display polarized emission compared to nano dots. Triangular prisms are good candidates for polarized optical properties and monodisperse triangular NCs are ideal for developing building blocks for novel three-dimensional superlattices due to its anisotropic dimension. Among triangular nanocrystals, CdS nanocrystals are less discussed for the past one decade of research due to the difficulty in its processing method. Though well studied very few methods for developing CdS triangular nanocrystals have been reported, and most are having drawbacks either due to the time consuming process or the products are combination of triangular as well as many other shaped NC or with trap emissions due to defects which are comparable to band emissions limits its applications in full scale. Here, we are presenting a novel method to develop 7 nm CdS triangular NCs that can solve the above mentioned problems, which would augment the usage of CdS triangular crystals for many applications, based on its anisotropic properties.

Structure and Ultrafast Dynamics of White-Light-Emitting CdSe Nanocrystals

International Nuclear Information System (INIS)

Bowers, Michael J.; McBride, James; Garrett, Maria Danielle; Sammons, Jessica A.; Dukes, Albert; Schreuder, Michael A.; Watt, Tony L.; Lupini, Andrew R.; Pennycook, Stephen J.; Rosenthal, Sandra

2009-01-01

White-light emission from ultrasmall CdSe nanocrystals offers an alternative approach to the realization of solid-state lighting as an appealing technology for consumers. Unfortunately, their extremely small size limits the feasibility of traditional methods for nanocrystal characterization. This paper reports the first images of their structure, which were obtained using aberration-corrected atomic number contrast scanning transmission electron microscopy (Z-STEM). With subangstrom resolution, Z-STEM is one of the few available methods that can be used to directly image the nanocrystal's structure. The initial images suggest that they are crystalline and approximately four lattice planes in diameter. In addition to the structure, for the first time, the exciton dynamics were measured at different wavelengths of the white-light spectrum using ultrafast fluorescence upconversion spectroscopy. The data suggest that a myriad of trap states are responsible for the broad-spectrum emission. It is hoped that the information presented here will provide a foundation for the future development and improvement of white-light-emitting nanocrystals.

Hydrogen storage in Pd nanocrystals covered with a metal-organic framework

Science.gov (United States)

Li, Guangqin; Kobayashi, Hirokazu; Taylor, Jared M.; Ikeda, Ryuichi; Kubota, Yoshiki; Kato, Kenichi; Takata, Masaki; Yamamoto, Tomokazu; Toh, Shoichi; Matsumura, Syo; Kitagawa, Hiroshi

2014-08-01

Hydrogen is an essential component in many industrial processes. As a result of the recent increase in the development of shale gas, steam reforming of shale gas has received considerable attention as a major source of H2, and the more efficient use of hydrogen is strongly demanded. Palladium is well known as a hydrogen-storage metal and an effective catalyst for reactions related to hydrogen in a variety of industrial processes. Here, we present remarkably enhanced capacity and speed of hydrogen storage in Pd nanocrystals covered with the metal-organic framework (MOF) HKUST-1 (copper(II) 1,3,5-benzenetricarboxylate). The Pd nanocrystals covered with the MOF have twice the storage capacity of the bare Pd nanocrystals. The significantly enhanced hydrogen storage capacity was confirmed by hydrogen pressure-composition isotherms and solid-state deuterium nuclear magnetic resonance measurements. The speed of hydrogen absorption in the Pd nanocrystals is also enhanced by the MOF coating.

Synthesis of colloidal metal nanocrystals in droplet reactors: the pros and cons of interfacial adsorption.

Science.gov (United States)

Zhang, Lei; Wang, Yi; Tong, Limin; Xia, Younan

2014-07-09

Droplet reactors have received considerable attention in recent years as an alternative route to the synthesis and potentially high-volume production of colloidal metal nanocrystals. Interfacial adsorption will immediately become an important issue to address when one seeks to translate a nanocrystal synthesis from batch reactors to droplet reactors due to the involvement of higher surface-to-volume ratios for the droplets and the fact that nanocrystals tend to be concentrated at the water-oil interface. Here we report a systematic study to compare the pros and cons of interfacial adsorption of metal nanocrystals during their synthesis in droplet reactors. On the one hand, interfacial adsorption can be used to generate nanocrystals with asymmetric shapes or structures, including one-sixth-truncated Ag octahedra and Au-Ag nanocups. On the other hand, interfacial adsorption has to be mitigated to obtain nanocrystals with uniform sizes and controlled shapes. We confirmed that Triton X-100, a nonionic surfactant, could effectively alleviate interfacial adsorption while imposing no impact on the capping agent typically needed for a shape-controlled synthesis. With the introduction of a proper surfactant, droplet reactors offer an attractive platform for the continuous production of colloidal metal nanocrystals.

Zero-reabsorption doped-nanocrystal luminescent solar concentrators.

Science.gov (United States)

Erickson, Christian S; Bradshaw, Liam R; McDowall, Stephen; Gilbertson, John D; Gamelin, Daniel R; Patrick, David L

2014-04-22

Optical concentration can lower the cost of solar energy conversion by reducing photovoltaic cell area and increasing photovoltaic efficiency. Luminescent solar concentrators offer an attractive approach to combined spectral and spatial concentration of both specular and diffuse light without tracking, but they have been plagued by luminophore self-absorption losses when employed on practical size scales. Here, we introduce doped semiconductor nanocrystals as a new class of phosphors for use in luminescent solar concentrators. In proof-of-concept experiments, visibly transparent, ultraviolet-selective luminescent solar concentrators have been prepared using colloidal Mn(2+)-doped ZnSe nanocrystals that show no luminescence reabsorption. Optical quantum efficiencies of 37% are measured, yielding a maximum projected energy concentration of ∼6× and flux gain for a-Si photovoltaics of 15.6 in the large-area limit, for the first time bounded not by luminophore self-absorption but by the transparency of the waveguide itself. Future directions in the use of colloidal doped nanocrystals as robust, processable spectrum-shifting phosphors for luminescent solar concentration on the large scales required for practical application of this technology are discussed.

Enzyme-free electrochemical immunosensor configured with Au-Pd nanocrystals and N-doped graphene sheets for sensitive detection of AFP.

Science.gov (United States)

Zhao, Lifang; Li, Songjun; He, Jing; Tian, Guihong; Wei, Qin; Li, He

2013-11-15

A novel electrochemical immunosensor capable of enzyme-free detection of alpha fetoprotein (AFP) is reported. This immunosensor was fabricated in a sandwich-like format where catalytic Au-Pd nanocrystals and highly conductive N-doped graphene sheets were incorporated. The significant catalysis by Au-Pd nanocrystals toward hydrogen peroxide, along with the increased electron transfer by graphene sheets, caused signal generation and increased sensitivity, which enables the enzyme-free detection of AFP. With a low detection limit at 0.005 ng mL(-1), this novel immunosensor worked well over the broad linear range of 0.05-30 ng mL(-1). Unlike previously reported enzyme-based electrochemical immunosensors, which often involve the complicated steps for enzyme loading and necessary treatments to keep the activity of enzyme, this novel immunosensor is simple in nature and employed catalytic Au-Pd nanoparticles and highly conductive graphene, which thus enables reliable and sensitive detection for clinic usage. Copyright © 2013 Elsevier B.V. All rights reserved.

Improving polymer/nanocrystal hybrid solar cell performance via tuning ligand orientation at CdSe quantum dot surface.

Science.gov (United States)

Fu, Weifei; Wang, Ling; Zhang, Yanfang; Ma, Ruisong; Zuo, Lijian; Mai, Jiangquan; Lau, Tsz-Ki; Du, Shixuan; Lu, Xinhui; Shi, Minmin; Li, Hanying; Chen, Hongzheng

2014-11-12

Achieving superior solar cell performance based on the colloidal nanocrystals remains challenging due to their complex surface composition. Much attention has been devoted to the development of effective surface modification strategies to enhance electronic coupling between the nanocrystals to promote charge carrier transport. Herein, we aim to attach benzenedithiol ligands onto the surface of CdSe nanocrystals in the "face-on" geometry to minimize the nanocrystal-nanocrystal or polymer-nanocrystal distance. Furthermore, the "electroactive" π-orbitals of the benzenedithiol are expected to further enhance the electronic coupling, which facilitates charge carrier dissociation and transport. The electron mobility of CdSe QD films was improved 20 times by tuning the ligand orientation, and high performance poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT):CdSe nanocrystal hybrid solar cells were also achieved, showing a highest power conversion efficiency of 4.18%. This research could open up a new pathway to improve further the performance of colloidal nanocrystal based solar cells.

Nanocrystals of medium soluble actives--novel concept for improved dermal delivery and production strategy.

Science.gov (United States)

Zhai, Xuezhen; Lademann, Jürgen; Keck, Cornelia M; Müller, Rainer H

2014-08-15

After use in oral pharmaceutical products, nanocrystals are meanwhile applied to improve the dermal penetration of cosmetic actives (e.g. rutin, hesperidin) and of drugs. By now, nanocrystals are only dermally applied made from poorly soluble actives. The novel concept is to formulate nanocrystals also from medium soluble actives, and to apply a dermal formulation containing additionally nanocrystals. The nanocrystals should act as fast dissolving depot, increase saturation solubility and especially accumulate in the hair follicles, to further increase skin penetration. Caffeine was used as model compound with relevance to market products, and a particular process was developed for the production of caffeine nanocrystals to overcome the supersaturation related effect of crystal growth and fiber formation - typical with medium soluble compounds. It is based on low energy milling (pearl milling) in combination with low dielectric constant dispersion media (water-ethanol or ethanol-propylene glycol mixtures) and optimal stabilizers. Most successful was Carbopol(®) 981 (e.g. 20% caffeine in ethanol-propylene glycol 3:7 with 2% Carbopol, w/w). Nanocrystals with varied sizes can now be produced in a controlled process e.g. 660 nm (optimal for hair follicle accumulation) to 250 nm (optimal for fast dissolution). The short term test proved stability over 2 months of the present formulation being sufficient to perform in vivo testing of the novel concept. Copyright © 2014 Elsevier B.V. All rights reserved.

Colloidal Sb2S3 Nanocrystals: Synthesis, Characterization and Fabrication of Solid-State Semiconductor Sensitized Solar Cell

KAUST Repository

Abulikemu, Mutalifu

2015-12-26

Inorganic nanocrystals composed of earth-abundant and non-toxic elements are crucial to fabricated sustainable photovoltaic devices in large scale. In this study, various-shaped and different phases of antimony sulfide nanocrystals, which is composed of non-scarce and non-toxic elements, are synthesized using hot-injection colloidal method. The effect of various synthetic parameters on the final morphology is explored. Also, foreign ion (Chlorine) effects on the morphology of Sb2S3 nanocrystals have been observed. Structural, optical and morphological properties of the nanocrystals were investigated, and Sb2S3 nanocrystal-based solid-state semiconductor-sensitized solar cells were fabricated using as-prepared nanocrystals. We achieved promising power conversion efficiencies of 1.48%.

Colloidal Sb2S3 Nanocrystals: Synthesis, Characterization and Fabrication of Solid-State Semiconductor Sensitized Solar Cell

KAUST Repository

Abulikemu, Mutalifu; Del Gobbo, Silvano; Anjum, Dalaver H.; Malik, Mohammad A; Bakr, Osman

2015-01-01

Inorganic nanocrystals composed of earth-abundant and non-toxic elements are crucial to fabricated sustainable photovoltaic devices in large scale. In this study, various-shaped and different phases of antimony sulfide nanocrystals, which is composed of non-scarce and non-toxic elements, are synthesized using hot-injection colloidal method. The effect of various synthetic parameters on the final morphology is explored. Also, foreign ion (Chlorine) effects on the morphology of Sb2S3 nanocrystals have been observed. Structural, optical and morphological properties of the nanocrystals were investigated, and Sb2S3 nanocrystal-based solid-state semiconductor-sensitized solar cells were fabricated using as-prepared nanocrystals. We achieved promising power conversion efficiencies of 1.48%.

Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions

International Nuclear Information System (INIS)

Prtljaga, Nikola; D'Amato, Elvira; Pitanti, Alessandro; Guider, Romain; Froner, Elena; Larcheri, Silvia; Scarpa, Marina; Pavesi, Lorenzo

2011-01-01

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.

Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions

Science.gov (United States)

Prtljaga, Nikola; D'Amato, Elvira; Pitanti, Alessandro; Guider, Romain; Froner, Elena; Larcheri, Silvia; Scarpa, Marina; Pavesi, Lorenzo

2011-05-01

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.

Photoluminescence of hydrophilic silicon nanocrystals in aqueous solutions

Energy Technology Data Exchange (ETDEWEB)

Prtljaga, Nikola; D' Amato, Elvira; Pitanti, Alessandro; Guider, Romain; Froner, Elena; Larcheri, Silvia; Scarpa, Marina; Pavesi, Lorenzo, E-mail: nikolap@science.unitn.it [Department of Physics, University of Trento, Via Sommarive 14, I-38123 Trento (Italy)

2011-05-27

Stable aqueous solutions of undecylenic-acid-grafted silicon nanocrystals (Si-nc) were prepared. The time evolution of the photoluminescence properties of these hydrophilic silicon nanocrystals has been followed on different timescales (hours and days). On a short timescale (hours), Si-nc tend to agglomerate while the PL lineshape and intensity are stable. Agglomeration can be reduced by using suitable surfactants. On a long timescale (days), oxidation of Si-nc occurs even in the presence of surfactants. These two observations render Si-nc very useful as a labeling agent for biosensing.

Elucidating the Potential Biological Impact of Cellulose Nanocrystals

Directory of Open Access Journals (Sweden)

Sandra Camarero-Espinosa

2016-07-01

Full Text Available Cellulose nanocrystals exhibit an interesting combination of mechanical properties and physical characteristics, which make them potentially useful for a wide range of consumer applications. However, as the usage of these bio-based nanofibers increases, a greater understanding of human exposure addressing their potential health issues should be gained. The aim of this perspective is to highlight how knowledge obtained from studying the biological impact of other nanomaterials can provide a basis for future research strategies to deduce the possible human health risks posed by cellulose nanocrystals.

Solution-Phase Synthesis of SnSe Nanocrystals for Use in Solar Cells

KAUST Repository

Franzman, Matthew A.

2010-03-31

Nanocrystals of phase-pure tin(II) selenide (SnSe) were synthesized via a solution-phase route employing stoichiometric amounts of di-tert-butyl dlselenlde as a novel and facile selenium source. The direct band gap of the resulting nanocrystals (E8 = 1.71 eV) is significantly blue-shifted relative to the bulk value (E8 = 1.30 eV), a likely consequence of quantum confinement resulting from the relatively small average diameter of the nanocrystals (μD < 20 nm). Preliminary solar cell devices incorporating SnSe nanocrystals into a poly[2-methoxy5-(3\\',7\\'-d1methyloctyloxy)-1,4- phenylenev1nylene] matrix demonstrate a significant enhancement In quantum efficiency and short-circuit current density, suggesting that this earth-abundant material could be a valuable component In future photovoltaic devices. Copyright © 2010 American Chemical Society.

A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

Energy Technology Data Exchange (ETDEWEB)

Liu Yan [Jilin Province Research Center for Engineering and Technology of Spectral Analytical Instruments, Jilin University, Changchun 130023 (China); Shen Qihui; Shi Weiguang; Li Jixue; Liu Xiaoyang [State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012 (China); Yu Dongdong [1st Hopstail affiliated to Jilin University, Jilin University, Changchun 130023 (China); Zhou Jianguang [Research Center for Analytical Instrumentation, Zhejiang University, Hangzhou 310058 (China)], E-mail: liuxy@jlu.edu.cn, E-mail: jgzhou70@126.com

2008-06-18

One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660 nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.

A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

International Nuclear Information System (INIS)

Liu Yan; Shen Qihui; Shi Weiguang; Li Jixue; Liu Xiaoyang; Yu Dongdong; Zhou Jianguang

2008-01-01

One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660 nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals

Aqueous based synthesis of N-acetyl-L-cysteine capped ZnSe nanocrystals with intense blue emission

Science.gov (United States)

Soheyli, Ehsan; Sahraei, Reza; Nabiyouni, Gholamreza

2016-10-01

In this work a very simple reflux route for preparation of ZnSe nanocrystals with minor modification and faster preparation over conventional ones is introduced. X-ray diffraction analysis indicated that the ZnSe nanocrystals have a cubic structure. The complete disappearance of the S-H band in FT-IR spectrum of N-acetyl-L-cysteine capped ZnSe nanocrystals was an indication over formation of Zn-thiol covalent bonds at the surface of the nanocrystals which results in passivation of small nanocrystals. The strong size-quantization regime was responsible of significant blue shift in absorption/emission spectra. Using the well-known calculations, band gap and Urbach energy of the ZnSe nanocrystals were measured and their average size was estimated optically to be around 4.6 nm along with the TEM image. A dark blue emission with higher relative intensity of excitonic to trap emissions (compared to conventional method), very narrow excitonic emission peak of about 16 nm and remarkable stability was obtained from the ZnSe nanocrystals.

Infrared Emitting and Photoconducting Colloidal Silver Chalcogenide Nanocrystal Quantum Dots from a Silylamide-Promoted Synthesis

NARCIS (Netherlands)

Yarema, Maksym; Pichler, Stefan; Sytnyk, Mykhailo; Seyrkammer, Robert; Lechner, Rainer T.; Fritz-Popovski, Gerhard; Jarzab, Dorota; Szendrei, Krisztina; Resel, Roland; Korovyanko, Oleksandra; Loi, Maria Antonietta; Paris, Oskar; Hesser, Guenter; Heiss, Wolfgang; Hesser, Günter

Here, we present a hot injection synthesis of colloidal Ag chalcogenide nanocrystals (Ag(2)Se, Ag(2)Te, and Ag(2)S) that resulted in exceptionally small nanocrystal sizes in the range between 2 and 4 nm. Ag chalcogenide nanocrystals exhibit band gap energies within the near-infrared spectral region,

Semiconductor-nanocrystal/conjugated polymer thin films

Science.gov (United States)

Alivisatos, A. Paul; Dittmer, Janke J.; Huynh, Wendy U.; Milliron, Delia

2014-06-17

The invention described herein provides for thin films and methods of making comprising inorganic semiconductor-nanocrystals dispersed in semiconducting-polymers in high loading amounts. The invention also describes photovoltaic devices incorporating the thin films.

A single molecule switch based on two Pd nanocrystals linked by a ...

Indian Academy of Sciences (India)

in this single molecule system. 2. Experimental ... (b) Histogram showing size distribution of the nanocrystal in (a). (c) Micro- graph taken ... applied on one of the nanocrystals using the STM tip, a voltage drop is expected along the molecular ...

Properties of magnetically diluted nanocrystals prepared by mechanochemical route

International Nuclear Information System (INIS)

Balaz, P.; Skorvanek, I.; Fabian, M.; Kovac, J.; Steinbach, F.; Feldhoff, A.; Sepelak, V.; Jiang, J.; Satka, A.; Kovac, J.

2010-01-01

The bulk and surface properties of magnetically diluted Cd 0.6 Mn 0.4 S nanocrystals synthesized by solid state route in a planetary mill were studied. XRD, SEM, TEM (HRTEM), low-temperature N 2 sorption, nanoparticle size distribution as well as SQUID magnetometry methods have been applied. The measurements identified the aggregates of small nanocrystals, 5-10 nm in size. The homogeneity of produced particles with well developed specific surface area (15-66 m 2 g -1 ) was documented. The transition from the paramagnetic to the spin-glass-like phase has been observed below ∼40 K. The changes in the magnetic behaviour at low temperatures seem to be correlated with the formation of the new surface area as a consequence of milling. The magnetically diluted Cd 0.6 Mn 0.4 S nanocrystals are obtained in the simple synthesis step, making the process attractive for industrial applications.

Highly stable colloidal TiO{sub 2} nanocrystals with strong violet-blue emission

Energy Technology Data Exchange (ETDEWEB)

Ghamsari, Morteza Sasani, E-mail: msghamsari@yahoo.com [Laser & Optics Research School, NSTRI, 11155-3486 Tehran (Iran, Islamic Republic of); Gaeeni, Mohammad Reza [Laser & Optics Research School, NSTRI, 11155-3486 Tehran (Iran, Islamic Republic of); Han, Wooje; Park, Hyung-Ho [Department of Materials Science and Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749 (Korea, Republic of)

2016-10-15

Improved sol–gel method has been applied to prepare highly stable colloidal TiO{sub 2} nanocrystals. The synthesized titania nanocrystals exhibit strong emission in the violet-blue wavelength region. Very long evolution time was obtained by preventing the sol to gel conversion with reflux process. FTIR, XRD, UV–vis absorption, photoluminescence and high resolution transmission electron microscope (HRTEM) were used to study the optical properties, crystalline phase, morphology, shape and size of prepared TiO{sub 2} colloidal nanocrystals. HRTEM showed that the diameter of TiO{sub 2} colloidal nanocrystals is about 5 nm. Although the PL spectra show similar spectral features upon excitation wavelengths at 280, 300 and 350 nm, but their emission intensities are significantly different from each other. Photoluminescence quantum yield for TiO{sub 2} colloidal nanocrystals is estimated to be 49% with 280 nm excitation wavelength which is in agreement and better than reported before. Obtained results confirm that the prepared colloidal TiO{sub 2} sample has enough potential for optoelectronics applications.

Structural Phase Transition and Compressibility of CaF2 Nanocrystals under High Pressure

Directory of Open Access Journals (Sweden)

Jingshu Wang

2018-05-01

Full Text Available The structural phase transition and compressibility of CaF2 nanocrystals with size of 23 nm under high pressure were investigated by synchrotron X-ray diffraction measurement. A pressure-induced fluorite to α-PbCl2-type phase transition starts at 9.5 GPa and completes at 20.2 GPa. The phase-transition pressure is lower than that of 8 nm CaF2 nanocrystals and closer to bulk CaF2. Upon decompression, the fluorite and α-PbCl2-type structure co-exist at the ambient pressure. The bulk modulus B0 of the 23 nm CaF2 nanocrystals for the fluorite and α-PbCl2-type phase are 103(2 and 78(2 GPa, which are both larger than those of the bulk CaF2. The CaF2 nanocrystals exhibit obviously higher incompressibility compare to bulk CaF2. Further analysis demonstrates that the defect effect in our CaF2 nanocrystals plays a dominant role in the structural stability.

Preparation of ZnS semiconductor nanocrystals using pulsed laser ablation in aqueous surfactant solutions

International Nuclear Information System (INIS)

Choi, S-H; Sasaki, T; Shimizu, Y; Yoon, J-W; Nichols, W T; Sung, Y-E; Koshizaki, N

2007-01-01

Cubic ZnS semiconductor nanocrystals with the size of 2 to 5 nm were prepared by pulsed laser ablation in aqueous surfactant solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide without any further treatments. The obtained suspensions of the nanocrystals have broad photoluminescence emission from 375 to 600 nm. The abundance and emission intensity of the nanocrystals depend on the concentration of the surfactant in solution

An Experimental Study on the Shape Changes of TiO2 Nanocrystals Synthesized by Microemulsion-Solvothermal Method

Directory of Open Access Journals (Sweden)

Wei Kong

2011-01-01

Full Text Available Titanium dioxide (TiO2 nanocrystals of different shape were successfully synthesized in a new microemulsion system through a solvothermal process. The TiO2 nanocrystals were prepared from the reaction of tetrabutyl titanate (TBT, H2O, and oleic acid (OA, which were used as solvent and surfactant at 300∘C and 240∘C in a stainless steel autoclave. The sphere, polygon, and rhombus-shaped nanocrystals have been prepared at 300∘C and the dot- and- rod shaped nanocrystals have been synthesized at 240∘C. The effect of the reaction time on the shape and size of TiO2 nanocrystals in this method was studied in the present paper. The size distribution of TiO2 nanocrystals prepared at 300∘C for different hours is also studied. In addition, an attempt to describe the mechanism of shape change of TiO2 nanocrystals was presented in this paper.

Cellulose nanocrystals the next big nano-thing?

Science.gov (United States)

Postek, Michael T.; Vladar, Andras; Dagata, John; Farkas, Natalia; Ming, Bin; Sabo, Ronald; Wegner, Theodore H.; Beecher, James

2008-08-01

Biomass surrounds us from the smallest alga to the largest redwood tree. Even the largest trees owe their strength to a newly-appreciated class of nanomaterials known as cellulose nanocrystals (CNC). Cellulose, the world's most abundant natural, renewable, biodegradable polymer, occurs as whisker like microfibrils that are biosynthesized and deposited in plant material in a continuous fashion. Therefore, the basic raw materials for a future of new nanomaterials breakthroughs already abound in the environment and are available to be utilized in an array of future materials once the manufacturing processes and nanometrology are fully developed. This presentation will discuss some of the instrumentation, metrology and standards issues associated with nanomanufacturing of cellulose nanocrystals. The use of lignocellulosic fibers derived from sustainable, annually renewable resources as a reinforcing phase in polymeric matrix composites provides positive environmental benefits with respect to ultimate disposability and raw material use. Today we lack the essential metrology infrastructure that would enable the manufacture of nanotechnology-based products based on CNCs (or other new nanomaterial) to significantly impact the U.S. economy. The basic processes common to manufacturing - qualification of raw materials, continuous synthesis methods, process monitoring and control, in-line and off-line characterization of product for quality control purposes, validation by standard reference materials - are not generally in place for nanotechnology based products, and thus are barriers to innovation. One advantage presented by the study of CNCs is that, unlike other nanomaterials, at least, cellulose nanocrystal manufacturing is already a sustainable and viable bulk process. Literally tons of cellulose nanocrystals can be generated each day, producing other viable byproducts such as glucose (for alternative fuel) and gypsum (for buildings).There is an immediate need for the

Hydrogen-Bonded Organic Semiconductor Micro- And Nanocrystals: From Colloidal Syntheses to (Opto-)Electronic Devices

Science.gov (United States)

2014-01-01

Organic pigments such as indigos, quinacridones, and phthalocyanines are widely produced industrially as colorants for everyday products as various as cosmetics and printing inks. Herein we introduce a general procedure to transform commercially available insoluble microcrystalline pigment powders into colloidal solutions of variously sized and shaped semiconductor micro- and nanocrystals. The synthesis is based on the transformation of the pigments into soluble dyes by introducing transient protecting groups on the secondary amine moieties, followed by controlled deprotection in solution. Three deprotection methods are demonstrated: thermal cleavage, acid-catalyzed deprotection, and amine-induced deprotection. During these processes, ligands are introduced to afford colloidal stability and to provide dedicated surface functionality and for size and shape control. The resulting micro- and nanocrystals exhibit a wide range of optical absorption and photoluminescence over spectral regions from the visible to the near-infrared. Due to excellent colloidal solubility offered by the ligands, the achieved organic nanocrystals are suitable for solution processing of (opto)electronic devices. As examples, phthalocyanine nanowire transistors as well as quinacridone nanocrystal photodetectors, with photoresponsivity values by far outperforming those of vacuum deposited reference samples, are demonstrated. The high responsivity is enabled by photoinduced charge transfer between the nanocrystals and the directly attached electron-accepting vitamin B2 ligands. The semiconducting nanocrystals described here offer a cheap, nontoxic, and environmentally friendly alternative to inorganic nanocrystals as well as a new paradigm for obtaining organic semiconductor materials from commercial colorants. PMID:25253644

Encapsulated Silicon Nanocrystals Formed in Silica by Ion Beam Synthesis

International Nuclear Information System (INIS)

Choi, Han Woo; Woo, Hyung Joo; Kim, Joon Kon; Kim, Gi Dong; Hong, Wan; Ji, Young Yong

2004-01-01

The photoluminescence (PL) emission of Si nanocrystals synthesized by 400 keV Si ion implanted in SiO 2 is studied as a function of ion dose and annealing time. The formation of nanocrystals at around 600 nm from the surface was confirmed by RBS and HRTEM, and the Si nanocrystals showed a wide and very intense PL emission at 700-900 nm. The intensity of this emission showed a typical behaviour with a fast transitory increase to reach a saturation with the annealing time, however, the red shift increased continuously because of the Ostwald ripening. The oversaturation of dose derived a decrease of PL intensity because of the diminishment of quantum confinement. A strong enhancement of PL intensity by H passivation was confirmed also, and the possible mechanism is discussed

Broadband enhancement of infrared absorption in microbolometers using Ag nanocrystals

International Nuclear Information System (INIS)

Hyun, Jerome K.; Ahn, Chi Won; Kim, Woo Choong; Kim, Tae Hyun; Hyun, Moon Seop; Kim, Hee Yeoun; Park, Jae Hong; Lee, Won-Oh

2015-01-01

High performance microbolometers are widely sought for thermal imaging applications. In order to increase the performance limits of microbolometers, the responsivity of the device to broadband infrared (IR) radiation needs to be improved. In this work, we report a simple, quick, and cost-effective approach to modestly enhance the broadband IR response of the device by evaporating Ag nanocrystals onto the light entrance surface of the device. When irradiated with IR light, strong fields are built up within the gaps between adjacent Ag nanocrystals. These fields resistively generate heat in the nanocrystals and underlying substrate, which is transduced into an electrical signal via a resistive sensing element in the device. Through this method, we are able to enhance the IR absorption over a broadband spectrum and improve the responsivity of the device by ∼11%

High quality zinc-blende CdSe nanocrystals synthesized in a hexadecylamine-oleic acid-paraffin liquid mixture

Energy Technology Data Exchange (ETDEWEB)

Wang Lan, E-mail: lwang322@yahoo.com.cn [Department of Applied Physics, Harbin Institute of Technology, Harbin 150001 (China); Department of Physics, Harbin Medical University, Harbin 150081 (China); Sun Xiudong, E-mail: xdsun@hit.edu.cn [Department of Applied Physics, Harbin Institute of Technology, Harbin 150001 (China); Liu Wenjing [Department of Astronautic Science and Mechanics, Harbin Institute of Technology, Harbin 150001 (China); Liu Bingyi [Laboratory Center for the School of Pharmacy, Harbin Medical University, Harbin 150081 (China)

2010-03-15

Safe, common, and low-cost compounds were used as solvents for the non-tri-n-octylphosphine (TOP) synthesis of high quality CdSe nanocrystals (NCs) in open air. In oleic acid-paraffin liquid system, CdSe nanocrystals in the less common zinc-blende (ZB, cubic) crystal structure have been obtained. The effects of adding n-hexadecylamine (HDA) to different solutions were discussed. Stable, highly homogeneous and luminescent CdSe nanocrystals were formed by adding n-hexadecylamine to Cd solution rather than to Se solution. Without any size sorting, the size distribution of the nanocrystals can be readily controlled and the highest photoluminescence (PL) quantum efficiency (QE) of the nanocrystals was up to 20-30%.

High quality zinc-blende CdSe nanocrystals synthesized in a hexadecylamine-oleic acid-paraffin liquid mixture

International Nuclear Information System (INIS)

Wang Lan; Sun Xiudong; Liu Wenjing; Liu Bingyi

2010-01-01

Safe, common, and low-cost compounds were used as solvents for the non-tri-n-octylphosphine (TOP) synthesis of high quality CdSe nanocrystals (NCs) in open air. In oleic acid-paraffin liquid system, CdSe nanocrystals in the less common zinc-blende (ZB, cubic) crystal structure have been obtained. The effects of adding n-hexadecylamine (HDA) to different solutions were discussed. Stable, highly homogeneous and luminescent CdSe nanocrystals were formed by adding n-hexadecylamine to Cd solution rather than to Se solution. Without any size sorting, the size distribution of the nanocrystals can be readily controlled and the highest photoluminescence (PL) quantum efficiency (QE) of the nanocrystals was up to 20-30%.

GaAs nanocrystals: Structure and vibrational properties

International Nuclear Information System (INIS)

Nayak, J.; Sahu, S.N.; Nozaki, S.

2006-01-01

GaAs nanocrystals were grown on indium tin oxide substrate by an electrodeposition technique. Atomic force microscopic measurement indicates an increase in the size of the nanocrystal with decrease in the electrolysis current density accompanied by the change in the shape of the crystallite. Transmission electron microscopic measurements identify the crystallite sizes to be in the range of 10-15 nm and the crystal structure to be orthorhombic. On account of the quantum size effect, the first optical transition was blue shifted with respect to the band gap of the bulk GaAs and the excitonic peak appeared prominent. A localized phonon mode ascribed to certain point defect occurred in the room temperature micro-Raman spectrum

Colloidal nanocrystals for quality lighting and displays: milestones and recent developments

Directory of Open Access Journals (Sweden)

Erdem Talha

2016-06-01

Full Text Available Recent advances in colloidal synthesis of nanocrystals have enabled high-quality high-efficiency light-emitting diodes, displays with significantly broader color gamut, and optically-pumped lasers spanning the whole visible regime. Here we review these colloidal platforms covering the milestone studies together with recent developments. In the review, we focus on the devices made of colloidal quantum dots (nanocrystals, colloidal quantum rods (nanorods, and colloidal quantum wells (nanoplatelets as well as those of solution processed perovskites and phosphor nanocrystals. The review starts with an introduction to colloidal nanocrystal photonics emphasizing the importance of colloidal materials for light-emitting devices. Subsequently,we continue with the summary of important reports on light-emitting diodes, in which colloids are used as the color converters and then as the emissive layers in electroluminescent devices. Also,we review the developments in color enrichment and electroluminescent displays. Next, we present a summary of important reports on the lasing of colloidal semiconductors. Finally, we summarize and conclude the review presenting a future outlook.

Controllable synthesis of nickel bicarbonate nanocrystals with high homogeneity for a high-performance supercapacitor

Science.gov (United States)

Gu, Jianmin; Liu, Xin; Wang, Zhuang; Bian, Zhenpan; Jin, Cuihong; Sun, Xiao; Yin, Baipeng; Wu, Tianhui; Wang, Lin; Tang, Shoufeng; Wang, Hongchao; Gao, Faming

2017-08-01

The electrochemical performance of supercapacitors might be associated with the homogeneous structure of the electrode materials. However, the relationship between the degree of uniformity for the electrode materials and the electrochemical performance of the supercapacitor is not clear. Herein, we synthesize two types of nickel bicarbonate nanocrystals with different degrees of uniformity to investigate this relationship. As the electroactive material, the nickel bicarbonate nanocrystals with a homogeneous structure could provide a larger space and offer more exposed atoms for the electrochemical reaction than the nanocrystals with a heterogeneous structure. The homogeneous nickel bicarbonate nanocrystals exhibit better electrochemical performance and show excellent specific capacitance (1596 F g-1 at 2 A g-1 and 1260 F g-1 at 30 A g-1), which is approximately twice that of the heterogeneous nickel bicarbonate nanocrystals. The cycling stability for the homogeneity (˜80%) is higher than the inhomogeneity (˜61%) at a high current density of 5 A g-1.

Temperature dependent recombination dynamics in InP/ZnS colloidal nanocrystals

Science.gov (United States)

Shirazi, R.; Kopylov, O.; Kovacs, A.; Kardynał, B. E.

2012-08-01

In this letter, we investigate exciton recombination in InP/ZnS core-shell colloidal nanocrystals over a wide temperature range. Over the entire range between room temperature and liquid helium temperature, multi-exponential exciton decay curves are observed and well explained by the presence of bright and dark exciton states, as well as defect states. Two different types of defect are present: one located at the core-shell interface and the other on the surface of the nanocrystal. Based on the temperature dependent contributions of all four states to the total photoluminescence signal, we estimate that the four states are distributed within a 20 meV energy band in nanocrystals that emit at 1.82 eV.

Out- versus in-plane magnetic anisotropy of free Fe and Co nanocrystals

DEFF Research Database (Denmark)

Li, Dongzhe; Barreteau, Cyrille; Castell, Martin R.

2014-01-01

We report tight-binding and density functional theory calculations of magnetocrystalline anisotropy energy (MAE) of free Fe (body-centered-cubic) and Co (face-centered-cubic) slabs and nanocrystals. The nanocrystals are truncated square pyramids which can be grown experimentally by deposition...... of metal on a SrTiO3(001) substrate. For both elements our local analysis shows that the totalMAE of the nanocrystals is largely dominated by the contribution of (001) facets. However, while the easy axis of Fe(001) is out-of-plane, it is in-plane for Co(001). This has direct consequences on the magnetic...

Photoluminescence studies on Cd(1-x)Zn(x)S:Mn2+ nanocrystals.

Science.gov (United States)

Sethi, Ruchi; Kumar, Lokendra; Pandey, A C

2009-09-01

Highly monodispersed, undoped and doped with Mn2+, binary and ternary (CdS, ZnS, Cd(1-x)Zn(x)S) compound semiconductor nanocrystals have been synthesized by co-precipitation method using citric acid as a stabilizer. As prepared sample are characterized by X-ray diffraction, Small angle X-ray scattering, Transmission electron microscope, Optical absorption and Photoluminescence spectroscopy, for their optical and structural properties. X-ray diffraction, Small angle X-ray scattering and Transmission electron microscope results confirm the preparation of monodispersed nanocrystals. Photoluminescence studies show a significant blue shift in the wavelength with an increasing concentration of Zn in alloy nanocrystals.

Processing of Polymer Nanocomposites Reinforced with Polysaccharide Nanocrystals

Directory of Open Access Journals (Sweden)

Alain Dufresne

2010-06-01

Full Text Available Aqueous suspensions of polysaccharide (cellulose, chitin or starch nanocrystals can be prepared by acid hydrolysis of biomass. The main problem with their practical use is related to the homogeneous dispersion of these nanoparticles within a polymeric matrix. Water is the preferred processing medium. A new and interesting way for the processing of polysaccharide nanocrystals-based nanocomposites is their transformation into a co-continuous material through long chain surface chemical modification. It involves the surface chemical modification of the nanoparticles based on the use of grafting agents bearing a reactive end group and a long compatibilizing tail.

Preparation of ZnO nanocrystals via ultrasonic irradiation

DEFF Research Database (Denmark)

Qian, D.; Jiang, Jianzhong; Hansen, P. L.

2003-01-01

A simple and rapid process has been developed for the preparation of nanometer-sized ZnO crystals via ultrasonic irradiation, by which pure ZnO nanocrystals with an average size of 6 nm and narrow size distribution can be synthesized in a short time and without using any solvents for the precipit......A simple and rapid process has been developed for the preparation of nanometer-sized ZnO crystals via ultrasonic irradiation, by which pure ZnO nanocrystals with an average size of 6 nm and narrow size distribution can be synthesized in a short time and without using any solvents...

Simple eco-friendly synthesis of the surfactant free SnS nanocrystal toward the photoelectrochemical cell application.

Science.gov (United States)

Huang, Xiaoguang; Woo, Heechul; Wu, Peinian; Hong, Hyo Jin; Jung, Wan Gil; Kim, Bong-Joong; Vanel, Jean-Charles; Choi, Jin Woo

2017-11-28

A simple, low cost, non-toxic and eco-friendly pathway for synthesizing efficient sunlight-driven tin sulfide photocatalyst was studied. SnS nanocrystals were prepared by using mechanical method. The bulk SnS was obtained by evaporation of SnS nanocrystal solution. The synthesized samples were characterized by using XRD, SEM, TEM, UV-vis, and Raman analyses. Well crystallized SnS nanocrystals were verified and the electrochemical characterization was also performed under visible light irradiation. The SnS nanocrystals have shown remarkable photocurrent density of 7.6 mA cm -2 under 100 mW cm -2 which is about 10 times larger than that of the bulk SnS under notably stable operation conditions. Furthermore, the SnS nanocrystals presented higher stability than the bulk form. The IPCE(Incident photon to current conversion efficiency) of 9.3% at 420 nm was obtained for SnS nanocrystal photoanode which is strikingly higher than that of bulk SnS, 0.78%. This work suggests that the enhancement of reacting area by using SnS nanocrystal absorbers could give rise to the improvement of photoelectrochemical cell efficiency.

Strong blue emission from ZnO nanocrystals synthesized in acetone-based solvent

International Nuclear Information System (INIS)

Efafi, B.; Majles Ara, M.H.; Mousavi, S.S.

2016-01-01

In this research, ZnO nanocrystals were synthesized by an improved sol–gel method. UV–vis, FTIR and photoluminescence spectra of the ZnO solution synthesized by this route indicated different properties compared to the other preparation methods. It was observed from FTIR that the sol (prepared using acetone) with the low concentration contains a noticeable amount of the Zn–O bond. The PL spectrum with a strong blue emission confirmed that these nanocrystals are good candidate for use in applications where a monochromatic emission is required. To the best of our knowledge, monochromatic emission ZnO devices have been fabricated through high technology instruments but this paper introduces a simple method for preparation of ZnO with the high intensity blue peak. The size and morphology of ZnO nanocrystals have been studied using FESEM. The nanocrystal size was estimated about 70 nm which was in good agreement with XRD data. - Highlights: • Preparation of ZnO nanocrystals through a novel method by the use of acetone as the solvent. • Observation of the strong blue emission peak from the ZnO prepared solution. • Reduction of green emission in the synthesized sample compared to the other methods of preparation.

Strong blue emission from ZnO nanocrystals synthesized in acetone-based solvent

Energy Technology Data Exchange (ETDEWEB)

Efafi, B. [NanoPhotonics Lab., Physics Department, Kharazmi University, Tehran (Iran, Islamic Republic of); Departments of Physics, Iran University of Science & Technology, Tehran (Iran, Islamic Republic of); Majles Ara, M.H., E-mail: majlesara@gmail.com [NanoPhotonics Lab., Physics Department, Kharazmi University, Tehran (Iran, Islamic Republic of); Mousavi, S.S. [NanoPhotonics Lab., Physics Department, Kharazmi University, Tehran (Iran, Islamic Republic of)

2016-10-15

In this research, ZnO nanocrystals were synthesized by an improved sol–gel method. UV–vis, FTIR and photoluminescence spectra of the ZnO solution synthesized by this route indicated different properties compared to the other preparation methods. It was observed from FTIR that the sol (prepared using acetone) with the low concentration contains a noticeable amount of the Zn–O bond. The PL spectrum with a strong blue emission confirmed that these nanocrystals are good candidate for use in applications where a monochromatic emission is required. To the best of our knowledge, monochromatic emission ZnO devices have been fabricated through high technology instruments but this paper introduces a simple method for preparation of ZnO with the high intensity blue peak. The size and morphology of ZnO nanocrystals have been studied using FESEM. The nanocrystal size was estimated about 70 nm which was in good agreement with XRD data. - Highlights: • Preparation of ZnO nanocrystals through a novel method by the use of acetone as the solvent. • Observation of the strong blue emission peak from the ZnO prepared solution. • Reduction of green emission in the synthesized sample compared to the other methods of preparation.

Spontaneous emission enhancement of colloidal perovskite nanocrystals

Science.gov (United States)

Yang, Zhili; Waks, Edo

Halide perovskite semiconductors have emerged as prominent photovoltaic materials since their high conversion efficiency and promising light emitting materials in optoelectronics. In particular, easy-to-fabricated colloidal perovskite nanocrystals based on CsPbX3 quantum dots has been intensively investigated recently. Their luminescent wavelength could be tuned precisely by their chemical composition and size of growth. This opens new applications including light-emitting diodes, optical amplifiers and lasing since their promising performance as emitters. However, this potentially high-efficient emitter and gain material has not been fully investigated and realized in integrated photonic structures. Here we demonstrate Purcell enhancement effect of CsPbBr3 perovskite nanocrystals by coupling to an optimized photonic crystal nanobeam cavity as a first crucial step towards realization of integrated on-chip coherent light source with low energy consumption. We show clearly highly-enhanced photoluminescent spectrum and an averaged Purcell enhancement factor of 2.9 is achieved when they are coupled to nanobeam photonic crystal cavities compared to the ones on unpatterned surface in our lifetime measurement. Our success in enhancement of emission from CsPbX3 perovskite nanocrystals paves the way towards the realization of efficient light sources for integrated optoelectronic devices with low energy consumption.

Bi-continuous Multi-component Nanocrystal Superlattices for Solar Energy Conversion

Energy Technology Data Exchange (ETDEWEB)

Kagan, Cherie [University of Pennsylvania; Murray, Christopher [University of Pennsylvania; Kikkawa, James [University of Pennsylvania; Engheta, Nader [University of Pennsylvania

2017-06-14

Our SISGR program studied an emerging class of nanomaterials wherein different combinations of semiconductor or semiconductor and plasmonic nanocrystals (NCs) are self-assembled into three-dimensional multi-component superlattices. The NC assemblies were designed to form bicontinuous semiconductor NC sublattices with type-II energy offsets to drive charge separation onto electron and hole transporting sublattices for collection and introduce plasmonic NCs to increase solar absorption and charge separation. Our group is expert in synthesizing and assembling an extraordinary variety of artificial systems by tailoring the NC building blocks and the superlattice unit cell geometry. Under this DOE BES Materials Chemistry program, we introduced chemical methods to control inter-particle distance and to dope NC assemblies, which enabled our demonstration of strong electronic communication between NCs and the use of NC thin films as electronic materials. We synthesized, assembled and structurally, spectroscopically, and electrically probed NC superlattices to understand and manipulate the flow of energy and charge toward discovering the design rules and optimizing these complex architectures to create materials that efficiently convert solar radiation into electricity.

Gamma-ray imaging probes

International Nuclear Information System (INIS)

Wild, W.J.

1988-01-01

External nuclear medicine diagnostic imaging of early primary and metastatic lung cancer tumors is difficult due to the poor sensitivity and resolution of existing gamma cameras. Nonimaging counting detectors used for internal tumor detection give ambiguous results because distant background variations are difficult to discriminate from neighboring tumor sites. This suggests that an internal imaging nuclear medicine probe, particularly an esophageal probe, may be advantageously used to detect small tumors because of the ability to discriminate against background variations and the capability to get close to sites neighboring the esophagus. The design, theory of operation, preliminary bench tests, characterization of noise behavior and optimization of such an imaging probe is the central theme of this work

Microstructure, thermal properties and crystallinity of amadumbe starch nanocrystals.

Science.gov (United States)

Mukurumbira, Agnes; Mariano, Marcos; Dufresne, Alain; Mellem, John J; Amonsou, Eric O

2017-09-01

Amadumbe (Colocasia esculenta), commonly known as taro is a tropical tuber that produces starch-rich underground corms. In this study, the physicochemical properties of starch nanocrystals (SNC) prepared by acid hydrolysis of amadumbe starches were investigated. Two varieties of amadumbe corms were used for starch extraction. Amadumbe starches produced substantially high yield (25%) of SNC's. These nanocrystals appeared as aggregated and individual particles and possessed square-like platelet morphology with size: 50-100nm. FTIR revealed high peak intensities corresponding to OH stretch, CH stretch and H 2 O bending vibrations for SNCs compared to their native starch counterparts. Both the native starch and SNC exhibited the A-type crystalline pattern. However, amadumbe SNCs showed higher degree of crystallinity and slightly reduced melting temperatures than their native starches. Amadumbe SNCs presented similar thermal decomposition property as their native starches. Amadumbe starch nanocrystals may have potential application in biocomposite films due to their square-like platelet morphology. Copyright © 2017 Elsevier B.V. All rights reserved.

X-Ray Absorption Studies of Vanadium-Containing Metal Oxide Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Hohn, Keith, L.

2006-01-09

Metal oxide nanocrystals offer significant potential for use as catalysts or catalyst supports due to their high surface areas and unique chemical properties that result from the high number of exposed corners and edges. However, little is known about the catalytic activity of these materials, especially as oxidation catalysts. This research focused on the preparation, characterization and use of vanadium-containing nanocrystals as selective oxidation catalysts. Three vanadium-containing nanocrystals were prepared using a modified sol-gel procedure: V/MgO, V/SiO2, and vanadium phosphate (VPO). These represent active oxidation catalysts for a number of industrially relevant reactions. The catalysts were characterized by x-ray diffraction and Raman, UV-VIS, infrared and x-ray absorption spectroscopies with the goal of determining the primary structural and chemical differences between nanocrystals and microcrystals. The catalytic activity of these catalysts was also studied in oxidative dehydrogenation of butane and methanol oxidation to formaldehyde. V/MgO nanocrystals were investigated for activity in oxidative dehydrogenation of butane and compared to conventional V/MgO catalysts. Characterization of V/MgO catalysts using Raman spectroscopy and x-ray absorption spectroscopy showed that both types of catalysts contained magnesium orthovanadate at vanadium loadings below 15 weight%, but above that loading, magnesium pyrovanadate may have been present. In general, MgO nanocrystals had roughly half the crystal size and double the surface area of the conventional MgO. In oxidative dehydrogenation of butane, nanocrystalline V/MgO gave higher selectivity to butene than conventional V/MgO at the same conversion. This difference was attributed to differences in vanadium domain size resulting from the higher surface areas of the nanocrystalline support, since characterization suggested that similar vanadium phases were present on both types of catalysts. Experiments in

Twenty-fold plasmon-induced enhancement of radiative emission rate in silicon nanocrystals embedded in silicon dioxide

International Nuclear Information System (INIS)

Gardelis, S; Gianneta, V.; Nassiopoulou, A.G

2016-01-01

We report on a 20-fold enhancement of the integrated photoluminescence (PL) emission of silicon nanocrystals, embedded in a matrix of silicon dioxide, induced by excited surface plasmons from silver nanoparticles, which are located in the vicinity of the silicon nanocrystals and separated from them by a silicon dioxide layer of a few nanometers. The electric field enhancement provided by the excited surface plasmons increases the absorption cross section and the emission rate of the nearby silicon nanocrystals, resulting in the observed enhancement of the photoluminescence, mainly attributed to a 20-fold enhancement in the emission rate of the silicon nanocrystals. The observed remarkable improvement of the PL emission makes silicon nanocrystals very useful material for photonic, sensor and solar cell applications.

New crystal structures in hexagonal CuInS2 nanocrystals

Science.gov (United States)

Shen, Xiao; Hernández-Pagan, Emil A.; Zhou, Wu; Puzyrev, Yevgeniy S.; Idrobo, Juan C.; MacDonald, Janet E.; Pennycook, Stephen J.; Pantelides, Sokrates T.

2013-03-01

CuInS2 is one of the best candidate materials for solar energy harvesting. Its nanocrystals with a hexagonal lattice structure that is different from the bulk chalcopyrite phase have been synthesized by many groups. The structure of these CuInS2 nanocrystals has been previously identified as the wurtzite structure in which the copper and indium atoms randomly occupy the cation sites. Using first-principles total energy and electronic structure calculations based on density functional theory, UV-vis absorption spectroscopy, X-ray diffraction, and atomic resolution Z-contrast images obtained in an aberration-corrected scanning transmission electron microscope, we show that CuInS2 nanocrystals do not form random wurtzite structure. Instead, the CuInS2 nanocrystals consist of several wurtzite- related crystal structures with ordered cation sublattices, some of which are reported for the first time here. This work is supported by the NSF TN-SCORE (JEM), by NSF (WZ), by ORNL's Shared Research Equipment User Program (JCI) sponsored by DOE BES, by DOE BES Materials Sciences and Engineering Division (SJP, STP), and used resources of the National Energy Research Scientific Computing Center, supported by the DOE Office of Science under Contract No. DE-AC02-05CH11231.

Visualizing Current Flow at the Mesoscale in Disordered Assemblies of Touching Semiconductor Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Chen, Qinyi; Guest, Jeffrey R. [Center; Thimsen, Elijah

2017-07-12

The transport of electrons through assemblies of nanocrystals is important to performance in optoelectronic applications for these materials. Previous work has primarily focused on single nanocrystals or transitions between pairs of nanocrystals. There is a gap in knowledge of how large numbers of nanocrystals in an assembly behave collectively, and how this collective behavior manifests at the mesoscale. In this work, the variable range hopping (VRH) transport of electrons in disordered assemblies of touching, heavily doped ZnO nanocrystals was visualized at the mesoscale as a function of temperature both theoretically, using the model of Skinner, Chen and Shklovskii (SCS), and experimentally, with conductive atomic force microscopy on ultrathin films only a few particle layers thick. Agreement was obtained between the model and experiments, with a few notable exceptions. The SCS model predicts that a single network within the nanocrystal assembly, comprised of sites connected by small resistances, dominates conduction - namely the optimum band from variable range hopping theory. However, our experiments revealed that in addition to the optimum band, there are subnetworks that appear as additional peaks in the resistance histogram of conductive atomic force microscopy (CAFM) maps. Furthermore, the connections of these subnetworks to the optimum band change in time, such that some subnetworks become connected to the optimum band while others become disconnected and isolated from the optimum band; this observation appears to be an experimental manifestation of the ‘blinking’ phenomenon in our images of mesoscale transport.

Semiconductor nanocrystals dispersed in imidazolium-based ionic liquids: a spectroscopic and morphological investigation

International Nuclear Information System (INIS)

Panniello, Annamaria; Binetti, Enrico; Ingrosso, Chiara; Curri, M. Lucia; Agostiano, Angela; Tommasi, Raffaele; Striccoli, Marinella

2013-01-01

A growing interest is devoted to the study of imidazolium-based ionic liquids as innovative materials to combine with functional elements for advanced technological applications. Materials based on semiconductor and oxide nanocrystals in ionic liquids can be promising for their integration in lithium batteries, as well as in innovative solar cells. Although the physical chemical properties and the solvation dynamics of bare ionic liquids have been extensively studied, their combination with colloidal nanocrystals still remains almost unexplored. Here, the optical properties of organic-capped luminescent cadmium selenide nanocrystals coated by a shell of zinc sulfide (CdSe(ZnS)) dispersed in 1,3-dialkyl imidazolium ionic liquids have been investigated, also in dependence of the alkyl chain length on the imidazolium ring and of the anion nature, by using both time-integrated and time-resolved optical spectroscopy. The observed variations in decay profiles of the ionic liquid in presence of colloidal nanocrystals suggest that the dispersion of the nanostructures induces modifications in the ionic liquid structural order. Finally, atomic force microscopy analysis has provided insight into the topography of the investigated dispersions deposited as film, confirming the organization of the ionic liquids in super-structures, also upon nanocrystal incorporation.

Nanocrystal: a novel approach to overcome skin barriers for improved topical drug delivery.

Science.gov (United States)

Patel, Viral; Sharma, Om Prakash; Mehta, Tejal

2018-04-01

Skin is an important route of drug delivery for the treatment of various dermatological conditions. The advent of nanotechnology is paving the roadmaps for topical drug delivery by providing sustained release as well as maintaining a localized effect, outweighing the toxicity concern. Area covered: This review highlighted the morphology of skin, its barrier nature as well as drug penetration pathways after topical application of formulations. The existing methods to improve topical drug delivery, by infringing or permeating the skin barriers, are discussed. This context concretes the foundation to accentuate the need for the development of nanocrystal-based topical formulation. The mechanism of drug release, immediate as well as sustained release, after topical administration of drug nanocrystals is also elaborated. The special emphasis is given on the breakthrough achieved, in topical drug delivery using drug nanocrystals, so far in the plethora of literature, patents, and products, under clinical trial as well as in the market. Expert opinion: The current research on nanocrystals for topical drug delivery is highlighting the breakthroughs achieved so far. The output of these research envisages that topical nanocrystals based formulations can be a novel strategy for the drugs which are facing solubility, bioavailability and toxicity concerns.

Precipitation-lyophilization-homogenization (PLH) for preparation of clarithromycin nanocrystals: influencing factors on physicochemical properties and stability.

Science.gov (United States)

Morakul, Boontida; Suksiriworapong, Jiraphong; Leanpolchareanchai, Jiraporn; Junyaprasert, Varaporn Buraphacheep

2013-11-30

Nanocrystals is one of effective technologies used to improve solubility and dissolution behavior of poorly soluble drugs. Clarithromycin is classified in BCS class II having low bioavailability due to very low dissolution behavior. The main purpose of this study was to investigate an efficiency of clarithromycin nanocrystals preparation by precipitation-lyophilization-homogenization (PLH) combination method in comparison with high pressure homogenization (HPH) method. The factors influencing particle size reduction and physical stability were assessed. The results showed that the PLH technique provided an effective and rapid reduction of particle size of nanocrystals to 460 ± 10 nm with homogeneity size distribution after only the fifth cycle of homogenization, whereas the same size was attained after 30 cycles by the HPH method. The smallest nanocrystals were achieved by using the combination of poloxamer 407 (2%, w/v) and SLS (0.1%, w/v) as stabilizers. This combination could prevent the particle aggregation over 3-month storage at 4 °C. The results from SEM showed that the clarithromycin nanocrystals were in cubic-shaped similar to its initial particle morphology. The DSC thermogram and X-ray diffraction pattern of nanocrystals were not different from the original drug except for intensity of peaks which indicated the presenting of nanocrystals in the crystalline state and/or partial amorphous form. In addition, the dissolution of the clarithromycin nanocrystals was dramatically increased as compared to the coarse clarithromycin. Copyright © 2013 Elsevier B.V. All rights reserved.

Light-emitting diodes based on nontoxic zinc-alloyed silver-indium-sulfide (AIZS) nanocrystals

Science.gov (United States)

Bhaumik, Saikat; Guchhait, Asim; Pal, Amlan J.

2014-04-01

We report solution-processed growth of zinc-alloyed silver-indium-sulfide (AIZS) nanocrystals followed by fabrication and characterization of light-emitting diodes (LEDs) based on such nanostructures. While growing the low dimensional crystals, we vary the ratio between the silver and zinc contents that in turn tunes the bandgap and correspondingly their photoluminescence (PL) emission. We also dope the AIZS nanocrystals with manganese, so that their PL emission, which appears due to a radiative transition between the d-states of the dopants, becomes invariant in energy when the diameter of the quantum dots or the dopant concentration in the nanostructures varies. The LEDs fabricated with such undoped and manganese-doped AIZS nanocrystals emit electroluminescence (EL) that matches the PL spectrum of the respective nanomaterial. The results demonstrate examples of quantum dot LEDs (QDLEDs) based on nontoxic AIZS nanocrystals.

Characterization of CdSe-nanocrystals used in semiconductors for aerospace applications: Production and optical properties

Directory of Open Access Journals (Sweden)

Maroof A. Hegazy

2014-06-01

Full Text Available Semiconductor nanocrystals (NC’s are the materials with dimensions less than 10 nm. When the dimensions of nanocrystals are reduced the bulk bohr diameter, the photo generated electron-hole pair becomes confined and nanocrystal exhibits size dependent upon optical properties. This work is focused on the studying of CdSe semiconductor nanocrystals. These nanocrystals are considered as one of the most widely studies semiconductors because of their size – tunable optical properties from the visible spectrum. CdSe-nanocrystals are produced and obtained throughout the experimental setup initiated at Nano-NRIAG Unit (NNU, which has been constructed and assembled at NRIAG institute. This unit has a specific characterization for preparing chemical compositions, which may be used for solar cell fabrications and space science technology. The materials prepared included cadmium oxide and selinid have sizes ranging between 2.27 nm and 3.75 nm. CdSe-nanocrystals are synthesized in “TOP/TOPO (tri–octyl phosphine/tri–octyl phosphine oxide. Diagnostic tools, include UV analysis, TEM microscope, and X-ray diffraction, which are considered for the analytical studies of the obtained materials. The results show that, in this size regime, the generated particles have unique optical properties, which is achieved from the UV analysis. Also, the TEM image analysis shows the size and shape of the produced particles. These studies are carried out to optimize the photoluminescent efficiency of these nanoparticles. Moreover, the data revealed that, the grain size of nanocrystals is dependent upon the growth time in turn, it leads to a change in the energy gap. Some applications of this class of materials are outlined.

Paramagnetic behavior of Co doped TiO{sub 2} nanocrystals controlled by self-purification mechanism

Energy Technology Data Exchange (ETDEWEB)

Anitha, B. [Centre for Nanoscience and Nanotechnology, University of Kerala, Kariavattom, Thiruvananthapuram 695 581 (India); Khadar, M. Abdul, E-mail: mabdulkhadar@rediffmail.com [Centre for Nanoscience and Nanotechnology, University of Kerala, Kariavattom, Thiruvananthapuram 695 581 (India); Banerjee, Alok [UGC-DAE Consortium for Scientific Research (CSR), Khandwa Road, Indore 452 001 (India)

2016-07-15

Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO{sub 2} doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO{sub 2} along with weak intensity peaks of Co{sub 3}O{sub 4} for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO{sub 2} matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO{sub 2} nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co{sup 2+} ions and an increased presence of Co{sub 3}O{sub 4} phase near the surface of the TiO{sub 2} nanocrystals due to self-purification mechanism. - Graphical abstract: Variation of the intensity ratios of XRD peaks as a function of atomic ratio of Co. Inset: variation of structure factor for (101) reflection as a function of atomic ratio of Co. Display Omitted - Highlights: • Co doped TiO{sub 2} nanocrystals were synthesized by peroxide gel method. • HRTEM images showed Co doped TiO{sub 2} nanocrystals to be rod-like. • EPR spectra showed +2 oxidation states for Co in the samples. • Co doped TiO{sub 2} nanocrystals showed paramagnetic behavior.

Silver nanocrystal-decorated polyoxometalate single-walled nanotubes as nanoreactors for desulfurization catalysis at room temperature.

Science.gov (United States)

Zhang, Hao; Xu, Xiaobin; Lin, Haifeng; Ud Din, Muhammad Aizaz; Wang, Haiqing; Wang, Xun

2017-09-14

Ultrathin nanocrystals generally provide a remarkable catalytic performance due to their high specific surface area and exposure of certain active sites. However, deactivation caused by growth and gathering limits the catalytic application of ultrathin nanocrystals. Here we report Ag nanocrystal-decorated polyoxometalate (Ag-POM) single-walled nanotubes assembled via a concise, surfactant-free soaking method as a new kind of well-defined core-sheath nanoreactor. The diameter of Ag nanocrystals inside polyoxometalate nanotubes can be controlled via simply adjusting the reactant concentration. Ag-POM provided outstanding oxidative desulfurization (ODS) catalytic performance for aromatic sulfocompounds at room temperature. It was suggested that Ag nanocrystals decorated on the inner surface played a key role in adjusting the electronic distribution and enhancing the catalytic activity. The as-prepared Ag-POM nanotubes are promising candidate catalysts with enhanced performance for practical catalytic applications in the gasoline desulfurization industry.

In situ functionalization and PEO coating of iron oxide nanocrystals using seeded emulsion polymerization.

Science.gov (United States)

Kloust, Hauke; Schmidtke, Christian; Feld, Artur; Schotten, Theo; Eggers, Robin; Fittschen, Ursula E A; Schulz, Florian; Pöselt, Elmar; Ostermann, Johannes; Bastús, Neus G; Weller, Horst

2013-04-16

Herein we demonstrate that seeded emulsion polymerization is a powerful tool to produce multiply functionalized PEO coated iron oxide nanocrystals. Advantageously, by simple addition of functional surfactants, functional monomers, or functional polymerizable linkers-solely or in combinations thereof-during the seeded emulsion polymerization process, a broad range of in situ functionalized polymer-coated iron oxide nanocrystals were obtained. This was demonstrated by purposeful modulation of the zeta potential of encapsulated iron oxide nanocrystals and conjugation of a dyestuff. Successful functionalization was unequivocally proven by TXRF. Furthermore, the spatial position of the functional groups can be controlled by choosing the appropriate spacers. In conclusion, this methodology is highly amenable for combinatorial strategies and will spur rapid expedited synthesis and purposeful optimization of a broad scope of nanocrystals.

Self-Assembled Monolayers of CdSe Nanocrystals on Doped GaAs Substrates

DEFF Research Database (Denmark)

Marx, E.; Ginger, D.S.; Walzer, Karsten

2002-01-01

This letter reports the self-assembly and analysis of CdSe nanocrystal monolayers on both p- and a-doped GaAs substrates. The self-assembly was performed using a 1,6-hexanedithiol self-assembled monolayer (SAM) to link CdSe nanocrystals to GaAs substrates. Attenuated total reflection Fourier tran...

Fabrication of highly oriented D03-Fe3Si nanocrystals by solid-state dewetting of Si ultrathin layer

International Nuclear Information System (INIS)

Naito, Muneyuki; Nakagawa, Tatsuhiko; Machida, Nobuya; Shigematsu, Toshihiko; Nakao, Motoi; Sudoh, Koichi

2013-01-01

In this paper, highly oriented nanocrystals of Fe 3 Si with a D0 3 structure are fabricated on SiO 2 using ultrathin Si on insulator substrate. First, (001) oriented Si nanocrystals are formed on the SiO 2 layer by solid state dewetting of the top Si layer. Then, Fe addition to the Si nanocrystals is performed by reactive deposition epitaxy and post-deposition annealing at 500 °C. The structures of the Fe–Si nanocrystals are analyzed by cross-sectional transmission electron microscopy and nanobeam electron diffraction. We observe that Fe 3 Si nanocrystals with D0 3 , B2, and A2 structures coexist on the 1-h post-annealed samples. Prolonged annealing at 500 °C is effective in obtaining Fe 3 Si nanocrystals with a D0 3 single phase, thereby promoting structural ordering in the nanocrystals. We discuss the formation process of the highly oriented D0 3 -Fe 3 Si nanocrystals on the basis of the atomistic structural information. - Highlights: • Highly oriented Fe–Si nanocrystals (NCs) are fabricated by reactive deposition. • Si NCs formed by solid state dewetting of Si thin layers are used as seed crystals. • The structures of Fe–Si NCs are analyzed by nanobeam electron diffraction. • Most of Fe–Si NCs possess the D0 3 structure after post-deposition annealing

Noninjection Synthesis of CdS and Alloyed CdSxSe1−xNanocrystals Without Nucleation Initiators

Directory of Open Access Journals (Sweden)

Zou Yu

2010-01-01

Full Text Available Abstract CdS and alloyed CdSxSe1−x nanocrystals were prepared by a simple noninjection method without nucleation initiators. Oleic acid (OA was used to stabilize the growth of the CdS nanocrystals. The size of the CdS nanocrystals can be tuned by changing the OA/Cd molar ratios. On the basis of the successful synthesis of CdS nanocrystals, alloyed CdSxSe1−x nanocrystals can also be prepared by simply replacing certain amount of S precursor with equal amount of Se precursor, verified by TEM, XRD, EDX as well as UV–Vis absorption analysis. The optical properties of the alloyed CdSxSe1−x nanocrystals can be tuned by adjusting the S/Se feed molar ratios. This synthetic approach developed is highly reproducible and can be readily scaled up for potential industrial production.

Prospects of Colloidal Copper Chalcogenide Nanocrystals

NARCIS (Netherlands)

van der Stam, W.; Berends, A.C.; de Mello-Donega, Celso

2016-01-01

Over the past few years, colloidal copper chalcogenide nanocrystals (NCs) have emerged as promising alternatives to conventional Cd and Pb chalcogenide NCs. Owing to their wide size, shape, and composition tunability, Cu chalcogenide NCs hold great promise for several applications, such as

In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices.

Science.gov (United States)

Zhao, Lianfeng; Yeh, Yao-Wen; Tran, Nhu L; Wu, Fan; Xiao, Zhengguo; Kerner, Ross A; Lin, YunHui L; Scholes, Gregory D; Yao, Nan; Rand, Barry P

2017-04-25

Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CH 3 NH 3 PbI 3 red/near-infrared LEDs and CH 3 NH 3 PbBr 3 green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.

Tuning the morphology, stability and photocatalytic activity of TiO2 nanocrystal colloids by tungsten doping

International Nuclear Information System (INIS)

Xu, Haiping; Liao, Jianhua; Yuan, Shuai; Zhao, Yin; Zhang, Meihong; Wang, Zhuyi; Shi, Liyi

2014-01-01

Graphical abstract: - Highlights: • W 6+ -doped TiO 2 nanocrystal colloids were prepared by hydrothermal methods. • The properties of TiO 2 nanocrystal colloids can be tuned by tungsten doping. • W 6+ -doped TiO 2 nanocrystal colloids show higher stability and dispersity. • W 6+ -doped TiO 2 nanocrystal colloids show higher photocatalytic activity. - Abstract: The effects of tungsten doping on the morphology, stability and photocatalytic activity of TiO 2 nanocrystal colloids were investigated. The nanostructure, chemical state of Ti, W, O, and the properties of tungsten doped TiO 2 samples were investigated carefully by TEM, XRD, XPS, UV–vis, PL and photocatalytic degradation experiments. And the structure–activity relationship was discussed according to the analysis and measurement results. The analysis results reveal that the morphology, zeta potential and photocatalytic activity of TiO 2 nanocrystals can be easily tuned by changing the tungsten doping concentration. The tungsten doped TiO 2 colloid combines the characters of high dispersity and high photocatalytic activity

Optical properties and ensemble characteristics of size purified Silicon nanocrystals

Science.gov (United States)

Miller, Joseph Bradley

Nanotechnology is at the forefront of current scientific research and nanocrystals are being hailed as the 'artificial' atoms of the 21st century. Semiconducting silicon nanocrystals (SiNCs) are prime candidates for potential commercial applications because of silicon's already ubiquitous presence in the semiconductor industry, nontoxicity and abundance in nature. For realization of these potential applications, the properties and behavior of SiNCs need to be understood and enhanced. In this report, some of the main SiNC synthesis schemes are discussed, including those we are currently experimenting with to create our own SiNCs and the one utilized to create the SiNCs used in this study. The underlying physics that governs the unique behavior of SiNCs is then presented. The properties of the as-produced SiNCs are determined to depend strongly on surface passivation and environment. Size purification, an important aspect of nanomaterial utilization, was successfully performed on our SiNCs though density gradient ultracentrifugation. We demonstrate that the size-purified fractions exhibit an enhanced ability for colloidal self-assembly, with better aligned nanocrystal energy levels which promotes greater photostability in close-packed films and produces a slight increase in photoluminescence (PL) quantum yield. The qualities displayed by the fractions are exploited to form SiNC clusters that exhibit photostable PL. An analysis of SiNC cluster (from individual nanocrystals to collections of more than one thousand) blinking and PL shows an improvement in their PL emitting 'on' times. Pure SiNC films and SiNC-polymer nanocomposites are created and the dependence of their PL on temperature is measured. For such nanocomposites, the coupling between the 'coffee-ring' effect and liquid-liquid phase separation is also examined for ternary mixtures of solvent, polymer and semiconducting nanocrystal. We discover that with the right SiNC-polymer concentration and polymer

Formulation strategy and evaluation of nanocrystal piroxicam orally disintegrating tablets manufacturing by freeze-drying.

Science.gov (United States)

Lai, Francesco; Pini, Elena; Corrias, Francesco; Perricci, Jacopo; Manconi, Maria; Fadda, Anna Maria; Sinico, Chiara

2014-06-05

Piroxicam (PRX) is a non-steroidal anti-inflammatory drug characterized by a poor water solubility and consequently by a low oral bioavailability. In this work, different nanocrystal orally disintegrating tablets (ODT) were prepared to enhance piroxicam dissolution rate and saturation solubility. PRX nanocrystals were prepared by means of high pressure homogenization technique using poloxamer 188 as stabilizer. Three different ODTs were prepared with the same nanosuspension using different excipients in order to study their effect on the PRX dissolution properties. PRX nanocrystal size and zeta potential were determined by photon correlation spectroscopy. Additional characterization of PRX nanocrystal ODT was carried out by infrared spectroscopy, X-ray powder diffractometry, differential scanning calorimetry. Dissolution study was performed in distilled water (pH 5.5) and compared with PRX coarse suspension ODT, PRX/poloxamer 188 physical mixture, bulk PRX samples and a PRX commercial ODT. All PRX nanocrystal ODT formulations showed a higher drug dissolution rate than coarse PRX ODT. PRX nanocrystal ODT prepared using gelatin or croscarmellose as excipient showed a higher PRX dissolution rate compared with the commercial formulation and ODT prepared using xanthan gum. Overall results confirmed that improved PRX dissolution rate is due to the increased surface-to-volume ratio due to the nanosized drug particle but also revealed the important role of different excipients used. Copyright © 2014 Elsevier B.V. All rights reserved.

Reversible modulation of CsPbBr3 perovskite nanocrystal/gold nanoparticle heterostructures.

Science.gov (United States)

Chen, Shanshan; Lyu, Danya; Ling, Tao; Guo, Weiwei

2018-04-19

A facile strategy is illustrated to reversibly modulate CsPbBr3 perovskite nanocrystal/Au nanoparticle heterostructures with the reversible formation and fragmentation of gold nanoparticles anchored to the corners and surface of CsPbBr3 perovskite nanocrystals. The modulation process was performed under ambient conditions and could be conducted for cycles.

InP/ZnS nanocrystals for colour conversion in white light emitting diodes

DEFF Research Database (Denmark)

Shirazi, Roza

In this work a comprehensive study of a colloidal InP/ZnS nanocrystals (NC) as the colour conversion material for white light emitting diodes (WLED) is shown. Studied nanocrystals were synthesised by wet chemistry using one pot, hot injection method. A quantum efficiency (QE) of photoluminescence......, radiative and non-radiative recombination rates were determined and QE of 63% for the population of NCs that emit light was derived. A search for source of exciton losses in bright nanocrystals temperature resolved TRPL was studied and it revealed carrier trapping most likely at core-shell interface as well...... as at the surface and which competes with bright and dark exciton states. A presence of long-lived dark excitons and trapped charges lead to strong Auger recombination at high (relative to the trapping times) excitation. A colour conversion efficiency of the nanocrystals upon light absorption and in a process...

Shape-Controlled Synthesis of Colloidal Metal Nanocrystals: Thermodynamic versus Kinetic Products.

Science.gov (United States)

Xia, Younan; Xia, Xiaohu; Peng, Hsin-Chieh

2015-07-01

This Perspective provides a contemporary understanding of the shape evolution of colloidal metal nanocrystals under thermodynamically and kinetically controlled conditions. It has been extremely challenging to investigate this subject in the setting of one-pot synthesis because both the type and number of seeds involved would be changed whenever the experimental conditions are altered, making it essentially impossible to draw conclusions when comparing the outcomes of two syntheses conducted under different conditions. Because of the uncertainty about seeds, most of the mechanistic insights reported in literature for one-pot syntheses of metal nanocrystals with different shapes are either incomplete or ambiguous, and some of them might be misleading or even wrong. Recently, with the use of well-defined seeds for such syntheses, it became possible to separate growth from nucleation and therefore investigate the explicit role(s) played by a specific thermodynamic or kinetic parameter in directing the evolution of colloidal metal nanocrystals into a specific shape. Starting from single-crystal seeds enclosed by a mix of {100}, {111}, and {110} facets, for example, one can obtain colloidal nanocrystals with diversified shapes by adjusting various thermodynamic or kinetic parameters. The mechanistic insights learnt from these studies can also be extended to account for the products of conventional one-pot syntheses that involve self-nucleation only. The knowledge can be further applied to many other types of seeds with twin defects or stacking faults, making it an exciting time to design and synthesize colloidal metal nanocrystals with the shapes sought for a variety of fundamental studies and technologically important applications.

Bionanocomposite films based on plasticized PLA-PHB/cellulose nanocrystal blends.

Science.gov (United States)

Arrieta, M P; Fortunati, E; Dominici, F; López, J; Kenny, J M

2015-05-05

Optically transparent plasticized poly(lactic acid) (PLA) based bionanocomposite films intended for food packaging were prepared by melt blending. Materials were plasticized with 15wt% of acetyl(tributyl citrate) (ATBC) to improve the material processability and to obtain flexibile films. Poly(hydroxybutyrate) (PHB) was used to increase PLA crystallinity. The thermal stability of the PLA-PHB blends was improved by the addition of 5 wt% of cellulose nanocrystals (CNC) or modified cellulose nanocrystals (CNCs) synthesized from microcrystalline cellulose. The combination of ATBC and cellulose nanocrystals, mainly the better dispersed CNCs, improved the interaction between PLA and PHB. Thus, an improvement on the oxygen barrier and stretchability was achieved in PLA-PHB-CNCs-ATBC which also displayed somewhat UV light blocking effect. All bionanocomposite films presented appropriate disintegration in compost suggesting their possible applications as biodegradable packaging materials. Copyright © 2014 Elsevier Ltd. All rights reserved.

Resonance Raman spectra of wurtzite and zincblende CdSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Kelley, Anne Myers, E-mail: amkelley@ucmerced.edu [Chemistry and Chemical Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA 95343 (United States); Dai, Quanqin; Jiang, Zhong-jie; Baker, Joshua A.; Kelley, David F. [Chemistry and Chemical Biology, School of Natural Sciences, University of California, 5200 North Lake Road, Merced, CA 95343 (United States)

2013-08-30

Highlights: ► Very similar resonance Raman spectra of wurtzite and zincblende CdSe nanocrystals. ► First absolute resonance Raman cross-sections reported for CdSe nanocrystals. ► LO overtones suggest slightly stronger electron–phonon coupling in wurtzite form. - Abstract: Resonance Raman spectra and absolute differential Raman cross-sections have been measured for CdSe nanocrystals in both the wurtzite and zincblende crystal forms at four excitation wavelengths from 457.9 to 514.5 nm. The frequency and bandshape of the longitudinal optical (LO) phonon fundamental is essentially identical for both crystal forms at each excitation wavelength. The LO phonon overtone to fundamental intensity ratio appears to be slightly higher for the wurtzite form, which may suggest slightly stronger exciton–phonon coupling from the Fröhlich mechanism in the wurtzite form. The LO fundamental Raman cross-sections are very similar for both crystal forms at each excitation wavelength.

Observation of melting in 30 angstrom diameter CdS nanocrystals

International Nuclear Information System (INIS)

Goldstein, A.N.; Colvin, V.L.; Alivisatos, A.P.

1991-01-01

In this paper temperature dependent electron diffraction studies on 30 Angstrom diameter CdS nanocrystals are described. The linear thermal expansion coefficient of the nanocrystals is 2.75 * 10 -5 Angstrom/K, and the melting point is 575 K. These data are in contrast to bulk CdS which has a melting point of 1750 K and a linear expansion coefficient of 5.5 * 10 -6 Angstrom/K. The observed depression in the melting point of these semiconductor clusters is similar to effects observed in metals and molecular crystals, indicating that the phenomenon of reduced melting point in small systems is a general one regardless of the type of material. The observation of melting point depression in these clusters also has far reaching implications for the preparation of highly crystalline clusters of CdS, as well as for the use of these nanocrystals as precursors to thin films

Plasmon-induced carrier polarization in semiconductor nanocrystals

Science.gov (United States)

Yin, Penghui; Tan, Yi; Fang, Hanbing; Hegde, Manu; Radovanovic, Pavle V.

2018-06-01

Spintronics1 and valleytronics2 are emerging quantum electronic technologies that rely on using electron spin and multiple extrema of the band structure (valleys), respectively, as additional degrees of freedom. There are also collective properties of electrons in semiconductor nanostructures that potentially could be exploited in multifunctional quantum devices. Specifically, plasmonic semiconductor nanocrystals3-10 offer an opportunity for interface-free coupling between a plasmon and an exciton. However, plasmon-exciton coupling in single-phase semiconductor nanocrystals remains challenging because confined plasmon oscillations are generally not resonant with excitonic transitions. Here, we demonstrate a robust electron polarization in degenerately doped In2O3 nanocrystals, enabled by non-resonant coupling of cyclotron magnetoplasmonic modes11 with the exciton at the Fermi level. Using magnetic circular dichroism spectroscopy, we show that intrinsic plasmon-exciton coupling allows for the indirect excitation of the magnetoplasmonic modes, and subsequent Zeeman splitting of the excitonic states. Splitting of the band states and selective carrier polarization can be manipulated further by spin-orbit coupling. Our results effectively open up the field of plasmontronics, which involves the phenomena that arise from intrinsic plasmon-exciton and plasmon-spin interactions. Furthermore, the dynamic control of carrier polarization is readily achieved at room temperature, which allows us to harness the magnetoplasmonic mode as a new degree of freedom in practical photonic, optoelectronic and quantum-information processing devices.

Temperature-Dependent Physical and Memory Characteristics of Atomic-Layer-Deposited RuOx Metal Nanocrystal Capacitors

Directory of Open Access Journals (Sweden)

S. Maikap

2011-01-01

Full Text Available Physical and memory characteristics of the atomic-layer-deposited RuOx metal nanocrystal capacitors in an n-Si/SiO2/HfO2/RuOx/Al2O3/Pt structure with different postdeposition annealing temperatures from 850–1000°C have been investigated. The RuOx metal nanocrystals with an average diameter of 7 nm and a highdensity of 0.7 × 1012/cm2 are observed by high-resolution transmission electron microscopy after a postdeposition annealing temperature at 1000°C. The density of RuOx nanocrystal is decreased (slightly by increasing the annealing temperatures, due to agglomeration of multiple nanocrystals. The RuO3 nanocrystals and Hf-silicate layer at the SiO2/HfO2 interface are confirmed by X-ray photoelectron spectroscopy. For post-deposition annealing temperature of 1000°C, the memory capacitors with a small equivalent oxide thickness of ~9 nm possess a large hysteresis memory window of >5 V at a small sweeping gate voltage of ±5 V. A promising memory window under a small sweeping gate voltage of ~3 V is also observed due to charge trapping in the RuOx metal nanocrystals. The program/erase mechanism is modified Fowler-Nordheim (F-N tunneling of the electrons and holes from Si substrate. The electrons and holes are trapped in the RuOx nanocrystals. Excellent program/erase endurance of 106 cycles and a large memory window of 4.3 V with a small charge loss of ~23% at 85°C are observed after 10 years of data retention time, due to the deep-level traps in the RuOx nanocrystals. The memory structure is very promising for future nanoscale nonvolatile memory applications.

Depth-selective 2D-ACAR and coincidence Doppler investigation of embedded Au nanocrystals in MgO

International Nuclear Information System (INIS)

Eijt, S.W.H.; Veen, A. van; Falub, C.V.; Schut, H.; Huis, M.A. van; Mijnarends, P.E.

2004-01-01

We present a depth-selective 2D-ACAR and two-detector Doppler broadening study on Au nanocrystals in monocrystalline MgO(100), produced in sub-surface layers by ion implantation and subsequent thermal annealing to temperatures beyond the stability range of vacancy clusters in MgO. In contrast to the case of Li nanocrystals, it was found that positrons do not trap inside the Au nanocrystals, but only in defects at the nanocrystal-to-host interface (attached vacancy clusters). This is interpreted in terms of the positron affinity of Au, MgO and the defects. (orig.)

Depth-selective 2D-ACAR and coincidence Doppler investigation of embedded Au nanocrystals in MgO

Energy Technology Data Exchange (ETDEWEB)

Eijt, S.W.H.; Veen, A. van; Falub, C.V.; Schut, H.; Huis, M.A. van [Interfaculty Reactor Inst., Delft Univ. of Technology, Delft (Netherlands); Mijnarends, P.E. [Interfaculty Reactor Inst., Delft Univ. of Technology, Delft (Netherlands); Dept. of Physics, Northeastern Univ., Boston, MA (United States)

2004-07-01

We present a depth-selective 2D-ACAR and two-detector Doppler broadening study on Au nanocrystals in monocrystalline MgO(100), produced in sub-surface layers by ion implantation and subsequent thermal annealing to temperatures beyond the stability range of vacancy clusters in MgO. In contrast to the case of Li nanocrystals, it was found that positrons do not trap inside the Au nanocrystals, but only in defects at the nanocrystal-to-host interface (attached vacancy clusters). This is interpreted in terms of the positron affinity of Au, MgO and the defects. (orig.)

Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Gross, Dieter Konrad Michael

2013-11-08

Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

International Nuclear Information System (INIS)

Gross, Dieter Konrad Michael

2013-01-01

Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

Functionalized SiC nanocrystals for tuning of optical, thermal, mechanical and electrical properties of polyvinyl alcohol

DEFF Research Database (Denmark)

Saini, Isha; Sharma, Annu; Dhiman, Rajnish

2017-01-01

 MPa for PVA to 45 MPa for PVA-SiC nanocomposite film containing 0.023 wt% f-SiC nanocrystals at an applied load of 9.8 mN indicating improved interfacial interaction. Current-voltage analysis indicated an increase in conductivity of PVA with the introduction of f-SiC nanocrystals. The conduction......Polyvinyl alcohol (PVA)-SiC nanocomposite films were prepared by incorporating functionalized Silicon Carbide (f-SiC) nanocrystals in PVA matrix. Structural characterization of SiC nanocrystals before and after the functionalization was carried out using Fourier transform infrared spectroscopy...... (FTIR), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA). Transmission electron microscopy (TEM) and Scanning Electron Microscopy (SEM) were used to study the morphology and size distribution of f-SiC nanocrystals in PVA-SiC nanocomposite films. TEM and SEM images depict an improved...

Fundamental aspects of nucleation and growth in the solution-phase synthesis of germanium nanocrystals

KAUST Repository

Codoluto, Stephen C.; Baumgardner, William J.; Hanrath, Tobias

2010-01-01

Colloidal Ge nanocrystals (NCs) were synthesized via the solution phase reduction of germanium(ii) iodide. We report a systematic investigation of the nanocrystal nucleation and growth as a function of synthesis conditions including the nature

Au/ZnS core/shell nanocrystals as an efficient anode photocatalyst in direct methanol fuel cells.

Science.gov (United States)

Chen, Wei-Ta; Lin, Yin-Kai; Yang, Ting-Ting; Pu, Ying-Chih; Hsu, Yung-Jung

2013-10-04

Au/ZnS core/shell nanocrystals with controllable shell thicknesses were synthesized using a cysteine-assisted hydrothermal method. Incorporating Au/ZnS nanocrystals into the traditional Pt-catalyzed half-cell reaction led to a 43.3% increase in methanol oxidation current under light illumination, demonstrating their promising potential for metal/semiconductor hybrid nanocrystals as the anode photocatalyst in direct methanol fuel cells.

Photogenerated Exciton Dissociation in Highly Coupled Lead Salt Nanocrystal Assemblies

KAUST Repository

Choi, Joshua J.; Luria, Justin; Hyun, Byung-Ryool; Bartnik, Adam C.; Sun, Liangfeng; Lim, Yee-Fun; Marohn, John A.; Wise, Frank W.; Hanrath, Tobias

2010-01-01

Internanocrystal coupling induced excitons dissociation in lead salt nanocrystal assemblies is investigated. By combining transient photoluminescence spectroscopy, grazing incidence small-angle X-ray scattering, and time-resolved electric force microscopy, we show that excitons can dissociate, without the aid of an external bias or chemical potential gradient, via tunneling through a potential barrier when the coupling energy is comparable to the exciton binding energy. Our results have important implications for the design of nanocrystal-based optoelectronic devices. © 2010 American Chemical Society.

Photogenerated Exciton Dissociation in Highly Coupled Lead Salt Nanocrystal Assemblies

KAUST Repository

Choi, Joshua J.

2010-05-12

Internanocrystal coupling induced excitons dissociation in lead salt nanocrystal assemblies is investigated. By combining transient photoluminescence spectroscopy, grazing incidence small-angle X-ray scattering, and time-resolved electric force microscopy, we show that excitons can dissociate, without the aid of an external bias or chemical potential gradient, via tunneling through a potential barrier when the coupling energy is comparable to the exciton binding energy. Our results have important implications for the design of nanocrystal-based optoelectronic devices. © 2010 American Chemical Society.

Scanning Probe Microscopy at 650 °C in Air

DEFF Research Database (Denmark)

Hansen, Karin Vels; Jacobsen, Torben; Nørgaard, Anne-Mette

2009-01-01

The controlled atmosphere high temperature scanning probe microscope was designed to study the electrical properties of surfaces at elevated temperatures by using the probe as an electrode. The capability of a simultaneous acquisition of topographical and electrical data for the same surface area...

Shared probe design and existing microarray reanalysis using PICKY

Directory of Open Access Journals (Sweden)

Chou Hui-Hsien

2010-04-01

Full Text Available Abstract Background Large genomes contain families of highly similar genes that cannot be individually identified by microarray probes. This limitation is due to thermodynamic restrictions and cannot be resolved by any computational method. Since gene annotations are updated more frequently than microarrays, another common issue facing microarray users is that existing microarrays must be routinely reanalyzed to determine probes that are still useful with respect to the updated annotations. Results PICKY 2.0 can design shared probes for sets of genes that cannot be individually identified using unique probes. PICKY 2.0 uses novel algorithms to track sharable regions among genes and to strictly distinguish them from other highly similar but nontarget regions during thermodynamic comparisons. Therefore, PICKY does not sacrifice the quality of shared probes when choosing them. The latest PICKY 2.1 includes the new capability to reanalyze existing microarray probes against updated gene sets to determine probes that are still valid to use. In addition, more precise nonlinear salt effect estimates and other improvements are added, making PICKY 2.1 more versatile to microarray users. Conclusions Shared probes allow expressed gene family members to be detected; this capability is generally more desirable than not knowing anything about these genes. Shared probes also enable the design of cross-genome microarrays, which facilitate multiple species identification in environmental samples. The new nonlinear salt effect calculation significantly increases the precision of probes at a lower buffer salt concentration, and the probe reanalysis function improves existing microarray result interpretations.

Controlled synthesis of concave tetrahedral palladium nanocrystals by reducing Pd(acac)2 with carbon monoxide

International Nuclear Information System (INIS)

Zhu, Hai; Chi, Quan; Zhao, Yanxi; Li, Chunya; Tang, Heqing; Li, Jinlin; Huang, Tao; Liu, Hanfan

2012-01-01

Graphical abstract: By using CO as a reducing agent, uniform and well-defined concave tetrahedral Pd nanocrystals were successfully synthesized. CO flow rate was the most essential for the formation of the concave tetrahedral nanostructures. The morphologies and sizes of the final products can be well controlled by adjusting the flow rate of CO. Highlights: ► By using CO as a reducing agent, concave tetrahedral Pd nanocrystals were obtained. ► CO flow rate is critical to the formation of concave tetrahedral Pd nanocrystals. ► The selective adsorption of CO on (1 1 0) facets is essential to concave Pd tetrahedra. -- Abstract: CO reducing strategy to control the morphologies of palladium nanocrystals was investigated. By using CO as a reducing agent, uniform and well-defined concave tetrahedral Pd nanocrystals with a mean size of about 55 ± 2 nm were readily synthesized with Pd(acac) 2 as a precursor and PVP as a stabilizer. The structures of the as-prepared Pd nanocrystals were characterized by transmission electron microscopy (TEM), X-ray powder diffraction (XRD), ultraviolet–visible (UV–vis) absorption spectroscopy and electrochemical measurements. The results demonstrated that CO was the most essential for the formation of the concave tetrahedral Pd nanostructures. The morphologies and sizes of the final products can be well controlled by adjusting the flow rate of CO. The most appropriate CO flow rate, temperature and time for the formation of the ideal concave tetrahedral Pd nanocrystals was 0.033 mL s −1 , 100 °C and 3 h, respectively.

Synthesis of CdS nanocrystals with different morphologies via an ultraviolet irradiation route

International Nuclear Information System (INIS)

Yao Suwei; Han Yuxin; Liu Weixing; Zhang Weiguo; Wang Hongzhi

2007-01-01

A simple ultraviolet photochemical reduction synthetic approach to preparing CdS nanocrystals with different morphologies is described. Sodium dodecyl sulfate (SDS) was used as soft template for the chemical synthesis of CdS nanocrystals in a mixture solution at room temperature. It was found that the magnetic force stirring and the volume proportions of C 2 H 5 OH and H 2 O had marked influences on the morphology of CdS nanocrystals (such as spherical, acicular-like, rod-like and worm-like shapes). The formation of CdS is via precipitation of Cd 2+ ions with the homogeneously released S 2- ions from decomposition of thioacetamide under ultraviolet irradiation source. X-ray diffraction (XRD), scanning electron microscopy (SEM) and the ultraviolet-visible (UV-vis) absorption spectra were employed to characterize the products. This novel method is expected to produce various semiconductor nanocrystals with potential applications in the fields of materials science and photovoltaic cells, etc

Cellulose nanocrystal from pomelo (C. Grandis osbeck) albedo: Chemical, morphology and crystallinity evaluation

Energy Technology Data Exchange (ETDEWEB)

Zain, Nor Fazelin Mat; Yusop, Salma Mohamad [Food Science Program, School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Selangor (Malaysia); Ahmad, Ishak [Polymer Research Centre (PORCE), School of Chemical Sciences and Food Technology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Selangor (Malaysia)

2013-11-27

Citrus peel is one of the under-utilized waste materials that have potential in producing a valuable fibre, which are cellulose and cellulose nanocrystal. Cellulose was first isolated from pomelo (C. Grandis Osbeck) albedo by combination of alkali treatment and bleaching process, followed by acid hydrolysis (65% H{sub 2}SO{sub 4}, 45 °C, 45min) to produce cellulose nanocrystal. The crystalline, structural, morphological and chemical properties of both materials were studied. Result reveals the crystallinity index obtained from X-ray diffraction for cellulose nanocrystal was found higher than extracted cellulose with the value of 60.27% and 57.47%, respectively. Fourier transform infrared showed that the chemical treatments removed most of the hemicellulose and lignin from the pomelo albedo fibre. This has been confirmed further by SEM and TEM for their morphological studies. These results showed that cellulose and cellulose nanocrystal were successfully obtained from pomelo albedo and might be potentially used in producing functional fibres for food application.

Cellulose nanocrystal from pomelo (C. Grandis osbeck) albedo: Chemical, morphology and crystallinity evaluation

International Nuclear Information System (INIS)

Zain, Nor Fazelin Mat; Yusop, Salma Mohamad; Ahmad, Ishak

2013-01-01

Citrus peel is one of the under-utilized waste materials that have potential in producing a valuable fibre, which are cellulose and cellulose nanocrystal. Cellulose was first isolated from pomelo (C. Grandis Osbeck) albedo by combination of alkali treatment and bleaching process, followed by acid hydrolysis (65% H 2 SO 4 , 45 °C, 45min) to produce cellulose nanocrystal. The crystalline, structural, morphological and chemical properties of both materials were studied. Result reveals the crystallinity index obtained from X-ray diffraction for cellulose nanocrystal was found higher than extracted cellulose with the value of 60.27% and 57.47%, respectively. Fourier transform infrared showed that the chemical treatments removed most of the hemicellulose and lignin from the pomelo albedo fibre. This has been confirmed further by SEM and TEM for their morphological studies. These results showed that cellulose and cellulose nanocrystal were successfully obtained from pomelo albedo and might be potentially used in producing functional fibres for food application

Coupling Mo2C@C core-shell nanocrystals on 3D graphene hybrid aerogel for high-performance lithium ion battery

Science.gov (United States)

Xin, Hailin; Hai, Yang; Li, Dongzhi; Qiu, Zhaozheng; Lin, Yemao; Yang, Bo; Fan, Haosen; Zhu, Caizhen

2018-05-01

Hybrid aerogel by dispersing Mo2C@C core-shell nanocrystals into three-dimensional (3D) graphene (Mo2C@C-GA) has been successfully prepared through two-step methods. Firstly, carbon-coated MoO2 nanocrystals uniformly anchor on 3D graphene aerogel (MoO2@C-GA) via hydrothermal reaction. Then the MoO2@C-GA precursor is transformed into Mo2C@C-GA after the following carbonization process. Furthermore, the freeze-drying step plays an important role in the resulting pore size distribution of the porous networks. Moreover, graphene aerogels exhibit extremely low densities and superior electrical properties. When evaluated as anode material for lithium ion battery, Mo2C@C-GA delivers excellent rate capability and stable cycle performance when compared with C-GA and Mo2C nanoparticles. Mo2C@C-GA exhibits the initial discharge capacity of 1461.4 mA h g-1 at the current density of 0.1 A g-1, and retains a reversible capacity of 1089.8 mA h g-1 after 100 cycles at a current density of 0.1 A g-1. Even at high current density of 5 A g-1, a discharge capacity of 623.5 mA h g-1 can be still achieved. The excellent performance of Mo2C@C-GA could be attributed to the synergistic effect of Mo2C@C nanocrystals and the 3D graphene conductive network.

Chronotherapeutically Modulated Pulsatile System of Valsartan Nanocrystals-an In Vitro and In Vivo Evaluation.

Science.gov (United States)

Biswas, Nikhil; Kuotsu, Ketousetuo

2017-02-01

The objective was to improve the dissolution of valsartan by developing valsartan nanocrystals and design a pulsed release system for the chronotherapy of hypertension. Valsartan nanocrystals were prepared by sonication-anti-solvent precipitation method and lyophilized to obtain dry powder. Nanocrystals were directly compressed to minitablets and coated to achieve pulsatile valsartan release. Pharmacokinetic profiles of optimized and commercial formulations were compared in rabbit model. The mean particle size and PDI of the optimized nanocrystal batch V4 was reported as 211 nm and 0.117, respectively. DSC and PXRD analysis confirmed the crystalline nature of valsartan in nanocrystals. The dissolution extent of valsartan was markedly enhanced with both nanocrystals and minitablets as compared to pure valsartan irrespective of pH of the medium. Core minitablet V4F containing 5% w/w polyplasdone XL showed quickest release of valsartan, over 90% within 15 min. Coated formulation CV4F showed two spikes in release profile after successive lag times of 235 and 390 min. The pharmacokinetic study revealed that the bioavailability of optimized formulation (72.90%) was significantly higher than the commercial Diovan tablet (30.18%). The accelerated stability studies showed no significant changes in physicochemical properties, release behavior, and bioavialability of CV4F formulation. The formulation was successfully designed to achieve enhanced bioavailability and dual pulsatile release. Bedtime dosing will more efficiently control the circadian spikes of hypertension in the morning.

Hydrothermal synthesis, characterization and up/down-conversion luminescence of barium rare earth fluoride nanocrystals

International Nuclear Information System (INIS)

Jia, Li-Ping; Zhang, Qiang; Yan, Bing

2014-01-01

Graphical abstract: Lanthanide ions doped bare earth rare earth fluoride nanocrystals are synthesized by hydrothermal technology and characterized. The down/up-conversion luminescence of them are discussed. - Highlights: • Mixed hydrothermal system H 2 O–OA (EDA)–O-A(LO-A) is used for synthesis. • Barium rare earth fluoride nanocrystals are synthesized comprehensively. • Luminescence for down-conversion and up-conversion are obtained for these systems. - Abstract: Mixed hydrothermal system H 2 O–OA (EDA)–O-A(LO-A) is developed to synthesize barium rare earth fluorides nanocrystals (OA = oleylamine, EDA = ethylenediamine, O-A = oleic acid and LO-A = linoleic acid). They are presented as BaREF 5 (RE = Ce, Pr, Nd, Eu, Gd, Tb, Dy, Y, Tm, Lu) and Ba 2 REF 7 (RE = La, Sm, Ho, Er, Yb). The influence of reaction parameters (rare earth species, hydrothermal system and temperature) is checked on the phase and shape evolution of the fluoride nanocrystals. It is found that reaction time and temperature of these nanocrystals using EDA (180 °C, 6 h) is lower than those of them using OA (220 °C, 10 h). The photoluminescence properties of these fluorides activated by some rare earth ions (Nd 3+ , Eu 3+ , Tb 3+ ) are studied, and especially up-conversion luminescence of the four fluoride nanocrystal systems (Ba 2 LaF 7 :Yb, Tm(Er), Ba 2 REF 7 :Yb, Tm(Er) (RE = Gd, Y, Lu)) is observed

Nanocrystal synthesis and thin film formation for earth abundant photovoltaics

Science.gov (United States)

Carter, Nathaniel J.

Providing access to on-demand energy at the global scale is a grand challenge of our time. The fabrication of solar cells from nanocrystal inks comprising earth abundant elements represents a scalable and sustainable photovoltaic technology with the potential to meet the global demand for electricity. Solar cells with Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers are of particular interest due to the high absorption coefficient of CZTSSe, its band gap in the ideal range for efficient photovoltaic power conversion, and the relative abundance of its constituent elements in the earth's crust. Despite the promise of this material system, CZTSSe solar cell efficiencies reported throughout literature have failed to exceed 12.6%, principally due to the low open-circuit voltage (VOC) achieved in these devices compared to the absorber band gap. The work presented herein primarily aims to address the low VOC problem. First, the fundamental cause for such low VOC's is investigated. Interparticle compositional inhomogeneities identified in the synthesized CZTS nanocrystals and their effect on the absorber layer formation and device performance are characterized. Real-time energy-dispersive x-ray diffraction (EDXRD) elucidates the role of these inhomogeneities in the mechanism by which a film of CZTS nanocrystals converts into a dense absorber layer comprising micron-sized CZTSSe grains upon annealing in a selenium atmosphere (selenization). Additionally, a direct correlation between the nanocrystal inhomogeneities and the VOC in completed devices is observed. Detailed characterization of CZTSSe solar cells identifies electrical potential fluctuations in the CZTSSe absorber - due to spatial composition variations not unlike those observed in the nanocrystals - as a primary V OC inhibitor. Additional causes for low VOC's in CZTSSe solar cells proposed in the literature involve recombination at the interface between the CZTSSe absorber and: (1) the n-type, CdS buffer layer, or (2) the

Cellulose nanocrystal properties and their applications

Directory of Open Access Journals (Sweden)

mahdi jonoobi

2015-05-01

Full Text Available The main purpose of this work is to provide an overview of recent research in the area of cellulose nonmaterials production from different sources. Due to their abundance, their renewability, high strength and stiffness, being eco-friendly, and low weight; numerous studies have been reported on the isolation of cellulose nanomaterials from different cellulosic sources and their use in high performance applications. This work covers an introduction into the nano cellulose definition as well as used methods for isolation of nanomaterials (nanocrystals from various sources. The rod-like cellulose nanocrystals (CNC can be isolated from sources like wood, plant fibers, agriculture and industrial bio residues, tunicates, and bacterial cellulose using acid hydrolysis process. Following this, the paper focused on characterization methods, materials properties and structure. The current review is a comprehensive literature regarding the nano cellulose isolation and demonstrates the potential of cellulose nanomaterials to be used in a wide range of high-tech applications.

Novel green synthetic strategy to prepare ZnO nanocrystals using rambutan (Nephelium lappaceum L.) peel extract and its antibacterial applications.

Science.gov (United States)

Yuvakkumar, R; Suresh, J; Nathanael, A Joseph; Sundrarajan, M; Hong, S I

2014-08-01

In the present investigation, we report a sustainable novel green synthetic strategy to synthesis zinc oxide nanocrystals. This is the first report on sustainable biosynthesis of zinc oxide nanocrystals employing Nephelium lappaceum L., peel extract as a natural ligation agent. Green synthesis of zinc oxide nanocrystals was carried out via zinc-ellagate complex formation using rambutan peel wastes. The successful formation of zinc oxide nanocrystals was confirmed employing standard characterisation studies. A possible mechanism for the formation of ZnO nanocrystals with rambutan peel extract was also proposed. The prepared ZnO nanocrystals were coated on the cotton fabric and their antibacterial activity were analyzed. ZnO nanocrystals coated cotton showed good antibacterial activity towards Escherichia coli (E. coli), gram negative bacteria and Staphylococcus aureus (S. aureus), gram positive bacteria. Copyright © 2014 Elsevier B.V. All rights reserved.

Facile synthesis of ultrafine Co{sub 3}O{sub 4} nanocrystals embedded carbon matrices with specific skeletal structures as efficient non-enzymatic glucose sensors

Energy Technology Data Exchange (ETDEWEB)

Li, Mian; Han, Ce; Zhang, Yufan; Bo, Xiangjie, E-mail: baoxj133@nenu.edu.cn; Guo, Liping, E-mail: guolp078@nenu.edu.cn

2015-02-25

Highlights: • Novel hyperfine Co{sub 3}O{sub 4} nanocrystals decorated porous carbon matrixes. • Facile synthesis without use of any harmful dispersing reagents or surfactants. • High dispersion degree of Co{sub 3}O{sub 4} nanocrystals and excellent e{sup −} transport rates. • A large current sensitivity of 955.9 μA cm{sup −2} mM{sup −1} toward glucose. • Excellent anti-interference and stability for glucose detection. - Abstract: A facile, effective, and environmentally friendly method has been adopted for the first time to prepare tiny Co{sub 3}O{sub 4} nanocrystals embedded carbon matrices without using surfactants, harmful organic reagents or extreme conditions. Structural characterizations reveal that the size-controlled Co{sub 3}O{sub 4} nanocrystals are uniformly dispersed on carbon matrices. Electrochemical measurements reveal that Co{sub 3}O{sub 4}-ordered mesoporous carbon (OMC) can more efficiently catalyze glucose oxidation and acquire better detection parameters compared with those for the Co{sub 3}O{sub 4}-macroporous carbon, Co{sub 3}O{sub 4}-reduced graphene oxide, and free Co{sub 3}O{sub 4} nanoparticles (NPs) (such as: the large sensitivity (2597.5 μA cm{sup −2} mM{sup −1} between 0 and 0.8 mM and 955.9 μA cm{sup −2} mM{sup −1} between 0.9 and 7.0 mM), fast response time, wide linear range, good stability, and surpassingly selective capability to electroactive molecules or Cl{sup −}). Such excellent performances are attributed to the synergistic effect of the following three factors: (1) the high catalytic sites provided by the uniformly dispersed and size-controlled Co{sub 3}O{sub 4} nanocrystals embedded on OMC; (2) the excellent reactant transport efficiency caused by the abundant mesoporous structures of OMC matrix: (3) the improved electron transport in high electron transfer rate (confinement of the Co{sub 3}O{sub 4} NPs in nanoscale spaces ensured intimate contact between Co{sub 3}O{sub 4} nanocrystals and the

Composition-Dependent Energy Splitting between Bright and Dark Excitons in Lead Halide Perovskite Nanocrystals.

Science.gov (United States)

Chen, Lan; Li, Bin; Zhang, Chunfeng; Huang, Xinyu; Wang, Xiaoyong; Xiao, Min

2018-03-14

Perovskite semiconductor nanocrystals with different compositions have shown promise for applications in light-emitting devices. Dark excitonic states may suppress light emission from such nanocrystals by providing an additional nonradiative recombination channel. Here, we study the composition dependence of dark exciton dynamics in nanocrystals of lead halides by time-resolved photoluminescence spectroscopy at cryogenic temperatures. The presence of a spin-related dark state is revealed by magneto-optical spectroscopy. The energy splitting between bright and dark states is found to be highly sensitive to both halide elements and organic cations, which is explained by considering the effects of size confinement and charge screening, respectively, on the exchange interaction. These findings suggest the possibility of manipulating dark exciton dynamics in perovskite semiconductor nanocrystals by composition engineering, which will be instrumental in the design of highly efficient light-emitting devices.

Noscapinoids bearing silver nanocrystals augmented drug delivery, cytotoxicity, apoptosis and cellular uptake in B16F1, mouse melanoma skin cancer cells.

Science.gov (United States)

Soni, Naina; Jyoti, Kiran; Jain, Upendra Kumar; Katyal, Anju; Chandra, Ramesh; Madan, Jitender

2017-06-01

Noscapine (Nos) and reduced brominated analogue of noscapine (Red-Br-Nos) prevent cellular proliferation and induce apoptosis in cancer cells either alone or in combination with other chemotherapeutic drugs. However, owing to poor physicochemical properties, Nos and Red-Br-Nos have demonstrated their anticancer activity at higher and multiple doses. Therefore, in present investigation, silver nanocrystals of noscapinoids (Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals) were customized to augment drug delivery, cytotoxicity, apoptosis and cellular uptake in B16F1 mouse melanoma cancer cells. Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals were prepared separately by precipitation method. The mean particle size of Nos-Ag 2+ nanocrystals was measured to be 25.33±3.52nm, insignificantly (P>0.05) different from 27.43±4.51nm of Red-Br-Nos-Ag 2+ nanocrystals. Furthermore, zeta-potential of Nos-Ag 2+ nanocrystals was determined to be -25.3±3.11mV significantly (Pcellular uptake. The Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals exhibited an IC 50 of 16.6μM and 6.5μM, significantly (Pcellular morphological alterations in B16F1 cells upon internalization of Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals provided the evidences for accumulation within membrane-bound cytoplasmic vacuoles and in enlarged lysosomes and thus triggered mitochondria mediated apoptosis via caspase activation. Preliminary investigations substantiated that Nos-Ag 2+ nanocrystals and Red-Br-Nos-Ag 2+ nanocrystals must be further explored and utilized for the delivery of noscapinoids to melanoma cancer cells. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Adsorption behavior and current-voltage characteristics of CdSe nanocrystals on hydrogen-passivated silicon

DEFF Research Database (Denmark)

Walzer, Karsten; Quaade, Ulrich; Ginger, D.S.

2002-01-01

Using scanning tunneling microscopy and spectroscopy we have studied both the geometric distribution and the conduction properties of organic shell capped CdSe nanocrystals adsorbed on hydrogen-passivated Si(100). At submonolayer concentrations, the nanocrystal distribution on the surface was found...... found that the current through the MIS junction is limited by the nanocrystals only in one bias direction, while in the other bias direction the current is limited by the semiconducting substrate. This property may be of relevance for the construction of hybrid electronic devices combining semiconductor...

[Spectroscopic Research on Slag Nanocrystal Glass Ceramics Containing Rare Earth Elements].

Science.gov (United States)

Ouyang, Shun-li; Li, Bao-wei; Zhang, Xue-feng; Jia, Xiao-lin; Zhao, Ming; Deng, Lei-bo

2015-08-01

The research group prepared the high-performance slag nanocrystal glass ceramics by utilizing the valuable elements of the wastes in the Chinese Bayan Obo which are characterized by their symbiotic or associated existence. In this paper, inductively coupled plasma emission spectroscopy (ICP), X-ray diffraction (XRD), Raman spectroscopy (Raman) and scanning electron microscopy (SEM) are all used in the depth analysis for the composition and structure of the samples. The experiment results of ICP, XRD and SEM showed that the principal crystalline phase of the slag nanocrystal glass ceramics containing rare earth elements is diopside, its grain size ranges from 45 to 100 nm, the elements showed in the SEM scan are basically in consistent with the component analysis of ICP. Raman analysis indicated that its amorphous phase is a three-dimensional network structure composed by the structural unit of silicon-oxy tetrahedron with different non-bridging oxygen bonds. According to the further analysis, we found that the rare earth microelement has significant effect on the network structure. Compared the nanocrystal slag glass ceramic with the glass ceramics of similar ingredients, we found that generally, the Raman band wavenumber for the former is lower than the later. The composition difference between the glass ceramics and the slag nanocrystal with the similar ingredients mainly lies on the rare earth elements and other trace elements. Therefore, we think that the rare earth elements and other trace elements remains in the slag nanocrystal glass ceramics have a significant effect on the network structure of amorphous phase. The research method of this study provides an approach for the relationship among the composition, structure and performance of the glass ceramics.

Simultaneous phase and size control of upconversion nanocrystals through lanthanide doping

KAUST Repository

Wang, Feng

2010-02-25

Doping is a widely applied technological process in materials science that involves incorporating atoms or ions of appropriate elements into host lattices to yield hybrid materials with desirable properties and functions. For nanocrystalline materials, doping is of fundamental importance in stabilizing a specific crystallographic phase, modifying electronic properties, modulating magnetism as well as tuning emission properties. Here we describe a material system in which doping influences the growth process to give simultaneous control over the crystallographic phase, size and optical emission properties of the resulting nanocrystals. We show that NaYF 4 nanocrystals can be rationally tuned in size (down to ten nanometres), phase (cubic or hexagonal) and upconversion emission colour (green to blue) through use of trivalent lanthanide dopant ions introduced at precisely defined concentrations. We use first-principles calculations to confirm that the influence of lanthanide doping on crystal phase and size arises from a strong dependence on the size and dipole polarizability of the substitutional dopant ion. Our results suggest that the doping-induced structural and size transition, demonstrated here in NaYF 4 upconversion nanocrystals, could be extended to other lanthanide-doped nanocrystal systems for applications ranging from luminescent biological labels to volumetric three-dimensional displays. © 2010 Macmillan Publishers Limited. All rights reserved.

Influence of reductant and germanium concentration on the growth and stress development of germanium nanocrystals in silicon oxide matrix

International Nuclear Information System (INIS)

Chew, H G; Zheng, F; Choi, W K; Chim, W K; Foo, Y L; Fitzgerald, E A

2007-01-01

Germanium (Ge) nanocrystals have been synthesized by annealing co-sputtered SiO 2 -Ge samples in N 2 or forming gas (90% N 2 +10% H 2 ) at temperatures ranging from 700 to 1000 deg. C. We concluded that the annealing ambient, temperature and Ge concentration have a significant influence on the formation and evolution of the nanocrystals. We showed that a careful selective etching of the annealed samples in hydrofluoric acid solution enabled the embedded Ge nanocrystals to be liberated from the SiO 2 matrix. From the Raman results of the as-grown and the liberated nanocrystals, we established that the nanocrystals generally experienced compressive stress in the oxide matrix and the evolution of these stress states was intimately linked to the distribution, density, size and quality of the Ge nanocrystals

Thick-shell nanocrystal quantum dots

Science.gov (United States)

Hollingsworth, Jennifer A [Los Alamos, NM; Chen, Yongfen [Eugene, OR; Klimov, Victor I [Los Alamos, NM; Htoon, Han [Los Alamos, NM; Vela, Javier [Los Alamos, NM

2011-05-03

Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

Synthesis and charge storage properties of double-layered NiSi nanocrystals

International Nuclear Information System (INIS)

Yoon, Jong-Hwan

2010-01-01

Based on bidirectional diffusion of Ni atoms, double-layered nickel silicide (NiSi) nanocrystals (NCs) for multilevel charge storage were fabricated, and their charge storage properties were examined. The double layer was produced by long-term thermal annealing (for 4 h at 900 o C) of a sandwich structure comprised of a thin Ni film of 0.3 nm sandwiched between two silicon-rich oxide (SiO 1.36 ) layers. Transmission electron microscopic image clearly exhibits a distinct NiSi nanocrystal double layer with a gap of about 7 nm between the mean positions of particle distribution in each NC layer. Capacitance-voltage measurements on the metal/oxide/semiconductor (MOS) capacitors with the double-layered NiSi nanocrystals are shown to have the apparent two plateaus of charge storage, the large memory window of about 9 V and the improved charge retention stability.

Storage of optical excitations in colloidal semiconductor nanocrystals

International Nuclear Information System (INIS)

Kraus, Robert

2009-01-01

In the present theis it is described, how colloidal semiconductor nanocrystals can be used under influence of an electric field to store optical excitation energy at room temperature, to alter, and to supply controlledly. For this the photoluminescence emission of an ensemble of heterogeneous nanocrystals was manipulated and spectroscopically studied. The applied od-shaped particles consist of a spherical core of CdSe, on which an elongated shell of CdS is monocrystallinely be grown. The electron is in such an asymmetric geometry delocalized over the hole nanorod, whereas the hole because of the high potential barrier remains bound in the CdSe core. The wave-function overlap of the charge carriers can therefore be influenced both by the length of the nanorod and by an external electric field. In the regime of prompt fluorescence the manipulation of the charge-carrier separation by an electric field led to a suppression of the radiative recombination. As consequence a fluorescence suppression of about 40% could be observed. After the removal of the electric field the separation was reduced and the stored energy is in an fluorescence increasement directedly liberated again. The strength of the storage efficiency lies with the strength of the electric field in a linear connection. Furthermore in this time range a quantum-confined Stark effect of upt o 14 meV could be detected at room temperature, although the effect is complicated by the different orientations and sizes of the nanorods in the ensemble. Hereby it is of advance to can adress with the applied detection technique a subensemble of nanocrystals. Furthermore a significant storage of the ensmble emission by up to 100 μs conditioned by the electric electric fieldcould be demonstrated, which exceeds the fluorescence lifetime of these particles by the 10 5 fold. As also could be shown by experiments on CdSe/ZnS nanocrystals surface states play a relevent role for the emission dynamics of nanocrystals. The

Pd@Au core-shell nanocrystals with concave cubic shapes: kinetically controlled synthesis and electrocatalytic properties.

Science.gov (United States)

Zhang, Ling; Niu, Wenxin; Zhao, Jianming; Zhu, Shuyun; Yuan, Yali; Hua, Lianzhe; Xu, Guobao

2013-01-01

A new type of concave cubic Pd@Au core-shell nanocrystals is synthesized through a kinetically controlled growth process. Pd nanocubes of 56 nm are used as the inner core, and CTAC and Br(-) are used as the capping agent and selective adsorbent, respectively. A suitable ratio of HAuCl4 and cubic Pd seeds and the presence of Br(-) anions are critical to the growth of the concave cubic Pd@Au core-shell nanocrystals. The fast deposition rate on the corners of the cubic Pd seeds promotes the overgrowth of the Au outer shell along the direction, leading to the formation of concave cubic nanostructures. The reduction process is monitored by the surface plasmon resonance spectra of the nanocrystals, and the extinction band became broader and red shifted as the nanocrystals became larger. The electrocatalytic properties of the concave cubic Pd@Au core-shell nanocrystals were investigated with the cathodic electrochemiluminescence reaction of luminol and H2O2. A possible electrocatalytic mechanism was proposed and analyzed.

Origin of low quantum efficiency of photoluminescence of InP/ZnS nanocrystals

DEFF Research Database (Denmark)

Shirazi, Roza; Kovacs, Andras; Corell, Dennis Dan

2013-01-01

In this paper, we study the origin of a strong wavelength dependence of the quantum efficiency of InP/ZnS nanocrystals. We find that while the average size of the nanocrystals increased by 50%, resulting in longer emission wavelength, the quantum efficiency drops more than one order of magnitude...

A simple and sensitive fluorescent probe for specific detection of ...

Indian Academy of Sciences (India)

Yan-Fei Kang

A fluorescent probe, with simplicity of structure and convenience of synthesis, is capable of detecting ... Yan-Fei Kang et al. .... Pastore A, Federici G, Bertini E and Ptemonte F 2003 ... Urano Y 2010 New Strategies for Fluorescent Probe.

Silicon Nanocrystal Synthesis in Microplasma Reactor

Science.gov (United States)

Nozaki, Tomohiro; Sasaki, Kenji; Ogino, Tomohisa; Asahi, Daisuke; Okazaki, Ken

Nanocrystalline silicon particles with grains smaller than 5 nm are widely recognized as a key material in optoelectronic devices, lithium battery electrodes, and bio-medical labels. Another important characteristic is that silicon is an environmentally safe material that is used in numerous silicon technologies. To date, several synthesis methods such as sputtering, laser ablation, and plasma-enhanced chemical vapor deposition (PECVD) based on low-pressure silane chemistry (SiH4) have been developed for precise control of size and density distributions of silicon nanocrystals. In this study, we explore the possibility of microplasma technologies for efficient production of mono-dispersed nanocrystalline silicon particles on a micrometer-scale, continuous-flow plasma reactor operated at atmospheric pressure. Mixtures of argon, hydrogen, and silicon tetrachloride were activated using a very-high-frequency (144 MHz) power source in a capillary glass tube with volume of less than 1 μl. Fundamental plasma parameters of the microplasma were characterized using optical emission spectroscopy, which respectively indicated electron density of 1015 cm-3, argon excitation temperature of 5000 K, and rotational temperature of 1500 K. Such high-density non-thermal reactive plasma can decompose silicon tetrachloride into atomic silicon to produce supersaturated silicon vapor, followed by gas-phase nucleation via three-body collision: particle synthesis in high-density plasma media is beneficial for promoting nucleation processes. In addition, further growth of silicon nuclei can be terminated in a short-residence-time reactor. Micro-Raman scattering spectra showed that as-deposited particles are mostly amorphous silicon with a small fraction of silicon nanocrystals. Transmission electron micrography confirmed individual 3-15 nm silicon nanocrystals. Although particles were not mono-dispersed, they were well separated and not coagulated.

Semiconductor nanocrystals for novel optical applications

Science.gov (United States)

Moon, Jong-Sik

Inspired by the promise of enhanced spectral response, photorefractive polymeric composites photosensitized with semiconductor nanocrystals have emerged as an important class of materials. Here, we report on the photosensitization of photorefractive polymeric composites at visible wavelengths through the inclusion of narrow band-gap semiconductor nanocrystals composed of PbS. Through this approach, internal diffraction efficiencies in excess of 82%, two-beam-coupling gain coefficients in excess of 211 cm-1, and response times 34 ms have been observed, representing some of the best figures-of-merit reported on this class of materials. In addition to providing efficient photosensitization, however, extensive studies of these hybrid composites have indicated that the inclusion of nanocrystals also provides an enhancement in the charge-carrier mobility and subsequent reduction in the photorefractive response time. Through this approach with PbS as charge-carrier, unprecedented response times of 399 micros were observed, opening the door for video and other high-speed applications. It is further demonstrated that this improvement in response time occurs with little sacrifice in photorefractive efficiency and with internal diffraction efficiencies of 72% and two- beam-coupling gain coefficients of 500 cm-1 being measured. A thorough analysis of the experimental data is presented, supporting the hypothesized mechanism of the enhanced charge mobility without the accompaniment of superfluous traps. Finally, water soluble InP/ZnS and CdSe/ZnS quantum dots interacted with CPP and Herceptin to apply them as a bio-maker. Both of quantum dots showed the excellent potential for use in biomedical imaging and drug delivery applications. It is anticipated that these approaches can play a significant role in the eventual commercialization of these classes of materials.

Extracting hot carriers from photoexcited semiconductor nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Zhu, Xiaoyang

2014-12-10

This research program addresses a fundamental question related to the use of nanomaterials in solar energy -- namely, whether semiconductor nanocrystals (NCs) can help surpass the efficiency limits, the so-called “Shockley-Queisser” limit, in conventional solar cells. In these cells, absorption of photons with energies above the semiconductor bandgap generates “hot” charge carriers that quickly “cool” to the band edges before they can be utilized to do work; this sets the solar cell efficiency at a limit of ~31%. If instead, all of the energy of the hot carriers could be captured, solar-to-electric power conversion efficiencies could be increased, theoretically, to as high as 66%. A potential route to capture this energy is to utilize semiconductor nanocrystals. In these materials, the quasi-continuous conduction and valence bands of the bulk semiconductor become discretized due to confinement of the charge carriers. Consequently, the energy spacing between the electronic levels can be much larger than the highest phonon frequency of the lattice, creating a “phonon bottleneck” wherein hot-carrier relaxation is possible via slower multiphonon emission. For example, hot-electron lifetimes as long as ~1 ns have been observed in NCs grown by molecular beam epitaxy. In colloidal NCs, long lifetimes have been demonstrated through careful design of the nanocrystal interfaces. Due to their ability to slow electronic relaxation, semiconductor NCs can in principle enable extraction of hot carriers before they cool to the band edges, leading to more efficient solar cells.

Tuning light emission of PbS nanocrystals from infrared to visible range by cation exchange

KAUST Repository

Binetti, Enrico

2015-10-27

Colloidal semiconductor nanocrystals, with intense and sharp-line emission between red and near-infrared spectral regions, are of great interest for optoelectronic and bio-imaging applications. The growth of an inorganic passivation layer on nanocrystal surfaces is a common strategy to improve their chemical and optical stability and their photoluminescence quantum yield. In particular, cation exchange is a suitable approach for shell growth at the expense of the nanocrystal core size. Here, the cation exchange process is used to promote the formation of a CdS passivation layer on the surface of very small PbS nanocrystals (2.3 nm in diameter), blue shifting their optical spectra and yielding luminescent and stable nanostructures emitting in the range of 700–850 nm. Structural, morphological and compositional investigation confirms the nanocrystal size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Absorption and photoluminescence spectroscopy demonstrate the growth of a passivation layer with a decrease of the PbS core size, as inferred by the blue-shift of the excitonic peaks. The surface passivation strongly increases the photoluminescence intensity and the excited state lifetime. In addition, the nanocrystals reveal increased stability against oxidation over time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such highly luminescent nano-objects can find interesting applications in sensitized photovoltaic cells and light-emitting devices.

Tuning light emission of PbS nanocrystals from infrared to visible range by cation exchange

KAUST Repository

Binetti, Enrico; Striccoli, Marinella; Sibillano, Teresa; Giannini, Cinzia; Brescia, Rosaria; Falqui, Andrea; Comparelli, Roberto; Corricelli, Michela; Tommasi, Raffaele; Agostiano, Angela; Curri, M Lucia

2015-01-01

Colloidal semiconductor nanocrystals, with intense and sharp-line emission between red and near-infrared spectral regions, are of great interest for optoelectronic and bio-imaging applications. The growth of an inorganic passivation layer on nanocrystal surfaces is a common strategy to improve their chemical and optical stability and their photoluminescence quantum yield. In particular, cation exchange is a suitable approach for shell growth at the expense of the nanocrystal core size. Here, the cation exchange process is used to promote the formation of a CdS passivation layer on the surface of very small PbS nanocrystals (2.3 nm in diameter), blue shifting their optical spectra and yielding luminescent and stable nanostructures emitting in the range of 700–850 nm. Structural, morphological and compositional investigation confirms the nanocrystal size contraction after the cation-exchange process, while the PbS rock-salt crystalline phase is retained. Absorption and photoluminescence spectroscopy demonstrate the growth of a passivation layer with a decrease of the PbS core size, as inferred by the blue-shift of the excitonic peaks. The surface passivation strongly increases the photoluminescence intensity and the excited state lifetime. In addition, the nanocrystals reveal increased stability against oxidation over time. Thanks to their absorption and emission spectral range and the slow recombination dynamics, such highly luminescent nano-objects can find interesting applications in sensitized photovoltaic cells and light-emitting devices.

Connecting the dots : shedding light on the self-assembly of semiconductor nanocrystals with synchrotron X-ray scattering techniques

NARCIS (Netherlands)

Geuchies, J.J.

2017-01-01

We studied the formation of two-dimensional crystals from nanocrystals using X-ray scattering techniques. Inside these nanocrystals, with sizes between 5-10 nm, the atoms are ordered in an atomic lattice. We use the nanocrystals as building blocks to create larger lattices in two dimensions. By

Laser-induced luminescence of multilayer structures based on polyimides and CdSe and CdSe/ZnS nanocrystals

International Nuclear Information System (INIS)

Chistyakov, A A; Dayneko, S V; Zakharchenko, K V; Kolesnikov, V A; Tedoradze, M G; Mochalov, K E; Oleinikov, V A

2009-01-01

Laser-induced luminescence of multilayer structures based on the solids of CdSe and CdSe/ZnS nanocrystals, different organic semiconductors and on the layers of organic semiconductors with embedded nanocrystals has been investigated. Drastic decrease of luminescence quantum yield is observed in the films of CdSe nanocrystals on organic semiconductors compared to those on optical glasses. The luminescence of the nanocrystals in the matrices of organic semiconductors and in multilayer structures is shown to be suppressed. The effects observed are explained by the transfer of photogenerated carriers from the nanocrystals to the molecules of organic semiconductors. The presence of the charge transfer is confirmed by a drastic increase in the conductivity (by 2 – 4 orders of magnitude) and in photovoltaic effect at the presence of CdSe and CdSe/ZnS nanocrystals in the structures under investigation. The prospects of using the multilayer structures for development new materials for solar cells are discussed

Density functional theory study of atomic and electronic properties of defects in reduced anatase TiO2 nanocrystals

Science.gov (United States)

Morita, Kazuki; Yasuoka, Kenji

2018-03-01

Anatase TiO2 nanocrystals have received considerable attention owing to their promising applications in photocatalysis, photovoltaics, and fuel cells. Although experimental evidence has shown that the performance of nanocrystals can be significantly improved through reduction, the mechanistic basis of this enhancement remains unclear. To shed a light on the chemistry of reduced anatase TiO2 nanocrystals, density functional theory were used to investigate the properties of defects and excess electrons. We demonstrated that oxygen vacancies are stable both on the surface and at the sub-surface of the nanocrystal, while titanium interstitials prefer sub-surface sites. Different defect locations possessed different excess electron structures, which contributed to deep and shallow states in the band gap of the nanocrystals. Furthermore, valence band tailing was observed, resulting in band gap narrowing. The theoretical results presented here deepen our understanding, and show the potential of defects to considerably change the macroscopic properties of anatase TiO2 nanocrystals.

Density functional theory study of atomic and electronic properties of defects in reduced anatase TiO2 nanocrystals

Directory of Open Access Journals (Sweden)

Kazuki Morita

2018-03-01

Full Text Available Anatase TiO2 nanocrystals have received considerable attention owing to their promising applications in photocatalysis, photovoltaics, and fuel cells. Although experimental evidence has shown that the performance of nanocrystals can be significantly improved through reduction, the mechanistic basis of this enhancement remains unclear. To shed a light on the chemistry of reduced anatase TiO2 nanocrystals, density functional theory were used to investigate the properties of defects and excess electrons. We demonstrated that oxygen vacancies are stable both on the surface and at the sub-surface of the nanocrystal, while titanium interstitials prefer sub-surface sites. Different defect locations possessed different excess electron structures, which contributed to deep and shallow states in the band gap of the nanocrystals. Furthermore, valence band tailing was observed, resulting in band gap narrowing. The theoretical results presented here deepen our understanding, and show the potential of defects to considerably change the macroscopic properties of anatase TiO2 nanocrystals.

Chemically Addressable Perovskite Nanocrystals for Light-Emitting Applications

KAUST Repository

Sun, Haizhu; Yang, Zhenyu; Wei, Mingyang; Sun, Wei; Li, Xiyan; Ye, Shuyang; Zhao, Yongbiao; Tan, Hairen; Kynaston, Emily L.; Schon, Tyler B.; Yan, Han; Lu, Zheng-Hong; Ozin, Geoffrey A.; Sargent, Edward H.; Seferos, Dwight S.

2017-01-01

Whereas organic–inorganic hybrid perovskite nanocrystals (PNCs) have remarkable potential in the development of optoelectronic materials, their relatively poor chemical and colloidal stability undermines their performance in optoelectronic devices

Adhesion and internalization differences of COM nanocrystals on Vero cells before and after cell damage

Energy Technology Data Exchange (ETDEWEB)

Gan, Qiong-Zhi; Sun, Xin-Yuan; Ouyang, Jian-Ming, E-mail: toyjm@jnu.edu.cn

2016-02-01

The adhesion and internalization between African green monkey kidney epithelial (Vero) cells (before and after oxidative damage by hydrogen peroxide) and calcium oxalate monohydrate (COM) nanocrystals (97 ± 35 nm) were investigated so as to discuss the molecular and cellular mechanism of kidney stone formation. Scanning electron microscope (SEM) was used to observe the Vero–COM nanocrystal adhesion; the nanocrystal-cell adhesion was evaluated by measuring the content of malonaldehyde (MDA), the activity of superoxide dismutase (SOD), the expression level of cell surface osteopontin (OPN) and the change of Zeta potential. Confocal microscopy and flow cytometry were used for the observation and quantitative analysis of crystal internalization. In the process of adhesion, the cell viability and the SOD activity declined, the MDA content, Zeta potential, and the OPN expression level increased. The adhesive capacity of injured Vero was obviously stronger than normal cells; in addition the injured cells promoted the aggregation of COM nanocrystals. The capacity of normal cells to internalize crystals was obviously stronger than that of injured cells. Cell injury increased adhesive sites on cell surface, thereby facilitating the aggregation of COM nanocrystals and their attachment, which results in enhanced risk of calcium oxalate stone formation. - Graphical abstract: The adhesion and internalization differences between Vero cells before and after oxidative damage and calcium oxalate monohydrate nanocrystals were comparatively studied. - Highlights: • Adhesion capacity of injured Vero cells was stronger than normal cells. • Internalization capacity of injured Vero cells was weaker than normal cells. • Injured cells promoted the aggregation of COM nanocrystals. • COM adhesion could aggravate cell injury in both normal and injured cells.

Sub-2 nm SnO2 nanocrystals: A reduction/oxidation chemical reaction synthesis and optical properties

International Nuclear Information System (INIS)

Zhang Hui; Du Ning; Chen Bindi; Cui Tianfeng; Yang Deren

2008-01-01

A simple reduction/oxidation chemical solution approach at room temperature has been developed to synthesize ultrafine SnO 2 nanocrystals, in which NaBH 4 is used as a reducing agent instead of mineralizers such as sodium hydroxide, ammonia, and alcohol. The morphology, structure, and optical property of the ultrafine SnO 2 nanocrystals have been characterized by high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD), differential scanning calorimetry and thermogravimetric analysis (DSC-TGA), X-ray photoelectron spectroscopy (XPS) and UV-vis absorption spectroscopy. It is indicated that the uniform tetragonal ultrafine SnO 2 nanocrystals with the size below 2 nm have been fabricated at room temperature. The band gap of the ultrafine SnO 2 nanocrystals is about 4.1 eV, exhibiting 0.5 eV blue shift from that of the bulk SnO 2 (3.6 eV). Furthermore, the mechanism for the reduction/oxidation chemical reaction synthesis of the ultrafine SnO 2 nanocrystals has been preliminary presented

Hydrothermal Synthesis of PbTiO3 Nanocrystals with a pH-Adjusting Agent of Ammonia Solution

Science.gov (United States)

Li, Xinyi; Huang, Zhixiong; Zhang, Lianmeng; Guo, Dongyun

2018-05-01

The PbTiO3 nanocrystals were synthesized by a hydrothermal method, and ammonia solution was firstly used as a pH-adjusting agent. The effect of ammonia concentration on formation and morphologies of PbTiO3 nanocrystals was investigated. At low ammonia concentration (0-2.2 mol/L), no perovskite PbTiO3 phase was formed. When the ammonia concentration was 4.4 mol/L, the rod-like PbTiO3 nanocrystals with highly crystalline were successfully synthesized. As the ammonia concentration further increased to 13.2 mol/L, the flake-like PbTiO3 nanocrystals were formed.

Memory characteristics of silicon nitride with silicon nanocrystals as a charge trapping layer of nonvolatile memory devices

International Nuclear Information System (INIS)

Choi, Sangmoo; Yang, Hyundeok; Chang, Man; Baek, Sungkweon; Hwang, Hyunsang; Jeon, Sanghun; Kim, Juhyung; Kim, Chungwoo

2005-01-01

Silicon nitride with silicon nanocrystals formed by low-energy silicon plasma immersion ion implantation has been investigated as a charge trapping layer of a polycrystalline silicon-oxide-nitride-oxide-silicon-type nonvolatile memory device. Compared with the control sample without silicon nanocrystals, silicon nitride with silicon nanocrystals provides excellent memory characteristics, such as larger width of capacitance-voltage hysteresis, higher program/erase speed, and lower charge loss rate at elevated temperature. These improved memory characteristics are derived by incorporation of silicon nanocrystals into the charge trapping layer as additional accessible charge traps with a deeper effective trap energy level

Direct observation of shear–induced nanocrystal attachment and coalescence in CuZr-based metallic glasses: TEM investigation

International Nuclear Information System (INIS)

Hajlaoui, K.; Alrasheedi, Nashmi H.; Yavari, A.R.

2016-01-01

In-situ tensile straining tests were performed in a transmission electron microscope (TEM) to analyse the deformation processes in CuZr-based metallic glasses and to directly observe the phase transformation occurrence. We report evidence of shear induced coalescence of nanocrystals in the vicinity of deformed regions. Nanocrystals grow in shear bands, come into contact, being attached and progressively coalesce under applied shear stress. - Highlights: • In-situ tensile straining test in TEM was investigated on CuZr-Based metallic glass. • Strain induces nanocrystallization and subsequent attachment and coalescence of nanocrystals. • The coalescence of nanocrystals compensates strain softening in metallic glasses.

Hybridization of Single Nanocrystals of Cs4PbBr6 and CsPbBr3

OpenAIRE

Weerd, Chris de; Lin, Junhao; Gomez, Leyre; Fujiwara, Yasufumi; Suenaga, Kazutomo; Gregorkiewicz, Tom

2017-01-01

Nanocrystals of all-inorganic cesium lead halide perovskites (CsPbX3, X = Cl, Br, I) feature high absorption and efficient narrow-band emission which renders them promising for future generation of photovoltaic and optoelectronic devices. Colloidal ensembles of these nanocrystals can be conveniently prepared by chemical synthesis. However, in the case of CsPbBr3, its synthesis can also yield nanocrystals of Cs4PbBr6 and the properties of the two are easily confused. Here, we investigate in de...

Cellulose Nanocrystals Obtained from Rice By-Products and Their Binding Potential to Metallic Ions

Directory of Open Access Journals (Sweden)

Vanessa L. Albernaz

2015-01-01

Full Text Available The present study aimed to develop and optimize a method to obtain cellulose nanocrystals from the agricultural by-products rice husk and straw and to evaluate their electrostructural modifications in the presence of metallic ions. First, different particle formation conditions and routes were tested and analyzed by spectrophotometry, dynamic light scattering (DLS, and Zeta potential measurements. Then, electrostructural effects of ions Na(I, Cd(II, and Al(III on the optimized nanoparticles were analyzed by atomic force microscopy (AFM, scanning electron microscopy (SEM, and electrical conductivity (EC assessments. The produced cellulose nanocrystals adopted a rod-like shape. AFM height distribution and EC data indicated that the nanocrystals have more affinity in binding with Na(I > Al(III > Cd(II. These data suggest that the use of these cellulose nanocrystals in the bioremediation field is promising, both in metal sorption from wastewater and as an alternative for water desalination.

Generalized syntheses of nanocrystal-graphene hybrids in high-boiling-point organic solvents.

Science.gov (United States)

Pang, Danny Wei-Ping; Yuan, Fang-Wei; Chang, Yan-Cheng; Li, Guo-An; Tuan, Hsing-Yu

2012-08-07

Nanocrystal-graphene have been proposed as a new kind of promising hybrid for a wide range of application areas including catalysts, electronics, sensors, biomedicine, and energy storage, etc. Although a variety of methods have been developed for the preparation of hybrids, a facile and general synthetic approach is still highly required. In this study, nanocrystal-graphene hybrids were successfully synthesized in high-boiling-point organic solvents. Graphene oxide (GO) nanosheets were modified by oleylamine (OLA) to form a OLA-GO complex in order to be readily incorporated into hydrophobic synthesis. A rich library of highly crystalline nanocrystals, with types including noble metal, metal oxide, magnetic material and semiconductor were successfully grown on chemically converted graphene (CCG), which is simultaneously reduced from GO during the synthesis. High boiling-point solvents afford sufficient thermal energy to assure the high-quality crystalline nature of NCs, therefore the post-annealing process is obviated. Controlled experiments revealed that OLA-GO triggers heterogeneous nucleation and serves as excellent nuclei anchorage media. The protocol developed here brings one step closer to achieve "unity in diversity" on the preparation of nanocrystal-graphene hybrids.

Changes of the absorption cross section of Si nanocrystals with temperature and distance

Czech Academy of Sciences Publication Activity Database

Greben, M.; Khoroshyy, Petro; Gutsch, S.; Hiller, D.; Zacharias, M.; Valenta, J.

2017-01-01

Roč. 8, Nov 6 (2017), s. 2315-2323 ISSN 2190-4286 Institutional support: RVO:61388963 Keywords : absorption cross section * average lifetime * nanocrystal distance * photoluminescence decay * silicon nanocrystals Subject RIV: CF - Physical ; Theoretical Chemistry OBOR OECD: Physical chemistry Impact factor: 3.127, year: 2016 https://www.beilstein-journals.org/bjnano/articles/8/231

Formation and characterization of varied size germanium nanocrystals by electron microscopy, Raman spectroscopy, and photoluminescence

DEFF Research Database (Denmark)

Ou, Haiyan; Ou, Yiyu; Liu, Chuan

2011-01-01

Germanium nanocrystals are being extensively examined. Their unique optical properties (brought about by the quantum confinement effect) could potentially be applied in wide areas of nonlinear optics, light emission and solid state memory etc. In this paper, Ge nanocrystals embedded in a SiO2...... matrix were formed by complementary metal-oxide-semiconductor compatible technology, e.g. plasma enhanced chemical vapour deposition and annealing. Different sizes of the Ge nanocrystals were prepared and analyzed by transmission electron microscopy with respect to their size, distribution...... and crystallization. The samples of different size Ge nanocrystals embedded in the SiO2 matrix were characterized by Raman spectroscopy and photoluminescence. Interplayed size and strain effect of Ge nanocystals was demonstrated by Raman spectroscopy after excluding the thermal effect with proper excitation laser...

Theory of the thermodynamic influence of solution-phase additives in shape-controlled nanocrystal synthesis.

Science.gov (United States)

Qi, Xin; Fichthorn, Kristen A

2017-10-19

Though many experimental studies have documented that certain solution-phase additives can play a key role in the shape-selective synthesis of metal nanocrystals, the origins and mechanisms of this shape selectivity are still unclear. One possible role of such molecules is to thermodynamically induce the equilibrium shape of a nanocrystal by altering the interfacial free energies of the facets. Using a multi-scheme thermodynamic integration method that we recently developed [J. Chem. Phys., 2016, 145, 194108], we calculate the solid-liquid interfacial free energies γ sl and investigate the propensity to achieve equilibrium shapes in such syntheses. We first apply this method to Ag(100) and Ag(111) facets in ethylene glycol solution containing polyvinylpyrrolidone (PVP), to mimic the environment in polyol synthesis of Ag nanocrystals. We find that although PVP has a preferred binding to Ag(100), its selectivity is not sufficient to induce a thermodynamic preference for {100}-faceted nanocubes, as has been observed experimentally. This indicates that PVP promotes Ag nanocube formation kinetically rather than thermodynamically. We further quantify the thermodynamic influence of adsorbed solution-phase additives for generic molecules, by building a γ sl ratio/nanocrystal shape map as a function of zero-temperature binding energies. This map can be used to gauge the efficacy of candidate additive molecules for producing targeted thermodynamic nanocrystal shapes. The results indicate that only additives with a strong facet selectivity can impart significant thermodynamic-shape change. Therefore, many of the nanocrystals observed in experiments are likely kinetic products.

Advanced Branching Control and Characterization of Inorganic Semiconducting Nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Hughes, Steven Michael [Univ. of California, Berkeley, CA (United States)

2007-01-01

The ability to finely tune the size and shape of inorganic semiconducting nanocrystals is an area of great interest, as the more control one has, the more applications will be possible for their use. The first two basic shapes develped in nanocrystals were the sphere and the anistropic nanorod. the II_VI materials being used such as Cadmium Selenide (CdSe) and Cadmium Telluride (CdTe), exhibit polytypism, which allows them to form in either the hexagonally packed wurtzite or cubically packed zinc blende crystalline phase. The nanorods are wurtzite with the length of the rod growing along the c-axis. As this grows, stacking faults may form, which are layers of zinc blende in the otherwise wurtzite crystal. Using this polytypism, though, the first generation of branched crystals were developed in the form of the CdTe tetrapod. This is a nanocrystal that nucleates in the zincblend form, creating a tetrahedral core, on which four wurtzite arms are grown. This structure opened up the possibility of even more complex shapes and applications. This disseration investigates the advancement of branching control and further understanding the materials polytypism in the form of the stacking faults in nanorods.

Chemistry of the Colloidal Group II-VI Nanocrystal Synthesis

Energy Technology Data Exchange (ETDEWEB)

Liu, Haitao [Univ. of California, Berkeley, CA (United States)

2007-05-17

In the last two decades, the field of nanoscience andnanotechnology has witnessed tremendous advancement in the synthesis andapplication of group II-VI colloidal nanocrystals. The synthesis based onhigh temperature decomposition of organometallic precursors has becomeone of the most successful methods of making group II-VI colloidalnanocrystals. This methodis first demonstrated by Bawendi and coworkersin 1993 to prepare cadmium chalcogenide colloidal quantum dots and laterextended by others to prepare other group II-VI quantum dots as well asanisotropic shaped colloidal nanocrystals, such as nanorod and tetrapod.This dissertation focuses on the chemistry of this type of nanocrystalsynthesis. The synthesis of group II-VI nanocrystals was studied bycharacterizing the molecular structures of the precursors and productsand following their time evolution in the synthesis. Based on theseresults, a mechanism was proposed to account for the 2 reaction betweenthe precursors that presumably produces monomer for the growth ofnanocrystals. Theoretical study based on density functional theorycalculations revealed the detailed free energy landscape of the precursordecomposition and monomerformation pathway. Based on the proposedreaction mechanism, a new synthetic method was designed that uses wateras a novel reagent to control the diameter and the aspect ratio of CdSeand CdS nanorods.

Low-Temperature Electron Beam-Induced Transformations of Cesium Lead Halide Perovskite Nanocrystals

Science.gov (United States)

2017-01-01

Cesium lead halide perovskite (CsPbX3, with X = Br, Cl, I) nanocrystals have been found to undergo severe modifications under the high-energy electron beam irradiation of a transmission electron microscope (80/200 keV). In particular, in our previous work, together with halogen desorption, Pb2+ ions were found to be reduced to Pb0 and then diffused to form lead nanoparticles at temperatures above −40 °C. Here, we present a detailed irradiation study of CsPbBr3 nanocrystals at temperatures below −40 °C, a range in which the diffusion of Pb0 atoms/clusters is drastically suppressed. Under these conditions, the irradiation instead induces the nucleation of randomly oriented CsBr, CsPb, and PbBr2 crystalline domains. In addition to the Br desorption, which accompanies Pb2+ reduction at all the temperatures, Br is also desorbed from the CsBr and PbBr2 domains at low temperatures, leading to a more pronounced Br loss, thus the final products are mainly composed of Cs and Pb. The overall transformation involves the creation of voids, which coalesce upon further exposure, as demonstrated in both nanosheets and nanocuboids. Our results show that although low temperatures hinder the formation of Pb nanoparticles in CsPbBr3 nanocrystals when irradiated, the nanocrystals are nevertheless unstable. Consequently, we suggest that an optimum combination of temperature range, electron energy, and dose rate needs to be carefully chosen for the characterization of halide perovskite nanocrystals to minimize both the Pb nanoparticle formation and the structural decomposition. PMID:28983524

Model for efficient visible emission from Si nanocrystals ion beam synthesized in SiO{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Lopez, M. E-mail: mlopez@el.ub.es; Garrido, B.; Bonafos, C.; Perez-Rodriguez, A.; Morante, J.R.; Claverie, A

2001-05-01

The photoluminescence (PL) emission of Si nanocrystals ion beam synthesized in SiO{sub 2} is studied in this work as a function of annealing time and initial Si atomic excess (super-saturation). The optical properties of this system have been correlated with the characteristics of the nanocrystal population. The Si nanocrystals show a wide and very intense PL red/infrared emission. This emission peaks at about 1.7 eV for the low super-saturation range between 1% and 10% and shifts to the infrared for higher super-saturation (20% and 30%). Remarkably, there is a linear increase of PL intensity versus super-saturation in the low range. Moreover, the annealing kinetic studies show a typical behavior of PL intensity with annealing time, with a fast transitory increase that bends over to reach asymptotic saturation. The PL intensity saturation is satisfactorily explained by the Ostwald ripening stage of the nanocrystal population while the transient stage is a consequence of both nanocrystal growth and nanocrystal surface passivation mechanisms acting together. Indeed, electron spin resonance measurements demonstrate that the concentration of P{sub b} centers (Si dangling bonds) at the Si-SiO{sub 2} interface correlates inversely with PL intensity during most of the transient stage.

Pyridine-induced Dimensionality Change in Hybrid Perovskite Nanocrystals

KAUST Repository

Ahmed, Ghada H.

2017-05-02

Engineering the surface energy through careful manipulation of the surface chemistry is a convenient approach to control quantum confinement and structure dimensionality during nanocrystal growth. Here, we demonstrate that the introduction of pyridine during the synthesis of methylammonium lead bromide (MAPbBr) perovskite nanocrystals can transform three-dimensional (3D) cubes into two-dimensional (2D) nanostructures. Density functional theory (DFT) calculations show that pyridine preferentially binds to Pb atoms terminating the surface, driving the selective 2D growth of the nanostructures. These 2D nanostructures exhibit strong quantum confinement effects, high photoluminescence quantum yields in the visible spectral range, and efficient charge transfer to molecular acceptors. These qualities indicate the suitability of the synthesized 2D nanostructures for a wide range of optoelectronic applications.

Mega-electron-volt ion beam induced anisotropic plasmon resonance of silver nanocrystals in glass

NARCIS (Netherlands)

Penninkhof, JJ; Polman, A; Sweatlock, LA; Maier, SA; Atwater, HA; Vredenberg, AM; Kooi, BJ; Sweatlock, Luke A.; Maier, Stefan A.

2003-01-01

30 MeV Si ion beam irradiation of silica glass containing Ag nanocrystals causes alignment of Ag nanocrystals in arrays along the ion tracks. Optical transmission measurements show a large splitting of the surface plasmon resonance bands for polarizations longitudinal and transversal to the arrays.

Eco-friendly approach towards green synthesis of zinc oxide nanocrystals and its potential applications.

Science.gov (United States)

Velmurugan, Palanivel; Park, Jung-Hee; Lee, Sang-Myeong; Yi, Young-Joo; Cho, Min; Jang, Jum-Suk; Myung, Hyun; Bang, Keuk-Soo; Oh, Byung-Taek

2016-09-01

In the present study, we investigated a novel green route for synthesis of zinc oxide (ZnO) nanocrystals using Prunus × yedoensis Matsumura leaf extract as a reducing agent without using any surfactant or external energy. Standard characterization studies were carried out to confirm the obtained product using UV-Vis spectra, SEM-EDS, FTIR, TEM, and XRD. In addition, the synthesized ZnO nanocrystals were coated onto fabric and leather samples to study their bacteriostatic effect against odor-causing bacteria Brevibacterium linens and Staphylococcus epidermidis. Zinc oxide nanocrystal-coated fabric and leather showed good activity against both bacteria.

Phase diagrams of ferroelectric nanocrystals strained by an elastic matrix

Science.gov (United States)

Nikitchenko, A. I.; Azovtsev, A. V.; Pertsev, N. A.

2018-01-01

Ferroelectric crystallites embedded into a dielectric matrix experience temperature-dependent elastic strains caused by differences in the thermal expansion of the crystallites and the matrix. Owing to the electrostriction, these lattice strains may affect polarization states of ferroelectric inclusions significantly, making them different from those of a stress-free bulk crystal. Here, using a nonlinear thermodynamic theory, we study the mechanical effect of elastic matrix on the phase states of embedded single-domain ferroelectric nanocrystals. Their equilibrium polarization states are determined by minimizing a special thermodynamic potential that describes the energetics of an ellipsoidal ferroelectric inclusion surrounded by a linear elastic medium. To demonstrate the stability ranges of such states for a given material combination, we construct a phase diagram, where the inclusion’s shape anisotropy and temperature are used as two parameters. The ‘shape-temperature’ phase diagrams are calculated numerically for PbTiO3 and BaTiO3 nanocrystals embedded into representative dielectric matrices generating tensile (silica glass) or compressive (potassium silicate glass) thermal stresses inside ferroelectric inclusions. The developed phase maps demonstrate that the joint effect of thermal stresses and matrix-induced elastic clamping of ferroelectric inclusions gives rise to several important features in the polarization behavior of PbTiO3 and BaTiO3 nanocrystals. In particular, the Curie temperature displays a nonmonotonic variation with the ellipsoid’s aspect ratio, being minimal for spherical inclusions. Furthermore, the diagrams show that the polarization orientation with respect to the ellipsoid’s symmetry axis is controlled by the shape anisotropy and the sign of thermal stresses. Under certain conditions, the mechanical inclusion-matrix interaction qualitatively alters the evolution of ferroelectric states on cooling, inducing a structural transition

Passivation effects in B doped self-assembled Si nanocrystals

International Nuclear Information System (INIS)

Puthen Veettil, B.; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Zhang, Tian; Yang, Terry; Johnson, Craig; Conibeer, Gavin; Perez-Würfl, Ivan; McCamey, Dane

2014-01-01

Doping of semiconductor nanocrystals has enabled their widespread technological application in optoelectronics and micro/nano-electronics. In this work, boron-doped self-assembled silicon nanocrystal samples have been grown and characterised using Electron Spin Resonance and photoluminescence spectroscopy. The passivation effects of boron on the interface dangling bonds have been investigated. Addition of boron dopants is found to compensate the active dangling bonds at the interface, and this is confirmed by an increase in photoluminescence intensity. Further addition of dopants is found to reduce the photoluminescence intensity by decreasing the minority carrier lifetime as a result of the increased number of non-radiative processes

Organic-Inorganic Composites of Semiconductor Nanocrystals for Efficient Excitonics.

Science.gov (United States)

Guzelturk, Burak; Demir, Hilmi Volkan

2015-06-18

Nanocomposites of colloidal semiconductor nanocrystals integrated into conjugated polymers are the key to soft-material hybrid optoelectronics, combining advantages of both plastics and particles. Synergic combination of the favorable properties in the hybrids of colloidal nanocrystals and conjugated polymers offers enhanced performance and new functionalities in light-generation and light-harvesting applications, where controlling and mastering the excitonic interactions at the nanoscale are essential. In this Perspective, we highlight and critically consider the excitonic interactions in the organic-inorganic nanocomposites to achieve highly efficient exciton transfer through rational design of the nanocomposites. The use of strong excitonic interactions in optoelectronic devices can trigger efficiency breakthroughs in hybrid optoelectronics.

Growth of monodisperse nanocrystals of cerium oxide during synthesis and annealing

International Nuclear Information System (INIS)

Ghosh, Swapankumar; Divya, Damodaran; Remani, Kottayilpadi C.; Sreeremya, Thadathil S.

2010-01-01

Monodisperse cerium oxide nanocrystals have been successfully synthesised using simple ammonia precipitation technique from cerium(III) nitrate solution at different temperatures in the range 35-80 o C. The activation energy for growth of CeO 2 nanocrystals during the precipitation is calculated as 11.54 kJ/mol using Arrhenius plot. Average crystal diameter was obtained from XRD analysis, HR-TEM and light scattering (PCS). The analysis of size data from HR-TEM images and PCS clearly indicated the formation of highly crystalline CeO 2 particles in narrow size range. CeO 2 nanocrystals precipitated at 35 o C were further annealed at temperatures in the range 300-700 o C. The activation energy for crystal growth during annealing is also calculated and is close to the reported values. An effort is made to predict the mechanism of crystal growth during the precipitation and annealing.

Controlled Growth of ZnSe Nanocrystals by Tuning Reactivity and Amount of Zinc Precursor

Directory of Open Access Journals (Sweden)

Lai-Jun Zhang

2013-01-01

Full Text Available Zinc selenide (ZnSe nanocrystals were synthesized via a phosphine-free route using the highly reactive alkylamine-H2Se complex as selenium precursor and zinc precursors with different reactivity. The reactivity of zinc precursor was tuned by using three kinds of zinc carboxylates with different alkyl chain lengths, including zinc acetate, zinc nonanoate, and zinc stearate. The effect of the reactivity and the amount of zinc precursor on nucleation and growth of ZnSe nanocrystals were investigated by ultraviolet-visible absorption and photoluminescence spectra. Result indicates that the growth and optical property of the resulting ZnSe nanocrystals are strongly dependent on the alkyl chain length and the amount of the zinc carboxylates and both shorter alkyl chain length, and more amount of zinc carboxylate will lead to faster growth of ZnSe nanocrystals. This allows that the controlled growth and excellent optical property of high-quality ZnSe nanocrystals can be achieved by combining the different reactivity and the used amount of zinc precursor, such as by using stoichiometric and reactive Zn precursor and Se precursor or by using larger amount of more unreactive Zn precursor relative to the highly reactive alkylamine-H2Se complex precursor.

Effects of ultrasonic irradiation on crystallization and structural properties of EMT-type zeolite nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Ng, Eng-Poh, E-mail: epng@usm.my [School of Chemical Sciences, Universiti Sains Malaysia, USM, 11800 Penang (Malaysia); Awala, Hussein [Laboratoire Catalyse & Spectrochimie, CNRS-ENSICAEN, Université de Caen (France); Ghoy, Jia-Pei [School of Chemical Sciences, Universiti Sains Malaysia, USM, 11800 Penang (Malaysia); Vicente, Aurélie [Laboratoire Catalyse & Spectrochimie, CNRS-ENSICAEN, Université de Caen (France); Ling, Tau Chuan [Institute of Biological Sciences, Faculty of Science, University of Malaya (Malaysia); Ng, Yun Hau [School of Chemical Engineering, The University of New South Wales, Sydney (Australia); Mintova, Svetlana [Laboratoire Catalyse & Spectrochimie, CNRS-ENSICAEN, Université de Caen (France); Adam, Farook, E-mail: farook@usm.my [School of Chemical Sciences, Universiti Sains Malaysia, USM, 11800 Penang (Malaysia)

2015-06-01

Synthesis of EMT zeolite nanocrystals from rice husk ash biomass (RHA) under continuous ultrasonic irradiation is reported. The aging, nucleation and crystallization stages of EMT zeolite in the system were monitored at ambient temperature, and compared with the conventional hydrothermal method. It was found that ultrasonic wave induced rapid crystal growth of the nanosized EMT zeolite. Complete crystallization of EMT nanocrystals was achieved within 24 h which was much faster than conventional hydrothermal synthesis (36 h). Furthermore, XRD and TEM analyses revealed that more nuclei were formed during the nucleation stage, allowing the preparation of smaller zeolite nanocrystals with high crystallinity. The results also showed that sonocrystallization produced EMT zeolite with high yield (ca. 80%). The ultrasound-prepared EMT nanocrystals were also found to have high porosity and high hydrophilicity, making the material promising for water sorption applications including vapor sensing, heat pump and adsorption technologies. - Highlights: • Nanosized EMT zeolites are formed from rice husk ash under ultrasonic irradiation. • The effects of ultrasonic waves in nanosized EMT zeolite synthesis are studied. • Ultrasound induces rapid crystal growth and produces high zeolite yield. • Smaller zeolite nanocrystals with high crystallinity and large defect sites are obtained. • Improved surface hydrophilicity of crystals is beneficial for water sorption applications.

Nanocomposites Based on Luminescent Colloidal Nanocrystals and Polymeric Ionic Liquids towards Optoelectronic Applications

Directory of Open Access Journals (Sweden)

Annamaria Panniello

2014-01-01

Full Text Available Polymeric ionic liquids (PILs are an interesting class of polyelectrolytes, merging peculiar physical-chemical features of ionic liquids with the flexibility, mechanical stability and processability typical of polymers. The combination of PILs with colloidal semiconducting nanocrystals leads to novel nanocomposite materials with high potential for batteries and solar cells. We report the synthesis and properties of a hybrid nanocomposite made of colloidal luminescent CdSe nanocrystals incorporated in a novel ex situ synthesized imidazolium-based PIL, namely, either a poly(N-vinyl-3-butylimidazolium hexafluorophosphate or a homologous PIL functionalized with a thiol end-group exhibiting a chemical affinity with the nanocrystal surface. A capping exchange procedure has been implemented for replacing the pristine organic capping molecules of the colloidal CdSe nanocrystals with inorganic chalcogenide ions, aiming to disperse the nano-objects in the PILs, by using a common polar solvent. The as-prepared nanocomposites have been studied by TEM investigation, UV-Vis, steady-state and time resolved photoluminescence spectroscopy for elucidating the effects of the PIL functionalization on the morphological and optical properties of the nanocomposites.

Free radical scavenging properties of some wine probes

International Nuclear Information System (INIS)

Stasko, A.; Liptakova, M.; Malik, F.

1999-01-01

There are preliminary results of investigation of scavenging properties of 8 probes of Slovak wines (consisting of one reference, 3 probes of white wine and 4 probes of red wine). According to the literature so far, wine probes contain paramagnetic species (Mn 2+ , characterised with sextet spectrum, and a singlet line around g=2,00). In our probes we observed Mn 2+ signals, but no significant evidence for a single line of free radical was found. We can conclude that Mn 2+ content in the red wines is generally higher than in the white ones. Further, we investigated the scavenging activities of the probes adding solution of dinitropicryl hydrazyl (DPPH-stable radical) to them. Their ability to terminate free radicals resulted in the decrease of the final DPPH concentrations in the probes. The red wines have significantly higher capability to scavenge free radicals than the probes of white wines. (authors)

Charge separation and transfer in hybrid type II tunneling structures of CdTe and CdSe nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Gross, Dieter Konrad Michael

2013-11-08

Closely packed nanocrystal systems have been investigated in this thesis with respect to charge separation by charge carrier tunneling. Clustered and layered samples have been analyzed using PL-measurements and SPV-methods. The most important findings are reviewed in the following. A short outlook is also provided for potential further aspects and application of the presented results. The main purpose of this thesis was to find and quantify electronic tunneling transfer in closely packed self-assembled nanocrystal structures presenting quantum mechanical barriers of about 1 nm width. We successfully used hybrid assemblies of CdTe and CdSe nanocrystals where the expected type II alignment between CdTe and CdSe typically leads to a concentration of electrons in CdSe and holes in CdTe nanocrystals. We were able to prove the charge selectivity of the CdTe-CdSe nanocrystal interface which induces charge separation. We mainly investigated the effects related to the electron transfer from CdTe to CdSe nanocrystals. Closely packing was achieved by two independent methods: the disordered colloidal clustering in solution and the layered assembly on dry glass substrates. Both methods lead to an inter-particle distance of about 1 nm of mainly organic material which acts as a tunneling barrier. PL-spectroscopy was applied. The PL-quenching of the CdTe nanocrystals in hybrid assemblies indicates charge separation by electron transfer from CdTe to CdSe nanocrystals. A maximum quenching rate of up to 1/100 ps was measured leading to a significant global PL-quenching of up to about 70 % for the CdTe nanocrystals. It was shown that charge separation dynamics compete with energy transfer dynamics and that charge separation typically dominates. The quantum confinement effect was used to tune the energetic offset between the CdTe and CdSe nanocrystals. We thus observe a correlation of PL-quenching and offset of the energy states for the electron transfer. The investigated PL

Density-controllable nonvolatile memory devices having metal nanocrystals through chemical synthesis and assembled by spin-coating technique

International Nuclear Information System (INIS)

Wang Guangli; Chen Yubin; Shi Yi; Pu Lin; Pan Lijia; Zhang Rong; Zheng Youdou

2010-01-01

A novel two-step method is employed, for the first time, to fabricate nonvolatile memory devices that have metal nanocrystals. First, size-averaged Au nanocrystals are synthesized chemically; second, they are assembled into memory devices by a spin-coating technique at room temperature. This attractive approach makes it possible to tailor the diameter and control the density of nanocrystals individually. In addition, processes at room temperature prevent Au diffusion, which is a main concern for the application of metal nanocrystal-based memory. The experimental results, both the morphology characterization and the electrical measurements, reveal that there is an optimum density of nanocrystal monolayer to balance between long data retention and a large hysteresis memory window. At the same time, density-controllable devices could also feed the preferential emphasis on either memory window or retention time. All these facts confirm the advantages and novelty of our two-step method. (semiconductor devices)

Transparent ‘solution’ of ultrathin magnesium hydroxide nanocrystals for flexible and transparent nanocomposite films

International Nuclear Information System (INIS)

Wang, Jie-Xin; Sun, Qian; Chen, Bo; Zeng, Xiao-Fei; Zhang, Cong; Chen, Jian-Feng; Wu, Xi; Zou, Hai-Kui

2015-01-01

Transparent solutions of nanocrystals exhibit many unique properties, and are thus attractive materials for numerous applications. However, the synthesis of transparent nanocrystal solutions of magnesium hydroxide (MH) with wide applications is yet to be realized. Here, we report a facile two-step process, which includes a direct reactive precipitation in alcohol phase instead of aqueous phase combined with a successive surface modification, to prepare transparent alcohol solutions containing lamellar MH nanocrystals with an average size of 52 nm and an ultrathin thickness of 1–2 nm, which is the thinnest MH nanoplatelet reported in the literatures. Further, highly flexible and transparent nanocomposite films are fabricated with a solution mixing method by adding the transparent MH nanocrystal solutions into PVB solution. Considering the simplicity of the fabrication process, high transparency and good flexibility, this MH/polymer nanocomposite film is promising for flame-resistant applications in plastic electronics and optical devices with high transparency, such as flexible displays, optical filters, and flexible solar cells. (paper)

Hybridization of Single Nanocrystals of Cs4PbBr6 and CsPbBr3.

Science.gov (United States)

Weerd, Chris de; Lin, Junhao; Gomez, Leyre; Fujiwara, Yasufumi; Suenaga, Kazutomo; Gregorkiewicz, Tom

2017-09-07

Nanocrystals of all-inorganic cesium lead halide perovskites (CsPbX 3 , X = Cl, Br, I) feature high absorption and efficient narrow-band emission which renders them promising for future generation of photovoltaic and optoelectronic devices. Colloidal ensembles of these nanocrystals can be conveniently prepared by chemical synthesis. However, in the case of CsPbBr 3 , its synthesis can also yield nanocrystals of Cs 4 PbBr 6 and the properties of the two are easily confused. Here, we investigate in detail the optical characteristics of simultaneously synthesized green-emitting CsPbBr 3 and insulating Cs 4 PbBr 6 nanocrystals. We demonstrate that, in this case, the two materials inevitably hybridize, forming nanoparticles with a spherical shape. The actual amount of these Cs 4 PbBr 6 nanocrystals and nanohybrids increases for synthesis at lower temperatures, i.e., the condition typically used for the development of perovskite CsPbBr 3 nanocrystals with smaller sizes. We use state-of-the-art electron energy loss spectroscopy to characterize nanoparticles at the single object level. This method allows distinguishing between optical characteristics of a pure Cs 4 PbBr 6 and CsPbBr 3 nanocrystal and their nanohybrid. In this way, we resolve some of the recent misconceptions concerning possible visible absorption and emission of Cs 4 PbBr 6 . Our method provides detailed structural characterization, and combined with modeling, we conclusively identify the nanospheres as CsPbBr 3 /Cs 4 PbBr 6 hybrids. We show that the two phases are independent of each other's presence and merge symbiotically. Herein, the optical characteristics of the parent materials are preserved, allowing for an increased absorption in the UV due to Cs 4 PbBr 6 , accompanied by the distinctive efficient green emission resulting from CsPbBr 3 .

Colloidal synthesis of Cu-ZnO and Cu@CuNi-ZnO hybrid nanocrystals with controlled morphologies and multifunctional properties

Science.gov (United States)

Zeng, Deqian; Gong, Pingyun; Chen, Yuanzhi; Zhang, Qinfu; Xie, Qingshui; Peng, Dong-Liang

2016-06-01

Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications. The utilization of low-cost non-noble metals to construct novel metal-semiconductor hybrid nanocrystals is important and meaningful for their large-scale applications. In this study, a facile solution approach is developed for the synthesis of Cu-ZnO hybrid nanocrystals with well-controlled morphologies, including nanomultipods, core-shell nanoparticles, nanopyramids and core-shell nanowires. In the synthetic strategy, Cu nanocrystals formed in situ serve as seeds for the heterogeneous nucleation and growth of ZnO, and it eventually forms various Cu-ZnO hetero-nanostructures under different reaction conditions. These hybrid nanocrystals possess well-defined and stable heterostructure junctions. The ultraviolet-visible-near infrared spectra reveal morphology-dependent surface plasmon resonance absorption of Cu and the band gap absorption of ZnO. Furthermore, we construct a novel Cu@CuNi-ZnO ternary hetero-nanostructure by incorporating the magnetic metal Ni into the pre-synthesized colloidal Cu nanocrystals. Such hybrid nanocrystals possess a magnetic Cu-Ni intermediate layer between the ZnO shell and the Cu core, and exhibit ferromagnetic/superparamagnetic properties which expand their functionalities. Finally, enhanced photocatalytic activities are observed in the as-prepared non-noble metal-ZnO hybrid nanocrystals. This study not only provides an economical way to prepare high-quality morphology-controlled Cu-ZnO hybrid nanocrystals for potential applications in the fields of photocatalysis and photovoltaic devices, but also opens up new opportunities in designing ternary non-noble metal-semiconductor hybrid nanocrystals with multifunctionalities.Metal-semiconductor hybrid nanocrystals have received extensive attention owing to their multiple functionalities which can find wide technological applications

Observation of Quantum Confinement in Monodisperse Methylammonium Lead Halide Perovskite Nanocrystals Embedded in Mesoporous Silica.

Science.gov (United States)

Malgras, Victor; Tominaka, Satoshi; Ryan, James W; Henzie, Joel; Takei, Toshiaki; Ohara, Koji; Yamauchi, Yusuke

2016-10-13

Hybrid organic-inorganic metal halide perovskites have fascinating electronic properties and have already been implemented in various devices. Although the behavior of bulk metal halide perovskites has been widely studied, the properties of perovskite nanocrystals are less well-understood because synthesizing them is still very challenging, in part because of stability. Here we demonstrate a simple and versatile method to grow monodisperse CH 3 NH 3 PbBr x I x-3 perovskite nanocrystals inside mesoporous silica templates. The size of the nanocrystal is governed by the pore size of the templates (3.3, 3.7, 4.2, 6.2, and 7.1 nm). In-depth structural analysis shows that the nanocrystals maintain the perovskite crystal structure, but it is slightly distorted. Quantum confinement was observed by tuning the size of the particles via the template. This approach provides an additional route to tune the optical bandgap of the nanocrystal. The level of quantum confinement was modeled taking into account the dimensions of the rod-shaped nanocrystals and their close packing inside the channels of the template. Photoluminescence measurements on CH 3 NH 3 PbBr clearly show a shift from green to blue as the pore size is decreased. Synthesizing perovskite nanostructures in templates improves their stability and enables tunable electronic properties via quantum confinement. These structures may be useful as reference materials for comparison with other perovskites, or as functional materials in all solid-state light-emitting diodes.

Biocompatibility of bio based calcium carbonate nanocrystals ...

African Journals Online (AJOL)

Background: Currently, there has been extensive research interest for inorganic nanocrystals such as calcium phosphate, iron oxide, silicone, carbon nanotube and layered double hydroxide as a drug delivery system especially in cancer therapy. However, toxicological screening of such particles is paramount importance ...

In vitro and in vivo evaluation of SN-38 nanocrystals with different particle sizes

Directory of Open Access Journals (Sweden)

Chen M

2017-08-01

Full Text Available Min Chen,1,2 Wanqing Li,3 Xun Zhang,1 Ye Dong,1 Yabing Hua,1 Hui Zhang,1 Jing Gao,1 Liang Zhao,2 Ying Li,1 Aiping Zheng1 1State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Institute of Pharmacology and Toxicology, 2School of Pharmacy, Jinzhou Medical University, Jinzhou, 3School of Preclinical Medicine, Beijing University of Chinese Medicine, Beijing, People’s Republic of China Abstract: 7-Ethyl-10-hydroxycamptothecin (SN-38 is a potent broad-spectrum antitumor drug derived from irinotecan hydrochloride (CPT-11. Due to its poor solubility and instability of the active lactone ring, its clinical use is significantly limited. As one of the most promising formulations for poorly water-soluble drugs, nanocrystals have attracted increasing attention. In order to solve these problems and evaluate the antitumor effect of SN-38 in vitro and in vivo, two nanocrystals with markedly different particle sizes were prepared. Dynamic light scattering and transmission electron microscopy were used to investigate the two nanocrystals. The particle sizes of SN-38 nanocrystals A (SN-38/NCs-A and SN-38 nanocrystals B (SN-38/NCs-B were 229.5±1.99 and 799.2±14.44 nm, respectively. X-ray powder diffraction analysis showed that the crystalline state of SN-38 did not change in the size reduction process. An accelerated dissolution velocity of SN-38 was achieved by nanocrystals, and release rate of SN-38/NCs-A was significantly faster than that of SN-38/NCs-B. Cellular uptake, cellular cytotoxicity, pharmacokinetics, animal antitumor efficacy, and tissue distribution were subsequently examined. As a result, enhanced intracellular accumulation in HT1080 cells and cytotoxicity on different tumor cells were observed for SN-38/NCs-A compared to that for SN-38/NCs-B and solution. Besides, compared to the SN-38 solution, SN-38/NCs-A had a higher bioavailability after intravenous injection; while the bioavailability of SN-38/NCs-B was even lower than

Heterogeneous nucleation of amorphous alloys on catalytic nanoparticles to produce 2D patterned nanocrystal arrays

International Nuclear Information System (INIS)

Gangopadhyay, A K; Krishna, H; Favazza, C; Miller, C; Kalyanaraman, R

2007-01-01

Templates are widely used to produce artificial nanostructures. Here, laser-assisted self-organization has been used to form one- and two-dimensional (D) nanoarrays of Cu nanocrystals. Using these nanoarrays as a template, a 2D patterned ferromagnetic nanostructure of FeCrSi nanocrystals has been produced by heterogeneous nucleation and growth of nanocrystals by partial devitrification from an amorphous Fe 64.5 Cr 10 Si 13.5 B 9 Nb 3 alloy with the Cu nanoparticles acting as catalytic nucleation sites. The interaction among the ferromagnetic nanocrystals via the residual amorphous matrix can be controlled by suitable choice of the amorphous alloy composition. Although demonstrated for a ferromagnetic system, the processing method may have much wider applicability for producing artificial nanostructures of a wide variety of materials when materials-specific catalysts and amorphous alloy compositions are judiciously chosen

Size effect on the SHG properties of Cu-doped CdI2 nanocrystals

International Nuclear Information System (INIS)

Miah, M. Idrish

2009-01-01

Because the optically induced second harmonic generation (SHG) is prevented by symmetry in a centrosymmetric material, one needs to form noncentrosymmetric processes in order to observe the SHG. However, one of the efficient ways to enhance the noncentrosymmetricity of a material is to dope it with an appropriate impurity and amount. We grow Cu-doped CdI 2 layered nanocrystal structures from the mixture of CdI 2 and CuI using the standard Bridgman-Stockbarger method and investigate the nano-confined effects by studying the second-order optical effect via the measurements of SHG. The second-order susceptibility for the nanocrystals is calculated and the values at liquid helium temperature range from 0.38 to 0.83 pm V -1 for the thicknesses of 10-0.8 nm respectively. The size dependence demonstrates the nano-sized quantum-confined effect with a clear increase in the SHG with decreasing the thickness of the nanocrystal or crystal temperature. Since the local electron-phonon anharmonicity is described by third-order rank tensors in disordered systems, the SHG is very similar to that one introduced for the third-order optical susceptibility. It has been confirmed by observing the large photoluminescent yield of the pure crystals. The Raman scattering spectra taken for thin nanocrystals confirm the phonon modes originating from interlayer phonons crucially responsible for the observed effects. The obtained results show that the Cu-doped CdI 2 layered nanocrystals are promising materials for applications in optoelectronic nano-devices.

Trapping time of excitons in Si nanocrystals embedded in a SiO2 matrix

Science.gov (United States)

de Jong, E. M. L. D.; de Boer, W. D. A. M.; Yassievich, I. N.; Gregorkiewicz, T.

2017-05-01

Silicon (Si) nanocrystals (NCs) are of great interest for many applications, ranging from photovoltaics to optoelectonics. The photoluminescence quantum yield of Si NCs dispersed in SiO2 is limited, suggesting the existence of very efficient processes of nonradiative recombination, among which the formation of a self-trapped exciton state on the surface of the NC. In order to improve the external quantum efficiency of these systems, the carrier relaxation and recombination need to be understood more thoroughly. For that purpose, we perform transient-induced absorption spectroscopy on Si NCs embedded in a SiO2 matrix over a broad probe range for NCs of average sizes from 2.5 to 5.5 nm. The self-trapping of free excitons on surface-related states is experimentally and theoretically discussed and found to be dependent on the NC size. These results offer more insight into the self-trapped exciton state and are important to increase the optical performance of Si NCs.

Growth of monodisperse nanocrystals of cerium oxide during synthesis and annealing

Energy Technology Data Exchange (ETDEWEB)

Ghosh, Swapankumar, E-mail: swapankumar.ghosh2@mail.dcu.ie; Divya, Damodaran [National Institute for Interdisciplinary Science and Technology (NIIST), Council of Scientific and Industrial Research (CSIR) (India); Remani, Kottayilpadi C. [Sree Neelakanda Government Sanskrit College, Department of Chemistry (India); Sreeremya, Thadathil S. [National Institute for Interdisciplinary Science and Technology (NIIST), Council of Scientific and Industrial Research (CSIR) (India)

2010-06-15

Monodisperse cerium oxide nanocrystals have been successfully synthesised using simple ammonia precipitation technique from cerium(III) nitrate solution at different temperatures in the range 35-80 {sup o}C. The activation energy for growth of CeO{sub 2} nanocrystals during the precipitation is calculated as 11.54 kJ/mol using Arrhenius plot. Average crystal diameter was obtained from XRD analysis, HR-TEM and light scattering (PCS). The analysis of size data from HR-TEM images and PCS clearly indicated the formation of highly crystalline CeO{sub 2} particles in narrow size range. CeO{sub 2} nanocrystals precipitated at 35 {sup o}C were further annealed at temperatures in the range 300-700 {sup o}C. The activation energy for crystal growth during annealing is also calculated and is close to the reported values. An effort is made to predict the mechanism of crystal growth during the precipitation and annealing.

Dopant concentration dependent magnetism of Cu-doped TiO{sub 2} nanocrystals

Energy Technology Data Exchange (ETDEWEB)

Anitha, B.; Khadar, M. Abdul, E-mail: mabdulkhadar@rediffmail.com [University of Kerala, Centre for Nanoscience and Nanotechnology (India)

2016-06-15

Undoped and Cu-doped nanocrystals of TiO{sub 2} having the size range of 8–11 nm were synthesized by peroxide gel method. XRD analysis using Rietveld refinement confirmed anatase phase with a small percentage of rutile content for undoped TiO{sub 2} nanocrystals while a pure anatase phase with preferential growth along [004] direction was observed for nanocrystals of Cu-doped TiO{sub 2}. Variation in the intensity ratios of the XRD peaks of the doped samples compared to that of the undoped sample offered an evidence for the substitutional incorporation of Cu ions in the TiO{sub 2} lattice. The preferential growth of the nanocrystals along the [004] direction was verified using HRTEM analysis. Cu doping extended the optical absorption edge of TiO{sub 2} nanocrystals to the visible spectral region and caused a blue shift and broadening of the E{sub g} (1) Raman active mode of anatase TiO{sub 2}. Undoped TiO{sub 2} sample showed a weak ferromagnetism superimposed on a diamagnetic background while Cu-doped TiO{sub 2} samples exhibited a weak ferromagnetism in the low-field region with a paramagnetic component in the high-field region. The magnetic moment exhibited by the doped samples is interpreted as the resultant of a weak ferromagnetic moment in the low-field region arising from the presence of defects near the surface of TiO{sub 2} nanoparticles or from the interaction of the substituted Cu ions with the oxygen vacancies, and the paramagnetic contribution from the increased Cu dopant concentration near the surface of the particles arising from self-purification mechanism.

Accurate thermodynamic relations of the melting temperature of nanocrystals with different shapes and pure theoretical calculation

Energy Technology Data Exchange (ETDEWEB)

Zhu, Jinhua; Fu, Qingshan; Xue, Yongqiang, E-mail: xyqlw@126.com; Cui, Zixiang

2017-05-01

Based on the surface pre-melting model, accurate thermodynamic relations of the melting temperature of nanocrystals with different shapes (tetrahedron, cube, octahedron, dodecahedron, icosahedron, nanowire) were derived. The theoretically calculated melting temperatures are in relative good agreements with experimental, molecular dynamic simulation and other theoretical results for nanometer Au, Ag, Al, In and Pb. It is found that the particle size and shape have notable effects on the melting temperature of nanocrystals, and the smaller the particle size, the greater the effect of shape. Furthermore, at the same equivalent radius, the more the shape deviates from sphere, the lower the melting temperature is. The value of melting temperature depression of cylindrical nanowire is just half of that of spherical nanoparticle with an identical radius. The theoretical relations enable one to quantitatively describe the influence regularities of size and shape on the melting temperature and to provide an effective way to predict and interpret the melting temperature of nanocrystals with different sizes and shapes. - Highlights: • Accurate relations of T{sub m} of nanocrystals with various shapes are derived. • Calculated T{sub m} agree with literature results for nano Au, Ag, Al, In and Pb. • ΔT{sub m} (nanowire) = 0.5ΔT{sub m} (spherical nanocrystal). • The relations apply to predict and interpret the melting behaviors of nanocrystals.

Pressure-induced preferential growth of nanocrystals in amorphous Nd9Fe85B6

International Nuclear Information System (INIS)

Wu Wei; Li Wei; Sun Hongyu; Li Hui; Zhang Xiangyi; Li Xiaohong; Liu Baoting

2008-01-01

Control over the growth and crystallographic orientation of nanocrystals in amorphous alloys is of particular importance for the development of advanced nanocrystalline materials. In the present study, Nd 2 Fe 14 B nanocrystals with a strong crystallographic texture along the [410] direction have been produced in Nd-lean amorphous Nd 9 Fe 85 B 6 under a high pressure of 6 GPa at 923 K. This is attributed to the high pressure inducing the preferential growth of Nd 2 Fe 14 B nanocrystals in the alloy. The present study demonstrates the potential application of high-pressure technology in controlling nanocrystalline orientation in amorphous alloys

Laser induced broad band anti-Stokes white emission from LiYbF4 nanocrystals

Institute of Scientific and Technical Information of China (English)

L. Marciniak; R. Tomala; M. Stefanski; D. Hreniak; W. Strek

2016-01-01

Spectroscopic properties of tetragonal LiYbF4 nanocrystals under high dense NIR excitation at vacuum condition were in-vestigated. White, broad band emission covering whole visible part of the spectrum from LiYbF4 nanocrystals was observed. Its in-tensity strongly depended on the excitation power, excitation wavelength and ambient pressure. Temperature of the nanocrystals un-der 975 nm excitation was determined as a function of excitation power. Strong photo-induced current was observed from LiYbF4 pallet. The emission kinetic was analyzed. The mechanism of the anti-Stokes white emission was discussed in terms of the la-ser-induced charge transfer emission from Yb2+ states.

Essentially Trap-Free CsPbBr3 Colloidal Nanocrystals by Postsynthetic Thiocyanate Surface Treatment.

Science.gov (United States)

Koscher, Brent A; Swabeck, Joseph K; Bronstein, Noah D; Alivisatos, A Paul

2017-05-17

We demonstrate postsynthetic modification of CsPbBr 3 nanocrystals by a thiocyanate salt treatment. This treatment improves the quantum yield of both freshly synthesized (PLQY ≈ 90%) and aged nanocrystals (PLQY ≈ 70%) to within measurement error (2-3%) of unity, while simultaneously maintaining the shape, size, and colloidal stability. Additionally, the luminescence decay kinetics transform from multiexponential decays typical of nanocrystalline semiconductors with a distribution of trap sites, to a monoexponential decay, typical of single energy level emitters. Thiocyanate only needs to access a limited number of CsPbBr 3 nanocrystal surface sites, likely representing under-coordinated lead atoms on the surface, in order to have this effect.

Luminescence in Mn-doped CdS nanocrystals

Indian Academy of Sciences (India)

Wintec

and the Mn d levels occur at two different energies, allowed us to study the PL lifetime decay behaviour of both kinds of .... seen from the XRD analysis, the size of the nanocrystals .... levels couple to the CdS electronic states and the excited.

Electronic structure and magnetic properties of FeWO{sub 4} nanocrystals synthesized by the microwave-hydrothermal method

Energy Technology Data Exchange (ETDEWEB)

Almeida, M.A.P. [INCTMN-DQ-Universidade Federal de Sao Carlos, Sao Carlos, P.O. Box 676, 13565-905, SP (Brazil); Cavalcante, L.S., E-mail: laeciosc@bol.com.br [INCTMN-Universidade Estadual, Paulista, P.O. Box 355, 14801-907, Araraquara, SP (Brazil); Morilla-Santos, C.; Filho, P.N. Lisboa [MAv-Universidade Estadual, Paulista, P.O. Box 473, 17033-360, Bauru, SP (Brazil); Beltran, A.; Andres, J.; Gracia, L. [Department de Quimica Fisica i Analitica, Universitat Jaume I, E-12071 Castello (Spain); Longo, E. [INCTMN-DQ-Universidade Federal de Sao Carlos, Sao Carlos, P.O. Box 676, 13565-905, SP (Brazil); INCTMN-Universidade Estadual, Paulista, P.O. Box 355, 14801-907, Araraquara, SP (Brazil)

2012-11-15

This communication reports that FeWO{sub 4} nanocrystals were successfully synthesized by the microwave-hydrothermal method at 443 K for 1 h. The structure and shape of these nanocrystals were characterized by X-ray diffraction, Rietveld refinement, and transmission electron microscopy. The experimental results and first principles calculations were combined to explain the electronic structure and magnetic properties. Experimental data were obtained by magnetization measurements for different applied magnetic fields. Theoretical calculations revealed that magnetic properties of FeWO{sub 4} nanocrystals can be assigned to two magnetic orderings with parallel or antiparallel spins in adjacent chains. These factors are crucial to understanding of competition between ferro- and antiferromagnetic behavior. Highlights: Black-Right-Pointing-Pointer Monophasic FeWO{sub 4} nanocrystals were synthesized by the microwave-hydrothermal method. Black-Right-Pointing-Pointer Rietveld refinement and clusters model for monoclinic structure Black-Right-Pointing-Pointer Magnetic properties of FeWO{sub 4} nanocrystals at different temperatures.

Release kinetics and cell viability of ibuprofen nanocrystals produced by melt-emulsification.

Science.gov (United States)

Fernandes, A R; Dias-Ferreira, J; Cabral, C; Garcia, M L; Souto, E B

2018-06-01

The clinical use of poorly water-soluble drugs has become a big challenge in pharmaceutical development due to the compromised bioavailability of the drugs in vivo. Nanocrystals have been proposed as a formulation strategy to improve the dissolution properties of these drugs. The benefits of using nanocrystals in drug delivery, when compared to other nanoparticles, are related to their production facilities, simple structure, and suitability for a variety of administration routes. High pressure homogenization (HPH) is the most promising production process, which can be employed at low or high temperatures. Ibuprofen nanocrystals with a mean size below 175 nm, and polydispersity below 0.18, have been produced by melt-emulsification, followed by HPH. Two nanocrystal formulations, differing on the surfactant composition, have been produced, their in vitro ibuprofen release tested in Franz diffusion cells and adjusted to several kinetic models (zero order, first order, Higuchi, Hixson-Crowell, Korsmeyer-Peppas, Baker-Lonsdale and Weibull model). Cell viability was assessed at 3, 6 and 24 h of incubation on human epithelial colorectal cells (Caco-2) by AlamarBlue ® colorimetric assay. For both formulations, Caco-2 cells viability was dependent on the drug concentration and time of exposure. Copyright © 2018 Elsevier B.V. All rights reserved.

Hydroxyapatite nanocrystals: simple preparation, characterization and formation mechanism.

Science.gov (United States)

Mohandes, Fatemeh; Salavati-Niasari, Masoud; Fathi, Mohammadhossein; Fereshteh, Zeinab

2014-12-01

Crystalline hydroxyapatite (HAP) nanoparticles and nanorods have been successfully synthesized via a simple precipitation method. To control the shape and particle size of HAP nanocrystals, coordination ligands derived from 2-hydroxy-1-naphthaldehyde were first prepared, characterized by Fourier transform infrared (FT-IR) and proton nuclear magnetic resonance ((1)H-NMR) spectroscopies, and finally applied in the synthesis process of HAP. On the other hand, the HAP nanocrystals were also characterized by several techniques including powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). According to the FE-SEM and TEM micrographs, it was found that the morphology and crystallinity of the HAP powders depended on the coordination mode of the ligands. Copyright © 2014 Elsevier B.V. All rights reserved.

Preparation and nonlinear optical properties of indium nanocrystals in sodium borosilicate glass by the sol–gel route

International Nuclear Information System (INIS)

Zhong, Jiasong; Xiang, Weidong; Zhao, Haijun; Chen, Zhaoping; Liang, Xiaojuan; Zhao, Wenguang; Chen, Guoxin

2012-01-01

Graphical abstract: The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel methods. And the indium nanocrystals in tetragonal crystal system have formed uniformly in the glass, and the average diameter of indium nanocrystals is about 30 nm. The third-order optical nonlinear refractive index γ, absorption coefficient β, and susceptibility χ (3) of the glass are determined to be −4.77 × 10 −16 m 2 /W, 2.67 × 10 −9 m/W, and 2.81 × 10 −10 esu, respectively. Highlights: ► Indium nanocrystals embedded in glass matrix have been prepared by sol–gel route. ► The crystal structure and composition are investigated by XRD and XPS. ► Size and distribution of indium nanocrystals is determined by TEM. ► The third-order optical nonlinearity is investigated by using Z-scan technique. -- Abstract: The sodium borosilicate glass doped with indium nanocrystals have been successfully prepared by sol–gel route. The thermal stability behavior of the stiff gel is investigated by thermogravimetric (TG) and differential thermal (DTA) analysis. The crystal structure of the glass is characterized by X-ray powder diffraction (XRD). Particle composition is determined by X-ray photoelectron spectroscopy (XPS). Size and distribution of the nanocrystals are characterized by transmission electron microscopy (TEM) as well as high-resolution transmission electron microscopy (HRTEM). Results show that the indium nanocrystals in tetragonal crystal structure have formed in glass, and the average diameter is about 30 nm. Further, the glass is measured by Z-scan technique to investigate the nonlinear optical (NLO) properties. The third-order NLO coefficient χ (3) of the glass is determined to be 2.81 × 10 −10 esu. The glass with large third-order NLO coefficient is promising materials for applications in optical devices.

Licuri fibers characterization after treatment to produce cellulose nanocrystals

International Nuclear Information System (INIS)

Castro, E.G.; Oliveira, J.C.; Miranda, C.S.; Jose, N.M.

2014-01-01

Cellulose nanocrystals have been widely studied in the materials area due to their high aspect ratio, which is directly related to a good performance as mechanical reinforcement. Obtaining this nanocrystals from commercial bleached pulps, as eucalyptus, or microcrystalline cellulose is well studied. Trying to find new extraction sources, exploring better the huge variety of Brazil’s natural fibers and giving the opportunity of development to small communities, the present work verifies the influence of two bleaching methodologies, sodium hypochlorite or hydrogen peroxide, on licuri fibers. Previous washing and mercerization steps were performed before bleaching. The product of each step was analysed by: DSC, TGA, XRD, SEM and FTIR. The yield of each step was also calculated. (author)

Pyridine-induced Dimensionality Change in Hybrid Perovskite Nanocrystals

KAUST Repository

Ahmed, Ghada H.; Yin, Jun; Bose, Riya; Sinatra, Lutfan; Alarousu, Erkki; Yengel, Emre; AlYami, Noktan; Saidaminov, Makhsud I.; Zhang, Yuhai; Hedhili, Mohamed N.; Bakr, Osman; Bredas, Jean-Luc; Mohammed, Omar F.

2017-01-01

of pyridine during the synthesis of methylammonium lead bromide (MAPbBr) perovskite nanocrystals can transform three-dimensional (3D) cubes into two-dimensional (2D) nanostructures. Density functional theory (DFT) calculations show that pyridine preferentially

Heterogeneous nucleation of amorphous alloys on catalytic nanoparticles to produce 2D patterned nanocrystal arrays

Energy Technology Data Exchange (ETDEWEB)

Gangopadhyay, A K [Department of Physics, Washington University in St Louis, MO 63130 (United States); Krishna, H [Department of Physics, Washington University in St Louis, MO 63130 (United States); Favazza, C [Department of Physics, Washington University in St Louis, MO 63130 (United States); Miller, C [Center for Materials Innovation, Washington University in St Louis, MO 63130 (United States); Kalyanaraman, R [Department of Physics, Washington University in St Louis, MO 63130 (United States)

2007-12-05

Templates are widely used to produce artificial nanostructures. Here, laser-assisted self-organization has been used to form one- and two-dimensional (D) nanoarrays of Cu nanocrystals. Using these nanoarrays as a template, a 2D patterned ferromagnetic nanostructure of FeCrSi nanocrystals has been produced by heterogeneous nucleation and growth of nanocrystals by partial devitrification from an amorphous Fe{sub 64.5}Cr{sub 10}Si{sub 13.5}B{sub 9}Nb{sub 3} alloy with the Cu nanoparticles acting as catalytic nucleation sites. The interaction among the ferromagnetic nanocrystals via the residual amorphous matrix can be controlled by suitable choice of the amorphous alloy composition. Although demonstrated for a ferromagnetic system, the processing method may have much wider applicability for producing artificial nanostructures of a wide variety of materials when materials-specific catalysts and amorphous alloy compositions are judiciously chosen.

Patterned structures of in situ size controlled CdS nanocrystals in a polymer matrix under UV irradiation

International Nuclear Information System (INIS)

Fragouli, D; Pompa, P P; Caputo, G; Cingolani, R; Athanassiou, A; Resta, V; Laera, A M; Tapfer, L

2009-01-01

A method of in situ formation of patterns of size controlled CdS nanocrystals in a polymer matrix by pulsed UV irradiation is presented. The films consist of Cd thiolate precursors with different carbon chain lengths embedded in TOPAS polymer matrices. Under UV irradiation the precursors are photolyzed, driving to the formation of CdS nanocrystals in the quantum size regime, with size and concentration defined by the number of incident UV pulses, while the host polymer remains macroscopically/microscopically unaffected. The emission of the formed nanocomposite materials strongly depends on the dimensions of the CdS nanocrystals, thus, their growth at the different phases of the irradiation is monitored using spatially resolved photoluminescence by means of a confocal microscope. X-ray diffraction measurements verified the existence of the CdS nanocrystals, and defined their crystal structure for all the studied cases. The results are reinforced by transmission electron microscopy. It is proved that the selection of the precursor determines the efficiency of the procedure, and the quality of the formed nanocrystals. Moreover it is demonstrated that there is the possibility of laser induced formation of well-defined patterns of CdS nanocrystals, opening up new perspectives in the development of nanodevices.

Patterned structures of in situ size controlled CdS nanocrystals in a polymer matrix under UV irradiation

Energy Technology Data Exchange (ETDEWEB)

Fragouli, D; Pompa, P P; Caputo, G; Cingolani, R; Athanassiou, A [NNL-National Nanotechnology Laboratory, INFM, CNR, Via Arnesano, 73100 Lecce (Italy); Resta, V; Laera, A M; Tapfer, L [ENEA, Centro Ricerche Brindisi, SS7 Appia Km 706, I-72100 Brindisi (Italy)], E-mail: despina.fragouli@unile.it

2009-04-15

A method of in situ formation of patterns of size controlled CdS nanocrystals in a polymer matrix by pulsed UV irradiation is presented. The films consist of Cd thiolate precursors with different carbon chain lengths embedded in TOPAS polymer matrices. Under UV irradiation the precursors are photolyzed, driving to the formation of CdS nanocrystals in the quantum size regime, with size and concentration defined by the number of incident UV pulses, while the host polymer remains macroscopically/microscopically unaffected. The emission of the formed nanocomposite materials strongly depends on the dimensions of the CdS nanocrystals, thus, their growth at the different phases of the irradiation is monitored using spatially resolved photoluminescence by means of a confocal microscope. X-ray diffraction measurements verified the existence of the CdS nanocrystals, and defined their crystal structure for all the studied cases. The results are reinforced by transmission electron microscopy. It is proved that the selection of the precursor determines the efficiency of the procedure, and the quality of the formed nanocrystals. Moreover it is demonstrated that there is the possibility of laser induced formation of well-defined patterns of CdS nanocrystals, opening up new perspectives in the development of nanodevices.

Thermodynamic Study of the Interaction of Bovine Serum Albumin and Amino Acids with Cellulose Nanocrystals.

Science.gov (United States)

Lombardo, Salvatore; Eyley, Samuel; Schütz, Christina; van Gorp, Hans; Rosenfeldt, Sabine; Van den Mooter, Guy; Thielemans, Wim

2017-06-06

The interaction of bovine serum albumin (BSA) with sulfated, carboxylated, and pyridinium-grafted cellulose nanocrystals (CNCs) was studied as a function of the degree of substitution by determining the adsorption isotherm and by directly measuring the thermodynamics of interaction. The adsorption of BSA onto positively charged pyridinium-grafted cellulose nanocrystals followed Langmuirian adsorption with the maximum amount of adsorbed protein increasing linearly with increasing degree of substitution. The binding mechanism between the positively charged pyridinum-grafted cellulose nanocrystals and BSA was found to be endothermic and based on charge neutralization. A positive entropy of adsorption associated with an increase of the degree of disorder upon addition of BSA compensated for the unfavorable endothermic enthalpy and enabled formation of pyridinium-g-CNC-BSA complexes. The endothermic enthalpy of adsorption was further found to decrease as a function of increasing degree of substitution. Negatively charged cellulose nanocrystals bearing sulfate and/or carboxylic functionalities were found to not interact significantly with the BSA protein. To investigate in more detail the role of single amino acids in the adsorption of proteins onto cellulose nanocrystals, we also studied the interaction of different types of amino acids with CNCs, i.e., charged (lysine, aspartic acid), aromatic (tryptophan, tyrosine), and polar (serine) amino acids. We found that none of the single amino acids bound with CNCs irrespective of surface charge and that therefore the binding of proteins with CNCs appears to require larger amino acid sequences that induce a greater entropic contribution to stabilize binding. Single amino acids are thus not adsorbed onto cellulose nanocrystals.

Synthesis, Optical and Structural Properties of Copper Sulfide Nanocrystals from Single Molecule Precursors

Directory of Open Access Journals (Sweden)

Peter A. Ajibade

2017-02-01

Full Text Available We report the synthesis and structural studies of copper sulfide nanocrystals from copper (II dithiocarbamate single molecule precursors. The precursors were thermolysed in hexadecylamine (HDA to prepare HDA-capped CuS nanocrystals. The optical properties of the nanocrystals studied using UV–visible and photoluminescence spectroscopy showed absorption band edges at 287 nm that are blue shifted, and the photoluminescence spectra show emission curves that are red-shifted with respect to the absorption band edges. These shifts are as a result of the small crystallite sizes of the nanoparticles leading to quantum size effects. The structural studies were carried out using powder X-ray diffraction (XRD, transmission electron microscopy (TEM, scanning electron microscopy (SEM, energy dispersive X-ray spectroscopy (EDS, and atomic force microscopy. The XRD patterns indicates that the CuS nanocrystals are in hexagonal covellite crystalline phases with estimated particles sizes of 17.3–18.6 nm. The TEM images showed particles with almost spherical or rod shapes, with average crystallite sizes of 3–9.8 nm. SEM images showed morphology with ball-like microspheres on the surfaces, and EDS spectra confirmed the presence of CuS nanoparticles.

Azobenzene mesogens mediated preparation of SnS nanocrystals encapsulated with in-situ N-doped carbon and their enhanced electrochemical performance for lithium ion batteries application

International Nuclear Information System (INIS)

Wang Meng; Zhou Yang; Chen Dongzhong; Duan Junfei

2016-01-01

In this work, azobenzene mesogen-containing tin thiolates have been synthesized, which possess ordered lamellar structures persistent to higher temperature and serve as liquid crystalline precursors. Based on the preorganized tin thiolate precursors, SnS nanocrystals encapsulated with in-situ N-doped carbon layer have been achieved through a simple solventless pyrolysis process with the azobenzene mesogenic thiolate precursor served as Sn, S, N, and C sources simultaneously. Thus prepared nanocomposite materials as anode of lithium ion batteries present a large specific capacity of 604.6 mAh·g −1 at a current density of 100 mA·g −1 , keeping a high capacity retention up to 96% after 80 cycles, and display high rate capability due to the synergistic effect of well-dispersed SnS nanocrystals and N-doped carbon layer. Such encouraging results shed a light on the controlled preparation of advanced nanocomposites based on liquid crystalline metallomesogen precursors and may boost their novel intriguing applications. (special topic)

Enhancement of the photoelectric performance in inverted bulk heterojunction solid solar cell with inorganic nanocrystals

International Nuclear Information System (INIS)

Luan, Weiling; Zhang, Chengxi; Luo, Lingli; Yuan, Binxia; Jin, Lin; Kim, Yong-Sang

2017-01-01

Highlights: • Solid solar cells based on FeS_2 or PbS NCs showed power conversion efficiency (PCE) of 3.0% and 3.11%, respectively. • The FeS_2 NCs/polymer solar cells showed good time and thermal stability when exposed in air condition. • Ternary solid solar cells based on PbS NCs exhibited a higher short circuit current density (J_s_c). - Abstract: Nanocrystal/polymer solid solar cells have the advantages of low-cost, simple process, and flexible manufacture. In this work, ternary solid solar cells based on FeS_2 and PbS nanocrystals exhibited photovoltaic conversion efficiency of 3.0% and 3.1%, respectively. As a kind of semiconductor with optical absorption in the visible and near-infrared regions, FeS_2 nanocrystals matched well with the solar radiation spectrum. Furthermore, PbS Nanocrystals could increase the number of electrons, due to its multiple exciton effect. Additionally, the FeS_2 nanocrystals solar cells showed high stability, with 83.3% of its initial efficiency remained after 15 weeks of exposure in air, and kept good stable performance at 20–80 °C. The photovoltaic conversion efficiency fluctuation magnitudes were also found to be smaller than quantum-dot sensitized solar cell under the same conditions.

Confinement and surface effects on the physical properties of rhombohedral-shape hematite (α-Fe_2O_3) nanocrystals

International Nuclear Information System (INIS)

Luna, Carlos; Cuan-Guerra, Aída D.; Barriga-Castro, Enrique D.; Núñez, Nuria O.; Mendoza-Reséndez, Raquel

2016-01-01

Highlights: • Uniform rhombohedral hematite nanocrystals (RHNCs) have been obtained. • A detailed formation mechanism of these HNCS has been proposed. • Phonon confinement effects were revealed in the RHNCS vibrational bands. • Quantum confinement effects on the optical and electronic properties were found. - Abstract: Morphological, microstructural and vibrational properties of hematite (α-Fe_2O_3) nanocrystals with a rhombohedral shape and rounded edges, obtained by forced hydrolysis of iron(III) solutions under a fast nucleation, have been investigated in detail as a function of aging time. These studies allowed us to propose a detailed formation mechanism and revealed that these nanocrystals are composed of four {104} side facets, two {110} faces at the edges of the long diagonal of the nanocrystals and two {−441} facets as the top and bottom faces. Also, the presence of nanoscopic pores and fissures was evidenced. The vibrational bands of such nanocrystals were shifted to lower frequencies in comparison with bulk hematite ones as the nanocrystal size was reduced due to phonon confinement effects. Also, the indirect and direct transition band gaps displayed interesting dependences on the aging time arising from quantum confinement and surface effects

Drug nanocrystals for the formulation of poorly soluble drugs and its application as a potential drug delivery system

International Nuclear Information System (INIS)

Gao Lei; Zhang Dianrui; Chen Minghui

2008-01-01

Formulation of poorly soluble drugs is a general intractable problem in pharmaceutical field, especially those compounds poorly soluble in both aqueous and organic media. It is difficult to resolve this problem using conventional formulation approaches, so many drugs are abandoned early in discovery. Nanocrystals, a new carrier-free colloidal drug delivery system with a particle size ranging from 100 to 1000 nm, is thought as a viable drug delivery strategy to develop the poorly soluble drugs, because of their simplicity in preparation and general applicability. In this article, the product techniques of the nanocrystals were reviewed and compared, the special features of drug nanocrystals were discussed. The researches on the application of the drug nanocrystals to various administration routes were described in detail. In addition, as introduced later, the nanocrystals could be easily scaled up, which was the prerequisite to the development of a delivery system as a market product

Formation Mechanism of Ge Nanocrystals Embedded in SiO2 Studied by Fluorescence X-Ray Absorption Fine Structure

International Nuclear Information System (INIS)

Yan Wensheng; Li Zhongrui; Sun Zhihu; Wei Shiqiang; Kolobov, A. V.

2007-01-01

The formation mechanism of Ge nanocrystals for Ge (60 mol%) embedded in a SiO2 matrix grown on Si(001) and quartz-glass substrates was studied by fluorescence x-ray absorption fine structure (XAFS). It was found that the formation of Ge nanocrystals strongly depends on the properties of the substrate materials. In the as-prepared samples, Ge atoms exist in amorphous Ge and GeO2 phases. At the annealing temperature of 1073 K, on the quartz-glass substrate, Ge nanocrystals are only formed predominantly from the amorphous Ge phase in the as-prepared sample. However, on the Si(100) substrate the Ge nanocrystals are generated partly from amorphous Ge, and partly from GeO2 phases through the permutation reaction with Si substrate. Quantitative analysis revealed that about 10% of GeO2 in as-prepared sample permutated with Si in the wafer and formed Ge nanocrystals

Probing the structure of CuInS{sub 2}-ZnS core-shell and similar nanocrystals by Raman spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Dzhagan, Volodymyr, E-mail: dzhagan@isp.kiev.ua [Semiconductor Physics, Technische Universität Chemnitz, 09107 Chemnitz (Germany); V. E. Lashkaryov Institute of Semiconductors Physics, National Academy of Sciences of Ukraine, Kyiv 03028 (Ukraine); Kempken, Björn [Energy and Semiconductor Research Laboratory, Department of Physics, Carl von Ossietzky University of Oldenburg, 26111 Oldenburg (Germany); Valakh, Mykhailo [V. E. Lashkaryov Institute of Semiconductors Physics, National Academy of Sciences of Ukraine, Kyiv 03028 (Ukraine); Parisi, Jürgen; Kolny-Olesiak, Joanna [Energy and Semiconductor Research Laboratory, Department of Physics, Carl von Ossietzky University of Oldenburg, 26111 Oldenburg (Germany); Zahn, Dietrich R.T. [Semiconductor Physics, Technische Universität Chemnitz, 09107 Chemnitz (Germany)

2017-02-15

CuInS{sub 2}/ZnS core-shell and alloyed nanocrystals (NCs) are promising candidates for applications in biolabeling, photocatalysis, solar energy conversion, and light emitting diodes. The growth mechanism and subsequent internal structure of such heterogeneous NCs are therefore of crucial importance, as it strongly affects their optical and electronic properties. Here, we investigated using resonant Raman spectroscopy the structure of CuInS{sub 2}/ZnS and Cu-Zn-In-S/ZnS core-shell NCs, as well as the evolution of Cu{sub 2−x}S NCs into CuInS{sub 2}via the heterogeneous Cu{sub 2−x}S/CuInS{sub 2} phase. We demonstrate that the particular phases can be distinguished based on their characteristic Raman modes and tuning the exciting laser energy into resonance with the bandgap of the particular phase.

Electrical resistivity of nanocrystals in Fe-Al-Ga-P-B-Si-Cu alloy

International Nuclear Information System (INIS)

Pekala, K.; Jaskiewicz, P.; Nowinski, J.L.; Pekala, M.

2003-01-01

In new supercooled Fe 74 Al 4 Ga 2 P 11 B 4 Si 4 Cu 1 alloy the 10 nm size α-Fe(Si) nanocrystals are precipitated. Thermal stability is analyzed by the electron transport and magnetization measurements. Temperature variation of electrical resistivity of nanocrystals is determined and discussed for alloys with different initial crystalline fraction. Possible mechanism inhibiting the grain growth is presented

Grafted SiC nanocrystals

DEFF Research Database (Denmark)

Saini, Isha; Sharma, Annu; Dhiman, Rajnish

2017-01-01