WorldWideScience

Sample records for spin-polarized scanning tunnelling

  1. Spin-polarized scanning tunneling microscopy: breakthroughs and highlights.

    Science.gov (United States)

    Bode, Matthias

    2012-01-01

    The principle of scanning tunneling microscopy, an imaging method with atomic resolution capability invented by Binnig and Rohrer in 1982, can be adapted for surface magnetism studies by using magnetic probe tips. The contrast mechanism of this so-called spin-polarized scanning tunneling microscopy, or SP-STM, relies on the tunneling magneto-resistance effect, i.e. the tip-sample distance as well as the differential conductance depend on the relative magnetic orientation of tip and sample. To illustrate the working principle and the unique capabilities of SP-STM, this compilation presents some key experiments which have been performed on various magnetic surfaces, such as the topological antiferromagnet Cr(001), a double-layer of Fe which exhibits a stripe- domain pattern with about 50 nm periodicity, and the Mn monolayer on W(110), where the combination of experiment and theory reveal an antiferromagnetic spin cycloid. Recent experimental results also demonstrate the suitability of SP-STM for studies of dynamic properties, such as the spin relaxation time of single magnetic nanostructures.

  2. Compact scanning tunneling microscope for spin polarization measurements.

    Science.gov (United States)

    Kim, Seong Heon; de Lozanne, Alex

    2012-10-01

    We present a design for a scanning tunneling microscope that operates in ultrahigh vacuum down to liquid helium temperatures in magnetic fields up to 8 T. The main design philosophy is to keep everything compact in order to minimize the consumption of cryogens for initial cool-down and for extended operation. In order to achieve this, new ideas were implemented in the design of the microscope body, dewars, vacuum chamber, manipulators, support frame, and vibration isolation. After a brief description of these designs, the results of initial tests are presented.

  3. The impact of structural relaxation on spin polarization and magnetization reversal of individual nano structures studied by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Sander, Dirk; Phark, Soo-Hyon; Corbetta, Marco; Fischer, Jeison A; Oka, Hirofumi; Kirschner, Jürgen

    2014-10-01

    The application of low temperature spin-polarized scanning tunneling microscopy and spectroscopy in magnetic fields for the quantitative characterization of spin polarization, magnetization reversal and magnetic anisotropy of individual nano structures is reviewed. We find that structural relaxation, spin polarization and magnetic anisotropy vary on the nm scale near the border of a bilayer Co island on Cu(1 1 1). This relaxation is lifted by perimetric decoration with Fe. We discuss the role of spatial variations of the spin-dependent electronic properties within and at the edge of a single nano structure for its magnetic properties.

  4. In situ scanning tunneling microscope tip treatment device for spin polarization imaging

    Science.gov (United States)

    Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN

    2008-04-22

    A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.

  5. Spin-polarized tunneling with GaAs tips in scanning tunneling microscopy

    NARCIS (Netherlands)

    Prins, M.W.J.; Jansen, R.; Kempen, van H.

    1996-01-01

    We describe a model as well as experiments on spin-polarized tunneling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate

  6. Recent advances in atomic-scale spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Smith, Arthur R; Yang, Rong; Yang, Haiqiang; Dick, Alexey; Neugebauer, Joerg; Lambrecht, Walter R L

    2005-02-01

    The Mn3N2 (010) surface has been studied using spin-polarized scanning tunneling microscopy at the atomic scale. The principle objective of this work is to elucidate the properties and potential of this technique to measure atomic-scale magnetic structures. The experimental approach involves the use of a combined molecular beam epitaxy/scanning tunneling microscopy system that allows the study of atomically clean magnetic surfaces. Several key findings have been obtained. First, both magnetic and non-magnetic atomic-scale information has been obtained in a single spin-polarized image. Magnetic modulation of the height profile having an antiferromagnetic super-period of c = 12.14 A (6 atomic rows) together with a non-magnetic superstructure having a period of c/2 = 6.07 A (3 atomic rows) was observed. Methods of separation of magnetic and non-magnetic profiles are presented. Second, bias voltage-dependent spin-polarized images show a reversal of the magnetic modulation at a particular voltage. This reversal is clearly due to a change in the sign of the magnetic term in the tunnel current. Since this term depends on both the tip's as well as the sample's magnetic local density of states, the reversal can be caused by either the sample or the tip. Third, the shape of the line profile was found to vary with the bias voltage, which is related to the energy-dependent spin contribution from the 2 chemically inequivalent Mn sites on the surface. Overall, the results shown here expand the application of the method of spin-polarized scanning tunneling microscopy to measure atomic-scale magnetic structures. (c) 2005 Wiley-Liss, Inc.

  7. Spin-filter scanning tunneling microscopy : a novel technique for the analysis of spin polarization on magnetic surfaces and spintronic devices

    NARCIS (Netherlands)

    Vera Marun, I.J.

    2010-01-01

    This thesis deals with the development of a versatile technique to measure spin polarization with atomic resolution. A microscopy technique that can measure electronic spin polarization is relevant for characterization of magnetic nanostructures and spintronic devices. Scanning tunneling microscopy

  8. Vectorial mapping of noncollinear antiferromagnetic structure of semiconducting FeSe surface with spin-polarized scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Xiaole [Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Chen, Xianfeng [The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L., E-mail: clgao@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Luo, Weidong, E-mail: wdluo@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)

    2016-02-08

    Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.

  9. Vectorial mapping of noncollinear antiferromagnetic structure of semiconducting FeSe surface with spin-polarized scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Zhang, K. F.; Yang, Fang; Song, Y. R.; Zhang, Xiaole; Chen, Xianfeng; Liu, Canhua; Qian, Dong; Gao, C. L.; Jia, Jin-Feng; Luo, Weidong

    2016-01-01

    Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations

  10. New insights into nano-magnetism by spin-polarized scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sander, Dirk, E-mail: sander@mpi-halle.de [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale (Germany); Oka, Hirofumi; Corbetta, Marco; Stepanyuk, Valeri; Kirschner, Jürgen [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle/Saale (Germany)

    2013-08-15

    Highlights: ► We measure the magnetization reversal of individual nm small Co island by spin-STM. ► We identify an inhomogeneous magnetic anisotropy within a single Co island. ► The magnetic anisotropy near the rim is negligible as compared to 0.148 meV/atom at the island center. ► A crossover of the magnetization reversal from an exchange-spring behavior to domain wall formation is suggested. ► The impact of the observed spatial variation of the spin-dependent electronic properties on reversal is discussed. -- Abstract: We study the magnetization reversal and the position dependence of the spin-dependent electronic properties of nm small bilayer Co islands on Cu(1 1 1) by spin-polarized scanning tunneling microscopy in magnetic fields at low temperatures of 8 K. The analysis of the energy barrier of magnetization reversal from measurements of the switching field suggests a crossover of the magnetization reversal mode with increasing island size around 7500 atoms from exchange-spring behavior to domain wall formation. The quantitative analysis of the island size dependence of the energy barrier indicates an inhomogeneous magnetic anisotropy of the island. The island rim is magnetically soft, whereas the center shows a pronounced effective anisotropy of 0.148 meV/atom. We speculate that this inhomogeneity of the magnetic anisotropy might be a consequence of the spatial dependence of the spin-dependent electronic properties. We measure a spin-polarization and a tunnel magneto resistance ratio of opposite sign at the rim as compared to the island center.

  11. New insights into nano-magnetism by spin-polarized scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Sander, Dirk; Oka, Hirofumi; Corbetta, Marco; Stepanyuk, Valeri; Kirschner, Jürgen

    2013-01-01

    Highlights: ► We measure the magnetization reversal of individual nm small Co island by spin-STM. ► We identify an inhomogeneous magnetic anisotropy within a single Co island. ► The magnetic anisotropy near the rim is negligible as compared to 0.148 meV/atom at the island center. ► A crossover of the magnetization reversal from an exchange-spring behavior to domain wall formation is suggested. ► The impact of the observed spatial variation of the spin-dependent electronic properties on reversal is discussed. -- Abstract: We study the magnetization reversal and the position dependence of the spin-dependent electronic properties of nm small bilayer Co islands on Cu(1 1 1) by spin-polarized scanning tunneling microscopy in magnetic fields at low temperatures of 8 K. The analysis of the energy barrier of magnetization reversal from measurements of the switching field suggests a crossover of the magnetization reversal mode with increasing island size around 7500 atoms from exchange-spring behavior to domain wall formation. The quantitative analysis of the island size dependence of the energy barrier indicates an inhomogeneous magnetic anisotropy of the island. The island rim is magnetically soft, whereas the center shows a pronounced effective anisotropy of 0.148 meV/atom. We speculate that this inhomogeneity of the magnetic anisotropy might be a consequence of the spatial dependence of the spin-dependent electronic properties. We measure a spin-polarization and a tunnel magneto resistance ratio of opposite sign at the rim as compared to the island center

  12. Spin-polarized scanning tunneling microscopy and spectroscopy study of chromium on a Cr(001) surface.

    Science.gov (United States)

    Lagoute, J; Kawahara, S L; Chacon, C; Repain, V; Girard, Y; Rousset, S

    2011-02-02

    Several tens of chromium layers were deposited at 250 °C on a Cr(001) surface and investigated by spin-polarized scanning tunneling microscopy (SP-STM), Auger electron spectroscopy (AES) and scanning tunneling spectroscopy (STS). Chromium is found to grow with a mound-like morphology resulting from the stacking of several monolayers which do not uniformly cover the whole surface of the substrate. The terminal plane consists of an irregular array of Cr islands with lateral sizes smaller than 20 × 20 nm(2). Combined AES and STS measurements reveal the presence of a significant amount of segregants prior to and after deposition. A detailed investigation of the surface shows that it consists of two types of patches. Thanks to STS measurements, the two types of area have been identified as being either chromium pure or segregant rich. SP-STM experiments have evidenced that the antiferromagnetic layer coupling remains in the chromium mounds after deposition and is not significantly affected by the presence of the segregants.

  13. Joule heating and spin-transfer torque investigated on the atomic scale using a spin-polarized scanning tunneling microscope.

    Science.gov (United States)

    Krause, S; Herzog, G; Schlenhoff, A; Sonntag, A; Wiesendanger, R

    2011-10-28

    The influence of a high spin-polarized tunnel current onto the switching behavior of a superparamagnetic nanoisland on a nonmagnetic substrate is investigated by means of spin-polarized scanning tunneling microscopy. A detailed lifetime analysis allows for a quantification of the effective temperature rise of the nanoisland and the modification of the activation energy barrier for magnetization reversal, thereby using the nanoisland as a local thermometer and spin-transfer torque analyzer. Both the Joule heating and spin-transfer torque are found to scale linearly with the tunnel current. The results are compared to experiments performed on lithographically fabricated magneto-tunnel junctions, revealing a very high spin-transfer torque switching efficiency in our experiments.

  14. Spin-polarized scanning tunneling microscopy with quantitative insights into magnetic probes.

    Science.gov (United States)

    Phark, Soo-Hyon; Sander, Dirk

    2017-01-01

    Spin-polarized scanning tunneling microscopy and spectroscopy (spin-STM/S) have been successfully applied to magnetic characterizations of individual nanostructures. Spin-STM/S is often performed in magnetic fields of up to some Tesla, which may strongly influence the tip state. In spite of the pivotal role of the tip in spin-STM/S, the contribution of the tip to the differential conductance d I /d V signal in an external field has rarely been investigated in detail. In this review, an advanced analysis of spin-STM/S data measured on magnetic nanoislands, which relies on a quantitative magnetic characterization of tips, is discussed. Taking advantage of the uniaxial out-of-plane magnetic anisotropy of Co bilayer nanoisland on Cu(111), in-field spin-STM on this system has enabled a quantitative determination, and thereby, a categorization of the magnetic states of the tips. The resulting in-depth and conclusive analysis of magnetic characterization of the tip opens new venues for a clear-cut sub-nanometer scale spin ordering and spin-dependent electronic structure of the non-collinear magnetic state in bilayer high Fe nanoislands on Cu(111).

  15. Spin-polarized scanning tunneling spectroscopy of self-organized nanoscale Co islands on Au(111) surfaces.

    Science.gov (United States)

    Schouteden, K; Muzychenko, D A; Van Haesendonck, C

    2008-07-01

    Magnetic monolayer and bilayer Co islands of only a few nanometer in size were grown by atomic deposition on atomically flat Au(111) films. The islands were studied in situ by scanning tunneling microscopy (STM) and spectroscopy at low temperatures. Spin-resolved tunneling spectroscopy, using an STM tip with a magnetic coating, revealed that the Co islands exhibit a net magnetization perpendicular to the substrate surface due to the presence of spin-polarized d-states. A random distribution of islands with either upward or downward pointing magnetization was observed, without any specific correlation of magnetization orientation with island size or island height.

  16. Interface-induced chiral domain walls, spin spirals and skyrmions revealed by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    von Bergmann, Kirsten; Kubetzka, André; Pietzsch, Oswald; Wiesendanger, Roland

    2014-10-01

    The spin textures of ultra-thin magnetic layers exhibit surprising variety. The loss of inversion symmetry at the interface of the magnetic layer and substrate gives rise to the so-called Dzyaloshinskii-Moriya interaction which favors non-collinear spin arrangements with unique rotational sense. Here we review the application of spin-polarized scanning tunneling microscopy to such systems, which has led to the discovery of interface-induced chiral domain walls and spin spirals. Recently, different interface-driven skyrmion lattices have been found, and the writing as well as the deleting of individual skyrmions based on local spin-polarized current injection has been demonstrated. These interface-induced non-collinear magnetic states offer new exciting possibilities to study fundamental magnetic interactions and to tailor material properties for spintronic applications.

  17. Spin-polarized scanning-tunneling probe for helical Luttinger liquids.

    Science.gov (United States)

    Das, Sourin; Rao, Sumathi

    2011-06-10

    We propose a three-terminal spin-polarized STM setup for probing the helical nature of the Luttinger liquid edge state that appears in the quantum spin Hall system. We show that the three-terminal tunneling conductance depends on the angle (θ) between the magnetization direction of the tip and the local orientation of the electron spin on the edge while the two terminal conductance is independent of this angle. We demonstrate that chiral injection of an electron into the helical Luttinger liquid (when θ is zero or π) is associated with fractionalization of the spin of the injected electron in addition to the fractionalization of its charge. We also point out a spin current amplification effect induced by the spin fractionalization.

  18. Experimental verification of the rotational type of chiral spin spiral structures by spin-polarized scanning tunneling microscopy.

    Science.gov (United States)

    Haze, Masahiro; Yoshida, Yasuo; Hasegawa, Yukio

    2017-10-16

    We report on experimental verification of the rotational type of chiral spin spirals in Mn thin films on a W(110) substrate using spin-polarized scanning tunneling microscopy (SP-STM) with a double-axis superconducting vector magnet. From SP-STM images using Fe-coated W tips magnetized to the out-of-plane and [001] directions, we found that both Mn mono- and double-layers exhibit cycloidal rotation whose spins rotate in the planes normal to the propagating directions. Our results agree with the theoretical prediction based on the symmetry of the system, supporting that the magnetic structures are driven by the interfacial Dzyaloshinskii-Moriya interaction.

  19. Spin polarized electron tunneling and magnetoresistance in molecular junctions.

    Science.gov (United States)

    Szulczewski, Greg

    2012-01-01

    This chapter reviews tunneling of spin-polarized electrons through molecules positioned between ferromagnetic electrodes, which gives rise to tunneling magnetoresistance. Such measurements yield important insight into the factors governing spin-polarized electron injection into organic semiconductors, thereby offering the possibility to manipulate the quantum-mechanical spin degrees of freedom for charge carriers in optical/electrical devices. In the first section of the chapter a brief description of the Jullière model of spin-dependent electron tunneling is reviewed. Next, a brief description of device fabrication and characterization is presented. The bulk of the review highlights experimental studies on spin-polarized electron tunneling and magnetoresistance in molecular junctions. In addition, some experiments describing spin-polarized scanning tunneling microscopy/spectroscopy on single molecules are mentioned. Finally, some general conclusions and prospectus on the impact of spin-polarized tunneling in molecular junctions are offered.

  20. Thermal stability of tunneling spin polarization

    International Nuclear Information System (INIS)

    Kant, C.H.; Kohlhepp, J.T.; Paluskar, P.V.; Swagten, H.J.M.; Jonge, W.J.M. de

    2005-01-01

    We present a study of the thermal stability of tunneling spin polarization in Al/AlOx/ferromagnet junctions based on the spin-polarized tunneling technique, in which the Zeeman-split superconducting density of states in the Al electrode is used as a detector for the spin polarization. Thermal robustness of the polarization, which is of key importance for the performance of magnetic tunnel junction devices, is demonstrated for post-deposition anneal temperatures up to 500 o C with Co and Co 90 Fe 10 top electrodes, independent of the presence of an FeMn layer on top of the ferromagnet

  1. Co on Pt(111) studied by spin-polarized scanning tunneling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Meier, F.K.

    2006-07-01

    In this thesis the electronic properties of the bare Pt(111) surface, the structural, electronic, and magnetic properties of monolayer and double-layer high Co nanostructures as well as the spin-averaged electronic structure of single Co atoms on Pt(111) were studied by low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The experiments on the bare Pt(111) surface and on single Co atoms have been performed in an STM facility operating at temperatures of down to 0.3 K and at magnetic fields of up to 14 T under ultra-high vacuum conditions. The facility has been taken into operation within the time period of this thesis and its specifications were tested by STS measurements. These characterization measurements show a very high stability of the tunneling junction and an energy resolution of about 100 {mu}eV, which is close to the thermal limit. The investigation of the electronic structure of the bare Pt(111) surface reveals the existence of an unoccupied surface state. By a comparison of the measured dispersion to first-principles electronic structure calculations the state is assigned to an sp-derived surface band at the lower boundary of the projected bulk band gap. The surface state exhibits a strong spin-orbit coupling induced spin splitting. The close vicinity to the bulk bands leads to a strong linear contribution to the dispersion and thus to a deviant appearance in the density of states in comparison to the surface states of the (111) surfaces of noble metals. A detailed study of Co monolayer and double-layer nanostructures on the Pt(111) surface shows that both kinds of nanostructures exhibit a highly inhomogeneous electronic structure which changes at the scale of only a few Aa due to a strong stacking dependence with respect to the Pt(111) substrate. With the help of first principles calculations the different spectroscopic appearance for Co atoms within the Co monolayer is assigned to a stacking dependent hybridization of Co states

  2. Role of spin polarized tunneling in magnetoresistance and low

    Indian Academy of Sciences (India)

    Role of spin polarized tunneling in magnetoresistance and low temperature minimum of polycrystalline La1–KMnO3 ( = 0.05, 0.1, ... Manganites; magnetoresistance; low temperature resistivity; spin polarized tunneling. ... Current Issue

  3. Spin-polarized scanning electron microscopy

    International Nuclear Information System (INIS)

    Kohashi, Teruo

    2014-01-01

    Spin-Polarized Scanning Electron Microscopy (Spin SEM) is one way for observing magnetic domain structures taking advantage of the spin polarization of the secondary electrons emitted from a ferromagnetic sample. This principle brings us several excellent capabilities such as high-spatial resolution better than 10 nm, and analysis of magnetization direction in three dimensions. In this paper, the principle and the structure of the spin SEM is briefly introduced, and some examples of the spin SEM measurements are shown. (author)

  4. Spin polarization at the interface and tunnel magnetoresistance

    International Nuclear Information System (INIS)

    Itoh, H.; Inoue, J.

    2001-01-01

    We propose that interfacial states of imperfectly oxidized Al ions may exist in ferromagnetic tunnel junctions with Al-O barrier and govern both the spin polarization and tunnel conductance. It is shown that the spin polarization is positive independent of materials and correlates well with the tunnel magnetoresistance

  5. Real-space observation of a right-rotating inhomogeneous cycloidal spin spiral by spin-polarized scanning tunneling microscopy in a triple axes vector magnet.

    Science.gov (United States)

    Meckler, S; Mikuszeit, N; Pressler, A; Vedmedenko, E Y; Pietzsch, O; Wiesendanger, R

    2009-10-09

    Using spin-polarized scanning tunneling microscopy performed in a triple axes vector magnet, we show that the magnetic structure of the Fe double layer on W(110) is an inhomogeneous right-rotating cycloidal spin spiral. The magnitude of the Dzyaloshinskii-Moriya vector is extracted from the experimental data using micromagnetic calculations. The result is confirmed by comparison of the measured saturation field along the easy axis to the respective value as obtained from Monte Carlo simulations. We find that the Dzyaloshinskii-Moriya interaction is too weak to destabilize the single domain state. However, it can define the sense of rotation and the cycloidal spiral type once the single domain state is destabilized by dipolar interaction.

  6. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R., E-mail: smitha2@ohio.edu [Department of Physics and Astronomy, Nanoscale and Quantum Phenomena Institute, Ohio University, Athens, Ohio 45701 (United States)

    2014-04-15

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  7. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

    Science.gov (United States)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

    2014-04-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  8. Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy

    International Nuclear Information System (INIS)

    Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R.

    2014-01-01

    Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without

  9. Spin-Polarized Scanning Tunneling Microscope for Atomic-Scale Studies of Spin Transport, Spin Relaxation, and Magnetism in Graphene

    Science.gov (United States)

    2017-11-09

    Polarized Scanning Tunneling Microscope for Atomic-Scale Studies of Spin Transport, Spin Relaxation, and Magnetism in Graphene Report Term: 0-Other Email ...Principal: Y Name: Jay A Gupta Email : gupta.208@osu.edu Name: Roland K Kawakami Email : kawakami.15@osu.edu RPPR Final Report as of 13-Nov-2017...studies on films and devices. Optimization of the Cr tip will be the next important step to establish this technique. We are writing up these early

  10. A modular designed ultra-high-vacuum spin-polarized scanning tunneling microscope with controllable magnetic fields for investigating epitaxial thin films.

    Science.gov (United States)

    Wang, Kangkang; Lin, Wenzhi; Chinchore, Abhijit V; Liu, Yinghao; Smith, Arthur R

    2011-05-01

    A room-temperature ultra-high-vacuum scanning tunneling microscope for in situ scanning freshly grown epitaxial films has been developed. The core unit of the microscope, which consists of critical components including scanner and approach motors, is modular designed. This enables easy adaptation of the same microscope units to new growth systems with different sample-transfer geometries. Furthermore the core unit is designed to be fully compatible with cryogenic temperatures and high magnetic field operations. A double-stage spring suspension system with eddy current damping has been implemented to achieve ≤5 pm z stability in a noisy environment and in the presence of an interconnected growth chamber. Both tips and samples can be quickly exchanged in situ; also a tunable external magnetic field can be introduced using a transferable permanent magnet shuttle. This allows spin-polarized tunneling with magnetically coated tips. The performance of this microscope is demonstrated by atomic-resolution imaging of surface reconstructions on wide band-gap GaN surfaces and spin-resolved experiments on antiferromagnetic Mn(3)N(2)(010) surfaces.

  11. Spin-Polarization in Quasi-Magnetic Tunnel Junctions

    Science.gov (United States)

    Xie, Zheng-Wei; Li, Ling

    2017-05-01

    Spin polarization in ferromagnetic metal/insulator/spin-filter barrier/nonmagnetic metal, referred to as quasi-magnetic tunnel junctions, is studied within the free-electron model. Our results show that large positive or negative spin-polarization can be obtained at high bias in quasi-magnetic tunnel junctions, and within large bias variation regions, the degree of spin-polarization can be linearly tuned by bias. These linear variation regions of spin-polarization with bias are influenced by the barrier thicknesses, barrier heights and molecular fields in the spin-filter (SF) layer. Among them, the variations of thickness and heights of the insulating and SF barrier layers have influence on the value of spin-polarization and the linear variation regions of spin-polarization with bias. However, the variations of molecular field in the SF layer only have influence on the values of the spin-polarization and the influences on the linear variation regions of spin-polarization with bias are slight. Supported by the Key Natural Science Fund of Sichuan Province Education Department under Grant Nos 13ZA0149 and 16ZA0047, and the Construction Plan for Scientific Research Innovation Team of Universities in Sichuan Province under Grant No 12TD008.

  12. Observation of layered antiferromagnetism in self-assembled parallel NiSi nanowire arrays on Si(110) by spin-polarized scanning tunneling spectromicroscopy

    Science.gov (United States)

    Hong, Ie-Hong; Hsu, Hsin-Zan

    2018-03-01

    The layered antiferromagnetism of parallel nanowire (NW) arrays self-assembled on Si(110) have been observed at room temperature by direct imaging of both the topographies and magnetic domains using spin-polarized scanning tunneling microscopy/spectroscopy (SP-STM/STS). The topographic STM images reveal that the self-assembled unidirectional and parallel NiSi NWs grow into the Si(110) substrate along the [\\bar{1}10] direction (i.e. the endotaxial growth) and exhibit multiple-layer growth. The spatially-resolved SP-STS maps show that these parallel NiSi NWs of different heights produce two opposite magnetic domains, depending on the heights of either even or odd layers in the layer stack of the NiSi NWs. This layer-wise antiferromagnetic structure can be attributed to an antiferromagnetic interlayer exchange coupling between the adjacent layers in the multiple-layer NiSi NW with a B2 (CsCl-type) crystal structure. Such an endotaxial heterostructure of parallel magnetic NiSi NW arrays with a layered antiferromagnetic ordering in Si(110) provides a new and important perspective for the development of novel Si-based spintronic nanodevices.

  13. Spin-polarized inelastic tunneling through insulating barriers.

    Science.gov (United States)

    Lu, Y; Tran, M; Jaffrès, H; Seneor, P; Deranlot, C; Petroff, F; George, J-M; Lépine, B; Ababou, S; Jézéquel, G

    2009-05-01

    Spin-conserving hopping transport through chains of localized states has been evidenced by taking benefit of the high degree of spin-polarization of CoFeB-MgO-CoFeB magnetic tunnel junctions. In particular, our data show that relatively thick MgO barriers doped with boron favor the activation of spin-conserving inelastic channels through a chain of three localized states and leading to reduced magnetoresistance effects. We propose an extension of the Glazman-Matveev theory to the case of ferromagnetic reservoirs to account for spin-polarized inelastic tunneling through nonmagnetic localized states embedded in an insulating barrier.

  14. Resonant tunneling via spin-polarized barrier states in a magnetic tunnel junction

    NARCIS (Netherlands)

    Jansen, R.; Lodder, J.C.

    2000-01-01

    Resonant tunneling through states in the barrier of a magnetic tunnel junction has been analyzed theoretically for the case of a spin-polarized density of barrier states. It is shown that for highly spin-polarized barrier states, the magnetoresistance due to resonant tunneling is enhanced compared

  15. Spin-polarized tunneling through a ferromagnetic insulator

    NARCIS (Netherlands)

    Kok, M.; Kok, M.; Beukers, J.N.; Brinkman, Alexander

    2009-01-01

    The polarization of the tunnel conductance of spin-selective ferromagnetic insulators is modeled, providing a generalized concept of polarization including both the effects of electrode and barrier polarization. The polarization model is extended to take additional non-spin-polarizing insulating

  16. Spin polarized tunnelling investigation of nanometre Co clusters by means of a Ni bulk tip

    International Nuclear Information System (INIS)

    Rastei, M V; Bucher, J P

    2006-01-01

    A massive Ni tip is used in spin polarized scanning tunnelling microscopy (SP STM) to explore the magnetization state of nanometre Co clusters, self-organized on the Au(111) surface. Constant current STM images taken at 4.6 K show a bimodal distribution of the cluster heights, accounting for the spin polarization of the STM junction. The spin polarization of the tunnel junction as a function of the bias voltage is found to depend on the local density of states of the sample examined. Changing the vacuum barrier parameters by bringing the tip closer to the surface leads to a reduction in the tunnelling magnetoresistance that may be attributed to spin flip effects. (letter to the editor)

  17. Tunneling Spectroscopy Study of Spin-Polarized Quasiparticle Injection Effects in Cuparate/Manganite Heterostructures

    Science.gov (United States)

    Wei, J. Y. T.; Yeh, N. C.; Vasquez, R. P.

    1998-01-01

    Scanning tunneling spectroscopy was performed at 4.2K on epitaxial thin-film heterostructures comprising YBa2Cu3O7 and La0.7Ca0.3MnO3, to study the microscopic effects of spin-polarized quasiparticle injection from the half-metallic ferromagnetic manganite on the high-Tc cuprate superconductor.

  18. Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

    Energy Technology Data Exchange (ETDEWEB)

    Matsuyama, H., E-mail: matsu@phys.sci.hokudai.ac.jp [Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Nara, D.; Kageyama, R.; Honda, K.; Sato, T.; Kusanagi, K. [Department of Condensed Matter Physics, Graduate School of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Srinivasan, E. [Creative Research Institution (CRIS), Hokkaido University, Sapporo, Hokkaido 001-0021 (Japan); Koike, K. [Department of Physics, Faculty of Science, Hokkaido University, Sapporo, Hokkaido 060-0810 (Japan); Creative Research Institution (CRIS), Hokkaido University, Sapporo, Hokkaido 001-0021 (Japan)

    2016-03-15

    We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM) in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin image of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.

  19. Spin-polarized scanning tunneling microscopy experiments on the rough surface of a polycrystalline NiFe film with a fine magnetic tip sensitive to a well-defined magnetization component

    Directory of Open Access Journals (Sweden)

    H. Matsuyama

    2016-03-01

    Full Text Available We developed a micrometer-sized magnetic tip integrated onto the write head of a hard disk drive for spin-polarized scanning tunneling microscopy (SP-STM in the modulated tip magnetization mode. Using SP-STM, we measured a well-defined in-plane spin-component of the tunneling current of the rough surface of a polycrystalline NiFe film. The spin asymmetry of the NiFe film was about 1.3% within the bias voltage range of -3 to 1 V. We obtained the local spin component image of the sample surface, switching the magnetic field of the sample to reverse the sample magnetization during scanning. We also obtained a spin image of the rough surface of a polycrystalline NiFe film evaporated on the recording medium of a hard disk drive.

  20. Probing spin-polarized tunneling at high bias and temperature with a magnetic tunnel transistor

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Min, B.C.; Sanderink, Johannes G.M.; Lodder, J.C.; Jansen, R.

    2005-01-01

    The magnetic tunnel transistor (MTT) is a three terminal hybrid device that consists of a tunnel emitter, a ferromagnetic (FM) base, and a semiconductor collector. In the MTT with a FM emitter and a single FM base, spin-polarized hot electrons are injected into the base by tunneling. After

  1. Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field.

    Science.gov (United States)

    von Allwörden, Henning; Eich, Andreas; Knol, Elze J; Hermenau, Jan; Sonntag, Andreas; Gerritsen, Jan W; Wegner, Daniel; Khajetoorians, Alexander A

    2018-03-01

    We describe the design and performance of a scanning tunneling microscope (STM) that operates at a base temperature of 30 mK in a vector magnetic field. The cryogenics is based on an ultra-high vacuum (UHV) top-loading wet dilution refrigerator that contains a vector magnet allowing for fields up to 9 T perpendicular and 4 T parallel to the sample. The STM is placed in a multi-chamber UHV system, which allows in situ preparation and exchange of samples and tips. The entire system rests on a 150-ton concrete block suspended by pneumatic isolators, which is housed in an acoustically isolated and electromagnetically shielded laboratory optimized for extremely low noise scanning probe measurements. We demonstrate the overall performance by illustrating atomic resolution and quasiparticle interference imaging and detail the vibrational noise of both the laboratory and microscope. We also determine the electron temperature via measurement of the superconducting gap of Re(0001) and illustrate magnetic field-dependent measurements of the spin excitations of individual Fe atoms on Pt(111). Finally, we demonstrate spin resolution by imaging the magnetic structure of the Fe double layer on W(110).

  2. Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field

    Science.gov (United States)

    von Allwörden, Henning; Eich, Andreas; Knol, Elze J.; Hermenau, Jan; Sonntag, Andreas; Gerritsen, Jan W.; Wegner, Daniel; Khajetoorians, Alexander A.

    2018-03-01

    We describe the design and performance of a scanning tunneling microscope (STM) that operates at a base temperature of 30 mK in a vector magnetic field. The cryogenics is based on an ultra-high vacuum (UHV) top-loading wet dilution refrigerator that contains a vector magnet allowing for fields up to 9 T perpendicular and 4 T parallel to the sample. The STM is placed in a multi-chamber UHV system, which allows in situ preparation and exchange of samples and tips. The entire system rests on a 150-ton concrete block suspended by pneumatic isolators, which is housed in an acoustically isolated and electromagnetically shielded laboratory optimized for extremely low noise scanning probe measurements. We demonstrate the overall performance by illustrating atomic resolution and quasiparticle interference imaging and detail the vibrational noise of both the laboratory and microscope. We also determine the electron temperature via measurement of the superconducting gap of Re(0001) and illustrate magnetic field-dependent measurements of the spin excitations of individual Fe atoms on Pt(111). Finally, we demonstrate spin resolution by imaging the magnetic structure of the Fe double layer on W(110).

  3. Spin-polarized scanning tunneling microscopy of magnetic nanostructures at the example of bcc-Co/Fe(110), Fe/Mo(110), and copper phthalocyanine/Fe(1110); Spinpolarisierte Rastertunnelmikroskopie magnetischer Nanostrukturen am Beispiel von bcc-Co/Fe(110), Fe/Mo(110) und Kupfer-Phthalocyanin/Fe(110)

    Energy Technology Data Exchange (ETDEWEB)

    Methfessel, Torsten

    2010-12-09

    This thesis provides an introduction into the technique of spin-polarized scanning tunnelling microscopy and spectroscopy as an experimental method for the investigation of magnetic nanostructures. Experimental results for the spin polarized electronic structure depending on the crystal structure of ultrathin Co layers, and depending on the direction of the magnetization for ultrathin Fe layers are presented. High-resolution measurements show the position-dependent spin polarization on a single copper-phthalocyanine molecule deposited on a ferromagnetic surface. Co was deposited by molecular beam epitaxy on the (110) surface of the bodycentered cubic metals Cr and Fe. In contrast to previous reports in the literature only two layers of Co can be stabilized in the body-centered cubic (bcc) structure. The bcc-Co films on the Fe(110) surface show no signs of epitaxial distortions. Thicker layers reconstruct into a closed-packed structure (hcp / fcc). The bcc structure increases the spin-polarization of Co to P=62 % in comparison to hcp-Co (P=45 %). The temperature-dependent spin-reorientation of ultrathin Fe/Mo(110) films was investigated by spin-polarized spectroscopy. A reorientation of the magnetic easy axis from the [110] direction along the surface normal to the in-plane [001] axis is observed at T (13.2{+-}0.5) K. This process can be identified as a discontinuous reorientation transition, revealing two simultaneous minima of the free energy in a certain temperature range. The electronic structure of mono- and double-layer Fe/Mo(110) shows a variation with the reorientation of the magnetic easy axis and with the direction of the magnetization. The investigation of the spin-polarized charge transport through a copper-phthalocyanine molecule on the Fe/Mo(110) surface provides an essential contribution to the understanding of spin-transport at the interface between metal and organic molecule. Due to the interaction with the surface of the metal the HOMO-LUMO energy

  4. Tunnel spin polarization versus energy for clean and doped Al2O3 barriers

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the

  5. Tunnel Spin Polarization Versus Energy for Clean and Doped Al2O3 Barriers

    NARCIS (Netherlands)

    Park, B.G.; Banerjee, T.; Lodder, J.C.; Jansen, R.

    2007-01-01

    The variation of the tunnel spin-polarization (TSP) with energy is determined using a magnetic tunnel transistor, allowing quantification of the energy dependent TSP separately for both ferromagnet/insulator interfaces and direct correlation with the tunnel magnetoresistance (TMR) measured in the

  6. From epitaxial growth of ferrite thin films to spin-polarized tunnelling

    International Nuclear Information System (INIS)

    Moussy, Jean-Baptiste

    2013-01-01

    This paper presents a review of the research which is focused on ferrite thin films for spintronics. First, I will describe the potential of ferrite layers for the generation of spin-polarized currents. In the second step, the structural and chemical properties of epitaxial thin films and ferrite-based tunnel junctions will be presented. Particular attention will be given to ferrite systems grown by oxygen-assisted molecular beam epitaxy. The analysis of the structure and chemistry close to the interfaces, a key-point for understanding the spin-polarized tunnelling measurements, will be detailed. In the third part, the magnetic and magneto-transport properties of magnetite (Fe 3 O 4 ) thin films as a function of structural defects such as the antiphase boundaries will be explained. The spin-polarization measurements (spin-resolved photoemission, tunnel magnetoresistance) on this oxide predicted to be half-metallic will be discussed. Fourth, the potential of magnetic tunnel barriers, such as CoFe 2 O 4 , NiFe 2 O 4 or MnFe 2 O 4 , whose insulating behaviour and the high Curie temperatures make it exciting candidates for spin filtering at room temperature will be described. Spin-polarized tunnelling experiments, involving either Meservey–Tedrow or tunnel magnetoresistance measurements, will reveal significant spin-polarizations of the tunnelling current at low temperatures but also at room temperatures. Finally, I will mention a few perspectives with ferrite-based heterostructures. (topical review)

  7. Antiferromagnetic Spin Coupling between Rare Earth Adatoms and Iron Islands Probed by Spin-Polarized Tunneling.

    Science.gov (United States)

    Coffey, David; Diez-Ferrer, José Luis; Serrate, David; Ciria, Miguel; de la Fuente, César; Arnaudas, José Ignacio

    2015-09-03

    High-density magnetic storage or quantum computing could be achieved using small magnets with large magnetic anisotropy, a requirement that rare-earth iron alloys fulfill in bulk. This compelling property demands a thorough investigation of the magnetism in low dimensional rare-earth iron structures. Here, we report on the magnetic coupling between 4f single atoms and a 3d magnetic nanoisland. Thulium and lutetium adatoms deposited on iron monolayer islands pseudomorphically grown on W(110) have been investigated at low temperature with scanning tunneling microscopy and spectroscopy. The spin-polarized current indicates that both kind of adatoms have in-plane magnetic moments, which couple antiferromagnetically with their underlying iron islands. Our first-principles calculations explain the observed behavior, predicting an antiparallel coupling of the induced 5d electrons magnetic moment of the lanthanides with the 3d magnetic moment of iron, as well as their in-plane orientation, and pointing to a non-contribution of 4f electrons to the spin-polarized tunneling processes in rare earths.

  8. Theoretical consideration of spin-polarized resonant tunneling in magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Mu Haifeng; Zhu Zhengang; Zheng Qingrong; Jin Biao; Wang Zhengchuan; Su Gang

    2004-01-01

    A recent elegant experimental realization [S. Yuasa et al., Science 297 (2002) 234] of the spin-polarized resonant tunneling in magnetic tunnel junctions is interpreted in terms of a two-band model. It is shown that the tunnel magnetoresistance (TMR) decays oscillatorily with the thickness of the normal metal (NM) layer, being fairly in agreement with the experimental observation. The tunnel conductance is found to decay with slight oscillations with the increase of the NM layer thickness, which is also well consistent with the experiment. In addition, when the magnetizations of both ferromagnet electrodes are not collinearly aligned, TMR is found to exhibit sharp resonant peaks at some particular thickness of the NM layer. The peaked TMR obeys nicely a Gaussian distribution against the relative orientation of the magnetizations

  9. Spin-Polarized Tunneling through Chemical Vapor Deposited Multilayer Molybdenum Disulfide.

    Science.gov (United States)

    Dankert, André; Pashaei, Parham; Kamalakar, M Venkata; Gaur, Anand P S; Sahoo, Satyaprakash; Rungger, Ivan; Narayan, Awadhesh; Dolui, Kapildeb; Hoque, Md Anamul; Patel, Ram Shanker; de Jong, Michel P; Katiyar, Ram S; Sanvito, Stefano; Dash, Saroj P

    2017-06-27

    The two-dimensional (2D) semiconductor molybdenum disulfide (MoS 2 ) has attracted widespread attention for its extraordinary electrical-, optical-, spin-, and valley-related properties. Here, we report on spin-polarized tunneling through chemical vapor deposited multilayer MoS 2 (∼7 nm) at room temperature in a vertically fabricated spin-valve device. A tunnel magnetoresistance (TMR) of 0.5-2% has been observed, corresponding to spin polarization of 5-10% in the measured temperature range of 300-75 K. First-principles calculations for ideal junctions result in a TMR up to 8% and a spin polarization of 26%. The detailed measurements at different temperature, bias voltages, and density functional theory calculations provide information about spin transport mechanisms in vertical multilayer MoS 2 spin-valve devices. These findings form a platform for exploring spin functionalities in 2D semiconductors and understanding the basic phenomena that control their performance.

  10. Laser-assisted spin-polarized transport in graphene tunnel junctions

    International Nuclear Information System (INIS)

    Ding Kaihe; Zhu Zhengang; Berakdar, Jamal

    2012-01-01

    The Keldysh nonequilibrium Green’s function method is utilized to theoretically study spin-polarized transport through a graphene spin valve irradiated by a monochromatic laser field. It is found that the bias dependence of the differential conductance exhibits successive peaks corresponding to the resonant tunneling through the photon-assisted sidebands. The multi-photon processes originate from the combined effects of the radiation field and the graphene tunneling properties, and are shown to be substantially suppressed in a graphene spin valve which results in a decrease of the differential conductance for a high bias voltage. We also discuss the appearance of a dynamical gap around zero bias due to the radiation field. The gap width can be tuned by changing the radiation electric field strength and the frequency. This leads to a shift of the resonant peaks in the differential conductance. We also demonstrate numerically the dependences of the radiation and spin valve effects on the parameters of the external fields and those of the electrodes. We find that the combined effects of the radiation field, the graphene and the spin valve properties bring about an oscillatory behavior in the tunnel magnetoresistance, and this oscillatory amplitude can be changed by scanning the radiation field strength and/or the frequency. (paper)

  11. Spin polarization of tunneling current in barriers with spin-orbit coupling

    International Nuclear Information System (INIS)

    Fujita, T; Jalil, M B A; Tan, S G

    2008-01-01

    We present a general method for evaluating the maximum transmitted spin polarization and optimal spin axis for an arbitrary spin-orbit coupling (SOC) barrier system, in which the spins lie in the azimuthal plane and finite spin polarization is achieved by wavevector filtering of electrons. Besides momentum filtering, another prerequisite for finite spin polarization is asymmetric occupation or transmission probabilities of the eigenstates of the SOC Hamiltonian. This is achieved most efficiently by resonant tunneling through multiple SOC barriers. We apply our analysis to common SOC mechanisms in semiconductors: pure bulk Dresselhaus SOC, heterostructures with mixed Dresselhaus and Rashba SOC and strain-induced SOC. In particular, we find that the interplay between Dresselhaus and Rashba SOC effects can yield several advantageous features for spin filter and spin injector functions, such as increased robustness to wavevector spread of electrons

  12. Spin polarization of tunneling current in barriers with spin-orbit coupling.

    Science.gov (United States)

    Fujita, T; Jalil, M B A; Tan, S G

    2008-03-19

    We present a general method for evaluating the maximum transmitted spin polarization and optimal spin axis for an arbitrary spin-orbit coupling (SOC) barrier system, in which the spins lie in the azimuthal plane and finite spin polarization is achieved by wavevector filtering of electrons. Besides momentum filtering, another prerequisite for finite spin polarization is asymmetric occupation or transmission probabilities of the eigenstates of the SOC Hamiltonian. This is achieved most efficiently by resonant tunneling through multiple SOC barriers. We apply our analysis to common SOC mechanisms in semiconductors: pure bulk Dresselhaus SOC, heterostructures with mixed Dresselhaus and Rashba SOC and strain-induced SOC. In particular, we find that the interplay between Dresselhaus and Rashba SOC effects can yield several advantageous features for spin filter and spin injector functions, such as increased robustness to wavevector spread of electrons.

  13. Transmittance and Tunneling Current through a Trapezoidal Barrier under Spin Polarization Consideration

    Science.gov (United States)

    Noor, F. A.; Nabila, E.; Mardianti, H.; Ariani, T. I.; Khairurrijal

    2018-04-01

    The transmittance and tunneling current in heterostructures under spin polarization consideration were studied by employing a zinc-blended structure for the heterostructures. An electron tunnels through a potential barrier by applying a bias voltage to the barrier, which is called the trapezoidal potential barrier. In order to study the transmittance, an Airy wave function approach was employed to find the transmittance. The obtained transmittance was then utilized to compute the tunneling current by using a Gauss quadrature method. It was shown that the transmittances were asymmetric with the incident angle of the electron. It was also shown that the tunneling currents increased as the bias voltage increased.

  14. Electron-spin polarization in tunnel junctions with ferromagnetic EuS barriers

    International Nuclear Information System (INIS)

    Hao, X.; Moodera, J.S.; Meservey, R.

    1989-01-01

    The authors report here spin-polarized tunneling experiments using non-ferromagnetic electrodes and ferromagnetic EuS barriers. Because of the conduction band in EuS splits into spin-up and spin-down subbands when the temperature is below 16.7 K, the Curie temperature of EuS, the tunnel barrier for electrons with different spin directions is different, therefore giving rise to tunnel current polarization. The spin-filter effect, as it may be called, was observed earlier, directly or indirectly, by several groups: Esaki et al. made a tunneling study on junctions having EuS and EuSe barriers; Thompson et al. studied Schottky barrier tunneling between In and doped EuS; Muller et al. and Kisker et al. performed electron field emission experiments on EuS-coated tungsten tips. The field emission experiments gave a maximum polarization of (89 + 7)% for the emitted electrons. Although the previous tunneling studies did not directly show electron polarization, their results were explained by the same spin- filter effect. This work uses the spin-polarized tunneling technique to show directly that tunnel current is indeed polarized and polarization can be as high as 85%

  15. Semiclassical theory of the tunneling anomaly in partially spin-polarized compressible quantum Hall states

    Science.gov (United States)

    Chowdhury, Debanjan; Skinner, Brian; Lee, Patrick A.

    2018-05-01

    Electron tunneling into a system with strong interactions is known to exhibit an anomaly, in which the tunneling conductance vanishes continuously at low energy due to many-body interactions. Recent measurements have probed this anomaly in a quantum Hall bilayer of the half-filled Landau level, and shown that the anomaly apparently gets stronger as the half-filled Landau level is increasingly spin polarized. Motivated by this result, we construct a semiclassical hydrodynamic theory of the tunneling anomaly in terms of the charge-spreading action associated with tunneling between two copies of the Halperin-Lee-Read state with partial spin polarization. This theory is complementary to our recent work (D. Chowdhury, B. Skinner, and P. A. Lee, arXiv:1709.06091) where the electron spectral function was computed directly using an instanton-based approach. Our results show that the experimental observation cannot be understood within conventional theories of the tunneling anomaly, in which the spreading of the injected charge is driven by the mean-field Coulomb energy. However, we identify a qualitatively new regime, in which the mean-field Coulomb energy is effectively quenched and the tunneling anomaly is dominated by the finite compressibility of the composite Fermion liquid.

  16. Effect of Orbital Hybridization on Spin-Polarized Tunneling across Co/C60 Interfaces.

    Science.gov (United States)

    Wang, Kai; Strambini, Elia; Sanderink, Johnny G M; Bolhuis, Thijs; van der Wiel, Wilfred G; de Jong, Michel P

    2016-10-26

    The interaction between ferromagnetic surfaces and organic semiconductors leads to the formation of hybrid interfacial states. As a consequence, the local magnetic moment is altered, a hybrid interfacial density of states (DOS) is formed, and spin-dependent shifts of energy levels occur. Here, we show that this hybridization affects spin transport across the interface significantly. We report spin-dependent electronic transport measurements for tunnel junctions comprising C 60 molecular thin films grown on top of face-centered-cubic (fcc) epitaxial Co electrodes, an AlO x tunnel barrier, and an Al counter electrode. Since only one ferromagnetic electrode (Co) is present, spin-polarized transport is due to tunneling anisotropic magnetoresistance (TAMR). An in-plane TAMR ratio of approximately 0.7% has been measured at 5 K under application of a magnetic field of 800 mT. The magnetic switching behavior shows some remarkable features, which are attributed to the rotation of interfacial magnetic moments. This behavior can be ascribed to the magnetic coupling between the Co thin films and the newly formed Co/C 60 hybridized interfacial states. Using the Tedrow-Meservey technique, the tunnel spin polarization of the Co/C 60 interface was found to be 43%.

  17. Large positive spin polarization and giant inverse tunneling magnetoresistance in Fe/PbTiO3/Fe multiferroic tunnel junction

    International Nuclear Information System (INIS)

    Dai, Jian-Qing; Zhang, Hu; Song, Yu-Min

    2014-01-01

    We perform first-principles electronic structure and spin-dependent transport calculations of a multiferroic tunnel junction (MFTJ) with an epitaxial Fe/PbTiO 3 /Fe heterostructure. We predict a large positive spin-polarization (SP) and an intriguing giant inverse tunneling magnetoresistance (TMR) ratio in this tunnel junction. We demonstrate that the tunneling properties are determined by ferroelectric (FE) polarization screening and electronic reconstruction at the interface with lower electrostatic potential. The intricate complex band structure of PbTiO 3 , in particular the lowest decay rates concerning Pb 6p z and Ti 3d z2 states near the Γ ¯ point, gives rise to the large positive SP of the tunneling current in the parallel magnetic configuration. However, the giant inverse TMR ratio is attributed to the minority-spin electrons of the interfacial Ti 3d xz +3d yz orbitals which have considerably weight in the extended area around the Γ ¯ point at the Fermi energy and causes remarkable contributions to the conductance in the antiparallel magnetic configuration. - Highlights: • We study spin-dependent tunneling in Fe/PbTiO 3 /Fe multiferroic tunnel junction. • We find a large positive spin polarization in the parallel magnetic configuration. • An intriguing giant inverse TMR ratio (about −2000%) is predicted. • Complex band structure of PbTiO 3 causes the large positive spin polarization. • Negative TMR is due to minority-spin electrons of interfacial Ti d xz +d yz orbitals

  18. The tunneling magnetoresistance and spin-polarized optoelectronic properties of graphyne-based molecular magnetic tunnel junctions

    International Nuclear Information System (INIS)

    Yang, Zhi; Ouyang, Bin; Lan, Guoqing; Xu, Li-Chun; Liu, Ruiping; Liu, Xuguang

    2017-01-01

    Using density functional theory and the non-equilibrium Green’s function method, we investigate the spin-dependent transport and optoelectronic properties of the graphyne-based molecular magnetic tunnel junctions (MMTJs). We find that these MMTJs exhibit an outstanding tunneling magnetoresistance (TMR) effect. The TMR value is as high as 10 6 %. When the magnetization directions of two electrodes are antiparallel under positive or negative bias voltages, two kinds of pure spin currents can be obtained in the systems. Furthermore, under the irradiation of infrared, visible or ultraviolet light, spin-polarized photocurrents can be generated in the MMTJs, but the corresponding microscopic mechanisms are different. More importantly, if the magnetization directions of two electrodes are antiparallel, the photocurrents with different spins are spatially separated, appearing at different electrodes. This phenomenon provides a new way to simultaneously generate two spin currents. (paper)

  19. Manipulation of magnetic Skyrmions with a Scanning Tunneling Microscope

    OpenAIRE

    Wieser, R.

    2016-01-01

    The dynamics of a single magnetic Skyrmion in an atomic spin system under the influence of Scanning Tunneling Microscope is investigated by computer simulations solving the Landau-Lifshitz-Gilbert equation. Two possible scenarios are described: manipulation with aid of a spin-polarized tunneling current and by an electric field created by the scanning tunneling microscope. The dynamics during the creation and annihilation process is studied and the possibility to move single Skyrmions is showed.

  20. Spin-polarized currents in the tunnel contact of a normal conductor and a two-dimensional topological insulator

    International Nuclear Information System (INIS)

    Sukhanov, A. A.; Sablikov, V. A.

    2013-01-01

    The spin filtering of electrons tunneling from the edge states of a two-dimensional topological insulator into a normal conductor under a magnetic field (external or induced due to proximity to a magnetic insulator) is studied. Calculations are performed for a tunnel contact of finite length between the topological insulator and an electronic multimode quantum strip. It is shown that the flow of tunneling electrons is split in the strip, so that spin-polarized currents arise in its left and right branches. These currents can be effectively controlled by the contact voltage and the chemical potential of the system. The presence of a magnetic field, which splits the spin subbands of the electron spectrum in the strip, gives rise to switching of the spin current between the strip branches

  1. Partially spin-polarized Josephson tunneling between non-centrosymmetric superconductors like CePt3Si

    International Nuclear Information System (INIS)

    Mandal, S.S.; Mukherjee, S.P.

    2007-01-01

    Full text: The recent discovery of the superconductivity in the heavy fermionic compound CePt 3 Si have attracted much of the attention of the physics community. The presence of strong Rashba kind of spin-orbit coupling in them split the otherwise degenerate electronic band into two nondegenerate bands. This peculiarity in the band structure gives rise to complicated kind of order parameter whose exact nature is unknown till date. Traditionally Josephson junctions in superconductors draw interest both scientifically and its applicability in making devices. It has been used in several cases as a probe to the order parameter symmetry of the superconductor. It has also been studied in unconventional superconductors like spin-singlet cuprate and spin-triplet Sr 2 RuO 4 superconductors. However no Josephson junction between nonmagnetic superconductors is known to generate spin-polarized current. The purpose of this work is to theoretically show that the direction dependent tunneling matrix element across the junction between two recently discovered non-centrosymmetric superconductors like CePt 3 Si, leads to tunneling of both spin-singlet and spin-triplet Cooper pairs. As a consequence, nonvanishing spin-Josephson current is viable along with the usual charge-Josephson current. This novel spin-Josephson current depends on the relative angle xi between the axes of non-centrosymmetry {n} L and that {n} R in the left and right side of the junction respectively. This angular dependence may be used to make Josephson spin switch. (authors)

  2. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...

  3. Multiterminal semiconductor/ferromagnet probes for spin-filter scanning tunneling microscopy

    NARCIS (Netherlands)

    Vera Marun, I.J.; Jansen, R.

    2009-01-01

    We describe the fabrication of multiterminal semiconductor/ferromagnet probes for a new technique to study magnetic nanostructures: spin-filter scanning tunneling microscopy. We describe the principle of the technique, which is based on spin-polarized tunneling and subsequent analysis of the spin

  4. Spin-polarized spin excitation spectroscopy

    International Nuclear Information System (INIS)

    Loth, Sebastian; Lutz, Christopher P; Heinrich, Andreas J

    2010-01-01

    We report on the spin dependence of elastic and inelastic electron tunneling through transition metal atoms. Mn, Fe and Cu atoms were deposited onto a monolayer of Cu 2 N on Cu(100) and individually addressed with the probe tip of a scanning tunneling microscope. Electrons tunneling between the tip and the substrate exchange energy and spin angular momentum with the surface-bound magnetic atoms. The conservation of energy during the tunneling process results in a distinct onset threshold voltage above which the tunneling electrons create spin excitations in the Mn and Fe atoms. Here we show that the additional conservation of spin angular momentum leads to different cross-sections for spin excitations depending on the relative alignment of the surface spin and the spin of the tunneling electron. For this purpose, we developed a technique for measuring the same local spin with a spin-polarized and a non-spin-polarized tip by exchanging the last apex atom of the probe tip between different transition metal atoms. We derive a quantitative model describing the observed excitation cross-sections on the basis of an exchange scattering process.

  5. Modeling all-electrical detection of the inverse Edelstein effect by spin-polarized tunneling in a topological-insulator/ferromagnetic-metal heterostructure

    Science.gov (United States)

    Dey, Rik; Register, Leonard F.; Banerjee, Sanjay K.

    2018-04-01

    The spin-momentum locking of the surface states in a three-dimensional topological insulator (TI) allows a charge current on the surface of the TI induced by an applied spin current onto the surface, which is known as the inverse Edelstein effect (IEE), that could be achieved either by injecting pure spin current by spin-pumping from a ferromagnetic metal (FM) layer or by injecting spin-polarized charge current by direct tunneling of electrons from the FM to the TI. Here, we present a theory of the observed IEE effect in a TI-FM heterostructure for the spin-polarized tunneling experiments. If an electrical current is passed from the FM to the surface of the TI, because of density-of-states polarization of the FM, an effective imbalance of spin-polarized electrons occurs on the surface of the TI. Due to the spin-momentum helical locking of the surface states in the TI, a difference of transverse charge accumulation appears on the TI surface in a direction orthogonal to the direction of the magnetization of the FM, which is measured as a voltage difference. Here, we derive the two-dimensional transport equations of electrons on the surface of a diffusive TI, coupled to a FM, starting from the quantum kinetic equation, and analytically solve the equations for a rectangular geometry to calculate the voltage difference.

  6. Scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Binnig, G.; Rohrer, H.

    1983-01-01

    Based on vacuum tunneling, a novel type of microscope, the scanning tunneling microscope (STM) was developed. It has an unprecedented resolution in real space on an atomic scale. The authors review the important technical features, illustrate the power of the STM for surface topographies and discuss its potential in other areas of science and technology. (Auth.)

  7. Spin Polarization Inversion at Benzene-Absorbed Fe4N Surface

    KAUST Repository

    Zhang, Qian; Mi, Wenbo; Wang, Xiaocha; Wang, Xuhui

    2015-01-01

    We report a first-principle study on electronic structure and simulation of the spin-polarized scanning tunneling microscopy graphic of a benzene/Fe4N interface. Fe4N is a compound ferromagnet suitable for many spintronic applications. We found that, depending on the particular termination schemes and interface configurations, the spin polarization on the benzene surface shows a rich variety of properties ranging from cosine-type oscillation to polarization inversion. Spin-polarization inversion above benzene is resulting from the hybridizations between C pz and the out-of-plane d orbitals of Fe atom.

  8. Spin Polarization Inversion at Benzene-Absorbed Fe4N Surface

    KAUST Repository

    Zhang, Qian

    2015-05-27

    We report a first-principle study on electronic structure and simulation of the spin-polarized scanning tunneling microscopy graphic of a benzene/Fe4N interface. Fe4N is a compound ferromagnet suitable for many spintronic applications. We found that, depending on the particular termination schemes and interface configurations, the spin polarization on the benzene surface shows a rich variety of properties ranging from cosine-type oscillation to polarization inversion. Spin-polarization inversion above benzene is resulting from the hybridizations between C pz and the out-of-plane d orbitals of Fe atom.

  9. Spin-polarized SEM

    International Nuclear Information System (INIS)

    Konoto, Makoto

    2007-01-01

    Development of highly effective evaluation technology of magnetic structures on a nanometric scale is a key to understanding spintronics and related phenomena. A high-resolution spin-polarized scanning electron microscope (spin SEM) developed recently is quite suitable for probing such nanostructures because of the capability of analyzing local magnetization vectors in three dimensions. Utilizing the spin SEM, a layered antiferromagnetic structure with the 1nm-alternation of bilayer-sheet magnetization has been successfully resolved. The real-space imaging with full analysis of the temperature-dependent magnetization vectors will be demonstrated. (author)

  10. Ultrafast scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Botkin, D.A. [California Univ., Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley Lab., CA (United States)

    1995-09-01

    I have developed an ultrafast scanning tunneling microscope (USTM) based on uniting stroboscopic methods of ultrafast optics and scanned probe microscopy to obtain nanometer spatial resolution and sub-picosecond temporal resolution. USTM increases the achievable time resolution of a STM by more than 6 orders of magnitude; this should enable exploration of mesoscopic and nanometer size systems on time scales corresponding to the period or decay of fundamental excitations. USTM consists of a photoconductive switch with subpicosecond response time in series with the tip of a STM. An optical pulse from a modelocked laser activates the switch to create a gate for the tunneling current, while a second laser pulse on the sample initiates a dynamic process which affects the tunneling current. By sending a large sequence of identical pulse pairs and measuring the average tunnel current as a function of the relative time delay between the pulses in each pair, one can map the time evolution of the surface process. USTM was used to measure the broadband response of the STM`s atomic size tunnel barrier in frequencies from tens to hundreds of GHz. The USTM signal amplitude decays linearly with the tunnel junction conductance, so the spatial resolution of the time-resolved signal is comparable to that of a conventional STM. Geometrical capacitance of the junction does not appear to play an important role in the measurement, but a capacitive effect intimately related to tunneling contributes to the measured signals and may limit the ultimate resolution of the USTM.

  11. Switching Magnetism and Superconductivity with Spin-Polarized Current in Iron-Based Superconductor.

    Science.gov (United States)

    Choi, Seokhwan; Choi, Hyoung Joon; Ok, Jong Mok; Lee, Yeonghoon; Jang, Won-Jun; Lee, Alex Taekyung; Kuk, Young; Lee, SungBin; Heinrich, Andreas J; Cheong, Sang-Wook; Bang, Yunkyu; Johnston, Steven; Kim, Jun Sung; Lee, Jhinhwan

    2017-12-01

    We explore a new mechanism for switching magnetism and superconductivity in a magnetically frustrated iron-based superconductor using spin-polarized scanning tunneling microscopy (SPSTM). Our SPSTM study on single-crystal Sr_{2}VO_{3}FeAs shows that a spin-polarized tunneling current can switch the Fe-layer magnetism into a nontrivial C_{4} (2×2) order, which cannot be achieved by thermal excitation with an unpolarized current. Our tunneling spectroscopy study shows that the induced C_{4} (2×2) order has characteristics of plaquette antiferromagnetic order in the Fe layer and strongly suppresses superconductivity. Also, thermal agitation beyond the bulk Fe spin ordering temperature erases the C_{4} state. These results suggest a new possibility of switching local superconductivity by changing the symmetry of magnetic order with spin-polarized and unpolarized tunneling currents in iron-based superconductors.

  12. Magnetism in grain-boundary phase of a NdFeB sintered magnet studied by spin-polarized scanning electron microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Kohashi, Teruo, E-mail: teruo.kohashi.fc@hitachi.com; Motai, Kumi [Central Research Laboratory, Hitachi, Ltd., Hatoyama, Saitama 350-0395 (Japan); Nishiuchi, Takeshi; Hirosawa, Satoshi [Magnetic Materials Research Laboratory, Hitachi Metals Ltd., Osaka 618-0013 (Japan)

    2014-06-09

    The magnetism in the grain-boundary phase of a NdFeB sintered magnet was measured by spin-polarized scanning electron microscopy (spin SEM). A sample magnet was fractured in the ultra-high-vacuum chamber to avoid oxidation, and its magnetizations in the exposed grain-boundary phase on the fracture surface were evaluated through the spin polarization of secondary electrons. Spin-SEM images were taken as the fracture surface was milled gradually by argon ions, and the magnetization in the grain-boundary phase was quantitatively obtained separately from that of the Nd{sub 2}Fe{sub 14}B phase. The obtained magnetization shows that the grain-boundary phase of this magnet has substantial magnetization, which was confirmed to be ferromagnetic.

  13. Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions.

    Science.gov (United States)

    Bonell, F; Hauet, T; Andrieu, S; Bertran, F; Le Fèvre, P; Calmels, L; Tejeda, A; Montaigne, F; Warot-Fonrose, B; Belhadji, B; Nicolaou, A; Taleb-Ibrahimi, A

    2012-04-27

    In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with Δ(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.

  14. The possibility to determine a constant of spin-orbit interaction by scanning tunneling microscopy method

    International Nuclear Information System (INIS)

    Khotkevich, N.V.; Kolesnichenko, Yu.A.; Vovk, N.P.

    2016-01-01

    The electron tunneling from the quasi-two-dimensional (surface) states with the spin-orbit interaction into bulk-mode states is studied in the framework of a model of an infinitely thin inhomogeneous tunnel magnetic barrier. The influence of the scattering of quasi-two-dimensional electrons by a single magnetic defect on the tunnel current is analyzed. Analytic formulas for the conductance of a tunnel point-contact as a function of its distance from the defect are obtained. It is shown that the analysis of the local magnetization density around the defect by means of spin-polarized scanning tunneling microscopy allows finding the constant of spin orbit interaction.

  15. Scanning tunneling microscope nanoetching method

    Science.gov (United States)

    Li, Yun-Zhong; Reifenberger, Ronald G.; Andres, Ronald P.

    1990-01-01

    A method is described for forming uniform nanometer sized depressions on the surface of a conducting substrate. A tunneling tip is used to apply tunneling current density sufficient to vaporize a localized area of the substrate surface. The resulting depressions or craters in the substrate surface can be formed in information encoding patterns readable with a scanning tunneling microscope.

  16. When measured spin polarization is not spin polarization

    International Nuclear Information System (INIS)

    Dowben, P A; Wu Ning; Binek, Christian

    2011-01-01

    Spin polarization is an unusually ambiguous scientific idiom and, as such, is rarely well defined. A given experimental methodology may allow one to quantify a spin polarization but only in its particular context. As one might expect, these ambiguities sometimes give rise to inappropriate interpretations when comparing the spin polarizations determined through different methods. The spin polarization of CrO 2 and Cr 2 O 3 illustrate some of the complications which hinders comparisons of spin polarization values. (viewpoint)

  17. Scanning Tunneling Microscopy - image interpretation

    International Nuclear Information System (INIS)

    Maca, F.

    1998-01-01

    The basic ideas of image interpretation in Scanning Tunneling Microscopy are presented using simple quantum-mechanical models and supplied with examples of successful application. The importance is stressed of a correct interpretation of this brilliant experimental surface technique

  18. Investigation of non-collinear spin states with scanning tunneling microscopy.

    Science.gov (United States)

    Wulfhekel, W; Gao, C L

    2010-03-05

    Most ferromagnetic and antiferromagnetic substances show a simple collinear arrangement of the local spins. Under certain circumstances, however, the spin configuration is non-collinear. Scanning tunneling microscopy with its potential atomic resolution is an ideal tool for investigating these complex spin structures. Non-collinearity can be due to topological frustration of the exchange interaction, due to relativistic spin-orbit coupling or can be found in excited states. Examples for all three cases are given, illustrating the capabilities of spin-polarized scanning tunneling microscopy.

  19. Spin-polarized photoemission

    International Nuclear Information System (INIS)

    Johnson, Peter D.

    1997-01-01

    Spin-polarized photoemission has developed into a versatile tool for the study of surface and thin film magnetism. In this review, we examine the methodology of the technique and its application to a number of different problems, including both valence band and core level studies. After a detailed review of spin-polarization measurement techniques and the related experimental requirements we consider in detail studies of the bulk properties both above and below the Curie temperature. This section also includes a discussion of observations relating to unique metastable phases obtained via epitaxial growth. The application of the technique to the study of surfaces, both clean and adsorbate covered, is reviewed. The report then examines, in detail, studies of the spin-polarized electronic structure of thin films and the related interfacial magnetism. Finally, observations of spin-polarized quantum well states in non-magnetic thin films are discussed with particular reference to their mediation of the oscillatory exchange coupling in related magnetic multilayers. (author)

  20. The scanning tunneling microscope

    International Nuclear Information System (INIS)

    Salvan, F.

    1986-01-01

    A newly conceived microscope, based on a pure quantum phenomenon, is an ideal tool to study atom by atom the topography and properties of surfaces. Applications are presented: surface ''reconstruction'' of silicon, lamellar compound study, etc... Spectroscopy by tunnel effect will bring important information on electronic properties; it is presented with an application on silicon [fr

  1. Introduction to scanning tunneling microscopy

    CERN Document Server

    Chen, C Julian

    2008-01-01

    The scanning tunneling and the atomic force microscope, both capable of imaging individual atoms, were crowned with the Physics Nobel Prize in 1986, and are the cornerstones of nanotechnology today. This is a thoroughly updated version of this 'bible' in the field.

  2. Scanning Tunneling Optical Resonance Microscopy

    Science.gov (United States)

    Bailey, Sheila; Wilt, Dave; Raffaelle, Ryne; Gennett, Tom; Tin, Padetha; Lau, Janice; Castro, Stephanie; Jenkins, Philip; Scheiman, Dave

    2003-01-01

    Scanning tunneling optical resonance microscopy (STORM) is a method, now undergoing development, for measuring optoelectronic properties of materials and devices on the nanoscale by means of a combination of (1) traditional scanning tunneling microscopy (STM) with (2) tunable laser spectroscopy. In STORM, an STM tip probing a semiconductor is illuminated with modulated light at a wavelength in the visible-to-near-infrared range and the resulting photoenhancement of the tunneling current is measured as a function of the illuminating wavelength. The photoenhancement of tunneling current occurs when the laser photon energy is sufficient to excite charge carriers into the conduction band of the semiconductor. Figure 1 schematically depicts a proposed STORM apparatus. The light for illuminating the semiconductor specimen at the STM would be generated by a ring laser that would be tunable across the wavelength range of interest. The laser beam would be chopped by an achromatic liquid-crystal modulator. A polarization-maintaining optical fiber would couple the light to the tip/sample junction of a commercial STM. An STM can be operated in one of two modes: constant height or constant current. A STORM apparatus would be operated in the constant-current mode, in which the height of the tip relative to the specimen would be varied in order to keep the tunneling current constant. In this mode, a feedback control circuit adjusts the voltage applied to a piezoelectric actuator in the STM that adjusts the height of the STM tip to keep the tunneling current constant. The exponential relationship between the tunneling current and tip-to-sample distance makes it relatively easy to implement this mode of operation. The choice of method by which the photoenhanced portion of the tunneling current would be measured depends on choice of the frequency at which the input illumination would be modulated (chopped). If the frequency of modulation were low enough (typically tunneling current

  3. Seismic scanning tunneling macroscope - Theory

    KAUST Repository

    Schuster, Gerard T.

    2012-09-01

    We propose a seismic scanning tunneling macroscope (SSTM) that can detect the presence of sub-wavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of λ/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the point scatterer is in the near-field region; if the sub-wavelength scatterer is a spherical impedance discontinuity then the resolution will also be limited by the radius of the sphere. Therefore, superresolution imaging can be achieved as the scatterer approaches the source. This is analogous to an optical scanning tunneling microscope that has sub-wavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by imaging of near-field seismic energy.

  4. Seismic scanning tunneling macroscope - Theory

    KAUST Repository

    Schuster, Gerard T.; Hanafy, Sherif M.; Huang, Yunsong

    2012-01-01

    We propose a seismic scanning tunneling macroscope (SSTM) that can detect the presence of sub-wavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of λ/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the point scatterer is in the near-field region; if the sub-wavelength scatterer is a spherical impedance discontinuity then the resolution will also be limited by the radius of the sphere. Therefore, superresolution imaging can be achieved as the scatterer approaches the source. This is analogous to an optical scanning tunneling microscope that has sub-wavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by imaging of near-field seismic energy.

  5. Spin polarized deuterium

    International Nuclear Information System (INIS)

    Glyde, H.R.; Hernadi, S.I.

    1986-01-01

    Several ground state properties of (electron) spin-polarized deuterium (D) such as the energy, single quasiparticle energies and lifetimes, Landau parameters and sound velocities are evaluated. The calculations begin with the Kolos-Wolneiwicz potential and use the Galitskii-FeynmanHartree-Fock (GFHF) approximation. The deuteron nucleas has spin I = 1, and spin states I/sub z/ = 1,0,-1. We explore D 1 , D 2 and D 3 in which, respectively, one spin state only is populated, two states are equally populated, and three states are equally populated. We find the GFHF describes D 1 well, but D 2 and D 3 less well. The Landau parameters, F/sub L/, are small compared to liquid 3 He and very small for doubly polarized D 1 (i.e. the F/sub L/ decrease with nuclear polarization)

  6. Dynamic nuclear spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Stuhrmann, H B [GKSS-Forschungszentrum Geesthacht GmbH (Germany)

    1996-11-01

    Polarized neutron scattering from dynamic polarized targets has been applied to various hydrogenous materials at different laboratories. In situ structures of macromolecular components have been determined by nuclear spin contrast variation with an unprecedented precision. The experiments of selective nuclear spin depolarisation not only opened a new dimension to structural studies but also revealed phenomena related to propagation of nuclear spin polarization and the interplay of nuclear polarisation with the electronic spin system. The observation of electron spin label dependent nuclear spin polarisation domains by NMR and polarized neutron scattering opens a way to generalize the method of nuclear spin contrast variation and most importantly it avoids precontrasting by specific deuteration. It also likely might tell us more about the mechanism of dynamic nuclear spin polarisation. (author) 4 figs., refs.

  7. Tetrairon(III) Single Molecule Magnet Studied by Scanning Tunneling Microscopy and Spectroscopy

    Science.gov (United States)

    Oh, Youngtek; Jeong, Hogyun; Lee, Minjun; Kwon, Jeonghoon; Yu, Jaejun; Mamun, Shariful Islam; Gupta, Gajendra; Kim, Jinkwon; Kuk, Young

    2011-03-01

    Tetrairon(III) single-molecule magnet (SMM) on a clean Au(111) has studied using scanning tunneling microscopy (STM) and spectroscopy (STS) to understand quantum mechanical tunneling of magnetization and hysteresis of pure molecular origin. Before the STM studies, elemental analysis, proton nuclear magnetic resonance (NMR) measurement and Energy Dispersive X- ray Spectroscopy (EDS) were carried out to check the robustness of the sample. The STM image of this molecule shows a hexagonal shape, with a phenyl ring at the center and surrounding six dipivaloylmethane ligands. Two peaks are observed at 0.5 eV, 1.5 eV in the STS results, agreeing well with the first principles calculations. Spin-polarized scanning tunneling microscopy (SPSTM) measurements have been performed with a magnetic tip to get the magnetization image of the SMM. We could observe the antiferromagnetic coupling and a centered- triangular topology with six alkoxo bridges inside the molecule while applying external magnetic fields.

  8. Time-resolved scanning tunnelling microscopy

    NARCIS (Netherlands)

    van Houselt, Arie; Zandvliet, Henricus J.W.

    2010-01-01

    Scanning tunneling microscopy has revolutionized our ability to image, study, and manipulate solid surfaces on the size scale of atoms. One important limitation of the scanning tunneling microscope (STM) is, however, its poor time resolution. Recording a standard image with a STM typically takes

  9. Towards vortex imaging with scanning tunneling microscope

    International Nuclear Information System (INIS)

    Fuchs, Dan T.

    1994-02-01

    A low temperature, Besocke beetle type scanning tunneling microscope, with a scan range of 10 by 10 microns was built. The scanning tunneling microscope was calibrates for various temperatures and tested on several samples. Gold monolayers evaporated at 400 deg C were resolved and their dynamic behavior observed. Atomic resolution images of graphite were obtained. The scanning tunneling microscope was designed for future applications of vortex imaging in superconductors. The special design considerations for this application are discussed and the physics underlying it reviewed. (author)

  10. Scanning Tunneling Microscope For Use In Vacuum

    Science.gov (United States)

    Abel, Phillip B.

    1993-01-01

    Scanning tunneling microscope with subangstrom resolution developed to study surface structures. Although instrument used in air, designed especially for use in vacuum. Scanning head is assembly of small, mostly rigid components made of low-outgassing materials. Includes coarse-positioning mechanical-translation stage, on which specimen mounted by use of standard mounting stub. Tunneling tip mounted on piezoelectric fine-positioning tube. Application of suitable voltages to electrodes on piezoelectric tube controls scan of tunneling tip across surface of specimen. Electronic subsystem generates scanning voltages and collects data.

  11. Spin-polarized current generated by magneto-electrical gating

    International Nuclear Information System (INIS)

    Ma Minjie; Jalil, Mansoor Bin Abdul; Tan, Seng Ghee

    2012-01-01

    We theoretically study spin-polarized current through a single electron tunneling transistor (SETT), in which a quantum dot (QD) is coupled to non-magnetic source and drain electrodes via tunnel junctions, and gated by a ferromagnetic (FM) electrode. The I–V characteristics of the device are investigated for both spin and charge currents, based on the non-equilibrium Green's function formalism. The FM electrode generates a magnetic field, which causes a Zeeman spin-splitting of the energy levels in the QD. By tuning the size of the Zeeman splitting and the source–drain bias, a fully spin-polarized current is generated. Additionally, by modulating the electrical gate bias, one can effect a complete switch of the polarization of the tunneling current from spin-up to spin-down current, or vice versa. - Highlights: ► The spin polarized transport through a single electron tunneling transistor is systematically studied. ► The study is based on Keldysh non-equilibrium Green's function and equation of motion method. ► A fully spin polarized current is observed. ► We propose to reverse current polarization by the means of gate voltage modulation. ► This device can be used as a bi-polarization current generator.

  12. Thermovoltages in vacuum tunneling investigated by scanning tunneling microscopy

    OpenAIRE

    Hoffmann, D. H.; Rettenberger, Armin; Grand, Jean Yves; Läuger, K.; Leiderer, Paul; Dransfeld, Klaus; Möller, Rolf

    1995-01-01

    By heating the tunneling tip of a scanning tunneling microscope the thermoelectric properties of a variable vacuum barrier have been investigated. The lateral variation of the observed thermovoltage will be discussed for polycrystalline gold, stepped surfaces of silver, as well as for copper islands on silver.

  13. Theoretical approach to the scanning tunneling microscope

    International Nuclear Information System (INIS)

    Noguera, C.

    1990-01-01

    Within a one-electron approach, based on a Green's-function formalism, a nonperturbative expression for the tunneling current is obtained and used to discuss which spectroscopic information may be deduced from a scanning-tunneling-microscope experiment. It is shown up to which limits the voltage dependence of the tunneling current reproduces the local density of states at the surface, and how the reflection coefficients of the electronic waves at the surface may modify it

  14. Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging.

    Science.gov (United States)

    Hauptmann, Nadine; Gerritsen, Jan W; Wegner, Daniel; Khajetoorians, Alexander A

    2017-09-13

    Storing and accessing information in atomic-scale magnets requires magnetic imaging techniques with single-atom resolution. Here, we show simultaneous detection of the spin-polarization and exchange force with or without the flow of current with a new method, which combines scanning tunneling microscopy and noncontact atomic force microscopy. To demonstrate the application of this new method, we characterize the prototypical nanoskyrmion lattice formed on a monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing magnetic exchange force microscopy, demonstrating its applicability to noncollinear magnetic structures for the first time. Utilizing distance-dependent force and current spectroscopy, we quantify the exchange forces in comparison to the spin-polarization. For strongly spin-polarized tips, we distinguish different signs of the exchange force that we suggest arises from a change in exchange mechanisms between the probe and a skyrmion. This new approach may enable both nonperturbative readout combined with writing by current-driven reversal of atomic-scale magnets.

  15. NEW SCANNING DEVICE FOR SCANNING TUNNELING MICROSCOPE APPLICATIONS

    NARCIS (Netherlands)

    SAWATZKY, GA; Koops, Karl Richard

    A small, single piezo XYZ translator has been developed. The device has been used as a scanner for a scanning tunneling microscope and has been tested successfully in air and in UHV. Its simple design results in a rigid and compact scanning unit which permits high scanning rates.

  16. Comparison of Electron Transmittance and Tunneling Current through a Trapezoidal Potential Barrier with Spin Polarization Consideration by using Analytical and Numerical Approaches

    Science.gov (United States)

    Nabila, Ezra; Noor, Fatimah A.; Khairurrijal

    2017-07-01

    In this study, we report an analytical calculation of electron transmittance and polarized tunneling current in a single barrier heterostructure of a metal-GaSb-metal by considering the Dresselhaus spin orbit effect. Exponential function, WKB method and Airy function were used in calculating the electron transmittance and tunneling current. A Transfer Matrix Method, as a numerical method, was utilized as the benchmark to evaluate the analytical calculation. It was found that the transmittances calculated under exponential function and Airy function is the same as that calculated under TMM method at low electron energy. However, at high electron energy only the transmittance calculated under Airy function approach is the same as that calculated under TMM method. It was also shown that the transmittances both of spin-up and spin-down conditions increase as the electron energy increases for low energies. Furthermore, the tunneling current decreases with increasing the barrier width.

  17. Investigation into scanning tunnelling luminescence microscopy

    International Nuclear Information System (INIS)

    Manson-Smith, S.K.

    2001-01-01

    This work reports on the development of a scanning tunnelling luminescence (STL) microscope and its application to the study of Ill-nitride semiconductor materials used in the production of light emitting devices. STL microscopy is a technique which uses the high resolution topographic imaging capabilities of the scanning tunnelling microscope (STM) to generate high resolution luminescence images. The STM tunnelling current acts as a highly localised source of electrons (or holes) which generates luminescence in certain materials. Light generated at the STM tunnelling junction is collected concurrently with the height variation of the tunnelling probe as it is scanned across a sample surface, producing simultaneous topographic and luminescence images. Due to the very localised excitation source, high resolution luminescence images can be obtained. Spectroscopic resolution can be obtained by using filters. Additionally, the variation of luminescence intensity with tunnel current and with bias voltage can provide information on recombination processes and material properties. The design and construction of a scanning tunnelling luminescence microscope is described in detail. Operating under ambient conditions, the microscope has several novel features, including a new type of miniature inertial slider-based approach motor, large solid-angle light collection optical arrangement and a tip-height regulation system which requires the minimum of operator input. (author)

  18. Fiber coupled ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1997-01-01

    We report on a scanning tunneling microscope with a photoconductive gate in the tunneling current circuit. The tunneling tip is attached to a coplanar transmission line with an integrated photoconductive switch. The switch is illuminated through a fiber which is rigidly attached to the switch...... waveguide. The measurements show that the probe works as a transient voltage detector in contact and a capacitively coupled transient field detector in tunneling mode. We do not measure the transient voltage change in the ohmic tunneling current. In this sense, the spatial resolution for propagating...... substrate. By using a firmly attached fiber we achieve an excellent reproducibility and unconstrained positioning of the tip. We observe a transient signal with 2.9 ps pulse width in tunneling mode and 5 ps in contact mode. The instrument is applied to investigating the mode structure on a coplanar...

  19. Fluctuation Dominated Josephson Tunneling with a Scanning Tunneling Microscope

    International Nuclear Information System (INIS)

    Naaman, O.; Teizer, W.; Dynes, R. C.

    2001-01-01

    We demonstrate Josephson tunneling in vacuum tunnel junctions formed between a superconducting scanning tunneling microscope tip and a Pb film, for junction resistances in the range 50--300 k Omega. We show that the superconducting phase dynamics is dominated by thermal fluctuations, and that the Josephson current appears as a peak centered at small finite voltage. In the presence of microwave fields (f=15.0 GHz) the peak decreases in magnitude and shifts to higher voltages with increasing rf power, in agreement with theory

  20. A Student-Built Scanning Tunneling Microscope

    Science.gov (United States)

    Ekkens, Tom

    2015-01-01

    Many introductory and nanotechnology textbooks discuss the operation of various microscopes including atomic force (AFM), scanning tunneling (STM), and scanning electron microscopes (SEM). In a nanotechnology laboratory class, students frequently utilize microscopes to obtain data without a thought about the detailed operation of the tool itself.…

  1. Scanning tunneling microscope assembly, reactor, and system

    Science.gov (United States)

    Tao, Feng; Salmeron, Miquel; Somorjai, Gabor A

    2014-11-18

    An embodiment of a scanning tunneling microscope (STM) reactor includes a pressure vessel, an STM assembly, and three spring coupling objects. The pressure vessel includes a sealable port, an interior, and an exterior. An embodiment of an STM system includes a vacuum chamber, an STM reactor, and three springs. The three springs couple the STM reactor to the vacuum chamber and are operable to suspend the scanning tunneling microscope reactor within the interior of the vacuum chamber during operation of the STM reactor. An embodiment of an STM assembly includes a coarse displacement arrangement, a piezoelectric fine displacement scanning tube coupled to the coarse displacement arrangement, and a receiver. The piezoelectric fine displacement scanning tube is coupled to the coarse displacement arrangement. The receiver is coupled to the piezoelectric scanning tube and is operable to receive a tip holder, and the tip holder is operable to receive a tip.

  2. Mn concentration and quantum size effects on spin-polarized transport through CdMnTe based magnetic resonant tunneling diode.

    Science.gov (United States)

    Mnasri, S; Abdi-Ben Nasrallahl, S; Sfina, N; Lazzari, J L; Saïd, M

    2012-11-01

    Theoretical studies on spin-dependent transport in magnetic tunneling diodes with giant Zeeman splitting of the valence band are carried out. The studied structure consists of two nonmagnetic layers CdMgTe separated by a diluted magnetic semiconductor barrier CdMnTe, the hole is surrounded by two p-doped CdTe layers. Based on the parabolic valence band effective mass approximation and the transfer matrix method, the magnetization and the current densities for holes with spin-up and spin-down are studied in terms of the Mn concentration, the well and barrier thicknesses as well as the voltage. It is found that, the current densities depend strongly on these parameters and by choosing suitable values; this structure can be a good spin filter. Such behaviors are originated from the enhancement and suppression in the spin-dependent resonant states.

  3. Scanning tunneling microscopic images and scanning tunneling spectra for coupled rectangular quantum corrals

    International Nuclear Information System (INIS)

    Mitsuoka, Shigenori; Tamura, Akira

    2011-01-01

    Assuming that an electron confined by double δ-function barriers lies in a quasi-stationary state, we derived eigenstates and eigenenergies of the electron. Such an electron has a complex eigenenergy, and the imaginary part naturally leads to the lifetime of the electron associated with tunneling through barriers. We applied this point of view to the electron confined in a rectangular quantum corral (QC) on a noble metal surface, and obtained scanning tunneling microscopic images and a scanning tunneling spectrum consistent with experimental ones. We investigated the electron states confined in coupled QCs and obtained the coupled states constructed with bonding and anti-bonding states. Using those energy levels and wavefunctions we specified scanning tunneling microscope (STM) images and scanning tunneling spectra (STS) for the doubly and triply coupled QCs. In addition we pointed out the feature of resonant electron states associated with the same QCs at both ends of the triply coupled QCs.

  4. Injection of spin-polarized current into semiconductor

    International Nuclear Information System (INIS)

    Vedyayev, A.V.; Dieny, B.; Ryzhanova, N.V.; Zhukov, I.V.; Zhuravlev, M.Ye.; Lutz, H.O.

    2003-01-01

    A quantum-statistical theory of injection of spin-polarized current into a semiconductor in ferromagnet/tunnel barrier/semiconductor system is presented. The presence of Schottky barrier in the semiconductor is taken into account. The case of degenerated and non-degenerated semiconductors are considered. Both the diffusive and ballistic transport regime are investigated. The dependence of current polarization on barrier thickness and temperature is calculated

  5. Scanning Tunneling Spectroscope Use in Electrocatalysis Testing

    Science.gov (United States)

    Knutsen, Turid

    2010-01-01

    The relationship between the electrocatalytic properties of an electrode and its ability to transfer electrons between the electrode and a metallic tip in a scanning tunneling microscope (STM) is investigated. The alkaline oxygen evolution reaction (OER) was used as a test reaction with four different metallic glasses, Ni78Si8B14, Ni70Mo20Si5B5, Ni58Co20Si10B12, and Ni25Co50Si15B10, as electrodes. The electrocatalytic properties of the electrodes were determined. The electrode surfaces were then investigated with an STM. A clear relationship between the catalytic activity of an electrode toward the OER and its tunneling characteristics was found. The use of a scanning tunneling spectroscope (STS) in electrocatalytic testing may increase the efficiency of the optimization of electrochemical processes.

  6. Scanning Tunneling Spectroscope Use in Electrocatalysis Testing

    Directory of Open Access Journals (Sweden)

    Turid Knutsen

    2010-06-01

    Full Text Available The relationship between the electrocatalytic properties of an electrode and its ability to transfer electrons between the electrode and a metallic tip in a scanning tunneling microscope (STM is investigated. The alkaline oxygen evolution reaction (OER was used as a test reaction with four different metallic glasses, Ni78Si8B14, Ni70Mo20Si5B5, Ni58Co20Si10B12, and Ni25Co50Si15B10, as electrodes. The electrocatalytic properties of the electrodes were determined. The electrode surfaces were then investigated with an STM. A clear relationship between the catalytic activity of an electrode toward the OER and its tunneling characteristics was found. The use of a scanning tunneling spectroscope (STS in electrocatalytic testing may increase the efficiency of the optimization of electrochemical processes.

  7. Study of Scanning Tunneling Microscope control electronics

    International Nuclear Information System (INIS)

    Oliva, A.J.; Pancarobo, M.; Denisenko, N.; Aguilar, M.; Rejon, V.; Pena, J.L.

    1994-01-01

    A theoretical study of Scanning Tunneling Microscope control electronics is made. The knowledge of its behaviour allows us to determine accurately the region where the unstable operation could effect the measurements, and also to set the optimal working parameters. Each feedback circuitry compound is discussed as well as their mutual interaction. Different working conditions analysis and results are presented. (Author) 12 refs

  8. New directions in scanning-tunneling microscopy

    International Nuclear Information System (INIS)

    Ferrell, T.L.; Warmack, R.J.; Reddick, R.C.

    1989-01-01

    The tunneling of electrons in scanning-tunneling microscopy (STM) has permitted imaging of the electronic distribution about individual atoms on surfaces. The need for use of conducting surfaces in STM limits its applicability, and new forms of scanning microscopy have emerged as a result of interest in poorly conducting samples. Atomic force microscopy has demonstrated that the force between a surface and a probe tip can be used to image selected materials. Now being developed are magnetic probe STM's and photon tunneling microscopes in which the probe is a sharpened optical fiber. Also of great interest presently is the measurement of differential conductance of surfaces using electron STM's. This method supplies spectral information and contrast enhancement in images. At present there remains much theoretical work to be carried out in order to better characterize related data on inelastic electron tunneling, and valuable insight may be gained from data being gathered on the local work function of materials. As matters stand today, the key problems lie in determining tip and contamination effects, preparation of samples, and understanding conductivity mechanisms in very thin materials on conducting substrates. Resolution of these problems and introduction of new forms of scanning microscopy may permit novel and important applications in biology as well as surface science

  9. New approach towards imaging -DNA using scanning tunneling

    Indian Academy of Sciences (India)

    DNA; scanning tunneling microscopy; Langmuir Blodget technique; silanization. ... Scanning tunneling spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap region of -Si(111) which ... Current Issue

  10. Nuclear spin polarization of targets

    International Nuclear Information System (INIS)

    Happer, W.

    1990-01-01

    Lasers can be used to produce milligrams to grams of noble gas nuclei with spin polarizations in excess of 50%. These quantities are sufficient to be very useful targets in nuclear physics experiments. Alkali-metal atoms are used to capture the angular momentum of circularly polarized laser photons, and the alkali-metal atoms transfer their angular momentum to noble gas atoms in binary or three-body collisions. Non-radiative collisions between the excited alkali atoms and molecular quenching gases are essential to avoid radiation trapping. The spin exchange can involve gas-phase van der Waals molecules, consisting of a noble gas atom and an alkali metal atom. Surface chemistry is also of great importance in determining the wall-induced relaxation rates of the noble gases

  11. Scanning tunneling microscopy II further applications and related scanning techniques

    CERN Document Server

    Güntherodt, Hans-Joachim

    1995-01-01

    Scanning Tunneling Microscopy II, like its predecessor, presents detailed and comprehensive accounts of the basic principles and broad range of applications of STM and related scanning probe techniques. The applications discussed in this volume come predominantly from the fields of electrochemistry and biology. In contrast to those described in STM I, these studies may be performed in air and in liquids. The extensions of the basic technique to map other interactions are described in chapters on scanning force microscopy, magnetic force microscopy, and scanning near-field optical microscopy, together with a survey of other related techniques. Also described here is the use of a scanning proximal probe for surface modification. Together, the two volumes give a comprehensive account of experimental aspects of STM. They provide essential reading and reference material for all students and researchers involved in this field. In this second edition the text has been updated and new methods are discussed.

  12. Scanning tunneling microscopy II further applications and related scanning techniques

    CERN Document Server

    Güntherodt, Hans-Joachim

    1992-01-01

    Scanning Tunneling Microscopy II, like its predecessor, presents detailed and comprehensive accounts of the basic principles and broad range of applications of STM and related scanning probe techniques. The applications discussed in this volume come predominantly from the fields of electrochemistry and biology. In contrast to those described in Vol. I, these sudies may be performed in air and in liquids. The extensions of the basic technique to map other interactions are described inchapters on scanning force microscopy, magnetic force microscopy, scanning near-field optical microscopy, together with a survey of other related techniques. Also described here is the use of a scanning proximal probe for surface modification. Togehter, the two volumes give a comprehensive account of experimental aspcets of STM. They provide essentialreading and reference material for all students and researchers involvedin this field.

  13. Spontaneous spin polarization in quantum wires

    Energy Technology Data Exchange (ETDEWEB)

    Vasilchenko, A.A., E-mail: a_vas2002@mail.ru

    2015-12-04

    The total energy of a quasi-one-dimensional electron system was calculated using the density functional theory. In the absence of a magnetic field, we have found that ferromagnetic state occurs in the quantum wires. The phase diagram of the transition into the spin-polarized state is constructed. The critical electron density below which electrons are in spin-polarized state is estimated analytically. - Highlights: • Density functional theory used to study a spin-polarized state in quantum wires. • The Kohn–Sham equation for quasi-one-dimensional electrons solved numerically. • The phase diagram of the transition into the spin-polarized state is constructed. • The electron density below which electrons are in a spin-polarized state was found. • The critical density of electrons was estimated analytically.

  14. Spontaneous spin polarization in quantum wires

    International Nuclear Information System (INIS)

    Vasilchenko, A.A.

    2015-01-01

    The total energy of a quasi-one-dimensional electron system was calculated using the density functional theory. In the absence of a magnetic field, we have found that ferromagnetic state occurs in the quantum wires. The phase diagram of the transition into the spin-polarized state is constructed. The critical electron density below which electrons are in spin-polarized state is estimated analytically. - Highlights: • Density functional theory used to study a spin-polarized state in quantum wires. • The Kohn–Sham equation for quasi-one-dimensional electrons solved numerically. • The phase diagram of the transition into the spin-polarized state is constructed. • The electron density below which electrons are in a spin-polarized state was found. • The critical density of electrons was estimated analytically.

  15. Scanning Tunneling Spectroscopy of Potassium on Graphene

    Science.gov (United States)

    Cormode, Daniel; Leroy, Brian; Yankowitz, Matthew

    2012-02-01

    We investigate the effect of charged impurities on the electronic properties of large single crystal CVD grown graphene using scanning tunneling microscopy. Mono- and multilayer crystals were prepared by transferring graphene from copper onto exfoliated boron nitride flakes on 300 nm SiO2 substrates. The boron nitride provides an ultra flat surface for the graphene. Potassium atoms are controllably deposited on the graphene at low temperature by heating a nearby getter source. Scanning tunneling spectroscopy and transport measurements were performed in ultra high vacuum at 4.5 K. Transport measurements demonstrate the shifting of the Dirac point as the samples are doped, while STM measurements demonstrate the size, arrangement and local electronic influence of the potassium atoms.

  16. Atomic physics with the scanning tunneling microscope

    International Nuclear Information System (INIS)

    Kleber, M.; Bracher, C.; Riza, M.

    1999-01-01

    Backscattering of atomic beams above a given surface yields information similar to the one obtained from scanning the same surface with a scanning tunneling microscope (STM): In both cases the experimentally accessible quantity is the local density of states (LDOS) n(r,E) of the surface. For the case of backscattering, the LDOS at the turning point of the atom is an important ingredient of the potential between atom and surface. In experiments performed with an STM, the LDOS at the apex of an atomically sharp tip can be determined directly. Probing surfaces locally by an STM allows for the study of basic phenomena in atomic physics, with tunneling of electrons in three dimensions being a central issue

  17. New materials research for high spin polarized current

    International Nuclear Information System (INIS)

    Tezuka, Nobuki

    2012-01-01

    The author reports here a thorough investigation of structural and magnetic properties of Co 2 FeAl 0.5 Si 0.5 Heusler alloy films, and the tunnel magnetoresistance effect for junctions with Co 2 FeAl 0.5 Si 0.5 electrodes, spin injection into GaAs semiconductor from Co 2 FeAl 0.5 Si 0.5 , and spin filtering phenomena for junctions with CoFe 2 O 4 ferrite barrier. It was observed that tunnel magnetoresistance ratio up to 832%(386%) at 9 K (room temperature), which corresponds to the tunnel spin polarization of 0.90 (0.81) for the junctions using Co 2 FeAl 0.5 Si 0.5 Heusler electrodes by optimizing the fabrication condition. It was also found that the tunnel magnetoresistance ratio are almost the same between the junctions with Co 2 FeAl 0.5 Si 0.5 Heusler electrodes on Cr buffered (1 0 0) and (1 1 0) MgO substrates, which indicates that tunnel spin polarization of Co 2 FeAl 0.5 Si 0.5 for these two direction are almost the same. The next part of this paper is a spin filtering effect using a Co ferrite. The spin filtering effect was observed through a thin Co-ferrite barrier. The inverse type tunnel magnetoresistance ratio of −124% measured at 10 K was obtained. The inverse type magnetoresistance suggests the negative spin polarization of Co-ferrite barrier. The magnetoresistance ratio of −124% corresponds to the spin polarization of −0.77 by the Co-ferrite barrier. The last part is devoted to the spin injection from Co 2 FeAl 0.5 Si 0.5 into GaAs. The spin injection signal was clearly obtained by three terminal Hanle measurement. The spin relaxation time was estimated to be 380 ps measured at 5 K.

  18. Scanning tunneling spectroscopy study of DNA conductivity

    Czech Academy of Sciences Publication Activity Database

    Kratochvílová, Irena; Král, Karel; Bunček, M.; Nešpůrek, Stanislav; Todorciuc, Tatiana; Weiter, M.; Navrátil, J.; Schneider, Bohdan; Pavluch, J.

    2008-01-01

    Roč. 6, č. 3 (2008), s. 422-426 ISSN 1895-1082 R&D Projects: GA AV ČR KAN401770651; GA MŠk OC 137; GA AV ČR KAN400720701; GA AV ČR KAN200100801 Institutional research plan: CEZ:AV0Z10100520; CEZ:AV0Z40500505; CEZ:AV0Z40550506 Keywords : molecular electronics * DNA * scanning tunneling microscopy * conductivity * charge carrier transport Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 0.448, year: 2008

  19. Scanning tunneling spectroscopy of Pb thin films

    Energy Technology Data Exchange (ETDEWEB)

    Becker, Michael

    2010-12-13

    The present thesis deals with the electronic structure, work function and single-atom contact conductance of Pb thin films, investigated with a low-temperature scanning tunneling microscope. The electronic structure of Pb(111) thin films on Ag(111) surfaces is investigated using scanning tunneling spectroscopy (STS). Quantum size effects, in particular, quantum well states (QWSs), play a crucial role in the electronic and physical properties of these films. Quantitative analysis of the spectra yields the QWS energies as a function of film thickness, the Pb bulk-band dispersion in {gamma}-L direction, scattering phase shifts at the Pb/Ag interface and vacuum barrier as well as the lifetime broadening at anti {gamma}. The work function {phi} is an important property of surfaces, which influences catalytic reactivity and charge injection at interfaces. It controls the availability of charge carriers in front of a surface. Modifying {phi} has been achieved by deposition of metals and molecules. For investigating {phi} at the atomic scale, scanning tunneling microscopy (STM) has become a widely used technique. STM measures an apparent barrier height {phi}{sub a}, which is commonly related to the sample work function {phi}{sub s} by: {phi}{sub a}=({phi}{sub s}+{phi}{sub t}- vertical stroke eV vertical stroke)/2, with {phi}{sub t} the work function of the tunneling tip, V the applied tunneling bias voltage, and -e the electron charge. Hence, the effect of the finite voltage in STM on {phi}{sub a} is assumed to be linear and the comparison of {phi}{sub a} measured at different surface sites is assumed to yield quantitative information about work function differences. Here, the dependence of {phi}{sub a} on the Pb film thickness and applied bias voltage V is investigated. {phi}{sub a} is found to vary significantly with V. This bias dependence leads to drastic changes and even inversion of contrast in spatial maps of {phi}{sub a}, which are related to the QWSs in the Pb

  20. Scanning tunnel microscopy of semiconductor nanostructures

    International Nuclear Information System (INIS)

    Eder, C.

    1997-09-01

    In this work a scanning tunneling microscope (STM) is utilized as a surface sensitive tool for local characterization of internal potential profiles of GaAs/AlGaAs heterostructures. The STM is operated at variable temperatures under ambient conditions, i.e. either in air or in the variable temperature insert of a cryostat. Distinct local differences between current-voltage curves taken on inverted heterostructures, which were patterned by wet chemically etching, are found. The spectroscopic differences can be ascribed to the internal potential profile in the subsurface regions of the sample. Current imaging tunneling spectroscopy (CITS) is applied to study quantum wire regions. It is found that the magnitude of the CITS-current is an indirect measure of edge depletion zones, which are much larger at 4.2 K. Direct measurements of relevant energy levels in quantum structures were obtained by ballistic electron emission microscopy (BEEM). It is shown that this 3-terminal technique is an excellent tool for transport characterization of minibands formed in semiconductor superlattices. Furthermore, low dimensional electron gases are shown to act as very efficient collector electrodes at low temperatures. For the first time, BEEM experiments were performed at 4.2 K. The enhanced thermal resolution at 4.2 K allows an analysis of the relevant scattering processes. It is found that the collector current is strongly influenced by diffusive scattering at the metal/semiconductor interface. (author)

  1. Electron spin resonance scanning tunneling microscope

    International Nuclear Information System (INIS)

    Guo Yang; Li Jianmei; Lu Xinghua

    2015-01-01

    It is highly expected that the future informatics will be based on the spins of individual electrons. The development of elementary information unit will eventually leads to novel single-molecule or single-atom devices based on electron spins; the quantum computer in the future can be constructed with single electron spins as the basic quantum bits. However, it is still a great challenge in detection and manipulation of a single electron spin, as well as its coherence and entanglement. As an ideal experimental tool for such tasks, the development of electron spin resonance scanning tunneling microscope (ESR-STM) has attracted great attention for decades. This paper briefly introduces the basic concept of ESR-STM. The development history of this instrument and recent progresses are reviewed. The underlying mechanism is explored and summarized. The challenges and possible solutions are discussed. Finally, the prospect of future direction and applications are presented. (authors)

  2. Direct, coherent and incoherent intermediate state tunneling and scanning tunnel microscopy (STM)

    International Nuclear Information System (INIS)

    Halbritter, J.

    1997-01-01

    Theory and experiment in tunneling are still qualitative in nature, which hold true also for the latest developments in direct-, resonant-, coherent- and incoherent-tunneling. Those tunnel processes have recently branched out of the field of ''solid state tunnel junctions'' into the fields of scanning tunnel microscopy (STM), single electron tunneling (SET) and semiconducting resonant tunnel structures (RTS). All these fields have promoted the understanding of tunneling in different ways reaching from the effect of coherence, of incoherence and of charging in tunneling, to spin flip or inelastic effects. STM allows not only the accurate measurements of the tunnel current and its voltage dependence but, more importantly, the easy quantification via the (quantum) tunnel channel conductance and the distance dependence. This new degree of freedom entering exponentially the tunnel current allows an unique identification of individual tunnel channels and their quantification. In STM measurements large tunnel currents are observed for large distances d > 1 nm explainable by intermediate state tunneling. Direct tunneling with its reduced tunnel time and reduced off-site Coulomb charging bridges distances below 1 nm, only. The effective charge transfer process with its larger off-site and on-site charging at intermediate states dominates tunnel transfer in STM, biology and chemistry over distances in the nm-range. Intermediates state tunneling becomes variable range hopping conduction for distances larger than d > 2 nm, for larger densities of intermediate states n 1 (ε) and for larger temperatures T or voltages U, still allowing high resolution imaging

  3. Versatile spin-polarized electron source

    Science.gov (United States)

    Jozwiak, Chris; Park, Cheol -Hwan; Gotlieb, Kenneth; Louie, Steven G.; Hussain, Zahid; Lanzara, Alessandra

    2015-09-22

    One or more embodiments relate generally to the field of photoelectron spin and, more specifically, to a method and system for creating a controllable spin-polarized electron source. One preferred embodiment of the invention generally comprises: method for creating a controllable spin-polarized electron source comprising the following steps: providing one or more materials, the one or more materials having at least one surface and a material layer adjacent to said surface, wherein said surface comprises highly spin-polarized surface electrons, wherein the direction and spin of the surface electrons are locked together; providing at least one incident light capable of stimulating photoemission of said surface electrons; wherein the photon polarization of said incident light is tunable; and inducing photoemission of the surface electron states.

  4. Optical pumping production of spin polarized hydrogen

    International Nuclear Information System (INIS)

    Knize, R.J.; Happer, W.; Cecchi, J.L.

    1984-01-01

    There has been much interest recently in the production of large quantities of spin polarized hydrogen in various fields including controlled fusion, quantum fluids, high energy, and nuclear physics. One promising method for the development of large quantities of spin polarized hydrogen is the utilization of optical pumping with a laser. Optical pumping is a process where photon angular momentum is converted into electron and nuclear spin. The advent of tunable CW dye lasers (approx. 1 watt) allow the production of greater than 10 18 polarized atoms/sec. We have begun a program at Princeton to investigate the physics and technology of using optical pumping to produce large quantities of spin polarized hydrogen. Initial experiments have been done in small closed glass cells. Eventually, a flowing system, open target, or polarized ion source could be constructed

  5. Transient charging and discharging of spin-polarized electrons in a quantum dot

    DEFF Research Database (Denmark)

    De Souza, Fabricio; Leao, S.A.; Gester, R. M.

    2007-01-01

    We study spin-polarized transient transport in a quantum dot coupled to two ferromagnetic leads subjected to a rectangular bias voltage pulse. Time-dependent spin-resolved currents, occupations, spin accumulation, and tunneling magnetoresistance TMR are calculated using both nonequilibrium Green ...

  6. Scanning tunneling spectroscopy on superconducting proximity nanostructures

    International Nuclear Information System (INIS)

    Chapelier, C; Vinet, M; Lefloch, F

    2001-01-01

    We investigated the local density of states (LDOS) of a normal metal (N) in good electrical contact with a superconductor (S) as a function of the distance x to the NS interface. The sample consists of a pattern of alternate L = 1 mm wide strips of Au and Nb made by UV lithography. We used a low temperature scanning tunneling microscope and a lock-in detection technique to record simultaneously dI/dV(V,x) curves and the topographic profile z(x) at 1.5 K. We scanned along lines perpendicular to the strips. All the spectra show a dip near the Fermi energy, which spectral extension decreases from the superconducting gap Δ at the NS interface to zero at distances x >> ξ N where ξ N ≅ √hD N /2Δ ≅ 53nm is the coherence length in the normal metal. Our measurements are correctly described in the framework of the quasi-classical Green's function formalism. We numerically solved the 1D Usadel equation and extracted a decoherence time in gold of 4 ps. We also investigated the LDOS of small ridges of Au deposited on the top of the Nb lines. In this case, L ≤ ξ N and the spatial variations of the spectra depend on the exact shape of the Au ridge. However, our results are consistent with a predicted minigap related to the Thouless energy. (4. mesoscopic superconductivity)

  7. Regular Scanning Tunneling Microscope Tips can be Intrinsically Chiral

    International Nuclear Information System (INIS)

    Tierney, Heather L.; Murphy, Colin J.; Sykes, E. Charles H.

    2011-01-01

    We report our discovery that regular scanning tunneling microscope tips can themselves be chiral. This chirality leads to differences in electron tunneling efficiencies through left- and right-handed molecules, and, when using the tip to electrically excite molecular rotation, large differences in rotation rate were observed which correlated with molecular chirality. As scanning tunneling microscopy is a widely used technique, this result may have unforeseen consequences for the measurement of asymmetric surface phenomena in a variety of important fields.

  8. Regular scanning tunneling microscope tips can be intrinsically chiral.

    Science.gov (United States)

    Tierney, Heather L; Murphy, Colin J; Sykes, E Charles H

    2011-01-07

    We report our discovery that regular scanning tunneling microscope tips can themselves be chiral. This chirality leads to differences in electron tunneling efficiencies through left- and right-handed molecules, and, when using the tip to electrically excite molecular rotation, large differences in rotation rate were observed which correlated with molecular chirality. As scanning tunneling microscopy is a widely used technique, this result may have unforeseen consequences for the measurement of asymmetric surface phenomena in a variety of important fields.

  9. Scanning tunneling microscopy of hexagonal BN grown on graphite

    International Nuclear Information System (INIS)

    Fukumoto, H.; Hamada, T.; Endo, T.; Osaka, Y.

    1991-01-01

    The microscopic surface topography of thin BN x films grown on graphite by electron cyclotron resonance plasma chemical vapor deposition have been imaged with scanning tunneling microscopy in air. The scanning tunneling microscope has generated images of hexagonal BN with atomic resolution

  10. Small-size low-temperature scanning tunnel microscope

    International Nuclear Information System (INIS)

    Al'tfeder, I.B.; Khajkin, M.S.

    1989-01-01

    A small-size scanning tunnel microscope, designed for operation in transport helium-filled Dewar flasks is described. The microscope design contains a device moving the pin to the tested sample surface and a piezoelectric fine positioning device. High vibration protection of the microscope is provided by its suspension using silk threads. The small-size scanning tunnel microscope provides for atomic resolution

  11. Direct observation of atoms on surfaces by scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    Baldeschwieler, J.D.

    1989-01-01

    The scanning tunnelling microscope is a non-destructive means of achieving atomic level resolution of crystal surfaces in real space to elucidate surface structures, electronic properties and chemical composition. Scanning tunnelling microscope is a powerful, real space surface structure probe complementary to other techniques such as x-ray diffraction. 21 refs., 8 figs

  12. Spin-polarized fuel in ICF pellets

    International Nuclear Information System (INIS)

    Wakuta, Yoshihisa; Emoto, Nobuya; Nakao, Yasuyuki; Honda, Takuro; Honda, Yoshinori; Nakashima, Hideki.

    1990-01-01

    The use of parallel spin-polarized DT or D 3 He fuel increases the fusion cross-section by 50%. By implosion-burn simulation for inertially confined fusion (ICF) pellets of the spin-polarized fuels, we found that the input energy requirement could be reduced by nearly a fact of two. These pellets taken up here include large-high-aspect-ratio DT target proposed in ILE Osaka University and DT ignitor/D 3 He fuel pellet proposed by our group. We also found that the polarized state could survive during the implosion-burn phase. (author)

  13. Magnetoresistance through spin-polarized p states

    International Nuclear Information System (INIS)

    Papanikolaou, Nikos

    2003-01-01

    We present a theoretical study of the ballistic magnetoresistance in Ni contacts using first-principles, atomistic, electronic structure calculations. In particular we investigate the role of defects in the contact region with the aim of explaining the recently observed spectacular magnetoresistance ratio. Our results predict that the possible presence of spin-polarized oxygen in the contact region could explain conductance changes by an order of magnitude. Electronic transport essentially occurs through spin-polarized oxygen p states, and this mechanism gives a much higher magnetoresistance than that obtained assuming clean atomically sharp domain walls alone

  14. Photo-Induced Electron Spin Polarization in a Narrow Band Gap Semiconductor Nanostructure

    International Nuclear Information System (INIS)

    Peter, A. John; Lee, Chang Woo

    2012-01-01

    Photo-induced spin dependent electron transmission through a narrow gap InSb/InGa x Sb 1−x semiconductor symmetric well is theoretically studied using transfer matrix formulism. The transparency of electron transmission is calculated as a function of electron energy for different concentrations of gallium. Enhanced spin-polarized photon assisted resonant tunnelling in the heterostructure due to Dresselhaus and Rashba spin-orbit coupling induced splitting of the resonant level and compressed spin-polarization are observed. Our results show that Dresselhaus spin-orbit coupling is dominant for the photon effect and the computed polarization efficiency increases with the photon effect and the gallium concentration

  15. EDITORIAL: Three decades of scanning tunnelling microscopy that changed the course of surface science Three decades of scanning tunnelling microscopy that changed the course of surface science

    Science.gov (United States)

    Ramachandra Rao, M. S.; Margaritondo, Giorgio

    2011-11-01

    envisaged. AFM observations of thin-film surfaces give us a picture of surface topography and morphology and any visible defects. The growing importance of ultra-thin films for magnetic recording in hard disk drive systems requires an in-depth understanding of the fundamental mechanisms occurring during growth. This special issue of Journal of Physics D: Applied Physics covers all of the different aspects of SPM that illustrate the achievements of this methodology: nanoscale imaging and mapping (Chiang, and Douillard and Charra), piezoresponse force microscopy (Soergel) and STM engineering (Okuyama and Hamada, and Huang et al). Chiang takes the reader on a journey along the STM imaging of atoms and molecules on surfaces. Jesse and Kalinin explore the band excitations that occur during the corresponding processes. Jia et al propose STM and molecular beam epitaxy as a winning experimental combination at the interface of science and technology. Douillard and Charra describe the high-resolution mapping of plasmonic modes using photoemission and scanning tunnelling microscopy. Cricenti et al demonstrate the importance of SPM in material science and biology. Wiebe et al have probed atomic scale magnetism, revealed by spin polarized scanning tunnelling microscopy. In addition, Simon et al present Fourier transform scanning tunnelling spectroscopy and the possibility to obtain constant energy maps and band dispersion using local measurements. Lackinger and Heckl give a perspective of the use of STM to study covalent intermolecular coupling reactions on surfaces. Okuyama and Hamada investigated hydrogen bond imaging and engineering with STM. Soergel describes the study of substrate-dependent self-assembled CuPc molecules using piezo force microscope (PFM). We are very grateful to the authors and reviewers for the papers in this special issue of Journal of Physics D: Applied Physics. Their contributions have provided a comprehensive picture of the evolution, status and potential of

  16. Spin polarization of electrons in quantum wires

    OpenAIRE

    Vasilchenko, A. A.

    2013-01-01

    The total energy of a quasi-one-dimensional electron system is calculated using density functional theory. It is shown that spontaneous ferromagnetic state in quantum wire occurs at low one-dimensional electron density. The critical electron density below which electrons are in spin-polarized state is estimated analytically.

  17. Measuring voltage transients with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1997-01-01

    circuit, where the tunneling tip is directly connected to the current amplifier of the scanning tunneling microscope, this dependence is eliminated. Ail results can be explained with coupling through the geometrical capacitance of the tip-electrode junction. By illuminating the current......We use an ultrafast scanning tunneling microscope to resolve propagating voltage transients in space and time. We demonstrate that the previously observed dependence of the transient signal amplitude on the tunneling resistance was only caused by the electrical sampling circuit. With a modified...

  18. Tuning spin-polarized transport in organic semiconductors

    Science.gov (United States)

    Mattana, Richard; Galbiati, Marta; Delprat, Sophie; Tatay, Sergio; Deranlot, Cyrile; Seneor, Pierre; Petroff, Frederic

    Molecular spintronics is an emerging research field at the frontier between organic chemistry and the spintronics. Compared to traditional inorganic materials molecules are flexible and can be easily tailored by chemical synthesis. Due to their theoretically expected very long spin lifetime, they were first only seen as the ultimate media for spintronics devices. It was recently that new spintronics tailoring could arise from the chemical versatility brought by molecules. The hybridization between a ferromagnet and molecules induces a spin dependent broadening and energy shifting of the molecular orbitals leading to an induced spin polarization on the first molecular layer. This spin dependent hybridization can be used to tailor the spin dependent transport in organic spintronics devices. We have studied vertical Co/Alq3/Co organic spin valves. The negative magnetoresistance observed is the signature of different coupling strengths at the top and bottom interfaces. We have then inserted an inorganic tunnel barrier at the bottom interface in order to suppress the spin-dependent hybridization. In this case we restore a positive magnetoresistance. This demonstrates that at the bottom Co/Alq3 interface a stronger coupling occurs which induces an inversion of the spin polarization.

  19. Single-atom contacts with a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Kroeger, J; Neel, N; Sperl, A; Wang, Y F; Berndt, R

    2009-01-01

    The tip of a cryogenic scanning tunnelling microscope is used to controllably contact single atoms adsorbed on metal surfaces. The transition between tunnelling and contact is gradual for silver, while contact to adsorbed gold atoms is abrupt. The single-atom junctions are stable and enable spectroscopic measurements of, e.g., the Abrikosov-Suhl resonance of single Kondo impurities.

  20. Ultrafast terahertz scanning tunneling microscopy with atomic resolution

    DEFF Research Database (Denmark)

    Jelic, Vedran; Iwaszczuk, Krzysztof; Nguyen, Peter H.

    2016-01-01

    We demonstrate that ultrafast terahertz scanning tunneling microscopy (THz-STM) can probe single atoms on a silicon surface with simultaneous sub-nanometer and sub-picosecond spatio-temporal resolution. THz-STM is established as a new technique for exploring high-field non-equilibrium tunneling...

  1. Modulated photodetection with semiconductor tips in a scanning tunneling microscope

    NARCIS (Netherlands)

    Groeneveld, R.H.M.; Prins, M.W.J.; Kempen, van H.

    1995-01-01

    We report on the detection of modulated light power irradiated into the tunnel junction of a scanning tunneling microscope. When semiconductor tips are used we can distinguish three contributions to the measured current: photocurrent due to electron-hole pair generation at the apex of the tip, a

  2. Detection of picosecond electrical transients in a scanning tunneling microscope

    NARCIS (Netherlands)

    Groeneveld, R.H.M.; Rasing, T.H.M.; Kaufmann, L.M.F.; Smalbrugge, E.; Wolter, J.H.; Melloch, M.R.; Kempen, van H.

    1996-01-01

    We have developed a scanning tunneling microscope using an optoelectronic switch which gates the tunneling tip current. The switch is fabricated within several tens of microns from the tip by photolithography and an accurate cleavage method. We demonstrate this approach by detecting picosecond

  3. Photoelectrical properties of semiconductor tips in scanning tunneling microscopy

    NARCIS (Netherlands)

    Prins, M.W.J.; Jansen, R.; Groeneveld, R.H.M.; Gelder, Van A.P.; Kempen, van H.

    1996-01-01

    We describe a model as well as experiments on the electrical properties of a photoexcited tunnel junction between a metal and a semiconductor material, as is established in a scanning tunneling microscope. The model treats the case in which carrier transport is mediated by capture and relaxation in

  4. Surface physics studied by means of scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Besenbacher, F.; Laegsgaard, E.; Stensgaard, I.

    1993-01-01

    Scanning tunneling microscopy has been applied to study silicon crystal structures, oxygen on Cu (110), and real industrial catalyst surfaces. For the latter purpose an Atomic Force Microscope is being developed. (EG)

  5. New approach towards imaging λ-DNA using scanning tunneling ...

    Indian Academy of Sciences (India)

    Wintec

    spectroscopy (STS) at different stages depict a broad distribution of defect states in the bandgap ... DNA; scanning tunneling microscopy; Langmuir Blodget technique; silanization. 1. ... assembled monolayer (SAM) of C-8 silane gave stable.

  6. Antiresonance induced spin-polarized current generation

    Science.gov (United States)

    Yin, Sun; Min, Wen-Jing; Gao, Kun; Xie, Shi-Jie; Liu, De-Sheng

    2011-12-01

    According to the one-dimensional antiresonance effect (Wang X R, Wang Y and Sun Z Z 2003 Phys. Rev. B 65 193402), we propose a possible spin-polarized current generation device. Our proposed model consists of one chain and an impurity coupling to the chain. The energy level of the impurity can be occupied by an electron with a specific spin, and the electron with such a spin is blocked because of the antiresonance effect. Based on this phenomenon our model can generate the spin-polarized current flowing through the chain due to different polarization rates. On the other hand, the device can also be used to measure the generated spin accumulation. Our model is feasible with today's technology.

  7. SPIN-POLARIZED PHOTOCURRENT THROUGH QUANTUM DOT PHOTODETECTOR

    Directory of Open Access Journals (Sweden)

    Nguyen Van Hieu

    2017-11-01

    Full Text Available The theory of the photocurrent through the photodetector based on a two-level semiconductor quantum dot (QD is presented. The analytical expressions of the matrix elements of the electronic transitions generated by the absorption of the circularly polarized photons are derived in the lowest order of the perturbation theory with respect to the electron tunneling interaction as well as the electron-photon interaction. From these expressions the mechanism of the generation of the spin-polarized of electrons in the photocurrent is evident. It follows that the photodetector based on the two-level semiconductor QD can be used as the model of a source of highly spinpolarized electrons.

  8. Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope.

    Science.gov (United States)

    Nazin, G V; Wu, S W; Ho, W

    2005-06-21

    The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks corresponding to the individual vibronic states depends on the relative electron tunneling rates through the two barriers of the junction, as found by varying the vacuum gap tunneling rate by changing the height of the scanning tunneling microscope tip above the molecule. A simple, sequential tunneling model explains the observed trends.

  9. Development of the tunneling junction simulation environment for scanning tunneling microscope evaluation

    International Nuclear Information System (INIS)

    Gajewski, Krzysztof; Piasecki, Tomasz; Kopiec, Daniel; Gotszalk, Teodor

    2017-01-01

    Proper configuration of scanning tunneling microscope electronics plays an important role in the atomic scale resolution surface imaging. Device evaluation in the tunneling contact between scanning tip and sample may be prone to the surface quality or mechanical disturbances. Thus the use of tunneling junction simulator makes electronics testing more reliable and increases its repeatability. Here, we present the theoretical background enabling the proper selection of electronic components circuitry used as a tunneling junction simulator. We also show how to simulate mechanics related to the piezoelectric scanner, which is applied in real experiments. Practical use of the proposed simulator and its application in metrological characterization of the developed scanning tunneling microscope is also shown. (paper)

  10. Compact, single-tube scanning tunneling microscope with thermoelectric cooling.

    Science.gov (United States)

    Jobbins, Matthew M; Agostino, Christopher J; Michel, Jolai D; Gans, Ashley R; Kandel, S Alex

    2013-10-01

    We have designed and built a scanning tunneling microscope with a compact inertial-approach mechanism that fits inside the piezoelectric scanner tube. Rigid construction allows the microscope to be operated without the use of external vibration isolators or acoustic enclosures. Thermoelectric cooling and a water-ice bath are used to increase temperature stability when scanning under ambient conditions.

  11. Optical characterication of probes for photon scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Vohnsen, Brian; Bozhevolnyi, Sergey I.

    1999-01-01

    The photon scanning tunnelling microscope is a well-established member of the family of scanning near-field optical microscopes used for optical imaging at the sub-wavelength scale. The quality of the probes, typically pointed uncoated optical fibres, used is however difficult to evaluate...

  12. Structural monitoring of tunnels using terrestrial laser scanning

    NARCIS (Netherlands)

    Lindenbergh, R.C.; Uchanski, L.; Bucksch, A.; Van Gosliga, R.

    2009-01-01

    In recent years terrestrial laser scanning is rapidly evolving as a surveying technique for the monitoring of engineering objects like roof constructions, mines, dams, viaducts and tunnels. The advantage of laser scanning above traditional surveying methods is that it allows for the rapid

  13. Theory of high-resolution tunneling spin transport on a magnetic skyrmion

    OpenAIRE

    Palotás, Krisztián; Rózsa, Levente; Szunyogh, László

    2018-01-01

    Tunneling spin transport characteristics of a magnetic skyrmion are described theoretically in magnetic scanning tunneling microscopy (STM). The spin-polarized charge current in STM (SP-STM) and tunneling spin transport vector quantities, the longitudinal spin current and the spin transfer torque are calculated in high spatial resolution within the same theoretical framework. A connection between the conventional charge current SP-STM image contrasts and the magnitudes of the spin transport v...

  14. Transient measurements with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1998-01-01

    We use a photoconductively gated ultrafast scanning tunneling microscope to resolve laser-induced transients on transmission lines and photoconductors. The photoconductive switch on the tunneling probe is illuminated through a rigidly attached fiber. The use of the fiber enables us to scan across...... the transmission line while the change in delay time between pump beam (on the sample) and probe beam (on the probe) provides the temporal information. The investigated photoconductor sample is a low-temperature-grown GaAs layer placed on a sapphire substrate with a thin, semitransparent gold layer. In tunneling...... mode the probe is sensitive to laser-induced field changes in the semiconductor layer. Laser-induced transient signals of 2.2 ps widths are detected. As for the transmission lines, the signals can be explained by a capacitive coupling across the tunneling gap....

  15. Scanning Tunneling Spectroscopy on Electron-Boson Interactions in Superconductors

    OpenAIRE

    Schackert, Michael Peter

    2014-01-01

    This thesis describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  16. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Schackert, Michael Peter

    2014-07-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  17. Scanning tunneling spectroscopy on electron-boson interactions in superconductors

    CERN Document Server

    Schackert, Michael Peter

    2015-01-01

    This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

  18. Solid-State Quantum Computer Based on Scanning Tunneling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Berman, G. P.; Brown, G. W.; Hawley, M. E.; Tsifrinovich, V. I.

    2001-08-27

    We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field ({approx}10 T) and at low temperature {approx}1 K .

  19. Solid-State Quantum Computer Based on Scanning Tunneling Microscopy

    International Nuclear Information System (INIS)

    Berman, G. P.; Brown, G. W.; Hawley, M. E.; Tsifrinovich, V. I.

    2001-01-01

    We propose a solid-state nuclear-spin quantum computer based on application of scanning tunneling microscopy (STM) and well-developed silicon technology. It requires the measurement of tunneling-current modulation caused by the Larmor precession of a single electron spin. Our envisioned STM quantum computer would operate at the high magnetic field (∼10 T) and at low temperature ∼1 K

  20. Highly spin-polarized materials and devices for spintronics∗.

    Science.gov (United States)

    Inomata, Koichiro; Ikeda, Naomichi; Tezuka, Nobuki; Goto, Ryogo; Sugimoto, Satoshi; Wojcik, Marek; Jedryka, Eva

    2008-01-01

    The performance of spintronics depends on the spin polarization of the current. In this study half-metallic Co-based full-Heusler alloys and a spin filtering device (SFD) using a ferromagnetic barrier have been investigated as highly spin-polarized current sources. The multilayers were prepared by magnetron sputtering in an ultrahigh vacuum and microfabricated using photolithography and Ar ion etching. We investigated two systems of Co-based full-Heusler alloys, Co 2 Cr 1 - x Fe x Al (CCFA( x )) and Co 2 FeSi 1 - x Al x (CFSA( x )) and revealed the structure and magnetic and transport properties. We demonstrated giant tunnel magnetoresistance (TMR) of up to 220% at room temperature and 390% at 5 K for the magnetic tunnel junctions (MTJs) using Co 2 FeSi 0.5 Al 0.5 (CFSA(0.5)) Heusler alloy electrodes. The 390% TMR corresponds to 0.81 spin polarization for CFSA(0.5) at 5 K. We also investigated the crystalline structure and local structure around Co atoms by x-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analyses, respectively, for CFSA films sputtered on a Cr-buffered MgO (001) substrate followed by post-annealing at various temperatures in an ultrahigh vacuum. The disordered structures in CFSA films were clarified by NMR measurements and the relationship between TMR and the disordered structure was discussed. We clarified that the TMR of the MTJs with CFSA(0.5) electrodes depends on the structure, and is significantly higher for L2 1 than B2 in the crystalline structure. The second part of this paper is devoted to a SFD using a ferromagnetic barrier. The Co ferrite is investigated as a ferromagnetic barrier because of its high Curie temperature and high resistivity. We demonstrate the strong spin filtering effect through an ultrathin insulating ferrimagnetic Co-ferrite barrier at a low temperature. The barrier was prepared by the surface plasma oxidization of a CoFe 2 film deposited on a MgO (001) single crystal substrate, wherein the spinel

  1. Magnetic Switching of a Single Molecular Magnet due to Spin-Polarized Current

    OpenAIRE

    Misiorny, Maciej; Barnas, Józef

    2006-01-01

    Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic electrodes is investigated theoretically. Magnetic moments of the electrodes are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through a barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system as well as the spin relaxation times of the SMM are calculated f...

  2. Continuous control of spin polarization using a magnetic field

    Science.gov (United States)

    Gifford, J. A.; Zhao, G. J.; Li, B. C.; Tracy, Brian D.; Zhang, J.; Kim, D. R.; Smith, David J.; Chen, T. Y.

    2016-05-01

    The giant magnetoresistance (GMR) of a point contact between a Co/Cu multilayer and a superconductor tip varies for different bias voltage. Direct measurement of spin polarization by Andreev reflection spectroscopy reveals that the GMR change is due to a change in spin polarization. This work demonstrates that the GMR structure can be utilized as a spin source and that the spin polarization can be continuously controlled by using an external magnetic field.

  3. Continuous control of spin polarization using a magnetic field

    International Nuclear Information System (INIS)

    Gifford, J. A.; Zhao, G. J.; Li, B. C.; Tracy, Brian D.; Zhang, J.; Kim, D. R.; Smith, David J.; Chen, T. Y.

    2016-01-01

    The giant magnetoresistance (GMR) of a point contact between a Co/Cu multilayer and a superconductor tip varies for different bias voltage. Direct measurement of spin polarization by Andreev reflection spectroscopy reveals that the GMR change is due to a change in spin polarization. This work demonstrates that the GMR structure can be utilized as a spin source and that the spin polarization can be continuously controlled by using an external magnetic field.

  4. Continuous control of spin polarization using a magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Gifford, J. A.; Zhao, G. J.; Li, B. C.; Tracy, Brian D.; Zhang, J.; Kim, D. R.; Smith, David J.; Chen, T. Y., E-mail: tingyong.chen@asu.edu [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)

    2016-05-23

    The giant magnetoresistance (GMR) of a point contact between a Co/Cu multilayer and a superconductor tip varies for different bias voltage. Direct measurement of spin polarization by Andreev reflection spectroscopy reveals that the GMR change is due to a change in spin polarization. This work demonstrates that the GMR structure can be utilized as a spin source and that the spin polarization can be continuously controlled by using an external magnetic field.

  5. Bulk electron spin polarization generated by the spin Hall current

    OpenAIRE

    Korenev, V. L.

    2005-01-01

    It is shown that the spin Hall current generates a non-equilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known equilibrium polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

  6. Bulk electron spin polarization generated by the spin Hall current

    Science.gov (United States)

    Korenev, V. L.

    2006-07-01

    It is shown that the spin Hall current generates a nonequilibrium spin polarization in the interior of crystals with reduced symmetry in a way that is drastically different from the previously well-known “equilibrium” polarization during the spin relaxation process. The steady state spin polarization value does not depend on the strength of spin-orbit interaction offering possibility to generate relatively high spin polarization even in the case of weak spin-orbit coupling.

  7. Probing superconductors. Spectroscopic-imaging scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Hanaguri, Tetsuo

    2011-01-01

    Discovery of high-temperature superconductivity in a cuprate triggered developments of various spectroscopic tools which have been utilized to elucidate electronic states of this mysterious compound. Particularly, angle-resolved photoemission spectroscopy and scanning-tunneling microscopy/spectroscopy are improved considerably. It is now possible to map the superconducting gap in both momentum and real spaces using these two techniques. Here we review spectroscopic-imaging scanning tunneling microscopy which is able to explore momentum-space phase structure of the superconducting gap, as well as real-space structure. Applications of this technique to a cuprate and an iron-based superconductor are discussed. (author)

  8. Scanning tunneling spectroscopy under large current flow through the sample.

    Science.gov (United States)

    Maldonado, A; Guillamón, I; Suderow, H; Vieira, S

    2011-07-01

    We describe a method to make scanning tunneling microscopy/spectroscopy imaging at very low temperatures while driving a constant electric current up to some tens of mA through the sample. It gives a new local probe, which we term current driven scanning tunneling microscopy/spectroscopy. We show spectroscopic and topographic measurements under the application of a current in superconducting Al and NbSe(2) at 100 mK. Perspective of applications of this local imaging method includes local vortex motion experiments, and Doppler shift local density of states studies.

  9. Theory of high-resolution tunneling spin transport on a magnetic skyrmion

    Science.gov (United States)

    Palotás, Krisztián; Rózsa, Levente; Szunyogh, László

    2018-05-01

    Tunneling spin transport characteristics of a magnetic skyrmion are described theoretically in magnetic scanning tunneling microscopy (STM). The spin-polarized charge current in STM (SP-STM) and tunneling spin transport vector quantities, the longitudinal spin current and the spin transfer torque, are calculated in high spatial resolution within the same theoretical framework. A connection between the conventional charge current SP-STM image contrasts and the magnitudes of the spin transport vectors is demonstrated that enables the estimation of tunneling spin transport properties based on experimentally measured SP-STM images. A considerable tunability of the spin transport vectors by the involved spin polarizations is also highlighted. These possibilities and the combined theory of tunneling charge and vector spin transport pave the way for gaining deep insight into electric-current-induced tunneling spin transport properties in SP-STM and to the related dynamics of complex magnetic textures at surfaces.

  10. A nanoscale gigahertz source realized with Josephson scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Jäck, Berthold, E-mail: b.jaeck@fkf.mpg.de; Eltschka, Matthias; Assig, Maximilian; Etzkorn, Markus; Ast, Christian R. [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Hardock, Andreas [Institut für Theoretische Elektrotechnik, Technische Universität Hamburg-Harburg, 21079 Hamburg (Germany); Kern, Klaus [Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart (Germany); Institut de Physique de la Matière Condensée, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne (Switzerland)

    2015-01-05

    Using the AC Josephson effect in the superconductor-vacuum-superconductor tunnel junction of a scanning tunneling microscope (STM), we demonstrate the generation of GHz radiation. With the macroscopic STM tip acting as a λ/4-monopole antenna, we first show that the atomic scale Josephson junction in the STM is sensitive to its frequency-dependent environmental impedance in the GHz regime. Further, enhancing Cooper pair tunneling via excitations of the tip eigenmodes, we are able to generate high-frequency radiation. We find that for vanadium junctions, the enhanced photon emission can be tuned from about 25 GHz to 200 GHz and that large photon flux in excess of 10{sup 20 }cm{sup −2} s{sup −1} is reached in the tunnel junction. These findings demonstrate that the atomic scale Josephson junction in an STM can be employed as a full spectroscopic tool for GHz frequencies on the atomic scale.

  11. Commendable surface physics by means of scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Besenbacher, F.; Laegsgaard, E.; Stensgard, I.

    1995-01-01

    The scanning tunneling microscope, developed at the Aarhus University (Denmark) allows taking several STM images per second, as opposite to other similar microscopes, where the typical scanning time is 0,5-1 min. This new system enables collecting of important information concerning dynamic processes on the surfaces. The Aarhus microscope is very stable, hence atomic resolution is achievable even on close-packed metallic surfaces, while it is difficult to achieve by means of the conventional STM. (EG)

  12. Scanning tunneling spectroscopy on organic semiconductors : experiment and model

    NARCIS (Netherlands)

    Kemerink, M.; Alvarado, S.F.; Müller, P.; Koenraad, P.M.; Salemink, H.W.M.; Wolter, J.H.; Janssen, R.A.J.

    2004-01-01

    Scanning-tunneling spectroscopy expts. performed on conjugated polymer films are compared with three-dimensional numerical model calcns. for charge injection and transport. It is found that if a sufficiently sharp tip is used, the field enhancement near the tip apex leads to a significant increase

  13. Scanning-tunneling spectroscopy on conjugated polymer films

    NARCIS (Netherlands)

    Kemerink, M.; Alvarado, S.F.; Koenraad, P.M.; Janssen, R.A.J.; Salemink, H.W.M.; Wolter, J.H.; Blom, P.W.M.

    2003-01-01

    Scanning-tunneling spectroscopy experiments have been performed on conjugated polymer films and have been compared to a three-dimensional numerical model for charge injection and transport. It is found that field enhancement near the tip apex leads to significant changes in the injected current,

  14. Oxygen-free in situ scanning tunnelling microscopy

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Ulstrup, Jens

    2007-01-01

    Scanning tunneling microscopy under full electrochemical potential control (in situ STM) has been used extensively as an efficient method to characterize microstructures at solid/liquid interfaces at the atomic and molecular levels. However, under ambient conditions oxygen may interfere in open i...

  15. Photon scanning tunneling microscope in combination with a force microscope

    NARCIS (Netherlands)

    Moers, M.H.P.; Moers, M.H.P.; Tack, R.G.; van Hulst, N.F.; Bölger, B.; Bölger, B.

    1994-01-01

    The simultaneous operation of a photon scanning tunneling microscope with an atomic force microscope is presented. The use of standard atomic force silicon nitride cantilevers as near-field optical probes offers the possibility to combine the two methods. Vertical forces and torsion are detected

  16. Scanning tunneling microscope for magneto-optical imaging

    NARCIS (Netherlands)

    Prins, M.W.J.; Groeneveld, R.H.M.; Abraham, D.L.; Schad, R.; Kempen, van H.; Kesteren, van H.W.

    1996-01-01

    Images of magnetic bits written in a Pt/Co multilayer are presented. Using photosensitive semiconducting tips in a scanning tunneling microscope the surface topography as well as the polarization-dependent optical transmission are measured. Magnetic contrast is achieved by detection of the Faraday

  17. Design and calibration of a vacuum compatible scanning tunneling microscope

    Science.gov (United States)

    Abel, Phillip B.

    1990-01-01

    A vacuum compatible scanning tunneling microscope was designed and built, capable of imaging solid surfaces with atomic resolution. The single piezoelectric tube design is compact, and makes use of sample mounting stubs standard to a commercially available surface analysis system. Image collection and display is computer controlled, allowing storage of images for further analysis. Calibration results from atomic scale images are presented.

  18. Electromigration of single metal atoms observed by scanning tunneling microscopy

    NARCIS (Netherlands)

    Braun, K.-F.; Soe, W.H.; Flipse, C.F.J.

    2007-01-01

    The authors show in this letter that single metal atoms on a Ni(111) surface can be pushed by electromigration forces from a scanning tunneling microscope tip. This repulsive interaction is obsd. over a length scale of 6 nm. While for voltages above -300 mV the atoms are pulled by the microscope

  19. Fabrication of metallic nanowires with a scanning tunnelling microscope

    NARCIS (Netherlands)

    Kramer, N.; Kramer, N.; Birk, H.; Jorritsma, J.; Schönenberger, C.

    1995-01-01

    A procedure to pattern thin metal films on a nanometer scale with a scanning tunneling microscope (STM) operating in air is reported. A 30 nm film of hydrogenated amorphous silicon (a‐Si:H) is deposited on a 10 nm film of TaIr. Applying a negative voltage between the STM tip and the a‐Si:H film

  20. Detection of current-induced spin polarization in BiSbTeSe{sub 2} toplogical insulator

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Fan; Ghatak, Subhamoy; Taskin, Alexey; Ando, Yoichi [Institute of Physics II, University of Cologne (Germany); Ando, Yuichiro [Department of Electronic Science and Engineering, Kyoto University (Japan)

    2016-07-01

    Topological insulators (TIs) are a class of quantum matter which possess spin-momentum-locked Dirac Fermions on the surfaces. Due to the spin-momentum locking, spin polarization will be induced when a charge current flows through the surface of a TI. Such spin polarization can be detected by using a ferromagnetic tunneling contact as a detector. In this talk, we present our results measured in devices fabricated from BiSbTeSe{sub 2} flakes. Spin signals were observed in both n-type and p-type BiSbTeSe{sub 2} samples.

  1. Tunneling rates in electron transport through double-barrier molecular junctions in a scanning tunneling microscope

    OpenAIRE

    Nazin, G. V.; Wu, S. W.; Ho, W.

    2005-01-01

    The scanning tunneling microscope enables atomic-scale measurements of electron transport through individual molecules. Copper phthalocyanine and magnesium porphine molecules adsorbed on a thin oxide film grown on the NiAl(110) surface were probed. The single-molecule junctions contained two tunneling barriers, vacuum gap, and oxide film. Differential conductance spectroscopy shows that electron transport occurs via vibronic states of the molecules. The intensity of spectral peaks correspondi...

  2. Organic light emitting diodes with spin polarized electrodes

    NARCIS (Netherlands)

    Arisi, E.; Bergenti, I.; Dediu, V.; Loi, M.A.; Muccini, M.; Murgia, M.; Ruani, G.; Taliani, C.; Zamboni, R.

    2003-01-01

    Electrical and optical properties of Alq3 based organic light emitting diodes with normal and spin polarized electrodes are presented. Epitaxial semitransparent highly spin polarized La0.7Sr0.3MnO3 were used as hole injector, substituting the traditional indium tin oxide electrode. A comparison of

  3. Detecting Spin-Polarized Currents in Ballistic Nanostructures

    DEFF Research Database (Denmark)

    Potok, R.; Folk, J.; M. Marcus, C.

    2002-01-01

    We demonstrate a mesoscopic spin polarizer/analyzer system that allows the spin polarization of current from a quantum point contact in an in-plane magnetic field to be measured. A transverse focusing geometry is used to couple current from an emitter point contact into a collector point contact....

  4. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    Abstract. A theoretical model is presented in this paper for degree of spin polarization in a light emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different ...

  5. Spin polarization of electrons in a magnetic impurity doped ...

    Indian Academy of Sciences (India)

    A theoretical model is presented in this paper for degree of spin polarization in alight emitting diode (LED) whose epitaxial region contains quantum dots doped with magnetic impurity. The model is then used to investigate the effect of electron–phonon interaction on degree of spin polarization at different temperatures and ...

  6. Diffusion equation and spin drag in spin-polarized transport

    DEFF Research Database (Denmark)

    Flensberg, Karsten; Jensen, Thomas Stibius; Mortensen, Asger

    2001-01-01

    We study the role of electron-electron interactions for spin-polarized transport using the Boltzmann equation, and derive a set of coupled transport equations. For spin-polarized transport the electron-electron interactions are important, because they tend to equilibrate the momentum of the two-s...

  7. Kinetic equation for spin-polarized plasmas

    International Nuclear Information System (INIS)

    Cowley, S.C.; Kulsrud, R.M.; Valeo, E.

    1984-07-01

    The usual kinetic description of a plasma is extended to include variables to describe the spin. The distribution function, over phase-space and the new spin variables, provides a sufficient description of a spin-polarized plasma. The evolution equation for the distribution function is given. The equations derived are used to calculate depolarization due to four processes, inhomogeneous fields, collisions, collisions in inhomogeneous fields, and waves. It is found that depolarization by field inhomogeneity on scales large compared with the gyroradius is totally negligible. The same is true for collisional depolarization. Collisions in inhomogeneous fields yield a depolarization rate of order 10 -4 S -1 for deuterons and a negligible rate for tritons in a typical fusion reactor design. This is still sufficiently small on reactor time scales. However, small amplitude magnetic fluctuations (of order one gauss) resonant with the spin precession frequency can lead to significant depolarization (depolarises triton in ten seconds and deuteron in a hundred seconds.)

  8. Core Technology Development of Nuclear spin polarization

    International Nuclear Information System (INIS)

    Yoo, Byung Duk; Gwon, Sung Ok; Kwon, Duck Hee; Lee, Sung Man

    2009-12-01

    In order to study nuclear spin polarization, we need several core technologies such as laser beam source to polarize the nuclear spin, low pressured helium cell development whose surface is essential to maintain polarization otherwise most of the polarized helium relaxed in short time, development of uniform magnetic field system which is essential for reducing relaxation, efficient vacuum system, development of polarization measuring system, and development of pressure raising system about 1000 times. The purpose of this study is to develop resonable power of laser system, that is at least 5 watt, 1083 nm, 4GHz tuneable. But the limitation of this research fund enforce to develop amplifying system into 5 watt with 1 watt system utilizing laser-diod which is already we have in stock. We succeeded in getting excellent specification of fiber laser system with power of 5 watts, 2 GHz linewidth, more than 80 GHz tuneable

  9. Scanning tunneling microscopy III theory of STM and related scanning probe methods

    CERN Document Server

    Güntherodt, Hans-Joachim

    1996-01-01

    Scanning Tunneling Microscopy III provides a unique introduction to the theoretical foundations of scanning tunneling microscopy and related scanning probe methods. The different theoretical concepts developed in the past are outlined, and the implications of the theoretical results for the interpretation of experimental data are discussed in detail. Therefore, this book serves as a most useful guide for experimentalists as well as for theoreticians working in the filed of local probe methods. In this second edition the text has been updated and new methods are discussed.

  10. Scanning tunnel microscope with large vision field compatible with a scanning electron microscope

    International Nuclear Information System (INIS)

    Volodin, A.P.; Stepanyan, G.A.; Khajkin, M.S.; Ehdel'man, V.S.

    1989-01-01

    A scanning tunnel microscope (STM) with the 20μm vision field and 1nm resolution, designed to be compatible with a scanning electron microscope (SEM), is described. The sample scanning area is chosen within the 3x10mm limits with a 0.1-1μm step. The STM needle is moved automatically toward the sample surface from the maximum distance of 10mm until the tunneling current appears. Bimorphous elements of the KP-1 piezocorrector are used in the STM design. The device is installed on a table of SEM object holders

  11. Excitation of propagating surface plasmons with a scanning tunnelling microscope.

    Science.gov (United States)

    Wang, T; Boer-Duchemin, E; Zhang, Y; Comtet, G; Dujardin, G

    2011-04-29

    Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10  µm. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.

  12. Apparent Barrier Height in Scanning Tunneling Microscopy Revisited

    DEFF Research Database (Denmark)

    Olesen, L.; Brandbyge, Mads; Sørensen, Mads Reinholdt

    1996-01-01

    The apparent barrier height phi(ap), that is, the rate of change of the logarithm of the conductance with tip-sample separation in a scanning tunneling microscope (STM), has been measured for Ni, Pt, and Au single crystal surfaces. The results show that phi(ap) is constant until point contact...... is reached rather than decreasing at small tunneling gap distances, as previously reported. The findings for phi(ap) can be accounted for theoretically by including the relaxations of the tip-surface junction in an STM due to the strong adhesive forces at close proximity. These relaxation effects are shown...

  13. Seismic scanning tunneling macroscope - Elastic simulations and Arizona mine test

    KAUST Repository

    Hanafy, Sherif M.; Schuster, Gerard T.

    2012-01-01

    Elastic seismic simulations and field data tests are used to validate the theory of a seismic scanning tunneling macroscope (SSTM). For nearfield elastic simulation, the SSTM results show superresolution to be better than λ/8 if the only scattered data are used as input data. If the direct P and S waves are muted then the resolution of the scatterer locations are within about λ/5. Seismic data collected in an Arizona tunnel showed a superresolution limit of at least λ/19. These test results are consistent with the theory of the SSTM and suggest that the SSTM can be a tool used by geophysicists as a probe for near-field scatterers.

  14. Fabrication of silver tips for scanning tunneling microscope induced luminescence.

    Science.gov (United States)

    Zhang, C; Gao, B; Chen, L G; Meng, Q S; Yang, H; Zhang, R; Tao, X; Gao, H Y; Liao, Y; Dong, Z C

    2011-08-01

    We describe a reliable fabrication procedure of silver tips for scanning tunneling microscope (STM) induced luminescence experiments. The tip was first etched electrochemically to yield a sharp cone shape using selected electrolyte solutions and then sputter cleaned in ultrahigh vacuum to remove surface oxidation. The tip status, in particular the tip induced plasmon mode and its emission intensity, can be further tuned through field emission and voltage pulse. The quality of silver tips thus fabricated not only offers atomically resolved STM imaging, but more importantly, also allows us to perform challenging "color" photon mapping with emission spectra taken at each pixel simultaneously during the STM scan under relatively small tunnel currents and relatively short exposure time.

  15. Scanning tunneling microscopy and spectroscopy studies of graphite edges

    International Nuclear Information System (INIS)

    Niimi, Y.; Matsui, T.; Kambara, H.; Tagami, K.; Tsukada, M.; Fukuyama, Hiroshi

    2005-01-01

    We studied experimentally and theoretically the electronic local density of states (LDOS) near single-step edges at the surface of exfoliated graphite. In scanning tunneling microscopy measurements, we observed the (3x3)R30 o and honeycomb superstructures extending over 3-4-bar nm both from the zigzag and armchair edges. Calculations based on a density-functional-derived non-orthogonal tight-binding model show that these superstructures can coexist if the two types of edges admix each other in real graphite step edges. Scanning tunneling spectroscopy measurements near the zigzag edge reveal a clear peak in the LDOS at an energy below the Fermi energy by 20-bar meV. No such a peak was observed near the armchair edge. We concluded that this peak corresponds to the 'edge state' theoretically predicted for graphene ribbons, since a similar prominent LDOS peak due to the edge state is obtained by the first principles calculations

  16. Scanning tunneling microscopy: A powerful tool for surface analysis

    International Nuclear Information System (INIS)

    Walle, G.F.A. van de; Nelissen, B.J.; Soethout, L.L.; Kempen, H. van

    1987-01-01

    The invention of the Scanning Tunneling Microscope (STM) has opened a new area of surface analysis. A description of the principle of operation is given in this paper. Also the technical problems encountered and their solution are described. Two examples demonstrating the possibilities of the STM are presented: topographic and spectroscopic measurements on a stepped Ni (111) surface and photoconductive measurements on GaAs. (orig.)

  17. Application of piezoceramic materials in low temperature scanning tunnel microscope

    International Nuclear Information System (INIS)

    Volodin, A.P.; Panich, A.E.

    1989-01-01

    Temperature dependences of the voltage-to-movement conversion coefficients for piezoceramic domestic materials PKR and TsTS-19 are measured using a capacitance dilatometer in the 0.4< T<300K temperature range. Anisotropy of thermal expansion of materials determined by the polarization vector is observed. Some recommendations concerning the use of the given materials in low-temperature scanning tunnel microscopes are given

  18. Distinction of nuclear spin states with the scanning tunneling microscope.

    Science.gov (United States)

    Natterer, Fabian Donat; Patthey, François; Brune, Harald

    2013-10-25

    We demonstrate rotational excitation spectroscopy with the scanning tunneling microscope for physisorbed H(2) and its isotopes HD and D(2). The observed excitation energies are very close to the gas phase values and show the expected scaling with the moment of inertia. Since these energies are characteristic for the molecular nuclear spin states we are able to identify the para and ortho species of hydrogen and deuterium, respectively. We thereby demonstrate nuclear spin sensitivity with unprecedented spatial resolution.

  19. Extension of Seismic Scanning Tunneling Macroscope to Elastic Waves

    KAUST Repository

    Tarhini, Ahmad

    2017-11-06

    The theory for the seismic scanning tunneling macroscope is extended from acoustic body waves to elastic body-wave propagation. We show that, similar to the acoustic case, near-field superresolution imaging from elastic body waves results from the O(1/R) term, where R is the distance between the source and near-field scatterer. The higher-order contributions R−n for n>1 are cancelled in the near-field region for a point source with normal stress.

  20. Scanning tunneling microscopy - STM: history, principle, construction, and related techniques

    International Nuclear Information System (INIS)

    Ostadal, I.; Sobotik, P.

    1998-01-01

    The method of scanning tunneling microscopy (STM) is discussed. The principle of STM and some other related methods is highlighted, and spectroscopy using STM is dealt with. A brief summary is given of problems to be solved in microscope design, and the influence of these on the resolution obtained is presented. A comparison of STM with other methods used at present in the physics of thin films and surfaces confirms its irreplaceability

  1. Extension of Seismic Scanning Tunneling Macroscope to Elastic Waves

    KAUST Repository

    Tarhini, Ahmad; Guo, Bowen; Dutta, Gaurav; Schuster, Gerard T.

    2017-01-01

    The theory for the seismic scanning tunneling macroscope is extended from acoustic body waves to elastic body-wave propagation. We show that, similar to the acoustic case, near-field superresolution imaging from elastic body waves results from the O(1/R) term, where R is the distance between the source and near-field scatterer. The higher-order contributions R−n for n>1 are cancelled in the near-field region for a point source with normal stress.

  2. A scanning tunneling microscope for a dilution refrigerator.

    Science.gov (United States)

    Marz, M; Goll, G; Löhneysen, H v

    2010-04-01

    We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

  3. A combined scanning tunnelling microscope and x-ray interferometer

    Science.gov (United States)

    Yacoot, Andrew; Kuetgens, Ulrich; Koenders, Ludger; Weimann, Thomas

    2001-10-01

    A monolithic x-ray interferometer made from silicon and a scanning tunnelling microscope have been combined and used to calibrate grating structures with periodicities of 100 nm or less. The x-ray interferometer is used as a translation stage which moves in discrete steps of 0.192 nm, the lattice spacing of the silicon (220) planes. Hence, movements are traceable to the definition of the metre and the nonlinearity associated with the optical interferometers used to measure displacement in more conventional metrological scanning probe microscopes (MSPMs) removed.

  4. Evaluation of radiative spin polarization in an electron storage ring

    Energy Technology Data Exchange (ETDEWEB)

    Chao, A W [Stanford Linear Accelerator Center, CA (USA)

    1981-02-15

    We have developed a matrix formalism that provides an accurate way of evaluating the degree of spin polarization built up through the process of synchrotron radiation under a wide variety of storage ring operation conditions.

  5. Neutron stars with spin polarized self-interacting dark matter

    OpenAIRE

    Rezaei, Zeinab

    2018-01-01

    Dark matter, one of the important portion of the universe, could affect the visible matter in neutron stars. An important physical feature of dark matter is due to the spin of dark matter particles. Here, applying the piecewise polytropic equation of state for the neutron star matter and the equation of state of spin polarized self-interacting dark matter, we investigate the structure of neutron stars which are influenced by the spin polarized self-interacting dark matter. The behavior of the...

  6. SPATIAL REPARTITION OF CURRENT FLUCTUATIONS IN A SCANNING TUNNELING MICROSCOPE

    Directory of Open Access Journals (Sweden)

    Jerome Lagoute

    2011-05-01

    Full Text Available Scanning Tunneling Microscopy (STM is a technique where the surface topography of a conducting sample is probed by a scanning metallic tip. The tip-to-surface distance is controlled by monitoring the electronic tunneling current between the two metals. The aim of this work is to extend the temporal range of this instrument by characterising the time fluctuations of this current on different surfaces. The current noise power spectral density is dominated by a characteristic 1/f component, the physical origin of which is not yet clearly identified, despite a number of investigations. A new I-V preamplifier was developed in order to characterise these fluctuations of the tunnelling current and to obtain images of their spatial repartition. It is observed that their intensity is correlated with some topographical features. This information can be used to get insights on the physical phenomena involved that are not accessible by the usual STM set-up, which is limited to low frequencies.

  7. Theory and feasibility tests for a seismic scanning tunnelling macroscope

    KAUST Repository

    Schuster, Gerard T.

    2012-09-01

    We propose a seismic scanning tunnelling macroscope (SSTM) that can detect subwavelength scatterers in the near-field of either the source or the receivers. Analytic formulas for the time reverse mirror (TRM) profile associated with a single scatterer model show that the spatial resolution limit to be, unlike the Abbe limit of λ/2, independent of wavelength and linearly proportional to the source-scatterer separation as long as the scatterer is in the near-field region. This means that, as the scatterer approaches the source, imaging of the scatterer with super-resolution can be achieved. Acoustic and elastic simulations support this concept, and a seismic experiment in an Arizona tunnel shows a TRM profile with super-resolution adjacent to the fault location. The SSTM is analogous to the optical scanning tunnelling microscopes having subwavelength resolution. Scaled to seismic frequencies, it is theoretically possible to extract 100 Hz information from 20 Hz data by the imaging of near-field seismic energy.

  8. Excitation of propagating surface plasmons with a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Wang, T; Boer-Duchemin, E; Zhang, Y; Comtet, G; Dujardin, G

    2011-01-01

    Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10 μm. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.

  9. Excitation of propagating surface plasmons with a scanning tunnelling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Wang, T; Boer-Duchemin, E; Zhang, Y; Comtet, G; Dujardin, G, E-mail: Elizabeth.Boer-Duchemin@u-psud.fr [Institut des Sciences Moleculaire d' Orsay (ISMO), CNRS Universite Paris-Sud, 91405 Orsay (France)

    2011-04-29

    Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10 {mu}m. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.

  10. Optical and electrical characterization at the nanoscale with a transparent probe of a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Sychugov, Ilya; Omi, Hiroo; Murashita, Tooru; Kobayashi, Yoshihiro

    2009-01-01

    A new type of scanning probe microscope, combining features of the scanning tunnelling microscope, the scanning tunnelling luminescence microscope with a transparent probe and the aperture scanning near-field optical microscope, is described. Proof-of-concept experiments were performed under ultrahigh vacuum conditions at varying temperature on GaAs/AlAs heterostructures.

  11. EDITORIAL: New materials with high spin polarization: half-metallic Heusler compounds

    Science.gov (United States)

    Felser, Claudia; Hillebrands, Burkard

    2007-03-01

    thin film Appl. Phys. Lett. 88 262503 [6] Thomas A, Meyners D, Ebke D, Liu N-N, Sacher M D, Schmalhorst J, Reiss G, Ebert H, and Hütten A 2006 Inverted spin polarization of Heusler alloys for spintronic devices Appl. Phys. Lett. 89 012502 [7] Hillebrands B and Felser C 2006 Editorial: High-spin polarization of Heusler alloys J. Phys. D: Appl. Phys. 39 issue 5 http://stacks.iop.org/0022-3727/39/i=5 [8] Galanakis I, Mavropoulos Ph and Dederichs P H 2006 Electronic structure and Slater-Pauling behaviour in half-metallic Heusler alloys calculated from first principles J. Phys. D: Appl. Phys. 39 765 J. Phys. D: Appl. Phys. 39 765 [9] Kandpal H C, Felser C and Seshadri R 2006 Covalent bonding and the nature of band gaps in some half-Heusler compounds J. Phys. D: Appl. Phys. 39 776 [10] Kallmayer M, Elmers H J, Balke B, Wurmehl S, Emmerling F, Fecher G H and Felser C 2006 Magnetic properties of Co2Mn1-xFexSi Heusler alloys J. Phys. D: Appl. Phys. 39 786 [11] Attema J J, de Wijs G A and de Groot R A 2006 The continuing drama of the half-metal/semiconductor interface J. Phys. D: Appl. Phys. 39 793 [12] Leziac M, Mavropoulos Ph, Bihlmayer G and Blügel S 2006 Scanning tunnelling microscopy of surfaces of half-metals: an ab-initio study on NiMnSb(001) J. Phys. D: Appl. Phys. 39 797 [13] Wurmehl S, Fecher G H, Kroth K, Kronast F, Dürr H A, Takeda Y, Saitoh Y, Kobayashi K, Lin H-J, Schönhense G and Felser C 2006 Electronic structure and spectroscopy of the quaternary Heusler alloy Co2Cr1-xFexAl J. Phys. D: Appl. Phys. 39 803 [14] Inomata K, Okamura S, Miyazaki A, Kikuchi M, Tezuka N, Wojcik M and Jedryka E 2006 Structural and magnetic properties and tunnel magnetoresistance for Co2(Cr,Fe)Al and Co2FeSi full-Heusler alloys J. Phys. D: Appl. Phys. 39 816 [15] Yamamoto M, Marukame T, Ishikawa T, Matsuda K, Uemura T and Arita M 2006 Fabrication of fully epitaxial magnetic tunnel junctions using cobalt-based full-Heusler alloy thin film and their tunnel magnetoresistance

  12. Dynamical nuclear spin polarization induced by electronic current through double quantum dots

    International Nuclear Information System (INIS)

    Lopez-Monis, Carlos; Platero, Gloria; Inarrea, Jesus

    2011-01-01

    We analyse electron-spin relaxation in electronic transport through coherently coupled double quantum dots (DQDs) in the spin blockade regime. In particular, we focus on hyperfine (HF) interaction as the spin-relaxation mechanism. We pay special attention to the effect of the dynamical nuclear spin polarization induced by the electronic current on the nuclear environment. We discuss the behaviour of the electronic current and the induced nuclear spin polarization versus an external magnetic field for different HF coupling intensities and interdot tunnelling strengths. We take into account, for each magnetic field, all HF-mediated spin-relaxation processes coming from different opposite spin level approaches. We find that the current as a function of the external magnetic field shows a peak or a dip and that the transition from a current dip to a current peak behaviour is obtained by decreasing the HF coupling or by increasing the interdot tunnelling strength. We give a physical picture in terms of the interplay between the electrons tunnelling out of the DQD and the spin-flip processes due to the nuclear environment.

  13. Electric field effects in scanning tunneling microscope imaging

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Quaade, Ulrich; Grey, Francois

    1998-01-01

    We present a high-voltage extension of the Tersoff-Hamann theory of scanning tunneling microscope (STM) images, which includes the effect of the electric field between the tip and the sample. The theoretical model is based on first-principles electronic structure calculations and has no adjustable...... parameters. We use the method to calculate theoretical STM images of the monohydrate Si(100)-H(2x1) surface with missing hydrogen defects at -2V and find an enhanced corrugation due to the electric field, in good agreement with experimental images....

  14. Observation of diamond turned OFHC copper using Scanning Tunneling Microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Grigg, D.A.; Russell, P.E.; Dow, T.A.

    1988-12-01

    Diamond turned OFHC copper samples have been observed within the past few months using the Scanning Tunneling Microscope. Initial results have shown evidence of artifacts which may be used to better understand the diamond turning process. The STM`s high resolution capability and three dimensional data representation allows observation and study of surface features unobtainable with conventional profilometry systems. Also, the STM offers a better quantitative means by which to analyze surface structures than the SEM. This paper discusses findings on several diamond turned OFHC copper samples having different cutting conditions. Each sample has been cross referenced using STM and SEM.

  15. Near-field optical microscopy with a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Barbara, A.; Lopez-Rios, T.; Quemerais, P.

    2005-01-01

    A homemade apertureless near-field optical microscope using a scanning tunneling microscope (STM) is described. The experimental set-up simultaneously provides optical and topographic images of the sample. Technical details and features of the set-up are presented, together with results demonstrating the sub-wavelength resolution achieved as well as its sensitivity to dielectric contrasts. We show that the use of a STM permits to precisely control very small distances between the tip and the sample which is a great advantage to excite localized optical resonances between the tip and the surface

  16. Scanning tunneling spectroscopy of Co adsorbates on superconducting Pb nanostructures

    Energy Technology Data Exchange (ETDEWEB)

    Decker, Regis; Caminale, Michael; Oka, Hirofumi; Stepniak, Agnieszka; Leon Vanegas, Augusto A.; Sander, Dirk; Kirschner, Juergen [Max-Planck-Institut fuer Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany)

    2015-07-01

    Superconductivity in low-dimensional structures has become an active research area. In order to understand the superconducting pairing, long-standing work has been devoted to the pair breaking effect, where magnetic impurities break Cooper pair singlets. We performed scanning tunneling spectroscopy at low temperature on Co adsorbates on superconducting Pb nanoislands. On the Co adsorbates, we observe spectral features in the superconductor's energy gap, which we attribute to magnetic impurity induced bound states, a hallmark of the pair breaking effect. We discuss the response of the superconducting islands to the presence of Co adsorbates.

  17. Dark states in spin-polarized transport through triple quantum dot molecules

    Science.gov (United States)

    Wrześniewski, K.; Weymann, I.

    2018-02-01

    We study the spin-polarized transport through a triple-quantum-dot molecule weakly coupled to ferromagnetic leads. The analysis is performed by means of the real-time diagrammatic technique, including up to the second order of perturbation expansion with respect to the tunnel coupling. The emphasis is put on the impact of dark states on spin-resolved transport characteristics. It is shown that the interplay of coherent population trapping and cotunneling processes results in a highly nontrivial behavior of the tunnel magnetoresistance, which can take negative values. Moreover, a super-Poissonian shot noise is found in transport regimes where the current is blocked by the formation of dark states, which can be additionally enhanced by spin dependence of tunneling processes, depending on the magnetic configuration of the device. The mechanisms leading to those effects are thoroughly discussed.

  18. A High Rigidity and Precision Scanning Tunneling Microscope with Decoupled XY and Z Scans.

    Science.gov (United States)

    Chen, Xu; Guo, Tengfei; Hou, Yubin; Zhang, Jing; Meng, Wenjie; Lu, Qingyou

    2017-01-01

    A new scan-head structure for the scanning tunneling microscope (STM) is proposed, featuring high scan precision and rigidity. The core structure consists of a piezoelectric tube scanner of quadrant type (for XY scans) coaxially housed in a piezoelectric tube with single inner and outer electrodes (for Z scan). They are fixed at one end (called common end). A hollow tantalum shaft is coaxially housed in the XY -scan tube and they are mutually fixed at both ends. When the XY scanner scans, its free end will bring the shaft to scan and the tip which is coaxially inserted in the shaft at the common end will scan a smaller area if the tip protrudes short enough from the common end. The decoupled XY and Z scans are desired for less image distortion and the mechanically reduced scan range has the superiority of reducing the impact of the background electronic noise on the scanner and enhancing the tip positioning precision. High quality atomic resolution images are also shown.

  19. A High Rigidity and Precision Scanning Tunneling Microscope with Decoupled XY and Z Scans

    Directory of Open Access Journals (Sweden)

    Xu Chen

    2017-01-01

    Full Text Available A new scan-head structure for the scanning tunneling microscope (STM is proposed, featuring high scan precision and rigidity. The core structure consists of a piezoelectric tube scanner of quadrant type (for XY scans coaxially housed in a piezoelectric tube with single inner and outer electrodes (for Z scan. They are fixed at one end (called common end. A hollow tantalum shaft is coaxially housed in the XY-scan tube and they are mutually fixed at both ends. When the XY scanner scans, its free end will bring the shaft to scan and the tip which is coaxially inserted in the shaft at the common end will scan a smaller area if the tip protrudes short enough from the common end. The decoupled XY and Z scans are desired for less image distortion and the mechanically reduced scan range has the superiority of reducing the impact of the background electronic noise on the scanner and enhancing the tip positioning precision. High quality atomic resolution images are also shown.

  20. Atomic resolution ultrafast scanning tunneling microscope with scan rate breaking the resonant frequency of a quartz tuning fork resonator.

    Science.gov (United States)

    Li, Quanfeng; Lu, Qingyou

    2011-05-01

    We present an ultra-fast scanning tunneling microscope with atomic resolution at 26 kHz scan rate which surpasses the resonant frequency of the quartz tuning fork resonator used as the fast scan actuator. The main improvements employed in achieving this new record are (1) fully low voltage design (2) independent scan control and data acquisition, where the tuning fork (carrying a tip) is blindly driven to scan by a function generator with the scan voltage and tunneling current (I(T)) being measured as image data (this is unlike the traditional point-by-point move and measure method where data acquisition and scan control are switched many times).

  1. Graphene quantum dots probed by scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Morgenstern, Markus; Freitag, Nils; Nent, Alexander; Nemes-Incze, Peter; Liebmann, Marcus [II. Institute of Physics B and JARA-FIT, RWTH Aachen University, Aachen (Germany)

    2017-11-15

    Scanning tunneling spectroscopy results probing the electronic properties of graphene quantum dots are reviewed. After a short summary of the study of squared wave functions of graphene quantum dots on metal substrates, we firstly present data where the Landau level gaps caused by a perpendicular magnetic field are used to electrostatically confine electrons in monolayer graphene, which are probed by the Coulomb staircase revealing the consecutive charging of a quantum dot. It turns out that these quantum dots exhibit much more regular charging sequences than lithographically confined ones. Namely, the consistent grouping of charging peaks into quadruplets, both, in the electron and hole branch, portrays a regular orbital splitting of about 10meV. At low hole occupation numbers, the charging peaks are, partly, additionally grouped into doublets. The spatially varying energy separation of the doublets indicates a modulation of the valley splitting by the underlying BN substrate. We outline that this property might be used to eventually tune the valley splitting coherently. Afterwards, we describe graphene quantum dots with multiple contacts produced without lithographic resist, namely by local anodic oxidation. Such quantum dots target the goal to probe magnetotransport properties during the imaging of the corresponding wave functions by scanning tunneling spectroscopy. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  2. From Graphite to Graphene via Scanning Tunneling Microscopy

    Science.gov (United States)

    Qi, Dejun

    The primary objective of this dissertation is to study both graphene on graphite and pristine freestanding grapheme using scanning tunneling microscopy (STM) and density functional theory (DFT) simulation technique. In the experiment part, good quality tungsten metalic tips for experiment were fabricated using our newly developed tip making setup. Then a series of measurements using a technique called electrostatic-manipulation scanning tunneling microscopy (EM-STM) of our own development were performed on a highly oriented pyrolytic graphite (HOPG) surface. The electrostatic interaction between the STM tip and the sample can be tuned to produce both reversible and irreversible large-scale movement of the graphite surface. Under this influence, atomic-resolution STM images reveal that a continuous electronic transition between two distinct patterns can be systematically controlled. DFT calculations reveal that this transition can be related to vertical displacements of the top layer of graphite relative to the bulk. Evidence for horizontal shifts in the top layer of graphite is also presented. Excellent agreement is found between experimental STM images and those simulated using DFT. In addition, the EM-STM technique was also used to controllably and reversibly pull freestanding graphene membranes up to 35 nm from their equilibrium height. Atomic-scale corrugation amplitudes 20 times larger than the STM electronic corrugation for graphene on a substrate were observed. The freestanding graphene membrane responds to a local attractive force created at the STM tip as a highly conductive yet flexible grounding plane with an elastic restoring force.

  3. Spin-polarized hydrogen, deuterium, and tritium : I

    International Nuclear Information System (INIS)

    Haugen, M.; Ostgaard, E.

    1989-01-01

    The ground-state energy of spin-polarized hydrogen, deuterium and tritium is calculated by means of a modified variational lowest order constrained-variation method, and the calculations are done for five different two-body potentials. Spin-polarized H is not self-bound according to our theoretical results for the ground-state binding energy. For spin-polarized D, however, we obtain theoretical results for the ground-state binding energy per particle from -0.4 K at an equilibrium particle density of 0.25 σ -3 or a molar volume of 121 cm 3 /mol to +0.32 K at an equilibrium particle density of 0.21 σ -3 or a molar volume of 142 cm 3 /mol, where σ = 3.69 A (1A = 10 -10 m). It is, therefore, not clear whether spin-polarized deuterium should be self-bound or not. For spin-polarized T, we obtain theoretical results for the ground-state binding energy per particle from -4.73 K at an equilibrium particle density of 0.41 σ -3 or a molar volume of 74 cm 3 /mol to -1.21 K at an equilibrium particle density of 0.28 σ -3 or a molar volume of 109 cm 3 /mol. (Author) 27 refs., 9 figs., tab

  4. Postprocessing Algorithm for Driving Conventional Scanning Tunneling Microscope at Fast Scan Rates.

    Science.gov (United States)

    Zhang, Hao; Li, Xianqi; Chen, Yunmei; Park, Jewook; Li, An-Ping; Zhang, X-G

    2017-01-01

    We present an image postprocessing framework for Scanning Tunneling Microscope (STM) to reduce the strong spurious oscillations and scan line noise at fast scan rates and preserve the features, allowing an order of magnitude increase in the scan rate without upgrading the hardware. The proposed method consists of two steps for large scale images and four steps for atomic scale images. For large scale images, we first apply for each line an image registration method to align the forward and backward scans of the same line. In the second step we apply a "rubber band" model which is solved by a novel Constrained Adaptive and Iterative Filtering Algorithm (CIAFA). The numerical results on measurement from copper(111) surface indicate the processed images are comparable in accuracy to data obtained with a slow scan rate, but are free of the scan drift error commonly seen in slow scan data. For atomic scale images, an additional first step to remove line-by-line strong background fluctuations and a fourth step of replacing the postprocessed image by its ranking map as the final atomic resolution image are required. The resulting image restores the lattice image that is nearly undetectable in the original fast scan data.

  5. Postprocessing Algorithm for Driving Conventional Scanning Tunneling Microscope at Fast Scan Rates

    Directory of Open Access Journals (Sweden)

    Hao Zhang

    2017-01-01

    Full Text Available We present an image postprocessing framework for Scanning Tunneling Microscope (STM to reduce the strong spurious oscillations and scan line noise at fast scan rates and preserve the features, allowing an order of magnitude increase in the scan rate without upgrading the hardware. The proposed method consists of two steps for large scale images and four steps for atomic scale images. For large scale images, we first apply for each line an image registration method to align the forward and backward scans of the same line. In the second step we apply a “rubber band” model which is solved by a novel Constrained Adaptive and Iterative Filtering Algorithm (CIAFA. The numerical results on measurement from copper(111 surface indicate the processed images are comparable in accuracy to data obtained with a slow scan rate, but are free of the scan drift error commonly seen in slow scan data. For atomic scale images, an additional first step to remove line-by-line strong background fluctuations and a fourth step of replacing the postprocessed image by its ranking map as the final atomic resolution image are required. The resulting image restores the lattice image that is nearly undetectable in the original fast scan data.

  6. Spin inelastic electron tunneling spectroscopy on local spin adsorbed on surface.

    Science.gov (United States)

    Fransson, J

    2009-06-01

    The recent experimental conductance measurements taken on magnetic impurities on metallic surfaces, using scanning tunneling microscopy technique and suggesting occurrence of inelastic scattering processes, are theoretically addressed. We argue that the observed conductance signatures are caused by transitions between the spin states that have opened due to, for example, exchange coupling between the local spins and the tunneling electrons, and are directly interpretable in terms of inelastic transitions energies. Feasible measurements using spin-polarized scanning tunneling microscopy that would enable new information about the excitation spectrum of the local spins are discussed.

  7. A scanning tunneling microscope with a scanning range from hundreds of micrometers down to nanometer resolution.

    Science.gov (United States)

    Kalkan, Fatih; Zaum, Christopher; Morgenstern, Karina

    2012-10-01

    A beetle type stage and a flexure scanning stage are combined to form a two stages scanning tunneling microscope (STM). It operates at room temperature in ultrahigh vacuum and is capable of scanning areas up to 300 μm × 450 μm down to resolution on the nanometer scale. This multi-scale STM has been designed and constructed in order to investigate prestructured metallic or semiconducting micro- and nano-structures in real space from atomic-sized structures up to the large-scale environment. The principle of the instrument is demonstrated on two different systems. Gallium nitride based micropillars demonstrate scan areas up to hundreds of micrometers; a Au(111) surface demonstrates nanometer resolution.

  8. Spin polarized states in strongly asymmetric nuclear matter

    International Nuclear Information System (INIS)

    Isayev, A.A.; Yang, J.

    2004-01-01

    The possibility of appearance of spin polarized states in strongly asymmetric nuclear matter is analyzed within the framework of a Fermi liquid theory with the Skyrme effective interaction. The zero temperature dependence of the neutron and proton spin polarization parameters as functions of density is found for SLy4 and SLy5 effective forces. It is shown that at some critical density strongly asymmetric nuclear matter undergoes a phase transition to the state with the oppositely directed spins of neutrons and protons while the state with the same direction of spins does not appear. In comparison with neutron matter, even small admixture of protons strongly decreases the threshold density of spin instability. It is clarified that protons become totally polarized within a very narrow density domain while the density profile of the neutron spin polarization parameter is characterized by the appearance of long tails near the transition density

  9. An enhancement of spin polarization by multiphoton pumping in semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Miah, M. Idrish, E-mail: m.miah@griffith.edu.au [Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)

    2011-08-15

    Highlights: {yields} Multiphoton pumping and spin generation in semiconductors. {yields} Optical selection rules for inter-band transitions. {yields} Calculations of spin polarization using band-energy model and the second order perturbation theory. {yields} Enhancement of the electronic spin polarization. - Abstract: A pump-probe spectroscopic study has been carried out in zinc-blende bulk semiconductors. In the semiconductor samples, a spin-polarized carrier population is produced by the absorption of a monochromatic circularly polarized light beam with two-photon energy above the direct band gap in bulk semiconductors. The production of a carrier population with a net spin is a consequence of the optical selection rules for the heavy-hole and light-hole valence-to-conduction band transitions. This production is probed by the spin-dependent transmission of the samples in the time domain. The spin polarization of the conduction-band-electrons in dependences of delay of the probe beam as well as of pumping photon energy is estimated. The spin polarization is found to depolarize rapidly for pumping energy larger than the energy gap of the split-off band to the conduction band. From the polarization decays, the spin relaxation times are also estimated. Compared to one-photon pumping, the results, however, show that an enhancement of the spin-polarization is achieved by multiphoton excitation of the samples. The experimental results are compared with those obtained in calculations using second order perturbation theory of the spin transport model. A good agreement between experiment and theory is obtained. The observed results are discussed in details.

  10. An enhancement of spin polarization by multiphoton pumping in semiconductors

    International Nuclear Information System (INIS)

    Miah, M. Idrish

    2011-01-01

    Highlights: → Multiphoton pumping and spin generation in semiconductors. → Optical selection rules for inter-band transitions. → Calculations of spin polarization using band-energy model and the second order perturbation theory. → Enhancement of the electronic spin polarization. - Abstract: A pump-probe spectroscopic study has been carried out in zinc-blende bulk semiconductors. In the semiconductor samples, a spin-polarized carrier population is produced by the absorption of a monochromatic circularly polarized light beam with two-photon energy above the direct band gap in bulk semiconductors. The production of a carrier population with a net spin is a consequence of the optical selection rules for the heavy-hole and light-hole valence-to-conduction band transitions. This production is probed by the spin-dependent transmission of the samples in the time domain. The spin polarization of the conduction-band-electrons in dependences of delay of the probe beam as well as of pumping photon energy is estimated. The spin polarization is found to depolarize rapidly for pumping energy larger than the energy gap of the split-off band to the conduction band. From the polarization decays, the spin relaxation times are also estimated. Compared to one-photon pumping, the results, however, show that an enhancement of the spin-polarization is achieved by multiphoton excitation of the samples. The experimental results are compared with those obtained in calculations using second order perturbation theory of the spin transport model. A good agreement between experiment and theory is obtained. The observed results are discussed in details.

  11. Local tunneling spectroscopy of a Nb/InAs/Nb superconducting proximity system with a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Inoue, K.; Takayanagi, H.

    1991-01-01

    Local tunneling spectroscopy for a Nb/In/As/Nb superconducting proximity system was demonstrated with a low-temperature scanning tunneling microscope. It is found that the local electron density of states in the InAs region is spatially modulated by the neighboring superconductor Nb

  12. Molecular tips for scanning tunneling microscopy: intermolecular electron tunneling for single-molecule recognition and electronics.

    Science.gov (United States)

    Nishino, Tomoaki

    2014-01-01

    This paper reviews the development of molecular tips for scanning tunneling microscopy (STM). Molecular tips offer many advantages: first is their ability to perform chemically selective imaging because of chemical interactions between the sample and the molecular tip, thus improving a major drawback of conventional STM. Rational design of the molecular tip allows sophisticated chemical recognition; e.g., chiral recognition and selective visualization of atomic defects in carbon nanotubes. Another advantage is that they provide a unique method to quantify electron transfer between single molecules. Understanding such electron transfer is mandatory for the realization of molecular electronics.

  13. Spin-polarized photoemission from SiGe heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ferrari, A.; Bottegoni, F.; Isella, G.; Cecchi, S.; Chrastina, D.; Finazzi, M.; Ciccacci, F. [LNESS-Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano (Italy)

    2013-12-04

    We apply the principles of Optical Orientation to measure by Mott polarimetry the spin polarization of electrons photoemitted from different group-IV heterostructures. The maximum measured spin polarization, obtained from a Ge/Si{sub 0.31}Ge{sub 0.69} strained film, undoubtedly exceeds the maximum value of 50% attainable in bulk structures. The explanation we give for this result lies in the enhanced band orbital mixing between light hole and split-off valence bands as a consequence of the compressive strain experienced by the thin Ge layer.

  14. Design of a high-speed electrochemical scanning tunneling microscope.

    Science.gov (United States)

    Yanson, Y I; Schenkel, F; Rost, M J

    2013-02-01

    In this paper, we present a bottom-up approach to designing and constructing a high-speed electrochemical scanning tunneling microscope (EC-STM). Using finite element analysis (FEA) calculations of the frequency response of the whole mechanical loop of the STM, we analyzed several geometries to find the most stable one that could facilitate fast scanning. To test the FEA results, we conducted measurements of the vibration amplitudes using a prototype STM setup. Based on the FEA analysis and the measurement results, we identified the potentially most disturbing vibration modes that could impair fast scanning. By modifying the design of some parts of the EC-STM, we reduced the amplitudes as well as increased the resonance frequencies of these modes. Additionally, we designed and constructed an electrochemical flow-cell that allows STM imaging in a flowing electrolyte, and built a bi-potentiostat to achieve electrochemical potential control during the measurements. Finally, we present STM images acquired during high-speed imaging in air as well as in an electrochemical environment using our newly-developed EC-STM.

  15. Fully low voltage and large area searching scanning tunneling microscope

    International Nuclear Information System (INIS)

    Pang, Zongqiang; Wang, Jihui; Lu, Qingyou

    2009-01-01

    We present a novel scanning tunneling microscope (STM), which allows the tip to travel a large distance (millimeters) on the sample and take images (to find microscopic targets) anywhere it reaches without losing atomic resolution. This broad range searching capability, together with the coarse approach and scan motion, is all done with only one single piezoelectric tube scanner as well as with only low voltages (<15 V). Simple structure, low interference and high precision are thus achieved. To this end, a pillar and a tube scanner are mounted in parallel on a base with one ball glued on the pillar top and two balls glued on the scanner top. These three balls form a narrow triangle, which supports a triangular slider piece. By inertial stepping, the scanner can move the slider toward the pillar (coarse approach) or rotate the slider about the pillar (travel along sample surface). Since all the stepping motions are driven by the scanner's lateral bending which is large per unit voltage, high voltages are unnecessary. The technology is also applicable to scanning force microscopes (SFM) such as atomic force microscopes (AFM), etc

  16. Electronic structure classifications using scanning tunneling microscopy conductance imaging

    International Nuclear Information System (INIS)

    Horn, K.M.; Swartzentruber, B.S.; Osbourn, G.C.; Bouchard, A.; Bartholomew, J.W.

    1998-01-01

    The electronic structure of atomic surfaces is imaged by applying multivariate image classification techniques to multibias conductance data measured using scanning tunneling microscopy. Image pixels are grouped into classes according to shared conductance characteristics. The image pixels, when color coded by class, produce an image that chemically distinguishes surface electronic features over the entire area of a multibias conductance image. Such open-quotes classedclose quotes images reveal surface features not always evident in a topograph. This article describes the experimental technique used to record multibias conductance images, how image pixels are grouped in a mathematical, classification space, how a computed grouping algorithm can be employed to group pixels with similar conductance characteristics in any number of dimensions, and finally how the quality of the resulting classed images can be evaluated using a computed, combinatorial analysis of the full dimensional space in which the classification is performed. copyright 1998 American Institute of Physics

  17. A high stability and repeatability electrochemical scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Zhigang; Wang, Jihao; Lu, Qingyou, E-mail: qxl@ustc.edu.cn [High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026 (China); Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026 (China); Hou, Yubin [High Magnetic Field Laboratory, Chinese Academy of Sciences and University of Science and Technology of China, Hefei, Anhui 230026 (China)

    2014-12-15

    We present a home built electrochemical scanning tunneling microscope (ECSTM) with very high stability and repeatability. Its coarse approach is driven by a closely stacked piezo motor of GeckoDrive type with four rigid clamping points, which enhances the rigidity, compactness, and stability greatly. It can give high clarity atomic resolution images without sound and vibration isolations. Its drifting rates in XY and Z directions in solution are as low as 84 pm/min and 59 pm/min, respectively. In addition, repeatable coarse approaches in solution within 2 mm travel distance show a lateral deviation less than 50 nm. The gas environment can be well controlled to lower the evaporation rate of the cell, thus reducing the contamination and elongating the measurement time. Atomically resolved SO{sub 4}{sup 2−} image on Au (111) work electrode is demonstrated to show the performance of the ECSTM.

  18. A combined scanning tunneling microscope-atomic layer deposition tool.

    Science.gov (United States)

    Mack, James F; Van Stockum, Philip B; Iwadate, Hitoshi; Prinz, Fritz B

    2011-12-01

    We have built a combined scanning tunneling microscope-atomic layer deposition (STM-ALD) tool that performs in situ imaging of deposition. It operates from room temperature up to 200 °C, and at pressures from 1 × 10(-6) Torr to 1 × 10(-2) Torr. The STM-ALD system has a complete passive vibration isolation system that counteracts both seismic and acoustic excitations. The instrument can be used as an observation tool to monitor the initial growth phases of ALD in situ, as well as a nanofabrication tool by applying an electric field with the tip to laterally pattern deposition. In this paper, we describe the design of the tool and demonstrate its capability for atomic resolution STM imaging, atomic layer deposition, and the combination of the two techniques for in situ characterization of deposition.

  19. A high stability and repeatability electrochemical scanning tunneling microscope.

    Science.gov (United States)

    Xia, Zhigang; Wang, Jihao; Hou, Yubin; Lu, Qingyou

    2014-12-01

    We present a home built electrochemical scanning tunneling microscope (ECSTM) with very high stability and repeatability. Its coarse approach is driven by a closely stacked piezo motor of GeckoDrive type with four rigid clamping points, which enhances the rigidity, compactness, and stability greatly. It can give high clarity atomic resolution images without sound and vibration isolations. Its drifting rates in XY and Z directions in solution are as low as 84 pm/min and 59 pm/min, respectively. In addition, repeatable coarse approaches in solution within 2 mm travel distance show a lateral deviation less than 50 nm. The gas environment can be well controlled to lower the evaporation rate of the cell, thus reducing the contamination and elongating the measurement time. Atomically resolved SO4(2-) image on Au (111) work electrode is demonstrated to show the performance of the ECSTM.

  20. Fault detection by surface seismic scanning tunneling macroscope: Field test

    KAUST Repository

    Hanafy, Sherif M.

    2014-08-05

    The seismic scanning tunneling macroscope (SSTM) is proposed for detecting the presence of near-surface impedance anomalies and faults. Results with synthetic data are consistent with theory in that scatterers closer to the surface provide brighter SSTM profiles than those that are deeper. The SSTM profiles show superresolution detection if the scatterers are in the near-field region of the recording line. The field data tests near Gulf of Aqaba, Haql, KSA clearly show the presence of the observable fault scarp, and identify the subsurface presence of the hidden faults indicated in the tomograms. Superresolution detection of the fault is achieved, even when the 35 Hz data are lowpass filtered to the 5-10 Hz band.

  1. Fault detection by surface seismic scanning tunneling macroscope: Field test

    KAUST Repository

    Hanafy, Sherif M.; Schuster, Gerard T.

    2014-01-01

    The seismic scanning tunneling macroscope (SSTM) is proposed for detecting the presence of near-surface impedance anomalies and faults. Results with synthetic data are consistent with theory in that scatterers closer to the surface provide brighter SSTM profiles than those that are deeper. The SSTM profiles show superresolution detection if the scatterers are in the near-field region of the recording line. The field data tests near Gulf of Aqaba, Haql, KSA clearly show the presence of the observable fault scarp, and identify the subsurface presence of the hidden faults indicated in the tomograms. Superresolution detection of the fault is achieved, even when the 35 Hz data are lowpass filtered to the 5-10 Hz band.

  2. Scanning tunneling microscope with two-dimensional translator.

    Science.gov (United States)

    Nichols, J; Ng, K-W

    2011-01-01

    Since the invention of the scanning tunneling microscope (STM), it has been a powerful tool for probing the electronic properties of materials. Typically STM designs capable of obtaining resolution on the atomic scale are limited to a small area which can be probed. We have built an STM capable of coarse motion in two dimensions, the z- and x-directions which are, respectively, parallel and perpendicular to the tip. This allows us to image samples with very high resolution at sites separated by macroscopic distances. This device is a single unit with a compact design making it very stable. It can operate in either a horizontal or vertical configuration and at cryogenic temperatures.

  3. Molecules on vicinal Au surfaces studied by scanning tunnelling microscopy

    International Nuclear Information System (INIS)

    Kroeger, J; Neel, N; Jensen, H; Berndt, R; Rurali, R; Lorente, N

    2006-01-01

    Using low-temperature scanning tunnelling microscopy and spectroscopy we investigated the adsorption characteristics of 3,4,9,10-perylenetetracarboxylic-dianhydride and fullerenes on Au(788), Au(433), and Au(778). On Au(788) and Au(778), 3,4,9,10-perylenetetracarboxylic-dianhydride exhibits three coexisting superstructures, which do not reflect the periodicity of the hosting substrate. The adsorption on Au(433) leads to the formation of molecule chains along the step edges after annealing the sample. Fullerene molecules on Au(788) arrange in a mesh of islands, which extends over several hundreds of nanometres with an extraordinarily high periodicity. A combination of fullerene adsorption and annealing leads to facetting of Au(433) and the formation of extraordinarily long fullerene stripes

  4. Scanning tunneling microscope with a rotary piezoelectric stepping motor

    Science.gov (United States)

    Yakimov, V. N.

    1996-02-01

    A compact scanning tunneling microscope (STM) with a novel rotary piezoelectric stepping motor for coarse positioning has been developed. An inertial method for rotating of the rotor by the pair of piezoplates has been used in the piezomotor. Minimal angular step size was about several arcsec with the spindle working torque up to 1 N×cm. Design of the STM was noticeably simplified by utilization of the piezomotor with such small step size. A shaft eccentrically attached to the piezomotor spindle made it possible to push and pull back the cylindrical bush with the tubular piezoscanner. A linear step of coarse positioning was about 50 nm. STM resolution in vertical direction was better than 0.1 nm without an external vibration isolation.

  5. Simple and efficient scanning tunneling luminescence detection at low-temperature

    NARCIS (Netherlands)

    Keizer, J.G.; Garleff, J.K.; Koenraad, P.M.

    2009-01-01

    We have designed and built an optical system to collect light that is generated in the tunneling region of a low-temperature scanning tunneling microscope. The optical system consists of an in situ lens placed approximately 1.5 cm from the tunneling region and an ex situ optical lens system to

  6. Current-induced spin polarization in a spin-polarized two-dimensional electron gas with spin-orbit coupling

    International Nuclear Information System (INIS)

    Wang, C.M.; Pang, M.Q.; Liu, S.Y.; Lei, X.L.

    2010-01-01

    The current-induced spin polarization (CISP) is investigated in a combined Rashba-Dresselhaus spin-orbit-coupled two-dimensional electron gas, subjected to a homogeneous out-of-plane magnetization. It is found that, in addition to the usual collision-related in-plane parts of CISP, there are two impurity-density-free contributions, arising from intrinsic and disorder-mediated mechanisms. The intrinsic parts of spin polarization are related to the Berry curvature, analogous with the anomalous and spin Hall effects. For short-range collision, the disorder-mediated spin polarizations completely cancel the intrinsic ones and the total in-plane components of CISP equal those for systems without magnetization. However, for remote disorders, this cancellation does not occur and the total in-plane components of CISP strongly depend on the spin-orbit interaction coefficients and magnetization for both pure Rashba and combined Rashba-Dresselhaus models.

  7. Investigation of Current Induced Spin Polarization in III-V Semiconductor Epilayers

    Science.gov (United States)

    Luengo-Kovac, Marta

    In the development of a semiconductor spintronics device, a thorough understanding of spin dynamics in semiconductors is necessary. In particular, electrical control of electron spins is advantageous for its compatibility with present day electronics. In this thesis, we will discuss the electrical modification of the electron g-factor, which characterizes the strength of the interaction between a spin and a magnetic field, as well as investigate electrically generated spin polarizations as a function of various material parameters. We report on the modification of the electron g-factor by an in-plane electric field in an InGaAs epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to measure the g-factor independently of the spin-orbit fields. The g-factor increases from -0.4473(0.0001) at 0 V/cm to -0.4419( 0.0001) at 50 V/cm applied along the [110] crystal axis. A comparison of temperature and voltage dependent photoluminescence measurements indicate that minimal channel heating occurs at these voltages. Possible explanations for this g-factor modification are discussed, including an increase in the electron temperature that is independent of the lattice temperature and the modification of the donor-bound electron wave function by the electric field. The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InGaAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the spin polarization mechanism is extrinsic. Temperature-dependent measurements of the spin dephasing rates and mobilities were used to characterize the relative strengths of the intrinsic D

  8. Experiment on the melting pressure of spin polarized He3

    DEFF Research Database (Denmark)

    Chapellier, M.; Olsen, M.; Rasmussen, Finn Berg

    1981-01-01

    In liquid He in a Pomeranchuk cell, the melting curve has been observed to be suppressed, presumably in regions with a strong local spin polarization. In the temperature range 30-50 mK the observed suppression was 60-80 kPa. The corresponding local polarization is estimated, in a crude model...

  9. Current-Induced Spin Polarization at a Single Heterojunction

    NARCIS (Netherlands)

    Silov, A.; Blajnov, P.; Wolter, J.H.; Hey, R.; Ploog, K.; Averkiev, N.S.; Menendez, J.; Walle, van der C.G.

    2005-01-01

    We have experimentally achieved spin-polarization by a lateral current in a single non-magnetic semiconductor heterojunction. The effect does not require an applied magnetic field or ferromagnetic contacts. The current-induced spin orientation can be seen as the inverse of the circular

  10. Fusion with highly spin polarized HD and D2

    International Nuclear Information System (INIS)

    Honig, A.

    1992-01-01

    This report discusses the following topics relating to inertial confinement with spin polarized hydrogen targets: low temperature implementation of mating a target to omega; dilution-refrigerator cold-entry and retrieval system; target shell tensile strength characterization at low temperatures; and proton and deuteron spin-lattice relaxation measurements in HD in the millikelvin temperature range

  11. Dresselhaus spin-orbit coupling induced spin-polarization and resonance-split in n-well semiconductor superlattices

    International Nuclear Information System (INIS)

    Ye Chengzhi; Xue Rui; Nie, Y.-H.; Liang, J.-Q.

    2009-01-01

    Using the transfer matrix method, we investigate the electron transmission over multiple-well semiconductor superlattices with Dresselhaus spin-orbit coupling in the potential-well regions. The superlattice structure enhances the effect of spin polarization in the transmission spectrum. The minibands of multiple-well superlattices for electrons with different spin can be completely separated at the low incident energy, leading to the 100% spin polarization in a broad energy windows, which may be an effective scheme for realizing spin filtering. Moreover, for the transmission over n-quantum-well, it is observed that the resonance peaks in the minibands split into n-folds or (n-1)-folds depending on the well-width and barrier-thickness, which is different from the case of tunneling through n-barrier structure

  12. Light-free magnetic resonance force microscopy for studies of electron spin polarized systems

    International Nuclear Information System (INIS)

    Pelekhov, Denis V.; Selcu, Camelia; Banerjee, Palash; Chung Fong, Kin; Chris Hammel, P.; Bhaskaran, Harish; Schwab, Keith

    2005-01-01

    Magnetic resonance force microscopy is a scanned probe technique capable of three-dimensional magnetic resonance imaging. Its excellent sensitivity opens the possibility for magnetic resonance studies of spin accumulation resulting from the injection of spin polarized currents into a para-magnetic collector. The method is based on mechanical detection of magnetic resonance which requires low noise detection of cantilever displacement; so far, this has been accomplished using optical interferometry. This is undesirable for experiments on doped silicon, where the presence of light is known to enhance spin relaxation rates. We report a non-optical displacement detection scheme based on sensitive microwave capacitive readout

  13. Spin-polarized light-emitting diodes based on organic bipolar spin valves

    Science.gov (United States)

    Vardeny, Zeev Valentine; Nguyen, Tho Duc; Ehrenfreund, Eitan Avraham

    2017-10-25

    Spin-polarized organic light-emitting diodes are provided. Such spin-polarized organic light-emitting diodes incorporate ferromagnetic electrodes and show considerable spin-valve magneto-electroluminescence and magneto-conductivity responses, with voltage and temperature dependencies that originate from the bipolar spin-polarized space charge limited current.

  14. A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Shuai; Huang, Di [State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433 (China); Wu, Shiwei, E-mail: swwu@fudan.edu.cn [State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (MOE), and Department of Physics, Fudan University, Shanghai 200433 (China); Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433 (China)

    2016-06-15

    The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

  15. A cryogen-free low temperature scanning tunneling microscope capable of inelastic electron tunneling spectroscopy.

    Science.gov (United States)

    Zhang, Shuai; Huang, Di; Wu, Shiwei

    2016-06-01

    The design and performance of a cryogen-free low temperature scanning tunneling microscope (STM) housed in ultrahigh vacuum (UHV) are reported. The cryogen-free design was done by directly integrating a Gifford-McMahon cycle cryocooler to a Besocke-type STM, and the vibration isolation was achieved by using a two-stage rubber bellow between the cryocooler and a UHV-STM interface with helium exchange gas cooling. A base temperature of 15 K at the STM was achieved, with a possibility to further decrease by using a cryocooler with higher cooling power and adding additional low temperature stage under the exchange gas interface. Atomically sharp STM images and high resolution dI/dV spectra on various samples were demonstrated. Furthermore, we reported the inelastic tunneling spectroscopy on a single carbon monoxide molecule adsorbed on Ag(110) surface with a cryogen-free STM for the first time. Being totally cryogen-free, the system not only saves the running cost significantly but also enables uninterrupted data acquisitions and variable temperature measurements with much ease. In addition, the system is capable of coupling light to the STM junction by a pair of lens inside the UHV chamber. We expect that these enhanced capabilities could further broaden our views to the atomic-scale world.

  16. Spin polarization of graphene and h -BN on Co(0001) and Ni(111) observed by spin-polarized surface positronium spectroscopy

    Science.gov (United States)

    Miyashita, A.; Maekawa, M.; Wada, K.; Kawasuso, A.; Watanabe, T.; Entani, S.; Sakai, S.

    2018-05-01

    In spin-polarized surface positronium annihilation measurements, the spin polarizations of graphene and h -BN on Co(0001) were higher than those on Ni(111), while no significant differences were seen between graphene and h -BN on the same metal. The obtained spin polarizations agreed with those expected from first-principles calculations considering the positron wave function and the electron density of states from the first surface layer to the vacuum region. The higher spin polarizations of graphene and h -BN on Co(0001) as compared to Ni(111) simply reflect the spin polarizations of these metals. The comparable spin polarizations of graphene and h -BN on the same metal are attributed to the creation of similar electronic states due to the strong influence of the metals: the Dirac cone of graphene and the band gap of h -BN disappear as a consequence of d -π hybridization.

  17. An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging.

    Science.gov (United States)

    Diaconescu, Bogdan; Nenchev, Georgi; de la Figuera, Juan; Pohl, Karsten

    2007-10-01

    We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.

  18. Spectroscopic scanning tunneling microscopy insights into Fe-based superconductors

    International Nuclear Information System (INIS)

    Hoffman, Jennifer E

    2011-01-01

    In the first three years since the discovery of Fe-based high T c superconductors, scanning tunneling microscopy (STM) and spectroscopy have shed light on three important questions. First, STM has demonstrated the complexity of the pairing symmetry in Fe-based materials. Phase-sensitive quasiparticle interference (QPI) imaging and low temperature spectroscopy have shown that the pairing order parameter varies from nodal to nodeless s± within a single family, FeTe 1-x Se x . Second, STM has imaged C4 → C2 symmetry breaking in the electronic states of both parent and superconducting materials. As a local probe, STM is in a strong position to understand the interactions between these broken symmetry states and superconductivity. Finally, STM has been used to image the vortex state, giving insights into the technical problem of vortex pinning, and the fundamental problem of the competing states introduced when superconductivity is locally quenched by a magnetic field. Here we give a pedagogical introduction to STM and QPI imaging, discuss the specific challenges associated with extracting bulk properties from the study of surfaces, and report on progress made in understanding Fe-based superconductors using STM techniques.

  19. Scanning tunneling microscopy and spectroscopy of twisted trilayer graphene

    Science.gov (United States)

    Zuo, Wei-Jie; Qiao, Jia-Bin; Ma, Dong-Lin; Yin, Long-Jing; Sun, Gan; Zhang, Jun-Yang; Guan, Li-Yang; He, Lin

    2018-01-01

    Twist, as a simple and unique degree of freedom, could lead to enormous novel quantum phenomena in bilayer graphene. A small rotation angle introduces low-energy van Hove singularities (VHSs) approaching the Fermi level, which result in unusual correlated states in the bilayer graphene. It is reasonable to expect that the twist could also affect the electronic properties of few-layer graphene dramatically. However, such an issue has remained experimentally elusive. Here, by using scanning tunneling microscopy/spectroscopy (STM/STS), we systematically studied a twisted trilayer graphene (TTG) with two different small twist angles between adjacent layers. Two sets of VHSs, originating from the two twist angles, were observed in the TTG, indicating that the TTG could be simply regarded as a combination of two different twisted bilayers of graphene. By using high-resolution STS, we observed a split of the VHSs and directly imaged the spatial symmetry breaking of electronic states around the VHSs. These results suggest that electron-electron interactions play an important role in affecting the electronic properties of graphene systems with low-energy VHSs.

  20. Spin-polarized gapped Dirac spectrum of unsupported silicene

    Energy Technology Data Exchange (ETDEWEB)

    Podsiadły-Paszkowska, A., E-mail: agata.podsiadly@gmail.com; Krawiec, M., E-mail: mariusz.krawiec@umcs.pl

    2016-06-15

    Highlights: • Effects of spin–orbit interaction and atomic reconstruction of silicene on its electronic properties have been studied. • Spin-polarized gapped Dirac spectrum has been revealed. • Two different AFM phases have been obtained. - Abstract: We study effects of the spin–orbit interaction and the atomic reconstruction of silicene on its electronic spectrum. As an example we consider unsupported silicene pulled off from Pb(111) substrate. Using first principles density functional theory we show that the inversion symmetry broken arrangement of atoms and the spin–orbit interaction generate a spin-polarized electronic spectrum with an energy gap in the Dirac cone. These findings are particularly interesting in view of the quantum anomalous and quantum valley Hall effects and should be observable in weakly interacting silicene-substrate systems.

  1. Widespread spin polarization effects in photoemission from topological insulators

    Energy Technology Data Exchange (ETDEWEB)

    Jozwiak, C.; Chen, Y. L.; Fedorov, A. V.; Analytis, J. G.; Rotundu, C. R.; Schmid, A. K.; Denlinger, J. D.; Chuang, Y.-D.; Lee, D.-H.; Fisher, I. R.; Birgeneau, R. J.; Shen, Z.-X.; Hussain, Z.; Lanzara, A.

    2011-06-22

    High-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES) was performed on the three-dimensional topological insulator Bi{sub 2}Se{sub 3} using a recently developed high-efficiency spectrometer. The topological surface state's helical spin structure is observed, in agreement with theoretical prediction. Spin textures of both chiralities, at energies above and below the Dirac point, are observed, and the spin structure is found to persist at room temperature. The measurements reveal additional unexpected spin polarization effects, which also originate from the spin-orbit interaction, but are well differentiated from topological physics by contrasting momentum and photon energy and polarization dependencies. These observations demonstrate significant deviations of photoelectron and quasiparticle spin polarizations. Our findings illustrate the inherent complexity of spin-resolved ARPES and demonstrate key considerations for interpreting experimental results.

  2. Application of spin-polarized fuel to fusion reactions

    International Nuclear Information System (INIS)

    Wakuta, Y.; Nakao, Y.; Honda, T.; Honda, Y.; Nakashima, H.

    1990-01-01

    Studies on the application of the polarized fuel to the inertial fusion reaction have been carried out. It is shown that the use of the spin-polarized fuel D vector·T vector or D vector· 3 (He)vector reduces the irradiating laser power more than 50% compared with the use of the unpolarized fuel. The depolarization rate of the polarized fuel during the fusing process is found to be almost negligible. (author)

  3. Design and performance of a beetle-type double-tip scanning tunneling microscope

    International Nuclear Information System (INIS)

    Jaschinsky, Philipp; Coenen, Peter; Pirug, Gerhard; Voigtlaender, Bert

    2006-01-01

    A combination of a double-tip scanning tunneling microscope with a scanning electron microscope in ultrahigh vacuum environment is presented. The compact beetle-type design made it possible to integrate two independently driven scanning tunneling microscopes in a small space. Moreover, an additional level for coarse movement allows the decoupling of the translation and approach of the tunneling tip. The position of the two tips can be controlled from the millimeter scale down to 50 nm with the help of an add-on electron microscope. The instrument is capable of atomic resolution imaging with each tip

  4. Magnetic switching of a single molecular magnet due to spin-polarized current

    Science.gov (United States)

    Misiorny, Maciej; Barnaś, Józef

    2007-04-01

    Magnetic switching of a single molecular magnet (SMM) due to spin-polarized current flowing between ferromagnetic metallic leads (electrodes) is investigated theoretically. Magnetic moments of the leads are assumed to be collinear and parallel to the magnetic easy axis of the molecule. Electrons tunneling through the barrier between magnetic leads are coupled to the SMM via exchange interaction. The current flowing through the system, as well as the spin relaxation times of the SMM, are calculated from the Fermi golden rule. It is shown that spin of the SMM can be reversed by applying a certain voltage between the two magnetic electrodes. Moreover, the switching may be visible in the corresponding current-voltage characteristics.

  5. Spin polarized semimagnetic exciton-polariton condensate in magnetic field.

    Science.gov (United States)

    Król, Mateusz; Mirek, Rafał; Lekenta, Katarzyna; Rousset, Jean-Guy; Stephan, Daniel; Nawrocki, Michał; Matuszewski, Michał; Szczytko, Jacek; Pacuski, Wojciech; Piętka, Barbara

    2018-04-27

    Owing to their integer spin, exciton-polaritons in microcavities can be used for observation of non-equilibrium Bose-Einstein condensation in solid state. However, spin-related phenomena of such condensates are difficult to explore due to the relatively small Zeeman effect of standard semiconductor microcavity systems and the strong tendency to sustain an equal population of two spin components, which precludes the observation of condensates with a well defined spin projection along the axis of the system. The enhancement of the Zeeman splitting can be achieved by introducing magnetic ions to the quantum wells, and consequently forming semimagnetic polaritons. In this system, increasing magnetic field can induce polariton condensation at constant excitation power. Here we evidence the spin polarization of a semimagnetic polaritons condensate exhibiting a circularly polarized emission over 95% even in a moderate magnetic field of about 3 T. Furthermore, we show that unlike nonmagnetic polaritons, an increase on excitation power results in an increase of the semimagnetic polaritons condensate spin polarization. These properties open new possibilities for testing theoretically predicted phenomena of spin polarized condensate.

  6. Development of spin-polarized transmission electron microscope

    International Nuclear Information System (INIS)

    Kuwahara, M; Saitoh, K; Tanaka, N; Takeda, Y; Ujihara, T; Asano, H; Nakanishi, T

    2011-01-01

    In order to study spin related phenomena in nano-size materials, spin-polarized electron source (PES) has been employed for the incident beam in transmission electron microscope (TEM). The PES has been designed and constructed with optimizing for spin-polarized TEM. The illuminating system of TEM is also designed to focus the spin-polarized electron beam emitted from a semiconductor photocathode with a negative electron affinity (NEA) surface. The beam energy is set to below 40 keV which is lower energy type as a TEM, because the spin interaction with condensed matters is very small corresponding with a Coulomb interaction. The polarized electron gun has realized in an extra high vacuum (XHV) condition and high field gradient of 4 MV/m on a surface of photocathode. Furthermore, it demonstrated that 40-keV polarized electron beam was operated with a sub-milli second pulse mode by using the backside excitation type photocathode. This high performance PES will make it possible to observe dynamically a magnetic field images with high contrast and highspeed temporal imaging in TEM.

  7. Scanning tunneling microscopy studies of glucose oxidase on gold surface

    International Nuclear Information System (INIS)

    Losic, D.; Shapter, J.G.; Gooding, J.J.

    2002-01-01

    Full text: Three immobilization methods have been used for scanning tunneling microscopy (STM) studies of glucose oxidase (GOD) on gold. They are based on a) physical adsorption from solution, b) microcontact printing and c) covalent bonding onto self-assembled monolayers (SAM) of 3-mercaptopropionic acid (MPA). The STM images are used to provide information about the organization of individual GOD molecules and more densely packed monolayers of GOD on electrode surfaces, thus providing information of the role of interfacial structure on biosensor performance. The use of atomically flat gold substrates enables easy distinction of deposited enzyme features from the flat gold substrate. Microcontact printing is found to be a more reliable method than adsorption from solution for preparing individual GOD molecules on the gold surface STM images of printed samples reveal two different shapes of native GOD molecules. One is a butterfly shape with dimensions of 10 ± 1 nm x 6 ± 1 nm, assigned to the lying position of molecule while the second is an approximately spherical shape with dimensions of 6.5 ± 1 nm x 5 ± 1nm assigned to a standing position. Isolated clusters of 5 to 6 GOD molecules are also observed. With monolayer coverage, GOD molecules exhibit a tendency to organize themselves into a two dimensional array with adequate sample stability to obtain high-resolution STM images. Within these two-dimensional arrays are clearly seen repeating clusters of five to six enzyme molecules in a unit STM imaging of GOD monolayers covalently immobilized onto SAM (MPA) are considerably more difficult than when the enzyme is adsorbed directly onto the metal. Cluster structures are observed both high and low coverage despite the fact that native GOD is a negatively charged molecule. Copyright (2002) Australian Society for Electron Microscopy Inc

  8. Field-Induced Deformation as a Mechanism for Scanning Tunneling Microscopy Based Nanofabrication

    DEFF Research Database (Denmark)

    Hansen, Ole; Ravnkilde, Jan Tue; Quaade, Ulrich

    1998-01-01

    The voltage between tip and sample in a scanning tunneling microscope (STM) results in a large electric field localized near the tip apex. The mechanical stress due to this field can cause appreciable deformation of both tip and sample on the scale of the tunnel gap. We derive an approximate...

  9. Study of Nb-oxide Nb-Pb film structures by tunnel scanning microscope

    International Nuclear Information System (INIS)

    Golyamina, E.M.; Troyanovskij, A.M.

    1986-01-01

    The surface of niobium films, which were earlier used to create niobium-niobium oxide-lead film structures on their base, was investigated, using tunnel scanning microscope. The results obtained agree well with the observed properties of these structures, containing josephson and tunnel junctions

  10. Spectroscopy of surface adsorbed molecules (scanning tunneling microscopy). Progress report, May 1, 1985-April 30, 1986

    International Nuclear Information System (INIS)

    Coleman, R.V.

    1986-01-01

    A review of the scanning tunneling microscopy program is given. This article contains a description of the design and fabrication of the microscope in addition to description of studies which use the microscope: studies of charge-density waves and studies of tunnel junctions doped with metals and semiconductors. 48 refs., 26 figs

  11. Measurement of the vortex-core radius by scanning tunneling microscopy

    NARCIS (Netherlands)

    Hartmann, U.; Golubov, Alexandre Avraamovitch; Drechsler, T.; Kupriyanov, M. Yu; Heiden, C.

    1994-01-01

    Using a scanning tunneling microscope operated in a spectroscopic mode we imaged flux-line lattices in niobium diselenide at various external magnetic fields. From the evaluation of a large number of tunneling-current profiles taken across the individual vortices we deduced the dependence of the

  12. Spatio-temporal imaging of voltage pulses with an ultrafast scanning tunneling microscope

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Keil, Ulrich Dieter Felix; Hvam, Jørn Märcher

    1997-01-01

    Measurements on an ultrafast scanning tunneling microscope with simultaneous spatial and temporal resolution are presented. We show images of picosecond pulses propagating on a coplanar waveguide and resolve their mode structures. The influence of transmission line discontinuities on the mode...

  13. Scanning tunneling microscopy III theory of STM and related scanning probe methods

    CERN Document Server

    Güntherodt, Hans-Joachim

    1993-01-01

    While the first two volumes on Scanning Tunneling Microscopy (STM) and its related scanning probe (SXM) methods have mainly concentrated on intro­ ducing the experimental techniques, as well as their various applications in different research fields, this third volume is exclusively devoted to the theory of STM and related SXM methods. As the experimental techniques including the reproducibility of the experimental results have advanced, more and more theorists have become attracted to focus on issues related to STM and SXM. The increasing effort in the development of theoretical concepts for STM/SXM has led to considerable improvements in understanding the contrast mechanism as well as the experimental conditions necessary to obtain reliable data. Therefore, this third volume on STM/SXM is not written by theorists for theorists, but rather for every scientist who is not satisfied by just obtaining real­ space images of surface structures by STM/SXM. After a brief introduction (Chap. 1), N. D. Lang first co...

  14. Photothermal modulation of the gap distance in scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Amer, N.M.; Skumanich, A.; Ripple, D.

    1986-01-01

    We have employed the photothermal effect to modulate the gap distance in a tunneling microscope. In this approach, optical heating induces the expansion and buckling of laser-illuminated sample surface. The surface displacement can be modulated over a wide frequency range, and its height (typically <1 A-circle) can be varied by changing the illumination intensity and modulation frequency. This novel method provides an alternative means for performing tunneling spectroscopy and microscopy, and for determining work functions of materials

  15. Scanning tunnelling microscope imaging of nanoscale electron density gradients on the surface of GaAs

    International Nuclear Information System (INIS)

    Hamilton, B; Jacobs, J; Missous, M

    2003-01-01

    This paper is concerned with the scanning tunnelling microscope tunnelling conditions needed to produce constant current images dominated either by surface topology or by electronic effects. A model experimental structure was produced by cleaving a GaAs multiδ-doped layer in UHV and so projecting a spatially varying electron gas density onto the (110) surface. This cross sectional electron density varies on a nanometre scale in the [100] growth direction. The electronic structure and tunnelling properties of this system were modelled, and the tunnelling conditions favouring sensitivity to the surface electron gas density determined

  16. Superconducting phonon spectroscopy using a low-temperature scanning tunneling microscope

    Science.gov (United States)

    Leduc, H. G.; Kaiser, W. J.; Hunt, B. D.; Bell, L. D.; Jaklevic, R. C.

    1989-01-01

    The low-temperature scanning tunneling microscope (STM) system described by LeDuc et al. (1987) was used to observe the phonon density of states effects in a superconductor. Using techniques based on those employed in macroscopic tunneling spectroscopy, electron tunneling current-voltage (I-V) spectra were measured for NbN and Pb, and dI/dV vs V spectra were measured using standard analog derivative techniques. I-V measurements on NbN and Pb samples under typical STM conditions showed no evidence for multiparticle tunneling effects.

  17. Closed-loop conductance scanning tunneling spectroscopy: demonstrating the equivalence to the open-loop alternative.

    Science.gov (United States)

    Hellenthal, Chris; Sotthewes, Kai; Siekman, Martin H; Kooij, E Stefan; Zandvliet, Harold J W

    2015-01-01

    We demonstrate the validity of using closed-loop z(V) conductance scanning tunneling spectroscopy (STS) measurements for the determination of the effective tunneling barrier by comparing them to more conventional open-loop I(z) measurements. Through the development of a numerical model, the individual contributions to the effective tunneling barrier present in these experiments, such as the work function and the presence of an image charge, are determined quantitatively. This opens up the possibility of determining tunneling barriers of both vacuum and molecular systems in an alternative and more detailed manner.

  18. First-principles theory of inelastic currents in a scanning tunneling microscope

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Hu, Ben Yu-Kuang; Thirstrup, C.

    1998-01-01

    A first-principles theory of inelastic tunneling between a model probe tip and an atom adsorbed on a surface is presented, extending the elastic tunneling theory of Tersoff and Hamann. The inelastic current is proportional to the change in the local density of states at the center of the tip due...... to the addition of the adsorbate. We use the theory to investigate the vibrational heating of an adsorbate below a scanning tunneling microscopy tip. We calculate the desorption rate of PI from Si(100)-H(2 X 1) as a function of the sample bias and tunnel current, and find excellent a,agreement with recent...

  19. Surface confined metallosupramolecular architectures: formation and scanning tunneling microscopy characterization.

    Science.gov (United States)

    Li, Shan-Shan; Northrop, Brian H; Yuan, Qun-Hui; Wan, Li-Jun; Stang, Peter J

    2009-02-17

    Metallosupramolecular compounds have attracted a great deal of attention over the past two decades largely because of their unique, highly complex structural characteristics and their potential electronic, magnetic, optical, and catalytic properties. These molecules can be prepared with relative ease using coordination-driven self-assembly techniques. In particular, the use of electron-poor square-planar Pt(II) transition metals in conjunction with rigid, electron-rich pyridyl donors has enabled the spontaneous self-assembly of a rich library of 2D metallacyclic and 3D metallacage assemblies via the directional-bonding approach. With this progress in the preparation and characterization of metallosupramolecules, researchers have now turned their attention toward fully exploring and developing their materials properties. Assembling metallosupramolecular compounds on solid supports represents a vitally important step toward developing their materials properties. Surfaces provide a means of uniformly aligning and orienting these highly symmetric metallacycles and metallacages. This uniformity increases the level of coherence between molecules above that which can be achieved in the solution phase and provides a way to integrate adsorbed layers, or adlayers, into a solid-state materials setting. The dynamic nature of kinetically labile Pt(II)-N coordination bonds requires us to adjust deposition and imaging conditions to retain the assemblies' stability. Toward these aims, we have used scanning tunneling microscopy (STM) to image these adlayers and to understand the factors that govern surface self-assembly and the interactions that influence their structure and stability. This Account describes our efforts to deposit 2D rectangular and square metallacycles and 3D trigonal bipyramidal and chiral trigonal prism metallacages on highly oriented pyrolytic graphite (HOPG) and Au(111) substrates to give intact assemblies and ordered adlayers. We have investigated the effects

  20. Making Mn substitutional impurities in InAs using a scanning tunneling microscope.

    Science.gov (United States)

    Song, Young Jae; Erwin, Steven C; Rutter, Gregory M; First, Phillip N; Zhitenev, Nikolai B; Stroscio, Joseph A

    2009-12-01

    We describe in detail an atom-by-atom exchange manipulation technique using a scanning tunneling microscope probe. As-deposited Mn adatoms (Mn(ad)) are exchanged one-by-one with surface In atoms (In(su)) to create a Mn surface-substitutional (Mn(In)) and an exchanged In adatom (In(ad)) by an electron tunneling induced reaction Mn(ad) + In(su) --> Mn(In) + In(ad) on the InAs(110) surface. In combination with density-functional theory and high resolution scanning tunneling microscopy imaging, we have identified the reaction pathway for the Mn and In atom exchange.

  1. Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Oberbeck, Lars [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); TOTAL Marketing Services, New Energies, La Défense 10, 92069 Paris La Défense Cedex (France); Reusch, Thilo C. G.; Hallam, Toby; Simmons, Michelle Y., E-mail: n.curson@ucl.ac.uk, E-mail: michelle.simmons@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); Schofield, Steven R. [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); London Centre for Nanotechnology, UCL, London WC1H 0AH (United Kingdom); Department of Physics and Astronomy, UCL, London WC1E 6BT (United Kingdom); Curson, Neil J., E-mail: n.curson@ucl.ac.uk, E-mail: michelle.simmons@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales 2052 (Australia); London Centre for Nanotechnology, UCL, London WC1H 0AH (United Kingdom); Department of Electronic and Electrical Engineering, UCL, London WC1E 7JE (United Kingdom)

    2014-06-23

    We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

  2. Imaging of buried phosphorus nanostructures in silicon using scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Oberbeck, Lars; Reusch, Thilo C. G.; Hallam, Toby; Simmons, Michelle Y.; Schofield, Steven R.; Curson, Neil J.

    2014-01-01

    We demonstrate the locating and imaging of single phosphorus atoms and phosphorus dopant nanostructures, buried beneath the Si(001) surface using scanning tunneling microscopy. The buried dopant nanostructures have been fabricated in a bottom-up approach using scanning tunneling microscope lithography on Si(001). We find that current imaging tunneling spectroscopy is suited to locate and image buried nanostructures at room temperature and with residual surface roughness present. From these studies, we can place an upper limit on the lateral diffusion during encapsulation with low-temperature Si molecular beam epitaxy.

  3. Directional scanning tunneling spectroscopy in MgB2

    International Nuclear Information System (INIS)

    Iavarone, M.; Karapetrov, G.; Koshelev, A.E.; Kwok, W.K.; Crabtree, G.W.; Hinks, D.G.; Cook, R.; Kang, W.N.; Choi, E.M.; Kim, H.J.; Lee, S.I.

    2003-01-01

    The superconductivity in MgB 2 has a two-band character with the dominating band having a 2D character and the second band being isotropic in the three dimensions. We use tunneling microscopy and spectroscopy to reveal the two distinct energy gaps at Δ 1 =2.3 meV and Δ 2 =7.1 meV. Different spectral weights of the partial superconducting density of states are a reflection of different tunneling directions in this multi-band system. The results are consistent with the existence of two-band superconductivity in the presence of strong interband superconducting pair interaction and quasiparticle scattering. The temperature evolution of the tunneling spectra shows both gaps vanishing at the bulk T c

  4. POLARIZED BEAMS: 1 - Longitudinal electron spin polarization at HERA

    Energy Technology Data Exchange (ETDEWEB)

    Anon.

    1994-09-15

    Wednesday 4 May marked a turning point in the art of the manipulation of spins in electron storage rings: longitudinal electron spin polarization (with the spins oriented along the electrons' direction of motion) was established in the electron ring of HERA, the electronproton collider at DESY in Hamburg. A polarization level of about 55% was obtained and polarizations of over 60% were reproducibly obtained in the following days. The beam energy was 27.52 GeV, corresponding to half integer spin tune of 62.5.

  5. Generation and detection of spin polarization in parallel coupled double quantum dots connected to four terminals

    International Nuclear Information System (INIS)

    An, Xing-Tao; Mu, Hui-Ying; Li, Yu-Xian; Liu, Jian-Jun

    2011-01-01

    A four-terminal parallel double quantum dots (QDs) device is proposed to generate and detect the spin polarization in QDs. It is found that the spin accumulation in QDs and the spin-polarized currents in the upper and down leads can be generated when a bias voltage is applied between the left and right leads. It is more interesting that the spin polarization in the QDs can be detected using the upper and down leads. Moreover, the direction and magnitude of the spin polarization in the QDs, and in the upper and down leads can be tuned by the energy levels of QDs and the bias. -- Highlights: → The spin polarization in the quantum dots can be generated and controlled. → The spin polarization in quantum dots can be detected by the nonferromagnetic leads. → The system our studied is a discrete level spin Hall system.

  6. Determination of the spin polarization of a 4He+ ion beam

    International Nuclear Information System (INIS)

    Suzuki, T.; Yamauchi, Y.

    2008-01-01

    It was demonstrated that the spin polarization of a 4 He + ion beam (P He + ) can be determined from the spin dependence of the electron emission in the deexcitation process of spin-polarized He metastable atoms (He*, 2 3 S 1 ) and spin-polarized He + ions on Fe (100) surfaces. On Fe (100) surfaces, both He* and He + deexcite via Auger neutralization, and therefore, the spin asymmetry obtained from spin-polarized He + ion neutralization spectroscopy should be equal to that from spin-polarized metastable He* deexcitation spectroscopy. The spin polarization of He* was obtained from Stern-Gerlach measurements. P He + was finally determined to be 0.19±0.02

  7. Electron-Spin Filters Would Offer Spin Polarization Greater than 1

    Science.gov (United States)

    Ting, David Z.

    2009-01-01

    A proposal has been made to develop devices that would generate spin-polarized electron currents characterized by polarization ratios having magnitudes in excess of 1. Heretofore, such devices (denoted, variously, as spin injectors, spin polarizers, and spin filters) have typically offered polarization ratios having magnitudes in the approximate range of 0.01 to 0.1. The proposed devices could be useful as efficient sources of spin-polarized electron currents for research on spintronics and development of practical spintronic devices.

  8. Note: long-range scanning tunneling microscope for the study of nanostructures on insulating substrates.

    Science.gov (United States)

    Molina-Mendoza, Aday J; Rodrigo, José G; Island, Joshua; Burzuri, Enrique; Rubio-Bollinger, Gabino; van der Zant, Herre S J; Agraït, Nicolás

    2014-02-01

    The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

  9. Note: Long-range scanning tunneling microscope for the study of nanostructures on insulating substrates

    Energy Technology Data Exchange (ETDEWEB)

    Molina-Mendoza, Aday J., E-mail: aday.molina@uam.es [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Rodrigo, José G.; Rubio-Bollinger, Gabino [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Island, Joshua; Burzuri, Enrique; Zant, Herre S. J. van der [Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Agraït, Nicolás [Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Condensed Matter Physics Center (IFIMAC) and Instituto Universitario de Ciencia de Materiales “Nicolás Cabrera,” Universidad Autónoma de Madrid, Campus de Cantoblanco, E-28049 Madrid (Spain); Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, E-28049 Madrid (Spain)

    2014-02-15

    The scanning tunneling microscope (STM) is a powerful tool for studying the electronic properties at the atomic level, however, it is of relatively small scanning range and the fact that it can only operate on conducting samples prevents its application to study heterogeneous samples consisting of conducting and insulating regions. Here we present a long-range scanning tunneling microscope capable of detecting conducting micro and nanostructures on insulating substrates using a technique based on the capacitance between the tip and the sample and performing STM studies.

  10. Local X-ray magnetic circular dichroism study of Fe/Cu(111) using a tunneling smart tip

    Energy Technology Data Exchange (ETDEWEB)

    DiLullo, Andrew; Shirato, Nozomi; Cummings, Marvin [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Kersell, Heath; Chang, Hao [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rosenmann, Daniel; Miller, Dean; Freeland, John W. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Hla, Saw-Wai [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Ohio University, Athens, OH 45701 (United States); Rose, Volker, E-mail: vrose@anl.gov [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States)

    2016-01-28

    A tunneling smart tip of a synchrotron X-ray scanning tunneling microscope provides simultaneously localized topographic, elemental and magnetic information. Localized spectroscopy with simultaneous topographic, elemental and magnetic information is presented. A synchrotron X-ray scanning tunneling microscope has been employed for the local study of the X-ray magnetic circular dichroism at the Fe L{sub 2,3}-edges of a thin iron film grown on Cu(111). Polarization-dependent X-ray absorption spectra have been obtained through a tunneling smart tip that serves as a photoelectron detector. In contrast to conventional spin-polarized scanning tunneling microscopy, X-ray excitations provide magnetic contrast even with a non-magnetic tip. Intensity variations in the photoexcited tip current point to chemical variations within a single magnetic Fe domain.

  11. RKKY interaction in spin polarized armchair graphene nanoribbon

    Energy Technology Data Exchange (ETDEWEB)

    Rezania, Hamed, E-mail: rezania.hamed@gmail.com; Azizi, Farshad

    2016-11-01

    We present the Ruderman–Kittle–Kasuya–Yosida (RKKY) interaction in the presence of magnetic long range ordered armchair graphene nanoribbon. RKKY interaction as a function of distance between localized moments has been analyzed. It has been shown that a magnetic ordering along the z-axis mediates an anisotropic interaction which corresponds to a XXZ model interaction between two magnetic moments. In order to calculate the exchange interaction along arbitrary direction between two magnetic moments, we should obtain the static spin susceptibilities of armchair graphene nanoribbon. The spin susceptibility components are calculated using Green's function approach for tight binding model Hamiltonian. The effects of spin polarization on the dependence of exchange interaction on distance between moments are investigated via calculating correlation function of spin density operators. Our results show that the chemical potential impacts the spatial behavior of RKKY interaction. - Highlights: • Theoretical calculation of RKKY interaction of armchair graphene nanoribbon. • The investigation of the effect of spin polarization on RKKY interaction. • The investigation of electronic concentration on RKKY interaction of armchair graphene nanoribbon.

  12. Langmuir instability in partially spin polarized bounded degenerate plasma

    Science.gov (United States)

    Iqbal, Z.; Jamil, M.; Murtaza, G.

    2018-04-01

    Some new features of waves inside the cylindrical waveguide on employing the separated spin evolution quantum hydrodynamic model are evoked. Primarily, the instability of Langmuir wave due to the electron beam in a partially spin polarized degenerate plasma considering a nano-cylindrical geometry is discussed. Besides, the evolution of a new spin-dependent wave (spin electron acoustic wave) due to electron spin polarization effects in the real wave spectrum is elaborated. Analyzing the growth rate, it is found that in the absence of Bohm potential, the electron spin effects or exchange interaction reduce the growth rate as well as k-domain but the inclusion of Bohm potential increases both the growth rate and k-domain. Further, we investigate the geometry effects expressed by R and pon and find that they have opposite effects on the growth rate and k-domain of the instability. Additionally, how the other parameters like electron beam density or streaming speed of beam electrons influence the growth rate is also investigated. This study may find its applications for the signal analysis in solid state devices at nanoscales.

  13. A modular scanning tunneling microscope with an interchangeable elastic closed cell and external actuators

    International Nuclear Information System (INIS)

    Bjarnason, Elias H.; Arnalds, Unnar B.; Olafsson, Sveinn

    2006-01-01

    We introduce a novel modular cell based scanning tunneling microscope with external piezoelectric actuators. A tip and a sample are contained in a closed interchangeable cell, consisting of a stiff top plate and a bottom part, fastened together by an elastic material. The bottom part, containing a scanning tip, is fastened to a base unit while the top plate, containing a sample, is capable of scanning motion by external piezoelectric actuators mounted in the same base unit. The actuators are pre-loaded by the deformation of the elastic material of the cell, giving an increased stability. This design is expected to simplify the scanning tunneling microscope (STM) operation in difficult environments greatly by enclosing only the tip and sample in a small cell-module, which is pluggable to a scanning mechanism and other supportive functionalities. A frequency characterization and an image scan showing atomic resolution of highly oriented graphite in air, at room temperature, is presented

  14. Local imaging of high mobility two-dimensional electron systems with virtual scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Pelliccione, M. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106 (United States); Bartel, J.; Goldhaber-Gordon, D. [Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305 (United States); Sciambi, A. [Department of Applied Physics, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305 (United States); Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025 (United States); Pfeiffer, L. N.; West, K. W. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)

    2014-11-03

    Correlated electron states in high mobility two-dimensional electron systems (2DESs), including charge density waves and microemulsion phases intermediate between a Fermi liquid and Wigner crystal, are predicted to exhibit complex local charge order. Existing experimental studies, however, have mainly probed these systems at micron to millimeter scales rather than directly mapping spatial organization. Scanning probes should be well-suited to study the spatial structure of these states, but high mobility 2DESs are found at buried semiconductor interfaces, beyond the reach of conventional scanning tunneling microscopy. Scanning techniques based on electrostatic coupling to the 2DES deliver important insights, but generally with resolution limited by the depth of the 2DES. In this letter, we present our progress in developing a technique called “virtual scanning tunneling microscopy” that allows local tunneling into a high mobility 2DES. Using a specially designed bilayer GaAs/AlGaAs heterostructure where the tunnel coupling between two separate 2DESs is tunable via electrostatic gating, combined with a scanning gate, we show that the local tunneling can be controlled with sub-250 nm resolution.

  15. Selective scanning tunneling microscope light emission from rutile phase of VO2.

    Science.gov (United States)

    Sakai, Joe; Kuwahara, Masashi; Hotsuki, Masaki; Katano, Satoshi; Uehara, Yoichi

    2016-09-28

    We observed scanning tunneling microscope light emission (STM-LE) induced by a tunneling current at the gap between an Ag tip and a VO2 thin film, in parallel to scanning tunneling spectroscopy (STS) profiles. The 34 nm thick VO2 film grown on a rutile TiO2 (0 0 1) substrate consisted of both rutile (R)- and monoclinic (M)-structure phases of a few 10 nm-sized domains at room temperature. We found that STM-LE with a certain photon energy of 2.0 eV occurs selectively from R-phase domains of VO2, while no STM-LE was observed from M-phase. The mechanism of STM-LE from R-phase VO2 was determined to be an interband transition process rather than inverse photoemission or inelastic tunneling processes.

  16. Magnetic-field-controlled negative differential conductance in scanning tunneling spectroscopy of graphene npn junction resonators

    Science.gov (United States)

    Li, Si-Yu; Liu, Haiwen; Qiao, Jia-Bin; Jiang, Hua; He, Lin

    2018-03-01

    Negative differential conductance (NDC), characterized by the decreasing current with increasing voltage, has attracted continuous attention for its various novel applications. The NDC typically exists in a certain range of bias voltages for a selected system and controlling the regions of NDC in curves of current versus voltage (I -V ) is experimentally challenging. Here, we demonstrate a magnetic-field-controlled NDC in scanning tunneling spectroscopy of graphene npn junction resonators. The magnetic field not only can switch on and off the NDC, but also can continuously tune the regions of the NDC in the I -V curves. In the graphene npn junction resonators, magnetic fields generate sharp and pronounced Landau-level peaks with the help of the Klein tunneling of massless Dirac fermions. A tip of scanning tunneling microscope induces a relatively shift of the Landau levels in graphene beneath the tip. Tunneling between the misaligned Landau levels results in the magnetic-field-controlled NDC.

  17. Three-dimensional scanning force/tunneling spectroscopy at room temperature

    International Nuclear Information System (INIS)

    Sugimoto, Yoshiaki; Ueda, Keiichi; Abe, Masayuki; Morita, Seizo

    2012-01-01

    We simultaneously measured the force and tunneling current in three-dimensional (3D) space on the Si(111)-(7 × 7) surface using scanning force/tunneling microscopy at room temperature. The observables, the frequency shift and the time-averaged tunneling current were converted to the physical quantities of interest, i.e. the interaction force and the instantaneous tunneling current. Using the same tip, the local density of states (LDOS) was mapped on the same surface area at constant height by measuring the time-averaged tunneling current as a function of the bias voltage at every lateral position. LDOS images at negative sample voltages indicate that the tip apex is covered with Si atoms, which is consistent with the Si-Si covalent bonding mechanism for AFM imaging. A measurement technique for 3D force/current mapping and LDOS imaging on the equivalent surface area using the same tip was thus demonstrated. (paper)

  18. Tunneling spectroscopy study of YBa2Cu3O7 thin films using a cryogenic scanning tunneling microscope

    International Nuclear Information System (INIS)

    Wilkins, R.; Amman, M.; Soltis, R.E.; Ben-Jacob, E.; Jaklevic, R.C.

    1990-01-01

    We have measured reproducible tunneling spectra on YBa 2 Cu 3 O 7 (T c ∼85 K) thin films (thickness ∼2 μm) with a cryogenic scanning tunneling microscope. We find that the I-V curves are generally of three types. The most common type, featured in a large majority of the data, shows a region of high conductance at zero bias. The amplitude of this region is inversely proportional to the tunneling resistance between the tip and sample. It is possible that this can be explained in terms of Josephson effects within the films, although an alternative is given based on electronic self-energy corrections. Data showing capacitive charging steps are analyzed in terms of two ultrasmall tunnel junctions in series.. Theoretical fits to the data give specific values of the junction parameters that are consistent with the assumed geometry of the tip probing an individual grain of the film. The third type of I-V curves exhibits negative differential resistance. We conclude that this phenomenon is probably due to tunneling to localized states in the surface oxide. We also present and discuss data with energy-gap-like behavior; the best example gives Δ to be about 27 mV

  19. Development and trial measurement of synchrotron-radiation-light-illuminated scanning tunneling microscope

    International Nuclear Information System (INIS)

    Matsushima, Takeshi; Okuda, Taichi; Eguchi, Toyoaki; Ono, Masanori; Harasawa, Ayumi; Wakita, Takanori; Kataoka, Akira; Hamada, Masayuki; Kamoshida, Atsushi; Hasegawa, Yukio; Kinoshita, Toyohiko

    2004-01-01

    Scanning tunneling microscope (STM) study is performed under synchrotron-radiation-light illumination. The equipment is designed so as to achieve atomic resolution even under rather noisy conditions in the synchrotron radiation facility. By measuring photoexcited electron current by the STM tip together with the conventional STM tunneling current, Si 2p soft-x-ray absorption spectra are successfully obtained from a small area of Si(111) surface. The results are a first step toward realizing a new element-specific microscope

  20. Spin-dependent current in resonant tunneling diode with ferromagnetic GaMnN layers

    International Nuclear Information System (INIS)

    Tang, N.Y.

    2009-01-01

    The spin-polarized tunneling current through a double barrier resonant tunneling diode (RTD) with ferromagnetic GaMnN emitter/collector is investigated theoretically. Two distinct spin splitting peaks can be observed at current-voltage (I-V) characteristics at low temperature. The spin polarization decreases with the temperature due to the thermal effect of electron density of states. When charge polarization effect is considered at the heterostructure, the spin polarization is enhanced significantly. A highly spin-polarized current can be obtained depending on the polarization charge density.

  1. Effects of the finite duration of quantum tunneling in laser-assisted scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Hagmann, M.J.

    1994-01-01

    Previous measurements of tunnel conductance in heterostructures and experiments with Josephson junctions suggest quantum tunneling has a definite duration. The authors use semiclassical methods to determine the effects of this delay on the tunneling current in a laser-assisted STM. A planar-planar STM model is used with the exact multiple image potential, and the energy distribution for a free-electron metal. It is necessary to average over the phase at barrier entry, and iteration with back propagated solutions is required to obtain the transmission coefficients for evenly spaced phases and specified energies at barrier entry. The simulations suggest that the dependence of the tunneling current on the wavelength of illumination can serve as a basis for determining the duration of barrier traversal. A power flux density of 10 11 W/m 2 would be required at several wavelengths from 1 to 10 μm. It is possible that thermal effects could be separated from the modeled phenomena by determining the time dependence of the tunneling current with a pulsed laser

  2. Imaging by Electrochemical Scanning Tunneling Microscopy and Deconvolution Resolving More Details of Surfaces Nanomorphology

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov

    observed in high-resolution images of metallic nanocrystallites may be effectively deconvoluted, as to resolve more details of the crystalline morphology (see figure). Images of surface-crystalline metals indicate that more than a single atomic layer is involved in mediating the tunneling current......Upon imaging, electrochemical scanning tunneling microscopy (ESTM), scanning electrochemical micro-scopy (SECM) and in situ STM resolve information on electronic structures and on surface topography. At very high resolution, imaging processing is required, as to obtain information that relates...... to crystallographic-surface structures. Within the wide range of new technologies, those images surface features, the electrochemical scanning tunneling microscope (ESTM) provides means of atomic resolution where the tip participates actively in the process of imaging. Two metallic surfaces influence ions trapped...

  3. Probing Nanoscale Electronic and Magnetic Interaction with Scanning Tunneling Spectroscopy

    DEFF Research Database (Denmark)

    Bork, Jakob

    tunneling microscope (STM). Especially at low temperatures the Kondo resonance is used to probe magnetic interaction with ferromagnetic islands and between two atoms. The latter showing a crossover between Kondo screened atoms and antiferromagnetically coupled atoms close to the quantum critical point....... This is related to research in correlated electron materials such as studies of phase transitions in heavy fermion compounds and magnetic interaction in spintronic research. The capping of cobalt islands on Cu(111) with silver is investigated with STM and photoemission spectroscopy. It is shown that at low...

  4. Infrared spectroscopy of molecular submonolayers on surfaces by infrared scanning tunneling microscopy: tetramantane on Au111.

    Science.gov (United States)

    Pechenezhskiy, Ivan V; Hong, Xiaoping; Nguyen, Giang D; Dahl, Jeremy E P; Carlson, Robert M K; Wang, Feng; Crommie, Michael F

    2013-09-20

    We have developed a new scanning-tunneling-microscopy-based spectroscopy technique to characterize infrared (IR) absorption of submonolayers of molecules on conducting crystals. The technique employs a scanning tunneling microscope as a precise detector to measure the expansion of a molecule-decorated crystal that is irradiated by IR light from a tunable laser source. Using this technique, we obtain the IR absorption spectra of [121]tetramantane and [123]tetramantane on Au(111). Significant differences between the IR spectra for these two isomers show the power of this new technique to differentiate chemical structures even when single-molecule-resolved scanning tunneling microscopy (STM) images look quite similar. Furthermore, the new technique was found to yield significantly better spectral resolution than STM-based inelastic electron tunneling spectroscopy, and to allow determination of optical absorption cross sections. Compared to IR spectroscopy of bulk tetramantane powders, infrared scanning tunneling microscopy (IRSTM) spectra reveal narrower and blueshifted vibrational peaks for an ordered tetramantane adlayer. Differences between bulk and surface tetramantane vibrational spectra are explained via molecule-molecule interactions.

  5. Combined Scanning Nanoindentation and Tunneling Microscope Technique by Means of Semiconductive Diamond Berkovich Tip

    International Nuclear Information System (INIS)

    Lysenko, O; Novikov, N; Gontar, A; Grushko, V; Shcherbakov, A

    2007-01-01

    A combined Scanning Probe Microscope (SPM) - nanoindentation instrument enables submicron resolution indentation tests and in-situ scanning of structure surfaces. A newly developed technique is based on the scanning tunneling microscopy (STM) with integrated Berkovich diamond semiconductive tip. Diamond tips for a combined SPM were obtained using the developed procedure including the synthesis of the semiconductive borondoped diamond monocrystals by the temperature gradient method at high pressure - high temperature conditions and fabrication of the tips from these crystals considering their zonal structure. Separately grown semiconductive diamond single crystals were studied in order to find the best orientation of diamond crystals. Optimal scanning characteristics and experimental data errors were calculated by an analysis of the general functional dependence of the tunneling current from properties of the tip and specimen. Tests on the indentation and scanning of the gold film deposited on the silicon substrate employing the fabricated tips demonstrated their usability, acceptable resolution and sensitivity

  6. Scanning tunneling spectroscopy of CdSe nanocrystals covalently bound to GaAs

    DEFF Research Database (Denmark)

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

    2003-01-01

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

  7. Thin films of metal oxides on metal single crystals: Structure and growth by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Galloway, H.C.

    1995-12-01

    Detailed studies of the growth and structure of thin films of metal oxides grown on metal single crystal surfaces using Scanning Tunneling Microscopy (STM) are presented. The oxide overlayer systems studied are iron oxide and titanium oxide on the Pt(III) surface. The complexity of the metal oxides and large lattice mismatches often lead to surface structures with large unit cells. These are particularly suited to a local real space technique such as scanning tunneling microscopy. In particular, the symmetry that is directly observed with the STM elucidates the relationship of the oxide overlayers to the substrate as well as distinguishing, the structures of different oxides

  8. Scanning tunneling microscopy I general principles and applications to clean and adsorbate-covered surfaces

    CERN Document Server

    Wiesendanger, Roland

    1992-01-01

    Scanning Tunneling Microscopy I provides a unique introduction to a novel and fascinating technique that produces beautiful images of nature on an atomic scale. It is the first of three volumes that together offer a comprehensive treatment of scanning tunneling microscopy, its diverse applications, and its theoretical treatment. In this volume the reader will find a detailed description of the technique itself and of its applications to metals, semiconductors, layered materials, adsorbed molecules and superconductors. In addition to the many representative results reviewed, extensive references to original work will help to make accessible the vast body of knowledge already accumulated in this field.

  9. Interplay between spin polarization and color superconductivity in high density quark matter

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; da Providência, João; Providência, Constança

    2013-01-01

    Here, it is suggested that a four-point interaction of the tensor type may lead to spin polarization in quark matter at high density. It is found that the two-flavor superconducting phase and the spin polarized phase correspond to distinct local minima of a certain generalized thermodynamical pot...

  10. Laser driven source of spin polarized atomic deuterium and hydrogen

    International Nuclear Information System (INIS)

    Poelker, M.; Coulter, K.P.; Holt, R.J.

    1993-01-01

    Optical pumping of potassium atoms in the presence of a high magnetic field followed by spin exchange collisions with deuterium (hydrogen) is shown to yield a high flux of spin polarized atomic deuterium (hydrogen). The performance of the laser driven source has been characterized as a function of deuterium (hydrogen) flow rate, potassium density, pump laser power, and magnetic field. Under appropriate conditions, the authors have observed deuterium atomic polarization as high as 75% at a flow rate 4.2x10 17 atoms/second. Preliminary results suggest that high nuclear polarizations are obtained in the absence of weak field rf transitions as a result of a spin temperature distribution that evolves through frequent H-H (D-D) collisions

  11. Anomalous scattering of neutrons in spin-polarized media

    International Nuclear Information System (INIS)

    Bashkin, E.P.

    1989-01-01

    A new exchange mechanism of inelastic scattering with spin flip for slow neutrons propagating through a spin-polarized medium is studied. The scattering is accompanied by emission or absorption of thermal fluctuations of the transverse magnetization of the medium; the weakly damped Larmor precession of nuclear spins in the external magnetic field plays the main role in these fluctuations. Under the conditions of giant opalescence the effect is enormous and the corresponding cross sections are significantly greater than the standard elastic scattering cross sections. Thus in the case of 29 Si↑ and 3 He↑ under typical experimental conditions the cross sections of these inelastic processes are of the order of 10 5 -10 6 b

  12. Optically pumped electron spin polarized targets for use in the production of polarized ion beams

    International Nuclear Information System (INIS)

    Anderson, L.W.

    1979-01-01

    The production of relatively dense electron spin polarized alkali metal vapor targets by optical pumping with intense cw dye lasers is discussed. The target density and electron spin polarization depend on the dye laser intensity and bandwidth, the magnetic field at the target, and the electron spin depolarization time. For example in a magnetic field of 1.5 x 10 3 G, and using 1 W dye laser with a bandwidth of 10 10 Hz one can construct an electron spin polarized Na vapor target with a target thickness of 1.6 x 10 13 atoms/cm 2 and an average electron spin polarization of about 90% even though the Na atoms are completely depolarized at every wall collision. Possible uses of the electron spin polarized targets for the production of intense beams of polarized H - or 3 He - ions are discussed. (orig.)

  13. Electron ionization and spin polarization control of Fe atom adsorbed graphene irradiated by a femtosecond laser

    International Nuclear Information System (INIS)

    Yu, Dong; Jiang, Lan; Wang, Feng; Li, Xin; Qu, Liangti; Lu, Yongfeng

    2015-01-01

    We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons

  14. Three-Dimensional Laser Scanning for Geometry Documentation and Construction Management of Highway Tunnels during Excavation

    Science.gov (United States)

    Gikas, Vassilis

    2012-01-01

    Driven by progress in sensor technology, computer software and data processing capabilities, terrestrial laser scanning has recently proved a revolutionary technique for high accuracy, 3D mapping and documentation of physical scenarios and man-made structures. Particularly, this is of great importance in the underground space and tunnel construction environment as surveying engineering operations have a great impact on both technical and economic aspects of a project. This paper discusses the use and explores the potential of laser scanning technology to accurately track excavation and construction activities of highway tunnels. It provides a detailed overview of the static laser scanning method, its principles of operation and applications for tunnel construction operations. Also, it discusses the planning, execution, data processing and analysis phases of laser scanning activities, with emphasis given on geo-referencing, mesh model generation and cross-section extraction. Specific case studies are considered based on two construction sites in Greece. Particularly, the potential of the method is examined for checking the tunnel profile, producing volume computations and validating the smoothness/thickness of shotcrete layers at an excavation stage and during the completion of excavation support and primary lining. An additional example of the use of the method in the geometric documentation of the concrete lining formwork is examined and comparisons against dimensional tolerances are examined. Experimental comparisons and analyses of the laser scanning method against conventional surveying techniques are also considered. PMID:23112655

  15. Construction of a four tip scanning tunneling microscope/scanning electron microscope combination and conductivity measurements of silicide nanowires

    International Nuclear Information System (INIS)

    Zubkov, Evgeniy

    2013-01-01

    In this work the combination of a four-tip scanning tunneling microscope with a scanning electron microscope is presented. By means of this apparatus it is possible to perform the conductivity measurements on the in-situ prepared nanostructures in ultra-high vacuum. With the aid of a scanning electron microscope (SEM), it becomes possible to position the tunneling tips of the four-tip scanning tunneling microscope (STM), so that an arrangement for a four-point probe measurement on nanostructures can be obtained. The STM head was built according to the novel coaxial Beetle concept. This concept allows on the one hand, a very compact arrangement of the components of the STM and on the other hand, the new-built STM head has a good mechanical stability, in order to achieve atomic resolution with all four STM units. The atomic resolution of the STM units was confirmed by scanning a Si(111)-7 x 7 surface. The thermal drift during the STM operation, as well as the resonant frequencies of the mechanical structure of the STM head, were determined. The scanning electron microscope allows the precise and safe navigation of the tunneling tips on the sample surface. Multi tip spectroscopy with up to four STM units can be performed synchronously. To demonstrate the capabilities of the new-built apparatus the conductivity measurements were carried out on metallic yttrium silicide nanowires. The nanowires were prepared by the in-situ deposition of yttrium on a heated Si(110) sample surface. Current-voltage curves were recorded on the nanowires and on the wetting layer in-between. The curves indicate an existence of the Schottky barrier between the yttrium silicide nanowires and the silicon bulk. By means of the two-tip measurements with a gate, the insulating property of the Schottky barrier has been confirmed. Using this Schottky barrier, it is possible to limit the current to the nanowire and to prevent it from flowing through the silicon bulk. A four-tip resistance measurement

  16. Fabrication of tungsten tip for scanning tunneling microscope by the lever principle

    International Nuclear Information System (INIS)

    Wang Yang; Wang Huabin; Chinese Academy of Sciences, Beijing; Gong Jinlong; Zhu Dezhang

    2007-01-01

    A novel experimental setup was designed to fabricate tungsten tips for scanning tunneling microscope (STM), based on simple mechanical lever principle. The equipment can quickly separate the tip from electrolyte to avoid the further etching of the fine-shaped tungsten tip. The setup is advantageous for its simplicity over complex electronic control systems. The use result in scanning electron microscope demonstrates that the radius of the tip can reach 50 nm. The tip was applied to scan the surface of highly-oriented pyrolytic graphite, and the results were satisfactory. It is shown that the tip can be used for the scanning of atomically resolved images. (authors)

  17. Photon emission spectroscopy of NiAl(110) in the scanning tunneling microscope

    International Nuclear Information System (INIS)

    Nilius, N.; Ernst, N.; Freund, H.-J.; Johansson, P.

    2000-01-01

    Spectroscopic measurements have been carried out of the light emitted from the NiAl(110)/W tunnel junction of a scanning tunneling microscope. The data reveal two prominent emission lines in the visible and near-infrared region. Corresponding model calculations assign the observed light emission to the radiating decay of the tip-induced plasmon excited in the tip-sample cavity. In agreement with the theory, a low- and a high-energy mode of the plasmon can be distinguished in the experimental data. Since the excitation probability of the two modes is determined by the size of the tunnel cavity, it can be influenced by the radius of the tunnel tip. A blunted tip favors the observation conditions of the higher mode

  18. Transient measurements with an ultrafast scanning tunneling microscope on semiconductor surfaces

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1998-01-01

    We demonstrate: the use of an ultrafast scanning tunneling microscope on a semiconductor surface. Laser-induced transient signals with 1.8 ps rise time are detected, The investigated sample is a low-temperature grown GaAs layer plated on a sapphire substrate with a thin gold layer that serves as st...... bias contact, For comparison, the measurements are performed with the tip in contact to the sample as well as in tunneling above the surface, In contact and under bias, the transient signals are identified as a transient photocurrent, An additional signal is generated by a transient voltage induced...... by the nonuniform carrier density created by the absorption of the light (photo Dember effect). The transient depends in sign and in shape on the direction of optical excitation. This signal is the dominating transient in tunneling mode. The signals are explained by a capacitive coupling across the tunneling gap...

  19. Simultaneously measured signals in scanning probe microscopy with a needle sensor: frequency shift and tunneling current.

    Science.gov (United States)

    Morawski, Ireneusz; Voigtländer, Bert

    2010-03-01

    We present combined noncontact scanning force microscopy and tunneling current images of a platinum(111) surface obtained by means of a 1 MHz quartz needle sensor. The low-frequency circuit of the tunneling current was combined with a high-frequency signal of the quartz resonator enabling full electrical operation of the sensor. The frequency shift and the tunneling current were detected simultaneously, while the feedback control loop of the topography signal was fed using one of them. In both cases, the free signal that was not connected to the feedback loop reveals proportional-integral controller errorlike behavior, which is governed by the time derivative of the topography signal. A procedure is proposed for determining the mechanical oscillation amplitude by utilizing the tunneling current also including the average tip-sample work function.

  20. Local crystallography analysis for atomically resolved scanning tunneling microscopy images

    International Nuclear Information System (INIS)

    Lin, Wenzhi; Li, Qing; Belianinov, Alexei; Gai, Zheng; Baddorf, Arthur P; Pan, Minghu; Jesse, Stephen; Kalinin, Sergei V; Sales, Brian C; Sefat, Athena

    2013-01-01

    Scanning probe microscopy has emerged as a powerful and flexible tool for atomically resolved imaging of surface structures. However, due to the amount of information extracted, in many cases the interpretation of such data is limited to being qualitative and semi-quantitative in nature. At the same time, much can be learned from local atom parameters, such as distances and angles, that can be analyzed and interpreted as variations of local chemical bonding, or order parameter fields. Here, we demonstrate an iterative algorithm for indexing and determining atomic positions that allows the analysis of inhomogeneous surfaces. This approach is further illustrated by local crystallographic analysis of several real surfaces, including highly ordered pyrolytic graphite and an Fe-based superconductor FeTe 0.55 Se 0.45 . This study provides a new pathway to extract and quantify local properties for scanning probe microscopy images. (paper)

  1. Scanning tunneling spectroscopy on neutron irradiated MgB2 thin films

    International Nuclear Information System (INIS)

    Di Capua, Roberto; Salluzzo, Marco; Vaglio, Ruggero; Ferdeghini, Carlo; Ferrando, Valeria; Putti, Marina; Xi Xiaoxing; Aebersold, Hans U.

    2007-01-01

    Neutron irradiation was performed on MgB 2 thin films grown by hybrid physical chemical vapor deposition. Samples irradiated with different neutron fluences, having different critical temperatures, were studied by scanning tunneling spectroscopy in order to investigate the effect of the introduced disorder on the superconducting and spectroscopic properties. A monotonic increase of the π gap with increasing disorder was found

  2. Scanning tunneling spectroscopy on neutron irradiated MgB{sub 2} thin films

    Energy Technology Data Exchange (ETDEWEB)

    Di Capua, Roberto [University of Napoli and CNR-INFM/Coherentia, Via Cinthia, Naples I-80126 (Italy)], E-mail: rdicapua@na.infn.it; Salluzzo, Marco; Vaglio, Ruggero [University of Napoli and CNR-INFM/Coherentia, Via Cinthia, Naples I-80126 (Italy); Ferdeghini, Carlo [CNR-INFM/LAMIA, Via Dodecaneso 33, Genova I-16146 (Italy); Ferrando, Valeria [CNR-INFM/LAMIA, Via Dodecaneso 33, Genova I-16146 (Italy); Pennsylvania State University, University Park, PA 16802 (United States); Putti, Marina [CNR-INFM/LAMIA, Via Dodecaneso 33, Genova I-16146 (Italy); Xi Xiaoxing [Pennsylvania State University, University Park, PA 16802 (United States); Aebersold, Hans U. [Paul Scherrer Institut, Villigen CH-5232 (Switzerland)

    2007-09-01

    Neutron irradiation was performed on MgB{sub 2} thin films grown by hybrid physical chemical vapor deposition. Samples irradiated with different neutron fluences, having different critical temperatures, were studied by scanning tunneling spectroscopy in order to investigate the effect of the introduced disorder on the superconducting and spectroscopic properties. A monotonic increase of the {pi} gap with increasing disorder was found.

  3. Polarization contrast in photon scanning tunnelling microscopy combined with atomic force microscopy

    NARCIS (Netherlands)

    Propstra, K.; Propstra, K.; van Hulst, N.F.

    1995-01-01

    Photon scanning tunnelling microscopy combined with atomic force microscopy allows simultaneous acquisition and direct comparison of optical and topographical images, both with a lateral resolution of about 30 nm, far beyond the optical diffraction limit. The probe consists of a modified

  4. Optical detection of ballistic electrons injected by a scanning-tunneling microscope

    NARCIS (Netherlands)

    Kemerink, M.; Sauthoff, K.; Koenraad, P.M.; Gerritsen, J.W.; Kempen, van H.; Wolter, J.H.

    2001-01-01

    We demonstrate a spectroscopic technique which is based on ballistic injection of minority carriers from the tip of a scanning-tunneling microscope into a semiconductor heterostructure. By analyzing the resulting electroluminescence spectrum as a function of tip-sample bias, both the injection

  5. In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared...

  6. Submolecular Electronic Mapping of Single Cysteine Molecules by in Situ Scanning Tunneling Imaging

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Chi, Qijin; Nazmutdinov, R. R.

    2009-01-01

    We have used L-Cysteine (Cys) as a model system to study the surface electronic structures of single molecules at the submolecular level in aqueous buffer solution by a combination of electrochemical scanning tunneling microscopy (in situ STM), electrochemistry including voltammetry and chronocou...

  7. Adsorption of Cu phthalocyanine on Pt modified Ge(001): A scanning tunneling microscopy study

    NARCIS (Netherlands)

    Saedi, A.; Berkelaar, Robin P.; Kumar, Avijit; Poelsema, Bene; Zandvliet, Henricus J.W.

    2010-01-01

    The adsorption configurations of copper phthalocyanine (CuPc) molecules on platinum-modified Ge(001) have been studied using scanning tunneling microscopy. After deposition at room temperature and cooling down to 77 K the CuPc molecules are still dynamic. However, after annealing at 550±50 K, the

  8. Ionic channels in Langmuir-Blodgett films imaged by a scanning tunneling microscope.

    Science.gov (United States)

    Kolomytkin, O V; Golubok, A O; Davydov, D N; Timofeev, V A; Vinogradova, S A; Tipisev SYa

    1991-01-01

    The molecular structure of channels formed by gramicidin A in a lipid membrane was imaged by a scanning tunneling microscope operating in air. The mono- and bimolecular films of lipid with gramicidin A were deposited onto a highly oriented pyrolitic graphite substrate by the Langmuir-Blodgett technique. It has been shown that under high concentration gramicidin A molecules can form in lipid films a quasi-regular, densely packed structure. Single gramicidin A molecules were imaged for the first time as well. The cavity of 0.4 +/- 0.05 nm in halfwidth was found on the scanning tunneling microscopy image of the gramicidin A molecule. The results of direct observation obtained by means of scanning tunneling microscope are in good agreement with the known molecular model of gramicidin A. It was shown that gramicidin A molecules can exist in a lipid monolayer as individual molecules or combined into clusters. The results demonstrate that scanning tunneling microscope can be used for high spatial resolution study of ionic channel structure. Images FIGURE 1 FIGURE 2 FIGURE 4 FIGURE 5 PMID:1712239

  9. Observation of a Ag protrusion on a Ag2S island using a scanning tunneling microscope

    Directory of Open Access Journals (Sweden)

    Takeo Ohno

    2015-01-01

    Full Text Available A silver sulfide (Ag2S island as an ionic conductor in resistive switching memories was formed and a protrusion of silver from the Ag2S formed by an electrochemical reaction was observed using a scanning tunneling microscope.

  10. New design of a variable-temperature ultrahigh vacuum scanning tunneling microscope

    NARCIS (Netherlands)

    Mugele, Friedrich Gunther; Rettenberger, A.; Boneberg, J.; Leiderer, P.

    1998-01-01

    We present the design of a variable-temperature ultrahigh vacuum (UHV) scanning tunneling microscope which can be operated between 20 and 400 K. The microscope is mounted directly onto the heat exchanger of a He continuous flow cryostat without vibration isolation inside the UHV chamber. The coarse

  11. Imaging of surface plasmon polariton interference using phase-sensitive scanning tunneling microscope

    NARCIS (Netherlands)

    Jose, J.; Segerink, Franciscus B.; Korterik, Jeroen P.; Herek, Jennifer Lynn; Offerhaus, Herman L.

    2011-01-01

    We report the surface plasmon polariton interference, generated via a ‘buried’ gold grating, and imaged using a phase-sensitive Photon Scanning Tunneling Microscope (PSTM). The phase-resolved PSTM measurement unravels the complex surface plasmon polariton interference fields at the gold-air

  12. Field-based scanning tunneling microscope manipulation of antimony dimers on Si(001)

    NARCIS (Netherlands)

    Rogge, S.; Timmerman, R.H.; Scholte, P.M.L.O.; Geerligs, L.J.; Salemink, H.W.M.

    2001-01-01

    The manipulation of antimony dimers, Sb2, on the silicon (001) surface by means of a scanning tunneling microscope (STM) has been experimentally investigated. Directed hopping of the Sb2 dimers due the STM tip can dominate over the thermal motion at temperatures between 300 and 500 K. Statistics on

  13. Visible Light Emission from Atomic Scale Patterns Fabricated by the Scanning Tunneling Microscope

    DEFF Research Database (Denmark)

    Thirstrup, C.; Sakurai, M.; Stokbro, Kurt

    1999-01-01

    Scanning tunneling microscope (STM) induced light emission from artificial atomic scale structures comprising silicon dangling bonds on hydrogen-terminated Si(001) surfaces has been mapped spatially and analyzed spectroscopically in the visible spectral range. The light emission is based on a novel...

  14. Probing Field Distributions on Waveguide Structures with an Atomic Force/Photon Scanning Tunneling Microscope

    NARCIS (Netherlands)

    Borgonjen, E.G.; Borgonjen, E.G.; Moers, M.H.P.; Moers, M.H.P.; Ruiter, A.G.T.; van Hulst, N.F.

    1995-01-01

    A 'stand-alone' Photon Scanning Tunneling Microscope combined with an Atomic force Microscope, using a micro-fabricated silicon-nitride probe, is applied to the imaging of field distribution in integrated optical ridge waveguides. The electric field on the waveguide is locally probed by coupling to

  15. Scanning tunneling microscopy in TTF-TCNQ: Phase and amplitude modulated charge density waves

    DEFF Research Database (Denmark)

    Wang, Z.Z.; Gorard, J.C.; Pasquier, C.

    2003-01-01

    Charge density waves (CDWs) have been studied at the surface of a cleaved tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) single crystal using a low temperature scanning tunneling microscope (STM) under ultrahigh-vacuum conditions, between 300 and 33 K with molecular resolution. All CDW...

  16. Tip-Dependent Scanning Tunneling Microscopy Imaging of Ultrathin FeO Films on Pt(111)

    DEFF Research Database (Denmark)

    Merte, Lindsay Richard; Grabow, Lars C.; Peng, Guowen

    2011-01-01

    High-resolution scanning tunneling microscope (STM) images of moiré-structured FeO films on Pt(111) were obtained in a number of different tip-dependent imaging modes. For the first time, the STM images are distinguished and interpreted unambiguously with the help of distinct oxygen...

  17. A simple, ultrahigh vacuum compatible scanning tunneling microscope for use at variable temperatures

    NARCIS (Netherlands)

    Mugele, Friedrich Gunther; Kloos, Ch.; Leiderer, P.; Moller, R.

    1996-01-01

    We present the construction of a very compact scanning tunneling microscope (STM) which can be operated at temperatures between 4 and 350 K. The tip and a tiny tip holder are the only movable parts, whereas the sample and the piezoscanner are rigidly attached to the body of the STM. This leads to an

  18. Simultaneous topographic and elemental chemical and magnetic contrast in scanning tunneling microscopy

    Science.gov (United States)

    Rose, Volker; Preissner, Curt A; Hla, Saw-Wai; Wang, Kangkang; Rosenmann, Daniel

    2014-09-30

    A method and system for performing simultaneous topographic and elemental chemical and magnetic contrast analysis in a scanning, tunneling microscope. The method and system also includes nanofabricated coaxial multilayer tips with a nanoscale conducting apex and a programmable in-situ nanomanipulator to fabricate these tips and also to rotate tips controllably.

  19. Scanning tunneling microscopy studies of thin foil x-ray mirrors

    DEFF Research Database (Denmark)

    Christensen, Finn Erland; Besenbacher, Flemming; Garnaes, Jorgen

    1990-01-01

    In this paper scanning tunneling microscopy (STM) measurements of x-ray mirrors are presented. The x-ray mirrors are 0.3 mm thick dip-lacquered aluminum foils coated with gold by evaporation, as well as state-of-the-art polished surfaces coated with gold, platinum, or iridium. The measurements...

  20. Preparation of Chemically Etched Tips for Ambient Instructional Scanning Tunneling Microscopy

    Science.gov (United States)

    Zaccardi, Margot J.; Winkelmann, Kurt; Olson, Joel A.

    2010-01-01

    A first-year laboratory experiment that utilizes concepts of electrochemical tip etching for scanning tunneling microscopy (STM) is described. This experiment can be used in conjunction with any STM experiment. Students electrochemically etch gold STM tips using a time-efficient method, which can then be used in an instructional grade STM that…

  1. Dynamics of decanethiol self-assembled monolayers on Au(111) studied by Scanning tunnelling microscopy

    NARCIS (Netherlands)

    Wu, Hairong; Sotthewes, Kai; Kumar, Avijit; Vancso, Gyula J.; Schön, Peter Manfred; Zandvliet, Henricus J.W.

    2013-01-01

    We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (β, δ, χ*, and ) and a disordered phase (ε) were observed. Current–time traces with the feedback loop disabled

  2. Covalently Immobilised Cytochrome C Imaged by In Situ Scanning Tunnelling Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Olesen, Klaus G.; Danilov, Alexey I.

    1997-01-01

    In situ scanning tunnelling microscopy (STM) imaging of cytochrome c (cyt c) on polycrystalline Pt surfaces and on Au(lll) was achieved first by covalent immobilisation of 3-aminopropyltriethoxysilane (3-APTS) brought to react with oxide present on the Pt surfaces. Covalently bound 3-APTS forms...

  3. STM in liquids. A scanning tunneling microscopy exploration of the liquid-solid interface.

    NARCIS (Netherlands)

    Hulsken, B.

    2008-01-01

    This thesis reports of a series of atomic scale studies of the liquid-solid interface, carried out with a home-built liquid-cell Scanning Tunnelling Microscope (STM). The home-built liquid-cell STM is described in detail, and numerical simulations are performed to show that surfaces immersed in the

  4. Supramolecular chemistry at the liquid/solid interface probed by scanning tunnelling microscopy

    NARCIS (Netherlands)

    Feyter, S. De; Uji-i, H.; Mamdouh, W.; Miura, A.; Zhang, J.; Jonkheijm, P.; Schenning, A.P.H.J.; Meijer, E.W.; Chen, Z.; Wurthner, F.; Schuurmans, N.; Esch, J. van; Feringa, B.L.; Dulcey, A.E.; Percec, V.; Schryver, F.C. De

    2006-01-01

    The liquid/solid interface provides an ideal environment to investigate self-assembly phenomena, and scanning tunnelling microscopy (STM) is one of the preferred methodologies to probe the structure and the properties of physisorbed monolayers on the nanoscale. Physisorbed monolayers are of

  5. Surface x-ray scattering and scanning tunneling microscopy studies at the Au(111) electrode

    International Nuclear Information System (INIS)

    Ocko, B.M.; Magnussen, O.M.; Wang, J.X.; Adzic, R.R.

    1993-01-01

    This chapter reviews Surface X-ray Scattering and Scanning Tunneling Microscopy results carried out at the Au(111) surface under electrochemical conditions. Results are presented for the reconstructed surface, and for bromide and thallium monolayers. These examples are used to illustrate the complementary nature of the techniques

  6. Simultaneous scanning tunneling microscopy and synchrotron X-ray measurements in a gas environment

    NARCIS (Netherlands)

    Mom, R.V.; Onderwaater, W.G.; Rost, M.J.; Jankowski, M.; Wenzel, S.; Jacobse, L.; Alkemade, P.F.A.; Vandalon, V.; van Spronsen, M.A.; van Weeren, M.; Crama, B.; van der Tuijn, P.; Felici, R.; Kessels, W.M.M.; Carlà, F.; Frenken, J.W.M.; Groot, I.M.N.

    2017-01-01

    A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer

  7. Cytochrome C Dynamics at Gold and Glassy Carbon Surfaces Monitored by in Situ Scanning Tunnel Microscopy

    DEFF Research Database (Denmark)

    Andersen, Jens Enevold Thaulov; Møller, Per; Pedersen, Marianne Vind

    1995-01-01

    We have investigated the absorption of cytochrome c on gold and glassy carbon substrates by in situ scanning tunnel microscopy under potentiostatic control of both substrate and tip. Low ionic strength and potential ranges where no Faradaic current flows were used. Cyt c aggregates into flat...

  8. Magneto-optical Faraday effect probed in a scanning tunneling microscope

    NARCIS (Netherlands)

    Prins, M.W.J.; Wielen, van der M.C.M.M.; Abraham, D.L.; Kempen, van H.; Kesteren, van H.W.

    1994-01-01

    Semiconductor tips are used as local photodetectors in a scanning tunneling microscope. We demonstrate that this configuration is sensitive to small light intensity variations, as supported by a simple model. The principle is applied to the detection of Faraday ellipticity of a Pt/Co multilayer

  9. Spin-polarized states in neutron matter in a strong magnetic field

    International Nuclear Information System (INIS)

    Isayev, A. A.; Yang, J.

    2009-01-01

    Spin-polarized states in neutron matter in strong magnetic fields up to 10 18 G are considered in the model with the Skyrme effective interaction. By analyzing the self-consistent equations at zero temperature, it is shown that a thermodynamically stable branch of solutions for the spin-polarization parameter as a function of density corresponds to the negative spin polarization when the majority of neutron spins are oriented opposite to the direction of the magnetic field. Besides, beginning from some threshold density dependent on magnetic field strength, the self-consistent equations also have two other branches of solutions for the spin-polarization parameter with the positive spin polarization. The free energy corresponding to one of these branches turns out to be very close to that of the thermodynamically preferable branch. As a consequence, in a strong magnetic field, the state with the positive spin polarization can be realized as a metastable state in the high-density region in neutron matter, which, under decreasing density, at some threshold density changes to a thermodynamically stable state with the negative spin polarization.

  10. Spin-polarized transport properties of Fe atomic chain adsorbed on zigzag graphene nanoribbons

    International Nuclear Information System (INIS)

    Zhang, Z L; Chen, Y P; Xie, Y E; Zhang, M; Zhong, J X

    2011-01-01

    The spin-polarized transport properties of Fe atomic chain adsorbed on zigzag graphene nanoribbons (ZGNRs) are investigated using the density-functional theory in combination with the nonequilibrium Green's function method. We find that the Fe chain has drastic effects on spin-polarized transport properties of ZGNRs compared with a single Fe atom adsorbed on the ZGNRs. When the Fe chain is adsorbed on the centre of the ZGNR, the original semiconductor transforms into metal, showing a very wide range of spin-polarized transport. Particularly, the spin polarization around the Fermi level is up to 100%. This is because the adsorbed Fe chain not only induces many localized states but also has effects on the edge states of ZGNR, which can effectively modulate the spin-polarized transports. The spin polarization of ZGNRs is sensitive to the adsorption site of the Fe chain. When the Fe chain is adsorbed on the edge of ZGNR, the spin degeneracy of conductance is completely broken. The spin polarization is found to be more pronounced because the edge state of one edge is destroyed by the additional Fe chain. These results have direct implications for the control of the spin-dependent conductance in ZGNRs with the adsorption of Fe chains.

  11. High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

    International Nuclear Information System (INIS)

    Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Sheet, Goutam; Singh, Chandan K.; Kabir, Mukul; Thakur, Gohil S.; Haque, Zeba; Gupta, L. C.; Ganguli, Ashok K.

    2016-01-01

    CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

  12. High spin polarization and the origin of unique ferromagnetic ground state in CuFeSb

    Energy Technology Data Exchange (ETDEWEB)

    Sirohi, Anshu; Saha, Preetha; Gayen, Sirshendu; Gaurav, Abhishek; Jyotsna, Shubhra; Sheet, Goutam, E-mail: goutam@iisermohali.ac.in [Department of Physical Sciences, Indian Institute of Science Education and Research Mohali, Sector 81, S. A. S. Nagar, Manauli PO 140306 (India); Singh, Chandan K.; Kabir, Mukul [Department of Physics, Indian Institute of Science Education and Research, Pune 411008 (India); Thakur, Gohil S.; Haque, Zeba; Gupta, L. C. [Department of Chemistry, Indian Institute of Technology, New Delhi 110016 (India); Ganguli, Ashok K. [Department of Chemistry, Indian Institute of Technology, New Delhi 110016 (India); Institute of Nano Science & Technology, Mohali 160064 (India)

    2016-06-13

    CuFeSb is isostructural to the ferro-pnictide and chalcogenide superconductors and it is one of the few materials in the family that are known to stabilize in a ferromagnetic ground state. Majority of the members of this family are either superconductors or antiferromagnets. Therefore, CuFeSb may be used as an ideal source of spin polarized current in spin-transport devices involving pnictide and the chalcogenide superconductors. However, for that the Fermi surface of CuFeSb needs to be sufficiently spin polarized. In this paper we report direct measurement of transport spin polarization in CuFeSb by spin-resolved Andreev reflection spectroscopy. From a number of measurements using multiple superconducting tips we found that the intrinsic transport spin polarization in CuFeSb is high (∼47%). In order to understand the unique ground state of CuFeSb and the origin of large spin polarization at the Fermi level, we have evaluated the spin-polarized band structure of CuFeSb through first principles calculations. Apart from supporting the observed 47% transport spin polarization, such calculations also indicate that the Sb-Fe-Sb angles and the height of Sb from the Fe plane are strikingly different for CuFeSb than the equivalent parameters in other members of the same family thereby explaining the origin of the unique ground state of CuFeSb.

  13. Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope.

    Science.gov (United States)

    Hagmann, Mark J; Yarotski, Dmitry A; Mousa, Marwan S

    2017-04-01

    Quasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200 μm of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.

  14. Luminescence of Quantum Dots by Coupling with Nonradiative Surface Plasmon Modes in a Scanning Tunneling Microscope

    International Nuclear Information System (INIS)

    Romero, M.J.; van de Lagemaat, J.

    2009-01-01

    The electronic coupling between quantum dots (QDs) and surface plasmons (SPs) is investigated by a luminescence spectroscopy based on scanning tunneling microscopy (STM). We show that tunneling luminescence from the dot is excited by coupling with the nonradiative plasmon mode oscillating at the metallic tunneling gap formed during the STM operation. This approach to the SP excitation reveals aspects of the SP-QD coupling not accessible to the more conventional optical excitation of SPs. In the STM, luminescence from the dot is observed when and only when the SP is in resonance with the fundamental transition of the dot. The tunneling luminescence spectrum also suggests that excited SP-QD hybrid states can participate in the excitation of QD luminescence. Not only the SP excitation regulates the QD luminescence but the presence of the dot at the tunneling gap imposes restrictions to the SP that can be excited in the STM, in which the SP cannot exceed the energy of the fundamental transition of the dot. The superior SP-QD coupling observed in the STM is due to the tunneling gap acting as a tunable plasmonic resonator in which the dot is fully immersed.

  15. Spin-polarization reversal at the interface between benzene and Fe(100)

    KAUST Repository

    Goumri-Said, Souraya

    2013-01-03

    The spin-polarization at the interface between Fe(100) and a benzene is investigated theoretically using density functional theory for two positions of the organic molecule: planar and perpendicular with respect to the substrate. The electronic and magnetic properties as well as the spin-polarization close to the Fermi level strongly depend on the benzene position on the iron surface. An inversion of the spin-polarization is induced by p-d hybridization and charge transfer from the iron to the carbon sites in both configurations.

  16. Influence of temperature on spin polarization dynamics in dilute nitride semiconductors—Role of nonparamagnetic centers

    Energy Technology Data Exchange (ETDEWEB)

    Baranowski, M.; Misiewicz, J. [Laboratory for Optical Spectroscopy of Nanostructures, Department of Experimental Physics, Wroclaw University of Technology, Wybrzeze, Wyspianskiego 27, 50-370 Wroclaw (Poland)

    2015-10-21

    We report theoretical studies of spin polarization dynamics in dilute nitride semiconductors. We develop a commonly used rate equation model [Lagarde et al., Phys. Status Solidi A 204, 208 (2007) and Kunold et al. Phys. Rev. B 83, 165202 (2011)] to take into account the influence of shallow localizing states on the temperature dependence of spin polarization dynamics and a spin filtering effect. Presented investigations show that the experimentally observed temperature dependence of a spin polarization lifetime in dilute nitrides can be related to the electron capture process by shallow localizing states without paramagnetic properties. This process reduces the efficiency of spin filtering effect by deep paramagnetic centers, especially at low temperatures.

  17. Nuclear reactivity indices in the context of spin polarized density functional theory

    International Nuclear Information System (INIS)

    Cardenas, Carlos; Lamsabhi, Al Mokhtar; Fuentealba, Patricio

    2006-01-01

    In this work, the nuclear reactivity indices of density functional theory have been generalized to the spin polarized case and their relationship to electron spin polarized indices has been established. In particular, the spin polarized version of the nuclear Fukui function has been proposed and a finite difference approximation has been used to evaluate it. Applications to a series of triatomic molecules demonstrate the ability of the new functions to predict the geometrical changes due to a change in the spin multiplicity. The main equations in the different ensembles have also been presented

  18. Spin-polarization reversal at the interface between benzene and Fe(100)

    KAUST Repository

    Goumri-Said, Souraya; Benali Kanoun, Mohammed; Manchon, Aurelien; Schwingenschlö gl, Udo

    2013-01-01

    The spin-polarization at the interface between Fe(100) and a benzene is investigated theoretically using density functional theory for two positions of the organic molecule: planar and perpendicular with respect to the substrate. The electronic and magnetic properties as well as the spin-polarization close to the Fermi level strongly depend on the benzene position on the iron surface. An inversion of the spin-polarization is induced by p-d hybridization and charge transfer from the iron to the carbon sites in both configurations.

  19. Note: optical optimization for ultrasensitive photon mapping with submolecular resolution by scanning tunneling microscope induced luminescence.

    Science.gov (United States)

    Chen, L G; Zhang, C; Zhang, R; Zhang, X L; Dong, Z C

    2013-06-01

    We report the development of a custom scanning tunneling microscope equipped with photon collection and detection systems. The optical optimization includes the comprehensive design of aspherical lens for light collimation and condensing, the sophisticated piezo stages for in situ lens adjustment inside ultrahigh vacuum, and the fiber-free coupling of collected photons directly onto the ultrasensitive single-photon detectors. We also demonstrate submolecular photon mapping for the molecular islands of porphyrin on Ag(111) under small tunneling currents down to 10 pA and short exposure time down to 1.2 ms/pixel. A high quantum efficiency up to 10(-2) was also observed.

  20. Conductance of single atoms and molecules studied with a scanning tunnelling microscope

    International Nuclear Information System (INIS)

    Neel, N; Kroeger, J; Limot, L; Berndt, R

    2007-01-01

    The conductance of single atoms and molecules is investigated with a low-temperature scanning tunnelling microscope. In a controlled and reproducible way, clean Ag(111) surfaces, individual silver atoms on Ag(111) as well as individual C 60 molecules adsorbed on Cu(100) are contacted with the tip of the microscope. Upon contact the conductance changes discontinuously in the case of the tip-surface junction while the tip-atom and tip-molecule junctions exhibit a continuous transition from the tunnelling to the contact regime

  1. Fermi surface contours obtained from scanning tunneling microscope images around surface point defects

    International Nuclear Information System (INIS)

    Khotkevych-Sanina, N V; Kolesnichenko, Yu A; Van Ruitenbeek, J M

    2013-01-01

    We present a theoretical analysis of the standing wave patterns in scanning tunneling microscope (STM) images, which occur around surface point defects. We consider arbitrary dispersion relations for the surface states and calculate the conductance for a system containing a small-size tunnel contact and a surface impurity. We find rigorous theoretical relations between the interference patterns in the real-space STM images, their Fourier transforms and the Fermi contours of two-dimensional electrons. We propose a new method for reconstructing Fermi contours of surface electron states, directly from the real-space STM images around isolated surface defects. (paper)

  2. Energy gap and surface structure of superconducting diamond films probed by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Nishizaki, Terukazu; Takano, Yoshihiko; Nagao, Masanori; Takenouchi, Tomohiro; Kawarada, Hiroshi; Kobayashi, Norio

    2007-01-01

    We have performed scanning tunneling microscopy/spectroscopy (STM/STS) experiments on (1 1 1)-oriented epitaxial films of heavily boron-doped diamond at T = 0.47 K. The STM topography shows two kinds of atomic structures: a hydrogenated 1 x 1 structure, C(1 1 1)1 x 1:H, and an amorphous structure. On the C(1 1 1)1 x 1:H region, the tunneling spectra show superconducting property with the energy gap Δ = 0.83 meV. The obtained gap ratio 2Δ/k B T c = 3.57 is consistent with the weak-coupling BCS theory

  3. Spin polarization and magnetic effects in radical reactions

    International Nuclear Information System (INIS)

    Salikhov, K.M.; Molin, Yu.N.; Sagdeev, R.Z.; Buchachenko, A.L.

    1984-01-01

    Studies on the effects of chemically induced dynamic nuclear and electron polarizations (CIDNP and CIDEP), and magnetic effects in radical reactions, have given rise to a new rapidly-progressing field of chemical physics. It came into being about ten years ago and has been attracting the ever-growing attention of researchers in related areas. The present book is a fairly all-embracing review of the state of affairs in this field. The book presents the physical background (both theoretical and experimental) of CIDNP and CIDEP, of the effects of an external magnetic field and magnetic nuclear moment (magnetic isotope effects) on radical reactions in solutions. Great attention has been paid to the application of chemical spin polarization and magnetic effects to solving various problems of chemical kinetics, structural chemistry, molecular physics, magnetobiology, and radiospectroscopy. The book will be useful for physicists, chemists and biologists employing CIDNP, CIDEP and magnetic effects in their investigations, as well as for researchers in related fields of chemical physics. The book can be also recommended for postgraduates and senior undergraduate students. (Auth.)

  4. Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications

    International Nuclear Information System (INIS)

    Morawski, Ireneusz; Spiegelberg, Richard; Korte, Stefan; Voigtländer, Bert

    2015-01-01

    A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. The high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations

  5. Combined frequency modulated atomic force microscopy and scanning tunneling microscopy detection for multi-tip scanning probe microscopy applications

    Energy Technology Data Exchange (ETDEWEB)

    Morawski, Ireneusz [Peter Grünberg Institut (PGI-3) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich, 52425 Jülich (Germany); Institute of Experimental Physics, University of Wrocław, pl. M. Borna 9, 50-204 Wrocław (Poland); Spiegelberg, Richard; Korte, Stefan; Voigtländer, Bert [Peter Grünberg Institut (PGI-3) and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich, 52425 Jülich (Germany)

    2015-12-15

    A method which allows scanning tunneling microscopy (STM) tip biasing independent of the sample bias during frequency modulated atomic force microscopy (AFM) operation is presented. The AFM sensor is supplied by an electronic circuit combining both a frequency shift signal and a tunneling current signal by means of an inductive coupling. This solution enables a control of the tip potential independent of the sample potential. Individual tip biasing is specifically important in order to implement multi-tip STM/AFM applications. An extensional quartz sensor (needle sensor) with a conductive tip is applied to record simultaneously topography and conductivity of the sample. The high resonance frequency of the needle sensor (1 MHz) allows scanning of a large area of the surface being investigated in a reasonably short time. A recipe for the amplitude calibration which is based only on the frequency shift signal and does not require the tip being in contact is presented. Additionally, we show spectral measurements of the mechanical vibration noise of the scanning system used in the investigations.

  6. Spin-polarized charge transport in HgTe/CdTe quantum well topological insulator under a ferromagnetic metal strip

    Science.gov (United States)

    Wu, Zhenhua; Luo, Kun; Yu, Jiahan; Wu, Xiaobo; Lin, Liangzhong

    2018-02-01

    Electron tunneling through a single magnetic barrier in a HgTe topological insulator has been theoretically investigated. We find that the perpendicular magnetic field would not lead to spin-flip of the edge states due to the conservation of the angular moment. By tuning the magnetic field and the Fermi energy, the edge channels can be transited from switch-on states to switch-off states and the current from unpolarized states can be filtered to fully spin polarized states. These features offer us an efficient way to control charge/spin transport in a HgTe/CdTe quantum well, and pave a way to construct the nanoelectronic devices utilizing the topological edge states.

  7. Simultaneous scanning tunneling microscopy and synchrotron X-ray measurements in a gas environment.

    Science.gov (United States)

    Mom, Rik V; Onderwaater, Willem G; Rost, Marcel J; Jankowski, Maciej; Wenzel, Sabine; Jacobse, Leon; Alkemade, Paul F A; Vandalon, Vincent; van Spronsen, Matthijs A; van Weeren, Matthijs; Crama, Bert; van der Tuijn, Peter; Felici, Roberto; Kessels, Wilhelmus M M; Carlà, Francesco; Frenken, Joost W M; Groot, Irene M N

    2017-11-01

    A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer shield of the coaxial tips can be biased to deflect ions away from the tip core. When tunneling, the X-ray-induced current is separated from the regular, 'topographic' tunneling current using a novel high-speed separation scheme. We demonstrate the capabilities of the instrument by measuring the local X-ray-induced current on Au(1 1 1) in 800 mbar Ar. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. Fano Description of Single-Hydrocarbon Fluorescence Excited by a Scanning Tunneling Microscope.

    Science.gov (United States)

    Kröger, Jörg; Doppagne, Benjamin; Scheurer, Fabrice; Schull, Guillaume

    2018-06-13

    The detection of fluorescence with submolecular resolution enables the exploration of spatially varying photon yields and vibronic properties at the single-molecule level. By placing individual polycyclic aromatic hydrocarbon molecules into the plasmon cavity formed by the tip of a scanning tunneling microscope and a NaCl-covered Ag(111) surface, molecular light emission spectra are obtained that unravel vibrational progression. In addition, light spectra unveil a signature of the molecule even when the tunneling current is injected well separated from the molecular emitter. This signature exhibits a distance-dependent Fano profile that reflects the subtle interplay between inelastic tunneling electrons, the molecular exciton and localized plasmons in at-distance as well as on-molecule fluorescence. The presented findings open the path to luminescence of a different class of molecules than investigated before and contribute to the understanding of single-molecule luminescence at surfaces in a unified picture.

  9. In situ scanning tunnelling microscopy of redox molecules. Coherent electron transfer at large bias voltages

    DEFF Research Database (Denmark)

    Zhang, Jingdong; Kuznetsov, A.M.; Ulstrup, Jens

    2003-01-01

    Theories of in situ scanning tunnelling microscopy (STM) of molecules with redox levels near the substrate and tip Fermi levels point to 'spectroscopic' current-overpotential features. Prominent features require a narrow 'probing tip', i.e. a small bias voltage, eV(bias), compared...... a broad tunnelling current-overpotential range at a constant (large) bias voltage of +0.2 V. The current is found to be constant over a 0.25 V overpotential range, which covers roughly the range where the oxidised and reduced redox levels are located within the energy tip. STM contrast and apparent...... of previous theoretical work on in situ STM of redox molecules, to large bias voltages, \\eV(bias)\\ > E-r. Large bias voltages give tunnelling contrasts independent of the overpotential over a broad range, as both the oxidised and reduced redox levels are located within the 'energy tip' between the substrate...

  10. A compact atomic force-scanning tunneling microscope for studying microelectronics and environmental aerosols

    International Nuclear Information System (INIS)

    Chen, G.

    1996-06-01

    This dissertation describes the characteristics and the construction of a compact atomic force/scanning tunneling microscope (AFM/STM). The basics and the method of preparing a tunneling junction between a chemically etched tunneling tip and a micro-manufactured cantilever is outlined by analyzing the forces between tunneling tip and cantilever as well as between force-sensing tip and sample surfaces. To our best knowledge this instrument is the first one using a commercial cantilever with only one piezoelectric tube carrying the whole tunneling sensor. The feedback control system has been optimized after a careful analysis of the electronic loop characteristics. The mode of operation has been determined by analyzing the dynamic characteristics of the scan heads and by investigating the time characteristics of the data acquisition system. The vibration isolation system has been calibrated by analyzing the characteristics of the damping setup and the stiffness of the scan head. The calculated results agree well with the measured ones. Also, a software package for data acquisition and real time display as well as for image processing and three-dimensional visualization has been developed. With this home-made software package, the images can be processed by means of a convolution filter, a Wiener filter and other 2-D FFT filters, and can be displayed in different ways. Atomic resolution images of highly oriented pyrolytic graphite (HOPG) and graphite surfaces have been obtained in AFM and STM mode. New theoretical explanations have been given for the observed anomalous STM and AFM images of graphite by calculating the asymmetric distribution of quantum conductance and tip-surface forces on a graphite surface. This not only resolved the theoretical puzzles of STM and AFM of graphite, but also revealed the relation between atomic force microscopy and scanning tunneling microscopy of graphite. Applications of STM and AFM to micro-electronic devices have been investigated

  11. Spin-polarized ballistic conduction through correlated Au-NiMnSb-Au heterostructures

    KAUST Repository

    Morari, C.

    2017-11-20

    We examine the ballistic conduction through Au-NiMnSb-Au heterostructures consisting of up to four units of the half-metallic NiMnSb in the scattering region, using density functional theory (DFT) methods. For a single NiMnSb unit the transmission function displays a spin polarization of around 50% in a window of 1eV centered around the Fermi level. By increasing the number of layers, an almost complete spin polarization of the transmission is obtained in this energy range. Supplementing the DFT calculations with local electronic interactions, of Hubbard-type on the Mn sites, leads to a hybridization between the interface and many-body states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin polarization of the conduction electron transmission, which suggests that the hybridized interface and many-body induced states are localized.

  12. Peculiarities of spin polarization inversion at a thiophene/cobalt interface

    KAUST Repository

    Wang, Xuhui; Manchon, Aurelien; Schwingenschlö gl, Udo; Zhu, Zhiyong

    2013-01-01

    We perform ab initio calculations to investigate the spin polarization at the interface between a thiophene molecule and cobalt substrate. We find that the reduced symmetry in the presence of a sulfur atom (in the thiophene molecule) leads to a

  13. Modelization of nanospace interaction involving a ferromagnetic atom: a spin polarization effect study by thermogravimetric analysis.

    Science.gov (United States)

    Santhanam, K S V; Chen, Xu; Gupta, S

    2014-04-01

    Ab initio studies of ferromagnetic atom interacting with carbon nanotubes have been reported in the literature that predict when the interaction is strong, a higher hybridization with confinement effect will result in spin polarization in the ferromagnetic atom. The spin polarization effect on the thermal oxidation to form its oxide is modeled here for the ferromagnetic atom and its alloy, as the above studies predict the 4s electrons are polarized in the atom. The four models developed here provide a pathway for distinguishing the type of interaction that exists in the real system. The extent of spin polarization in the ferromagnetic atom has been examined by varying the amount of carbon nanotubes in the composites in the thermogravimetric experiments. In this study we report the experimental results on the CoNi alloy which appears to show selective spin polarization. The products of the thermal oxidation has been analyzed by Fourier Transform Infrared Spectroscopy.

  14. a New Approach for Subway Tunnel Deformation Monitoring: High-Resolution Terrestrial Laser Scanning

    Science.gov (United States)

    Li, J.; Wan, Y.; Gao, X.

    2012-07-01

    With the improvement of the accuracy and efficiency of laser scanning technology, high-resolution terrestrial laser scanning (TLS) technology can obtain high precise points-cloud and density distribution and can be applied to high-precision deformation monitoring of subway tunnels and high-speed railway bridges and other fields. In this paper, a new approach using a points-cloud segmentation method based on vectors of neighbor points and surface fitting method based on moving least squares was proposed and applied to subway tunnel deformation monitoring in Tianjin combined with a new high-resolution terrestrial laser scanner (Riegl VZ-400). There were three main procedures. Firstly, a points-cloud consisted of several scanning was registered by linearized iterative least squares approach to improve the accuracy of registration, and several control points were acquired by total stations (TS) and then adjusted. Secondly, the registered points-cloud was resampled and segmented based on vectors of neighbor points to select suitable points. Thirdly, the selected points were used to fit the subway tunnel surface with moving least squares algorithm. Then a series of parallel sections obtained from temporal series of fitting tunnel surfaces were compared to analysis the deformation. Finally, the results of the approach in z direction were compared with the fiber optical displacement sensor approach and the results in x, y directions were compared with TS respectively, and comparison results showed the accuracy errors of x, y, z directions were respectively about 1.5 mm, 2 mm, 1 mm. Therefore the new approach using high-resolution TLS can meet the demand of subway tunnel deformation monitoring.

  15. A NEW APPROACH FOR SUBWAY TUNNEL DEFORMATION MONITORING: HIGH-RESOLUTION TERRESTRIAL LASER SCANNING

    Directory of Open Access Journals (Sweden)

    J. Li

    2012-07-01

    Full Text Available With the improvement of the accuracy and efficiency of laser scanning technology, high-resolution terrestrial laser scanning (TLS technology can obtain high precise points-cloud and density distribution and can be applied to high-precision deformation monitoring of subway tunnels and high-speed railway bridges and other fields. In this paper, a new approach using a points-cloud segmentation method based on vectors of neighbor points and surface fitting method based on moving least squares was proposed and applied to subway tunnel deformation monitoring in Tianjin combined with a new high-resolution terrestrial laser scanner (Riegl VZ-400. There were three main procedures. Firstly, a points-cloud consisted of several scanning was registered by linearized iterative least squares approach to improve the accuracy of registration, and several control points were acquired by total stations (TS and then adjusted. Secondly, the registered points-cloud was resampled and segmented based on vectors of neighbor points to select suitable points. Thirdly, the selected points were used to fit the subway tunnel surface with moving least squares algorithm. Then a series of parallel sections obtained from temporal series of fitting tunnel surfaces were compared to analysis the deformation. Finally, the results of the approach in z direction were compared with the fiber optical displacement sensor approach and the results in x, y directions were compared with TS respectively, and comparison results showed the accuracy errors of x, y, z directions were respectively about 1.5 mm, 2 mm, 1 mm. Therefore the new approach using high-resolution TLS can meet the demand of subway tunnel deformation monitoring.

  16. Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics

    DEFF Research Database (Denmark)

    Christiansen, Jesper; Morgenstern, K.; Schiøtz, Jakob

    2002-01-01

    The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations, the simulati......The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations......, the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width...

  17. Creation of stable molecular junctions with a custom-designed scanning tunneling microscope.

    Science.gov (United States)

    Lee, Woochul; Reddy, Pramod

    2011-12-02

    The scanning tunneling microscope break junction (STMBJ) technique is a powerful approach for creating single-molecule junctions and studying electrical transport in them. However, junctions created using the STMBJ technique are usually mechanically stable for relatively short times (scanning tunneling microscope that enables the creation of metal-single molecule-metal junctions that are mechanically stable for more than 1 minute at room temperature. This stability is achieved by a design that minimizes thermal drift as well as the effect of environmental perturbations. The utility of this instrument is demonstrated by performing transition voltage spectroscopy-at the single-molecule level-on Au-hexanedithiol-Au, Au-octanedithiol-Au and Au-decanedithiol-Au junctions.

  18. Creation of stable molecular junctions with a custom-designed scanning tunneling microscope

    International Nuclear Information System (INIS)

    Lee, Woochul; Reddy, Pramod

    2011-01-01

    The scanning tunneling microscope break junction (STMBJ) technique is a powerful approach for creating single-molecule junctions and studying electrical transport in them. However, junctions created using the STMBJ technique are usually mechanically stable for relatively short times (<1 s), impeding detailed studies of their charge transport characteristics. Here, we report a custom-designed scanning tunneling microscope that enables the creation of metal–single molecule–metal junctions that are mechanically stable for more than 1 minute at room temperature. This stability is achieved by a design that minimizes thermal drift as well as the effect of environmental perturbations. The utility of this instrument is demonstrated by performing transition voltage spectroscopy—at the single-molecule level—on Au–hexanedithiol–Au, Au–octanedithiol–Au and Au–decanedithiol–Au junctions.

  19. Tip preparation for usage in an ultra-low temperature UHV scanning tunneling microscope

    Directory of Open Access Journals (Sweden)

    S. Ernst, S. Wirth, M. Rams, V. Dolocan and F. Steglich

    2007-01-01

    Full Text Available This work deals with the preparation and characterization of tungsten tips for the use in UHV low-temperature scanning tunneling microscopy and spectroscopy (STM and STS, respectively. These specific environments require in situ facilities for tip conditioning, for further sharpening of the tips, as well as for reliable tip characterization. The implemented conditioning methods include direct resistive annealing, annealing by electron bombardment, and self-sputtering with noble gas ions. Moreover, results from in situ tip characterization by field emission and STM experiments were compared to ex situ scanning electron microscopy. Using the so-prepared tips, high resolution STM images and tunneling spectra were obtained in a temperature range from ambient down to 350 mK, partially with applied magnetic field, on a variety of materials.

  20. Scanning Tunneling Microscopy Analysis of a Pentacene/Graphene/SiC(0001) system

    Science.gov (United States)

    Yost, Andrew; Suzer, Ozgun; Smerdon, Joseph; Chien, Teyu; Guest, Jeffrey

    2014-03-01

    A complete understanding of the structure of molecular assemblies, as well as an understanding of donor-acceptor interactions is crucial in the development of emergent molecular electronics technologies such as organic photovoltaics. The pentacene (C22H14) is a good electron donor in Pentacene-C60 system, which is a model system of an organic photovoltaic cell.. Here we present scanning tunneling microscopy studies of the pentacene(Pn) molecule on Graphene(G) that is epitaxially grown on SiC(0001). In addition to the morphologies reported in literature, several new structures of Pn on on G/SiC(0001) were observed with different periodicity and registry both in monolayer and bilayer coverages of molecules on the surface. Preliminary scanning tunneling spectroscopy of the molecular system is also discussed; well-isolated states and a large HOMO-LUMO gap indicate the Pn is weakly coupled to the grapheme and underlying substrate.

  1. Radio frequency scanning tunneling spectroscopy for single-molecule spin resonance.

    Science.gov (United States)

    Müllegger, Stefan; Tebi, Stefano; Das, Amal K; Schöfberger, Wolfgang; Faschinger, Felix; Koch, Reinhold

    2014-09-26

    We probe nuclear and electron spins in a single molecule even beyond the electromagnetic dipole selection rules, at readily accessible magnetic fields (few mT) and temperatures (5 K) by resonant radio-frequency current from a scanning tunneling microscope. We achieve subnanometer spatial resolution combined with single-spin sensitivity, representing a 10 orders of magnitude improvement compared to existing magnetic resonance techniques. We demonstrate the successful resonant spectroscopy of the complete manifold of nuclear and electronic magnetic transitions of up to ΔI(z)=±3 and ΔJ(z)=±12 of single quantum spins in a single molecule. Our method of resonant radio-frequency scanning tunneling spectroscopy offers, atom-by-atom, unprecedented analytical power and spin control with an impact on diverse fields of nanoscience and nanotechnology.

  2. Fusion with highly spin polarized HD and D2

    International Nuclear Information System (INIS)

    Honig, A.; Letzring, S.; Skupsky, S.

    1993-01-01

    Our experimental efforts over the past 5 years have been aimed at cazrying out ICF shots with spin-polarized 0 fuel. We successfully prepared polarized 0 in HD, and solved the problems of loading target shells with our carefully prepared isotopic -rnixt.l.l?-es, polarizing them so that the 0 polarization remains metastably frozen-in for about half a day, and carrying out the various cold transfer requirements at Syracuse, where the target is prepared, and at Rochester, where the cold target is inserted fusion chamber. Upon shooting the accurately positioned unpolarized high density cold target, no neutron yield was observed. Inspection inside the OMEGA tank after the shot indicated the absence of neutron yield was dus to mal-timing or insufficient retraction rate of OMEGA'S fast shroud mechanism, resulting in interception of at least 20 of the 24 laser beams by the faulty shroud. In spits of this, all alements of the complex experiment we originally undertook have been successfully demonstrated, and the cold retrieval concepts and methods we developed are being utilized on the ICF upgrades at Rochester and at Livermore. In addition to the solution of the interface problems, we obtained novel results on polymer shell characteristics at low temperatures, and continuation of these experiments is c = ently supported by KLUP. Extensive additional mappings were ca=ied out of nuclear spin relaxation rates of H and D in solid HD in the temperature-magnetic field rangs of 0.01 to 4.2K and 0 - 13 Tesla. New phenomena were discovered, such as association of impurity clustering with very low temperature motion, and inequality of the growth-rate and decay-rate of the magnetization

  3. Fusion with highly spin polarized HD and D2

    International Nuclear Information System (INIS)

    Honig, A.; Letzring, S.; Skupsky, S.

    1993-01-01

    The experimental efforts over the past 5 years have been aimed at carrying out ICF shots with spin-polarized D fuel. The authors successfully prepared polarized D in HD, and solved the problems of loading target shells with their carefully prepared isotopic mixtures, polarizing them so that the D polarization remains metastably frozen-in for about half a day, and carrying out the various cold transfer requirements at Syracuse, where the target is prepared, and at Rochester, where the cold target is inserted into the OMEGA fusion chamber. A principal concern during this past year was overcoming difficulties encountered in maintaining the integrity of the fragile cold target during the multitude of cold-transfers required for the experiment. These difficulties arose from insufficient rigidity of the cold transfer systems, which were constrained to be of small diameter by the narrow central access bore of the dilution refrigerator, and were exacerbated by the multitude of required target shell manipulations between different environments, each with different coupling geometry, including target shell permeation, polarization, storage, transport, retrieval and insertion into OMEGA. The authors did solve all of these problems, and were able to position a cold, high density but unpolarized target with required precision in OMEGA. Upon shooting the accurately positioned unpolarized high density cold target, no neutron yield was observed. Inspection inside the OMEGA tank after the shot indicated the absence of neutron yield was due to mal-timing or insufficient retraction rate of OMEGA's fast shroud mechanism, resulting in interception of at least 20 of the 24 laser beams by the faulty shroud. In spite of this, all elements of the complex experiment the authors originally undertook have been successfully demonstrated, and the cold retrieval concepts and methods they developed are being utilized on the ICF upgrades at Rochester and at Livermore

  4. Estimate of spin polarization for PEP using generalized transformation matrices

    International Nuclear Information System (INIS)

    Chao, A.W.

    1978-04-01

    The spin polarization for PEP has been estimated before by using simplified models. The main difficulty in the previous estimates is that the strength of depolarization effects caused by various electromagnetic field errors could not be specified accurately. To overcome this difficulty, a matrix formalism for depolarization calculation was developed recently. One basic ingredient of this theory is to represent an electron by an 8-dimensional state vector, X = (x,x',y,y',z,δ,α,β) where the first six coordinates are the usual transverse and longitudinal canonical coordinates, while α and β are the two components of the electron's spin vector perpendicular to the equilibrium direction of polarization /cflx n/. The degree of depolarization is specified by 1/2(α 2 + β 2 ). The state vector X will be transformed by an 8 x 8 matrix as the electron passes through a beam-line element such as a bending magnet or an rf cavity. From any position s, one multiplies successively the 8 x 8 matrices around one revolution of the storage ring to obtain the total transformation T(s). Any impulse perturbation ΔX to the electron's state vector occurring at s will be transformed repeatedly by T(s) as the electron circulates around the storage ring. Another basic ingredient is to decompose ΔX into 8 eigenstate components with eigenvectors determined from T(s). Six of these eigenstate components corresponding to the space states will be damped out by the usual radiation damping. The projections of ΔX onto the remaining two spin eigenstates are directly related to the loss of polarization due to the impulse perturbation ΔX. Depolarization effects can thus be calculated directly once all perturbations are specified. 7 refs., 4 figs

  5. The spin polarized linear response from density functional theory: Theory and application to atoms

    Energy Technology Data Exchange (ETDEWEB)

    Fias, Stijn, E-mail: sfias@vub.ac.be; Boisdenghien, Zino; De Proft, Frank; Geerlings, Paul [General Chemistry (ALGC), Vrije Universiteit Brussel (Free University Brussels – VUB), Pleinlaan 2, 1050 Brussels (Belgium)

    2014-11-14

    Within the context of spin polarized conceptual density functional theory, the spin polarized linear response functions are introduced both in the [N, N{sub s}] and [N{sub α}, N{sub β}] representations. The mathematical relations between the spin polarized linear response functions in both representations are examined and an analytical expression for the spin polarized linear response functions in the [N{sub α}, N{sub β}] representation is derived. The spin polarized linear response functions were calculated for all atoms up to and including argon. To simplify the plotting of our results, we integrated χ(r, r′) to a quantity χ(r, r{sup ′}), circumventing the θ and ϕ dependence. This allows us to plot and to investigate the periodicity throughout the first three rows in the periodic table within the two different representations. For the first time, χ{sub αβ}(r, r{sup ′}), χ{sub βα}(r, r{sup ′}), and χ{sub SS}(r, r{sup ′}) plots have been calculated and discussed. By integration of the spin polarized linear response functions, different components to the polarisability, α{sub αα}, α{sub αβ}, α{sub βα}, and α{sub ββ} have been calculated.

  6. Theoretical analysis of a dual-probe scanning tunneling microscope setup on graphene

    DEFF Research Database (Denmark)

    Settnes, Mikkel; Power, Stephen R.; Petersen, Dirch Hjorth

    2014-01-01

    Experimental advances allow for the inclusion of multiple probes to measure the transport properties of a sample surface. We develop a theory of dual-probe scanning tunneling microscopy using a Green's function formalism, and apply it to graphene. Sampling the local conduction properties at finite...... to different scattering processes. We compute the conductance maps of graphene systems with different edge geometries or height fluctuations to determine the effects of nonideal graphene samples on dual-probe measurements. © 2014 American Physical Society....

  7. Robust procedure for creating and characterizing the atomic structure of scanning tunneling microscope tips.

    Science.gov (United States)

    Tewari, Sumit; Bastiaans, Koen M; Allan, Milan P; van Ruitenbeek, Jan M

    2017-01-01

    Scanning tunneling microscopes (STM) are used extensively for studying and manipulating matter at the atomic scale. In spite of the critical role of the STM tip, procedures for controlling the atomic-scale shape of STM tips have not been rigorously justified. Here, we present a method for preparing tips in situ while ensuring the crystalline structure and a reproducibly prepared tip structure up to the second atomic layer. We demonstrate a controlled evolution of such tips starting from undefined tip shapes.

  8. Scanning tunneling spectroscopy on heavy-fermion systems; Rastertunnelspektroskopie an Schwere-Fermionen-Systemen

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, Stefan

    2011-06-24

    in the framework of this thesis different heavy-fermion systems were studied by means of scanning tunneling microscopy and spectroscopy. In the experiment two main topics existed. On the one hand the heavy-fermion superconductivity in the compounds CeCu{sub 2}Si{sub 2}, CeCoIn{sub 5}, and on the other hand the Kondo effect in the Kondo-lattice system YbRh{sub 2}Si{sub 2}.

  9. Single-step electrochemical method for producing very sharp Au scanning tunneling microscopy tips

    International Nuclear Information System (INIS)

    Gingery, David; Buehlmann, Philippe

    2007-01-01

    A single-step electrochemical method for making sharp gold scanning tunneling microscopy tips is described. 3.0M NaCl in 1% perchloric acid is compared to several previously reported etchants. The addition of perchloric acid to sodium chloride solutions drastically shortens etching times and is shown by transmission electron microscopy to produce very sharp tips with a mean radius of curvature of 15 nm

  10. Measurements with an ultrafast scanning tunnelling microscope on photoexcited semiconductor layers

    DEFF Research Database (Denmark)

    Keil, Ulrich Dieter Felix; Jensen, Jacob Riis; Hvam, Jørn Märcher

    1998-01-01

    Summary form only given. We demonstrate the use of a ultrafast scanning tunnelling microscopes (USTM) for detecting laser-induced field transients on semiconductor layers. In principle, the instrument can detect transient field changes thus far observed as far-field THz radiation in the near......-field regime and resolve small signal sources. For photoexcited low temperature (LT) GaAs we can explain the signal by a diffusion current driven by the laser-induced carrier density gradient...

  11. Mapping atomic contact between pentacene and a Au surface using scanning tunneling spectroscopy.

    Science.gov (United States)

    Song, Young Jae; Lee, Kyuho; Kim, Seong Heon; Choi, Byoung-Young; Yu, Jaejun; Kuk, Young

    2010-03-10

    We mapped spatially varying intramolecular electronic structures on a pentacene-gold interface using scanning tunneling spectroscopy. Along with ab initio calculations based on density functional theory, we found that the directional nature of the d orbitals of Au atoms plays an important role in the interaction at the pentacene-gold contact. The gold-induced interface states are broadened and shifted by various pentacene-gold distances determined by the various registries of a pentacene molecule on a gold substrate.

  12. Spin- and energy-dependent tunneling through a single molecule with intramolecular spatial resolution.

    Science.gov (United States)

    Brede, Jens; Atodiresei, Nicolae; Kuck, Stefan; Lazić, Predrag; Caciuc, Vasile; Morikawa, Yoshitada; Hoffmann, Germar; Blügel, Stefan; Wiesendanger, Roland

    2010-07-23

    We investigate the spin- and energy-dependent tunneling through a single organic molecule (CoPc) adsorbed on a ferromagnetic Fe thin film, spatially resolved by low-temperature spin-polarized scanning tunneling microscopy. Interestingly, the metal ion as well as the organic ligand show a significant spin dependence of tunneling current flow. State-of-the-art ab initio calculations including also van der Waals interactions reveal a strong hybridization of molecular orbitals and substrate 3d states. The molecule is anionic due to a transfer of one electron, resulting in a nonmagnetic (S=0) state. Nevertheless, tunneling through the molecule exhibits a pronounced spin dependence due to spin-split molecule-surface hybrid states.

  13. Atomic resolution scanning tunneling microscopy in a cryogen free dilution refrigerator at 15 mK

    International Nuclear Information System (INIS)

    Haan, A. M. J. den; Wijts, G. H. C. J.; Galli, F.; Oosterkamp, T. H.; Usenko, O.; Baarle, G. J. C. van; Zalm, D. J. van der

    2014-01-01

    Pulse tube refrigerators are becoming more common, because they are cost efficient and demand less handling than conventional (wet) refrigerators. However, a downside of a pulse tube system is the vibration level at the cold-head, which is in most designs several micrometers. We implemented vibration isolation techniques which significantly reduced vibration levels at the experiment. These optimizations were necessary for the vibration sensitive magnetic resonance force microscopy experiments at milli-kelvin temperatures for which the cryostat is intended. With these modifications we show atomic resolution scanning tunneling microscopy on graphite. This is promising for scanning probe microscopy applications at very low temperatures

  14. Multiple-scanning-probe tunneling microscope with nanoscale positional recognition function.

    Science.gov (United States)

    Higuchi, Seiji; Kuramochi, Hiromi; Laurent, Olivier; Komatsubara, Takashi; Machida, Shinichi; Aono, Masakazu; Obori, Kenichi; Nakayama, Tomonobu

    2010-07-01

    Over the past decade, multiple-scanning-probe microscope systems with independently controlled probes have been developed for nanoscale electrical measurements. We developed a quadruple-scanning-probe tunneling microscope (QSPTM) that can determine and control the probe position through scanning-probe imaging. The difficulty of operating multiple probes with submicrometer precision drastically increases with the number of probes. To solve problems such as determining the relative positions of the probes and avoiding of contact between the probes, we adopted sample-scanning methods to obtain four images simultaneously and developed an original control system for QSPTM operation with a function of automatic positional recognition. These improvements make the QSPTM a more practical and useful instrument since four images can now be reliably produced, and consequently the positioning of the four probes becomes easier owing to the reduced chance of accidental contact between the probes.

  15. Tunnel magnetoresistance in double spin filter junctions

    International Nuclear Information System (INIS)

    Saffarzadeh, Alireza

    2003-01-01

    We consider a new type of magnetic tunnel junction, which consists of two ferromagnetic tunnel barriers acting as spin filters (SFs), separated by a nonmagnetic metal (NM) layer. Using the transfer matrix method and the free-electron approximation, the dependence of the tunnel magnetoresistance (TMR) on the thickness of the central NM layer, bias voltage and temperature in the double SF junction are studied theoretically. It is shown that the TMR and electron-spin polarization in this structure can reach very large values under suitable conditions. The highest value of the TMR can reach 99%. By an appropriate choice of the thickness of the central NM layer, the degree of spin polarization in this structure will be higher than that of the single SF junctions. These results may be useful in designing future spin-polarized tunnelling devices

  16. Low Temperature Electrical Spin Injection from Highly Spin Polarized Co₂CrAl Heusler Alloy into p-Si.

    Science.gov (United States)

    Kar, Uddipta; Panda, J; Nath, T K

    2018-06-01

    The low temperature spin accumulation in p-Si using Co2CrAl/SiO2 tunnel junction has been investigated in detail. The heterojunction has been fabricated using electron beam evaporation (EBE) technique. The 3-terminal contacts in Hanle geometry has been made for spin transport measurements. The electrical transport properties have been investigated at different isothermal conditions in the temperature range of 10-300 K. The current-voltage characteristics of the junction shows excellent rectifying magnetic diode like behaviour in lower temperature range (below 200 K). At higher temperature, the junction shows nonlinear behaviour without rectifying characteristics. We have observed spin accumulation signal in p-Si semiconductor using SiO2/Co2CrAl tunnel junction in the low temperature regime (30-100 K). Hence the highly spin polarized Full Heusler alloys compounds, like Co2CrAl etc., are very attractive and can act as efficient tunnel device for spin injection in the area of spintronics devices in near future. The estimated spin life time is τ = 54 pS and spin diffusion length inside p-Si is LSD = 289 nm at 30 K for this heterostructure.

  17. Scanning tunnelling microscope light emission: Finite temperature current noise and over cut-off emission.

    Science.gov (United States)

    Kalathingal, Vijith; Dawson, Paul; Mitra, J

    2017-06-14

    The spectral distribution of light emitted from a scanning tunnelling microscope junction not only bears its intrinsic plasmonic signature but is also imprinted with the characteristics of optical frequency fluc- tuations of the tunnel current. Experimental spectra from gold-gold tunnel junctions are presented that show a strong bias (V b ) dependence, curiously with emission at energies higher than the quantum cut-off (eV b ); a component that decays monotonically with increasing bias. The spectral evolution is explained by developing a theoretical model for the power spectral density of tunnel current fluctuations, incorporating finite temperature contribution through consideration of the quantum transport in the system. Notably, the observed decay of the over cut-off emission is found to be critically associated with, and well explained in terms of the variation in junction conductance with V b . The investigation highlights the scope of plasmon-mediated light emission as a unique probe of high frequency fluctuations in electronic systems that are fundamental to the electrical generation and control of plasmons.

  18. Near-Field Enhanced Photochemistry of Single Molecules in a Scanning Tunneling Microscope Junction.

    Science.gov (United States)

    Böckmann, Hannes; Gawinkowski, Sylwester; Waluk, Jacek; Raschke, Markus B; Wolf, Martin; Kumagai, Takashi

    2018-01-10

    Optical near-field excitation of metallic nanostructures can be used to enhance photochemical reactions. The enhancement under visible light illumination is of particular interest because it can facilitate the use of sunlight to promote photocatalytic chemical and energy conversion. However, few studies have yet addressed optical near-field induced chemistry, in particular at the single-molecule level. In this Letter, we report the near-field enhanced tautomerization of porphycene on a Cu(111) surface in a scanning tunneling microscope (STM) junction. The light-induced tautomerization is mediated by photogenerated carriers in the Cu substrate. It is revealed that the reaction cross section is significantly enhanced in the presence of a Au tip compared to the far-field induced process. The strong enhancement occurs in the red and near-infrared spectral range for Au tips, whereas a W tip shows a much weaker enhancement, suggesting that excitation of the localized plasmon resonance contributes to the process. Additionally, using the precise tip-surface distance control of the STM, the near-field enhanced tautomerization is examined in and out of the tunneling regime. Our results suggest that the enhancement is attributed to the increased carrier generation rate via decay of the excited near-field in the STM junction. Additionally, optically excited tunneling electrons also contribute to the process in the tunneling regime.

  19. Size-dependent energy levels of InSb quantum dots measured by scanning tunneling spectroscopy.

    Science.gov (United States)

    Wang, Tuo; Vaxenburg, Roman; Liu, Wenyong; Rupich, Sara M; Lifshitz, Efrat; Efros, Alexander L; Talapin, Dmitri V; Sibener, S J

    2015-01-27

    The electronic structure of single InSb quantum dots (QDs) with diameters between 3 and 7 nm was investigated using atomic force microscopy (AFM) and scanning tunneling spectroscopy (STS). In this size regime, InSb QDs show strong quantum confinement effects which lead to discrete energy levels on both valence and conduction band states. Decrease of the QD size increases the measured band gap and the spacing between energy levels. Multiplets of equally spaced resonance peaks are observed in the tunneling spectra. There, multiplets originate from degeneracy lifting induced by QD charging. The tunneling spectra of InSb QDs are qualitatively different from those observed in the STS of other III-V materials, for example, InAs QDs, with similar band gap energy. Theoretical calculations suggest the electron tunneling occurs through the states connected with L-valley of InSb QDs rather than through states of the Γ-valley. This observation calls for better understanding of the role of indirect valleys in strongly quantum-confined III-V nanomaterials.

  20. Creation, transport and detection of imprinted magnetic solitons stabilized by spin-polarized current

    Science.gov (United States)

    Loreto, R. P.; Moura-Melo, W. A.; Pereira, A. R.; Zhang, X.; Zhou, Y.; Ezawa, M.; de Araujo, C. I. L.

    2018-06-01

    With the recent proposition of skyrmion utilization in racetrack memories at room temperature, skyrmionics has become a very attractive field. However, for the stability of skyrmions, it is essential to incorporate the Dzyaloshinskii-Moriya interaction (DMI) and the out-of-plane magnetic field into the system. In this work, we explore a system without these interactions. First, we propose a controlled way for the creation of magnetic skyrmions and skyrmioniums imprinted on a ferromagnetic nanotrack via a nanopatterned nanodisk with the magnetic vortex state. Then we investigate the detachment of the imprinted spin textures from the underneath of the nanodisk, as well as its transport by the spin-transfer torque imposed by spin-polarized current pulses applied in the nanotrack. A prominent feature of the moving imprinted spin texture is that its topological number Q is oscillating around the averaged value of Q = 0 as if it is a resonant state between the skyrmions with Q = ± 1 and the bubble with Q = 0 . We may call it a resonant magnetic soliton (RMS). A RMS moves along a straight line since it is free from the skyrmion Hall effect. In our studied device, the same electrodes are employed to realize the imprinted spin texture detachment and its transport. In addition, we have investigated the interaction between the RMS and a magnetic tunnel junction sensor, where the passing of the RMS in the nanotrack can be well detected. Our results would be useful for the development of novel spintronic devices based on moveable spin textures.

  1. Spin polarized and density modulated phases in symmetric electron-electron and electron-hole bilayers.

    Science.gov (United States)

    Kumar, Krishan; Moudgil, R K

    2012-10-17

    We have studied symmetric electron-electron and electron-hole bilayers to explore the stable homogeneous spin phase and the feasibility of inhomogeneous charge-/spin-density ground states. The former is resolved by comparing the ground-state energies in states of different spin polarizations, while the latter is resolved by searching for a divergence in the wavevector-dependent static charge/spin susceptibility. For this endeavour, we have used the dielectric approach within the self-consistent mean-field theory of Singwi et al. We find that the inter-layer interactions tend to change an abrupt spin-polarization transition of an isolated layer into a nearly gradual one, even though the partially spin-polarized phases are not clearly stable within the accuracy of our calculation. The transition density is seen to decrease with a reduction in layer spacing, implying a suppression of spin polarization by inter-layer interactions. Indeed, the suppression shows up distinctly in the spin susceptibility computed from the spin-polarization dependence of the ground-state energy. However, below a critical layer spacing, the unpolarized liquid becomes unstable against a charge-density-wave (CDW) ground state at a density preceding full spin polarization, with the transition density for the CDW state increasing on further reduction in the layer spacing. Due to attractive e-h correlations, the CDW state is found to be more pronounced in the e-h bilayer. On the other hand, the static spin susceptibility diverges only in the long-wavelength limit, which simply represents a transition to the homogeneous spin-polarized phase.

  2. Facile synthesis and electron transport properties of NiO nanostructures investigated by scanning tunneling microscopy

    Directory of Open Access Journals (Sweden)

    Govind Mallick

    2017-08-01

    Full Text Available Due to their unique chemical, thermal, electronic and photonic properties, low -dimensional transition metal oxides, especially NiO, have attracted great deal of attention for potential applications in a wide range of technologies, such as, sensors, electrochromic coatings and self-healing materials. However, their synthesis involves multi-step complex procedures that in addition to being expensive, further introduce impurities. Here we present a low cost facile approach to synthesize uniform size NiO nanoparticles (NPs from hydrothermally grown Ni(OH2. Detailed transmission electron microscopic analysis reveal the average size of NiO NPs to be around 29 nm. The dimension of NiO NP is also corroborated by the small area scanning tunneling microscope (STM measurements. Further, we investigate electron transport characteristics of newly synthesized Ni(OH2 and NiO nanoparticles on p-type Si substrate using scanning tunneling microscopy. The conductivity of Ni(OH2 and NiO are determined to be 1.46x10-3 S/cm and 2.37x10-5 S/cm, respectively. The NiO NPs exhibit a lower voltage window (∼0.7 V electron tunneling than the parent Ni(OH2.

  3. Nanomanipulation and nanofabrication with multi-probe scanning tunneling microscope: from individual atoms to nanowires.

    Science.gov (United States)

    Qin, Shengyong; Kim, Tae-Hwan; Wang, Zhouhang; Li, An-Ping

    2012-06-01

    The wide variety of nanoscale structures and devices demands novel tools for handling, assembly, and fabrication at nanoscopic positioning precision. The manipulation tools should allow for in situ characterization and testing of fundamental building blocks, such as nanotubes and nanowires, as they are built into functional devices. In this paper, a bottom-up technique for nanomanipulation and nanofabrication is reported by using a 4-probe scanning tunneling microscope (STM) combined with a scanning electron microscope (SEM). The applications of this technique are demonstrated in a variety of nanosystems, from manipulating individual atoms to bending, cutting, breaking carbon nanofibers, and constructing nanodevices for electrical characterizations. The combination of the wide field of view of SEM, the atomic position resolution of STM, and the flexibility of multiple scanning probes is expected to be a valuable tool for rapid prototyping in the nanoscience and nanotechnology.

  4. Note: long range and accurate measurement of deep trench microstructures by a specialized scanning tunneling microscope.

    Science.gov (United States)

    Ju, Bing-Feng; Chen, Yuan-Liu; Zhang, Wei; Zhu, Wule; Jin, Chao; Fang, F Z

    2012-05-01

    A compact but practical scanning tunneling microscope (STM) with high aspect ratio and high depth capability has been specially developed. Long range scanning mechanism with tilt-adjustment stage is adopted for the purpose of adjusting the probe-sample relative angle to compensate the non-parallel effects. A periodical trench microstructure with a pitch of 10 μm has been successfully imaged with a long scanning range up to 2.0 mm. More innovatively, a deep trench with depth and step height of 23.0 μm has also been successfully measured, and slope angle of the sidewall can approximately achieve 67°. The probe can continuously climb the high step and exploring the trench bottom without tip crashing. The new STM could perform long range measurement for the deep trench and high step surfaces without image distortion. It enables accurate measurement and quality control of periodical trench microstructures.

  5. New directions in point-contact spectroscopy based on scanning tunneling microscopy techniques (Review Article)

    International Nuclear Information System (INIS)

    Tartaglini, E.; Verhagen, T.G.A.; Galli, F.; Trouwborst, M.L.; Aarts, J.; Van-Ruitebbeek, J.M.; Muller, R.; Shiota, T.

    2013-01-01

    Igor Yanson showed 38 years ago for the first time a point-contact measurement where he probed the energy resolved spectroscopy of the electronic scattering inside the metal. Since this first measurement, the pointcontact spectroscopy (PCS) technique improved enormously. The application of the scanning probe microscopy (SPM) techniques in the late 1980s allowed achieving contacts with a diameter of a single atom. With the introduction of the mechanically controlled break junction technique, even spectroscopy on freely suspended chains of atoms could be performed. In this paper, we briefly review the current developments of PCS and show recent experiments in advanced scanning PCS based on SPM techniques. We describe some results obtained with both needle-anvil type of point contacts and scanning tunneling microscopy (STM). We also show our first attempt to lift up with a STM a chain of single gold atoms from a Au(110) surface.

  6. Scanning tunneling microscopy measurements of the spin Hall effect in tungsten films by using iron-coated tungsten tips

    Directory of Open Access Journals (Sweden)

    Ting Xie

    2018-05-01

    Full Text Available Scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying tungsten films have been conducted. An asymmetry of the tunneling current with respect to the change of the direction of the bias current through a tungsten film has been observed. It is argued that this asymmetry is a manifestation of the spin Hall effect in the current-carrying tungsten film. Nanoscale variations of this asymmetry across the tungsten film have been studied by using the scanning tunneling microscopy technique.

  7. Scanning tunneling microscopy measurements of the spin Hall effect in tungsten films by using iron-coated tungsten tips

    Science.gov (United States)

    Xie, Ting; Dreyer, Michael; Bowen, David; Hinkel, Dan; Butera, R. E.; Krafft, Charles; Mayergoyz, Isaak

    2018-05-01

    Scanning tunneling microscopy experiments using iron-coated tungsten tips and current-carrying tungsten films have been conducted. An asymmetry of the tunneling current with respect to the change of the direction of the bias current through a tungsten film has been observed. It is argued that this asymmetry is a manifestation of the spin Hall effect in the current-carrying tungsten film. Nanoscale variations of this asymmetry across the tungsten film have been studied by using the scanning tunneling microscopy technique.

  8. Scanning tunnelling spectroscopy of low pentacene coverage on the Ag/Si(111)-(√3 x √3) surface

    International Nuclear Information System (INIS)

    Guaino, Ph; Cafolla, A A; McDonald, O; Carty, D; Sheerin, G; Hughes, G

    2003-01-01

    The low coverage S1 phase of pentacene deposited on Ag/Si(111)-(√3 x √3) has been investigated at room temperature by scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS). Current-voltage data were acquired simultaneously with STM images for this phase. The normalized conductivity reveals two pronounced peaks at -1.10 and +2.25 V relative to the Fermi level. These peaks are attributed to resonant tunnelling through the highest occupied molecular orbital and lowest unoccupied molecular orbital molecular levels of the pentacene layer. The electronic properties of this interface are discussed in relation to results obtained for pentacene adsorbed on other metallic surfaces

  9. Molecular electronics of a single photosystem I reaction center: Studies with scanning tunneling microscopy and spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Lee, I.; Lee, J.W.; Warmack, R.J.; Allison, D.P.; Greenbaum, E. [Oak Ridge National Lab., TN (United States)

    1995-03-14

    Thylakoids and photosystem I (PSI) reaction centers were imaged by scanning tunneling microscopy. The thylakoids were isolated from spinach chloroplasts, and PSI reaction centers were extracted from thylakoid membranes. Because thylakoids are relatively thick nonconductors, they were sputter-coated with Pd/Au before imaging. PSI photosynthetic centers and chemically platinized PSI were investigated without sputter-coating. They were mounted on flat gold substrates that had been treated with mercaptoacetic acid to help bind the proteins. With tunneling spectroscopy, the PSI centers displayed a semiconductor-like response with a band gap of 1.8 eV. Lightly platinized (platinized for 1 hr) centers displayed diode-like conduction that resulted in dramatic contrast changes between images taken with opposite bias voltages. The electronic properties of this system were stable under long-term storage. 42 refs., 7 figs.

  10. Haptic-STM: a human-in-the-loop interface to a scanning tunneling microscope.

    Science.gov (United States)

    Perdigão, Luís M A; Saywell, Alex

    2011-07-01

    The operation of a haptic device interfaced with a scanning tunneling microscope (STM) is presented here. The user moves the STM tip in three dimensions by means of a stylus attached to the haptic instrument. The tunneling current measured by the STM is converted to a vertical force, applied to the stylus and felt by the user, with the user being incorporated into the feedback loop that controls the tip-surface distance. A haptic-STM interface of this nature allows the user to feel atomic features on the surface and facilitates the tactile manipulation of the adsorbate/substrate system. The operation of this device is demonstrated via the room temperature STM imaging of C(60) molecules adsorbed on an Au(111) surface in ultra-high vacuum.

  11. A variable-temperature scanning tunneling microscope capable of single-molecule vibrational spectroscopy

    International Nuclear Information System (INIS)

    Stipe, B.C.; Rezaei, M.A.; Ho, W.

    1999-01-01

    The design and performance of a variable-temperature scanning tunneling microscope (STM) is presented. The microscope operates from 8 to 350 K in ultrahigh vacuum. The thermally compensated STM is suspended by springs from the cold tip of a continuous flow cryostat and is completely surrounded by two radiation shields. The design allows for in situ dosing and irradiation of the sample as well as for the exchange of samples and STM tips. With the STM feedback loop off, the drift of the tip-sample spacing is approximately 0.001 Angstrom/min at 8 K. It is demonstrated that the STM is well-suited for the study of atomic-scale chemistry over a wide temperature range, for atomic-scale manipulation, and for single-molecule inelastic electron tunneling spectroscopy (IETS). copyright 1999 American Institute of Physics

  12. Construction and performance of a dilution-refrigerator based spectroscopic-imaging scanning tunneling microscope.

    Science.gov (United States)

    Singh, U R; Enayat, M; White, S C; Wahl, P

    2013-01-01

    We report on the set-up and performance of a dilution-refrigerator based spectroscopic imaging scanning tunneling microscope. It operates at temperatures below 10 mK and in magnetic fields up to 14T. The system allows for sample transfer and in situ cleavage. We present first-results demonstrating atomic resolution and the multi-gap structure of the superconducting gap of NbSe(2) at base temperature. To determine the energy resolution of our system we have measured a normal metal/vacuum/superconductor tunneling junction consisting of an aluminum tip on a gold sample. Our system allows for continuous measurements at base temperature on time scales of up to ≈170 h.

  13. Density-matrix approach for the electroluminescence of molecules in a scanning tunneling microscope.

    Science.gov (United States)

    Tian, Guangjun; Liu, Ji-Cai; Luo, Yi

    2011-04-29

    The electroluminescence (EL) of molecules confined inside a nanocavity in the scanning tunneling microscope possesses many intriguing but unexplained features. We present here a general theoretical approach based on the density-matrix formalism to describe the EL from molecules near a metal surface induced by both electron tunneling and localized surface plasmon excitations simultaneously. It reveals the underlying physical mechanism for the external bias dependent EL. The important role played by the localized surface plasmon on the EL is highlighted. Calculations for porphyrin derivatives have reproduced corresponding experimental spectra and nicely explained the observed unusual large variation of emission spectral profiles. This general theoretical approach can find many applications in the design of molecular electronic and photonic devices.

  14. Resonant-enhanced spectroscopy of molecular rotations with a scanning tunneling microscope.

    Science.gov (United States)

    Natterer, Fabian Donat; Patthey, François; Brune, Harald

    2014-07-22

    We use rotational excitation spectroscopy with a scanning tunneling microscope to investigate the rotational properties of molecular hydrogen and its isotopes physisorbed on the surfaces of graphene and hexagonal boron nitride (h-BN), grown on Ni(111), Ru(0001), and Rh(111). The rotational excitation energies are in good agreement with ΔJ = 2 transitions of freely spinning p-H2 and o-D2 molecules. The variations of the spectral line shapes for H2 among the different surfaces can be traced back to a molecular resonance-mediated tunneling mechanism. Our data for H2/h-BN/Rh(111) suggest a local intrinsic gating on this surface due to lateral static dipoles. Spectra on a mixed monolayer of H2, HD, and D2 display all three J = 0 → 2 rotational transitions, irrespective of tip position, thus pointing to a multimolecule excitation, or molecular mobility in the physisorbed close-packed layer.

  15. Chiral Majorana fermion modes regulated by a scanning tunneling microscope tip

    Science.gov (United States)

    Zhou, Yan-Feng; Hou, Zhe; Zhang, Ying-Tao; Sun, Qing-Feng

    2018-03-01

    The Majorana fermion can be described by a real wave function with only two phases (zero and π ) which provide a controllable degree of freedom. We propose a strategy to regulate the phase of the chiral Majorana state by coupling with a scanning tunneling microscope tip in a system consisting of a quantum anomalous Hall insulator coupled with a superconductor. With the change in the chemical potential, the chiral Majorana state can be tuned alternately between zero and π , in which the perfect normal tunneling and perfect crossed Andreev reflection appear, respectively. The perfect crossed Andreev reflection, by which a Cooper pair can be split into two electrons going into different terminals completely, leads to a pumping current and distinct quantized resistances. These findings may provide a signature of Majorana fermions and pave a feasible avenue to regulate the phase of the Majorana state.

  16. MgB2 energy gap determination by scanning tunnelling spectroscopy

    International Nuclear Information System (INIS)

    Heitmann, T W; Bu, S D; Kim, D M; Choi, J H; Giencke, J; Eom, C B; Regan, K A; Rogado, N; Hayward, M A; He, T; Slusky, J S; Khalifah, P; Haas, M; Cava, R J; Larbalestier, D C; Rzchowski, M S

    2004-01-01

    We report scanning tunnelling spectroscopy (STS) measurements of the gap properties of both ceramic MgB 2 and c-axis oriented epitaxial MgB 2 thin films. Both show a temperature dependent zero bias conductance peak and evidence for two superconducting gaps. We report tunnelling spectroscopy of superconductor-insulator-superconductor (S-I-S) junctions formed in two ways in addition to normal metal-insulator-superconductor (N-I-S) junctions. We find a gap δ = 2.2-2.8 meV, with spectral features and temperature dependence that are consistent between S-I-S junction types. In addition, we observe evidence of a second, larger gap, δ 7.2 meV, consistent with a proposed two-band model

  17. Quantum nature of protons in water probed by scanning tunneling microscopy and spectroscopy

    Science.gov (United States)

    Guo, Jing; Lü, Jing-Tao; Feng, Yexin; Chen, Ji; Peng, Jinbo; Lin, Zeren; Meng, Xiangzhi; Wang, Zhichang; Li, Xin-Zheng; Wang, En-Ge; Jiang, Ying; Jing-Tao Lü Team; Xin-Zheng Li Team

    The complexity of hydrogen-bonding interaction largely arises from the quantum nature of light hydrogen nuclei, which has remained elusive for decades. Here we report the direct assessment of nuclear quantum effects on the strength of a single hydrogen bond formed at a water-salt interface, using tip-enhanced inelastic electron tunneling spectroscopy (IETS) based on a low-temperature scanning tunneling microscope (STM). The IETS signals are resonantly enhanced by gating the frontier orbitals of water via a chlorine-terminated STM tip, such that the hydrogen-bonding strength can be determined with unprecedentedly high accuracy from the redshift in the O-H stretching frequency of water. Isotopic substitution experiments combined with quantum simulations reveal that the anharmonic quantum fluctuations of hydrogen nuclei weaken the weak hydrogen bonds and strengthen the relatively strong ones. However, this trend can be completely reversed when the hydrogen bond is strongly coupled to the polar atomic sites of the surface.

  18. Dual descriptors within the framework of spin-polarized density functional theory.

    Science.gov (United States)

    Chamorro, E; Pérez, P; Duque, M; De Proft, F; Geerlings, P

    2008-08-14

    Spin-polarized density functional theory (SP-DFT) allows both the analysis of charge-transfer (e.g., electrophilic and nucleophilic reactivity) and of spin-polarization processes (e.g., photophysical changes arising from electron transitions). In analogy with the dual descriptor introduced by Morell et al. [J. Phys. Chem. A 109, 205 (2005)], we introduce new dual descriptors intended to simultaneously give information of the molecular regions where the spin-polarization process linking states of different multiplicity will drive electron density and spin density changes. The electronic charge and spin rearrangement in the spin forbidden radiative transitions S(0)-->T(n,pi(*)) and S(0)-->T(pi,pi(*)) in formaldehyde and ethylene, respectively, have been used as benchmark examples illustrating the usefulness of the new spin-polarization dual descriptors. These quantities indicate those regions where spin-orbit coupling effects are at work in such processes. Additionally, the qualitative relationship between the topology of the spin-polarization dual descriptors and the vertical singlet triplet energy gap in simple substituted carbene series has been also discussed. It is shown that the electron density and spin density rearrangements arise in agreement with spectroscopic experimental evidence and other theoretical results on the selected target systems.

  19. Injection and detection of a spin-polarized current in a light-emitting diode

    Science.gov (United States)

    Fiederling, R.; Keim, M.; Reuscher, G.; Ossau, W.; Schmidt, G.; Waag, A.; Molenkamp, L. W.

    1999-12-01

    The field of magnetoelectronics has been growing in practical importance in recent years. For example, devices that harness electronic spin-such as giant-magnetoresistive sensors and magnetoresistive memory cells-are now appearing on the market. In contrast, magnetoelectronic devices based on spin-polarized transport in semiconductors are at a much earlier stage of development, largely because of the lack of an efficient means of injecting spin-polarized charge. Much work has focused on the use of ferromagnetic metallic contacts, but it has proved exceedingly difficult to demonstrate polarized spin injection. More recently, two groups have reported successful spin injection from an NiFe contact, but the observed effects of the spin-polarized transport were quite small (resistance changes of less than 1%). Here we describe a different approach, in which the magnetic semiconductor BexMnyZn1-x-ySe is used as a spin aligner. We achieve injection efficiencies of 90% spin-polarized current into a non-magnetic semiconductor device. The device used in this case is a GaAs/AlGaAs light-emitting diode, and spin polarization is confirmed by the circular polarization state of the emitted light.

  20. Unique spin-polarized transmission effects in a QD ring structure

    Science.gov (United States)

    Hedin, Eric; Joe, Yong

    2010-10-01

    Spintronics is an emerging field in which the spin of the electron is used for switching purposes and to communicate information. In order to obtain spin-polarized electron transmission, the Zeeman effect is employed to produce spin-split energy states in quantum dots which are embedded in the arms of a mesoscopic Aharonov-Bohm (AB) ring heterostructure. The Zeeman splitting of the QD energy levels can be induced by a parallel magnetic field, or by a perpendicular field which also produces AB-effects. The combination of these effects on the transmission resonances of the structure is studied analytically and several parameter regimes are identified which produce a high degree of spin-polarized output. Contour and line plots of the weighted spin polarization as a function of electron energy and magnetic field are presented to visualize the degree of spin-polarization. Taking advantage of these unique parameter regimes shows the potential promise of such devices for producing spin-polarized currents.

  1. Conductivity of a spin-polarized two-dimensional hole gas at very low temperature

    Energy Technology Data Exchange (ETDEWEB)

    Dlimi, S., E-mail: kaaouachi21@yahoo.fr; Kaaouachi, A. El, E-mail: kaaouachi21@yahoo.fr; Limouny, L., E-mail: kaaouachi21@yahoo.fr; Sybous, A.; Narjis, A.; Errai, M.; Daoudi, E. [Research Group ESNPS , Physics department, University Ibn Zohr, Faculty of Sciences, B.P 8106, Hay Dakhla, 80000 Agadir (Morocco); Idrissi, H. El [Faculté des Sciences et Techniques de Mohammedia, Département de physique. BP 146 Quartier Yasmina Mohammedia (Morocco); Zatni, A. [Laboratoire MSTI. Ecole de technologied' Agadir, B.P33/S Agadir (Morocco)

    2014-01-27

    In the ballistic regime where k{sub B}Tτ / ħ ≥1, the temperature dependence of the metallic conductivity in a two-dimensional hole system of gallium arsenide, is found to change non-monotonically with the degree of spin polarization. In particular, it fades away just before the onset of complete spin polarization, but reappears again in the fully spin-polarized state, being, however, suppressed relative to the zero magnetic field case. The analysis of the degree of suppression can distinguish between screening and interaction-based theories. We show that in a fully polarized spin state, the effects of disorder are dominant and approach a strong localization regime, which is contrary to the behavior of 2D electron systems in a weakly disordered unpolarized state. It was found that the elastic relaxation time correction, depending on the temperature, changed significantly with the degree of spin polarization, to reach a minimum just below the start of the spin-polarized integer, where the conductivity is practically independent of temperature.

  2. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces

    International Nuclear Information System (INIS)

    Krueger, David

    2009-01-01

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  3. Development of a scanning tunneling potentiometry system for measurement of electronic transport at short length scales

    Science.gov (United States)

    Rozler, Michael

    It is clear that complete understanding of macroscopic properties of materials is impossible without a thorough knowledge of behavior at the smallest length scales. While the past 25 years have witnessed major advances in a variety of techniques that probe the nanoscale properties of matter, electrical transport measurements -- the heart of condensed matter research -- have lagged behind, never progressing beyond bulk measurements. This thesis describes a scanning tunneling potentiometry (STP) system developed to simultaneously map the transport-related electrochemical potential distribution of a biased sample along with its surface topography, extending electronic transport measurements to the nanoscale. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining atomic scale STM imaging, all at scan sizes of up to 15 microns. A mm-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. Use of carefully selected model materials, combined with excellent topographic and voltage resolution has allowed us to distinguish measurement artifacts caused by surface roughness from true potentiometric features, a major problem in previous STP measurements. The measurements demonstrate that STP can produce physically meaningful results for homogeneous transport as well as non-uniform conduction dominated by material microstructures. Measurements of several physically interesting materials systems are presented as well, revealing new behaviors at the smallest length sales. The results establish scanning tunneling potentiometry as a useful tool for physics and

  4. Scanning Tunneling Microscopy Evidence for the Dissociation of Carbon Monoxide on Ruthenium Steps

    DEFF Research Database (Denmark)

    Tison, Yann; Nielsen, Kenneth; Mowbray, Duncan J.

    2012-01-01

    –Tropsch processes under certain conditions, has been debated for years. Here, scanning tunneling microscopy (STM) and density functional theory (DFT) are used to clarify the role of monatomic steps in the splitting of CO on a stepped Ru(0 1 54) crystal, which displays alternating steps with either 4-fold or 3-fold...... symmetry. After CO doses at elevated temperatures, the STM images reveal step decorations characteristic of atomic oxygen resulting from CO dissociation on every second step. The comparison of the STM images with the results of DFT calculations shows that the step decoration occurs on the steps displaying...

  5. Dysprosium disilicide nanostructures on silicon(001) studied by scanning tunneling microscopy and transmission electron microscopy

    International Nuclear Information System (INIS)

    Ye Gangfeng; Nogami, Jun; Crimp, Martin A.

    2006-01-01

    The microstructure of self-assembled dysprosium silicide nanostructures on silicon(001) has been studied by scanning tunneling microscopy and transmission electron microscopy. The studies focused on nanostructures that involve multiple atomic layers of the silicide. Cross-sectional high resolution transmission electron microscopy images and fast Fourier transform analysis showed that both hexagonal and orthorhombic/tetragonal silicide phases were present. Both the magnitude and the anisotropy of lattice mismatch between the silicide and the substrate play roles in the morphology and epitaxial growth of the nanostructures formed

  6. Transport properties of magnetic atom bridges controlled by a scanning tunneling microscope

    International Nuclear Information System (INIS)

    Nakanishi, H.; Kishi, T.; Kasai, H.; Komori, F.; Okiji, A.

    2003-01-01

    We have investigated the transport and magnetic properties of the atom bridge made from magnetic materials, which is the atom-scale wire constructed between a scanning tunneling microscope (STM) tip and a solid surface, by the use of ab initio calculations. In the case of the twisted ladder structure atom bridge made of Fe, we have found that the magnetic state of the bridge changes from ferromagnetic to paramagnetic, as we compress the bridge in length. We report the spin dependent quantized conductance of the bridge. And we discuss the origin of a change in transport properties as we compress the bridge in length

  7. Development of a scanning tunneling microscope combined with a synchrotron radiation light source

    International Nuclear Information System (INIS)

    Hasegawa, Yukio; Okuda, Taichi; Eguchi, Toyoaki; Matsushima, Takeshi; Harasawa, Ayumi; Akiyama, Kotone; Kinoshita, Toyohiko

    2005-01-01

    We have developed a scanning tunneling microscope (STM) combined with a synchrotron-radiation light source (SR-STM) aiming at elemental analysis in a spatial resolution of STM. Using SR-STM atomically resolved STM images under the irradiation and also X-ray adsorption spectra clearly showing an adsorption edge of a substrate were successfully obtained by detecting photo-emitted electrons with the STM tip. In order to focus the probing area of the photo-induced current, a glass-coated metal tip sharpened with focused ion beam was used as a probe. The present situation and prospects of the instrument are discussed in this review. (author)

  8. Atomic force microscope-assisted scanning tunneling spectroscopy under ambient conditions.

    Science.gov (United States)

    Vakhshouri, Amin; Hashimoto, Katsushi; Hirayama, Yoshiro

    2014-12-01

    We have developed a method of atomic force microscopy (AFM)-assisted scanning tunneling spectroscopy (STS) under ambient conditions. An AFM function is used for rapid access to a selected position prior to performing STS. The AFM feedback is further used to suppress vertical thermal drift of the tip-sample distance during spectroscopy, enabling flexible and stable spectroscopy measurements at room temperature. © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

  9. Low temperature ultrahigh vacuum cross-sectional scanning tunneling microscope for luminescence measurements

    International Nuclear Information System (INIS)

    Khang, Yoonho; Park, Yeonjoon; Salmeron, Miquel; Weber, Eicke R.

    1999-01-01

    We have constructed a scanning tunneling microscope with simultaneous light collection capabilities in order to investigate the opto-electronic properties of semiconductors. The microscope has in situ sample cleavage mechanism for cross-sectional sample. In order to reach low temperature (4 K), we used a specially designed cryostat. The efficiency of light collection generated in the tip-surface junction was greatly improved by use of a small parabolic mirror with the tip located at its focal point. (c) 1999 American Institute of Physics

  10. Self-navigation of a scanning tunneling microscope tip toward a micron-sized graphene sample.

    Science.gov (United States)

    Li, Guohong; Luican, Adina; Andrei, Eva Y

    2011-07-01

    We demonstrate a simple capacitance-based method to quickly and efficiently locate micron-sized conductive samples, such as graphene flakes, on insulating substrates in a scanning tunneling microscope (STM). By using edge recognition, the method is designed to locate and to identify small features when the STM tip is far above the surface, allowing for crash-free search and navigation. The method can be implemented in any STM environment, even at low temperatures and in strong magnetic field, with minimal or no hardware modifications.

  11. Robust procedure for creating and characterizing the atomic structure of scanning tunneling microscope tips

    Directory of Open Access Journals (Sweden)

    Sumit Tewari

    2017-11-01

    Full Text Available Scanning tunneling microscopes (STM are used extensively for studying and manipulating matter at the atomic scale. In spite of the critical role of the STM tip, procedures for controlling the atomic-scale shape of STM tips have not been rigorously justified. Here, we present a method for preparing tips in situ while ensuring the crystalline structure and a reproducibly prepared tip structure up to the second atomic layer. We demonstrate a controlled evolution of such tips starting from undefined tip shapes.

  12. Probing the atomic structure of metallic nanoclusters with the tip of a scanning tunneling microscope.

    Science.gov (United States)

    Schouteden, Koen; Lauwaet, Koen; Janssens, Ewald; Barcaro, Giovanni; Fortunelli, Alessandro; Van Haesendonck, Chris; Lievens, Peter

    2014-02-21

    Preformed Co clusters with an average diameter of 2.5 nm are produced in the gas phase and are deposited under controlled ultra-high vacuum conditions onto a thin insulating NaCl film on Au(111). Relying on a combined experimental and theoretical investigation, we demonstrate visualization of the three-dimensional atomic structure of the Co clusters by high-resolution scanning tunneling microscopy (STM) using a Cl functionalized STM tip that can be obtained on the NaCl surface. More generally, use of a functionalized STM tip may allow for systematic atomic structure determination with STM of nanoparticles that are deposited on metal surfaces.

  13. A functional renormalization group application to the scanning tunneling microscopy experiment

    Directory of Open Access Journals (Sweden)

    José Juan Ramos Cárdenas

    2015-12-01

    Full Text Available We present a study of a system composed of a scanning tunneling microscope (STM tip coupled to an absorbed impurity on a host surface using the functional renormalization group (FRG. We include the effect of the STM tip as a correction to the self-energy in addition to the usual contribution of the host surface in the wide band limit. We calculate the differential conductance curves at two different lateral distances from the quantum impurity and find good qualitative agreement with STM experiments where the differential conductance curves evolve from an antiresonance to a Lorentzian shape.

  14. Plasmon-mediated circularly polarized luminescence of GaAs in a scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Mühlenberend, Svenja; Gruyters, Markus; Berndt, Richard, E-mail: berndt@physik.uni-kiel.de [Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität zu Kiel, 24098 Kiel (Germany)

    2015-12-14

    The electroluminescence from p-type GaAs(110) in a scanning tunneling microscope has been investigated at 6 K. Unexpectedly, high degrees of circular polarization have often been observed with ferromagnetic Ni tips and also with paramagnetic W and Ag tips. The data are interpreted in terms of two distinct excitation mechanisms. Electron injection generates intense luminescence with low polarization. Plasmon-mediated generation of electron-hole pairs leads to less intense emission, which, however, is highly polarized for many tips.

  15. Current–Voltage Characterization of Individual As-Grown Nanowires Using a Scanning Tunneling Microscope

    Science.gov (United States)

    2013-01-01

    Utilizing semiconductor nanowires for (opto)electronics requires exact knowledge of their current–voltage properties. We report accurate on-top imaging and I–V characterization of individual as-grown nanowires, using a subnanometer resolution scanning tunneling microscope with no need for additional microscopy tools, thus allowing versatile application. We form Ohmic contacts to InP and InAs nanowires without any sample processing, followed by quantitative measurements of diameter dependent I–V properties with a very small spread in measured values compared to standard techniques. PMID:24059470

  16. A scanning tunneling microscope break junction method with continuous bias modulation.

    Science.gov (United States)

    Beall, Edward; Yin, Xing; Waldeck, David H; Wierzbinski, Emil

    2015-09-28

    Single molecule conductance measurements on 1,8-octanedithiol were performed using the scanning tunneling microscope break junction method with an externally controlled modulation of the bias voltage. Application of an AC voltage is shown to improve the signal to noise ratio of low current (low conductance) measurements as compared to the DC bias method. The experimental results show that the current response of the molecule(s) trapped in the junction and the solvent media to the bias modulation can be qualitatively different. A model RC circuit which accommodates both the molecule and the solvent is proposed to analyze the data and extract a conductance for the molecule.

  17. Note: A quartz cell with Pt single crystal bead electrode for electrochemical scanning tunneling microscope measurements.

    Science.gov (United States)

    Xia, Zhigang; Wang, Jihao; Hou, Yubin; Lu, Qingyou

    2014-09-01

    In this paper, we provide and demonstrate a design of a unique cell with Pt single crystal bead electrode for electrochemical scanning tunneling microscope (ECSTM) measurements. The active metal Pt electrode can be protected from air contamination during the preparation process. The transparency of the cell allows the tip and bead to be aligned by direct observation. Based on this, a new and effective alignment method is introduced. The high-quality bead preparations through this new cell have been confirmed by the ECSTM images of Pt (111).

  18. First-principles modelling of scanning tunneling microscopy using non-equilibrium Green's functions

    DEFF Research Database (Denmark)

    Lin, H.P.; Rauba, J.M.C.; Thygesen, Kristian Sommer

    2010-01-01

    The investigation of electron transport processes in nano-scale architectures plays a crucial role in the development of surface chemistry and nano-technology. Experimentally, an important driving force within this research area has been the concurrent refinements of scanning tunneling microscopy...... into account. As an illustrating example we apply the NEGF-STM method to the Si(001)(2x1):H surface with sub-surface P doping and discuss the results in comparison to the Bardeen and Tersoff-Hamann methods....

  19. Scanning tunneling microscopy of monoatomic gold chains on vicinal Si(335) surface: experimental and theoretical study

    Energy Technology Data Exchange (ETDEWEB)

    Krawiec, M.; Kwapinski, T.; Jalochowski, M. [Institute of Physics and Nanotechnology Center, M. Curie-Sklodowska University, pl. M. Curie-Sklodowskiej 1, 20-031 Lublin (Poland)

    2005-02-01

    We study electronic and topographic properties of the Si(335) surface, containing Au wires parallel to the steps. We use scanning tunneling microscopy (STM) supplemented by reflection of high energy electron diffraction (RHEED) technique. The STM data show the space and voltage dependent oscillations of the distance between STM tip and the surface which can be explained within one band tight binding Hubbard model. We calculate the STM current using nonequilibrium Keldysh Green function formalism. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Epitaxial clusters studied by synchrotron x-ray diffraction and scanning tunneling microscopy

    DEFF Research Database (Denmark)

    Nielsen, M.; Feidenhans'l, R.; Rasmussen, F.B.

    1998-01-01

    Nanoscale clusters are often formed during heteroepitaxial crystal growth. Misfit between the lattice parameter of the substrate and the adsorbate stimulates the formation of regular clusters with a characteristic size. The well-known "hut-clusters" formed during the growth of Ge on Si(001) are a...... similar to the "hut clusters". We demonstrate that X-ray diffraction in combination with scanning tunneling microscopy can be used to determine the fundamental properties of such clusters. (C) 1998 Elsevier Science B.V. All rights reserved....

  1. Real-Space Analysis of Scanning Tunneling Microscopy Topography Datasets Using Sparse Modeling Approach

    Science.gov (United States)

    Miyama, Masamichi J.; Hukushima, Koji

    2018-04-01

    A sparse modeling approach is proposed for analyzing scanning tunneling microscopy topography data, which contain numerous peaks originating from the electron density of surface atoms and/or impurities. The method, based on the relevance vector machine with L1 regularization and k-means clustering, enables separation of the peaks and peak center positioning with accuracy beyond the resolution of the measurement grid. The validity and efficiency of the proposed method are demonstrated using synthetic data in comparison with the conventional least-squares method. An application of the proposed method to experimental data of a metallic oxide thin-film clearly indicates the existence of defects and corresponding local lattice distortions.

  2. Observation and Manipulation of Polymers by Scanning Tunneling and Atomic Force Microscopy

    Science.gov (United States)

    1988-07-13

    Observation and Manipulation of Polymers by Scanning Tunneling and Atomic Force Microscooy 12. PERSONAL AUTHOR(S) M.M. Dovek, T.R. Albrecht, S.W.J. Kuan, C.A...COUNT FIELD GOP SU8 -GROUP 19. ABSTRACT (Continue on reverse if ncosay and kIti1I by block numbor) ~AM\\~ v~~\\~A Dhe properties of monolayer films of...organic materi s are importantl i--V~ ety of technologies. We have employed the STM and AFM t study’ LanD~ ..-odgett films of a varie ’ty of polymers

  3. Current-voltage characterization of individual as-grown nanowires using a scanning tunneling microscope.

    Science.gov (United States)

    Timm, Rainer; Persson, Olof; Engberg, David L J; Fian, Alexander; Webb, James L; Wallentin, Jesper; Jönsson, Andreas; Borgström, Magnus T; Samuelson, Lars; Mikkelsen, Anders

    2013-11-13

    Utilizing semiconductor nanowires for (opto)electronics requires exact knowledge of their current-voltage properties. We report accurate on-top imaging and I-V characterization of individual as-grown nanowires, using a subnanometer resolution scanning tunneling microscope with no need for additional microscopy tools, thus allowing versatile application. We form Ohmic contacts to InP and InAs nanowires without any sample processing, followed by quantitative measurements of diameter dependent I-V properties with a very small spread in measured values compared to standard techniques.

  4. Scanning tunneling spectroscopy of MoS2 monolayer in presence of ethanol gas

    Science.gov (United States)

    Hosseini, Seyed Ali; Iraji zad, Azam; Berahman, Masoud; Aghakhani Mahyari, Farzaneh; Shokouh, Seyed Hossein Hosseini

    2018-04-01

    Due to high surface to volume ratio and tunable band gap, two dimensional (2D) layered materials such as MoS2, is good candidate for gas sensing applications. This research mainly focuses on variation of Density of States (DOS) of MoS2 monolayes caused by ethanol adsorption. The nanosheets are synthesized by liquid exfoliation, and then using Scanning Tunneling Spectroscopy (STS) and Density Functional Theory (DFT), local electronic characteristic such as DOS and band gap in non-vacuum condition are analyzed. The results show that ethanol adsorption enhances DOS and deform orbitals near the valence and conduction bands that increase transport of carriers on the sheet.

  5. Production of spin-polarized unstable nuclei by using polarized electron capture process

    International Nuclear Information System (INIS)

    Shimizu, S.

    1998-01-01

    Measurements of emitted radiation from spin polarized nuclei are used to get information on electromagnetic moment of ground state unstable nuclei together with spin or parity state of excited states of their decayed (daughter) nuclei. These data are known to be useful for experimental investigation into the structure of unstable nuclei far from the stability line. The present study aims to establish a general method applicable to 11 Be and 16 N nuclei. To produce spin polarization, a new method in which the electron spin polarization of Rb is firstly produced by laser pumping, then the electron is transferred to the unstable nuclear beam (RNB) when they passes through the Rb vapor is proposed. Finally the polarized RNB will be implanted into superfluid helium to remain with a long spin-relaxation time. Future experimental set up for the above measurement adopted in the available radioactive nuclear beam facilities is briefly described. (Ohno, S.)

  6. Nuclear spin polarized H and D by means of spin-exchange optical pumping

    Science.gov (United States)

    Stenger, Jörn; Grosshauser, Carsten; Kilian, Wolfgang; Nagengast, Wolfgang; Ranzenberger, Bernd; Rith, Klaus; Schmidt, Frank

    1998-01-01

    Optically pumped spin-exchange sources for polarized hydrogen and deuterium atoms have been demonstrated to yield high atomic flow and high electron spin polarization. For maximum nuclear polarization the source has to be operated in spin temperature equilibrium, which has already been demonstrated for hydrogen. In spin temperature equilibrium the nuclear spin polarization PI equals the electron spin polarization PS for hydrogen and is even larger than PS for deuterium. We discuss the general properties of spin temperature equilibrium for a sample of deuterium atoms. One result are the equations PI=4PS/(3+PS2) and Pzz=PSṡPI, where Pzz is the nuclear tensor polarization. Furthermore we demonstrate that the deuterium atoms from our source are in spin temperature equilibrium within the experimental accuracy.

  7. Design and performance of a spin-polarized electron energy loss spectrometer with high momentum resolution

    Energy Technology Data Exchange (ETDEWEB)

    Vasilyev, D.; Kirschner, J. [Max-Planck-Institut für Mikrostrukturphysik, Weinberg 2, 06120 Halle (Germany)

    2016-08-15

    We describe a new “complete” spin-polarized electron energy loss spectrometer comprising a spin-polarized primary electron source, an imaging electron analyzer, and a spin analyzer of the “spin-polarizing mirror” type. Unlike previous instruments, we have a high momentum resolution of less than 0.04 Å{sup −1}, at an energy resolution of 90-130 meV. Unlike all previous studies which reported rather broad featureless data in both energy and angle dependence, we find richly structured spectra depending sensitively on small changes of the primary energy, the kinetic energy after scattering, and of the angle of incidence. The key factor is the momentum resolution.

  8. Effects of spin-polarized current on pulse field-induced precessional magnetization reversal

    Directory of Open Access Journals (Sweden)

    Guang-fu Zhang

    2012-12-01

    Full Text Available We investigate effects of a small DC spin-polarized current on the pulse field-induced precessional magnetization reversal in a thin elliptic magnetic element by micromagnetic simulations. We find that the spin-polarized current not only broadens the time window of the pulse duration, in which a successful precessional reversal is achievable, but also significantly suppresses the magnetization ringing after the reversal. The pulse time window as well as the decay rate of the ringing increase with increasing the current density. When a spin-polarized current with 5 MA/cm2 is applied, the time window increases from 80 ps to 112 ps, and the relaxation time of the ringing decreases from 1.1 ns to 0.32 ns. Our results provide useful information to achieve magnetic nanodevices based on precessional switching.

  9. Spin-Polarized Hybridization at the interface between different 8-hydroxyquinolates and the Cr(001) surface

    Science.gov (United States)

    Wang, Jingying; Deloach, Andrew; Dougherty, Daniel B.; Dougherty Lab Team

    Organic materials attract a lot of attention due to their promising applications in spintronic devices. It is realized that spin-polarized metal/organic interfacial hybridization plays an important role to improve efficiency of organic spintronic devices. Hybridized interfacial states help to increase spin injection at the interface. Here we report spin-resolved STM measurements of single tris(8-hydroxyquinolinato) aluminum molecules adsorbed on the antiferromagnetic Cr(001). Our observations show a spin-polarized interface state between Alq3 and Cr(001). Tris(8-hydroxyquinolinato) chromium has also been studied and compared with Alq3, which exhibits different spin-polarized hybridization with the Cr(001) surface state than Alq3. We attribute the differences to different character of molecular orbitals in the two different quinolates.

  10. Spin Dynamics in Highly Spin Polarized Co1-xFexS2

    Science.gov (United States)

    Hoch, Michael J. R.; Kuhns, Philip L.; Moulton, William G.; Reyes, Arneil P.; Lu, Jun; Wang, Lan; Leighton, Chris

    2006-09-01

    Highly spin polarized or half-metallic systems are of considerable current interest because of their potential for spin injection in spintronics applications. The ferromagnet (FM) CoS2 is close to being a half-metal. Recent theoretical and experimental work has shown that the alloys Co1-xFexS2 (0.07 < x < 0.9) are highly spin polarized at low temperatures. The Fe concentration may be used to tune the spin polarization. Using 59Co FM- NMR we have investigated the spin dynamics in this family of alloys and have obtained information on the evolution of the d-band density of states at the Fermi level with x in the range 0 to 0.3. The results are compared with available theoretical predictions.

  11. Scanning tunneling spectroscopy on vortex cores in high-T{sub c} superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Hoogenboom, B.W.; Maggio-Aprile, I.; Fischer, Oe. [Geneva Univ. (Switzerland). Dept. de Physique de la Matiere Condensee; Renner, C. [NEC Research Inst., Princeton, NJ (United States)

    2002-07-01

    Scanning tunneling spectroscopy (STS) with its unique capacity for tunneling spectroscopy with sub-nanometer spatial resolution, has opened new ways to look at the flux lines and their distribution in superconductors. In contrast to all other imaging techniques, which are sensitive to the local magnetic field, STM relies on local changes in the density of states near the Fermi level to generate a real space image of the vortex distribution. It is thus sensitive to the vortex cores, which in high temperature superconductors have a size approaching the interatomic distances. The small size of the vortex cores and the anisotropic character of the high temperature superconductors allow pinning to play a large role in determining the vortex core positions. Vortex hopping between different pinning sites, again down to a sub-nanometer scale, has been studied by STM imaging as a function of time. These studies give microscopic indications for quantum tunneling of vortices. Moreover, STM provides new insights into the detailed electronic vortex core structure, revealing localized quasiparticles. (orig.)

  12. Calibration of tip and sample temperature of a scanning tunneling microscope using a superconductive sample

    Energy Technology Data Exchange (ETDEWEB)

    Stocker, Matthias; Pfeifer, Holger; Koslowski, Berndt, E-mail: berndt.koslowski@uni-ulm.de [Institute of Solid State Physics, University of Ulm, D-89069 Ulm (Germany)

    2014-05-15

    The temperature of the electrodes is a crucial parameter in virtually all tunneling experiments. The temperature not only controls the thermodynamic state of the electrodes but also causes thermal broadening, which limits the energy resolution. Unfortunately, the construction of many scanning tunneling microscopes inherits a weak thermal link between tip and sample in order to make one side movable. Such, the temperature of that electrode is badly defined. Here, the authors present a procedure to calibrate the tip temperature by very simple means. The authors use a superconducting sample (Nb) and a standard tip made from W. Due to the asymmetry in the density of states of the superconductor (SC)—normal metal (NM) tunneling junction, the SC temperature controls predominantly the density of states while the NM controls the thermal smearing. By numerically simulating the I-V curves and numerically optimizing the tip temperature and the SC gap width, the tip temperature can be accurately deduced if the sample temperature is known or measureable. In our case, the temperature dependence of the SC gap may serve as a temperature sensor, leading to an accurate NM temperature even if the SC temperature is unknown.

  13. Calibration of tip and sample temperature of a scanning tunneling microscope using a superconductive sample

    International Nuclear Information System (INIS)

    Stocker, Matthias; Pfeifer, Holger; Koslowski, Berndt

    2014-01-01

    The temperature of the electrodes is a crucial parameter in virtually all tunneling experiments. The temperature not only controls the thermodynamic state of the electrodes but also causes thermal broadening, which limits the energy resolution. Unfortunately, the construction of many scanning tunneling microscopes inherits a weak thermal link between tip and sample in order to make one side movable. Such, the temperature of that electrode is badly defined. Here, the authors present a procedure to calibrate the tip temperature by very simple means. The authors use a superconducting sample (Nb) and a standard tip made from W. Due to the asymmetry in the density of states of the superconductor (SC)—normal metal (NM) tunneling junction, the SC temperature controls predominantly the density of states while the NM controls the thermal smearing. By numerically simulating the I-V curves and numerically optimizing the tip temperature and the SC gap width, the tip temperature can be accurately deduced if the sample temperature is known or measureable. In our case, the temperature dependence of the SC gap may serve as a temperature sensor, leading to an accurate NM temperature even if the SC temperature is unknown

  14. Tunneling Mode of Scanning Electrochemical Microscopy: Probing Electrochemical Processes at Single Nanoparticles.

    Science.gov (United States)

    Sun, Tong; Wang, Dengchao; Mirkin, Michael V

    2018-06-18

    Electrochemical experiments at individual nanoparticles (NPs) can provide new insights into their structure-activity relationships. By using small nanoelectrodes as tips in a scanning electrochemical microscope (SECM), we recently imaged individual surface-bound 10-50 nm metal NPs. Herein, we introduce a new mode of SECM operation based on tunneling between the tip and a nanoparticle immobilized on the insulating surface. The obtained current vs. distance curves show the transition from the conventional feedback response to electron tunneling between the tip and the NP at separation distances of less than about 3 nm. In addition to high-resolution imaging of the NP topography, the tunneling mode enables measurement of the heterogeneous kinetics at a single NP without making an ohmic contact with it. The developed method should be useful for studying the effects of nanoparticle size and geometry on electrocatalytic activity in real-world applications. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

    International Nuclear Information System (INIS)

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

    2014-01-01

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

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2014-04-15

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

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

    Science.gov (United States)

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

    2014-04-01

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

  18. Note: Electron energy spectroscopy mapping of surface with scanning tunneling microscope.

    Science.gov (United States)

    Li, Meng; Xu, Chunkai; Zhang, Panke; Li, Zhean; Chen, Xiangjun

    2016-08-01

    We report a novel scanning probe electron energy spectrometer (SPEES) which combines a double toroidal analyzer with a scanning tunneling microscope to achieve both topography imaging and electron energy spectroscopy mapping of surface in situ. The spatial resolution of spectroscopy mapping is determined to be better than 0.7 ± 0.2 μm at a tip sample distance of 7 μm. Meanwhile, the size of the field emission electron beam spot on the surface is also measured, and is about 3.6 ± 0.8 μm in diameter. This unambiguously demonstrates that the spatial resolution of SPEES technique can be much better than the size of the incident electron beam.

  19. Note: Electron energy spectroscopy mapping of surface with scanning tunneling microscope

    Energy Technology Data Exchange (ETDEWEB)

    Li, Meng; Xu, Chunkai, E-mail: xuck@ustc.edu.cn, E-mail: xjun@ustc.edu.cn; Zhang, Panke; Li, Zhean; Chen, Xiangjun, E-mail: xuck@ustc.edu.cn, E-mail: xjun@ustc.edu.cn [Hefei National Laboratory for Physical Science at Microscale and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, China and Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China, Hefei 230026 (China)

    2016-08-15

    We report a novel scanning probe electron energy spectrometer (SPEES) which combines a double toroidal analyzer with a scanning tunneling microscope to achieve both topography imaging and electron energy spectroscopy mapping of surface in situ. The spatial resolution of spectroscopy mapping is determined to be better than 0.7 ± 0.2 μm at a tip sample distance of 7 μm. Meanwhile, the size of the field emission electron beam spot on the surface is also measured, and is about 3.6 ± 0.8 μm in diameter. This unambiguously demonstrates that the spatial resolution of SPEES technique can be much better than the size of the incident electron beam.

  20. Note: Electron energy spectroscopy mapping of surface with scanning tunneling microscope

    International Nuclear Information System (INIS)

    Li, Meng; Xu, Chunkai; Zhang, Panke; Li, Zhean; Chen, Xiangjun

    2016-01-01

    We report a novel scanning probe electron energy spectrometer (SPEES) which combines a double toroidal analyzer with a scanning tunneling microscope to achieve both topography imaging and electron energy spectroscopy mapping of surface in situ. The spatial resolution of spectroscopy mapping is determined to be better than 0.7 ± 0.2 μm at a tip sample distance of 7 μm. Meanwhile, the size of the field emission electron beam spot on the surface is also measured, and is about 3.6 ± 0.8 μm in diameter. This unambiguously demonstrates that the spatial resolution of SPEES technique can be much better than the size of the incident electron beam.

  1. Ultra compact multitip scanning tunneling microscope with a diameter of 50 mm.

    Science.gov (United States)

    Cherepanov, Vasily; Zubkov, Evgeny; Junker, Hubertus; Korte, Stefan; Blab, Marcus; Coenen, Peter; Voigtländer, Bert

    2012-03-01

    We present a multitip scanning tunneling microscope (STM) where four independent STM units are integrated on a diameter of 50 mm. The coarse positioning of the tips is done under the control of an optical microscope or scanning electron microscopy in vacuum. The heart of this STM is a new type of piezoelectric coarse approach called KoalaDrive. The compactness of the KoalaDrive allows building a four-tip STM as small as a single-tip STM with a drift of less than 0.2 nm/min at room temperature and lowest resonance frequencies of 2.5 kHz (xy) and 5.5 kHz (z). We present as examples of the performance of the multitip STM four point measurements of silicide nanowires and graphene.

  2. Variable-temperature independently driven four-tip scanning tunneling microscope

    International Nuclear Information System (INIS)

    Hobara, Rei; Nagamura, Naoka; Hasegawa, Shuji; Matsuda, Iwao; Yamamoto, Yuko; Miyatake, Yutaka; Nagamura, Toshihiko

    2007-01-01

    The authors have developed an ultrahigh vacuum (UHV) variable-temperature four-tip scanning tunneling microscope (STM), operating from room temperature down to 7 K, combined with a scanning electron microscope (SEM). Four STM tips are mechanically and electrically independent and capable of positioning in arbitrary configurations in nanometer precision. An integrated controller system for both of the multitip STM and SEM with a single computer has also been developed, which enables the four tips to operate either for STM imaging independently and for four-point probe (4PP) conductivity measurements cooperatively. Atomic-resolution STM images of graphite were obtained simultaneously by the four tips. Conductivity measurements by 4PP method were also performed at various temperatures with the four tips in square arrangement with direct contact to the sample surface

  3. Spontaneous spin-polarization and phase transition in the relativistic approach

    International Nuclear Information System (INIS)

    Maruyama, Tomoyuki; Tatsumi, Toshitaka

    2001-01-01

    We study the spin-polarization mechanism in the highly dense nuclear matter with the relativistic mean-field approach. In the relativistic Hartree-Fock framework we find that there are two kinds of spin-spin interaction channels, which are the axial-vector and tensor exchange ones. If each interaction is strong and different sign, the system loses the spherical symmetry and holds the spin-polarization in the high-density region. When the axial-vector interaction is negative enough, the system holds ferromagnetism. (author)

  4. Generation and control of spin-polarized photocurrents in GaMnAs heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Bezerra, Anibal T., E-mail: anibal@df.ufscar.br; Farinas, Paulo F.; Studart, Nelson [Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, SP (Brazil); DISSE - Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores, CNPq/MCT, Rio de Janeiro, RJ (Brazil); Castelano, Leonardo K. [Departamento de Física, Universidade Federal de São Carlos, 13565-905 São Carlos, SP (Brazil); Degani, Marcos H.; Maialle, Marcelo Z. [Faculdade de Ciências Aplicadas, Universidade Estadual de Campinas, 13484-350 Limeira, SP (Brazil); DISSE - Instituto Nacional de Ciência e Tecnologia de Nanodispositivos Semicondutores, CNPq/MCT, Rio de Janeiro, RJ (Brazil)

    2014-01-13

    Photocurrents are calculated for a specially designed GaMnAs semiconductor heterostructure. The results reveal regions in the infrared range of the energy spectrum, in which the proposed structure is remarkably spin-selective. For such photon energies, the generated photocurrents are strongly spin-polarized. Application of a relatively small static bias in the growth direction of the structure is predicted to efficiently reverse the spin-polarization for some photon energies. This behavior suggests the possibility of conveniently simple switching mechanisms. The physics underlying the results is studied and understood in terms of the spin-dependent properties emerging from the particular potential profile of the structure.

  5. A qualitative study of spin polarization effect in defect tuned Co/graphene/Co nanostructures

    Science.gov (United States)

    Mandal, Sumit; Saha, Shyamal K.

    2014-10-01

    Theoretical reports predict that in contact with a ferromagnetic giant spin, spin polarization evolves in defective graphene since defects in graphene act as local spin moments. We have synthesized different Co/graphene/Co nano spin valve like structures tuning the degree of defect applying ultrasonic vibration and characterized them by Raman spectroscopy. Initially with increasing ID/IG ratio in Raman spectra, antiferromagnetic coupling between the Co nanosheets on either sides of graphene enhances leading to betterment in spin transport through graphene. But for highest ID/IG, a totally new phenomenon called antiferro quadrupolar ordering (AFQ) takes place which eventually reduces the spin polarization effect.

  6. Hardness and softness reactivity kernels within the spin-polarized density-functional theory

    International Nuclear Information System (INIS)

    Chamorro, Eduardo; De Proft, Frank; Geerlings, Paul

    2005-01-01

    Generalized hardness and softness reactivity kernels are defined within a spin-polarized density-functional theory (SP-DFT) conceptual framework. These quantities constitute the basis for the global, local (i.e., r-position dependent), and nonlocal (i.e., r and r ' -position dependents) indices devoted to the treatment of both charge-transfer and spin-polarization processes in such a reactivity framework. The exact relationships between these descriptors within a SP-DFT framework are derived and the implications for chemical reactivity in such context are outlined

  7. Peculiarities of spin polarization inversion at a thiophene/cobalt interface

    KAUST Repository

    Wang, Xuhui

    2013-03-20

    We perform ab initio calculations to investigate the spin polarization at the interface between a thiophene molecule and cobalt substrate. We find that the reduced symmetry in the presence of a sulfur atom (in the thiophene molecule) leads to a strong spatial dependence of the spin polarization of the molecule. The two carbon atoms far from the sulfur acquire a polarization opposite to that of the substrate, while the carbon atoms bonded directly to sulfur possess the same polarization as the substrate. We determine the origin of this peculiar spin interface property as well as its impact on the spin transport.

  8. Magnetic x-ray circular dichroism in spin-polarized photoelectron diffraction

    International Nuclear Information System (INIS)

    Waddill, G.D.; Tobin, J.G.

    1994-01-01

    The first structural determination with spin-polarized, energy-dependent photoelectron diffraction using circularly-polarized x-rays is reported for Fe films on Cu(001). Circularly-polarized x-rays produced spin-polarized photoelectrons from the Fe 2p doublet, and intensity asymmetries in the 2p 3/2 level are observed. Fully spin-specific multiple scattering calculations reproduced the experimentally-determined energy and angular dependences. A new analytical procedure which focuses upon intensity variations due to spin-dependent diffraction is introduced. A sensitivity to local geometric and magnetic structure is demonstrated

  9. Construction of the spin-polarized slow positron beam with the RI source

    Energy Technology Data Exchange (ETDEWEB)

    Nakajyo, Terunobu; Tashiro, Mutsumi; Kanazawa, Ikuzo [Tokyo Gakugei Univ., Koganei (Japan); Komori, Fumio; Murata, Yoshimasa; Ito, Yasuo

    1997-03-01

    The electrostatic slow-positron beam is constructed by using {sup 22}Na source. We design the electrostatic lens, the system of the detector, and the Wien filter for the experiment`s system of the spin-polarized slow positron beam. The reemitted spin-polarized slow-positron spectroscopy is proposed for studying magnetic thin films and magnetic multilayers. We calculated the depolarized positron fractions in the Fe thin film Fe(10nm)/Cu(substrate) and the multilayers Cu(1nm)/Fe(10nm)/Cu(substrate). (author)

  10. High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat.

    Science.gov (United States)

    Hackley, Jason D; Kislitsyn, Dmitry A; Beaman, Daniel K; Ulrich, Stefan; Nazin, George V

    2014-10-01

    We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale.

  11. High-stability cryogenic scanning tunneling microscope based on a closed-cycle cryostat

    Energy Technology Data Exchange (ETDEWEB)

    Hackley, Jason D.; Kislitsyn, Dmitry A.; Beaman, Daniel K.; Nazin, George V., E-mail: gnazin@uoregon.edu [Department of Chemistry and Biochemistry, 1253 University of Oregon, Eugene, Oregon 97403 (United States); Ulrich, Stefan [RHK Technology, Inc., 1050 East Maple Road, Troy, Michigan 48083 (United States)

    2014-10-15

    We report on the design and operation of a cryogenic ultra-high vacuum (UHV) scanning tunneling microscope (STM) coupled to a closed-cycle cryostat (CCC). The STM is thermally linked to the CCC through helium exchange gas confined inside a volume enclosed by highly flexible rubber bellows. The STM is thus mechanically decoupled from the CCC, which results in a significant reduction of the mechanical noise transferred from the CCC to the STM. Noise analysis of the tunneling current shows current fluctuations up to 4% of the total current, which translates into tip-sample distance variations of up to 1.5 picometers. This noise level is sufficiently low for atomic-resolution imaging of a wide variety of surfaces. To demonstrate this, atomic-resolution images of Au(111) and NaCl(100)/Au(111) surfaces, as well as of carbon nanotubes deposited on Au(111), were obtained. Thermal drift analysis showed that under optimized conditions, the lateral stability of the STM scanner can be as low as 0.18 Å/h. Scanning Tunneling Spectroscopy measurements based on the lock-in technique were also carried out, and showed no detectable presence of noise from the closed-cycle cryostat. Using this cooling approach, temperatures as low as 16 K at the STM scanner have been achieved, with the complete cool-down of the system typically taking up to 12 h. These results demonstrate that the constructed CCC-coupled STM is a highly stable instrument capable of highly detailed spectroscopic investigations of materials and surfaces at the atomic scale.

  12. A compact combined ultrahigh vacuum scanning tunnelling microscope (UHV STM) and near-field optical microscope

    International Nuclear Information System (INIS)

    Woolley, R A J; Hayton, J A; Cavill, S; Ma, Jin; Beton, P H; Moriarty, P

    2008-01-01

    We have designed and constructed a hybrid scanning near-field optical microscope (SNOM)–scanning tunnelling microscope (STM) instrument which operates under ultrahigh vacuum (UHV) conditions. Indium tin oxide (ITO)-coated fibre-optic tips capable of high quality STM imaging and tunnelling spectroscopy are fabricated using a simple and reliable method which foregoes the electroless plating strategy previously employed by other groups. The fabrication process is reproducible, producing robust tips which may be exchanged under UHV conditions. We show that controlled contact with metal surfaces considerably enhances the STM imaging capabilities of fibre-optic tips. Light collection (from the cleaved back face of the ITO-coated fibre-optic tip) and optical alignment are facilitated by a simple two-lens arrangement where the in-vacuum collimation/collection lens may be adjusted using a slip-stick motor. A second in-air lens focuses the light (which emerges from the UHV system as a parallel beam) onto a cooled CCD spectrograph or photomultiplier tube. The application of the instrument to combined optical and electronic spectroscopy of Au and GaAs surfaces is discussed

  13. Probing Single Nanometer-scale Particles with Scanning Tunneling Microscopy and Spectroscopies

    International Nuclear Information System (INIS)

    McCarty, G.S.; Love, J.C.; Kushmerick, J.G.; Charles, L.F.; Keating, C.D.; Toleno, B.J.; Lyn, M.E.; Castleman, A.W.; Natan, M.J.; Weiss, P.S.

    1999-01-01

    Scanning tunneling microscopy can be used to isolate single particles on surfaces for further study. Local optical and electronic properties coupled with topographic information collected by the scanning tunneling microscope (STM) give insight into the intrinsic properties of the species under study. Since each spectroscopic measurement is done on a single particle, each sample is 'monodisperse', regardless of the degree of heterogeneity of the original preparation. We illustrate this with three example systems - a metal cluster of known atomic structure, metal nanoparticles dispersed from colloid suspensions, and metallocarbohedrenes (Met-Cars) deposited with other reaction products. Au and Ag nanoparticles were imaged using a photon emission STM. The threshold voltage, the lowest bias voltage at which photons are produced, was determined for Au nanoparticles. Electronic spectra of small clusters of Ni atoms on MoS 2 were recorded. Preliminary images of Zr-based Met-Car-containing soot were obtained on Au and MoS 2 substrates and partial electronic spectra were recorded of these possible Met-Car particles

  14. Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

    Science.gov (United States)

    Jung, Han Sae; Tsai, Hsin-Zon; Wong, Dillon; Germany, Chad; Kahn, Salman; Kim, Youngkyou; Aikawa, Andrew S.; Desai, Dhruv K.; Rodgers, Griffin F.; Bradley, Aaron J.; Velasco, Jairo; Watanabe, Kenji; Taniguchi, Takashi; Wang, Feng; Zettl, Alex; Crommie, Michael F.

    2015-01-01

    Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene’s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene's electronic structure in the presence of a charged impurity. The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene’s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices. PMID:26273961

  15. Dielectric breakdown of ultrathin aluminum oxide films induced by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Magtoto, N. P.; Niu, C.; Ekstrom, B. M.; Addepalli, S.; Kelber, J. A.

    2000-01-01

    Dielectric breakdown of 7-Aa-thick Al 2 O 3 (111) films grown on Ni 3 Al(111) under ultrahigh vacuum conditions is induced by increasing the bias voltage on the scanning tunneling microscopy tip under constant current feedback. Breakdown is marked by the precipitous retreat of the tip from the surface, and the formation of an elevated feature in the scanning tunneling microscopy image, typically greater than 5 nm high and ∼100 nm in diameter. Constant height measurements performed at tip/sample distances of 1 nm or less yield no tip/substrate physical interaction, indicating that such features do not result from mass transport. Consistent with this, current/voltage measurements within the affected regions indicate linear behavior, in contrast to a band gap of 1.5 eV observed at unaffected regions of the oxide surface. A threshold electric field value of 11±1 MV cm -1 is required to induce breakdown, in good agreement with extrapolated values from capacitance measurements on thicker oxides. (c) 2000 American Institute of Physics

  16. Scanning tunneling microscopy on iron-chalcogenide superconductor Fe(Se, Te) single crystal

    International Nuclear Information System (INIS)

    Ukita, R.; Sugimoto, A.; Ekino, T.

    2011-01-01

    We show scanning tunneling microscopy/spectroscopy (STM/STS) results of Fe(Se, Te). STM topography shows square arrangements of spots with the lattice spacing 0.37 nm. Te and Se atoms are randomly distributed in the STM topography. The STM topography of FeTe exhibits clusters of separated iron atoms. We have investigated the iron-chalcogenide superconductor Fe(Se, Te) using a low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) technique. STM topography at 4.9 K shows clear regular square arrangements of spots with the lattice spacing ∼0.37 nm, from which what we observe are attributed to Se or Te atomic plane. In the topography, brighter and darker atomic spots are randomly distributed, which are most probably due to Te and Se atoms, respectively. For the FeTe compound, the topography exhibits clusters of the bright spots probably arising from separated iron atoms distributing over several Te lattice sites. The STS measurements clarify the existence of the large-size gap with 2Δ = 0.4-0.6 eV.

  17. Temperature Dependent Electron Transport Properties of Gold Nanoparticles and Composites: Scanning Tunneling Spectroscopy Investigations.

    Science.gov (United States)

    Patil, Sumati; Datar, Suwarna; Dharmadhikari, C V

    2018-03-01

    Scanning tunneling spectroscopy (STS) is used for investigating variations in electronic properties of gold nanoparticles (AuNPs) and its composite with urethane-methacrylate comb polymer (UMCP) as function of temperature. Films are prepared by drop casting AuNPs and UMCP in desired manner on silicon substrates. Samples are further analyzed for morphology under scanning electron microscopy (SEM) and atomic force microscopy (AFM). STS measurements performed in temperature range of 33 °C to 142 °C show systematic variation in current versus voltage (I-V) curves, exhibiting semiconducting to metallic transition/Schottky behavior for different samples, depending upon preparation method and as function of temperature. During current versus time (I-t) measurement for AuNPs, random telegraphic noise is observed at room temperature. Random switching of tunneling current between two discrete levels is observed for this sample. Power spectra derived from I-t show 1/f2 dependence. Statistical analysis of fluctuations shows exponential behavior with time width τ ≈ 7 ms. Local density of states (LDOS) plots derived from I-V curves of each sample show systematic shift in valance/conduction band edge towards/away from Fermi level, with respect to increase in temperature. Schottky emission is best fitted electron emission mechanism for all samples over certain range of bias voltage. Schottky plots are used to calculate barrier heights and temperature dependent measurements helped in measuring activation energies for electron transport in all samples.

  18. Manipulating individual dichlorotin phthalocyanine molecules on Cu(100) surface at room temperature by scanning tunneling microscopy

    International Nuclear Information System (INIS)

    Li, Chao; Xiang, Feifei; Wang, Zhongping; Liu, Xiaoqing; Jiang, Danfeng; Wang, Li; Wang, Guang; Zhang, Xueao; Chen, Wei

    2014-01-01

    Single molecule manipulations have been achieved on dichlorotin phthalocyanine(SnCl 2 Pc) molecules adsorbed on Cu (100) at room temperature. Scanning tunneling microscopy observations directly demonstrate that the individual SnCl 2 Pc molecules can be moved along the [100] direction on Cu(100) surface by employing a scanning tunneling microscope tip fixed at the special position of the molecules. The orientation of the molecule can be switched between two angles of ±28° with respect to the [011] surface direction in the same way. Dependences of the probability of molecular motion on the distances between the tip and the molecules reveal that the mechanism for such manipulation of a SnCl 2 Pc molecule is dominated by the repulsive interactions between the tip and the molecules. With the assistance of this manipulation process, a prototype molecular storage array with molecular orientation as information carrier and an artificial hydrogen bonded supramolecular structure have been constructed on the surface. (paper)

  19. Realization of a four-step molecular switch in scanning tunneling microscope manipulation of single chlorophyll-a molecules

    Science.gov (United States)

    Iancu, Violeta; Hla, Saw-Wai

    2006-01-01

    Single chlorophyll-a molecules, a vital resource for the sustenance of life on Earth, have been investigated by using scanning tunneling microscope manipulation and spectroscopy on a gold substrate at 4.6 K. Chlorophyll-a binds on Au(111) via its porphyrin unit while the phytyl-chain is elevated from the surface by the support of four CH3 groups. By injecting tunneling electrons from the scanning tunneling microscope tip, we are able to bend the phytyl-chain, which enables the switching of four molecular conformations in a controlled manner. Statistical analyses and structural calculations reveal that all reversible switching mechanisms are initiated by a single tunneling-electron energy-transfer process, which induces bond rotation within the phytyl-chain. PMID:16954201

  20. Shot noise as a probe of spin-polarized transport through single atoms

    DEFF Research Database (Denmark)

    Burtzlaff, Andreas; Weismann, Alexander; Brandbyge, Mads

    2015-01-01

    Single atoms on Au(111) surfaces have been contacted with the Au tip of a low temperature scanning tunneling microscope. The shot noise of the current through these contacts has been measured up to frequencies of 120 kHz and Fano factors have been determined to characterize the transport channels...

  1. A scanning tunneling microscopy based potentiometry technique and its application to the local sensing of the spin Hall effect

    Directory of Open Access Journals (Sweden)

    Ting Xie

    2017-12-01

    Full Text Available A scanning tunneling microscopy based potentiometry technique for the measurements of the local surface electric potential is presented. A voltage compensation circuit based on this potentiometry technique is developed and employed to maintain a desired tunneling voltage independent of the bias current flow through the film. The application of this potentiometry technique to the local sensing of the spin Hall effect is outlined and some experimental results are reported.

  2. Spin-polarized quantum transport properties through flexible phosphorene

    Science.gov (United States)

    Chen, Mingyan; Yu, Zhizhou; Xie, Yiqun; Wang, Yin

    2016-10-01

    We report a first-principles study on the tunnel magnetoresistance (TMR) and spin-injection efficiency (SIE) through phosphorene with nickel electrodes under the mechanical tension and bending on the phosphorene region. Both the TMR and SIE are largely improved under these mechanical deformations. For the uniaxial tension (ɛy) varying from 0% to 15% applied along the armchair transport (y-)direction of the phosphorene, the TMR ratio is enhanced with a maximum of 107% at ɛy = 10%, while the SIE increases monotonously from 8% up to 43% with the increasing of the strain. Under the out-of-plane bending, the TMR overall increases from 7% to 50% within the bending ratio of 0%-3.9%, and meanwhile the SIE is largely improved to around 70%, as compared to that (30%) of the flat phosphorene. Such behaviors of the TMR and SIE are mainly affected by the transmission of spin-up electrons in the parallel configuration, which is highly dependent on the applied mechanical tension and bending. Our results indicate that the phosphorene based tunnel junctions have promising applications in flexible electronics.

  3. The Utilization of Spin Polarized Photoelectron Spectroscopy as a Probe of Electron Correlation with an Ultimate Goal of Pu

    International Nuclear Information System (INIS)

    Tobin, James; Yu, Sung; Chung, Brandon; Morton, Simon; Komesu, Takashi; Waddill, George

    2008-01-01

    We are developing the technique of spin-polarized photoelectron spectroscopy as a probe of electron correlation with the ultimate goal of resolving the Pu electronic structure controversy. Over the last several years, we have demonstrated the utility of spin polarized photoelectron spectroscopy for determining the fine details of the electronic structure in complex systems such as those shown in the paper.

  4. Tuning Fermi level of Cr{sub 2}CoZ (Z=Al and Si) inverse Heusler alloys via Fe-doping for maximum spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mukhtiyar [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Saini, Hardev S. [Department of Physics, Panjab University, Chandigarh-160014 (India); Thakur, Jyoti [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India); Reshak, Ali H. [New Technologies—Research Center, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); Center of Excellence Geopolymer and Green Technology, School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra-136119, Haryana (India)

    2014-12-15

    We report full potential treatment of electronic and magnetic properties of Cr{sub 2−x}Fe{sub x}CoZ (Z=Al, Si) Heusler alloys where x=0.0, 0.25, 0.5, 0.75 and 1.0, based on density functional theory (DFT). Both parent alloys (Cr{sub 2}CoAl and Cr{sub 2}CoSi) are not half-metallic frromagnets. The gradual replacement of one Cr sublattice with Fe induces the half-metallicity in these systems, resulting maximum spin polarization. The half-metallicity starts to appear in Cr{sub 2−x}Fe{sub x}CoAl and Cr{sub 2−x}Fe{sub x}CoSi with x=0.50 and x=0.25, respectively, and the values of minority-spin gap and half-metallic gap or spin-flip gap increase with further increase of x. These gaps are found to be maximum for x=1.0 for both cases. An excellent agreement between the structural properties of CoFeCrAl with available experimental study is obtained. The Fermi level tuning by Fe-doping makes these alloys highly spin polarized and thus these can be used as promising candidates for spin valves and magnetic tunnelling junction applications. - Highlights: • Tuning of E{sub F} in Cr{sub 2}CoZ (Z=Al, Si) has been demonstrated via Fe doping. • Effect of Fe doping on half-metallicity and magnetism have been discussed. • The new alloys have a potential of being used as spin polarized electrodes.

  5. Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields

    International Nuclear Information System (INIS)

    Lima, E A; Weiss, B P; Bruno, A C; Carvalho, H R

    2014-01-01

    Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7 µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x–y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz 1/2 between 0.1 and 10 Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10 –14  A m 2 , a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays. (paper)

  6. Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields

    Science.gov (United States)

    Lima, E. A.; Bruno, A. C.; Carvalho, H. R.; Weiss, B. P.

    2014-10-01

    Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7 µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x-y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz1/2 between 0.1 and 10 Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10-14 A m2, a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays.

  7. 3D laser scanning techniques applying to tunnel documentation and geological mapping at Aespoe hard rock laboratory, Sweden

    International Nuclear Information System (INIS)

    Feng, Q.; Wang, G.; Roeshoff, K.

    2008-01-01

    3D terrestrial laser scanning is nowadays one of the most attractive methods to applying for 3D mapping and documentation of rock faces and tunnels, and shows the most potential to improve the data quality and provide some good solutions in rock engineering projects. In this paper, the state-of-the-art methods are described for different possibility to tunnel documentation and geological mapping based on 3D laser scanning data. Some results are presented from the case study performed at the Hard Rock Laboratory, Aespoe run by SKB, Swedish Nuclear Fuel and Waste Management Co. Comparing to traditional methods, 3D laser scanning techniques can not only provide us with a rapid and 3D digital way for tunnel documentation, but also create a potential chance to achieve high quality data, which might be beneficial to different rock engineering project procedures, including field data acquisition, data processing, data retrieving and management, and also modeling and design. (authors)

  8. Spin polarization in top pair production in association with two photons at NLO+PS

    CERN Document Server

    Luisoni, Gionata

    2018-01-01

    This talk focuses on the impact of top-quark spin polarization effects in Higgs boson production in association with a top-quark pair, where the Higgs boson decays to two photons. Predictions for the signal are compared with direct top-quark pair production in association with two photons at NLO+PS.

  9. Cross sections and spin polarizations of electrons elastically scattered from oriented molecules (CH3I)

    International Nuclear Information System (INIS)

    Fink, M.; Ross, A.W.; Fink, R.J.

    1989-01-01

    Elastic differential cross sections and spin polarizations for electrons elastically scattered from CH 3 I are calculated using the independent atom model. Three molecular orientations with respect to the incident electron wavevector are considered - first, the molecule is oriented randomly, second, the electron wave front and molecular bond are parallel, and third, the wavefront and the bond axis are perpendicular. It will be seen to what extent orientational averaging weakens features of the cross section and spin polarization. The calculations show that cross section and spin polarization measurements are a possible tool for determining the degree of molecular orientation. There is no degeneracy between I-C and C-I in cross section and spin polarization measurements. The results presented here for 200 eV and 600 eV electrons scattered by CH 3 I should be considered as a case study and it should be possible to find molecules and electron energies for which even more dramatic differences between the various orientations between the molecules and the electrons can be expected. (orig.)

  10. On the theory of elastic scattering of spin polarized electrons from ferromagnets

    International Nuclear Information System (INIS)

    Helman, J.S.

    1984-01-01

    The first Born approximation supposedly inadequate for dealing with elastic scattering of spin polarized electrons on ferromagnets is reconsidered. It is found that when used in conjunction with a spin dependent pseudopotential, it can describe the gross features of the ansisotropy. (Author) [pt

  11. On the theory of elastic scattering of spin polarized electrons from ferromagnets

    International Nuclear Information System (INIS)

    Helman, J.S.; Baltenspenger, W.

    1984-01-01

    The first Born approximation supposedly inadequate for dealing with the elastic scattering of spin polarized electrons on ferromagnets is reconsidered. It is found that when used in conjunction with a spin dependent pseudo-potential, it can describe the gross features of the anisotropy. (author) [pt

  12. Spin-polarized ballistic conduction through correlated Au-NiMnSb-Au heterostructures

    KAUST Repository

    Morari, C.; Appelt, W. H.; Ö stlin, A.; Prinz-Zwick, A.; Schwingenschlö gl, Udo; Eckern, U.; Chioncel, L.

    2017-01-01

    calculations with local electronic interactions, of Hubbard-type on the Mn sites, leads to a hybridization between the interface and many-body states. The significant reduction of the spin polarization seen in the density of states is not apparent in the spin

  13. Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts

    DEFF Research Database (Denmark)

    Hu, C.-M.; Nitta, Junsaku; Jensen, Ane

    2001-01-01

    Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spi...

  14. Spin polarization in top pair production in association with two photons at NLO+PS

    CERN Document Server

    Luisoni, Gionata

    2017-01-01

    This talk focuses on the impact of top-quark spin polarization effects in Higgs boson production in association with a top-quark pair, where the Higgs boson decays to two photons. Predictions for the signal are compared with direct top-quark pair production in association with two photons at NLO+PS.

  15. Spin-polarized versus chiral condensate in quark matter at finite temperature and density

    DEFF Research Database (Denmark)

    Matsuoka, Hiroaki; Tsue, Yasuhiko; da Providencia, Joao

    2016-01-01

    It is shown that the spin-polarized condensate appears in quark matter at high baryon density and low temperature due to the tensor-type four-point interaction in the Nambu-Jona-Lasiniotype model as a low-energy effective theory of quantum chromodynamics. It is indicated within this low-energy ef...

  16. Spin polarization versus color–flavor locking in high-density quark matter

    DEFF Research Database (Denmark)

    Tsue, Yasuhiko; da Providência, João; Providência, Constança

    2015-01-01

    It is shown that spin polarization with respect to each flavor in three-flavor quark matter occurs instead of color–flavor locking at high baryon density by using the Nambu–Jona-Lasinio model with four-point tensor-type interaction. Also, it is indicated that the order of phase transition between...

  17. The HERA polarimeter and the first observation of electron spin polarization at HERA

    International Nuclear Information System (INIS)

    Barber, D.P.; Bremer, H.D.; Boege, M.; Brinkmann, R.; Gianfelice-Wendt, E.; Kaiser, H.; Klanner, R.; Lewin, H.C.; Meyners, N.; Vogel, W.; Brueckner, W.; Buescher, C.; Dueren, M.; Gaul, H.G.; Muecklich, A.; Neunreither, F.; Rith, K.; Scholz, C.; Steffens, E.; Veltri, M.; Wander, W.; Zapfe, K.; Zetsche, F.; Chapman, M.; Milner, R.; Coulter, K.; Delheij, P.P.J.; Haeusser, O.; Henderson, R.; Levy, P.; Vetterli, M.; Gressmann, H.; Janke, T.; Micheel, B.; Westphal, D.; Kaiser, R.; Losev, L.; Nowak, W.D.

    1992-10-01

    Electron spin polarizations of about 8% were observed at HERA in November 1991. In runs during 1992 utilizing special orbit corrections, polarization values close to 60% have been achieved. In this paper the polarimeter, the machine conditions, the data analysis, the first results and plans for future measurements are described. (orig.)

  18. A scanning tunneling microscope capable of imaging specified micron-scale small samples.

    Science.gov (United States)

    Tao, Wei; Cao, Yufei; Wang, Huafeng; Wang, Kaiyou; Lu, Qingyou

    2012-12-01

    We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt∕Ir wire to an isolated individual 32.5 × 32.5 μm(2) graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure.

  19. A scanning tunneling microscope capable of imaging specified micron-scale small samples

    Science.gov (United States)

    Tao, Wei; Cao, Yufei; Wang, Huafeng; Wang, Kaiyou; Lu, Qingyou

    2012-12-01

    We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt/Ir wire to an isolated individual 32.5 × 32.5 μm2 graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure.

  20. Scanning tunnel microscopic image of tungsten (100) and (110) real surfaces and nature of conduction electron reflection

    International Nuclear Information System (INIS)

    Pryadkin, S.L.; Tsoj, V.S.

    1988-01-01

    The electrically polished (100) and (110) surfaces of tungsten are studied with the aid of a scanning tunnel microscope at atmospheric pressure. The (110) surface consists of a large number of atomically plane terraces whereas the (100) surface is faceted. The scanning tunnel microscope data can explain such results of experiments on transverse electron focussing as the strong dependence of the probability for specular reflection of conduction electrons scattered by the (100) surface on the electron de Broglie wavelength and the absence of a dependence of the probability for specular reflection on the wavelength for the (110) surface