Direct Bandgap Group IV Materials

Science.gov (United States)

2016-01-21

AFRL-AFOSR-JP-TR-2017-0049 Direct Bandgap group IV Materials Hung Hsiang Cheng NATIONAL TAIWAN UNIVERSITY Final Report 01/21/2016 DISTRIBUTION A...NAME(S) AND ADDRESS(ES) NATIONAL TAIWAN UNIVERSITY 1 ROOSEVELT RD. SEC. 4 TAIPEI CITY, 10617 TW 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING...14. ABSTRACT Direct bandgap group IV materials have been long sought for in both academia and industry for the implementation of photonic devices

Densely Aligned Graphene Nanoribbon Arrays and Bandgap Engineering

Energy Technology Data Exchange (ETDEWEB)

Su, Justin [Stanford Univ., CA (United States); Chen, Changxin [Stanford Univ., CA (United States); Gong, Ming [Stanford Univ., CA (United States); Kenney, Michael [Stanford Univ., CA (United States)

2017-01-04

Graphene has attracted great interest for future electronics due to its high mobility and high thermal conductivity. However, a two-dimensional graphene sheet behaves like a metal, lacking a bandgap needed for the key devices components such as field effect transistors (FETs) in digital electronics. It has been shown that, partly due to quantum confinement, graphene nanoribbons (GNRs) with ~2 nm width can open up sufficient bandgaps and evolve into semiconductors to exhibit high on/off ratios useful for FETs. However, a challenging problem has been that, such ultra-narrow GNRs (~2 nm) are difficult to fabricate, especially for GNRs with smooth edges throughout the ribbon length. Despite high on/off ratios, these GNRs show very low mobility and low on-state conductance due to dominant scattering effects by imperfections and disorders at the edges. Wider GNRs (>5 nm) show higher mobility, higher conductance but smaller bandgaps and low on/off ratios undesirable for FET applications. It is highly desirable to open up bandgaps in graphene or increase the bandgaps in wide GNRs to afford graphene based semiconductors for high performance (high on-state current and high on/off ratio) electronics. Large scale ordering and dense packing of such GNRs in parallel are also needed for device integration but have also been challenging thus far. It has been shown theoretically that uniaxial strains can be applied to a GNR to engineer its bandgap. The underlying physics is that under uniaxial strain, the Dirac point moves due to stretched C-C bonds, leading to an increase in the bandgap of armchair GNRs by up to 50% of its original bandgap (i.e. bandgap at zero strain). For zigzag GNRs, due to the existence of the edge states, changes of bandgap are smaller under uniaxial strain and can be increased by ~30%. This work proposes a novel approach to the fabrication of densely aligned graphene nanoribbons with highly smooth edges afforded by anisotropic etching and uniaxial strain for

True photonic band-gap mode-control in VCSEL structures

DEFF Research Database (Denmark)

Romstad, F.; Madsen, M.; Birkedal, Dan

2003-01-01

Photonic band-gap mode confinement in novel nano-structured large area VCSEL structures is confirmed by the amplified spontaneous emission spectrum. Both guide and anti-guide VCSEL structures are experimentally characterised to verify the photonic band-gap effect.......Photonic band-gap mode confinement in novel nano-structured large area VCSEL structures is confirmed by the amplified spontaneous emission spectrum. Both guide and anti-guide VCSEL structures are experimentally characterised to verify the photonic band-gap effect....

Wide Bandgap Extrinsic Photoconductive Switches

Energy Technology Data Exchange (ETDEWEB)

Sullivan, James S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

2013-07-03

Semi-insulating Gallium Nitride, 4H and 6H Silicon Carbide are attractive materials for compact, high voltage, extrinsic, photoconductive switches due to their wide bandgap, high dark resistance, high critical electric field strength and high electron saturation velocity. These wide bandgap semiconductors are made semi-insulating by the addition of vanadium (4H and 6HSiC) and iron (2H-GaN) impurities that form deep acceptors. These deep acceptors trap electrons donated from shallow donor impurities. The electrons can be optically excited from these deep acceptor levels into the conduction band to transition the wide bandgap semiconductor materials from a semi-insulating to a conducting state. Extrinsic photoconductive switches with opposing electrodes have been constructed using vanadium compensated 6H-SiC and iron compensated 2H-GaN. These extrinsic photoconductive switches were tested at high voltage and high power to determine if they could be successfully used as the closing switch in compact medical accelerators.

Bandgap Optimization of Perovskite Semiconductors for Photovoltaic Applications.

Science.gov (United States)

Xiao, Zewen; Zhou, Yuanyuan; Hosono, Hideo; Kamiya, Toshio; Padture, Nitin P

2018-02-16

The bandgap is the most important physical property that determines the potential of semiconductors for photovoltaic (PV) applications. This Minireview discusses the parameters affecting the bandgap of perovskite semiconductors that are being widely studied for PV applications, and the recent progress in the optimization of the bandgaps of these materials. Perspectives are also provided for guiding future research in this area. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wide bandgap engineering of (AlGa)2O3 films

International Nuclear Information System (INIS)

Zhang, Fabi; Saito, Katsuhiko; Tanaka, Tooru; Nishio, Mitsuhiro; Guo, Qixin; Arita, Makoto

2014-01-01

Bandgap tunable (AlGa) 2 O 3 films were deposited on sapphire substrates by pulsed laser deposition (PLD). The deposited films are of high transmittance as measured by spectrophotometer. The Al content in films is almost the same as that in targets. The measurement of bandgap energies by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy is proved to be valid for determining the bandgap of (AlGa) 2 O 3 films as it is in good agreement with the bandgap values from transmittance spectra. The measured bandgap of (AlGa) 2 O 3 films increases continuously with the Al content covering the whole Al content range from about 5 to 7 eV, indicating PLD is a promising growth technology for growing bandgap tunable (AlGa) 2 O 3 films.

High-efficiency, monolithic, multi-bandgap, tandem photovoltaic energy converters

Science.gov (United States)

Wanlass, Mark W [Golden, CO

2011-11-29

A monolithic, multi-bandgap, tandem solar photovoltaic converter has at least one, and preferably at least two, subcells grown lattice-matched on a substrate with a bandgap in medium to high energy portions of the solar spectrum and at least one subcell grown lattice-mismatched to the substrate with a bandgap in the low energy portion of the solar spectrum, for example, about 1 eV.

Terahertz spectroscopy of three-dimensional photonic band-gap crystals

International Nuclear Information System (INIS)

Oezbay, E.; Michel, E.; Tuttle, G.; Biswas, R.; Ho, K.M.; Bostak, J.; Bloom, D.M.

1994-01-01

We have fabricated and built three-dimensional photonic band-gap crystals with band-gap frequencies larger than 500 GHz. We built the crystals by stacking micromachined (110) silicon wafers. The transmission and dispersion characteristics of the structures were measured by an all-electronic terahertz spectroscopy setup. The experimental results were in good agreement with theoretical calculations. To our knowledge, our new crystal has the highest reported photonic band-gap frequency

Tensile-strain effect of inducing the indirect-to-direct band-gap transition and reducing the band-gap energy of Ge

Energy Technology Data Exchange (ETDEWEB)

Inaoka, Takeshi, E-mail: inaoka@phys.u-ryukyu.ac.jp; Furukawa, Takuro; Toma, Ryo; Yanagisawa, Susumu [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan)

2015-09-14

By means of a hybrid density-functional method, we investigate the tensile-strain effect of inducing the indirect-to-direct band-gap transition and reducing the band-gap energy of Ge. We consider [001], [111], and [110] uniaxial tensility and (001), (111), and (110) biaxial tensility. Under the condition of no normal stress, we determine both normal compression and internal strain, namely, relative displacement of two atoms in the primitive unit cell, by minimizing the total energy. We identify those strain types which can induce the band-gap transition, and evaluate the critical strain coefficient where the gap transition occurs. Either normal compression or internal strain operates unfavorably to induce the gap transition, which raises the critical strain coefficient or even blocks the transition. We also examine how each type of tensile strain decreases the band-gap energy, depending on its orientation. Our analysis clearly shows that synergistic operation of strain orientation and band anisotropy has a great influence on the gap transition and the gap energy.

Electrically tunable liquid crystal photonic bandgap fiber laser

DEFF Research Database (Denmark)

Olausson, Christina Bjarnal Thulin; Scolari, Lara; Wei, Lei

2010-01-01

We demonstrate electrical tunability of a fiber laser by using a liquid crystal photonic bandgap fiber. Tuning of the laser is achieved by combining the wavelength filtering effect of a liquid crystal photonic bandgap fiber device with an ytterbium-doped photonic crystal fiber. We fabricate an al...

An Unusual Strong Visible-Light Absorption Band in Red Anatase TiO2 Photocatalyst Induced by Atomic Hydrogen-Occupied Oxygen Vacancies.

Science.gov (United States)

Yang, Yongqiang; Yin, Li-Chang; Gong, Yue; Niu, Ping; Wang, Jian-Qiang; Gu, Lin; Chen, Xingqiu; Liu, Gang; Wang, Lianzhou; Cheng, Hui-Ming

2018-02-01

Increasing visible light absorption of classic wide-bandgap photocatalysts like TiO 2 has long been pursued in order to promote solar energy conversion. Modulating the composition and/or stoichiometry of these photocatalysts is essential to narrow their bandgap for a strong visible-light absorption band. However, the bands obtained so far normally suffer from a low absorbance and/or narrow range. Herein, in contrast to the common tail-like absorption band in hydrogen-free oxygen-deficient TiO 2 , an unusual strong absorption band spanning the full spectrum of visible light is achieved in anatase TiO 2 by intentionally introducing atomic hydrogen-mediated oxygen vacancies. Combining experimental characterizations with theoretical calculations reveals the excitation of a new subvalence band associated with atomic hydrogen filled oxygen vacancies as the origin of such band, which subsequently leads to active photo-electrochemical water oxidation under visible light. These findings could provide a powerful way of tailoring wide-bandgap semiconductors to fully capture solar light. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Advances in photonic bandgap fiber functionality

DEFF Research Database (Denmark)

Lyngsøe, Jens Kristian

In order to take advantage of the many intriguing optical properties of photonic bandgap fibers, there are some technological challenges that have to be addressed. Among other things this includes transmission loss and the fibers ability to maintain field polarization. The work presented in this ......In order to take advantage of the many intriguing optical properties of photonic bandgap fibers, there are some technological challenges that have to be addressed. Among other things this includes transmission loss and the fibers ability to maintain field polarization. The work presented...

Wide Bandgap Extrinsic Photoconductive Switches

Energy Technology Data Exchange (ETDEWEB)

Sullivan, James S. [State Univ. of New York (SUNY), Plattsburgh, NY (United States); Univ. of California, Davis, CA (United States)

2012-01-20

Photoconductive semiconductor switches (PCSS) have been investigated since the late 1970s. Some devices have been developed that withstand tens of kilovolts and others that switch hundreds of amperes. However, no single device has been developed that can reliably withstand both high voltage and switch high current. Yet, photoconductive switches still hold the promise of reliable high voltage and high current operation with subnanosecond risetimes. Particularly since good quality, bulk, single crystal, wide bandgap semiconductor materials have recently become available. In this chapter we will review the basic operation of PCSS devices, status of PCSS devices and properties of the wide bandgap semiconductors 4H-SiC, 6H-SiC and 2H-GaN.

Optimum design of band-gap beam structures

DEFF Research Database (Denmark)

Olhoff, Niels; Niu, Bin; Cheng, Gengdong

2012-01-01

The design of band-gap structures receives increasing attention for many applications in mitigation of undesirable vibration and noise emission levels. A band-gap structure usually consists of a periodic distribution of elastic materials or segments, where the propagation of waves is impeded...... or significantly suppressed for a range of external excitation frequencies. Maximization of the band-gap is therefore an obvious objective for optimum design. This problem is sometimes formulated by optimizing a parameterized design model which assumes multiple periodicity in the design. However, it is shown...... in the present paper that such an a priori assumption is not necessary since, in general, just the maximization of the gap between two consecutive natural frequencies leads to significant design periodicity. The aim of this paper is to maximize frequency gaps by shape optimization of transversely vibrating...

Doped phosphorene for hydrogen capture: A DFT study

Science.gov (United States)

Zhang, Hong-ping; Hu, Wei; Du, Aijun; Lu, Xiong; Zhang, Ya-ping; Zhou, Jian; Lin, Xiaoyan; Tang, Youhong

2018-03-01

Hydrogen capture and storage is the core of hydrogen energy application. With its high specific surface area, direct bandgap, and variety of potential applications, phosphorene has attracted much research interest. In this study, density functional theory (DFT) is utilized to study the interactions between doped phosphorenes and hydrogen molecules. The effects of different dopants and metallic or nonmetallic atoms on phosphorene/hydrogen interactions is systematically studied by adsorption energy, electron density difference, partial density of states analysis, and Hirshfeld population. Our results indicate that the metallic dopants Pt, Co, and Ni can help to improve the hydrogen capture ability of phosphorene, whereas the nonmetallic dopants have no effect on it. Among the various metallic dopants, Pt performs very differently, such that it can help to dissociate H2 on phosphorene. Specified doped phosphorene could be a promising candidate for hydrogen storage, with behaviors superior to those of intrinsic graphene sheet.

Micromachined millimeter-wave photonic band-gap crystals

International Nuclear Information System (INIS)

Oezbay, E.; Michel, E.; Tuttle, G.; Biswas, R.; Sigalas, M.; Ho, K.

1994-01-01

We have developed a new technique for fabricating three-dimensional photonic band-gap crystals. Our method utilizes an orderly stacking of micromachined (110) silicon wafers to build the periodic structure. A structure with a full three-dimensional photonic band gap centered near 100 GHz was measured, with experimental results in good agreement with theoretical predictions. This basic approach described should be extendable to build structures with photonic band-gap frequencies ranging from 30 GHz to 3 THz

Thermal tunability of photonic bandgaps in liquid crystal infiltrated microstructured polymer optical fibers

DEFF Research Database (Denmark)

Yuan, Scott Wu; Wei, Lei; Alkeskjold, Thomas Tanggaard

2009-01-01

We demonstrate the photonic bandgap effect and the thermal tunability of bandgaps in microstructured polymer optical fibers infiltrated with liquid crystal. Two liquid crystals with opposite sign of the temperature gradient of the ordinary refractive index (E7 and MDA-00- 1444) are used to demons......We demonstrate the photonic bandgap effect and the thermal tunability of bandgaps in microstructured polymer optical fibers infiltrated with liquid crystal. Two liquid crystals with opposite sign of the temperature gradient of the ordinary refractive index (E7 and MDA-00- 1444) are used...... to demonstrate that both signs of the thermal tunability of the bandgaps are possible. The useful bandgaps are ultimately bounded to the visible range by the transparency window of the polymer....

Recent Advances in Wide-Bandgap Photovoltaic Polymers.

Science.gov (United States)

Cai, Yunhao; Huo, Lijun; Sun, Yanming

2017-06-01

The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fullerene-based low-density superhard materials with tunable bandgaps

Science.gov (United States)

Cao, Ai-Hua; Zhao, Wen-Juan; Gan, Li-Hua

2018-06-01

Four carbon allotropes built from tetrahedral symmetrical fullerenes C28 and C40 are predicted to be superhard materials with mass density around that of water, and all of them are porous semiconductors. Both the bandgaps and hardness decrease with increasing ratio of sp2 hybridized carbon atoms. The mechanical and thermodynamic stabilities of C28- and C40-based allotropes at zero pressure are confirmed by a variety of state-of-the-art theoretical calculations. The evolution trend of bandgap found here suggests that one can obtain low-density hard materials with tunable bandgaps by substituting the carbon atom in diamond with different Td-symmetrical non-IPR fullerene Cn.

Cat-CVD-prepared oxygen-rich μc-Si:H for wide-bandgap material

International Nuclear Information System (INIS)

Matsumoto, Yasuhiro; Ortega, Mauricio; Peza, Juan-Manuel; Reyes, Mario-Alfredo; Escobosa, Arturo

2005-01-01

Microcrystalline phase-involved oxygen-rich a-Si:H (hydrogenated amorphous silicon) films have been obtained using catalytic chemical vapor deposition (Cat-CVD) process. Pure SiH 4 (silane), H 2 (hydrogen), and O 2 (oxygen) gases were introduced in the chamber by maintaining a pressure of 0.1 Torr. A tungsten catalyzer was fixed at temperatures of 1750 and 1950 deg. C for film deposition on glass and crystalline silicon substrates at 200 deg. C. As revealed from X-ray diffraction spectra, the microcrystalline phase appears for oxygen-rich a-Si:H samples deposited at a catalyzer temperature of 1950 deg. C. However, this microcrystalline phase tends to disappear for further oxygen incorporation. The oxygen content in the deposited films was corroborated by FTIR analysis revealing Si-O-Si bonds and typical Si-H bonding structures. The optical bandgap of the sample increases from 2.0 to 2.7 eV with oxygen gas flow and oxygen incorporation to the deposited films. In the present thin film deposition conditions, no strong tungsten filament degradation was observed after a number of sample preparations

Research on bandgaps in two-dimensional phononic crystal with two resonators.

Science.gov (United States)

Gao, Nansha; Wu, Jiu Hui; Yu, Lie

2015-02-01

In this paper, the bandgap properties of a two-dimensional phononic crystal with the two resonators is studied and embedded in a homogenous matrix. The resonators are not connected with the matrix but linked with connectors directly. The dispersion relationship, transmission spectra, and displacement fields of the eigenmodes of this phononic crystal are studied with finite-element method. In contrast to the phononic crystals with one resonators and hollow structure, the proposed structures with two resonators can open bandgaps at lower frequencies. This is a very interesting and useful phenomenon. Results show that, the opening of the bandgaps is because of the local resonance and the scattering interaction between two resonators and matrix. An equivalent spring-pendulum model can be developed in order to evaluate the frequencies of the bandgap edge. The study in this paper is beneficial to the design of opening and tuning bandgaps in phononic crystals and isolators in low-frequency range. Copyright © 2014 Elsevier B.V. All rights reserved.

New Light-Harvesting Materials Using Accurate and Efficient Bandgap Calculations

DEFF Research Database (Denmark)

Castelli, Ivano Eligio; Hüser, Falco; Pandey, Mohnish

2014-01-01

Electronic bandgap calculations are presented for 2400 experimentally known materials from the Materials Project database and the bandgaps, obtained with different types of functionals within density functional theory and (partial) self-consistent GW approximation, are compared for 20 randomly...

Analysis of phononic bandgap structures with dissipation

DEFF Research Database (Denmark)

Andreassen, Erik; Jensen, Jakob Søndergaard

2013-01-01

and longer wavelengths, we show that the two formulations produce nearly identical results in terms of propagation constant and wave decay. We use the k(ω)-formulation to compute loss factors with dissipative bandgap materials for steady-state wave propagation and create simplified diagrams that unify...... the spatial loss factor from dissipative and bandgap effects. Additionally, we demonstrate the applicability of the k(ω)-formulation for the computation of the band diagram for viscoelastic composites and compare the computed loss factors for low frequency wave propagation to existing results based on quasi...

Strain-Modulated Bandgap and Piezo-Resistive Effect in Black Phosphorus Field-Effect Transistors.

Science.gov (United States)

Zhang, Zuocheng; Li, Likai; Horng, Jason; Wang, Nai Zhou; Yang, Fangyuan; Yu, Yijun; Zhang, Yu; Chen, Guorui; Watanabe, Kenji; Taniguchi, Takashi; Chen, Xian Hui; Wang, Feng; Zhang, Yuanbo

2017-10-11

Energy bandgap largely determines the optical and electronic properties of a semiconductor. Variable bandgap therefore makes versatile functionality possible in a single material. In layered material black phosphorus, the bandgap can be modulated by the number of layers; as a result, few-layer black phosphorus has discrete bandgap values that are relevant for optoelectronic applications in the spectral range from red, in monolayer, to mid-infrared in the bulk limit. Here, we further demonstrate continuous bandgap modulation by mechanical strain applied through flexible substrates. The strain-modulated bandgap significantly alters the density of thermally activated carriers; we for the first time observe a large piezo-resistive effect in black phosphorus field-effect transistors (FETs) at room temperature. The effect opens up opportunities for future development of electromechanical transducers based on black phosphorus, and we demonstrate an ultrasensitive strain gauge constructed from black phosphorus thin crystals.

Efficient CsF interlayer for high and low bandgap polymer solar cell

Science.gov (United States)

Mitul, Abu Farzan; Sarker, Jith; Adhikari, Nirmal; Mohammad, Lal; Wang, Qi; Khatiwada, Devendra; Qiao, Qiquan

2018-02-01

Low bandgap polymer solar cells have a great deal of importance in flexible photovoltaic market to absorb sun light more efficiently. Efficient wide bandgap solar cells are always available in nature to absorb visible photons. The development and incorporation of infrared photovoltaics (IR PV) with wide bandgap solar cells can improve overall solar device performance. Here, we have developed an efficient low bandgap polymer solar cell with CsF as interfacial layer in regular structure. Polymer solar cell devices with CsF shows enhanced performance than Ca as interfacial layer. The power conversion efficiency of 4.5% has been obtained for PDPP3T based polymer solar cell with CsF as interlayer. Finally, an optimal thickness with CsF as interfacial layer has been found to improve the efficiency in low bandgap polymer solar cells.

Single-graded CIGS with narrow bandgap for tandem solar cells.

Science.gov (United States)

Feurer, Thomas; Bissig, Benjamin; Weiss, Thomas P; Carron, Romain; Avancini, Enrico; Löckinger, Johannes; Buecheler, Stephan; Tiwari, Ayodhya N

2018-01-01

Multi-junction solar cells show the highest photovoltaic energy conversion efficiencies, but the current technologies based on wafers and epitaxial growth of multiple layers are very costly. Therefore, there is a high interest in realizing multi-junction tandem devices based on cost-effective thin film technologies. While the efficiency of such devices has been limited so far because of the rather low efficiency of semitransparent wide bandgap top cells, the recent rise of wide bandgap perovskite solar cells has inspired the development of new thin film tandem solar devices. In order to realize monolithic, and therefore current-matched thin film tandem solar cells, a bottom cell with narrow bandgap (~1 eV) and high efficiency is necessary. In this work, we present Cu(In,Ga)Se 2 with a bandgap of 1.00 eV and a maximum power conversion efficiency of 16.1%. This is achieved by implementing a gallium grading towards the back contact into a CuInSe 2 base material. We show that this modification significantly improves the open circuit voltage but does not reduce the spectral response range of these devices. Therefore, efficient cells with narrow bandgap absorbers are obtained, yielding the high current density necessary for thin film multi-junction solar cells.

Transmission properties of hollow-core photonic bandgap fibers

DEFF Research Database (Denmark)

Falk, Charlotte Ijeoma; Hald, Jan; Petersen, Jan C.

2010-01-01

Variations in optical transmission of four types of hollow-core photonic bandgap fibers are measured as a function of laser frequency. These variations influence the potential accuracy of gas sensors based on molecular spectroscopy in hollow-core fibers.......Variations in optical transmission of four types of hollow-core photonic bandgap fibers are measured as a function of laser frequency. These variations influence the potential accuracy of gas sensors based on molecular spectroscopy in hollow-core fibers....

Ultrasensitive tunability of the direct bandgap of 2D InSe flakes via strain engineering

Science.gov (United States)

Li, Yang; Wang, Tianmeng; Wu, Meng; Cao, Ting; Chen, Yanwen; Sankar, Raman; Ulaganathan, Rajesh K.; Chou, Fangcheng; Wetzel, Christian; Xu, Cheng-Yan; Louie, Steven G.; Shi, Su-Fei

2018-04-01

InSe, a member of the layered materials family, is a superior electronic and optical material which retains a direct bandgap feature from the bulk to atomically thin few-layers and high electronic mobility down to a single layer limit. We, for the first time, exploit strain to drastically modify the bandgap of two-dimensional (2D) InSe nanoflakes. We demonstrated that we could decrease the bandgap of a few-layer InSe flake by 160 meV through applying an in-plane uniaxial tensile strain to 1.06% and increase the bandgap by 79 meV through applying an in-plane uniaxial compressive strain to 0.62%, as evidenced by photoluminescence (PL) spectroscopy. The large reversible bandgap change of ~239 meV arises from a large bandgap change rate (bandgap strain coefficient) of few-layer InSe in response to strain, ~154 meV/% for uniaxial tensile strain and ~140 meV/% for uniaxial compressive strain, representing the most pronounced uniaxial strain-induced bandgap strain coefficient experimentally reported in 2D materials. We developed a theoretical understanding of the strain-induced bandgap change through first-principles DFT and GW calculations. We also confirmed the bandgap change by photoconductivity measurements using excitation light with different photon energies. The highly tunable bandgap of InSe in the infrared regime should enable a wide range of applications, including electro-mechanical, piezoelectric and optoelectronic devices.

Bandgap Engineering of Double Perovskites for One- and Two-photon Water Splitting

DEFF Research Database (Denmark)

Castelli, Ivano Eligio; Thygesen, Kristian Sommer; Jacobsen, Karsten Wedel

2013-01-01

Computational screening is becoming increasingly useful in the search for new materials. We are interested in the design of new semiconductors to be used for light harvesting in a photoelectrochemical cell. In the present paper, we study the double perovskite structures obtained by combining 46...... stable cubic perovskites which was found to have a finite bandgap in a previous screening-study. The four-metal double perovskite space is too large to be investigated completely. For this reason we propose a method for combining different metals to obtain a desired bandgap. We derive some bandgap design...... rules on how to combine two cubic perovskites to generate a new combination with a larger or smaller bandgap compared with the constituent structures. Those rules are based on the type of orbitals involved in the conduction bands and on the size of the two cubic bandgaps. We also see that a change...

Optically controlled photonic bandgap structures for microstrip circuits

International Nuclear Information System (INIS)

Cadman, Darren Arthur

2003-01-01

This thesis is concerned with the optical control of microwave photonic bandgap circuits using high resistivity silicon. Photoconducting processes that occur within silicon are investigated. The influence of excess carrier density on carrier mobility and lifetime is examined. In addition, electron-hole pair recombination mechanisms (Shockley-Read-Hall, Auger, radiative and surface) are investigated. The microwave properties of silicon are examined, in particular the variation of silicon reflectivity with excess carrier density. Filtering properties of microstrip photonic bandgap structures and how they may be controlled optically are studied. A proof-of-concept microstrip photonic bandgap structure with optical control is designed, simulated and measured. With no optical illumination incident upon the silicon, the microstrip photonic bandgap structure's filtering properties are well-defined; a 3dB stopband width of 2.6GHz, a 6dB bandwidth of 2GHz and stopband depth of -11.6dB at the centre frequency of 9.9GHz. When the silicon is illuminated, the structure's filtering properties are suppressed. Under illumination the experimental results display an increase in S 21 of 6.5dB and a reduction in S 11 of more than 10dB at 9.9GHz. A comparison of measured and simulated results reveal that the photogenerated excess carrier density is between 4 x 10 15 cm -3 and 1.1 x 10 16 cm -3 . (author)

Liquid Crystal photonic Bandgap Fiber Devices

DEFF Research Database (Denmark)

Wei, Lei

In this Ph.D. thesis, an experimental investigation of liquid crystal photonic bandgap (LCPBG) fiber devices and applications is presented. Photonic crystal fibers (PCFs) consist of a cladding microstructure with periodic index variations and a core defined by a defect of the structure. The prese......In this Ph.D. thesis, an experimental investigation of liquid crystal photonic bandgap (LCPBG) fiber devices and applications is presented. Photonic crystal fibers (PCFs) consist of a cladding microstructure with periodic index variations and a core defined by a defect of the structure...... of each LCPBG fiber. Finally, the applications for LCPBG fiber devices based on the on-chip platform design have been demonstrated in realizing microwave true-time delay and creating an electrically tunable fiber laser. Referatet mailes...

Water-Dependent Photonic Bandgap in Silica Artificial Opals

OpenAIRE

Gallego-Gomez, Francisco; Blanco, Alvaro; Canalejas-Tejero, Victor; Lopez, Cefe

2011-01-01

Some characteristics of silica-based structuresa-like the photonic properties of artificial opals formed by silica spheresa-can be greatly affected by the presence of adsorbed water. The reversible modification of the water content of an opal is investigated here by moderate heating (below 300 °C) and measuring in situ the changes in the photonic bandgap. Due to reversible removal of interstitial water, large blueshifts of 30 nm and a bandgap narrowing of 7% are observed. The latter is partic...

Surface- and interface-engineered heterostructures for solar hydrogen generation

Science.gov (United States)

Chen, Xiangyan; Li, Yanrui; Shen, Shaohua

2018-04-01

Photoelectrochemical (PEC) water splitting based on semiconductor photoelectrodes provides a promising platform for reducing environmental pollution and solving the energy crisis by developing clean, sustainable and environmentally friendly hydrogen energy. In this context, metal oxides with their advantages including low cost, good chemical stability and environmental friendliness, have attracted extensive attention among the investigated candidates. However, the large bandgap, poor charge transfer ability and high charge recombination rate limit the PEC performance of metal oxides as photoelectrodes. To solve this limitation, many approaches toward enhanced PEC water splitting performance, which focus on surface and interface engineering, have been presented. In this topical review, we concentrate on the heterostructure design of some typical metal oxides with narrow bandgaps (e.g. Fe2O3, WO3, BiVO4 and Cu2O) as photoelectrodes. An overview of the surface- and interface-engineered heterostructures, including semiconductor heterojunctions, surface protection, surface passivation and cocatalyst decoration, will be given to introduce the recent advances in metal oxide heterostructures for PEC water splitting. This article aims to provide fundamental references and principles for designing metal oxide heterostructures with high activity and stability as photoelectrodes for PEC solar hydrogen generation.

Physical properties and analytical models of band-to-band tunneling in low-bandgap semiconductors

International Nuclear Information System (INIS)

Shih, Chun-Hsing; Dang Chien, Nguyen

2014-01-01

Low-bandgap semiconductors, such as InAs and InSb, are widely considered to be ideal for use in tunnel field-effect transistors to ensure sufficient on-current boosting at low voltages. This work elucidates the physical and mathematical considerations of applying conventional band-to-band tunneling models in low-bandgap semiconductors, and presents a new analytical alternative for practical use. The high-bandgap tunneling generates most at maximum field region with shortest tunnel path, whereas the low-bandgap generations occur dispersedly because of narrow tunnel barrier. The local electrical field associated with tunneling-electron numbers dominates in low-bandgap materials. This work proposes decoupled electric-field terms in the pre-exponential factor and exponential function of generation-rate expressions. Without fitting, the analytical results and approximated forms exhibit great agreements with the sophisticated forms both in high- and low-bandgap semiconductors. Neither nonlocal nor local field is appropriate to be used in numerical simulations for predicting the tunneling generations in a variety of low- and high-bandgap semiconductors

Multi-fidelity machine learning models for accurate bandgap predictions of solids

International Nuclear Information System (INIS)

Pilania, Ghanshyam; Gubernatis, James E.; Lookman, Turab

2016-01-01

Here, we present a multi-fidelity co-kriging statistical learning framework that combines variable-fidelity quantum mechanical calculations of bandgaps to generate a machine-learned model that enables low-cost accurate predictions of the bandgaps at the highest fidelity level. Additionally, the adopted Gaussian process regression formulation allows us to predict the underlying uncertainties as a measure of our confidence in the predictions. In using a set of 600 elpasolite compounds as an example dataset and using semi-local and hybrid exchange correlation functionals within density functional theory as two levels of fidelities, we demonstrate the excellent learning performance of the method against actual high fidelity quantum mechanical calculations of the bandgaps. The presented statistical learning method is not restricted to bandgaps or electronic structure methods and extends the utility of high throughput property predictions in a significant way.

Effect of hydrogen on the diode properties of reactively sputtered amorphous silicon Schottky barrier structures

International Nuclear Information System (INIS)

Morel, D.L.; Moustakas, T.D.

1981-01-01

The diode properties of reactively sputtered hydrogenated amorphous silicon Schottky barrier structures (a-SiH/sub x/ /Pt) have been investigated. We find a systematic relation between the changes in the open circuit voltage, the barrier height, and the diode quality factor. These results are accounted for by assuming that hydrogen incorporation into the amorphous silicon network removes states from the top of the valence band and sharpens the valence-band tail. Interfacial oxide layers play a significant role in the low hydrogen content, and low band-gap regime

Resonance fluorescence spectrum in a two-band photonic bandgap crystal

Science.gov (United States)

Lee, Ray-Kuang; Lai, Yinchieh

2003-05-01

Steady state resonance fluorescence spectra from a two-level atom embedded in a photonic bandgap crystal and resonantly driven by a classical pump light are calculated. The photonic crystal is considered to be with a small bandgap which is in the order of magnitude of the Rabi frequency and is modeled by the anisotropic two-band dispersion relation. Non-Markovian noises caused by the non-uniform distribution of photon density states near the photonic bandgap are taken into account by a new approach which linearizes the optical Bloch equations by using the Liouville operator expansion. Fluorescence spectra that only exhibit sidebands of the Mollow triplet are found, indicating that there is no coherent Rayleigh scattering process.

Photonic bandgap narrowing in conical hollow core Bragg fibers

Energy Technology Data Exchange (ETDEWEB)

Ozturk, Fahri Emre; Yildirim, Adem; Kanik, Mehmet [UNAM-National Nanotechnology Research Center, Bilkent University, 06800 Ankara (Turkey); Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Bayindir, Mehmet, E-mail: bayindir@nano.org.tr [UNAM-National Nanotechnology Research Center, Bilkent University, 06800 Ankara (Turkey); Institute of Materials Science and Nanotechnology, Bilkent University, 06800 Ankara (Turkey); Department of Physics, Bilkent University, 06800 Ankara (Turkey)

2014-08-18

We report the photonic bandgap engineering of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightly smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap. A narrow transmission bandwidth is particularly desirable in hollow waveguide mid-infrared sensing schemes, where broadband light is coupled to the fiber and the analyte vapor is introduced into the hollow core to measure infrared absorption. We carried out sensing simulations using the absorption spectrum of isopropyl alcohol vapor to demonstrate the importance of narrow bandgap fibers in chemical sensing applications.

High-Temperature Electronics: A Role for Wide Bandgap Semiconductors?

Science.gov (United States)

Neudeck, Philip G.; Okojie, Robert S.; Chen, Liang-Yu

2002-01-01

It is increasingly recognized that semiconductor based electronics that can function at ambient temperatures higher than 150 C without external cooling could greatly benefit a variety of important applications, especially-in the automotive, aerospace, and energy production industries. The fact that wide bandgap semiconductors are capable of electronic functionality at much higher temperatures than silicon has partially fueled their development, particularly in the case of SiC. It appears unlikely that wide bandgap semiconductor devices will find much use in low-power transistor applications until the ambient temperature exceeds approximately 300 C, as commercially available silicon and silicon-on-insulator technologies are already satisfying requirements for digital and analog very large scale integrated circuits in this temperature range. However, practical operation of silicon power devices at ambient temperatures above 200 C appears problematic, as self-heating at higher power levels results in high internal junction temperatures and leakages. Thus, most electronic subsystems that simultaneously require high-temperature and high-power operation will necessarily be realized using wide bandgap devices, once the technology for realizing these devices become sufficiently developed that they become widely available. Technological challenges impeding the realization of beneficial wide bandgap high ambient temperature electronics, including material growth, contacts, and packaging, are briefly discussed.

In Situ Measurement of Local Hydrogen Production Rate by Bubble-Evolved Recording

Directory of Open Access Journals (Sweden)

Xiaowei Hu

2013-01-01

Full Text Available Hydrogen visibly bubbles during photocatalytic water splitting under illumination with above-bandgap radiation, which provides a direct measurement of local gas-evolving reaction rate. In this paper, optical microscopy of superfield depth was used for recording the hydrogen bubble growth on Cd0.5Zn0.5S photocatalyst in reaction liquid and illuminated with purple light. By analyzing change of hydrogen bubble size as a function of time, we understood that hydrogen bubble growth experienced two periods, which were inertia effect dominated period and diffusion effect dominated period, respectively. The tendency of hydrogen bubble growth was similar to that of the gas bubble in boiling, while the difference in bubble diameter and growth time magnitude was great. Meanwhile, we obtained the local hydrogen production rate on photocatalyst active site by measuring hydrogen bubble growth variation characteristics. This method makes it possible to confirm local actual hydrogen evolution rate quantitatively during photocatalytic water splitting.

Low-bandgap polymer photovoltaic cells

NARCIS (Netherlands)

Duren, van J.K.J.; Dhanabalan, A.; Hal, van P.A.; Janssen, R.A.J.

2001-01-01

A-novel low-bandgap conjugated polymer (PTPTB, Eg = ~1.6 eV), consisting of alternating electron-rich N-dodecyl-2,5-bis(2'-thienyl)pyrrole (TPT) and electron-deficient 2,1,3-benzothiadiazole (B) units, as a donor material is studied together with a soluble fullerene derivative (PCBM) as acceptor to

Below-bandgap photoreflection spectroscopy of semiconductor laser structures

International Nuclear Information System (INIS)

Sotnikov, Aleksandr E; Chernikov, Maksim A; Ryabushkin, Oleg A; Trubenko, P; Moshegov, N; Ovchinnikov, A

2004-01-01

A new method of modulated light reflection - below-bandgap photoreflection, is considered. Unlike the conventional photoreflection method, the proposed method uses optical pumping by photons of energy smaller than the bandgap of any layer of a semiconductor structure under study. Such pumping allows one to obtain the modulated reflection spectrum for all layers of the structure without excitation of photoluminescence. This method is especially promising for the study of wide-gap semiconductors. The results of the study of semiconductor structures used in modern high-power multimode semiconductor lasers are presented. (laser applications and other topics in quantum electronics)

Hydrogen production through microheterogeneous photocatalysis of hydrogen sulfide cleavage. The thiosulfate cycle

Energy Technology Data Exchange (ETDEWEB)

Borgarello, E; Serpone, N; Graetzel, M; Pelizzetti, E

1985-01-01

Cleavage of hydrogen sulfide into hydrogen and sulfur occurs in alkaline aqueous CdS dispersions under visible light illumination. Small quantities of a noble metal catalyst (RuO/sub 2/) loaded onto 'naked' CdS particles markedly improve the yield of hydrogen formation. The effect of RuO/sub 2/ is ascribed to catalysis of electron transfer to proton. Simultaneous and efficient photogeneration of hydrogen and thiosulfate occurs in CdS dispersions containing both sulfite and bisulfide (or sulfide) ions. Electron transfer from the conduction band of CdS to that of TiO/sub 2/ particles occurs in alkaline suspensions containing these HS/sup -/ ions and has been exploited to improve the performance of a system achieving decomposition of H/sub 2/S by visible light. Equally important is a recent finding that the performance of a system containing 'naked' CdS in combination with RuO/sub 2/-loaded TiO/sub 2/ particles is far better than that of CdS/RuO/sub 2/ alone. Additionally, conduction band electrons produced by bandgap excitation of TiO/sub 2/ particles efficiently reduce thiosulfate to sulfide and sulfite. The valence band process in alklaine TiO/sub 2/ dispersions is thought to involve oxidation of S/sub 2/O/sub 3//sup 2 -/ to tetrathionate, S/sub 4/O/sub 6//sup 2 -/, which quantitatively dismutates into sulfite and thiosulfate. The photodriven disproportionation of thiosulfate into sulfide and sulfate is of great interest in systems that photochemically cleave hydrogen sulfide into hydrogen and sulfur. (author).

Anomalous band-gap bowing of AlN1−xPx alloy

International Nuclear Information System (INIS)

Winiarski, M.J.; Polak, M.; Scharoch, P.

2013-01-01

Highlights: •Structural and electronic properties of AlN 1−x P x from first principles. •The supercell and the virtual crystall approximation methods applied and compared. •Anomalously high band-gap bowing found. •Similarities of band-gap behavior to that in BN 1−x P x noticed. •Performance of MBJLDA with the pseudopotential approach discussed. -- Abstract: Electronic structure of zinc blende AlN 1−x P x alloy has been calculated from first principles. Structural optimization has been performed within the framework of LDA and the band-gaps calculated with the modified Becke–Jonson (MBJLDA) method. Two approaches have been examined: the virtual crystal approximation (VCA) and the supercell-based calculations (SC). The composition dependence of the lattice parameter obtained from the SC obeys Vegard’s law whereas the volume optimization in the VCA leads to an anomalous bowing of the lattice constant. A strong correlation between the band-gaps and the structural parameter in the VCA method has been observed. On the other hand, in the SC method the supercell size and atoms arrangement (clustered vs. uniform) appear to have a great influence on the computed band-gaps. In particular, an anomalously big band-gap bowing has been found in the case of a clustered configuration with relaxed geometry. Based on the performed tests and obtained results some general features of MBJLDA are discussed and its performance for similar systems predicted

Energy level alignment and sub-bandgap charge generation in polymer:fullerene bulk heterojunction solar cells.

Science.gov (United States)

Tsang, Sai-Wing; Chen, Song; So, Franky

2013-05-07

Using charge modulated electroabsorption spectroscopy (CMEAS), for the first time, the energy level alignment of a polymer:fullerene bulk heterojunction photovoltaic cell is directly measured. The charge-transfer excitons generated by the sub-bandgap optical pumping are coupled with the modulating electric field and introduce subtle changes in optical absorption in the sub-bandgap region. This minimum required energy for sub-bandgap charge genreation is defined as the effective bandgap. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Coulomb engineering of the bandgap and excitons in two-dimensional materials

Science.gov (United States)

Raja, Archana; Chaves, Andrey; Yu, Jaeeun; Arefe, Ghidewon; Hill, Heather M.; Rigosi, Albert F.; Berkelbach, Timothy C.; Nagler, Philipp; Schüller, Christian; Korn, Tobias; Nuckolls, Colin; Hone, James; Brus, Louis E.; Heinz, Tony F.; Reichman, David R.; Chernikov, Alexey

2017-01-01

The ability to control the size of the electronic bandgap is an integral part of solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning the energies of the electronic states based on the unusual strength of the Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering the surrounding dielectric environment, one can tune the electronic bandgap and the exciton binding energy in monolayers of WS2 and WSe2 by hundreds of meV. We exploit this behaviour to present an in-plane dielectric heterostructure with a spatially dependent bandgap, as an initial step towards the creation of diverse lateral junctions with nanoscale resolution. PMID:28469178

Multi-cavity locally resonant structure with the low frequency and broad band-gaps

Directory of Open Access Journals (Sweden)

Jiulong Jiang

2016-11-01

Full Text Available A multi-cavity periodic structure with the characteristic of local resonance was proposed in the paper. The low frequency band-gap structure was comparatively analyzed by the finite element method (FEM and electric circuit analogy (ECA. Low frequency band-gap can be opened through the dual influence of the coupling’s resonance in the cavity and the interaction among the couplings between structures. Finally, the influence of the structural factors on the band-gap was analyzed. The results show that the structure, which is divided into three parts equally, has a broader effective band-gap below the frequency of 200 Hz. It is also proved that reducing the interval between unit structures can increase the intensity of the couplings among the structures. And in this way, the width of band-gap would be expanded significantly. Through the parameters adjustment, the structure enjoys a satisfied sound insulation effect below the frequency of 500Hz. In the area of low frequency noise reduction, the structure has a lot of potential applications.

A Direct Bandgap Copper-Antimony Halide Perovskite.

Science.gov (United States)

Vargas, Brenda; Ramos, Estrella; Pérez-Gutiérrez, Enrique; Alonso, Juan Carlos; Solis-Ibarra, Diego

2017-07-12

Since the establishment of perovskite solar cells (PSCs), there has been an intense search for alternative materials to replace lead and improve their stability toward moisture and light. As single-metal perovskite structures have yielded unsatisfactory performances, an alternative is the use of double perovskites that incorporate a combination of metals. To this day, only a handful of these compounds have been synthesized, but most of them have indirect bandgaps and/or do not have bandgaps energies well-suited for photovoltaic applications. Here we report the synthesis and characterization of a unique mixed metal ⟨111⟩-oriented layered perovskite, Cs 4 CuSb 2 Cl 12 (1), that incorporates Cu 2+ and Sb 3+ into layers that are three octahedra thick (n = 3). In addition to being made of abundant and nontoxic elements, we show that this material behaves as a semiconductor with a direct bandgap of 1.0 eV and its conductivity is 1 order of magnitude greater than that of MAPbI 3 (MA = methylammonium). Furthermore, 1 has high photo- and thermal-stability and is tolerant to humidity. We conclude that 1 is a promising material for photovoltaic applications and represents a new type of layered perovskite structure that incorporates metals in 2+ and 3+ oxidation states, thus significantly widening the possible combinations of metals to replace lead in PSCs.

Actively doped solid core Photonic Bandgap Fiber

DEFF Research Database (Denmark)

Broeng, Jes; Olausson, Christina Bjarnal Thulin; Lyngsøe, Jens Kristian

2010-01-01

Solid photonic bandgap fibers offer distributed spectral filtering with extraordinary high suppression. This opens new possibilities of artificially tailoring the gain spectrum of fibers. We present record-performance of such fibers and outline their future applications....

Bandgap tunability at single-layer molybdenum disulphide grain boundaries

KAUST Repository

Huang, Yu Li

2015-02-17

Two-dimensional transition metal dichalcogenides have emerged as a new class of semiconductor materials with novel electronic and optical properties of interest to future nanoelectronics technology. Single-layer molybdenum disulphide, which represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle energy gap to be 2.40±0.05 eV for single-layer, 2.10±0.05 eV for bilayer and 1.75±0.05 eV for trilayer molybdenum disulphide, which were directly grown on a graphite substrate by chemical vapour deposition method. More interestingly, we report an unexpected bandgap tunability (as large as 0.85±0.05 eV) with distance from the grain boundary in single-layer molybdenum disulphide, which also depends on the grain misorientation angle. This work opens up new possibilities for flexible electronic and optoelectronic devices with tunable bandgaps that utilize both the control of two-dimensional layer thickness and the grain boundary engineering.

Optical devices based on liquid crystal photonic bandgap fibers

DEFF Research Database (Denmark)

Alkeskjold, Thomas Tanggaard

2005-01-01

the waveguiding mechanism of LC filled PCFs. The principle of tunable fibers based on LCs is thereafter discussed and an alignment and coating study of LC in capillaries is presented. Next, the Liquid Crystal Photonic BandGap (LCPBG) fiber is presented and the waveguiding mechanism is analyzed through plane...... hole. The presence of a LC in the holes of the PCF transforms the fiber from a Total Internal Reflection (TIR) guiding type into a Photonic BandGap (PBG) guiding type, where light is confined to the silica core by coherent scattering from the LC-billed holes. The high dielectric and optical anisotropy...

Experimental Methods for Implementing Graphene Contacts to Finite Bandgap Semiconductors

DEFF Research Database (Denmark)

Meyer-Holdt, Jakob

Present Ph.D. thesis describes my work on implanting graphene as electrical contact to finite bandgap semiconductors. Different transistor architectures, types of graphene and finite bandgap semiconductors have been employed. The device planned from the beginning of my Ph.D. fellowship...... contacts to semiconductor nanowires, more specifically, epitaxially grown InAs nanowires. First, we tried a top down method where CVD graphene was deposited on substrate supported InAs nanowires followed by selective graphene ashing to define graphene electrodes. While electrical contact between...

Complete three-dimensional photonic bandgap in a simple cubic structure

International Nuclear Information System (INIS)

Lin, Shawn-Yu; Fleming, J. G.; Lin, Robin; Sigalas, M. M.; Biswas, R.; Ho, K. M.

2001-01-01

The creation of a three-dimensional (3D) photonic crystal with simple cubic (sc) symmetry is important for applications in the signal routing and 3D waveguiding of light. With a simple stacking scheme and advanced silicon processing, a 3D sc structure was constructed from a 6-in. silicon wafer. The sc structure is experimentally shown to have a complete 3D photonic bandgap in the infrared wavelength. The finite size effect is also observed, accounting for a larger absolute photonic bandgap

First-principles study of bandgap tuning in Ge1-xPbxSe

Science.gov (United States)

Lohani, Himanshu

2018-03-01

Narrow bandgap and its tuning are important aspects of materials for their technological applications. In this context group IV-VI semiconductors are one of the interesting candidates. In this paper, we explore the possibility of bandgap tuning in one of the family member of this family GeSe by using isoelectronic Pb doping. Our study is first-principles based electronic structure calculations of Ge1-xPbxSe. This study reveals that the Ge-p and Se-p states are strongly hybridized in GeSe and shows a gap in the DOS at Ef in GeSe. This gap reduces systematically with simultaneous enhancement of the states in the near Ef region as a function of Pb doping. This leads tuning of the indirect bandgap in GeSe via Pb doping. The results of the indirect bandgap decrement are consistent with the experimental findings. We propose a mechanism where the electrostatic effect of dopant Pb cation could be responsible for these changes in the electronic structure of GeSe.

Device Modeling of the Performance of Cu(In,GaSe2 Solar Cells with V-Shaped Bandgap Profiles

Directory of Open Access Journals (Sweden)

Shou-Yi Kuo

2014-01-01

Full Text Available The effect of Cu(In,GaSe2 (CIGS with V-shaped bandgap on device performance is investigated in detail. A series of Ga/(In+Ga ratio are set to study the influence of V-shaped bandgap profile on the electricity of CIGS thin film solar cells. The modeling of device current density-voltage (J-V curve and bandgap grading profile corresponded well to measurement results. Detailed characteristic and modeling results show that an increased gradient of bandgap from valley to the buffer layer CdS will result in a barrier and lead to an enhanced recombination in the valley. This phenomenon can be modified by the back electric field resulting from a gradient bandgap from valley (bandgap minimum to the Mo back contact. These results indicate CIGS-based solar cells can achieve higher performance by optimizing the V-shaped bandgap profile.

Compact electrically controlled broadband liquid crystal photonic bandgap fiber polarizer

DEFF Research Database (Denmark)

Wei, Lei; Alkeskjold, Thomas Tanggaard; Bjarklev, Anders Overgaard

2009-01-01

An electrically controlled liquid crystal photonic-bandgap fiber polarizer is experimentally demonstrated. A maximum 21.3dB electrically tunable polarization extinction ratio is achieved with 45° rotatable transmission axis as well as switched on and off in 1300nm–1600nm.......An electrically controlled liquid crystal photonic-bandgap fiber polarizer is experimentally demonstrated. A maximum 21.3dB electrically tunable polarization extinction ratio is achieved with 45° rotatable transmission axis as well as switched on and off in 1300nm–1600nm....

Towards double-functionalized small diamondoids: selective electronic band-gap tuning

International Nuclear Information System (INIS)

Adhikari, Bibek; Fyta, Maria

2015-01-01

Diamondoids are nanoscale diamond-like cage structures with hydrogen terminations, which can occur in various sizes and with a diverse type of modifications. In this work, we focus on the structural alterations and the effect of doping and functionalization on the electronic properties of diamondoids, from the smallest adamantane to heptamantane. The results are based on quantum mechanical calculations. We perform a self-consistent study, starting with doping the smallest diamondoid, adamantane. Boron, nitrogen, silicon, oxygen, and phosphorus are chosen as dopants at sites which have been previously optimized and are also consistent with the literature. At a next step, an amine- and a thiol- group are separately used to functionalize the adamantane molecule. We mainly focus on a double functionalization of diamondoids up to heptamantane using both these atomic groups. The effect of isomeration in the case of tetramantane is also studied. We discuss the higher efficiency of a double-functionalization compared to doping or a single-functionalization of diamondoids in tuning the electronic properties, such as the electronic band-gap, of modified small diamondoids in view of their novel nanotechnological applications. (paper)

A Polarization Maintaining Filter based on a Liquid-Crystal-Photonic-Bandgap-Fiber

DEFF Research Database (Denmark)

Scolari, Lara; Olausson, Christina Bjarnal Thulin; Turchinovich, Dmitry

2008-01-01

A polarization maintaining filter based on a liquid-crystal-photonic-bandgap-fiber is demonstrated. Its polarization extinction ratio is 14 dB at 1550 nm. Its tunability is 150 nm.......A polarization maintaining filter based on a liquid-crystal-photonic-bandgap-fiber is demonstrated. Its polarization extinction ratio is 14 dB at 1550 nm. Its tunability is 150 nm....

Optimal design of tunable phononic bandgap plates under equibiaxial stretch

International Nuclear Information System (INIS)

Hedayatrasa, Saeid; Abhary, Kazem; Uddin, M S; Guest, James K

2016-01-01

Design and application of phononic crystal (PhCr) acoustic metamaterials has been a topic with tremendous growth of interest in the last decade due to their promising capabilities to manipulate acoustic and elastodynamic waves. Phononic controllability of waves through a particular PhCr is limited only to the spectrums located within its fixed bandgap frequency. Hence the ability to tune a PhCr is desired to add functionality over its variable bandgap frequency or for switchability. Deformation induced bandgap tunability of elastomeric PhCr solids and plates with prescribed topology have been studied by other researchers. Principally the internal stress state and distorted geometry of a deformed phononic crystal plate (PhP) changes its effective stiffness and leads to deformation induced tunability of resultant modal band structure. Thus the microstructural topology of a PhP can be altered so that specific tunability features are met through prescribed deformation. In the present study novel tunable PhPs of this kind with optimized bandgap efficiency-tunability of guided waves are computationally explored and evaluated. Low loss transmission of guided waves throughout thin walled structures makes them ideal for fabrication of low loss ultrasound devices and structural health monitoring purposes. Various tunability targets are defined to enhance or degrade complete bandgaps of plate waves through macroscopic tensile deformation. Elastomeric hyperelastic material is considered which enables recoverable micromechanical deformation under tuning finite stretch. Phononic tunability through stable deformation of phononic lattice is specifically required and so any topology showing buckling instability under assumed deformation is disregarded. Nondominated sorting genetic algorithm (GA) NSGA-II is adopted for evolutionary multiobjective topology optimization of hypothesized tunable PhP with square symmetric unit-cell and relevant topologies are analyzed through finite

Bandgap engineering and charge separation in two-dimensional GaS-based van der Waals heterostructures for photocatalytic water splitting

Science.gov (United States)

Wang, Biao; Kuang, Anlong; Luo, Xukai; Wang, Guangzhao; Yuan, Hongkuan; Chen, Hong

2018-05-01

Two-dimensional (2D) gallium sulfide (GaS), hexagonal boron nitride (h-BN) and graphitic carbon nitride (g-C3N4) have been fabricated and expected to be promising photocatalysts under ultraviolet irradiation. Here, we employ hybrid density functional calculations to explore the potential of the 2D GaS-based heterojunctions GaS/h-BN (g-C3N4) for the design of efficient water redox photocatalysts. Both heterostructures can be formed via van der Waals (vdW) interaction and are direct bandgap semiconductors, whose bandgaps are reduced comparing with isolated GaS, h-BN or g-C3N4 monolayers and whose bandedges straddle water redox potentials. Furthermore, the optical absorption of GaS/h-BN (g-C3N4) heterostructures is observably enhanced in the ultraviolet-visible (UV-vis) light range. The electron-hole pairs in GaS/h-BN (g-C3N4) heterostructures are completely separated from different layers. In addition, the in-plane biaxial strain can effectively modulate the electronic properties of GaS/h-BN (g-C3N4) heterostructures. Thus the GaS/h-BN (g-C3N4) heterostructures are anticipated to be promising candidates for photocatalytic water splitting to produce hydrogen.

Thermally controlled mid-IR band-gap engineering in all-glass chalcogenide microstructured fibers: a numerical study

DEFF Research Database (Denmark)

Barh, Ajanta; Varshney, Ravi K.; Pal, Bishnu P.

2017-01-01

Presence of photonic band-gap (PBG) in an all-glass low refractive index (RI) contrast chalcogenide (Ch) microstructured optical fibers (MOFs) is investigated numerically. The effect of external temperature on the position of band-gap is explored to realize potential fiber-based wavelength filters....... Then the temperature sensitivity of band-gaps is investigated to design fiber-based mid-IR wavelength filters/sensors....

Passive band-gap reconfiguration born from bifurcation asymmetry.

Science.gov (United States)

Bernard, Brian P; Mann, Brian P

2013-11-01

Current periodic structures are constrained to have fixed energy transmission behavior unless active control or component replacement is used to alter their wave propagation characteristics. The introduction of nonlinearity to generate multiple stable equilibria is an alternative strategy for realizing distinct energy propagation behaviors. We investigate the creation of a reconfigurable band-gap system by implementing passive switching between multiple stable states of equilibrium, to alter the level of energy attenuation in response to environmental stimuli. The ability to avoid potentially catastrophic loads is demonstrated by tailoring the bandpass and band-gap regions to coalesce for two stable equilibria and varying an external load parameter to trigger a bifurcation. The proposed phenomenon could be utilized in remote or autonomous applications where component modifications and active control are impractical.

Tuning the hybridization bandgap by meta-molecules with in-unit interaction

Energy Technology Data Exchange (ETDEWEB)

Chen, Yongqiang; Li, Yunhui, E-mail: liyunhui@tongji.edu.cn; Wu, Qian; Jiang, Haitao; Zhang, Yewen; Chen, Hong [Key Laboratory of Advanced Micro-Structured Materials, Ministry of Education, School of Physics Science and Engineering, Tongji University, Shanghai 200092 (China)

2015-09-07

In this paper, we demonstrate that the hybridization bandgap (HBG) can be tuned conveniently by deep subwavelength meta-molecules with in-unit interaction. Spontaneous-emission-cancellation-like (SEC-like) effect is realized in a meta-molecule by introducing the destructive interference of two detuned meta-atoms. The meta-atoms consisting of subwavelength zero-index-metamaterial-based resonators are side-coupled to a microstrip. Compared to conventional HBG configurations, the presence of in-unit interaction between meta-atoms provides more flexibility in tuning the bandgap properties, keeping the device volume almost unchanged. Both numerical simulations and microwave experiments confirm that the width, depth, and spectrum shape of HBG can be tuned by simply introducing SEC-like interaction into the meta-molecule. Due to these features, our design may be promising to be applied in microwave or optics communications systems with strict limitation of device volume and flexible bandgap properties.

Simultaneous high crystallinity and sub-bandgap optical absorptance in hyperdoped black silicon using nanosecond laser annealing

Energy Technology Data Exchange (ETDEWEB)

Franta, Benjamin, E-mail: bafranta@gmail.com; Pastor, David; Gandhi, Hemi H.; Aziz, Michael J.; Mazur, Eric [School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138 (United States); Rekemeyer, Paul H.; Gradečak, Silvija [Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)

2015-12-14

Hyperdoped black silicon fabricated with femtosecond laser irradiation has attracted interest for applications in infrared photodetectors and intermediate band photovoltaics due to its sub-bandgap optical absorptance and light-trapping surface. However, hyperdoped black silicon typically has an amorphous and polyphasic polycrystalline surface that can interfere with carrier transport, electrical rectification, and intermediate band formation. Past studies have used thermal annealing to obtain high crystallinity in hyperdoped black silicon, but thermal annealing causes a deactivation of the sub-bandgap optical absorptance. In this study, nanosecond laser annealing is used to obtain high crystallinity and remove pressure-induced phases in hyperdoped black silicon while maintaining high sub-bandgap optical absorptance and a light-trapping surface morphology. Furthermore, it is shown that nanosecond laser annealing reactivates the sub-bandgap optical absorptance of hyperdoped black silicon after deactivation by thermal annealing. Thermal annealing and nanosecond laser annealing can be combined in sequence to fabricate hyperdoped black silicon that simultaneously shows high crystallinity, high above-bandgap and sub-bandgap absorptance, and a rectifying electrical homojunction. Such nanosecond laser annealing could potentially be applied to non-equilibrium material systems beyond hyperdoped black silicon.

Optimal design of lossy bandgap structures

DEFF Research Database (Denmark)

Jensen, Jakob Søndergaard

2004-01-01

The method of topology optimization is used to design structures for wave propagation with one lossy material component. Optimized designs for scalar elastic waves are presented for mininimum wave transmission as well as for maximum wave energy dissipation. The structures that are obtained...... are of the 1D or 2D bandgap type depending on the objective and the material parameters....

Emergence of an enslaved phononic bandgap in a non-equilibrium pseudo-crystal

Science.gov (United States)

Bachelard, Nicolas; Ropp, Chad; Dubois, Marc; Zhao, Rongkuo; Wang, Yuan; Zhang, Xiang

2017-08-01

Material systems that reside far from thermodynamic equilibrium have the potential to exhibit dynamic properties and behaviours resembling those of living organisms. Here we realize a non-equilibrium material characterized by a bandgap whose edge is enslaved to the wavelength of an external coherent drive. The structure dynamically self-assembles into an unconventional pseudo-crystal geometry that equally distributes momentum across elements. The emergent bandgap is bestowed with lifelike properties, such as the ability to self-heal to perturbations and adapt to sudden changes in the drive. We derive an exact analytical solution for both the spatial organization and the bandgap features, revealing the mechanism for enslavement. This work presents a framework for conceiving lifelike non-equilibrium materials and emphasizes the potential for the dynamic imprinting of material properties through external degrees of freedom.

Emergence of an enslaved phononic bandgap in a non-equilibrium pseudo-crystal.

Science.gov (United States)

Bachelard, Nicolas; Ropp, Chad; Dubois, Marc; Zhao, Rongkuo; Wang, Yuan; Zhang, Xiang

2017-08-01

Material systems that reside far from thermodynamic equilibrium have the potential to exhibit dynamic properties and behaviours resembling those of living organisms. Here we realize a non-equilibrium material characterized by a bandgap whose edge is enslaved to the wavelength of an external coherent drive. The structure dynamically self-assembles into an unconventional pseudo-crystal geometry that equally distributes momentum across elements. The emergent bandgap is bestowed with lifelike properties, such as the ability to self-heal to perturbations and adapt to sudden changes in the drive. We derive an exact analytical solution for both the spatial organization and the bandgap features, revealing the mechanism for enslavement. This work presents a framework for conceiving lifelike non-equilibrium materials and emphasizes the potential for the dynamic imprinting of material properties through external degrees of freedom.

Stability and bandgaps of layered perovskites for one- and two-photon water splitting

DEFF Research Database (Denmark)

Castelli, Ivano Eligio; García Lastra, Juan Maria; Hüser, Falco

2013-01-01

in the Ruddlesden–Popper phase of the layered perovskite structure. Based on screening criteria for the stability, bandgaps and band edge positions, we suggest 20 new materials for the light harvesting photo-electrode of a one-photon water splitting device and 5 anode materials for a two-photon device with silicon...... as photo-cathode. In addition, we explore a simple rule relating the bandgap of the perovskite to the number of octahedra in the layered structure and the B-metal ion. Finally, the quality of the GLLB-SC potential used to obtain the bandgaps, including the derivative discontinuity, is validated against G0W......0@LDA gaps for 20 previously identified oxides and oxynitrides in the cubic perovskite structure....

Hybrid functional calculations of potential hydrogen storage material: Complex dimagnesium iron hydride

KAUST Repository

Ul Haq, Bakhtiar

2014-06-01

By employing the state of art first principles approaches, comprehensive investigations of a very promising hydrogen storage material, Mg 2FeH6 hydride, is presented. To expose its hydrogen storage capabilities, detailed structural, elastic, electronic, optical and dielectric aspects have been deeply analysed. The electronic band structure calculations demonstrate that Mg2FeH6 is semiconducting material. The obtained results of the optical bandgap (4.19 eV) also indicate that it is a transparent material for ultraviolet light, thus demonstrating its potential for optoelectronics application. The calculated elastic properties reveal that Mg2FeH6 is highly stiff and stable hydride. Finally, the calculated hydrogen (H2) storage capacity (5.47 wt.%) within a reasonable formation energy of -78 kJ mol-1, at room temperature, can be easily achievable, thus making Mg2FeH6 as potential material for practical H2 storage applications. Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Influence of interface preparation on minority carrier lifetime for low bandgap tandem solar cell materials

Energy Technology Data Exchange (ETDEWEB)

Szabo, Nadine; Sagol, B. Erol; Seidel, Ulf; Schwarzburg, Klaus; Hannappel, Thomas [Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Berlin (Germany)

2010-07-01

III-V semiconductor compounds grown by MOVPE are implemented in todays state-of-the-art third generation multi-junction solar cells. The current record multi junction solar cell grown on germanium, having Ge, Ga(In)As and GaInP as subcells, reached a record efficiency of 41.6%. The efficiency of these multi junction solar cells could be significantly increased, if its low bandgap Ge subcell would be replaced by a more efficient tandem. For this purpose the low bandgap materials InGaAs and InGaAsP are suitable. The bandgap composition of these materials allows a better yield of the solar spectrum. Based on InGaAs/InGaAsP absorber materials we have developed a low bandgap tandem solar cell with optimized bandgaps. Results of time resolved photoluminescence (TRPL) for the IR-bandgap compounds InGaAsP (1.03 eV)/InGaAs (0.73 eV) are presented. The lifetime of minority carriers is one of the most important properties of solar cell absorber materials. We show on the example of the low band gap tandem cell how the choice of the materials, the quality of the bulk, the optimization of the band gap energies and the preparation of the critical interfaces are essential to build a high efficiency solar cell. The quality of the bulk and the preparation of the critical interfaces are essential for the growth of the double heterostructure (DHS).

Pressure-Induced Bandgap Optimization in Lead-Based Perovskites with Prolonged Carrier Lifetime and Ambient Retainability

Energy Technology Data Exchange (ETDEWEB)

Liu, Gang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Kong, Lingping [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Gong, Jue [Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb IL 60115 USA; Yang, Wenge [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Mao, Ho-kwang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Hu, Qingyang [Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Liu, Zhenxian [Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Schaller, Richard D. [Center for Nanoscale Materials, Argonne National Laboratory, Argonne IL 60439 USA; Zhang, Dongzhou [Hawai' i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai' i at Manoa, Honolulu HI 96822 USA; Xu, Tao [Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb IL 60115 USA

2016-12-05

Bond length and bond angle exhibited by valence electrons is essential to the core of chemistry. Using lead-based organic–inorganic perovskite compounds as an exploratory platform, it is demonstrated that the modulation of valence electrons by compression can lead to discovery of new properties of known compounds. Yet, despite its unprecedented progress, further efficiency boost of lead-based organic–inorganic perovskite solar cells is hampered by their wider bandgap than the optimum value according to the Shockley–Queisser limit. By modulating the valence electron wavefunction with modest hydraulic pressure up to 2.1 GPa, the optimized bandgap for single-junction solar cells in lead-based perovskites, for the first time, is achieved by narrowing the bandgap of formamidinium lead triiodide (HC(NH2)2PbI3) from 1.489 to 1.337 eV. Strikingly, such bandgap narrowing is partially retained after the release of pressure to ambient, and the bandgap narrowing is also accompanied with double-prolonged carrier lifetime. With First-principles simulation, this work opens a new dimension in basic chemical understanding of structural photonics and electronics and paves an alternative pathway toward better photovoltaic materials-by-design.

Pressure-Induced Bandgap Optimization in Lead-Based Perovskites with Prolonged Carrier Lifetime and Ambient Retainability

Energy Technology Data Exchange (ETDEWEB)

Liu, Gang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Kong, Lingping [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Gong, Jue [Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb IL 60115 USA; Yang, Wenge [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Mao, Ho-kwang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203 China; Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Hu, Qingyang [Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Liu, Zhenxian [Geophysical Laboratory, Carnegie Institution of Washington, Washington DC 20015 USA; Schaller, Richard D. [Center for Nanoscale Materials, Argonne National Laboratory, Argonne IL 60439 USA; Zhang, Dongzhou [Hawai' i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai' i at Manoa, Honolulu HI 96822 USA; Xu, Tao [Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb IL 60115 USA

2016-12-05

Bond length and bond angle exhibited by valence electrons is essential to the core of chemistry. Using lead-based organic–inorganic perovskite compounds as an exploratory platform, it is demonstrated that the modulation of valence electrons by compression can lead to discovery of new properties of known compounds. Yet, despite its unprecedented progress, further efficiency boost of lead-based organic–inorganic perovskite solar cells is hampered by their wider bandgap than the optimum value according to the Shockley–Queisser limit. By modulating the valence electron wavefunction with modest hydraulic pressure up to 2.1 GPa, the optimized bandgap for single-junction solar cells in lead-based perovskites, for the first time, is achieved by narrowing the bandgap of formamidinium lead triiodide (HC(NH₂)₂PbI₃) from 1.489 to 1.337 eV. Strikingly, such bandgap narrowing is partially retained after the release of pressure to ambient, and the bandgap narrowing is also accompanied with double-prolonged carrier lifetime. With First-principles simulation, this work opens a new dimension in basic chemical understanding of structural photonics and electronics and paves an alternative pathway toward better photovoltaic materials-by-design.

Bandgap tunability at single-layer molybdenum disulphide grain boundaries

KAUST Repository

Huang, Yu Li; Chen, Yifeng; Zhang, Wenjing; Quek, Su Ying; Chen, Chang-Hsiao; Li, Lain-Jong; Hsu, Wei-Ting; Chang, Wen-Hao; Zheng, Yu Jie; Chen, Wei; Wee, Andrew T. S.

2015-01-01

represents a prototype two-dimensional transition metal dichalcogenide, has an electronic bandgap that increases with decreasing layer thickness. Using high-resolution scanning tunnelling microscopy and spectroscopy, we measure the apparent quasiparticle

Effects of corrugation shape on frequency band-gaps for longitudinal wave motion in a periodic elastic layer

DEFF Research Database (Denmark)

Sorokin, Vladislav

2016-01-01

The paper concerns determining frequency band-gaps for longitudinal wave motion in a periodic waveguide. The waveguide may be considered either as an elastic layer with variable thickness or as a rod with variable cross section. As a result, widths and locations of all frequency band-gaps are det......The paper concerns determining frequency band-gaps for longitudinal wave motion in a periodic waveguide. The waveguide may be considered either as an elastic layer with variable thickness or as a rod with variable cross section. As a result, widths and locations of all frequency band......, harmonic in the corrugation series. The revealed insights into the mechanism of band-gap formation can be used to predict locations and widths of all frequency band-gaps featured by any corrugation shape. These insights are general and can be valid also for other types of wave motion in periodic structures...

Two-dimensional Kagome photonic bandgap waveguide

DEFF Research Database (Denmark)

Nielsen, Jens Bo; Søndergaard, Thomas; Libori, Stig E. Barkou

2000-01-01

The transverse-magnetic photonic-bandgap-guidance properties are investigated for a planar two-dimensional (2-D) Kagome waveguide configuration using a full-vectorial plane-wave-expansion method. Single-moded well-localized low-index guided modes are found. The localization of the optical modes...... is investigated with respect to the width of the 2-D Kagome waveguide, and the number of modes existing for specific frequencies and waveguide widths is mapped out....

Structure and optical bandgap relationship of π-conjugated systems.

Directory of Open Access Journals (Sweden)

André Leitão Botelho

Full Text Available In bulk heterojunction photovoltaic systems both the open-circuit voltage as well as the short-circuit current, and hence the power conversion efficiency, are dependent on the optical bandgap of the electron-donor material. While first-principles methods are computationally intensive, simpler model Hamiltonian approaches typically suffer from one or more flaws: inability to optimize the geometries for their own input; absence of general, transferable parameters; and poor performance for non-planar systems. We introduce a set of new and revised parameters for the adapted Su-Schrieffer-Heeger (aSSH Hamiltonian, which is capable of optimizing geometries, along with rules for applying them to any [Formula: see text]-conjugated system containing C, N, O, or S, including non-planar systems. The predicted optical bandgaps show excellent agreement to UV-vis spectroscopy data points from literature, with a coefficient of determination [Formula: see text], a mean error of -0.05 eV, and a mean absolute deviation of 0.16 eV. We use the model to gain insights from PEDOT, fused thiophene polymers, poly-isothianaphthene, copolymers, and pentacene as sources of design rules in the search for low bandgap materials. Using the model as an in-silico design tool, a copolymer of benzodithiophenes along with a small-molecule derivative of pentacene are proposed as optimal donor materials for organic photovoltaics.

Monolithic all-PM femtosecond Yb-doped fiber laser using photonic bandgap fibers

DEFF Research Database (Denmark)

Liu, Xiaomin; Lægsgaard, Jesper; Turchinovich, Dmitry

2009-01-01

We present a monolithic Yb fiber laser, dispersion managed by an all-solid photonic bandgap fiber, and pulse compressed in a hollow-core photonic crystal fiber. The laser delivers 9 nJ, 275-fs long pulses at 1035 nm.......We present a monolithic Yb fiber laser, dispersion managed by an all-solid photonic bandgap fiber, and pulse compressed in a hollow-core photonic crystal fiber. The laser delivers 9 nJ, 275-fs long pulses at 1035 nm....

First principle analyses of direct bandgap solar cells with absorbing substrates versus mirrors

Energy Technology Data Exchange (ETDEWEB)

Kirk, Alexander P. [School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Kirk, Wiley P. [Department of Materials Science and Engineering, University of Texas at Arlington, Arlington, Texas 76019 (United States)

2013-11-07

Direct bandgap InP, GaAs, CdTe, and Ga{sub 0.5}In{sub 0.5}P solar cells containing backside mirrors as well as parasitically absorbing substrates are analyzed for their limiting open circuit voltage and power conversion efficiency with comparison to record solar cells. From the principle of detailed balance, it is shown quantitatively that mirror solar cells have greater voltage and power conversion efficiency than their substrate counterparts. Next, the radiative recombination coefficient and maximum radiative lifetime of GaAs mirror and substrate solar cells are calculated and compared to the nonradiative Auger and Shockley-Read-Hall (SRH) lifetimes. Mirror solar cells have greater radiative lifetime than their substrate variants. Auger lifetime exceeds radiative lifetime for both substrate and mirror cells while SRH lifetime may be less or greater than radiative lifetime depending on trap concentration and capture cross section. Finally, the change in free energy of the photogenerated carriers is analyzed in a comparison between InP, GaAs, CdTe, and Ga{sub 0.5}In{sub 0.5}P mirror and substrate solar cells in order to characterize the relationship between solar photon quality and free energy management in solar cells with differing bandgaps. Wider bandgap visible threshold Ga{sub 0.5}In{sub 0.5}P solar cells make better use of the available change in free energy of the photogenerated charge carriers, even when normalized to the bandgap energy, than narrower bandgap near-IR threshold InP, GaAs, and CdTe solar cells.

Design of photonic bandgap fibers by topology optimization

DEFF Research Database (Denmark)

Dühring, Maria Bayard; Sigmund, Ole; Feurer, Thomas

2010-01-01

A method based on topology optimization is presented to design the cross section of hollow-core photonic bandgap fibers for minimizing energy loss by material absorption. The optical problem is modeled by the timeharmonic wave equation and solved with the finite element program Comsol Multiphysics...

Bandgap tuning with thermal residual stresses induced in a quantum dot.

Science.gov (United States)

Kong, Eui-Hyun; Joo, Soo-Hyun; Park, Hyun-Jin; Song, Seungwoo; Chang, Yong-June; Kim, Hyoung Seop; Jang, Hyun Myung

2014-09-24

Lattice distortion induced by residual stresses can alter electronic and mechanical properties of materials significantly. Herein, a novel way of the bandgap tuning in a quantum dot (QD) by lattice distortion is presented using 4-nm-sized CdS QDs grown on a TiO2 particle as an application example. The bandgap tuning (from 2.74 eV to 2.49 eV) of a CdS QD is achieved by suitably adjusting the degree of lattice distortion in a QD via the tensile residual stresses which arise from the difference in thermal expansion coefficients between CdS and TiO2. The idea of bandgap tuning is then applied to QD-sensitized solar cells, achieving ≈60% increase in the power conversion efficiency by controlling the degree of thermal residual stress. Since the present methodology is not limited to a specific QD system, it will potentially pave a way to unexplored quantum effects in various QD-based applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Relation between bandgap and resistance drift in amorphous phase change materials.

Science.gov (United States)

Rütten, Martin; Kaes, Matthias; Albert, Andreas; Wuttig, Matthias; Salinga, Martin

2015-12-01

Memory based on phase change materials is currently the most promising candidate for bridging the gap in access time between memory and storage in traditional memory hierarchy. However, multilevel storage is still hindered by the so-called resistance drift commonly related to structural relaxation of the amorphous phase. Here, we present the temporal evolution of infrared spectra measured on amorphous thin films of the three phase change materials Ag4In3Sb67Te26, GeTe and the most popular Ge2Sb2Te5. A widening of the bandgap upon annealing accompanied by a decrease of the optical dielectric constant ε∞ is observed for all three materials. Quantitative comparison with experimental data for the apparent activation energy of conduction reveals that the temporal evolution of bandgap and activation energy can be decoupled. The case of Ag4In3Sb67Te26, where the increase of activation energy is significantly smaller than the bandgap widening, demonstrates the possibility to identify new phase change materials with reduced resistance drift.

Design for maximum band-gaps in beam structures

DEFF Research Database (Denmark)

Olhoff, Niels; Niu, Bin; Cheng, Gengdong

2012-01-01

This paper aims to extend earlier optimum design results for transversely vibrating Bernoulli-Euler beams by determining new optimum band-gap beam structures for (i) different combinations of classical boundary conditions, (ii) much larger values of the orders n and n-1 of adjacent upper and lower...

Quasiperiodic one-dimensional photonic crystals with adjustable multiple photonic bandgaps.

Science.gov (United States)

Vyunishev, Andrey M; Pankin, Pavel S; Svyakhovskiy, Sergey E; Timofeev, Ivan V; Vetrov, Stepan Ya

2017-09-15

We propose an elegant approach to produce photonic bandgap (PBG) structures with multiple photonic bandgaps by constructing quasiperiodic photonic crystals (QPPCs) composed of a superposition of photonic lattices with different periods. Generally, QPPC structures exhibit both aperiodicity and multiple PBGs due to their long-range order. They are described by a simple analytical expression, instead of quasiperiodic tiling approaches based on substitution rules. Here we describe the optical properties of QPPCs exhibiting two PBGs that can be tuned independently. PBG interband spacing and its depth can be varied by choosing appropriate reciprocal lattice vectors and their amplitudes. These effects are confirmed by the proof-of-concept measurements made for the porous silicon-based QPPC of the appropriate design.

Direct bandgap silicon: tensile-strained silicon nanocrystals

Czech Academy of Sciences Publication Activity Database

Kůsová, Kateřina; Hapala, Prokop; Valenta, J.; Jelínek, Pavel; Cibulka, Ondřej; Ondič, Lukáš; Pelant, Ivan

2014-01-01

Roč. 1, č. 2 (2014), "1300042-1"-"1300042-9" ISSN 2196-7350 R&D Projects: GA ČR(CZ) GBP108/12/G108; GA ČR GPP204/12/P235; GA ČR GAP204/10/0952 Institutional support: RVO:68378271 Keywords : silicon nanocrystals * badstructure * light emission * direct bandgap * surface capping Subject RIV: BM - Solid Matter Physics ; Magnetism

Advances in wide bandgap SiC for optoelectronics

DEFF Research Database (Denmark)

Ou, Haiyan; Ou, Yiyu; Argyraki, Aikaterini

2014-01-01

Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication...

Analysis of optical band-gap shift in impurity doped ZnO thin films by using nonparabolic conduction band parameters

International Nuclear Information System (INIS)

Kim, Won Mok; Kim, Jin Soo; Jeong, Jeung-hyun; Park, Jong-Keuk; Baik, Young-Jun; Seong, Tae-Yeon

2013-01-01

Polycrystalline ZnO thin films both undoped and doped with various types of impurities, which covered the wide carrier concentration range of 10 16 –10 21 cm −3 , were prepared by magnetron sputtering, and their optical-band gaps were investigated. The experimentally measured optical band-gap shifts were analyzed by taking into account the carrier density dependent effective mass determined by the first-order nonparabolicity approximation. It was shown that the measured shifts in optical band-gaps in ZnO films doped with cationic dopants, which mainly perturb the conduction band, could be well represented by theoretical estimation in which the band-gap widening due to the band-filling effect and the band-gap renormalization due to the many-body effect derived for a weakly interacting electron-gas model were combined and the carrier density dependent effective mass was incorporated. - Highlights: ► Optical band-gaps of polycrystalline ZnO thin films were analyzed. ► Experimental carrier concentration range covered from 10 16 to 10 21 cm −3 . ► Nonparabolic conduction band parameters were used in theoretical analysis. ► The band-filling and the band-gap renormalization effects were considered. ► The measured optical band-gap shifts corresponded well with the calculated ones

Fluctuations of electrical and mechanical properties of diamond induced by interstitial hydrogen

Science.gov (United States)

Zhuang, Chun-Qiang; Liu, Lei

2015-01-01

While experimental evidence demonstrates that the presence of hydrogen (H) impurities in diamond films plays a significant role in determining their physical properties, the small radius of the H atom makes detecting such impurities quite a challenging task. In the present work, first-principles calculations were employed to provide an insight into the effects of the interstitial hydrogen on the electrical and mechanical properties of diamond crystals at the atomic level. The migrated pathways of the interstitial hydrogen are dictated by energetic considerations. Some new electronic states are formed near the Fermi level. The interstitial hydrogen markedly narrows the bandgap of the diamond and weakens the diamond crystal. The obvious decrement of the critical strain clearly implies the presence of an H-induced embrittlement effect. Project supported by the Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges under Beijing Municipality, China (Grant No. IDHT20140504), the National Natural Science Foundation of China (Grant No. 51402009), and the Foundation for Young Scholars of Beijing University of Technology, China.

Impact of hydrogen dilution on optical properties of intrinsic hydrogenated amorphous silicon films prepared by high density plasma chemical vapor deposition for solar cell applications

Science.gov (United States)

Chen, Huai-Yi; Lee, Yao-Jen; Chang, Chien-Pin; Koo, Horng-Show; Lai, Chiung-Hui

2013-01-01

P-i-n single-junction hydrogenated amorphous silicon (a-Si:H) thin film solar cells were successfully fabricated in this study on a glass substrate by high density plasma chemical vapor deposition (HDP-CVD) at low power of 50 W, low temperature of 200°C and various hydrogen dilution ratios (R). The open circuit voltage (Voc ), short circuit current density (Jsc ), fill factor (FF) and conversion efficiency (η) of the solar cell as well as the refractive index (n) and absorption coefficient (α) of the i-layer at 600 nm wavelength rise with increasing R until an abrupt drop at high hydrogen dilution, i.e. R > 0.95. However, the optical energy bandgap (Eg ) of the i-layer decreases with the R increase. Voc and α are inversely correlated with Eg . The hydrogen content affects the i-layer and p/i interface quality of the a-Si:H thin film solar cell with an optimal value of R = 0.95, which corresponds to solar cell conversion efficiency of 3.85%. The proposed a-Si:H thin film solar cell is expected to be improved in performance.

Complete low-frequency bandgap in a two-dimensional phononic crystal with spindle-shaped inclusions

Science.gov (United States)

Ting, Wang; Hui, Wang; Mei-Ping, Sheng; Qing-Hua, Qin

2016-04-01

A two-dimensional phononic crystal (PC) structure possessing a relatively low frequency range of complete bandgap is presented. The structure is composed of periodic spindle-shaped plumbum inclusions in a rubber matrix which forms a square lattice. The dispersion relation, transmission spectrum and displacement field are studied using the finite element method in conjunction with the Bloch theorem. Numerical results show that the present PC structure can achieve a large complete bandgap in a relatively low frequency range compared with two inclusions of different materials, which is useful in low-frequency noise and vibration control and can be designed as a low frequency acoustic filter and waveguides. Moreover, the transmission spectrum and effective mass are evaluated to validate the obtained band structure. It is interesting to see that within the band gap the effective mass becomes negative, resulting in an imaginary wave speed and wave exponential attenuation. Finally, sensitivity analysis of the effect of geometrical parameters of the presented PC structure on the lowest bandgap is performed to investigate the variations of the bandgap width and frequency. Project supported by the China Scholarship Council.

Systematic design of phononic band-gap materials and structures by topology optimization

DEFF Research Database (Denmark)

Sigmund, Ole; Jensen, Jakob Søndergaard

2003-01-01

Phononic band-gap materials prevent elastic waves in certain frequency ranges from propagating, and they may therefore be used to generate frequency filters, as beam splitters, as sound or vibration protection devices, or as waveguides. In this work we show how topology optimization can be used...... to design and optimize periodic materials and structures exhibiting phononic band gaps. Firstly, we optimize infinitely periodic band-gap materials by maximizing the relative size of the band gaps. Then, finite structures subjected to periodic loading are optimized in order to either minimize the structural...

Graded band-gap engineering for increased efficiency in CZTS solar cells

Science.gov (United States)

Ferhati, H.; Djeffal, F.

2018-02-01

In this paper, we propose a potential high efficiency Cu2ZnSn(S,Se)4/CdS (CZTS) solar cell design based on graded band-gap engineering that can offer the benefits of improved absorption behavior and reduced recombination effects. Moreover, a new hybrid approach based on analytical modeling and Particle Swarm Optimization (PSO) is proposed to determinate the optimal band-gap profile of the amended CZTS absorber layer to achieve further efficiency enhancement. It is found that the proposed design exhibits superior performance, where a high efficiency of 16.9% is recorded for the optimized solar cell with a relative improvement of 92%, compared with the reference cell efficiency of 8.8%. Likewise, the optimized CZTS solar cell with a graded band-gap enables achieving a higher open circuit voltage of 889 mV, a short-circuit current of 28.5 mA and a fill factor of 66%. Therefore, the optimized CZTS-based solar cell with graded-band gap paradigm pinpoints a new path toward recording high-efficiency thin-film solar cells through enhancing carrier collection and reducing the recombination rate.

Temperature-modified photonic bandgap in colloidal photonic crystals fabricated by vinyl functionalized silica spheres

International Nuclear Information System (INIS)

Deng Tiansong; Zhang Junyan; Zhu Kongtao; Zhang Qifeng; Wu Jinlei

2011-01-01

Graphical abstract: A thermal annealing procedure was described for fine modifying the photonic bandgap properties of colloidal photonic crystals, which were self-assembled from vinyl-functionalized silica spheres by a gravity sedimentation process. Highlights: → We described a thermal annealing procedure for fine modifying the photonic bandgap properties of colloidal photonic crystals. → The position of its stop band had more than 25% blue shift by annealing the sample from 60 to 600 deg. C. → The annealing temperature and the Bragg peak values have a linear relationship in the 120-440 deg. C range. → The effects provide a simple and controllable method for modifying the photonic bandgap properties of colloidal photonic crystals. - Abstract: A thermal annealing procedure for fine modifying the photonic bandgap properties of colloidal photonic crystals was described. The colloidal photonic crystals were assembled from monodisperse vinyl functionalized silica spheres by a gravity sedimentation process. The samples diffract light following Bragg's law combined with Snell's law. By annealing the sample at temperatures in the range of 60-600 deg. C, the position of its stop band shifted from 943 to 706 nm. It had more than 25% blue shift. In addition, the annealing temperature and the Bragg peak values have a linear relationship in the 120-440 deg. C range. Fourier transform infrared (FT-IR) spectra and thermo-gravimetric analysis (TGA) curves of vinyl functionalized silica spheres confirmed the above results. The effects provide a simple and controllable method for modifying the photonic bandgap properties of colloidal photonic crystals.

Semi-transparent polymer solar cells with excellent sub-bandgap transmission for third generation photovoltaics

KAUST Repository

Beiley, Zach M.

2013-10-07

Semi-transparent organic photovoltaics are of interest for a variety of photovoltaic applications, including solar windows and hybrid tandem photovoltaics. The figure shows a photograph of our semi-transparent solar cell, which has a power conversion efficiency of 5.0%, with an above bandgap transmission of 34% and a sub-bandgap transmission of 81%. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced Impurity-Free Intermixing Bandgap Engineering for InP-Based Photonic Integrated Circuits

Science.gov (United States)

Cui, Xiao; Zhang, Can; Liang, Song; Zhu, Hong-Liang; Hou, Lian-Ping

2014-04-01

Impurity-free intermixing of InGaAsP multiple quantum wells (MQW) using sputtering Cu/SiO2 layers followed by rapid thermal processing (RTP) is demonstrated. The bandgap energy could be modulated by varying the sputtering power and time of Cu, RTP temperature and time to satisfy the demands for lasers, modulators, photodetector, and passive waveguides for the photonic integrated circuits with a simple procedure. The blueshift of the bandgap wavelength of MQW is experimentally investigated on different sputtering and annealing conditions. It is obvious that the introduction of the Cu layer could increase the blueshift more greatly than the common impurity free vacancy disordering technique. A maximum bandgap blueshift of 172 nm is realized with an annealing condition of 750°C and 200s. The improved technique is promising for the fabrication of the active/passive optoelectronic components on a single wafer with simple process and low cost.

Solar-Driven Hydrogen Peroxide Production Using Polymer-Supported Carbon Dots as Heterogeneous Catalyst

Science.gov (United States)

Gogoi, Satyabrat; Karak, Niranjan

2017-10-01

Safe, sustainable, and green production of hydrogen peroxide is an exciting proposition due to the role of hydrogen peroxide as a green oxidant and energy carrier for fuel cells. The current work reports the development of carbon dot-impregnated waterborne hyperbranched polyurethane as a heterogeneous photo-catalyst for solar-driven production of hydrogen peroxide. The results reveal that the carbon dots possess a suitable band-gap of 2.98 eV, which facilitates effective splitting of both water and ethanol under solar irradiation. Inclusion of the carbon dots within the eco-friendly polymeric material ensures their catalytic activity and also provides a facile route for easy catalyst separation, especially from a solubilizing medium. The overall process was performed in accordance with the principles of green chemistry using bio-based precursors and aqueous medium. This work highlights the potential of carbon dots as an effective photo-catalyst.

Effects of Ge- and Sb-doping and annealing on the tunable bandgaps of SnS films

Energy Technology Data Exchange (ETDEWEB)

Hsu, Hsuan-Tai; Chiang, Ming-Hung; Huang, Chen-Hao [Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan (China); Lin, Wen-Tai, E-mail: wtlin@mail.ncku.edu.tw [Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan (China); Fu, Yaw-Shyan [Department of Greenergy, National University of Tainan, Tainan 700, Taiwan (China); Guo, Tzung-Fang [Department of Photonics, Advanced Optoelectronic Technology Center, National Cheng Kung University, Tainan 701, Taiwan (China)

2015-06-01

SnS, Ge- and Sb-doped SnS films with single orthorhombic SnS phase were fabricated via solvothermal routes and subsequent spin-coating, respectively. The substitution solubilities of Ge and Sb in SnS are about 6 and 5 at.%, respectively. The bandgaps of Ge- and Sb-doped SnS films can be tuned in the ranges of 1.25–1.35 and 1.30–1.39 eV, respectively. The possible mechanisms for the tunable bandgaps of Ge- and Sb-doped SnS films are discussed. For the Ge- and Sb-doped SnS films subjected to annealing at 200–350 °C in N{sub 2}, the bandgaps of 200 °C-annealed films remain unchanged, while those of 300 °C- and 350 °C-annealed films decrease with the annealing temperature because of the evaporation of Ge and Sb respectively. - Highlights: • Ge- and Sb-doped SnS films were fabricated via spin-coating. • The solubilities of Ge and Sb in SnS are about 6 and 5 at.%, respectively. • The bandgaps of SnS films can be tuned by Ge and Sb doping respectively. • Annealing above 300 °C reduces the bandgaps of Ge- and Sb-doped SnS films.

Silica-air photonic crystal fiber design that permits waveguiding by a true photonic bandgap effect

DEFF Research Database (Denmark)

Barkou, Stig Eigil; Broeng, Jes; Bjarklev, Anders Overgaard

1999-01-01

A theoretical investigation of a novel type of optical fiber is presented. The operation of the fiber relies entirely on wave guidance through the photonic bandgap effect and not on total internal reflection, thereby distinguishing that fiber from all other known fibers, including recently studied...... photonic crystal fibers. The novel fiber has a central low-index core region and a cladding consisting of a silica background material with air holes situated within a honeycomb lattice structure. We show the existence of photonic bandgaps for the silica–air cladding structure and demonstrate how light can...... be guided at the central low-index core region for a well-defined frequency that falls inside the photonic bandgap region of the cladding structure....

Small-bandgap semiconducting polymers with high near-infrared photoresponse

NARCIS (Netherlands)

Hendriks, K.H.; Li, W.; Wienk, M.M.; Janssen, R.A.J.

2014-01-01

Lowering the optical bandgap of conjugated polymers while maintaining a high efficiency for photoinduced charge transfer to suitable electron acceptors such as fullerene has remained a formidable challenge in the area of organic photovoltaics. Here we present the synthesis and application of a

CMOS bandgap references and temperature sensors and their applications

NARCIS (Netherlands)

Wang, G.

2005-01-01

Two main parts have been presented in this thesis: device characterization and circuit. In integrated bandgap references and temperature sensors, the IC(VBE, characteristics of bipolar transistors are used to generate the basic signals with high accuracy. To investigate the possibilities to

Single-nanowire, low-bandgap hot carrier solar cells with tunable open-circuit voltage

Science.gov (United States)

Limpert, Steven; Burke, Adam; Chen, I.-Ju; Anttu, Nicklas; Lehmann, Sebastian; Fahlvik, Sofia; Bremner, Stephen; Conibeer, Gavin; Thelander, Claes; Pistol, Mats-Erik; Linke, Heiner

2017-10-01

Compared to traditional pn-junction photovoltaics, hot carrier solar cells offer potentially higher efficiency by extracting work from the kinetic energy of photogenerated ‘hot carriers’ before they cool to the lattice temperature. Hot carrier solar cells have been demonstrated in high-bandgap ferroelectric insulators and GaAs/AlGaAs heterostructures, but so far not in low-bandgap materials, where the potential efficiency gain is highest. Recently, a high open-circuit voltage was demonstrated in an illuminated wurtzite InAs nanowire with a low bandgap of 0.39 eV, and was interpreted in terms of a photothermoelectric effect. Here, we point out that this device is a hot carrier solar cell and discuss its performance in those terms. In the demonstrated devices, InP heterostructures are used as energy filters in order to thermoelectrically harvest the energy of hot electrons photogenerated in InAs absorber segments. The obtained photovoltage depends on the heterostructure design of the energy filter and is therefore tunable. By using a high-resistance, thermionic barrier, an open-circuit voltage is obtained that is in excess of the Shockley-Queisser limit. These results provide generalizable insight into how to realize high voltage hot carrier solar cells in low-bandgap materials, and therefore are a step towards the demonstration of higher efficiency hot carrier solar cells.

Band-gap tunable dielectric elastomer filter for low frequency noise

Science.gov (United States)

Jia, Kun; Wang, Mian; Lu, Tongqing; Zhang, Jinhua; Wang, Tiejun

2016-05-01

In the last decades, diverse materials and technologies for sound insulation have been widely applied in engineering. However, suppressing the noise radiation at low frequency still remains a challenge. In this work, a novel membrane-type smart filter, consisting of a pre-stretched dielectric elastomer membrane with two compliant electrodes coated on the both sides, is presented to control the low frequency noise. Since the stiffness of membrane dominates its acoustic properties, sound transmission band-gap of the membrane filter can be tuned by adjusting the voltage applied to the membrane. The impedance tube experiments have been carried out to measure the sound transmission loss (STL) of the filters with different electrodes, membrane thickness and pre-stretch conditions. The experimental results show that the center frequency of sound transmission band-gap mainly depends on the stress in the dielectric elastomer, and a large band-gap shift (more than 60 Hz) can be achieved by tuning the voltage applied to the 85 mm diameter VHB4910 specimen with pre-stretch {λ }0=3. Based on the experimental results and the assumption that applied electric field is independent of the membrane behavior, 3D finite element analysis has also been conducted to calculate the membrane stress variation. The sound filter proposed herein may provide a promising facility to control low frequency noise source with tonal characteristics.

Wide-bandgap epitaxial heterojunction windows for silicon solar cells

Science.gov (United States)

Landis, Geoffrey A.; Loferski, Joseph J.; Beaulieu, Roland; Sekula-Moise, Patricia A.; Vernon, Stanley M.

1990-01-01

It is shown that the efficiency of a solar cell can be improved if minority carriers are confined by use of a wide-bandgap heterojunction window. For silicon (lattice constant a = 5.43 A), nearly lattice-matched wide-bandgap materials are ZnS (a = 5.41 A) and GaP (a = 5.45 A). Isotype n-n heterojuntions of both ZnS/Si and GaP/Si were grown on silicon n-p homojunction solar cells. Successful deposition processes used were metalorganic chemical vapor deposition (MO-CVD) for GaP and ZnS, and vacuum evaporation of ZnS. Planar (100) and (111) and texture-etched - (111)-faceted - surfaces were used. A decrease in minority-carrier surface recombination compared to a bare surface was seen from increased short-wavelength spectral response, increased open-circuit voltage, and reduced dark saturation current, with no degradation of the minority carrier diffusion length.

Water-dependent photonic bandgap in silica artificial opals.

Science.gov (United States)

Gallego-Gómez, Francisco; Blanco, Alvaro; Canalejas-Tejero, Victor; López, Cefe

2011-07-04

Some characteristics of silica--based structures-like the photonic properties of artificial opals formed by silica spheres--can be greatly affected by the presence of adsorbed water. The reversible modification of the water content of an opal is investigated here by moderate heating (below 300 °C) and measuring in situ the changes in the photonic bandgap. Due to reversible removal of interstitial water, large blueshifts of 30 nm and a bandgap narrowing of 7% are observed. The latter is particularly surprising, because water desorption increases the refractive index contrast, which should lead instead to bandgap broadening. A quantitative explanation of this experiment is provided using a simple model for water distribution in the opal that assumes a nonclose-packed fcc structure. This model further predicts that, at room temperature, about 50% of the interstitial water forms necks between nearest-neighbor spheres, which are separated by 5% of their diameter. Upon heating, dehydration predominantly occurs at the sphere surfaces (in the opal voids), so that above 65 °C the remaining water resides exclusively in the necks. A near-close-packed fcc arrangement is only achieved above 200 °C. The high sensitivity to water changes exhibited by silica opals, even under gentle heating of few degrees, must be taken into account for practical applications. Remarkably, accurate control of the distance between spheres--from 16 to 1 nm--is obtained with temperature. In this study, novel use of the optical properties of the opal is made to infer quantitative information about water distribution within silica beads and dehydration phenomena from simple reflection spectra. Taking advantage of the well-defined opal morphology, this approach offers a simple tool for the straightforward investigation of generic adsorption-desorption phenomena, which might be extrapolated to many other fields involving capillary condensation. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGa

Creation of tunable absolute bandgaps in a two-dimensional anisotropic photonic crystal modulated by a nematic liquid crystal

International Nuclear Information System (INIS)

Liu Chenyang

2008-01-01

Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable absolute bandgap in a two-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic-dielectric cylinder in the liquid crystal medium is studied by solving Maxwell's equations using the plane wave expansion method. The photonic band structures are found to exhibit absolute bandgaps for the square and triangular lattices. Numerical simulations show that the absolute bandgaps can be continuously tuned in the square and triangular lattices consisting of anisotropic-dielectric cylinders by infiltrating nematic liquid crystals. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits

TiO2/ZnS/CdS Nanocomposite for Hydrogen Evolution and Orange II Dye Degradation

Directory of Open Access Journals (Sweden)

Václav Štengl

2011-01-01

Full Text Available TiO2/ZnS/CdS composites for photocatalytic hydrogen production from water were prepared by homogeneous hydrolysis of aqueous solutions mixture of TiOSO4, ZnSO4, and CdSO4 with thioacetamide. Hydrogen evolution was observed in the presence of palladium and platinum nanoparticles deposited on TiO2/ZnS/CdS composites. The morphology was obtained by scanning electron microscopy, the nitrogen adsorption-desorption was used for determination of surface area (BET and porosity. The method of UV-VIS diffuse reflectance spectroscopy was employed to estimate band-gap energies of prepared TiO2/ZnS/CdS nano-composites. The photocatalytic activity of the prepared samples were assessed by photocatalytic decomposition of Orange II dye in an aqueous slurry under UV irradiation at 365 nm wavelength and visible light up to 400 nm wavelength. Doped titanium dioxide by the CdS increased band-gap energy and doping with ZnS increased photocatalytic activity. The best photocatalytic activity for H2 evolution shows sample named TiZnCd7 on surface deposited with palladium, which contains 20.21% TiO2, 78.5% ZnS, and 1.29% CdS.

Plasmonically Enhanced Reflectance of Heat Radiation from Low-Bandgap Semiconductor Microinclusions.

Science.gov (United States)

Tang, Janika; Thakore, Vaibhav; Ala-Nissila, Tapio

2017-07-18

Increased reflectance from the inclusion of highly scattering particles at low volume fractions in an insulating dielectric offers a promising way to reduce radiative thermal losses at high temperatures. Here, we investigate plasmonic resonance driven enhanced scattering from microinclusions of low-bandgap semiconductors (InP, Si, Ge, PbS, InAs and Te) in an insulating composite to tailor its infrared reflectance for minimizing thermal losses from radiative transfer. To this end, we compute the spectral properties of the microcomposites using Monte Carlo modeling and compare them with results from Fresnel equations. The role of particle size-dependent Mie scattering and absorption efficiencies, and, scattering anisotropy are studied to identify the optimal microinclusion size and material parameters for maximizing the reflectance of the thermal radiation. For composites with Si and Ge microinclusions we obtain reflectance efficiencies of 57-65% for the incident blackbody radiation from sources at temperatures in the range 400-1600 °C. Furthermore, we observe a broadbanding of the reflectance spectra from the plasmonic resonances due to charge carriers generated from defect states within the semiconductor bandgap. Our results thus open up the possibility of developing efficient high-temperature thermal insulators through use of the low-bandgap semiconductor microinclusions in insulating dielectrics.

Photoelectrochemical Hydrogen Production

Energy Technology Data Exchange (ETDEWEB)

Hu, Jian

2013-12-23

The objectives of this project, covering two phases and an additional extension phase, were the development of thin film-based hybrid photovoltaic (PV)/photoelectrochemical (PEC) devices for solar-powered water splitting. The hybrid device, comprising a low-cost photoactive material integrated with amorphous silicon (a-Si:H or a-Si in short)-based solar cells as a driver, should be able to produce hydrogen with a 5% solar-to-hydrogen conversion efficiency (STH) and be durable for at least 500 hours. Three thin film material classes were studied and developed under this program: silicon-based compounds, copper chalcopyrite-based compounds, and metal oxides. With the silicon-based compounds, more specifically the amorphous silicon carbide (a-SiC), we achieved a STH efficiency of 3.7% when the photoelectrode was coupled to an a-Si tandem solar cell, and a STH efficiency of 6.1% when using a crystalline Si PV driver. The hybrid PV/a-SiC device tested under a current bias of -3~4 mA/cm{sup 2}, exhibited a durability of up to ~800 hours in 0.25 M H{sub 2}SO{sub 4} electrolyte. Other than the PV driver, the most critical element affecting the photocurrent (and hence the STH efficiency) of the hybrid PV/a-SiC device was the surface energetics at the a-SiC/electrolyte interface. Without surface modification, the photocurrent of the hybrid PEC device was ~1 mA/cm{sup 2} or lower due to a surface barrier that limits the extraction of photogenerated carriers. We conducted an extensive search for suitable surface modification techniques/materials, of which the deposition of low work function metal nanoparticles was the most successful. Metal nanoparticles of ruthenium (Ru), tungsten (W) or titanium (Ti) led to an anodic shift in the onset potential. We have also been able to develop hybrid devices of various configurations in a monolithic fashion and optimized the current matching via altering the energy bandgap and thickness of each constituent cell. As a result, the short

Theoretical prediction of sandwiched two-dimensional phosphide binary compound sheets with tunable bandgaps and anisotropic physical properties

Science.gov (United States)

Zhang, C. Y.; Yu, M.

2018-03-01

Atomic layers of GaP and InP binary compounds with unique anisotropic structural, electronic and mechanical properties have been predicted from first-principle molecular dynamics simulations. These new members of the phosphide binary compound family stabilize to a sandwiched two-dimensional (2D) crystalline structure with orthorhombic lattice symmetry and high buckling of 2.14 Å-2.46 Å. Their vibration modes are similar to those of phosphorene with six Raman active modes ranging from ˜80 cm-1 to 400 cm-1. The speeds of sound in their phonon dispersions reflect anisotropy in their elastic constants, which was further confirmed by their strong directional dependence of Young’s moduli and effective nonlinear elastic moduli. They show wide bandgap semiconductor behavior with fundamental bandgaps of 2.89 eV for GaP and 2.59 eV for InP, respectively, even wider than their bulk counterparts. Such bandgaps were found to be tunable under strain. In particular, a direct-indirect bandgap transition was found under certain strains along zigzag or biaxial orientations, reflecting their promising applications in strain-induced bandgap engineering in nanoelectronics and photovoltaics. Feasible pathways to realize these novel 2D phosphide compounds are also proposed.

Optical spectroscopy and imaging of the higher energy excitons and bandgap of monolayer MoS2

Science.gov (United States)

Borys, Nicholas; Bao, Wei; Barnard, Edward; Ko, Changhyun; Tongay, Sefaatin; Wu, Junqiao; Yang, Li; Schuck, P. James

Monolayer MoS2 (ML-MoS2) exhibits a rich manifold of excitons that dictate optoelectronic performance and functionality. Disentangling these states, which include the quasi-particle bandgap, is critical for developing 2D optoelectronic devices that operate beyond the optical bandgap. Whereas photoluminescence (PL) spectroscopy only probes the lowest-energy radiative state and absorption spectroscopy fails to discriminate energetically degenerate states, photoluminescence excitation (PLE) spectroscopy selectively probes only the excited states that thermalize to the emissive ground state exciton. Using PLE spectroscopy of ML-MoS2, we identify the Rydberg series of the exciton A and exciton B states as well as signatures of the quasi-particle bandgap and coupling between the indirect C exciton and the lowest-energy A exciton, which have eluded previous PLE studies. The assignment of these states is confirmed with density functional theory. Mapping the PLE spectrum reveals spatial variations of the higher-energy exciton manifold and quasi-particle bandgap which mirror the heterogeneity in the PL but also indicate variations in local exciton thermalization processes and chemical potentials.

High-Power Yb-Doped Solid-Core Photonic Bandgap Fiber Amplifier at 1150-1200nm

DEFF Research Database (Denmark)

Maruyama, H.; Shirakawa, A.; Ueda, K.

2008-01-01

Solid-core photonic-bandgap fiber amplification at the long-wavelength edge of ytterbium band is reported. A 32W output at 1156nm with a 66% slope efficiency and 9.1W output at 1178nm were succesfully obtained.......Solid-core photonic-bandgap fiber amplification at the long-wavelength edge of ytterbium band is reported. A 32W output at 1156nm with a 66% slope efficiency and 9.1W output at 1178nm were succesfully obtained....

In- and Ga-based inorganic double perovskites with direct bandgaps for photovoltaic applications.

Science.gov (United States)

Dai, Jun; Ma, Liang; Ju, Minggang; Huang, Jinsong; Zeng, Xiao Cheng

2017-08-16

Double perovskites in the form of A 2 B'B''X 6 (A = Cs, B' = Ag, B'' = Bi) have been reported as potential alternatives to lead-containing organometal trihalide perovskites. However, all double perovskites synthesized to date exhibit indirect bandgaps >1.95 eV, which are undesirable for photovoltaic and optoelectronic applications. Herein, we report a comprehensive computer-aided screening of In- and Ga-based double perovskites for potential photovoltaic applications. To this end, several preconditions are implemented for the screening of optimal candidates, which include structural stability, electronic bandgaps, and optical absorption. Importantly, four In- and Ga-based double perovskites are identified to possess direct bandgaps within the desirable range of 0.9-1.6 eV for photovoltaic applications. Dominant optical absorption of the four double perovskites is found to be in the UV range. The structural and thermal stability of the four double perovskites are examined using both the empirical Goldschmidt ratio and convex-hull calculations. Only Cs 2 AgInBr 6 is predicted to be thermodynamically stable.

Automating Energy Bandgap Measurements in Semiconductors Using LabVIEW

Science.gov (United States)

Garg, Amit; Sharma, Reena; Dhingra, Vishal

2010-01-01

In this paper, we report the development of an automated system for energy bandgap and resistivity measurement of a semiconductor sample using Four-Probe method for use in the undergraduate laboratory of Physics and Electronics students. The automated data acquisition and analysis system has been developed using National Instruments USB-6008 DAQ…

Light Absorption Enhancement of Silicon-Based Photovoltaic Devices with Multiple Bandgap Structures of Porous Silicon

Directory of Open Access Journals (Sweden)

Kuen-Hsien Wu

2015-09-01

Full Text Available Porous-silicon (PS multi-layered structures with three stacked PS layers of different porosity were prepared on silicon (Si substrates by successively tuning the electrochemical-etching parameters in an anodization process. The three PS layers have different optical bandgap energy and construct a triple-layered PS (TLPS structure with multiple bandgap energy. Photovoltaic devices were fabricated by depositing aluminum electrodes of Schottky contacts on the surfaces of the developed TLPS structures. The TLPS-based devices exhibit broadband photoresponses within the spectrum of the solar irradiation and get high photocurrent for the incident light of a tungsten lamp. The improved spectral responses of devices are owing to the multi-bandgap structures of TLPS, which are designed with a layered configuration analog to a tandem cell for absorbing a wider energy range of the incidental sun light. The large photocurrent is mainly ascribed to an enhanced light-absorption ability as a result of applying nanoporous-Si thin films as the surface layers to absorb the short-wavelength light and to improve the Schottky contacts of devices. Experimental results reveal that the multi-bandgap PS structures produced from electrochemical-etching of Si wafers are potentially promising for development of highly efficient Si-based solar cells.

Band structure of germanium carbides for direct bandgap silicon photonics

Energy Technology Data Exchange (ETDEWEB)

Stephenson, C. A., E-mail: cstephe3@nd.edu; Stillwell, R. A.; Wistey, M. A. [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); O' Brien, W. A. [Rigetti Quantum Computing, 775 Heinz Avenue, Berkeley, California 94710 (United States); Penninger, M. W. [Honeywell UOP, Des Plaines, Illinois 60016 (United States); Schneider, W. F. [Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Gillett-Kunnath, M. [Department of Chemistry, Syracuse University, Syracuse, New York 13244 (United States); Zajicek, J. [Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Yu, K. M. [Department of Physics and Materials Science, City University of Hong Kong, Hong Kong (China); Kudrawiec, R. [Institute of Physics, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw (Poland)

2016-08-07

Compact optical interconnects require efficient lasers and modulators compatible with silicon. Ab initio modeling of Ge{sub 1−x}C{sub x} (x = 0.78%) using density functional theory with HSE06 hybrid functionals predicts a splitting of the conduction band at Γ and a strongly direct bandgap, consistent with band anticrossing. Photoreflectance of Ge{sub 0.998}C{sub 0.002} shows a bandgap reduction supporting these results. Growth of Ge{sub 0.998}C{sub 0.002} using tetrakis(germyl)methane as the C source shows no signs of C-C bonds, C clusters, or extended defects, suggesting highly substitutional incorporation of C. Optical gain and modulation are predicted to rival III–V materials due to a larger electron population in the direct valley, reduced intervalley scattering, suppressed Auger recombination, and increased overlap integral for a stronger fundamental optical transition.

Hydrothermal synthesis of core–shell TiO_2 to enhance the photocatalytic hydrogen evolution

International Nuclear Information System (INIS)

Jiang, Jinghui; Zhou, Han; Zhang, Fan; Fan, Tongxiang; Zhang, Di

2016-01-01

Graphical abstract: Core–shell TiO_2 with interior cavity was synthesized by a hydrothermal approach to enhance the photocatalytic performance. - Highlights: • Core–shell TiO_2 with interior cavity can be synthesized by hydrothermal approach. • Multiple reflection of incident light in cavity can increase the absorption. • Rutile can optimize the bandgap and delay the charge recombination. - Abstract: A hydrothermal approach was designed to synthesize core–shell TiO_2 with interior cavity by making sodium dodecyl sulfonate (SDS) as the surfactant and the mixture of water and ethanol as the solvent. The control experiment of solvent reveals ethanol and water are responsible for the formation of sphere and interior cavity, respectively. Besides, SDS can assist the growth of core–shell structure, and the sizes of sphere and interior cavity can be tuned by regulating the reaction time or temperature. UV–vis absorption proves core–shell structure with interior cavity can increase the absorption of incident light to enhance the optical activity of final product. The calculated bandgap and photoluminescence (PL) analyses reveal the coexistence of rutile in final product can optimize the bandgap to 3.03 eV and delay the charge recombination. As a result, an effective photocatalytic hydrogen evolution under full spectrum irradiation can be harvested by the as-synthesized core–shell spheres to reach a quantum yield, approximately 9.57% at 340 nm wavelength.

Visible light photoreactivity from hybridization states between carbon nitride bandgap states and valence states in Nb and Ti oxides

Energy Technology Data Exchange (ETDEWEB)

Lee, Hosik, E-mail: hosiklee@gmail.com [School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology (UNIST), Unist-gil 100 Eonyang-eup, Ulsan 689-798 (Korea, Republic of); Ohno, Takahisa, E-mail: OHNO.Takahisa@nims.go.jp [Global Research Center for Environment and Energy based on Nanomaterials Science (GREEN), National Institute for Material Science, 1-2-1 Sengen, Tsukuba (Japan); Computational Materials Science Unit (CMSU), National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0047 (Japan)

2013-03-29

Highlights: ► Origin of bandgap reduction for visible photoreactivity is suggested. ► Carbon nitride adsorption in interlayer space can induce the bandgap reduction. ► The electronic structures are studied by density functional theory calculations. - Abstract: For better efficiency as photocatalysts, N-doping for visible light reactivity has been intensively studied in Lamellar niobic and titanic solid acids (HNb{sub 3}O{sub 8}, H{sub 2}Ti{sub 4}O{sub 9}), and its microscopic structures have been debated in this decade. We calculate the layered solid acids’ structures and bandgaps. Bandgap reduction by carbon nitride adsorption in interlayer space is observed computationally. It originates from localized nitrogen states which form delocalized top-valence states by hybridizing with the host oxygen states and can contribute to photo-current.

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

Linewidth of Cyclotron Absorption in Band-Gap Graphene: Relaxation Time Approximation vs. Monte Carlo Method

OpenAIRE

S.V. Kryuchkov; E.I. Kukhar’; D.V. Zav’yalov

2015-01-01

The power of the elliptically polarized electromagnetic radiation absorbed by band-gap graphene in presence of constant magnetic field is calculated. The linewidth of cyclotron absorption is shown to be non-zero even if the scattering is absent. The calculations are performed analytically with the Boltzmann kinetic equation and confirmed numerically with the Monte Carlo method. The dependence of the linewidth of the cyclotron absorption on temperature applicable for a band-gap graphene in the...

Origin of unusual bandgap shift and dual emission in organic-inorganic lead halide perovskites.

Science.gov (United States)

Dar, M Ibrahim; Jacopin, Gwénolé; Meloni, Simone; Mattoni, Alessandro; Arora, Neha; Boziki, Ariadni; Zakeeruddin, Shaik Mohammed; Rothlisberger, Ursula; Grätzel, Michael

2016-10-01

Emission characteristics of metal halide perovskites play a key role in the current widespread investigations into their potential uses in optoelectronics and photonics. However, a fundamental understanding of the molecular origin of the unusual blueshift of the bandgap and dual emission in perovskites is still lacking. In this direction, we investigated the extraordinary photoluminescence behavior of three representatives of this important class of photonic materials, that is, CH 3 NH 3 PbI 3 , CH 3 NH 3 PbBr 3 , and CH(NH 2 ) 2 PbBr 3 , which emerged from our thorough studies of the effects of temperature on their bandgap and emission decay dynamics using time-integrated and time-resolved photoluminescence spectroscopy. The low-temperature (photoluminescence of CH 3 NH 3 PbI 3 and CH 3 NH 3 PbBr 3 reveals two distinct emission peaks, whereas that of CH(NH 2 ) 2 PbBr 3 shows a single emission peak. Furthermore, irrespective of perovskite composition, the bandgap exhibits an unusual blueshift by raising the temperature from 15 to 300 K. Density functional theory and classical molecular dynamics simulations allow for assigning the additional photoluminescence peak to the presence of molecularly disordered orthorhombic domains and also rationalize that the unusual blueshift of the bandgap with increasing temperature is due to the stabilization of the valence band maximum. Our findings provide new insights into the salient emission properties of perovskite materials, which define their performance in solar cells and light-emitting devices.

Optimization and experimental validation of stiff porous phononic plates for widest complete bandgap of mixed fundamental guided wave modes

Science.gov (United States)

Hedayatrasa, Saeid; Kersemans, Mathias; Abhary, Kazem; Uddin, Mohammad; Van Paepegem, Wim

2018-01-01

Phononic crystal plates (PhPs) have promising application in manipulation of guided waves for design of low-loss acoustic devices and built-in acoustic metamaterial lenses in plate structures. The prominent feature of phononic crystals is the existence of frequency bandgaps over which the waves are stopped, or are resonated and guided within appropriate defects. Therefore, maximized bandgaps of PhPs are desirable to enhance their phononic controllability. Porous PhPs produced through perforation of a uniform background plate, in which the porous interfaces act as strong reflectors of wave energy, are relatively easy to produce. However, the research in optimization of porous PhPs and experimental validation of achieved topologies has been very limited and particularly focused on bandgaps of flexural (asymmetric) wave modes. In this paper, porous PhPs are optimized through an efficient multiobjective genetic algorithm for widest complete bandgap of mixed fundamental guided wave modes (symmetric and asymmetric) and maximized stiffness. The Pareto front of optimization is analyzed and variation of bandgap efficiency with respect to stiffness is presented for various optimized topologies. Selected optimized topologies from the stiff and compliant regimes of Pareto front are manufactured by water-jetting an aluminum plate and their promising bandgap efficiency is experimentally observed. An optimized Pareto topology is also chosen and manufactured by laser cutting a Plexiglas (PMMA) plate, and its performance in self-collimation and focusing of guided waves is verified as compared to calculated dispersion properties.

All-PM monolithic fs Yb-fiber laser, dispersion-managed with all-solid photonic bandgap fiber

DEFF Research Database (Denmark)

Liu, Xiaomin; Lægsgaard, Jesper; Turchinovich, Dmitry

2009-01-01

All-in-fiber SESAM-modelocked self-starting fiber laser is demonstrated. Cavity dispersion is managed by a spliced-in PM all-solid photonic bandgap fiber. The laser directly delivers 1.25 nJ pulses of 280 fs duration.......All-in-fiber SESAM-modelocked self-starting fiber laser is demonstrated. Cavity dispersion is managed by a spliced-in PM all-solid photonic bandgap fiber. The laser directly delivers 1.25 nJ pulses of 280 fs duration....

Fabrication and characterization of porous-core honeycomb bandgap THz fibers

DEFF Research Database (Denmark)

Bao, Hualong; Nielsen, Kristian; Rasmussen, Henrik K.

We have fabricated a porous-core honeycomb fiber in the cyclic olefin copolymer (COC) Topas® by drill-draw technology [1]. A cross-sectional image of the fabricated fiber is shown in the left Panel of Fig. 1. Simulation of the electromagnetic properties of the fiber shows two wide bandgaps within......-TDS system (Picometrix T-Ray 4000). The reference pulse before coupling into the fiber is shown in Fig. 1(a) and the time trace of the THz pulse after propagation through a 5-cm long segment of fiber is shown in Fig. 1(b) (blue curve). After adding some water on the outside of the fiber surface......, the transmitted pulse experiences less pronounced oscillations at times later than 20 ps ( red curve in Fig. 1(b)). Figs. 1(c) and (d) show the short-time Fourier transforms of the two time-domain traces in Fig. 1(b), overlaid with the calculated group delay in the two bandgaps (black squares). The frequencies...

Intermediate Bandgap Solar Cells From Nanostructured Silicon

Energy Technology Data Exchange (ETDEWEB)

Black, Marcie [Bandgap Engineering, Lincoln, MA (United States)

2014-10-30

This project aimed to demonstrate increased electronic coupling in silicon nanostructures relative to bulk silicon for the purpose of making high efficiency intermediate bandgap solar cells using silicon. To this end, we formed nanowires with controlled crystallographic orientation, small diameter, <111> sidewall faceting, and passivated surfaces to modify the electronic band structure in silicon by breaking down the symmetry of the crystal lattice. We grew and tested these silicon nanowires with <110>-growth axes, which is an orientation that should produce the coupling enhancement.

Structural and electronic properties of hydrogen adsorptions on BC3 sheet and graphene: a comparative study

International Nuclear Information System (INIS)

Chuang, Feng-Chuan; Huang, Zhi-Quan; Lin, Wen-Huan; Albao, Marvin A; Su, Wan-Sheng

2011-01-01

We have systematically investigated the effect of hydrogen adsorption on a single BC 3 sheet as well as graphene using first-principles calculations. Specifically, a comparative study of the energetically favorable atomic configurations for both H-adsorbed BC 3 sheets and graphene at different hydrogen concentrations ranging from 1/32 to 4/32 ML and 1/8 to 1 ML was undertaken. The preferred hydrogen arrangement on the single BC 3 sheet and graphene was found to have the same property as that of the adsorbed H atoms on the neighboring C atoms on the opposite sides of the sheet. Moreover, at low coverage of H, the pattern of hydrogen adsorption on the BC 3 shows a proclivity toward formation on the same ring, contrasting their behavior on graphene where they tend to form the elongated zigzag chains instead. Lastly, both the hydrogenated BC 3 sheet and graphene exhibit alternation of semiconducting and metallic properties as the H concentration is increased. These results suggest the possibility of manipulating the bandgaps in a single BC 3 sheet and graphene by controlling the H concentrations on the BC 3 sheet and graphene.

Ultrasonic bandgaps in 3D-printed periodic ceramic microlattices

Czech Academy of Sciences Publication Activity Database

Kruisová, Alena; Ševčík, Martin; Seiner, Hanuš; Sedlák, Petr; Román-Manso, B.; Miranzo, P.; Belmonte, M.; Landa, Michal

January (2018), s. 91-100 ISSN 0041-624X R&D Projects: GA ČR GA17-01618S Institutional support: RVO:61388998 Keywords : phononic crystals * ceramic s * additive manufacturing * bandgaps * wave propagation * finite elements method Subject RIV: BI - Acoustics OBOR OECD: Applied mechanics Impact factor: 2.327, year: 2016 http://dx.doi.org/10.1016/j.ultras.2017.07.017

Electromagnetic interference reduction using electromagnetic bandgap structures in packages, enclosures, cavities, and antennas

Science.gov (United States)

Mohajer Iravani, Baharak

Electromagnetic interference (EMI) is a source of noise problems in electronic devices. The EMI is attributed to coupling between sources of radiation and components placed in the same media such as package or chassis. This coupling can be either through conducting currents or through radiation. The radiation of electromagnetic (EM) fields is supported by surface currents. Thus, minimizing these surface currents is considered a major and critical step to suppress EMI. In this work, we present novel strategies to confine surface currents in different applications including packages, enclosures, cavities, and antennas. The efficiency of present methods of EM noise suppression is limited due to different drawbacks. For example, the traditional use of lossy materials and absorbers suffers from considerable disadvantages including mechanical and thermal reliability leading to limited life time, cost, volume, and weight. In this work, we consider the use of Electromagnetic Band Gap (EBG) structures. These structures are suitable for suppressing surface currents within a frequency band denoted as the bandgap. Their design is straight forward, they are inexpensive to implement, and they do not suffer from the limitations of the previous methods. A new method of EM noise suppression in enclosures and cavity-backed antennas using mushroom-type EBG structures is introduced. The effectiveness of the EBG as an EMI suppresser is demonstrated using numerical simulations and experimental measurements. To allow integration of EBGs in printed circuit boards and packages, novel miniaturized simple planar EBG structures based on use of high-k dielectric material (epsilonr > 100) are proposed. The design consists of meander lines and patches. The inductive meander lines serve to provide current continuity bridges between the capacitive patches. The high-k dielectric material increases the effective capacitive load substantially in comparison to commonly used material with much lower

Defects induced luminescence and tuning of bandgap energy narrowing in ZnO nanoparticles doped with Li ions

KAUST Repository

Awan, Saif Ullah; Hasanain, S. K.; Hassnain Jaffari, G.; Anjum, Dalaver H.; Qurashi, Umar S.

2014-01-01

Microstructural and optical properties of Zn1-yLiyO (0.00 ≤y ≤0.10) nanoparticles are investigated. Li incorporation leads to substantial changes in the structural characterization. From micro-structural analysis, no secondary phases or clustering of Li was detected. Elemental maps confirmed homogeneous distribution of Li in ZnO. Sharp UV peak due to the recombination of free exciton and defects based luminescence broad visible band was observed. The transition from the conduction band to Zinc vacancy defect level in photoluminescence spectra is found at 518±2.5nm. The yellow luminescence was observed and attributed to Li related defects in doped samples. With increasing Li doping, a decrease in energy bandgap was observed in the range 3.26±0.014 to 3.17±0.018eV. The bandgap narrowing behavior is explained in terms of the band tailing effect due to structural disorder, carrier-impurities, carrier-carrier, and carrier-phonon interactions. Tuning of the bandgap energy in this class of wide bandgap semiconductor is very important for room temperature spintronics applications and optical devices. © 2014 AIP Publishing LLC.

Defects induced luminescence and tuning of bandgap energy narrowing in ZnO nanoparticles doped with Li ions

KAUST Repository

Awan, Saif Ullah

2014-08-28

Microstructural and optical properties of Zn1-yLiyO (0.00 ≤y ≤0.10) nanoparticles are investigated. Li incorporation leads to substantial changes in the structural characterization. From micro-structural analysis, no secondary phases or clustering of Li was detected. Elemental maps confirmed homogeneous distribution of Li in ZnO. Sharp UV peak due to the recombination of free exciton and defects based luminescence broad visible band was observed. The transition from the conduction band to Zinc vacancy defect level in photoluminescence spectra is found at 518±2.5nm. The yellow luminescence was observed and attributed to Li related defects in doped samples. With increasing Li doping, a decrease in energy bandgap was observed in the range 3.26±0.014 to 3.17±0.018eV. The bandgap narrowing behavior is explained in terms of the band tailing effect due to structural disorder, carrier-impurities, carrier-carrier, and carrier-phonon interactions. Tuning of the bandgap energy in this class of wide bandgap semiconductor is very important for room temperature spintronics applications and optical devices. © 2014 AIP Publishing LLC.

Self-stabilization of a mode-locked femtosecond fiber laser using a photonic bandgap fiber

DEFF Research Database (Denmark)

Liu, Xiaomin; Lægsgaard, Jesper; Turchinovich, Dmitry

2010-01-01

We demonstrate a self-stabilization mechanism of a semiconductor saturable absorber mode-locked linearcavity Yb-doped fiber laser using an intracavity photonic bandgap fiber. This mechanism relies on the spectral shift of the laser pulses to a spectral range of higher anomalous dispersion...... and higher loss of the photonic bandgap fiber, as a reaction to the intracavity power buildup. This, in particular, results in a smaller cavity loss for the stably mode-locked laser, as opposed to the Q-switched mode-locking scenario. The laser provides stable 39–49 pJ pulses of around 230 fs duration at 29...

Origins of visible-light emissions in hydrogen-coated silicon nanocrystals: Role of passivating coating

International Nuclear Information System (INIS)

Tit, Nacir; Yamani, Z.H.; Graham, J.; Ayesh, A.

2010-01-01

We present a theoretical investigation of the electronic and optical properties of hydrogen-coated silicon nanocrystals (Si:H NCs). On one hand, the density-functional theory (DFT) is used to both calculate the total energy and relax the NCs. On a second hand, the tight-binding method, which includes the minimal sp 3 -basis set within the second-nearest-neighbor interaction scheme, is applied to calculate the electronic structures, oscillator strength (OS) and recombination rate (RR) versus the NC size, coating and atomic relaxation. Three main findings are reported: (i) The quantum confinement in these NCs do follow similar rule to the case of a single-particle in a box, where the confinement energy decays in power-law with the increasing NC's size. (ii) The coating is shown to play the essential role in creation of large band-gap energy lying within the visible-light energy spectrum. (iii) The surface atomic relaxation is found to reduce the band-gap energy by about 150 meV and enhance both OS and RR. Our claims are corroborated by the available experimental data.

Nanoscale probing of bandgap states on oxide particles using electron energy-loss spectroscopy

Energy Technology Data Exchange (ETDEWEB)

Liu, Qianlang [School for the Engineering of Matter, Transport and Energy, Arizona State University, 85287 AZ (United States); March, Katia [Laboratoire de Physique des Solides, Bâtiment 510, Université Paris-Sud, 91405 Orsay Cedex (France); Crozier, Peter A., E-mail: CROZIER@asu.edu [School for the Engineering of Matter, Transport and Energy, Arizona State University, 85287 AZ (United States)

2017-07-15

Surface and near-surface electronic states were probed with nanometer spatial resolution in MgO and TiO{sub 2} anatase nanoparticles using ultra-high energy resolution electron energy-loss spectroscopy (EELS) coupled to a scanning transmission electron microscope (STEM). This combination allows the surface electronic structure determined with spectroscopy to be correlated with nanoparticle size, morphology, facet etc. By acquiring the spectra in aloof beam mode, radiation damage to the surface can be significantly reduced while maintaining the nanometer spatial resolution. MgO and TiO{sub 2} showed very different bandgap features associated with the surface/sub-surface layer of the nanoparticles. Spectral simulations based on dielectric theory and density of states models showed that a plateau feature found in the pre-bandgap region in the spectra from (100) surfaces of 60 nm MgO nanocubes is consistent with a thin hydroxide surface layer. The spectroscopy shows that this hydroxide species gives rise to a broad filled surface state at 1.1 eV above the MgO valence band. At the surfaces of TiO{sub 2} nanoparticles, pronounced peaks were observed in the bandgap region, which could not be well fitted to defect states. In this case, the high refractive index and large particle size may make Cherenkov or guided light modes the likely causes of the peaks. - Highlights: • Bandgap states detected with aloof beam monochromated EELS on oxide nanoparticle surfaces. • Dielectric theory applied to simulate the spectra and interpret surface structure. • Density of states models also be employed to understand the surface electronic structure. • In MgO, one states associate with water species was found close to the valence band edge. • In anatase, two mid-gap states associated with point defects were found.

Probing defect states in polycrystalline GaN grown on Si(111) by sub-bandgap laser-excited scanning tunneling spectroscopy

Science.gov (United States)

Hsiao, F.-M.; Schnedler, M.; Portz, V.; Huang, Y.-C.; Huang, B.-C.; Shih, M.-C.; Chang, C.-W.; Tu, L.-W.; Eisele, H.; Dunin-Borkowski, R. E.; Ebert, Ph.; Chiu, Y.-P.

2017-01-01

We demonstrate the potential of sub-bandgap laser-excited cross-sectional scanning tunneling microscopy and spectroscopy to investigate the presence of defect states in semiconductors. The characterization method is illustrated on GaN layers grown on Si(111) substrates without intentional buffer layers. According to high-resolution transmission electron microscopy and cathodoluminescence spectroscopy, the GaN layers consist of nanoscale wurtzite and zincblende crystallites with varying crystal orientations and hence contain high defect state densities. In order to discriminate between band-to-band excitation and defect state excitations, we use sub-bandgap laser excitation. We probe a clear increase in the tunnel current at positive sample voltages during sub-bandgap laser illumination for the GaN layer with high defect density, but no effect is found for high quality GaN epitaxial layers. This demonstrates the excitation of free charge carriers at defect states. Thus, sub-bandgap laser-excited scanning tunneling spectroscopy is a powerful complimentary characterization tool for defect states.

Theoretical evaluation of maximum electric field approximation of direct band-to-band tunneling Kane model for low bandgap semiconductors

Science.gov (United States)

Dang Chien, Nguyen; Shih, Chun-Hsing; Hoa, Phu Chi; Minh, Nguyen Hong; Thi Thanh Hien, Duong; Nhung, Le Hong

2016-06-01

The two-band Kane model has been popularly used to calculate the band-to-band tunneling (BTBT) current in tunnel field-effect transistor (TFET) which is currently considered as a promising candidate for low power applications. This study theoretically clarifies the maximum electric field approximation (MEFA) of direct BTBT Kane model and evaluates its appropriateness for low bandgap semiconductors. By analysing the physical origin of each electric field term in the Kane model, it has been elucidated in the MEFA that the local electric field term must be remained while the nonlocal electric field terms are assigned by the maximum value of electric field at the tunnel junction. Mathematical investigations have showed that the MEFA is more appropriate for low bandgap semiconductors compared to high bandgap materials because of enhanced tunneling probability in low field regions. The appropriateness of the MEFA is very useful for practical uses in quickly estimating the direct BTBT current in low bandgap TFET devices.

Wild Band Edges: The Role of Bandgap Grading and Band-Edge Fluctuations in High-Efficiency Chalcogenide Devices: Preprint

Energy Technology Data Exchange (ETDEWEB)

Repins, Ingrid; Mansfield, Lorelle; Kanevce, Ana; Jensen, Soren A.; Kuciauskas, Darius; Glynn, Stephen; Barnes, Teresa; Metzger, Wyatt; Burst, James; Jiang, Chun-Sheng; Dippo, Patricia; Harvey, Steve; Teeter, Glenn; Perkins, Craig; Egaas, Brian; Zakutayev, Andriy; Alsmeier, J.-H.; Lussky, T.; Korte, L.; Wilks, R. G.; Bar, M.; Yan, Y.; Lany, Stephan; Zawadzki, Pawel; Park, Ji-Sang; Wei, Suhuai

2016-06-16

Band-edge effects -- including grading, electrostatic fluctuations, bandgap fluctuations, and band tails -- affect chalcogenide device efficiency. These effects now require more careful consideration as efficiencies increase beyond 20%. Several aspects of the relationships between band-edge phenomena and device performance for NREL absorbers are examined. For Cu(In,Ga)Se2 devices, recent increases in diffusion length imply changes to optimum bandgap profile. The origin, impact, and modification of electrostatic and bandgap fluctuations are also discussed. The application of the same principles to devices based on CdTe, kesterites, and emerging absorbers (Cu2SnS3, CuSbS2), considering differences in materials properties and defect formation energies, is examined.

A 98 W 1178 nm Yb-doped solid-core photonic bandgap fiber oscillator

International Nuclear Information System (INIS)

Fan, Xinyan; Chen, Mingchen; Shirakawa, Akira; Ueda, Ken-ichi; Olausson, Christina B; Broeng, Jes

2013-01-01

A high-power ytterbium-doped solid-core photonic bandgap fiber laser directly oscillating at 1178 nm is reported. The sharp-cut bandpass distributed filtering effect of photonic bandgap fiber can suppress amplified spontaneous emission (ASE) in the conventional high-gain spectral region. The oscillator is composed of a high reflection fiber Bragg grating spliced with a 39 m gain fiber and a Fresnel fiber end surface. A model based on rate equations is investigated numerically. A record output power of 98 W is achieved with a slope efficiency of 54%. The laser linewidth is 0.5 nm. The spectrum at 98 W indicates that ASE and parasitic lasing are suppressed effectively. (letter)

Broadband optically controlled switching effect in a microfluid-filled photonic bandgap fiber

International Nuclear Information System (INIS)

Guo, Junqi; Liu, Yan-ge; Wang, Zhi; Luo, Mingming; Huang, Wei; Liu, Xiaoqi; Han, Tingting

2016-01-01

Broadband optically controlled switching in a microfluid-filled photonic bandgap fiber (MF-PBGF) was observed and investigated. The MF-PBGF was formed by infusing a temperature-sensitive high-index fluid into all of the cladding holes of a microstructured optical fiber (MOF). The fiber was then side pumped with a 532 nm continuous wave laser. An extinction ratio of greater than 20 dB at most of the bandgap wavelengths (more than 200 nm) was obtained with a switching power of ∼147 mW. Theoretical and experimental investigations revealed that the effect originated from changes in the temperature gradient induced by heat absorption of the fiber coating with laser illumination. These investigations offer a new and simple approach to achieve wideband and flexible all-optical fiber switching devices without using any photosensitive materials. (paper)

Analysis of multifunctional piezoelectric metastructures for low-frequency bandgap formation and energy harvesting

Science.gov (United States)

Sugino, C.; Erturk, A.

2018-05-01

Vibration-based energy harvesting is a growing field for generating low-power electricity to use in wireless electronic devices, such as the sensor networks used in structural health monitoring applications. Locally resonant metastructures, which are structures that comprise locally resonant metamaterial components, enable bandgap formation at wavelengths much longer than the lattice size, for critical applications such as low-frequency vibration attenuation in flexible structures. This work aims to bridge the domains of energy harvesting and locally resonant metamaterials to form multifunctional structures that exhibit both low-power electricity generation and vibration attenuation capabilities. A fully coupled electromechanical modeling framework is developed for two characteristic systems and their modal analysis is presented. Simulations are performed to explore the vibration and electrical power frequency response maps for varying electrical load resistance, and optimal loading conditions are presented. Case studies are presented to understand the interaction of bandgap formation and energy harvesting capabilities of this new class of multifunctional energy-harvesting locally resonant metastructures. It is shown that useful energy can be harvested from locally resonant metastructures without significantly diminishing their dramatic vibration attenuation in the locally resonant bandgap. Thus, integrating energy harvesters into a locally resonant metastructure enables a new potential for multifunctional locally resonant metastructures that can host self-powered sensors.

Physical ageing in the above-bandgap photoexposured glassy arsenic selenides

Energy Technology Data Exchange (ETDEWEB)

Kozdras, A [Faculty of Physics of Opole University of Technology, 75, Ozimska str., Opole, PL-45370 (Poland); Golovchak, R [Lviv Scientific Research Institute of Materials of SRC ' Carat' , 202, Stryjska str., Lviv, UA-79031 (Ukraine); Shpotyuk, O [Lviv Scientific Research Institute of Materials of SRC ' Carat' , 202, Stryjska str., Lviv, UA-79031 (Ukraine)

2007-08-15

Physical ageing induced by above-bandgap light illumination is studied in glassy As-Se using differential scanning calorimetry. It is shown that measurable effect like to known short-term physical ageing is observed only in Se-rich glasses. The kinetics of this effect is compared with that caused by natural storage in a dark.

Physical ageing in the above-bandgap photoexposured glassy arsenic selenides

International Nuclear Information System (INIS)

Kozdras, A; Golovchak, R; Shpotyuk, O

2007-01-01

Physical ageing induced by above-bandgap light illumination is studied in glassy As-Se using differential scanning calorimetry. It is shown that measurable effect like to known short-term physical ageing is observed only in Se-rich glasses. The kinetics of this effect is compared with that caused by natural storage in a dark

Space-coiling fractal metamaterial with multi-bandgaps on subwavelength scale

Science.gov (United States)

Man, Xianfeng; Liu, Tingting; Xia, Baizhan; Luo, Zhen; Xie, Longxiang; Liu, Jian

2018-06-01

Acoustic metamaterials are remarkably different from conventional materials, as they can flexibly manipulate and control the propagation of sound waves. Unlike the locally resonant metamaterials introduced in earlier studies, we designed an ultraslow artificial structure with a sound speed much lower than that in air. In this paper, the space-coiling approach is proposed for achieving artificial metamaterial for extremely low-frequency airborne sound. In addition, the self-similar fractal technique is utilized for designing space-coiling Mie-resonance-based metamaterials (MRMMs) to obtain a band-dispersive spectrum. The band structures of two-dimensional (2D) acoustic metamaterials with different fractal levels are illustrated using the finite element method. The low-frequency bandgap can easily be formed, and multi-bandgap properties are observed in high-level fractals. Furthermore, the designed MRMMs with higher order fractal space coiling shows a good robustness against irregular arrangement. Besides, the proposed artificial structure was found to modify and control the radiation field arbitrarily. Thus, this work provides useful guidelines for the design of acoustic filtering devices and acoustic wavefront shaping applications on the subwavelength scale.

Hydrogen Gas Sensing Characteristics of Nanostructured NiO Thin Films Synthesized by SILAR Method

Science.gov (United States)

Karaduman, Irmak; Çorlu, Tugba; Yıldırım, M. Ali; Ateş, Aytunç; Acar, Selim

2017-07-01

Nanostructured NiO thin films have been synthesized by a facile, low-cost successive ionic layer adsorption and reaction (SILAR) method, and the effects of the film thickness on their hydrogen gas sensing properties investigated. The samples were characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD) analysis, and energy-dispersive x-ray analysis. The XRD results revealed that the crystallinity improved with increasing thickness, exhibiting polycrystalline structure. SEM studies showed that all the films covered the glass substrate well. According to optical absorption measurements, the optical bandgap decreased with increasing film thickness. The gas sensing properties of the nanostructured NiO thin films were studied as a function of operating temperature and gas concentration. The samples showed good sensing performance of H2 gas with high response. The maximum response was 75% at operating temperature of 200°C for hydrogen gas concentration of 40 ppm. These results demonstrate that nanostructured NiO thin films synthesized by the SILAR method have potential for application in hydrogen detection.

Quantum state propagation in linear photonic bandgap structures

International Nuclear Information System (INIS)

Severini, S; Tricca, D; Sibilia, C; Bertolotti, M; Perina, Jan

2004-01-01

In this paper we investigate the propagation of a generic quantum state in a corrugated waveguide, which reproduces a photonic bandgap structure. We find the conditions that assure the outcoming state to preserve the quantum properties of the incoming state. Then, focusing on a particular quantum state (realized by two counter-propagating coherent states), we study the possibility of preserving the quantum properties of this particular double coherent state even in the presence of absorption phenomena during propagation in the structure

CdS/TiO2 photoanodes via solution ion transfer method for highly efficient solar hydrogen generation

Science.gov (United States)

Krishna Karuturi, Siva; Yew, Rowena; Reddy Narangari, Parvathala; Wong-Leung, Jennifer; Li, Li; Vora, Kaushal; Tan, Hark Hoe; Jagadish, Chennupati

2018-03-01

Cadmium sulfide (CdS) is a unique semiconducting material for solar hydrogen generation applications with a tunable, narrow bandgap that straddles water redox potentials. However, its potential towards efficient solar hydrogen generation has not yet been realized due to low photon-to-current conversions, high charge carrier recombination and the lack of controlled preparation methods. In this work, we demonstrate a highly efficient CdS/TiO2 heterostructured photoelectrode using atomic layer deposition and solution ion transfer reactions. Enabled by the well-controlled deposition of CdS nanocrystals on TiO2 inverse opal (TiIO) nanostructures using the proposed method, a saturation photocurrent density of 9.1 mA cm-2 is realized which is the highest ever reported for CdS-based photoelectrodes. We further demonstrate that the passivation of a CdS surface with an ultrathin amorphous layer (˜1.5 nm) of TiO2 improves the charge collection efficiency at low applied potentials paving the way for unassisted solar hydrogen generation.

On the mechanism of bandgap formation in locally resonant finite elastic metamaterials

Science.gov (United States)

Sugino, Christopher; Leadenham, Stephen; Ruzzene, Massimo; Erturk, Alper

2016-10-01

Elastic/acoustic metamaterials made from locally resonant arrays can exhibit bandgaps at wavelengths much longer than the lattice size for various applications spanning from low-frequency vibration/sound attenuation to wave guiding and filtering in mechanical and electromechanical devices. For an effective use of such locally resonant metamaterial concepts in finite structures, it is required to bridge the gap between the lattice dispersion characteristics and modal behavior of the host structure with its resonators. To this end, we develop a novel argument for bandgap formation in finite-length elastic metamaterial beams, relying on the modal analysis and the assumption of infinitely many resonators. We show that the dual problem to wave propagation through an infinite periodic beam is the modal analysis of a finite beam with an infinite number of resonators. A simple formula that depends only on the resonator natural frequency and total mass ratio is derived for placing the bandgap in a desired frequency range, yielding an analytical insight and a rule of thumb for design purposes. A method for understanding the importance of a resonator location and mass is discussed in the context of a Riemann sum approximation of an integral, and a method for determining the optimal number of resonators for a given set of boundary conditions and target frequency is introduced. The simulations of the theoretical framework are validated by experiments for bending vibrations of a locally resonant cantilever beam.

Fabrication and characterization of an all-solid tellurite-phosphate photonic bandgap fiber.

Science.gov (United States)

Cheng, Tonglei; Sakai, Yukiko; Suzuki, Takenobu; Ohishi, Yasutake

2015-05-01

We present an all-solid tellurite-phosphate photonic bandgap fiber (PBGF) with two layers of high-index rods (TeO2-Li2O-WO3-MoO3-Nb2O5, TLWMN) in the cladding (TeO2-ZnO-Li2O-K2O-Al2O3-P2O5, TZLKAP). TLWMN and TZLKAP glasses have good compatibility for fabricating the all-solid PBGF. Photonic bandgap (PBG) properties are calculated by the plane wave expansion method (PWM), and the results agree well with the measured transmission spectrum. Furthermore, the modal field patterns are measured at ∼1300 and 1520 nm, respectively. The light is confined to the core at ∼1300  nm and lost in the cladding at ∼1520  nm, which match well with the calculated modal field intensities.

Hydrogenation of Penta-Graphene Leads to Unexpected Large Improvement in Thermal Conductivity.

Science.gov (United States)

Wu, Xufei; Varshney, Vikas; Lee, Jonghoon; Zhang, Teng; Wohlwend, Jennifer L; Roy, Ajit K; Luo, Tengfei

2016-06-08

Penta-graphene (PG) has been identified as a novel two-dimensional (2D) material with an intrinsic bandgap, which makes it especially promising for electronics applications. In this work, we use first-principles lattice dynamics and iterative solution of the phonon Boltzmann transport equation (BTE) to determine the thermal conductivity of PG and its more stable derivative, hydrogenated penta-graphene (HPG). As a comparison, we also studied the effect of hydrogenation on graphene thermal conductivity. In contrast to hydrogenation of graphene, which leads to a dramatic decrease in thermal conductivity, HPG shows a notable increase in thermal conductivity, which is much higher than that of PG. Considering the necessity of using the same thickness when comparing thermal conductivity values of different 2D materials, hydrogenation leads to a 63% reduction in thermal conductivity for graphene, while it results in a 76% increase for PG. The high thermal conductivity of HPG makes it more thermally conductive than most other semiconducting 2D materials, such as the transition metal chalcogenides. Our detailed analyses show that the primary reason for the counterintuitive hydrogenation-induced thermal conductivity enhancement is the weaker bond anharmonicity in HPG than PG. This leads to weaker phonon scattering after hydrogenation, despite the increase in the phonon scattering phase space. The high thermal conductivity of HPG may inspire intensive research around HPG and other derivatives of PG as potential materials for future nanoelectronic devices. The fundamental physics understood from this study may open up a new strategy to engineer thermal transport properties of other 2D materials by controlling bond anharmonicity via functionalization.

Photonic bandgap structure of 3-D fcc silica nanospheres

Energy Technology Data Exchange (ETDEWEB)

Woo, Y. K.; Ha, N. Y.; Hwang, Ji Soo; Chang, H. J.; Wu, J. W. [Dept. of Physics, Ewha Womans University, Seoul (Korea, Republic of)

2002-07-01

Photonic crystal is an artificial optical material with a periodic dielectric potential, hence exhibiting a bandgap for a propagating electromagnetic wave. We fabricated crystal possessing 3-D fcc opal structure from silica nanospheres. The crystals are self-assembled on a flat glass by evaporating the solvent in the nanosphere suspension at the room temperature. The suspension consists of silica nanospheres with a diameter of 200 nm. The microscopic arrangement of nanospheres is identified by a scanning electron microscope, the resulting structure being fcc.Transmission spectrum of the fabricated photonic crystal in the visible and near-infrared regions is measured at different incident angles to find the distinct Bragg peaks, analysis of which further confirmed the fcc structure of the photonic crystal. From the optical microscopic image, we find that the opal domain varies from 30 μm to 125 μm in size. In order to relate the observed Bragg peaks with the microscopic arrangement of silica nanospheres, we introduced the scalar wave approximation, where the electric field in the medium is treated as a scalar rather than a vector quantity. It is found that the theoretical prediction of the position of bandgap is in a good agreement with the experimental measurement.

Photonic bandgap structure of 3-D fcc silica nanospheres

International Nuclear Information System (INIS)

Woo, Y. K.; Ha, N. Y.; Hwang, Ji Soo; Chang, H. J.; Wu, J. W.

2002-01-01

Photonic crystal is an artificial optical material with a periodic dielectric potential, hence exhibiting a bandgap for a propagating electromagnetic wave. We fabricated crystal possessing 3-D fcc opal structure from silica nanospheres. The crystals are self-assembled on a flat glass by evaporating the solvent in the nanosphere suspension at the room temperature. The suspension consists of silica nanospheres with a diameter of 200 nm. The microscopic arrangement of nanospheres is identified by a scanning electron microscope, the resulting structure being fcc.Transmission spectrum of the fabricated photonic crystal in the visible and near-infrared regions is measured at different incident angles to find the distinct Bragg peaks, analysis of which further confirmed the fcc structure of the photonic crystal. From the optical microscopic image, we find that the opal domain varies from 30 μm to 125 μm in size. In order to relate the observed Bragg peaks with the microscopic arrangement of silica nanospheres, we introduced the scalar wave approximation, where the electric field in the medium is treated as a scalar rather than a vector quantity. It is found that the theoretical prediction of the position of bandgap is in a good agreement with the experimental measurement.

Nanoscale probing of bandgap states on oxide particles using electron energy-loss spectroscopy.

Science.gov (United States)

Liu, Qianlang; March, Katia; Crozier, Peter A

2017-07-01

Surface and near-surface electronic states were probed with nanometer spatial resolution in MgO and TiO 2 anatase nanoparticles using ultra-high energy resolution electron energy-loss spectroscopy (EELS) coupled to a scanning transmission electron microscope (STEM). This combination allows the surface electronic structure determined with spectroscopy to be correlated with nanoparticle size, morphology, facet etc. By acquiring the spectra in aloof beam mode, radiation damage to the surface can be significantly reduced while maintaining the nanometer spatial resolution. MgO and TiO 2 showed very different bandgap features associated with the surface/sub-surface layer of the nanoparticles. Spectral simulations based on dielectric theory and density of states models showed that a plateau feature found in the pre-bandgap region in the spectra from (100) surfaces of 60nm MgO nanocubes is consistent with a thin hydroxide surface layer. The spectroscopy shows that this hydroxide species gives rise to a broad filled surface state at 1.1eV above the MgO valence band. At the surfaces of TiO 2 nanoparticles, pronounced peaks were observed in the bandgap region, which could not be well fitted to defect states. In this case, the high refractive index and large particle size may make Cherenkov or guided light modes the likely causes of the peaks. Copyright © 2016 Elsevier B.V. All rights reserved.

Tunable polarisation-maintaining filter based on liquid crystal photonic bandgap fibre

DEFF Research Database (Denmark)

Scolari, Lara; Olausson, Christina Bjarnal Thulin; Weirich, Johannes

2008-01-01

A tunable and polarisation-maintaining all-in-fibre filter based on a liquid crystal photonic bandgap fibre is demonstrated. Its polarisation extinction ratio reaches 14 dB at 1550 nm wavelength. Its spectral tunability range spans over 250 nm in the temperature range 30–70°C. The measured...

A model for the direct-to-indirect band-gap transition in monolayer ...

Indian Academy of Sciences (India)

Abstract. A monolayer of MoSe2 is found to be a direct band-gap semiconductor. We show, ... In order to determine appropriate basis for the tight-binding model, the Mo and Se ..... RD thanks the Council of Scientific and Industrial Research.

GW quasiparticle bandgaps of anatase TiO2 starting from DFT + U.

Science.gov (United States)

Patrick, Christopher E; Giustino, Feliciano

2012-05-23

We investigate the quasiparticle band structure of anatase TiO(2), a wide gap semiconductor widely employed in photovoltaics and photocatalysis. We obtain GW quasiparticle energies starting from density-functional theory (DFT) calculations including Hubbard U corrections. Using a simple iterative procedure we determine the value of the Hubbard parameter yielding a vanishing quasiparticle correction to the fundamental bandgap of anatase TiO(2). The bandgap (3.3 eV) calculated using this optimal Hubbard parameter is smaller than the value obtained by applying many-body perturbation theory to standard DFT eigenstates and eigenvalues (3.7 eV). We extend our analysis to the rutile polymorph of TiO(2) and reach similar conclusions. Our work highlights the role of the starting non-interacting Hamiltonian in the calculation of GW quasiparticle energies in TiO(2) and suggests an optimal Hubbard parameter for future calculations.

Spectroscopic studies on novel donor-acceptor and low band-gap polymeric semiconductors

International Nuclear Information System (INIS)

Cravino, A.

2002-11-01

Novel low band-gap conjugated polymeric semiconductors as well as conjugated electron donor chains carrying electron acceptor substituents were electrochemically prepared and investigated by means of different spectroscopic techniques. Using in situ FTIR and ESR spectroelectrochemistry, the spectroscopic features of injected positive charges are found to be different as opposed to the negative charge carriers on the same conjugated polymer. These results, for which the theoretical models so far developed do not account, demonstrate the different structure and delocalization of charge carriers with opposite signs. In addition, vibrational spectroscopy results proof the enhanced 'quinoid' character of low band-gap conjugated chains. Excited state spectroscopy was applied to study photoexcitations in conjugated polymers carrying tetracyanoanthraquinone type or fullerene moieties. This novel class of materials, hereafter called double-cable polymers, was found promising as alternative to the conjugated polymer:fullerene mixtures currently used for the preparation of 'bulk-heterojunction' polymeric solar cells. (author)

Ab initio study of the bandgap engineering of Al1−xGaxN for optoelectronic applications

KAUST Repository

Amin, B.; Ahmad, Iftikhar; Maqbool, M.; Goumri-Said, S.; Ahmad, R.

2011-01-01

A theoretical study of Al1−xGaxN, based on the full-potential linearized augmented plane wave method, is used to investigate the variations in the bandgap,optical properties, and nonlinear behavior of the compound with the change in the Ga concentration. It is found that the bandgap decreases with the increase in Ga. A maximum value of 5.50 eV is determined for the bandgap of pure AlN, which reaches a minimum value of 3.0 eV when Al is completely replaced by Ga. The static index of refraction and dielectric constant decreases with the increase in the bandgap of the material, assigning a high index of refraction to pure GaN when compared to pure AlN. The refractive index drops below 1 for higher energy photons, larger than 14 eV. The group velocity of these photons is larger than the vacuum velocity of light. This astonishing result shows that at higher energies the optical properties of the material shifts from linear to nonlinear. Furthermore, frequency dependent reflectivity and absorption coefficients show that peak values of the absorption coefficient and reflectivity shift toward lower energy in the ultraviolet (UV) spectrum with the increase in Ga concentration. This comprehensive theoretical study of the optoelectronic properties predicts that the material can be effectively used in the optical devices working in the visible and UV spectrum.

Ab initio study of the bandgap engineering of Al1−xGaxN for optoelectronic applications

KAUST Repository

Amin, B.

2011-01-19

A theoretical study of Al1−xGaxN, based on the full-potential linearized augmented plane wave method, is used to investigate the variations in the bandgap,optical properties, and nonlinear behavior of the compound with the change in the Ga concentration. It is found that the bandgap decreases with the increase in Ga. A maximum value of 5.50 eV is determined for the bandgap of pure AlN, which reaches a minimum value of 3.0 eV when Al is completely replaced by Ga. The static index of refraction and dielectric constant decreases with the increase in the bandgap of the material, assigning a high index of refraction to pure GaN when compared to pure AlN. The refractive index drops below 1 for higher energy photons, larger than 14 eV. The group velocity of these photons is larger than the vacuum velocity of light. This astonishing result shows that at higher energies the optical properties of the material shifts from linear to nonlinear. Furthermore, frequency dependent reflectivity and absorption coefficients show that peak values of the absorption coefficient and reflectivity shift toward lower energy in the ultraviolet (UV) spectrum with the increase in Ga concentration. This comprehensive theoretical study of the optoelectronic properties predicts that the material can be effectively used in the optical devices working in the visible and UV spectrum.

Optical bandgap of semiconductor nanostructures: Methods for experimental data analysis

Science.gov (United States)

Raciti, R.; Bahariqushchi, R.; Summonte, C.; Aydinli, A.; Terrasi, A.; Mirabella, S.

2017-06-01

Determination of the optical bandgap (Eg) in semiconductor nanostructures is a key issue in understanding the extent of quantum confinement effects (QCE) on electronic properties and it usually involves some analytical approximation in experimental data reduction and modeling of the light absorption processes. Here, we compare some of the analytical procedures frequently used to evaluate the optical bandgap from reflectance (R) and transmittance (T) spectra. Ge quantum wells and quantum dots embedded in SiO2 were produced by plasma enhanced chemical vapor deposition, and light absorption was characterized by UV-Vis/NIR spectrophotometry. R&T elaboration to extract the absorption spectra was conducted by two approximated methods (single or double pass approximation, single pass analysis, and double pass analysis, respectively) followed by Eg evaluation through linear fit of Tauc or Cody plots. Direct fitting of R&T spectra through a Tauc-Lorentz oscillator model is used as comparison. Methods and data are discussed also in terms of the light absorption process in the presence of QCE. The reported data show that, despite the approximation, the DPA approach joined with Tauc plot gives reliable results, with clear advantages in terms of computational efforts and understanding of QCE.

Electromagnetically induced photonic bandgap in hot Cs atoms

International Nuclear Information System (INIS)

Li, D. W.; Zhang, L.; Su, X. M.; Zhuo, Z. C.; Kim, J. B

2010-01-01

Three-level Λ-type thermal Cs atoms are used to demonstrate the phenomenon of a photonic bandgap induced by quantum coherence with a standing wave (SW). We observed the transmitted signals of probe field driven by several kinds of SW, which are formed by a strong forward-traveling field and a backward-traveling field when a mirror reflects the forward-traveling beam. Considering Doppler inhomogeneous broadenings with a SW drive, we employ Fourier transformation to solve density-matrix equations for simulation results. The simulation results are found to be consistent with the experimental results.

Systematic Bandgap Engineering of Graphene Quantum Dots and Applications for Photocatalytic Water Splitting and CO2 Reduction.

Science.gov (United States)

Yan, Yibo; Chen, Jie; Li, Nan; Tian, Jingqi; Li, Kaixin; Jiang, Jizhou; Liu, Jiyang; Tian, Qinghua; Chen, Peng

2018-04-24

Graphene quantum dots (GQDs), which is the latest addition to the nanocarbon material family, promise a wide spectrum of applications. Herein, we demonstrate two different functionalization strategies to systematically tailor the bandgap structures of GQDs whereby making them snugly suitable for particular applications. Furthermore, the functionalized GQDs with a narrow bandgap and intramolecular Z-scheme structure are employed as the efficient photocatalysts for water splitting and carbon dioxide reduction under visible light. The underlying mechanisms of our observations are studied and discussed.

Band Engineering Small Bandgap p-Type Semiconductors: Investigations of their Optical and Photoelectrochemical Properties

Science.gov (United States)

Zoellner, Brandon

Mixed-metal oxides containing Mn(II), Cu(I), Ta(V), Nb(V), and V(V) were investigated for their structures and properties as new p-type semiconductors and in the potential applications involving the photocatalytic conversion of water into hydrogen and oxygen. Engineering of the bandgaps was achieved by combining metal cations that have halffilled (Mn 3d5) or filled (Cu 3d10) d-orbitals together with metal cations that have empty (V/Nb/Ta 3/4/5 d0) d-orbitals. The research described herein focuses on the synthesis, optical, electronic, and photocatalytic properties of the metal-oxide semiconductors MnV2O6, Cu3VO 4, CuNb1-xTaxO3, and Cu5(Ta1-xNbx)11O30. Powder X-ray diffraction was used to probe their phase purity as well as atomic-level crystallographic details, i.e. shifts of lattice parameters, chemical compositions, and changes in local bonding environments. Optical measurements revealed visible-light bandgap sizes of ˜1.17 eV (Cu3VO4), ˜1.45 eV (MnV2O6), ˜1.89-1.97 eV (CuNb1-xTa xO3), and ˜1.97-2.50 eV (Cu5(Ta1-xNb x)11O30). The latter two were found to systematically vary as a function of composition. Electrochemical impedance spectroscopy measurements of MnV2O6 and Cu3VO 4 provided the first experimental characterization of the energetic positions of the valence and conduction bands with respect to the water oxidation and reduction potentials, as well as confirmed the p-type nature of each semiconductor. The valence and conduction band energies were found to be suitable for driving either one or both of the water-splitting half reaction (i.e. 2H+ → H2 and 2H2O → O2 + 4H+). Photoelectrochemical measurements on polycrystalline films of the Cu(I)-based semiconductors under visible-light irradiation produced cathodic currents indicative of p-type semiconductor character and chemical reduction at their surfaces in the electrolyte solution. The stability of the photocurrents was increased by the addition of CuO oxide particles either externally deposited or

The Tunable Bandgap of AB-Stacked Bilayer Graphene on SiO2 with H2O Molecule Adsorption

International Nuclear Information System (INIS)

Wang Tao; Guo Qing; Liu Yan; Wang Wen-Bo; Sheng Kuang; Ao Zhi-Min; Yu Bin

2011-01-01

The atomic and electronic structures of AB-stacking bilayer graphene (BLG) in the presence of H 2 O molecules are investigated by density functional theory calculations. For free-standing BLG, the bandgap is opened to 0.101 eV with a single H 2 O molecule adsorbed on its surface. The perfectly suspended BLG is sensitive to H 2 O adsorbates, which break the BLG lattice symmetry and open an energy gap. While a single H 2 O molecule is adsorbed on the BLG surface with a SiO 2 substrate, the bandgap widens to 0.363 eV. Both the H 2 O molecule adsorption and the oxide substrate contribute to the BLG bandgap opening. The phenomenon is interpreted with the charge transfer process in 2D carbon nanostructures. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Effect of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency

International Nuclear Information System (INIS)

Ding Xueyong; Li Hongfan; Lv Zhensu

2012-01-01

Based on the mode-coupling method, numerical analysis is presented to demonstrate the influence of ripple taper on band-gap overlap in a coaxial Bragg structure operating at terahertz frequency. Results show that the interval between the band-gaps of the competing mode and the desired working mode is narrowed by use of positive-taper ripples, but is expanded if negative-taper ripples are employed, and the influence of the negative-taper ripples is obviously more advantageous than the positive-taper ripples; the band-gap overlap of modes can be efficiently separated by use of negative-taper ripples. The residual side-lobes of the frequency response in a coaxial Bragg structure with ripple taper also can be effectively suppressed by employing the windowing-function technique. These peculiarities provide potential advantage in constructing a coaxial Bragg cavity with high quality factor for single higher-order-mode operation of a high-power free-electron maser in the terahertz frequency range.

Photocatalytic hydrogen generation from water under visible light using core/shell nano-catalysts.

Science.gov (United States)

Wang, X; Shih, K; Li, X Y

2010-01-01

A microemulsion technique was employed to synthesize nano-sized photocatalysts with a core (CdS)/shell (ZnS) structure. The primary particles of the photocatalysts were around 10 nm, and the mean size of the catalyst clusters in water was about 100 nm. The band gaps of the catalysts ranged from 2.25 to 2.46 eV. The experiments of photocatalytic H(2) generation showed that the catalysts (CdS)(x)/(ZnS)(1-x) with x ranging from 0.1 to 1 were able to produce hydrogen from water photolysis under visible light. The catalyst with x=0.9 had the highest rate of hydrogen production. The catalyst loading density also influenced the photo-hydrogen production rate, and the best catalyst concentration in water was 1 g L(-1). The stability of the nano-catalysts in terms of size, morphology and activity was satisfactory during an extended test period for a specific hydrogen production rate of 2.38 mmol g(-1) L(-1) h(-1) and a quantum yield of 16.1% under visible light (165 W Xe lamp, lambda>420 nm). The results demonstrate that the (CdS)/(ZnS) core/shell nano-particles are a novel photo-catalyst for renewable hydrogen generation from water under visible light. This is attributable to the large band-gap ZnS shell that separates the electron/hole pairs generated by the CdS core and hence reduces their recombinations.

Electronic band-gap modified passive silicon optical modulator at telecommunications wavelengths.

Science.gov (United States)

Zhang, Rui; Yu, Haohai; Zhang, Huaijin; Liu, Xiangdong; Lu, Qingming; Wang, Jiyang

2015-11-13

The silicon optical modulator is considered to be the workhorse of a revolution in communications. In recent years, the capabilities of externally driven active silicon optical modulators have dramatically improved. Self-driven passive modulators, especially passive silicon modulators, possess advantages in compactness, integration, low-cost, etc. Constrained by a large indirect band-gap and sensitivity-related loss, the passive silicon optical modulator is scarce and has been not advancing, especially at telecommunications wavelengths. Here, a passive silicon optical modulator is fabricated by introducing an impurity band in the electronic band-gap, and its nonlinear optics and applications in the telecommunications-wavelength lasers are investigated. The saturable absorption properties at the wavelength of 1.55 μm was measured and indicates that the sample is quite sensitive to light intensity and has negligible absorption loss. With a passive silicon modulator, pulsed lasers were constructed at wavelengths at 1.34 and 1.42 μm. It is concluded that the sensitive self-driven passive silicon optical modulator is a viable candidate for photonics applications out to 2.5 μm.

Direct-Indirect Nature of the Bandgap in Lead-Free Perovskite Nanocrystals

KAUST Repository

Zhang, Yuhai

2017-06-23

With record efficiencies achieved in lead halide perovskite-based photovoltaics, urgency has shifted toward finding alternative materials that are stable and less toxic. Bismuth-based perovskite materials are currently one of the most promising candidates among those alternatives. However, the band structures of these materials, including the nature of the bandgaps, remain elusive due to extremely low photoluminescence quantum yield (PLQY) and scattering issues in their thin-film form. Here, we reveal the specific nature of the material\\'s electronic transitions by realizing monodisperse colloidal nanocrystals (NCs) of hexagonal-phase Cs3Bi2X9 perovskites, which afford well-resolved PL features. Interestingly, the PL profile exhibits a dual-spectral feature at room temperature with comparable intensities, based on which we propose an exciton recombination process involving both indirect and direct transitions simultaneously-an observation further supported by temperature-dependent and density functional theory (DFT) calculations. Our findings provide experimental and theoretical insights into the nature of the bandgaps in bismuth halide materials-essential information for assessing their viability in solar cells and optoelectronics.

Hydrogen Bonding and Stability of Hybrid Organic-Inorganic Perovskites

KAUST Repository

El-Mellouhi, Fedwa

2016-09-08

In the past few years, the efficiency of solar cells based on hybrid organic–inorganic perovskites has exceeded the level needed for commercialization. However, existing perovskites solar cells (PSCs) suffer from several intrinsic instabilities, which prevent them from reaching industrial maturity, and stabilizing PSCs has become a critically important problem. Here we propose to stabilize PSCs chemically by strengthening the interactions between the organic cation and inorganic anion of the perovskite framework. In particular, we show that replacing the methylammonium cation with alternative protonated cations allows an increase in the stability of the perovskite by forming strong hydrogen bonds with the halide anions. This interaction also provides opportunities for tuning the electronic states near the bandgap. These mechanisms should have a universal character in different hybrid organic–inorganic framework materials that are widely used.

Hydrogen Bonding and Stability of Hybrid Organic-Inorganic Perovskites

KAUST Repository

El-Mellouhi, Fedwa; Marzouk, Asma; Bentria, El Tayeb; Rashkeev, Sergey N.; Kais, Sabre; Alharbi, Fahhad H.

2016-01-01

In the past few years, the efficiency of solar cells based on hybrid organic–inorganic perovskites has exceeded the level needed for commercialization. However, existing perovskites solar cells (PSCs) suffer from several intrinsic instabilities, which prevent them from reaching industrial maturity, and stabilizing PSCs has become a critically important problem. Here we propose to stabilize PSCs chemically by strengthening the interactions between the organic cation and inorganic anion of the perovskite framework. In particular, we show that replacing the methylammonium cation with alternative protonated cations allows an increase in the stability of the perovskite by forming strong hydrogen bonds with the halide anions. This interaction also provides opportunities for tuning the electronic states near the bandgap. These mechanisms should have a universal character in different hybrid organic–inorganic framework materials that are widely used.

Triple photonic band-gap structure dynamically induced in the presence of spontaneously generated coherence

International Nuclear Information System (INIS)

Gao Jinwei; Bao Qianqian; Wan Rengang; Cui Cuili; Wu Jinhui

2011-01-01

We study a cold atomic sample coherently driven into the five-level triple-Λ configuration for attaining a dynamically controlled triple photonic band-gap structure. Our numerical calculations show that three photonic band gaps with homogeneous reflectivities up to 92% can be induced on demand around the probe resonance by a standing-wave driving field in the presence of spontaneously generated coherence. All these photonic band gaps are severely malformed with probe reflectivities declining rapidly to very low values when spontaneously generated coherence is gradually weakened. The triple photonic band-gap structure can also be attained in a five-level chain-Λ system of cold atoms in the absence of spontaneously generated coherence, which however requires two additional traveling-wave fields to couple relevant levels.

Effects of Plasma Hydrogenation on Trapping Properties of Dislocations in Heteroepitaxial InP/GaAs

Science.gov (United States)

Ringel, S. A.; Chatterjee, B.

1994-01-01

In previous work, we have demonstrated the effectiveness of a post-growth hydrogen plasma treatment for passivating the electrical activity of dislocations in metalorganic chemical vapor deposition (MOCVD) grown InP on GaAs substrates by a more than two order of magnitude reduction in deep level concentration and an improvement in reverse bias leakage current by a factor of approx. 20. These results make plasma hydrogenation an extremely promising technique for achieving high efficiency large area and light weight heteroepitaxial InP solar cells for space applications. In this work we investigate the carrier trapping process by dislocations in heteroepitaxial InP/GaAs and the role of hydrogen passivation on this process. It is shown that the charge trapping kinetics of dislocations after hydrogen passivation are significantly altered, approaching point defect-like behavior consistent with a transformation from a high concentration of dislocation-related defect bands within the InP bandgap to a low concentration of individual deep levels after hydrogen passivation. It is further shown that the "apparent" activation energies of dislocation related deep levels, before and after passivation, reduce by approx. 70 meV as DLTS fill pulse times are increased from 1 usec. to 1 msec. A model is proposed which explains these effects based on a reduction of Coulombic interaction between individual core sites along the dislocation cores by hydrogen incorporation. Knowledge of the trapping properties in these specific structures is important to develop optimum, low loss heteroepitaxial InP cells.

Wide bandgap collector III-V double heterojunction bipolar transistors

International Nuclear Information System (INIS)

Flitcroft, R.M.

2000-10-01

This thesis is devoted to the study and development of Heterojunction Bipolar Transistors (HBTs) designed for high voltage operation. The work concentrates on the use of wide bandgap III-V semiconductor materials as the collector material and their associated properties influencing breakdown, such as impact ionisation coefficients. The work deals with issues related to incorporating a wide bandgap collector into double heterojunction structures such as conduction band discontinuities at the base-collector junction and results are presented which detail, a number of methods designed to eliminate the effects of such discontinuities. In particular the use of AlGaAs as the base material has been successful in eliminating the conduction band spike at this interface. A method of electrically injecting electrons into the collector has been employed to investigate impact ionisation in GaAs, GaInP and AlInP which has used the intrinsic gain of the devices to extract impact ionisation coefficients over a range of electric fields beyond the scope of conventional optical injection techniques. This data has enabled the study of ''dead space'' effects in HBT collectors and have been used to develop an analytical model of impact ionisation which has been incorporated into an existing Ebers-Moll HBT simulator. This simulator has been shown to accurately reproduce current-voltage characteristics in both the devices used in this work and for external clients. (author)

Reducing support loss in micromechanical ring resonators using phononic band-gap structures

Energy Technology Data Exchange (ETDEWEB)

Hsu, Feng-Chia; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin [Industrial Technology Research Institute-South, Tainan 709, Taiwan (China); Hsu, Jin-Chen, E-mail: fengchiahsu@itri.org.t, E-mail: hsujc@yuntech.edu.t [Department of Mechanical Engineering, National Yunlin University of Science and Technology, Douliou, Yunlin 64002, Taiwan (China)

2011-09-21

In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

Reducing support loss in micromechanical ring resonators using phononic band-gap structures

International Nuclear Information System (INIS)

Hsu, Feng-Chia; Huang, Tsun-Che; Wang, Chin-Hung; Chang, Pin; Hsu, Jin-Chen

2011-01-01

In micromechanical resonators, energy loss via supports into the substrates may lead to a low quality factor. To eliminate the support loss, in this paper a phononic band-gap structure is employed. We demonstrate a design of phononic-crystal (PC) strips used to support extensional wine-glass mode ring resonators to increase the quality factor. The PC strips are introduced to stop elastic-wave propagation by the band-gap and deaf-band effects. Analyses of resonant characteristics of the ring resonators and the dispersion relations, eigenmodes, and transmission properties of the PC strips are presented. With the proposed resonator architecture, the finite-element simulations show that the leaky power is effectively reduced and the stored energy inside the resonators is enhanced simultaneously as the operating frequencies of the resonators are within the band gap or deaf bands. Realization of a high quality factor micromechanical ring resonator with minimized support loss is expected.

Shape optimization of solid-air porous phononic crystal slabs with widest full 3D bandgap for in-plane acoustic waves

Science.gov (United States)

D'Alessandro, Luca; Bahr, Bichoy; Daniel, Luca; Weinstein, Dana; Ardito, Raffaele

2017-09-01

The use of Phononic Crystals (PnCs) as smart materials in structures and microstructures is growing due to their tunable dynamical properties and to the wide range of possible applications. PnCs are periodic structures that exhibit elastic wave scattering for a certain band of frequencies (called bandgap), depending on the geometric and material properties of the fundamental unit cell of the crystal. PnCs slabs can be represented by plane-extruded structures composed of a single material with periodic perforations. Such a configuration is very interesting, especially in Micro Electro-Mechanical Systems industry, due to the easy fabrication procedure. A lot of topologies can be found in the literature for PnCs with square-symmetric unit cell that exhibit complete 2D bandgaps; however, due to the application demand, it is desirable to find the best topologies in order to guarantee full bandgaps referred to in-plane wave propagation in the complete 3D structure. In this work, by means of a novel and fast implementation of the Bidirectional Evolutionary Structural Optimization technique, shape optimization is conducted on the hole shape obtaining several topologies, also with non-square-symmetric unit cell, endowed with complete 3D full bandgaps for in-plane waves. Model order reduction technique is adopted to reduce the computational time in the wave dispersion analysis. The 3D features of the PnC unit cell endowed with the widest full bandgap are then completely analyzed, paying attention to engineering design issues.

Fabrication of a three-dimensional photonic band-gap crystal of air-spheres in a titania matrix

Science.gov (United States)

Diop, M.; Maurin, G.; Tork, Amir; Lessard, Roger A.

2003-02-01

A three-dimensional (3D) colloidal crystal have been grown from an aqueous colloidal solution of highly monodisperse submicrometer-sized polystyrene spheres using a self-assembly processing technique. The electromagnetic waves diffracted by this crystal can interfere and give rise to a photonic band-gap. However, due to the low refractive index contrast within this material the band-gap is incomplete. By filling the voids between the spheres of the colloidal crystal with titania and removing the polystyrene beads by sublimation, we obtained an inverse-opal structure with an increased refractive index contrast showing strong opalescence.

A computational study on the energy bandgap engineering in performance enhancement of CdTe thin film solar cells

Directory of Open Access Journals (Sweden)

Ameen M. Ali

Full Text Available In this study, photovoltaic properties of CdTe thin film in the configuration of n-SnO2/n-CdS/p-CdTe/p-CdTe:Te/metal have been studied by numerical simulation software named “Analysis of Microelectronic and Photonic Structure” (AMPS-1D. A modified structure for CdTe thin film solar cell has been proposed by numerical analysis with the insertion of a back contact buffer layer (CdTe:Te. This layer can serve as a barrier that will decelerate the copper diffusion in CdTe solar cell. Four estimated energy bandgap relations versus the Tellurium (Te concentrations and the (CdTe:Te layer thickness have been examined thoroughly during simulation. Correlation between energy bandgap with the CdTe thin film solar cell performance has also been established. Keywords: Numerical modelling, CdTe thin film, Solar cell, AMPS-1D, Bandgap

Effect of background dielectric on TE-polarized photonic bandgap of metallodielectric photonic crystals using Dirichlet-to-Neumann map method.

Science.gov (United States)

Sedghi, Aliasghar; Rezaei, Behrooz

2016-11-20

Using the Dirichlet-to-Neumann map method, we have calculated the photonic band structure of two-dimensional metallodielectric photonic crystals having the square and triangular lattices of circular metal rods in a dielectric background. We have selected the transverse electric mode of electromagnetic waves, and the resulting band structures showed the existence of photonic bandgap in these structures. We theoretically study the effect of background dielectric on the photonic bandgap.

Large bandgap narrowing in rutile TiO2 aimed towards visible light applications and its correlation with vacancy-type defects history and transformation

Science.gov (United States)

Nair, Radhika V.; Gayathri, P. K.; Siva Gummaluri, Venkata; Nambissan, P. M. G.; Vijayan, C.

2018-01-01

Extension of photoactivity of TiO2 to the visible region is achievable via effective control over the intrinsic defects such as oxygen and Ti vacancies, which has several applications in visible photocatalysis and sensing. We present here the first observation of an apparent bandgap narrowing and bandgap tuning effect due to vacancy cluster transformation in rutile TiO2 structures to 1.84 eV from the bulk bandgap of 3 eV. A gradual transformation of divacancies (V Ti-O) to tri vacancies ({{V}Ti-O-T{{i-}}} ) achieved through a controlled solvothermal scheme appears to result in an apparent narrowing bandgap and tunability, as supported by positron annihilation lifetime and electron paramagnetic resonance spectroscopy measurements. Visible photocatalytic activity of the samples is demonstrated in terms of photodegradation of rhodamine B dye molecules.

Soliton formation in hollow-core photonic bandgap fibers

DEFF Research Database (Denmark)

Lægsgaard, Jesper

2009-01-01

of an approximate scaling relation is tested. It is concluded that compression of input pulses of several ps duration and sub-MW peak power can lead to a formation of solitons with ∼100 fs duration and multi-megawatt peak powers. The dispersion slope of realistic hollow-core fibers appears to be the main obstacle......The formation of solitons upon compression of linearly chirped pulses in hollow-core photonic bandgap fibers is investigated numerically. The dependence of soliton duration on the chirp and power of the input pulse and on the dispersion slope of the fiber is investigated, and the validity...

Regioregular narrow-bandgap-conjugated polymers for plastic electronics

Science.gov (United States)

Ying, Lei; Huang, Fei; Bazan, Guillermo C.

2017-03-01

Progress in the molecular design and processing protocols of semiconducting polymers has opened significant opportunities for the fabrication of low-cost plastic electronic devices. Recent studies indicate that field-effect transistors and organic solar cells fabricated using narrow-bandgap regioregular polymers with translational symmetries in the direction of the backbone vector often outperform those containing analogous regiorandom polymers. This review addresses the cutting edge of regioregularity chemistry, in particular how to control the spatial distribution in the molecular structures and how this order translates to more ordered bulk morphologies. The effect of regioregularity on charge transport and photovoltaic properties is also outlined.

Contributions of oxygen vacancies and titanium interstitials to band-gap states of reduced titania

Science.gov (United States)

Li, Jingfeng; Lazzari, Rémi; Chenot, Stéphane; Jupille, Jacques

2018-01-01

The spectroscopic fingerprints of the point defects of titanium dioxide remain highly controversial. Seemingly indisputable experiments lead to conflicting conclusions in which oxygen vacancies and titanium interstitials are alternately referred to as the primary origin of the Ti 3 d band-gap states. We report on experiments performed by electron energy loss spectroscopy whose key is the direct annealing of only the very surface of rutile TiO2(110 ) crystals and the simultaneous measurement of its temperature via the Bose-Einstein loss/gain ratio. By surface preparations involving reactions with oxygen and water vapor, in particular, under electron irradiation, vacancy- and interstitial-related band-gap states are singled out. Off-specular measurements reveal that both types of defects contribute to a unique charge distribution that peaks in subsurface layers with a common dispersive behavior.

Photonic bandgap fiber lasers and multicore fiber lasers for next generation high power lasers

DEFF Research Database (Denmark)

Shirakawa, A.; Chen, M.; Suzuki, Y.

2014-01-01

Photonic bandgap fiber lasers are realizing new laser spectra and nonlinearity mitigation that a conventional fiber laser cannot. Multicore fiber lasers are a promising tool for power scaling by coherent beam combination. © 2014 OSA....

Synthesis and characterization of a low bandgap conjugated polymer for bulk heterojunction photovoltaic cells

NARCIS (Netherlands)

Dhanabalan, A.; Duren, van J.K.J.; Hal, van P.A.; Dongen, van J.L.J.; Janssen, R.A.J.

2001-01-01

Low optical bandgap conjugated polymers may improve the efficiency of organic photovoltaic devices by increasing the absorption in the visible and near infrared region of the solar spectrum. Here we demonstrate that condensation polymerization of

Halogenation of SiC for band-gap engineering and excitonic functionalization

Science.gov (United States)

Drissi, L. B.; Ramadan, F. Z.; Lounis, S.

2017-11-01

The optical excitation spectra and excitonic resonances are investigated in systematically functionalized SiC with Fluorine and/or Chlorine utilizing density functional theory in combination with many-body perturbation theory. The latter is required for a realistic description of the energy band-gaps as well as for the theoretical realization of excitons. Structural, electronic and optical properties are scrutinized and show the high stability of the predicted two-dimensional materials. Their realization in laboratory is thus possible. Large band-gaps of the order of 4 eV are found in the so-called GW approximation, with the occurrence of bright excitons, optically active in the four investigated materials. Their binding energies vary from 0.9 eV to 1.75 eV depending on the decoration choice and in one case, a dark exciton is foreseen to exist in the fully chlorinated SiC. The wide variety of opto-electronic properties suggest halogenated SiC as interesting materials with potential not only for solar cell applications, anti-reflection coatings or high-reflective systems but also for a possible realization of excitonic Bose-Einstein condensation.

Defect Characterization, Imaging, and Control in Wide-Bandgap Semiconductors and Devices

Science.gov (United States)

Brillson, L. J.; Foster, G. M.; Cox, J.; Ruane, W. T.; Jarjour, A. B.; Gao, H.; von Wenckstern, H.; Grundmann, M.; Wang, B.; Look, D. C.; Hyland, A.; Allen, M. W.

2018-03-01

Wide-bandgap semiconductors are now leading the way to new physical phenomena and device applications at nanoscale dimensions. The impact of defects on the electronic properties of these materials increases as their size decreases, motivating new techniques to characterize and begin to control these electronic states. Leading these advances have been the semiconductors ZnO, GaN, and related materials. This paper highlights the importance of native point defects in these semiconductors and describes how a complement of spatially localized surface science and spectroscopy techniques in three dimensions can characterize, image, and begin to control these electronic states at the nanoscale. A combination of characterization techniques including depth-resolved cathodoluminescence spectroscopy, surface photovoltage spectroscopy, and hyperspectral imaging can describe the nature and distribution of defects at interfaces at both bulk and nanoscale surfaces, their metal interfaces, and inside nanostructures themselves. These features as well as temperature and mechanical strain inside wide-bandgap device structures at the nanoscale can be measured even while these devices are operating. These advanced capabilities enable several new directions for describing defects at the nanoscale, showing how they contribute to device degradation, and guiding growth processes to control them.

Tunable Bandgap and Optical Properties of Black Phosphorene Nanotubes

Directory of Open Access Journals (Sweden)

Chunmei Li

2018-02-01

Full Text Available Black phosphorus (BP, a new two-dimensional material, has been the focus of scientists’ attention. BP nanotubes have potential in the field of optoelectronics due to their low-dimensional effects. In this work, the bending strain energy, electronic structure, and optical properties of BP nanotubes were investigated by using the first-principles method based on density functional theory. The results show that these properties are closely related to the rolling direction and radius of the BP nanotube. All the calculated BP nanotube properties show direct bandgaps, and the BP nanotubes with the same rolling direction express a monotone increasing trend in the value of bandgap with a decrease in radius, which is a stacking effect of the compression strain on the inner atoms and the tension strain on the outer atoms. The bending strain energy of the zigzag phosphorene nanotubes (zPNTs is higher than that of armchair phosphorene nanotubes (aPNT with the same radius of curvature due to the anisotropy of the BP’s structure. The imaginary part of the dielectric function, the absorption range, reflectivity, and the imaginary part of the refractive index of aPNTs have a wider range than those of zPNTs, with higher values overall. As a result, tunable BP nanotubes are suitable for optoelectronic devices, such as lasers and diodes, which function in the infrared and ultra-violet regions, and for solar cells and photocatalysis.

Multiple bandgap combination of thin film photovoltaic cells and a photoanode for efficient hydrogen and oxygen generation by water splitting

Energy Technology Data Exchange (ETDEWEB)

Avachat, Upendra S.; Jahagirdar, Anant H.; Dhere, Neelkanth G. [Florida Solar Energy Center (FSEC), University of Central Florida 1679 Clearlake Road, Cocoa, FL, 32922-5703 (United States)

2006-09-22

The objective of this research is to develop cheaper and more efficient photoelectrochemical (PEC) cells for the production of highly pure hydrogen and oxygen by water splitting. FSEC PV Materials Lab has developed PEC set up consisting of two thin film photovoltaic (PV) cells, a RuS{sub 2} photoanode for efficient oxygen evolution and a platinum cathode for hydrogen evolution. A p-type transparent-conducting layer is prepared at the back of PV cell to transmit unabsorbed infrared photons onto the photoanode for efficient oxygen evolution. This paper presents the preparation and characterization of p- type ZnTe:Cu transparent conducting back layer and PEC cell. (author)

Postgrowth tuning of the bandgap of single-layer molybdenum disulfide films by sulfur/selenium exchange.

Science.gov (United States)

Ma, Quan; Isarraraz, Miguel; Wang, Chen S; Preciado, Edwin; Klee, Velveth; Bobek, Sarah; Yamaguchi, Koichi; Li, Emily; Odenthal, Patrick Michael; Nguyen, Ariana; Barroso, David; Sun, Dezheng; von Son Palacio, Gretel; Gomez, Michael; Nguyen, Andrew; Le, Duy; Pawin, Greg; Mann, John; Heinz, Tony F; Rahman, Talat Shahnaz; Bartels, Ludwig

2014-05-27

We demonstrate bandgap tuning of a single-layer MoS2 film on SiO2/Si via substitution of its sulfur atoms by selenium through a process of gentle sputtering, exposure to a selenium precursor, and annealing. We characterize the substitution process both for S/S and S/Se replacement. Photoluminescence and, in the latter case, X-ray photoelectron spectroscopy provide direct evidence of optical band gap shift and selenium incorporation, respectively. We discuss our experimental observations, including the limit of the achievable bandgap shift, in terms of the role of stress in the film as elucidated by computational studies, based on density functional theory. The resultant films are stable in vacuum, but deteriorate under optical excitation in air.

Evolution of the structure and hydrogen bonding configuration in annealed hydrogenated a-Si/a-Ge multilayers and layers

International Nuclear Information System (INIS)

Frigeri, C.; Nasi, L.; Serenyi, M.; Khanh, N.Q.; Csik, A.; Szekrenyes, Zs.; Kamaras, K.

2012-01-01

Complete text of publication follows. Among the present available renewable energy sources, energy harvesting from sunlight by means of photovoltaic cells is the most attractive one. In order to win over the traditional energy resources both efficiency and cost effectiveness of photovoltaic conversion must be optimized as far as possible. Efficiency is basically improved by the use of multijunction cells containing semiconductors with different band-gap. In this respect, the III-V compounds guarantee the highest efficiency, up to 41.6 %, but they are quite expensive. The latter drawback also affects other compounds like CdTe and CuIn 1-x Ga x Se 2 (CIGS). Si based solar devices have lower efficiency but are much more cost effective. They can use either crystalline or amorphous Si thin layers or Si nanoparticles. As to the thin films, amorphous Si (a-Si) is preferred to crystalline Si as it has a wider band-gap (1.7 instead of 1.1 eV) thus harvesting a larger portion of solar energy. A tandem cell is formed by using a-SiGe which has a smaller band-gap tunable between 1.1 and 1.7 eV depending on the Ge content. The best value should be 1.4 eV since the material properties seem to degrade below this value whilst the photo-conductivity drops after light soaking if the band gap exceeds 1.4 eV. A key issue of amorphous Si, Ge and SiGe is the high density of defects in the band-gap mostly due to dangling bonds whose density is particularly high (even up to 5 x10 19 cm -3 ) since the lattice is significantly disordered with distorted bond angles and lengths. This increases the probability of rupture of the Si-Si (Ge-Ge) bonds, i.e., formation of dangling bonds. Owing to the fact that hydrogen with its single electron structure can close the dangling bonds, their density can be reduced even by 4 orders of magnitude by doping with hydrogen. However, H is unstable in the host lattice. In fact, several findings showed its evolution from the thin layer upon annealing and that

Opto-electronics of PbS quantum dot and narrow bandgap polymer blends

NARCIS (Netherlands)

Kahmann, Simon; Mura, Andrea; Protesescu, Loredana; Kovalenko, Maksym V.; Brabec, Christoph J.; Loi, Maria A.

2015-01-01

Here we report on the interaction between the narrow bandgap polymer [2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta-[2,1-b;3,4-b]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and lead sulphide (PbS) colloidal quantum dots (CQDs) upon photoexcitation. We show that the presence of both materials

High bandgap III-V alloys for high efficiency optoelectronics

Energy Technology Data Exchange (ETDEWEB)

Alberi, Kirstin; Mascarenhas, Angelo; Wanlass, Mark

2017-01-10

High bandgap alloys for high efficiency optoelectronics are disclosed. An exemplary optoelectronic device may include a substrate, at least one Al.sub.1-xIn.sub.xP layer, and a step-grade buffer between the substrate and at least one Al.sub.1-xIn.sub.xP layer. The buffer may begin with a layer that is substantially lattice matched to GaAs, and may then incrementally increase the lattice constant in each sequential layer until a predetermined lattice constant of Al.sub.1-xIn.sub.xP is reached.

Mode Division Multiplexing Exploring Hollow-Core Photonic Bandgap Fibers

DEFF Research Database (Denmark)

Xu, Jing; Lyngso, Jens Kristian; Leick, Lasse

2013-01-01

We review our recent exploratory investigations on mode division multiplexing using hollow-core photonic bandgap fibers (HC-PBGFs). Compared with traditional multimode fibers, HC-PBGFs have several attractive features such as ultra-low nonlinearities, low-loss transmission window around 2 µm etc....... After having discussed the potential and challenges of using HC-PBGFs as transmission fibers for mode multiplexing applications, we will report a number of recent proof-of-concept results obtained in our group using direct detection receivers. The first one is the transmission of two 10.7 Gbit/s non...

Effects of weak nonlinearity on dispersion relations and frequency band-gaps of periodic structures

DEFF Research Database (Denmark)

Sorokin, Vladislav; Thomsen, Jon Juel

2015-01-01

of these for nonlinear problems is impossible or cumbersome, since Floquet theory is applicable for linear systems only. Thus the nonlinear effects for periodic structures are not yet fully uncovered, while at the same time applica-tions may demand effects of nonlinearity on structural response to be accounted for....... The present work deals with analytically predicting dynamic responses for nonlinear continuous elastic periodic structures. Specifically, the effects of weak nonlinearity on the dispersion re-lation and frequency band-gaps of a periodic Bernoulli-Euler beam performing bending os-cillations are analyzed......The analysis of the behaviour of linear periodic structures can be traced back over 300 years, to Sir Isaac Newton, and still attracts much attention. An essential feature of periodic struc-tures is the presence of frequency band-gaps, i.e. frequency ranges in which waves cannot propagate...

Efficient low bandgap polymer solar cell with ordered heterojunction defined by nanoimprint lithography.

Science.gov (United States)

Yang, Yi; Mielczarek, Kamil; Zakhidov, Anvar; Hu, Walter

2014-11-12

In this work, we demonstrate the feasibility of using nanoimprint lithography (NIL) to make efficient low bandgap polymer solar cells with well-ordered heterojunction. High quality low bandgap conjugated polymer 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) nanogratings are fabricated using this technique for the first time. The geometry effect of PCPDTBT nanostructures on the solar cell performance is investigated by making PCPDTBT/C70 solar cells with different feature sizes of PCPDTBT nanogratings. It is found that the power conversion efficiency (PCE) increases with increasing nanograting height, PCPDTBT/C70 junction area, and decreasing nanograting width. We also find that NIL makes PCPDTBT chains interact more strongly and form an improved structural ordering. Solar cells made on the highest aspect ratio PCPDTBT nanostructures are among the best reported devices using the same material with a PCE of 5.5%.

Metallic photonic band-gap materials

International Nuclear Information System (INIS)

Sigalas, M.M.; Chan, C.T.; Ho, K.M.; Soukoulis, C.M.

1995-01-01

We calculate the transmission and absorption of electromagnetic waves propagating in two-dimensional (2D) and 3D periodic metallic photonic band-gap (PBG) structures. For 2D systems, there is substantial difference between the s- and p-polarized waves. The p-polarized waves exhibit behavior similar to the dielectric PBG's. But, the s-polarized waves have a cutoff frequency below which there are no propagating modes. For 3D systems, the results are qualitatively the same for both polarizations but there are important differences related to the topology of the structure. For 3D structures with isolated metallic scatterers (cermet topology), the behavior is similar to that of the dielectric PBG's, while for 3D structures with the metal forming a continuous network (network topology), there is a cutoff frequency below which there are no propagating modes. The systems with the network topology may have some interesting applications for frequencies less than about 1 THz where the absorption can be neglected. We also study the role of the defects in the metallic structures

Photolithography of thick photoresist coating for electrically controlled liquid crystal photonic bandgap fibre devices

DEFF Research Database (Denmark)

Wei, Lei; Khomtchenko, Elena; Alkeskjold, Thomas Tanggaard

2009-01-01

Thick photoresist coating for electrode patterning in an anisotropically etched V-groove is investigated for electrically controlled liquid crystal photonic bandgap fibre devices. The photoresist step coverage at the convex corners is compared with and without soft baking after photoresist spin...

Correlation between Photoluminescence and Carrier Transport and a Simple In Situ Passivation Method for High-Bandgap Hybrid Perovskites.

Science.gov (United States)

Stoddard, Ryan J; Eickemeyer, Felix T; Katahara, John K; Hillhouse, Hugh W

2017-07-20

High-bandgap mixed-halide hybrid perovskites have higher open-circuit voltage deficits and lower carrier diffusion lengths than their lower-bandgap counterparts. We have developed a ligand-assisted crystallization (LAC) technique that introduces additives in situ during the solvent wash and developed a new method to dynamically measure the absolute intensity steady-state photoluminescence and the mean carrier diffusion length simultaneously. The measurements reveal four distinct regimes of material changes and show that photoluminescence brightening often coincides with losses in carrier transport, such as in degradation or phase segregation. Further, the measurements enabled optimization of LAC on the 1.75 eV bandgap FA 0.83 Cs 0.17 Pb(I 0.66 Br 0.34 ) 3 , resulting in an enhancement of the photoluminescence quantum yield (PLQY) of over an order of magnitude, an increase of 80 meV in the quasi-Fermi level splitting (to 1.29 eV), an increase in diffusion length by a factor of 3.5 (to over 1 μm), and enhanced open-circuit voltage and short-circuit current from photovoltaics fabricated from the LAC-treated films.

Transitions of bandgap and built-in stress for sputtered HfZnO thin films after thermal treatments

Energy Technology Data Exchange (ETDEWEB)

Li, Chih-Hung; Chen, Jian-Zhang [Institute of Applied Mechanics, National Taiwan University, Taipei City 10617, Taiwan (China); Cheng, I-Chun [Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei City 10617, Taiwan (China)

2013-08-28

HfZnO thin films with various Hf contents are sputter-deposited on glass substrates from Hf{sub x}Zn{sub 1−x}O (x = 0, 2.5, 5, 7.5, and 10 at. %) targets at room temperature. The incorporation of Hf in the ZnO film leads to the amorphorization of the materials. The amorphous structures of high-Hf-content films remain after annealing at 600 °C for 30 min. The built-in stresses of as-deposited films are compressive. As the annealing temperature increases, the stresses are relaxed and even become tensile. The films exhibit a high transmission of 80% in the visible region. The optical bandgap increases with the Hf content, but it decreases with the annealing temperature. This can be attributed to the alteration of strain (stress) status in the films and atomic substitution. The reduction of bandgap partly results from the grain growth, which is due to the quantum confinement effect of the small grains. Hf doping increases the resistivity of ZnO owing to the disorder of the material structure and the higher bandgap, which result in more carrier traps and less thermally excited carriers in the conduction bands.

Bandgap engineering of Cu2CdxZn1−xSnS4 alloy for photovoltaic applications: A complementary experimental and first-principles study

KAUST Repository

Xiao, Zhen-Yu

2013-11-11

We report on bandgap engineering of an emerging photovoltaic material of Cu2CdxZn1-xSnS4 (CCZTS) alloy. CCZTS alloy thin films with different Cd contents and single kesterite phase were fabricated using the sol-gel method. The optical absorption measurements indicate that the bandgap of the kesterite CCZTS alloy can be continuously tuned in a range of 1.55-1.09 eV as Cd content varied from x = 0 to 1. Hall effect measurements suggest that the hole concentration of CCZTS films decreases with increasing Cd content. The CCZTS-based solar cell with x = 0.47 demonstrates a power conversion efficiency of 1.2%. Our first-principles calculations based on the hybrid functional method demonstrate that the bandgap of the kesterite CCZTS alloy decreases monotonically with increasing Cd content, supporting the experimental results. Furthermore, Cu2ZnSnS4/Cu 2CdSnS4 interface has a type-I band-alignment with a small valence-band offset, explaining the narrowing of the bandgap of CCZTS as the Cd content increases. Our results suggest that CCZTS alloy is a potentially suitable material to fabricate high-efficiency multi-junction tandem solar cells with different bandgap-tailored absorption layers. © 2013 AIP Publishing LLC.

Controlling spin-dependent tunneling by bandgap tuning in epitaxial rocksalt MgZnO films.

Science.gov (United States)

Li, D L; Ma, Q L; Wang, S G; Ward, R C C; Hesjedal, T; Zhang, X-G; Kohn, A; Amsellem, E; Yang, G; Liu, J L; Jiang, J; Wei, H X; Han, X F

2014-12-02

Widespread application of magnetic tunnel junctions (MTJs) for information storage has so far been limited by the complicated interplay between tunnel magnetoresistance (TMR) ratio and the product of resistance and junction area (RA). An intricate connection exists between TMR ratio, RA value and the bandgap and crystal structure of the barrier, a connection that must be unravelled to optimise device performance and enable further applications to be developed. Here, we demonstrate a novel method to tailor the bandgap of an ultrathin, epitaxial Zn-doped MgO tunnel barrier with rocksalt structure. This structure is attractive due to its good Δ1 spin filtering effect, and we show that MTJs based on tunable MgZnO barriers allow effective balancing of TMR ratio and RA value. In this way spin-dependent transport properties can be controlled, a key challenge for the development of spintronic devices.

High-Temperature, Wirebondless, Ultra-Compact Wide Bandgap Power Semiconductor Modules for Space Power Systems, Phase I

Data.gov (United States)

National Aeronautics and Space Administration — Silicon carbide (SiC) and other wide band-gap semiconductors offer great promise of high power rating, high operating temperature, simple thermal management, and...

Transmission properties of hollow-core photonic bandgap fibers in relation to molecular spectroscopy

DEFF Research Database (Denmark)

Falk, Charlotte Ijeoma; Hald, Jan; Petersen, Jan C.

2010-01-01

The transmission properties of five types of hollow-core photonic bandgap fibers (HC-PBFs) are characterized in the telecom wavelength range around 1:5 μm. The variations in optical transmission are measured as a function of laser frequency over a 2GHz scan range as well as a function of time over...

LETTER TO THE EDITOR: Green emission and bandgap narrowing due to two-photon excitation in thin film CdS formed by spray pyrolysis

Science.gov (United States)

Ullrich, B.; Schroeder, R.

2001-08-01

Thin (10 µm) film CdS on Pyrex® formed by spray pyrolysis is excited below the gap at 804 nm with 200 fs laser pulses at room temperature. Excitation intensities up to 250 GW cm-2 evoke green bandgap emission due to two-photon transitions. This two-photon photoluminescence does not show a red emission contribution in contrast to the single-photon excited emission, which is dominated by broad emission in the red spectral range. It is demonstrated that two-photon excitation causes photo-induced bandgap narrowing due to Debye screening. At 250 GW cm-2 bandgap narrowing of 47 meV is observed, which corresponds to an excited electron density of 1.6×1018 cm-3.

Medium-Bandgap Small-Molecule Donors Compatible with Both Fullerene and Nonfullerene Acceptors.

Science.gov (United States)

Huo, Yong; Yan, Cenqi; Kan, Bin; Liu, Xiao-Fei; Chen, Li-Chuan; Hu, Chen-Xia; Lau, Tsz-Ki; Lu, Xinhui; Sun, Chun-Lin; Shao, Xiangfeng; Chen, Yongsheng; Zhan, Xiaowei; Zhang, Hao-Li

2018-03-21

Much effort has been devoted to the development of new donor materials for small-molecule organic solar cells due to their inherent advantages of well-defined molecular weight, easy purification, and good reproducibility in photovoltaic performance. Herein, we report two small-molecule donors that are compatible with both fullerene and nonfullerene acceptors. Both molecules consist of an (E)-1,2-di(thiophen-2-yl)ethane-substituted (TVT-substituted) benzo[1,2-b:4,5-b']dithiophene (BDT) as the central unit, and two rhodanine units as the terminal electron-withdrawing groups. The central units are modified with either alkyl side chains (DRBDT-TVT) or alkylthio side chains (DRBDT-STVT). Both molecules exhibit a medium bandgap with complementary absorption and proper energy level offset with typical acceptors like PC 71 BM and IDIC. The optimized devices show a decent power conversion efficiency (PCE) of 6.87% for small-molecule organic solar cells and 6.63% for nonfullerene all small-molecule organic solar cells. Our results reveal that rationally designed medium-bandgap small-molecule donors can be applied in high-performance small-molecule organic solar cells with different types of acceptors.

Freedom from band-gap slavery: from diode lasers to quantum cascade lasers

Science.gov (United States)

Capasso, Federico

2010-02-01

Semiconductor heterostructure lasers, for which Alferov and Kromer received part of the Nobel Prize in Physics in 2000, are the workhorse of technologies such as optical communications, optical recording, supermarket scanners, laser printers and fax machines. They exhibit high performance in the visible and near infrared and rely for their operation on electrons and holes emitting photons across the semiconductor bandgap. This mechanism turns into a curse at longer wavelengths (mid-infrared) because as the bandgap, shrinks laser operation becomes much more sensitive to temperature, material defects and processing. Quantum Cascade Laser (QCL), invented in 1994, rely on a radically different process for light emission. QCLs are unipolar devices in which electrons undergo transitions between quantum well energy levels and are recycled through many stages emitting a cascade of photons. Thus by suitable tailoring of the layers' thickness, using the same heterostructure material, they can lase across the molecular fingerprint region from 3 to 25 microns and beyond into the far-infrared and submillimiter wave spectrum. High power cw room temperature QCLs and QCLs with large continuous single mode tuning range have found many applications (infrared countermeasures, spectroscopy, trace gas analysis and atmospheric chemistry) and are commercially available. )

Complex layered materials and periodic electromagnetic band-gap structures: Concepts, characterizations, and applications

Science.gov (United States)

Mosallaei, Hossein

The main objective of this dissertation is to characterize and create insight into the electromagnetic performances of two classes of composite structures, namely, complex multi-layered media and periodic Electromagnetic Band-Gap (EBG) structures. The advanced and diversified computational techniques are applied to obtain their unique propagation characteristics and integrate the results into some novel applications. In the first part of this dissertation, the vector wave solution of Maxwell's equations is integrated with the Genetic Algorithm (GA) optimization method to provide a powerful technique for characterizing multi-layered materials, and obtaining their optimal designs. The developed method is successfully applied to determine the optimal composite coatings for Radar Cross Section (RCS) reduction of canonical structures. Both monostatic and bistatic scatterings are explored. A GA with hybrid planar/curved surface implementation is also introduced to efficiently obtain the optimal absorbing materials for curved structures. Furthermore, design optimization of the non-uniform Luneburg and 2-shell spherical lens antennas utilizing modal solution/GA-adaptive-cost function is presented. The lens antennas are effectively optimized for both high gain and suppressed grating lobes. The second part demonstrates the development of an advanced computational engine, which accurately computes the broadband characteristics of challenging periodic electromagnetic band-gap structures. This method utilizes the Finite Difference Time Domain (FDTD) technique with Periodic Boundary Condition/Perfectly Matched Layer (PBC/PML), which is efficiently integrated with the Prony scheme. The computational technique is successfully applied to characterize and present the unique propagation performances of different classes of periodic structures such as Frequency Selective Surfaces (FSS), Photonic Band-Gap (PBG) materials, and Left-Handed (LH) composite media. The results are

Electrical and Optical Measurements of the Bandgap Energy of a Light-Emitting Diode

Science.gov (United States)

Petit, Matthieu; Michez, Lisa; Raimundo, Jean-Manuel; Dumas, Philippe

2016-01-01

Semiconductor materials are at the core of electronics. Most electronic devices are made of semiconductors. The operation of these components is well described by quantum physics which is often a difficult concept for students to understand. One of the intrinsic parameters of semiconductors is their bandgap energy E[subscript g]. In the case of…

Planar Circularly Symmetric Electromagnetic Band-Gap Antennas for Low Cost High Performance Integrated Antennas

NARCIS (Netherlands)

Neto, A.; LLombart, N.; Gerini, G.; Maagt, P.J. de

2009-01-01

The use of Planar Circularly Symmetric (PCS) Electromagnetic Band-Gap (EBG) structures for optimizing the performances of single antenna elements and arrays is been discussed. The key advantage of using this sort of super structures is that they are planar and thus very cheap to manufacture with

Planar circularly symmetric Electromagnetic Band-Gap antennas for low cost high performance integrated antennas

NARCIS (Netherlands)

Neto, A.; Llombart, N.; Gerini, G.; de Maagt, P.J.I.

2009-01-01

The use of planar circularly symmetric (PCS) electromagnetic band-gap (EBG) structures for optimizing the performances of single antenna elements and arrays is been discussed. The key advantage of using this sort of super structures is that they are planar and thus very cheap to manufacture with

Wide and ultra-wide bandgap oxides: where paradigm-shift photovoltaics meets transparent power electronics

Science.gov (United States)

Pérez-Tomás, Amador; Chikoidze, Ekaterine; Jennings, Michael R.; Russell, Stephen A. O.; Teherani, Ferechteh H.; Bove, Philippe; Sandana, Eric V.; Rogers, David J.

2018-03-01

Oxides represent the largest family of wide bandgap (WBG) semiconductors and also offer a huge potential range of complementary magnetic and electronic properties, such as ferromagnetism, ferroelectricity, antiferroelectricity and high-temperature superconductivity. Here, we review our integration of WBG and ultra WBG semiconductor oxides into different solar cells architectures where they have the role of transparent conductive electrodes and/or barriers bringing unique functionalities into the structure such above bandgap voltages or switchable interfaces. We also give an overview of the state-of-the-art and perspectives for the emerging semiconductor β- Ga2O3, which is widely forecast to herald the next generation of power electronic converters because of the combination of an UWBG with the capacity to conduct electricity. This opens unprecedented possibilities for the monolithic integration in solar cells of both self-powered logic and power electronics functionalities. Therefore, WBG and UWBG oxides have enormous promise to become key enabling technologies for the zero emissions smart integration of the internet of things.

Development of Radiation-hard Bandgap Reference and Temperature Sensor in CMOS 130 nm Technology

CERN Document Server

Kuczynska, Marika; Bugiel, Szymon; Firlej, Miroslaw; Fiutowski, Tomasz; Idzik, Marek; Michelis, Stefano; Moron, Jakub; Przyborowski, Dominik; Swientek, Krzysztof

2015-01-01

A stable reference voltage (or current) source is a standard component of today's microelectronics systems. In particle physics experiments such reference is needed in spite of harsh ionizing radiation conditions, i.e. doses exceeding 100 Mrads and fluences above 1e15 n/cm2. After such radiation load a bandgap reference using standard p-n junction of bipolar transistor does not work properly. Instead of using standard p-n junctions, two enclosed layout transistor (ELTMOS) structures are used to create radiation-hard diodes: the ELT bulk diode and the diode obtained using the ELTMOS as dynamic threshold transistor (DTMOS). In this paper we have described several sub-1V references based on ELTMOS bulk diode and DTMOS based diode, using CMOS 130 nm process. Voltage references the structures with additional PTAT (Proportional To Absolute Temperature) output for temperature measurements were also designed. We present and compare post-layout simulations of the developed bandgap references and temperature sensors, w...

Structural correlations in the generation of polaron pairs in low-bandgap polymers for photovoltaics

Science.gov (United States)

Tautz, Raphael; da Como, Enrico; Limmer, Thomas; Feldmann, Jochen; Egelhaaf, Hans-Joachim; von Hauff, Elizabeth; Lemaur, Vincent; Beljonne, David; Yilmaz, Seyfullah; Dumsch, Ines; Allard, Sybille; Scherf, Ullrich

2012-07-01

Polymeric semiconductors are materials where unique optical and electronic properties often originate from a tailored chemical structure. This allows for synthesizing conjugated macromolecules with ad hoc functionalities for organic electronics. In photovoltaics, donor-acceptor co-polymers, with moieties of different electron affinity alternating on the chain, have attracted considerable interest. The low bandgap offers optimal light-harvesting characteristics and has inspired work towards record power conversion efficiencies. Here we show for the first time how the chemical structure of donor and acceptor moieties controls the photogeneration of polaron pairs. We show that co-polymers with strong acceptors show large yields of polaron pair formation up to 24% of the initial photoexcitations as compared with a homopolymer (η=8%). π-conjugated spacers, separating the donor and acceptor centre of masses, have the beneficial role of increasing the recombination time. The results provide useful input into the understanding of polaron pair photogeneration in low-bandgap co-polymers for photovoltaics.

Towards efficient solar-to-hydrogen conversion: Fundamentals and recent progress in copper-based chalcogenide photocathodes

Directory of Open Access Journals (Sweden)

Chen Yubin

2016-09-01

Full Text Available Photoelectrochemical (PEC water splitting for hydrogen generation has been considered as a promising route to convert and store solar energy into chemical fuels. In terms of its large-scale application, seeking semiconductor photoelectrodes with high efficiency and good stability should be essential. Although an enormous number of materials have been explored for solar water splitting in the last several decades, challenges still remain for the practical application. P-type copper-based chalcogenides, such as Cu(In, GaSe2 and Cu2ZnSnS4, have shown impressive performance in photovoltaics due to narrow bandgaps, high absorption coefficients, and good carrier transport properties. The obtained high efficiencies in photovoltaics have promoted the utilization of these materials into the field of PEC water splitting. A comprehensive review on copper-based chalcogenides for solar-to-hydrogen conversion would help advance the research in this expanding area. This review will cover the physicochemical properties of copper-based chalco-genides, developments of various photocathodes, strategies to enhance the PEC activity and stability, introductions of tandem PEC cells, and finally, prospects on their potential for the practical solar-to-hydrogen conversion. We believe this review article can provide some insights of fundamentals and applications of copper-based chalco-genide thin films for PEC water splitting.

Tunable Bandgap Opening in the Proposed Structure of Silicon Doped Graphene

OpenAIRE

Azadeh, Mohammad S. Sharif; Kokabi, Alireza; Hosseini, Mehdi; Fardmanesh, Mehdi

2011-01-01

A specific structure of doped graphene with substituted silicon impurity is introduced and ab. initio density-functional approach is applied for energy band structure calculation of proposed structure. Using the band structure calculation for different silicon sites in the host graphene, the effect of silicon concentration and unit cell geometry on the bandgap of the proposed structure is also investigated. Chemically silicon doped graphene results in an energy gap as large as 2eV according t...

Microstructured and Photonic Bandgap Fibers for Applications in the Resonant Bio- and Chemical Sensors

Directory of Open Access Journals (Sweden)

Maksim Skorobogatiy

2009-01-01

Full Text Available We review application of microstructured and photonic bandgap fibers for designing resonant optical sensors of changes in the value of analyte refractive index. This research subject has recently invoked much attention due to development of novel fiber types, as well as due to development of techniques for the activation of fiber microstructure with functional materials. Particularly, we consider two sensors types. The first sensor type employs hollow core photonic bandgap fibers where core guided mode is confined in the analyte filled core through resonant effect in the surrounding periodic reflector. The second sensor type employs metalized microstructured or photonic bandgap waveguides and fibers, where core guided mode is phase matched with a plasmon propagating at the fiber/analyte interface. In resonant sensors one typically employs fibers with strongly nonuniform spectral transmission characteristics that are sensitive to changes in the real part of the analyte refractive index. Moreover, if narrow absorption lines are present in the analyte transmission spectrum, due to Kramers-Kronig relation this will also result in strong variation in the real part of the refractive index in the vicinity of an absorption line. Therefore, resonant sensors allow detection of minute changes both in the real part of the analyte refractive index (10−6–10−4 RIU, as well as in the imaginary part of the analyte refractive index in the vicinity of absorption lines. In the following we detail various resonant sensor implementations, modes of operation, as well as analysis of sensitivities for some of the common transduction mechanisms for bio- and chemical sensing applications. Sensor designs considered in this review span spectral operation regions from the visible to terahertz.

Electrically pumped edge-emitting photonic bandgap semiconductor laser

Science.gov (United States)

Lin, Shawn-Yu; Zubrzycki, Walter J.

2004-01-06

A highly efficient, electrically pumped edge-emitting semiconductor laser based on a one- or two-dimensional photonic bandgap (PBG) structure is described. The laser optical cavity is formed using a pair of PBG mirrors operating in the photonic band gap regime. Transverse confinement is achieved by surrounding an active semiconductor layer of high refractive index with lower-index cladding layers. The cladding layers can be electrically insulating in the passive PBG mirror and waveguide regions with a small conducting aperture for efficient channeling of the injection pump current into the active region. The active layer can comprise a quantum well structure. The quantum well structure can be relaxed in the passive regions to provide efficient extraction of laser light from the active region.

A superhard sp3 microporous carbon with direct bandgap

Science.gov (United States)

Pan, Yilong; Xie, Chenlong; Xiong, Mei; Ma, Mengdong; Liu, Lingyu; Li, Zihe; Zhang, Shuangshuang; Gao, Guoying; Zhao, Zhisheng; Tian, Yongjun; Xu, Bo; He, Julong

2017-12-01

Carbon allotropes with distinct sp, sp2, and sp3 hybridization possess various different properties. Here, a novel all-sp3 hybridized tetragonal carbon, namely the P carbon, was predicted by the evolutionary particle swarm structural search. It demonstrated a low density among all-sp3 carbons, due to the corresponding distinctive microporous structure. P carbon is thermodynamically stable than the known C60 and could be formed through the single-walled carbon nanotubes (SWCNTs) compression. P carbon is a direct bandgap semiconductor displaying a strong and superhard nature. The unique combination of electrical and mechanical properties constitutes P carbon a potential superhard material for semiconductor industrial fields.

Improvement of the quality of a-SiGe:H films

Energy Technology Data Exchange (ETDEWEB)

Sadamoto, M.; Saitoh, K.; Ishiguro, N.; Yanagawa, N.; Tanaka, H.; Fukuda, S.; Ashida, Y.; Fukuda, N. [Central Research Institute, Mitsui Toatsu Chemicals Inc., Sakae-ku, Yokohama (Japan)

1996-05-15

The ADHT (alternately repeating deposition and hydrogen plasma treatment) method and the DLE (deposition of low emission) method were developed for the formation of high quality a-SiGe:H (hydrogenated amorphous silicon germanium) films. High photosensitivity was obtained by the ADHT and DLE methods, with a wide range of optical bandgaps between 1.3 eV and 1.7 eV, higher than those of films obtained by the hydrogen dilution method. It was also proved that these films were solar cell device-grade. A conversion efficiency of 8.9% was obtained with a bandgap of 1.6 eV by the ADHT method, and a conversion efficiency of 8.2% and a short circuit current of 20.4 mA/cm{sup 2} were obtained with a bandgap of 1.47 eV by the DLE method

A 158 fs 5.3 nJ fiber-laser system at 1 mu m using photonic bandgap fibers for dispersion control and pulse compression

DEFF Research Database (Denmark)

Nielsen, C.K.; Jespersen, Kim Giessmann; Keiding, S.R.

2006-01-01

We demonstrate a 158 fs 5.3 nJ mode-locked laser system based on a fiber oscillator, fiber amplifier and fiber compressor. Dispersion compensation in the fiber oscillator was obtained with a solid-core photonic bandgap (SC-PBG) fiber spliced to standard fibers, and external compression is obtained...... with a hollow-core photonic bandgap (HC-PBG) fiber....

Influence of band-gap grading on luminescence properties of Cu(In,Ga)Se{sub 2}

Energy Technology Data Exchange (ETDEWEB)

Haarstrich, Jakob; Metzner, Heiner; Ronning, Carsten [Institut fuer Festkoerperphysik, Friedrich Schiller Universitaet Jena, Max-Wien-Platz 1, 07743 Jena (Germany); Rissom, Thorsten; Kaufmann, Christian A.; Schock, Hans-Werner [Helmholtz-Zentrum Berlin fuer Materialien und Energie, Solar Energy Research, Institute for Technology, Lise-Meitner-Campus, Hahn-Meitner-Platz 1, 14109 Berlin (Germany); Undisz, Andreas [Institute for Material Science and Technology, Metallic Materials, Friedrich-Schiller-University Jena, Loebdergraben 32, 07743 Jena (Germany)

2011-07-01

Cathodoluminescence (CL) has been measured on Cu(In,Ga)Se{sub 2} with Ga-grading as it is used in high-efficiency thin-film solar cells at 10 K in both cross-section and plain view configuration. In cross-section geometry, we show that the vertical profile of the emission energy represents the Ga-profile in the film and, thus, we are able to measure the band-gap grading present by means of CL methods. At the same time, we observe a strong drift of excited charge carriers towards the minimum of the band-gap which can be explained by the Ga-grading. It is shown by voltage-dependent CL, how these results directly influence the interpretation of luminescence spectra obtained on Ga-graded Cu(In,Ga)Se{sub 2} and, thus, they will have to be considered as a basis for all forthcoming investigations on this topic.

Design of a Polymer-Based Hollow-Core Bandgap Fiber for Low-Loss Terahertz Transmission

DEFF Research Database (Denmark)

Barh, Ajanta; Varshney, Ravi K.; Pal, Bishnu P.

2016-01-01

wavelength-scale circular air holes in a hexagonal pattern, embedded in a uniform Teflon matrix. The THz guidance in this fiber is achieved by exploiting the photonic bandgap (PBG) effect. In our low index contrast Teflon-air (1.44:1) hexagonal periodic lattice, the PBG appears only for a certain range...

Shape and phase evolution from CsPbBr3 perovskite nanocubes to tetragonal CsPb2Br5 nanosheets with an indirect bandgap.

Science.gov (United States)

Li, Guopeng; Wang, Hui; Zhu, Zhifeng; Chang, Yajing; Zhang, Ting; Song, Zihang; Jiang, Yang

2016-09-13

Tetragonal CsPb 2 Br 5 nanosheets were obtained by an oriented attachment of orthorhombic CsPbBr 3 nanocubes, involving a lateral shape evolution from octagonal to square. Meanwhile, the experimental results, together with DFT simulation results, indicated that the tetragonal CsPb 2 Br 5 is an indirect bandgap semiconductor that is PL-inactive with a bandgap of 2.979 eV.

Bose-Einstein condensates in optical lattices: Band-gap structure and solitons

International Nuclear Information System (INIS)

Louis, Pearl J. Y.; Kivshar, Yuri S.; Ostrovskaya, Elena A.; Savage, Craig M.

2003-01-01

We analyze the existence and stability of spatially extended (Bloch-type) and localized states of a Bose-Einstein condensate loaded into an optical lattice. In the framework of the Gross-Pitaevskii equation with a periodic potential, we study the band-gap structure of the matter-wave spectrum in both the linear and nonlinear regimes. We demonstrate the existence of families of spatially localized matter-wave gap solitons, and analyze their stability in different band gaps, for both repulsive and attractive atomic interactions

Millijoule Pulse Energy Second Harmonic Generation With Single-Stage Photonic Bandgap Rod Fiber Laser

DEFF Research Database (Denmark)

Laurila, Marko; Saby, Julien; Alkeskjold, Thomas Tanggaard

2011-01-01

In this paper, we demonstrate, for the first time, a single-stage Q-switched single-mode (SM) ytterbium-doped rod fiber laser delivering record breaking pulse energies at visible and UV light. We use a photonic bandgap rod fiber with a mode field diameter of 59μm based on a new distributed...

Hydrogen and oxygen isotope exchange reactions over illuminated and nonilluminated TiO2

International Nuclear Information System (INIS)

Sato, S.

1987-01-01

Hydrogen isotope exchange between H 2 , gaseous H 2 O, and the surface hydroxyls of TiO 2 , and oxygen isotope exchange between O 2 , CO 2 , CO, H 2 O vapor, and the hydroxyls over TiO 3 were studied at room temperature in the dark and under illumination. Hydrogen isotope exchange between H 2 O and the hydroxyls occurred rapidly in the dark, but the exchange involving H 2 did not occur at all even under illumination. Oxygen isotope exchange among H 2 O vapor, CO 2 , and the hydroxyls easily took place in the dark, but the exchange involving O 2 required band-gap illumination. Dioxygen isotope equilibration was much faster than the other photoexchange reactions. Although the oxygen exchange between O 2 and illuminated TiO 2 has been considered to involve lattice-oxygen exchange, the present experiments revealed that the hydroxyls of TiO 2 mainly participate in the exchange reaction. The oxygen exchange between O 2 and H 2 O vapor was strongly inhibited by H 2 O vapor itself probably because oxygen adsorption was retarded by adsorbed water. Oxygen in CO was not exchanged with the other substrates under any conditions tested

Free-carrier-compensated charged domain walls produced with super-bandgap illumination in insulating ferroelectrics

Czech Academy of Sciences Publication Activity Database

Bednyakov, Petr; Sluka, T.; Tagantsev, A.; Damjanovic, D.; Setter, N.

2016-01-01

Roč. 28, č. 43 (2016), s. 9498-9503 ISSN 0935-9648 R&D Projects: GA ČR GA15-04121S Institutional support: RVO:68378271 Keywords : super-bandgap illumination * charged domain walls * ferroelectric BaTiO 3 * free-carrier generation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 19.791, year: 2016

Bandgap modulation in photoexcited topological insulator Bi{sub 2}Te{sub 3} via atomic displacements

Energy Technology Data Exchange (ETDEWEB)

Hada, Masaki, E-mail: hadamasaki@okayama-u.ac.jp [Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530 (Japan); Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan); Norimatsu, Katsura; Tsuruta, Tetsuya; Igarashi, Kyushiro; Kayanuma, Yosuke; Sasagawa, Takao; Nakamura, Kazutaka G. [Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Tanaka, Sei' ichi; Ishikawa, Tadahiko; Koshihara, Shin-ya [Department of Chemistry and Materials Science, Tokyo Institute of Technology, Tokyo 152-8551 (Japan); Keskin, Sercan [The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761 (Germany); Miller, R. J. Dwayne [The Max Planck Institute for the Structure and Dynamics of Matter, The Hamburg Centre for Ultrafast Imaging, University of Hamburg, Hamburg 22761 (Germany); Departments of Chemistry and Physics, University of Toronto, Toronto M5S 3H6 (Canada); Onda, Ken [PRESTO, Japan Science and Technology Agency, Kawaguchi 332-0012 (Japan); Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226-8502 (Japan)

2016-07-14

The atomic and electronic dynamics in the topological insulator (TI) Bi{sub 2}Te{sub 3} under strong photoexcitation were characterized with time-resolved electron diffraction and time-resolved mid-infrared spectroscopy. Three-dimensional TIs characterized as bulk insulators with an electronic conduction surface band have shown a variety of exotic responses in terms of electronic transport when observed under conditions of applied pressure, magnetic field, or circularly polarized light. However, the atomic motions and their correlation between electronic systems in TIs under strong photoexcitation have not been explored. The artificial and transient modification of the electronic structures in TIs via photoinduced atomic motions represents a novel mechanism for providing a comparable level of bandgap control. The results of time-domain crystallography indicate that photoexcitation induces two-step atomic motions: first bismuth and then tellurium center-symmetric displacements. These atomic motions in Bi{sub 2}Te{sub 3} trigger 10% bulk bandgap narrowing, which is consistent with the time-resolved mid-infrared spectroscopy results.

Radiation resistant low bandgap InGaAsP solar cell for multi-junction solar cells

International Nuclear Information System (INIS)

Khan, Aurangzeb; Yamaguchi, Masafumi; Dharmaras, Nathaji; Yamada, Takashi; Tanabe, Tatsuya; Takagishi, Shigenori; Itoh, Hisayoshi; Ohshima, Takeshi

2001-01-01

We have explored the superior radiation tolerance of metal organic chemical vapor deposition (MOCVD) grown, low bandgap, (0.95eV) InGaAsP solar cells as compared to GaAs-on-Ge cells, after 1 MeV electron irradiation. The minority carrier injection due to forward bias and light illumination under low concentration ratio, can lead to enhanced recovery of radiation damage in InGaAsP n + -p junction solar cells. An injection anneal activation energy (0.58eV) of the defects involved in damage/recovery of the InGaAsP solar cells has been estimated from the resultant recovery of the solar cell properties following minority carrier injection. The results suggest that low bandgap radiation resistant InGaAsP (0.95eV) lattice matched to InP substrates provide an alternative to use as bottom cells in multi-junction solar cells instead of less radiation ressitant conventional GaAs based solar cells for space applications. (author)

Semiconductor Metal-Organic Frameworks: Future Low-Bandgap Materials.

Science.gov (United States)

Usman, Muhammad; Mendiratta, Shruti; Lu, Kuang-Lieh

2017-02-01

Metal-organic frameworks (MOFs) with low density, high porosity, and easy tunability of functionality and structural properties, represent potential candidates for use as semiconductor materials. The rapid development of the semiconductor industry and the continuous miniaturization of feature sizes of integrated circuits toward the nanometer (nm) scale require novel semiconductor materials instead of traditional materials like silicon, germanium, and gallium arsenide etc. MOFs with advantageous properties of both the inorganic and the organic components promise to serve as the next generation of semiconductor materials for the microelectronics industry with the potential to be extremely stable, cheap, and mechanically flexible. Here, a perspective of recent research is provided, regarding the semiconducting properties of MOFs, bandgap studies, and their potential in microelectronic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Hyperuniform Disordered photonic bandgap materials, from 2D to 3D, and their applications

Science.gov (United States)

Man, Weining; Florescu, Marian; Sahba, Shervin; Sellers, Steven

Recently, hyperuniform disordered systems attracted increasing attention due to their unique physical properties and the potential possibilities of self-assembling them. We had introduced a class of 2D hyperuniform disordered (HUD) photonic bandgap (PBG) materials enabled by a novel constrained optimization method for engineering the material's isotropic photonic bandgap. The intrinsic isotropy in these disordered structures is an inherent advantage associated with the lack of crystalline order, offering unprecedented freedom for functional defect design impossible to achieve in photonic crystals. Beyond our previous experimental work using macroscopic samples with microwave radiation, we demonstrated functional devices based on submicron-scale planar hyperuniform disordered PBG structures further highlight their ability to serve as highly compact, flexible and energy-efficient platforms for photonic integrated circuits. We further extended the design, fabrication, and characterization of the disordered photonic system into 3D. We also identify local self-uniformity as a novel measure of a disordered network's internal structural similarity, which we found crucial for photonic band gap formation. National Science Foundations award DMR-1308084.

Bandgap engineering of the Lu{sub x}Y{sub 1−x}PO{sub 4} mixed crystals

Energy Technology Data Exchange (ETDEWEB)

Levushkina, V.S., E-mail: viktoriia.levushkina@ut.ee [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Physics Faculty, Moscow State University, Leninskiye Gory 1-2, 11991 Moscow (Russian Federation); Spassky, D.A. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); Skobeltsyn Institute of Nuclear Physics, Moscow State University, Leninskiye Gory 1-2, 11991 Moscow (Russian Federation); Aleksanyan, E.M. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); A. Alikhanyan National Science Laboratory, Yerevan Physics Institute, Alikhanyan Yeghbayrneri St. 2, 0036 Yerevan (Armenia); Brik, M.G. [Institute of Physics, University of Tartu, Ravila 14c, 50411 Tartu (Estonia); College of Sciences, Chongqing University of Posts and Telecommunications, 400065 Chongqing (China); Institute of Physics, Jan Dlugosz University, Armii Krajowej 13/15, PL-42200 Czestochowa (Poland); Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warsaw (Poland); Tretyakova, M.S.; Zadneprovski, B.I. [Central Research and Development Institute of Chemistry and Mechanics, Nagatinskaya St. 16a, 115487 Moscow (Russian Federation); Belsky, A.N. [Institute of Light and Matter, CNRS, University Lyon1, 69622 Villeurbanne (France)

2016-03-15

Bandgap modification of the Lu{sub x}Y{sub 1−x}PO{sub 4} mixed crystals has been studied by thermostimulated luminescence (TSL) and ab-initio calculation methods. Doping of Lu{sub x}Y{sub 1−x}PO{sub 4} with Ce{sup 3+} allowed to follow up the changes of electron traps depth, caused by the modification of the bottom of conduction band. The observed gradual shift of the most intensive TSL peaks to higher temperatures with increase of x value was connected with the high-energy shift of the conduction band bottom. According to the band structure calculations the bottom of the conduction band is formed by the 5d and 4d states of Lu and Y, respectively. Therefore, substitution of one cation by another is responsible for the observed variation of the electronic and optical properties. Doping with Eu{sup 3+} was used to study the modification of the hole traps and the top of the valence band in Lu{sub x}Y{sub 1−x}PO{sub 4}. The independence of the TSL peaks position on x value in Lu{sub x}Y{sub 1−x}PO{sub 4}:Eu{sup 3+} allows to conclude that the top of the valence band is negligibly affected by the cation substitution. According to the band structure calculations the top of the valence band is formed by the O 2p electronic states, which are not affected by the cation substitution. The resulting increase of the bandgap with x value is confirmed by the data of ab-initio calculations. - Highlights: • Band structure modification with x in Lu{sub x}Y{sub 1−x}PO{sub 4}:RE{sup 3+} (RE=Ce, Eu) is studied. • Depth of electron traps is affected by the bandgap modification. • Increase of bandgap with x is due to the shift of conduction band bottom.

Waveguidance by the photonic bandgap effect in optical fibres

DEFF Research Database (Denmark)

Broeng, Jes; Søndergaard, Thomas; Barkou, Stig Eigil

1999-01-01

Photonic crystals form a new class of intriguing building blocks to be utilized in future optoelectronics and electromagnetics. One of the most exciting possiblilties offered by phtonic crystals is the realization of new types of electromagnetic waveguides. In the optical domain, the most mature...... technology for such photonic bandgap (PBG) waveguides is in optical fibre configurations. These new fibres can be classified in a fundamentally different way to all optical waveguides and possess radically different guiding properties due to PBG guidance, as opposed to guidance by total internal refelction....... In this paper we summarize and review our theoretical work demonstrating the underlying physical principles of PBG guiding optical fibres and discuss some of their unique waveguiding properties....

Single-mode ytterbium-doped large-mode-area photonic bandgap rod fiber amplifier

DEFF Research Database (Denmark)

Alkeskjold, Thomas Tanggaard; Scolari, Lara; Broeng, Jes

2011-01-01

bandgap structure. The structure allows resonant coupling of higher-order modes from the core and acts as a spatially Distributed Mode Filter (DMF). With this approach, we demonstrate passive SM performance in an only ~50cm long and straight ytterbium-doped rod fiber. The amplifier has a mode field...... diameter of ∼59Lim at 1064nm and exhibits a pump absorption of 27dB/m at 976nm. © 2011 Optical Society of America....

Investigation on bandgap, diffraction, interference, and refraction effects of photonic crystal structure in GaN/InGaN LEDs for light extraction.

Science.gov (United States)

Patra, Saroj Kanta; Adhikari, Sonachand; Pal, Suchandan

2014-06-20

In this paper, we have made a clear differentiation among bandgap, diffraction, interference, and refraction effects in photonic crystal structures (PhCs). For observing bandgap, diffraction, and refraction effects, PhCs are considered on the top p-GaN surface of light emitting diodes (LEDs), whereas for interference effect, hole type PhCs are considered to be embedded within n-GaN layer of LED. From analysis, it is observed that at a particular lattice periodicity, for which bandgap lies within the wavelength of interest shows a significant light extraction due to inhibition of guided mode. Beyond a certain periodicity, diffraction effect starts dominating and light extraction improves further. The interference effect is observed in embedded photonic crystal LEDs, where depth of etching supports constructive interference of outward light waves. We have also shed light on refraction effects exhibited by the PhCs and whether negative refraction properties of PhCs may be useful in case of LED light extraction.

Structural, optical, and electronic studies of wide-bandgap lead halide perovskites

KAUST Repository

Comin, Riccardo; Walters, Grant; Thibau, Emmanuel Sol; Voznyy, Oleksandr; Lu, Zheng-Hong; Sargent, Edward H.

2015-01-01

© The Royal Society of Chemistry 2015. We investigate the family of mixed Br/Cl organolead halide perovskites which enable light emission in the blue-violet region of the visible spectrum. We report the structural, optical and electronic properties of this air-stable family of perovskites, demonstrating full bandgap tunability in the 400-550 nm range and enhanced exciton strength upon Cl substitution. We complement this study by tracking the evolution of the band levels across the gap, thereby providing a foundational framework for future optoelectronic applications of these materials.

Analysis of photonic band-gap (PBG) structures using the FDTD method

DEFF Research Database (Denmark)

Tong, M.S.; Cheng, M.; Lu, Y.L.

2004-01-01

In this paper, a number of photonic band-gap (PBG) structures, which are formed by periodic circuit elements printed oil transmission-line circuits, are studied by using a well-known numerical method, the finite-difference time-domain (FDTD) method. The results validate the band-stop filter...... behavior of these structures, and the computed results generally match well with ones published in the literature. It is also found that the FDTD method is a robust, versatile, and powerful numerical technique to perform such numerical studies. The proposed PBG filter structures may be applied in microwave...

Demonstration of suppressed phonon tunneling losses in phononic bandgap shielded membrane resonators for high-Q optomechanics.

Science.gov (United States)

Tsaturyan, Yeghishe; Barg, Andreas; Simonsen, Anders; Villanueva, Luis Guillermo; Schmid, Silvan; Schliesser, Albert; Polzik, Eugene S

2014-03-24

Dielectric membranes with exceptional mechanical and optical properties present one of the most promising platforms in quantum opto-mechanics. The performance of stressed silicon nitride nanomembranes as mechanical resonators notoriously depends on how their frame is clamped to the sample mount, which in practice usually necessitates delicate, and difficult-to-reproduce mounting solutions. Here, we demonstrate that a phononic bandgap shield integrated in the membrane's silicon frame eliminates this dependence, by suppressing dissipation through phonon tunneling. We dry-etch the membrane's frame so that it assumes the form of a cm-sized bridge featuring a 1-dimensional periodic pattern, whose phononic density of states is tailored to exhibit one, or several, full band gaps around the membrane's high-Q modes in the MHz-range. We quantify the effectiveness of this phononic bandgap shield by optical interferometry measuring both the suppressed transmission of vibrations, as well as the influence of frame clamping conditions on the membrane modes. We find suppressions up to 40 dB and, for three different realized phononic structures, consistently observe significant suppression of the dependence of the membrane's modes on sample clamping-if the mode's frequency lies in the bandgap. As a result, we achieve membrane mode quality factors of 5 × 10(6) with samples that are tightly bolted to the 8 K-cold finger of a cryostat. Q × f -products of 6 × 10(12) Hz at 300 K and 14 × 10(12) Hz at 8 K are observed, satisfying one of the main requirements for optical cooling of mechanical vibrations to their quantum ground-state.

Compact and portable multiline UV and visible Raman lasers in hydrogen-filled HC-PCF.

Science.gov (United States)

Wang, Y Y; Couny, F; Light, P S; Mangan, B J; Benabid, F

2010-04-15

We report on the realization of compact UV visible multiline Raman lasers based on two types of hydrogen-filled hollow-core photonic crystal fiber. The first, with a large pitch Kagome lattice structure, offers a broad spectral coverage from near IR through to the much sought after yellow, deep-blue and UV, whereas the other, based on photonic bandgap guidance, presents a pump conversion concentrated in the visible region. The high Raman efficiency achieved through these fibers allows for compact, portable diode-pumped solid-state lasers to be used as pumps. Each discrete component of this laser system exhibits a spectral density several orders of magnitude larger than what is achieved with supercontinuum sources and a narrow linewidth, making it an ideal candidate for forensics and biomedical applications.

Theory of adiabatic pressure-gradient soliton compression in hollow-core photonic bandgap fibers

DEFF Research Database (Denmark)

Lægsgaard, Jesper; Roberts, John

2009-01-01

Adiabatic soliton compression by means of a pressure gradient in a hollow-core photonic bandgap fiber is investigated theoretically and numerically. It is shown that the dureation of the compressed pulse is limited mainly by the interplay between third-order dispersion and the Raman-induced soliton...... frequency shift. Analytical expressions for this limit are derived and compared with results of detailed numerical simulations for a realistic fiber structure....

SiC Sensors in Extreme Environments: Real-time Hydrogen Monitoring for Energy Plant Applications

Science.gov (United States)

Ghosh, Ruby

2008-03-01

Clean, efficient energy production, such as the gasification of coal (syngas), requires physical and chemical sensors for exhaust gas monitoring as well as real-time control of the combustion process. Wide-bandgap semiconducting materials systems can meet the sensing demands in these extreme environments consisting of chemically corrosive gases at high temperature and pressure. We have developed a SiC based micro-sensor for detection of hydrogen containing species with millisecond response at 600 C. The sensor is a Pt-SiO2-SiC device with a dense Pt catalytic sensing film, capable of withstanding months of continuous high temperature operation. The device was characterized in robust sensing module that is compatible with an industrial reactor. We report on the performance of the SiC sensor in a simulated syngas ambient at 370 C containing the common interferants CO2, CH4 and CO [1]. In addition we demonstrate that hours of exposure to >=1000 ppm H2S and 15% water vapor does not degrade the sensor performance. To elucidate the mechanisms responsible for the hydrogen response of the sensor we have modeled the hydrogen adsorptions kinetics at the internal Pt-SiO2 interface, using both the Tempkin and Langmuir isotherms. Under the conditions appropriate for energy plant applications, the response of our sensor is significantly larger than that obtained from ultra-high vacuum electrochemical sensor measurements at high temperatures. We will discuss the role of morphology, at the nano to micro scale, on the enhanced catalytic activity observed for our Pt sensing films in response to a heated hydrogen gas stream at atmospheric pressure. [1] R. Loloee, B. Chorpening, S. Beers & R. Ghosh, Hydrogen monitoring for power plant applications using SiC sensors, Sens. Actuators B:Chem. (2007), doi:10.1016/j.snb.2007.07.118

Modelling and measurement of bandgap behaviour in medium-wavelength IR InAs/InAs0.815Sb0.185 strained-layer superlattices

Science.gov (United States)

Letka, Veronica; Keen, James; Craig, Adam; Marshall, Andrew R. J.

2017-10-01

InAs/InAs1-xSbx type-II strained-layer superlattices (SLS) are a structure with potential infrared detection applications, owing to its tunable bandgap and suppressed Auger recombination. A series of medium-wavelength infrared (MWIR) InAs/InAs0.815Sb0.185 SLS structures, grown as undoped absorption epilayers on GaAs, were fabricated using molecular beam epitaxy in order to study the dependence of the ground state transitions on temperature and superlattice period thickness. Photoluminescence peaks at 4 K were obtained with the use of a helium-cooled micro-PL system and an InSb detector, and temperature-dependent absorption spectra were measured in the range 77 K - 300 K on a Fourier Transform Infrared (FTIR) spectrometer, equipped with a 1370 K blackbody source and a DTGS detector. An nBn device sample with the absorber structure identical to one of the undoped samples was also grown and processed with the goal of measuring temperature-dependent spectral response. A model for superlattice band alignment was also devised, incorporating the Bir-Pikus transformation results for uniaxial and biaxial strain, and the Einstein oscillator model for bandgap temperature dependence. Absorption coefficients of several 1000 cm-1 throughout the entire MWIR range are found for all samples, and temperature dependence of the bandgaps is extracted and compared to the model. This and photoluminescence data also demonstrate bandgap shifts consistent with the different superlattice periods of the three samples.

Understanding Electrically Active Interface Formation on Wide Bandgap Semiconductors through Molecular Beam Epitaxy Using Fe3O 4 for Spintronics as a Base Case

Science.gov (United States)

Hamedani Golshan, Negar

Nanoelectronics, complex heterostructures, and engineered 3D matrix materials are quickly advancing from research possibilities to manufacturing challenges for applications ranging from high-power devices to solar cells to any number of novel multifunctional sensors and controllers. Formation of an abrupt and effective interface is one of the basic requirements for integration of functional materials on different types of semiconductors (from silicon to the wide bandgaps) which can significantly impact the functionality of nanoscale electronic devices. To realize the potential of next-generation electronics, the understanding and control of those initial stages of film layer formation must be understood and translated to a process that can control the initial stages of film deposition. Thin film Fe3O4 has attracted much attention as a material for exploring the potential of spintronics in next-generation information technologies. Synthesis of highly spin-polarized material as spin sources, in combination with wide bandgap semiconductors which have a long spin relaxation time in addition to functionality in high-temperature, high-power, and high-frequency environments, would enhance the performance of today's spintronic devices. Spinel ferrite Fe3O4 has a high Curie temperature of 858 K and it is predicted to possess half-metallic properties, i.e. 100% spin polarization at the Fermi level, which can lead to ultrahigh tunneling magnetoresistance at room temperature. However, these properties have been very difficult to realize in thin film form, and device design strategies require high-quality thin films of Fe3O4. The most common reason reported in literature for the failure of the films to achieve theoretical performance is that the growth techniques used today produce films with antiphase boundaries (APB). These APBs have a strong antiferromagnetic coupling that negatively impact the magnetic and transport properties of epitaxial Fe 3O4 films. Therefore, greater

Two Regimes of Bandgap Red Shift and Partial Ambient Retention in Pressure-Treated Two-Dimensional Perovskites

Energy Technology Data Exchange (ETDEWEB)

Liu, Gang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China; Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States; Kong, Lingping [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China; Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States; Guo, Peijun [Center; Stoumpos, Constantinos C. [Department; Hu, Qingyang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China; Liu, Zhenxian [Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States; Cai, Zhonghou [Advanced; Gosztola, David J. [Center; Mao, Ho-kwang [Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China; Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, United States; Kanatzidis, Mercouri G. [Department; Schaller, Richard D. [Center; Department

2017-10-09

The discovery of elevated environmental stability in two-dimensional (2D) Ruddlesden–Popper hybrid perovskites represents a significant advance in low-cost, high-efficiency light absorbers. In comparison to 3D counterparts, 2D perovskites of organo-lead-halides exhibit wider, quantum-confined optical bandgaps that reduce the wavelength range of light absorption. Here, we characterize the structural and optical properties of 2D hybrid perovskites as a function of hydrostatic pressure. We observe bandgap narrowing with pressure of 633 meV that is partially retained following pressure release due to an atomic reconfiguration mechanism. We identify two distinct regimes of compression dominated by the softer organic and less compressible inorganic sublattices. Our findings, which also include PL enhancement, correlate well with density functional theory calculations and establish structure–property relationships at the atomic scale. These concepts can be expanded into other hybrid perovskites and suggest that pressure/strain processing could offer a new route to improved materials-by-design in applications.

Band-gap analysis of a novel lattice with a hierarchical periodicity using the spectral element method

Science.gov (United States)

Wu, Zhijing; Li, Fengming; Zhang, Chuanzeng

2018-05-01

Inspired by the hierarchical structures of butterfly wing surfaces, a new kind of lattice structures with a two-order hierarchical periodicity is proposed and designed, and the band-gap properties are investigated by the spectral element method (SEM). The equations of motion of the whole structure are established considering the macro and micro periodicities of the system. The efficiency of the SEM is exploited in the modeling process and validated by comparing the results with that of the finite element method (FEM). Based on the highly accurate results in the frequency domain, the dynamic behaviors of the proposed two-order hierarchical structures are analyzed. An original and interesting finding is the existence of the distinct macro and micro stop-bands in the given frequency domain. The mechanisms for these two types of band-gaps are also explored. Finally, the relations between the hierarchical periodicities and the different types of the stop-bands are investigated by analyzing the parametrical influences.

Control of electric field in CdZnTe radiation detectors by above-bandgap light

International Nuclear Information System (INIS)

Franc, J.; Dědič, V.; Rejhon, M.; Zázvorka, J.; Praus, P.; Touš, J.; Sellin, P. J.

2015-01-01

We have studied the possibility of above bandgap light induced depolarization of CdZnTe planar radiation detector operating under high flux of X-rays by Pockels effect measurements. In this contribution, we show a similar influence of X-rays at 80 kVp and LED with a wavelength of 910 nm irradiating the cathode on polarization of the detector due to an accumulation of a positive space charge of trapped photo-generated holes. We have observed the depolarization of the detector under simultaneous cathode-site illumination with excitation LED at 910 nm and depolarization above bandgap LED at 640 nm caused by trapping of drifting photo-generated electrons. Although the detector current is quite high during this depolarization, we have observed that it decreases relatively fast to its initial value after switching off the depolarizing light. In order to get detailed information about physical processes present during polarization and depolarization and, moreover, about associated deep levels, we have performed the Pockels effect infrared spectral scanning measurements of the detector without illumination and under illumination in polarized and optically depolarized states

Control of electric field in CdZnTe radiation detectors by above-bandgap light

Energy Technology Data Exchange (ETDEWEB)

Franc, J.; Dědič, V.; Rejhon, M.; Zázvorka, J.; Praus, P. [Institute of Physics of Charles University, Prague (Czech Republic); Touš, J. [Crytur Ltd., Turnov (Czech Republic); Sellin, P. J. [Department of Physics, University of Surrey, Guildford (United Kingdom)

2015-04-28

We have studied the possibility of above bandgap light induced depolarization of CdZnTe planar radiation detector operating under high flux of X-rays by Pockels effect measurements. In this contribution, we show a similar influence of X-rays at 80 kVp and LED with a wavelength of 910 nm irradiating the cathode on polarization of the detector due to an accumulation of a positive space charge of trapped photo-generated holes. We have observed the depolarization of the detector under simultaneous cathode-site illumination with excitation LED at 910 nm and depolarization above bandgap LED at 640 nm caused by trapping of drifting photo-generated electrons. Although the detector current is quite high during this depolarization, we have observed that it decreases relatively fast to its initial value after switching off the depolarizing light. In order to get detailed information about physical processes present during polarization and depolarization and, moreover, about associated deep levels, we have performed the Pockels effect infrared spectral scanning measurements of the detector without illumination and under illumination in polarized and optically depolarized states.

First-principle approach based bandgap engineering for cubic boron nitride doped with group IIA elements

Science.gov (United States)

Li, Yubo; Wang, Pengtao; Hua, Fei; Zhan, Shijie; Wang, Xiaozhi; Luo, Jikui; Yang, Hangsheng

2018-03-01

Electronic properties of cubic boron nitride (c-BN) doped with group IIA elements were systematically investigated using the first principle calculation based on density functional theory. The electronic bandgap of c-BN was found to be narrowed when the impurity atom substituted either the B (IIA→B) or the N (IIA→N) atom. For IIA→B, a shallow accept level degenerated into valence band (VB); while for IIA→N, a shallow donor level degenerated conduction band (CB). In the cases of IIBe→N and IIMg→N, deep donor levels were also induced. Moreover, a zigzag bandgap narrowing pattern was found, which is in consistent with the variation pattern of dopants' radius of electron occupied outer s-orbital. From the view of formation energy, the substitution of B atom under N-rich conditions and the substitution of N atom under B-rich conditions were energetically favored. Our simulation results suggested that Mg and Ca are good candidates for p-type dopants, and Ca is the best candidate for n-type dopant.

Compact electromagnetic bandgap structures for notch band in ultra-wideband applications.

Science.gov (United States)

Rotaru, Mihai; Sykulski, Jan

2010-01-01

This paper introduces a novel approach to create notch band filters in the front-end of ultra-wideband (UWB) communication systems based on electromagnetic bandgap (EBG) structures. The concept presented here can be implemented in any structure that has a microstrip in its configuration. The EBG structure is first analyzed using a full wave electromagnetic solver and then optimized to work at WLAN band (5.15-5.825 GHz). Two UWB passband filters are used to demonstrate the applicability and effectiveness of the novel EBG notch band feature. Simulation results are provided for two cases studied.

Structure and optical band-gap energies of Ba0.5Sr0.5TiO3 thin films fabricated by RF magnetron plasma sputtering

International Nuclear Information System (INIS)

Xu, Zhimou; Suzuki, Masato; Yokoyama, Shin

2005-01-01

The structure and optical band-gap energies of Ba 0.5 Sr 0.5 TiO 3 (BST0.5) thin films prepared on SiO 2 /Si and fused quartz substrates by RF magnetron plasma sputtering were studied in terms of deposition temperature and film thickness. Highly (100)-oriented BST0.5 thin films were successfully sputtered on a Si substrate with an approximately 1.0-μm-thick SiO 2 layer at a deposition temperature of above 450degC. The optical transmittance of BST0.5 thin films weakly depended on the magnitude of X-ray diffraction (XRD) peak intensity. This is very helpful for monolithic integration of BST0.5 films for electrooptical functions directly onto a SiO 2 /Si substrate. The band-gap energies showed a strong dependence on the deposition temperature and film thickness. It was mainly related to the quantum size effect and the influence of the crystallinity of thin films, such as grain boundaries, grain size, oriented growth, and the existence of an amorphous phase. The band-gap energy values, which were much larger than those of single crystals, decreased with the increase in the deposition temperature and the thickness of BST0.5 thin films. The band-gap energy of 311-nm-thick amorphous BST0.5 thin film was about 4.45 eV and that of (100)-oriented BST0.5 thin film with a thickness of 447 nm was about 3.89 eV. It is believed that the dependence of the band-gap energies of the thin films on the crystallinity for various values of deposition temperature and film thickness means that there could be application in integrated optical devices. (author)

Stable Inverted Low-Bandgap Polymer Solar Cells with Aqueous Solution Processed Low-Temperature ZnO Buffer Layers

Directory of Open Access Journals (Sweden)

Chunfu Zhang

2016-01-01

Full Text Available Efficient inverted low-bandgap polymer solar cells with an aqueous solution processed low-temperature ZnO buffer layer have been investigated. The low-bandgap material PTB-7 is employed so that more solar light can be efficiently harvested, and the aqueous solution processed ZnO electron transport buffer layer is prepared at 150°C so that it can be compatible with the roll-to-roll process. Power conversion efficiency (PCE of the inverted device reaches 7.12%, which is near the control conventional device. More importantly, the inverted device shows a better stability, keeping more than 90% of its original PCE after being stored for 625 hours, while PCE of the conventional device is only 75% of what it was. In addition, it is found that the ZnO thin film annealed in N2 can obviously increase PCE of the inverted device further to 7.26%.

Plasma Reflection in Multigrain Layers of Narrow-Bandgap Semiconductors

Science.gov (United States)

Zhukov, N. D.; Shishkin, M. I.; Rokakh, A. G.

2018-04-01

Qualitatively similar spectral characteristics of plasma-resonance reflection in the region of 15-25 μm were obtained for layers of electrodeposited submicron particles of InSb, InAs, and GaAs and plates of these semiconductors ground with M1-grade diamond powder. The most narrow-bandgap semiconductor InSb (intrinsic absorption edge ˜7 μm) is characterized by an absorption band at 2.1-2.3 μm, which is interpreted in terms of the model of optical excitation of electrons coupled by the Coulomb interaction. The spectra of a multigrain layer of chemically deposited PbS nanoparticles (50-70 nm) exhibited absorption maxima at 7, 10, and 17 μm, which can be explained by electron transitions obeying the energy-quantization rules for quantum dots.

III-N Wide Bandgap Deep-Ultraviolet Lasers and Photodetectors

KAUST Repository

Detchprohm, T.

2016-11-05

The III-N wide-bandgap alloys in the AlInGaN system have many important and unique electrical and optical properties which have been exploited to develop deep-ultraviolet (DUV) optical devices operating at wavelengths < 300 nm, including light-emitting diodes, optically pumped lasers, and photodetectors. In this chapter, we review some aspects of the development and current state of the art of these DUV materials and devices. We describe the growth of III-N materials in the UV region by metalorganic chemical vapor deposition as well as the properties of epitaxial layers and heterostructure devices. In addition, we discuss the simulation and design of DUV laser diodes, the processing of III-N optical devices, and the description of the current state of the art of DUV lasers and photodetectors.

Analysis of photonic band-gap structures in stratified medium

DEFF Research Database (Denmark)

Tong, Ming-Sze; Yinchao, Chen; Lu, Yilong

2005-01-01

in electromagnetic and microwave applications once the Maxwell's equations are appropriately modeled. Originality/value - The method validates its values and properties through extensive studies on regular and defective 1D PBG structures in stratified medium, and it can be further extended to solving more......Purpose - To demonstrate the flexibility and advantages of a non-uniform pseudo-spectral time domain (nu-PSTD) method through studies of the wave propagation characteristics on photonic band-gap (PBG) structures in stratified medium Design/methodology/approach - A nu-PSTD method is proposed...... in solving the Maxwell's equations numerically. It expands the temporal derivatives using the finite differences, while it adopts the Fourier transform (FT) properties to expand the spatial derivatives in Maxwell's equations. In addition, the method makes use of the chain-rule property in calculus together...

Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide

KAUST Repository

Li, Yangyang

2017-12-16

Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long-wavelength regimes. In this work, the discovery of orthorhombic-structured Ti2O3 films is reported as a unique narrow-bandgap (≈0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well-known corundum-structured Ti2O3 polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti2O3 thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti2O3 polymorph is found to be n-type with a very high electron concentration, while the bulk-type trigonal-structured Ti2O3 is p-type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti2O3, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti2O3, which is confirmed by X-ray magnetic circular dichroism measurements. Using first-principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti2O3. The room-temperature ferromagnetism observed in orthorhombic-structured Ti2O3, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases.

Orthorhombic Ti2O3: A Polymorph-Dependent Narrow-Bandgap Ferromagnetic Oxide

KAUST Repository

Li, Yangyang; Weng, Yakui; Yin, Xinmao; Yu, Xiaojiang; Sarath Kumar, S. R.; Wehbe, Nimer; Wu, Haijun; Alshareef, Husam N.; Pennycook, Stephen J.; Breese, Mark B. H.; Chen, Jingsheng; Dong, Shuai; Wu, Tao

2017-01-01

Magnetic semiconductors are highly sought in spintronics, which allow not only the control of charge carriers like in traditional electronics, but also the control of spin states. However, almost all known magnetic semiconductors are featured with bandgaps larger than 1 eV, which limits their applications in long-wavelength regimes. In this work, the discovery of orthorhombic-structured Ti2O3 films is reported as a unique narrow-bandgap (≈0.1 eV) ferromagnetic oxide semiconductor. In contrast, the well-known corundum-structured Ti2O3 polymorph has an antiferromagnetic ground state. This comprehensive study on epitaxial Ti2O3 thin films reveals strong correlations between structure, electrical, and magnetic properties. The new orthorhombic Ti2O3 polymorph is found to be n-type with a very high electron concentration, while the bulk-type trigonal-structured Ti2O3 is p-type. More interestingly, in contrast to the antiferromagnetic ground state of trigonal bulk Ti2O3, unexpected ferromagnetism with a transition temperature well above room temperature is observed in the orthorhombic Ti2O3, which is confirmed by X-ray magnetic circular dichroism measurements. Using first-principles calculations, the ferromagnetism is attributed to a particular type of oxygen vacancies in the orthorhombic Ti2O3. The room-temperature ferromagnetism observed in orthorhombic-structured Ti2O3, demonstrates a new route toward controlling magnetism in epitaxial oxide films through selective stabilization of polymorph phases.

Cu2I2Se6: A Metal-Inorganic Framework Wide-Bandgap Semiconductor for Photon Detection at Room Temperature.

Science.gov (United States)

Lin, Wenwen; Stoumpos, Constantinos C; Kontsevoi, Oleg Y; Liu, Zhifu; He, Yihui; Das, Sanjib; Xu, Yadong; McCall, Kyle M; Wessels, Bruce W; Kanatzidis, Mercouri G

2018-02-07

Cu 2 I 2 Se 6 is a new wide-bandgap semiconductor with high stability and great potential toward hard radiation and photon detection. Cu 2 I 2 Se 6 crystallizes in the rhombohedral R3̅m space group with a density of d = 5.287 g·cm -3 and a wide bandgap E g of 1.95 eV. First-principles electronic band structure calculations at the density functional theory level indicate an indirect bandgap and a low electron effective mass m e * of 0.32. The congruently melting compound was grown in centimeter-size Cu 2 I 2 Se 6 single crystals using a vertical Bridgman method. A high electric resistivity of ∼10 12 Ω·cm is readily achieved, and detectors made of Cu 2 I 2 Se 6 single crystals demonstrate high photosensitivity to Ag Kα X-rays (22.4 keV) and show spectroscopic performance with energy resolutions under 241 Am α-particles (5.5 MeV) radiation. The electron mobility is measured by a time-of-flight technique to be ∼46 cm 2 ·V -1 ·s -1 . This value is comparable to that of one of the leading γ-ray detector materials, TlBr, and is a factor of 30 higher than mobility values obtained for amorphous Se for X-ray detection.

Widely bandgap tunable amorphous Cd–Ga–O oxide semiconductors exhibiting electron mobilities ≥10 cm{sup 2 }V{sup −1 }s{sup −1}

Energy Technology Data Exchange (ETDEWEB)

Yanagi, Hiroshi, E-mail: hyanagi@yamanashi.ac.jp [Graduate Faculty of Interdisciplinary Research, University of Yamanashi, 4-4-37 Takeda, Kofu, Yamanashi 400-8510 (Japan); Sato, Chiyuki; Kimura, Yota [Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, 4-4-37 Takeda, Kofu, Yamanashi 400-8510 (Japan); Suzuki, Issei; Omata, Takahisa [Division of Material and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Kamiya, Toshio [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Materials Research Center for Element Strategy, Tokyo Institute of Technology, Mailbox S2-16, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Hosono, Hideo [Materials and Structures Laboratory, Tokyo Institute of Technology, Mailbox R3-4, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Materials Research Center for Element Strategy, Tokyo Institute of Technology, Mailbox S2-16, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan); Frontier Research Center, Tokyo Institute of Technology, Mailbox S2-16, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503 (Japan)

2015-02-23

Amorphous oxide semiconductors exhibit large electron mobilities; however, their bandgaps are either too large for solar cells or too small for deep ultraviolet applications depending on the materials system. Herein, we demonstrate that amorphous Cd–Ga–O semiconductors display bandgaps covering the entire 2.5–4.3 eV region while maintaining large electron mobilities ≥10 cm{sup 2 }V{sup −1 }s{sup −1}. The band alignment diagram obtained by ultraviolet photoemission spectroscopy and the bandgap values reveal that these semiconductors form type-II heterojunctions with p-type Cu{sub 2}O, which is suitable for solar cells and solar-blind ultraviolet sensors.

Effects of indirect bandgap top cells in a monolithic cascade cell structure

Science.gov (United States)

Curtis, H. B.; Godlewski, M. P.

1982-01-01

The effect of having a slightly indirect top cell in a three junction cascade monolithic stack is calculated. The minority carrier continuity equations are utilized to calculate individual junction performance. Absorption coefficient curves for general III-V compounds are calculated for a variety of direct and indirect gap materials. The results indicate that for a small excursion into the indirect region, (about 0.1 eV), the loss of efficiency is acceptably small (less than 2.5 percent) and considerably less than attempting to make the top junction a smaller direct bandgap.

Hydrogen system (hydrogen fuels feasibility)

International Nuclear Information System (INIS)

Guarna, S.

1991-07-01

This feasibility study on the production and use of hydrogen fuels for industry and domestic purposes includes the following aspects: physical and chemical properties of hydrogen; production methods steam reforming of natural gas, hydrolysis of water; liquid and gaseous hydrogen transportation and storage (hydrogen-hydride technology); environmental impacts, safety and economics of hydrogen fuel cells for power generation and hydrogen automotive fuels; relevant international research programs

Design of a Rad-Hard eFuse Trimming Circuit for Bandgap Voltage Reference for LHC Experiments Upgrades

CERN Document Server

Besirli, Mustafa; Koukab, Adil; Michelis, Stefano

A precise and stable reference voltage is required to generate a stable output voltage in DC/DC converters. This reference voltage must be independent of temperature, power supply, radiation, intrinsic technology mismatch and process variation. This master's thesis reports the development of a rad-hard bandgap voltage reference with electrical fuse (eFuse) based analog calibration circuit in a commercial 130nm technology. According to the test results, the maximum error in the bandgap voltage (300mV in this application) was reduced from ±30mV to less than ±0.6mV thanks to the eFuse trimming. A temperature, power supply, radiation, mismatch and process-independent reference voltage was generated to provide reference voltage to first (bPOL12V) and second (bPOL2V5) stage DC/DC converters. This circuit will be integrated in bPOL12V and bPOL2V5 converters for high-luminosity LHC upgrades.

Angle-dependent bandgap engineering in gated graphene superlattices

Energy Technology Data Exchange (ETDEWEB)

García-Cervantes, H.; Sotolongo-Costa, O. [Centro de Investigación en Ciencias, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Gaggero-Sager, L. M. [CIICAp, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Naumis, G. G. [Instituto Física, Depto. de Física-Química, Universidad Nacional Autónoma de México (UNAM). Apdo. Postal 20-364, 01000, México D.F., México (Mexico); Rodríguez-Vargas, I., E-mail: isaac@fisica.uaz.edu.mx [Centro de Investigación en Ciencias, IICBA, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Col. Chamilpa, 62209 Cuernavaca, Morelos, México (Mexico); Unidad Académica de Física, Universidad Autónoma de Zacatecas, Calzada Solidaridad Esquina Con Paseo La Bufa S/N, 98060 Zacatecas, Zac., México (Mexico)

2016-03-15

Graphene Superlattices (GSs) have attracted a lot of attention due to its peculiar properties as well as its possible technological implications. Among these characteristics we can mention: the extra Dirac points in the dispersion relation and the highly anisotropic propagation of the charge carriers. However, despite the intense research that is carried out in GSs, so far there is no report about the angular dependence of the Transmission Gap (TG) in GSs. Here, we report the dependence of TG as a function of the angle of the incident Dirac electrons in a rather simple Electrostatic GS (EGS). Our results show that the angular dependence of the TG is intricate, since for moderated angles the dependence is parabolic, while for large angles an exponential dependence is registered. We also find that the TG can be modulated from meV to eV, by changing the structural parameters of the GS. These characteristics open the possibility for an angle-dependent bandgap engineering in graphene.

Angle-dependent bandgap engineering in gated graphene superlattices

International Nuclear Information System (INIS)

García-Cervantes, H.; Sotolongo-Costa, O.; Gaggero-Sager, L. M.; Naumis, G. G.; Rodríguez-Vargas, I.

2016-01-01

Graphene Superlattices (GSs) have attracted a lot of attention due to its peculiar properties as well as its possible technological implications. Among these characteristics we can mention: the extra Dirac points in the dispersion relation and the highly anisotropic propagation of the charge carriers. However, despite the intense research that is carried out in GSs, so far there is no report about the angular dependence of the Transmission Gap (TG) in GSs. Here, we report the dependence of TG as a function of the angle of the incident Dirac electrons in a rather simple Electrostatic GS (EGS). Our results show that the angular dependence of the TG is intricate, since for moderated angles the dependence is parabolic, while for large angles an exponential dependence is registered. We also find that the TG can be modulated from meV to eV, by changing the structural parameters of the GS. These characteristics open the possibility for an angle-dependent bandgap engineering in graphene.

Effect of Non-Stoichiometric Solution Chemistry on Improving the Performance of Wide-Bandgap Perovskite Solar Cells

Energy Technology Data Exchange (ETDEWEB)

Zhu, Kai [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Yang, Mengjin [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Kim, Donghoe [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Li, Zhen [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Reid, Obadiah G [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Yu, Yue [University of Toledo; Song, Zhaoning [University of Toledo; Zhao, Dewei [University of Toledo; Wang, Changlei [University of Toledo; Li, Liwei [ENN Energy Research Institute; ENN Solar Energy Co., Ltd.; Meng, Yuan [ENN Energy Research Institute; ENN Solar Energy Co., Ltd.; Guo, Ted [ENN Energy Research Institute; ENN Solar Energy Co., Ltd.; Yan, Yanfa [University of Toledo

2017-10-18

A high-efficiency wide-bandgap (WBG) perovskite solar cell is critical for developing perovskite-related (e.g., all-perovskite, perovskite/Si, or perovskite/Cu(In,Ga)Se2) tandem devices. Here, we demonstrate the use of non-stoichiometric precursor chemistry with excess methylammonium halides (MAX; X = I, Br, or Cl) for preparing high-quality ~1.75-eV FA0.83Cs0.17Pb(I0.6Br0.4)3 perovskite solar cells. Among various methylammonium halides, using excess MABr in the non-stoichiometric precursor exhibits the strongest effect on improving perovskite crystallographic properties and device characteristics without affecting the perovskite composition. In contrast, using excess MAI significantly reduces the bandgap of perovskite due to the replacement of Br with I. Using 40% excess MABr, we demonstrate a single-junction WBG perovskite solar cell with stabilized efficiency of 16.4%. We further demonstrate a 20.3%-efficient 4-terminal tandem device by using a 14.7%-efficient semi-transparent WBG perovskite top cell and an 18.6%-efficient unfiltered (5.6%-efficient filtered) Si bottom cell.

Mode division multiplexing over 19-cell hollow-core photonic bandgap fibre by employing integrated mode multiplexer

NARCIS (Netherlands)

Chen, H.; Uden, van R.G.H.; Okonkwo, C.M.; Jung, Y.; Wheeler, N.V.; Fokoua, E.N.; Baddela, N.; Petrovich, M.N.; Poletti, F.; Richardson, D.J.; Raz, O.; Waardt, de H.; Koonen, A.M.J.

2014-01-01

A photonic integrated mode coupler based on silicon-on-insulator is employed for mode division multiplexing (MDM) over a 193 m 19-cell hollow-core photonic bandgap fibre (HC-PBGF) with a -3 dB bandwidth >120 nm. Robust MDM transmissions using LP01 and LP11 modes, and two degenerate LP11 modes (LP11a

Synthesis of Isothianaphthene (ITN and 3,4-Ethylenedioxy-Thiophene (EDOT-Based Low-Bandgap Liquid Crystalline Conjugated Polymers

Directory of Open Access Journals (Sweden)

Hiromasa Goto

2013-05-01

Full Text Available Copolymers, consisting of isothianaphthene and phenylene derivatives with liquid crystal groups, were synthesized via Migita-Kosugi-Stille polycondensation reaction. IR absorption, UV-vis optical absorption, and PL spectroscopy measurements were carried out. Thermotropic liquid crystallinity of the polymers with bandgap of ~2.5 eV was confirmed.

Light and Electrically Induced Phase Segregation and Its Impact on the Stability of Quadruple Cation High Bandgap Perovskite Solar Cells.

Science.gov (United States)

Duong, The; Mulmudi, Hemant Kumar; Wu, YiLiang; Fu, Xiao; Shen, Heping; Peng, Jun; Wu, Nandi; Nguyen, Hieu T; Macdonald, Daniel; Lockrey, Mark; White, Thomas P; Weber, Klaus; Catchpole, Kylie

2017-08-16

Perovskite material with a bandgap of 1.7-1.8 eV is highly desirable for the top cell in a tandem configuration with a lower bandgap bottom cell, such as a silicon cell. This can be achieved by alloying iodide and bromide anions, but light-induced phase-segregation phenomena are often observed in perovskite films of this kind, with implications for solar cell efficiency. Here, we investigate light-induced phase segregation inside quadruple-cation perovskite material in a complete cell structure and find that the magnitude of this phenomenon is dependent on the operating condition of the solar cell. Under short-circuit and even maximum power point conditions, phase segregation is found to be negligible compared to the magnitude of segregation under open-circuit conditions. In accordance with the finding, perovskite cells based on quadruple-cation perovskite with 1.73 eV bandgap retain 94% of the original efficiency after 12 h operation at the maximum power point, while the cell only retains 82% of the original efficiency after 12 h operation at the open-circuit condition. This result highlights the need to have standard methods including light/dark and bias condition for testing the stability of perovskite solar cells. Additionally, phase segregation is observed when the cell was forward biased at 1.2 V in the dark, which indicates that photoexcitation is not required to induce phase segregation.

Band-gap engineering by molecular mechanical strain-induced giant tuning of the luminescence in colloidal amorphous porous silicon nanostructures

KAUST Repository

Mughal, Asad Jahangir; El Demellawi, Jehad K.; Chaieb, Saharoui

2014-01-01

reported. In this letter, we report on a 100 nm modulation in the emission of freestanding colloidal amorphous porous silicon nanostructures via band-gap engineering. The mechanism responsible for this tunable modulation, which is independent of the size

Incorporation of Furan into Low Band-Gap Polymers for Efficient Solar Cells

KAUST Repository

Woo, Claire H.

2010-11-10

The design, synthesis, and characterization of the first examples of furan-containing low band-gap polymers, PDPP2FT and PDPP3F, with substantial power conversion efficiencies in organic solar cells are reported. Inserting furan moieties in the backbone of the conjugated polymers enables the use of relatively small solubilizing side chains because of the significant contribution of the furan rings to overall polymer solubility in common organic solvents. Bulk heterojunction solar cells fabricated from furan-containing polymers and PC71BM as the acceptor showed power conversion efficiencies reaching 5.0%. © 2010 American Chemical Society.

Incorporation of Furan into Low Band-Gap Polymers for Efficient Solar Cells

KAUST Repository

Woo, Claire H.; Beaujuge, Pierre M.; Holcombe, Thomas W.; Lee, Olivia P.; Fréchet, Jean M. J.

2010-01-01

The design, synthesis, and characterization of the first examples of furan-containing low band-gap polymers, PDPP2FT and PDPP3F, with substantial power conversion efficiencies in organic solar cells are reported. Inserting furan moieties in the backbone of the conjugated polymers enables the use of relatively small solubilizing side chains because of the significant contribution of the furan rings to overall polymer solubility in common organic solvents. Bulk heterojunction solar cells fabricated from furan-containing polymers and PC71BM as the acceptor showed power conversion efficiencies reaching 5.0%. © 2010 American Chemical Society.

High-directivity planar antenna using controllable photonic bandgap material at microwave frequencies

International Nuclear Information System (INIS)

de Lustrac, A.; Gadot, F.; Akmansoy, E.; Brillat, T.

2001-01-01

In this letter, we experimentally demonstrate the capability of a controllable photonic bandgap (CPBG) material to conform the emitted radiation of a planar antenna at 12 GHz. The CPBG material is a variable conductance lattice fabricated with high-frequency PIN diodes soldered along metallic stripes on dielectric printed boards. Depending on the diode bias, the emitted radiation of the antenna can be either transmitted or totally reflected by the material. In the transmission state, the antenna radiation is spatially filtered by the CPBG material in a sharp beam perpendicular to the surface of the material. [copyright] 2001 American Institute of Physics

Novel start-up circuit with enhanced power-up characteristic for bandgap references

DEFF Research Database (Denmark)

Tuan Vu, Cao; Wisland, Dag T.; Lande, Tor Sverre

This paper presents a new start-up circuit for low-power bandgap reference (BGR) voltage generators. The BGR is designed for providing a stable 0.3 V power supply for application in low power wireless sensor nodes. The BGR has an enhanced power-up characteristic and demonstrates a reduction...... of the total stand-by current. Simulated results confirm that the proposed start-up circuit does not affect the performance of the BGR even though the supply voltage (VDD) is higher and has more stable power-up characteristic than the conventional start-up circuits. The new start-up circuit is designed with 65...

Rationally Controlled Synthesis of CdSexTe1-x Alloy Nanocrystals and Their Application in Efficient Graded Bandgap Solar Cells.

Science.gov (United States)

Wen, Shiya; Li, Miaozi; Yang, Junyu; Mei, Xianglin; Wu, Bin; Liu, Xiaolin; Heng, Jingxuan; Qin, Donghuan; Hou, Lintao; Xu, Wei; Wang, Dan

2017-11-08

CdSe x Te 1-x semiconductor nanocrystals (NCs), being rod-shaped/irregular dot-shaped in morphology, have been fabricated via a simple hot-injection method. The NCs composition is well controlled through varying molar ratios of Se to Te precursors. Through changing the composition of the CdSe x Te 1-x NCs, the spectral absorption of the NC thin film between 570-800 nm is proved to be tunable. It is shown that the bandgap of homogeneously alloyed CdSe x Te 1-x active thin film is nonlinearly correlated with the different compositions, which is perceived as optical bowing. The solar cell devices based on CdSe x Te 1-x NCs with the structure of ITO/ZnO/CdSe/CdSe x Te 1-x /MoO x /Au and the graded bandgap ITO/ZnO/CdSe( w / o )/CdSe x Te 1-x /CdTe/MoO x /Au are systematically evaluated. It was found that the performance of solar cells degrades almost linearly with the increase of alloy NC film thickness with respect to ITO/ZnO/CdSe/CdSe 0.2 Te 0.8 /MoO x /Au. From another perspective, in terms of the graded bandgap structure of ITO/ZnO/CdSe/CdSe x Te 1-x /CdTe/MoO x /Au, the performance is improved in contrast with its single-junction analogues. The graded bandgap structure is proved to be efficient when absorbing spectrum and the solar cells fabricated under the structure of ITO/ZnO/CdSe 0.8 Te 0.2 /CdSe 0.2 Te 0.8 /CdTe/MoO x /Au indicate power conversion efficiency (PCE) of 6.37%, a value among the highest for solution-processed inversely-structured CdSe x Te 1-x NC solar cells. As the NC solar cells are solution-processed under environmental conditions, they are promising for fabricating solar cells at low cost, roll by roll and in large area.

Bandgap Engineering of 1300 nm Quantum Dots/Quantum Well Nanostructures Based Devices

KAUST Repository

Alhashim, Hala H.

2016-05-29

The main objectives of this thesis are to develop viable process and/or device technologies for bandgap tuning of 1300-nm InGaAs/GaAs quantum-dot (QD) laser structures, and broad linewidth 1300-nm InGaAsP/InP quantum well (QW) superluminescent diode structures. The high performance bandgap-engineered QD laser structures were achieved by employing quantum-dot intermixing (QDI) based on impurity free vacancy diffusion (IFVD) technique for eventual seamless active-passive integration, and bandgap-tuned lasers. QDI using various dielectric-capping materials, such as HfO2, SrTiO3, TiO2, Al2O3 and ZnO, etc, were experimented in which the resultant emission wavelength can be blueshifted to ∼ 1100 nm ─ 1200 nm range depending on process conditions. The significant results extracted from the PL characterization were used to perform an extensive laser characterization. The InAs/GaAs quantum-dot lasers with QDs transition energies were blueshifted by ~185 nm, and lasing around ~1070 – 1190 nm was achieved. Furthermore, from the spectral analysis, a simultaneous five-state lasing in the InAs/InGaAs intermixed QD laser was experimentally demonstrated for the first time in the very important wavelength range from 1030 to 1125 nm. The QDI methodology enabled the facile formation of a plethora of devices with various emission wavelengths suitable for a wide range of applications in the infrared. In addition, the wavelength range achieved is also applicable for coherent light generation in the green – yellow – orange visible wavelength band via frequency doubling, which is a cost-effective way of producing compact devices for pico-projectors, semiconductor laser based solid state lighting, etc. [1, 2] In QW-based superluminescent diode, the problem statement lies on achieving a flat-top and ultra-wide emission bandwidth. The approach was to design an inhomogeneous active region with a comparable simultaneous emission from different transition states in the QW stacks, in

The hydrogen; L'hydrogene

Energy Technology Data Exchange (ETDEWEB)

NONE

2004-07-01

The hydrogen as an energy system represents nowadays a main challenge (in a scientific, economical and environmental point of view). The physical and chemical characteristics of hydrogen are at first given. Then, the challenges of an hydrogen economy are explained. The different possibilities of hydrogen production are described as well as the distribution systems and the different possibilities of hydrogen storage. Several fuel cells are at last presented: PEMFC, DMFC and SOFC. (O.M.)

Polarizing Ytterbium-Doped all-Solid Photonic Bandgap Fiber with 1150 micrometers2 Effective Mode Area

Science.gov (United States)

2015-02-11

RESPONSIBLE PERSON 19b. TELEPHONE NUMBER Liang Dong Fanting Kong,, Guancheng Gu,, Thomas W. Hawkins ,, Joshua Parsons, Maxwell Jones,, Christopher...Dunn,, Monica T. Kalichevsky-Dong,, Benjamin Pulford,, Iyad Dajani,, Kunimasa Saitoh,, Stephen P. Palese,, Eric Cheung,, Liang Dong c. THIS PAGE The...ytterbium-doped all-solid photonic bandgap fiber with ~1150µm2 effective mode area Fanting Kong,1,* Guancheng Gu,1 Thomas W. Hawkins ,1 Joshua Parsons

Efficient H2 production over Au/graphene/TiO2 induced by surface plasmon resonance of Au and band-gap excitation of TiO2

International Nuclear Information System (INIS)

Liu, Yang; Yu, Hongtao; Wang, Hua; Chen, Shuo; Quan, Xie

2014-01-01

Highlights: • Both surface plasmon resonance and band-gap excitation were used for H 2 production. • Au/Gr/TiO 2 composite photocatalyst was synthesized. • Au/Gr/TiO 2 exhibited enhancement of light absorption and charge separation. • H 2 production rate of Au/Gr/TiO 2 was about 2 times as high as that of Au/TiO 2 . - Abstract: H 2 production over Au/Gr/TiO 2 composite photocatalyst induced by surface plasmon resonance of Au and band-gap excitation of TiO 2 using graphene (Gr) as an electron acceptor has been investigated. Electron paramagnetic resonance study indicated that, in this composite, Gr collected electrons not only from Au with surface plasmon resonance but also from TiO 2 with band-gap excitation. Surface photovoltage and UV–vis absorption measurements revealed that compared with Au/TiO 2 , Au/Gr/TiO 2 displayed more effective photogenerated charge separation and higher optical absorption. Benefiting from these advantages, the H 2 production rate of Au/Gr/TiO 2 composite with Gr content of 1.0 wt% and Au content of 2.0 wt% was about 2 times as high as that of Au/TiO 2 . This work represents an important step toward the efficient application of both surface plasmon resonance and band-gap excitation on the way to converting solar light into chemical energy

Experimental investigation of backreflection at air-core photonic bandgap fiber terminations

Science.gov (United States)

Xu, Xiaobin; Yan, Ming; Wu, Chunxiao; Song, Ningfang; Zhang, Chunxi

2017-07-01

Backreflection from the termination of air-core photonic bandgap fibers (PBFs) is experimentally investigated based on a range-extended Mach-Zehnder and Michelson hybrid (M2) interferometer. For primary waves generated by the fundamental modes, the reflectivity is about -90 dB; for secondary waves caused by other modes, the reflectivity is less than -80 dB when compared to the intensity of the primary wave and -20 to -50 dB when compared to their own incident intensity. To suppress the reflection, 3-centimeter PBF at the end is filled with alcohol through the capillary effect, and this proposed method is shown to be much more convenient and effective than the conventional angle cleaving method.

In vivo imaging of the morphology and changes in pH along the gastrointestinal tract of Japanese medaka by photonic band-gap hydrogel microspheres

International Nuclear Information System (INIS)

Du, Xuemin; Lei, Ngai-Yu; Hu, Peng; Lei, Zhang; Ong, Daniel Hock-Chun; Ge, Xuewu; Zhang, Zhicheng; Lam, Michael Hon-Wah

2013-01-01

Graphical abstract: -- Highlights: •Fabrication of pH-responsive photonic colloidal crystalline microspheres. •Specific photonic band-gap responses occurred in the pH range of 4–5. •Remarkably low in vivo toxicity to Japanese medaka (Oryzia latipes). •In vivo imaging of the morphology and pH along GI tract of Japanese medaka. •Demonstrates bio-imaging potentials of stimuli-responsive photonic materials. -- Abstract: Colloidal crystalline microspheres with photonic band-gap properties responsive to media pH have been developed for in vivo imaging purposes. These colloidal crystalline microspheres were constructed from monodispersed core–shell nano-size particles with poly(styrene-co-acrylic acid) (PS-co-PAA) cores and poly(acrylic acid-co-N-isopropylacrylamide) (PAA-co-PNIPAM) hydrogel shells cross-linked by N,N′-methylenebisacrylamide. A significant shift in the photonic band-gap properties of these colloidal crystalline microspheres was observed in the pH range of 4–5. This was caused by the discontinuous volume phase transition of the hydrogel coating, due to the protonation/deprotonation of its acrylic acid moieties, on the core–shell nano-sized particles within the microspheres. The in vivo imaging capability of these pH-responsive photonic microspheres was demonstrated on a test organism – Japanese medaka, Oryzia latipes – in which the morphology and change in pH along their gastrointestinal (GI) tracts were revealed under an ordinary optical microscope. This work illustrates the potential of stimuli-responsive photonic band-gap materials in tissue-/organ-level in vivo bio-imaging

Band-gap measurements of bulk and nanoscale hematite by soft x-ray spectroscopy

DEFF Research Database (Denmark)

Gilbert, B.; Frandsen, Cathrine; Maxey, E.R.

2009-01-01

Chemical and photochemical processes at semiconductor surfaces are highly influenced by the size of the band gap, and ability to control the band gap by particle size in nanomaterials is part of their promise. The combination of soft x-ray absorption and emission spectroscopies provides band......-gap determination in bulk and nanoscale itinerant electron semiconductors such as CdS and ZnO, but this approach has not been established for materials such as iron oxides that possess band-edge electronic structure dominated by electron correlations. We performed soft x-ray spectroscopy at the oxygen K...

Investigating the electronic properties of multi-junction ZnS/CdS/CdTe graded bandgap solar cells

Energy Technology Data Exchange (ETDEWEB)

Olusola, O.I., E-mail: olajideibk@yahoo.com [Electronic Materials and Sensors Group, Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield S1 1WB (United Kingdom); Department of Physics, School of Science, The Federal University of Technology, Akure (FUTA), P.M.B. 704 (Nigeria); Madugu, M.L.; Dharmadasa, I.M. [Electronic Materials and Sensors Group, Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield S1 1WB (United Kingdom)

2017-04-15

The fabrication of multi-junction graded bandgap solar cells have been successfully implemented by electroplating three binary compound semiconductors from II-VI family. The three semiconductor materials grown by electroplating techniques are ZnS, CdS and CdTe thin films. The electrical conductivity type and energy bandgap of each of the three semiconductors were determined using photoelectrochemical (PEC) cell measurement and UV–Vis spectrophotometry techniques respectively. The PEC cell results show that all the three semiconductor materials have n-type electrical conductivity. These two material characterisation techniques were considered in this paper in order to establish the relevant energy band diagram for device results, analysis and interpretation. Solar cells with the device structure glass/FTO/n-ZnS/n-CdS/n-CdTe/Au were then fabricated and characterised using current-voltage (I-V) and capacitance-voltage (C-V) techniques. From the I-V characteristics measurement, the fabricated device structures yielded an open circuit voltage (V{sub oc}) of 670 mV, short circuit current density (J{sub sc}) of 41.5 mA cm{sup −2} and fill-factor (FF) of 0.46 resulting in ∼12.8% efficiency when measured at room temperature under AM1.5 illumination conditions. The device structure showed an excellent rectification factor (RF) of 10{sup 4.3} and ideality factor (n) of 1.88. The results obtained from the C-V measurement also showed that the device structures have a moderate doping level of 5.2 × 10{sup 15} cm{sup −3}. - Highlights: • Electroplating of n-ZnS, n-CdS and n-CdTe binary compound semiconductors. • Fabrication of Schottky barrier solar cells from glass/FTO/n-ZnS/n-CdS/n-CdTe/Au. • Development of multi-junction graded bandgap solar cells using n-n-n structures.

Gamma irradiation of minimal latency Hollow-Core Photonic Bandgap Fibres

CERN Document Server

Olanterae, L; Richardson, D J; Vasey, F; Wooler, J P; Petrovich, M N; Wheeler, N V; Poletti, F; Troska, J

2013-01-01

Hollow-Core Photonic-Bandgap Fibres (HC-PBGFs) offer several distinct advantages over conventional fibres, such as low latency and radiation hardness; properties that make HC-PBGFs interesting for the high energy physics community. This contribution presents the results from a gamma irradiation test carried out using a new type of HC-PBGF that combines sufficiently low attenuation over distances that are compatible with high energy physics applications together with a transmission bandwidth that covers the 1550 nm region. The radiation induced attenuation of the HC-PBGF was two orders of magnitude lower than that of a conventional fibre during a 67.5 h exposure to gamma-rays, resulting in a radiation-induced attenuation of only 2.1 dB/km at an accumulated dose of 940 kGy.

Sub-bandgap photonic base current method for characterization of interface states at heterointerfaces in heterojunction bipolar transistors

International Nuclear Information System (INIS)

Shin, H. T.; Kim, K. H.; Kim, K. S.

2004-01-01

In this paper, we propose a novel photonic base current analysis method to characterize the interface states in heterojunction bipolar transistors (HBTs) by using the photonic I-V characteristics under sub-bandgap photonic excitation. For the photonic current-voltage characterization of HBTs, an optical source with a photon energy less than the bandgap energy of Al 0.3 Ga 0.7 As and GaAs (E ph = 0.95 eV g,AlGaAs = 1.79 eV, E g,GaAs = 1.45 eV) is employed for the characterization of the interface states distributed in the photo-responsive energy band (E C - 0.95 ≤ E it ≤ E C ) in emitter-base heterojunction at HBTs. The proposed novel method, which is applied to bipolar junction transistors for the first time, is simple, and an accurate analysis of interface traps in HBTs is possible. By using the photonic base-current and the dark-base-current, we qualitatively analyze the interface trap at the Al 0.3 Ga 0.7 As/GaAs heterojunction interface in HBTs.

Optical tuning of photonic bandgaps in dye-doped nematic liquid crystal photonic crystal fibers

DEFF Research Database (Denmark)

Alkeskjold, Thomas Tanggaard; Bjarklev, Anders Overgaard; Hermann, David Sparre

2005-01-01

An all-optical modulator is demonstrated, which utilizes a pulsed 532 nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. In order to investigate the time response of the LCPBG fiber device, a low-power CW probe...... laser was coupled into the fiber together with the pulsed pump laser of 2.3 mW and we have demonstrated a modulation frequency of up to 2 kHz....

Continuously tunable devices based on electrical control of dual-frequency liquid crystal filled photonic bandgap fibers

DEFF Research Database (Denmark)

Scolari, Lara; Alkeskjold, Thomas Tanggaard; Riishede, Jesper

2005-01-01

We present an electrically controlled photonic bandgap fiber device obtained by infiltrating the air holes of a photonic crystal fiber (PCF) with a dual-frequency liquid crystal (LC) with pre-tilted molecules. Compared to previously demonstrated devices of this kind, the main new feature of this ...... in the same device. We investigate the dynamics of this device and demonstrate a birefringence controller based on this principle....

Detection of the scintillation light emitted from direct-bandgap compound semiconductors by a Si avalanche photodiode at 150 mK

International Nuclear Information System (INIS)

Yasumune, Takashi; Takayama, Nobuyasu; Maehata, Keisuke; Ishibashi, Kenji; Umeno, Takahiro

2008-01-01

In this work, the direct-bandgap compound semiconductor materials are irradiated by α particles emitted from 241 Am for the detection of scintillation light at the temperature of 150 mK. For the irradiation experiment, two disk shaped samples were fabricated from an epoxy resin mixed with the powder of PbI 2 and CuI, respectively. Each disk-samples was cooled down to 150 mK by a compact liquid helium-free dilution refrigerator. A Si avalanche photodiode (APD) was employed for detecting the scintillation light emitted from the disk-sample inside the refrigerator. The detection signal current of Si APD was converted into the voltage pulses by a charge sensitive preamplifier. The voltage pulses of the scintillation light emitted from the direct-bandgap semiconductors were observed at the temperature of 150 mK. (author)

Optical characterization and bandgap engineering of flat and wrinkle-textured FA0.83Cs0.17Pb(I1-xBrx)3 perovskite thin films

Science.gov (United States)

Tejada, A.; Braunger, S.; Korte, L.; Albrecht, S.; Rech, B.; Guerra, J. A.

2018-05-01

The complex refractive indices of formamidinium cesium lead mixed-halide [FA0.83Cs0.17Pb(I1- xBrx)3] perovskite thin films of compositions ranging from x = 0 to 0.4, with both flat and wrinkle-textured surface topographies, are reported. The films are characterized using a combination of variable angle spectroscopic ellipsometry and spectral transmittance in the wavelength range of 190 nm to 850 nm. Optical constants, film thicknesses and roughness layers are obtained point-by-point by minimizing a global error function, without using optical dispersion models, and including topographical information supplied by a laser confocal microscope. To evaluate the bandgap engineering potential of the material, the optical bandgaps and Urbach energies are then accurately determined by applying a band fluctuation model for direct semiconductors, which considers both the Urbach tail and the fundamental band-to-band absorption region in a single equation. With this information, the composition yielding the optimum bandgap of 1.75 eV for a Si-perovskite tandem solar cell is determined.

Sub-bandgap response of graphene/SiC Schottky emitter bipolar phototransistor examined by scanning photocurrent microscopy

Science.gov (United States)

Barker, Bobby G., Jr.; Chava, Venkata Surya N.; Daniels, Kevin M.; Chandrashekhar, M. V. S.; Greytak, Andrew B.

2018-01-01

Graphene layers grown epitaxially on SiC substrates are attractive for a variety of sensing and optoelectronic applications because the graphene acts as a transparent, conductive, and chemically responsive layer that is mated to a wide-bandgap semiconductor with large breakdown voltage. Recent advances in control of epitaxial growth and doping of SiC epilayers have increased the range of electronic device architectures that are accessible with this system. In particular, a recently-introduced Schottky-emitter bipolar phototransistor (SEPT) based on an epitaxial graphene (EG) emitter grown on a p-SiC base epilayer has been found to exhibit a maximum common emitter current gain of 113 and a UV responsivity of 7.1 A W-1. The behavior of this device, formed on an n +-SiC substrate that serves as the collector, was attributed to a very large minority carrier injection efficiency at the EG/p-SiC Schottky contact. This large minority carrier injection efficiency is in turn related to the large built-in potential found at a EG/p-SiC Schottky junction. The high performance of this device makes it critically important to analyze the sub bandgap visible response of the device, which provides information on impurity states and polytype inclusions in the crystal. Here, we employ scanning photocurrent microscopy (SPCM) with sub-bandgap light as well as a variety of other techniques to clearly demonstrate a localized response based on the graphene transparent electrode and an approximately 1000-fold difference in responsivity between 365 nm and 444 nm excitation. A stacking fault propagating from the substrate/epilayer interface, assigned as a single layer of the 8H-SiC polytype within the 4H-SiC matrix, is found to locally increase the photocurrent substantially. The discovery of this polytype heterojunction opens the potential for further development of heteropolytype devices based on the SEPT architecture.

Colloidal Engineering for Infrared-Bandgap Solution-Processed Quantum Dot Solar Cells

Science.gov (United States)

Kiani, Amirreza

harvesting for the first time. Addition of short bromothiol ligands during the synthesis significantly reduces the agglomeration of 1 eV bandgap CQDs and maintains efficient charge extraction into the selective electrodes. The devices can augment the performance of the best silicon cells by 7 power points where 0.8 additive power points are demonstrated experimentally. A tailored solution exchanged process developed for 1 eV bandgap CQDs results in air-stable IR PV devices with improved manufacturability. The process utilizes a tailored combination of lead iodide (PbI2) and ammonium acetate for the solution exchange and hexylamine + MEK as the final solvent to yield solar thick films with the filtered (1100 nm and beyond) performance of 0.4%. This thesis pushes the limit of CQD device applications to waste heat recovery. I demonstrate successful harvesting of low energy photons emitted from a hot object by designing and developing the first solution-processed thermophotovoltaic devices. These devices are comprised of 0.7 eV bandgap CQDs that successfully harvest photons emitted from an 800°C heat source.

High-Temperature, Wirebondless, Ultracompact Wide Bandgap Power Semiconductor Modules

Science.gov (United States)

Elmes, John

2015-01-01

Silicon carbide (SiC) and other wide bandgap semiconductors offer great promise of high power rating, high operating temperature, simple thermal management, and ultrahigh power density for both space and commercial power electronic systems. However, this great potential is seriously limited by the lack of reliable high-temperature device packaging technology. This Phase II project developed an ultracompact hybrid power module packaging technology based on the use of double lead frames and direct lead frame-to-chip transient liquid phase (TLP) bonding that allows device operation up to 450 degC. The new power module will have a very small form factor with 3-5X reduction in size and weight from the prior art, and it will be capable of operating from 450 degC to -125 degC. This technology will have a profound impact on power electronics and energy conversion technologies and help to conserve energy and the environment as well as reduce the nation's dependence on fossil fuels.

Growth of Bulk Wide Bandgap Semiconductor Crystals and Their Potential Applications

Science.gov (United States)

Chen, Kuo-Tong; Shi, Detang; Morgan, S. H.; Collins, W. Eugene; Burger, Arnold

1997-01-01

Developments in bulk crystal growth research for electro-optical devices in the Center for Photonic Materials and Devices since its establishment have been reviewed. Purification processes and single crystal growth systems employing physical vapor transport and Bridgman methods were assembled and used to produce high purity and superior quality wide bandgap materials such as heavy metal halides and II-VI compound semiconductors. Comprehensive material characterization techniques have been employed to reveal the optical, electrical and thermodynamic properties of crystals, and the results were used to establish improved material processing procedures. Postgrowth treatments such as passivation, oxidation, chemical etching and metal contacting during the X-ray and gamma-ray device fabrication process have also been investigated and low noise threshold with improved energy resolution has been achieved.

Photo-Detection on Narrow-Bandgap High-Mobility 2D Semiconductors

Science.gov (United States)

Charnas, Adam; Qiu, Gang; Deng, Yexin; Wang, Yixiu; Du, Yuchen; Yang, Lingming; Wu, Wenzhuo; Ye, Peide

Photo-detection and energy harvesting device concepts have been demonstrated widely in 2D materials such as graphene, TMDs, and black phosphorus. In this work, we demonstrate anisotropic photo-detection achieved using devices fabricated from hydrothermally grown narrow-bandgap high-mobility 2D semiconductor. Back-gated FETs were fabricated by transferring the 2D flakes onto a Si/SiO2 substrate and depositing various metal contacts across the flakes to optimize the access resistance for optoelectronic devices. Photo-responsivity was measured and mapped by slightly biasing the devices and shining a laser spot at different locations of the device to observe and map the resulting photo-generated current. Optimization of the Schottky barrier height for both n and p at the metal-2D interfaces using asymmetric contact engineering was performed to improve device performance.

Subwavelength wave manipulation in a thin surface-wave bandgap crystal.

Science.gov (United States)

Gao, Zhen; Wang, Zhuoyuan; Zhang, Baile

2018-01-01

It has been recently reported that the unit cell of wire media metamaterials can be tailored locally to shape the flow of electromagnetic waves at deep-subwavelength scales [Nat. Phys.9, 55 (2013)NPAHAX1745-247310.1038/nphys2480]. However, such bulk structures have a thickness of at least the order of wavelength, thus hindering their applications in the on-chip compact plasmonic integrated circuits. Here, based upon a Sievenpiper "mushroom" array [IEEE Trans. Microwave Theory Tech.47, 2059 (1999)IETMAB0018-948010.1109/22.798001], which is compatible with standard printed circuit board technology, we propose and experimentally demonstrate the subwavelength manipulation of surface waves on a thin surface-wave bandgap crystal with a thickness much smaller than the wavelength (1/30th of the operating wavelength). Functional devices including a T-shaped splitter and sharp bend are constructed with good performance.

Hydrogen energy

International Nuclear Information System (INIS)

2005-03-01

This book consists of seven chapters, which deals with hydrogen energy with discover and using of hydrogen, Korean plan for hydrogen economy and background, manufacturing technique on hydrogen like classification and hydrogen manufacture by water splitting, hydrogen storage technique with need and method, hydrogen using technique like fuel cell, hydrogen engine, international trend on involving hydrogen economy, technical current for infrastructure such as hydrogen station and price, regulation, standard, prospect and education for hydrogen safety and system. It has an appendix on related organization with hydrogen and fuel cell.

Enhanced photocathodic behaviors of Pb(Zr{sub 0.20}Ti{sub 0.80})O{sub 3} films on Si substrates for hydrogen production

Energy Technology Data Exchange (ETDEWEB)

Cheng, Xiaorong; Dong, Wen; Zheng, Fengang; Fang, Liang; Shen, Mingrong, E-mail: mrshen@suda.edu.cn [College of Physics, Optoelectronics and Energy, Collaborative Innovation Center of Suzhou Nano Science and Technology, Photovoltaic Research Institute of Soochow University & Canadian Solar Inc., and Jiangsu Key Laboratory of Thin Films, Soochow University, 1 Shizi Street, Suzhou 215006 (China)

2015-06-15

Wide bandgap ferroelectric Pb(Zr{sub 0.20}Ti{sub 0.80})O{sub 3} films were deposited on indium tin oxide (ITO) coated Si-pn{sup +} substrates with an intention to form efficient Si-pn{sup +}/ITO/Pb(Zr,Ti)O{sub 3} (PZT) photocathode for hydrogen production. Depolarization electric field generated in PZT film due to poling can drive the photogenerated electrons from Si-pn{sup +} junction to PZT film, resulting in enhanced photoelectrochemical activity of the photocathode. Comparing the electrode with as-prepared PZT film, the photocurrent increased from −100 μA cm{sup −2} to −1.2 mA cm{sup −2} at 0 V vs. reversible hydrogen electrode (RHE) and the onset potential from 0.36 V to 0.7 V vs. RHE under 100 mW cm{sup −2} illumination, manifesting the great advantage of depolarization electric field in driving the photogenerated carriers not only in the ferroelectric film but also on the interface of different semiconductors.

Influence of air pressure on soliton formation in hollow-core photonic bandgap fibers

DEFF Research Database (Denmark)

Lægsgaard, Jesper; Roberts, Peter John

2009-01-01

Abstract Soliton formation during dispersive compression of chirped few-picosecond pulses at the microjoule level in a hollow-core photonic bandgap (HC-PBG) fiber is studied by numerical simulations. Long-pass filtering of the emerging frequency-shifted solitons is investigated with the objective...... of obtaining pedestal-free output pulses. Particular emphasis is placed on the influence of the air pressure in the HC-PBG fiber. It is found that a reduction in air pressure enables an increase in the fraction of power going into the most redshifted soliton and also improves the quality of the filtered pulse...

Crystal orientation dependence of the optical bandgap of (1 - x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 single crystals

International Nuclear Information System (INIS)

Wan Xinming; Zhao Xiangyong; Chan, H.L.W.; Choy, C.L.; Luo Haosu

2005-01-01

The transmission spectra of rhombohedral 0.71Pb(Mg 1/3 Nb 2/3 )O 3 -0.29PbTiO 3 (PMN-0.29PT) and tetragonal PMN-0.38PT single crystals were obtained in the main crystallographic directions , and . The absorption coefficients were computed and the optical bandgaps were calculated in both direct and indirect transitions. The energy of phonons contributing in the indirect transition was also calculated. For PMN-0.38PT single crystal in all the three directions, the values of direct bandgaps E gd are all slightly lower than those of PMN-0.29PT single crystal, while the indirect bandgaps E gi are all higher. For different crystallographic directions, the values of E gi for -direction are lower compared with and directions, both for PMN-0.29PT and PMN-0.38PT single crystals. Some discussions about the B-site cation d-orbits and the O-anion 2p orbits that determine the basic energy level of the single crystals are presented. The optical transition mechanism was also discussed

Doping of wide-bandgap titanium-dioxide nanotubes: optical, electronic and magnetic properties

Science.gov (United States)

Alivov, Yahya; Singh, Vivek; Ding, Yuchen; Cerkovnik, Logan Jerome; Nagpal, Prashant

2014-08-01

Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO2) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications.Doping semiconductors is an important step for their technological application. While doping bulk semiconductors can be easily achieved, incorporating dopants in semiconductor nanostructures has proven difficult. Here, we report a facile synthesis method for doping titanium-dioxide (TiO2) nanotubes that was enabled by a new electrochemical cell design. A variety of optical, electronic and magnetic dopants were incorporated into the hollow nanotubes, and from detailed studies it is shown that the doping level can be easily tuned from low to heavily-doped semiconductors. Using desired dopants - electronic (p- or n-doped), optical (ultraviolet bandgap to infrared absorption in co-doped nanotubes), and magnetic (from paramagnetic to ferromagnetic) properties can be tailored, and these technologically important nanotubes can be useful for a variety of applications in photovoltaics, display technologies, photocatalysis, and spintronic applications. Electronic supplementary information (ESI) available: See DOI: 10.1039/c4nr02417f

Trifluoromethyl-Substituted Large Band-Gap Polytriphenylamines for Polymer Solar Cells with High Open-Circuit Voltages

Directory of Open Access Journals (Sweden)

Shuwang Yi

2018-01-01

Full Text Available Two large band-gap polymers (PTPACF and PTPA2CF based on polytriphenylamine derivatives with the introduction of electron-withdrawing trifluoromethyl groups were designed and prepared by Suzuki polycondensation reaction. The chemical structures, thermal, optical and electrochemical properties were characterized in detail. From the UV-visible absorption spectra, the PTPACF and PTPA2CF showed the optical band gaps of 2.01 and 2.07 eV, respectively. The cyclic voltammetry (CV measurement displayed the deep highest occupied molecular orbital (HOMO energy levels of −5.33 and −5.38 eV for PTPACF and PTPA2CF, respectively. The hole mobilities, determined by field-effect transistor characterization, were 2.5 × 10−3 and 1.1 × 10−3 cm2 V−1 S−1 for PTPACF and PTPA2CF, respectively. The polymer solar cells (PSCs were tested under the conventional device structure of ITO/PEDOT:PSS/polymer:PC71BM/PFN/Al. All of the PSCs showed the high open circuit voltages (Vocs with the values approaching 1 V. The PTPACF and PTPA2CF based PSCs gave the power conversion efficiencies (PCEs of 3.24% and 2.40%, respectively. Hence, it is a reliable methodology to develop high-performance large band-gap polymer donors with high Vocs through the feasible side-chain modification.

Tuning Bandgap of p-Type Cu2Zn(Sn, Ge)(S, Se)4 Semiconductor Thin Films via Aqueous Polymer-Assisted Deposition.

Science.gov (United States)

Yi, Qinghua; Wu, Jiang; Zhao, Jie; Wang, Hao; Hu, Jiapeng; Dai, Xiao; Zou, Guifu

2017-01-18

Bandgap engineering of kesterite Cu 2 Zn(Sn, Ge)(S, Se) 4 with well-controlled stoichiometric composition plays a critical role in sustainable inorganic photovoltaics. Herein, a cost-effective and reproducible aqueous solution-based polymer-assisted deposition approach is developed to grow p-type Cu 2 Zn(Sn, Ge)(S, Se) 4 thin films with tunable bandgap. The bandgap of Cu 2 Zn(Sn, Ge)(S, Se) 4 thin films can be tuned within the range 1.05-1.95 eV using the aqueous polymer-assisted deposition by accurately controlling the elemental compositions. One of the as-grown Cu 2 Zn(Sn, Ge)(S, Se) 4 thin films exhibits a hall coefficient of +137 cm 3 /C. The resistivity, concentration and carrier mobility of the Cu 2 ZnSn(S, Se) 4 thin film are 3.17 ohm·cm, 4.5 × 10 16 cm -3 , and 43 cm 2 /(V·S) at room temperature, respectively. Moreover, the Cu 2 ZnSn(S, Se) 4 thin film when used as an active layer in a solar cell leads to a power conversion efficiency of 3.55%. The facile growth of Cu 2 Zn(Sn, Ge)(S, Se) 4 thin films in an aqueous system, instead of organic solvents, provides great promise as an environmental-friendly platform to fabricate a variety of single/multi metal chalcogenides for the thin film industry and solution-processed photovoltaic devices.

Efficient Sub-Bandgap Light Absorption and Signal Amplification in Silicon Photodetectors

Science.gov (United States)

Liu, Yu-Hsin

This thesis focuses on two areas in silicon photodetectors, the first being enhancing the sub-bandgap light absorption of IR wavelenghts in silicon, and the second being intrinsic signal amplification in silicon photodetectors. Both of these are achieved using heavily doped p-n junction devices which create localized states that relax the k-selection rule of indirect bandgap material. The probability of transitions between impurity band and the conduction/valence band would be much more efficient than the one between band-to-band transition. The waveguide-coupled epitaxial p-n photodetector was demonstrated for 1310 nm wavelength detection. Incorporated with the Franz-Keldysh effect and the quasi-confined epitaxial layer design, an absorption coefficient around 10 cm-1 has been measured and internal quantum efficiency nearly 100% at -2.5V. The absorption coefficient is calculated from the wave function of the electron and hole in p-n diode. The heavily doped impurity wave function can be formulated as a delta function, and the quasi-confined conduction band energy states, and the wave function on each level can be obtained from the Silvaco software. The calculated theoretical absorption coefficient increases with the increasing applied bias and the doping concentration, which matches the experimental results. To solve the issues of large excess noise and high operation bias for avalanche photodiodes based on impact ionization, I presented a detector using the Cycling Excitation Process (CEP) for signal amplification. This can be realized in a heavily doped and highly compensated Si p-n junction, showing ultra high gain about 3000 at very low bias (<4 V), and possessing an intrinsic, phonon-mediated regulation process to keep the device stable without any quenching device required in today's Geiger-mode avalanche detectors. The CEP can be formulated with the rate equations in conduction bands and impurity states. The gain expression, which is a function of the

Small-bandgap polymer solar cells with unprecedented short-circuit current density and high fill factor.

Science.gov (United States)

Choi, Hyosung; Ko, Seo-Jin; Kim, Taehyo; Morin, Pierre-Olivier; Walker, Bright; Lee, Byoung Hoon; Leclerc, Mario; Kim, Jin Young; Heeger, Alan J

2015-06-03

Small-bandgap polymer solar cells (PSCs) with a thick bulk heterojunction film of 340 nm exhibit high power conversion efficiencies of 9.40% resulting from high short-circuit current density (JSC ) of 20.07 mA cm(-2) and fill factor of 0.70. This remarkable efficiency is attributed to maximized light absorption by the thick active layer and minimized recombination by the optimized lateral and vertical morphology through the processing additive. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Measurement of dissolved hydrogen and hydrogen gas transfer in a hydrogen-producing reactor

Energy Technology Data Exchange (ETDEWEB)

Shizas, I.; Bagley, D.M. [Toronto Univ., ON (Canada). Dept. of Civil Engineering

2004-07-01

This paper presents a simple method to measure dissolved hydrogen concentrations in the laboratory using standard equipment and a series of hydrogen gas transfer tests. The method was validated by measuring hydrogen gas transfer parameters for an anaerobic reactor system that was purged with 10 per cent carbon dioxide and 90 per cent nitrogen using a coarse bubble diffuser stone. Liquid samples from the reactor were injected into vials and hydrogen was allowed to partition between the liquid and gaseous phases. The concentration of dissolved hydrogen was determined by comparing the headspace injections onto a gas chromatograph and a standard curve. The detection limit was 1.0 x 10{sup -5} mol/L of dissolved hydrogen. The gas transfer rate for hydrogen in basal medium and anaerobic digester sludge was used to validate the method. Results were compared with gas transfer models. In addition to monitoring dissolved hydrogen in reactor systems, this method can help improve hydrogen production potential. 1 ref., 4 figs.

High frequency modulation circuits based on photoconductive wide bandgap switches

Science.gov (United States)

Sampayan, Stephen

2018-02-13

Methods, systems, and devices for high voltage and/or high frequency modulation. In one aspect, an optoelectronic modulation system includes an array of two or more photoconductive switch units each including a wide bandgap photoconductive material coupled between a first electrode and a second electrode, a light source optically coupled to the WBGP material of each photoconductive switch unit via a light path, in which the light path splits into multiple light paths to optically interface with each WBGP material, such that a time delay of emitted light exists along each subsequent split light path, and in which the WBGP material conducts an electrical signal when a light signal is transmitted to the WBGP material, and an output to transmit the electrical signal conducted by each photoconductive switch unit. The time delay of the photons emitted through the light path is substantially equivalent to the time delay of the electrical signal.

FIBER AND INTEGRATED OPTICS: Bandgap modes in a coupled waveguide array

Science.gov (United States)

Usievich, B. A.; Nurligareev, D. Kh; Svetikov, V. V.; Sychugov, V. A.

2009-08-01

This work examines a waveguide array that consists of ten Nb2O5/SiO2 double layers and supports a 0.63-μm surface wave. The deposition of a Nb2O5 capping layer on top of the waveguide array enables a marked increase in the wave field intensity on its surface. The efficiency of surface-wave excitation in the Kretschmann configuration can be optimised by adjusting the number of double layers. We analyse the behaviour of the Bragg mode in relation to the thickness of the layer exposed to air and the transition of this mode from the second allowed band to the first through the bandgap of the system. In addition, the conventional leaky mode converts to a surface mode and then to a guided mode.

Cation-induced band-gap tuning in organohalide perovskites: interplay of spin-orbit coupling and octahedra tilting.

Science.gov (United States)

Amat, Anna; Mosconi, Edoardo; Ronca, Enrico; Quarti, Claudio; Umari, Paolo; Nazeeruddin, Md K; Grätzel, Michael; De Angelis, Filippo

2014-06-11

Organohalide lead perovskites have revolutionized the scenario of emerging photovoltaic technologies. The prototype MAPbI3 perovskite (MA = CH3NH3(+)) has dominated the field, despite only harvesting photons above 750 nm (∼1.6 eV). Intensive research efforts are being devoted to find new perovskites with red-shifted absorption onset, along with good charge transport properties. Recently, a new perovskite based on the formamidinium cation ((NH2)2CH(+) = FA) has shown potentially superior properties in terms of band gap and charge transport compared to MAPbI3. The results have been interpreted in terms of the cation size, with the larger FA cation expectedly delivering reduced band-gaps in Pb-based perovskites. To provide a full understanding of the interplay among size, structure, and organic/inorganic interactions in determining the properties of APbI3 perovskites, in view of designing new materials and fully exploiting them for solar cells applications, we report a fully first-principles investigation on APbI3 perovskites with A = Cs(+), MA, and FA. Our results evidence that the tetragonal-to-quasi cubic structural evolution observed when moving from MA to FA is due to the interplay of size effects and enhanced hydrogen bonding between the FA cations and the inorganic matrix altering the covalent/ionic character of Pb-I bonds. Most notably, the observed cation-induced structural variability promotes markedly different electronic and optical properties in the MAPbI3 and FAPbI3 perovskites, mediated by the different spin-orbit coupling, leading to improved charge transport and red-shifted absorption in FAPbI3 and in general in pseudocubic structures. Our theoretical model constitutes the basis for the rationale design of new and more efficient organohalide perovskites for solar cells applications.

Dependence of hydrogen-induced lattice defects and hydrogen embrittlement of cold-drawn pearlitic steels on hydrogen trap state, temperature, strain rate and hydrogen content

International Nuclear Information System (INIS)

Doshida, Tomoki; Takai, Kenichi

2014-01-01

The effects of the hydrogen state, temperature, strain rate and hydrogen content on hydrogen embrittlement susceptibility and hydrogen-induced lattice defects were evaluated for cold-drawn pearlitic steel that absorbed hydrogen in two trapping states. Firstly, tensile tests were carried out under various conditions to evaluate hydrogen embrittlement susceptibility. The results showed that peak 2 hydrogen, desorbed at temperatures above 200 °C as determined by thermal desorption analysis (TDA), had no significant effect on hydrogen embrittlement susceptibility. In contrast, hydrogen embrittlement susceptibility increased in the presence of peak 1 hydrogen, desorbed from room temperature to 200 °C as determined by TDA, at temperatures higher than −30 °C, at lower strain rates and with higher hydrogen content. Next, the same effects on hydrogen-induced lattice defects were also evaluated by TDA using hydrogen as a probe. Peak 2 hydrogen showed no significant effect on either hydrogen-induced lattice defects or hydrogen embrittlement susceptibility. It was found that hydrogen-induced lattice defects formed under the conditions where hydrogen embrittlement susceptibility increased. This relationship indicates that hydrogen embrittlement susceptibility was higher under the conditions where the formation of hydrogen-induced lattice defects tended to be enhanced. Since hydrogen-induced lattice defects formed by the interaction between hydrogen and strain were annihilated by annealing at a temperature of 200 °C, they were presumably vacancies or vacancy clusters. One of the common atomic-level changes that occur in cold-drawn pearlitic steel showing higher hydrogen embrittlement susceptibility is the formation of vacancies and vacancy clusters

Noise filtering in a multi-channel system using a tunable liquid crystal photonic bandgap fiber

DEFF Research Database (Denmark)

Petersen, Martin Nordal; Scolari, Lara; Tokle, Torger

2008-01-01

This paper reports on the first application of a liquid crystal infiltrated photonic bandgap fiber used as a tunable filter in an optical transmission system. The device allows low-cost amplified spontaneous emission (ASE) noise filtering and gain equalization with low insertion loss and broad...... tunability. System experiments show that the use of this filter increases for times the distance over which the optical signal-to-noise ratio (OSNR) is sufficient for error-free transmission with respect to the case in which no filtering is used....

Hydrogen sensor

Science.gov (United States)

Duan, Yixiang; Jia, Quanxi; Cao, Wenqing

2010-11-23

A hydrogen sensor for detecting/quantitating hydrogen and hydrogen isotopes includes a sampling line and a microplasma generator that excites hydrogen from a gas sample and produces light emission from excited hydrogen. A power supply provides power to the microplasma generator, and a spectrometer generates an emission spectrum from the light emission. A programmable computer is adapted for determining whether or not the gas sample includes hydrogen, and for quantitating the amount of hydrogen and/or hydrogen isotopes are present in the gas sample.

Hail hydrogen

International Nuclear Information System (INIS)

Hairston, D.

1996-01-01

After years of being scorned and maligned, hydrogen is finding favor in environmental and process applications. There is enormous demand for the industrial gas from petroleum refiners, who need in creasing amounts of hydrogen to remove sulfur and other contaminants from crude oil. In pulp and paper mills, hydrogen is turning up as hydrogen peroxide, displacing bleaching agents based on chlorine. Now, new technologies for making hydrogen have the industry abuzz. With better capabilities of being generated onsite at higher purity levels, recycled and reused, hydrogen is being prepped for a range of applications, from waste reduction to purification of Nylon 6 and hydrogenation of specialty chemicals. The paper discusses the strong market demand for hydrogen, easier routes being developed for hydrogen production, and the use of hydrogen in the future

Near-bandgap optical properties of pseudomorphic GeSn alloys grown by molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

D' Costa, Vijay Richard, E-mail: vdcosta@asu.edu; Wang, Wei; Yeo, Yee-Chia, E-mail: eleyeoyc@nus.edu.sg [Department of Electrical and Computer Engineering, National University of Singapore, Singapore 117583 (Singapore)

2016-08-14

We investigated the compositional dependence of the near-bandgap dielectric function and the E{sub 0} critical point in pseudomorphic Ge{sub 1-x}Sn{sub x} alloys grown on Ge (100) substrate by molecular beam epitaxy. The complex dielectric functions were obtained using spectroscopic ellipsometry from 0.5 to 4.5 eV at room temperature. Analogous to the E{sub 1} and E{sub 1}+Δ{sub 1} transitions, a model consisting of the compositional dependence of relaxed alloys along with the strain contribution predicted by the deformation potential theory fully accounts for the observed compositional dependence in pseudomorphic alloys.

Band-gap narrowing of TiO2 films induced by N-doping

International Nuclear Information System (INIS)

Nakano, Y.; Morikawa, T.; Ohwaki, T.; Taga, Y.

2006-01-01

N-doped TiO 2 films were deposited on n + -GaN/Al 2 O 3 substrates by reactive magnetron sputtering and subsequently crystallized by annealing at 550 o C in flowing N 2 gas. The N-doping concentration was ∼8.8%, as determined from X-ray photoelectron spectroscopy measurements. Deep-level optical spectroscopy measurements revealed two characteristic deep levels located at 1.18 and 2.48 eV below the conduction band. The 1.18 eV level is probably attributable to the O vacancy state and can be active as an efficient generation-recombination center. Additionally, the 2.48 eV band is newly introduced by the N-doping and contributes to band-gap narrowing by mixing with the O 2p valence band

Compression of realistic laser pulses in hollow-core photonic bandgap fibers

DEFF Research Database (Denmark)

Lægsgaard, Jesper; Roberts, John

2009-01-01

Dispersive compression of chirped few-picosecond pulses at the microjoule level in a hollow-core photonic bandgap fiber is studied numerically. The performance of ideal parabolic input pulses is compared to pulses from a narrowband picosecond oscillator broadened by self-phase modulation during...... amplification. It is shown that the parabolic pulses are superior for compression of high-quality femtosecond pulses up to the few-megawatts level. With peak powers of 5-10 MW or higher, there is no significant difference in power scaling and pulse quality between the two pulse types for comparable values...... of power, duration, and bandwidth. The same conclusion is found for the peak power and energy of solitons formed beyond the point of maximal compression. Long-pass filtering of these solitons is shown to be a promising route to clean solitonlike output pulses with peak powers of several MW....

Bandgap Engineering of Lead-Free Double Perovskite Cs2 AgBiBr6 through Trivalent Metal Alloying.

Science.gov (United States)

Du, Ke-Zhao; Meng, Weiwei; Wang, Xiaoming; Yan, Yanfa; Mitzi, David B

2017-07-03

The double perovskite family, A 2 M I M III X 6 , is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH 3 NH 3 PbI 3 . Given the generally large indirect band gap within most known double perovskites, band-gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs 2 AgBiBr 6 as host, band-gap engineering through alloying of In III /Sb III has been demonstrated in the current work. Cs 2 Ag(Bi 1-x M x )Br 6 (M=In, Sb) accommodates up to 75 % In III with increased band gap, and up to 37.5 % Sb III with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs 2 Ag(Bi 0.625 Sb 0.375 )Br 6 . Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultrafast carrier dynamics unravel role of surface ligands and metal domain size on the photocatalytic hydrogen evolution efficiency of Au-tipped CdS nanorods: an ultrafast transient absorption spectroscopy study

Science.gov (United States)

Ben-Shahar, Yuval; Kriegel, Ilka; Scotognella, Francesco; Waiskopf, Nir; Dal Conte, Stefano; Moretti, Luca; Cerullo, Giulio; Rabani, Eran; Banin, Uri

2017-02-01

Semiconductor-metal hybrid nanostructures are interesting materials for photocatalysis. Their tunable properties offer a highly controllable platform to design light-induced charge separation, a key to their function in photocatalytic water splitting. Hydrogen evolution quantum yields are influenced by factors as size, shape, material and morphology of the system, additionally the surface coating or the metal domain size play a dominant role. In this paper we present a study on a well-defined model system of Au-tipped CdS nanorods. We use transient absorption spectroscopy to get insights into the charge carrier dynamics after photoexcitation of the bandgap of CdS nanorods. The study of charge transfer processes combined with the hydrogen evolution efficiency unravels the effects of surface coating and the gold tip size on the photocatalytic efficiency. Differences in efficiency with various surface ligands are primarily ascribed to the effects of surface passivation. Surface trapping of charge carriers is competing with effective charge separation, a prerequisite for photocatalysis, leading to the observed lower hydrogen production quantum yields. Interestingly, non-monotonic hydrogen evolution efficiency with size of the gold tip is observed, resulting in an optimal metal domain size for the most efficient photocatalysis. These results are explained by the sizedependent interplay of the metal domain charging and the relative band-alignments. Taken together our findings are of major importance for the potential application of hybrid nanoparticles as photocatalysts.

Analysis of sub-bandgap losses in TiO2 coating deposited via single and dual ion beam deposition

Czech Academy of Sciences Publication Activity Database

Žídek, Karel; Hlubuček, Jiří; Horodyská, Petra; Budasz, Jiří; Václavík, Jan

2017-01-01

Roč. 626, March (2017), s. 60-65 ISSN 0040-6090 R&D Projects: GA MŠk(CZ) LO1206 Institutional support: RVO:61389021 Keywords : Ion beam deposition * Titanium dioxide * Optical coating * Sub-bandgap losses * Urbach tail Subject RIV: BH - Optics, Masers, Lasers OBOR OECD: Optics (including laser optics and quantum optics) Impact factor: 1.879, year: 2016 http://www.sciencedirect.com/science/article/pii/S0040609017301256

Hydrogen molecules and hydrogen-related defects in crystalline silicon

Science.gov (United States)

Fukata, N.; Sasaki, S.; Murakami, K.; Ishioka, K.; Nakamura, K. G.; Kitajima, M.; Fujimura, S.; Kikuchi, J.; Haneda, H.

1997-09-01

We have found that hydrogen exists in molecular form in crystalline silicon treated with hydrogen atoms in the downstream of a hydrogen plasma. The vibrational Raman line of hydrogen molecules is observed at 4158 cm-1 for silicon samples hydrogenated between 180 and 500 °C. The assignment of the Raman line is confirmed by its isotope shift to 2990 cm-1 for silicon treated with deuterium atoms. The Raman intensity has a maximum for hydrogenation at 400 °C. The vibrational Raman line of the hydrogen molecules is broad and asymmetric. It consists of at least two components, possibly arising from hydrogen molecules in different occupation sites in crystalline silicon. The rotational Raman line of hydrogen molecules is observed at 590 cm-1. The Raman band of Si-H stretching is observed for hydrogenation temperatures between 100 and 500 °C and the intensity has a maximum for hydrogenation at 250 °C.

Wide-range tunable bandgap in Bi1−xCaxFe1−yTiyO3−δ nanoparticles via oxygen vacancy induced structural modulations at room temperature

International Nuclear Information System (INIS)

Mocherla, Pavana S V; Sudakar, C; Gautam, Sanjeev; Chae, Keun Hwa; Rao, M S Ramachandra

2015-01-01

We demonstrate that oxygen vacancies (V O ) produced by aliovalent (Ca 2+ ) doping in BiFeO 3 (BCFO) and associated structural changes due to V O ordering result in systematic alteration of the bandgap (E g ) over a wide range from 1.5 eV to 2.3 eV. By contrast, the change in the bandgap of a Ca 2+ and Ti 4+ co-doped BiFeO 3 (BCFTO) system, wherein the V O formation is suppressed, is negligible. These contrastive results strongly confirm the role of oxygen vacancies in altering the bandgap of BCFO. Irrespective of doping, microstrain, which is found to be large (0.3 to 1.2%) below a critical size (d c ∼ 60 nm) also produces a small, yet linear change in the bandgap (E g from 2.0 to 2.3 eV). The cubic phase stabilizes gradually in BCFO for x > 0.1 through an orthorhombic phase (for 0.05 < x < 0.1), whereas it directly transforms for x > 0.1 in BCFTO. This change in BCFO at 300 K suggests a high-pressure-like (or high-temperature-like) effect of the oxygen vacancies and dopants on the structure. Systematic variations in the relative intensities and peak positions of Fe d–d transitions in BCFO reveal the local changes in Fe–O–Fe coordination. These results along with XANES and HRTEM studies substantiate the observed structural changes. (paper)

Hydrogen concentration control utilizing a hydrogen permeable membrane

International Nuclear Information System (INIS)

Keating, S.J. Jr.

1976-01-01

The concentration of hydrogen in a fluid mixture is controlled to a desired concentration by flowing the fluid through one chamber of a diffusion cell separated into two chambers by a hydrogen permeable membrane. A gradient of hydrogen partial pressure is maintained across the membrane to cause diffusion of hydrogen through the membrane to maintain the concentration of hydrogen in the fluid mixture at the predetermined level. The invention has particular utility for the purpose of injecting into and/or separating hydrogen from the reactor coolant of a nuclear reactor system

Research and development of photovoltaic power system. Optimization of bandgap of chalcopyrite semiconductors; Taiyoko hatsuden system no kenkyu kaihatsu. Kinseitaihaba no saitekika no kenkyu

Energy Technology Data Exchange (ETDEWEB)

Konagai, M [Tokyo Institute of Technology, Tokyo (Japan). Faculty of Engineering

1994-12-01

This paper reports the result obtained during fiscal 1994 on research on research on optimization of bandgap in thin film compound solar cells. In research on Cu(InGa)Se2 thin film solar cells by using a gas phase selenide making process, discussions were given on optimizing the following three processes: a process to raise temperature of a precursor film formed at a substrate temperature of about 150{degree}C, a selenide making process to perform annealing at about 500{degree}C, and a temperature reducing process. Good characteristics were obtained when selenium amount in the precursor is about 50%. In a bandgap control viewpoint, it was found that the conversion efficiency decreases rapidly when Ga composition is higher than 50%. A conversion efficiency of 14.9% was obtained to date at the Ga/(In+Ga) ratio of 0.4. In research on Cu(InGa)Se2 thin film solar cells by using a simultaneous deposition method, a conversion efficiency of 13.5% was obtained at a bandgap width of about 1.3 eV during research on manufacturing ZnO/CdS/Cu(InGa)Se2 thin film solar cells by using the simultaneous deposition method. Research has been carried out on manufacturing Cu(InGa)Se2 thin film solar cells using ZnSe interface layers. 8 figs.

Photocatalytic reforming of biomass for hydrogen production

NARCIS (Netherlands)

Ripken, R.M.; de Boer, V.J.H.W.; Gardeniers, J.G.E.; le Gac, S.

2017-01-01

Here, we describe a novel microfluidic device to determine the required bandgap for the photocatalytic reforming of biomass model substrates (ethylene glycol, glycerol, xylose and xylitol) in water. Furthermore, this device is applied to eventually elucidate the reaction mechanism of aqueous

Hydrogen safety

International Nuclear Information System (INIS)

Frazier, W.R.

1991-01-01

The NASA experience with hydrogen began in the 1950s when the National Advisory Committee on Aeronautics (NACA) research on rocket fuels was inherited by the newly formed National Aeronautics and Space Administration (NASA). Initial emphasis on the use of hydrogen as a fuel for high-altitude probes, satellites, and aircraft limited the available data on hydrogen hazards to small quantities of hydrogen. NASA began to use hydrogen as the principal liquid propellant for launch vehicles and quickly determined the need for hydrogen safety documentation to support design and operational requirements. The resulting NASA approach to hydrogen safety requires a joint effort by design and safety engineering to address hydrogen hazards and develop procedures for safe operation of equipment and facilities. NASA also determined the need for rigorous training and certification programs for personnel involved with hydrogen use. NASA's current use of hydrogen is mainly for large heavy-lift vehicle propulsion, which necessitates storage of large quantities for fueling space shots and for testing. Future use will involve new applications such as thermal imaging

Hydrogen isotope effect through Pd in hydrogen transport pipe

International Nuclear Information System (INIS)

Tamaki, Masayoshi

1992-01-01

This investigation concerns hydrogen system with hydrogen transport pipes for transportation, purification, isotope separation and storage of hydrogen and its isotopes. A principle of the hydrogen transport pipe (heat pipe having hydrogen transport function) was proposed. It is comprised of the heat pipe and palladium alloy tubes as inlet, outlet, and the separation membrane of hydrogen. The operation was as follows: (1) gas was introduced into the heat pipe through the membrane in the evaporator; (2) the introduced gas was transported toward the condenser by the vapor flow; (3) the transported gas was swept and compressed to the end of the condenser by the vapor pressure; and (4) the compressed gas was exhausted from the heat pipe through the membrane in the condenser. The characteristics of the hydrogen transport pipe were examined for various working conditions. Basic performance concerning transportation, evacuation and compression was experimentally verified. Isotopic dihydrogen gases (H 2 and D 2 ) were used as feed gas for examining the intrinsic performance of the isotope separation by the hydrogen transport pipe. A simulated experiment for hydrogen isotope separation was carried out using a hydrogen-helium gas mixture. The hydrogen transport pipe has a potential for isotope separation and purification of hydrogen, deuterium and tritium in fusion reactor technology. (author)

Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates

International Nuclear Information System (INIS)

Lumb, M. P.; Yakes, M. K.; Schmieder, K. J.; Affouda, C. A.; Walters, R. J.; González, M.; Bennett, M. F.; Herrera, M.; Delgado, F. J.; Molina, S. I.

2016-01-01

In this work, the electrical performance of strain-balanced quantum well tunnel junctions with varying designs is presented. Strain-balanced quantum well tunnel junctions comprising compressively strained InAlAs wells and tensile-strained InAlAs barriers were grown on InP substrates using solid-source molecular beam epitaxy. The use of InAlAs enables InP-based tunnel junction devices to be produced using wide bandgap layers, enabling high electrical performance with low absorption. The impact of well and barrier thickness on the electrical performance was investigated, in addition to the impact of Si and Be doping concentration. Finally, the impact of an InGaAs quantum well at the junction interface is presented, enabling a peak tunnel current density of 47.6 A/cm 2 to be realized.

Characterizing Surfaces of the Wide Bandgap Semiconductor Ilmenite with Scanning Probe Microcopies

Science.gov (United States)

Wilkins, R.; Powell, Kirk St. A.

1997-01-01

Ilmenite (FeTiO3) is a wide bandgap semiconductor with an energy gap of about 2.5eV. Initial radiation studies indicate that ilmenite has properties suited for radiation tolerant applications, as well as a variety of other electronic applications. Two scanning probe microscopy methods have been used to characterize the surface of samples taken from Czochralski grown single crystals. The two methods, atomic force microscopy (AFM) and scanning tunneling microscopy (STM), are based on different physical principles and therefore provide different information about the samples. AFM provides a direct, three-dimensional image of the surface of the samples, while STM give a convolution of topographic and electronic properties of the surface. We will discuss the differences between the methods and present preliminary data of each method for ilmenite samples.

Wide bandgap Mg-doped ZnAlO thin films for optoelectronic applications

International Nuclear Information System (INIS)

Gupta, R.K.; Ghosh, K.; Patel, R.; Kahol, P.K.

2009-01-01

Magnesium-doped ZnAlO thin films were grown on quartz substrate by ablating the sintered target with a KrF excimer laser. The effect of growth temperature from 30 deg. C to 700 deg. C on structural, optical, and electrical properties has been studied. These films are highly transparent in visible spectrum with average transmittance of 82%. The films grown at low temperature are amorphous while films grown at high temperature are crystalline in nature. These films are highly oriented along (0 0 2) direction. The electrical conductivity, carrier concentration, and electron mobility is found to increase with increase in temperature and then decreases with further increase in temperature. The bandgap is found to vary from 3.86 eV to 4.00 eV for various films

Wide bandgap, strain-balanced quantum well tunnel junctions on InP substrates

Energy Technology Data Exchange (ETDEWEB)

Lumb, M. P. [The George Washington University, Washington, DC 20037 (United States); US Naval Research Laboratory, Washington, DC 20375 (United States); Yakes, M. K.; Schmieder, K. J.; Affouda, C. A.; Walters, R. J. [US Naval Research Laboratory, Washington, DC 20375 (United States); González, M.; Bennett, M. F. [Sotera Defense Solutions, Annapolis Junction, Maryland 20701 (United States); US Naval Research Laboratory, Washington, DC 20375 (United States); Herrera, M.; Delgado, F. J.; Molina, S. I. [University of Cádiz, 11510, Puerto Real, Cádiz (Spain)

2016-05-21

In this work, the electrical performance of strain-balanced quantum well tunnel junctions with varying designs is presented. Strain-balanced quantum well tunnel junctions comprising compressively strained InAlAs wells and tensile-strained InAlAs barriers were grown on InP substrates using solid-source molecular beam epitaxy. The use of InAlAs enables InP-based tunnel junction devices to be produced using wide bandgap layers, enabling high electrical performance with low absorption. The impact of well and barrier thickness on the electrical performance was investigated, in addition to the impact of Si and Be doping concentration. Finally, the impact of an InGaAs quantum well at the junction interface is presented, enabling a peak tunnel current density of 47.6 A/cm{sup 2} to be realized.

Simulation of push-pull inverter using wide bandgap devices

Science.gov (United States)

Al-badri, Mustafa; Matin, Mohammed A.

2016-09-01

This paper discusses the use of wide bandgap devices (SiC-MOSFET) in the design of a push-pull inverter which provides inexpensive low power dc-ac inverters. The parameters used were 1200V SiC MOSFET(C2M0040120D) made by power company ROHM. This modeling was created using parameters that were provided from a device datasheet. The spice model is provided by this company to study the effect of adding this component on push-pull inverter ordinary circuit and compared results between SiC MOSFET and silicon MOSFET (IRFP260M). The results focused on Vout and Vmos stability as well as on output power and MOSFET power loss because it is a very crucial aspect on DC-AC inverter design. These results are done using the National Instrument simulation program (Multisim 14). It was found that power loss is better in the 12 and 15 vdc inverter. The Vout in the SIC MOSFET circuit shows more stability in the high current low resistance load in comparison to the Silicon MOSFET circuit and this will improve the overall performance of the circuit.

Future hydrogen markets for large-scale hydrogen production systems

International Nuclear Information System (INIS)

Forsberg, Charles W.

2007-01-01

The cost of delivered hydrogen includes production, storage, and distribution. For equal production costs, large users (>10 6 m 3 /day) will favor high-volume centralized hydrogen production technologies to avoid collection costs for hydrogen from widely distributed sources. Potential hydrogen markets were examined to identify and characterize those markets that will favor large-scale hydrogen production technologies. The two high-volume centralized hydrogen production technologies are nuclear energy and fossil energy with carbon dioxide sequestration. The potential markets for these technologies are: (1) production of liquid fuels (gasoline, diesel and jet) including liquid fuels with no net greenhouse gas emissions and (2) peak electricity production. The development of high-volume centralized hydrogen production technologies requires an understanding of the markets to (1) define hydrogen production requirements (purity, pressure, volumes, need for co-product oxygen, etc.); (2) define and develop technologies to use the hydrogen, and (3) create the industrial partnerships to commercialize such technologies. (author)

Hydrogen embrittlement due to hydrogen-inclusion interactions

International Nuclear Information System (INIS)

Yu, H.Y.; Li, J.C.M.

1976-01-01

Plastic flow around inclusions creates elastic misfit which attracts hydrogen towards the regions of positive dilatation. Upon decohesion of the inclusion-matrix interface, the excess hydrogen escapes into the void and can produce sufficient pressure to cause void growth by plastic deformation. This mechanism of hydrogen embrittlement can be used to understand the increase of ductility with temperature, the decrease of ductility with hydrogen content, and the increase of ductility with the ultimate strength of the matrix. An examination of the effect of the shape of spheroid inclusion reveals that rods are more susceptible to hydrogen embrittlement than disks. The size of the inclusion is unimportant while the volume fraction of inclusions plays the usual role

Magnonic band structure, complete bandgap, and collective spin wave excitation in nanoscale two-dimensional magnonic crystals

International Nuclear Information System (INIS)

Kumar, D.; Barman, A.; Kłos, J. W.; Krawczyk, M.

2014-01-01

We present the observation of a complete bandgap and collective spin wave excitation in two-dimensional magnonic crystals comprised of arrays of nanoscale antidots and nanodots, respectively. Considering that the frequencies dealt with here fall in the microwave band, these findings can be used for the development of suitable magnonic metamaterials and spin wave based signal processing. We also present the application of a numerical procedure, to compute the dispersion relations of spin waves for any high symmetry direction in the first Brillouin zone. The results obtained from this procedure have been reproduced and verified by the well established plane wave method for an antidot lattice, when magnetization dynamics at antidot boundaries are pinned. The micromagnetic simulation based method can also be used to obtain iso–frequency contours of spin waves. Iso–frequency contours are analogous of the Fermi surfaces and hence, they have the potential to radicalize our understanding of spin wave dynamics. The physical origin of bands, partial and full magnonic bandgaps have been explained by plotting the spatial distribution of spin wave energy spectral density. Although, unfettered by rigid assumptions and approximations, which afflict most analytical methods used in the study of spin wave dynamics, micromagnetic simulations tend to be computationally demanding. Thus, the observation of collective spin wave excitation in the case of nanodot arrays, which can obviate the need to perform simulations, may also prove to be valuable

Hydrogen molecules and hydrogen-related defects in crystalline silicon

OpenAIRE

Fukata, N.; Sasak, S.; Murakami, K.; Ishioka, K.; Nakamura, K. G.; Kitajima, M.; Fujimura, S.; Kikuchi, J.; Haneda, H.

1997-01-01

We have found that hydrogen exists in molecular form in crystalline silicon treated with hydrogen atoms in the downstream of a hydrogen plasma. The vibrational Raman line of hydrogen molecules is observed at 4158cm-1 for silicon samples hydrogenated between 180 and 500 °C. The assignment of the Raman line is confirmed by its isotope shift to 2990cm-1 for silicon treated with deuterium atoms. The Raman intensity has a maximum for hydrogenation at 400 °C. The vibrational Raman line of the hydro...

Why hydrogen; Pourquoi l'hydrogene?

Energy Technology Data Exchange (ETDEWEB)

NONE

2004-02-01

The energy consumption increase and the associated environmental risks, led to develop new energy sources. The authors present the potentialities of the hydrogen in this context of energy supply safety. They detail the today market and the perspectives, the energy sources for the hydrogen production (fossils, nuclear and renewable), the hydrogen transport, storage, distribution and conversion, the application domains, the associated risks. (A.L.B.)

Beyond Donor-Acceptor (D-A) Approach: Structure-Optoelectronic Properties-Organic Photovoltaic Performance Correlation in New D-A1 -D-A2 Low-Bandgap Conjugated Polymers.

Science.gov (United States)

Chochos, Christos L; Drakopoulou, Sofia; Katsouras, Athanasios; Squeo, Benedetta M; Sprau, Christian; Colsmann, Alexander; Gregoriou, Vasilis G; Cando, Alex-Palma; Allard, Sybille; Scherf, Ullrich; Gasparini, Nicola; Kazerouni, Negar; Ameri, Tayebeh; Brabec, Christoph J; Avgeropoulos, Apostolos

2017-04-01

Low-bandgap near-infrared polymers are usually synthesized using the common donor-acceptor (D-A) approach. However, recently polymer chemists are introducing more complex chemical concepts for better fine tuning of their optoelectronic properties. Usually these studies are limited to one or two polymer examples in each case study so far, though. In this study, the dependence of optoelectronic and macroscopic (device performance) properties in a series of six new D-A 1 -D-A 2 low bandgap semiconducting polymers is reported for the first time. Correlation between the chemical structure of single-component polymer films and their optoelectronic properties has been achieved in terms of absorption maxima, optical bandgap, ionization potential, and electron affinity. Preliminary organic photovoltaic results based on blends of the D-A 1 -D-A 2 polymers as the electron donor mixed with the fullerene derivative [6,6]-phenyl-C 71 -butyric acid methyl ester demonstrate power conversion efficiencies close to 4% with short-circuit current densities (J sc ) of around 11 mA cm -2 , high fill factors up to 0.70, and high open-circuit voltages (V oc s) of 0.70 V. All the devices are fabricated in an inverted architecture with the photoactive layer processed in air with doctor blade technique, showing the compatibility with roll-to-roll large-scale manufacturing processes. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Bandgap engineering of lead-free double perovskite Cs_2AgBiBr_6 through trivalent metal alloying

International Nuclear Information System (INIS)

Du, Ke-zhao; Mitzi, David B.; Meng, Weiwei; Wang, Xiaoming; Yan, Yanfa

2017-01-01

The double perovskite family, A_2M"IM"I"I"IX_6, is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH_3NH_3PbI_3. Given the generally large indirect band gap within most known double perovskites, band-gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs_2AgBiBr_6 as host, band-gap engineering through alloying of In"I"I"I/Sb"I"I"I has been demonstrated in the current work. Cs_2Ag(Bi_1_-_xM_x)Br_6 (M=In, Sb) accommodates up to 75 % In"I"I"I with increased band gap, and up to 37.5 % Sb"I"I"I with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs_2Ag(Bi_0_._6_2_5Sb_0_._3_7_5)Br_6. Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

Hydrogen Embrittlement

Science.gov (United States)

Woods, Stephen; Lee, Jonathan A.

2016-01-01

Hydrogen embrittlement (HE) is a process resulting in a decrease in the fracture toughness or ductility of a metal due to the presence of atomic hydrogen. In addition to pure hydrogen gas as a direct source for the absorption of atomic hydrogen, the damaging effect can manifest itself from other hydrogen-containing gas species such as hydrogen sulfide (H2S), hydrogen chloride (HCl), and hydrogen bromide (HBr) environments. It has been known that H2S environment may result in a much more severe condition of embrittlement than pure hydrogen gas (H2) for certain types of alloys at similar conditions of stress and gas pressure. The reduction of fracture loads can occur at levels well below the yield strength of the material. Hydrogen embrittlement is usually manifest in terms of singular sharp cracks, in contrast to the extensive branching observed for stress corrosion cracking. The initial crack openings and the local deformation associated with crack propagation may be so small that they are difficult to detect except in special nondestructive examinations. Cracks due to HE can grow rapidly with little macroscopic evidence of mechanical deformation in materials that are normally quite ductile. This Technical Memorandum presents a comprehensive review of experimental data for the effects of gaseous Hydrogen Environment Embrittlement (HEE) for several types of metallic materials. Common material screening methods are used to rate the hydrogen degradation of mechanical properties that occur while the material is under an applied stress and exposed to gaseous hydrogen as compared to air or helium, under slow strain rates (SSR) testing. Due to the simplicity and accelerated nature of these tests, the results expressed in terms of HEE index are not intended to necessarily represent true hydrogen service environment for long-term exposure, but rather to provide a practical approach for material screening, which is a useful concept to qualitatively evaluate the severity of

Bandgap-customizable germanium using lithographically determined biaxial tensile strain for silicon-compatible optoelectronics.

Science.gov (United States)

Sukhdeo, David S; Nam, Donguk; Kang, Ju-Hyung; Brongersma, Mark L; Saraswat, Krishna C

2015-06-29

Strain engineering has proven to be vital for germanium-based photonics, in particular light emission. However, applying a large permanent biaxial tensile strain to germanium has been a challenge. We present a simple, CMOS-compatible technique to conveniently induce a large, spatially homogenous strain in circular structures patterned within germanium nanomembranes. Our technique works by concentrating and amplifying a pre-existing small strain into a circular region. Biaxial tensile strains as large as 1.11% are observed by Raman spectroscopy and are further confirmed by photoluminescence measurements, which show enhanced and redshifted light emission from the strained germanium. Our technique allows the amount of biaxial strain to be customized lithographically, allowing the bandgaps of different germanium structures to be independently customized in a single mask process.

Bandgap characteristics of 2D plasma photonic crystal with oblique incidence: TM case

International Nuclear Information System (INIS)

Xie Ying-Tao; Yang Li-Xia

2011-01-01

A novel periodic boundary condition (PBC), that is the constant transverse wavenumber (CTW) method, is introduced to solve the time delay in the transverse plane with oblique incidence. Based on the novel PBC, the FDTD/PBC algorithm is proposed to study periodic structure consisting of plasma and vacuum. Then the reflection coefficient for the plasma slab from the FDTD/PBC algorithm is compared with the analytic results to show the validity of our technique. Finally, the reflection coefficients for the plasma photonic crystals are calculated using the FDTD/PBC algorithm to study the variation of bandgap characteristics with the incident angle and the plasma parameters. Thus it has provided the guiding sense for the actual manufacturing plasma photonic crystal. (general)

Fuel Cell and Hydrogen Technology Validation | Hydrogen and Fuel Cells |

Science.gov (United States)

NREL Fuel Cell and Hydrogen Technology Validation Fuel Cell and Hydrogen Technology Validation The NREL technology validation team works on validating hydrogen fuel cell electric vehicles; hydrogen fueling infrastructure; hydrogen system components; and fuel cell use in early market applications such as

Wide Bandgap Semiconductor Detector Optimization for Flash X-Ray Measurements

Energy Technology Data Exchange (ETDEWEB)

Roecker, Caleb Daniel [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Schirato, Richard C. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

2017-11-17

Charge trapping, resulting in a decreased and spatially dependent electric field, has long been a concern for wide bandgap semiconductor detectors. While significant work has been performed to characterize this degradation at varying temperatures and radiation environments, this work concentrates upon examining the event-to-event response in a flash X-ray environment. The following work investigates if charge trapping is a problem for CZT detectors, with particular emphasis on flash X-ray radiation fields at cold temperatures. Results are compared to a non-flash radiation field, using an Am-241 alpha source and similar temperature transitions. Our ability to determine if a response change occurred was hampered by the repeatability of our flash X-ray systems; a small response change was observed with the Am-241 source. Due to contrast of these results, we are in the process of revisiting the Am-241 measurements in the presence of a high radiation environment. If the response change is more pronounced in the high radiation environment, a similar test will be performed in the flash X-ray environment.

Hydrogen program overview

Energy Technology Data Exchange (ETDEWEB)

Gronich, S. [Dept. of Energy, Washington, DC (United States). Office of Utility Technologies

1997-12-31

This paper consists of viewgraphs which summarize the following: Hydrogen program structure; Goals for hydrogen production research; Goals for hydrogen storage and utilization research; Technology validation; DOE technology validation activities supporting hydrogen pathways; Near-term opportunities for hydrogen; Market for hydrogen; and List of solicitation awards. It is concluded that a full transition toward a hydrogen economy can begin in the next decade.

The prospects for hydrogen as an energy carrier: an overview of hydrogen energy and hydrogen energy systems

International Nuclear Information System (INIS)

Rosen, Marc A.; Koohi-Fayegh, Seama

2016-01-01

Hydrogen is expected to play a key role as an energy carrier in future energy systems of the world. As fossil-fuel supplies become scarcer and environmental concerns increase, hydrogen is likely to become an increasingly important chemical energy carrier and eventually may become the principal chemical energy carrier. When most of the world's energy sources become non-fossil based, hydrogen and electricity are expected to be the two dominant energy carriers for the provision of end-use services. In such a ''hydrogen economy,'' the two complementary energy carriers, hydrogen and electricity, are used to satisfy most of the requirements of energy consumers. A transition era will bridge the gap between today's fossil-fuel economy and a hydrogen economy, in which non-fossil-derived hydrogen will be used to extend the lifetime of the world's fossil fuels - by upgrading heavy oils, for instance - and the infrastructure needed to support a hydrogen economy is gradually developed. In this paper, the role of hydrogen as an energy carrier and hydrogen energy systems' technologies and their economics are described. Also, the social and political implications of hydrogen energy are examined, and the questions of when and where hydrogen is likely to become important are addressed. Examples are provided to illustrate key points. (orig.)

Hydrogen economy

Energy Technology Data Exchange (ETDEWEB)

Pahwa, P.K.; Pahwa, Gulshan Kumar

2013-10-01

In the future, our energy systems will need to be renewable and sustainable, efficient and cost-effective, convenient and safe. Hydrogen has been proposed as the perfect fuel for this future energy system. The availability of a reliable and cost-effective supply, safe and efficient storage, and convenient end use of hydrogen will be essential for a transition to a hydrogen economy. Research is being conducted throughout the world for the development of safe, cost-effective hydrogen production, storage, and end-use technologies that support and foster this transition. This book discusses hydrogen economy vis-a-vis sustainable development. It examines the link between development and energy, prospects of sustainable development, significance of hydrogen energy economy, and provides an authoritative and up-to-date scientific account of hydrogen generation, storage, transportation, and safety.

Hydrogen detector

International Nuclear Information System (INIS)

Kumagaya, Hiromichi; Yoshida, Kazuo; Sanada, Kazuo; Chigira, Sadao.

1994-01-01

The present invention concerns a hydrogen detector for detecting water-sodium reaction. The hydrogen detector comprises a sensor portion having coiled optical fibers and detects hydrogen on the basis of the increase of light transmission loss upon hydrogen absorption. In the hydrogen detector, optical fibers are wound around and welded to the outer circumference of a quartz rod, as well as the thickness of the clad layer of the optical fiber is reduced by etching. With such procedures, size of the hydrogen detecting sensor portion can be decreased easily. Further, since it can be used at high temperature, diffusion rate is improved to shorten the detection time. (N.H.)

Wide Bandgap Semiconductor Opportunities in Power Electronics

Energy Technology Data Exchange (ETDEWEB)

Das, Sujit [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Marlino, Laura D. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Armstrong, Kristina O. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2018-01-01

The report objective is to explore the Wide Bandgap (WBG) Power Electronics (PE) market, applications, and potential energy savings in order to identify key areas where further resources and investments of the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (DOE EERE) would have the most impact on U.S. competiveness. After considering the current market, several potential near-term application areas were identified as having significant market and energy savings potential with respect to clean energy applications: (1) data centers (uninterruptible power supplies and server power supplies); (2) renewable energy generation (photovoltaic-solar and wind); (3) motor drives (industrial, commercial and residential); (4) rail traction; and, (5) hybrid and electric vehicles (traction and charging). After the initial explorative analyses, it became clear that, SiC, not GaN, would be the principal WBG power device material for the chosen markets in the near future. Therefore, while GaN is discussed when appropriate, this report focuses on SiC devices, other WBG applications (e.g., solid-state transformers, combined heat and power, medical, and wireless power), the GaN market, and GaN specific applications (e.g., LiDAR, 5G) will be explored at a later date. In addition to the market, supply and value chain analyses addressed in Section 1 of this report, a SWOT (Strength, Weakness, Opportunity, Threat) analysis and potential energy savings analysis was conducted for each application area to identify the major potential WBG application area(s) with a U.S. competitiveness opportunity in the future.

Reconfigurable origami sonic barriers with tunable bandgaps for traffic noise mitigation

Science.gov (United States)

Thota, M.; Wang, K. W.

2017-10-01

An origami sonic barrier composed of cylindrical inclusions attached onto an origami sheet is proposed. The idea allows for tunable sound blocking properties for application in attenuating complex traffic noise spectra. Folding of the underlying origami sheet transforms the periodicity of the inclusions between different Bravais lattices, viz. between a square and a hexagonal lattice, and such significant lattice re-configuration leads to drastic tuning of dispersion characteristics. The wave tuning capabilities are corroborated via performing theoretical and numerical investigations using a plane wave expansion method and an acoustic simulation package of COMSOL, while experiments are performed on a one-seventh scaled-down model of origami sonic barrier to demonstrate the lattice re-configuration between different Bravais lattices and the associated bandgap adaptability. Good sound blocking performance in the frequency range of traffic noise spectra combined with less efforts, required for actuating one-degree of freedom folding mechanism, makes the origami sonic barrier a potential candidate for mitigating complex traffic noise.

Heterovalent Dopant Incorporation for Bandgap and Type Engineering of Perovskite Crystals

KAUST Repository

Abdelhady, Ahmed L.

2016-01-02

Controllable doping of semiconductors is a fundamental technological requirement for electronic and optoelectronic devices. As intrinsic semiconductors, hybrid perovskites have so far been a phenomenal success in photovoltaics. The inability to dope these materials heterovalently (or aliovalently) has greatly limited their wider utilizations in electronics. Here we show an efficient in situ chemical route that achieves the controlled incorporation of trivalent cations (Bi3+, Au3+, or In3+) by exploiting the retrograde solubility behavior of perovskites. We term the new method dopant incorporation in the retrograde regime. We achieve Bi3+ incorporation that leads to bandgap tuning (∼300 meV), 104 fold enhancement in electrical conductivity, and a change in the sign of majority charge carriers from positive to negative. This work demonstrates the successful incorporation of dopants into perovskite crystals while preserving the host lattice structure, opening new avenues to tailor the electronic and optoelectronic properties of this rapidly emerging class of solution-processed semiconductors. © 2016 American Chemical Society.

Band-gap creation by icosahedral symmetry in nearly-free-electron materials

International Nuclear Information System (INIS)

Carlsson, A.E.

1993-01-01

A series of numerical electronic density-of-states calculations is performed for rational approximants to a model one-electron potential based on icosahedrally arranged plane-wave components. It is found that high-order approximants can have band gaps even if the low-order approximants do not; furthermore, the magnitude of the gap increases with the order of the approximant. The results are interpreted via a two- and three-wave analysis of the energy eigenvalues at the pseudo-Jones-zone faces and edges. It is also found that the mechanism of band-gap reduction in the rational approximants is the presence of a small density of gap states. An analytic calculation shows that these gap states result from a splitting of threefold and pseudothreefold states at the valence-band edge when the icosahedral symmetry is broken. The splitting is proportional to the error with which the ratio between the approximant indices approximates τ, the golden mean. Finally, an application to the AlCuLi system is presented

Heterovalent Dopant Incorporation for Bandgap and Type Engineering of Perovskite Crystals

KAUST Repository

Abdelhady, Ahmed L.; Saidaminov, Makhsud I.; Banavoth, Murali; Adinolfi, Valerio; Voznyy, Oleksandr; Katsiev, Khabiboulakh; Alarousu, Erkki; Comin, Riccardo; Dursun, Ibrahim; Sinatra, Lutfan; Sargent, Edward H.; Mohammed, Omar F.; Bakr, Osman

2016-01-01

Controllable doping of semiconductors is a fundamental technological requirement for electronic and optoelectronic devices. As intrinsic semiconductors, hybrid perovskites have so far been a phenomenal success in photovoltaics. The inability to dope these materials heterovalently (or aliovalently) has greatly limited their wider utilizations in electronics. Here we show an efficient in situ chemical route that achieves the controlled incorporation of trivalent cations (Bi3+, Au3+, or In3+) by exploiting the retrograde solubility behavior of perovskites. We term the new method dopant incorporation in the retrograde regime. We achieve Bi3+ incorporation that leads to bandgap tuning (∼300 meV), 104 fold enhancement in electrical conductivity, and a change in the sign of majority charge carriers from positive to negative. This work demonstrates the successful incorporation of dopants into perovskite crystals while preserving the host lattice structure, opening new avenues to tailor the electronic and optoelectronic properties of this rapidly emerging class of solution-processed semiconductors. © 2016 American Chemical Society.

Investigation of the open-circuit voltage in wide-bandgap InGaP-host InP quantum dot intermediate-band solar cells

Science.gov (United States)

Aihara, Taketo; Tayagaki, Takeshi; Nagato, Yuki; Okano, Yoshinobu; Sugaya, Takeyoshi

2018-04-01

To analyze the open-circuit voltage (V oc) in intermediate-band solar cells, we investigated the current-voltage characteristics in wide-bandgap InGaP-based InP quantum dot (QD) solar cells. From the temperature dependence of the current-voltage curves, we show that the V oc in InP QD solar cells increases with decreasing temperature. We use a simple diode model to extract V oc at the zero-temperature limit, V 0, and the temperature coefficient C of the solar cells. Our results show that, while the C of InP QD solar cells is slightly larger than that of the reference InGaP solar cells, V 0 significantly decreases and coincides with the bandgap energy of the InP QDs rather than that of the InGaP host. This V 0 indicates that the V oc reduction in the InP QD solar cells is primarily caused by the breaking of the Fermi energy separation between the QDs and the host semiconductor in intermediate-band solar cells, rather than by enhanced carrier recombination.

Aluminum doping of CuInSe{sub 2} synthesized by solution process and its effect on structure, morphology, and bandgap tuning

Energy Technology Data Exchange (ETDEWEB)

Yan, Zhi; Deng, Weizhi; Zhang, Xia; Yuan, Qian; Deng, Peiran; Sun, Lei [Material Engineering College, Shanghai University of Engineering Science (China); Liang, Jun [School of Advanced Materials, Peking University Shenzhen Graduate School, Shenzhen University Town (China)

2014-11-15

Al-doped CuInSe{sub 2} material is prepared by a low-cost wet chemical process. The key properties of Al-doped CuInSe{sub 2} as a successful solar cell material are investigated, such as crystal structure, morphology, optical properties, and bandgap. In situ X-ray diffraction measurements indicate that the doping of Al has induced noticeable lattice distortion. The material shows excellent thermal stability up to 600 C annealing temperature. By increasing the Al-doping concentration, the crystal unit-cell parameter of the material becomes smaller and the change of crystal structure leads to an increase of the grain size and surface roughness. The bandgap of Al-doped CuInSe{sub 2} can be continuously tuned in a range of 1.07-1.67 eV as Al/(Al + In) content ratio varies from 0 to 0.49. Finally, the effect mechanism on the properties of CuInSe{sub 2} after Al doping is discussed based on the ionic radius, crystal structure, and bonding state. (copyright 2014 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

The prospects for hydrogen as an energy carrier: an overview of hydrogen energy and hydrogen energy systems

Energy Technology Data Exchange (ETDEWEB)

Rosen, Marc A.; Koohi-Fayegh, Seama [Ontario Univ., Oshawa, ON (Canada). Inst. of Technology

2016-02-15

Hydrogen is expected to play a key role as an energy carrier in future energy systems of the world. As fossil-fuel supplies become scarcer and environmental concerns increase, hydrogen is likely to become an increasingly important chemical energy carrier and eventually may become the principal chemical energy carrier. When most of the world's energy sources become non-fossil based, hydrogen and electricity are expected to be the two dominant energy carriers for the provision of end-use services. In such a ''hydrogen economy,'' the two complementary energy carriers, hydrogen and electricity, are used to satisfy most of the requirements of energy consumers. A transition era will bridge the gap between today's fossil-fuel economy and a hydrogen economy, in which non-fossil-derived hydrogen will be used to extend the lifetime of the world's fossil fuels - by upgrading heavy oils, for instance - and the infrastructure needed to support a hydrogen economy is gradually developed. In this paper, the role of hydrogen as an energy carrier and hydrogen energy systems' technologies and their economics are described. Also, the social and political implications of hydrogen energy are examined, and the questions of when and where hydrogen is likely to become important are addressed. Examples are provided to illustrate key points. (orig.)

Elastic Wave Control Beyond Band-Gaps: Shaping the Flow of Waves in Plates and Half-Spaces with Subwavelength Resonant Rods

Directory of Open Access Journals (Sweden)

Andrea Colombi

2017-08-01

Full Text Available In metamaterial science, local resonance and hybridization are key phenomena strongly influencing the dispersion properties; the metasurface discussed in this article created by a cluster of resonators, subwavelength rods, atop an elastic surface being an exemplar with these features. On this metasurface, band-gaps, slow or fast waves, negative refraction, and dynamic anisotropy can all be observed by exploring frequencies and wavenumbers from the Floquet–Bloch problem and by using the Brillouin zone. These extreme characteristics, when appropriately engineered, can be used to design and control the propagation of elastic waves along the metasurface. For the exemplar we consider, two parameters are easily tuned: rod height and cluster periodicity. The height is directly related to the band-gap frequency and, hence, to the slow and fast waves, while the periodicity is related to the appearance of dynamic anisotropy. Playing with these two parameters generates a gallery of metasurface designs to control the propagation of both flexural waves in plates and surface Rayleigh waves for half-spaces. Scalability with respect to the frequency and wavelength of the governing physical laws allows the application of these concepts in very different fields and over a wide range of lengthscales.

Breath Hydrogen Produced by Ingestion of Commercial Hydrogen Water and Milk

OpenAIRE

Shimouchi, Akito; Nose, Kazutoshi; Yamaguchi, Makoto; Ishiguro, Hiroshi; Kondo, Takaharu

2009-01-01

Objective: To compare how and to what extent ingestion of hydrogen water and milk increase breath hydrogen in adults.Methods: Five subjects without specific diseases, ingested distilled or hydrogen water and milk as a reference material that could increase breath hydrogen. Their end-alveolar breath hydrogen was measured.Results: Ingestion of hydrogen water rapidly increased breath hydrogen to the maximal level of approximately 40 ppm 10–15 min after ingestion and thereafter rapidly decrease...

Hydrogen - From hydrogen to energy production

International Nuclear Information System (INIS)

Klotz, Gregory

2005-01-01

More than a century ago, Jules Verne wrote in 'The Mysterious Island' that water would one day be employed as fuel: 'Hydrogen and oxygen, which constitute it, used singly or together, will furnish an inexhaustible source of heat and light'. Today, the 'water motor' is not entirely the dream of a writer. Fiction is about to become fact thanks to hydrogen, which can be produced from water and when burned in air itself produces water. Hydrogen is now at the heart of international research. So why do we have such great expectations of hydrogen? 'Hydrogen as an energy system is now a major challenge, both scientifically and from an environmental and economic point of view'. Dominated as it is by fossil fuels (oil, gas and coal), our current energy system has left a dual threat hovering over our environment, exposing the planet to the exhaustion of its natural reserves and contributing to the greenhouse effect. If we want sustainable development for future generations, it is becoming necessary to diversify our methods of producing energy. Hydrogen is not, of course, a source of energy, because first it has to be produced. But it has the twofold advantage of being both inexhaustible and non-polluting. So in the future, it should have a very important role to play. (author)

Hydrogen fuel. Uses

International Nuclear Information System (INIS)

Darkrim-Lamari, F.; Malbrunot, P.

2006-01-01

Hydrogen is a very energetic fuel which can be used in combustion to generate heat and mechanical energy or which can be used to generate electricity and heat through an electrochemical reaction with oxygen. This article deals with the energy conversion, the availability and safety problems linked with the use of hydrogen, and with the socio-economical consequences of a generalized use of hydrogen: 1 - hydrogen energy conversion: hydrogen engines, aerospace applications, fuel cells (principle, different types, domains of application); 2 - hydrogen energy availability: transport and storage (gas pipelines, liquid hydrogen, adsorbed and absorbed hydrogen in solid materials), service stations; 3 - hazards and safety: flammability, explosibility, storage and transport safety, standards and regulations; 4 - hydrogen economy; 5 - conclusion. (J.S.)

Tensile strain induced narrowed bandgap of TiO{sub 2} films: Utilizing the two-way shape memory effect of TiNiNb substrate and in-situ mechanical bending

Energy Technology Data Exchange (ETDEWEB)

Du, Minshu, E-mail: dms1223@126.com [Department of Materials Science and Engineering, China University of Petroleum at Beijing, Beijing, 102249 (China); Center for Electrochemistry, Department of Chemistry, The University of Texas at Austin, Austin, Texas, 78712 (United States); Cui, Lishan; Wan, Qiong [Department of Materials Science and Engineering, China University of Petroleum at Beijing, Beijing, 102249 (China)

2016-05-15

Graphical abstract: - Highlights: • Imposed tensile strain to anatase TiO{sub 2} nanofilm by using the two-way shape memory effect of NiTiNb substrate. • Imposed tensile strain to rutile TiO{sub 2} thin film by in-situ mechanical bending. • Tauc plot based on the PEC-tested auction spectrum was utilized to precisely determine the bandgap of TiO{sub 2}. • Tensile strain narrowed the bandgap of anatase TiO{sub 2} by 60 meV and rutile TiO{sub 2} by 70 meV. • Tensile strain contributes to a 1.5 times larger photocurrent for the water oxidation reaction. - Abstract: Elastic strain is one of the methods to alter the band gap of semiconductors. However, relevant experimental work is limited due to the difficulty in imposing strain. Two new methods for imposing tensile strain to TiO{sub 2} film were introduced here. One is by utilizing the two-way shape memory effect of NiTiNb substrate, and the other method is in-situ mechanical bending. The former method succeeded in imposing 0.4% tensile strain to anatase TiO{sub 2} nanofilm, and strain narrowed the bandgap of TiO{sub 2} by 60 meV. The latter method enabled rutile TiO{sub 2} thin film under the 0.5% biaxially tensile-strained state, which contributes to a narrowed bandgap with ΔE{sub g} of 70 meV. Also, photocurrents of both strained TiO{sub 2} films increased by 1.5 times compared to the strain-free films, which indirectly verified the previous DFT prediction proposed by Thulin and Guerra in 2008 that tensile strain could improve the mobility and separation of photo-excite carriers.

Solar hydrogen production: renewable hydrogen production by dry fuel reforming

Science.gov (United States)

Bakos, Jamie; Miyamoto, Henry K.

2006-09-01

SHEC LABS - Solar Hydrogen Energy Corporation constructed a pilot-plant to demonstrate a Dry Fuel Reforming (DFR) system that is heated primarily by sunlight focusing-mirrors. The pilot-plant consists of: 1) a solar mirror array and solar concentrator and shutter system; and 2) two thermo-catalytic reactors to convert Methane, Carbon Dioxide, and Water into Hydrogen. Results from the pilot study show that solar Hydrogen generation is feasible and cost-competitive with traditional Hydrogen production. More than 95% of Hydrogen commercially produced today is by the Steam Methane Reformation (SMR) of natural gas, a process that liberates Carbon Dioxide to the atmosphere. The SMR process provides a net energy loss of 30 to 35% when converting from Methane to Hydrogen. Solar Hydrogen production provides a 14% net energy gain when converting Methane into Hydrogen since the energy used to drive the process is from the sun. The environmental benefits of generating Hydrogen using renewable energy include significant greenhouse gas and criteria air contaminant reductions.

Carbon Dioxide-Free Hydrogen Production with Integrated Hydrogen Separation and Storage.

Science.gov (United States)

Dürr, Stefan; Müller, Michael; Jorschick, Holger; Helmin, Marta; Bösmann, Andreas; Palkovits, Regina; Wasserscheid, Peter

2017-01-10

An integration of CO 2 -free hydrogen generation through methane decomposition coupled with hydrogen/methane separation and chemical hydrogen storage through liquid organic hydrogen carrier (LOHC) systems is demonstrated. A potential, very interesting application is the upgrading of stranded gas, for example, gas from a remote gas field or associated gas from off-shore oil drilling. Stranded gas can be effectively converted in a catalytic process by methane decomposition into solid carbon and a hydrogen/methane mixture that can be directly fed to a hydrogenation unit to load a LOHC with hydrogen. This allows for a straight-forward separation of hydrogen from CH 4 and conversion of hydrogen to a hydrogen-rich LOHC material. Both, the hydrogen-rich LOHC material and the generated carbon on metal can easily be transported to destinations of further industrial use by established transport systems, like ships or trucks. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Production of hydrogen from organic waste via hydrogen sulfide

International Nuclear Information System (INIS)

McMahon, M.; Davis, B.R.; Roy, A.; Daugulis, A.

2007-01-01

In this paper an integrated process is proposed that converts organic waste to hydrogen via hydrogen sulphide. The designed bioreactor has achieved high volumetric productivities comparable to methanogenic bioreactors. Proposed process has advantages of bio-methane production and is more resilient to process upset. Thermochemical conversion of hydrogen sulphide to hydrogen is exothermic and also requires smaller plant infrastructure

Effect of single point defects on the confinement losses of air-guiding photonic bandgap fibers

Institute of Scientific and Technical Information of China (English)

Shi Wei-Hua; Zhao Yan; Qian Li-Guo; Chen He-Ming

2012-01-01

The confinement losses in air-guiding photonic bandgap fibers (PBGFs) with air hole missing are studied with the full-vector finite-element method.It is confirmed that there are two loss peaks (1.555 and 1.598 μm) if there is a hole missing in the cladding far from the core.The closer to the core the hole missing is,the larger the confinement losses are,and even no mode could propagate in the core.The main power of the fundamental mode leaks from the core to the cladding defect.The quality of PBGFs can be improved through controlling the number and position of defects.

The Lamb wave bandgap variation of a locally resonant phononic crystal subjected to thermal deformation

Science.gov (United States)

Zhu, Yun; Li, Zhen; Li, Yue-ming

2018-05-01

A study on dynamical characteristics of a ternary locally resonant phononic crystal (PC) plate (i.e., hard scatterer with soft coating periodically disperse in stiff host matrix) is carried out in this paper. The effect of thermal deformation on the structure stiffness, which plays an important role in the PC's dynamical characteristics, is considered. Results show that both the start and the stop frequency of bandgap shift to higher range with the thermal deformation. In particular, the characteristics of band structure change suddenly at critical buckling temperature. The effect of thermal deformation could be utilized for tuning of phononic band structures, which can promote their design and further applications.

Morphology effects on the bandgap of silicon nanocrystals—Numerically modelled by a full multi-grid method

Science.gov (United States)

Puthen Veettil, Binesh; König, Dirk; Huang, Shujuan; Patterson, Robert; Conibeer, Gavin

2017-02-01

Silicon nanocrystals embedded in a dielectric matrix have been considered a potential candidate for many optoelectronic and photovoltaic applications and have been under vigorous study in recent years. One of the main properties of interest in this application is the absorption bandgap, which is determined by the quantum confinement of silicon nanocrystals. The ability to predict the absorption bandgap is a key step in designing an optimum solar cell using this material. Although several higher level algorithms are available to predict the electronic confinement in these nanocrystals, most of them make regular-shape assumptions for the ease of computation. In this work, we present a model for the accurate prediction of the quantum confinement in silicon nanocrystals of non-regular shape by employing an efficient, self-consistent Full-Multi-Grid method. Confined energies in spherical, elongated, and arbitrarily shaped nanocrystals are calculated. The excited level calculations quantify the wavefunction coupling and energy level splitting arising due to the proximity of dots. The splitting magnitude was found to be as high as 0.1 eV for the 2 nm size silicon quantum dots. The decrease in confinement energy due to the elongation of dots was found to be more than 0.2 eV, and the trend was similar for different dielectric materials. Theoretical predictions were compared to the results from optical and structural characterisation and found to be in agreement. The loss of degeneracy in highly asymmetric quantum dots, such as a "horse-shoe" shaped quantum dot, significantly affects the excited state energies.

Near-infrared sub-bandgap all-silicon photodetectors: state of the art and perspectives.

Science.gov (United States)

Casalino, Maurizio; Coppola, Giuseppe; Iodice, Mario; Rendina, Ivo; Sirleto, Luigi

2010-01-01

Due to recent breakthroughs, silicon photonics is now the most active discipline within the field of integrated optics and, at the same time, a present reality with commercial products available on the market. Silicon photodiodes are excellent detectors at visible wavelengths, but the development of high-performance photodetectors on silicon CMOS platforms at wavelengths of interest for telecommunications has remained an imperative but unaccomplished task so far. In recent years, however, a number of near-infrared all-silicon photodetectors have been proposed and demonstrated for optical interconnect and power-monitoring applications. In this paper, a review of the state of the art is presented. Devices based on mid-bandgap absorption, surface-state absorption, internal photoemission absorption and two-photon absorption are reported, their working principles elucidated and their performance discussed and compared.

Near-Infrared Sub-Bandgap All-Silicon Photodetectors: State of the Art and Perspectives

Directory of Open Access Journals (Sweden)

Luigi Sirleto

2010-11-01

Full Text Available Due to recent breakthroughs, silicon photonics is now the most active discipline within the field of integrated optics and, at the same time, a present reality with commercial products available on the market. Silicon photodiodes are excellent detectors at visible wavelengths, but the development of high-performance photodetectors on silicon CMOS platforms at wavelengths of interest for telecommunications has remained an imperative but unaccomplished task so far. In recent years, however, a number of near-infrared all-silicon photodetectors have been proposed and demonstrated for optical interconnect and power-monitoring applications. In this paper, a review of the state of the art is presented. Devices based on mid-bandgap absorption, surface-state absorption, internal photoemission absorption and two-photon absorption are reported, their working principles elucidated and their performance discussed and compared.

Fuel Cell and Hydrogen Technologies Program | Hydrogen and Fuel Cells |

Science.gov (United States)

NREL Fuel Cell and Hydrogen Technologies Program Fuel Cell and Hydrogen Technologies Program Through its Fuel Cell and Hydrogen Technologies Program, NREL researches, develops, analyzes, and validates fuel cell and hydrogen production, delivery, and storage technologies for transportation

Synthesis of highly non-stoichiometric Cu{sub 2}ZnSnS{sub 4} nanoparticles with tunable bandgaps

Energy Technology Data Exchange (ETDEWEB)

Hamanaka, Yasushi, E-mail: hamanaka@nitech.ac.jp; Oyaizu, Wataru; Kawase, Masanari [Nagoya Institute of Technology, Department of Materials Science and Engineering (Japan); Kuzuya, Toshihiro [Muroran Institute of Technology, College of Design and Manufacturing Technology (Japan)

2017-01-15

Non-stoichiometric Cu{sub 2}ZnSnS{sub 4} nanoparticles with average diameters of 4–15 nm and quasi-polyhedral shape were successfully synthesized by a colloidal method. We found that a non-stoichiometric composition of Zn to Cu in Cu{sub 2}ZnSnS{sub 4} nanoparticles yielded a correlation where Zn content increased with a decrease in Cu content, suggesting formation of lattice defects relating to Cu and Zn, such as a Cu vacancy (V{sub Cu}), antisite with Zn replacing Cu (Zn{sub Cu}), and/or defect cluster of V{sub Cu} and Zn{sub Cu}. The bandgap energy of Cu{sub 2}ZnSnS{sub 4} nanoparticles systematically varies between 1.56 and 1.83 eV depending on the composition ratios of Cu and Zn, resulting in a wider bandgap for Cu-deficient Cu{sub 2}ZnSnS{sub 4} nanoparticles. These characteristics can be ascribed to the modification in electronic band structures due to formation of V{sub Cu} and Zn{sub Cu} on the analogy of ternary copper chalcogenide, chalcopyrite CuInSe{sub 2}, in which the top of the valence band shifts downward with decreasing Cu contents, because much like the structure of CuInSe{sub 2}, the top of the valence band is composed of a Cu 3d orbital in Cu{sub 2}ZnSnS{sub 4}.

Hydrogen Village : creating hydrogen and fuel cell communities

International Nuclear Information System (INIS)

Smith, G.R.

2009-01-01

The Hydrogen Village (H2V) is a collaborative public-private partnership administered through Hydrogen and Fuel Cells Canada and funded by the Governments of Canada and Ontario. This end user-driven, market development program accelerates the commercialization of hydrogen and fuel cell (FC) technologies throughout the Greater Toronto Area (GTA). The program targets 3 specific aspects of market development, notably deployment of near market technologies in community based stationary and mobile applications; development of a coordinated hydrogen delivery and equipment service infrastructure; and societal factors involving corporate policy and public education. This presentation focused on lessons learned through outreach programs and the deployment of solid oxide fuel cell (SOFC) heat and power generation; indoor and outdoor fuel cell back up power systems; fuel cell-powered forklifts, delivery vehicles, and utility vehicles; hydrogen internal combustion engine powered shuttle buses, sedans, parade float; hydrogen production/refueling stations in the downtown core; and temporary fuel cell power systems

Light and gas confinement in hollow-core photonic crystal fibre based photonic microcells

DEFF Research Database (Denmark)

Benabid, F.; Roberts, John; Couny, F.

2009-01-01

guides via a photonic bandgap and the other guides by virtue of an inhibited coupling between core and cladding mode constituents. For the former fibre type, we explore how the bandgap is formed using a photonic analogue of the tight-binding model and how it is related to the anti-resonant reflection...... on electromagnetically induced transparency in a rubidium filled hollow-core photonic crystal fibre, the CW-pumped hydrogen Raman laser and the generation of multi-octave spanning stimulated Raman scattering spectral combs....

All-silica photonic bandgap fibre with zero dispersion and a large mode area at 730 nm

DEFF Research Database (Denmark)

Riishede, Jesper; Lægsgaard, Jesper; Broeng, Jes

2004-01-01

A theoretical analysis of a photonic bandgap fibre, consisting of a pure silica background with a triangular lattice of Ge-doped high-index rods, is presented. This novel fibre design guides a single, well-confined mode in a core region made from undoped silica. The fibre is found to have positive...... waveguide dispersion, which may be used to shift the zero-dispersion wavelength down to 730 nm, while maintaining an effective mode area of 17 $mu@-m$+2$/. This is an order of magnitude larger than what may be achieved in highly non-linear index-guiding microstructured fibres with comparable zero...

Hydrogen energy assessment

Energy Technology Data Exchange (ETDEWEB)

Salzano, F J; Braun, C [eds.

1977-09-01

The purpose of this assessment is to define the near term and long term prospects for the use of hydrogen as an energy delivery medium. Possible applications of hydrogen are defined along with the associated technologies required for implementation. A major focus in the near term is on industrial uses of hydrogen for special applications. The major source of hydrogen in the near term is expected to be from coal, with hydrogen from electric sources supplying a smaller fraction. A number of potential applications for hydrogen in the long term are identified and the level of demand estimated. The results of a cost benefit study for R and D work on coal gasification to hydrogen and electrolytic production of hydrogen are presented in order to aid in defining approximate levels of R and D funding. A considerable amount of data is presented on the cost of producing hydrogen from various energy resources. A key conclusion of the study is that in time hydrogen is likely to play a role in the energy system; however, hydrogen is not yet competitive for most applications when compared to the cost of energy from petroleum and natural gas.

Composition and optical properties tunability of hydrogenated silicon carbonitride thin films deposited by reactive magnetron sputtering

Science.gov (United States)

Bachar, A.; Bousquet, A.; Mehdi, H.; Monier, G.; Robert-Goumet, C.; Thomas, L.; Belmahi, M.; Goullet, A.; Sauvage, T.; Tomasella, E.

2018-06-01

Radiofrequency reactive magnetron sputtering was used to deposit hydrogenated amorphous silicon carbonitride (a-SiCxNy:H) at 400 °C by sputtering a silicon target under CH4 and N2 reactive gas mixture. Rutherford backscattering spectrometry revealed that the change of reactive gases flow rate (the ratio R = FN2/(FN2+FCH4)) induced a smooth chemical composition tunability from a silicon carbide-like film for R = 0 to a silicon nitride-like one at R = 1 with a large area of silicon carbonitrides between the two regions. The deconvolution of Fourier Transform InfraRed and X-ray photoelectron spectroscopy spectrum highlighted a shift of the chemical environment of the deposited films corresponding to the changes seen by RBS. The consequence of these observations is that a control of refractive index in the range of [1.9-2.5] at λ = 633 nm and optical bandgap in the range [2 eV-3.8 eV] have been obtained which induces that these coatings can be used as antireflective coatings in silicon photovoltaic cells.

Bandgap engineering of Cu2CdxZn1−xSnS4 alloy for photovoltaic applications: A complementary experimental and first-principles study

KAUST Repository

Xiao, Zhen-Yu; Li, Yong-Feng; Yao, Bin; Deng, Rui; Ding, Zhan-Hui; Wu, Tao; Yang, Gang; Li, Chun-Ran; Dong, Zi-Yuan; Liu, Lei; Zhang, Li-Gong; Zhao, Hai-Feng

2013-01-01

We report on bandgap engineering of an emerging photovoltaic material of Cu2CdxZn1-xSnS4 (CCZTS) alloy. CCZTS alloy thin films with different Cd contents and single kesterite phase were fabricated using the sol-gel method. The optical absorption

II-VI Narrow-Bandgap Semiconductors for Optoelectronics

Science.gov (United States)

Baker, Ian

The field of narrow-gap II-VI materials is dominated by the compound semiconductor mercury cadmium telluride, (Hg1-x Cd x Te or MCT), which supports a large industry in infrared detectors, cameras and infrared systems. It is probably true to say that HgCdTe is the third most studied semiconductor after silicon and gallium arsenide. Hg1-x Cd x Te is the material most widely used in high-performance infrared detectors at present. By changing the composition x the spectral response of the detector can be made to cover the range from 1 μm to beyond 17 μm. The advantages of this system arise from a number of features, notably: close lattice matching, high optical absorption coefficient, low carrier generation rate, high electron mobility and readily available doping techniques. These advantages mean that very sensitive infrared detectors can be produced at relatively high operating temperatures. Hg1-x Cd x Te multilayers can be readily grown in vapor-phase epitaxial processes. This provides the device engineer with complex doping and composition profiles that can be used to further enhance the electro-optic performance, leading to low-cost, large-area detectors in the future. The main purpose of this chapter is to describe the applications, device physics and technology of II-VI narrow-bandgap devices, focusing on HgCdTe but also including Hg1-x Mn x Te and Hg1-x Zn x Te. It concludes with a review of the research and development programs into third-generation infrared detector technology (so-called GEN III detectors) being performed in centers around the world.

Hydrogen separation process

Science.gov (United States)

Mundschau, Michael [Longmont, CO; Xie, Xiaobing [Foster City, CA; Evenson, IV, Carl; Grimmer, Paul [Longmont, CO; Wright, Harold [Longmont, CO

2011-05-24

A method for separating a hydrogen-rich product stream from a feed stream comprising hydrogen and at least one carbon-containing gas, comprising feeding the feed stream, at an inlet pressure greater than atmospheric pressure and a temperature greater than 200.degree. C., to a hydrogen separation membrane system comprising a membrane that is selectively permeable to hydrogen, and producing a hydrogen-rich permeate product stream on the permeate side of the membrane and a carbon dioxide-rich product raffinate stream on the raffinate side of the membrane. A method for separating a hydrogen-rich product stream from a feed stream comprising hydrogen and at least one carbon-containing gas, comprising feeding the feed stream, at an inlet pressure greater than atmospheric pressure and a temperature greater than 200.degree. C., to an integrated water gas shift/hydrogen separation membrane system wherein the hydrogen separation membrane system comprises a membrane that is selectively permeable to hydrogen, and producing a hydrogen-rich permeate product stream on the permeate side of the membrane and a carbon dioxide-rich product raffinate stream on the raffinate side of the membrane. A method for pretreating a membrane, comprising: heating the membrane to a desired operating temperature and desired feed pressure in a flow of inert gas for a sufficient time to cause the membrane to mechanically deform; decreasing the feed pressure to approximately ambient pressure; and optionally, flowing an oxidizing agent across the membrane before, during, or after deformation of the membrane. A method of supporting a hydrogen separation membrane system comprising selecting a hydrogen separation membrane system comprising one or more catalyst outer layers deposited on a hydrogen transport membrane layer and sealing the hydrogen separation membrane system to a porous support.

Hydrogen energy stations: along the roadside to the hydrogen economy

International Nuclear Information System (INIS)

Clark, W.W.; Rifkin, J.; O'Connor, T.; Swisher, J.; Lipman, T.; Rambach, G.

2005-01-01

Hydrogen has become more than an international topic of discussion within government and among industry. With the public announcements from the European Union and American governments and an Executive Order from the Governor of California, hydrogen has become a ''paradigm change'' targeted toward changing decades of economic and societal behaviours. The public demand for clean and green energy as well as being ''independent'' or not located in political or societal conflict areas, has become paramount. The key issues are the commitment of governments through public policies along with corporations. Above all, secondly, the advancement of hydrogen is regional as it depends upon infrastructure and fuel resources. Hence, the hydrogen economy, to which the hydrogen highway is the main component, will be regional and creative. New jobs, businesses and opportunities are already emerging. And finally, the costs for the hydrogen economy are critical. The debate as to hydrogen being 5 years away from being commercial and available in the marketplace versus needing more research and development contradicts the historical development and deployment of any new technology be it bio-science, flat panel displays, computers or mobile phones. The market drivers are government regulations and standards soon thereafter matched by market forces and mass production. Hydrogen is no different. What this paper does is describes is how the hydrogen highway is the backbone to the hydrogen economy by becoming, with the next five years, both regional and commercial through supplying stationary power to communities. Soon thereafter, within five to ten years, these same hydrogen stations will be serving hundreds and then thousands of hydrogen fuel powered vehicles. Hydrogen is the fuel for distributed energy generation and hence positively impacts the future of public and private power generators. The paradigm has already changed. (author)

Canadian Hydrogen Association workshop on building Canadian strength with hydrogen systems. Proceedings

International Nuclear Information System (INIS)

2006-01-01

The Canadian Hydrogen Association workshop on 'Building Canadian Strength with Hydrogen Systems' was held in Montreal, Quebec, Canada on October 19-20, 2006. Over 100 delegates attended the workshop and there were over 50 presentations made. The Canadian Hydrogen Association (CHA) promotes the development of a hydrogen infrastructure and the commercialization of new, efficient and economic methods that accelerate the adoption of hydrogen technologies that will eventually replace fossil-based energy systems to reduce greenhouse gas emissions. This workshop focused on defining the strategic direction of research and development that will define the future of hydrogen related energy developments across Canada. It provided a forum to strengthen the research, development and innovation linkages among government, industry and academia to build Canadian strength with hydrogen systems. The presentations described new technologies and the companies that are making small scale hydrogen and hydrogen powered vehicles. Other topics of discussion included storage issues, hydrogen safety, competition in the hydrogen market, hydrogen fuel cell opportunities, nuclear-based hydrogen production, and environmental impacts

Hydrogen in metals

CSIR Research Space (South Africa)

Carter, TJ

2001-04-01

Full Text Available .J. Cartera,*, L.A. Cornishb aAdvanced Engineering & Testing Services, MATTEK, CSIR, Private Bag X28, Auckland Park 2006, South Africa bSchool of Process and Materials Engineering, University of the Witwatersrand, Private Bag 3, P.O. WITS 2050, South Africa... are contrasted, and an unusual case study of hydrogen embrittlement of an alloy steel is presented. 7 2001 Published by Elsevier Science Ltd. Keywords: Hydrogen; Hydrogen-assisted cracking; Hydrogen damage; Hydrogen embrittlement 1. Introduction Hydrogen suC128...

Hydrogen-Assisted IC Engine Combustion as a Route to Hydrogen Implementation

Energy Technology Data Exchange (ETDEWEB)

Andre Boehman; Daniel Haworth

2008-09-30

The 'Freedom Car' Initiative announced by the Bush Administration has placed a significant emphasis on development of a hydrogen economy in the United States. While the hydrogen-fueled fuel-cell vehicle that is the focus of the 'Freedom Car' program would rely on electrochemical energy conversion, and despite the large amount of resources being devoted to its objectives, near-term implementation of hydrogen in the transportation sector is not likely to arise from fuel cell cars. Instead, fuel blending and ''hydrogen-assisted'' combustion are more realizable pathways for wide-scale hydrogen utilization within the next ten years. Thus, a large potential avenue for utilization of hydrogen in transportation applications is through blending with natural gas, since there is an existing market for natural-gas vehicles of various classes, and since hydrogen can provide a means of achieving even stricter emissions standards. Another potential avenue is through use of hydrogen to 'assist' diesel combustion to permit alternate combustion strategies that can achieve lower emissions and higher efficiency. This project focused on developing the underlying fundamental information to support technologies that will facilitate the introduction of coal-derived hydrogen into the market. Two paths were envisioned for hydrogen utilization in transportation applications. One is for hydrogen to be mixed with other fuels, specifically natural gas, to enhance performance in existing natural gas-fueled vehicles (e.g., transit buses) and provide a practical and marketable avenue to begin using hydrogen in the field. A second is to use hydrogen to enable alternative combustion modes in existing diesel engines, such as homogeneous charge compression ignition, to permit enhanced efficiency and reduced emissions. Thus, this project on hydrogen-assisted combustion encompassed two major objectives: (1) Optimization of hydrogen-natural gas mixture

Vanadium alloy membranes for high hydrogen permeability and suppressed hydrogen embrittlement

International Nuclear Information System (INIS)

Kim, Kwang Hee; Park, Hyeon Cheol; Lee, Jaeho; Cho, Eunseog; Lee, Sang Mock

2013-01-01

The structural properties and hydrogen permeation characteristics of ternary vanadium–iron–aluminum (V–Fe–Al) alloy were investigated. To achieve not only high hydrogen permeability but also strong resistance to hydrogen embrittlement, the alloy composition was modulated to show high hydrogen diffusivity but reduced hydrogen solubility. We demonstrated that matching the lattice constant to the value of pure V by co-alloying lattice-contracting and lattice-expanding elements was quite effective in maintaining high hydrogen diffusivity of pure V

Technical files. Hydrogen memento; Fiches techniques. Memento de l'hydrogene

Energy Technology Data Exchange (ETDEWEB)

NONE

2002-07-01

This document is a compilation of 30 technical files about hydrogen and its related technologies. These files cover the following aspects: general considerations (world energy consumption growth, contribution of developing countries, atmospheric pollution and greenhouse effect, health impacts, actions implemented at the world scale, role of hydrogen); glossary and acronyms; units used and conversions; world energy situation (primary production, sectoral consumption, demand trends, environmental impact, situation of fossil fuel reserves); French energy situation (primary sources, energy independence ratio, electric power status, evolutions and trends of the French energy demand); fuel cells; basic data on hydrogen (thermodynamic properties and data); hydrogen production by water electrolysis, application to small capacity systems; thermochemical water dissociation; water photo-electrolysis; hydrogen pipeline networks in the world; mechanical energy production; hydrogen thermal engines; aeronautic applications; research laboratories; industrial actors of the hydrogen sector (companies, activities, geographical situation, financial structure, strategy, R and D, cooperations, projects etc..); hydrogen flammability and explosiveness; transport and storage safety; standards and regulations about hydrogen safety in France, in Europe and in the rest of the world; hydrogen programs in the world; the programs financed by the European Union; the German programs; the programs in Island, France and UK; the programs in North America; the Japanese programs; table of the main recent R and D projects per type of program; light vehicles with fuel cells; the Daimler-Chrysler program. (J.S.)

Method for absorbing hydrogen using an oxidation resisant organic hydrogen getter

Science.gov (United States)

Shepodd, Timothy J [Livermore, CA; Buffleben, George M [Tracy, CA

2009-02-03

A composition for removing hydrogen from an atmosphere, comprising a mixture of a polyphenyl ether and a hydrogenation catalyst, preferably a precious metal catalyst, and most preferably platinum, is disclosed. This composition is stable in the presence of oxygen, will not polymerize or degrade upon exposure to temperatures in excess of 200.degree. C., or prolonged exposure to temperatures in the range of 100-300.degree. C. Moreover, these novel hydrogen getter materials can be used to efficiently remove hydrogen from mixtures of hydrogen/inert gas (e.g., He, Ar, N.sub.2), hydrogen/ammonia atmospheres, such as may be encountered in heat exchangers, and hydrogen/carbon dioxide atmospheres. Water vapor and common atmospheric gases have no adverse effect on the ability of these getter materials to absorb hydrogen.

Hydrogenation properties of Zr films under various conditions of hydrogen plasma

CERN Document Server

Yan Guo Qiang; Zhou Zhu Ying; Zhao Guo Qing; Hu Pei Gang; Luo Shun Zhong; Peng Shu Ming; Ding Wei; Long Xing Gui

2002-01-01

The hydrogenation properties of Zr samples with and without an Ni overlayer under various plasma conditions were investigated by means of non-Rutherford backscattering and elastic recoil detection analysis. The theoretical maximum hydrogen capacity, 66.7 at%, could be achieved at a hydrogen absolute pressure of approx 2 Pa and a substrate temperature of approx 393K for a plasma irradiation of only 10 min; this was significantly greater than that for gas hydrogenation under the same hydrogen pressure and substrate temperature. It was also found that the C and O contamination on the sample surface strongly influences the hydrogenation, and that the maximum equilibrium hydrogen content drops dramatically with the increasing total contamination. In addition, the influence of the Ni overlayer on the plasma hydrogenation is discussed

The hydrogen village: building hydrogen and fuel cell opportunities

International Nuclear Information System (INIS)

Smith, R.

2006-01-01

The presentation addressed the progress the Hydrogen Village Program has made in its first 24 months of existence and will provide an understanding of the development of new markets for emerging Hydrogen and Fuel Cell technologies based on first hand, real world experience. The Hydrogen Village (H2V) is an End User driven, Market Development Program designed to accelerate the sustainable commercialization of hydrogen and fuel cell technologies through awareness, education and early deployments throughout the greater Toronto area (GTA). The program is a collaborative public-private partnership of some 35 companies from a broad cross section of industry administered through Hydrogen and Fuel Cells Canada and funded by the Governments of Canada and Ontario. The intent of the H2V is to develop markets for Hydrogen and Fuel Cell technologies that benefit the local and global community. The following aspects of market development are specifically targeted: 1) Deployments: of near market technologies in all aspects of community life (stationary and mobile). All applications must be placed within the community and contact peoples in their day-to-day activity. End user involvement is critical to ensure that the applications chosen have a commercial justification and contribute to the complementary growth of the market. 2) Development: of a coordinated hydrogen delivery and equipment service infrastructure. The infrastructure will develop following the principles of conservation and sustainability. 3) Human and societal factors: - Public and Corporate policy, public education, Codes/ Standards/ Regulations - Opportunity for real world implementation and feedback on developing codes and standards - Build awareness among regulatory groups, public, and the media. The GTA Hydrogen Village is already well under way with strategically located projects covering a wide range of hydrogen and fuel cell applications including: Residential heat and power generation using solid oxide

Bandgap Engineering of InP QDs Through Shell Thickness and Composition

Energy Technology Data Exchange (ETDEWEB)

Dennis, Allison M. [Los Alamos National Laboratory; Mangum, Benjamin D. [Los Alamos National Laboratory; Piryatinski, Andrei [Los Alamos National Laboratory; Park, Young-Shin [Los Alamos National Laboratory; Htoon, Han [Los Alamos National Laboratory; Hollingsworth, Jennifer A. [Los Alamos National Laboratory

2012-06-21

Fields as diverse as biological imaging and telecommunications utilize the unique photophysical and electronic properties of nanocrystal quantum dots (NQDs). The development of new NQD compositions promises material properties optimized for specific applications, while addressing material toxicity. Indium phosphide (InP) offers a 'green' alternative to the traditional cadmium-based NQDs, but suffers from extreme susceptibility to oxidation. Coating InP cores with more stable shell materials significantly improves nanocrystal resistance to oxidation and photostability. We have investigated several new InP-based core-shell compositions, correlating our results with theoretical predictions of their optical and electronic properties. Specifically, we can tailor the InP core-shell QDs to a type-I, quasi-type-II, or type-II bandgap structure with emission wavelengths ranging from 500-1300 nm depending on the shell material used (ZnS, ZnSe, CdS, or CdSe) and the thickness of the shell. Single molecule microscopy assessments of photobleaching and blinking are used to correlate NQD properties with shell thickness.

Hydrogen Filling Station

Energy Technology Data Exchange (ETDEWEB)

Boehm, Robert F; Sabacky, Bruce; Anderson II, Everett B; Haberman, David; Al-Hassin, Mowafak; He, Xiaoming; Morriseau, Brian

2010-02-24

Hydrogen is an environmentally attractive transportation fuel that has the potential to displace fossil fuels. The Freedom CAR and Freedom FUEL initiatives emphasize the importance of hydrogen as a future transportation fuel. Presently, Las Vegas has one hydrogen fueling station powered by natural gas. However, the use of traditional sources of energy to produce hydrogen does not maximize the benefit. The hydrogen fueling station developed under this grant used electrolysis units and solar energy to produce hydrogen fuel. Water and electricity are furnished to the unit and the output is hydrogen and oxygen. Three vehicles were converted to utilize the hydrogen produced at the station. The vehicles were all equipped with different types of technologies. The vehicles were used in the day-to-day operation of the Las Vegas Valley Water District and monitoring was performed on efficiency, reliability and maintenance requirements. The research and demonstration utilized for the reconfiguration of these vehicles could lead to new technologies in vehicle development that could make hydrogen-fueled vehicles more cost effective, economical, efficient and more widely used. In order to advance the development of a hydrogen future in Southern Nevada, project partners recognized a need to bring various entities involved in hydrogen development and deployment together as a means of sharing knowledge and eliminating duplication of efforts. A road-mapping session was held in Las Vegas in June 2006. The Nevada State Energy Office, representatives from DOE, DOE contractors and LANL, NETL, NREL were present. Leadership from the National hydrogen Association Board of Directors also attended. As a result of this session, a roadmap for hydrogen development was created. This roadmap has the ability to become a tool for use by other road-mapping efforts in the hydrogen community. It could also become a standard template for other states or even countries to approach planning for a hydrogen

Analysis of hydrogen content and distribution in hydrogen storage alloys using neutron radiography

International Nuclear Information System (INIS)

Sakaguchi, Hiroki; Hatakeyama, Keisuke; Satake, Yuichi; Esaka, Takao; Fujine, Shigenori; Yoneda, Kenji; Kanda, Keiji

2000-01-01

Small amounts of hydrogen in hydrogen storage alloys, such as Mg 2 Ni, were detected using neutron radiography (NRG). Hydrogen concentrations in a hydrogenated solid solution were determined by this technique. Furthermore, we were able to obtain NRG images for an initial stage of hydrogen absorption in the hydrogen storage alloys. NRG would be a new measurement method to clarify the behavior of hydrogen in hydrogen storage alloys. (author)

Liquid-phase chemical hydrogen storage: catalytic hydrogen generation under ambient conditions.

Science.gov (United States)

Jiang, Hai-Long; Singh, Sanjay Kumar; Yan, Jun-Min; Zhang, Xin-Bo; Xu, Qiang

2010-05-25

There is a demand for a sufficient and sustainable energy supply. Hence, the search for applicable hydrogen storage materials is extremely important owing to the diversified merits of hydrogen energy. Lithium and sodium borohydride, ammonia borane, hydrazine, and formic acid have been extensively investigated as promising hydrogen storage materials based on their relatively high hydrogen content. Significant advances, such as hydrogen generation temperatures and reaction kinetics, have been made in the catalytic hydrolysis of aqueous lithium and sodium borohydride and ammonia borane as well as in the catalytic decomposition of hydrous hydrazine and formic acid. In this Minireview we briefly survey the research progresses in catalytic hydrogen generation from these liquid-phase chemical hydrogen storage materials.

Interface passivation and trap reduction via hydrogen fluoride for molybdenum disulfide on silicon oxide back-gate transistors

Science.gov (United States)

Hu, Yaoqiao; San Yip, Pak; Tang, Chak Wah; Lau, Kei May; Li, Qiang

2018-04-01

Layered semiconductor molybdenum disulfide (MoS2) has recently emerged as a promising material for flexible electronic and optoelectronic devices because of its finite bandgap and high degree of gate control. Here, we report a hydrogen fluoride (HF) passivation technique for improving the carrier mobility and interface quality of chemical vapor deposited monolayer MoS2 on a SiO2/Si substrate. After passivation, the fabricated MoS2 back-gate transistors demonstrate a more than double improvement in average electron mobility, a reduced gate hysteresis gap of 3 V, and a low interface trapped charge density of ˜5.8 × 1011 cm-2. The improvements are attributed to the satisfied interface dangling bonds, thus a reduction of interface trap states and trapped charges. Surface x-ray photoelectron spectroscopy analysis and first-principles simulation were performed to verify the HF passivation effect. The results here highlight the necessity of a MoS2/dielectric passivation strategy and provides a viable route for enhancing the performance of MoS2 nano-electronic devices.

Process for exchanging hydrogen isotopes between gaseous hydrogen and water

International Nuclear Information System (INIS)

Hindin, S.G.; Roberts, G.W.

1977-01-01

A process is described for exchanging isotopes (particularly tritium) between water and gaseous hydrogen. Isotope depleted gaseous hydrogen and water containing a hydrogen isotope are introduced into the vapour phase in a first reaction area. The steam and gaseous hydrogen are brought into contact with a supported metal catalyst in this area in a parallel flow at a temperature range of around 225 and 300 0 C. An effluent flow comprising a mixture of isotope enriched gaseous hydrogen and depleted steam is evacuated from this area and the steam condensed into liquid water [fr

Hydrogen energy applications

International Nuclear Information System (INIS)

Okken, P.A.

1992-10-01

For the Energy and Material consumption Scenarios (EMS), by which emission reduction of CO 2 and other greenhouse gases can be calculated, calculations are executed by means of the MARKAL model (MARket ALlocation, a process-oriented dynamic linear programming model to minimize the costs of the energy system) for the Netherlands energy economy in the period 2000-2040, using a variable CO 2 emission limit. The results of these calculations are published in a separate report (ECN-C--92-066). The use of hydrogen can play an important part in the above-mentioned period. An overview of several options to produce or use hydrogen is given and added to the MARKAL model. In this report techno-economical data and estimates were compiled for several H 2 -application options, which subsequently also are added to the MARKAL model. After a brief chapter on hydrogen and the impact on the reduction of CO 2 emission attention is paid to stationary and mobile applications. The stationary options concern the mixing of natural gas with 10% hydrogen, a 100% substitution of natural gas by hydrogen, the use of a direct steam generator (combustion of hydrogen by means of pure oxygen, followed by steam injection to produce steam), and the use of fuel cells. The mobile options concern the use of hydrogen in the transportation sector. In brief, attention is paid to a hydrogen passenger car with an Otto engine, and a hydrogen passenger car with a fuel cell, a hybrid (metal)-hydride car, a hydrogen truck, a truck with a methanol fuel cell, a hydrogen bus, an inland canal boat with a hydrogen fuel cell, and finally a hydrogen airplane. 2 figs., 15 tabs., 1 app., 26 refs

Bandgap engineering of lead-free double perovskite Cs{sub 2}AgBiBr{sub 6} through trivalent metal alloying

Energy Technology Data Exchange (ETDEWEB)

Du, Ke-zhao; Mitzi, David B. [Department of Mechanical Engineering and Materials Science, and Department of Chemistry, Duke University, Durham, NC (United States); Meng, Weiwei; Wang, Xiaoming; Yan, Yanfa [Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, OH (United States)

2017-07-03

The double perovskite family, A{sub 2}M{sup I}M{sup III}X{sub 6}, is a promising route to overcome the lead toxicity issue confronting the current photovoltaic (PV) standout, CH{sub 3}NH{sub 3}PbI{sub 3}. Given the generally large indirect band gap within most known double perovskites, band-gap engineering provides an important approach for targeting outstanding PV performance within this family. Using Cs{sub 2}AgBiBr{sub 6} as host, band-gap engineering through alloying of In{sup III}/Sb{sup III} has been demonstrated in the current work. Cs{sub 2}Ag(Bi{sub 1-x}M{sub x})Br{sub 6} (M=In, Sb) accommodates up to 75 % In{sup III} with increased band gap, and up to 37.5 % Sb{sup III} with reduced band gap; that is, enabling ca. 0.41 eV band gap modulation through introduction of the two metals, with smallest value of 1.86 eV for Cs{sub 2}Ag(Bi{sub 0.625}Sb{sub 0.375})Br{sub 6}. Band structure calculations indicate that opposite band gap shift directions associated with Sb/In substitution arise from different atomic configurations for these atoms. Associated photoluminescence and environmental stability of the three-metal systems are also assessed. (copyright 2017 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

Hydrogen millennium

International Nuclear Information System (INIS)

Bose, T.K.; Benard, P.

2000-05-01

The 10th Canadian Hydrogen Conference was held at the Hilton Hotel in Quebec City from May 28 to May 31, 2000. The topics discussed included current drivers for the hydrogen economy, the international response to these drivers, new initiatives, sustainable as well as biological and hydrocarbon-derived production of hydrogen, defense applications of fuel cells, hydrogen storage on metal hydrides and carbon nanostructures, stationary power and remote application, micro-fuel cells and portable applications, marketing aspects, fuel cell modeling, materials, safety, fuel cell vehicles and residential applications. (author)

Modification of hydrogen determinator for total hydrogen analysis in irradiated zircaloy cladding tube

International Nuclear Information System (INIS)

Park, Soon Dal; Choi, Kwnag Soon; Kim, Jong Goo; Joe, Kih Soo; Kim, Won Ho

1999-01-01

A hydrogen determinator was modified and installed in the glove box to analyse total hydrogen content in irradiated zircaloy tube. The analysis method of hydrogen is Inert Gas Fusion(IGF)-Thermal Conductivity Detection(TCD). The hydrogen recoveries of no tin method using Ti and Zr matrix standards, respectively, were available within 3 μg of hydrogen. Also the smaller size of sample showed the better hydrogen recovery. It was found that the hydrogen standard of Ti matrix is available to hydrogen analysis in zircaloy sample. The mean radioactivity of irradiated zircaloy sample was 10 mR/hr and hydrogen concentration was 130 ppm

Hydrogen exchange

DEFF Research Database (Denmark)

Jensen, Pernille Foged; Rand, Kasper Dyrberg

2016-01-01

Hydrogen exchange (HX) monitored by mass spectrometry (MS) is a powerful analytical method for investigation of protein conformation and dynamics. HX-MS monitors isotopic exchange of hydrogen in protein backbone amides and thus serves as a sensitive method for probing protein conformation...... and dynamics along the entire protein backbone. This chapter describes the exchange of backbone amide hydrogen which is highly quenchable as it is strongly dependent on the pH and temperature. The HX rates of backbone amide hydrogen are sensitive and very useful probes of protein conformation......, as they are distributed along the polypeptide backbone and form the fundamental hydrogen-bonding networks of basic secondary structure. The effect of pressure on HX in unstructured polypeptides (poly-dl-lysine and oxidatively unfolded ribonuclease A) and native folded proteins (lysozyme and ribonuclease A) was evaluated...

Decoration of PbS nanoparticles on Al-doped ZnO nanorod array thin film with hydrogen treatment as a photoelectrode for solar water splitting

Energy Technology Data Exchange (ETDEWEB)

Hsu, Chih-Hsiung; Chen, Chao-Hong [Department of Chemical Engineering and Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan, ROC (China); Chen, Dong-Hwang, E-mail: chendh@mail.ncku.edu.tw [Department of Chemical Engineering and Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan, ROC (China)

2013-03-25

Highlights: ► AZO nanorod array thin film is used as a photoanode for solar water splitting. ► Hydrogen treatment and sensitization by PbS nanoparticles enhance photocurrent. ► A novel ITO/FTO-free composite photoelectrode is developed. ► The pre-fabrication and use of an extra TCO thin film substrate is unnecessary. -- Abstract: Al-doped ZnO (AZO) nanorod arrays thin film with hydrogen treatment is directly used as a photoelectrode for solar water splitting without an extra transparent conducting oxide (TCO) thin film because it possesses the functions of TCO thin film and photoactive 1-dimensional nanostructured semiconductor simultaneously. To enhance the absorption in the visible region, PbS nanoparticles decorated the AZO nanorods via successive ionic layer adsorption and reaction route. The PbS nanoparticles have a face-centered cubic structure and their decoration does not destroy the 1-dimensional morphology of AZO nanorod arrays. With increasing the cycle number of PbS nanoparticles decoration, the grain size and loading of PbS nanoparticles become larger gradually which leads to lower energy bandgap and stronger absorption. A maximum photocurrent density of 1.65 mW cm{sup −2} is obtained when the cycle number is 20, which is much higher than those without PbS nanoparticles sensitization or hydrogen treatment. This demonstrates that the AZO nanorod array thin film with hydrogen treatment can be directly used as a photoelectrode without an extra TCO thin film. Because the use of expensive metals can be avoided and the pre-fabrication of TCO thin film substrate is necessary no more, the fabrication of such a composite photoelectrode becomes simple and low-cost. So, it has great potentials in solar water splitting after sensitization by quantum dots capable of visible light absorption.

Hydrogen energy systems studies

Energy Technology Data Exchange (ETDEWEB)

Ogden, J.M.; Kreutz, T.G.; Steinbugler, M. [Princeton Univ., NJ (United States)] [and others

1996-10-01

In this report the authors describe results from technical and economic assessments carried out during the past year with support from the USDOE Hydrogen R&D Program. (1) Assessment of technologies for small scale production of hydrogen from natural gas. Because of the cost and logistics of transporting and storing hydrogen, it may be preferable to produce hydrogen at the point of use from more readily available energy carriers such as natural gas or electricity. In this task the authors assess near term technologies for producing hydrogen from natural gas at small scale including steam reforming, partial oxidation and autothermal reforming. (2) Case study of developing a hydrogen vehicle refueling infrastructure in Southern California. Many analysts suggest that the first widespread use of hydrogen energy is likely to be in zero emission vehicles in Southern California. Several hundred thousand zero emission automobiles are projected for the Los Angeles Basin alone by 2010, if mandated levels are implemented. Assuming that hydrogen vehicles capture a significant fraction of this market, a large demand for hydrogen fuel could evolve over the next few decades. Refueling a large number of hydrogen vehicles poses significant challenges. In this task the authors assess near term options for producing and delivering gaseous hydrogen transportation fuel to users in Southern California including: (1) hydrogen produced from natural gas in a large, centralized steam reforming plant, and delivered to refueling stations via liquid hydrogen truck or small scale hydrogen gas pipeline, (2) hydrogen produced at the refueling station via small scale steam reforming of natural gas, (3) hydrogen produced via small scale electrolysis at the refueling station, and (4) hydrogen from low cost chemical industry sources (e.g. excess capacity in refineries which have recently upgraded their hydrogen production capacity, etc.).

Questioning hydrogen

International Nuclear Information System (INIS)

Hammerschlag, Roel; Mazza, Patrick

2005-01-01

As an energy carrier, hydrogen is to be compared to electricity, the only widespread and viable alternative. When hydrogen is used to transmit renewable electricity, only 51% can reach the end user due to losses in electrolysis, hydrogen compression, and the fuel cell. In contrast, conventional electric storage technologies allow between 75% and 85% of the original electricity to be delivered. Even when hydrogen is extracted from gasified coal (with carbon sequestration) or from water cracked in high-temperature nuclear reactors, more of the primary energy reaches the end user if a conventional electric process is used instead. Hydrogen performs no better in mobile applications, where electric vehicles that are far closer to commercialization exceed fuel cell vehicles in efficiency, cost and performance. New, carbon-neutral energy can prevent twice the quantity of GHG's by displacing fossil electricity than it can by powering fuel cell vehicles. The same is true for new, natural gas energy. New energy resources should be used to displace high-GHG electric generation, not to manufacture hydrogen

On the Integration of Wide Band-gap Semiconductors in Single Phase Boost PFC Converters

DEFF Research Database (Denmark)

Hernandez Botella, Juan Carlos

Power semiconductor technology has dominated the evolution of switched mode power supplies (SMPS). Advances in silicon (Si) technology, as the introduction of metal oxide field effect transistor (MOSFET), isolated gate bipolar transistors (IGBT), superjunction vertical structures and Schottky...... diodes, or the introduction of silicon carbide (SiC) diodes, provided large steps in miniaturization and efficiency improvement of switched mode power converters. Gallium nitride (GaN) and SiC semiconductor devices have already been around for some years. The first one proliferated due to the necessity...... of high frequency operation in optoelectronics applications. On the other hand, Schottky SiC power diodes were introduced in 2001 as an alternative to eliminate reverse recovery issues in Si rectifiers. Wide band-gap semiconductors offer an increased electrical field strength and electron mobility...

Radiation resistance of wide-bandgap semiconductor power transistors

Energy Technology Data Exchange (ETDEWEB)

Hazdra, Pavel; Popelka, Stanislav [Department of Microelectronics, Czech Technical University in Prague (Czech Republic)

2017-04-15

Radiation resistance of state-of-the-art commercial wide-bandgap power transistors, 1700 V 4H-SiC power MOSFETs and 200 V GaN HEMTs, to the total ionization dose was investigated. Transistors were irradiated with 4.5 MeV electrons with doses up to 2000 kGy. Electrical characteristics and introduced defects were characterized by current-voltage (I-V), capacitance-voltage (C-V), and deep level transient spectroscopy (DLTS) measurements. Results show that already low doses of 4.5 MeV electrons (>1 kGy) cause a significant decrease in threshold voltage of SiC MOSFETs due to embedding of the positive charge into the gate oxide. On the other hand, other parameters like the ON-state resistance are nearly unchanged up to the dose of 20 kGy. At 200 kGy, the threshold voltage returns back close to its original value, however, the ON-state resistance increases and transconductance is lowered. This effect is caused by radiation defects introduced into the low-doped drift region which decrease electron concentration and mobility. GaN HEMTs exhibit significantly higher radiation resistance. They keep within the datasheet specification up to doses of 2000 kGy. Absence of dielectric layer beneath the gate and high concentration of carriers in the two dimensional electron gas channel are the reasons of higher radiation resistance of GaN HEMTs. Their degradation then occurs at much higher doses due to electron mobility degradation. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Hydrogen in oxygen-free, phosphorus-doped copper-Charging techniques, hydrogen contents and modelling of hydrogen diffusion and depth profile

International Nuclear Information System (INIS)

Martinsson, Aasa; Sandstroem, Rolf; Lilja, Christina

2013-01-01

In Sweden spent nuclear fuel is planned to be disposed of by encapsulating in cast iron inserts protected by a copper shell. The copper can be exposed to hydrogen released during corrosion processes in the inserts. If the hydrogen is taken up by the copper, it could lead to hydrogen embrittlement. Specimens from oxygen-free copper have been hydrogen charged using two different methods. The purpose was to investigate how hydrogen could be introduced into copper in a controlled way. The thermal charging method resulted in a reduction of the initial hydrogen content. After electrochemical charging of cylindrical specimens, the measured hydrogen content was 2.6 wt. ppm which should compared with 0.6 wt. ppm before charging. The retained hydrogen after two weeks was reduced by nearly 40%. Recently the paper 'Hydrogen depth profile in phosphorus-doped, oxygen-free copper after cathodic charging' (Martinsson and Sandstrom, 2012) has been published. The paper describes experimental results for bulk specimens as well as presenting a model. Almost all the hydrogen is found to be located less than 100 μm from the surface. This model is used to interpret the experimental results on foils in the present report. Since the model is fully based on fundamental equations, it can be used to analyse what happens in new situations. In this report the effect of the charging intensity, the grain size, the critical nucleus size for hydrogen bubble formation as well as the charging time are analysed

Hydrogen in oxygen-free, phosphorus-doped copper - Charging techniques, hydrogen contents and modelling of hydrogen diffusion and depth profile

Energy Technology Data Exchange (ETDEWEB)

Martinsson, Aasa [Swerea KIMAB, Kista (Sweden); Sandstroem, Rolf [Swerea KIMAB, Kista (Sweden); Div. of Materials Science and Engineering, KTH Royal Institute of Technology, Stockholm (Sweden); Lilja, Christina [Swedish Nuclear Fuel and Waste Management Co., Stockholm (Sweden)

2013-01-15

In Sweden spent nuclear fuel is planned to be disposed of by encapsulating in cast iron inserts protected by a copper shell. The copper can be exposed to hydrogen released during corrosion processes in the inserts. If the hydrogen is taken up by the copper, it could lead to hydrogen embrittlement. Specimens from oxygen-free copper have been hydrogen charged using two different methods. The purpose was to investigate how hydrogen could be introduced into copper in a controlled way. The thermal charging method resulted in a reduction of the initial hydrogen content. After electrochemical charging of cylindrical specimens, the measured hydrogen content was 2.6 wt. ppm which should compared with 0.6 wt. ppm before charging. The retained hydrogen after two weeks was reduced by nearly 40%. Recently the paper 'Hydrogen depth profile in phosphorus-doped, oxygen-free copper after cathodic charging' (Martinsson and Sandstrom, 2012) has been published. The paper describes experimental results for bulk specimens as well as presenting a model. Almost all the hydrogen is found to be located less than 100 {mu}m from the surface. This model is used to interpret the experimental results on foils in the present report. Since the model is fully based on fundamental equations, it can be used to analyse what happens in new situations. In this report the effect of the charging intensity, the grain size, the critical nucleus size for hydrogen bubble formation as well as the charging time are analysed.

Hydrogen at the Rooftop: Compact CPV-Hydrogen system to Convert Sunlight to Hydrogen

KAUST Repository

Burhan, Muhammad

2017-12-27

Despite being highest potential energy source, solar intermittency and low power density make it difficult for solar energy to compete with the conventional power plants. Highly efficient concentrated photovoltaic (CPV) system provides best technology to be paired with the electrolytic hydrogen production, as a sustainable energy source with long term energy storage. However, the conventional gigantic design of CPV system limits its market and application to the open desert fields without any rooftop installation scope, unlike conventional PV. This makes CPV less popular among solar energy customers. This paper discusses the development of compact CPV-Hydrogen system for the rooftop application in the urban region. The in-house built compact CPV system works with hybrid solar tracking of 0.1° accuracy, ensured through proposed double lens collimator based solar tracking sensor. With PEM based electrolyser, the compact CPV-hydrogen system showed 28% CPV efficiency and 18% sunlight to hydrogen (STH) efficiency, for rooftop operation in tropical region of Singapore. For plant designers, the solar to hydrogen production rating of 217 kWh/kg has been presented with 15% STH daily average efficiency, recorded from the long term field operation of the system.

Hydrogen at the Rooftop: Compact CPV-Hydrogen system to Convert Sunlight to Hydrogen

KAUST Repository

Burhan, Muhammad; Wakil Shahzad, Muhammad; Ng, Kim Choon

2017-01-01

Despite being highest potential energy source, solar intermittency and low power density make it difficult for solar energy to compete with the conventional power plants. Highly efficient concentrated photovoltaic (CPV) system provides best technology to be paired with the electrolytic hydrogen production, as a sustainable energy source with long term energy storage. However, the conventional gigantic design of CPV system limits its market and application to the open desert fields without any rooftop installation scope, unlike conventional PV. This makes CPV less popular among solar energy customers. This paper discusses the development of compact CPV-Hydrogen system for the rooftop application in the urban region. The in-house built compact CPV system works with hybrid solar tracking of 0.1° accuracy, ensured through proposed double lens collimator based solar tracking sensor. With PEM based electrolyser, the compact CPV-hydrogen system showed 28% CPV efficiency and 18% sunlight to hydrogen (STH) efficiency, for rooftop operation in tropical region of Singapore. For plant designers, the solar to hydrogen production rating of 217 kWh/kg has been presented with 15% STH daily average efficiency, recorded from the long term field operation of the system.

Trapping and detrapping of hydrogen in graphite materials exposed to hydrogen gas

International Nuclear Information System (INIS)

Atsumi, Hisao; Iseki, Michio; Shikama, Tatsuo.

1994-01-01

Measurements of hydrogen solubility have been performed for several unirradiated and neutron-irradiated graphite (and CFC) samples at temperatures between 973 and 1323 K under a ∼10 kPa hydrogen atmosphere. The hydrogen dissolution process has been studied and it is discussed here. The values of hydrogen solubility vary substantially among the samples up to about a factor of 16. A strong correlation has been observed between the values of hydrogen solubility and the degrees of graphitization determined by X-ray diffraction technique. The relation can be extended even for the neutron irradiated samples. Hydrogen dissolution into graphite can be explained with the trapping of hydrogen at defect sites (e.g. dangling carbon bonds) considering an equilibrium reaction between hydrogen molecules and the trapping sites. The migration of hydrogen in graphite is speculated to result from a sequence of detrapping and retrapping events with high energy activation processes. (author)

Technical files. Hydrogen memento; Fiches techniques. Memento de l'hydrogene

Energy Technology Data Exchange (ETDEWEB)

NONE

2002-07-01

This document is a compilation of 30 technical files about hydrogen and its related technologies. These files cover the following aspects: general considerations (world energy consumption growth, contribution of developing countries, atmospheric pollution and greenhouse effect, health impacts, actions implemented at the world scale, role of hydrogen); glossary and acronyms; units used and conversions; world energy situation (primary production, sectoral consumption, demand trends, environmental impact, situation of fossil fuel reserves); French energy situation (primary sources, energy independence ratio, electric power status, evolutions and trends of the French energy demand); fuel cells; basic data on hydrogen (thermodynamic properties and data); hydrogen production by water electrolysis, application to small capacity systems; thermochemical water dissociation; water photo-electrolysis; hydrogen pipeline networks in the world; mechanical energy production; hydrogen thermal engines; aeronautic applications; research laboratories; industrial actors of the hydrogen sector (companies, activities, geographical situation, financial structure, strategy, R and D, cooperations, projects etc..); hydrogen flammability and explosiveness; transport and storage safety; standards and regulations about hydrogen safety in France, in Europe and in the rest of the world; hydrogen programs in the world; the programs financed by the European Union; the German programs; the programs in Island, France and UK; the programs in North America; the Japanese programs; table of the main recent R and D projects per type of program; light vehicles with fuel cells; the Daimler-Chrysler program. (J.S.)

Process for exchanging hydrogen isotopes between gaseous hydrogen and water

International Nuclear Information System (INIS)

Hindin, S. G.; Roberts, G. W.

1980-01-01

A process for exchanging isotopes of hydrogen, particularly tritium, between gaseous hydrogen and water is provided whereby gaseous hydrogen depeleted in tritium and liquid or gaseous water containing tritium are reacted in the presence of a metallic catalyst

BIG hydrogen: hydrogen technology in the oil and gas sector

International Nuclear Information System (INIS)

2006-01-01

The BIG Hydrogen workshop was held in Calgary, Alberta, Canada on February 13, 2006. About 60 representatives of industry, academia and government attended this one-day technical meeting on hydrogen production for the oil and gas industry. The following themes were identified from the presentations and discussion: the need to find a BIG hydrogen replacement for Steam Methane Reformer (SMR) because of uncertainty regarding cost and availability of natural gas, although given the maturity of SMR process (reliability, known capital cost) how high will H2 prices have to rise?; need for a national strategy to link the near-term and the longer-term hydrogen production requirements, which can take hydrogen from chemical feedstock to energy carrier; and in the near-term Canada should get involved in demonstrations and build expertise in large hydrogen systems including production and carbon capture and sequestration

Florida Hydrogen Initiative

Energy Technology Data Exchange (ETDEWEB)

Block, David L

2013-06-30

The Florida Hydrogen Initiative (FHI) was a research, development and demonstration hydrogen and fuel cell program. The FHI program objectives were to develop Florida?s hydrogen and fuel cell infrastructure and to assist DOE in its hydrogen and fuel cell activities The FHI program funded 12 RD&D projects as follows: Hydrogen Refueling Infrastructure and Rental Car Strategies -- L. Lines, Rollins College This project analyzes strategies for Florida's early stage adaptation of hydrogen-powered public transportation. In particular, the report investigates urban and statewide network of refueling stations and the feasibility of establishing a hydrogen rental-car fleet based in Orlando. Methanol Fuel Cell Vehicle Charging Station at Florida Atlantic University ? M. Fuchs, EnerFuel, Inc. The project objectives were to design, and demonstrate a 10 kWnet proton exchange membrane fuel cell stationary power plant operating on methanol, to achieve an electrical energy efficiency of 32% and to demonstrate transient response time of less than 3 milliseconds. Assessment of Public Understanding of the Hydrogen Economy Through Science Center Exhibits, J. Newman, Orlando Science Center The project objective was to design and build an interactive Science Center exhibit called: ?H2Now: the Great Hydrogen Xchange?. On-site Reformation of Diesel Fuel for Hydrogen Fueling Station Applications ? A. Raissi, Florida Solar Energy Center This project developed an on-demand forecourt hydrogen production technology by catalytically converting high-sulfur hydrocarbon fuels to an essentially sulfur-free gas. The removal of sulfur from reformate is critical since most catalysts used for the steam reformation have limited sulfur tolerance. Chemochromic Hydrogen Leak Detectors for Safety Monitoring ? N. Mohajeri and N. Muradov, Florida Solar Energy Center This project developed and demonstrated a cost-effective and highly selective chemochromic (visual) hydrogen leak detector for safety

New efficient hydrogen process production from organosilane hydrogen carriers derivatives

Energy Technology Data Exchange (ETDEWEB)

Brunel, Jean Michel [Unite URMITE, UMR 6236 CNRS, Faculte de Medecine et de Pharmacie, Universite de la Mediterranee, 27 boulevard Jean Moulin, 13385 Marseille 05 (France)

2010-04-15

While the source of hydrogen constitutes a significant scientific challenge, addressing issues of hydrogen storage, transport, and delivery is equally important. None of the current hydrogen storage options, liquefied or high pressure H{sub 2} gas, metal hydrides, etc.. satisfy criteria of size, costs, kinetics, and safety for use in transportation. In this context, we have discovered a methodology for the production of hydrogen on demand, in high yield, under kinetic control, from organosilane hydrogen carriers derivatives and methanol as co-reagent under mild conditions catalyzed by a cheap ammonium fluoride salt. Finally, the silicon by-products can be efficiently recycle leading to an environmentally friendly source of energy. (author)

The Lattice Compatibility Theory LCT: Physical and Chemical Arguments from the Growth Behavior of Doped Compounds in terms of Bandgap Distortion and Magnetic Effects

Directory of Open Access Journals (Sweden)

K. Boubaker

2013-01-01

Full Text Available Physical and chemical arguments for the recently discussed materials-related Lattice Compatibility Theory are presented. The discussed arguments are based on some differences of Mn ions incorporation kinetics inside some compounds. These differences have been evaluated and quantified in terms of alteration of bandgap edges, magnetic patterns, and Faraday effect.

Effect of hydrogen coverage on hydrogenation of o-cresol on Pt(111)

Science.gov (United States)

Li, Yaping; Liu, Zhimin; Crossley, Steven P.; Jentoft, Friederike C.; Wang, Sanwu

2018-06-01

The conversion of phenolics over metal catalysts is an important process for upgrading biofuels. With density functional calculations, hydrogenation of o-cresol on the hydrogen-covered Pt(111) surface was investigated. The results show that the coverage of hydrogen plays a significant role in the reaction rate while it does not affect the reaction selectivity. The reaction barriers of the hydrogenation process leading to the formation of both 2-methyl-cyclohexanone (the intermediate product) and 2-methyl-cyclohexanol (the final product) at high H coverages (∼1 ML) are found to be smaller by 0.14-0.69 eV than those at lower H coverages (∼1/25 ML). After both hydrogen and cresol are adsorbed on Pt(111) from their initial gas phase state, the reaction energy of each hydrogenation step on the surface is also dependent on the hydrogen coverage. On the H-covered Pt(111) surface, most steps of hydrogenation involve exothermic reactions when the hydrogen coverage is high while they are endothermic reactions at low hydrogen coverages. The differences in reaction rate and reaction energy between high and low H coverages can be understood with the coverage-dependent bonding strength and configurations.

Microvoid channel polymer photonic crystals with large infrared stop gaps and a multitude of higher-order bandgaps fabricated by femtosecond laser drilling in solid resin

International Nuclear Information System (INIS)

Straub, M.; Ventura, M.; Gu, M.

2004-01-01

Photosensitive polymer materials are ideally suited for laser-induced micro- and nanostructuring, as structural and compositional changes are achieved already under exposure to moderate intensities of high-repetition rate ultrashort-pulsed light. Photonic crystals with bandgaps in the infrared or the visible spectral region are a particularly interesting application, because highly correlated structural elements at a size of only a few hundred nanometers are required. We fabricated infrared photonic crystals based on microvoid channels inside solid polymer material. Femtosecond-pulsed visible light was focused into UV-cured Norland NOA63 resin by a high numerical aperture objective. In the focal spot microexplosions drive the material out of the center of the focus. Void channels of 0.7-1.3 μm diameter are generated by translating the sample along a preprogrammed pathway. Woodpile structures of void channels at layer spacings of 1.6-2.6 μm and in-plane channel spacings of 1.2-1.3 μm allowed for bandgap-induced suppression of infrared transmission in the stacking direction of as much as 86% by only 20 layers. As these structures are highly correlated and do not contain many imperfections, up to three higher-order stop gaps are observed. Consistent with theory, the number and gapwidth of higher-order gaps strongly increases with the ratio between layer- and in-plane spacing. Due to their low refractive index contrast and the missing interconnectivity of voids our structures do not provide complete photonic bandgaps. However, their manifold of sizable higher-order gaps allows for the engineering of photonic stop gaps down to the near-infrared wavelength region using comparatively large structural dimensions

Disappearance of dielectric anomaly in spite of presence of structural phase transition in reduced BaTiO3: Effect of defect states within the bandgap

Science.gov (United States)

Sagdeo, Archna; Nagwanshi, Anjali; Pokhriyal, Preeti; Sinha, A. K.; Rajput, Parasmani; Mishra, Vikash; Sagdeo, P. R.

2018-04-01

We report the structural, optical, ferroelectric, and dielectric properties of reduced BaTiO3 samples. For this purpose, oxygen vacancies in BaTiO3 are created by heating these samples with a Ti metal in a vacuum environment at different temperatures. It is observed that with an increase in oxygen deficiencies, the c/a ratio decreases as compared to that of the oxygen treated sample. The ferroelectric properties of the oxygen deficient samples are visibly different as compared to those of the oxygen treated sample. The disappearance of the P-E loop and the anomaly in the temperature variation of the dielectric constant have been observed; however, the structural phase transition corresponding to ferroelectric phase transitions still persists. Thus, it appears that the anomaly in dielectric data and the presence of the P-E loop are getting masked possibly by the Maxwell-Wagner effect. The presence of Ti+3 states in the prepared samples has been confirmed by X-ray absorption near edge structure measurements. The Kubelka-Munk optical absorption shows the presence of extra states below fundamental transition, indicating the emergence of new electronic states within the bandgap, which might be due to Ti+3 states. These new states appear at different energy positions, and with different intensities for different samples, which are reduced in the presence of Ti. These new states within the bandgap appear to modify the electronic structure, thereby reducing the overall bandgap, and hence, they seem to modify the ferroelectric and dielectric properties of the samples. Our results may be treated as experimental evidence for theoretically proposed defect states in oxygen deficient or reduced BaTiO3.

Hydrogen distribution in a containment with a high-velocity hydrogen-steam source

International Nuclear Information System (INIS)

Bloom, G.R.; Muhlestein, L.D.; Postma, A.K.; Claybrook, S.W.

1982-09-01

Hydrogen mixing and distribution tests are reported for a modeled high velocity hydrogen-steam release from a postulated small pipe break or release from a pressurizer relief tank rupture disk into the lower compartment of an Ice Condenser Plant. The tests, which in most cases used helium as a simulant for hydrogen, demonstrated that the lower compartment gas was well mixed for both hydrogen release conditions used. The gas concentration differences between any spatial locations were less than 3 volume percent during the hydrogen/steam release period and were reduced to less than 0.5 volume percent within 20 minutes after termination of the hydrogen source. The high velocity hydrogen/steam jet provided the dominant mixing mechanism; however, natural convection and forced air recirculation played important roles in providing a well mixed atmosphere following termination of the hydrogen source. 5 figures, 4 tables

Large bandgap blueshifts in the InGaP/InAlGaP laser structure using novel strain-induced quantum well intermixing

Energy Technology Data Exchange (ETDEWEB)

Al-Jabr, A. A.; Majid, M. A.; Alias, M. S.; Ng, T. K.; Ooi, B. S., E-mail: boon.ooi@kaust.edu.sa [Photonics Laboratory, King Abdullah University of Science & Technology (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia (KSA) (Saudi Arabia); Anjum, D. H. [Advanced Nanofabrication, Imaging and Characterization Core Facilities, (KAUST), Thuwal 23955-6900, Kingdom of Saudi Arabia (KSA) (Saudi Arabia)

2016-04-07

We report on a novel quantum well intermixing (QWI) technique that induces a large degree of bandgap blueshift in the InGaP/InAlGaP laser structure. In this technique, high external compressive strain induced by a thick layer of SiO{sub 2} cap with a thickness ≥1 μm was used to enhance QWI in the tensile-strained InGaP/InAlGaP quantum well layer. A bandgap blueshift as large as 200 meV was observed in samples capped with 1-μm SiO{sub 2} and annealed at 1000 °C for 120 s. To further enhance the degree of QWI, cycles of annealing steps were applied to the SiO{sub 2} cap. Using this method, wavelength tunability over the range of 640 nm to 565 nm (∼250 meV) was demonstrated. Light-emitting diodes emitting at red (628 nm), orange (602 nm), and yellow (585 nm) wavelengths were successfully fabricated on the intermixed samples. Our results show that this new QWI method technique may pave the way for the realization of high-efficiency orange and yellow light-emitting devices based on the InGaP/InAlGaP material system.

Novel developments in hydrogen storage, hydrogen activation and ionic liquids

Energy Technology Data Exchange (ETDEWEB)

Doroodian, Amir

2010-12-03

This dissertation is divided into three chapters. Recently, metal-free hydrogen activation using phosphorous compounds has been reported in science magazine. We have investigated the interaction between hydrogen and phosphorous compounds in presence of strong Lewis acids (chapter one). A new generation of metal-free hydrogen activation, using amines and strong Lewis acids with sterically demanding nature, was already developed in our group. Shortage of high storage capacity using large substitution to improve sterical effect led us to explore the amine borane derivatives, which are explained in chapter two. Due to the high storage capacity of hydrogen in aminoborane derivatives, we have explored these materials to extend hydrogen release. These compounds store hydrogen as proton and hydride on adjacent atoms or ions. These investigations resulted in developing hydrogen storage based on ionic liquids containing methyl guanidinium cation. Then we have continued to develop ionic liquids based on methyl guanidinium cation with different anions, such as tetrafluoro borate (chapter three). We have replaced these anions with transition metal anions to investigate hydrogen bonding and catalytic activity of ionic liquids. This chapter illustrates the world of ionic liquid as a green solvent for organic, inorganic and catalytic reactions and combines the concept of catalysts and solvents based on ionic liquids. The catalytic activity is investigated particularly with respect to the interaction with CO{sub 2}. (orig.)

Unusual hydrogen bonding in L-cysteine hydrogen fluoride.

Science.gov (United States)

Minkov, V S; Ghazaryan, V V; Boldyreva, E V; Petrosyan, A M

2015-08-01

L-Cysteine hydrogen fluoride, or bis(L-cysteinium) difluoride-L-cysteine-hydrogen fluoride (1/1/1), 2C3H8NO2S(+)·2F(-)·C3H7NO2S·HF or L-Cys(+)(L-Cys···L-Cys(+))F(-)(F(-)...H-F), provides the first example of a structure with cations of the 'triglycine sulfate' type, i.e. A(+)(A···A(+)) (where A and A(+) are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter-ion. The salt crystallizes in the monoclinic system with the space group P2(1). The dimeric (L-Cys···L-Cys(+)) cation and the dimeric (F(-)···H-F) anion are formed via strong O-H···O or F-H···F hydrogen bonds, respectively, with very short O···O [2.4438 (19) Å] and F···F distances [2.2676 (17) Å]. The F···F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O-H···F type, formed by a L-cysteinium cation and a fluoride ion. The corresponding O···F distance of 2.3412 (19) Å seems to be the shortest among O-H···F and F-H···O hydrogen bonds known to date. The single-crystal X-ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above-mentioned hydrogen bonds.

Hydrogen production using Rhodopseudomonas palustris WP 3-5 with hydrogen fermentation reactor effluent

International Nuclear Information System (INIS)

Chi-Mei Lee; Kuo-Tsang Hung

2006-01-01

The possibility of utilizing the dark hydrogen fermentation stage effluents for photo hydrogen production using purple non-sulfur bacteria should be elucidated. In the previous experiments, Rhodopseudomonas palustris WP3-5 was proven to efficiently produce hydrogen from the effluent of hydrogen fermentation reactors. The highest hydrogen production rate was obtained at a HRT value of 48 h when feeding a 5 fold effluent dilution from anaerobic hydrogen fermentation. Besides, hydrogen production occurred only when the NH 4 + concentration was below 17 mg-NH 4 + /l. Therefore, for successful fermentation effluent utilization, the most important things were to decrease the optimal HRT, increase the optimal substrate concentration and increase the tolerable ammonia concentration. In this study, a lab-scale serial photo-bioreactor was constructed. The reactor overall hydrogen production efficiency with synthetic wastewater exhibiting an organic acid profile identical to that of anaerobic hydrogen fermentation reactor effluent and with effluent from two anaerobic hydrogen fermentation reactors was evaluated. (authors)

Metal hydrides for hydrogen storage in nickel hydrogen batteries

International Nuclear Information System (INIS)

Bittner, H.F.; Badcock, C.C.; Quinzio, M.V.

1984-01-01

Metal hydride hydrogen storage in nickel hydrogen (Ni/H 2 ) batteries has been shown to increase battery energy density and improve battery heat management capabilities. However the properties of metal hydrides in a Ni/H 2 battery environment, which contains water vapor and oxygen in addition to the hydrogen, have not been well characterized. This work evaluates the use of hydrides in Ni/H 2 batteries by fundamental characterization of metal hydride properties in a Ni/H 2 cell environment. Hydrogen sorption properties of various hydrides have been measured in a Ni/H 2 cell environment. Results of detailed thermodynamic and kinetic studies of hydrogen sorption in LaNi 5 in a Ni/H 2 cell environment are presented. Long-term cycling studies indicate that degradation of the hydride can be minimized by cycling between certain pressure limits. A model describing the mechanism of hydride degradation is presented

Hydrogen, energy of the future?

International Nuclear Information System (INIS)

Alleau, Th.

2007-01-01

A cheap, non-polluting energy with no greenhouse gas emissions and unlimited resources? This is towards this fantastic future that this book brings us, analyzing the complex but promising question of hydrogen. The scientific and technical aspects of production, transport, storage and distribution raised by hydrogen are thoroughly reviewed. Content: I) Energy, which solutions?: 1 - hydrogen, a future; 2 - hydrogen, a foreseeable solution?; II) Hydrogen, an energy vector: 3 - characteristics of hydrogen (physical data, quality and drawbacks); 4 - hydrogen production (from fossil fuels, from water, from biomass, bio-hydrogen generation); 5 - transport, storage and distribution of hydrogen; 6 - hydrogen cost (production, storage, transport and distribution costs); III) Fuel cells and ITER, utopias?: 7 - molecular hydrogen uses (thermal engines and fuel cells); 8 - hydrogen and fusion (hydrogen isotopes, thermonuclear reaction, ITER project, fusion and wastes); IV) Hydrogen acceptability: 9 - risk acceptability; 10 - standards and regulations; 11 - national, European and international policies about hydrogen; 12 - big demonstration projects in France and in the rest of the world; conclusion. (J.S.)

A new type of hydrogen generator-HHEG (high-compressed hydrogen energy generator)

International Nuclear Information System (INIS)

Harada, H.; Tojima, K.; Takeda, M.; Nakazawa, T.

2004-01-01

'Full text:' We have developed a new type of hydrogen generator named HHEG (High-compressed Hydrogen Energy Generator). HHEG can produce 35 MPa high-compressed hydrogen for fuel cell vehicle without any mechanical compressor. HHEG is a kind of PEM(proton exchange membrane)electrolysis. It was well known that compressed hydrogen could be generated by water electrolysis. However, the conventional electrolysis could not generate 35 MPa or higher pressure that is required for fuel cell vehicle, because electrolysis cell stack is destroyed in such high pressure. In HHEG, the cell stack is put in high-pressure vessel and the pressure difference of oxygen and hydrogen that is generated by the cell stack is always kept at nearly zero by an automatic compensator invented by Mitsubishi Corporation. The cell stack of HHEG is not so special one, but it is not broken under such high pressure, because the automatic compensator always offsets the force acting on the cell stack. Hydrogen for fuel cell vehicle must be produce by no emission energy such as solar and atomic power. These energies are available as electricity. So, water electrolysis is the only way of producing hydrogen fuel. Hydrogen fuel is also 35 MPa high-compressed hydrogen and will become 70 MPa in near future. But conventional mechanical compressor is not useful for such high pressure hydrogen fuel, because of the short lifetime and high power consumption. Construction of hydrogen station network is indispensable in order to come into wide use of fuel cell vehicles. For such network contraction, an on-site type hydrogen generator is required. HHEG can satisfy above these requirements. So we can conclude that HHEG is the only way of realizing the hydrogen economy. (author)

Effect of composition on diffusible hydrogen content and hydrogen assisted cracking of steel welds

International Nuclear Information System (INIS)

Albert, S.K.; Ramasubbu, V.; Bhaduri, A.K.; Parvathavarthini, N.

2008-01-01

Study of hydrogen assisted cracking and measurement of diffusible hydrogen content in different Cr-Mo steel welds showed that for identical conditions, susceptibility to cracking increased and diffusible hydrogen content decreased with increase in alloy content. Hydrogen permeation studies showed that hydrogen diffusivity decreases and solubility increases with increase in alloy content. Thus decrease in diffusible hydrogen content with increase in alloying is attributed to increase in apparent solubility and decrease in apparent diffusivity of hydrogen with increase in alloy content. Analysis of the results indicates that variation of diffusible hydrogen content and apparent diffusivity of hydrogen with alloy content can be represented as a function of alloy composition. (author)

New hydrogen technologies

International Nuclear Information System (INIS)

1992-01-01

This report presents an overview of the overall hydrogen system. There are separate sections for production, distribution, transport, storage; and applications of hydrogen. The most important methods for hydrogen production are steam reformation of natural gas and electrolysis of water. Of the renewable energy options, production of hydrogen by electrolysis using electricity from wind turbines or by gasification of biomass were found to be the most economic for Finland. Direct use of this electricity or the production of liquid fuels from biomass will be competing alternatives. When hydrogen is produced in the solar belt or where there is cheap hydropower it must be transported over long distances. The overall energy consumed for the transport is from 25 to 40 % of the initial available energy. Hydrogen storage can be divided into stationary and mobile types. The most economic, stationary, large scale hydrogen storage for both long and short periods is underground storage. When suitable sites are not available, then pressure vessels are the best for short period and liquid H 2 for long period. Vehicle storage of hydrogen is by either metal hydrides or liquid H 2 . Hydrogen is a very versatile energy carrier. It can be used to produce heat directly in catalytic burners without flame, to produce electricity in fuel cells with high efficiency for use in vehicles or for peak power shaving, as a fuel component with conventional fuels to reduce emissions, as a way to store energy and as a chemical reagent in reactions

Hydrogen production by Cyanobacteria

Directory of Open Access Journals (Sweden)

Chaudhuri Surabhi

2005-12-01

Full Text Available Abstract The limited fossil fuel prompts the prospecting of various unconventional energy sources to take over the traditional fossil fuel energy source. In this respect the use of hydrogen gas is an attractive alternate source. Attributed by its numerous advantages including those of environmentally clean, efficiency and renew ability, hydrogen gas is considered to be one of the most desired alternate. Cyanobacteria are highly promising microorganism for hydrogen production. In comparison to the traditional ways of hydrogen production (chemical, photoelectrical, Cyanobacterial hydrogen production is commercially viable. This review highlights the basic biology of cynobacterial hydrogen production, strains involved, large-scale hydrogen production and its future prospects. While integrating the existing knowledge and technology, much future improvement and progress is to be done before hydrogen is accepted as a commercial primary energy source.

Hydrogen Fuelling Stations

DEFF Research Database (Denmark)

Rothuizen, Erasmus Damgaard

. A system consisting of one high pressure storage tank is used to investigate the thermodynamics of fuelling a hydrogen vehicle. The results show that the decisive parameter for how the fuelling proceeds is the pressure loss in the vehicle. The single tank fuelling system is compared to a cascade fuelling......This thesis concerns hydrogen fuelling stations from an overall system perspective. The study investigates thermodynamics and energy consumption of hydrogen fuelling stations for fuelling vehicles for personal transportation. For the study a library concerning the components in a hydrogen fuelling...... station has been developed in Dymola. The models include the fuelling protocol (J2601) for hydrogen vehicles made by Society of Automotive Engineers (SAE) and the thermodynamic property library CoolProp is used for retrieving state point. The components in the hydrogen fuelling library are building up...

Liquid hydrogen properties

International Nuclear Information System (INIS)

Choi, Jung Woon; Kim, Y. J.; Lee, K. H.; Kim, H. I.; Han, K. Y.; Park, J.H.

2004-03-01

The purpose of this report is to provide the input data, whose characteristic is thermodynamic and transport, in the form of equation for the thermo-hydraulic calculations using hydrogen as a working substance. The considered data in this report are particularly focused on the properties of para-hydrogen and of equilibrium-hydrogen around the working temperature range of the HANARO-CNS. The discussed properties of hydrogen are, in turn, the pressure of saturated vapors, the density, the heat of vaporization, thermal conductivity, viscosity, and heat capacity. Several equations to fit the above-mentioned experimental data allow calculating the various properties of liquid hydrogen with high accuracy at all considered temperatures

Dynamics of hydrogen in hydrogenated amorphous silicon

Indian Academy of Sciences (India)

is mobile and can easily move through the material). Hydrogen diffuses ... The determination of the relationship of light-enhanced hydrogen motion to ... term is negligible, and using the thermodynamic relation given below f(c) = kBT .... device-applications problematic but the normal state can be recovered by a thermal an-.

Muonium/muonic hydrogen formation in atomic hydrogen

Indian Academy of Sciences (India)

The muonium/muonic hydrogen atom formation in ± –H collisions is investigated, using a two-state approximation in a time dependent formalism. It is found that muonium cross-section results are similar to the cross-section results obtained for positronium formation in + –H collision. Muonic hydrogen atom formation ...

Compact Design of an Electrically Tunable and Rotatable Polarizer Based on a Liquid Crystal Photonic Bandgap Fiber

DEFF Research Database (Denmark)

Wei, Lei; Alkeskjold, Thomas Tanggaard; Bjarklev, Anders Overgaard

2009-01-01

In this letter, a compact electrically controlled broadband liquid crystal (LC) photonic bandgap fiber polarizer is designed and fabricated. A good fiber coupling quality between two single-mode fibers and one 10-mm-long LC-filled photonic crystal fiber is obtained and protected by using SU-8 fiber...... fixing structures during the device assembly. The total insertion loss of this all-in-fiber device is 2.7 dB. An electrically tunable polarization extinction ratio of 21.3 dB is achieved with 45$^{circ}$ rotatable transmission axis as well as switched on and off in the wavelength range of 1300–1600 nm....

On the solubility of hydrogen in the systems titanium-aluminium-hydrogen, titanium-vanadium-hydrogen and titanium-aluminium-vanadium-hydrogen in the temperature region of 800 to 1,0000C at hydrogen pressures of 0.1 to 400 mm.Hg

International Nuclear Information System (INIS)

Kauder, G.W.

1973-01-01

The hydrogen concentrations on Ti-Al, Ti-V and Ti-Al-V alloys were determined in the temperature region from 800 to 1,000 0 C and at hydrogen pressures of 0.1 to 400 mm.Hg using a gravimetric measuring process. The thus obtained results allowed the drawing of hydrogen activity slopes in the titanium rich corner of the systems titanium-hydrogen, titanium-aluminium-hydrogen, titanium-vanadium-hydrogen and such for the technical titanium alloys Ti-6Al-4V and Ti-6Al-6V. In spite of the antagonistic effects of the elements aluminium and vanadium on the stabilization of the α and β phase regions of titanium, a hydrogen-activity-increasing effect was always found in which the aluminium influence was greater than that of vanadium. Breaks occured in the hydrogen activity curves and phase boundaries, and phase regions were determined over their positions. Isothermal phase diagrams for the titanium-rich corner of the system titanium-aluminium-hydrogen at 800, 850 and 900 0 C and for the titanium-rich corner of the titanium-vanadium-hydrogen system at 900, 950 and 1,000 0 C were drawn up from the hydrogen activity curves. (orig./LH) [de

Industrial implications of hydrogen

International Nuclear Information System (INIS)

Pressouyre, G.M.

1982-01-01

Two major industrial implications of hydrogen are examined: problems related to the effect of hydrogen on materials properties (hydrogen embrittlement), and problems related to the use and production of hydrogen as a future energy vector [fr

Bandgap optimization of two-dimensional photonic crystals using semidefinite programming and subspace methods

International Nuclear Information System (INIS)

Men, H.; Nguyen, N.C.; Freund, R.M.; Parrilo, P.A.; Peraire, J.

2010-01-01

In this paper, we consider the optimal design of photonic crystal structures for two-dimensional square lattices. The mathematical formulation of the bandgap optimization problem leads to an infinite-dimensional Hermitian eigenvalue optimization problem parametrized by the dielectric material and the wave vector. To make the problem tractable, the original eigenvalue problem is discretized using the finite element method into a series of finite-dimensional eigenvalue problems for multiple values of the wave vector parameter. The resulting optimization problem is large-scale and non-convex, with low regularity and non-differentiable objective. By restricting to appropriate eigenspaces, we reduce the large-scale non-convex optimization problem via reparametrization to a sequence of small-scale convex semidefinite programs (SDPs) for which modern SDP solvers can be efficiently applied. Numerical results are presented for both transverse magnetic (TM) and transverse electric (TE) polarizations at several frequency bands. The optimized structures exhibit patterns which go far beyond typical physical intuition on periodic media design.

Biomimetic hydrogen production

Energy Technology Data Exchange (ETDEWEB)

Krassen, Henning

2009-05-15

Hydrogenases catalyze the reduction of protons to molecular hydrogen with outstanding efficiency. An electrode surface which is covered with active hydrogenase molecules becomes a promising alternative to platinum for electrochemical hydrogen production. To immobilize the hydrogenase on the electrode, the gold surface was modified by heterobifunctional molecules. A thiol headgroup on one side allowed the binding to the gold surface and the formation of a self-assembled monolayer. The other side of the molecules provided a surface with a high affinity for the hydrogenase CrHydA1 from Chlamydomonas reinhardtii. With methylviologen as a soluble energy carrier, electrons were transferred from carboxy-terminated electrodes to CrHydA1 and conducted to the active site (H-cluster), where they reduce protons to molecular hydrogen. A combined approach of surface-enhanced infrared absorption spectroscopy, gas chromatography, and surface plasmon resonance allowed quantifying the hydrogen production on a molecular level. Hydrogen was produced with a rate of 85 mol H{sub 2} min{sup -1} mol{sup -1}. On a 1'- benzyl-4,4'-bipyridinum (BBP)-terminated surface, the electrons were mediated by the monolayer and no soluble electron carrier was necessary to achieve a comparable hydrogen production rate (approximately 50% of the former system). The hydrogen evolution potential was determined to be -335 mV for the BBP-bound hydrogenase and -290 mV for the hydrogenase which was immobilized on a carboxy-terminated mercaptopropionic acid SAM. Therefore, both systems significantly reduce the hydrogen production overpotential and allow electrochemical hydrogen production at an energy level which is close to the commercially applied platinum electrodes (hydrogen evolution potential of -270 mV). In order to couple hydrogen production and photosynthesis, photosystem I (PS1) from Synechocystis PCC 6803 and membrane-bound hydrogenase (MBH) from Ralstonia eutropha were bound to each other

Ultrafine hydrogen storage powders

Science.gov (United States)

Anderson, Iver E.; Ellis, Timothy W.; Pecharsky, Vitalij K.; Ting, Jason; Terpstra, Robert; Bowman, Robert C.; Witham, Charles K.; Fultz, Brent T.; Bugga, Ratnakumar V.

2000-06-13

A method of making hydrogen storage powder resistant to fracture in service involves forming a melt having the appropriate composition for the hydrogen storage material, such, for example, LaNi.sub.5 and other AB.sub.5 type materials and AB.sub.5+x materials, where x is from about -2.5 to about +2.5, including x=0, and the melt is gas atomized under conditions of melt temperature and atomizing gas pressure to form generally spherical powder particles. The hydrogen storage powder exhibits improved chemcial homogeneity as a result of rapid solidfication from the melt and small particle size that is more resistant to microcracking during hydrogen absorption/desorption cycling. A hydrogen storage component, such as an electrode for a battery or electrochemical fuel cell, made from the gas atomized hydrogen storage material is resistant to hydrogen degradation upon hydrogen absorption/desorption that occurs for example, during charging/discharging of a battery. Such hydrogen storage components can be made by consolidating and optionally sintering the gas atomized hydrogen storage powder or alternately by shaping the gas atomized powder and a suitable binder to a desired configuration in a mold or die.

Canadian hydrogen safety program

International Nuclear Information System (INIS)

MacIntyre, I.; Tchouvelev, A.V.; Hay, D.R.; Wong, J.; Grant, J.; Benard, P.

2007-01-01

The Canadian hydrogen safety program (CHSP) is a project initiative of the Codes and Standards Working Group of the Canadian transportation fuel cell alliance (CTFCA) that represents industry, academia, government, and regulators. The Program rationale, structure and contents contribute to acceptance of the products, services and systems of the Canadian Hydrogen Industry into the Canadian hydrogen stakeholder community. It facilitates trade through fair insurance policies and rates, effective and efficient regulatory approval procedures and accommodation of the interests of the general public. The Program integrates a consistent quantitative risk assessment methodology with experimental (destructive and non-destructive) failure rates and consequence-of-release data for key hydrogen components and systems into risk assessment of commercial application scenarios. Its current and past six projects include Intelligent Virtual Hydrogen Filling Station (IVHFS), Hydrogen clearance distances, comparative quantitative risk comparison of hydrogen and compressed natural gas (CNG) refuelling options; computational fluid dynamics (CFD) modeling validation, calibration and enhancement; enhancement of frequency and probability analysis, and Consequence analysis of key component failures of hydrogen systems; and fuel cell oxidant outlet hydrogen sensor project. The Program projects are tightly linked with the content of the International Energy Agency (IEA) Task 19 Hydrogen Safety. (author)

The energy carrier hydrogen

International Nuclear Information System (INIS)

Anon.

1992-01-01

The potential of hydrogen to be used as a clean fuel for the production of heat and power, as well as for the propulsion of aeroplanes and vehicles, is described, in particular for Germany. First, attention is paid to the application of hydrogen as a basic material for the (petro)chemical industry, as an indirect energy source for (petro)chemical processes, and as a direct energy source for several purposes. Than the importance of hydrogen as an energy carrier in a large-scale application of renewable energy sources is discussed. Next an overview is given of new and old hydrogen production techniques from fossil fuels, biomass, or the electrolysis of water. Energetic applications of hydrogen in the transportation sector and the production of electric power and heat are mentioned. Brief descriptions are given of techniques to store hydrogen safely. Finally attention is paid to hydrogen research in Germany. Two hydrogen projects, in which Germany participates, are briefly dealt with: the Euro-Quebec project (production of hydrogen by means of hydropower), and the HYSOLAR project (hydrogen production by means of solar energy). 18 figs., 1 tab., 7 refs

Nanodiamond for hydrogen storage: temperature-dependent hydrogenation and charge-induced dehydrogenation.

Science.gov (United States)

Lai, Lin; Barnard, Amanda S

2012-02-21

Carbon-based hydrogen storage materials are one of hottest research topics in materials science. Although the majority of studies focus on highly porous loosely bound systems, these systems have various limitations including use at elevated temperature. Here we propose, based on computer simulations, that diamond nanoparticles may provide a new promising high temperature candidate with a moderate storage capacity, but good potential for recyclability. The hydrogenation of nanodiamonds is found to be easily achieved, in agreement with experiments, though we find the stability of hydrogenation is dependent on the morphology of nanodiamonds and surrounding environment. Hydrogenation is thermodynamically favourable even at high temperature in pure hydrogen, ammonia, and methane gas reservoirs, whereas water vapour can help to reduce the energy barrier for desorption. The greatest challenge in using this material is the breaking of the strong covalent C-H bonds, and we have identified that the spontaneous release of atomic hydrogen may be achieved through charging of hydrogenated nanodiamonds. If the degree of induced charge is properly controlled, the integrity of the host nanodiamond is maintained, which indicates that an efficient and recyclable approach for hydrogen release may be possible. This journal is © The Royal Society of Chemistry 2012

Hydrogen-metal systems

International Nuclear Information System (INIS)

Wenzl, H.; Springer, T.

1976-01-01

A survey is given on the alloys of metal crystals with hydrogen. The system niobium-hydrogen and its properties are especially dealt with: diffusion and heat of solution of hydrogen in the host crystal, phase diagram, coherent and incoherent phase separation, application of metal-hydrogen systems in technology. Furthermore, examples from research work in IFF (Institut fuer Festkoerperforschung) of the Nuclear Research Plant, Juelich, in the field of metal-H systems are given in summary form. (GSC) [de

Electric arc hydrogen heaters

International Nuclear Information System (INIS)

Zasypin, I.M.

2000-01-01

The experimental data on the electric arc burning in hydrogen are presented. Empirical and semiempirical dependences for calculating the arc characteristics are derived. An engineering method of calculating plasma torches for hydrogen heating is proposed. A model of interaction of a hydrogen arc with a gas flow is outlined. The characteristics of plasma torches for heating hydrogen and hydrogen-bearing gases are described. (author)

Investigation of hydrogen bubbles behavior in tungsten by high-flux hydrogen implantation

Science.gov (United States)

Zhao, Jiangtao; Meng, Xuan; Guan, Xingcai; Wang, Qiang; Fang, Kaihong; Xu, Xiaohui; Lu, Yongkai; Gao, Jun; Liu, Zhenlin; Wang, Tieshan

2018-05-01

Hydrogen isotopes retention and bubbles formation are critical issues for tungsten as plasma-facing material in future fusion reactors. In this work, the formation and growing up behavior of hydrogen bubbles in tungsten were investigated experimentally. The planar TEM samples were implanted by 6.0keV hydrogens to a fluence of 3.38 ×1018 H ṡ cm-2 at room temperature, and well-defined hydrogen bubbles were observed by TEM. It was demonstrated that hydrogen bubbles formed when exposed to a fluence of 1.5 ×1018 H ṡ cm-2 , and the hydrogen bubbles grew up with the implantation fluence. In addition, the bubbles' size appeared larger with higher beam flux until saturated at a certain flux, even though the total fluence was kept the same. Finally, in order to understand the thermal annealing effect on the bubbles behavior, hydrogen-implanted samples were annealed at 400, 600, 800, and 1000 °C for 3 h. It was obvious that hydrogen bubbles' morphology changed at temperatures higher than 800 °C.

Liquid hydrogen in Japan

Energy Technology Data Exchange (ETDEWEB)

Yasumi, S. [Iwatani Corp., Osaka (Japan). Dept. of Overseas Business Development

2009-07-01

Japan's Iwatani Corporation has focused its attention on hydrogen as the ultimate energy source in future. Unlike the United States, hydrogen use and delivery in liquid form is extremely limited in the European Union and in Japan. Iwatani Corporation broke through industry stereotypes by creating and building Hydro Edge Co. Ltd., Japan's largest liquid hydrogen plant. It was established in 2006 as a joint venture between Iwatani and Kansai Electric Power Group in Osaka. Hydro Edge is Japan's first combined liquid hydrogen and ASU plant, and is fully operational. Liquid oxygen, liquid nitrogen and liquid argon are separated from air using the cryogenic energy of liquefied natural gas fuel that is used for power generation. Liquid hydrogen is produced efficiently and simultaneously using liquid nitrogen. Approximately 12 times as much hydrogen in liquid form can be transported and supplied as pressurized hydrogen gas. This technology is a significant step forward in the dissemination and expansion of hydrogen in a hydrogen-based economy.

Hydrogen as automotive fuel

International Nuclear Information System (INIS)

Dini, D.; Ciancia, A.; Pede, G.; Sglavo, V.; ENEA, Rome

1992-01-01

An assessment of the technical/economic feasibility of the use of hydrogen as an automotive fuel is made based on analyses of the following: the chemical- physical properties of hydrogen in relation to its use in internal combustion engines; the modifications necessary to adapt internal combustion engines to hydrogen use; hydrogen fuel injection systems - with water vapour injection, cryogenic injection, and the low or high pressure injection of hydrogen directly into the combustion chamber; the current commercialization status of hydrogen automotive fuels; energy efficiency ratings; environmental impacts; in-vehicle storage systems - involving the use of hydrides, high pressure systems and liquid hydrogen storage systems; performance in terms of pay-load ratio; autonomous operation; and operating costs. The paper concludes that, considering current costs for hydrogen fuel production, distribution and use, at present, the employment of hydrogen fuelled vehicles is feasible only in highly polluted urban environments where the innovative vehicle's air pollution abatement characteristics would justify its high operating costs as compared with those of conventional automotive alternatives

Design of UWB Monopole Antenna with Dual Notched Bands Using One Modified Electromagnetic-Bandgap Structure

Science.gov (United States)

Xu, Ziqiang

2013-01-01

A modified electromagnetic-bandgap (M-EBG) structure and its application to planar monopole ultra-wideband (UWB) antenna are presented. The proposed M-EBG which comprises two strip patch and an edge-located via can perform dual notched bands. By properly designing and placing strip patch near the feedline, the proposed M-EBG not only possesses a simple structure and compact size but also exhibits good band rejection. Moreover, it is easy to tune the dual notched bands by altering the dimensions of the M-EBG. A demonstration antenna with dual band-notched characteristics is designed and fabricated to validate the proposed method. The results show that the proposed antenna can satisfy the requirements of VSWR WLAN) at 3.5 GHz and 5.5 GHz, respectively. PMID:24170984

Nuclear electrolytic hydrogen

International Nuclear Information System (INIS)

Barnstaple, A.G.; Petrella, A.J.

1982-05-01

An extensive study of hydrogen supply has recently been carried out by Ontario Hydro which indicates that electrolytic hydrogen produced from nuclear electricity could offer the lowest cost option for any future large scale hydrogen supply in the Province of Ontario, Canada. This paper provides a synopsis of the Ontario Hydro study, a brief overview of the economic factors supporting the study conclusion and discussion of a number of issues concerning the supply of electrolytic hydrogen by electric power utilities

Review of iron oxide for photo electrode application in water splitting

International Nuclear Information System (INIS)

Amir Memar; Mohammad Kassim

2009-01-01

Full text: The use of the photoelectrochemical (PEC) route in hydrogen production is a promising, valuable, clean and efficient way of storing solar energy for use in hydrogen-powered fuel cells. Iron oxide (α-Fe 2 O 3 ) is an attractive photo electrode in PEC cell due to its constructive bandgap of ∼ 2.2 eV, lying in the visible region. This paper presents a review of the different methods of Fe2O3 thin film production and the characterization of the thin film and its application for photo-electrochemical hydrogen production. (author)

Limits for hydrogen production of a solar - hydrogen system in Cuernavaca, Mexico

International Nuclear Information System (INIS)

Arriaga, H.L.G.; Gutierrez, S.L.; Cano, U.

2006-01-01

In this work experimental data are used in order to estimate the production of hydrogen as a function of irradiance of a direct-interconnection of solar panel system with a SPE (Solid Polymer Electrolyte) electrolyzer (also Solar-Hydrogen system). The solar - hydrogen system, consists of a photovoltaic solar array of 36 panels (75 Watts each) of monocrystalline silicon interconnected with an electrolyzer stack of 25 cells (around 100 cm 2 of geometrical area) with a maximum hydrogen production of 1 Nm 3 /h. By the use of voltage, current density, energy consumption values of the whole solar-hydrogen system, an average efficiency up to 5% was estimated and an average of 3,800 NL of hydrogen per day can be expected. Also the maximum hydrogen production for the months of July and December (sunniest and least sunny months in the location) is predicted. (authors)

Limits for hydrogen production of a solar - hydrogen system in Cuernavaca, Mexico

Energy Technology Data Exchange (ETDEWEB)

Arriaga, H.L.G.; Gutierrez, S.L.; Cano, U. [Instituto de Investigaciones Electricas Av. Reforma 113, col. Palmira c.p.62490 Cuernavaca Morelos (Mexico)

2006-07-01

In this work experimental data are used in order to estimate the production of hydrogen as a function of irradiance of a direct-interconnection of solar panel system with a SPE (Solid Polymer Electrolyte) electrolyzer (also Solar-Hydrogen system). The solar - hydrogen system, consists of a photovoltaic solar array of 36 panels (75 Watts each) of monocrystalline silicon interconnected with an electrolyzer stack of 25 cells (around 100 cm{sup 2} of geometrical area) with a maximum hydrogen production of 1 Nm{sup 3}/h. By the use of voltage, current density, energy consumption values of the whole solar-hydrogen system, an average efficiency up to 5% was estimated and an average of 3,800 NL of hydrogen per day can be expected. Also the maximum hydrogen production for the months of July and December (sunniest and least sunny months in the location) is predicted. (authors)

Simulation of hydrogen and hydrogen-assisted propane ignition in Pt catalyzed microchannel

Energy Technology Data Exchange (ETDEWEB)

Seshadri, Vikram; Kaisare, Niket S. [Department of Chemical Engineering, Indian Institute of Technology - Madras, Chennai 600 036 (India)

2010-11-15

This paper deals with self-ignition of catalytic microburners from ambient cold-start conditions. First, reaction kinetics for hydrogen combustion is validated with experimental results from the literature, followed by validation of a simplified pseudo-2D microburner model. The model is then used to study the self-ignition behavior of lean hydrogen/air mixtures in a Platinum-catalyzed microburner. Hydrogen combustion on Pt is a very fast reaction. During cold start ignition, hydrogen conversion reaches 100% within the first few seconds and the reactor dynamics are governed by the ''thermal inertia'' of the microburner wall structure. The self-ignition property of hydrogen can be used to provide the energy required for propane ignition. Two different modes of hydrogen-assisted propane ignition are considered: co-feed mode, where the microburner inlet consists of premixed hydrogen/propane/air mixtures; and sequential feed mode, where the inlet feed is switched from hydrogen/air to propane/air mixtures after the microburner reaches propane ignition temperature. We show that hydrogen-assisted ignition is equivalent to selectively preheating the inlet section of the microburner. The time to reach steady state is lower at higher equivalence ratio, lower wall thermal conductivity, and higher inlet velocity for both the ignition modes. The ignition times and propane emissions are compared. Although the sequential feed mode requires slightly higher amount of hydrogen, the propane emissions are at least an order of magnitude lower than the other ignition modes. (author)

Metallic hydrogen research

International Nuclear Information System (INIS)

Burgess, T.J.; Hawke, R.S.

1978-01-01

Theoretical studies predict that molecular hydrogen can be converted to the metallic phase at very high density and pressure. These conditions were achieved by subjecting liquid hydrogen to isentropic compression in a magnetic-flux compression device. Hydrogen became electrically conducting at a density of about 1.06 g/cm 3 and a calculated pressure of about 2 Mbar. In the experimental device, a cylindrical liner, on implosion by high explosive, compresses a magnetic flux which in turn isentropically compresses a hydrogen sample; coaxial conical anvils prevent escape of the sample during compression. One anvil contains a coaxial cable that uses alumina ceramic as an insulator; this probe allows continuous measurement of the electrical conductivity of the hydrogen. A flash x-ray radiograph exposed during the experiment records the location of the sample-tube boundaries and permits calculation of the sample density. The theoretical underpinnings of the metallic transition of hydrogen are briefly summarized, and the experimental apparatus and technique, analytical methods, and results are described. 9 figures

Numerical analysis on hydrogen stratification and post-inerting of hydrogen risk

International Nuclear Information System (INIS)

Peng, Cheng; Tong, Lili; Cao, Xuewu

2016-01-01

Highlights: • A three-dimensional computational model was built and the applicability was discussed. • The formation of helium stratification was further studied. • Three influencing factors on the post-inerting of hydrogen risk were analyzed. - Abstract: In the case of severe accidents, the risk of hydrogen explosion threatens the integrity of the nuclear reactor containment. According to nuclear regulations, hydrogen control is required to ensure the safe operation of the nuclear reactor. In this study, the method of Computational Fluid Dynamics (CFD) has been applied to analyze process of hydrogen stratification and the post-inerting of hydrogen risk in the Large-Scale Gas Mixing Facility. A three-dimensional computational model was built and the applicability of different turbulence models was discussed. The result shows that the helium concentration calculated by the standard k–ε turbulence model is closest to the experiment data. Through analyzing the formation of helium stratification at different injection velocities, it is found that when the injection mass flow is constant and the injection velocity of helium increases, the mixture of helium and air is enhanced while there is rarely influence on the formation of helium stratification. In addition, the influences of mass flow rate, injection location and direction and inert gas on the post-inerting of hydrogen risk have been analyzed and the results are as follows: with the increasing of mass flow rate, the mitigation effect of nitrogen on hydrogen risk will be further improved; there is an obvious local difference between the mitigation effects of nitrogen on hydrogen risk in different injection directions and locations; when the inert gas is injected at the same mass flow rate, the mitigation effect of steam on hydrogen risk is better than that of nitrogen. This study can provide technical support for the mitigation of hydrogen risk in the small LWR containment.

Evaluation of hydrogen demonstration systems (Task 18 of IEA Implementing Agreement on Hydrogen)

Energy Technology Data Exchange (ETDEWEB)

Baker, J N; Carter, S

2005-07-01

Task 18 aims to gather information about the integration of hydrogen into society around the world. As part of subtask B (demonstration projects), EA Technology Limited collected information and data on specific UK hydrogen demonstration projects and case studies. The work involved desk research, a literature review, telephone conversations and meetings with developers and operators of hydrogen-related projects in the UK. Various examples were identified in phase 1 that were either proposed, planned, under construction, commissioned or operational. The main demonstration activities described in the report are: the Clean Urban Transport for Europe (CUTE) refuelling station at Hornchurch in Essex; the Hydrogen and Renewables Integration (HARI) project at West Beacon Farm, Leicestershire; the Promoting Unst Renewable Energy (PURE) project on Unst in the Shetland Isles; the Hunterston Hydrogen Project in North Ayrshire, Scotland; and the Tees Valley Hydrogen Project. The CUTE, HARI and PURE projects were selected for inclusion in the overall Task 18 workplan. The report also covers developments associated with the Fuel Cell House, the Hydrogen Office, INEOS Chlor, the London Hydrogen Partnership and the Wales Hydrogen Project.

Hydrogen in amorphous silicon

International Nuclear Information System (INIS)

Peercy, P.S.

1980-01-01

The structural aspects of amorphous silicon and the role of hydrogen in this structure are reviewed with emphasis on ion implantation studies. In amorphous silicon produced by Si ion implantation of crystalline silicon, the material reconstructs into a metastable amorphous structure which has optical and electrical properties qualitatively similar to the corresponding properties in high-purity evaporated amorphous silicon. Hydrogen studies further indicate that these structures will accomodate less than or equal to 5 at.% hydrogen and this hydrogen is bonded predominantly in a monohydride (SiH 1 ) site. Larger hydrogen concentrations than this can be achieved under certain conditions, but the excess hydrogen may be attributed to defects and voids in the material. Similarly, glow discharge or sputter deposited amorphous silicon has more desirable electrical and optical properties when the material is prepared with low hydrogen concentration and monohydride bonding. Results of structural studies and hydrogen incorporation in amorphous silicon were discussed relative to the different models proposed for amorphous silicon

Transient shielded liquid hydrogen containers

International Nuclear Information System (INIS)

Varghese, A.P.; Herring, R.H.

1990-01-01

The storage of hydrogen in the liquid phase has been limited in duration due to the thermal performance constraints of conventional Liquid Hydrogen containers available. Conventional Liquid Hydrogen containers lose hydrogen because of their relatively high heat leak and variations in usage pattern of hydrogen due to shutdowns. Local regulations also discourage venting of hydrogen. Long term storage of Liquid Hydrogen without product loss was usually accomplished using Liquid Nitrogen sacrificial shields. This paper reports on a new low heat leak container developed and patented that will extend the storage time of liquid hydrogen by five hundred percent. The principle of operation of the Transient Shields which makes the extraordinary performance of this container feasible is described in this paper. Also covered are the impact of this new container on present applications of hydrogen and the new opportunities afforded to Liquid hydrogen in the world hydrogen market

Handheld hydrogen - a new concept for hydrogen storage

DEFF Research Database (Denmark)

Johannessen, Tue; Sørensen, Rasmus Zink

2005-01-01

A method of hydrogen storage using metal ammine complexes in combination with an ammonia decomposition catalyst is presented. This dense hydrogen storage material has high degree of safety compared to all the other available alternatives. This technology reduces the safety hazards of using liquid...

Hydrogen energy for beginners

CERN Document Server

2013-01-01

This book highlights the outstanding role of hydrogen in energy processes, where it is the most functional element due to its unique peculiarities that are highlighted and emphasized in the book. The first half of the book covers the great natural hydrogen processes in biology, chemistry, and physics, showing that hydrogen is a trend that can unite all natural sciences. The second half of the book is devoted to the technological hydrogen processes that are under research and development with the aim to create the infrastructure for hydrogen energetics. The book describes the main features of hydrogen that make it inalienable player in processes such as fusion, photosynthesis, and metabolism. It also covers the methods of hydrogen production and storage, highlighting at the same time the exclusive importance of nanotechnologies in those processes.

Reactivity of hydrogen contained in Raney nickel for ethylene hydrogenation studied by means of a tritium tracer

International Nuclear Information System (INIS)

Miyatani, Daisaku; Takeuchi, Toyosaburo.

1979-01-01

Reactivity of hydrogen contained in Raney nickel with ethylene was studied by using a tritium tracer. Hydrogen in Raney nickel was previously labeled with tritium and distinguished from hydrogen introduced during the hydrogenation reaction. The reactivity of the contained hydrogen was determined by measurement of the radioactivity of ethane produced in the hydrogenation. Ethylene reacted with hydrogen in Raney nickel for no supply of hydrogen during the hydrogenation. However, when ethylene was hydrogenated by both hydrogen in Raney nickel and introduced hydrogen, over 99% of the ethylene reacted with the introduced hydrogen and hardly reacted with the contained hydrogen. (author)

IEA Hydrogen Implementing Agreement: Three Decades of Collaborative Hydrogen R and D

International Nuclear Information System (INIS)

Nick Beck; Mary-Rose de Valladares

2006-01-01

Created in 1977 and now in its Second Generation of Hydrogen R, D and D, the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) is the oldest, largest international collaboration on hydrogen Research, Development and Demonstration (RD and D). As a global resource for technical expertise in hydrogen R, D and D, the HIA has expanded worldwide opportunities for hydrogen by undertaking 21 annexes (or tasks) on hydrogen production, storage, analysis of integrated systems and related topics with its 19 member countries. Related topics include hydrogen safety, conversion, economics and markets. The majority of the HIA's R and D portfolio has focused on longer term, pre-competitive R, D and D issues. Of the 21 annexes undertaken by the HIA, 15 are now complete. The HIA is also committed to outreach in support of both its core R and D activities and related issues such as regulation and infrastructure. As ever, the HIA welcomes collaboration and liaison with interested groups in the public and private sectors. (authors)

Hydrogen energy systems studies

Energy Technology Data Exchange (ETDEWEB)

Ogden, J.M.; Steinbugler, M.; Dennis, E. [Princeton Univ., NJ (United States)] [and others

1995-09-01

For several years, researchers at Princeton University`s Center for Energy and Environmental Studies have carried out technical and economic assessments of hydrogen energy systems. Initially, we focussed on the long term potential of renewable hydrogen. More recently we have explored how a transition to renewable hydrogen might begin. The goal of our current work is to identify promising strategies leading from near term hydrogen markets and technologies toward eventual large scale use of renewable hydrogen as an energy carrier. Our approach has been to assess the entire hydrogen energy system from production through end-use considering technical performance, economics, infrastructure and environmental issues. This work is part of the systems analysis activity of the DOE Hydrogen Program. In this paper we first summarize the results of three tasks which were completed during the past year under NREL Contract No. XR-11265-2: in Task 1, we carried out assessments of near term options for supplying hydrogen transportation fuel from natural gas; in Task 2, we assessed the feasibility of using the existing natural gas system with hydrogen and hydrogen blends; and in Task 3, we carried out a study of PEM fuel cells for residential cogeneration applications, a market which might have less stringent cost requirements than transportation. We then give preliminary results for two other tasks which are ongoing under DOE Contract No. DE-FG04-94AL85803: In Task 1 we are assessing the technical options for low cost small scale production of hydrogen from natural gas, considering (a) steam reforming, (b) partial oxidation and (c) autothermal reforming, and in Task 2 we are assessing potential markets for hydrogen in Southern California.

Hydrogen as automotive fuel

International Nuclear Information System (INIS)

Ambrosini, G.; Ciancia, A.; Pede, G.; Brighigna, M.

1993-01-01

Hydrogen fueled vehicles may just be the answer to the air pollution problem in highly polluted urban environments where the innovative vehicle's air pollution abatement characteristics would justify its high operating costs as compared with those of conventional automotive alternatives. This paper examines the feasibility of hydrogen as an automotive fuel by analyzing the following aspects: the chemical-physical properties of hydrogen in relation to its use in internal combustion engines; the modifications necessary to adapt internal combustion engines to hydrogen use; hydrogen fuel injection systems; current production technologies and commercialization status of hydrogen automotive fuels; energy efficiency ratings; environmental impacts; in-vehicle storage systems - involving the use of hydrides, high pressure systems and liquid hydrogen storage systems; performance in terms of pay-load ratio; autonomous operation; and operating costs. With reference to recent trial results being obtained in the USA, an assessment is also made of the feasibility of the use of methane-hydrogen mixtures as automotive fuels. The paper concludes with a review of progress being made by ENEA (the Italian Agency for New Technology, Energy and the Environment) in the development of fuel storage and electronic fuel injection systems for hydrogen powered vehicles

Band-gap sensitive adsorption of fluorine molecules on sidewalls of carbon nanotubes: an ab initio study

International Nuclear Information System (INIS)

Choi, Woon Ih; Park, Sohee; Kim, Tae-Eun; Park, Noejung; Lee, Kwang-Ryeol; Lee, Young Hee; Ihm, Jisoon; Han, Seungwu

2006-01-01

We report from ab initio calculations that the band-gap sensitive side-wall functionalization of a carbon nanotube is feasible with the fluorine molecule (F 2 ), which can provide a route to the extraction of semiconducting nanotubes by etching away metallic ones. In the small diameter cases like (11, 0) and (12, 0), the nanotubes are easily functionalized with F 2 regardless of their electronic properties. As the diameter becomes larger, however, the fluorination is favoured on metallic CNTs with smaller activation barriers than those of semiconducting ones. Our results suggest that low-temperature exposure to F 2 molecules in the gas phase can make a dominant portion of fluorinated metallic nanotubes and unfluorinated semiconducting ones. This is consistent with recent experimental reports

Hydrogen-based electrochemical energy storage

Science.gov (United States)

Simpson, Lin Jay

2013-08-06

An energy storage device (100) providing high storage densities via hydrogen storage. The device (100) includes a counter electrode (110), a storage electrode (130), and an ion conducting membrane (120) positioned between the counter electrode (110) and the storage electrode (130). The counter electrode (110) is formed of one or more materials with an affinity for hydrogen and includes an exchange matrix for elements/materials selected from the non-noble materials that have an affinity for hydrogen. The storage electrode (130) is loaded with hydrogen such as atomic or mono-hydrogen that is adsorbed by a hydrogen storage material such that the hydrogen (132, 134) may be stored with low chemical bonding. The hydrogen storage material is typically formed of a lightweight material such as carbon or boron with a network of passage-ways or intercalants for storing and conducting mono-hydrogen, protons, or the like. The hydrogen storage material may store at least ten percent by weight hydrogen (132, 134) at ambient temperature and pressure.

LARGE-SCALE PRODUCTION OF HYDROGEN BY NUCLEAR ENERGY FOR THE HYDROGEN ECONOMY

International Nuclear Information System (INIS)

SCHULTZ, K.R.; BROWN, L.C.; BESENBRUCH, G.E.; HAMILTON, C.J.

2003-01-01

OAK B202 LARGE-SCALE PRODUCTION OF HYDROGEN BY NUCLEAR ENERGY FOR THE HYDROGEN ECONOMY. The ''Hydrogen Economy'' will reduce petroleum imports and greenhouse gas emissions. However, current commercial hydrogen production processes use fossil fuels and releases carbon dioxide. Hydrogen produced from nuclear energy could avoid these concerns. The authors have recently completed a three-year project for the US Department of Energy whose objective was to ''define an economically feasible concept for production of hydrogen, by nuclear means, using an advanced high-temperature nuclear reactor as the energy source''. Thermochemical water-splitting, a chemical process that accomplishes the decomposition of water into hydrogen and oxygen, met this objective. The goal of the first phase of this study was to evaluate thermochemical processes which offer the potential for efficient, cost-effective, large-scale production of hydrogen and to select one for further detailed consideration. The authors selected the Sulfur-Iodine cycle, In the second phase, they reviewed all the basic reactor types for suitability to provide the high temperature heat needed by the selected thermochemical water splitting cycle and chose the helium gas-cooled reactor. In the third phase they designed the chemical flowsheet for the thermochemical process and estimated the efficiency and cost of the process and the projected cost of producing hydrogen. These results are summarized in this paper

A study of potential high band-gap photovoltaic materials for a two step photon intermediate technique in fission energy conversion. Final report

Energy Technology Data Exchange (ETDEWEB)

Prelas, M.A.

1996-01-24

This report describes progress made to develop a high bandgap photovoltaic materials for direct conversion to electricity of excimer radiation produced by fission energy pumped laser. This report summarizes the major achievements in sections. The first section covers n-type diamond. The second section covers forced diffusion. The third section covers radiation effects. The fourth section covers progress in Schottky barrier and heterojunction photovoltaic cells. The fifth section covers cell and reactor development.

Hydrogen gas detector

International Nuclear Information System (INIS)

Bohl, T.L.

1982-01-01

A differential thermocouple hydrogen gas detector has one thermocouple junction coated with an activated palladium or palladium-silver alloy catalytic material to allow heated hydrogen gas to react with the catalyst and raise the temperature of that junction. The other juction is covered with inert glass or epoxy resin, and does not experience a rise in temperature in the presence of hydrogen gas. A coil heater may be mounted around the thermocouple junctions to heat the hydrogen, or the gas may be passed through a heated block prior to exposing it to the thermocouples

Sustainable hydrogen production

Energy Technology Data Exchange (ETDEWEB)

Block, D.L.; Linkous, C.; Muradov, N.

1996-01-01

This report describes the Sustainable Hydrogen Production research conducted at the Florida Solar Energy Center (FSEC) for the past year. The report presents the work done on the following four tasks: Task 1--production of hydrogen by photovoltaic-powered electrolysis; Task 2--solar photocatalytic hydrogen production from water using a dual-bed photosystem; Task 3--development of solid electrolytes for water electrolysis at intermediate temperatures; and Task 4--production of hydrogen by thermocatalytic cracking of natural gas. For each task, this report presents a summary, introduction/description of project, and results.

Atomic hydrogen reactor

International Nuclear Information System (INIS)

Massip de Turville, C.M.D.

1982-01-01

Methods are discussed of generating heat in an atomic hydrogen reactor which involve; the production of atomic hydrogen by an electrical discharge, the capture of nascent neutrons from atomic hydrogen in a number of surrounding steel alloy tubes having a high manganese content to produce 56 Mn, the irradiation of atomic hydrogen by the high energy antineutrinos from the beta decay of 56 Mn to yield nascent neutrons, and the removal of the heat generated by the capture of nascent neutrons by 55 Mn and the beta decay of 56 Mn. (U.K.)

Kicking the habit[Hydrogen fuel

Energy Technology Data Exchange (ETDEWEB)

Jones, N.; Lawton, G.; Pearce, F.

2000-11-25

This article focuses on the use of clean non-polluting hydrogen fuel as opposed to the use of fossil fuels which ties western nations to the Middle East. Details are given of Iceland's plans to use hydrogen fuelled buses, cars, trucks and trawlers, car manufacturers' options of using internal combustion engines burning hydrogen and hydrogen fuel cells, and the production of hydrogen using electrolysis of water and steam reforming of hydrocarbons. The 'Green Dream' of pollution-free hydrogen production, the use of solar energy for renewable hydrogen production in California, and problems associated with hydrogen storage are discussed.

Hydrogen highway

International Nuclear Information System (INIS)

Anon

2008-01-01

The USA Administration would like to consider the US power generating industry as a basis ensuring both the full-scale production of hydrogen and the widespread use of the hydrogen related technological processes into the economy [ru

High density hydrogen research

International Nuclear Information System (INIS)

Hawke, R.S.

1977-01-01

The interest in the properties of very dense hydrogen is prompted by its abundance in Saturn and Jupiter and its importance in laser fusion studies. Furthermore, it has been proposed that the metallic form of hydrogen may be a superconductor at relatively high temperatures and/or exist in a metastable phase at ambient pressure. For ten years or more, laboratories have been developing the techniques to study hydrogen in the megabar region (1 megabar = 100 GPa). Three major approaches to study dense hydrogen experimentally have been used, static presses, shockwave compression, and magnetic compression. Static tchniques have crossed the megabar threshold in stiff materials but have not yet been convincingly successful in very compressible hydrogen. Single and double shockwave techniques have improved the precision of the pressure, volume, temperature Equation of State (EOS) of molecular hydrogen (deuterium) up to near 1 Mbar. Multiple shockwave and magnetic techniques have compressed hydrogen to several megabars and densities in the range of the metallic phase. The net result is that hydrogen becomes conducting at a pressure between 2 and 4 megabars. Hence, the possibility of making a significant amount of hydrogen into a metal in a static press remains a formidable challenge. The success of such experiments will hopefully answer the questions about hydrogen's metallic vs. conducting molecular phase, superconductivity, and metastability. 4 figures, 15 references

The hydrogen highway

International Nuclear Information System (INIS)

Grigg, A.

2004-01-01

'Full text:' The Hydrogen Highway in British Columbia, Canada, is a coordinated, large-scale demonstration and deployment program aimed at accelerating the commercialization of hydrogen and fuel cell technologies and products. It will be a showcase for fuel cell vehicles, refuelling stations and stationary power systems leading up to the 2010 Olympic and Paralympic Winter Games in Whistler, BC. The Hydrogen Highway is designed to help address many of the challenges to commercialization identified in the Canadian Fuel Cell Commercialization Roadmap. The project will create an early adopter network of hydrogen and fuel cell microenvironments where technology developers and users can learn about the technical, economic, environmental and social impacts of products. The Hydrogen Highway will give the public and potential purchasers an opportunity to feel, touch and see the new technology, as well as provide the industry with a venue in which to develop industry standards and supply chains of materials and components. While demonstration and deployment programs are a recognized and necessary component in the process to commercialize hydrogen and fuel cell technologies, there is no handbook describing how it should be done. This paper will describe the history, objectives, project details and some of the challenges associated with establishing Canada's Hydrogen Highway. (author)

The hydrogen highway

Energy Technology Data Exchange (ETDEWEB)

Grigg, A. [Fuel Cells Canada, Vancouver, British Columbia (Canada)

2004-07-01

'Full text:' The Hydrogen Highway in British Columbia, Canada, is a coordinated, large-scale demonstration and deployment program aimed at accelerating the commercialization of hydrogen and fuel cell technologies and products. It will be a showcase for fuel cell vehicles, refuelling stations and stationary power systems leading up to the 2010 Olympic and Paralympic Winter Games in Whistler, BC. The Hydrogen Highway is designed to help address many of the challenges to commercialization identified in the Canadian Fuel Cell Commercialization Roadmap. The project will create an early adopter network of hydrogen and fuel cell microenvironments where technology developers and users can learn about the technical, economic, environmental and social impacts of products. The Hydrogen Highway will give the public and potential purchasers an opportunity to feel, touch and see the new technology, as well as provide the industry with a venue in which to develop industry standards and supply chains of materials and components. While demonstration and deployment programs are a recognized and necessary component in the process to commercialize hydrogen and fuel cell technologies, there is no handbook describing how it should be done. This paper will describe the history, objectives, project details and some of the challenges associated with establishing Canada's Hydrogen Highway. (author)

Hydrogen

Directory of Open Access Journals (Sweden)

John O’M. Bockris

2011-11-01

Full Text Available The idea of a “Hydrogen Economy” is that carbon containing fuels should be replaced by hydrogen, thus eliminating air pollution and growth of CO2 in the atmosphere. However, storage of a gas, its transport and reconversion to electricity doubles the cost of H2 from the electrolyzer. Methanol made with CO2 from the atmosphere is a zero carbon fuel created from inexhaustible components from the atmosphere. Extensive work on the splitting of water by bacteria shows that if wastes are used as the origin of feed for certain bacteria, the cost for hydrogen becomes lower than any yet known. The first creation of hydrogen and electricity from light was carried out in 1976 by Ohashi et al. at Flinders University in Australia. Improvements in knowledge of the structure of the semiconductor-solution system used in a solar breakdown of water has led to the discovery of surface states which take part in giving rise to hydrogen (Khan. Photoelectrocatalysis made a ten times increase in the efficiency of the photo production of hydrogen from water. The use of two electrode cells; p and n semiconductors respectively, was first introduced by Uosaki in 1978. Most photoanodes decompose during the photoelectrolysis. To avoid this, it has been necessary to create a transparent shield between the semiconductor and its electronic properties and the solution. In this way, 8.5% at 25 °C and 9.5% at 50 °C has been reached in the photo dissociation of water (GaP and InAs by Kainthla and Barbara Zeleney in 1989. A large consortium has been funded by the US government at the California Institute of Technology under the direction of Nathan Lewis. The decomposition of water by light is the main aim of this group. Whether light will be the origin of the post fossil fuel supply of energy may be questionable, but the maximum program in this direction is likely to come from Cal. Tech.

Hydrogen.

Science.gov (United States)

Bockris, John O'M

2011-11-30

The idea of a "Hydrogen Economy" is that carbon containing fuels should be replaced by hydrogen, thus eliminating air pollution and growth of CO₂ in the atmosphere. However, storage of a gas, its transport and reconversion to electricity doubles the cost of H₂ from the electrolyzer. Methanol made with CO₂ from the atmosphere is a zero carbon fuel created from inexhaustible components from the atmosphere. Extensive work on the splitting of water by bacteria shows that if wastes are used as the origin of feed for certain bacteria, the cost for hydrogen becomes lower than any yet known. The first creation of hydrogen and electricity from light was carried out in 1976 by Ohashi et al. at Flinders University in Australia. Improvements in knowledge of the structure of the semiconductor-solution system used in a solar breakdown of water has led to the discovery of surface states which take part in giving rise to hydrogen (Khan). Photoelectrocatalysis made a ten times increase in the efficiency of the photo production of hydrogen from water. The use of two electrode cells; p and n semiconductors respectively, was first introduced by Uosaki in 1978. Most photoanodes decompose during the photoelectrolysis. To avoid this, it has been necessary to create a transparent shield between the semiconductor and its electronic properties and the solution. In this way, 8.5% at 25 °C and 9.5% at 50 °C has been reached in the photo dissociation of water (GaP and InAs) by Kainthla and Barbara Zeleney in 1989. A large consortium has been funded by the US government at the California Institute of Technology under the direction of Nathan Lewis. The decomposition of water by light is the main aim of this group. Whether light will be the origin of the post fossil fuel supply of energy may be questionable, but the maximum program in this direction is likely to come from Cal. Tech.

Hydrogen and its challenges

International Nuclear Information System (INIS)

Schal, M.

2008-01-01

The future of hydrogen as a universal fuel is in jeopardy unless we are able to produce it through an environment-friendly way and at a competitive cost. Today almost all the hydrogen used in the world is produced by steam reforming of natural gas. This process releases 8 tonnes of CO 2 per tonne of hydrogen produced. Other means of producing hydrogen are the hydrolysis, the very high temperature hydrolysis, and the direct chemical dissociation of water, these processes are greener than steam reforming but less efficient. About one hundred buses in the world operate on fuel cells fed by hydrogen, but it appears that the first industrial use of hydrogen at great scale will be for the local generation of electricity. Globally the annual budget for research concerning hydrogen is 4.4 milliard (10 9 ) euros worldwide. (A.C.)

Hydrogen production methods

International Nuclear Information System (INIS)

Hammerli, M.

1982-07-01

Old, present and new proceses for producing hydrogen are assessed critically. The emphasis throughout is placed on those processes which could be commercially viable before the turn of the century for large-scale hydrogen manufacture. Electrolysis of water is the only industrial process not dependent on fossil resources for large-scale hydrogen production and is likely to remain so for the next two or three decades. While many new processes, including those utilizing sunlight directly or indirectly, are presently not considered to be commercially viable for large-scale hydrogen production, research and development effort is needed to enhance our understanding of the nature of these processes. Water vapour electrolysis is compared with thermochemical processes: the former has the potential for displacing all other processes for producing hydrogen and oxygen from water

Synthesis of hydrogen-carbon clathrate material and hydrogen evolution therefrom at moderate temperatures and pressures

Science.gov (United States)

Lueking, Angela [State College, PA; Narayanan, Deepa [Redmond, WA

2011-03-08

A process for making a hydrogenated carbon material is provided which includes forming a mixture of a carbon source, particularly a carbonaceous material, and a hydrogen source. The mixture is reacted under reaction conditions such that hydrogen is generated and/or released from the hydrogen source, an amorphous diamond-like carbon is formed, and at least a portion of the generated and/or released hydrogen associates with the amorphous diamond-like carbon, thereby forming a hydrogenated carbon material. A hydrogenated carbon material including a hydrogen carbon clathrate is characterized by evolution of molecular hydrogen at room temperature at atmospheric pressure in particular embodiments of methods and compositions according to the present invention.

Examining hydrogen transitions.

Energy Technology Data Exchange (ETDEWEB)

Plotkin, S. E.; Energy Systems

2007-03-01

This report describes the results of an effort to identify key analytic issues associated with modeling a transition to hydrogen as a fuel for light duty vehicles, and using insights gained from this effort to suggest ways to improve ongoing modeling efforts. The study reported on here examined multiple hydrogen scenarios reported in the literature, identified modeling issues associated with those scenario analyses, and examined three DOE-sponsored hydrogen transition models in the context of those modeling issues. The three hydrogen transition models are HyTrans (contractor: Oak Ridge National Laboratory), MARKAL/DOE* (Brookhaven National Laboratory), and NEMS-H2 (OnLocation, Inc). The goals of these models are (1) to help DOE improve its R&D effort by identifying key technology and other roadblocks to a transition and testing its technical program goals to determine whether they are likely to lead to the market success of hydrogen technologies, (2) to evaluate alternative policies to promote a transition, and (3) to estimate the costs and benefits of alternative pathways to hydrogen development.

Bandgap engineering of InGaAsP/InP laser structure by photo-absorption-induced point defects

Science.gov (United States)

Kaleem, Mohammad; Nazir, Sajid; Saqib, Nazar Abbas

2016-03-01

Integration of photonic components on the same photonic wafer permits future optical communication systems to be dense and advanced performance. This enables very fast information handling between photonic active components interconnected through passive optical low loss channels. We demonstrate the UV-Laser based Quantum Well Intermixing (QWI) procedure to engineer the band-gap of compressively strained InGaAsP/InP Quantum Well (QW) laser material. We achieved around 135nm of blue-shift by simply applying excimer laser (λ= 248nm). The under observation laser processed material also exhibits higher photoluminescence (PL) intensity. Encouraging experimental results indicate that this simple technique has the potential to produce photonic integrated devices and circuits.

Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

International Nuclear Information System (INIS)

Bory, Benjamin F.; Wang, Jingxin; Janssen, René A. J.; Meskers, Stefan C. J.; Gomes, Henrique L.; De Leeuw, Dago M.

2014-01-01

Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron–hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 10 25 /m 3 . The electroformed alkali halide layer can be considered as a highly doped semiconductor with metallic transport characteristics

Europe - the first hydrogen economy?