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Sample records for low-dimensional semiconductor structures

  1. Time-resolved spectroscopy of low-dimensional semiconductor structures

    NASA Astrophysics Data System (ADS)

    Murphy, Joseph R.

    This dissertation is a survey of ultrafast time-resolved optical measurements conducted on a variety of low-dimensional semiconductor systems to further the understanding of the dynamic behavior in the following systems: ZnMnTe/ZnSe quantum dots, ZnTe/ZnMnSe quantum dots, InGaAs quantum wells, CdMnSe colloidal quantum dots, multi-shell CdSe/CdMnS/CdS colloidal nanoplatelets, and graphene and graphene-related solutions and films. Using time-resolved photoluminescence to study epitaxially-grown ZnTe and ZnMnTe quantum dots in corresponding ZnMnSe and ZnSe matrices, the location dependence of manganese ions in respect to magnetic polaron formation is shown. The structure with manganese ions located in the matrix exhibited magnetic polaron behavior consistent with previous literature, whereas the structure with the magnetic ions located within the quantum dots exhibited unconventional magnetic polaron properties. These properties, including temperature and magnetic field insensitivity, were explained through the use of a model that predicted an increased internal magnetic field due to a decreased effective volume of the magnetic polaron and a higher effective temperature due to laser heating. Magneto-time-resolved photoluminescence measurements on a system of colloidal CdMnSe quantum dots show that the magnetic polaron properties differ significantly from the epitaxially grown quantum dots. First the timescales at which the magnetic polaron forms and the polarization saturates are different by more than an order of magnitude, and second, the magnetic polaron energy exhibited step-like behavior as the strength of the externally applied magnetic field is increased. The field dependent MP formation energy that is observed experimentally is explained as due to the breaking of the antiferromagnetic coupling of Mn dimers within the QDs. This model is further verified by the observation of quantized behavior in the Zeeman energy splitting. Through the use of magneto

  2. Correlation of Photocatalytic Activity with Band Structure of Low-dimensional Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Meng, Fanke

    Photocatalytic hydrogen generation by water splitting is a promising technique to produce clean and renewable solar fuel. The development of effective semiconductor photocatalysts to obtain efficient photocatalytic activity is the key objective. However, two critical reasons prevent wide applications of semiconductor photocatalysts: low light usage efficiency and high rates of charge recombination. In this dissertation, several low-dimensional semiconductors were synthesized with hydrothermal, hydrolysis, and chemical impregnation methods. The band structures of the low-dimensional semiconductor materials were engineered to overcome the above mentioned two shortcomings. In addition, the correlation between the photocatalytic activity of the low-dimensional semiconductor materials and their band structures were studied. First, we studied the effect of oxygen vacancies on the photocatalytic activity of one-dimensional anatase TiO2 nanobelts. Given that the oxygen vacancy plays a significant role in band structure and photocatalytic performance of semiconductors, oxygen vacancies were introduced into the anatase TiO2 nanobelts during reduction in H2 at high temperature. The oxygen vacancies of the TiO2 nanobelts boosted visible-light-responsive photocatalytic activity but weakened ultraviolet-light-responsive photocatalytic activity. As oxygen vacancies are commonly introduced by dopants, these results give insight into why doping is not always beneficial to the overall photocatalytic performance despite increases in absorption. Second, we improved the photocatalytic performance of two-dimensional lanthanum titanate (La2Ti2 O7) nanosheets, which are widely studied as an efficient photocatalyst due to the unique layered crystal structure. Nitrogen was doped into the La2Ti2O7 nanosheets and then Pt nanoparticles were loaded onto the La2Ti2O7 nanosheets. Doping nitrogen narrowed the band gap of the La2Ti 2O7 nanosheets by introducing a continuum of states by the valence

  3. Toward Ultrafast Spin Dynamics in Low Dimensional Semiconductors

    NASA Astrophysics Data System (ADS)

    Chiu, Yi-Hsin

    Since the discovery of long spin relaxation times of itinerant electrons up to 100 nanoseconds and spin diffusion lengths over 100 mum in GaAs, extraordinary advances in semiconductor spintronics have been made in the past one and half decades. Incorporating spins in semiconductors requires the following essential capabilities: (i) injection of spins into semiconductors, (ii) manipulation of spins, and (iii) sensitive detection of spin coherence. The solutions to these challenges lie in a deeper understanding of spin interactions and spin relaxation in semiconductors as well as appropriate tools to probe spin dynamics. In particular, recent experiments have suggested the important role of dimensionality in spin dynamics. For example, spin-orbit interaction, the dominant source of spin relaxation in most II-VI and III-V semiconductors, has been shown to be significantly suppressed in reduced dimensions. Low-dimensional semiconductors are therefore appealing candidates for exploring spin physics and device applications. This dissertation aims at exploring spin dynamics in low dimensional semiconductor systems using time-resolved optical techniques. The time resolution allows for a direct measurement of the equilibrium and non-equilibrium carrier spins and various spin interactions in the time domain. Optical approaches are also a natural fit for probing optically active nanostructures where electric approaches can often encounter challenges. For instance, fabricating electric contacts with nanostructures is a proven challenge because of their reduced size and modified electronic structure. This dissertation is divided into three sections targeting an ultimate goal of employing optical methods to explore spin dynamics in low dimensional semiconductors. First, the time-resolved Kerr rotation technique is employed to study spin relaxation in Fe/MgO/GaAs heterostructures. The results reveal rich interactions between the GaAs electron spins, nuclear spins, and the

  4. Thermal transport in low dimensional semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Bohorquez-Ballen, Jaime

    We have performed a first principles density functional theory (DFT) calculations to study the thermal conductivity in ZnO nanotubes, ZnO nanowires, and Si/Ge shell-core nanowires. We found the equilibrium configuration and the electric band structure of each nanostructure using DFT, the interatomic force constants and the phonon dispersion relations were calculated using DFPT as implemented in Quantum Espresso. In order to fundamentally understand the effect of atomic arrangements, we calculated the phonon conductance in a ballistic approach using a Green's function method. All ZnO nanostructures studied exhibit semiconducting behavior, with direct bandgap at the Gamma point. The calculated values for the bandgaps were larger than the value of the bandgap of the bulk ZnO. We were able to identify phonon modes in which the motion of Zn atoms is significant when it is compared with the motion of oxygen atoms. The thermal conductivity depends on the diameter of the nanowires and nanotubes and it is dramatically affected when the nanowire or nanotube is doped with Ga. For Si/Ge nanowires, the slope and the curvature of acoustic modes in the phonon dispersion relation increases when the diameter increases. For nanowires with the same number of atoms, the slope and curvature of acoustic modes depends on the concentration of Si atoms. We were able to identify phonon modes in which the motion of core atoms is significant when it is compared with motion of atoms on the nanowire's shell. The thermal conductivity in these nanostructures depends on the nanowire's diameter and on the Si atoms concentration.

  5. Thermoelectric Transport in Bismuth Telluride Nanoplates, Semiconductor Nanowires, and Silicide Nanocomposites: Effects of Low Dimensionality, Surface States, Interface Structures, and Crystal Complexity

    NASA Astrophysics Data System (ADS)

    Shi, Li

    2012-02-01

    This presentation will review recent measurement results of thermoelectric properties of individual bismuth telluride nanoplates, semiconductor nanowires, and silicide nanocomposites. In experiments with these realistic nanostructured materials, a number of factors influence the transport properties. For example, unintentional doping, interface roughness and impurities can often obscure the predicted effects of the low-dimensional electronic density of states and the protected surface states, the latter of which have been suggested for bismuth telluride and other thermoelectric materials, now also referred as topological insulators. Similarly, impurities and defects as well as contact thermal resistance can play an important role in phonon transport in nanostructures, making it nontrivial to quantify the actual effects of phonon-surface scattering and other intriguing low-dimensional phonon transport phenomena. Because of these experimental complications, diverse theoretical interpretations of experimental results have appeared in the literature, and will be discussed. Moreover, the effects of twin defects and crystal complexity on thermoelectric transport in nanostructures will be examined based on measurement results of III-V and silicide nanostructures.

  6. Ultrafast electronic transport in low dimensional semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Choi, Hyunyong; Norris, Theodore B.; Faist, Jérôme; Capasso, Federico

    2009-02-01

    Ultrafast time-resolved pump-probe measurements are used to study low energy excitations and dynamics of electronic transport in various semiconductor nanostructures. In quantum cascade lasers, we observe ultrafast gain recovery dynamics due to electronic transport in the structures. In particular, the nature of electronic transport had been addressed by using ultrafast optical techniques. Sub-picosecond resonant tunneling injection from the quantum cascade laser injector ground state into the upper lasing state was found to be incoherent due to strong dephasing in the active subband. We also observed the strong coupling of the electronic transport to the intra-cavity photon density, which we term "photon-driven transport". Note that this invited paper reviews the details of our recent observations (H. Choi et al., Phys. Rev. Lett., 100, 167401, 2008 and H. Choi, et al., Appl. Phys. Lett. 92, 122114 (2008)).

  7. Quantum Effects in the Thermoelectric Power Factor of Low-Dimensional Semiconductors

    NASA Astrophysics Data System (ADS)

    Hung, Nguyen T.; Hasdeo, Eddwi H.; Nugraha, Ahmad R. T.; Dresselhaus, Mildred S.; Saito, Riichiro

    2016-07-01

    We theoretically investigate the interplay between the confinement length L and the thermal de Broglie wavelength Λ to optimize the thermoelectric power factor of semiconducting materials. An analytical formula for the power factor is derived based on the one-band model assuming nondegenerate semiconductors to describe quantum effects on the power factor of the low-dimensional semiconductors. The power factor is enhanced for one- and two-dimensional semiconductors when L is smaller than Λ of the semiconductors. In this case, the low-dimensional semiconductors having L smaller than their Λ will give a better thermoelectric performance compared to their bulk counterpart. On the other hand, when L is larger than Λ , bulk semiconductors may give a higher power factor compared to the lower dimensional ones.

  8. Quantum Effects in the Thermoelectric Power Factor of Low-Dimensional Semiconductors.

    PubMed

    Hung, Nguyen T; Hasdeo, Eddwi H; Nugraha, Ahmad R T; Dresselhaus, Mildred S; Saito, Riichiro

    2016-07-15

    We theoretically investigate the interplay between the confinement length L and the thermal de Broglie wavelength Λ to optimize the thermoelectric power factor of semiconducting materials. An analytical formula for the power factor is derived based on the one-band model assuming nondegenerate semiconductors to describe quantum effects on the power factor of the low-dimensional semiconductors. The power factor is enhanced for one- and two-dimensional semiconductors when L is smaller than Λ of the semiconductors. In this case, the low-dimensional semiconductors having L smaller than their Λ will give a better thermoelectric performance compared to their bulk counterpart. On the other hand, when L is larger than Λ, bulk semiconductors may give a higher power factor compared to the lower dimensional ones. PMID:27472126

  9. Quantum Effects in the Thermoelectric Power Factor of Low-Dimensional Semiconductors.

    PubMed

    Hung, Nguyen T; Hasdeo, Eddwi H; Nugraha, Ahmad R T; Dresselhaus, Mildred S; Saito, Riichiro

    2016-07-15

    We theoretically investigate the interplay between the confinement length L and the thermal de Broglie wavelength Λ to optimize the thermoelectric power factor of semiconducting materials. An analytical formula for the power factor is derived based on the one-band model assuming nondegenerate semiconductors to describe quantum effects on the power factor of the low-dimensional semiconductors. The power factor is enhanced for one- and two-dimensional semiconductors when L is smaller than Λ of the semiconductors. In this case, the low-dimensional semiconductors having L smaller than their Λ will give a better thermoelectric performance compared to their bulk counterpart. On the other hand, when L is larger than Λ, bulk semiconductors may give a higher power factor compared to the lower dimensional ones.

  10. Detection of Defect-Induced Magnetism in Low-Dimensional ZnO Structures by Magnetophotocurrent.

    PubMed

    Lorite, Israel; Kumar, Yogesh; Esquinazi, Pablo; Zandalazini, Carlos; de Heluani, Silvia Perez

    2015-09-01

    The detection of defect-induced magnetic order in single low-dimensional oxide structures is in general difficult because of the relatively small yield of magnetically ordered regions. In this work, the effect of an external magnetic field on the transient photocurrent measured after light irradiation on different ZnO samples at room temperature is studied. It has been found that a magnetic field produces a change in the relaxation rate of the transient photocurrent only in magnetically ordered ZnO samples. This rate can decrease or increase with field, depending on whether the magnetically ordered region is in the bulk or only at the surface of the ZnO sample. The phenomenon reported here is of importance for the development of magneto-optical low-dimensional oxides devices and provides a new guideline for the detection of magnetic order in low-dimensional magnetic semiconductors.

  11. Antitumor activity of low-dimensional alumina structures

    NASA Astrophysics Data System (ADS)

    Korovin, M. S.; Fomenko, A. N.

    2016-08-01

    Nano-dimensional materials have recently attracted much attention with respect to their potential role in medicine. Physical mechanisms of interaction of nanoparticles with tumor cells will help to develop new methods for cancer disease treatment. Based on aluminum oxide phases, positively charged low-dimensional structures have different shape: agglomerates of nanosheets, nameplates, cone-shaped nanoaggregates were synthesized with the help of aluminum nanoparticles. The cytotoxicity effect of these low-dimensional structures on A549, HeLa, MDA, PyMT tumor cells was studied. It was shown that agglomerates of nanosheets were more toxic for investigating cell lines. Agglomerates of nanosheets had a medium toxic effect at a concentration of 10 mg/ml while nameplates and cone-shaped nanoaggregates were nontoxic. The toxic effect of agglomerates of nanosheets correlates with their shape, mainly the presence of multiple edges.

  12. Quantum theory of the electronic and optical properties of low-dimensional semiconductor systems

    NASA Astrophysics Data System (ADS)

    Lau, Wayne Heung

    This thesis examines the electronic and optical properties of low-dimensional semiconductor systems. A theory is developed to study the electron-hole generation-recombination process of type-II semimetallic semiconductor heterojunctions based on a 3 x 3 k·p matrix Hamiltonian (three-band model) and an 8 x 8 k·p matrix Hamiltonian (eight-band model). A novel electron-hole generation and recombination process, which is called activationless generation-recombination process, is predicted. It is demonstrated that the current through the type-II semimetallic semiconductor heterojunctions is governed by the activationless electron-hole generation-recombination process at the heterointerfaces, and that the current-voltage characteristics are essentially linear. A qualitative agreement between theory and experiments is observed. The numerical results of the eight-band model are compared with those of the threeband model. Based on a lattice gas model, a theory is developed to study the influence of a random potential on the ionization equilibrium conditions for bound electron-hole pairs (excitons) in III--V semiconductor heterostructures. It is demonstrated that ionization equilibrium conditions for bound electron-hole pairs change drastically in the presence of strong disorder. It is predicted that strong disorder promotes dissociation of excitons in III--V semiconductor heterostructures. A theory of polariton (photon dressed by phonon) spontaneous emission in a III--V semiconductor doped with semiconductor quantum dots (QDs) or quantum wells (QWs) is developed. For the first time, superradiant and subradiant polariton spontaneous emission phenomena in a polariton-QD (QW) coupled system are predicted when the resonance energies of the two identical QDs (QWs) lie outside the polaritonic energy gap. It is also predicted that when the resonance energies of the two identical QDs (QWs) lie inside the polaritonic energy gap, spontaneous emission of polariton in the polariton

  13. Low-dimensional dynamics of structured random networks

    NASA Astrophysics Data System (ADS)

    Aljadeff, Johnatan; Renfrew, David; Vegué, Marina; Sharpee, Tatyana O.

    2016-02-01

    Using a generalized random recurrent neural network model, and by extending our recently developed mean-field approach [J. Aljadeff, M. Stern, and T. Sharpee, Phys. Rev. Lett. 114, 088101 (2015), 10.1103/PhysRevLett.114.088101], we study the relationship between the network connectivity structure and its low-dimensional dynamics. Each connection in the network is a random number with mean 0 and variance that depends on pre- and postsynaptic neurons through a sufficiently smooth function g of their identities. We find that these networks undergo a phase transition from a silent to a chaotic state at a critical point we derive as a function of g . Above the critical point, although unit activation levels are chaotic, their autocorrelation functions are restricted to a low-dimensional subspace. This provides a direct link between the network's structure and some of its functional characteristics. We discuss example applications of the general results to neuroscience where we derive the support of the spectrum of connectivity matrices with heterogeneous and possibly correlated degree distributions, and to ecology where we study the stability of the cascade model for food web structure.

  14. Semiconductor structure

    NASA Technical Reports Server (NTRS)

    Hovel, Harold J. (Inventor); Woodall, Jerry M. (Inventor)

    1979-01-01

    A technique for fabricating a semiconductor heterostructure by growth of a ternary semiconductor on a binary semiconductor substrate from a melt of the ternary semiconductor containing less than saturation of at least one common ingredient of both the binary and ternary semiconductors wherein in a single temperature step the binary semiconductor substrate is etched, a p-n junction with specific device characteristics is produced in the binary semiconductor substrate by diffusion of a dopant from the melt and a region of the ternary semiconductor of precise conductivity type and thickness is grown by virtue of a change in the melt characteristics when the etched binary semiconductor enters the melt.

  15. Nanoscale control of low-dimensional spin structures in manganites

    NASA Astrophysics Data System (ADS)

    Jing, Wang; Iftikhar, Ahmed Malik; Renrong, Liang; Wen, Huang; Renkui, Zheng; Jinxing, Zhang

    2016-06-01

    Due to the upcoming demands of next-generation electronic/magnetoelectronic devices with low-energy consumption, emerging correlated materials (such as superconductors, topological insulators and manganites) are one of the highly promising candidates for the applications. For the past decades, manganites have attracted great interest due to the colossal magnetoresistance effect, charge-spin-orbital ordering, and electronic phase separation. However, the incapable of deterministic control of those emerging low-dimensional spin structures at ambient condition restrict their possible applications. Therefore, the understanding and control of the dynamic behaviors of spin order parameters at nanoscale in manganites under external stimuli with low energy consumption, especially at room temperature is highly desired. In this review, we collected recent major progresses of nanoscale control of spin structures in manganites at low dimension, especially focusing on the control of their phase boundaries, domain walls as well as the topological spin structures (e.g., skyrmions). In addition, capacitor-based prototype spintronic devices are proposed by taking advantage of the above control methods in manganites. This capacitor-based structure may provide a new platform for the design of future spintronic devices with low-energy consumption. Project supported by the National Basic Research Program of China (Grant No. 2014CB920902), the National Natural Science Foundation of China (Grant Nos. 61306105 and 51572278), the Information Science and Technology (TNList) Cross-discipline Foundation from Tsinghua National Laboratory, China and the Fund from the State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China, Chengdu 610054, China.

  16. Low-dimensional transport and large thermoelectric power factors in bulk semiconductors by band engineering of highly directional electronic states.

    PubMed

    Bilc, Daniel I; Hautier, Geoffroy; Waroquiers, David; Rignanese, Gian-Marco; Ghosez, Philippe

    2015-04-01

    Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but less by maximizing the power factor. The latter imposes apparently conflicting requirements on the band structure: a narrow energy distribution and a low effective mass. Quantum confinement in nanostructures and the introduction of resonant states were suggested as possible solutions to this paradox, but with limited success. Here, we propose an original approach to fulfill both requirements in bulk semiconductors. It exploits the highly directional character of some orbitals to engineer the band structure and produce a type of low-dimensional transport similar to that targeted in nanostructures, while retaining isotropic properties. Using first-principle calculations, the theoretical concept is demonstrated in Fe2YZ Heusler compounds, yielding power factors 4 to 5 times larger than in classical thermoelectrics at room temperature. Our findings are totally generic and rationalize the search of alternative compounds with similar behavior. Beyond thermoelectricity, these might be relevant also in the context of electronic, superconducting, or photovoltaic applications. PMID:25884131

  17. Low-dimensional transport and large thermoelectric power factors in bulk semiconductors by band engineering of highly directional electronic states.

    PubMed

    Bilc, Daniel I; Hautier, Geoffroy; Waroquiers, David; Rignanese, Gian-Marco; Ghosez, Philippe

    2015-04-01

    Thermoelectrics are promising for addressing energy issues but their exploitation is still hampered by low efficiencies. So far, much improvement has been achieved by reducing the thermal conductivity but less by maximizing the power factor. The latter imposes apparently conflicting requirements on the band structure: a narrow energy distribution and a low effective mass. Quantum confinement in nanostructures and the introduction of resonant states were suggested as possible solutions to this paradox, but with limited success. Here, we propose an original approach to fulfill both requirements in bulk semiconductors. It exploits the highly directional character of some orbitals to engineer the band structure and produce a type of low-dimensional transport similar to that targeted in nanostructures, while retaining isotropic properties. Using first-principle calculations, the theoretical concept is demonstrated in Fe2YZ Heusler compounds, yielding power factors 4 to 5 times larger than in classical thermoelectrics at room temperature. Our findings are totally generic and rationalize the search of alternative compounds with similar behavior. Beyond thermoelectricity, these might be relevant also in the context of electronic, superconducting, or photovoltaic applications.

  18. On the current drive capability of low dimensional semiconductors: 1D versus 2D

    DOE PAGESBeta

    Zhu, Y.; Appenzeller, J.

    2015-10-29

    Low-dimensional electronic systems are at the heart of many scaling approaches currently pursuit for electronic applications. Here, we present a comparative study between an array of one-dimensional (1D) channels and its two-dimensional (2D) counterpart in terms of current drive capability. Lastly, our findings from analytical expressions derived in this article reveal that under certain conditions an array of 1D channels can outperform a 2D field-effect transistor because of the added degree of freedom to adjust the threshold voltage in an array of 1D devices.

  19. On the Current Drive Capability of Low Dimensional Semiconductors: 1D versus 2D.

    PubMed

    Zhu, Y; Appenzeller, J

    2015-12-01

    Low-dimensional electronic systems are at the heart of many scaling approaches currently pursuit for electronic applications. Here, we present a comparative study between an array of one-dimensional (1D) channels and its two-dimensional (2D) counterpart in terms of current drive capability. Our findings from analytical expressions derived in this article reveal that under certain conditions an array of 1D channels can outperform a 2D field-effect transistor because of the added degree of freedom to adjust the threshold voltage in an array of 1D devices.

  20. Structural phase transitions in low-dimensional ion crystals

    SciTech Connect

    Fishman, Shmuel; Chiara, Gabriele de; Calarco, Tommaso; Morigi, Giovanna

    2008-02-01

    A chain of singly charged particles, confined by a harmonic potential, exhibits a sudden transition to a zigzag configuration when the radial potential reaches a critical value, depending on the particle number. This structural change is a phase transition of second order, whose order parameter is the crystal displacement from the chain axis. We study analytically the transition using Landau theory and find full agreement with numerical predictions by Schiffer [Phys. Rev. Lett. 70, 818 (1993)] and Piacente et al. [Phys. Rev. B 69, 045324 (2004)]. Our theory allows us to determine analytically the system's behavior at the transition point.

  1. Bose-Einstein condensation in low dimensional layered structures

    NASA Astrophysics Data System (ADS)

    Salas, Patricia; Solis, M. A.

    2008-03-01

    Bose-Einstein condensation critical temperature, among other thermodynamic properties are reported for an ideal boson gas inside layered structures created by trapping potential of the Kronig-Penney type. We start with a big box where we introduce the Kronig-Penney potential in three directions to get a honey comb of cubes of side a size and walls of variable penetrability (P=mV0ab/^2), with bosons instead of bees. We are able to reduce the dimensions of the cubes to simulate bosons inside quantum dots. The critical temperature, starting from that of an ideal boson gas inside the big box, decreases as the small cube wall impenetrability increases arriving to a tiny but different from zero when the penetrability is zero (P-->∞). We also calculate the internal energy and the specific heat, and compare them to the ones obtained for the case of the same Kronig-Penney potential in one direction (simulating layers), and two directions (nanotubes).

  2. Low-dimensional semiconductor superlattices formed by geometric control over nanocrystal attachment.

    PubMed

    Evers, Wiel H; Goris, Bart; Bals, Sara; Casavola, Marianna; de Graaf, Joost; van Roij, René; Dijkstra, Marjolein; Vanmaekelbergh, Daniël

    2013-06-12

    Oriented attachment, the process in which nanometer-sized crystals fuse by atomic bonding of specific crystal facets, is expected to be more difficult to control than nanocrystal self-assembly that is driven by entropic factors or weak van der Waals attractions. Here, we present a study of oriented attachment of PbSe nanocrystals that counteract this tuition. The reaction was studied in a thin film of the suspension casted on an immiscible liquid at a given temperature. We report that attachment can be controlled such that it occurs with one type of facets exclusively. By control of the temperature and particle concentration we obtain one- or two-dimensional PbSe single crystals, the latter with a honeycomb or square superimposed periodicity in the nanometer range. We demonstrate the ability to convert these PbSe superstructures into other semiconductor compounds with the preservation of crystallinity and geometry.

  3. Spontaneous appearance of a low-dimensional magnetic electron system on semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Sawada, Keisuke; Iwata, Jun-Ichi; Oshiyama, Atsushi

    2016-06-01

    We report on the large-scale density-functional calculations that show the emergence of the spin-polarized ground states in nanofacets self-organized on SiC (0001) surfaces. We first reveal that the nanofacet formed by bunching of single bilayer steps induces peculiar electron states localized at but extended along step edges, showing the flat-band characteristics. The electron states are of C-dangling-bond characters mixed with the back-bond character of neighboring edge Si atoms. We find that the resulting flat bands lead to the spin polarization near the step edges by H passivation of the terrace Si atoms. Interestingly, either ferromagnetic or antiferromagnetic chains appear along the step edges on the SiC nanofacet and the location of such magnetic chains can be controlled by manipulating the H passivation of atoms near the step edges. These findings open a possibility of the appearance of new magnetic functions on the covalent semiconductor surfaces without magnetic elements.

  4. Harnessing Sparse and Low-Dimensional Structures for Robust Clustering of Imagery Data

    ERIC Educational Resources Information Center

    Rao, Shankar Ramamohan

    2009-01-01

    We propose a robust framework for clustering data. In practice, data obtained from real measurement devices can be incomplete, corrupted by gross errors, or not correspond to any assumed model. We show that, by properly harnessing the intrinsic low-dimensional structure of the data, these kinds of practical problems can be dealt with in a uniform…

  5. A low-dimensional model for large-scale coherent structures

    NASA Astrophysics Data System (ADS)

    Bai, Kunlun; Ji, Dandan; Brown, Eric

    2015-11-01

    We demonstrate a methodology to predict the dynamics of the large-scale coherent structures in turbulence using a simple low dimensional stochastic model proposed by Brown and Ahlers (Phys. Fluids, 2008). The model terms are derived from the Navier-Stokes equations, including a potential term depending on the geometry of the system. The model has previously described several dynamical modes of the large-scale circulation (LSC) in turbulent Rayleigh-Bénard convection. Here we test a model prediction for the existence of a new mode where the LSC stochastically changes direction to align with different diagonals of a cubic container. The model successfully predicts the switching rate of the LSC at different tilting conditions. The success of the prediction of the switching mode demonstrates that a low-dimensional turbulent model can quantitatively predict the existence and properties of different dynamical states that result from boundary geometry.

  6. Room temperature light emission from the low-dimensional semiconductors AZrPS{sub 6} ( A = K, Rb, Cs).

    SciTech Connect

    Banerjee, S.; Szarko, J. M.; Yuhas, B. D.; Malliakas, C. D.; Chen, L. X.; Kanatzidis, M. G.

    2010-03-29

    The new semiconducting thiophosphate compounds KZrPS{sub 6}, RbZrPS{sub 6}, and CsZrPS{sub 6} exhibit red light emission at room temperature. The materials have longer photoluminescence lifetimes than most of the inorganic chalcogenide semiconductors. They can be solution processed into thin films for potential device fabrication.

  7. Low Dimensional Tools for Flow-Structure Interaction Problems: Application to Micro Air Vehicles

    NASA Technical Reports Server (NTRS)

    Schmit, Ryan F.; Glauser, Mark N.; Gorton, Susan A.

    2003-01-01

    A low dimensional tool for flow-structure interaction problems based on Proper Orthogonal Decomposition (POD) and modified Linear Stochastic Estimation (mLSE) has been proposed and was applied to a Micro Air Vehicle (MAV) wing. The method utilizes the dynamic strain measurements from the wing to estimate the POD expansion coefficients from which an estimation of the velocity in the wake can be obtained. For this experiment the MAV wing was set at five different angles of attack, from 0 deg to 20 deg. The tunnel velocities varied from 44 to 58 ft/sec with corresponding Reynolds numbers of 46,000 to 70,000. A stereo Particle Image Velocimetry (PIV) system was used to measure the wake of the MAV wing simultaneously with the signals from the twelve dynamic strain gauges mounted on the wing. With 20 out of 2400 POD modes, a reasonable estimation of the flow flow was observed. By increasing the number of POD modes, a better estimation of the flow field will occur. Utilizing the simultaneously sampled strain gauges and flow field measurements in conjunction with mLSE, an estimation of the flow field with lower energy modes is reasonable. With these results, the methodology for estimating the wake flow field from just dynamic strain gauges is validated.

  8. Hot-carrier solar cells using low-dimensional quantum structures

    SciTech Connect

    Watanabe, Daiki; Kasamatsu, Naofumi; Harada, Yukihiro; Kita, Takashi

    2014-10-27

    We propose a high-conversion-efficiency solar cell (SC) utilizing the hot carrier (HC) population in an intermediate-band (IB) of a quantum dot superlattice (QDSL) structure. The bandgap of the host semiconductor in this device plays an important role as an energy-selective barrier for HCs in the QDSLs. According to theoretical calculation using the detailed balance model with an air mass 1.5 spectrum, the optimum IB energy is determined by a trade-off relation between the number of HCs with energy exceeding the conduction-band edge and the number of photons absorbed by the valence band−IB transition. Utilizing experimental data of HC temperature in InAs/GaAs QDSLs, the maximum conversion efficiency under maximum concentration (45 900 suns) has been demonstrated to increase by 12.6% as compared with that for a single-junction GaAs SC.

  9. EMRS Spring Meeting 2014 Symposium D: Phonons and fluctuations in low dimensional structures

    NASA Astrophysics Data System (ADS)

    2014-11-01

    The E-MRS 2014 Spring meeting, held from 26-30th May 2014 in Lille included the Symposium D entitled ''Phonons and Fluctuations in Low Dimensional Structures'', the first edition of its kind. The symposium was organised in response to the increasing interest in the study of phonons in the context of advances in condensed matter physics, electronics, experimental methods and theory and, in particular, the transfer of energy across atomic interfaces and the propagation of energy in the nm-scale. Steering heat by light or vice versa and examining nano-scale energy conversion (as in thermoelectricity and harvesting e.g. in biological systems) are two aspects that share the underlying science of energy processes across atomic interfaces and energy propagation in the nanoscale and or in confined systems. The nanometer scale defies several of the bulk relationships as confinement of electrons and phonons, locality and non-equilibrium become increasingly important. The propagation of phonons as energy carriers impacts not only heat transfer, but also the very concept and handling of temperature in non-equilibrium and highly localised conditions. Much of the needed progress depends on the materials studied and this symposium targeted the interface material aspects as well as the emerging concepts to advance in this field. The symposium had its origins in a series of meetings and seminars including: (1) the first Phonon Engineering Workshop, funded by Catalan Institute for Research and Advanced Studies (ICREA), the then MICINN, the CNRS, VTT, and several EU projects, held in Saint Feliu de Guixols (Girona, Spain) from 24th to 27th of May 2010 with 65 participants from Europe, the USA and Japan; (2) the first Phonons and Fluctuations workshop, held in Paris on 8th and 9th November 2010, supported by French, Spanish and Finnish national projects and EU projects, attended by about 50 researchers; (3) the second Phonon and Fluctuations workshop, held in Paris on 8th and 9th

  10. From 1D chain to 3D network: A theoretical study on TiO{sub 2} low dimensional structures

    SciTech Connect

    Guo, Ling-ju; He, Tao; Zeng, Zhi

    2015-06-14

    We have performed a systematic study on a series of low dimensional TiO{sub 2} nanostructures under density functional theory methods. The geometries, stabilities, growth mechanism, and electronic structures of 1D chain, 2D ring, 2D ring array, and 3D network of TiO{sub 2} nanostructures are analyzed. Based on the Ti{sub 2}O{sub 4} building unit, a series of 1D TiO{sub 2} nano chains and rings can be built. Furthermore, 2D ring array and 3D network nanostructures can be constructed from 1D chains and rings. Among non-periodic TiO{sub 2} chain and ring structures, one series of ring structures is found to be more stable. The geometry model of the 2D ring arrays and 3D network structures in this work has provided a theoretical understanding on the structure information in experiments. Based on these semiconductive low dimensional structures, moreover, it can help to understand and design new hierarchical TiO{sub 2} nanostructure in the future.

  11. Semiconductor structure and devices

    NASA Technical Reports Server (NTRS)

    Dinkel, Nancy A. (Inventor); Goldstein, Bernard (Inventor); Ettenberg, Michael (Inventor)

    1987-01-01

    Semiconductor devices such as lasers which include a substrate with a channel therein with a clad layer overlying the substrate and filling the channel exhibit irregularities such as terraces in the surface of the clad layer which are detrimental to device performance. These irregularities are substantially eliminated by forming the channel in a surface of a buffer layer greater than about 4 micrometers thick on the substrate and forming the clad layer over the buffer layer and the channel. CW lasers incorporating the principles of the invention exhibit the highest output power in a single spatial mode and maximum output power which have been observed to date.

  12. Extracting Low-Dimensional Latent Structure from Time Series in the Presence of Delays.

    PubMed

    Lakshmanan, Karthik C; Sadtler, Patrick T; Tyler-Kabara, Elizabeth C; Batista, Aaron P; Yu, Byron M

    2015-09-01

    Noisy, high-dimensional time series observations can often be described by a set of low-dimensional latent variables. Commonly used methods to extract these latent variables typically assume instantaneous relationships between the latent and observed variables. In many physical systems, changes in the latent variables manifest as changes in the observed variables after time delays. Techniques that do not account for these delays can recover a larger number of latent variables than are present in the system, thereby making the latent representation more difficult to interpret. In this work, we introduce a novel probabilistic technique, time-delay gaussian-process factor analysis (TD-GPFA), that performs dimensionality reduction in the presence of a different time delay between each pair of latent and observed variables. We demonstrate how using a gaussian process to model the evolution of each latent variable allows us to tractably learn these delays over a continuous domain. Additionally, we show how TD-GPFA combines temporal smoothing and dimensionality reduction into a common probabilistic framework. We present an expectation/conditional maximization either (ECME) algorithm to learn the model parameters. Our simulations demonstrate that when time delays are present, TD-GPFA is able to correctly identify these delays and recover the latent space. We then applied TD-GPFA to the activity of tens of neurons recorded simultaneously in the macaque motor cortex during a reaching task. TD-GPFA is able to better describe the neural activity using a more parsimonious latent space than GPFA, a method that has been used to interpret motor cortex data but does not account for time delays. More broadly, TD-GPFA can help to unravel the mechanisms underlying high-dimensional time series data by taking into account physical delays in the system. PMID:26079746

  13. Extracting Low-Dimensional Latent Structure from Time Series in the Presence of Delays

    PubMed Central

    Lakshmanan, Karthik C.; Sadtler, Patrick T.; Tyler-Kabara, Elizabeth C.; Batista, Aaron P.; Yu, Byron M.

    2015-01-01

    Noisy, high-dimensional time series observations can often be described by a set of low-dimensional latent variables. Commonly-used methods to extract these latent variables typically assume instantaneous relationships between the latent and observed variables. In many physical systems, changes in the latent variables manifest as changes in the observed variables after time delays. Techniques that do not account for these delays can recover a larger number of latent variables than are present in the system, thereby making the latent representation more difficult to interpret. In this work, we introduce a novel probabilistic technique, time-delay Gaussian-process factor analysis (TD-GPFA), that performs dimensionality reduction in the presence of a different time delay between each pair of latent and observed variables. We demonstrate how using a Gaussian process to model the evolution of each latent variable allows us to tractably learn these delays over a continuous domain. Additionally, we show how TD-GPFA combines temporal smoothing and dimensionality reduction into a common probabilistic framework. We present an Expectation/Conditional Maximization Either (ECME) algorithm to learn the model parameters. Our simulations demonstrate that when time delays are present, TD-GPFA is able to correctly identify these delays and recover the latent space. We then applied TD-GPFA to the activity of tens of neurons recorded simultaneously in the macaque motor cortex during a reaching task. TD-GPFA is able to better describe the neural activity using a more parsimonious latent space than GPFA, which is a method that has been used to interpret motor cortex data, but does not account for time delays. More broadly, TD-GPFA can help to unravel the mechanisms underlying high-dimensional time series data by taking into account physical delays in the system. PMID:26079746

  14. Semiconductor alloys - Structural property engineering

    NASA Technical Reports Server (NTRS)

    Sher, A.; Van Schilfgaarde, M.; Berding, M.; Chen, A.-B.

    1987-01-01

    Semiconductor alloys have been used for years to tune band gaps and average bond lengths to specific applications. Other selection criteria for alloy composition, and a growth technique designed to modify their structural properties, are presently considered. The alloys Zn(1-y)Cd(y)Te and CdSe(y)Te(1-y) are treated as examples.

  15. Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene

    PubMed Central

    Chen, H.-H.; Su, S. H.; Chang, S.-L.; Cheng, B.-Y.; Chen, S. W.; Chen, H.-Y.; Lin, M.-F.; Huang, J. C. A.

    2015-01-01

    To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices. PMID:26100604

  16. Tailoring low-dimensional structures of bismuth on monolayer epitaxial graphene

    NASA Astrophysics Data System (ADS)

    Chen, H.-H.; Su, S. H.; Chang, S.-L.; Cheng, B.-Y.; Chen, S. W.; Chen, H.-Y.; Lin, M.-F.; Huang, J. C. A.

    2015-06-01

    To improve graphene-based multifunctional devices at nanoscale, a stepwise and controllable fabrication procedure must be elucidated. Here, a series of structural transition of bismuth (Bi) adatoms, adsorbed on monolayer epitaxial graphene (MEG), is explored at room temperature. Bi adatoms undergo a structural transition from one-dimensional (1D) linear structures to two-dimensional (2D) triangular islands and such 2D growth mode is affected by the corrugated substrate. Upon Bi deposition, a little charge transfer occurs and a characteristic peak can be observed in the tunneling spectrum, reflecting the distinctive electronic structure of the Bi adatoms. When annealed to ~500 K, 2D triangular Bi islands aggregate into Bi nanoclusters (NCs) of uniform size. A well-controlled fabrication method is thus demonstrated. The approaches adopted herein provide perspectives for fabricating and characterizing periodic networks on MEG and related systems, which are useful in realizing graphene-based electronic, energy, sensor and spintronic devices.

  17. Semiconductor devices having a recessed electrode structure

    DOEpatents

    Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth

    2015-05-26

    An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.

  18. Method and structure for passivating semiconductor material

    DOEpatents

    Pankove, Jacques I.

    1981-01-01

    A structure for passivating semiconductor material comprises a substrate of crystalline semiconductor material, a relatively thin film of carbon disposed on a surface of the crystalline material, and a layer of hydrogenated amorphous silicon deposited on the carbon film.

  19. Interplay between electronic and structural degrees of freedom in quarter-filled low dimensional conductors

    NASA Astrophysics Data System (ADS)

    Pouget, Jean-Paul

    2015-03-01

    We review the basic aspects of the charge density wave (CDW) and bond order wave (BOW) instabilities observed in one dimension (1D) organic conductors at either the 2kF and/or 4kF critical wave vectors. We start by recalling the main features of the coupled structural/electronic Peierls instabilities observed in donor-acceptor (D-A) charge transfer (CT) salts. Then we consider the specific case of 2:1 salts D2X where X is a monovalent anion. We show that the incipient CDW/BOW instabilities of the Bechgaard and Fabre salts are those of the parent quarter-filled CT salts TMTSF-DMTCNQ and TMTTF-DMTCNQ respectively. We also consider more specifically the influence of specific features of D2X salts such as the stack dimerization, the Fermi surface warping and the coupling to the anions. Then we discuss more generally the role of the anions in the Bechgaard and Fabre salts by pointing out the influence of polarization and charge displacement induced by the anion shift. Finally we show that some of these features are also relevant to understand the subtle interplay between structural and electronic degrees of freedom in 2D quarter-filled organic salts such as the (BEDT-TTF)2X series.

  20. Nanoscale and proximity effects on low-dimensional helical magnetic structures

    NASA Astrophysics Data System (ADS)

    Sandratskii, Leonid; Fisher, J.; Park, S.; Ouazi, S.; Sander, D.; Kirschner, J.

    We combine symmetry arguments, first-principles calculations and spin-resolved STS measurements to study a 2D helical magnet of some nm extension in proximity to ferromagnetic Co and vacuum regions. Considering the prototypical helical 2D system, an Fe bilayer with intrinsic helical spin structure (1), we report a non-uniform distortion of the spin helix which depends on the lateral extension of the bilayer and on the proximity to either Co or vacuum. The proximity effect manifests itself in different modifications of the magnetic and electronic structures of Fe in vicinity of the interfaces with Co and vacuum. These nanosize and proximity effects have not been discussed before. We demonstrate that, in contrast to an ideal helix of infinite length, the lack of symmetry of the nm-long distorted Fe spin helix, induces an energy dependence of the direction of the electronic magnetization which is revealed in the measured energy dependence of the spin-asymmetry of the differential tunneling conductance. (1) Phark, S. H.; Fischer, J. A.; Corbetta, M.; Sander, D.; Nakamura, K. & Kirschner, J. Reduced-dimensionality-induced helimagnetism in iron nanoislands Nat Commun 5 (2014) 5183.

  1. Effect of low-dimensional alumina structures on viability of L 929 cells

    SciTech Connect

    Fomenko, Alla N. Korovin, Matvey S. Bakina, Olga V. Kazantsev, Sergey O. Glazkova, Elena A. Svarovskaya, Natalia V. Lozhkomoev, Aleksandr S.

    2015-10-27

    In the study, we estimated the cytotoxicity of alumina nanoparticles differing in shape (nanofibers, nanoplates, nanosheets, agglomerates of nanosheets) and close in physicochemical properties (particle size, specific surface area, phase composition, and zeta potential). The alumina structures were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) data, low-temperature nitrogen adsorption, and dynamic light scattering (DLS). The cytotoxicity was estimated on fibroblast cells of the L929 line. It was found that a more adverse effect on the cells was exerted by alumina nanofibers and nanosheets. The action of nanosheets on the cells was inhibitory and was of about the same level, irrespective of the observation period. The effect of alumina nanosheet agglomerates and nanoplates on the cell proliferation was weak even at an exposure time of 72 h.

  2. Structure and dynamics in low-dimensional guest-host systems

    SciTech Connect

    Fischer, J.E. . Dept. of Materials Science)

    1992-04-01

    New synthetic materials continue to be discovered at a rapid rate. Many of these can be broadly described as guest-host systems, in the sense that a range of compositions is accessible by selectively inserting heteroatoms or molecules into the interstitial sites in an otherwise pure starting material. The premier examples are layer intercalates (graphite, transition metal di- and trichalocogenides, silicate clays) and doped polymers (notably polyacetylene). With a somewhat broader definition of intercaiation, one might include the high-{Tc} cuprate superconductors (variable oxygen and alkaline earth concentrations), ion-exchanged beta-alumina and related defect oxides, and alkali metal-doped buckminsterfullerene (C{sub 60}). The interest in these material families for energy applications is directly attributable to the guest-in-a-host feature, either by exploiting guest ion mobility in electrochemical devices or by tuning/optimizing properties via control of guest concentration and sublattice structure. This document is a progress report covering the first 25 months (6/89 to 7/91) of the present 3-year period. Part IV describes the proposed research 6/1/92--5/31/95.

  3. On the structure of positive maps. II. Low dimensional matrix algebras

    NASA Astrophysics Data System (ADS)

    Majewski, Władysław A.; Tylec, Tomasz I.

    2013-07-01

    We use a new idea that emerged in the examination of exposed positive maps between matrix algebras to investigate in more detail the differences and similarities between unital positive maps on M2 ({C}) and M3({C}). Our main tool stems from classical Grothendieck theorem on tensor product of Banach spaces and is an older and more general version of Choi-Jamiołkowski isomorphism between positive maps and block positive Choi matrices. It takes into account the correct topology on the latter set that is induced by the uniform topology on positive maps. In this setting, we show that in M2({C}) case a large class of nice positive maps can be generated from the small set of maps represented by self-adjoint unitaries, 2Px with x maximally entangled vector and p⊗ {1} with p rank 1 projector. We indicate problems with passing this result to M3({C}) case. Among similarities, in both M2({C}) and M3({C}) cases any unital positive map represented by self-adjoint unitary is unitarily equivalent to the transposition map. Consequently, we obtain a large family of exposed maps. Furthermore, for M3({C}) there appear new non-trivial class of maps represented by Choi matrices with square equal to a projector. We examine this case. We also investigate a convex structure of the Choi map, the first example of non-decomposable map. As a result the nature of the Choi map will be explained.

  4. Low dimensional quantum paramagnets

    NASA Astrophysics Data System (ADS)

    Hong, Tao

    A quantum paramagnet is a material with interacting spins that possesses a paramagnetic ground state and an energy gap to all excitations. This dissertation focuses on studying the magnetic excitation spectrum and the quantum critical phenomena of such low dimensional quantum paramagnet systems. Inelastic neutron scattering (INS) measurements of Cu(Quinoxaline)Br 2 was performed on a partially deuterated powder sample. Magnetic neutron scattering was identified above an energy gap of 1.9 meV. Consideration of the sharp spectral max imum and wave vector dependence of the scattering and polymeric structure further identifies the material as a two-legged spin-1/2 ladder. The continuous uniform transformation theory provides an excellent account of the data with leg exchange J‖ =2.0 meV and the rung exchange J⊥ =3.3 meV. INS study of (2,3 - dimethylpyridinium)2CuBr4 (DIMPY) in both powder and single crystalline form are presented to understand the origin of the spin gap and what is the right spin Hamiltonian. Magnetic excitations are found above a 0.3 meV energy gap. The excitation only disperses along the a-direction with a bandwidth that exceeds 1.7 meV. The conclusion to be a S=1/2 two-legged spin ladder is supported by the material structure and INS measurement. External magnetic field drives the system into a critical region and induced low energy excitation continuum above critical field was studied. Piperazinium Hexachlorodicuprate (PHCC) is a two-dimensional antiferromagnet. We studied the behavior in the vicinity of the quantum critical point (QCP) where the spin gap is closed by an applied magnetic field by INS. The energy and damping of the low energy excitations were measured in the vicinity of the QCP where both quantities become strongly temperature dependent, which can be successfully described by a selfconsistent Hartree-Fock theory of strongly interacting bosons developed by Sachdev and Dunkel. A preliminary study of hydrostatic pressure effects

  5. Band structure engineering in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Schwarze, Martin; Tress, Wolfgang; Beyer, Beatrice; Gao, Feng; Scholz, Reinhard; Poelking, Carl; Ortstein, Katrin; Günther, Alrun A.; Kasemann, Daniel; Andrienko, Denis; Leo, Karl

    2016-06-01

    A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors.

  6. Band structure engineering in organic semiconductors.

    PubMed

    Schwarze, Martin; Tress, Wolfgang; Beyer, Beatrice; Gao, Feng; Scholz, Reinhard; Poelking, Carl; Ortstein, Katrin; Günther, Alrun A; Kasemann, Daniel; Andrienko, Denis; Leo, Karl

    2016-06-17

    A key breakthrough in modern electronics was the introduction of band structure engineering, the design of almost arbitrary electronic potential structures by alloying different semiconductors to continuously tune the band gap and band-edge energies. Implementation of this approach in organic semiconductors has been hindered by strong localization of the electronic states in these materials. We show that the influence of so far largely ignored long-range Coulomb interactions provides a workaround. Photoelectron spectroscopy confirms that the ionization energies of crystalline organic semiconductors can be continuously tuned over a wide range by blending them with their halogenated derivatives. Correspondingly, the photovoltaic gap and open-circuit voltage of organic solar cells can be continuously tuned by the blending ratio of these donors. PMID:27313043

  7. The 6th International Conference on Modulated Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    1993-08-01

    This workbook contains unreferred manuscripts of papers which will be presented at conference. The topics covered include the following: growth of wires and dots; transport properties in low dimensional systems; growth characterization transport; growth characterization and phonons; quantum wells -- electrical properties; vertical transport -- resonant tunneling; quantum wells, superlattices -- optical properties; metal/semiconductors and type 2 interfaces; atomic scale characterization; electronic excitation -- superlattices; and optical properties.

  8. PREFACE: Dynamics of low-dimensional systems Dynamics of low-dimensional systems

    NASA Astrophysics Data System (ADS)

    Bernasconi, M.; Miret-Artés, S.; Toennies, J. P.

    2012-03-01

    With the development of techniques for high-resolution inelastic helium atom scattering (HAS), electron scattering (EELS) and neutron spin echo spectroscopy, it has become possible, within approximately the last thirty years, to measure the dispersion curves of surface phonons in insulators, semiconductors and metals. In recent years, the advent of new experimental techniques such as 3He spin-echo spectroscopy, scanning inelastic electron tunnel spectroscopy, inelastic x-ray scattering spectroscopy and inelastic photoemission have extended surface phonon spectroscopy to a variety of systems. These include ultra-thin metal films, adsorbates at surface and elementary processes where surface phonons play an important role. Other important directions have been actively pursued in the past decade: the dynamics of stepped surfaces and clusters grown on metal surfaces, due to their relevance in many dynamical and chemical processes at surfaces, including heterogeneous catalysis; clusters; diffusion etc. The role of surface effects in these processes has been conjectured since the early days of surface dynamics, although only now is the availability of ab initio approaches providing those conjectures with a microscopic basis. Last but not least, the investigation of non-adiabatic effects, originating for instance from the hybridization (avoided crossing) of the surface phonons branches with the quasi 1D electron-hole excitation branch, is also a challenging new direction. Furthermore, other elementary oscillations such as surface plasmons are being actively investigated. The aforementioned experimental breakthroughs have been accompanied by advances in the theoretical study of atom-surface interaction. In particular, in the past decade first principles calculations based on density functional perturbation theory have boosted the theoretical study of the dynamics of low-dimensional systems. Phonon dispersion relations of clean surfaces, the dynamics of adsorbates, and the

  9. Method of transferring strained semiconductor structure

    DOEpatents

    Nastasi, Michael A.; Shao, Lin

    2009-12-29

    The transfer of strained semiconductor layers from one substrate to another substrate involves depositing a multilayer structure on a substrate having surface contaminants. An interface that includes the contaminants is formed in between the deposited layer and the substrate. Hydrogen atoms are introduced into the structure and allowed to diffuse to the interface. Afterward, the deposited multilayer structure is bonded to a second substrate and is separated away at the interface, which results in transferring a multilayer structure from one substrate to the other substrate. The multilayer structure includes at least one strained semiconductor layer and at least one strain-induced seed layer. The strain-induced seed layer can be optionally etched away after the layer transfer.

  10. The amazing story of semiconductor surface structures

    NASA Astrophysics Data System (ADS)

    Duke, C. B.

    1995-12-01

    A brief indication of the history of the determination and prediction of the structure of semiconductor surfaces is given. Only clean surfaces are considered, although adsorbate structures exhibit analogous features. Many of these surfaces are reconstructed, i.e., the symmetry of their surface structure is lower than that of the corresponding bulk lattice plane. During the 1980s and 1990s, the detailed atomic geometries of many of these structures were determined. They exhibit a wide variety of atomic motifs, many of which are not familiar from either small molecule geometries or solid state structures. Theoretical predictions exist for a few of the most heavily studied structures, but even in these cases not all the details of the structures are accepted. The enormous literature on this topic can be comprehended by recognizing that the surface regions of semiconductors constitute a new class of two dimensional chemical compounds, restricted by the requirement that they fit epitaxically on the bulk crystalline substrate. Five principles govern the formation of these compounds for clean tetrahedrally coordinated semiconductors, guiding even a novice to a rudimentary understanding of the origin of the observed rich variety of surface structures. In the case of the cleavage surfaces additional scaling laws are satisfied which further buttress the concept that these surfaces are two dimensional compounds governed by coordination chemistry considerations which are distinct from those appropriate for either molecules or bulk solids.

  11. Ability of a low-dimensional model to predict geometry-dependent dynamics of large-scale coherent structures in turbulence.

    PubMed

    Bai, Kunlun; Ji, Dandan; Brown, Eric

    2016-02-01

    We test the ability of a general low-dimensional model for turbulence to predict geometry-dependent dynamics of large-scale coherent structures, such as convection rolls. The model consists of stochastic ordinary differential equations, which are derived as a function of boundary geometry from the Navier-Stokes equations [Brown and Ahlers, Phys. Fluids 20, 075101 (2008); Phys. Fluids 20, 105105 (2008)]. We test the model using Rayleigh-Bénard convection experiments in a cubic container. The model predicts a mode in which the alignment of a convection roll stochastically crosses a potential barrier to switch between diagonals. We observe this mode with a measured switching rate within 30% of the prediction. PMID:26986423

  12. Ability of a low-dimensional model to predict geometry-dependent dynamics of large-scale coherent structures in turbulence.

    PubMed

    Bai, Kunlun; Ji, Dandan; Brown, Eric

    2016-02-01

    We test the ability of a general low-dimensional model for turbulence to predict geometry-dependent dynamics of large-scale coherent structures, such as convection rolls. The model consists of stochastic ordinary differential equations, which are derived as a function of boundary geometry from the Navier-Stokes equations [Brown and Ahlers, Phys. Fluids 20, 075101 (2008); Phys. Fluids 20, 105105 (2008)]. We test the model using Rayleigh-Bénard convection experiments in a cubic container. The model predicts a mode in which the alignment of a convection roll stochastically crosses a potential barrier to switch between diagonals. We observe this mode with a measured switching rate within 30% of the prediction.

  13. Bulk anisotropic excitons in type-II semiconductors built with 1D and 2D low-dimensional structures

    NASA Astrophysics Data System (ADS)

    Coyotecatl, H. A.; Del Castillo-Mussot, M.; Reyes, J. A.; Vazquez, G. J.; Montemayor-Aldrete, J. A.; Reyes-Esqueda, J. A.; Cocoletzi, G. H.

    2005-08-01

    We used a simple variational approach to account for the difference in the electron and hole effective masses in Wannier-Mott excitons in type-II semiconducting heterostructures in which the electron is constrained in an one-dimensional quantum wire (1DQW) and the hole is in a two-dimensional quantum layer (2DQL) perpendicular to the wire or viceversa. The resulting Schrodinger equation is similar to that of a 3D bulk exciton because the number of free (nonconfined) variables is three; two coming from the 2DQL and one from the 1DQW. In this system the effective electron-hole interaction depends on the confinement potentials.

  14. Local structure and lattice dynamics study of low dimensional materials using atomic pair distribution function and high energy resolution inelastic x-ray scattering

    NASA Astrophysics Data System (ADS)

    Shi, Chenyang

    Structure and dynamics lie at the heart of the materials science. A detailed knowledge of both subjects would be foundational in understanding the materials' properties and predicting their potential applications. However, the task becomes increasingly dicult as the particle size is reduced to the nanometer scale. For nanostructured materials their laboratory x-ray scattering patterns are overlapped and broadened, making structure determination impossible. Atomic pair distribution function technique based on either synchrotron x-ray or neutron scattering data is known as the tool of choice for probing local structures. However, to solve the "structure problem" in low-dimensional materials with PDF is still challenging. For example for 2D materials of interest in this thesis the crystallographic modeling approach often yields unphysical thermal factors along stacking direction where new chemical intuitions about their actual structures and new modeling methodology/program are needed. Beyond this, lattice dynamical investigations on nanosized particles are extremely dicult. Laboratory tools such as Raman and infra-red only probe phonons at Brillouin zone center. Although in literature there are a great number of theoretical studies of their vibrational properties based on either empirical force elds or density functional theory, various approximations made in theories make the theoretical predictions less reliable. Also, there lacks the direct experiment result to validate the theory against. In this thesis, we studied the structure and dynamics of a wide variety of technologically relevant low-dimensional materials through synchrotron based x-ray PDF and high energy resolution inelastic x-ray scattering (HERIX) techniques. By collecting PDF data and employing advanced modeling program such as DiPy-CMI, we successfully determined the atomic structures of (i) emerging Ti3C2, Nb4C3 MXenes (transition metal carbides and/or nitrides) that are promising for energy storage

  15. Structural and electronic properties of Ce overlayers and low-dimensional Pt-Ce alloys on Pt\\{111\\}

    NASA Astrophysics Data System (ADS)

    Baddeley, Christopher J.; Stephenson, Andrew W.; Hardacre, Christopher; Tikhov, Mintcho; Lambert, Richard M.

    1997-11-01

    The structural, thermal, chemisorptive, and electronic properties of Ce on Pt\\{111\\} are studied by photoemission, Auger spectroscopy, scanning tunnel microscope (STM), and low-energy electron diffraction (LEED). Stranski-Krastanov-like growth of low-density Ce layers is accompanied by substantial valence charge transfer from Ce to Pt: in line with this, the measured dipole moment and polarizability of adsorbed Ce at low coverages are 7.2×10-30 C m and ~1.3×10-29 m3, respectively. Pt-Ce intermixing commences at ~400 K and with increasing temperature a sequence of five different ordered surface alloys evolves. The symmetry, periodicities, and rotational epitaxy observed by LEED are in good accord with the STM data which reveal the true complexity of the system. The various bimetallic surface phases are based on growth of crystalline Pt5Ce, a hexagonal layer structure consisting of alternating layers of Pt2Ce and Kagomé nets of Pt atoms. This characteristic ABAB layered arrangement of the surface alloys is clearly imaged, and chemisorption data permit a distinction to be made between the more reactive Pt2Ce layer and the less reactive Pt Kagomé net. Either type of layer can appear at the surface as the terminating structure, thicker films exhibiting unit mesh parameters characteristic of the bulk alloy.

  16. Structure and dynamics in low-dimensional guest-host systems. Progress report, June 1, 1990--May 31, 1992

    SciTech Connect

    Fischer, J.E.

    1992-04-01

    New synthetic materials continue to be discovered at a rapid rate. Many of these can be broadly described as guest-host systems, in the sense that a range of compositions is accessible by selectively inserting heteroatoms or molecules into the interstitial sites in an otherwise pure starting material. The premier examples are layer intercalates (graphite, transition metal di- and trichalocogenides, silicate clays) and doped polymers (notably polyacetylene). With a somewhat broader definition of intercaiation, one might include the high-{Tc} cuprate superconductors (variable oxygen and alkaline earth concentrations), ion-exchanged beta-alumina and related defect oxides, and alkali metal-doped buckminsterfullerene (C{sub 60}). The interest in these material families for energy applications is directly attributable to the guest-in-a-host feature, either by exploiting guest ion mobility in electrochemical devices or by tuning/optimizing properties via control of guest concentration and sublattice structure. This document is a progress report covering the first 25 months (6/89 to 7/91) of the present 3-year period. Part IV describes the proposed research 6/1/92--5/31/95.

  17. Semiconductor structures for repeated velocity overshoot

    NASA Astrophysics Data System (ADS)

    Cooper, J. A., Jr.; Capasso, F.; Thornber, K. K.

    1982-12-01

    The conditions required for obtaining repeated velocity overshoot in semiconductors are discussed. Two classes of structures that provide these conditions are considered. The structures are seen as holding promise for achieving average drift velocities well in excess of the maximum steady-state velocity over distances ranging from submicron to tens of microns. In structures of the first class, the stairstep in potential is achieved by using a graded bandgap that is similar to the avalanche photodetector described by Williams et al. (1982), where the composition is graded from GaAs to Al(0.2)Ga(0.8)As. The second class of structures uses alternating planar doped charge sheets, as described by Malik et al. (1980).

  18. The structure and morphology of semiconductor nanocrystals

    SciTech Connect

    Kadavanich, A V

    1997-11-01

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

  19. Low dimensional magnetism

    NASA Astrophysics Data System (ADS)

    Kjall, Jonas Alexander

    quantum Hall phases for bosons can be obtained, and the phases nu = 1/2 and nu = 2/3 have the edge spectra predicted by the chiral Luttinger liquid theory. Also, some of the traditional experimental techniques for detecting magnetic order and dynamics in solid state materials, like neutron scattering has had somewhat of a renaissance lately. In a recent experiment on CoNb2O 6, Coldea et. al. found for the first time experimental evidence of the exceptional Lie algebra E8. The emergence of this symmetry was theoretically predicted long ago for the transverse quantum Ising chain in the presence of a weak longitudinal field. We consider an accurate microscopic model of CoNb2O6 incorporating additional couplings and calculate numerically the dynamical structure function using a recently developed matrix-product-state method. The excitation spectra show bound states characteristic of the weakly broken E8 symmetry. We compare the observed bound state signatures in this model to those found in the transverse Ising chain in a longitudinal field and to experimental data. Finally, we investigate the ground state phase diagram of a related quantum spin chain, the S = 2 XXZ chain with single-ion anisotropy. The interest in this system comes mainly from connecting the highly quantum mechanical spin-1 phase diagram with the classical S = infinity phase diagram. While most of these questions where believed to have been satisfactorily answered mainly with DMRG, some recent studies have questioned some of the conclusions. We use several of the recent advances within DMRG and perform a detailed analysis of the whole phase diagram. We extend the phase diagram by considering different types of single ion anisotropies which help us to answer two important questions: First we show that one can adiabatically move from the isotropic Heisenberg point to the so-called large-D phase with a continuous change of the Hamiltonian. Second, we can tune the model into a predicted intermediate phase which

  20. Electronic states of semiconductor-metal-semiconductor quantum-well structures

    NASA Technical Reports Server (NTRS)

    Huberman, M. L.; Maserjian, J.

    1988-01-01

    Quantum-size effects are calculated in thin layered semiconductor-metal-semiconductor structures using an ideal free-electron model for the metal layer. The results suggest new quantum-well structures having device applications. Structures with sufficiently high-quality interfaces should exhibit effects such as negative differential resistance due to tunneling between allowed states. Similarly, optical detection by intersubband absorption may be possible. Ultrathin metal layers are predicted to behave as high-density dopant sheets.

  1. Electronic structure of low-dimensional 4d(5) oxides: interplay of ligand distortions, overall lattice anisotropy, and spin-orbit interactions.

    PubMed

    Katukuri, Vamshi M; Roszeitis, Karla; Yushankhai, Viktor; Mitrushchenkov, Alexander; Stoll, Hermann; van Veenendaal, Michel; Fulde, Peter; van den Brink, Jeroen; Hozoi, Liviu

    2014-05-19

    The electronic structure of the low-dimensional 4d(5) oxides Sr2RhO4 and Ca3CoRhO6 is herein investigated by embedded-cluster quantum chemistry calculations. A negative tetragonal-like t2g splitting is computed in Sr2RhO4 and a negative trigonal-like splitting is predicted for Ca3CoRhO6, in spite of having positive tetragonal distortions in the former material and cubic oxygen octahedra in the latter. Our findings bring to the foreground the role of longer-range crystalline anisotropy in generating noncubic potentials that compete with local distortions of the ligand cage, an issue not addressed in standard textbooks on crystal-field theory. We also show that sizable t2g(5)-t2g(4)eg(1) couplings via spin-orbit interactions produce in Sr2RhO4 ⟨Z⟩ = ⟨Σ(i)l(i)·s(i)⟩ ground-state expectation values significantly larger than 1, quite similar to theoretical and experimental data for 5d(5) spin-orbit-driven oxides such as Sr2IrO4. On the other hand, in Ca3CoRhO6, the ⟨Z⟩ values are lower because of larger t2g-eg splittings. Future X-ray magnetic circular dichroism experiments on these 4d oxides will constitute a direct test for the ⟨Z⟩ values that we predict here, the importance of many-body t2g-eg couplings mediated by spin-orbit interactions, and the role of low-symmetry fields associated with the extended surroundings. PMID:24779549

  2. Electrical transport engineering of semiconductor superlattice structures

    NASA Astrophysics Data System (ADS)

    Shokri, Aliasghar

    2014-04-01

    We investigate the influence of doping concentration on band structures of electrons and electrical transmission in a typical aperiodic semiconductor superlattice consisting of quantum well and barrier layers, theoretically. For this purpose, we assume that each unit cell of the superlattice contains alternately two types of material GaAs (as a well) and GaAlAs (as a barrier) with six sublayers of two materials. Our calculations are based on the generalized Kronig-Penny (KP) model and the transfer matrix method within the framework of the parabolic conductance band effective mass approximation in the coherent regime. This model reduces the numerical calculation time and enables us to use the transfer matrix method to investigate transport in the superlattices. We show that by varying the doping concentration and geometrical parameters, one can easily block the transmission of the electrons. The numerical results may be useful in designing of nanoenergy filter devices.

  3. Metal Insulator Semiconductor Structures on Gallium Arsenide.

    NASA Astrophysics Data System (ADS)

    Connor, Sean Denis

    Available from UMI in association with The British Library. The compound semiconductor gallium arsenide and its associated aluminium alloys have been the subject of intensive research in recent years. These materials offer the advantage of high electron mobilities coupled with the ability to be 'barrier engineered' leading to high injection efficiencies in bipolar devices. From a technological viewpoint however these materials are difficult to work with and device realisation is a major problem. Both thermal and anodic oxidation of these materials fail to produce a dielectric of sufficient quality for device applications and as a result devices tend to be complex non planar, mesa structures. A technique is proposed whereby the electrical interface is separated from the dielectric by means of a thin layer of AlGaAs, carrier confinement in the active GaAs region being maintained by the potential barriers to holes and electrons formed by the GaAs-AlGaAs junction. The integrity of these barriers is maintained by the provision of a suitable 'capping' dielectric. The electrical characteristics of various dielectric systems on GaAs have been investigated by means of current -voltage, capacitance-voltage and electronic breakdown measurements. Transport mechanisms for leakage current through these systems are identified and the interface properties (viz Fermi level pinning etc.) assessed by means of a direct comparison between experimental capacitance-voltage curves and theoretical data obtained from classical theory. As a technique for producing a convenient, in house 'capping' dielectric with good electrical and mechanical properties, the plasma anodisation of deposited aluminium films has been investigated. The anodisation parameters have been optimised for oxidation of these films in a microwave sustained oxygen plasma to give alumina films of around 500 A. A qualitative model for the anodisation process, involving linear and parabolic growth kinetics is proposed and

  4. Semiconductor wire array structures, and solar cells and photodetectors based on such structures

    SciTech Connect

    Kelzenberg, Michael D.; Atwater, Harry A.; Briggs, Ryan M.; Boettcher, Shannon W.; Lewis, Nathan S.; Petykiewicz, Jan A.

    2014-08-19

    A structure comprising an array of semiconductor structures, an infill material between the semiconductor materials, and one or more light-trapping elements is described. Photoconverters and photoelectrochemical devices based on such structure also described.

  5. Electrochemical Characterization of Semiconductor Materials and Structures

    NASA Technical Reports Server (NTRS)

    1997-01-01

    For a period covering October 1, 1995 through August 12, 1996, the research group at CSU has conducted theoretical and experimental research on "Electrochemical Characterization of Semiconductor Materials and Structures. " The objective of this investigation was to demonstrate the applicability of electrochemical techniques for characterization of complex device structures based on InP and GaAs, Ge, InGaAs, InSb, InAs and InSb, including: (1) accurate EC-V net majority carrier concentration depth profiling, and (2) surface and bulk structural and electrical type defect densities. Our motivation for this R&D effort was as follows: "Advanced space solar cells and ThermoPhotoVoltaic (TPV) cells are fabricated using a large variety of III-V materials based on InP and GaAs for solar cells and low bandgap materials such as Ge, InGaAs, InAs and InSb for TPV applications. At the present time for complex device structures using these materials, however, there is no simple way to assess the quality of these structures prior to device fabrication. Therefore, process optimization is a very time consuming and a costly endeavor". Completion of this R&D effort would have had unquestionable benefits for space solar cell and TPV cells, since electrochemical characterization of the above cell structures, if properly designed can provide many useful structural and electrical material information virtually at any depth inside various layers and at the interfaces. This, could have been applied for step-by-step process optimization, which could have been used for fabrication of new generation high efficiency, low cost space PV and TPV cells.

  6. PREFACE: Dynamics of low-dimensional systems Dynamics of low-dimensional systems

    NASA Astrophysics Data System (ADS)

    Bernasconi, M.; Miret-Artés, S.; Toennies, J. P.

    2012-03-01

    With the development of techniques for high-resolution inelastic helium atom scattering (HAS), electron scattering (EELS) and neutron spin echo spectroscopy, it has become possible, within approximately the last thirty years, to measure the dispersion curves of surface phonons in insulators, semiconductors and metals. In recent years, the advent of new experimental techniques such as 3He spin-echo spectroscopy, scanning inelastic electron tunnel spectroscopy, inelastic x-ray scattering spectroscopy and inelastic photoemission have extended surface phonon spectroscopy to a variety of systems. These include ultra-thin metal films, adsorbates at surface and elementary processes where surface phonons play an important role. Other important directions have been actively pursued in the past decade: the dynamics of stepped surfaces and clusters grown on metal surfaces, due to their relevance in many dynamical and chemical processes at surfaces, including heterogeneous catalysis; clusters; diffusion etc. The role of surface effects in these processes has been conjectured since the early days of surface dynamics, although only now is the availability of ab initio approaches providing those conjectures with a microscopic basis. Last but not least, the investigation of non-adiabatic effects, originating for instance from the hybridization (avoided crossing) of the surface phonons branches with the quasi 1D electron-hole excitation branch, is also a challenging new direction. Furthermore, other elementary oscillations such as surface plasmons are being actively investigated. The aforementioned experimental breakthroughs have been accompanied by advances in the theoretical study of atom-surface interaction. In particular, in the past decade first principles calculations based on density functional perturbation theory have boosted the theoretical study of the dynamics of low-dimensional systems. Phonon dispersion relations of clean surfaces, the dynamics of adsorbates, and the

  7. Synthesis, structure and magnetic properties of low dimensional spin systems in the 3d transition metal oxides and superconductivity in magnesium borate

    NASA Astrophysics Data System (ADS)

    Rogado, Nyrissa S.

    The major part of this thesis deals with the synthesis and magnetic characterization of low dimensional spin systems in the 3d transition metal oxides. Such systems are of interest due to the simplicity of their structures, allowing theoretical modeling of their electronic and magnetic behavior. Exotic properties are also often encountered. Studies involving layered magnetic materials based on triangle lattices, in particular, have resulted in many observations of unusual low temperature spin dynamics, and have presented new challenges for the theoretical understanding of magnetic systems. The magnetic properties of some compounds exhibiting these triangle-based lattices are described here in detail. BaNi2V2O8 is a spin-1 antiferromagnet on a honeycomb net. Susceptibility chi(T), specific heat C(T), and neutron diffraction measurements on this compound reveal the onset of antiferromagnetic (AFM) long-range ordering (LRO) close to 50 K. Diffuse diffraction peaks that are characteristic of two-dimensional (2D) short-range order are also observed up to 100 K. chi(T) of Ba(Ni1-xMgx)2V 2O8 shows the gradual disappearance of LRO with doping. Ni3V2O8, Co3V2O 8, and beta-Cu3V2O8 have spin-1, spin-3/2, and spin-1/2 magnetic lattices that are a new anisotropic variant of the Kagome net, wherein edge-sharing MO6 octahedra form the rises and rungs of a "Kagome staircase". The anisotropy largely relieves the geometric frustration, but results in rich magnetic behavior. Characterization of the magnetization of polycrystalline samples of Ni 3V2O8 and Co3V2O8 reveals that the compounds are ferrimagnetic in character. C(T) show four distinct magnetic phase transitions below 9 K for Ni3V2O 8 and two below 11 K for Co3V2O8. In the case of beta-Cu3V2O8, chi(T) and C(T) show the onset of short-range ordering at approximately 75 K, and a magnetic phase transition with the characteristics of antiferromagnetism at around 29 K. The second part of this thesis describes the bulk synthesis of

  8. Two-mode dynamics in different semiconductor laser structures

    NASA Astrophysics Data System (ADS)

    Scirè, Alessandro; Sorel, Marc; Colet, Pere; Tessone, Claudio Juan; Mirasso, Claudio R.; San Miguel, Maxi

    2006-04-01

    We review three two-mode models for different semiconductor laser structures: Vertical-Cavity Surface-Emitting Lasers (VCSELs), Twin-Stripe Semiconductor-Lasers (TSSL), and Semiconductor Ring Lasers (SRL). The VCSELs model and TSSL model display rich dynamic behavior when a saturable absorber is embedded in the cavity. VCSELs with saturable absorber showed polarization chaos, which found applications in encoded communications; TSSLs with saturable absorber show coherent locked states as well as chaotic behavior; and SRLs show a complex two-mode dynamics giving rise to bidirectional operation, alternate oscillations and spontaneous symmetry breaking toward quasi-unidirectional bistable solutions, with potential applications to all-optical switching.

  9. Printable semiconductor structures and related methods of making and assembling

    DOEpatents

    Nuzzo, Ralph G.; Rogers, John A.; Menard, Etienne; Lee, Keon Jae; Khang, Dahl-Young; Sun, Yugang; Meitl, Matthew; Zhu, Zhengtao; Ko, Heung Cho; Mack, Shawn

    2010-09-21

    The present invention provides a high yield pathway for the fabrication, transfer and assembly of high quality printable semiconductor elements having selected physical dimensions, shapes, compositions and spatial orientations. The compositions and methods of the present invention provide high precision registered transfer and integration of arrays of microsized and/or nanosized semiconductor structures onto substrates, including large area substrates and/or flexible substrates. In addition, the present invention provides methods of making printable semiconductor elements from low cost bulk materials, such as bulk silicon wafers, and smart-materials processing strategies that enable a versatile and commercially attractive printing-based fabrication platform for making a broad range of functional semiconductor devices.

  10. Printable semiconductor structures and related methods of making and assembling

    DOEpatents

    Nuzzo, Ralph G.; Rogers, John A.; Menard, Etienne; Lee, Keon Jae; Khang, Dahl-Young; Sun, Yugang; Meitl, Matthew; Zhu, Zhengtao; Ko, Heung Cho; Mack, Shawn

    2011-10-18

    The present invention provides a high yield pathway for the fabrication, transfer and assembly of high quality printable semiconductor elements having selected physical dimensions, shapes, compositions and spatial orientations. The compositions and methods of the present invention provide high precision registered transfer and integration of arrays of microsized and/or nanosized semiconductor structures onto substrates, including large area substrates and/or flexible substrates. In addition, the present invention provides methods of making printable semiconductor elements from low cost bulk materials, such as bulk silicon wafers, and smart-materials processing strategies that enable a versatile and commercially attractive printing-based fabrication platform for making a broad range of functional semiconductor devices.

  11. Printable semiconductor structures and related methods of making and assembling

    DOEpatents

    Nuzzo, Ralph G.; Rogers, John A.; Menard, Etienne; Lee, Keon Jae; Khang; , Dahl-Young; Sun, Yugang; Meitl, Matthew; Zhu, Zhengtao; Ko, Heung Cho; Mack, Shawn

    2013-03-12

    The present invention provides a high yield pathway for the fabrication, transfer and assembly of high quality printable semiconductor elements having selected physical dimensions, shapes, compositions and spatial orientations. The compositions and methods of the present invention provide high precision registered transfer and integration of arrays of microsized and/or nanosized semiconductor structures onto substrates, including large area substrates and/or flexible substrates. In addition, the present invention provides methods of making printable semiconductor elements from low cost bulk materials, such as bulk silicon wafers, and smart-materials processing strategies that enable a versatile and commercially attractive printing-based fabrication platform for making a broad range of functional semiconductor devices.

  12. Screenable contact structure and method for semiconductor devices

    DOEpatents

    Ross, Bernd

    1980-08-26

    An ink composition for deposition upon the surface of a semiconductor device to provide a contact area for connection to external circuitry is disclosed, the composition comprising an ink system containing a metal powder, a binder and vehicle, and a metal frit. The ink is screened onto the semiconductor surface in the desired pattern and is heated to a temperature sufficient to cause the metal frit to become liquid. The metal frit dissolves some of the metal powder and densifies the structure by transporting the dissolved metal powder in a liquid sintering process. The sintering process typically may be carried out in any type of atmosphere. A small amount of dopant or semiconductor material may be added to the ink systems to achieve particular results if desired.

  13. Synchronization of semiconductor laser arrays with 2D Bragg structures

    NASA Astrophysics Data System (ADS)

    Baryshev, V. R.; Ginzburg, N. S.

    2016-08-01

    A model of a planar semiconductor multi-channel laser is developed. In this model two-dimensional (2D) Bragg mirror structures are used for synchronizing radiation of multiple laser channels. Coupling of longitudinal and transverse waves can be mentioned as the distinguishing feature of these structures. Synchronization of 20 laser channels is demonstrated with a semi-classical approach based on Maxwell-Bloch equations.

  14. Electrochemical Characterization of Semiconductor Materials and Structures

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The objective of this investigation was to demonstrate the applicability of electrochemical techniques for characterization of complex device structures based on InP and GaAs, Ge, InGaAs, InSb, InAs and InSb, including: (1) accurate EC-V net majority carrier concentration depth profiling, and (2) surface and bulk structural and electrical type defect densities. Our motivation for this R&D effort was as follows: Advanced space solar cells and thermophotovoltaic (TPV) cells are fabricated using a large variety of III-V materials based on InP and GaAs for solar cells and low bandgap materials such as Ge, InGaAs, InAs and InSb for TPV applications. At the present time for complex device structures using these materials, however, there is no simple way to assess the quality of these structures prior to device fabrication. Therefore, process optimization is a very time consuming and a costly endeavor. Completion of this R&D effort would have had unquestionable benefits for space solar cell and TPV cells, since electrochemical characterization of the above cell structures, if properly designed can provide many useful structural and electrical material information virtually at any depth inside various layers and at the interfaces. This, could have been applied for step-by-step process optimization, which could have been used for fabrication of new generation high efficiency, low cost space PV and TPV cells. The four projects were as follows: (1) Electrochemical characterization of Germanium Substrates and Structures for TPV and other Device applications; (2) Electrochemical characterization of InP and GaAs based structures grown on InP, GaAs, and Si of Ge substrates for space solar cell applications; (3) Electrochemical characterization of InGaAs based structures grown on Ge Substrates,using InP as a buffer layer for TPV applications; (4) Electrochemical characterization of InSb and InAs bases structures for TPV applications.

  15. Supervised dimension reduction of intrinsically low-dimensional data.

    PubMed

    Vlassis, Nikos; Motomura, Yoichi; Kröse, Ben

    2002-01-01

    High-dimensional data generated by a system with limited degrees of freedom are often constrained in low-dimensional manifolds in the original space. In this article, we investigate dimension-reduction methods for such intrinsically low-dimensional data through linear projections that preserve the manifold structure of the data. For intrinsically one dimensional data, this implies projecting to a curve on the plane with as few intersections as possible. We are proposing a supervised projection pursuit method that can be regarded as an extension of the single-index model for nonparametric regression. We show results from a toy and two robotic applications. PMID:11747538

  16. Low-dimensional Te-based nanostructures.

    PubMed

    Wang, Qisheng; Safdar, Muhammad; Wang, Zhenxing; He, Jun

    2013-07-26

    Low-dimensional Te-based nanomaterials have attracted intense attention in recent years due to their novel physical properties including surface-state effects, photoelectricity, phase changes, and thermoelectricity. The recent development of synthesis methods of low-dimensional Te-based nanostructures is reviewed, such as van der Waals expitaxial growth and template-assisted solution-phase deposition. In addition, the unique properties of these materials, such as tunable surface states, high photoresponsivity, fast phase change, and high thermoelectricity figure of merit, are reviewed. The potential applications of low-dimensional Te-based nanostructures are broad but particularly promising for nanoscale electronic and photoelectronic devices. PMID:24048978

  17. Interface Structure of MoO3 on Organic Semiconductors

    PubMed Central

    White, Robin T.; Thibau, Emmanuel S.; Lu, Zheng-Hong

    2016-01-01

    We have systematically studied interface structure formed by vapor-phase deposition of typical transition metal oxide MoO3 on organic semiconductors. Eight organic hole transport materials have been used in this study. Ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy are used to measure the evolution of the physical, chemical and electronic structure of the interfaces at various stages of MoO3 deposition on these organic semiconductor surfaces. For the interface physical structure, it is found that MoO3 diffuses into the underlying organic layer, exhibiting a trend of increasing diffusion with decreasing molecular molar mass. For the interface chemical structure, new carbon and molybdenum core-level states are observed, as a result of interfacial electron transfer from organic semiconductor to MoO3. For the interface electronic structure, energy level alignment is observed in agreement with the universal energy level alignment rule of molecules on metal oxides, despite deposition order inversion. PMID:26880185

  18. Electronic Structure of II-Vi Semiconductors and Their Alloys

    NASA Astrophysics Data System (ADS)

    Wei, Su-Huai

    The II-VI semiconductors ZnXVI, CdXVI, and HgXVI are known to have a metal d band inside the main valence band. Using all-electron self-consistent electronic structure techniques, we study their effects on valence properties. For II-VI semiconductors, we find that p-d repulsion and hybridization (i) lower the band gaps, (ii) alter the sign of the crystal-field splitting, (iii) reduce the spin-orbit splitting, (iv) change the valence band offset between common-anion semiconductors, and (v) increase the equilibrium lattice parameters, p-d repulsion is also shown to be responsible for the anomalously small band gaps in chalcopyrites, and for the negative exchange splitting in MnTe. We also study the electronic structure of ordered and random II-VI substitutional alloys and identify the mechanism for their band gap narrowing. The random {A_{1-x}^{II}B_{x}^{II}C^{VI}} alloys are represented by the "special quasirandom structures." We show how chemical and structural perturbations lead to (i) distinct A-like and B-like features in the density of states and (ii) different C-like features associated with fluctuations in the local environments around the common sublattice.

  19. Magnetic structure of the low-dimensional magnet NaCu{sub 2}O{sub 2}: {sup 63,65}Cu and {sup 23}Na NMR studies

    SciTech Connect

    Sadykov, A. F. Gerashchenko, A. P.; Piskunov, Yu. V.; Ogloblichev, V. V.; Smol’nikov, A. G.; Verkhovskii, S. V.; Buzlukov, A. L.; Arapova, I. Yu.; Furukawa, Y.; Yakubovskii, A. Yu.; Bush, A. A.

    2014-11-15

    The magnetic structure of a quasi-one-dimensional frustrated NaCu{sub 2}O{sub 2} magnet single crystal is studied by NMR. The spatial orientation of the planar spin spirals in the copper-oxygen Cu{sup 2+}-O chains is determined, and its evolution as a function of the applied magnetic field direction is analyzed.

  20. Low-dimensional compounds containing cyanido groups. XXVIII. Crystal structure, spectroscopic and magnetic properties of two copper(II) tetracyanidoplatinate complexes with 1,2-diaminopropane

    SciTech Connect

    Vavra, Martin; Potočňák, Ivan; Dušek, Michal; Čižmár, Erik; Ozerov, Mykhaylo; Zvyagin, Sergei A.

    2015-05-15

    Violet crystals of ([Cu(pn){sub 2}]{sub 2}[Pt(CN){sub 4}])[Pt(CN){sub 4}]·2H{sub 2}O (1, pn=1,2-diaminopropane) and blue crystals of [Cu(pn)Pt(CN){sub 4}]{sub n}·nH{sub 2}O (2) were prepared under hydrothermal conditions and characterized using elemental analysis, IR and UV–vis spectroscopy and by X-ray crystal structure analysis. Different number of ν(C≡N) absorption bands of these two compounds reflects their different structures. An X-ray crystal structure analysis has shown that complex 1 is of ionic character and is formed from trinuclear [Cu(pn){sub 2}–Pt(CN){sub 4}–Cu(pn){sub 2}]{sup 2+} complex cation and discrete [Pt(CN){sub 4}]{sup 2–} anion together with two molecules of crystal water. On the other hand, complex 2 is of polymeric character and is formed by 2D networks of [Cu(pn)Pt(CN){sub 4}]{sub n} composition and completed by n molecules of crystal water. Magnetic measurements show the presence of a weak antiferromagnetic exchange interaction in complex 1 (Θ=–0.2 K), while the magnetic susceptibility of complex 2 is well described by the model of uniform S=1/2 spin chain with exchange interaction J/k{sub B}=–1.64 K. - Graphical abstract: Two complexes of different structural types from the system Cu(II) – 1,2–diaminopropane – [Pt(CN){sub 4}]{sup 2–} have been isolated. These were characterized by IR and UV–VIS spectroscopy, X–ray crystal structure analysis together with the magnetic measurements. On one hand ([Cu(pn){sub 2}]{sub 2}[Pt(CN){sub 4}])[Pt(CN){sub 4}]∙2H{sub 2}O is of ionic character and is formed from trinuclear complex cation and discrete anion together with two molecules of crystal water. On the other hand, [Cu(pn)Pt(CN){sub 4}]{sub n}∙nH{sub 2}O is of polymeric character and is formed by 2D networks of [Cu(pn)Pt(CN){sub 4}]{sub n} composition and completed by n molecules of crystal water. - Highlights: • Two complexes of different compositions from one system have been isolated. • First complex is of

  1. Spin Hall effect in doped semiconductor structures.

    PubMed

    Tse, Wang-Kong; Das Sarma, S

    2006-02-10

    In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as sigma(xy)SJ/sigma(xy)SS approximately (h/tau)/epsilonF, with tau being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining sigma(s)/sigma(c) approximately 10(-3)-10(-4), where sigma(s(c)) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

  2. Spin Hall Effect in Doped Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Das Sarma, Sankar

    2006-03-01

    We present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump (SJ) and skew-scattering (SS) contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show their effects scale as σxy^SJ/σxy^SS ˜(/τ)/ɛF, where τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n-doped and p-doped 3D and 2D GaAs structures, obtaining analytical formulas for the SJ and SS contributions. Moreover, the ratio of the spin Hall conductivity to longitudinal conductivity is found as σs/σc˜10-3-10-4, in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)] in n-doped 3D GaAs system.

  3. Spin Hall Effect in Doped Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Tse, Wang-Kong; Das Sarma, S.

    2006-02-01

    In this Letter we present a microscopic theory of the extrinsic spin Hall effect based on the diagrammatic perturbation theory. Side-jump and skew-scattering contributions are explicitly taken into account to calculate the spin Hall conductivity, and we show that their effects scale as σxySJ/σxySS˜(ℏ/τ)/ɛF, with τ being the transport relaxation time. Motivated by recent experimental work we apply our theory to n- and p-doped 3D and 2D GaAs structures, obtaining σs/σc˜10-3-10-4, where σs(c) is the spin Hall (charge) conductivity, which is in reasonable agreement with the recent experimental results of Kato et al. [Science 306, 1910 (2004)]SCIEAS0036-807510.1126/science.1105514 in n-doped 3D GaAs system.

  4. Confinement and Diffusion Effects in Dynamical Nuclear Polarization in Low Dimensional Nanostructures

    NASA Astrophysics Data System (ADS)

    Henriksen, Dan; Tifrea, Ionel

    2012-02-01

    We investigate the dynamic nuclear polarization as it results from the hyperfine coupling between nonequilibrium electronic spins and nuclear spins in semiconductor nanostructures. The natural confinement provided by low dimensional nanostructures is responsible for an efficient nuclear spin - electron spin hyperfine coupling [1] and for a reduced value of the nuclear spin diffusion constant [2]. In the case of optical pumping, the induced nuclear spin polarization is position dependent even in the presence of nuclear spin diffusion. This effect should be measurable via optically induced nuclear magnetic resonance or time-resolved Faraday rotation experiments. We discuss the implications of our calculations for the case of GaAs quantum well structures.[4pt] [1] I. Tifrea and M. E. Flatt'e, Phys. Rev. B 84, 155319 (2011).[0pt] [2] A. Malinowski and R. T. Harley, Solid State Commun. 114, 419 (2000).

  5. Electron Liquids in Semiconductor Quantum Structures

    SciTech Connect

    Aron Pinczuk

    2009-05-25

    The groups led by Stormer and Pinczuk have focused this project on goals that seek the elucidation of novel many-particle effects that emerge in two-dimensional electron systems (2DES) as the result from fundamental quantum interactions. This experimental research is conducted under extreme conditions of temperature and magnetic field. From the materials point of view, the ultra-high mobility systems in GaAs/AlGaAs quantum structures continue to be at the forefront of this research. The newcomer materials are based on graphene, a single atomic layer of graphite. The graphene research is attracting enormous attention from many communities involved in condensed matter research. The investigated many-particle phenomena include the integer and fractional quantum Hall effect, composite fermions, and Dirac fermions, and a diverse group of electron solid and liquid crystal phases. The Stormer group performed magneto-transport experiments and far-infrared spectroscopy, while the Pinczuk group explores manifestations of such phases in optical spectra.

  6. Low dimensional worm-holes

    NASA Astrophysics Data System (ADS)

    Samardzija, Nikola

    1995-01-01

    A simple three dimensional physical model is proposed to qualitatively address a particular type of dynamics evolving on toroidal structures. In the phase space this dynamics creates appearance of a worm-hole through which a chaotic, quasiperiodic and periodic behaviors are formed. An intriguing topological property of such a system is that it possesses no steady state solutions. As such, it opens some interesting questions in the bifurcation theory. The model also offers a novel qualitative tool for explaining some recently reported experimental and simulation results observed in physics, chemistry and biology.

  7. Evidence of low-dimensional antiferromagnetic ordering and crystal structure in the R sub 2 BaNiO sub 5 ( R =Y,Er) oxides

    SciTech Connect

    Amador, J.; Gutierrez-Puebla, E.; Monge, M.A.; Rasines, I.; Ruriaaz-Valero, C. ); Fernandez, F.; Saez-Puche, R. ); Campa, J.A. )

    1990-11-01

    Crystals of {ital R}{sub 2}BaNiO{sub 5} ({ital R}=Y,Er) have been grown, and their structures have been established by single-crystal x-ray diffraction. Both compounds crystallize in the Nd{sub 2}BaNiO{sub 5} structure type, with one-dimensional chains of vertex-sharing NiO{sub 6} octahedra in the direction of the {bold a} axis. These octahedra show an unusual twofold distortion: The Ni-O distances to the two axial oxygen atoms are considerably shorter, 0.3 A, than those to the four equatorial oxygens, and these oxygens are distorted from the right angles of a regular octahedron to 79.0(2){degree} or 77.7(6){degree}, respectively. As a result of this, Ni-O(axial)-Ni distances are very short, 3.76 and 3.75 A for {ital R}=Y and Er, respectively. X-ray powder diffraction data and the results of magnetic measurements for both oxides are given. The structural features mentioned elucidate why Ni{sup 2+} ions in polycrystalline Y{sub 2}BaNiO{sub 5} behave as a monodimensional system in which they become antiferromagnetically ordered below 300 K. Besides that, the ferromagnetic interactions that operate below 40 K can be due to tridimensional interchain interactions and/or the presence of ferromagnetic impurities. The estimated Neel temperature for Y{sub 2}BaNiO{sub 5}, higher than that reported for Y{sub 2}BaCuO{sub 5}, is explained by the promotion of the superexchange Ni-O-Ni interactions along the chains of flattened NiO{sub 6} octahedra sharing corners. In Er{sub 2}BaNiO{sub 5} both effects are masked by the strong paramagnetic signal of Er{sup 3+}, and a maximum observed at 15.6 K for the susceptibility is attributed to tridimensional ordering of the Er{sup 3+} cations.

  8. Low-dimensional coordination polymeric structures in alkali metal complex salts of the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D).

    PubMed

    Smith, Graham

    2015-02-01

    The Li, Rb and Cs complexes with the herbicide (2,4-dichlorophenoxy)acetic acid (2,4-D), namely poly[[aqua[μ3-(2,4-dichlorophenoxy)acetato-κ(3)O(1):O(1):O(1')]lithium(I)] dihydrate], {[Li(C8H5Cl2O3)(H2O)]·2H2O}n, (I), poly[μ-aqua-bis[μ3-(2,4-dichlorophenoxy)acetato-κ(4)O(1):O(1'):O(1'),Cl(2)]dirubidium(I)], [Rb2(C8H5Cl2O3)2(H2O)]n, (II), and poly[μ-aqua-bis[μ3-(2,4-dichlorophenoxy)acetato-κ(5)O(1):O(1'):O(1'),O(2),Cl(2)]dicaesium(I)], [Cs2(C8H5Cl2O3)2(H2O)]n, (III), respectively, have been determined and their two-dimensional polymeric structures are described. In (I), the slightly distorted tetrahedral LiO4 coordination involves three carboxylate O-atom donors, of which two are bridging, and a monodentate aqua ligand, together with two water molecules of solvation. Conjoined six-membered ring systems generate a one-dimensional coordination polymeric chain which extends along b and interspecies water O-H...O hydrogen-bonding interactions give the overall two-dimensional layers which lie parallel to (001). In hemihydrate complex (II), the irregular octahedral RbO5Cl coordination about Rb(+) comprises a single bridging water molecule which lies on a twofold rotation axis, a bidentate O(carboxy),Cl-chelate interaction and three bridging carboxylate O-atom bonding interactions from the 2,4-D ligand. A two-dimensional coordination polymeric layer structure lying parallel to (100) is formed through a number of conjoined cyclic bridges, including a centrosymmetric four-membered Rb2O2 ring system with an Rb...Rb separation of 4.3312 (5) Å. The coordinated water molecule forms intralayer aqua-carboxylate O-H...O hydrogen bonds. Complex (III) comprises two crystallographically independent (Z' = 2) irregular CsO6Cl coordination centres, each comprising two O-atom donors (carboxylate and phenoxy) and a ring-substituted Cl-atom donor from the 2,4-D ligand species in a tridentate chelate mode, two O-atom donors from bridging carboxylate groups and one from a

  9. Structural properties of bismuth-bearing semiconductor alloys

    NASA Technical Reports Server (NTRS)

    Berding, M. A.; Sher, A.; Chen, A. B.

    1986-01-01

    The structural properties of bismuth-bearing III-V semiconductor alloys are addressed. Because the Bi compounds are not known to form zincblende structures, only the anion-substituted alloys InPBi, InAsBi, and InSbBi are considered candidates as narrow-gap semiconductors. Miscibility calculations indicate that InSbBi will be the most miscible, and InPBi, with the large lattice mismatch of the constituents, will be the most difficult to mix. Calculations of the hardness of the Bi compounds indicate that, once formed, the InPBi alloy will be harder than the other Bi alloys, and substantially harder than the currently favored narrow-gap semiconductor HgCdTe. Thus, although InSbBi may be an easier material to prepare, InPBi promises to be a harder material. Growth of the Bi compounds will require high effective growth temperatures, probably attainable only through the use of nonequilibrium energy-assisted epitaxial growth techniques.

  10. Structural properties of bismuth-bearing semiconductor alloys

    NASA Technical Reports Server (NTRS)

    Berding, M. A.; Sher, A.; Chen, A.-B.; Miller, W. E.

    1988-01-01

    The structural properties of bismuth-bearing III-V semiconductor alloys InPBi, InAsBi, and InSbBi were studied theoretically. Bond energies, bond lengths, and strain coefficients were calculated for pure AlBi, GaBi, and InBi compounds and their alloys, and predictions were made for the mixing enthalpies, miscibility gaps, and critical metastable-to-stable material transition temperatures. Miscibility calculations indicate that InSbBi will be the most miscible, and the InPBi will be the the most difficult to mix. However, calculations of the hardness of the Bi compounds indicate that, once formed, the InPBi alloy will be harder than the other Bi alloys and substantially harder than the currently favored narrow-gap semiconductor HgCdTe.

  11. Low Dimensionality Effects in Complex Magnetic Oxides

    NASA Astrophysics Data System (ADS)

    Kelley, Paula J. Lampen

    Complex magnetic oxides represent a unique intersection of immense technological importance and fascinating physical phenomena originating from interwoven structural, electronic and magnetic degrees of freedom. The resulting energetically close competing orders can be controllably selected through external fields. Competing interactions and disorder represent an additional opportunity to systematically manipulate the properties of pure magnetic systems, leading to frustration, glassiness, and other novel phenomena while finite sample dimension plays a similar role in systems with long-range cooperative effects or large correlation lengths. A rigorous understanding of these effects in strongly correlated oxides is key to manipulating their functionality and device performance, but remains a challenging task. In this dissertation, we examine a number of problems related to intrinsic and extrinsic low dimensionality, disorder, and competing interactions in magnetic oxides by applying a unique combination of standard magnetometry techniques and unconventional magnetocaloric effect and transverse susceptibility measurements. The influence of dimensionality and disorder on the nature and critical properties of phase transitions in manganites is illustrated in La0.7 Ca0.3MnO3, in which both size reduction to the nanoscale and chemically-controlled quenched disorder are observed to induce a progressive weakening of the first-order nature of the transition, despite acting through the distinct mechanisms of surface effects and site dilution. In the second-order material La0.8Ca0.2MnO3, a strong magnetic field is found to drive the system toward its tricritical point as competition between exchange interactions in the inhomogeneous ground state is suppressed. In the presence of large phase separation stabilized by chemical disorder and long-range strain, dimensionality has a profound effect. With the systematic reduction of particle size in microscale-phase-separated (La, Pr

  12. Band structure of core-shell semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Pistol, Mats-Erik; Pryor, Craig

    2009-03-01

    We present band structures of strained core-shell nanowires composed of zincblende III-V (binary) semiconductors. We consider all combinations of AlN, GaN, InN, and all combinations of AlP, GaP, AlAs, GaAs, InP, InAs, AlSb, GaSb, and InSb. We compute the γ- and X-conduction band minima as well as the valence band maximum, all as functions of the core and shell radii. The calculations were performed using continuum elasticity theory for the strain, eight-band strain-dependent k.p theory for the γ-point energies, and single band approximation for the X-point conduction minima. We identify structures with type-I, type-II and type-III band alignment, as well as systems in which one material becomes metallic due to a negative band-gap. We identify structures that may support exciton crystals with and without photoexcitation. We have also computed the effective masses, from which the confinement energy may be estimated. All the results [Pistol and Pryor, Phys. Rev. B 78, 115319] are available in graphical and tabular form at www.semiconductor.physics.uiowa.edu

  13. Low-Dimensional Topological Crystalline Insulators.

    PubMed

    Wang, Qisheng; Wang, Feng; Li, Jie; Wang, Zhenxing; Zhan, Xueying; He, Jun

    2015-09-01

    Topological crystalline insulators (TCIs) are recently discovered topological phase with robust surface states residing on high-symmetry crystal surfaces. Different from conventional topological insulators (TIs), protection of surface states on TCIs comes from point-group symmetry instead of time-reversal symmetry in TIs. The distinct properties of TCIs make them promising candidates for the use in novel spintronics, low-dissipation quantum computation, tunable pressure sensor, mid-infrared detector, and thermoelectric conversion. However, similar to the situation in TIs, the surface states are always suppressed by bulk carriers, impeding the exploitation of topology-induced quantum phenomenon. One effective way to solve this problem is to grow low-dimensional TCIs which possess large surface-to-volume ratio, and thus profoundly increase the carrier contribution from topological surface states. Indeed, through persistent effort, researchers have obtained unique quantum transport phenomenon, originating from topological surface states, based on controllable growth of low-dimensional TCIs. This article gives a comprehensive review on the recent progress of controllable synthesis and topological surface transport of low-dimensional TCIs. The possible future direction about low-dimensional TCIs is also briefly discussed at the end of this paper.

  14. Polar semiconductor heterojunction structure energy band diagram considerations

    NASA Astrophysics Data System (ADS)

    Lin, Shuxun; Wen, Cheng P.; Wang, Maojun; Hao, Yilong

    2016-03-01

    The unique nature of built-in electric field induced positive/negative charge pairs of polar semiconductor heterojunction structure has led to a more realistic device model for hexagonal III-nitride HEMT. In this modeling approach, the distribution of charge carriers is dictated by the electrostatic potential profile instead of Femi statistics. The proposed device model is found suitable to explain peculiar properties of GaN HEMT structures, including: (1) Discrepancy in measured conventional linear transmission line model (LTLM) sheet resistance and contactless sheet resistance of GaN HEMT with thin barrier layer. (2) Below bandgap radiation from forward biased Nickel Schottky barrier diode on GaN HEMT structure. (3) GaN HEMT barrier layer doping has negligible effect on transistor channel sheet charge density.

  15. Modeling and Simulation of Semiconductor Quantum Well Structures and Lasers

    NASA Technical Reports Server (NTRS)

    Ning, Cun-Zheng; Saini, Subbash (Technical Monitor)

    1998-01-01

    In this talk I will cover two aspects of modeling and simulation efforts at NASA Ames Research Center. In the quantum well structure simulation, we typically start from the quantum mechanical calculation of the quantum well structures for the confined/and unconfined eigen states and functions. A bandstructure calculation of the k*p type is then performed for the confined valence states. This information is then used to computer the optical gain and refractive index of the quantum well structures by solving the linearized multiband semiconductor Bloch equations with the many-body interactions included. In our laser simulation, we typically solve the envelope equations for the laser field in space-time domain, coupled with a reduced set of material equations using the microscopic calculation of the first step. Finally I will show some examples of both aspects of simulation and modeling.

  16. Transport in two-dimensional modulation-doped semiconductor structures

    NASA Astrophysics Data System (ADS)

    Das Sarma, S.; Hwang, E. H.; Kodiyalam, S.; Pfeiffer, L. N.; West, K. W.

    2015-05-01

    We develop a theory for the maximum achievable mobility in modulation-doped 2D GaAs-AlGaAs semiconductor structures by considering the momentum scattering of the 2D carriers by the remote ionized dopants, which must invariably be present in order to create the 2D electron gas at the GaAs-AlGaAs interface. The minimal model, assuming first-order Born scattering by random quenched remote dopant ions as the only scattering mechanism, gives a mobility much lower (by a factor of 3 or more) than that observed experimentally in many ultrahigh-mobility modulation-doped 2D systems, establishing convincingly that the model of uncorrelated scattering by independent random remote quenched dopant ions is often unable to describe the physical system quantitively. We theoretically establish that the consideration of spatial correlations in the remote dopant distribution can enhance the mobility by (up to) several orders of magnitudes in experimental samples. The precise calculation of the carrier mobility in ultrapure modulation-doped 2D semiconductor structures thus depends crucially on the unknown spatial correlations among the dopant ions in the doping layer which may manifest sample to sample variations even for nominally identical sample parameters (i.e., density, well width, etc.), depending on the details of the modulation-doping growth conditions.

  17. Effect of hydrogen passivation on the electronic structure of ionic semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Deng, Hui-Xiong; Li, Shu-Shen; Li, Jingbo; Wei, Su-Huai

    2012-05-01

    In theoretical studies of thin film and nanostructured semiconductors, pseudohydrogen (PH) is widely used to passivate the surface dangling bonds. Based on these calculations, it is often believed that nanostructured semiconductors, due to quantum confinement, have a larger band gap than their bulk counterparts. Using first-principles band structure theory calculation and comparing systematically the differences between PH-passivated and real-hydrogen-passivated (RH-passivated) semiconductor surfaces and nanocrystals, we show that, unlike PH passivation that always increases the band gap with respect to the bulk value, RH passivation of the nanostructured semiconductors can either increase or decrease the band gap, depending on the ionicity of the nanocompounds. The differences between PH and RH passivations decreases when the covalency of the semiconductor increases and can be explained using a band coupling model. This observation greatly increases the tunability of nanostructured semiconductor properties, especially for wide-gap ionic semiconductors.

  18. Monolithic integrated high-T.sub.c superconductor-semiconductor structure

    NASA Technical Reports Server (NTRS)

    Burns, Michael J. (Inventor); de la Houssaye, Paul R. (Inventor); Garcia, Graham A. (Inventor); Russell, Stephen D. (Inventor); Clayton, Stanley R. (Inventor); Barfknecht, Andrew T. (Inventor)

    2000-01-01

    A method for the fabrication of active semiconductor and high-temperature superconducting device of the same substrate to form a monolithically integrated semiconductor-superconductor (MISS) structure is disclosed. A common insulating substrate, preferably sapphire or yttria-stabilized zirconia, is used for deposition of semiconductor and high-temperature superconductor substructures. Both substructures are capable of operation at a common temperature of at least 77 K. The separate semiconductor and superconductive regions may be electrically interconnected by normal metals, refractory metal silicides, or superconductors. Circuits and devices formed in the resulting MISS structures display operating characteristics which are equivalent to those of circuits and devices prepared on separate substrates.

  19. Physical structure and inversion charge at a semiconductor interface with a crystalline oxide.

    PubMed

    McKee, R A; Walker, F J; Chisholm, M F

    2001-07-20

    We show that the physical and electrical structure and hence the inversion charge for crystalline oxides on semiconductors can be understood and systematically manipulated at the atomic level. Heterojunction band offset and alignment are adjusted by atomic-level structural and chemical changes, resulting in the demonstration of an electrical interface between a polar oxide and a semiconductor free of interface charge. In a broader sense, we take the metal oxide semiconductor device to a new and prominent position in the solid-state electronics timeline. It can now be extensively developed using an entirely new physical system: the crystalline oxides-on-semiconductors interface.

  20. Method for making a monolithic integrated high-T.sub.c superconductor-semiconductor structure

    NASA Technical Reports Server (NTRS)

    Burns, Michael J. (Inventor); de la Houssaye, Paul R. (Inventor); Garcia, Graham A. (Inventor); Russell, Stephen D. (Inventor); Clayton, Stanley R. (Inventor); Barfknecht, Andrew T. (Inventor)

    2000-01-01

    A method for the fabrication of active semiconductor and high-temperature perconducting devices on the same substrate to form a monolithically integrated semiconductor-superconductor (MISS) structure is disclosed. A common insulating substrate, preferably sapphire or yttria-stabilized zirconia, is used for deposition of semiconductor and high-temperature superconductor substructures. Both substructures are capable of operation at a common temperature of at least 77 K. The separate semiconductor and superconductive regions may be electrically interconnected by normal metals, refractory metal silicides, or superconductors. Circuits and devices formed in the resulting MISS structures display operating characteristics which are equivalent to those of circuits and devices prepared on separate substrates.

  1. Density driven structural transformations in amorphous semiconductor clathrates

    DOE PAGESBeta

    Tulk, Christopher A.; dos Santos, Antonio M.; Neuefeind, Joerg C.; Molaison, Jamie J.; Sales, Brian C.; Honkimaeki, Veijo

    2015-01-16

    The pressure induced crystalline collapse at 14.7 GPa and polyamorphic structures of the semiconductor clathrate Sr8Ga16Ge30 are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicate that this feature is associated with gradual cage collapse and breakdown of the tetrahedral structure with themore » consequent systematic lengthening of the nearest-neighbor framework bonds. This suggests an overall local coordination change to an even higher density amorphous form. Upon recovery from high pressure, the sample remains amorphous, and while there is some indication of the guest-host cage reforming, it doesn't seem that the tetrahedral coordination is recovered. As such, the compresion-decompression process in this systems gives rise to three distict amorphous forms.« less

  2. Density driven structural transformations in amorphous semiconductor clathrates

    SciTech Connect

    Tulk, Christopher A.; dos Santos, Antonio M.; Neuefeind, Joerg C.; Molaison, Jamie J.; Sales, Brian C.; Honkimaeki, Veijo

    2015-01-16

    The pressure induced crystalline collapse at 14.7 GPa and polyamorphic structures of the semiconductor clathrate Sr8Ga16Ge30 are reported up to 35 GPa. In-situ total scattering measurements under pressure allow the direct microscopic inspection of the mechanisms associated with pressure induced amorphization in these systems, as well as the structure of the recovered phase. It is observed that, between 14.7 and 35 GPa the second peak in the structure factor function gradually disappears. Analysis of the radial distribution function extracted from those data indicate that this feature is associated with gradual cage collapse and breakdown of the tetrahedral structure with the consequent systematic lengthening of the nearest-neighbor framework bonds. This suggests an overall local coordination change to an even higher density amorphous form. Upon recovery from high pressure, the sample remains amorphous, and while there is some indication of the guest-host cage reforming, it doesn't seem that the tetrahedral coordination is recovered. As such, the compresion-decompression process in this systems gives rise to three distict amorphous forms.

  3. Electronic Properties of Low-Dimensional Materials Under Periodic Potential

    NASA Astrophysics Data System (ADS)

    Jamei, Mehdi

    In the quest for the further miniaturization of electronic devices, numerous fabrication techniques have been developed. The semiconductor industry has been able to manifest miniaturization in highly complex and ultra low-power integrated circuits and devices, transforming almost every aspect of our lives. However, we may have come very close to the end of this trend. While advanced machines and techniques may be able to overcome technological barriers, theoretical and fundamental barriers are inherent to the top-down miniaturization approach and cannot be circumvented. As a result, the need for novel and natural alternatives to replace old materials is valued now more than ever. Fortunately, there exists a large group of materials that essentially has low-dimensional (quasi-one- or quasi-two-dimensional) structures. Graphene, a two-dimensional form of carbon, which has attracted a lot of attention in recent years, is a perfect example of a prime material from this group. Niobium tri-selenide (NbSe3), from a family of trichalcogenides, has a highly anisotropic structure and electrical conductivity. At sufficiently low temperatures, NbSe3 also exhibits two independent "sliding charge density waves"-- an exciting phenomenon, which could be altered by changing the overall size of the material. In NbSe3 (and Blue Bronze K0.3MoO3 which has a similar structure and electrical behavior), the effect of a periodic potential could be seen in creating a charge density wave (CDW) that is incommensurate to the underlying lattice. The required periodic potential is provided by the crystal ions when ordered in a particular way. The consequence is a peculiar non-linear conductivity behavior, as well as a unique narrow-band noise spectrum. Theoretical and experimental studies have concluded that the dynamic properties of resulting CDW are directly related to the crystal impurity density, and other pinning potentials. Therefore, reducing the overall size of the crystal could

  4. Low-dimensional chaos in turbulence

    NASA Technical Reports Server (NTRS)

    Vastano, John A.

    1989-01-01

    Direct numerical simulations are being performed on two different fluid flows in an attempt to discover the mechanism underlying the transition to turbulence in each. The first system is Taylor-Couette flow; the second, two-dimensional flow over an airfoil. Both flows exhibit a gradual transition to high-dimensional turbulence through low-dimensional chaos. The hope is that the instabilities leading to chaos will be easier to relate to physical processes in this case, and that the understanding of these mechanisms can then be applied to a wider array of turbulent systems.

  5. Low dimensional modeling of wall turbulence

    NASA Astrophysics Data System (ADS)

    Aubry, Nadine

    2015-11-01

    In this talk we will review the original low dimensional dynamical model of the wall region of a turbulent boundary layer [Aubry, Holmes, Lumley and Stone, Journal of Fluid Dynamics 192, 1988] and discuss its impact on the field of fluid dynamics. We will also invite a few researchers who would like to make brief comments on the influence Lumley had on their research paths. In collaboration with Philip Holmes, Program in Applied and Computational Mathematics and Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ.

  6. Low-dimensional Representation of Error Covariance

    NASA Technical Reports Server (NTRS)

    Tippett, Michael K.; Cohn, Stephen E.; Todling, Ricardo; Marchesin, Dan

    2000-01-01

    Ensemble and reduced-rank approaches to prediction and assimilation rely on low-dimensional approximations of the estimation error covariances. Here stability properties of the forecast/analysis cycle for linear, time-independent systems are used to identify factors that cause the steady-state analysis error covariance to admit a low-dimensional representation. A useful measure of forecast/analysis cycle stability is the bound matrix, a function of the dynamics, observation operator and assimilation method. Upper and lower estimates for the steady-state analysis error covariance matrix eigenvalues are derived from the bound matrix. The estimates generalize to time-dependent systems. If much of the steady-state analysis error variance is due to a few dominant modes, the leading eigenvectors of the bound matrix approximate those of the steady-state analysis error covariance matrix. The analytical results are illustrated in two numerical examples where the Kalman filter is carried to steady state. The first example uses the dynamics of a generalized advection equation exhibiting nonmodal transient growth. Failure to observe growing modes leads to increased steady-state analysis error variances. Leading eigenvectors of the steady-state analysis error covariance matrix are well approximated by leading eigenvectors of the bound matrix. The second example uses the dynamics of a damped baroclinic wave model. The leading eigenvectors of a lowest-order approximation of the bound matrix are shown to approximate well the leading eigenvectors of the steady-state analysis error covariance matrix.

  7. Plasmonically-enhanced mid-infrared photoluminescence in a metal/narrow-gap semiconductor structure

    NASA Astrophysics Data System (ADS)

    Lu, Pengqi; Cai, Chunfeng; Zhang, Bingpo; Liu, Bozhi; Wu, Huizhen; Bi, Gang; Si, Jianxiao

    2016-05-01

    We report the enhancement of the mid-infrared (MIR) luminescence intensity in a nanoscale metal/semiconductor structure by the coupling of surface plasmon polaritons (SPPs) with excitons in a narrow-gap semiconductor. The SPPs are efficiently excited by the total internal reflection photons at a metal/semiconductor interface. The intense electric field induced by SPPs, in turn, greatly changes the radiative recombination rates of the excitons generated by the pumping laser and thus the MIR luminescence intensity. The finding avails the understanding of fundamental science of SPs in narrow-gap semiconductors and the development of novel MIR devices.

  8. Nanoscale electrodeposition of low-dimensional metal phases and clusters

    NASA Astrophysics Data System (ADS)

    Staikov, Georgi

    2016-07-01

    The present status of the problem of electrochemical formation of low-dimensional metal phases is reviewed. The progress in this field achieved in the last two decades is discussed on the basis of experimental results obtained in selected electrochemical systems with well defined single crystal substrates. The influence of crystallographic orientation and surface inhomogeneities of foreign substrates on the mechanism of formation and the atomic structure of two-dimensional (2D) metal phases in the underpotential deposition range is considered. The localized electrodeposition of metal nanoclusters on solid state surfaces applying the STM-tip as a nanoelectrode is demonstrated.

  9. Mechanical properties of low dimensional materials

    NASA Astrophysics Data System (ADS)

    Saini, Deepika

    Recent advances in low dimensional materials (LDMs) have paved the way for unprecedented technological advancements. The drive to reduce the dimensions of electronics has compelled researchers to devise newer techniques to not only synthesize novel materials, but also tailor their properties. Although micro and nanomaterials have shown phenomenal electronic properties, their mechanical robustness and a thorough understanding of their structure-property relationship are critical for their use in practical applications. However, the challenges in probing these mechanical properties dramatically increase as their dimensions shrink, rendering the commonly used techniques inadequate. This dissertation focuses on developing techniques for accurate determination of elastic modulus of LDMs and their mechanical responses under tensile and shear stresses. Fibers with micron-sized diameters continuously undergo tensile and shear deformations through many phases of their processing and applications. Significant attention has been given to their tensile response and their structure-tensile properties relations are well understood, but the same cannot be said about their shear responses or the structure-shear properties. This is partly due to the lack of appropriate instruments that are capable of performing direct shear measurements. In an attempt to fill this void, this dissertation describes the design of an inexpensive tabletop instrument, referred to as the twister, which can measure the shear modulus (G) and other longitudinal shear properties of micron-sized individual fibers. An automated system applies a pre-determined twist to the fiber sample and measures the resulting torque using a sensitive optical detector. The accuracy of the instrument was verified by measuring G for high purity copper and tungsten fibers. Two industrially important fibers, IM7 carbon fiber and KevlarRTM 119, were found to have G = 17 and 2.4 GPa, respectively. In addition to measuring the shear

  10. Investigation of Semiconductor Surface Structure by Transmission Ion Channeling.

    NASA Astrophysics Data System (ADS)

    Lyman, Paul Francis

    The primary thrust of this dissertation is the investigation of the composition and structure of two important surface systems on Si, and the study of how this structure evolves under the influence of ion bombardment or film growth. I have studied the initial stages of oxidation of Si immediately following removal of a surface oxide by an HF etch. I have also studied the structure of Ge deposited on clean Si(100) at low temperatures. These systems are of considerable technological interest, but were chosen because they naturally pose fundamental questions regarding physical and chemical processes at surfaces. In the study of the oxidation of Si, I have focused on the influence of the bombarding ion beam in altering the structure and composition of the surface layer. Thus, the system then provides a natural vehicle to study ion-induced chemistry. In the study of low-temperature growth of Ge, I have focused on the structure of the Ge layer and the evolution of that structure upon further deposition or upon heating. This simple system is a model one for observing strained semiconductor heteroepitaxial growth. The primary probe for these studies was transmission channeling of MeV ions. The sensitivity of this technique to correlations between the substrate and an overlayer allowed us to make the following observations. The O, Si and H bound in the thin oxide formed after an HF etch and H_2O rinse occupy preferred positions with respect to the Si matrix. Upon ion bombardment, the O further reacts with the Si (the reaction proceeds linearly with the ion fluence) and the portion of the H that is uncorrelated to the substrate is preferentially desorbed. For the case of Ge growth on Si(100)-(2 x 1) at room temperature, a substantial fraction of the Ge films is strained to occupy sites having the lattice constant of the Si substrate (pseudomorphic growth). A model for film growth is proposed in which pseudomorphic domains constitute roughly half of the Ge films up to a

  11. A microwave resonance investigation of quantum confined structures and defects in crystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Janssen, Griet

    In this work, high frequency (W-band, 95 GHz) Electron Paramagnetic Resonance spectroscopy (EPR) and Optically Detected Magnetic Resonance (ODMR) have been used as the principal tools to investigate quantum confined structures and defects in crystalline semiconductors. The low dimensional structures discussed in this work could be successfully examined with magnetic resonance techniques thanks to the high sensitivity of ODMR in combination with the application of high microwave frequencies. The advantage of the latter, compared to more conventional frequencies, is the increased Zeeman resolution, the improved sensitivity and the relaxation of the life time requirements. Our W-band setup was extended with a fiber bundle accessory to allow optical excitation of and light collection from a sample in the standard cylindrical cavity of a W-band spectrometer. This optical fiber bundle approach was shown to be efficient for ODMR experiments, even at low laser excitation powers. Microwave resonance transitions have been observed in a thin In(Ga)As/GaAs layer with shallowly formed quantum dots. The optical detection technique, combined with the application of high microwave frequencies and a long exciton lifetime, allowed for the first observation of microwave resonances in semiconductor quantum dots grown with epitaxial techniques. The microwave resonances revealed the cyclotron resonance of the electrons in the two-dimensional wetting layer, corresponding to an effective mass of 0.053m0. Further magnetic resonance transitions between spin states of the holes confined in the shallow dots were observed and an inhomogeneity in the quantum dot plane, either in the shape of or in the strain on the shallow quantum dots was derived. The W-band ODMR study of AgCl nanocrystals embedded in a crystalline KCl matrix, which was combined with atomic force microscopy (AFM) and continuous-wave and time-resolved photoluminescence measurements, revealed the high complexity of this system

  12. Growth and metal-oxide-semiconductor field-effect transistors of corundum-structured alpha indium oxide semiconductors

    NASA Astrophysics Data System (ADS)

    Kaneko, Kentaro; Ito, Yoshito; Uchida, Takayuki; Fujita, Shizuo

    2015-09-01

    The growth of corundum-structured α-In2O3, showing an X-ray diffraction (0006) rocking curve full-width at half maximum of 185 arcsec and electron Hall mobility of 130 cm2 V-1 s-1, was demonstrated on a sapphire substrate with an α-Ga2O3 buffer layer. An MOSFET of α-In2O3 exhibited pinch-off characteristics and an on-off ratio of drain current of 106. The use of mist chemical vapor deposition for the insulator-semiconductor structure was advantageous for low-cost devices.

  13. Temperature dependence of the electronic structure of semiconductors and insulators

    SciTech Connect

    Poncé, S. Gillet, Y.; Laflamme Janssen, J.; Gonze, X.; Marini, A.; Verstraete, M.

    2015-09-14

    The renormalization of electronic eigenenergies due to electron-phonon coupling (temperature dependence and zero-point motion effect) is sizable in many materials with light atoms. This effect, often neglected in ab initio calculations, can be computed using the perturbation-based Allen-Heine-Cardona theory in the adiabatic or non-adiabatic harmonic approximation. After a short description of the recent progresses in this field and a brief overview of the theory, we focus on the issue of phonon wavevector sampling convergence, until now poorly understood. Indeed, the renormalization is obtained numerically through a slowly converging q-point integration. For non-zero Born effective charges, we show that a divergence appears in the electron-phonon matrix elements at q → Γ, leading to a divergence of the adiabatic renormalization at band extrema. This problem is exacerbated by the slow convergence of Born effective charges with electronic wavevector sampling, which leaves residual Born effective charges in ab initio calculations on materials that are physically devoid of such charges. Here, we propose a solution that improves this convergence. However, for materials where Born effective charges are physically non-zero, the divergence of the renormalization indicates a breakdown of the adiabatic harmonic approximation, which we assess here by switching to the non-adiabatic harmonic approximation. Also, we study the convergence behavior of the renormalization and develop reliable extrapolation schemes to obtain the converged results. Finally, the adiabatic and non-adiabatic theories, with corrections for the slow Born effective charge convergence problem (and the associated divergence) are applied to the study of five semiconductors and insulators: α-AlN, β-AlN, BN, diamond, and silicon. For these five materials, we present the zero-point renormalization, temperature dependence, phonon-induced lifetime broadening, and the renormalized electronic band structure.

  14. Growth, structural, electronic and optical characterization of nitride semiconductors

    NASA Astrophysics Data System (ADS)

    Constantin, Costel

    This project investigates the growth, optical, electronic, surface, magnetic and bulk properties of scandium gallium nitride on Sapphire(0001), manganese scandium nitride on MgO(001), heterostructures of cubic gallium nitride and scandium nitride on Mg(001), and chromium nitride on MgO(001) grown by radio frequency molecular beam epitaxy. The growth of ScxGa1- xN films has been performed at a substrate temperature of 650°C. The diffraction and optical experiments confirm the existence of two main regimes of growth; for high Sc concentration (x ≥ 0.54), a rocksalt crystal structure is obtained. For low x ( x ≤ 0.17), a wurtzite-like crystal structure is observed with local lattice distortions at the sites where the Sc atoms incorporate substitutionally into the Ga sites. The growth of MnxSc1- xN films, with x = 0.03-0.05, has been performed at a substrate temperature of ˜500°C. A rocksalt structure is observed for the MnxSc1-xN films. Magnetic measurements preformed on the Mn0.03Sc0.97 N film show ferromagnetic with a TC ˜ 50 K. As the manganese concentration is increased to x = 0.05, the ferromagnetism is reduced. The growth of heterostructures c-GaN(001)/ScN(001)/MgO(001) and ScN(001)/c-GaN(001)/MgO(001) adopt a cubical symmetry of the MgO(001) substrate. The zincblend c-GaN grown atop of ScN(001) shows a smoother surface (predominantly 2D growth) as compared to the rocksalt ScN(001) grown on atop of c-GaN(001). The growth of stoichiometric CrN(001) films is performed at a substrate temperature of 450°C. A novel growth method of highly crystalline stoichiometric CrN(001) films has been proposed. The room temperature scanning tunneling microscopy together with resistivity versus temperature experiments reveal the electronic behavior of CrN(001) films to be metallic below T N ≃ 270 K, and semiconductor above TN.

  15. Tuning Surface Properties of Low Dimensional Materials via Strain Engineering.

    PubMed

    Yang, Shengchun; Liu, Fuzhu; Wu, Chao; Yang, Sen

    2016-08-01

    The promising and versatile applications of low dimensional materials are largely due to their surface properties, which along with their underlying electronic structures have been well studied. However, these materials may not be directly useful for applications requiring properties other than their natal ones. In recent years, strain has been shown to be an additionally useful handle to tune the physical and chemical properties of materials by changing their geometric and electronic structures. The strategies for producing strain are summarized. Then, the electronic structure of quasi-two dimensional layered non-metallic materials (e.g., graphene, MX2, BP, Ge nanosheets) under strain are discussed. Later, the strain effects on catalytic properties of metal-catalyst loaded with strain are focused on. Both experimental and computational perspectives for dealing with strained systems are covered. Finally, an outlook on engineering surface properties utilizing strain is provided. PMID:27376498

  16. Tuning Surface Properties of Low Dimensional Materials via Strain Engineering.

    PubMed

    Yang, Shengchun; Liu, Fuzhu; Wu, Chao; Yang, Sen

    2016-08-01

    The promising and versatile applications of low dimensional materials are largely due to their surface properties, which along with their underlying electronic structures have been well studied. However, these materials may not be directly useful for applications requiring properties other than their natal ones. In recent years, strain has been shown to be an additionally useful handle to tune the physical and chemical properties of materials by changing their geometric and electronic structures. The strategies for producing strain are summarized. Then, the electronic structure of quasi-two dimensional layered non-metallic materials (e.g., graphene, MX2, BP, Ge nanosheets) under strain are discussed. Later, the strain effects on catalytic properties of metal-catalyst loaded with strain are focused on. Both experimental and computational perspectives for dealing with strained systems are covered. Finally, an outlook on engineering surface properties utilizing strain is provided.

  17. Rf linearity in low dimensional nanowire mosfets

    NASA Astrophysics Data System (ADS)

    Razavieh, Ali

    linear Id-Vgs characteristics with a constant gm of which is independent of the choice of channel material when operated under high enough drain voltages. Unique scaling potential of nanowires in terms of body thickness, channel length, and oxide thickness makes nanowire transistors an excellent device structure of choice to operate in 1-D ballistic transport regime in the QCL. A set of guidelines is provided for material parameters and device dimensions for nanowire FETs, which meet the three criteria of i) 1-D transport ii) operation in the QCL iii) ballistic transport, and challenges and limitations of fulfilling any of the above transport conditions from materials point of view are discussed. This work also elaborates how a non-ideal device, one that approaches but does not perfectly fulfill criteria i) through iii), can be analyzed in terms of its linearity performance. In particular the potential of silicon based devices will be discussed in this context, through mixture of experiment and simulation. 1-D transport is successfully achieved in the lab. QCL is simulated through back calculation of the band movement of the transistors in on-state. Quasi-ballistic transport conditions can be achieved by cooling down the samples to 77K. Since, ballistic transport is challenging to achieve for practical channel lengths in today's leading semiconductor device technologies the effect of carrier back-scattering on RF linearity is explored through third order intercept point (IIP3) analysis. These findings show that for the devices which operate in the QCL, while 1-D sub-bands are involved in carrier transport, current linearity is directly related to the nature of the dominant scattering mechanism in the channel, and can be improved by proper choice of channel material in order to enforce a specific scattering mechanism to prevail in the channel. Usually, in semiconductors, the dominant scattering mechanism in the channel is the superposition of different mechanisms

  18. Superfluidity and Chaos in low dimensional circuits.

    PubMed

    Arwas, Geva; Vardi, Amichay; Cohen, Doron

    2015-01-01

    The hallmark of superfluidity is the appearance of "vortex states" carrying a quantized metastable circulating current. Considering a unidirectional flow of particles in a ring, at first it appears that any amount of scattering will randomize the velocity, as in the Drude model, and eventually the ergodic steady state will be characterized by a vanishingly small fluctuating current. However, Landau and followers have shown that this is not always the case. If elementary excitations (e.g. phonons) have higher velocity than that of the flow, simple kinematic considerations imply metastability of the vortex state: the energy of the motion cannot dissipate into phonons. On the other hand if this Landau criterion is violated the circulating current can decay. Below we show that the standard Landau and Bogoliubov superfluidity criteria fail in low-dimensional circuits. Proper determination of the superfluidity regime-diagram must account for the crucial role of chaos, an ingredient missing from the conventional stability analysis. Accordingly, we find novel types of superfluidity, associated with irregular or chaotic or breathing vortex states. PMID:26315272

  19. The structure of constitutive equations for semiconductor devices

    SciTech Connect

    Buchanan, G.R.; Girrens, S.P.; Bennett, J.G.

    1987-01-01

    The fundamental equations that describe carrier transport in semiconductor materials are developed using the methods of continuum mixture theory and Maxwell's equations for electrodynamics. There are five basic equations that govern the behavior of current flux, electrostatic potential, electrons, and holes. The bahavior of the electrical chemical potentials are introduced and their relation to the current flux is discussed.

  20. Building Structural Complexity in Semiconductor Nanocrystals through Chemical Transformations

    SciTech Connect

    Sadtler, Bryce F

    2009-05-01

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

  1. A spectroscopic method for the evaluation of surface passivation treatments on metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Walsh, Lee A.; Hurley, Paul K.; Lin, Jun; Cockayne, Eric; O'Regan, T. P.; Woicik, Joseph C.; Hughes, Greg

    2014-05-01

    Combined hard x-ray photoelectron spectroscopy (HAXPES) and electrical characterisation measurements have been shown to provide complementary information on the electrical performance of Si and GaAs based metal-oxide-semiconductor (MOS) structures. The results obtained indicate that surface potential changes at the semiconductor/dielectric interface due to the presence of different work function metals can be detected from HAXPES measurements. Changes in the semiconductor band bending at zero gate voltage and the flat band voltage values derived from C-V measurements are in agreement with the semiconductor core level shifts measured from the HAXPES spectra. These results highlight the potential application of this measurement approach in the evaluation of the efficacy of surface passivation treatments: HAXPES—hard x-ray photoelectron spectroscopy; C-V—capacitance voltage; Dit—interface state density; BE—binding energy, at reducing defect states densities in MOS structures.

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

    SciTech Connect

    Hamad, K.S.

    2000-05-01

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

  3. Semiconductor structures having electrically insulating and conducting portions formed from an AlSb-alloy layer

    DOEpatents

    Spahn, Olga B.; Lear, Kevin L.

    1998-01-01

    A semiconductor structure. The semiconductor structure comprises a plurality of semiconductor layers formed on a substrate including at least one layer of a III-V compound semiconductor alloy comprising aluminum (Al) and antimony (Sb), with at least a part of the AlSb-alloy layer being chemically converted by an oxidation process to form superposed electrically insulating and electrically conducting portions. The electrically insulating portion formed from the AlSb-alloy layer comprises an oxide of aluminum (e.g. Al.sub.2 O.sub.3), while the electrically conducting portion comprises Sb. A lateral oxidation process allows formation of the superposed insulating and conducting portions below monocrystalline semiconductor layers for forming many different types of semiconductor structures having particular utility for optoelectronic devices such as light-emitting diodes, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodetectors and optical modulators (waveguide and surface normal), and for electronic devices such as heterojunction bipolar transistors, field-effect transistors and quantum-effect devices. The invention is expected to be particularly useful for forming light-emitting devices for use in the 1.3-1.6 .mu.m wavelength range, with the AlSb-alloy layer acting to define an active region of the device and to effectively channel an electrical current therein for efficient light generation.

  4. Modeling of metal-ferroelectric-insulator-semiconductor structure considering the effects of interface traps

    NASA Astrophysics Data System (ADS)

    Sun, Jing; Shi, Xiao Rong; Zheng, Xue Jun; Tian, Li; Zhu, Zhe

    2015-06-01

    An improved model, in which the interface traps effects are considered, is developed by combining with quantum mechanical model, dipole switching theory and silicon physics of metal-oxide-semiconductor structure to describe the electrical properties of metal-ferroelectric-insulator-semiconductor (MFIS) structure. Using the model, the effects of the interface traps on the surface potential (ϕSi) of the semiconductor, the low frequency (LF) capacitance-voltage (C-V) characteristics and memory window of MFIS structure are simulated, and the results show that the ϕSi- V and LF C-V curves are shifted toward the positive-voltage direction and the memory window become worse as the density of the interface trap states increases. This paper is expected to provide some guidance to the design and performance improvement of MFIS structure devices. In addition, the improved model can be integrated into electronic design automation (EDA) software for circuit simulation.

  5. Predicted band structures of III-V semiconductors in the wurtzite phase

    SciTech Connect

    De, A.; Pryor, Craig E.

    2010-04-15

    While non-nitride III-V semiconductors typically have a zinc-blende structure, they may also form wurtzite crystals under pressure or when grown as nanowhiskers. This makes electronic structure calculation difficult since the band structures of wurtzite III-V semiconductors are poorly characterized. We have calculated the electronic band structure for nine III-V semiconductors in the wurtzite phase using transferable empirical pseudopotentials including spin-orbit coupling. We find that all the materials have direct gaps. Our results differ significantly from earlier ab initio calculations, and where experimental results are available (InP, InAs, and GaAs) our calculated band gaps are in good agreement. We tabulate energies, effective masses, and linear and cubic Dresselhaus zero-field spin-splitting coefficients for the zone-center states. The large zero-field spin-splitting coefficients we find may facilitate the development of spin-based devices.

  6. Nonlinear quantum transport in low-dimensional electronic devices

    NASA Astrophysics Data System (ADS)

    Barrios, Andres Javier

    The study of transport processes in low-dimensional semiconductors requires a rigorous quantum mechanical treatment. However, a full-fledged quantum transport theory of electrons (or holes) in semiconductors of small scale, applicable in the presence of external fields of arbitrary strength, is still not available. In the literature, different approaches have been proposed, including: (a) the semiclassical Boltzmann equation, (b) perturbation theory based on Keldysh's Green functions, and (c) the Quantum Boltzmann Equation (QBE), previously derived by Van Vliet and coworkers, applicable in the realm of Kubo's Linear Response Theory (LRT). In the present work, we follow the method originally proposed by Van Wet in LRT. The Hamiltonian in this approach is of the form: H = H 0(E, B) + lambdaV, where H0 contains the externally applied fields, and lambdaV includes many-body interactions. This Hamiltonian differs from the LRT Hamiltonian, H = H0 - AF(t) + lambdaV, which contains the external field in the field-response part, -AF(t). For the nonlinear problem, the eigenfunctions of the system Hamiltonian, H0(E, B), include the external fields without any limitation on strength. In Part A of this dissertation, both the diagonal and nondiagonal Master equations are obtained after applying projection operators to the von Neumann equation for the density operator in the interaction picture, and taking the Van Hove limit, (lambda → 0, t → infinity, so that (lambda2 t)n remains finite). Similarly, the many-body current operator J is obtained from the Heisenberg equation of motion. In Part B, the Quantum Boltzmann Equation is obtained in the occupation-number representation for an electron gas, interacting with phonons or impurities. On the one-body level, the current operator obtained in Part A leads to the Generalized Calecki current for electric and magnetic fields of arbitrary strength. Furthermore, in this part, the LRT results for the current and conductance are

  7. Synthesis and characterization of low-dimensional molecular magnetic materials

    NASA Astrophysics Data System (ADS)

    Liu, Chen

    This dissertation presents experimental results from the synthesis and structural, magnetic characterization of representative low-dimensional molecule-based magnetic materials. Most of the materials reported in this dissertation, both coordination polymers and cuprate, are obtained as the result of synthesizing and characterizing spin ladder systems; except the material studied in Chapter 2, ferricenyl(III)trisferrocenyl(II)borate, which is not related to the spin ladder project. The interest in spin ladder systems is due to the discovery of high-temperature superconductivity in doped cuprates possessing ladder-like structures, and it is hoped that investigation of the magnetic behavior of ladder-like structures will help us understand the mechanism of high-temperature superconductivity. Chapter 1 reviews fundamental knowledge of molecular magnetism, general synthetic strategies for low-dimensional coordination polymers, and a brief introduction to the current status of research on spin ladder systems. Chapter 2 presents a modified synthetic procedure of a previously known monomeric complex, ferricenyl(III)trisferrocenyl(II)borate, 1. Its magnetic properties were characterized and previous results have been disproved. Chapter 3 investigates the magnetism of [CuCl2(CH3CN)] 2, 2, a cuprate whose structure consists of isolated noninterpenetrating ladders formed by the stacking of Cu(II) dimers. This material presents an unexpected ferromagnetic interaction both within the dimeric units and between the dimers, and this behavior has been rationalized based on the effect of its terminal nonbridging ligands. In Chapter 4, the synthesis and magnetism of two ladder-like coordination polymers, [Co(NO3)2(4,4'-bipyridine) 1.5(MeCN)]n, 3, and Ni2(2,6-pyridinedicarboxylic acid)2(H2O)4(pyrazine), 4, are reported. Compound 3 possesses a covalent one-dimensional ladder structure in which Co(II) ions are bridged through bipyridine molecules. Compared to the materials discussed in

  8. Studies on Structure Property Relations in Printed Polymer Semiconductors

    NASA Astrophysics Data System (ADS)

    Mahadevapuram, Nikhila; Ahmadi Vaselabadi, Saeed; Reza Shakarisaz, David; Strzalka, Joseph; Ruchhoeft, Paul; Stein, Gila

    2014-03-01

    Printed polymer semiconductors can be used in systems which require precise control on domain placements and for sequential casting like in sensors, multi color light-emitting diodes or tandem solar cells. Morphology in polymer semiconductors places an important role on carrier mobility. Polymer crystals help in charge transport. In this work, we used helium ion beam lithography to irradiate polymer films and study crystallinity and carrier mobility. Thin films of poly (3-hexylthiphene) P3HT were irradiated with helium ion beam and light absorption properties were measured using UV-Vis spectroscopy. Crystal orientations in irradiated P3HT films were investigated using grazing incidence wide angle X-ray scattering (GIWAXS). Degree of crystallinity in irradiated polymer films were estimated by constructing pole figures. Charge mobility was estimated from device measurements. It was observed that the light absorption properties were retained in irradiated polymer films. Irradiation can influence both crystal orientations and charge mobility as a function of exposure dose. In summary, polymer crystallinity can be independently varied using this technique and a better understanding of the charge transport and device function can be established.

  9. Low-Dimensional Network Formation in Molten Sodium Carbonate.

    PubMed

    Wilding, Martin C; Wilson, Mark; Alderman, Oliver L G; Benmore, Chris; Weber, J K R; Parise, John B; Tamalonis, Anthony; Skinner, Lawrie

    2016-01-01

    Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (F(x)(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to F(x)(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na(+) ions.

  10. Low-Dimensional Network Formation in Molten Sodium Carbonate.

    PubMed

    Wilding, Martin C; Wilson, Mark; Alderman, Oliver L G; Benmore, Chris; Weber, J K R; Parise, John B; Tamalonis, Anthony; Skinner, Lawrie

    2016-01-01

    Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (F(x)(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to F(x)(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na(+) ions. PMID:27080401

  11. Low-Dimensional Network Formation in Molten Sodium Carbonate

    PubMed Central

    Wilding, Martin C.; Wilson, Mark; Alderman, Oliver L. G.; Benmore, Chris; Weber, J. K. R.; Parise, John B.; Tamalonis, Anthony; Skinner, Lawrie

    2016-01-01

    Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (Fx(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to Fx(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na+ ions. PMID:27080401

  12. Low-Dimensional Network Formation in Molten Sodium Carbonate

    NASA Astrophysics Data System (ADS)

    Wilding, Martin C.; Wilson, Mark; Alderman, Oliver L. G.; Benmore, Chris; Weber, J. K. R.; Parise, John B.; Tamalonis, Anthony; Skinner, Lawrie

    2016-04-01

    Molten carbonates are highly inviscid liquids characterized by low melting points and high solubility of rare earth elements and volatile molecules. An understanding of the structure and related properties of these intriguing liquids has been limited to date. We report the results of a study of molten sodium carbonate (Na2CO3) which combines high energy X-ray diffraction, containerless techniques and computer simulation to provide insight into the liquid structure. Total structure factors (Fx(Q)) are collected on the laser-heated carbonate spheres suspended in flowing gases of varying composition in an aerodynamic levitation furnace. The respective partial structure factor contributions to Fx(Q) are obtained by performing molecular dynamics simulations treating the carbonate anions as flexible entities. The carbonate liquid structure is found to be heavily temperature-dependent. At low temperatures a low-dimensional carbonate chain network forms, at T = 1100 K for example ~55% of the C atoms form part of a chain. The mean chain lengths decrease as temperature is increased and as the chains become shorter the rotation of the carbonate anions becomes more rapid enhancing the diffusion of Na+ ions.

  13. Recent progress in III-V based ferromagnetic semiconductors: Band structure, Fermi level, and tunneling transport

    SciTech Connect

    Tanaka, Masaaki; Ohya, Shinobu Nam Hai, Pham

    2014-03-15

    Spin-based electronics or spintronics is an emerging field, in which we try to utilize spin degrees of freedom as well as charge transport in materials and devices. While metal-based spin-devices, such as magnetic-field sensors and magnetoresistive random access memory using giant magnetoresistance and tunneling magnetoresistance, are already put to practical use, semiconductor-based spintronics has greater potential for expansion because of good compatibility with existing semiconductor technology. Many semiconductor-based spintronics devices with useful functionalities have been proposed and explored so far. To realize those devices and functionalities, we definitely need appropriate materials which have both the properties of semiconductors and ferromagnets. Ferromagnetic semiconductors (FMSs), which are alloy semiconductors containing magnetic atoms such as Mn and Fe, are one of the most promising classes of materials for this purpose and thus have been intensively studied for the past two decades. Here, we review the recent progress in the studies of the most prototypical III-V based FMS, p-type (GaMn)As and its heterostructures with focus on tunneling transport, Fermi level, and bandstructure. Furthermore, we cover the properties of a new n-type FMS, (In,Fe)As, which shows electron-induced ferromagnetism. These FMS materials having zinc-blende crystal structure show excellent compatibility with well-developed III-V heterostructures and devices.

  14. Theoretical discovery of stable structures of group III-V monolayers: The materials for semiconductor devices

    SciTech Connect

    Suzuki, Tatsuo

    2015-11-23

    Group III-V compounds are very important as the materials of semiconductor devices. Stable structures of the monolayers of group III-V binary compounds have been discovered by using first-principles calculations. The primitive unit cell of the discovered structures is a rectangle, which includes four group-III atoms and four group-V atoms. A group-III atom and its three nearest-neighbor group-V atoms are placed on the same plane; however, these connections are not the sp{sup 2} hybridization. The bond angles around the group-V atoms are less than the bond angle of sp{sup 3} hybridization. The discovered structure of GaP is an indirect transition semiconductor, while the discovered structures of GaAs, InP, and InAs are direct transition semiconductors. Therefore, the discovered structures of these compounds have the potential of the materials for semiconductor devices, for example, water splitting photocatalysts. The discovered structures may become the most stable structures of monolayers which consist of other materials.

  15. Local Atomic Structure of Semiconductor Alloys Using Pair Distribution Function Analysis

    SciTech Connect

    Billinge, S.J.L.; Thorpe, M.F.

    2002-06-24

    We have been taking advantage of recent experimental developments, which involve utilizing diffraction data from x-rays or neutrons out to very large wave-vectors, to obtain a detailed structural characterization of semiconductor alloys. This approach allows an accurate Pair Distribution Function (PDF) to be obtained to 20A and beyond and reveals the local structure of the alloy directly. These data can be modeled explicitly to learn about local correlations and short-range order in materials. We are combining theory, modeling and experiments to study a range of materials from semiconductors to thermoelectrics and proton conductors.

  16. Multiple trapping on a comb structure as a model of electron transport in disordered nanostructured semiconductors

    SciTech Connect

    Sibatov, R. T. Morozova, E. V.

    2015-05-15

    A model of dispersive transport in disordered nanostructured semiconductors has been proposed taking into account the percolation structure of a sample and joint action of several mechanisms. Topological and energy disorders have been simultaneously taken into account within the multiple trapping model on a comb structure modeling the percolation character of trajectories. The joint action of several mechanisms has been described within random walks with a mixture of waiting time distributions. Integral transport equations with fractional derivatives have been obtained for an arbitrary density of localized states. The kinetics of the transient current has been calculated within the proposed new model in order to analyze time-of-flight experiments for nanostructured semiconductors.

  17. Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors

    PubMed Central

    Wang, Jianwei; Zhang, Yong

    2016-01-01

    When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430

  18. Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors.

    PubMed

    Wang, Jianwei; Zhang, Yong

    2016-01-01

    When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III-V, and II-VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain-low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side. PMID:27090430

  19. Topologic connection between 2-D layered structures and 3-D diamond structures for conventional semiconductors

    NASA Astrophysics Data System (ADS)

    Wang, Jianwei; Zhang, Yong

    2016-04-01

    When coming to identify new 2D materials, our intuition would suggest us to look from layered instead of 3D materials. However, since graphite can be hypothetically derived from diamond by stretching it along its [111] axis, many 3D materials can also potentially be explored as new candidates for 2D materials. Using a density functional theory, we perform a systematic study over the common Group IV, III–V, and II–VI semiconductors along different deformation paths to reveal new structures that are topologically connected to but distinctly different from the 3D parent structure. Specifically, we explore two major phase transition paths, originating respectively from wurtzite and NiAs structure, by applying compressive and tensile strain along the symmetry axis, and calculating the total energy changes to search for potential metastable states, as well as phonon spectra to examine the structural stability. Each path is found to further split into two branches under tensile strain–low buckled and high buckled structures, which respectively lead to a low and high buckled monolayer structure. Most promising new layered or planar structures identified include BeO, GaN, and ZnO on the tensile strain side, Ge, Si, and GaP on the compressive strain side.

  20. Quasiparticle band structure of the almost-gapless transition-metal-based Heusler semiconductors

    NASA Astrophysics Data System (ADS)

    Tas, M.; Şaşıoǧlu, E.; Galanakis, I.; Friedrich, C.; Blügel, S.

    2016-05-01

    Transition-metal-based Heusler semiconductors are promising materials for a variety of applications ranging from spintronics to thermoelectricity. Employing the G W approximation within the framework of the FLAPW method, we study the quasiparticle band structure of a number of such compounds being almost gapless semiconductors. We find that in contrast to the s p -electron based semiconductors such as Si and GaAs, in these systems, the many-body corrections have a minimal effect on the electronic band structure and the energy band gap increases by less than 0.2 eV, which makes the starting point density functional theory (DFT) a good approximation for the description of electronic and optical properties of these materials. Furthermore, the band gap can be tuned either by the variation of the lattice parameter or by the substitution of the s p -chemical element.

  1. Structure-Dependent Spin Polarization in Polymorphic CdS:Y Semiconductor Nanocrystals.

    PubMed

    Wang, Pan; Xiao, Bingxin; Zhao, Rui; Ma, Yanzhang; Zhang, Mingzhe

    2016-03-01

    Searching for the polymorphic semiconductor nanocrystals would provide precise and insightful structure-spin polarization correlations and meaningful guidance for designing and synthesizing high spin-polarized spintronic materials. Herein, the high spin polarization is achieved in polymorphic CdS:Y semiconductor nanocrystals. The high-pressure polymorph of rock-salt CdS:Y nanocrystals has been recovered at ambient conditions synthesized by the wurtzite CdS:Y nanocrystals as starting material under 5.2 GPa and 300 °C conditions. The rock-salt CdS:Y polymorph displays more robust room-temperature ferromagnetism than wurtzite sample, which can reach the ferromagnetic level of conventional semiconductors doped with magnetic transition-metal ions, mainly due to the significantly enhanced spin configuration and defect states. Therefore, crystal structure directly governs the spin configuration, which determines the degree of spin polarization. This work can provide experimental and theoretical methods for designing the high spin-polarized semiconductor nanocrystals, which is important for applications in semiconductor spintronics. PMID:26905093

  2. Semiconductor structures having electrically insulating and conducting portions formed from an AlSb-alloy layer

    DOEpatents

    Spahn, O.B.; Lear, K.L.

    1998-03-10

    The semiconductor structure comprises a plurality of semiconductor layers formed on a substrate including at least one layer of a III-V compound semiconductor alloy comprising aluminum (Al) and antimony (Sb), with at least a part of the AlSb-alloy layer being chemically converted by an oxidation process to form superposed electrically insulating and electrically conducting portions. The electrically insulating portion formed from the AlSb-alloy layer comprises an oxide of aluminum (e.g., Al{sub 2}O{sub 3}), while the electrically conducting portion comprises Sb. A lateral oxidation process allows formation of the superposed insulating and conducting portions below monocrystalline semiconductor layers for forming many different types of semiconductor structures having particular utility for optoelectronic devices such as light-emitting diodes, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodetectors and optical modulators (waveguide and surface normal), and for electronic devices such as heterojunction bipolar transistors, field-effect transistors and quantum-effect devices. The invention is expected to be particularly useful for forming light-emitting devices for use in the 1.3--1.6 {mu}m wavelength range, with the AlSb-alloy layer acting to define an active region of the device and to effectively channel an electrical current therein for efficient light generation. 10 figs.

  3. Structure-Dependent Spin Polarization in Polymorphic CdS:Y Semiconductor Nanocrystals.

    PubMed

    Wang, Pan; Xiao, Bingxin; Zhao, Rui; Ma, Yanzhang; Zhang, Mingzhe

    2016-03-01

    Searching for the polymorphic semiconductor nanocrystals would provide precise and insightful structure-spin polarization correlations and meaningful guidance for designing and synthesizing high spin-polarized spintronic materials. Herein, the high spin polarization is achieved in polymorphic CdS:Y semiconductor nanocrystals. The high-pressure polymorph of rock-salt CdS:Y nanocrystals has been recovered at ambient conditions synthesized by the wurtzite CdS:Y nanocrystals as starting material under 5.2 GPa and 300 °C conditions. The rock-salt CdS:Y polymorph displays more robust room-temperature ferromagnetism than wurtzite sample, which can reach the ferromagnetic level of conventional semiconductors doped with magnetic transition-metal ions, mainly due to the significantly enhanced spin configuration and defect states. Therefore, crystal structure directly governs the spin configuration, which determines the degree of spin polarization. This work can provide experimental and theoretical methods for designing the high spin-polarized semiconductor nanocrystals, which is important for applications in semiconductor spintronics.

  4. Fundamental properties and applications of low- dimensional materials

    NASA Astrophysics Data System (ADS)

    Kim, Philip

    1999-11-01

    Physics in reduced dimensions has attracted much attention during the last decades owing to the discovery of new phenomena in low-dimensional materials and their potential importance in device applications. The unique properties of these low dimensional materials have been generally understood by considering the increased role of fluctuations and singularities in physical quantities due to the reduction in available phase space. In this thesis, I have investigated the fundamental physical properties of several low dimensional materials and have presented a technological application of these materials. Magnetic flux lines in high temperature superconductors (HTSCs) can be effectively treated as 2+1 dimensional systems due to the large anisotropy of HTSCs. The microscopic structure of the magnetic flux line lattice in Bi 2Sr2CaCu2O8 + x superconducting single crystals was studied at temperatures up to 77 K by Bitter magnetic decoration technique. Analysis of structural correlations shows that the flux line lattices are in the hexatic phase for the high temperature and low field regime, and enables us to estimate the flux line lattice freezing temperature. In addition, dislocation-free decoration images containing up to 80,000 vortices, which are two orders of magnitude larger number than that of previous studies, have been obtained. Analyses of these large length new data shows that the observed flux line lattices are in the random manifold regime with a roughening exponent of 0.44 for length scales up to 80-100 lattice constants. At larger length scales, the data exhibit nonequilibrium features that persist for different cooling rates and field histories. Charge density waves in transition-metal dichalcogenides are a good example of a two dispensional electronic system. A scanning tunneling microscope (STM) was used to fabricate T-phase tantalum diselenide (TaSe2) nanocrystals with sizes ranging from 7 to more than 100 nanometers within the surface layer of 2H phase

  5. Efficient light emission from inorganic and organic semiconductor hybrid structures by energy-level tuning

    PubMed Central

    Schlesinger, R.; Bianchi, F.; Blumstengel, S.; Christodoulou, C.; Ovsyannikov, R.; Kobin, B.; Moudgil, K.; Barlow, S.; Hecht, S.; Marder, S.R.; Henneberger, F.; Koch, N.

    2015-01-01

    The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach. PMID:25872919

  6. Disorder-related effects in electron systems of low dimensionality

    NASA Astrophysics Data System (ADS)

    Gramada, Apostol

    1999-08-01

    This dissertation reports on research we have done on different topics in the physics of low-dimensional disordered electron systems. For two-dimensional systems in the presence of a magnetic field, we approach aspects related to the delocalized states (levitation, structure and position in multilayer systems) and the problem of generation of high harmonics of the cyclotron resonance. We estimate that the delocalized state ``levitate'' away from the center of the Landau level as the inverse of the fourth power of the magnetic field. In a two-layer system, the delocalized states repel each other in a manner similar to the usual level repulsion in quantum mechanics. We calculate the position and structure of the delocalized states. In the limit of the weak magnetic field, we establish the physics and develop the quantitative theory which explain the recent observation of the enhancement of the harmonics of the cyclotron resonance in this limit. For the case of one-dimensional systems, we study the effect of inhomogeneity on the tunnel density of states in a Luttinger liquid. We show that for a periodic inhomogeneity, an additional anomaly develops in the electron density of states and we find its position and magnitude. In the case of a disordered inhomogeneity, the plasmons associated with the low-energy excitations of the system become localized and, as a consequence, the correlator of the fluctuations of the densities of states is modified, acquiring an oscillatory dependence on the distance.

  7. Method of multilayer semiconductor structures cross section preparation for transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Karasyov, Vladimir Y.; Skornyakov, Alexander V.; Kuznetsov, Mikhail G.

    1995-09-01

    The transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) are frequently applied for defects and failures ULCI analysis. The preparation of the electron transparent big area flat- parallel semiconductor thin films is needed. The simple and speed automated method of the thin films (less 10 micrometers ) and cross-sections of the multilayer semiconductor structures and devices preparation is described in this paper. It is based on the mechanical and chem- mechanical grinding and polishing of the semiconductor sample with a free abrasive. This method allows to form the flat-parallel and composition uniform thin films with electron transparent area more that 2 mm2 after ion-etching treatment. The original equipment which consists of a local treatment unit, planar treatment unit and wire saw unit is developed.

  8. Semiconductor structural damage attendant to contact formation in III-V solar cells

    NASA Technical Reports Server (NTRS)

    Fatemi, Navid S.; Weizer, Victor G.

    1991-01-01

    In order to keep the resistive losses in solar cells to a minimum, it is often necessary for the ohmic contacts to be heat treated to lower the metal-semiconductor contact resistivity to acceptable values. Sintering of the contacts, however can result in extensive mechanical damage of the semiconductor surface under the metallization. An investigation of the detailed mechanisms involved in the process of contact formation during heat treatment may control the structural damage incurred by the semiconductor surface to acceptable levels, while achieving the desired values of contact resistivity for the ohmic contacts. The reaction kinetics of sintered gold contacts to InP were determined. It was found that the Au-InP interaction involves three consecutive stages marked by distinct color changes observed on the surface of the Au, and that each stage is governed by a different mechanism. A detailed description of these mechanisms and options to control them are presented.

  9. SEMICONDUCTOR DEVICES: Trench gate IGBT structure with floating P region

    NASA Astrophysics Data System (ADS)

    Mengliang, Qian; Zehong, Li; Bo, Zhang; Zhaoji, Li

    2010-02-01

    A new trench gate IGBT structure with a floating P region is proposed, which introduces a floating P region into the trench accumulation layer controlled IGBT (TAC-IGBT). The new structure maintains a low on-state voltage drop and large forward biased safe operating area (FBSOA) of the TAC-IGBT structure while reduces the leakage current and improves the breakdown voltage. In addition, it enlarges the short circuit safe operating area (SCSOA) of the TAC-IGBT, and is simple in fabrication and design. Simulation results indicate that, for IGBT structures with a breakdown voltage of 1200 V, the leakage current of the new trench gate IGBT structure is one order of magnitude lower than the TAC-IGBT structure and the breakdown voltage is 150 V higher than the TAC-IGBT.

  10. Electronic structure of the organic semiconductor copper phthalocyanine: experiment and theory.

    PubMed

    Aristov, V Yu; Molodtsova, O V; Maslyuk, V V; Vyalikh, D V; Zhilin, V M; Ossipyan, Yu A; Bredow, T; Mertig, I; Knupfer, M

    2008-01-21

    The electronic structure of the organic semiconductor copper-phthalocyanine (CuPc) has been determined by a combination of conventional and resonant photoemission, near-edge x-ray absorption, as well as by the first-principles calculations. The experimentally obtained electronic valence band structure of CuPc is in very good agreement with the calculated density of states results, allowing the derivation of detailed site specific information.

  11. Flexible perovskite solar cells based on the metal-insulator-semiconductor structure.

    PubMed

    Wei, Jing; Li, Heng; Zhao, Yicheng; Zhou, Wenke; Fu, Rui; Pan, Huiyue; Zhao, Qing

    2016-09-14

    The metal-insulator-semiconductor (MIS) structure is applied to perovskite solar cells, in which the traditional compact layer TiO2 is replaced by Al2O3 as the hole blocking material to realize an all-low-temperature process. Flexible devices based on this structure are also realized with excellent flexibility, which hold 85% of their initial efficiency after bending 100 times. PMID:27524362

  12. Near Surface Structure of Organic Semiconductor Tetracene Single Crystal

    NASA Astrophysics Data System (ADS)

    Wakabayashi, Yusuke; Morisaki, Hazuki; Kimura, Tsuyoshi; Miwa, Kazumoto; Koretsune, Takashi; Takeya, Jun

    2014-03-01

    Electric conduction in organic crystals is highly anisotropic because of the anisotropic molecular orbitals. Crystal structure governs the transfer through the overlap integral among the highest occupied (or lowest unoccupied) molecular orbitals. In case of organic devices, the place where electrons conduct is the interface. Therefore, the surface structure of organic single crystals is relevant. Surface relaxation of the structure of rubrene single crystal was firstly observed by means of surface x-ray diffraction a few years ago. This time we performed similar measurement on tetracene single crystal, whose molecular shape has large similarity with rubrene while the crystal structure is very different. Tetracene single crystal was grown by the physical vapor transport method, and the surface x-ray diffraction experiments were performed at BL-3A and 4C of the Photon Factory, KEK, Japan. Obtained electron density profile shows a large structural deformation at the surface layer of tetracene.

  13. Release strategies for making transferable semiconductor structures, devices and device components

    SciTech Connect

    Rogers, John A; Nuzzo, Ralph G; Meitl, Matthew; Ko, Heung Cho; Yoon, Jongseung; Menard, Etienne; Baca, Alfred J

    2014-11-25

    Provided are methods for making a device or device component by providing a multilayer structure having a plurality of functional layers and a plurality of release layers and releasing the functional layers from the multilayer structure by separating one or more of the release layers to generate a plurality of transferable structures. The transferable structures are printed onto a device substrate or device component supported by a device substrate. The methods and systems provide means for making high-quality and low-cost photovoltaic devices, transferable semiconductor structures, (opto-)electronic devices and device components.

  14. Release strategies for making transferable semiconductor structures, devices and device components

    DOEpatents

    Rogers, John A.; Nuzzo, Ralph G.; Meitl, Matthew; Ko, Heung Cho; Yoon, Jongseung; Menard, Etienne; Baca, Alfred J.

    2011-04-26

    Provided are methods for making a device or device component by providing a multilayer structure having a plurality of functional layers and a plurality of release layers and releasing the functional layers from the multilayer structure by separating one or more of the release layers to generate a plurality of transferable structures. The transferable structures are printed onto a device substrate or device component supported by a device substrate. The methods and systems provide means for making high-quality and low-cost photovoltaic devices, transferable semiconductor structures, (opto-)electronic devices and device components.

  15. Release strategies for making transferable semiconductor structures, devices and device components

    DOEpatents

    Rogers, John A.; Nuzzo, Ralph G.; Meitl, Matthew; Ko, Heung Cho; Yoon, Jongseung; Menard, Etienne; Baca, Alfred J.

    2016-05-24

    Provided are methods for making a device or device component by providing a multi layer structure having a plurality of functional layers and a plurality of release layers and releasing the functional layers from the multilayer structure by separating one or more of the release layers to generate a plurality of transferable structures. The transferable structures are printed onto a device substrate or device component supported by a device substrate. The methods and systems provide means for making high-quality and low-cost photovoltaic devices, transferable semiconductor structures, (opto-)electronic devices and device components.

  16. Low dimensional dynamics in birdsong production

    NASA Astrophysics Data System (ADS)

    Amador, Ana; Mindlin, Gabriel B.

    2014-12-01

    The way in which information about behavior is represented at different levels of the motor pathway, remains among the fundamental unresolved problems of motor coding and sensorimotor integration. Insight into this matter is essential for understanding complex learned behaviors such as speech or birdsong. A major challenge in motor coding has been to identify an appropriate framework for characterizing behavior. In this work we discuss a novel approach linking biomechanics and neurophysiology to explore motor control of songbirds. We present a model of song production based on gestures that can be related to physiological parameters that the birds can control. This physical model for the vocal structures allows a reduction in the dimensionality of the behavior, being a powerful approach for studying sensorimotor integration. Our results also show how dynamical systems models can provide insight into neurophysiological analysis of vocal motor control. In particular, our work challenges the actual understanding of how the motor pathway of the songbird systems works and proposes a novel perspective to study neural coding for song production.

  17. Dynamic colloidal assembly pathways via low dimensional models

    NASA Astrophysics Data System (ADS)

    Yang, Yuguang; Thyagarajan, Raghuram; Ford, David M.; Bevan, Michael A.

    2016-05-01

    Here we construct a low-dimensional Smoluchowski model for electric field mediated colloidal crystallization using Brownian dynamic simulations, which were previously matched to experiments. Diffusion mapping is used to infer dimensionality and confirm the use of two order parameters, one for degree of condensation and one for global crystallinity. Free energy and diffusivity landscapes are obtained as the coefficients of a low-dimensional Smoluchowski equation to capture the thermodynamics and kinetics of microstructure evolution. The resulting low-dimensional model quantitatively captures the dynamics of different assembly pathways between fluid, polycrystal, and single crystals states, in agreement with the full N-dimensional data as characterized by first passage time distributions. Numerical solution of the low-dimensional Smoluchowski equation reveals statistical properties of the dynamic evolution of states vs. applied field amplitude and system size. The low-dimensional Smoluchowski equation and associated landscapes calculated here can serve as models for predictive control of electric field mediated assembly of colloidal ensembles into two-dimensional crystalline objects.

  18. Observations on ion track structure in semiconductors : a phenomenological study

    NASA Technical Reports Server (NTRS)

    Selva, L. E.; Wallace, R. E.

    2001-01-01

    An ion track structure model at the nanometer scale is presented. The model is based on electrostatic principles and is supported by observed experimental results conducted on power MOSFETs. The model predicts the existence of a transient induced electric field following the passage of an energetic heavy ion. There are two segments to the field (a radial and an axial component). It is the interaction of this transient electric field with the local environment that can trigger a catastrophic failure.

  19. Low-dimensional compounds containing cyano groups. XVII. Crystal structure, spectroscopic, thermal and magnetic properties of [Cu(bmen){sub 2}][Pt(CN){sub 4}] (bmen=N,N'-dimethylethylenediamine)

    SciTech Connect

    Potocnak, Ivan Vavra, Martin; Cizmar, Erik; Kajnakova, Marcela; Radvakova, Alena; Steinborn, Dirk; Zvyagin, Sergei A.; Wosnitza, Jochen; Feher, Alexander

    2009-01-15

    The synthesis, structural analysis, spectroscopic studies, susceptibility and specific-heat measurements of {l_brace}[Cu(bmen){sub 2}][Pt(CN){sub 4}]{r_brace}{sub n} (bmen=N,N'-dimethylethylenediamine) are presented. X-ray crystal-structure analysis revealed that the [Pt(CN){sub 4}]{sup 2-} building blocks are combined with [Cu(bmen){sub 2}]{sup 2+} units to form a chain-like structure along the a axis. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane belonging to two molecules of bidentate bmen ligands with average Cu-N distance of 2.043(18) A. The axial positions are occupied by two nitrogen atoms from bridging [Pt(CN){sub 4}]{sup 2-} anions at a longer axial Cu-N distance of 2.490(4) A. The compound is characterized by the presence of a weak antiferromagnetic exchange coupling J/k{sub B}=0.6 K. Despite the one-dimensional (1D) character of the structure, the analysis of the magnetic properties and specific heat at very low temperatures shows that [Cu(bmen){sub 2}][Pt(CN){sub 4}] behaves as a two-dimensional (2D) square-lattice Heisenberg magnet with weak interlayer coupling. - Graphical abstract: The synthesis, structural analysis, spectroscopic studies, susceptibility and specific-heat measurements of {l_brace}[Cu(bmen){sub 2}][Pt(CN){sub 4}]{r_brace}{sub n} (bmen=N,N'-dimethylethylenediamine) are presented. X-ray crystal-structure analysis revealed that the [Pt(CN){sub 4}]{sup 2-} building blocks are combined with [Cu(bmen){sub 2}]{sup 2+} units to form a chain-like structure. The compound is characterized by the presence of a weak antiferromagnetic exchange coupling J/k{sub B}=-0.6 K. Despite the one-dimensional character of the structure, the analysis of the magnetic properties and specific heat at very low temperatures shows that [Cu(bmen){sub 2}][Pt(CN){sub 4}] behaves as a two-dimensional square-lattice Heisenberg magnet with weak interlayer coupling.

  20. Fabrication of lateral electrodes on semiconductor nanowires through structurally matched insulation for functional optoelectronics.

    PubMed

    Sheng, Yun; Sun, Huabin; Wang, Jianyu; Gao, Fan; Wang, Junzhuan; Pan, Lijia; Pu, Lin; Zheng, Youdou; Shi, Yi

    2013-01-18

    A strategy of using structurally matched alumina insulation to produce lateral electrodes on semiconductor nanowires is presented. Nanowires in the architecture are structurally matched with alumina insulation using selective anodic oxidation. Lateral electrodes are fabricated by directly evaporating metallic atoms onto the opposite sides of the nanowires. The integrated architecture with lateral electrodes propels carriers to transport them across nanowires and is crucially beneficial to the injection/extraction in optoelectronics. The matched architecture and the insulating properties of the alumina layer are investigated experimentally. ZnO nanowires are functionalized into an ultraviolet photodiode as an example. The present strategy successfully implements an advantageous architecture and is significant in developing diverse semiconductor nanowires in optoelectronic applications.

  1. Fabrication of lateral electrodes on semiconductor nanowires through structurally matched insulation for functional optoelectronics

    NASA Astrophysics Data System (ADS)

    Sheng, Yun; Sun, Huabin; Wang, Jianyu; Gao, Fan; Wang, Junzhuan; Pan, Lijia; Pu, Lin; Zheng, Youdou; Shi, Yi

    2013-01-01

    A strategy of using structurally matched alumina insulation to produce lateral electrodes on semiconductor nanowires is presented. Nanowires in the architecture are structurally matched with alumina insulation using selective anodic oxidation. Lateral electrodes are fabricated by directly evaporating metallic atoms onto the opposite sides of the nanowires. The integrated architecture with lateral electrodes propels carriers to transport them across nanowires and is crucially beneficial to the injection/extraction in optoelectronics. The matched architecture and the insulating properties of the alumina layer are investigated experimentally. ZnO nanowires are functionalized into an ultraviolet photodiode as an example. The present strategy successfully implements an advantageous architecture and is significant in developing diverse semiconductor nanowires in optoelectronic applications.

  2. Dynamics of carrier recombination in a semiconductor laser structure

    SciTech Connect

    Dzhioev, R. I. Kavokin, K. V.; Kusrayev, Yu. G.; Poletaev, N. K.

    2015-11-15

    Carrier-recombination dynamics is studied by the method of optical orientation at room temperature in the active layer of a laser diode structure. The dependence of the degree of electron-spin orientation on the excitation density is attributed to saturation of the nonradiative-recombination channel. The time of electron capture at recombination centers is determined to be τ{sub e} = 5 × 10{sup –9} s. The temperature of nonequilibrium electrons heated by a He–Ne laser is estimated.

  3. Low-dimensional compounds containing cyano groups. XIV. Crystal structure, spectroscopic, thermal and magnetic properties of [CuL {sub 2}][Pt(China){sub 4}] complexes (L=ethylenediamine or N,N-dimethylethylenediamine)

    SciTech Connect

    Potocnak, Ivan . E-mail: ivan.potocnak@upjs.sk; Vavra, Martin; Cizmar, Erik; Tibenska, Katarina; Orendacova, Alzbeta; Steinborn, Dirk; Wagner, Christoph; Dusek, Michal; Fejfarova, Karla; Schmidt, Harry; Muller, Thomas; Orendac, Martin; Feher, Alexander

    2006-07-15

    Violet crystals of [Cu(en){sub 2}][Pt(China){sub 4}] and blue crystals of [Cu(dmen){sub 2}][Pt(China){sub 4}] were crystallized from the water-methanol solution containing CuCl{sub 2}.2H{sub 2}O, ethylenediamine (en) or N,N-dimethylethylenediamine (dmen) and K{sub 2}[Pt(China){sub 4}].3H{sub 2}O. Both compounds were characterized using elemental analysis, infrared and UV-VIS spectroscopy, magnetic measurements, specific heat measurements and thermal analysis. X-ray structure analysis revealed chain-like structure in both compounds. The covalent chains are built of Cu(II) ions linked by [Pt(China){sub 4}]{sup 2-} anions in the [111] and [101] direction, respectively. The Cu(II) atoms are hexacoordinated by four nitrogen atoms in the equatorial plane from two molecules of bidentate ligands L with average Cu-N distance of 2.022(2) and 2.049(4) A, respectively. Axial positions are occupied by two nitrogen atoms from bridging [Pt(China){sub 4}]{sup 2-} anions at longer Cu-N distance of 2.537(2) and 2.600(5) A, respectively. Both materials are characterized by the presence of weak antiferromagnetic exchange coupling. Despite the one-dimensional (1D) character of the structure, the analysis of magnetic properties and specific heat at very low temperatures shows that [Cu(en){sub 2}][Pt(China){sub 4}] behaves as two-dimensional (2D) spatially anisotropic square lattice Heisenberg magnet, while more pronounced influence of interlayer coupling is observed in [Cu(dmen){sub 2}][Pt(China){sub 4}]. - Graphical abstract: Chain-like structure in [Cu(en){sub 2}][Pt(China){sub 4}] (R=H) and [Cu(dmen){sub 2}][Pt(China){sub 4}] (R=CH{sub 3}) compounds.

  4. Relating chemical structure to the mechanical and electrical properties in organic crystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Reyes-Martinez, Marcos; Crosby, Alfred; Briseno, Alejandro

    2015-03-01

    The study of the physical properties of organic single crystals (OSCs) has allowed the advent of a new generation of high-performance organic electronic devices. Despite the profound knowledge of the structural and electrical properties of OSCs, there is little research on their mechanical properties and the effects of strain on their electrical properties. This presentation brings new understanding of the intrinsic mechanical properties of organic semiconductors and the effect of deformation in charge transport phenomena. We utilize rubrene single crystals as model systems. Due to the limited dimensions of crystals and the associated handling difficulty, the wrinkling instability is chosen as a metrology tool for the in-plane elastic constants. To elucidate the effects of mechanical strain on charge transport, we take advantage of wrinkling as a unique way to strain the conducting channel of field-effect transistors in a non-destructive, reversible, and predictable manner and demonstrate the mechanical modulation of field-effect mobility. Our contributions are the first to quantitatively correlate the crystal structure and the mechanical properties of OSCs, as well as the first to study their electro-mechanical behavior. They also represent a significant step forward in structure-function relationships in organic semiconductors and lay the foundation for the effective use of organic semiconductors in mechanically demanding applications such as pressure sensors and electronic skins.

  5. Electrical properties of hybrid (ferromagnetic metal)-(layered semiconductor) Ni/p-GaSe structures

    SciTech Connect

    Bakhtinov, A. P. Vodopyanov, V. N.; Kovalyuk, Z. D.; Netyaga, V. V.; Lytvyn, O. S.

    2010-02-15

    Two-barrier Ni/n-Ga2Se3/p-GaSe structures with nanoscale Ni-alloy grains caused by reactions at the 'metal-layered semiconductor' interface were formed after growing Ni layers on the p-GaSe (0001) surface. Current-voltage and capacitance-voltage characteristics of hybrid structures were studied in the temperature range of 220-350 K. The dependence of the impedance spectra on the bias voltage was studied at various temperatures. The frequency dependences of the impedance at high frequencies (f = 10{sup 6} Hz) are discussed in terms of the phenomena of spin injection and extraction in structures with an ultrathin spin-selective Ni/n-Ga{sub 2}Se{sub 3} barrier and the effects of spin diffusion and relaxation in the semiconductor substrate. The room-temperature phenomena of the Coulomb blockade and negative differential capacitance were detected. These phenomena are explained based on an analysis of transport processes in a narrow region near the 'ferromagnetic metal-semiconductor' interface, where nanoscale grains are arranged.

  6. Electronic Structure of the Organic Semiconductor Copper Tetraphenylporphyrin (CuTPP)

    SciTech Connect

    Reid, I.; Zhang, Y; Demasi, A; Blueser, A; Piper, L; Downes, J; Matsuura, A; Hughes, G; Smith, K

    2009-01-01

    The electronic structure of thin films of the organic semiconductor copper tetraphenylporphyrin (CuTPP) has been studied using synchrotron radiation-excited resonant soft X-ray emission spectroscopy (RSXE), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, and X-ray photoemission spectroscopy (XPS). The C and N partial density of states for both the valence and conduction band electronic structure has been determined, while XPS was used to provide information on the chemical composition and the oxidation states of the copper. Good agreement was found between the experimental measurements of the valence and conduction bands and the results of density functional theory calculations.

  7. Electronic structure of ferromagnetic semiconductor material on the monoclinic and rhombohedral ordered double perovskites La{sub 2}FeCoO{sub 6}

    SciTech Connect

    Fuh, Huei-Ru; Chang, Ching-Ray; Weng, Ke-Chuan; Wang, Yin-Kuo

    2015-05-07

    Double perovskite La{sub 2}FeCoO{sub 6} with monoclinic structure and rhombohedra structure show as ferromagnetic semiconductor based on density functional theory calculation. The ferromagnetic semiconductor state can be well explained by the superexchange interaction. Moreover, the ferromagnetic semiconductor state remains under the generalized gradient approximation (GGA) and GGA plus onsite Coulomb interaction calculation.

  8. Magnons in disordered nonstoichiometric low-dimensional magnets

    NASA Astrophysics Data System (ADS)

    Buczek, Paweł; Sandratskii, Leonid M.; Buczek, Nadine; Thomas, Stefan; Vignale, Giovanni; Ernst, Arthur

    2016-08-01

    We study spin excitation spectra of one-, two-, and three-dimensional magnets featuring nonmagnetic defects at a wide range of concentrations. Taking the Heisenberg model as the starting point, we tackle the problem by both direct numerical simulations in large supercells and using a semianalytic coherent-potential approximation. We consider the properties of the excitations in both direct and reciprocal spaces. In the limits of the concentration c of the magnetic atoms tending to 0 or 1 the properties of the spin excitations are similar in all three dimensions. In the case of a low concentration of magnetic atoms the spin excitation spectra are dominated by the modes confined in the real space to single atoms or small clusters and delocalized in the reciprocal space. In the limit of c tending to 1, we obtain the spin-wave excitations delocalized in the real space and localized in the reciprocal space. However, for the intermediate concentrations the properties of the spin excitations are strongly dimensionality dependent. We pay particular attention to the formation, with increase of c , of the Lorentzian-shaped peaks in the spectral densities of the spin excitations, which can be regarded as magnon states with a finite lifetime given by the width of the peaks. In general, low-dimensional magnets are more strongly affected by the presence of nonmagnetic impurities than their bulk counterparts. The details of the electronic structure, varying with the dimensionality and the concentration, substantially influence the spin excitation spectra of real materials, as we show in the example of the FeAl alloy.

  9. Low-dimensional CdS/CdTe multiple-quantum well heterostructure for optical refrigeration

    NASA Astrophysics Data System (ADS)

    Tarín-Cordero, Julio C.; Villa-Angulo, Rafael; Villa-Angulo, José R.; Villa-Angulo, Carlos

    2015-01-01

    The major challenge for semiconductors to achieve temperatures below 10 K by luminescence upconversion, is that at these lattice temperatures the acoustic phonon component dominates and the scattering rate becomes comparable to the band-to-band radiative transition rate. This problem can be significantly alleviated by employing quantum-confined systems, where relaxation of wave-vector conservation in the confined direction reduces material conductivity by nearly three orders of magnitude. Although previous studies have reported theoretical and experimental analyses of cooling characteristics for bulk semiconductors, the electron band-to-band transition due to photon absorption or photon emission under cooling conditions in quantum-confined semiconductor systems which exhibit quantum effects at the dimensions of several nanometers have not been completely analyzed in conventional theoretical studies. We realized a numerical investigation of optical cooling conditions for a low-dimensional CdS/CdTe multiple-quantum well heterostructure where injected carriers in the active region are quantum mechanically confined in one dimension. Effects of such quantum mechanically confined carriers on photon absorption and photoluminescence (PL) were analyzed under cooling conditions. Most importantly, the CdS/CdTe heterostructure absorption and PL spectra for cooling conditions were defined in terms of the active layer width and number of quantum wells in the complete heterostructure.

  10. Magnetic structure of low-dimensional LiCu{sub 2}O{sub 2} multiferroic according to {sup 63,65}Cu and {sup 7}Li NMR studies

    SciTech Connect

    Sadykov, A. F. Gerashchenko, A. P.; Piskunov, Yu. V.; Ogloblichev, V. V.; Smol'nikov, A. G.; Verkhovskii, S. V.; Yakubovskii, A. Yu.; Tishchenko, E. A.; Bush, A. A.

    2012-10-15

    The complex NMR study of the magnetic structure of LiCu{sub 2}O{sub 2} multiferroic has been performed. It has been shown that the spin spirals in LiCu{sub 2}O{sub 2} are beyond the ab, bc, and ac crystallographic planes. The external magnetic field applied along the c axis of the crystal does not change the spatial orientation of spirals in Cu{sup 2+} chains. A magnetic field of H{sub 0} = 94 kOe applied along the a and b axes rotates the planes of spin spirals in chains, tending to orient the normal n of spirals along the external magnetic field. The rotation angle of the planes of the magnetic moments are maximal at H{sub 0} Double-Vertical-Line b.

  11. Structure Analysis of Composition Modulation in Epitaxially-Grown III-V Semiconductor Alloys

    NASA Astrophysics Data System (ADS)

    Ishimaru, Manabu; Hasegawa, Shigehiko; Asahi, Hajime; Sato, Kazuhisa; Konno, Toyohiko J.

    2013-11-01

    It has been reported that composition modulation is naturally formed in some of the epitaxially-grown thin films. Structural characterization of these materials is necessary for controlling their nanostructures precisely. Here, we prepared epitaxially-grown III-V semiconductor alloys and characterized their atomistic structures by means of diffraction crystallography and electron microscopy techniques. As a consequence, we found that the following quantum well structures are spontaneously formed: (1) ultrashort period lateral composition modulation (LCM) with a modulation period of ˜1 nm; (2) complex vertical composition modulated (VCM) structures consisting of two modulated structures with a different period (˜4 and ˜25 nm). The former LCM structure is created via nanoscale phase separation at the growth surface, while the shorter-period modulation in the later VCM structure is induced by rotating a substrate through an inhomogeneous distribution of the anion flux within a chamber.

  12. Graphene-based hybrid structures combined with functional materials of ferroelectrics and semiconductors

    NASA Astrophysics Data System (ADS)

    Jie, Wenjing; Hao, Jianhua

    2014-05-01

    Fundamental studies and applications of 2-dimensional (2D) graphene may be deepened and broadened via combining graphene sheets with various functional materials, which have been extended from the traditional insulator of SiO2 to a versatile range of dielectrics, semiconductors and metals, as well as organic compounds. Among them, ferroelectric materials have received much attention due to their unique ferroelectric polarization. As a result, many attractive characteristics can be shown in graphene/ferroelectric hybrid systems. On the other hand, graphene can be integrated with conventional semiconductors and some newly-discovered 2D layered materials to form distinct Schottky junctions, yielding fascinating behaviours and exhibiting the potential for various applications in future functional devices. This review article is an attempt to illustrate the most recent progress in the fabrication, operation principle, characterization, and promising applications of graphene-based hybrid structures combined with various functional materials, ranging from ferroelectrics to semiconductors. We focus on mechanically exfoliated and chemical-vapor-deposited graphene sheets integrated in numerous advanced devices. Some typical hybrid structures have been highlighted, aiming at potential applications in non-volatile memories, transparent flexible electrodes, solar cells, photodetectors, and so on.

  13. Theory of the electronic structure of substitutional semiconductor alloys: Analytical approaches

    SciTech Connect

    Zakharov, A. Yu.

    2015-07-15

    Methods of predicting the electronic structure of disordered semiconductor alloys involving mainly isoelectronic substitution are reviewed. Special emphasis is placed on analytical methods of studying currently available models of alloys. An approximate equation for the localization threshold of electronic states in the Lifshitz model is considered, and the inaccuracy of this equation is estimated. The contributions of the perturbation potential of an individual impurity and of crystal-lattice distortions in the vicinity of the impurity center are analyzed on the basis of the Faddeev equations. The contributions of intrinsic impurity potentials and volume effects to the formation of the electronic structure of semiconductor alloys are esti- mated. Methods of calculating matrix elements of the perturbation potentials of isoelectronic impurities in alloys with consideration for deformation effects are considered. The procedure of calculating the compositional dependence of the band gap of multicomponent alloys is described. A comparative analysis of various methods for predicting the formation of electronic states bound at individual isoelectronic impurities in semiconductors is conducted. The theory of the energy spectrum of charged impurities in isoelectronic alloys is presented.

  14. Study of the structure of passivated vanadium-titanium alloys and their semiconductor properties.

    PubMed

    Bachmann, T; Vonau, W; John, P

    2002-10-01

    The possibility of investigating the photocurrent behavior and structure of electrochemically prepared passive films on metallic titanium and on binary vanadium-titanium alloys has been demonstrated. The semiconductor properties were characterized by measuring the dependence of the photocurrent on the wavelength of the incident light and on the electrode potential. The results showed the oxide layers to be n-type semiconductors with a bandgap between 2.6 and 3.3 eV and a flatband potential of approximately -300 to +400 mV (relative to the SCE). The results were interpreted in terms of the corrosion characteristics of the materials. XPS measurements on pure vanadium and some alloys are presented. Several properties were used to characterize the passive surface of these materials. The V(2)O(5) and TiO(2) content decreases with increasing depth.

  15. Structurally controllable spin spatial splitter in a hybrid ferromagnet and semiconductor nanostructure

    SciTech Connect

    Lu, Mao-Wang Cao, Xue-Li; Huang, Xin-Hong; Jiang, Ya-Qing; Li, Shuai

    2014-05-07

    We theoretically investigate modulation of a tunable δ-potential to the lateral displacement of electrons across a magnetically modulated semiconductor nanostructure. Experimentally, this nanostructure can be produced by depositing a nanosized ferromagnetic stripe with in-plane magnetization on top of a semiconductor heterostructure, while the δ-potential can be realized by means of the atomic layer doping technique. Theoretical analysis reveals that this δ-doping can break the intrinsic symmetry in nanostructure and a considerable spin polarization in the lateral displacement will appear. Numerical calculations demonstrate that both magnitude and sign of spin polarization can be manipulated by changing the height and/or position of the δ-doping, giving rise to a structurally tunable spin spatial splitter.

  16. Physical model for trap-assisted inelastic tunneling in metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Jiménez-Molinos, F.; Palma, A.; Gámiz, F.; Banqueri, J.; López-Villanueva, J. A.

    2001-10-01

    A physical model for trap-assisted inelastic tunnel current through potential barriers in semiconductor structures has been developed. The model is based on the theory of multiphonon transitions between detrapped and trapped states and the only fitting parameters are those of the traps (energy level and concentration) and the Huang-Rhys factor. Therefore, dependences of the trapping and detrapping processes on the bias, position, and temperature can be obtained with this model. The results of the model are compared with experimental data of stress induced leakage current in metal-oxide-semiconductor devices. The average energy loss has been obtained and an interpretation is given of the curves of average energy loss versus oxide voltage. This allows us to identify the entrance of the assisted tunnel current in the Fowler-Nordheim regime. In addition, the dependence of the tunnel current and average energy loss on the model parameters has been studied.

  17. Low-dimensional compounds containing bioactive ligands. Part VI: Synthesis, structures, in vitro DNA binding, antimicrobial and anticancer properties of first row transition metal complexes with 5-chloro-quinolin-8-ol.

    PubMed

    Potočňák, Ivan; Vranec, Peter; Farkasová, Veronika; Sabolová, Danica; Vataščinová, Michaela; Kudláčová, Júlia; Radojević, Ivana D; Čomić, Ljiljana R; Markovic, Bojana Simovic; Volarevic, Vladislav; Arsenijevic, Nebojsa; Trifunović, Srećko R

    2016-01-01

    A series of new 3d metal complexes with 5-chloro-quinolin-8-ol (ClQ), [Mn(ClQ)2] (1), [Fe(ClQ)3] (2), [Co(ClQ)2(H2O)2] (3), [Ni(ClQ)2(H2O)2] (4), [Cu(ClQ)2] (5), [Zn(ClQ)2(H2O)2] (6), [Mn(ClQ)3]·DMF (7) and [Co(ClQ)3]·DMF·(EtOH)0.35 (8) (DMF=N,N-dimethylformamide), has been synthesized and characterized by elemental analysis, IR spectroscopy and TG-DTA thermal analysis. X-ray structure analysis of 7 and 8 revealed that these molecular complexes contain three chelate ClQ molecules coordinated to the central atoms in a deformed octahedral geometry and free space between the complex units is filled by solvated DMF and ethanol molecules. Antimicrobial activity of 1-6 was tested by determining the minimum inhibitory concentration and minimum microbicidal concentration against 12 strains of bacteria and 5 strains of fungi. The intensity of antimicrobial action varies depending on the group of microorganism and can be sorted: 1>ClQ>6>3/4>2>5. Complexes 1-6 exhibit high cytotoxic activity against MDA-MB, HCT-116 and A549 cancer cell lines. Among them, complex 2 is significantly more cytotoxic against MDA-MB cells than cisplatin at all tested concentrations and is not cytotoxic against control mesenchymal stem cells indicating that this complex seems to be a good candidate for future pharmacological evaluation. Interaction of 1-6 with DNA was investigated using UV-VIS spectroscopy, fluorescence spectroscopy and agarose gel electrophoresis. The binding studies indicate that 1-6 can interact with CT-DNA through intercalation; complex 2 has the highest binding affinity. Moreover, complexes 1-6 inhibit the catalytic activity of topoisomerase I.

  18. INTRODUCTION: Physics of Low-dimensional Systems: Nobel Symposium 73

    NASA Astrophysics Data System (ADS)

    Lundqvist, Stig

    1989-01-01

    The physics of low-dimensional systems has developed in a remarkable way over the last decade and has accelerated over the last few years, in particular because of the discovery of the new high temperature superconductors. The new developments started more than fifteen years ago with the discovery of the unexpected quasi-one-dimensional character of the TTF-TCNQ. Since then the field of conducting quasi-one-dimensional organic systems have been rapidly growing. Parallel to the experimental work there has been an important theoretical development of great conceptual importance, such as charge density waves, soliton-like excitations, fractional charges, new symmetry properties etc. A new field of fundamental importance was the discovery of the Quantum Hall Effect in 1980. This field is still expanding with new experimental and theoretical discoveries. In 1986, then, came the totally unexpected discovery of high temperature superconductivity which started an explosive development. The three areas just mentioned formed the main themes of the Symposium. They do not in any way exhaust the progress in low-dimensional physics. We should mention the recent important development with both two-dimensional and one-dimensional and even zero-dimensional structures (quantum dots). The physics of mesoscopic systems is another important area where the low dimensionality is a key feature. Because of the small format of this Symposium we could unfortunately not cover these areas. A Nobel Symposium provides an excellent opportunity to bring together a group of prominent scientists for a stimulating exchange of new ideas and results. The Nobel Symposia are very small meetings by invitation only and the number of key international participants is typically in the range 25-40. These Symposia are arranged through a special Nobel Symposium Committee after proposal from individuals. This Symposium was sponsored by the Nobel Foundation through its Nobel Symposium Fund with grants from The

  19. Unusual nonlinear current-voltage characteristics of a metal-intrinsic semiconductor-metal barrierless structure

    NASA Astrophysics Data System (ADS)

    Meriuts, A. V.; Gurevich, Yu. G.

    2015-03-01

    A nonlinear model for the electric current in a metal-intrinsic semiconductor-metal structure without potential barriers in contacts is considered using a drift diffusion approach. An analytical solution of the continuity equations and the current-voltage characteristic for various recombination rates in the contacts are obtained. It is shown that the current-voltage characteristics of such a structure exhibit not only linear behavior, corresponding to Ohm's law, but may also possess properties of current-voltage characteristics of the rectifier diode. It is also possible current-voltage characteristics with saturation in both forward and backward directions. Physical model that explains the obtained results is proposed.

  20. Development of plenoptic infrared camera using low dimensional material based photodetectors

    NASA Astrophysics Data System (ADS)

    Chen, Liangliang

    Infrared (IR) sensor has extended imaging from submicron visible spectrum to tens of microns wavelength, which has been widely used for military and civilian application. The conventional bulk semiconductor materials based IR cameras suffer from low frame rate, low resolution, temperature dependent and highly cost, while the unusual Carbon Nanotube (CNT), low dimensional material based nanotechnology has been made much progress in research and industry. The unique properties of CNT lead to investigate CNT based IR photodetectors and imaging system, resolving the sensitivity, speed and cooling difficulties in state of the art IR imagings. The reliability and stability is critical to the transition from nano science to nano engineering especially for infrared sensing. It is not only for the fundamental understanding of CNT photoresponse induced processes, but also for the development of a novel infrared sensitive material with unique optical and electrical features. In the proposed research, the sandwich-structured sensor was fabricated within two polymer layers. The substrate polyimide provided sensor with isolation to background noise, and top parylene packing blocked humid environmental factors. At the same time, the fabrication process was optimized by real time electrical detection dielectrophoresis and multiple annealing to improve fabrication yield and sensor performance. The nanoscale infrared photodetector was characterized by digital microscopy and precise linear stage in order for fully understanding it. Besides, the low noise, high gain readout system was designed together with CNT photodetector to make the nano sensor IR camera available. To explore more of infrared light, we employ compressive sensing algorithm into light field sampling, 3-D camera and compressive video sensing. The redundant of whole light field, including angular images for light field, binocular images for 3-D camera and temporal information of video streams, are extracted and

  1. Low-dimensional ScO2 with tunable electronic and magnetic properties: first-principles studies.

    PubMed

    Zhang, Hui; Tong, Chuan-Jia; Wu, Jian; Yin, Wen-Jin; Zhang, Yan-Ning

    2016-01-13

    Transition metal dichalcogenides (TMDs) have attracted extensive attention due to their appealing properties for device applications. In this work, we explored the structure stability, electronic structure and magnetism of low-dimensional scandium dioxides, ScO2, by using the first-principles calculations. The results demonstrate that bulk ScO2, monolayers and nanoribbons (NRs) are thermodynamically stable, implying a high possibility of fabricating ScO2 nanocrystals in experiments. Despite the metallic characteristics of bulk ScO2, low-dimensional ScO2 possesses various electronic behaviors that can be further modulated by crystal structure and dimensionality. The results also show that the ground states of ScO2 monolayers and NRs are ferromagnetic (FM) with about 1 μ B per ScO2 formula. Our studies expand a new realm in low-dimensional TMDs, with tunable electronic and magnetic properties. PMID:26571138

  2. Low-dimensional ScO2 with tunable electronic and magnetic properties: first-principles studies

    NASA Astrophysics Data System (ADS)

    Zhang, Hui; Tong, Chuan-Jia; Wu, Jian; Yin, Wen-Jin; Zhang, Yan-Ning

    2016-01-01

    Transition metal dichalcogenides (TMDs) have attracted extensive attention due to their appealing properties for device applications. In this work, we explored the structure stability, electronic structure and magnetism of low-dimensional scandium dioxides, ScO2, by using the first-principles calculations. The results demonstrate that bulk ScO2, monolayers and nanoribbons (NRs) are thermodynamically stable, implying a high possibility of fabricating ScO2 nanocrystals in experiments. Despite the metallic characteristics of bulk ScO2, low-dimensional ScO2 possesses various electronic behaviors that can be further modulated by crystal structure and dimensionality. The results also show that the ground states of ScO2 monolayers and NRs are ferromagnetic (FM) with about 1 μ B per ScO2 formula. Our studies expand a new realm in low-dimensional TMDs, with tunable electronic and magnetic properties.

  3. Compound semiconductor alloys: From atomic-scale structure to bandgap bowing

    SciTech Connect

    Schnohr, C. S.

    2015-09-15

    Compound semiconductor alloys such as In{sub x}Ga{sub 1−x}As, GaAs{sub x}P{sub 1−x}, or CuIn{sub x}Ga{sub 1−x}Se{sub 2} are increasingly employed in numerous electronic, optoelectronic, and photonic devices due to the possibility of tuning their properties over a wide parameter range simply by adjusting the alloy composition. Interestingly, the material properties are also determined by the atomic-scale structure of the alloys on the subnanometer scale. These local atomic arrangements exhibit a striking deviation from the average crystallographic structure featuring different element-specific bond lengths, pronounced bond angle relaxation and severe atomic displacements. The latter, in particular, have a strong influence on the bandgap energy and give rise to a significant contribution to the experimentally observed bandgap bowing. This article therefore reviews experimental and theoretical studies of the atomic-scale structure of III-V and II-VI zincblende alloys and I-III-VI{sub 2} chalcopyrite alloys and explains the characteristic findings in terms of bond length and bond angle relaxation. Different approaches to describe and predict the bandgap bowing are presented and the correlation with local structural parameters is discussed in detail. The article further highlights both similarities and differences between the cubic zincblende alloys and the more complex chalcopyrite alloys and demonstrates that similar effects can also be expected for other tetrahedrally coordinated semiconductors of the adamantine structural family.

  4. The control of stoichiometry in Epitaxial semiconductor structures. Interfacial Chemistry: Property relations. A workshop review

    NASA Technical Reports Server (NTRS)

    Bachmann, Klaus J.

    1995-01-01

    A workshop on the control of stoichiometry in epitaxial semiconductor structures was held on August 21-26, 1995 in the hotel Stutenhaus at Vesser in Germany. The secluded location of the workshop in the forest of Thuringia and its informal style stimulated extensive private discussions among the participants and promoted new contacts between young scientists from Eastern and Western Europe and the USA. Topics addressed by the presentations were interactions of precursors to heteroepitaxy and doping with the substrate surface, the control of interfacial properties under the conditions of heteroepitaxy for selected materials systems, methods of characterization of interfaces and native point defects in semiconductor heterostructures and an in depth evaluation of the present status of the control and characterization of the point defect chemistry for one specific semiconductor (ZnGeP2), including studies of both heterostructures and bulk single crystals. The selected examples of presentations and comments given here represent individual choices - made by the author to highlight major points of the discussions.

  5. Application of Low Dimensional Manifolds in NO(x) Prediction

    NASA Technical Reports Server (NTRS)

    Norris, A. T.

    1997-01-01

    A new post-processing technique has been developed, based on the Intrinsic Low Dimensional Manifold (ILDM) method of Maas and Pope. The ILDM method is a dynamical systems approach to the simplification of large chemical kinetic mechanisms. By identifying low-dimensional attracting manifolds, the method allows complex full mechanisms to be parameterized by just a few variables: In effect, generating reduced chemical mechanisms by an automatic procedure. These resulting mechanisms however, still retain all the species used in the full mechanism. The NO(x) post-processor takes an ILDM reduced mechanism and attempts to map this mechanism to the results of a CFD calculation. This mapping allows the NO(x) concentrations at each grid node to be obtained from the ILDM reduced mechanism, as well as other trace species of interest. Because a mapping procedure is used, this method is very fast, being able to process one million node calculations in just a few minutes.

  6. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating

    PubMed Central

    Li, Yao; Duerloo, Karel-Alexander N.; Wauson, Kerry; Reed, Evan J.

    2016-01-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for MoxW1−xTe2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices. PMID:26868916

  7. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating.

    PubMed

    Li, Yao; Duerloo, Karel-Alexander N; Wauson, Kerry; Reed, Evan J

    2016-01-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for Mo(x)W(1-x)Te2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices. PMID:26868916

  8. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating

    NASA Astrophysics Data System (ADS)

    Li, Yao; Duerloo, Karel-Alexander N.; Wauson, Kerry; Reed, Evan J.

    2016-02-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for MoxW1-xTe2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices.

  9. Structural semiconductor-to-semimetal phase transition in two-dimensional materials induced by electrostatic gating.

    PubMed

    Li, Yao; Duerloo, Karel-Alexander N; Wauson, Kerry; Reed, Evan J

    2016-01-01

    Dynamic control of conductivity and optical properties via atomic structure changes is of technological importance in information storage. Energy consumption considerations provide a driving force towards employing thin materials in devices. Monolayer transition metal dichalcogenides are nearly atomically thin materials that can exist in multiple crystal structures, each with distinct electrical properties. By developing new density functional-based methods, we discover that electrostatic gating device configurations have the potential to drive structural semiconductor-to-semimetal phase transitions in some monolayer transition metal dichalcogenides. Here we show that the semiconductor-to-semimetal phase transition in monolayer MoTe2 can be driven by a gate voltage of several volts with appropriate choice of dielectric. We find that the transition gate voltage can be reduced arbitrarily by alloying, for example, for Mo(x)W(1-x)Te2 monolayers. Our findings identify a new physical mechanism, not existing in bulk materials, to dynamically control structural phase transitions in two-dimensional materials, enabling potential applications in phase-change electronic devices.

  10. Empirical low-dimensional manifolds in composition space

    NASA Astrophysics Data System (ADS)

    Yang, Yue; Pope, Stephen B.; Chen, Jacqueline H.

    2012-11-01

    To reduce the computational cost of turbulent combustion simulations with a detailed chemical mechanism, it is useful to find a low-dimensional manifold in composition space that can approximate the full system dynamics. Most previous low-dimensional manifolds in turbulent combustion are based on the governing conservation equations or thermochemistry and their application involves certain assumptions. On the other hand, empirical low-dimensional manifolds (ELDMs) are constructed based on samples of the compositions observed in experiments or in direct numerical simulation (DNS). Plane and curved ELDMs can be obtained using principal component analysis (PCA) and multivariate adaptive spline regression (MARS), respectively. Both PCA and MARS are applied to the DNS datasets of a non-premixed CO/H2 temporally evolving jet flame (Hawkes et al., 2007) and an ethylene lifted jet flame (Yoo et al., 2011). We observe that it requires very high dimensions to represent the species mass fractions accurately by a plane ELDM, while better accuracy can be achieved by curved ELDMs with lower dimensions. In addition, the effect of differential diffusion on ELDMs is examined in large-eddy simulations with PDF modeling. This work is supported in part by the Combustion Energy Frontier Research Center funded by the DOE.

  11. Impedance analysis of Al2O3/H-terminated diamond metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Liao, Meiyong; Liu, Jiangwei; Sang, Liwen; Coathup, David; Li, Jiangling; Imura, Masataka; Koide, Yasuo; Ye, Haitao

    2015-02-01

    Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al2O3 is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed.

  12. Comparison of the coherence properties of superradiance and laser emission in semiconductor structures

    SciTech Connect

    Vasil'ev, Petr P; Penty, R V; White, I H

    2012-12-31

    The coherence properties of a transient electron - hole state developing during superradiance emission in semiconductor laser structures have been studied experimentally using a Michelson interferometer and Young's classic double-slit configuration. The results demonstrate that, in the lasers studied, the first-order correlation function, which quantifies spatial coherence, approaches unity for superradiant emission and is 0.2 - 0.5 for laser emission. The supercoherence is due to long-range ordering upon the superradiant phase transition. (special issue devoted to the 90th anniversary of n.g. basov)

  13. Defect-driven interfacial electronic structures at an organic/metal-oxide semiconductor heterojunction.

    PubMed

    Winget, Paul; Schirra, Laura K; Cornil, David; Li, Hong; Coropceanu, Veaceslav; Ndione, Paul F; Sigdel, Ajaya K; Ginley, David S; Berry, Joseph J; Shim, Jaewon; Kim, Hyungchui; Kippelen, Bernard; Brédas, Jean-Luc; Monti, Oliver L A

    2014-07-16

    The electronic structure of the hybrid interface between ZnO and the prototypical organic semiconductor PTCDI is investigated via a combination of ultraviolet and X-ray photoelectron spectroscopy (UPS/XPS) and density functional theory (DFT) calculations. The interfacial electronic interactions lead to a large interface dipole due to substantial charge transfer from ZnO to 3,4,9,10-perylenetetracarboxylicdiimide (PTCDI), which can be properly described only when accounting for surface defects that confer ZnO its n-type properties. PMID:24830796

  14. Fabrication of Smooth Patterned Structures of Refractory Metals, Semiconductors, and Oxides via Template Stripping

    PubMed Central

    2013-01-01

    The template-stripping method can yield smooth patterned films without surface contamination. However, the process is typically limited to coinage metals such as silver and gold because other materials cannot be readily stripped from silicon templates due to strong adhesion. Herein, we report a more general template-stripping method that is applicable to a larger variety of materials, including refractory metals, semiconductors, and oxides. To address the adhesion issue, we introduce a thin gold layer between the template and the deposited materials. After peeling off the combined film from the template, the gold layer can be selectively removed via wet etching to reveal a smooth patterned structure of the desired material. Further, we demonstrate template-stripped multilayer structures that have potential applications for photovoltaics and solar absorbers. An entire patterned device, which can include a transparent conductor, semiconductor absorber, and back contact, can be fabricated. Since our approach can also produce many copies of the patterned structure with high fidelity by reusing the template, a low-cost and high-throughput process in micro- and nanofabrication is provided that is useful for electronics, plasmonics, and nanophotonics. PMID:24001174

  15. Superheating Suppresses Structural Disorder in Layered BiI3 Semiconductors Grown by the Bridgman Method

    SciTech Connect

    Johns, Paul M.; Sulekar, Soumitra; Yeo, Shinyoung; Baciak, James E.; Bliss, Mary; Nino, Juan C.

    2016-01-01

    The susceptibility of layered structures to stacking faults is a problem in some of the more attractive semiconductor materials for ambient-temperature radiation detectors. In the work presented here, Bridgman-grown BiI3 layered single crystals are investigated to understand and eliminate this structural disorder, which reduces radiation detector performance. The use of superheating gradients has been shown to improve crystal quality in non-layered semiconductor crystals; thus the technique was here explored to improve the growth of BiI3. When investigating the homogeneity of non-superheated crystals, highly geometric void defects were found to populate the bulk of the crystals. Applying a superheating gradient to the melt prior to crystal growth improved structural quality and decreased defect density from the order of 4600 voids per cm3 to 300 voids per cm3. Corresponding moderate improvements to electronic properties also resulted from the superheat gradient method of crystal growth. Comparative measurements through infrared microscopy, etch-pit density, x-ray rocking curves, and sheet resistivity readings show that superheat gradients in BiI3 growth led to higher quality crystals.

  16. Fabrication of smooth patterned structures of refractory metals, semiconductors, and oxides via template stripping.

    PubMed

    Park, Jong Hyuk; Nagpal, Prashant; McPeak, Kevin M; Lindquist, Nathan C; Oh, Sang-Hyun; Norris, David J

    2013-10-01

    The template-stripping method can yield smooth patterned films without surface contamination. However, the process is typically limited to coinage metals such as silver and gold because other materials cannot be readily stripped from silicon templates due to strong adhesion. Herein, we report a more general template-stripping method that is applicable to a larger variety of materials, including refractory metals, semiconductors, and oxides. To address the adhesion issue, we introduce a thin gold layer between the template and the deposited materials. After peeling off the combined film from the template, the gold layer can be selectively removed via wet etching to reveal a smooth patterned structure of the desired material. Further, we demonstrate template-stripped multilayer structures that have potential applications for photovoltaics and solar absorbers. An entire patterned device, which can include a transparent conductor, semiconductor absorber, and back contact, can be fabricated. Since our approach can also produce many copies of the patterned structure with high fidelity by reusing the template, a low-cost and high-throughput process in micro- and nanofabrication is provided that is useful for electronics, plasmonics, and nanophotonics.

  17. Electromagnetic waves reflection, transmission and absorption by graphene-magnetic semiconductor-graphene sandwich-structure in magnetic field: Faraday geometry

    NASA Astrophysics Data System (ADS)

    Kuzmin, Dmitry A.; Bychkov, Igor V.; Shavrov, Vladimir G.

    2014-11-01

    Electrodynamic properties of the graphene-magnetic semiconductor-graphene sandwich-structure have been investigated theoretically with taking into account the dissipation processes. Influence of graphene layers on electromagnetic waves propagation in graphene-semi-infinte magnetic semiconductor and graphene-magnetic semiconductor-graphene sandwich-structure has been analyzed. Frequency and field dependences of the reflectance, transmittance and absorbtance of electromagnetic waves by such structure have been calculated. The size effects associated with the thickness of the structure have been analyzed. The possibility of efficient control of electrodynamic properties of graphene-magnetic semiconductor-graphene sandwich-structure by an external magnetic field has been shown.

  18. Materials Science and Technology, Volume 4, Electronic Structure and Properties of Semiconductors

    NASA Astrophysics Data System (ADS)

    Schröter, Wolfgang

    1996-12-01

    This volume spans the field of semiconductor physics, with particular emphasis on concepts relevant to semiconductor technology. From the Contents: Lannoo: Band Theory Applied to Semiconductors. Ulbrich: Optical Properties and Charge Transport. Watkins: Intrinsic Point Defects in Semiconductors. Feichtinger: Deep Centers in Semiconductors. Gösele/Tan: Equilibria, Nonequilibria, Diffusion, and Precipitation. Alexander/Teichler: Dislocations. Thibault/Rouvière/Bourret: Grain Boundaries in Semiconductors. Ourmazd/Hull/Tung: Interfaces. Chang: The Hall Effect in Quantum Wires. Street/Winer: Material Properties of Hydrogenated Amorphous Silicon. Schröter/Seibt/Gilles: High-Temperature Properties of 3d Transition Elements in Silicon.

  19. Modeling and simulation of nano-scale electronics based on novel low dimensional materials

    NASA Astrophysics Data System (ADS)

    Lu, Yang

    Semiconductor technology has entered the nano-scale era, in which the featuring size of transistors is well below 100nm. Traditional Si-device has maintained the high speed development for about half a century, characterized by Moore's law. Nowadays, Si-based devices are still the main stream technology, semiconductor industry have invested a lot of efforts to maintain its vitality. However, its physical limits are inevitable. New device concepts have been proposed to upgrade or complement the current Si technology, in order to meet the new challenges in nano-scale electronics. Carbon based materials, from carbon nanotube to graphene, have added new possibilities to this drama. In this paper, graphene based electronics are explored numerically. It also added several chapters on other low dimensional materials such as topological insulators and TMDCs, due to the similarities of their Hamiltonian to graphene system ,and their present popularity in physics community. For all these devices, Nonequilibrium green's function (NEGF) method severs as the framework to capture the quantum transport feature in nano-scale. (Abstract shortened by UMI.).

  20. Valence band structure of binary chalcogenide vitreous semiconductors by high-resolution XPS

    SciTech Connect

    Kozyukhin, S.; Golovchak, R.; Kovalskiy, A.; Shpotyuk, O.; Jain, H.

    2011-04-15

    High-resolution X-ray photoelectron spectroscopy (XPS) is used to study regularities in the formation of valence band electronic structure in binary As{sub x}Se{sub 100-x}, As{sub x}S{sub 100-x}, Ge{sub x}Se{sub 100-x} and Ge{sub x}S{sub 100-x} chalcogenide vitreous semiconductors. It is shown that the highest occupied energetic states in the valence band of these materials are formed by lone pair electrons of chalcogen atoms, which play dominant role in the formation of valence band electronic structure of chalcogen-rich glasses. A well-expressed contribution from chalcogen bonding p electrons and more deep s orbitals are also recorded in the experimental valence band XPS spectra. Compositional dependences of the observed bands are qualitatively analyzed from structural and compositional points of view.

  1. Direct probing of band-structure Berry phase in diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Granada, M.; Lucot, D.; Giraud, R.; Lemaître, A.; Ulysse, C.; Waintal, X.; Faini, G.

    2015-06-01

    We report on experimental evidence of the Berry phase accumulated by the charge-carrier wave function in single-domain nanowires made from a (Ga, Mn)(As, P) diluted ferromagnetic semiconductor layer. Its signature on the mesoscopic transport measurements is revealed as unusual patterns in the magnetoconductance that are clearly distinguished from the universal conductance fluctuations. We show that these patterns appear in a magnetic field region where the magnetization rotates coherently and are related to a change in the band-structure Berry phase as the magnetization direction changes. They should thus be considered a band-structure Berry phase fingerprint of the effective magnetic monopoles in the momentum space. We argue that this is an efficient method to vary the band structure in a controlled way and to probe it directly. Hence, (Ga, Mn)As appears to be a very interesting test bench for new concepts based on this geometrical phase.

  2. Investigation on Photoelectric Behavior of Metal-Insulator-Semiconductor Structure Based on Titania Nanotubes Arrays

    NASA Astrophysics Data System (ADS)

    Wang, Lili; Panaitescu, Eugen; Richter, Christiaan; Menon, Latika

    2014-03-01

    Titanium dioxide (TiO2) has attracted great interest as an inexpensive, earth-abundant and environment-friendly anode material for next generation photovoltaic devices and the metal-insulator-semiconductor (MIS) concept is one of the most promising approaches for improving solar cell cost effectiveness (in /W). We investigated hybrid MIS structures of semiconducting ordered titania nanotube arrays integrated with insulating iron oxide or copper oxide layers and metallic copper. The morphological and structural properties of the samples were analyzed by scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy with elemental mapping, and X-ray diffraction. The nanotubular morphology represents a step change from the current thin film approach, providing significantly larger surface area while facilitating the charge separation and electron transport. Photoelectric behavior of the new structures was estimated by transient response, quantum efficiency and spectral response, and a solar simulator was used for recording the photovoltaic response.

  3. Fabrication of Nanovoid-Imbedded Bismuth Telluride with Low Dimensional System

    NASA Technical Reports Server (NTRS)

    Chu, Sang-Hyon (Inventor); Choi, Sang H. (Inventor); Kim, Jae-Woo (Inventor); Park, Yeonjoon (Inventor); Elliott, James R. (Inventor); King, Glen C. (Inventor); Stoakley, Diane M. (Inventor)

    2013-01-01

    A new fabrication method for nanovoids-imbedded bismuth telluride (Bi--Te) material with low dimensional (quantum-dots, quantum-wires, or quantum-wells) structure was conceived during the development of advanced thermoelectric (TE) materials. Bismuth telluride is currently the best-known candidate material for solid-state TE cooling devices because it possesses the highest TE figure of merit at room temperature. The innovative process described here allows nanometer-scale voids to be incorporated in Bi--Te material. The final nanovoid structure such as void size, size distribution, void location, etc. can be also controlled under various process conditions.

  4. Synthesis, characterization, and properties of low-dimensional nanostructured materials

    NASA Astrophysics Data System (ADS)

    Hu, Xianluo

    2007-05-01

    Nanometer scale structures represent an exciting and rapidly expanding area of research. Studies on new physical/chemical properties and applications of nanomaterials and nanostructures are possible only when nanostructured materials are made available with desired size, morphology, crystal and microstructure, and composition. Thus, controlled synthesis of nanomaterials is the essential aspect of nanotechnology. This thesis describes the development of simple and versatile solution-based approaches to synthesize low-dimensional nanostructures. The first major goal of this research is to design and fabricate morphology-controlled alpha-Fe 2O3 nanoarchitectures in aqueous solution through a programmed microwave-assisted hydrothermal route, taking advantage of microwave irradiation and hydrothermal effects. Free-standing alpha-Fe2O3 nanorings are prepared by hydrolysis of FeCl3 in the presence of phosphate ions. The as-formed architecture of alpha-Fe2O 3 nanorings is an exciting new member in the family of iron oxide nanostructures. Our preliminary results demonstrate that sensors made of the alpha-Fe 2O3 nanorings exhibit high sensitivity not only for bio-sensing of hydrogen peroxide in a physiological solution but also for gas-sensing of alcohol vapor at room temperature. Moreover, monodisperse alpha-Fe 2O3 nanocrystals with continuous aspect-ratio tuning and fine shape control are achieved by controlling the experimental conditions. The as-formed alpha-Fe2O3 exhibits shape-dependent infrared optical properties. The growth process of colloidal alpha-Fe 2O3 crystals in the presence of phosphate ions is discussed. In addition, through an efficient microwave-assisted hydrothermal process, self-assembled hierarchical alpha-Fe2O3 nanoarchitectures are synthesized on a large scale. The second major goal of this research is to develop convenient microwave-hydrothermal approaches for the fabrication of carbon-based nanocomposites: (1) A one-pot solution-phase route, namely

  5. The preparation of organic infrared semiconductor phthalocyanine gadolinium (III) and its optical and structural characterizations

    NASA Astrophysics Data System (ADS)

    Tang, Li-bin; Ji, Rong-bin; Song, Li-yuan; Chen, Xue-mei; Ma, Yu; Wang, Yi-feng; Qian, Ming; Song, Lei; Su, Hai-ying; Zhuang, Ji-sheng; Yang, Rui-yu

    2009-07-01

    In order to increase the species of organic infrared semiconductor, we synthesized organic infrared semiconductor phthalocyanine gadolinium by using o-phthalodinitrile and GdCl3 as reactants, ammonium molybdate as catalyzer. Under light and dark field modes of microscope, the translucency emerald-like powder of phthalocyanine gadolinium has been observed, the size of the small grain for the sample is around 5μm in diameter, the size of larger grain may reach to several tens of microns. The main vibrational peaks in FT-IR spectrum and Raman spectrum have been assigned. Elementary analysis shows that the experimental data of phthalocyanine gadolinium in the main agree with those of calculated data. The UV-Vis absorption spectrum of the sample indicates the sandwich-like structure of phthalocyanine gadolinium. The organic infrared semiconductor phthalocyanine gadolinium thin film on quartz substrate has been prepared with our synthesized powdered sample by using solution method. The characterizations of XRD and UV-Vis-NIR absorption have been carried out for the phthalocyanine gadolinium thin film on quartz substrate, XRD shows that phthalocyanine gadolinium diffractions occur at 2θ=6.851,8.290 and 8.820 degrees, the corresponding plane spacings (d) for the diffraction peaks are 12.8921, 10.6570, and 10.0176Å.The diffraction peaks locate at low diffraction angle, suggesting that the molecular size of the phthalocyanine gadolinium is big that causes the large spacing of crystal planes. The UV-Vis-NIR absorption of phthalocyanine gadolinium thin film on quartz substrate implies that within near infrared band there is a absorption in the 1.3~2.0μm wavelength range peaked at ca. 1.75μm, indicating the important potential application value of phthalocyanine gadolinium in the field of organic infrared optoelectronics.

  6. Photoluminescence polarization anisotropy for studying long-range structural ordering within semiconductor multi-atomic alloys and organic crystals

    SciTech Connect

    Prutskij, T.; Percino, J.; Orlova, T.; Vavilova, L.

    2013-12-04

    Long-range structural ordering within multi-component semiconductor alloys and organic crystals leads to significant optical anisotropy and, in particular, to anisotropy of the photoluminescence (PL) emission. The PL emission of ternary and quaternary semiconductor alloys is polarized if there is some amount of the atomic ordering within the crystal structure. We analyze the polarization of the PL emission from the quaternary GaInAsP semiconductor alloy grown by Liquid Phase Epitaxy (LPE) and conclude that it could be caused by low degree atomic ordering within the crystal structure together with the thermal biaxial strain due to difference between the thermal expansion coefficients of the layer and the substrate. We also study the state of polarization of the PL from organic crystals in order to identify different features of the crystal PL spectrum.

  7. Structure-fluctuation-induced abnormal thermoelectric properties in semiconductor copper selenide

    SciTech Connect

    Liu, Huili; Shi, Xun; Kirkham, Melanie J; Wang, Hsin; Li, Qiang; Uher, Ctirad; Zhang, Wenqing; Chen, Lidong

    2013-01-01

    Thermoelectric effects and related technologies have attracted a great interest due to the world-wide energy harvesting. Thermoelectricity has usually been considered in the context of stable material phases. Here we report that the fluctuation of structures during the second-order phase transition in Cu2Se semiconductor breaks the conventional trends of thermoelectric transports in normal phases, leading to a critically phase-transition-enhanced thermoelectric figure of merit zT above unity at 400K, a three times larger value than for the normal phases. Dynamic structural transformations introduce intensive fluctuations and extreme complexity, which enhance the carrier entropy and thus the thermopower, and strongly scatter carriers and phonons as well to make their transports behave critically.

  8. One-step photoembossing for submicrometer surface relief structures in liquid crystal semiconductors.

    PubMed

    Liedtke, Alicia; Lei, Chunhong; O'Neill, Mary; Dyer, Peter E; Kitney, Stuart P; Kelly, Stephen M

    2010-06-22

    We report a new single-step method to directly imprint nanometer-scale structures on photoreactive organic semiconductors. A surface relief grating is spontaneously formed when a light-emitting, liquid crystalline, and semiconducting thin film is irradiated by patterned light generated using a phase mask. Grating formation requires no postannealing nor wet etching so there is potential for high-throughput fabrication. The structured film is cross-linked for robustness. Gratings deeper than the original film thickness are made with periods as small as 265 nm. Grating formation is attributed to mass transfer, enhanced by self-assembly, from dark to illuminated regions. A photovoltaic device incorporating the grating is discussed.

  9. Synchrotron Studies of Narrow Band and Low-Dimensional Materials. Final Report for July 1, 1990---December 31, 2002

    SciTech Connect

    Allen, J. W.

    2003-05-13

    This report summarizes a 12-year program of various kinds of synchrotron spectroscopies directed at the electronic structures of narrow band and low-dimensional materials that display correlated electron behaviors such as metal-insulator transitions, mixed valence, superconductivity, Kondo moment quenching, heavy Fermions, and non-Fermi liquid properties.

  10. Optical properties and electronic band structure of AgGaTe2 chalcopyrite semiconductor.

    PubMed

    Arai, Shinya; Ozaki, Shunji; Adachi, Sadao

    2010-02-10

    The optical properties of AgGaTe(2) chalcopyrite semiconductor are studied by optical absorption, spectroscopic ellipsometry (SE), and thermoreflectance (TR) spectroscopy. Optical absorption spectra suggest that AgGaTe(2) is a direct-gap semiconductor having a bandgap of approximately 1.2 eV at T=300 K. The pseudodielectric-function spectra of AgGaTe(2) are determined by SE in the range between E=1.2 and 5.2 eV for both states of polarization. These spectra reveal distinct structures at energies of the critical points in the Brillouin zone. The TR spectra are also measured in the E=1.0-5.3 eV ranges at T=20 K-300 K. The spin-orbit and crystal-field splitting parameters of AgGaTe(2) are determined to be Delta(so)=0.70 eV and Delta(cr)=-0.23 eV, respectively.

  11. Electronic Structure of Hydrogen Donors in Semiconductors and Insulators Probed by Muon Spin Rotation

    NASA Astrophysics Data System (ADS)

    Shimomura, Koichiro; Ito, Takashi U.

    2016-09-01

    Hydrogen in semiconductors and insulators plays a crucial role in their electric conductivity. Substantial experimental and theoretical efforts have been made to establish this hypothesis in the last decade, and the muon spin rotation technique has played a pioneering role. Positive muons implanted into such low-carrier systems often form a muonium (an analogue of hydrogen, the bound state of a positive muon and an electron). Although its dynamical aspect may be different from the heavier hydrogen, the electronic structure of the muonium is expected to be identical to that of hydrogen after a small correction of the reduced mass (˜0.4%). Since the discovery of a shallow muonium in CdS, its properties have been intensively studied in many semiconductors and insulators, and then it was interpreted as a possible origin of n-type conductivity under the context of a classical shallow donor model. In this article, we will describe the principle of muonium experiments and survey recent achievements in this field.

  12. Thickness dependent electronic structure and morphology of rubrene thin films on metal, semiconductor, and dielectric substrates

    NASA Astrophysics Data System (ADS)

    Sinha, Sumona; Mukherjee, M.

    2013-08-01

    The evolution of the electronic structure and morphology of rubrene thin films on noble-metal, semiconductor and dielectric substrates have been investigated as a function of thickness of deposited films by using photoelectron spectroscopy and atomic force microscopy. The clean polycrystalline Au and Ag were used as noble-metals, whereas, H passivated and SiO2 coated Si (100) were used as semiconductors and dielectric substrates. Discussion and comparison on interface dipole, energy level alignment, and surface morphology for the four cases are presented. The formation of dipole at metallic interfaces is found to occur due to push back effect. S parameter obtained from the variation of barrier height with the change of work function of the contacting metal indicates moderately weak interaction between rubrene and the metal substrates. The thickness dependent energy level alignment of the physisorbed rubrene films on different substrates is explained by a dielectric model in terms of electrostatic screening of photo-holes or photoemission final state relaxation energy. Films on all the substrates are found to grow following Stranski-Krastnov type growth mode and are more ordered at higher coverage.

  13. Response characteristics of a low-dimensional model neuron.

    PubMed

    Cartling, B

    1996-11-15

    It is shown that a low-dimensional model neuron with a response time constant smaller than the membrane time constant closely reproduces the activity and excitability behavior of a detailed conductance-based model of Hodgkin-Huxley type. The fast response of the activity variable also makes it possible to reduce the model to a one-dimensional model, in particular for typical conditions. As an example, the reduction to a single-variable model from a multivariable conductance-based model of a neocortical pyramidal cell with somatic input is demonstrated. The conditions for avoiding a spurious damped oscillatory response to a constant input are derived, and it is shown that a limit-cycle response cannot occur. The capability of the low-dimensional model to approximate higher-dimensional models accurately makes it useful for describing complex dynamics of nets of interconnected neurons. The simplicity of the model facilitates analytic studies, elucidations of neurocomputational mechanisms, and applications to large-scale systems.

  14. Behavioral diversity in microbes and low-dimensional phenotypic spaces.

    PubMed

    Jordan, David; Kuehn, Seppe; Katifori, Eleni; Leibler, Stanislas

    2013-08-20

    Systematic studies of phenotypic diversity--required for understanding evolution--lag behind investigations of genetic diversity. Here we develop a quantitative approach to studying behavioral diversity, which we apply to swimming of the ciliate Tetrahymena. We measure the full-lifetime behavior of hundreds of individual organisms at high temporal resolution, over several generations and in diverse nutrient conditions. To characterize population diversity and temporal variability we introduce a unique statistical framework grounded in the notion of a phenotypic space of behaviors. We show that this space is effectively low dimensional with dimensions that correlate with a two-state "roaming and dwelling" model of swimming behavior. Temporal variability over the lifetime of an individual is correlated with the fraction of time spent roaming whereas diversity between individuals is correlated with the speed of roaming. Quantifying the dynamics of behavioral variation shows that behavior over the lifetime of an individual is strongly nonstationary. Analysis of behavioral dynamics between generations reveals complex patterns of behavioral heritability that point to the importance of considering correlations beyond mothers and daughters. Our description of a low-dimensional behavioral space should enable the systematic study of the evolutionary and ecological bases of phenotypic constraints. Future experimental and theoretical studies of behavioral diversity will have to account for the possibility of nonstationary and environmentally dependent behavioral dynamics that we observe.

  15. Test for low-dimensional determinism in electroencephalograms

    NASA Astrophysics Data System (ADS)

    Jeong, Jaeseung; Kim, Moo Seong; Kim, Soo Yong

    1999-07-01

    We tested low-dimensional determinism in an electroencephalogram (EEG), based on the fact that smoothness (continuity) on an embedded phase space is enough to imply determinism within time series. A modified version of the method developed by Salvino and Cawley [Phys. Rev. Lett. 73, 1091 (1994)] was used. In our method, we chose a box randomly and then estimated the mean directional element in the box containing the d+1 data points, where d is the embedding dimension. The global average for the mean local directional elements over the boxes, W, is a measure for smoothness. The nonlinear noise reduction method developed by Sauer [Physica D 58, 193 (1992)] is then applied to the EEG. We also compared the results for the EEG with those for its surrogate data. We found that the W values for the noise-reduced EEG had stable values around 0.35, which means that the EEG is not a low-dimensional deterministic signal. However, this method may not be applicable to the time series generated from high-dimensional deterministic systems. We cannot exclude the possibility that the determinism in the EEG may be too high-dimensional to be detected with current methods.

  16. Effect of the accumulation of excess Ni atoms in the crystal structure of the intermetallic semiconductor n-ZrNiSn

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Stadnyk, Yu. V.; Hlil, E. K.; Krajovskii, V. Ya.; Horyn, A. M.

    2013-07-15

    The crystal structure, electron density distribution, and energy, kinetic, and magnetic properties of the n-ZrNiSn intermetallic semiconductor heavily doped with a Ni impurity are investigated. The effect of the accumulation of an excess number of Ni{sub 1+x} atoms in tetrahedral interstices of the crystal structure of the semiconductor is found and the donor nature of such structural defects that change the properties of the semiconductor is established. The results obtained are discussed within the Shklovskii-Efros model of a heavily doped and strongly compensated semiconductor.

  17. Magneto-Optical Characterization of Compound Semiconductors

    NASA Astrophysics Data System (ADS)

    Agool, Ibrahim R.

    Available from UMI in association with The British Library. The subject matter of this thesis lies within the area of the physics of semiconductor crystals and more particularly is concerned with the characterization of compound semiconductors using the magneto-optical excitation studies for their importance in the field of device technology. In the first part of this thesis a full study is reported for bulk indium phosphide which is important as substrate material for device fabrication. Measurements have shown that the MCD-ODMR technique is a powerful tool in the investigation of ground state transitions of bulk substrate semiconductors. It has also been shown that the optical technique can be used to explore native defects and transition metal ions in semiconductors. It is also shown in the thesis that an important method used in the characterization of semiconductor superlattices is the use of CO_2 optically pumped far-infrared lasers for studies in quantum wells. This method described as optically detected cyclotron resonance (ODCR), where FIR induced changes in luminescence intensity at resonance has allowed the investigation of non-parabolicity and subband structure for both conduction and valence bands in GaAs. ODCR results at FIR frequencies are compared with measurements performed at microwave frequencies. We have demonstrated that the sensitivity and resolution of FIR-ODCR allows the investigation of multilayer (low dimensional) GaAs/GaAlAs systems with different well widths, where one can monitor the emission from each well independently and examine the effective mass versus well thickness. For the first time we have observed the exchange interaction between donor and acceptor pairs. A Hall Effect system is described for the electrical characterization of doped ZnSe grown at Heriot-Watt University using molecular beam epitaxy (MBE) for new optoelectronic devices such as blue light emitting diodes and blue lasers.

  18. The defect mode in a low-dimensional waveguide microwave photonic crystal

    NASA Astrophysics Data System (ADS)

    Usanov, D. A.; Skripal', A. V.; Posadskii, V. N.; Tyazhlov, V. S.; Baykin, A. V.

    2016-05-01

    It is shown that the violation of periodicity in a low-dimensional waveguide microwave photonic crystal, in which the periodic structure is formed by dielectric layers and adjacent metal plates partly overlapping the waveguide cross section and forming capacitive gaps between the plate edge and wide wall of the waveguide, leads to the appearance of a defect (impurity) mode. It is established that the defect mode position on the frequency scale significantly depends on both the thickness of "disturbed" dielectric layer and the capacitive gap width of diaphragms.

  19. Fabrication of microdevices with integrated nanowires for investigating low-dimensional phonon transport.

    PubMed

    Hippalgaonkar, Kedar; Huang, Baoling; Chen, Renkun; Sawyer, Karma; Ercius, Peter; Majumdar, Arun

    2010-11-10

    Phonons in low-dimensional structures with feature sizes on the order of the phonon wavelength may be coherently scattered by the boundary. This may give rise to a new regime of heat conduction, which can impact thermal energy transport and conversion. Traditional methods used to investigate phonon transport in one-dimensional structures suffer from uncertainty due to contact resistance, defects, and limited control over sample dimensions. We have developed a new batch-fabrication technique for suspended microdevices with integrated silicon nanowires from silicon-on-insulator (SOI) wafers. The nanowires are defect-free and have extremely high aspect ratios (length/critical dimension >2000). The nanowire dimensions (length and critical dimension) can be precisely controlled during fabrication. With these novel devices, phonon transport in silicon nanowires is systematically investigated. The room temperature thermal conductivity of nanowires with critical width around 80 nm is about 20 W/(m K) and much lower than that in smooth VLS wires. This suggests that the surface morphology of the structures has a significant effect on the thermal conductivity, but this phenomenon is not currently understood. This fabrication technique can also be used for thermal transport investigation in a wide-range of low-dimensional structures. PMID:20939585

  20. Structural Design Principle of Small-Molecule Organic Semiconductors for Metal-Free, Visible-Light-Promoted Photocatalysis.

    PubMed

    Wang, Lei; Huang, Wei; Li, Run; Gehrig, Dominik; Blom, Paul W M; Landfester, Katharina; Zhang, Kai A I

    2016-08-01

    Herein, we report on the structural design principle of small-molecule organic semiconductors as metal-free, pure organic and visible light-active photocatalysts. Two series of electron-donor and acceptor-type organic semiconductor molecules were synthesized to meet crucial requirements, such as 1) absorption range in the visible region, 2) sufficient photoredox potential, and 3) long lifetime of photogenerated excitons. The photocatalytic activity was demonstrated in the intermolecular C-H functionalization of electron-rich heteroaromates with malonate derivatives. A mechanistic study of the light-induced electron transport between the organic photocatalyst, substrate, and the sacrificial agent are described. With their tunable absorption range and defined energy-band structure, the small-molecule organic semiconductors could offer a new class of metal-free and visible light-active photocatalysts for chemical reactions.

  1. Common-path depth-filtered digital holography for high resolution imaging of buried semiconductor structures

    NASA Astrophysics Data System (ADS)

    Finkeldey, Markus; Schellenberg, Falk; Gerhardt, Nils C.; Paar, Christof; Hofmann, Martin R.

    2016-03-01

    We investigate digital holographic microscopy (DHM) in reflection geometry for non-destructive 3D imaging of semiconductor devices. This technique provides high resolution information of the inner structure of a sample while maintaining its integrity. To illustrate the performance of the DHM, we use our setup to localize the precise spots for laser fault injection, in the security related field of side-channel attacks. While digital holographic microscopy techniques easily offer high resolution phase images of surface structures in reflection geometry, they are typically incapable to provide high quality phase images of buried structures due to the interference of reflected waves from different interfaces inside the structure. Our setup includes a sCMOS camera for image capture, arranged in a common-path interferometer to provide very high phase stability. As a proof of principle, we show sample images of the inner structure of a modern microcontroller. Finally, we compare our holographic method to classic optical beam induced current (OBIC) imaging to demonstrate its benefits.

  2. Structure and stability of semiconductor tip apexes for atomic force microscopy.

    PubMed

    Pou, P; Ghasemi, S A; Jelinek, P; Lenosky, T; Goedecker, S; Perez, R

    2009-07-01

    The short range force between the tip and the surface atoms, that is responsible for atomic-scale contrast in atomic force microscopy (AFM), is mainly controlled by the tip apex. Thus, the ability to image, manipulate and chemically identify single atoms in semiconductor surfaces is ultimately determined by the apex structure and its composition. Here we present a detailed and systematic study of the most common structures that can be expected at the apex of the Si tips used in experiments. We tackle the determination of the structure and stability of Si tips with three different approaches: (i) first principles simulations of small tip apexes; (ii) simulated annealing of a Si cluster; and (iii) a minima hopping study of large Si tips. We have probed the tip apexes by making atomic contacts between the tips and then compared force-distance curves with the experimental short range forces obtained with dynamic force spectroscopy. The main conclusion is that although there are multiple stable solutions for the atomically sharp tip apexes, they can be grouped into a few types with characteristic atomic structures and properties. We also show that the structure of the last atomic layers in a tip apex can be both crystalline and amorphous. We corroborate that the atomically sharp tips are thermodynamically stable and that the tip-surface interaction helps to produce the atomic protrusion needed to get atomic resolution.

  3. Electronic-Structure Theory of Organic Semiconductors: Charge-Transport Parameters and Metal/Organic Interfaces

    NASA Astrophysics Data System (ADS)

    Coropceanu, Veaceslav; Li, Hong; Winget, Paul; Zhu, Lingyun; Brédas, Jean-Luc

    2013-07-01

    We focus this review on the theoretical description, at the density functional theory level, of two key processes that are common to electronic devices based on organic semiconductors (such as organic light-emitting diodes, field-effect transistors, and solar cells), namely charge transport and charge injection from electrodes. By using representative examples of current interest, our main goal is to introduce some of the reliable theoretical methodologies that can best depict these processes. We first discuss the evaluation of the microscopic parameters that determine charge-carrier transport in organic molecular crystals, i.e., electronic couplings and electron-vibration couplings. We then examine the electronic structure at interfaces between an organic layer and a metal or conducting oxide electrode, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.

  4. InAs-based metal-oxide-semiconductor structure formation in low-energy Townsend discharge

    NASA Astrophysics Data System (ADS)

    Aksenov, M. S.; Kokhanovskii, A. Yu.; Polovodov, P. A.; Devyatova, S. F.; Golyashov, V. A.; Kozhukhov, A. S.; Prosvirin, I. P.; Khandarkhaeva, S. E.; Gutakovskii, A. K.; Valisheva, N. A.; Tereshchenko, O. E.

    2015-10-01

    We developed and applied a method of InAs passivation in the low-energy plasma of Townsend discharge. The controlled interface oxidation in the Ar:O2:CF4 gas mixture under visualization of gas discharge plasma allowed growing thin homogeneous films in the range of 5-15 nm thickness. Oxidation with the addition of CF4 in gas-discharge plasma led to the formation of In and As oxyfluorides with a wide insulating gap and isostructural interface with unpinned Fermi level behavior. The metal-oxide-semiconductor structure showed excellent capacitance-voltage characteristics: small frequency dispersion (<15 mV), density of interface states (Dit) in the gap below 5 × 1010 eV-1cm-2, and fixed charge (Qfix) below 5 × 1011 cm-2.

  5. The Effects of Inversion Asymmetry on Diluted Magnetic Semiconductors with the Zincblende Structure.

    NASA Astrophysics Data System (ADS)

    Nobel, Jan Alan

    The energy bands of a zincblende structure semiconductor in a magnetic field are modelled. The model is used to investigate the effects of the standard k cdot p parameters with exchange included on the energy bands of Hg_{rm 1-x}Mn _{rm x}Te and Hg _{rm 1-x}Mn _{rm x}Se in a magnetic field. The various parameters for the model are studied and the most influential parameters determined. The effect of these parameters on the periodicity, in inverse magnetic field, of the crossing of the Fermi energy with the magnetic energy bands is examined. The resulting periodicity is compared to experimental values determined from Shubnikov-de Hass (ShdH) data to verify that the presently accepted values of the standard parameters do reproduce this periodicity. The model also includes the parameters normally neglected in the standard k cdot p treatment, specifically one warping and four inversion asymmetry parameters (IAPs). The IAPs and warping are examined using 408 x 408 k cdot p matrices. This allows us to study the effects of the four IAPs individually as well as collectively on the ShdH oscillations in Hg_{0.975}Mn _{0.025}Se over the temperature range 1.40 K to 3.40 K. From this process, we are able to determine a new set of exchange parameters, alpha and beta, and for the first time, a set of inversion asymmetry parameters which demonstrate the temperature dependence of the ShdH oscillations in diluted magnetic semiconductors. We use this new set of parameters to determine the small k-space band structure, the Fermi surface, and the k_{rm z} effective mass ratio as a function of field for Hg_ {0.975}Mn_{0.025} Se. We further use these IAPs to calculate the semimetal to semiconductor transition, cyclotron mass ratios and effective Lande g-factors for Hg_{0.975 }Mn_{0.025}Se, Hg_{0.95}Mn_ {0.05}Te, and Hg_{0.94 }Mn_{0.06}Te. For Hg_{0.95}Mn_ {0.05}Te the calculated magnetic energy bands using IAPs are used to study the resulting ShdH frequencies at different Fermi energies

  6. Million Atom Pseudopotential Manybody Theory of Electronic Structure and Spectroscopy of Semiconductor Quantum Dots

    NASA Astrophysics Data System (ADS)

    Zunger, Alex

    2003-03-01

    Semiconductor Quantum Dots that are of sufficient structural quality (good crystallinity, surface passivation, size uniformity) to produce ultra sharp spectroscopic lines worthy of a detailed theoretical effort tend to be rather BIG, containing thousands to million atoms. Yet, in this size regime, the only theoretical methods available are effective-mass based, particle-in-a-box approaches, that neglect multi-band and inter-valley coupling, leading to significant qualitative errors.(A. Zunger,Phys. Stat. Sol. (a) 190), 467 (2002). While LDA-based methods are capable of solving the Single-Particle problem even for ˜1,000 atom dots, the all important many-body problem can be currently addressed only for considerably smaller dots. I will present here a computational alternative which addresses both the single-particle and the Manybody parts of the problem for 10^3 to 10^6 atom dots .The method is applicable both to ``free Standing" (e.g. colloidal) dots of CdSe, InP, InAs and Si, as well as to the strained, ``self-assembled" epitaxial dots of, e.g., InGaAs/GaAs. It is based on a ``Linear Combination of Bulk Bands" (LCBB) approach that expands the dot states in terms of plane wave based (pseudopotential) Bloch states throughout the Brillouin zone. The manybody part is treated via Configuration Interaction. I will illustrate how this method addresses some of the recent striking experimental observations on semiconductor quantum dots:(i) Scaling laws for band gaps and exchange interactions (ii) Rapid Auger transitions in colloidal dots (iii) Coulomb Blocade and Spin Blockade in colloidal dots (iv) Charged Excitons (e.g. Trions) in Self-assembled dots, and (v) excitonic Fine-Structure in self assembled dots.

  7. Electronic structure of narrow gap semiconductors: Understanding gap formation and thermoelectric properties

    NASA Astrophysics Data System (ADS)

    Larson, Paul Melvin

    Electronic band structure calculations are invaluable theoretical tools to understand structural, transport, and optical properties of materials. We have used this tool in the search for new high performance thermoelectric materials, which are usually narrow-gap semiconductors. We have studied the electronic structures of these systems both to understand which properties of the band structure are most important for thermoelectric properties and the nature of the gap formation. Narrow-gap semiconductors lie between metals and wide-gap semiconductors, so understanding the nature of the gap formation is very important. The small band gaps in the systems we have studied generally arise from hybridization between different bands. We have used the local density approximation (LDA) and the generalized gradient approximation (GGA) within density functional theory (DFT). These have been implemented using the full-potential linearized augmented planewave (FLAPW) method within the WIEN97 package. This state-of-the-art method is among the most accurate methods for calculating the electronic structure of solids. We have studied four classes of compounds. These include the half-Heusler compounds, the ternary Zintl-phase compounds, the simple chalcogenides, and the complex chalcogenides. The ternary half-Heusler compounds, considered having a stuffed NaCl structure, show promising thermoelectric properties. The band gap formation is understood by starting with the semi-metallic binary NaCl compounds from which they are formed. Adding the transition (or noble) metal atom causes a strong p-d hybridization near the Fermi energy which opens up the band gap. This hybridization also leads to highly anisotropic effective masses at the conduction band minimum which are found in the best thermoelectric materials. Similar band gap formation is found in the ternary Zintl-phase compounds which are considered a stuffed Th3P4 structure. The band gaps in these ternary compounds are larger than

  8. Low-Dimensional Chaos in an Instance of Epilepsy

    NASA Astrophysics Data System (ADS)

    Babloyantz, A.; Destexhe, A.

    1986-05-01

    Using a time series obtained from the electroencephalogram recording of a human epileptic seizure, we show the existence of a chaotic attractor, the latter being the direct consequence of the deterministic nature of brain activity. This result is compared with other attractors seen in normal human brain dynamics. A sudden jump is observed between the dimensionalities of these brain attractors 4.05 ± 0.05 for deep sleep) and the very low dimensionality of the epileptic state (2.05 ± 0.09). The evaluation of the autocorrelation function and of the largest Lyapunov exponent allows us to sharpen further the main features of underlying dynamics. Possible implications in biological and medical research are briefly discussed.

  9. Learning Low-Dimensional Representations of Medical Concepts.

    PubMed

    Choi, Youngduck; Chiu, Chill Yi-I; Sontag, David

    2016-01-01

    We show how to learn low-dimensional representations (embeddings) of a wide range of concepts in medicine, including diseases (e.g., ICD9 codes), medications, procedures, and laboratory tests. We expect that these embeddings will be useful across medical informatics for tasks such as cohort selection and patient summarization. These embeddings are learned using a technique called neural language modeling from the natural language processing community. However, rather than learning the embeddings solely from text, we show how to learn the embeddings from claims data, which is widely available both to providers and to payers. We also show that with a simple algorithmic adjustment, it is possible to learn medical concept embeddings in a privacy preserving manner from co-occurrence counts derived from clinical narratives. Finally, we establish a methodological framework, arising from standard medical ontologies such as UMLS, NDF-RT, and CCS, to further investigate the embeddings and precisely characterize their quantitative properties. PMID:27570647

  10. Learning Low-Dimensional Representations of Medical Concepts

    PubMed Central

    Choi, Youngduck; Chiu, Chill Yi-I; Sontag, David

    2016-01-01

    We show how to learn low-dimensional representations (embeddings) of a wide range of concepts in medicine, including diseases (e.g., ICD9 codes), medications, procedures, and laboratory tests. We expect that these embeddings will be useful across medical informatics for tasks such as cohort selection and patient summarization. These embeddings are learned using a technique called neural language modeling from the natural language processing community. However, rather than learning the embeddings solely from text, we show how to learn the embeddings from claims data, which is widely available both to providers and to payers. We also show that with a simple algorithmic adjustment, it is possible to learn medical concept embeddings in a privacy preserving manner from co-occurrence counts derived from clinical narratives. Finally, we establish a methodological framework, arising from standard medical ontologies such as UMLS, NDF-RT, and CCS, to further investigate the embeddings and precisely characterize their quantitative properties. PMID:27570647

  11. Electronic Structures of Free-Standing Nanowires made from Indirect Bandgap Semiconductor Gallium Phosphide

    PubMed Central

    Liao, Gaohua; Luo, Ning; Chen, Ke-Qiu; Xu, H. Q.

    2016-01-01

    We present a theoretical study of the electronic structures of freestanding nanowires made from gallium phosphide (GaP)—a III-V semiconductor with an indirect bulk bandgap. We consider [001]-oriented GaP nanowires with square and rectangular cross sections, and [111]-oriented GaP nanowires with hexagonal cross sections. Based on tight binding models, both the band structures and wave functions of the nanowires are calculated. For the [001]-oriented GaP nanowires, the bands show anti-crossing structures, while the bands of the [111]-oriented nanowires display crossing structures. Two minima are observed in the conduction bands, while the maximum of the valence bands is always at the Γ-point. Using double group theory, we analyze the symmetry properties of the lowest conduction band states and highest valence band states of GaP nanowires with different sizes and directions. The band state wave functions of the lowest conduction bands and the highest valence bands of the nanowires are evaluated by spatial probability distributions. For practical use, we fit the confinement energies of the electrons and holes in the nanowires to obtain an empirical formula. PMID:27307081

  12. Electronic Structures of Free-Standing Nanowires made from Indirect Bandgap Semiconductor Gallium Phosphide.

    PubMed

    Liao, Gaohua; Luo, Ning; Chen, Ke-Qiu; Xu, H Q

    2016-01-01

    We present a theoretical study of the electronic structures of freestanding nanowires made from gallium phosphide (GaP)-a III-V semiconductor with an indirect bulk bandgap. We consider [001]-oriented GaP nanowires with square and rectangular cross sections, and [111]-oriented GaP nanowires with hexagonal cross sections. Based on tight binding models, both the band structures and wave functions of the nanowires are calculated. For the [001]-oriented GaP nanowires, the bands show anti-crossing structures, while the bands of the [111]-oriented nanowires display crossing structures. Two minima are observed in the conduction bands, while the maximum of the valence bands is always at the Γ-point. Using double group theory, we analyze the symmetry properties of the lowest conduction band states and highest valence band states of GaP nanowires with different sizes and directions. The band state wave functions of the lowest conduction bands and the highest valence bands of the nanowires are evaluated by spatial probability distributions. For practical use, we fit the confinement energies of the electrons and holes in the nanowires to obtain an empirical formula. PMID:27307081

  13. Electronic Structures of Free-Standing Nanowires made from Indirect Bandgap Semiconductor Gallium Phosphide

    NASA Astrophysics Data System (ADS)

    Liao, Gaohua; Luo, Ning; Chen, Ke-Qiu; Xu, H. Q.

    2016-06-01

    We present a theoretical study of the electronic structures of freestanding nanowires made from gallium phosphide (GaP)—a III-V semiconductor with an indirect bulk bandgap. We consider [001]-oriented GaP nanowires with square and rectangular cross sections, and [111]-oriented GaP nanowires with hexagonal cross sections. Based on tight binding models, both the band structures and wave functions of the nanowires are calculated. For the [001]-oriented GaP nanowires, the bands show anti-crossing structures, while the bands of the [111]-oriented nanowires display crossing structures. Two minima are observed in the conduction bands, while the maximum of the valence bands is always at the Γ-point. Using double group theory, we analyze the symmetry properties of the lowest conduction band states and highest valence band states of GaP nanowires with different sizes and directions. The band state wave functions of the lowest conduction bands and the highest valence bands of the nanowires are evaluated by spatial probability distributions. For practical use, we fit the confinement energies of the electrons and holes in the nanowires to obtain an empirical formula.

  14. Electronic Structures of Free-Standing Nanowires made from Indirect Bandgap Semiconductor Gallium Phosphide.

    PubMed

    Liao, Gaohua; Luo, Ning; Chen, Ke-Qiu; Xu, H Q

    2016-06-16

    We present a theoretical study of the electronic structures of freestanding nanowires made from gallium phosphide (GaP)-a III-V semiconductor with an indirect bulk bandgap. We consider [001]-oriented GaP nanowires with square and rectangular cross sections, and [111]-oriented GaP nanowires with hexagonal cross sections. Based on tight binding models, both the band structures and wave functions of the nanowires are calculated. For the [001]-oriented GaP nanowires, the bands show anti-crossing structures, while the bands of the [111]-oriented nanowires display crossing structures. Two minima are observed in the conduction bands, while the maximum of the valence bands is always at the Γ-point. Using double group theory, we analyze the symmetry properties of the lowest conduction band states and highest valence band states of GaP nanowires with different sizes and directions. The band state wave functions of the lowest conduction bands and the highest valence bands of the nanowires are evaluated by spatial probability distributions. For practical use, we fit the confinement energies of the electrons and holes in the nanowires to obtain an empirical formula.

  15. Nonlinear ion acoustic dissipative shock structure with exchange-correlation effects in quantum semiconductor plasmas

    NASA Astrophysics Data System (ADS)

    Hussain, S.; Akhtar, N.

    2016-09-01

    Ion acoustic shocks in the electron-hole-ion semiconductor plasmas have been studied. The quantum recoil effects, exchange-correlation effects and degenerate pressure of electrons and holes are included. The ion species are considered classical and their dissipation is taken into account via the dynamic viscosity. The Korteweg de Vries Burgers equation is derived by using reductive perturbation approach. The excitation of shock waves in different semiconductor plasmas is pointed out. For numerical analyses, the plasma parameters of different semiconductors are considered. The impact of variation of the plasma parameters on the strength of the shock wave in the semiconductor plasmas is discussed.

  16. Low-dimensional functionality of complex network dynamics: Neurosensory integration in the Caenorhabditiselegans connectome

    NASA Astrophysics Data System (ADS)

    Kunert, James; Shlizerman, Eli; Kutz, J. Nathan

    2014-05-01

    We develop a biophysical model of neurosensory integration in the model organism Caenorhabditis elegans. Building on experimental findings on the neuron conductances and their resolved connectome, we posit the first full dynamic model of the neural voltage excitations that allows for a characterization of network structures which link input stimuli to neural proxies of behavioral responses. Full connectome simulations of neural responses to prescribed inputs show that robust, low-dimensional bifurcation structures drive neural voltage activity modes. Comparison of these modes with experimental studies allows us to link these network structures to behavioral responses. Thus the underlying bifurcation structures discovered, i.e., induced Hopf bifurcations, are critical in explaining behavioral responses such as swimming and crawling.

  17. Energy-pressure relation for low-dimensional gases

    NASA Astrophysics Data System (ADS)

    Mancarella, Francesco; Mussardo, Giuseppe; Trombettoni, Andrea

    2014-10-01

    A particularly simple relation of proportionality between internal energy and pressure holds for scale-invariant thermodynamic systems (with Hamiltonians homogeneous functions of the coordinates), including classical and quantum - Bose and Fermi - ideal gases. One can quantify the deviation from such a relation by introducing the internal energy shift as the difference between the internal energy of the system and the corresponding value for scale-invariant (including ideal) gases. After discussing some general thermodynamic properties associated with the scale-invariance, we provide criteria for which the internal energy shift density of an imperfect (classical or quantum) gas is a bounded function of temperature. We then study the internal energy shift and deviations from the energy-pressure proportionality in low-dimensional models of gases interpolating between the ideal Bose and the ideal Fermi gases, focusing on the Lieb-Liniger model in 1d and on the anyonic gas in 2d. In 1d the internal energy shift is determined from the thermodynamic Bethe ansatz integral equations and an explicit relation for it is given at high temperature. Our results show that the internal energy shift is positive, it vanishes in the two limits of zero and infinite coupling (respectively the ideal Bose and the Tonks-Girardeau gas) and it has a maximum at a finite, temperature-depending, value of the coupling. Remarkably, at fixed coupling the energy shift density saturates to a finite value for infinite temperature. In 2d we consider systems of Abelian anyons and non-Abelian Chern-Simons particles: as it can be seen also directly from a study of the virial coefficients, in the usually considered hard-core limit the internal energy shift vanishes and the energy is just proportional to the pressure, with the proportionality constant being simply the area of the system. Soft-core boundary conditions at coincident points for the two-body wavefunction introduce a length scale, and induce a

  18. Structure and electronic properties features of amorphous chalhogenide semiconductor films prepared by ion-plasma spraying

    SciTech Connect

    Korobova, N. Timoshenkov, S.; Almasov, N.; Prikhodko, O.; Tsendin, K.

    2014-10-21

    Structure of amorphous chalcogenide semiconductor glassy As-S-Se films, obtained by high-frequency (HF) ion-plasma sputtering has been investigated. It was shown that the length of the atomic structure medium order and local structure were different from the films obtained by thermal vacuum evaporation. Temperature dependence of dark conductivity, as well as the dependence of the spectral transmittance has been studied. Conductivity value was determined at room temperature. Energy activation conductivity and films optical band gap have been calculated. Temperature and field dependence of the drift mobility of charge carriers in the HF As-S-Se films have been shown. Bipolarity of charge carriers drift mobility has been confirmed. Absence of deep traps for electrons in the As{sub 40}Se{sub 30}S{sub 30} spectrum of localized states for films obtained by HF plasma ion sputtering was determined. Bipolar drift of charge carriers was found in amorphous As{sub 40}Se{sub 30}S{sub 30} films obtained by ion-plasma sputtering of high-frequency, unlike the films of these materials obtained by thermal evaporation.

  19. Structural and magnetic properties of a prospective spin gapless semiconductor MnCrVAl

    NASA Astrophysics Data System (ADS)

    Huh, Y.; Gilbert, S.; Kharel, P.; Jin, Y.; Lukashev, P.; Valloppilly, S.; Sellmyer, D. J.

    Recently a new class of material, spin gapless semiconductors (SGS), has attracted much attention because of their potential for spintronic devices. We have synthesized a Heusler compound, MnCrVAl, which is theoretically predicted to exhibit SGS by arc melting, rapid quenching and thermal annealing. First principles calculations are employed to describe its structural, electronic and magnetic properties. X-ray diffraction indicates that the rapidly quenched samples crystallize in the disordered cubic structure. The crystal structure is stable against heat treatment up to 650oC. The samples show very small saturation magnetization, 0.3 emu/g, at room temperature under high magnetic field, 30 kOe. Above room temperature, the magnetization increases with increasing temperature undergoing a magnetic transition at 560oC, similar to an antiferromagnetic-to-paramagnetic transition. The prospect of this material for spintronic applications will be discussed. This research is supported by SDSU Academic/Scholarly Excellence Fund, and Research/Scholarship Support Fund. Research at UNL is supported by DOE (DE-FG02-04ER46152, synthesis, characterization), NSF (ECCS-1542182, facilities), and NRI.

  20. Spin-Orbit Coupling in Hybrid Semiconductor Structures: From Majorana Fermions to Topological Insulators

    NASA Astrophysics Data System (ADS)

    Scharf, Benedikt

    Hybrid semiconductor structures with strong spin-orbit coupling are responsible for many fascinating phenomena. Topological states in systems of reduced dimensionality, in particular, offer many intriguing possibilities, both for fundamental research as well as for potential applications. In this talk, we describe the importance of the interplay of spin-orbit coupling (SOC) and the sample geometry in realizing exotic Majorana fermions (MFs) in quantum dots and rings and discuss several schemes to detect MFs. An effective SOC from the magnetic textures provided by magnetic tunnel junctions could enable a versatile control of MFs and their adiabatic exchange. We show that in 2D topological insulators (TIs), such as inverted HgTe/CdTe QWs, helical quantum spin Hall (QSH) states persist even at finite magnetic fields below a critical magnetic field above which only quantum Hall (QH) states can be found. We propose magneto-optical absorption measurements to probe the magnetic-field induced transition between the QSH and QH regimes. This measurement scheme is robust against perturbations such as additional SOC due to bulk or structure-inversion asymmetry. Finally, tunnel junctions based on the surfaces of 3D TIs are presented. These junctions can exhibit giant tunneling anomalous Hall (TAH) currents and negative differential TAH conductance, which makes them an attractive and versatile system for spintronic applications.

  1. Quantum interference measurement of spin interactions in a bio-organic/semiconductor device structure

    DOE PAGESBeta

    Deo, Vincent; Zhang, Yao; Soghomonian, Victoria; Heremans, Jean J.

    2015-03-30

    Quantum interference is used to measure the spin interactions between an InAs surface electron system and the iron center in the biomolecule hemin in nanometer proximity in a bio-organic/semiconductor device structure. The interference quantifies the influence of hemin on the spin decoherence properties of the surface electrons. The decoherence times of the electrons serve to characterize the biomolecule, in an electronic complement to the use of spin decoherence times in magnetic resonance. Hemin, prototypical for the heme group in hemoglobin, is used to demonstrate the method, as a representative biomolecule where the spin state of a metal ion affects biologicalmore » functions. The electronic determination of spin decoherence properties relies on the quantum correction of antilocalization, a result of quantum interference in the electron system. Spin-flip scattering is found to increase with temperature due to hemin, signifying a spin exchange between the iron center and the electrons, thus implying interactions between a biomolecule and a solid-state system in the hemin/InAs hybrid structure. The results also indicate the feasibility of artificial bioinspired materials using tunable carrier systems to mediate interactions between biological entities.« less

  2. Quantum interference measurement of spin interactions in a bio-organic/semiconductor device structure

    SciTech Connect

    Deo, Vincent; Zhang, Yao; Soghomonian, Victoria; Heremans, Jean J.

    2015-03-30

    Quantum interference is used to measure the spin interactions between an InAs surface electron system and the iron center in the biomolecule hemin in nanometer proximity in a bio-organic/semiconductor device structure. The interference quantifies the influence of hemin on the spin decoherence properties of the surface electrons. The decoherence times of the electrons serve to characterize the biomolecule, in an electronic complement to the use of spin decoherence times in magnetic resonance. Hemin, prototypical for the heme group in hemoglobin, is used to demonstrate the method, as a representative biomolecule where the spin state of a metal ion affects biological functions. The electronic determination of spin decoherence properties relies on the quantum correction of antilocalization, a result of quantum interference in the electron system. Spin-flip scattering is found to increase with temperature due to hemin, signifying a spin exchange between the iron center and the electrons, thus implying interactions between a biomolecule and a solid-state system in the hemin/InAs hybrid structure. The results also indicate the feasibility of artificial bioinspired materials using tunable carrier systems to mediate interactions between biological entities.

  3. Raman spectrum of Cu2CdSnSe4 stannite structure semiconductor compound

    NASA Astrophysics Data System (ADS)

    Rincón, C.; Quintero, M.; Moreno, E.; Power, Ch.; Quintero, E.; Henao, J. A.; Macías, M. A.

    2015-12-01

    Raman spectrum of Cu2CdSnSe4 quaternary semiconductor compounds with tetragonal stannite-type structure (space group I 4 bar 2m), a material which has been recognized recently as a potential candidate for thermoelectric applications, has been studied. Most of the fourteen Raman lines expected for this compound according to group theory analysis were observed in the spectrum. Besides to the two strongest A1-symmetry stannite modes at 172 and 192 cm-1 originated from the motion of Se anion around the Cu and Sn cations which remain at rest, the leftover observed Raman lines were tentatively assigned to specific eigenmodes of the stannite crystal structure by comparing these line frequencies with those obtained for this compound from IR measurements as well as with those calculated Raman modes for the Cu2ZnSnSe4 stannite-compound reported in the literature. Two spurious Raman lines related to the presence in this compound of SnSe and SnSe2 minority secondary phases have also been found in the Raman spectrum.

  4. Low-dimensional carbon and MXene-based electrochemical capacitor electrodes

    NASA Astrophysics Data System (ADS)

    Yoon, Yeoheung; Lee, Keunsik; Lee, Hyoyoung

    2016-04-01

    Due to their unique structure and outstanding intrinsic physical properties such as extraordinarily high electrical conductivity, large surface area, and various chemical functionalities, low-dimension-based materials exhibit great potential for application in electrochemical capacitors (ECs). The electrical properties of electrochemical capacitors are determined by the electrode materials. Because energy charge storage is a surface process, the surface properties of the electrode materials greatly influence the electrochemical performance of the cell. Recently, graphene, a single layer of sp2-bonded carbon atoms arrayed into two-dimensional carbon nanomaterial, has attracted wide interest as an electrode material for electrochemical capacitor applications due to its unique properties, including a high electrical conductivity and large surface area. Several low-dimensional materials with large surface areas and high conductivity such as onion-like carbons (OLCs), carbide-derived carbons (CDCs), carbon nanotubes (CNTs), graphene, metal hydroxide, transition metal dichalcogenides (TMDs), and most recently MXene, have been developed for electrochemical capacitors. Therefore, it is useful to understand the current issues of low-dimensional materials and their device applications.

  5. Low-dimensional carbon and MXene-based electrochemical capacitor electrodes.

    PubMed

    Yoon, Yeoheung; Lee, Keunsik; Lee, Hyoyoung

    2016-04-29

    Due to their unique structure and outstanding intrinsic physical properties such as extraordinarily high electrical conductivity, large surface area, and various chemical functionalities, low-dimension-based materials exhibit great potential for application in electrochemical capacitors (ECs). The electrical properties of electrochemical capacitors are determined by the electrode materials. Because energy charge storage is a surface process, the surface properties of the electrode materials greatly influence the electrochemical performance of the cell. Recently, graphene, a single layer of sp(2)-bonded carbon atoms arrayed into two-dimensional carbon nanomaterial, has attracted wide interest as an electrode material for electrochemical capacitor applications due to its unique properties, including a high electrical conductivity and large surface area. Several low-dimensional materials with large surface areas and high conductivity such as onion-like carbons (OLCs), carbide-derived carbons (CDCs), carbon nanotubes (CNTs), graphene, metal hydroxide, transition metal dichalcogenides (TMDs), and most recently MXene, have been developed for electrochemical capacitors. Therefore, it is useful to understand the current issues of low-dimensional materials and their device applications. PMID:26988574

  6. Features of high-frequency measurements of the impedance of metal-insulator-semiconductor structures with an ultrathin oxide

    SciTech Connect

    Goldman, E. I.; Levashova, A. I.; Levashov, S. A.; Chucheva, G. V.

    2015-04-15

    The possibilities of using the data of high-frequency measurements of the impedance of metal-oxide-semiconductor structures with an ultrathin insulating layer for determining the parameters of the semiconductor and the tunneling characteristics of the insulator are considered. If the accuracy of the experiment makes it possible to record both the active and reactive impedance components, the thickness of the surface depletion layer, the resistance of the semiconductor base portion, the differential tunnel conductivity of the insulating layer, and the differential tunneling-stimulated current of the generation of electron-hole pairs are calculated using the values of the capacitance and conduction of the structure measured at two frequencies. In the case, where the values of the active component of the impedance is beyond the accuracy of measurements, analysis of the parameters is possible upon four-frequency organization of the experiment from the values of only the capacitances with an increased accuracy of their measurements. A test for the necessary accuracy of data of such an experiment is formulated. If the test fails, it is possible to determine only the capacitance of the surface depletion layer in the semiconductor and, in this case, it is sufficient to implement only the single-frequency experiment.

  7. Structural Investigation of Biological and Semiconductor Nanostructures with Nonlinear Multicontrast Microscopy

    NASA Astrophysics Data System (ADS)

    Cisek, Richard

    Physical and functional properties of advanced nano-composite materials and biological structures are determined by self-organized atoms and molecules into nanostructures and in turn by microscopic organization of the nanostructures into assemblies of higher structural complexity. Therefore, microscopes are indispensable tools for structural investigations at various levels of organization. In this work, novel nonlinear optical microscopy methods were developed to non-invasively study structural organization at the nanoscopic and microscopic levels. Atomic organization of semiconductor nanowires, molecular organization of amylose biocrystallites in starch granules, and microscopic organization of several photosynthetic organisms was elucidated. The structure of ZnSe nanowires, key components in many modern nanodevices, was investigated using polarization harmonic generation microscopy. Based on nonlinear optical properties of the different crystal lattices, zinc blende and wurtzite nanowires were differentiated, and the three-dimensional orientation of the zinc blende nanowires could be found. The structure of starch granules, a model biocrystal, important in food as well as health sciences, was also investigated using polarization harmonic microscopy. The study was combined with ab initio calculations using the crystal structures of amylose A and B, revealing that second harmonic signals originate from the hydroxide and hydrogen bonds in the starch granules. Visualization of several photosynthetic organisms including the green algae, Chlamydomonas reinhardtii, two species of cyanobacteria, Leptolyngbya sp. and Anabaena sp., aggregates of light-harvesting pigment-protein complexes as well as chloroplasts from green plants were also explored, revealing that future nonlinear microscopy applications could include structural studies of cell walls, the Chlamydomonas eyespot, and photosynthetic membranes. In this study, several nonlinear optical microscopy modalities

  8. Low-Dimensional Feature Representation for Instrument Identification

    NASA Astrophysics Data System (ADS)

    Ihara, Mizuki; Maeda, Shin-Ichi; Ikeda, Kazushi; Ishii, Shin

    For monophonic music instrument identification, various feature extraction and selection methods have been proposed. One of the issues toward instrument identification is that the same spectrum is not always observed even in the same instrument due to the difference of the recording condition. Therefore, it is important to find non-redundant instrument-specific features that maintain information essential for high-quality instrument identification to apply them to various instrumental music analyses. For such a dimensionality reduction method, the authors propose the utilization of linear projection methods: local Fisher discriminant analysis (LFDA) and LFDA combined with principal component analysis (PCA). After experimentally clarifying that raw power spectra are actually good for instrument classification, the authors reduced the feature dimensionality by LFDA or by PCA followed by LFDA (PCA-LFDA). The reduced features achieved reasonably high identification performance that was comparable or higher than those by the power spectra and those achieved by other existing studies. These results demonstrated that our LFDA and PCA-LFDA can successfully extract low-dimensional instrument features that maintain the characteristic information of the instruments.

  9. Low-Dimensional Dynamical Models of Thermal Convection

    NASA Technical Reports Server (NTRS)

    Liakopoulos, Anthony

    1996-01-01

    A low-dimensional dynamic model for transitional buoyancy-driven flow in a differentially heated tall enclosure is presented. The full governing partial differential equations with the associated boundary conditions are solved by a spectral element method for a cavity of aspect ratio A=20. Proper orthogonal decomposition is applied to the oscillatory solution at Prandtl number Pr=P tau (omega) = 0.71 and Grashof number G tau (omega) = 3.2 x 10 (exp 4) to construct empirical eigenfunctions. Using the four most energetic empirical eigenfunctions for the velocity and temperature as basis functions and applying Galerkin's method, a reduced model consisting of eight nonlinear ordinary differential equations is obtained. Close to the 'design' conditions (P tau(omega) G tau(omega)), the low-order model (LOM) predictions are in excellent agreement with the predictions of the full model. In particular, the critical Grashof number at the onset of the first temporal flow instability (Hopf bifurcation) was well as the frequency and amplitude of oscillations at supercritical conditions are in excellent agreement with the predictions of the full model. Far from the 'design' conditions, the LOM predicts the existence of multiple stable steady solutions at large values of G tau, and a unique stable steady solution at small values of G tau, and exhibits hysteretic behavior that is qualitatively similar to that observed in direct numerical simulations based on the full model.

  10. Efimov-Like Behaviour in Low-Dimensional Polymer Models

    NASA Astrophysics Data System (ADS)

    Mura, Federica; Bhattacharjee, Somendra M.; Maji, Jaya; Masetto, Mario; Seno, Flavio; Trovato, Antonio

    2016-10-01

    In the quantum Efimov effect, identical bosons form infinitely many bound trimer states at the bound dimer dissociation threshold, with their energy spectrum obeying a universal geometrical scaling law. Inspired by the formal correspondence between the possible trajectories of a quantum particle and the possible conformations of a polymer chain, the existence of a triple-stranded DNA bound state when a double-stranded DNA is not stable was recently predicted by modelling three directed polymer chains in low-dimensional lattices, both fractal (d<1) and euclidean (d=1). A finite melting temperature for double-stranded DNA requires in d≤ 2 the introduction of a weighting factor penalizing the formation of denaturation bubbles, that is non-base paired portions of DNA. The details of how bubble weighting is defined for a three-chain system were shown to crucially affect the presence of Efimov-like behaviour on a fractal lattice. Here we assess the same dependence on the euclidean 1+1 lattice, by setting up the transfer matrix method for three infinitely long chains confined in a finite size geometry. This allows us to discriminate unambiguously between the absence of Efimov-like behaviour and its presence in a very narrow temperature range, in close correspondence with what was already found on the fractal lattice. When present, however, no evidence is found for triple-stranded bound states other than the ground state at the two-chain melting temperature.

  11. A low-dimensional analogue of holographic baryons

    NASA Astrophysics Data System (ADS)

    Bolognesi, Stefano; Sutcliffe, Paul

    2014-04-01

    Baryons in holographic QCD correspond to topological solitons in the bulk. The most prominent example is the Sakai-Sugimoto model, where the bulk soliton in the five-dimensional spacetime of AdS-type can be approximated by the flat space self-dual Yang-Mills instanton with a small size. Recently, the validity of this approximation has been verified by comparison with the numerical field theory solution. However, multi-solitons and solitons with finite density are currently beyond numerical field theory computations. Various approximations have been applied to investigate these important issues and have led to proposals for finite density configurations that include dyonic salt and baryonic popcorn. Here we introduce and investigate a low-dimensional analogue of the Sakai-Sugimoto model, in which the bulk soliton can be approximated by a flat space sigma model instanton. The bulk theory is a baby Skyrme model in a three-dimensional spacetime with negative curvature. The advantage of the lower-dimensional theory is that numerical simulations of multi-solitons and finite density solutions can be performed and compared with flat space instanton approximations. In particular, analogues of dyonic salt and baryonic popcorn configurations are found and analysed.

  12. Features of the band structure and conduction mechanisms in the n-HfNiSn semiconductor heavily doped with Ru

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Stadnyk, Yu. V.; Korzh, R. O.; Krayovskyy, V. Ya.; Horyn, A. M.

    2014-12-15

    The crystal and electronic structure and energy and kinetic properties of the n-HfNiSn semiconductor heavily doped with a Ru acceptor impurity are investigated in the temperature and Ru concentration ranges T = 80–400 K and N{sub A}{sup Ru} ≈ 9.5 × 10{sup 19}−5.7 × 10{sup 20} cm{sup −3} (x = 0–0.03), respectively. The mechanism of structural-defect generation is established, which changes the band gap and degree of compensation of the semiconductor and consists in the simultaneous concentration reduction and elimination of donor structural defects by means of the displacement of ∼1% of Ni atoms from the Hf (4a) positions, the generation of acceptor structural defects upon the substitution of Ru atoms for Ni atoms in the 4c positions, and the generation of donor defects in the form of vacancies in the Sn (4b) positions. The calculated electronic structure of HfNi{sub 1−x}Ru{sub x}Sn is consistent with the experiment. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

  13. Features of the band structure and conduction mechanisms of n-HfNiSn semiconductor heavily Lu-doped

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Kaczorowski, D.; Stadnyk, Yu. V.; Korzh, R. O.; Krayovskyy, V. Ya.; Kovbasyuk, T. M.

    2015-03-15

    The crystal and electronic structures, energy, kinetic, and magnetic characteristics of n-HfNiSn semiconductor heavily doped with a Lu acceptor impurity in the ranges T = 80–400 K and N{sub A}{sup Lu} ≈ 1.9 × 10{sup 20}−1.9 × 10{sup 21} cm{sup −3} (x = 0.01–0.10) at H ≤ 10 kG is studied. The nature of the structural-defect generation mechanism leading to changes in the band gap and the degree of semiconductor compensation is determined. Its essence is the simultaneous reduction and elimination of donor-type structural defects due to the displacement of ∼1% of Ni atoms from the Hf (4a) site, the generation of acceptor-type structural defects by substituting Ni atoms with Lu atoms at the 4c site, and the generation of donor-type defects such as vacancies at the Sn (4b) site. The results of calculations of the electronic structure of Hf{sub 1−x}Lu{sub x}NiSn are in agreement with experimental data. The results are discussed within the model of a heavily doped and compensated Shklovskii-Efros semiconductor.

  14. Controlled buckling structures in semiconductor interconnects and nanomembranes for stretchable electronics

    DOEpatents

    Rogers, John A; Meitl, Matthew; Sun, Yugang; Ko, Heung Cho; Carlson, Andrew; Choi, Won Mook; Stoykovich, Mark; Jiang, Hanqing; Huang, Yonggang; Nuzzo, Ralph G; Zhu, Zhengtao; Menard, Etienne; Khang, Dahl-Young

    2014-05-20

    In an aspect, the present invention provides stretchable, and optionally printable, components such as semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed or otherwise deformed, and related methods of making or tuning such stretchable components. Stretchable semiconductors and electronic circuits preferred for some applications are flexible, in addition to being stretchable, and thus are capable of significant elongation, flexing, bending or other deformation along one or more axes. Further, stretchable semiconductors and electronic circuits of the present invention are adapted to a wide range of device configurations to provide fully flexible electronic and optoelectronic devices.

  15. Controlled buckling structures in semiconductor interconnects and nanomembranes for stretchable electronics

    DOEpatents

    Rogers, John A.; Meitl, Matthew; Sun, Yugang; Ko, Heung Cho; Carlson, Andrew; Choi, Won Mook; Stoykovich, Mark; Jiang, Hanqing; Huang, Yonggang; Nuzzo, Ralph G.; Lee, Keon Jae; Zhu, Zhengtao; Menard, Etienne; Khang, Dahl-Young; Kan, Seong Jun; Ahn, Jong Hyun; Kim, Hoon-sik

    2012-07-10

    In an aspect, the present invention provides stretchable, and optionally printable, components such as semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed or otherwise deformed, and related methods of making or tuning such stretchable components. Stretchable semiconductors and electronic circuits preferred for some applications are flexible, in addition to being stretchable, and thus are capable of significant elongation, flexing, bending or other deformation along one or more axes. Further, stretchable semiconductors and electronic circuits of the present invention are adapted to a wide range of device configurations to provide fully flexible electronic and optoelectronic devices.

  16. Controlling Light-Matter Interaction in Semiconductors with Hybrid Nano-Structures

    NASA Astrophysics Data System (ADS)

    Gehl, Michael R.

    Nano-structures, such as photonic crystal cavities and metallic antennas, allow one to focus and store optical energy into very small volumes, greatly increasing light-matter interactions. These structures produce resonances which are typically characterized by how well they confine energy both temporally (quality factor -- Q) and spatially (mode volume -- V). In order to observe non-linear effects, modified spontaneous emission (e.g. Purcell enhancement), or quantum effects (e.g. vacuum Rabi splitting), one needs to maximize the ratio of Q/V while also maximizing the coupling between the resonance and the active medium. In this dissertation I will discuss several projects related by the goal of controlling light-matter interactions using such nano-structures. In the first portion of this dissertation I will discuss the deterministic placement of self-assembled InAs quantum dots, which would allow one to precisely position an optically-active material, for maximum interaction, inside of a photonic crystal cavity. Additionally, I will discuss the use of atomic layer deposition to tune and improve both the resonance wavelength and quality factor of silicon based photonic crystal cavities. Moving from dielectric materials to metals allows one to achieve mode-volumes well below the diffraction limit. The quality factor of these resonators is severely limited by Ohmic loss in the metal; however, the small mode-volume still allows for greatly enhanced light-matter interaction. In the second portion of this dissertation I will investigate the coupling between an array of metallic resonators (antennas) and a nearby semiconductor quantum well. Using time-resolved pump-probe measurements I study the properties of the coupled system and compare the results to a model which allows one to quantitatively compare various antenna geometries.

  17. A new solution chemical method to make low dimensional thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Ding, Zhongfen

    2001-11-01

    Bismuth telluride and its alloys are currently the best thermoelectric materials known at room temperature and are therefore used for portable solid-state refrigeration. If the thermal electric figure of merit ZT could be improved by a factor of about 3, quiet and rugged solid-state devices could eventually replace conventional compressor based cooling systems. In order to test a theory that improved one-dimensional or two-dimensional materials could enhance ZT due to lower thermal conductivity, we are developing solution processing methods to make low dimensional materials. Bismuth telluride and its p-type and n-type alloys have layered structures consisting of 5 atom thick Te-Bi-Te-Bi-Te sheets, each sheet about 10 A thick. Lithium ions are intercalated into the layered materials using liquid ammonia. The lithium-intercalated materials are then exfoliated in water to form colloidal suspensions with narrow particle size distributions and are stable for more than 24 hours. The layers are then deposited on substrates, which after annealing at low temperatures, form highly c-axis oriented thin films. The exfoliated layers can potentially be restacked with other ions or layered materials in between the sheets to form novel structures. The restacked layers when treated with nitric acid and sonication form high yield nanorod structured materials. This new intercalation and exfoliation followed by sonication method could potentially be used for many other layered materials to make nanorod structured materials. The low dimensional materials are characterized by powder X-ray diffraction, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), inductively coupled plasma (ICP) and dynamic light scattering.

  18. Synthesis and Structure Determination of Ferromagnetic Semiconductors LaAMnSnO6 (A = Sr Ba)

    SciTech Connect

    T Yang; T Perkisas; J Hadermann; M Croft; A Ignatov; M Greenblatt

    2011-12-31

    LaAMnSnO{sub 6} (A = Sr, Ba) have been synthesized by high temperature solid-state reactions under dynamic 1% H{sub 2}/Ar flow. Rietveld refinements on room temperature powder X-ray diffraction data indicate that LaSrMnSnO{sub 6} crystallizes in the GdFeO{sub 3}-structure, with space group Pnma and, combined with transmission electron microscopy, LaBaMnSnO{sub 6} in Imma. Both space groups are common in disordered double-perovskites. The Mn{sup 3+} and Sn{sup 4+} ions whose valence states were confirmed by X-ray absorption spectroscopy, are completely disordered over the B-sites and the BO{sub 6} octahedra are slightly distorted. LaAMnSnO{sub 6} are ferromagnetic semiconductors with a T{sub C} = 83 K for the Sr- and 66 K for the Ba-compound. The title compounds, together with the previously reported LaCaMnSnO{sub 6} provide an interesting example of progression from Pnma to Imma as the tolerance factor increases. An analysis of the relationship between space group and tolerance factor for the series LaAMnMO{sub 6} (A = Ca, Sr, Ba; M = Sn, Ru) provides a better understanding of the symmetry determination for double perovskites.

  19. Interacting quasi-band theory for electronic states in compound semiconductor alloys: Wurtzite structure

    NASA Astrophysics Data System (ADS)

    Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

    2016-05-01

    This paper reports on the electronic states of compound semiconductor alloys of wurtzite structure calculated by the recently proposed interacting quasi-band (IQB) theory combined with empirical sp3 tight-binding models. Solving derived quasi-Hamiltonian 24 × 24 matrix that is characterized by the crystal parameters of the constituents facilitates the calculation of the conduction and valence bands of wurtzite alloys for arbitrary concentrations under a unified scheme. The theory is applied to III-V and II-VI wurtzite alloys: cation-substituted Al1- x Ga x N and Ga1- x In x N and anion-substituted CdS1- x Se x and ZnO1- x S x . The obtained results agree well with the experimental data, and are discussed in terms of mutual mixing between the quasi-localized states (QLS) and quasi-average bands (QAB): the latter bands are approximately given by the virtual crystal approximation (VCA). The changes in the valence and conduction bands, and the origin of the band gap bowing are discussed on the basis of mixing character.

  20. Theory of structure and hyperfine properties of anomalous muonium in elemental semiconductors: Diamond, silicon, and germanium

    SciTech Connect

    Sahoo, N.; Sulaiman, S. B.; Mishra, K. C.; Das, T. P.

    1989-06-15

    A number of possible models for the anomalous muonium (Mu/sup */)center in the elemental semiconductors diamond, silicon, and germanium areinvestigated in detail, both with respect to their stabilities and abilities toexplain the extensive available experimental hyperfine-interaction data, thelatter being the major focus of the present work. Using the unrestrictedHartree-Fock cluster procedure, the electronic structures and potential-energycurves associated with muon positions are obtained for the different models.The results are utilized to obtain hyperfine properties associated with themuon and its neighboring nuclei, including vibrational effects associated withthe muon. Our results show that stability considerations favor both thevacancy-associated (VA) and bond-centered (BC) models for Mu/sup */.The VA model explains all the experimentally observed features of the muonhyperfine properties and provides reasonably good quantitative agreement withexperiment. However, questions remain regarding its formation and ability toexplain level-crossing resonance (LCR) data. On the other hand, although the BCmodel appears to explain the experimental features from LCR measurements, inits present form, it seriously overestimates the strengths of the muonhyperfine interactions as compared to experiment, by more than an order ofmagnitude in some cases. Additionally, it does not explain the trend fromdiamond through germanium. On the basis of the results in this paper for the VAand BC models, the direction for future investigations for understanding thenature of the Mu/sup */ center is commented on.

  1. Multi-immunosensors based on electrolite-insulator-semiconductor structures for determination of some herbicides

    NASA Astrophysics Data System (ADS)

    Starodub, Nickolaj F.; Starodub, Valentyna M.; Krivenchuk, Vladimir E.; Shapovalenko, Valentyna F.

    2002-02-01

    New type of the multi-immune sensor was elaborated. It is based on electrolyte-insulator-semiconductors structures and intended for determination of such herbicides as simazine, atrazine and 2,4-D. The specific antibodies were immobilized on nitrocellulose disks, which were placed in measuring cells. The analysis was fulfilled by sequential saturation of antibodies, left unbound after their exposure to native herbicide in investigated sample, with labelled herbicide. If horse radish peroxidase (HRP) was used as label the sensitivity of this multi-immune sensor was about 5 and 1.25 (mu) g/L for simazine and 2,4-D, respectively. At the changing of HRP by (beta) -glucose oxidase the sensitivity of analysis of these herbicides increased approximately in 5 times. The linear plots of the registered concentrations were in the range of 1,0-150,0 and 0,25-150,0 ng/mL for simazine and 2,4-D respectively. It was recommended to use the developed immune sensor for wide screening of herbicides in environment. The ways for increasing of its sensitivity were proposed.

  2. Interacting quasi-band theory for electronic states in compound semiconductor alloys: Wurtzite structure

    NASA Astrophysics Data System (ADS)

    Kishi, Ayaka; Oda, Masato; Shinozuka, Yuzo

    2016-05-01

    This paper reports on the electronic states of compound semiconductor alloys of wurtzite structure calculated by the recently proposed interacting quasi-band (IQB) theory combined with empirical sp3 tight-binding models. Solving derived quasi-Hamiltonian 24 × 24 matrix that is characterized by the crystal parameters of the constituents facilitates the calculation of the conduction and valence bands of wurtzite alloys for arbitrary concentrations under a unified scheme. The theory is applied to III–V and II–VI wurtzite alloys: cation-substituted Al1‑ x Ga x N and Ga1‑ x In x N and anion-substituted CdS1‑ x Se x and ZnO1‑ x S x . The obtained results agree well with the experimental data, and are discussed in terms of mutual mixing between the quasi-localized states (QLS) and quasi-average bands (QAB): the latter bands are approximately given by the virtual crystal approximation (VCA). The changes in the valence and conduction bands, and the origin of the band gap bowing are discussed on the basis of mixing character.

  3. First-Principles Study on Electronic Structure of TiO2-Based Dilute Magnetic Semiconductors

    NASA Astrophysics Data System (ADS)

    Kizaki, Hidetoshi; Toyoda, Masayuki; Sato, Kazunori; Katayama-Yoshida, Hiroshi

    2008-03-01

    We investigate the electronic structure in rutile-TiO2-based dilute magnetic semiconductors (DMS) within self-interaction- corrected local density approximation (SIC-LDA). These results are compared with those calculated within standard LDA. Although the calculated band-gap energy and energetic position of Ti 3d bands are different in the LDA and the SIC-LDA, half-metallic density of states is predicted in transition- metal-doped TiO2 for both methods. While the LDA calculations predict high-spin state only for Fe-doped one, in the SIC-LDA calculations high-spin state is realized in V-, Cr- and Mn-doped one and low-spin state is realized in Fe- and Co- doped one. However, the absorption and soft x-ray magnetic circular dichroism measurements in (Ti0.97, Co0.03)O2-δ indicate the Co^2+ high-spin state in the D2h-symmetry crystal field at the Ti site. These experimental results do not agree with our calculated results. We will discuss the origin of the discrepancy between the theoretical predictions and the experimental observations. In addition, we will discuss the ferromagnetism in TiO2-based DMS.

  4. Structure of the Surface States at Topological Insulator-Semiconductor Interfaces

    NASA Astrophysics Data System (ADS)

    Asmar, Mahmoud M.; Sheehy, Daniel; Vekhter, Ilya

    Topologically-protected surface states of three-dimensional topological insulators (TIs) are characterized by spin and momentum locking. In the simplest picture the emergent two dimensional semimetal displays opposite helicities around the point of degeneracy. Possible applications of TIs rely on forming interfaces with other materials, such as semiconductors or superconductors. In such heterostructures, the dispersion and quantum numbers of the surface states become not only dependent on bulk properties but also on the specifics of the boundaries between the TI and the material in contact. Making use of the three dimensional k . p Hamiltonian describing TIs, and taking in to account surface potentials compatible with the symmetries of the TI and the semiconducting material, we find the effects of the latter on the energy-momentum dispersion and spin structure of the surface state and explore the consequences this may have on physical observables. Supported by: NSF Grant No. DMR-1105339, NSF Grant No. DMR-1410741 and NSF Grant No. DMR-1151717.

  5. Structural, magnetic, and transport properties of (Zn,V)Te semiconductors

    NASA Astrophysics Data System (ADS)

    Wang, Weigang; Ni, Chaoying; Zhu, Tao; Zhang, Huiwu; Xiao, John Q.

    2006-04-01

    Vanadium-doped ZnTe has been predicted to be one of the candidates for ferromagnetic semiconductors with a high Curie temperature [K. Sato and H. Katayama-Yoshida, Semicond. Sci. Technol. 17, 367 (2002)]. In this paper, we report the structural, magnetic, and transport properties of (Zn,V)Te films prepared by magnetron sputtering. Samples were fabricated on both GaAs and thermally oxidized silicon substrate at elevated temperature. Oriented sample (100) can be achieved on GaAs substrates and only polycrystalline samples are observed on Si substrates. X-ray diffraction (XRD) and transmission electron spectroscopy (TEM) show no magnetic precipitates in the (Zn,V)Te film. The magnetization measurement shows that the oriented sample is paramagnetic at 5 K, while films on Si substrate shows weak ferromagnetism at 5 K. The sign of magnetoresistance (MR=[R(H)-R(0)]/R(0)) gradually changes from negative to positive with temperature, and positive MR at high temperatures shows H2 dependence, indicating ordinary MR effect. It is believed the observed negative MR corresponds to the ferromagnetic ordering at lower temperature.

  6. Asymmetrically contacted germanium photodiode using a metal-interlayer-semiconductor-metal structure for extremely large dark current suppression.

    PubMed

    Zang, Hwan-Jun; Kim, Gwang-Sik; Park, Gil-Jae; Choi, Yong-Soo; Yu, Hyun-Yong

    2016-08-15

    In this study, we proposed germanium (Ge) metal-interlayer-semiconductor-metal (MISM) photodiodes (PD), with an anode of a metal-interlayer-semiconductor (MIS) contact and a cathode of a metal-semiconductor (MS) contact, to efficiently suppress the dark current of Ge PD. We selected titanium dioxide (TiO2) as an interlayer material for the MIS contact, due to its large valence band offset and negative conduction band offset to Ge. We significantly suppress the dark current of Ge PD by introducing the MISM structure with a TiO2 interlayer, as this enhances the hole Schottky barrier height, and thus acts as a large barrier for holes. In addition, it collects photo-generated carriers without degradation, due to its negative conduction band offset to Ge. This reduces the dark current of Ge MISM PDs by ×8000 for 7-nm-thick TiO2 interlayer, while its photo current is still comparable to that of Ge metal-semiconductor-metal (MSM) PDs. Furthermore, the proposed Ge PD shows ×6,600 improvement of the normalized photo-to-dark-current ratio (NPDR) at a wavelength of 1.55 μm. The proposed Ge MISM PD shows considerable promise for low power and high sensitivity Ge-based optoelectronic applications. PMID:27519063

  7. Proton tunneling in low dimensional cesium silicate LDS-1

    SciTech Connect

    Matsui, Hiroshi Iwamoto, Kei; Mochizuki, Dai; Osada, Shimon; Asakura, Yusuke; Kuroda, Kazuyuki

    2015-07-14

    In low dimensional cesium silicate LDS-1 (monoclinic phase of CsHSi{sub 2}O{sub 5}), anomalous infrared absorption bands observed at 93, 155, 1210, and 1220 cm{sup −1} are assigned to the vibrational mode of protons, which contribute to the strong hydrogen bonding between terminal oxygen atoms of silicate chain (O–O distance = 2.45 Å). The integrated absorbance (oscillator strength) for those modes is drastically enhanced at low temperatures. The analysis of integrated absorbance employing two different anharmonic double-minimum potentials makes clear that proton tunneling through the potential barrier yields an energy splitting of the ground state. The absorption bands at 93 and 155 cm{sup −1}, which correspond to the different vibrational modes of protons, are attributed to the optical transition between the splitting levels (excitation from the ground state (n = 0) to the first excited state (n = 1)). Moreover, the absorption bands at 1210 and 1220 cm{sup −1} are identified as the optical transition from the ground state (n = 0) to the third excited state (n = 3). Weak Coulomb interactions in between the adjacent protons generate two types of vibrational modes: symmetric mode (93 and 1210 cm{sup −1}) and asymmetric mode (155 and 1220 cm{sup −1}). The broad absorption at 100–600 cm{sup −1} reveals an emergence of collective mode due to the vibration of silicate chain coupled not only with the local oscillation of Cs{sup +} but also with the proton oscillation relevant to the second excited state (n = 2)

  8. Electrodynamic response properties of low-dimensional conductors

    NASA Astrophysics Data System (ADS)

    Brown, Brian Lewis

    Two classes of low-dimensional materials are examined to expand current knowledge on their potentially useful electrical and/or optical properties. First, complex AC conductance measurements from 0.01 to 50 GHz, across temperatures of 4.2 to 300 K and magnetic fields up to 2.0 T were made on textile sheets of highly aligned multi-wall carbon nanotubes drawn from 329, 420 and 520 microm-high forests. The AC conductance of sheets with strands oriented parallel and perpendicular to the electric field polarization is roughly modeled by a shunt capacitance in parallel with a frequency-independent conductance, with no inductive contribution. This is consistent with diffusive Drude AC conduction up to 50 GHz. Further, AC conductance is found to be essentially independent of temperature and magnetic field. The absence of temperature dependence implies elastic defect and impurity scattering is dominant in these materials, while a lack of magnetoconductance suggests uncompensated single band conduction with no coherent weak localization backscattering. Second, the effect of Cr doping on properties of Cr(x)V(1-x)O2 thin films across the metal-insulator transition (MIT) has been studied. Resistance, Hall effect and infrared reflectance show Cr doping systematically increases the transition temperature Tc from 59 C at x=0 to 70 C at x=0.11, but the effect appears to saturate. This is in contrast to a prior study of bulk ceramic samples where the transition temperature increased without saturation for chromium doping fractions up to x=0.20. Results also show conductance changes across the MIT for the Cr(x)V(1-x)O2 thin films to be largely due to increases in carrier density rather than mobility, consistent with theoretical expectations.

  9. Structural defect generation and band-structure features in the HfNi{sub 1−x}Co{sub x}Sn semiconductor

    SciTech Connect

    Romaka, V. A.; Rogl, P.; Romaka, V. V.; Stadnyk, Yu. V.; Krayovskyy, V. Ya.; Kaczorowski, D.; Nakonechnyy, I. N.; Goryn, A. M.

    2015-08-15

    The crystal and electronic structure and magnetic, energy, and kinetic properties of the n-HfNiSn semiconductor heavily doped with the Co acceptor impurity (HfNi{sub 1−x}Co{sub x}Sn) are investigated in the temperature and Co concentration ranges T = 80–400 K and N{sub A}{sup Co} ≈ 9.5 × 10{sup 19}-5.7 × 10{sup 21} cm{sup −3} (x = 0.005–0.30), respectively, and under magnetic field H ≤ 10 kOe. It is established that the degree of compensation of the semiconductor changes due to transformation of the crystal structure upon doping, which leads to the generation of acceptor and donor structural defects. The calculated electronic structure is consistent with the experiment; the HfNi{sub 1−x}Co{sub x}Sn semiconductor is shown to be a promising thermoelectric material. The results obtained are discussed within the Shklovsky-Efros model for a heavily doped and compensated semiconductor.

  10. Ab initio description of the diluted magnetic semiconductor Ga1-xMnxAs: Ferromagnetism, electronic structure, and optical response

    NASA Astrophysics Data System (ADS)

    Craco, L.; Laad, M. S.; Müller-Hartmann, E.

    2003-12-01

    Motivated by a study of various experiments describing the electronic and magnetic properties of the diluted magnetic semiconductor Ga1-xMnxAs, we investigate its physical response in detail using a combination of first-principles band structure with methods based on dynamical mean field theory to incorporate strong, dynamical correlations, and intrinsic as well as extrinsic disorder in one single theoretical picture. We show how ferromagnetism is driven by double exchange (DE), in agreement with very recent observations, along with a good quantitative description of the details of the electronic structure, as probed by scanning tunneling microscopy and optical conductivity. Our results show how ferromagnetism can be driven by DE even in diluted magnetic semiconductors with small carrier concentration.

  11. Effect of realistic metal electronic structure on the lower limit of contact resistivity of epitaxial metal-semiconductor contacts

    SciTech Connect

    Hegde, Ganesh Chris Bowen, R.

    2014-08-04

    The effect of realistic metal electronic structure on the lower limit of resistivity in [100] oriented n-Si is investigated using full band Density Functional Theory and Semi-Empirical Tight Binding calculations. It is shown that the “ideal metal” assumption may fail in some situations and, consequently, underestimate the lower limit of contact resistivity in n-Si by at least an order of magnitude at high doping concentrations. The mismatch in transverse momentum space in the metal and the semiconductor, the so-called “valley filtering effect,” is shown to be sensitive to the details of the transverse boundary conditions for the unit cells used. The results emphasize the need for explicit inclusion of the metal atomic and electronic structure in the atomistic modeling of transport across metal-semiconductor contacts.

  12. A first principles study of the lattice stability of diamond-structure semiconductors under intense laser irradiation

    SciTech Connect

    Feng Shiquan; Zhao Jianling; Cheng Xinlu

    2013-01-14

    Using density-functional linear-response theory, we calculated the phonon dispersion curves for the diamond structural elemental semiconductors of Ge, C and zinc-blende structure semiconductors of GaAs, InSb at different electronic temperatures. We found that the transverse-acoustic phonon frequencies of C and Ge become imaginary as the electron temperature is elevated, which means the lattices of C and Ge become unstable under intense laser irradiation. These results are very similar with previous theoretical and experimental results for Si. For GaAs and InSb, not only can be obtained the similar results for their transverse-acoustic modes, but also their LO-TO splitting gradually decreases as the electronic temperature is increased. It means that the electronic excitation weakens the strength of the ionicity of ionic crystal under intense laser irradiation.

  13. Electromagnetic metamaterial-inspired band gap and perfect transmission in semiconductor and graphene-based electronic and photonic structures

    NASA Astrophysics Data System (ADS)

    Mahdy, M. R. C.; Al Sayem, Ayed; Shahriar, Arif; Shawon, Jubayer; Al-Quaderi, Golam Dastegir; Jahangir, Ifat; Matin, M. A.

    2016-04-01

    In this article, at first we propose a unified and compact classification of single negative electromagnetic metamaterial-based perfect transmission unit cells. The classes are named as: type-A, -B and -C unit cells. Then based on the classification, we have extended these ideas in semiconductor and graphene regimes. For type-A: Based on the idea of electromagnetic Spatial Average Single Negative bandgap, novel bandgap structures have been proposed for electron transmission in semiconductor heterostructures. For type-B: with dielectric-graphene-dielectric structure, almost all angle transparency is achieved for both polarizations of electromagnetic wave in the terahertz frequency range instead of the conventional transparency in the microwave frequency range. Finally the application of the gated dielectric-graphene-dielectric has been demonstrated for the modulation and switching purpose.

  14. Design of nanophotonic, hot-electron solar-blind ultraviolet detectors with a metal-oxide-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Wang, Zhiyuan; Wang, Xiaoxin; Liu, Jifeng

    2014-12-01

    Solar-blind ultraviolet (UV) detection refers to photon detection specifically in the wavelength range of 200 nm-320 nm. Without background noises from solar radiation, it has broad applications from homeland security to environmental monitoring. The most commonly used solid state devices for this application are wide band gap (WBG) semiconductor photodetectors (Eg > 3.5 eV). However, WBG semiconductors are difficult to grow and integrate with Si readout integrated circuits (ROICs). In this paper, we design a nanophotonic metal-oxide-semiconductor structure on Si for solar-blind UV detectors. Instead of using semiconductors as the active absorber, we use Sn nano-grating structures to absorb UV photons and generate hot electrons for internal photoemission across the Sn/SiO2 interfacial barrier, thereby generating photocurrent between the metal and the n-type Si region upon UV excitation. Moreover, the transported hot electron has an excess kinetic energy >3 eV, large enough to induce impact ionization and generate another free electron in the conduction band of n-Si. This process doubles the quantum efficiency. On the other hand, the large metal/oxide interfacial energy barrier (>3.5 eV) also enables solar-blind UV detection by blocking the less energetic electrons excited by visible photons. With optimized design, ˜75% UV absorption and hot electron excitation can be achieved within the mean free path of ˜20 nm from the metal/oxide interface. This feature greatly enhances hot electron transport across the interfacial barrier to generate photocurrent. The simple geometry of the Sn nano-gratings and the MOS structure make it easy to fabricate and integrate with Si ROICs compared to existing solar-blind UV detection schemes. The presented device structure also breaks through the conventional notion that photon absorption by metal is always a loss in solid-state photodetectors, and it can potentially be extended to other active metal photonic devices.

  15. Dopant in Near-Surface Semiconductor Layers of Metal-Insulator-Semiconductor Structures Based on Graded-Gap p-Hg0.78Cd0.22Te Grown by Molecular-Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.

    2016-02-01

    Peculiarities in determining the dopant concentration and dopant distribution profile in the near-surface layer of a semiconductor are investigated by measuring the admittance of metal-insulator-semiconductor structures (MIS structures) based on p-Hg0.78Cd0.22Te grown by molecular beam epitaxy. The dopant concentrations in the near-surface layer of the semiconductor are determined by measuring the admittance of MIS structures in the frequency range of 50 kHz to 1 MHz. It is shown that in this frequency range, the capacitance-voltage characteristics of MIS structures based on p-Hg0.78Cd0.22Te with a near-surface graded gap layer demonstrate a high-frequency behavior with respect to the recharge time of surface states located near the Fermi level for an intrinsic semiconductor. The formation time of the inversion layer is decreased by less than two times, if a near-surface graded-gap layer is created. The dopant distribution profile in the near-surface layer of the semiconductor is found, and it is shown that for structures based on p-Hg0.78Cd0.22Te with a near-surface graded-gap layer, the dopant concentration has a minimum near the interface with the insulator. For MIS structure based on n-Hg0.78Cd0.22Te, the dopant concentration is more uniformly distributed in the near-surface layer of the semiconductor.

  16. Specific evidence of low-dimensional continuous attractor dynamics in grid cells.

    PubMed

    Yoon, Kijung; Buice, Michael A; Barry, Caswell; Hayman, Robin; Burgess, Neil; Fiete, Ila R

    2013-08-01

    We examined simultaneously recorded spikes from multiple rat grid cells, to explain mechanisms underlying their activity. Among grid cells with similar spatial periods, the population activity was confined to lie close to a two-dimensional (2D) manifold: grid cells differed only along two dimensions of their responses and otherwise were nearly identical. Relationships between cell pairs were conserved despite extensive deformations of single-neuron responses. Results from novel environments suggest such structure is not inherited from hippocampal or external sensory inputs. Across conditions, cell-cell relationships are better conserved than responses of single cells. Finally, the system is continually subject to perturbations that, were the 2D manifold not attractive, would drive the system to inhabit a different region of state space than observed. These findings have strong implications for theories of grid-cell activity and substantiate the general hypothesis that the brain computes using low-dimensional continuous attractors. PMID:23852111

  17. The geodynamo as a low-dimensional deterministic system at the edge of chaos

    NASA Astrophysics Data System (ADS)

    Ryan, D. A.; Sarson, G. R.

    2008-08-01

    We perform non-linear time series analysis tests on the SINT 2000 paleomagnetic record of the Earth's virtual axial dipole moment for the past 2 Ma, and find evidence of low-dimensional deterministic chaos. We reconstruct the phase space attractor using embedded time delay vectors, and compare the result with reconstructions from time series of a turbulent mean-field dynamo model, which exhibits a similar attractor structure. Considered alongside evidence of 1/f noise and lognormality in the paleomagnetic record, this suggests an important role for multiplicative noise, which may maintain the dynamo at the edge of chaos. In contrast to characterisations of geomagnetic reversals as stochastic processes, this work supports their interpretation as the outcome of a deterministic dynamical system.

  18. Low dimensional magnetic solids and single crystal elpasolites: Need for improved crystal growing techniques

    NASA Technical Reports Server (NTRS)

    Good, M. L.; Watkins, S.; Schwartz, R. W.

    1979-01-01

    The need for extensive crystal growing experiments to develop techniques for preparing crystals suitable for magnetic anisotropy measurements and detailed X-ray and neutron diffraction studies is rationalized on the basis of the unique magnetic properties of the materials and their hydrogen bonded structures which have many features in common with metalloenzyme and metalloprotein active sites. Single crystals of the single and mixed lanthanide species are prepared by the Bridgeman technique of gradient solidification of molten samples. The effects of crystal imperfections on the optical properties of these materials are an important part of the projected research. A series of a-amido acid complexes of first row transition metals were prepared which crystallize as infinite linear chains and exhibit low dimensional magnetic ordering (one or two) at temperature below 40 K.

  19. Low-dimensional hyperthin FeS2 nanostructures for efficient and stable hydrogen evolution electrocatalysis

    DOE PAGESBeta

    Jasion, Daniel; Qiao, Qiao; Barforoush, Joseph M.; Zhu, Yimei; Ren, Shenqiang; Leonard, Kevin C.

    2015-10-05

    We report a scalable, solution-processing method for synthesizing low-dimensional hyperthin FeS2 nanostructures, and we show that 2D FeS2 disc nanostructures are an efficient and stable hydrogen evolution electrocatalyst. By changing the Fe:S ratio in the precursor solution, we were able to preferentially synthesize either 1D wire or 2D disc nanostructures. The 2D FeS2 disc structure has the highest electrocatalytic activity for the hydrogen evolution reaction, comparable to platinum in neutral pH conditions. Moreover, the ability of the FeS2 nanostructures to generate hydrogen was confirmed by scanning electrochemical microscopy, and the 2D disc nanostructures were able to generate hydrogen for overmore » 125 h.« less

  20. High-frequency capacitance-voltage characteristics of the heterogeneous structure based on the model of spherical semiconductor particles in a dielectric

    NASA Astrophysics Data System (ADS)

    Tonkoshkur, A. S.; Ivanchenko, A. V.

    2016-08-01

    The dependence of the parameters of the capacitance effect in heterogeneous dispersed two-component structures based on semiconductors from the bulk fraction of the semiconductor component is modeled. The used method for determining the changes of the energy bands bending on the surface of the spherical semiconductor particle by applying dc electric field allowed to calculate the changes of the dipole moment and effective (taking into account the polarization of the free charge) dielectric constant of this semiconductor particle. This result allowed to use the known models of the dielectric constant of two-component structures for the description of the capacitance field effect in the heterogeneous structures. The relations allowing to estimate the value of the bulk donor concentration in the semiconductor component of the matrix of the heterogeneous system and the statistical mixture have been obtained. The approbation of the obtained calculation relations to evaluate the donor concentration in the ZnO grains of zinc oxide varistor ceramics leads to the correct values that are consistent with estimates of other methods and models. It is established that the sensitivity of the relative dielectric constant to the applied dc electric field is dependent on the bulk fraction of the semiconductor particles in the heterogeneous structures. The bulk fraction of the semiconductor particles significantly affects on the dielectric constant beginning with the values from ˜0.8 for matrix systems and ˜0.33 for statistical mixtures.

  1. Transport and optical properties of low-dimensional complex systems

    NASA Astrophysics Data System (ADS)

    Iurov, Andrii

    Over the last five years of my research work, I, my research was mainly concerned with certain crucial tunneling, transport and optical properties of novel low-dimensional graphitic and carbon-based materials as well as topological insulators. Both single-electron and many-body problems were addressed. We investigated the Dirac electrons transmission through a potential barrier in the presence of circularly polarized light. An anomalous photon-assisted enhanced transmission is predicted and explained in a comparison with the well-known Klein paradox. It is demonstrated that the perfect transmission for nearly-head-on collision in an infinite graphene is suppressed in gapped dressed states of electrons, which is further accompanied by shift of peaks as a function of the incident angle away from the head-on collision. We calculate the energy bands for graphene monolayers when electrons move through a periodic electrostatic potential in the presence of a uniform perpendicular magnetic field. We clearly demonstrate the quantum fractal nature of the energy bands at reasonably low magnetic fields. We present results for the energy bands as functions of both wave number and magnetic flux through the unit cells of the resulting moiŕe superlattice. This feature is also observed at extremely high magnetic fields. We have discovered a novel feature in the plasmon excitations for a pair of Coulomb-coupled non-concentric spherical two-dimensional electron gases (S2DEGs). Our results show that the plasmon excitations for such pairs depend on the orientation with respect to the external electromagnetic probe field. The origin of this anisotropy of the inter-sphere Coulomb interaction is due to the directional asymmetry of the electrostatic coupling of electrons in excited states which depend on both the angular momentum quantum number L and its projection M on the axis of quantization taken as the probe E-field direction. Such an effect from the plasmon spatial correlation is

  2. Determination of Fowler-Nordheim tunneling parameters in Metal-Oxide-Semiconductor structure including oxide field correction using a vertical optimization method

    NASA Astrophysics Data System (ADS)

    Toumi, S.; Ouennoughi, Z.; Strenger, K. C.; Frey, L.

    2016-08-01

    Current conduction mechanisms through a Metal-Oxide-Semiconductor structure are characterized via Fowler-Nordheim (FN) plots. The extraction of the FN parameters like the electron/hole effective mass in oxide mox and in semiconductor msc, the barrier height at the semiconductor-oxide interface ϕB, and the correction oxide voltage Vcorr for a MOS structure is made using a vertical optimization process on the current density without any assumption about ϕB or mox. An excellent agreement is obtained between the FN plots calculated with the FN parameters extracted using a vertical optimization process with the experimental one.

  3. Enhancing the Thermoelectric Figure of Merit by Low-Dimensional Electrical Transport in Phonon-Glass Crystals.

    PubMed

    Mi, Xue-Ya; Yu, Xiaoxiang; Yao, Kai-Lun; Huang, Xiaoming; Yang, Nuo; Lü, Jing-Tao

    2015-08-12

    Low-dimensional electronic and glassy phononic transport are two important ingredients of highly efficient thermoelectric materials, from which two branches of thermoelectric research have emerged. One focuses on controlling electronic transport in the low dimension, while the other focuses on multiscale phonon engineering in the bulk. Recent work has benefited much from combining these two approaches, e.g., phonon engineering in low-dimensional materials. Here we propose to employ the low-dimensional electronic structure in bulk phonon-glass crystals as an alternative way to increase the thermoelectric efficiency. Through first-principles electronic structure calculations and classical molecular dynamics simulations, we show that the π-π-stacking bis(dithienothiophene) molecular crystal is a natural candidate for such an approach. This is determined by the nature of its chemical bonding. Without any optimization of the material parameters, we obtained a maximum room-temperature figure of merit, ZT, of 1.48 at optimal doping, thus validating our idea.

  4. Solution processable semiconductor thin films: Correlation between morphological, structural, optical and charge transport properties

    NASA Astrophysics Data System (ADS)

    Isik, Dilek

    This Ph.D. thesis is a result of multidisciplinary research bringing together fundamental concepts in thin film engineering, materials science, materials processing and characterization, electrochemistry, microfabrication, and device physics. Experiments were conducted by tackling scientific problems in the field of thin films and interfaces, with the aim to correlate the morphology, crystalline structure, electronic structure of thin films with the functional properties of the films and the performances of electronic devices based thereon. Furthermore, novel strategies based on interfacial phenomena at electrolyte/thin film interfaces were explored and exploited to control the electrical conductivity of the thin films. Three main chemical systems were the object of the studies performed during this Ph.D., two types of organic semiconductors (azomethine-based oligomers and polymers and soluble pentacene derivatives) and one metal oxide semiconductor (tungsten trioxide, WO3). To explore the morphological properties of the thin films, atomic force microscopy was employed. The morphological properties were further investigated by hyperspectral fluorescence microscopy and tentatively correlated to the charge transport properties of the films. X-ray diffraction (Grazing incidence XRD, GIXRD) was used to investigate the crystallinity of the film and the effect of the heat treatment on such crystallinity, as well as to understand the molecular arrangement of the organic molecules in the thin film. The charge transport properties of the films were evaluated in thin film transistor configuration. For electrolyte gated thin film transistors, time dependent transient measurements were conducted, in parallel to more conventional transistor characterizations, to explore the specific effects played on the gating by the anion and cation constituting the electrolyte. The capacitances of the electrical double layers at the electrolyte/WO3 interface were obtained from

  5. Inter-band optoelectronic properties in quantum dot structure of low band gap III-V semiconductors

    SciTech Connect

    Dey, Anup; Maiti, Biswajit; Chanda, Debasree

    2014-04-14

    A generalized theory is developed to study inter-band optical absorption coefficient (IOAC) and material gain (MG) in quantum dot structures of narrow gap III-V compound semiconductor considering the wave-vector (k{sup →}) dependence of the optical transition matrix element. The band structures of these low band gap semiconducting materials with sufficiently separated split-off valance band are frequently described by the three energy band model of Kane. This has been adopted for analysis of the IOAC and MG taking InAs, InSb, Hg{sub 1−x}Cd{sub x}Te, and In{sub 1−x}Ga{sub x}As{sub y}P{sub 1−y} lattice matched to InP, as example of III–V compound semiconductors, having varied split-off energy band compared to their bulk band gap energy. It has been found that magnitude of the IOAC for quantum dots increases with increasing incident photon energy and the lines of absorption are more closely spaced in the three band model of Kane than those with parabolic energy band approximations reflecting the direct the influence of energy band parameters. The results show a significant deviation to the MG spectrum of narrow-gap materials having band nonparabolicity compared to the parabolic band model approximations. The results reflect the important role of valence band split-off energies in these narrow gap semiconductors.

  6. Development of epitaxial AlxSc1-xN for artificially structured metal/semiconductor superlattice metamaterials

    DOE PAGESBeta

    Sands, Timothy D.; Stach, Eric A.; Saha, Bivas; Saber, Sammy; Naik, Gururaj V.; Boltasseva, Alexandra; Kvam, Eric P.

    2015-02-01

    Epitaxial nitride rocksalt metal/semiconductor superlattices are emerging as a novel class of artificially structured materials that have generated significant interest in recent years for their potential application in plasmonic and thermoelectric devices. Though most nitride metals are rocksalt, nitride semiconductors in general have hexagonal crystal structure. We report rocksalt aluminum scandium nitride (Al,Sc)N alloys as the semiconducting component in epitaxial rocksalt metal/semiconductor superlattices. The AlxSc1-xN alloys when deposited directly on MgO substrates are stabilized in a homogeneous rocksalt (single) phase when x < 0.51. Employing 20 nm TiN as a seed layer on MgO substrates, the homogeneity range for stabilizingmore » the rocksalt phase has been extended to x < 0.82 for a 120 nm film. The rocksalt AlxSc1-xN alloys show moderate direct bandgap bowing with a bowing parameter, B = 1.41 ± 0.19 eV. The direct bandgap of metastable rocksalt AlN is extrapolated to be 4.70 ± 0.20 eV. The tunable lattice parameter, bandgap, dielectric permittivity, and electronic properties of rocksalt AlxSc1-xN alloys enable high quality epitaxial rocksalt metal/AlxSc1-xN superlattices with a wide range of accessible metamaterials properties.« less

  7. Extended line defects in BN, GaN, and AlN semiconductor materials: Graphene-like structures

    NASA Astrophysics Data System (ADS)

    Camacho-Mojica, Dulce C.; López-Urías, Florentino

    2016-05-01

    The extended line defect (ELD) mimicking grain boundaries in two-dimensional systems is theoretically investigated in BN, GaN, and AlN semiconductor materials with a single layer honeycomb structure. The ELD consists of octagonal-square membered rings. Density functional calculations of the electronic density of states, scanning tunneling microscopy and transmission electron microscopy image simulations are analyzed. Our results revealed that the ELDs are stable in all considered monolayers. In addition, electronic density of states calculations demonstrated that in gap states are emerged when ELD is incorporated into the honeycomb structures. Finally, results on armchair nanoribbons with bare-edges and hydrogenated edges are discussed.

  8. Physical properties of low-dimensional sp 2 -based carbon nanostructures

    NASA Astrophysics Data System (ADS)

    Meunier, V.; Souza Filho, A. G.; Barros, E. B.; Dresselhaus, M. S.

    2016-04-01

    The last two decades have witnessed a tremendous growth in the development and understanding of sp 2 carbon-based nanostructures. The impact of this research has led to a number of fundamental discoveries that have played a central role in the understanding of many aspects of materials physics and their applications. Much of this progress has been enabled by the development of new techniques to prepare, modify, and assemble low-dimensional materials into devices. The field has also benefited greatly from much progress in theoretical and computational modeling, as well as from advances in characterization techniques developed to probe and manipulate single atomic layers, nanoribbons, and nanotubes. Some of the most fundamental physical properties of sp2 carbon-based nanostructures are reviewed and their role as model systems for solid-state physics in one and two dimensions is highlighted. The objective of this review is to provide a thorough account on current understanding of how the details of the atomic structure affect phonons, electrons, and transport in these nanomaterials. The review starts with a description of the behavior of single-layer and few-layer graphene and then expands into the analysis of nanoribbons and nanotubes in terms of their reduced dimensionality and curvature. How the properties can be modified and tailored for specific applications is then discussed. The review concludes with a historical perspective and considers some open questions concerning future directions in the physics of low-dimensional systems and their impact on continued advances in solid-state physics, and also looks beyond carbon nanosystems.

  9. Electronic Band Structures of the Highly Desirable III-V Semiconductors: TB-mBJ DFT Studies

    NASA Astrophysics Data System (ADS)

    Rehman, Gul; Shafiq, M.; Saifullah; Ahmad, Rashid; Jalali-Asadabadi, S.; Maqbool, M.; Khan, Imad; Rahnamaye-Aliabad, H.; Ahmad, Iftikhar

    2016-07-01

    The correct band gaps of semiconductors are highly desirable for their effective use in optoelectronic and other photonic devices. However, the experimental and theoretical results of the exact band gaps are quite challenging and sometimes tricky. In this article, we explore the electronic band structures of the highly desirable optical materials, III-V semiconductors. The main reason of the ineffectiveness of the theoretical band gaps of these compounds is their mixed bonding character, where large proportions of electrons reside outside atomic spheres in the intestinal regions, which are challenging for proper theoretical treatment. In this article, the band gaps of the compounds are revisited and successfully reproduced by properly treating the density of electrons using the recently developed non-regular Tran and Blaha's modified Becke-Johnson (nTB-mBJ) approach. This study additionally suggests that this theoretical scheme could also be useful for the band gap engineering of the III-V semiconductors. Furthermore, the optical properties of these compounds are also calculated and compared with the experimental results.

  10. Toward High Performance Integrated Semiconductor Micro and Nano Lasers Enabled by Transparent Conducting Materials: from Thick Structure to Thin Film

    NASA Astrophysics Data System (ADS)

    Ou, Fang

    Integrated semiconductor lasers working at the wavelength around 1.3 microm and 1.55 microm are of great interest for the research of photonic integrated circuit (PIC) since they are the crucial components for optical communications and many other applications. To satisfy the requirement of the next generation optical communication and computing systems, integrated semiconductor lasers are expected to have high device performance like very low lasing threshold, high output powers, high speed and possibility of being integrated with electronics. This dissertation focuses on the design and realization of InP based high performance electrically pumped integrated semiconductor lasers. In the dissertation, we first design the tall structure based electrically pumped integrated micro-lasers. Those lasers are capable of giving >10 mW output power with a moderate low threshold current density (0.5--5 kA/cm 2). Besides, a new enhanced radiation loss based coupler design is demonstrated to realize single directional output for curvilinear cavities. Second, the thin film structure based integrated semiconductor laser designs are proposed. Both structures use the side conduction geometry to enable the electrical injection into the thin film laser cavity. The performance enhancement of the thin film structure based lasers is analyzed compared to the tall structure. Third, we investigate the TCO materials. CdO deposited by PLD and In 2O3 deposited by IAD are studied from aspects of their physical, optical and electrical properties. Those materials can give a wide range of tunability in their conductivity (1--5000 S/cm) and optical transparency (loss 200--5000 cm-1), which is of great interest in realizing novel nanophotonic devices. In addition, the electrical contact properties of those materials to InP are also studied. Experiment result shows that both CdO and In2O3 can achieve good ohmic contact to n-InP with contact resistance as low as 10-6O·cm 2. At last, we investigate

  11. Centrifugation-based Purification of Emerging Low-dimensional Materials and Their Thin-film Applications

    NASA Astrophysics Data System (ADS)

    Seo, Jung Woo

    Polydispersity in low-dimensional materials offers many interesting challenges and properties. In particular, the one- and two-dimensional carbon allotropes such as carbon nanotubes and graphene have demonstrated exquisite optoelectronic properties that are highly sensitive to their physical structures, where subtle variations in diameter and thickness render them with significantly different electronic band structures. Thus, the carbon nanomaterials have been the subject of extensive studies that address their polydispersity issues. Among these, solution-phase, buoyant density-based methods such as density gradient ultracentrifugation have been widely utilized to enrich subpopulations of carbon nanotubes and graphene with narrow distribution in diameter and thickness, enabling their applications in various next-generation thin-film devices. In this thesis, I present further advancement of centrifugation-based processing methods for emerging low-dimensional materials through systematic utilization of previously explored surfactant systems, development of novel surfactant types, and study of correlation between the chemical structure of surfactants and the dispersion and optoelectronic properties of the nanomaterials. First, I employ an iterative density gradient ultracentrifugation with a combination of anionic surfactants and addition of excess counter-ions to achieve isolation of novel diameter species of semiconducting single-walled carbon nanotubes. The purification of carbon nanotubes with simultaneous, ultrahigh-purity refinement in electronic type and diameter distribution leads to collaborative studies on heat distribution characteristics and diameter-dependent direct current and radio frequency performances in monodisperse carbon nanotube thin-film transistors. Next, I develop the use of non-ionic polymeric surfactants for centrifugation-based processes. Specifically, I utilize polypropylene and polyethylene oxide-based block copolymers with density

  12. Low Dimensional Oxygen Vacancy Ordering and Diffusion in SrCrO3-δ

    NASA Astrophysics Data System (ADS)

    Ong, Phuong Vu; Sushko, Peter V.; Physical; Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 9 Team

    Oxygen vacancies (VO) are known to strongly affect the structure and electronic properties of complex oxides. An ability to control local concentration and spatial distribution of the vacancies, as well as stability and dimensionality of their aggregates, would enable generating novel materials functionalities, such as fast directional charge and mass transport. We use first-principles simulations to study mechanisms of formation, aggregation and diffusion of oxygen vacancies in SrCrO3-δ. We found that at low concentrations oxygen vacancies have a tendency to aggregate into one-dimensional (1D) structures oriented along a [110] direction. These VO clusters induce rearrangements of oxide ions and conversion of Cr-centered perovskite lattice octahedra into tetrahedra. In turn, aggregation of these 1D VO clusters enables formation of 2D vacancy aggregates parallel to the (111) plane of the cubic perovskite lattice. We provide a simple physical picture for the formation and growth of such low-dimensional VO-structures. Moreover, we found mechanisms of VO migration which enable a diffusion and expansion of the VO-structures with low activation energies. Our results elucidate the atomic-scale mechanisms of efficient and reversible reduction and oxidation process observed in this material. These mechanisms could be extended to other complex oxides and used in design of high performance electrolytes and cathodes.

  13. Probing Electronic, Structural, and Charge Transfer Properties of Organic Semiconductor/Inorganic Oxide Interfaces Using Field-Effect Transistors

    NASA Astrophysics Data System (ADS)

    Spalenka, Josef Wade

    Interfaces between organic semiconductors and inorganic oxides provide the functionality for devices including field-effect transistors (FETs) and organic photovoltaics. Organic FETs are sensitive to the physical structure and electronic properties of the few molecular layers of material at the interface between the semiconducting channel and the gate dielectric, and provide quantitative information such as the field-effect mobility of charge carriers and the concentration of trapped charge. In this thesis, FET interfaces between organic small-molecule semiconductors and SiO2, and donor/acceptor interfaces between organic small-molecules and the wide bandgap semiconductor ZnO are studied using electrical measurements of field-effect transistor devices. Monolayer-scale films of dihexyl sexithiophene are shown to have higher hole mobility than other monolayer organic semiconductors, and the origin of the high mobility is discussed. Studies of the crystal structure of the monolayer using X-ray structural probes and atomic force microscopy reveal the crystal structure is different in the monolayer regime compared to thicker films and bulk crystals. Progress and remaining challenges are discussed for in situ X-ray diffraction studies of the dynamic changes in the local crystal structure in organic monolayers due to charge carriers generated during the application of electric fields from the gate electrode in working FETs. Studies were conducted of light sensitive organic/inorganic interfaces that are modified with organic molecules grafted to the surface of ZnO nanoparticles and thin films. These interfaces are models for donor/acceptor interfaces in photovoltaics. The process of exciton dissociation at the donor/acceptor interface was sensitive to the insulating or semiconducting molecules grafted to the ZnO, and the photoinduced charge transfer process is measured by the threshold voltage shift of FETs during illumination. Charge transfer between light sensitive donor

  14. Solution processable semiconductor thin films: Correlation between morphological, structural, optical and charge transport properties

    NASA Astrophysics Data System (ADS)

    Isik, Dilek

    This Ph.D. thesis is a result of multidisciplinary research bringing together fundamental concepts in thin film engineering, materials science, materials processing and characterization, electrochemistry, microfabrication, and device physics. Experiments were conducted by tackling scientific problems in the field of thin films and interfaces, with the aim to correlate the morphology, crystalline structure, electronic structure of thin films with the functional properties of the films and the performances of electronic devices based thereon. Furthermore, novel strategies based on interfacial phenomena at electrolyte/thin film interfaces were explored and exploited to control the electrical conductivity of the thin films. Three main chemical systems were the object of the studies performed during this Ph.D., two types of organic semiconductors (azomethine-based oligomers and polymers and soluble pentacene derivatives) and one metal oxide semiconductor (tungsten trioxide, WO3). To explore the morphological properties of the thin films, atomic force microscopy was employed. The morphological properties were further investigated by hyperspectral fluorescence microscopy and tentatively correlated to the charge transport properties of the films. X-ray diffraction (Grazing incidence XRD, GIXRD) was used to investigate the crystallinity of the film and the effect of the heat treatment on such crystallinity, as well as to understand the molecular arrangement of the organic molecules in the thin film. The charge transport properties of the films were evaluated in thin film transistor configuration. For electrolyte gated thin film transistors, time dependent transient measurements were conducted, in parallel to more conventional transistor characterizations, to explore the specific effects played on the gating by the anion and cation constituting the electrolyte. The capacitances of the electrical double layers at the electrolyte/WO3 interface were obtained from

  15. Impedance analysis of Al{sub 2}O{sub 3}/H-terminated diamond metal-oxide-semiconductor structures

    SciTech Connect

    Liao, Meiyong; Liu, Jiangwei; Imura, Masataka; Koide, Yasuo; Sang, Liwen; Coathup, David; Li, Jiangling; Ye, Haitao

    2015-02-23

    Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al{sub 2}O{sub 3} is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed.

  16. Structural and phase transformation of A{sup III}B{sup V}(100) semiconductor surface in interaction with selenium

    SciTech Connect

    Bezryadin, N. N.; Kotov, G. I. Kuzubov, S. V.

    2015-03-15

    Surfaces of GaAs(100), InAs(100), and GaP(100) substrates thermally treated in selenium vapor have been investigated by transmission electron microscopy and electron probe X-ray microanalysis. Some specific features and regularities of the formation of A{sub 3}{sup III}B{sub 4}{sup VI} (100)c(2 × 2) surface phases and thin layers of gallium or indium selenides A{sub 2}{sup III}B{sub 3}{sup VI} (100) on surfaces of different A{sup III}B{sup V}(100) semiconductors are discussed within the vacancy model of surface atomic structure.

  17. Translation symmetry breakdown in low-dimensional lattices of pentagonal rings.

    PubMed

    Avramov, Paul; Demin, Victor; Luo, Ming; Choi, Cheol Ho; Sorokin, Pavel B; Yakobson, Boris; Chernozatonskii, Leonid

    2015-11-19

    The mechanism of translation symmetry breakdown in newly proposed low-dimensional carbon pentagon-constituted nanostructures (e.g., pentagraphene) with multiple sp(2)/sp(3) sublattices was studied by GGA DFT, DFTB, and model potential approaches. It was found that finite nanoclusters suffer strong uniform unit cell bending followed by breaking of crystalline lattice linear translation invariance caused by structural mechanical stress. It was shown that 2D sp(2)/sp(3) nanostructures are correlated transition states between two symmetrically equivalent bent structures. At DFT level of theory the distortion energy of the flakes (7.5 × 10(-2) eV/atom) is much higher the energy of dynamical stabilization of graphene. Strong mechanical stress prevents stabilization of the nanoclusters on any type of supports by either van der Waals or covalent bonding and should lead to formation of pentatubes, nanorings, or nanofoams rather than infinite nanoribbons or nanosheets. Formation of two-layered pentagraphene structures leads to compensation of the stress and stabilization of flat finite pentaflakes. PMID:26582476

  18. Energy resolved electrochemical impedance spectroscopy for electronic structure mapping in organic semiconductors

    NASA Astrophysics Data System (ADS)

    Nádaždy, V.; Schauer, F.; Gmucová, K.

    2014-10-01

    We introduce an energy resolved electrochemical impedance spectroscopy method to map the electronic density of states (DOS) in organic semiconductor materials. The method consists in measurement of the charge transfer resistance of a semiconductor/electrolyte interface at a frequency where the redox reactions determine the real component of the impedance. The charge transfer resistance value provides direct information about the electronic DOS at the energy given by the electrochemical potential of the electrolyte, which can be adjusted using an external voltage. A simple theory for experimental data evaluation is proposed, along with an explanation of the corresponding experimental conditions. The method allows mapping over unprecedentedly wide energy and DOS ranges. Also, important DOS parameters can be determined directly from the raw experimental data without the lengthy analysis required in other techniques. The potential of the proposed method is illustrated by tracing weak bond defect states induced by ultraviolet treatment above the highest occupied molecular orbital in a prototypical σ-conjugated polymer, poly[methyl(phenyl)silylene]. The results agree well with those of our previous DOS reconstruction by post-transient space-charge-limited-current spectroscopy, which was, however, limited to a narrow energy range. In addition, good agreement of the DOS values measured on two common π-conjugated organic polymer semiconductors, polyphenylene vinylene and poly(3-hexylthiophene), with the rather rare previously published data demonstrate the accuracy of the proposed method.

  19. Energy resolved electrochemical impedance spectroscopy for electronic structure mapping in organic semiconductors

    SciTech Connect

    Nádaždy, V. Gmucová, K.; Schauer, F.

    2014-10-06

    We introduce an energy resolved electrochemical impedance spectroscopy method to map the electronic density of states (DOS) in organic semiconductor materials. The method consists in measurement of the charge transfer resistance of a semiconductor/electrolyte interface at a frequency where the redox reactions determine the real component of the impedance. The charge transfer resistance value provides direct information about the electronic DOS at the energy given by the electrochemical potential of the electrolyte, which can be adjusted using an external voltage. A simple theory for experimental data evaluation is proposed, along with an explanation of the corresponding experimental conditions. The method allows mapping over unprecedentedly wide energy and DOS ranges. Also, important DOS parameters can be determined directly from the raw experimental data without the lengthy analysis required in other techniques. The potential of the proposed method is illustrated by tracing weak bond defect states induced by ultraviolet treatment above the highest occupied molecular orbital in a prototypical σ-conjugated polymer, poly[methyl(phenyl)silylene]. The results agree well with those of our previous DOS reconstruction by post-transient space-charge-limited-current spectroscopy, which was, however, limited to a narrow energy range. In addition, good agreement of the DOS values measured on two common π-conjugated organic polymer semiconductors, polyphenylene vinylene and poly(3-hexylthiophene), with the rather rare previously published data demonstrate the accuracy of the proposed method.

  20. Semiconductor device PN junction fabrication using optical processing of amorphous semiconductor material

    SciTech Connect

    Sopori, Bhushan; Rangappan, Anikara

    2014-11-25

    Systems and methods for semiconductor device PN junction fabrication are provided. In one embodiment, a method for fabricating an electrical device having a P-N junction comprises: depositing a layer of amorphous semiconductor material onto a crystalline semiconductor base, wherein the crystalline semiconductor base comprises a crystalline phase of a same semiconductor as the amorphous layer; and growing the layer of amorphous semiconductor material into a layer of crystalline semiconductor material that is epitaxially matched to the lattice structure of the crystalline semiconductor base by applying an optical energy that penetrates at least the amorphous semiconductor material.

  1. Epitaxial MoS2/GaN structures to enable vertical 2D/3D semiconductor heterostructure devices

    NASA Astrophysics Data System (ADS)

    Ruzmetov, D.; Zhang, K.; Stan, G.; Kalanyan, B.; Eichfeld, S.; Burke, R.; Shah, P.; O'Regan, T.; Crowne, F.; Birdwell, A. G.; Robinson, J.; Davydov, A.; Ivanov, T.

    MoS2/GaN structures are investigated as a building block for vertical 2D/3D semiconductor heterostructure devices that utilize a 3D substrate (GaN) as an active component of the semiconductor device without the need of mechanical transfer of the 2D layer. Our CVD-grown monolayer MoS2 has been shown to be epitaxially aligned to the GaN lattice which is a pre-requisite for high quality 2D/3D interfaces desired for efficient vertical transport and large area growth. The MoS2 coverage is nearly 50 % including isolated triangles and monolayer islands. The GaN template is a double-layer grown by MOCVD on sapphire and allows for measurement of transport perpendicular to the 2D layer. Photoluminescence, Raman, XPS, Kelvin force probe microscopy, and SEM analysis identified high quality monolayer MoS2. The MoS2/GaN structures electrically conduct in the out-of-plane direction and across the van der Waals gap, as measured with conducting AFM (CAFM). The CAFM current maps and I-V characteristics are analyzed to estimate the MoS2/GaN contact resistivity to be less than 4 Ω-cm2 and current spreading in the MoS2 monolayer to be approx. 1 μm in diameter. Epitaxial MoS2/GaN heterostructures present a promising platform for the design of energy-efficient, high-speed vertical devices incorporating 2D layered materials with 3D semiconductors.

  2. Local atomic and magnetic structure of dilute magnetic semiconductor (Ba ,K ) (Zn,Mn ) 2As2

    NASA Astrophysics Data System (ADS)

    Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; Banerjee, Soham; Chen, Bijuan; Jin, Changqing; Feygenson, Mikhail; Uemura, Yasutomo J.; Billinge, Simon J. L.

    2016-09-01

    We have studied the atomic and magnetic structure of the dilute ferromagnetic semiconductor system (Ba ,K )(Zn ,Mn )2As2 through atomic and magnetic pair distribution function analysis of temperature-dependent x-ray and neutron total scattering data. We detected a change in curvature of the temperature-dependent unit cell volume of the average tetragonal crystallographic structure at a temperature coinciding with the onset of ferromagnetic order. We also observed the existence of a well-defined local orthorhombic structure on a short length scale of ≲5 Å , resulting in a rather asymmetrical local environment of the Mn and As ions. Finally, the magnetic PDF revealed ferromagnetic alignment of Mn spins along the crystallographic c axis, with robust nearest-neighbor ferromagnetic correlations that exist even above the ferromagnetic ordering temperature. We discuss these results in the context of other experiments and theoretical studies on this system.

  3. Expressive body movement responses to music are coherent, consistent, and low dimensional.

    PubMed

    Amelynck, Denis; Maes, Pieter-Jan; Martens, Jean Pierre; Leman, Marc

    2014-12-01

    Embodied music cognition stresses the role of the human body as mediator for the encoding and decoding of musical expression. In this paper, we set up a low dimensional functional model that accounts for 70% of the variability in the expressive body movement responses to music. With the functional principal component analysis, we modeled individual body movements as a linear combination of a group average and a number of eigenfunctions. The group average and the eigenfunctions are common to all subjects and make up what we call the commonalities. An individual performance is then characterized by a set of scores (the individualities), one score per eigenfunction. The model is based on experimental data which finds high levels of coherence/consistency between participants when grouped according to musical education. This shows an ontogenetic effect. Participants without formal musical education focus on the torso for the expression of basic musical structure (tempo). Musically trained participants decode additional structural elements in the music and focus on body parts having more degrees of freedom (such as the hands). Our results confirm earlier studies that different body parts move differently along with the music. PMID:25415938

  4. Expressive body movement responses to music are coherent, consistent, and low dimensional.

    PubMed

    Amelynck, Denis; Maes, Pieter-Jan; Martens, Jean Pierre; Leman, Marc

    2014-12-01

    Embodied music cognition stresses the role of the human body as mediator for the encoding and decoding of musical expression. In this paper, we set up a low dimensional functional model that accounts for 70% of the variability in the expressive body movement responses to music. With the functional principal component analysis, we modeled individual body movements as a linear combination of a group average and a number of eigenfunctions. The group average and the eigenfunctions are common to all subjects and make up what we call the commonalities. An individual performance is then characterized by a set of scores (the individualities), one score per eigenfunction. The model is based on experimental data which finds high levels of coherence/consistency between participants when grouped according to musical education. This shows an ontogenetic effect. Participants without formal musical education focus on the torso for the expression of basic musical structure (tempo). Musically trained participants decode additional structural elements in the music and focus on body parts having more degrees of freedom (such as the hands). Our results confirm earlier studies that different body parts move differently along with the music.

  5. Comparison of the electronic structure of amorphous versus crystalline indium gallium zinc oxide semiconductor: structure, tail states and strain effects

    NASA Astrophysics Data System (ADS)

    de Jamblinne de Meux, A.; Pourtois, G.; Genoe, J.; Heremans, P.

    2015-11-01

    We study the evolution of the structural and electronic properties of crystalline indium gallium zinc oxide (IGZO) upon amorphization by first-principles calculation. The bottom of the conduction band (BCB) is found to be constituted of a pseudo-band of molecular orbitals that resonate at the same energy on different atomic sites. They display a bonding character between the s orbitals of the metal sites and an anti-bonding character arising from the interaction between the oxygen and metal s orbitals. The energy level of the BCB shifts upon breaking of the crystal symmetry during the amorphization process, which may be attributed to the reduction of the coordination of the cationic centers. The top of the valence band (TVB) is constructed from anti-bonding oxygen p orbitals. In the amorphous state, they have random orientation, in contrast to the crystalline state. This results in the appearance of localized tail states in the forbidden gap above the TVB. Zinc is found to play a predominant role in the generation of these tail states, while gallium hinders their formation. Last, we study the dependence of the fundamental gap and effective mass of IGZO on mechanical strain. The variation of the gap under strain arises from the enhancement of the anti-bonding interaction in the BCB due to the modification of the length of the oxygen-metal bonds and/or to a variation of the cation coordination. This effect is less pronounced for the amorphous material compared to the crystalline material, making amorphous IGZO a semiconductor of choice for flexible electronics. Finally, the effective mass is found to increase upon strain, in contrast to regular materials. This counterintuitive variation is due to the reduction of the electrostatic shielding of the cationic centers by oxygen, leading to an increase of the overlaps between the metal orbitals at the origin of the delocalization of the BCB. For the range of strain typically met in flexible electronics, the induced

  6. Method for restoring the resistance of indium oxide semiconductors after heating while in sealed structures

    DOEpatents

    Seager, Carleton H.; Evans, Jr., Joseph Tate

    1998-01-01

    A method for counteracting increases in resistivity encountered when Indium Oxide resistive layers are subjected to high temperature annealing steps during semiconductor device fabrication. The method utilizes a recovery annealing step which returns the Indium Oxide layer to its original resistivity after a high temperature annealing step has caused the resistivity to increase. The recovery anneal comprises heating the resistive layer to a temperature between 100.degree. C. and 300.degree. C. for a period of time that depends on the annealing temperature. The recovery is observed even when the Indium Oxide layer is sealed under a dielectric layer.

  7. Electronic Structure and Valence of Mn impurities in III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Schulthess, Thomas C.

    2003-11-01

    Mn doped III-V semiconductors have recently become very popular materials since they are ferromagnetic at reasonably high temperatures and in some cases show carrier induced magnetism, where the Curie temperature can be altered by changes in the carrier concentration. It is expected that these materials will play an important role in Spintronics devices. Substitutional Mn impurities in III-V semiconductors can acquire either a divalent or a trivalent configuration. For example, it is generally accepted that Mn in GaAs is in a (d^5+h) configuration with five occupied Mn d-orbitals and a delocalized hole in the valence band. In contrast, Mn in GaN is believed to be in a d^4 configuration with a deep impurity state that has d-character. But there have recently been some discussions about the possibility of having some Mn ion in GaN assuming a divalent (d^5+h) type configuration. In order to achieve carrier induced ferromagnetism, the desired state of the Mn ions in III-V semiconductors is the (d^5+h) configuration. We have therefore performed ab-initio calculations of the Mn valence when it substitutes Ga in various III-V semiconductor hosts. We use the self-interaction corrected local spin density (SIC-LSD) method which is able to treat localized impurity orbitals properly. In particular we find that the method is capable of predicting the (d^5+h) state of Mn in GaAs. For Mn in GaP and GaN the calculations predict a trivalent d^4 state in the idealized system. The energy differences between d^4 and (d^5+h) configurations in GaP are, however, very small. Introduction of defects or donors does change the valence of Mn in GaP, favoring the divalent state under certain circumstances. Work done in collaboration with W. Temmerman and S. Szotek, Daresbury Laboratory, G. M. Stocks, ORNL, and W. H. Butler, MINT Center University of Alabama. This work supported by the Defense Advanced Research Agency and by DOE Office of Science trough ASCR/MICS and BES/DMSE under Contract No

  8. Method for restoring the resistance of indium oxide semiconductors after heating while in sealed structures

    DOEpatents

    Seager, C.H.; Evans, J.T. Jr.

    1998-11-24

    A method is described for counteracting increases in resistivity encountered when Indium Oxide resistive layers are subjected to high temperature annealing steps during semiconductor device fabrication. The method utilizes a recovery annealing step which returns the Indium Oxide layer to its original resistivity after a high temperature annealing step has caused the resistivity to increase. The recovery anneal comprises heating the resistive layer to a temperature between 100 C and 300 C for a period of time that depends on the annealing temperature. The recovery is observed even when the Indium Oxide layer is sealed under a dielectric layer. 1 fig.

  9. Multi-line triggering and interdigitated electrode structure for photoconductive semiconductor switches

    DOEpatents

    Mar, Alan; Zutavern, Fred J.; Loubriel, Guillermo

    2007-02-06

    An improved photoconductive semiconductor switch comprises multiple-line optical triggering of multiple, high-current parallel filaments between the switch electrodes. The switch can also have a multi-gap, interdigitated electrode for the generation of additional parallel filaments. Multi-line triggering can increase the switch lifetime at high currents by increasing the number of current filaments and reducing the current density at the contact electrodes in a controlled manner. Furthermore, the improved switch can mitigate the degradation of switching conditions with increased number of firings of the switch.

  10. Low dimensional GaAs/air vertical microcavity lasers

    SciTech Connect

    Gessler, J.; Steinl, T.; Fischer, J.; Höfling, S.; Schneider, C.; Kamp, M.; Mika, A.; Sęk, G.; Misiewicz, J.

    2014-02-24

    We report on the fabrication of gallium arsenide (GaAs)/air distributed Bragg reflector microresonators with indium gallium arsenide quantum wells. The structures are studied via momentum resolved photoluminescence spectroscopy which allows us to investigate a pronounced optical mode quantization of the photonic dispersion. We can extract a length parameter from these quantized states whose upper limit can be connected to the lateral physical extension of the microcavity via analytical calculations. Laser emission from our microcavity under optical pumping is observed in power dependent investigations.

  11. Fabrication, structural characterization and photoluminescence of Q-1D semiconductor ZnS hierarchical nanostructures.

    PubMed

    Zhang, Jun; Yang, Yongdong; Jiang, Feihong; Li, Jianping; Xu, Baolong; Wang, Xichang; Wang, Shumei

    2006-05-28

    Quasi-one-dimensional semiconductor ZnS hierarchical nanostructures have been fabricated by thermal evaporation of a mixture of ZnS nanopowders and Sn powders. Sn nanoparticles are located at or close to the tips of the nanowires (or nanoneedles) and served as the catalyst for quasi-one-dimensional ZnS nanostructure growth by a vapour-liquid-solid mechanism. The morphology and microstructure of the ZnS hierarchical nanostructures were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The results show that a large number of ZnS nanoneedles were formed on the outer shells of a long and straight ZnS axial nanowire. The ZnS axial nanowires grow along the [001] direction, and ZnS nanoneedles are aligned over the surface of the ZnS nanowire in the radial direction. The room temperature photoluminescence spectrum exhibits a UV weak emission centred at 337 nm and one blue emission centred at 436 nm from the as-synthesized single-crystalline semiconductor ZnS hierarchical nanostructures. PMID:21727526

  12. Reflection of Transverse Waves in a Structure "Dielectric-Piezoelectric Semiconductor with Current"

    NASA Astrophysics Data System (ADS)

    Lyamshev, L. M.; Shevyakhov, N. S.

    2000-05-01

    Reflection of a plane monochromatic transverse wave by the boundary of the acoustic contact of a dielectric with a hexagonal piezoelectric semiconductor in the presence of a longitudinal charge drift is treated in the small-signal approximation within the framework of the hydrodynamic description of a charge carrier plasma. A procedure of selecting the branches with allowance for the conversion of the quasi-acoustic mode (a refracted transverse wave) into plasma-acoustic disturbances, both in-leaking at the boundary or out-leaking from it, is proposed for the determination of the solution under the conditions of a supersonic drift and “overcritical” angles of incidence. Beyond the restrictions of White’s theory of ultrasonic wave propagation in piezoelectric semiconductors, it is demonstrated that this technique removes the defects of the solutions obtained earlier in the form of discontinuities in angular dependences of the modulus of the reflection coefficient of a transverse wave in the vicinity of the “critical” angle of incidence and leads to a solution that does not contain a resonance singularity of a polar type.

  13. Structural and optical properties of silicon metal-oxide-semiconductor light-emitting devices

    NASA Astrophysics Data System (ADS)

    Xu, Kaikai; Zhang, Zhengyuan; Zhang, Zhengping

    2016-01-01

    A silicon p-channel metal oxide semiconductor field-effect transistor (Si-PMOSFET) that is fully compatible with the standard complementary metal oxide semiconductor process is investigated based on the phenomenon of optical radiation observed in the reverse-biased p-n junction in the Si-PMOSFET device. The device can be used either as a two-terminal silicon diode light-emitting device (Si-diode LED) or as a three-terminal silicon gate-controlled diode light-emitting device (Si gate-controlled diode LED). It is seen that the three-terminal operating mode could provide much higher power transfer efficiency than the two-terminal operating mode. A new solution based on the concept of a theoretical quantum efficiency model combined with calculated results is proposed for interpreting the evidence of light intensity reduction at high operating voltages. The Si-LED that can be easily integrated into CMOS fabrication process is an important step toward optical interconnects.

  14. Evidence of low dimensional chaos in renal blood flow control in genetic and experimental hypertension

    NASA Astrophysics Data System (ADS)

    Yip, K.-P.; Marsh, D. J.; Holstein-Rathlou, N.-H.

    1995-01-01

    We applied a surrogate data technique to test for nonlinear structure in spontaneous fluctuations of hydrostatic pressure in renal tubules of hypertensive rats. Tubular pressure oscillates at 0.03-0.05 Hz in animals with normal blood pressure, but the fluctuations become irregular with chronic hypertension. Using time series from rats with hypertension we produced surrogate data sets to test whether they represent linearly correlated noise or ‘static’ nonlinear transforms of a linear stochastic process. The correlation dimension and the forecasting error were used as discriminating statistics to compare surrogate with experimental data. The results show that the original experimental time series can be distinguished from both linearly and static nonlinearly correlated noise, indicating that the nonlinear behavior is due to the intrinsic dynamics of the system. Together with other evidence this strongly suggests that a low dimensional chaotic attractor governs renal hemodynamics in hypertension. This appears to be the first demonstration of a transition to chaotic dynamics in an integrated physiological control system occurring in association with a pathological condition.

  15. Nontrivial ferrimagnetism on the low-dimensional quantum spin systems with frustration

    NASA Astrophysics Data System (ADS)

    Shimokawa, Tokuro; Nakano, Hiroki; Sakai, Toru

    2013-03-01

    In low-dimensional quantum spin systems with frustration, nontrivial magnetisms often occur due to strong quantum fluctuation. Ferrimagnetism in non-frustrated systems is well-known to occur from the mechanism based on the Marshall-Lieb-Mattis theorem. This type of ferrimagnetism is called ``Lieb-Mattis (LM) type.'' Recently, the occurrence of nontrivial ferrimagnetism has been reported in some one-dimensional Heisenberg spin systems with frustration, in which the continuous change of spontaneous magnetization and the incommensurate modulation in local magnetization are observed. This type is called ``non-Lieb-Mattis (NLM) type.'' In this study, we tackle a problem whether the NLM ferrimagnetism occurs or not in higher dimensional systems. We investigate the S =1/2 Heisenberg models on the spatially anisotropic two-dimensional (2D) kagome lattice and on the quasi-one-dimensional (Q1D) kagome strip lattices by the numerical diagonalization and density matrix renormalization group methods. The Q1D models share the same structure in their inner part with the spatially anisotropic 2D kagome lattice; we examine two cases with respect to strip width. We will discuss the relationship between the ground-state properties of the Q1D lattices and those of the 2D lattice.

  16. Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure

    NASA Astrophysics Data System (ADS)

    Naumov, P.; Barkalov, O.; Mirhosseini, H.; Felser, C.; Medvedev, S. A.

    2016-09-01

    Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4–300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range.

  17. Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure.

    PubMed

    Naumov, P; Barkalov, O; Mirhosseini, H; Felser, C; Medvedev, S A

    2016-09-28

    Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4-300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range. PMID:27439023

  18. Atomic and electronic structures evolution of the narrow band gap semiconductor Ag2Se under high pressure

    NASA Astrophysics Data System (ADS)

    Naumov, P.; Barkalov, O.; Mirhosseini, H.; Felser, C.; Medvedev, S. A.

    2016-09-01

    Non-trivial electronic properties of silver telluride and other chalcogenides, such as the presence of a topological insulator state, electronic topological transitions, metallization, and the possible emergence of superconductivity under pressure have attracted attention in recent years. In this work, we studied the electronic properties of silver selenide (Ag2Se). We performed direct current electrical resistivity measurements, in situ Raman spectroscopy, and synchrotron x-ray diffraction accompanied by ab initio calculations to explore pressure-induced changes to the atomic and electronic structure of Ag2Se. The temperature dependence of the electrical resistivity was measured up to 30 GPa in the 4-300 K temperature interval. Resistivity data showed an unusual increase in the thermal energy gap of phase I, which is a semiconductor under ambient conditions. Recently, a similar effect was reported for the 3D topological insulator Bi2Se3. Raman spectroscopy studies revealed lattice instability in phase I indicated by the softening of observed vibrational modes with pressure. Our hybrid functional band structure calculations predicted that phase I of Ag2Se would be a narrow band gap semiconductor, in accordance with experimental results. At a pressure of ~7.5 GPa, Ag2Se underwent a structural transition to phase II with an orthorhombic Pnma structure. The temperature dependence of the resistivity of Ag2Se phase II demonstrated its metallic character. Ag2Se phase III, which is stable above 16.5 GPa, is also metallic according to the resistivity data. No indication of the superconducting transition is found above 4 K in the studied pressure range.

  19. Heat capacity and sound velocities of low dimensional Fermi gases

    NASA Astrophysics Data System (ADS)

    Salas, P.; Solis, M. A.

    2014-03-01

    We report the heat capacity ratio and sound velocities for an interactionless Fermi gas immersed in periodic structures such as penetrable multilayers or multitubes created by one (planes) or two perpendicular (tubes) external Dirac comb potentials. The isobaric specific heat of the fermion gas presents the dimensional crossover previously observed in the isochoric specific heat - from 3D to 2D or to 1D -. The quotient between the two quantities has a prominent bump related to the confinement, and as the temperature increases, it goes towards the monoatomic classical gas value 5/3. We present the isothermal and the adiabatic sound velocities of the fermion gas which show anomalous behavior at temperatures below TF due to the dimensionality of the system, while at higher temperatures again we recover the behavior of a classical Fermi gas. Furthermore, as the temperature goes to zero the sound velocity has a finite value, as expected.

  20. First Principles Electronic Structure of Mn doped GaAs, GaP, and GaN Semiconductors

    SciTech Connect

    Schulthess, Thomas C; Temmerman, Walter M; Szotek, Zdzislawa; Svane, Axel; Petit, Leon

    2007-01-01

    We present first-principles electronic structure calculations of Mn doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn-d levels in GaAs. We find good agreement between computed values and estimates from photoemisison experiments.

  1. High-frequency spin-valve effect in a ferromagnet-semiconductor-ferromagnet structure based on precession of the injected spins.

    PubMed

    Bratkovsky, A M; Osipov, V V

    2004-03-01

    A new mechanism of magnetoresistance, based on tunneling emission of spin-polarized electrons from ferromagnets (FM) into semiconductors (S) and precession of electron spin in the semiconductor layer under external magnetic field, is described. The FM-S-FM structure is considered, which includes very thin heavily doped (delta-doped) layers at FM-S interfaces. At certain parameters the structure is highly sensitive at room temperature to variations of the field with frequencies up to 100 GHz. The current oscillates with the field, and its relative amplitude is determined only by the spin polarizations of FM-S junctions. PMID:15089518

  2. Superresolution Structure Optical Disk with Semiconductor-Doped Glass Mask Layer Containing CdSe Nanoparticles

    NASA Astrophysics Data System (ADS)

    Yeh, Tung‑Ti; Wang, Jr‑Hau; Hsieh, Tsung‑Eong; Shieh, Han‑Ping D.

    2006-02-01

    In this work, we demonstrate a distinct superresolution phenomenon and signal properties of an optical disk with a semiconductor-doped glass (SDG) mask layer containing CdSe nanoparticles. It was found that the 69 nm marks could be consistently retrieved at reading power (Pr) = 4 mW with carrier-to-noise ratio (CNR) = 13.56 dB. The signals were clearly resolved with CNRs nearly equal to 40 dB at Pr=4 mW when the recorded marks were larger than 100 nm. The cyclability test indicated that the CdSe-SiO2 SDG layer might serve as a stable and reliable optical mask layer in 105 readout cycles.

  3. Multianalyte biosensor based on pH-sensitive ZnO electrolyte-insulator-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Haur Kao, Chyuan; Chen, Hsiang; Ling Lee, Ming; Chun Liu, Che; Ueng, Herng-Yih; Cheng Chu, Yu; Jie Chen, Yu; Ming Chang, Kow

    2014-05-01

    Multianalyte electrolyte-insulator-semiconductor (EIS) sensors with a ZnO sensing membrane annealed on silicon substrate for use in pH sensing were fabricated. Material analyses were conducted using X-ray diffraction and atomic force microscopy to identify optimal treatment conditions. Sensing performance for various ions of Na+, K+, urea, and glucose was also tested. Results indicate that an EIS sensor with a ZnO membrane annealed at 600 °C exhibited good performance with high sensitivity and a low drift rate compared with all other reported ZnO-based pH sensors. Furthermore, based on well-established pH sensing properties, pH-ion-sensitive field-effect transistor sensors have also been developed for use in detecting urea and glucose ions. ZnO-based EIS sensors show promise for future industrial biosensing applications.

  4. Simulations of terahertz pulse emission from thin-film semiconductor structures

    NASA Astrophysics Data System (ADS)

    Semichaevsky, Andrey

    The photo-Dember effect is the formation of transient electric dipoles due to the interaction of semiconductors with ultrashort optical pulses. Typically the optically-induced dipole moments vary on the ns- or ps- scales, leading to the emission of electromagnetic pulses with terahertz (THz) bandwidths. One of the applications of the photo-Dember effect is a photoconductive dipole antenna (PDA). This work presents a computational model of a PDA based on Maxwell's equations coupled to the Boltzmann transport equation. The latter is solved semiclassically for the doped GaAs using a continuum approach. The emphasis is on the accurate prediction of the emitted THz pulse shape and bandwidth, particularly when materials are doped with a rare-earth metal such as erbium or terbium that serve as carrier recombination centers. Field-dependent carrier mobility is determined from particle-based simulations. Some of the previous experimental results are used as a basis for comparison with our model.

  5. 3D mapping of nanoscale electric potentials in semiconductor structures using electron-holographic tomography

    NASA Astrophysics Data System (ADS)

    Wolf, Daniel; Lubk, Axel; Prete, Paola; Lovergine, Nico; Lichte, Hannes

    2016-09-01

    Off-axis electron holography (EH) is a powerful method for mapping projected electric potentials, such as built-in potentials in semiconductor devices, in two dimensions (2D) at nanometer resolution. However, not well-defined thickness profiles, surface effects, and composition changes of the sample under investigation complicate the interpretation of the projected potentials. Here, we demonstrate how these problems can be overcome by combining EH with tomographic techniques, that is, electron holographic tomography (EHT), reconstructing electric potentials in 3D. We present EHT reconstructions of an n-type MOSFET including its dopant-related built-in potentials inside the device, as well as of a GaAs/AlGaAs core-multishell nanowire containing a 5 nm thick quantum well tube.

  6. Structural and optical properties of thin films of Cu(In,Ga)Se2 semiconductor compounds

    NASA Astrophysics Data System (ADS)

    Mudryi, A. V.; Gremenok, V. F.; Karotki, A. V.; Zalesski, V. B.; Yakushev, M. V.; Luckert, F.; Martin, R.

    2010-07-01

    The chemical composition of Cu(In,Ga)Se2 (CIGS) semiconductor compounds is analyzed by local x-ray spectral microanalysis and scanning Auger electron spectroscopy. X-ray diffraction analysis reveals a difference in the predominant orientation of CIGS films depending on the technological conditions under which they are grown. The chemical composition is found to have a strong effect on the shift in the self-absorption edge of CIGS compounds. It is shown that a change in the relative proportion of Ga and In in CIGS semiconducting compounds leads to a change in the band gap Eg for this material in the 1.05-1.72 eV spectral range at 4.2 K.

  7. Multianalyte biosensor based on pH-sensitive ZnO electrolyte–insulator–semiconductor structures

    SciTech Connect

    Haur Kao, Chyuan; Chun Liu, Che; Ueng, Herng-Yih; Chen, Hsiang Cheng Chu, Yu; Jie Chen, Yu; Ling Lee, Ming; Ming Chang, Kow

    2014-05-14

    Multianalyte electrolyte–insulator–semiconductor (EIS) sensors with a ZnO sensing membrane annealed on silicon substrate for use in pH sensing were fabricated. Material analyses were conducted using X-ray diffraction and atomic force microscopy to identify optimal treatment conditions. Sensing performance for various ions of Na{sup +}, K{sup +}, urea, and glucose was also tested. Results indicate that an EIS sensor with a ZnO membrane annealed at 600 °C exhibited good performance with high sensitivity and a low drift rate compared with all other reported ZnO-based pH sensors. Furthermore, based on well-established pH sensing properties, pH-ion-sensitive field-effect transistor sensors have also been developed for use in detecting urea and glucose ions. ZnO-based EIS sensors show promise for future industrial biosensing applications.

  8. Self-Interaction Corrections to the Electronic Structure of II-VI and III-V Nitride Semiconductors

    NASA Astrophysics Data System (ADS)

    Pollmann, J.

    1998-03-01

    II-VI and group-III nitride semiconductors have paramount technological potential for applications in micro- and optoelectronics. A most accurate description of their bulk electronic structure as a basis for studying defect properties, band-edge properties in respective ternary or quaternary alloys and electronic properties of their surfaces and interfaces is of major importance, therefore. Standard LDA band-structure calculations for these wide-band-gap compounds using nonlocal normconserving pseudopotentials yield gap energies and semicore d-band positions that are largely at variance with experimental data. Actually, InN even turns out to be a semimetal with a negative gap of about --0.4 eV in standard LDA, in contrast to the experimental gap of 1.9 eV. To improve the theoretical basis for the above mentioned studies, we have developed self-interaction- and relaxation-corrected pseudopotentials (SIRC-PPs) which are very efficient and physically well-founded. The properties of the constituent atoms are incorporated in these SIRC-PPs as accurately as possible from the start by taking atomic SIC contributions and electronic relaxation in the atoms fully into account. By this construction, we arrive at very useful pseudopotentials and effective one-particle Hamiltonians for the solids that can readily be employed in ab-initio LDA codes. This approach is computationally not more involved than any LDA calculation and, nevertheless, overcomes to a large extent the above mentioned shortcomings of standard LDA calculations employing 'state-of-the-art' pseudopotentials. Applications of our approach to II-VI and group-III nitride semiconductors have shown very gratifying results. The approach has also proven very useful for Hg-chalcogenides, as well as, for Ag- and Cu-halides. The calculations yield band structures, d-band positions, gap energies, densities of states, lattice constants, bulk moduli and effective masses in very good agreement with experiment. Due to the

  9. Semiconductor active plasmonics

    NASA Astrophysics Data System (ADS)

    Mendach, Stefan; Nötzel, Richard

    2013-12-01

    Plasmonics is a research area in nanophotonics attracting increasing interest due to the potential applications in sensing and detecting, sub-wavelength confinement of light, integrated circuits, and many others. In particular, when plasmonic structures such as metal nanostructures or highly doped semiconductor particles are combined with active semiconductor materials and nanostructures, novel exciting physics and applications arise. This special section on semiconductor active plasmonics covers several of the most important and complementary directions in the field. First is the modification of the optical properties of a semiconductor nanostructure due to the close proximity of a metallic film or nanostructure. These arise from the formation hybrid plasmon/exciton states and may lead to enhanced spontaneous emission rates, directional far field emission patterns, strong coupling phenomena, and many more. Second is the realization of sub-wavelength scale nanolasers by coupling a semiconductor gain medium with a plasmonic metallic cavity. Particular emphasis is given on the major technical challenges in the fabrication of these nanolasers, such as device patterning, surface passivation, and metal deposition. While the above topics address mainly active structures and devices operating in the visible or near-infrared wavelength region, in the third, the enhanced THz extinction by periodic arrays of semiconductor particles is discussed. This is based on the build-up of surface plasmon resonances in the doped semiconductor particles which can be resonantly coupled and widely tuned by the carrier density in the semiconductor. We believe these highly diverse aspects give insight into the wide variety of new physics and applications that semiconductor active plasmonics is offering. Finally, we would like to thank the IOP editorial staff, in particular Alice Malhador, for their support, and we would also like to thank the contributors for their efforts and participation

  10. Structural stability at high pressure, electronic, and magnetic properties of BaFZnAs: A new candidate of host material of diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Bi-Juan, Chen; Zheng, Deng; Xian-Cheng, Wang; Shao-Min, Feng; Zhen, Yuan; Si-Jia, Zhang; Qing-Qing, Liu; Chang-Qing, Jin

    2016-07-01

    The layered semiconductor BaFZnAs with the tetragonal ZrCuSiAs-type structure has been successfully synthesized. Both the in-situ high-pressure synchrotron x-ray diffraction and the high-pressure Raman scattering measurements demonstrate that the structure of BaFZnAs is stable under pressure up to 17.5 GPa at room temperature. The resistivity and the magnetic susceptibility data show that BaFZnAs is a non-magnetic semiconductor. BaFZnAs is recommended as a candidate of the host material of diluted magnetic semiconductor. Project supported by the National Natural Science Foundation of China and Project of Ministry of Science and Technology of China.

  11. A method to characterize the dielectric and interfacial properties of metal-insulator-semiconductor structures by microwave measurement

    NASA Astrophysics Data System (ADS)

    Lue, Hang-Ting; Tseng, Tseung-Yuen; Huang, Guo-Wei

    2002-04-01

    We have developed a method to investigate the dielectric and interfacial properties of gate dielectric thin films by microwave measurement. Ba0.5Sr0.5TiO3 (BST) thin films were deposited on 10 Ω cm (normal) and 10 k Ω cm [high-resistivity, (HR)] silicon substrates at the same time by rf magnetron sputtering. For the BST/HR-silicon, coplanar waveguides (CPW) were fabricated and measured at microwave frequencies with thru-reflect-line calibration while capacitance (C-V) measurements were carried out for BST/normal silicon. From the phase change of CPW transmission line and the maximum capacitance in C-V measurement, the dielectric constants of both the BST thin film and interface layer can be determined. Furthermore, the behaviors of insertion loss versus bias voltage were investigated. The results indicate that our method can provide useful information to study the dielectric and interfacial properties of metal-insulator-semiconductor structures.

  12. Experimental methods of post-growth tuning of the excitonic fine structure splitting in semiconductor quantum dots

    PubMed Central

    2012-01-01

    Deterministic sources of polarization entangled photon pairs on demand are considered as important building blocks for quantum communication technology. It has been demonstrated that semiconductor quantum dots (QDs), which exhibit a sufficiently small excitonic fine structure splitting (FSS) can be used as triggered, on-chip sources of polarization entangled photon pairs. As-grown QDs usually do not have the required values of the FSS, making the availability of post-growth tuning techniques highly desired. This article reviews the effect of different post-growth treatments and external fields on the FSS such as thermal annealing, magnetic fields, the optical Stark effect, electric fields, and anisotropic stress. As a consequence of the tuning of the FSS, for some tuning techniques a rotation of the polarization of the emitted light is observed. The joint modification of polarization orientation and FSS can be described by an anticrossing of the bright excitonic states. PMID:22726724

  13. Quenched disorder forbids discontinuous transitions in nonequilibrium low-dimensional systems.

    PubMed

    Villa Martín, Paula; Bonachela, Juan A; Muñoz, Miguel A

    2014-01-01

    Quenched disorder affects significantly the behavior of phase transitions. The Imry-Ma-Aizenman-Wehr-Berker argument prohibits first-order or discontinuous transitions and their concomitant phase coexistence in low-dimensional equilibrium systems in the presence of random fields. Instead, discontinuous transitions become rounded or even continuous once disorder is introduced. Here we show that phase coexistence and first-order phase transitions are also precluded in nonequilibrium low-dimensional systems with quenched disorder: discontinuous transitions in two-dimensional systems with absorbing states become continuous in the presence of quenched disorder. We also study the universal features of this disorder-induced criticality and find them to be compatible with the universality class of the directed percolation with quenched disorder. Thus, we conclude that first-order transitions do not exist in low-dimensional disordered systems, not even in genuinely nonequilibrium systems with absorbing states.

  14. Low-Dimensional Polyoxometalate Molecules/Tantalum Oxide Hybrids for Non-Volatile Capacitive Memories.

    PubMed

    Balliou, Angelika; Papadimitropoulos, Giorgos; Skoulatakis, George; Kennou, Stella; Davazoglou, Dimitrios; Gardelis, Spiros; Glezos, Nikos

    2016-03-23

    Transition-metal-oxide hybrids composed of high surface-to-volume ratio Ta2O5 matrices and a molecular analogue of transition metal oxides, tungsten polyoxometalates ([PW12O40](3-)), are introduced herein as a charge storage medium in molecular nonvolatile capacitive memory cells. The polyoxometalate molecules are electrostatically self-assembled on a low-dimensional Ta2O5 matrix, functionalized with an aminosilane molecule with primary amines as the anchoring moiety. The charge trapping sites are located onto the metal framework of the electron-accepting molecular entities as well as on the molecule/oxide interfaces which can immobilize negatively charged mobile oxygen vacancies. The memory characteristics of this novel nanocomposite were tested using no blocking oxide for extraction of structure-specific characteristics. The film was formed on top of the 3.1 nm-thick SiO2/n-Si(001) substrates and has been found to serve as both SiO2/Si interface states' reducer (i.e., quality enhancer) and electron storage medium. The device with the polyoxometalates sandwiched between two Ta2O5 films results in enhanced internal scattering of carriers. Thanks to this, it exhibits a significantly larger memory window than the one containing the plain hybrid and comparable retention time, resulting in a memory window of 4.0 V for the write state and a retention time around 10(4) s without blocking medium. Differential distance of molecular trapping centers from the cell's gate and electronic coupling to the space charge region of the underlying Si substrate were identified as critical parameters for enhanced electron trapping for the first time in such devices. Implementing a numerical electrostatic model incorporating structural and electronic characteristics of the molecular nodes derived from scanning probe and spectroscopic characterization, we are able to interpret the hybrid's electrical response and gain some insight into the electrostatics of the trapping medium. PMID

  15. The role of stress and diffusion in structure formation in semiconductors

    NASA Astrophysics Data System (ADS)

    Bouville, Mathieu

    This dissertation addresses two aspects of the theory and simulation of stress-diffusion coupling in semiconductors. The first part is a study of the role of kinetics in the formation of pits in stressed thin films. The second part describes how atomic-scale calculations can be used to extract the thermodynamic and elastic properties of point-defects. For both aspects, there exists an interaction between phenomena at the atomic and macroscopic scales and the formation of both point-defects and surface features depends on the stress state of the system. Recently, pit nucleation has been observed in a variety of semiconductor thin films. We present a model for pit nucleation in which the adatom concentration plays a central role in controlling the morphological development of the surface. Although pits relieve elastic energy more efficiently than islands, pit nucleation can be prevented by a high adatom concentration. Three-dimensional islands act as adatom sinks and the lower adatom density in their vicinity promotes pit nucleation. Thermodynamic considerations predict several different growth regimes in which pits may nucleate at different stages of growth depending on the growth conditions and materials system. When kinetics are taken into account, the model predicts a wide range of possible morphologies: planar films, islands alone, island nucleation followed by pit nucleation, and pits alone. The model shows good agreement with experimental observations in III-V systems given the uncertainties in quantifying experimental parameters such as the surface energy. The same stresses which lead to the nucleation of surface features can have a significant effect on the stability of dopant profiles by altering diffusivities and by inducing chemical potential gradients. We perform empirical calculations regarding a simple model point-defect, a vacancy in the Stillinger Weber model of silicon. In the context of these calculations we devise a method to extract the strength

  16. Diode having trenches in a semiconductor region

    DOEpatents

    Palacios, Tomas Apostol; Lu, Bin; Matioli, Elison de Nazareth

    2016-03-22

    An electrode structure is described in which conductive regions are recessed into a semiconductor region. Trenches may be formed in a semiconductor region, such that conductive regions can be formed in the trenches. The electrode structure may be used in semiconductor devices such as field effect transistors or diodes. Nitride-based power semiconductor devices are described including such an electrode structure, which can reduce leakage current and otherwise improve performance.

  17. Structure and method for controlling band offset and alignment at a crystalline oxide-on-semiconductor interface

    DOEpatents

    McKee, Rodney A.; Walker, Frederick J.

    2003-11-25

    A crystalline oxide-on-semiconductor structure and a process for constructing the structure involves a substrate of silicon, germanium or a silicon-germanium alloy and an epitaxial thin film overlying the surface of the substrate wherein the thin film consists of a first epitaxial stratum of single atomic plane layers of an alkaline earth oxide designated generally as (AO).sub.n and a second stratum of single unit cell layers of an oxide material designated as (A'BO.sub.3).sub.m so that the multilayer film arranged upon the substrate surface is designated (AO).sub.n (A'BO.sub.3).sub.m wherein n is an integer repeat of single atomic plane layers of the alkaline earth oxide AO and m is an integer repeat of single unit cell layers of the A'BO.sub.3 oxide material. Within the multilayer film, the values of n and m have been selected to provide the structure with a desired electrical structure at the substrate/thin film interface that can be optimized to control band offset and alignment.

  18. Photoelectric energy conversion of plasmon-generated hot carriers in metal-insulator-semiconductor structures.

    PubMed

    García de Arquer, F Pelayo; Mihi, Agustín; Kufer, Dominik; Konstantatos, Gerasimos

    2013-04-23

    Plasmonic excitation in metals has received great attention for light localization and control of light-matter interactions at the nanoscale with a plethora of applications in absorption enhancement, surface-enhanced Raman scattering, or biosensing. Electrically active plasmonic devices, which had remained underexplored, have recently become a growing field of interest. In this report we introduce a metal-insulator-semiconductor heterostructure for plasmo-electric energy conversion, a novel architecture to harvest hot-electrons derived from plasmonic excitations. We demonstrate external quantum efficiency (EQE) of 4% at 460 nm using a Ag nanostructured electrode and EQE of 1.3% at 550 nm employing a Au nanostructured electrode. The insulator interfacial layer has been found to play a crucial role in interface passivation, a requisite in photovoltaic applications to achieving both high open-circuit voltages (0.5 V) and fill-factors (0.5), but its introduction simultaneously modifies hot-electron injection and transport. We investigate the influence passivation has on these processes for different material configurations, and characterize different types of transport depending on the initial plasmon energy band, reporting power conversion efficiencies of 0.03% for nanopatterned silver electrodes. PMID:23495769

  19. Structural disorder and magnetism in the spin-gapless semiconductor CoFeCrAl

    NASA Astrophysics Data System (ADS)

    Choudhary, Renu; Kharel, Parashu; Valloppilly, Shah R.; Jin, Yunlong; O'Connell, Andrew; Huh, Yung; Gilbert, Simeon; Kashyap, Arti; Sellmyer, D. J.; Skomski, Ralph

    2016-05-01

    Disordered CoFeCrAl and CoFeCrSi0.5Al0.5 alloys have been investigated experimentally and by first-principle calculations. The melt-spun and annealed samples all exhibit Heusler-type superlattice peaks, but the peak intensities indicate a substantial degree of B2-type chemical disorder. Si substitution reduces the degree of this disorder. Our theoretical analysis also considers several types of antisite disorder (Fe-Co, Fe-Cr, Co-Cr) in Y-ordered CoFeCrAl and partial substitution of Si for Al. The substitution transforms the spin-gapless semiconductor CoFeCrAl into a half-metallic ferrimagnet and increases the half-metallic band gap by 0.12 eV. Compared CoFeCrAl, the moment of CoFeCrSi0.5Al0.5 is predicted to increase from 2.01 μB to 2.50 μB per formula unit, in good agreement with experiment.

  20. Simulation of plasma based semiconductor processing using block structured locally refined grids

    SciTech Connect

    Wake, D.D.

    1998-01-01

    We have described a new numerical method for plasma simulation. Calculations have been presented which show that the method is accurate and suggest the regimes in which the method provides savings in CPU time and memory requirements. A steady state simulation of a four centimeter domain was modeled with sheath scale (150 microns) resolution using only 40 grid points. Simulations of semiconductor processing equipment have been performed which imply the usefulness of the method for engineering applications. It is the author`s opinion that these accomplishments represent a significant contribution to plasma simulation and the efficient numerical solution of certain systems of non-linear partial differential equations. More work needs to be done, however, for the algorithm to be of practical use in an engineering environment. Despite our success at avoiding the dielectric relaxation timestep restrictions the algorithm is still conditionally stable and requires timesteps which are relatively small. This represents a prohibitive runtime for steady state solutions on high resolution grids. Current research suggests that these limitations may be overcome and the use of much larger timesteps will be possible.

  1. Isotopically controlled semiconductors

    SciTech Connect

    Haller, E.E.

    2004-11-15

    A review of recent research involving isotopically controlled semiconductors is presented. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, can be considered the most important one for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples. Manuel Cardona, the longtime editor-in-chief of Solid State Communications has been and continues to be one of the major contributors to this field of solid state physics and it is a great pleasure to dedicate this review to him.

  2. Low dimensional homeochaos in coevolving host-parasitoid dimorphic populations: Extinction thresholds under local noise

    NASA Astrophysics Data System (ADS)

    Sardanyés, Josep

    2011-10-01

    A discrete time model describing the population dynamics of coevolution between host and parasitoid haploid populations with a dimorphic matching allele coupling is investigated under both determinism and stochastic population disturbances. The role of the properties of the attractors governing the survival of both populations is analyzed considering equal mutation rates and focusing on host and parasitoid growth rates involving chaos. The purely deterministic model reveals a wide range of ordered and chaotic Red Queen dynamics causing cyclic and aperiodic fluctuations of haplotypes within each species. A Ruelle-Takens-Newhouse route to chaos is identified by increasing both host and parasitoid growth rates. From the bifurcation diagram structure and from numerical stability analysis, two different types of chaotic sets are roughly differentiated according to their size in phase space and to their largest Lyapunov exponent: the Confined and Expanded attractors. Under the presence of local population noise, these two types of attractors have a crucial role in the survival of both coevolving populations. The chaotic confined attractors, which have a low largest positive Lyapunov exponent, are shown to involve a very low extinction probability under the influence of local population noise. On the contrary, the expanded chaotic sets (with a higher largest positive Lyapunov exponent) involve higher host and parasitoid extinction probabilities under the presence of noise. The asynchronies between haplotypes in the chaotic regime combined with low dimensional homeochaos tied to the confined attractors is suggested to reinforce the long-term persistence of these coevolving populations under the influence of stochastic disturbances. These ideas are also discussed in the framework of spatially-distributed host-parasitoid populations.

  3. Probing Carrier Transport and Structure-Property Relationship of Highly Ordered Organic Semiconductors at the Two-Dimensional Limit.

    PubMed

    Zhang, Yuhan; Qiao, Jingsi; Gao, Si; Hu, Fengrui; He, Daowei; Wu, Bing; Yang, Ziyi; Xu, Bingchen; Li, Yun; Shi, Yi; Ji, Wei; Wang, Peng; Wang, Xiaoyong; Xiao, Min; Xu, Hangxun; Xu, Jian-Bin; Wang, Xinran

    2016-01-01

    One of the basic assumptions in organic field-effect transistors, the most fundamental device unit in organic electronics, is that charge transport occurs two dimensionally in the first few molecular layers near the dielectric interface. Although the mobility of bulk organic semiconductors has increased dramatically, direct probing of intrinsic charge transport in the two-dimensional limit has not been possible due to excessive disorders and traps in ultrathin organic thin films. Here, highly ordered single-crystalline mono- to tetralayer pentacene crystals are realized by van der Waals (vdW) epitaxy on hexagonal BN. We find that the charge transport is dominated by hopping in the first conductive layer, but transforms to bandlike in subsequent layers. Such an abrupt phase transition is attributed to strong modulation of the molecular packing by interfacial vdW interactions, as corroborated by quantitative structural characterization and density functional theory calculations. The structural modulation becomes negligible beyond the second conductive layer, leading to a mobility saturation thickness of only ∼3  nm. Highly ordered organic ultrathin films provide a platform for new physics and device structures (such as heterostructures and quantum wells) that are not possible in conventional bulk crystals.

  4. Impact of graphene-graphite films on electrical properties of Al2O3 metal-insulator-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Choi, Kyeong-Keun; Kee, Jong; Park, Chan-Gyung; Kim, Deok-kee

    2016-08-01

    The diffusion barrier property of directly grown graphene-graphite films between Al2O3 films and Si substrates was evaluated using metal-insulator-semiconductor (MIS) structures. The roughness, morphology, sheet resistance, Raman spectrum, chemical composition, and breakdown field strength of the films were investigated after rapid thermal annealing. About 2.5-nm-thick graphene-graphite films effectively blocked the formation of the interfacial layer between Al2O3 films and Si, which was confirmed by the decreased breakdown field strength of graphene-graphite film structures. After annealing at 975 °C for 90 s, the increase in the mean breakdown field strength of the structure with the ˜2.5-nm-thick graphene-graphite film was about 91% (from 8.7 to 16.6 MV/cm), while that without the graphene-graphite film was about 187% (from 11.2 to 32.1 MV/cm). Si atom diffusion into Al2O3 films was reduced by applying the carbon-based diffusion barrier.

  5. Impact of graphene–graphite films on electrical properties of Al2O3 metal–insulator–semiconductor structure

    NASA Astrophysics Data System (ADS)

    Choi, Kyeong-Keun; Kee, Jong; Park, Chan-Gyung; Kim, Deok-kee

    2016-08-01

    The diffusion barrier property of directly grown graphene–graphite films between Al2O3 films and Si substrates was evaluated using metal–insulator–semiconductor (MIS) structures. The roughness, morphology, sheet resistance, Raman spectrum, chemical composition, and breakdown field strength of the films were investigated after rapid thermal annealing. About 2.5-nm-thick graphene–graphite films effectively blocked the formation of the interfacial layer between Al2O3 films and Si, which was confirmed by the decreased breakdown field strength of graphene–graphite film structures. After annealing at 975 °C for 90 s, the increase in the mean breakdown field strength of the structure with the ∼2.5-nm-thick graphene–graphite film was about 91% (from 8.7 to 16.6 MV/cm), while that without the graphene–graphite film was about 187% (from 11.2 to 32.1 MV/cm). Si atom diffusion into Al2O3 films was reduced by applying the carbon-based diffusion barrier.

  6. Semiconductor sensors

    NASA Technical Reports Server (NTRS)

    Gatos, Harry C. (Inventor); Lagowski, Jacek (Inventor)

    1977-01-01

    A semiconductor sensor adapted to detect with a high degree of sensitivity small magnitudes of a mechanical force, presence of traces of a gas or light. The sensor includes a high energy gap (i.e., .about. 1.0 electron volts) semiconductor wafer. Mechanical force is measured by employing a non-centrosymmetric material for the semiconductor. Distortion of the semiconductor by the force creates a contact potential difference (cpd) at the semiconductor surface, and this cpd is determined to give a measure of the force. When such a semiconductor is subjected to illumination with an energy less than the energy gap of the semiconductors, such illumination also creates a cpd at the surface. Detection of this cpd is employed to sense the illumination itself or, in a variation of the system, to detect a gas. When either a gas or light is to be detected and a crystal of a non-centrosymmetric material is employed, the presence of gas or light, in appropriate circumstances, results in a strain within the crystal which distorts the same and the distortion provides a mechanism for qualitative and quantitative evaluation of the gas or the light, as the case may be.

  7. Synchrotron Studies of Quantum Emergence in Non-Low Dimensional Materials Final Report

    SciTech Connect

    James W. Allen

    2011-08-26

    This document is the final report of research performed under U.S. DOE Award Number DE-FG02-07ER46379, entitled Synchrotron Studies of Quantum Emergence in Non-Low Dimensional Materials. It covers the full period of the award, from June 1, 2007 through May 31, 2011.

  8. Iii-V Compound Semiconductor Integrated Charge Storage Structures for Dynamic and Non-Volatile Memory Elements

    NASA Astrophysics Data System (ADS)

    Hetherington, Dale Laird

    This thesis presents an investigation into a novel group of GaAs charge storage devices. These devices, which are an integration of bipolar and junction field effect transistor structures were conceived, designed, fabricated, and tested within this study. The purpose was to analyse new types of charge storage devices, which are suitable for fabrication and lead to the development of dynamic and nonvolatile memories in III-V compound semiconductors. Currently, III-V semiconductor storage devices consist only of capacitors, where data is destroyed during reading and electrical erasure is difficult. In this work, four devices types were demonstrated that exhibit nondestructive reading, and three of the prototypes can be electrically erased. All types use the junction field effect transistor (JFET) for charge sensing, with each having different bipolar or epitaxial layer structure controlling the junction gate. The bottom epitaxial layer in each case served as the JFET channel. Two of the device types have three alternately doped layers, while the remaining two have four alternately doped layers. In all cases, removal of majority carriers from the middle layers constitutes stored charge. The missing carriers deplete the current carrying a region of the JFET channel. Drain current of the JFET becomes an indicator of stored charge. The basic function of each JFET memory element type is independent of interchanging n- and p- type doping within the structure type. Some performance advantage can be realized, however, by sensing with an n-type channel as compared to p- type due to increased carrier mobility. All device types exhibit storage time characteristics of order ten seconds. Devices are constructed in epitaxial layers grown by molecular beam epitaxy (MBE) reactors. The design of the epitaxial layers is an intrinsic part, together with the electrical design, of the storage device concept. These concepts are implemented first with photolithography masks which are used

  9. Two-body physics in quasi-low-dimensional atomic gases under spin-orbit coupling

    NASA Astrophysics Data System (ADS)

    Wang, Jing-Kun; Yi, Wei; Zhang, Wei

    2016-06-01

    One of the most dynamic directions in ultracold atomic gas research is the study of low-dimensional physics in quasi-low-dimensional geometries, where atoms are confined in strongly anisotropic traps. Recently, interest has significantly intensified with the realization of synthetic spin-orbit coupling (SOC). As a first step toward understanding the SOC effect in quasi-low-dimensional systems, the solution of two-body problems in different trapping geometries and different types of SOC has attracted great attention in the past few years. In this review, we discuss both the scattering-state and the bound-state solutions of two-body problems in quasi-one and quasi-two dimensions. We show that the degrees of freedom in tightly confined dimensions, in particular with the presence of SOC, may significantly affect system properties. Specifically, in a quasi-one-dimensional atomic gas, a one-dimensional SOC can shift the positions of confinement-induced resonances whereas, in quasitwo- dimensional gases, a Rashba-type SOC tends to increase the two-body binding energy, such that more excited states in the tightly confined direction are occupied and the system is driven further away from a purely two-dimensional gas. The effects of the excited states can be incorporated by adopting an effective low-dimensional Hamiltonian having the form of a two-channel model. With the bare parameters fixed by two-body solutions, this effective Hamiltonian leads to qualitatively different many-body properties compared to a purely low-dimensional model.

  10. Strained-bond semiconductors

    NASA Astrophysics Data System (ADS)

    Dow, John D.

    1994-05-01

    Theories of strained-bond semiconductors and superconductors have been developed that promise to have significant impact on future electronic devices of interest to the Air Force. These include: (1) development of a theory of high-temperature superconductivity based on the idea of strained-layer superlattices, (2) elucidation of the physics of doping in Type-2 semiconductor superlattices, which is now central to the development of high-speed field-effect transistors, (3) a theory of dimerization and reconstruction on (001) semiconductor surfaces, (4) theory of Mobius transforms as applied to physics and remote sensing, (5) new understanding of how defects affect the vibrational properties of semiconductors, (6) new methods of efficiently computing the trajectories of atoms in semiconductors by a priori molecular dynamics, (7) elucidation of the criteria affecting quantum-well luminescence from Si, (8) models of the effects of vacancies in large-gap Al(x)Ga(1-x)N alloys, (9) physics of rare-earth-doped silicon, (10) models of Co adsorption to silicon surfaces, (11) theories of how defects affect the properties of large band-gap superlattices, and (12) models of the effects of electronic structure on the properties of semiconductors.

  11. Two-dimensional device modeling and analysis of GaInAs metal-semiconductor-metal photodiode structures

    NASA Astrophysics Data System (ADS)

    Averin, S.; Sachot, R.; Hugi, J.; de Fays, M.; Ilegems, M.

    1996-08-01

    A two-dimensional self-consistent time-dependent simulation technique has been developed to investigate electron-hole transport processes in the active region of metal-semiconductor-metal (MSM) interdigitated photodiode structures and to analyze their high-speed response. The distribution of the electric field inside the MSM device is determined by numerically solving the two-dimensional Poisson's equation by the modified fast elliptic solver method. A set of superparticles photogenerated at a particular wavelength is analyzed with a given initial distribution of the potential and given boundary conditions, and the evolution of the particles is traced in time through the active region of the MSM device. Circuit loading, electric field effects in the MSM structure with various finger separations, background doping, carrier trapping, and recombination are included in the simulation program. Owing to miniaturization of devices, the classical scaling laws lose their validity while various performance degrading effects appear. The simulations show that the main problem in MSM devices with a small contact separation is the low electric field penetration depth. This results in different electron and hole collection rates and in a poor response time. The trade-off between the high-speed response and the internal quantum efficiency is examined and ways to improve the high-speed response are indicated. Modeling results are compared with experimental data on Ga0.47In0.53As based MSM photodiodes.

  12. Magnetic domain structure study of a ferromagnetic semiconductor using a home-made low temperature scanning Hall probe microscope

    NASA Astrophysics Data System (ADS)

    Kweon, Seongsoo; de Lozanne, Alex; Samarth, Nitin

    2008-03-01

    GaMnAs is a ferromagnetic semiconductor actively studied for basic research and for the possibility of application to spintronic devices. To study the local magnetic properties of this material the magnetic force microscope (MFM) is too invasive (by affecting the domains in the sample) or not sensitive enough (due to the weak magnetization of the GaMnAs). We have therefore built a scanning Hall probe microscope (SHPM) to complement our MFM studies. We use a lock-in amplifier to supply a bias current of 1-10μA and to measure the Hall voltage. We calibrated this home-made SHPM with a computer hard disk sample. Comparing images of this sample obtained with MFM and SHPM we show that our home-made SHPM is operating well. We observed the domain structure of 30-nm thick Ga0.94Mn0.06As epilayer grown on a 700nm-thick In0.13Ga0.87As buffer covering a GaAs substrate. We will study the magnetic domain structure as a function of temperature with varying external magnetic fields.

  13. Tunable electronic structure in dilute magnetic semiconductor Sr{sub 3}SnO/c-YSZ/Si (001) epitaxial heterostructures

    SciTech Connect

    Lee, Y. F.; Narayan, J.; Schwartz, J.

    2014-10-28

    We report a systematic study of the structural, physical, and chemical properties of epitaxial thin films of emerging dilute magnetic semiconductor (DMS) Sr{sub 3}SnO (SSO) integrated with Si (100) prepared by various post-growth annealing treatments. The transport properties of these films are primarily governed by oxygen vacancies and the results are explained with the variable-range hopping model. The increased oxygen vacancy concentration generated by post-growth vacuum annealing results in a shorter hopping distance and reduced hopping energy and Coulomb gap, leading to lower resistivity; oxygen annealing shows the opposite effects. The work function ranges from 4.54 to 4.02 eV and shows a negative linear relationship with oxygen vacancy concentration, accompanied by a 0.42 eV shift in the surface Fermi level. The transport and ultraviolet photoelectron spectroscopy probes agree quantitatively on measurement of the resistivity and surface electronic structure. The results provide a direct and consistent explanation that the property changes in the bulk and at the surface are primarily attributed to oxygen vacancies, which are believed to be the carriers in the SSO thin films. The ability to manipulate the work function and oxygen vacancy concentration in epitaxial DMS SSO thin films offers great potential for the development of spintronic devices.

  14. Local structure of amorphous GaN{sub 1-x}As{sub x} semiconductor alloys across the composition range

    SciTech Connect

    Levander, A. X.; Dubon, O. D.; Wu, J.; Yu, K. M.; Liliental-Weber, Z.; Walukiewicz, W.; Novikov, S. V.; Foxon, C. T.

    2013-06-28

    Typically only dilute (up to {approx}10%) highly mismatched alloys can be grown due to the large differences in atomic size and electronegativity of the host and the alloying elements. We have overcome the miscibility gap of the GaN{sub 1-x}As{sub x} system using low temperature molecular beam epitaxy. In the intermediate composition range (0.10 < x < 0.75), the resulting alloys are amorphous. To gain a better understanding of the amorphous structure, the local environment of the As and Ga atoms was investigated using extended x-ray absorption fine structure (EXAFS). The EXAFS analysis shows a high concentration of dangling bonds compared to the crystalline binary endpoint compounds of the alloy system. The disorder parameter was larger for amorphous films compared to crystalline references, but comparable with other amorphous semiconductors. By examining the Ga local environment, the dangling bond density and disorder associated with As-related and N-related bonds could be decoupled. The N-related bonds had a lower dangling bond density and lower disorder.

  15. Instability analysis of charges trapped in the oxide of metal-ultra thin oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Aziz, A.; Kassmi, K.; Maimouni, R.; Olivié, F.; Sarrabayrouse, G.; Martinez, A.

    2005-09-01

    In this paper, we present the theoretical and experimental results of the influence of a charge trapped in ultra-thin oxide of metal/ultra-thin oxide/semiconductor structures (MOS) on the I(Vg) current-voltage characteristics when the conduction is of the Fowler-Nordheim (FN) tunneling type. The charge, which is negative, is trapped near the cathode (metal/oxide interface) after constant current injection by the metal (Vg<0). Of particular interest is the influence on the Δ Vg(Vg) shift over the whole I(Vg) characteristic at high field (greater than the injection field (>12.5 MV/cm)). It is shown that the charge centroid varies linearly with respect to the voltage Vg. The behavior at low field (<12.5 MV/cm) is analyzed in référence A. Aziz, K. Kassmi, Ka. Kassmi, F. Olivié, Semicond. Sci. Technol. 19, 877 (2004) and considers that the trapped charge centroid is fixed. The results obtained make it possible to analyze the influence of the injected charge and the applied field on the centroid position of the trapped charge, and to highlight the charge instability in the ultra-thin oxide of MOS structures.

  16. Nonlinear optical response of semiconductor-nanocrystals-embedded photonic band gap structure

    SciTech Connect

    Liao, Chen; Zhang, Huichao; Tang, Luping; Zhou, Zhiqiang; Lv, Changgui; Cui, Yiping; Zhang, Jiayu

    2014-04-28

    Colloidal CdSe/ZnS core/shell nanocrystals (NCs), which were dispersed in SiO{sub 2} sol, were utilized to fabricate a SiO{sub 2}:NCs/TiO{sub 2} all-dielectric photonic band gap (PBG) structure. The third-order nonlinear refractive index (n{sub 2}) of the PBG structure was nearly triple of that of the SiO{sub 2}:NCs film due to the local field enhancement in the PBG structure. The photoinduced change in refractive index (Δn) could shift the PBG band edge, so the PBG structure would show significant transmission modification, whose transmission change was ∼17 folds of that of the SiO{sub 2}:NCs film. Under excitation of a 30 GW/cm{sup 2} femtosecond laser beam, a transmission decrease of 80% was realized.

  17. Experimental investigation of a shielded complementary Metal-Oxide Semiconductor (MOS) structure

    NASA Technical Reports Server (NTRS)

    Lin, H. C.; Halsor, J. L.

    1974-01-01

    A shielded integrated complimentary MOS transistor structure is described which is used to prevent field inversion in the region not occupied by the gates and which permits the use of a thinner field oxide, reduces the chip area, and has provision for simplified multilayer connections. The structure is used in the design of a static shift register and results in a 20% reduction in area.

  18. Low-dimensional hyperthin FeS2 nanostructures for efficient and stable hydrogen evolution electrocatalysis

    SciTech Connect

    Jasion, Daniel; Qiao, Qiao; Barforoush, Joseph M.; Zhu, Yimei; Ren, Shenqiang; Leonard, Kevin C.

    2015-10-05

    We report a scalable, solution-processing method for synthesizing low-dimensional hyperthin FeS2 nanostructures, and we show that 2D FeS2 disc nanostructures are an efficient and stable hydrogen evolution electrocatalyst. By changing the Fe:S ratio in the precursor solution, we were able to preferentially synthesize either 1D wire or 2D disc nanostructures. The 2D FeS2 disc structure has the highest electrocatalytic activity for the hydrogen evolution reaction, comparable to platinum in neutral pH conditions. Moreover, the ability of the FeS2 nanostructures to generate hydrogen was confirmed by scanning electrochemical microscopy, and the 2D disc nanostructures were able to generate hydrogen for over 125 h.

  19. Low-dimensional multiplexing: the magneto-optical Kerr effect in an individual FeCoCu nanowire

    NASA Astrophysics Data System (ADS)

    Torres-Torres, C.

    2016-01-01

    Due to their selective and fascinating effects, metallic nanoparticles have become a very significant topic for science. A modification in morphology and structure of low-dimensional materials can result in extraordinary ultrafast physical phenomena. New findings related to electronic, optical and magnetic processes have emerged from surface plasmon resonance excitations in nanoparticles. Moreover, multi-functional systems can be obtained from the integration of different elements in a nanostructured configuration. Recently, Palmero et al (2015 Nanotechnology 26 461001) have reported magneto-optical Kerr effect explorations in individual FeCuCo nanowires; the influence of tailored morphologies exhibited by particular samples was analyzed. An important magnetization reversal action was revealed and it was concluded that the demagnetization may be responsible for vortex domain wall propagation. The report can provide a solid base for future research and immediate applications in modern spintronics or magnetic data storage can be contemplated.

  20. Low-dimensional multiplexing: the magneto-optical Kerr effect in an individual FeCoCu nanowire.

    PubMed

    Torres-Torres, C

    2016-01-22

    Due to their selective and fascinating effects, metallic nanoparticles have become a very significant topic for science. A modification in morphology and structure of low-dimensional materials can result in extraordinary ultrafast physical phenomena. New findings related to electronic, optical and magnetic processes have emerged from surface plasmon resonance excitations in nanoparticles. Moreover, multi-functional systems can be obtained from the integration of different elements in a nanostructured configuration. Recently, Palmero et al (2015 Nanotechnology 26 461001) have reported magneto-optical Kerr effect explorations in individual FeCuCo nanowires; the influence of tailored morphologies exhibited by particular samples was analyzed. An important magnetization reversal action was revealed and it was concluded that the demagnetization may be responsible for vortex domain wall propagation. The report can provide a solid base for future research and immediate applications in modern spintronics or magnetic data storage can be contemplated. PMID:26650433

  1. Solution-based growth and structural characterization of homo- and heterobranched semiconductor nanowires.

    PubMed

    Dong, Angang; Tang, Rui; Buhro, William E

    2007-10-10

    Colloidal homobranched ZnSe nanowires (NWs) and heterobranched CdSe-ZnSe NWs are successfully synthesized by combining a sequential seeding strategy with the solution-liquid-solid (SLS) growth process. We have developed an efficient approach to deposit secondary bismuth nanoparticles onto the NW backbone to induce the subsequent SLS branch growth. The density, length, and diameter of branches are rationally controlled by varying reaction conditions. Structural characterization reveals that crystalline branches grow epitaxially from the backbone in both homo- and heterobranched NWs. Two different branching structures are observed in the CdSe-ZnSe heterobranched NWs, owing to the phase admixture, i.e., cubic and hexagonal crystal structures, coexisting in the CdSe NW backbones. These branched NWs with well-designed architectures are expected to have potential as three-dimensional building blocks in the fabrication of nanoscale electronics and photonics.

  2. Measuring and Predicting the Internal Structure of Semiconductor Nanocrystals through Raman Spectroscopy.

    PubMed

    Mukherjee, Prabuddha; Lim, Sung Jun; Wrobel, Tomasz P; Bhargava, Rohit; Smith, Andrew M

    2016-08-31

    Nanocrystals composed of mixed chemical domains have diverse properties that are driving their integration in next-generation electronics, light sources, and biosensors. However, the precise spatial distribution of elements within these particles is difficult to measure and control, yet profoundly impacts their quality and performance. Here we synthesized a unique series of 42 different quantum dot nanocrystals, composed of two chemical domains (CdS:CdSe), arranged in 7 alloy and (core)shell structural classes. Chemometric analyses of far-field Raman spectra accurately classified their internal structures from their vibrational signatures. These classifications provide direct insight into the elemental arrangement of the alloy as well as an independent prediction of fluorescence quantum yield. This nondestructive, rapid approach can be broadly applied to greatly enhance our capacity to measure, predict and monitor multicomponent nanomaterials for precise tuning of their structures and properties. PMID:27472011

  3. Examination of the local structure in composite and lowdimensional semiconductor by X-ray Absorption Spectroscopy

    SciTech Connect

    Lawniczak-Jablonska, K.; Demchenko, I.N.; Piskorska, E.; Wolska,A.; Talik, E.; Zakharov, D.N.; Liliental-Weber, Z.

    2006-09-25

    X-ray absorption methods have been successfully used to obtain quantitative information about local atomic composition of two different materials. X-ray Absorption Near Edge Structure analysis and X-Ray Photoelectron Spectroscopy allowed us to determine seven chemical compounds and their concentrations in c-BN composite. Use of Extended X-ray Absorption Fine Structure in combination with Transmission Electron Microscopy enabled us to determine the composition and size of buried Ge quantum dots. It was found that the quantum dots consisted out of pure Ge core covered by 1-2 monolayers of a layer rich in Si.

  4. Ellipsometric study of metal-organic chemically vapor deposited III-V semiconductor structures

    NASA Technical Reports Server (NTRS)

    Alterovitz, Samuel A.; Sekula-Moise, Patricia A.; Sieg, Robert M.; Drotos, Mark N.; Bogner, Nancy A.

    1992-01-01

    An ellipsometric study of MOCVD-grown layers of AlGaAs and InGaAs in thick films and strained layer complex structures is presented. It is concluded that the ternary composition of thick nonstrained layers can be accurately determined to within experimental errors using numerical algorithms. In the case of complex structures, thickness of all layers and the alloy composition of nonstrained layers can be determined simultaneously, provided that the correlations between parameters is no higher than 0.9.

  5. Structural and electronic properties of GaAs and GaP semiconductors

    SciTech Connect

    Rani, Anita; Kumar, Ranjan

    2015-05-15

    The Structural and Electronic properties of Zinc Blende phase of GaAs and GaP compounds are studied using self consistent SIESTA-code, pseudopotentials and Density Functional Theory (DFT) in Local Density Approximation (LDA). The Lattice Constant, Equillibrium Volume, Cohesive Energy per pair, Compressibility and Band Gap are calculated. The band gaps calcultated with DFT using LDA is smaller than the experimental values. The P-V data fitted to third order Birch Murnaghan equation of state provide the Bulk Modulus and its pressure derivatives. Our Structural and Electronic properties estimations are in agreement with available experimental and theoretical data.

  6. Investigation of the structure of an amorphous As-Se semiconductor system by relaxation methods

    SciTech Connect

    Castro, R. A. Bordovsky, V. A.; Grabko, G. I.; Taturevich, T. V.

    2011-12-15

    The results of a complex investigation into dark-current relaxation in the long-time region of an MIM structure based on an As-Se thin-film chalcogenide system are presented. The values of parameters describing the electronic processes ocurring in the contact layers of the investigated compounds are estimated. The coincidence of the nature of conductivity and charge-accumulation mechanisms is revealed. The relaxation-time distribution function is calculated, and its structural sensitivity to such technological factors as the change in the composition stoichiometry and the method for manufacturing experimental samples is established.

  7. Electronic structure and phase stability of oxide semiconductors: Performance of dielectric-dependent hybrid functional DFT, benchmarked against G W band structure calculations and experiments

    NASA Astrophysics Data System (ADS)

    Gerosa, Matteo; Bottani, Carlo Enrico; Caramella, Lucia; Onida, Giovanni; Di Valentin, Cristiana; Pacchioni, Gianfranco

    2015-04-01

    We investigate band gaps, equilibrium structures, and phase stabilities of several bulk polymorphs of wide-gap oxide semiconductors ZnO, TiO2,ZrO2, and WO3. We are particularly concerned with assessing the performance of hybrid functionals built with the fraction of Hartree-Fock exact exchange obtained from the computed electronic dielectric constant of the material. We provide comparison with more standard density-functional theory and GW methods. We finally analyze the chemical reduction of TiO2 into Ti2O3 , involving a change in oxide stoichiometry. We show that the dielectric-dependent hybrid functional is generally good at reproducing both ground-state (lattice constants, phase stability sequences, and reaction energies) and excited-state (photoemission gaps) properties within a single, fully ab initio framework.

  8. Structure and magnetic properties of Co-doped ZnO dilute magnetic semiconductors synthesized via hydrothermal method

    NASA Astrophysics Data System (ADS)

    Ghosh, K.; Kahol, P. K.; Bhamidipati, S.; Das, N.; Khanra, S.; Wanekaya, A.; Delong, R.

    2012-07-01

    Using X-Ray Diffraction, Scanning Electron Microscopy, and Superconducting Quantum Interference Device magnetometer, detailed structural, morphological, and magnetic properties are reported on undoped and cobalt doped ZnO Dilute Magnetic Semiconductors, which were prepared by the hydrothermal method. Synthesis of undoped ZnO and cobalt-doped ZnO nanorods was carried out using aqueous solutions of Zn(NO3)2ṡ6H2O, Co(C2H3OO)2ṡ4H2O, and NH4OH as hydrolytic catalyst. Samples of different sizes and shapes were synthesized by varying process parameters such as solution molarity (0.05M, 0.15M, 0.3M, 0.5M), pH of the precursors in the range 8-11, growth temperature (100°-130°C), growth time (3-6 hrs), and annealing time. Optimum synthesis parameters to grow ZnO and cobalt-doped ZnO nanorods have been obtained. These nanorods show paramagnetic-like behavior. Our results do not indicate ferromagnetism behavior, unlike reported in thin films and nanocrystalline samples. The differences are likely due to the possible role of nanoparticle size, shape, and different oxygen vacancy concentrations.

  9. Device modeling of perovskite solar cells based on structural similarity with thin film inorganic semiconductor solar cells

    NASA Astrophysics Data System (ADS)

    Minemoto, Takashi; Murata, Masashi

    2014-08-01

    Device modeling of CH3NH3PbI3-xCl3 perovskite-based solar cells was performed. The perovskite solar cells employ a similar structure with inorganic semiconductor solar cells, such as Cu(In,Ga)Se2, and the exciton in the perovskite is Wannier-type. We, therefore, applied one-dimensional device simulator widely used in the Cu(In,Ga)Se2 solar cells. A high open-circuit voltage of 1.0 V reported experimentally was successfully reproduced in the simulation, and also other solar cell parameters well consistent with real devices were obtained. In addition, the effect of carrier diffusion length of the absorber and interface defect densities at front and back sides and the optimum thickness of the absorber were analyzed. The results revealed that the diffusion length experimentally reported is long enough for high efficiency, and the defect density at the front interface is critical for high efficiency. Also, the optimum absorber thickness well consistent with the thickness range of real devices was derived.

  10. Electronic structure of MoO3 insertion layer at the interface between organic semiconductor and indium tin oxide (ITO).

    NASA Astrophysics Data System (ADS)

    Ding, Huanjun; Irfan, Irfan; Gao, Yongli; So, Frank

    2009-03-01

    We have investigated the electronic structure of the interfaces formed by inserting thin layer of MoO3 in between indium tin oxide (ITO) and different organic semiconductors, such as aluminium phthalocyanine chloride (AlPcCl) and copper phthalocyanine (CuPc), with photoemission and inverse photoemission spectroscopy (PES and IPES). The presents of MoO3 layer at the interface increases the workfunction dramatically. As a result, the organic HOMO is almost aligned with the Fermi level (Ef) at the AlPc-Cl/MoO3 interface. For thicker AlPc-Cl layers, gradual band bending is observed. However, the recovery of the HOMO is incomplete for AlPc-Cl thickness of 200 å, leading to a great reduction of the hole injection barrier compare to the case without MoO3. Similar situation is found in case of CuPc/MoO3, although the energy levels are almost fully recovered for CuPc film thicker than 200 å. The energy level alignment of these interfaces will be discussed to explain the improvement induced by MoO3 layer in device performance.

  11. Metal-Semiconductor Transition Concomitant with a Structural Transformation in Tetrahedrite Cu12Sb4S13

    NASA Astrophysics Data System (ADS)

    Tanaka, Hiromi I.; Suekuni, Koichiro; Umeo, Kazunori; Nagasaki, Toshiki; Sato, Hitoshi; Kutluk, Galif; Nishibori, Eiji; Kasai, Hidetaka; Takabatake, Toshiro

    2016-01-01

    The tetrahedrite Cu12Sb4S13 undergoes a metal-semiconductor transition (MST) at TMST = 85 K, whose mechanism remains elusive. Our Cu 2p X-ray photoemission spectroscopy study revealed the monovalent state of Cu ions occupying the two sites in this compound. This fact excludes the possibilities of previously proposed antiferromagnetic order and Jahn-Teller instability inherent in a divalent Cu system. A synchrotron X-ray diffraction study has revealed that the body-centered cubic cell of Cu12Sb4S13 transforms into a body-centered 2a × 2a × 2c tetragonal supercell below TMST, where the cell volume per formula unit expands by 0.25%. We have further studied pressure effects on the MST as well as the effects of the substitution of As for Sb. The application of pressure above 1 GPa completely inhibits the MST and leads to a metallic state, suggesting that the low-temperature structure with a larger volume becomes unstable under pressure. The As substitution also reduces the volume and suppresses the MST but the full substitution induces another transition at 124 K.

  12. Raman spectra of Cu2BIICIV X4 VI magnetic quaternary semiconductor compounds with tetragonal stannite type structure

    NASA Astrophysics Data System (ADS)

    Rincón, C.; Quintero, M.; Power, Ch.; Moreno, E.; Quintero, E.; Henao, J. A.; Macías, M. A.; Morocoima, M.

    2015-05-01

    A comparative study of the Raman spectra of Cu2BIICIV S4 VI and Cu2BIICIV Se4 VI (where B = Mn or Fe) magnetic quaternary semiconductor compounds with stannite-type structure (I 4 ¯ 2m) has been done. Most of the fourteen Raman lines expected for these materials were observed in the spectra. The two strongest lines observed have been assigned to the IR inactive A11 and A12 stannite modes that originated from the motion of the S or Se anion around the Cu and CIV cations remaining at rest. The shift in the frequency of these two lines of about 150 cm-1 to lower energies observed in Cu2BIICIV Se4 VI compounds as compared to those in Cu2BIICIV S4 VI ones, can then be explained as due to the anion mass effect. Based on the fact that values of these frequencies depend mainly on anion mass and bond-stretching forces between nearest-neighbor atoms, the vibrational frequencies v ¯ (A12) and v ¯ (A12) of both modes for several Cu2BIICIV X4 VI stannite compounds (where X = S, Se, or Te) very close to the experimental data reported for these materials were calculated from a simple model that relates these stretching forces to the anion-cation bond-distances.

  13. Symmetry breaking in semiconductor nanocrystals via kinetic-controlled surface diffusion: a strategy for manipulating the junction structure.

    PubMed

    Wang, Xixi; Liu, Maochang; Chen, Yubin; Fu, Wenlong; Wang, Bin; Guo, Liejin

    2016-09-21

    The synthesis of semiconductor nanocrystals is usually limited to high-level symmetry, as constrained by the inherent, for example, face-centered cubic or hexagonal close-packed lattices of the crystals. Herein, we report a robust approach for breaking the symmetry of the CdS lattice and obtaining high-quality CdS ultrathin monopods, bipods, tripods, and tetrapods. The success relies on manipulating reaction kinetics by dropwise addition of a precursor solution, which permits deterministic control over the number of CdS monomers in the reaction solution. With rapid monomer supply by fast precursor injection, growth was restricted to only one {111} facet of the nascent CdS tetrahedron to produce an asymmetric ultrathin monopod (a zinc-blende tip with a wurtzite arm). Otherwise, growth monomers could access adjacent {111} facets through surface diffusion and thus lead to the switch of the growth pattern from asymmetric to symmetric to generate an ultrathin multipod (a zinc-blende tip/core with multi-wurtzite arms). These symmetry-controlled photocatalysts were characterized by a fine-tuned zinc blende-wurtzite intergrowth type-II homojunction. After evaluating their structure-dependent solar-hydrogen-production properties, the CdS ultrathin monopod with an appropriate length for controllable charge transportation showed the highest photocatalytic activity. PMID:27539367

  14. Structural, optical and electrical properties of tin oxide thin films for application as a wide band gap semiconductor

    SciTech Connect

    Sethi, Riti; Ahmad, Shabir; Aziz, Anver; Siddiqui, Azher Majid

    2015-08-28

    Tin oxide (SnO) thin films were synthesized using thermal evaporation technique. Ultra pure metallic tin was deposited on glass substrates using thermal evaporator under high vacuum. The thickness of the tin deposited films was kept at 100nm. Subsequently, the as-deposited tin films were annealed under oxygen environment for a period of 3hrs to obtain tin oxide films. To analyse the suitability of the synthesized tin oxide films as a wide band gap semiconductor, various properties were studied. Structural parameters were studied using XRD and SEM-EDX. The optical properties were studied using UV-Vis Spectrophotometry and the electrical parameters were calculated using the Hall-setup. XRD and SEM confirmed the formation of SnO phase. Uniform texture of the film can be seen through the SEM images. Presence of traces of unoxidised Sn has also been confirmed through the XRD spectra. The band gap calculated was around 3.6eV and the optical transparency around 50%. The higher value of band gap and lower value of optical transparency can be attributed to the presence of unoxidised Sn. The values of resistivity and mobility as measured by the Hall setup were 78Ωcm and 2.92cm{sup 2}/Vs respectively. The reasonable optical and electrical parameters make SnO a suitable candidate for optoelectronic and electronic device applications.

  15. Low-dimensional dynamics in observables from complex and higher-dimensional systems

    NASA Astrophysics Data System (ADS)

    Baptista, Murilo S.; Caldas, Iberê L.; Baptista, Mauricio S.; Baptista, Cassio S.; Ferreira, André A.; Heller, Maria Vittoria A. P.

    2000-11-01

    We analyze fluctuating observables of high-dimensional systems as the New York Stock Market S &P 500 index, the amino-acid sequence in the M. genitalium DNA, the maximum temperature of the San Francisco Bay area, and the toroidal magneto plasma potential. The probability measures of these fluctuations are obtained by the statistical analysis of a rescaling combination of the first Poincaré return time of a low-dimensional chaotic system. This result indicates that it is possible to use a measure of a low-dimensional chaotic attractor to describe a measure of these complex systems. Moreover, within this description we determine scaling power laws for average measurements of the analyzed fluctuations.

  16. Carrier Multiplication in Semiconductor Nanocrystals: Theoretical Screening of Candidate Materials Based on Band-Structure Effects

    SciTech Connect

    Luo, J. W.; Franceschetti, A.; Zunger, A.

    2008-01-01

    Direct carrier multiplication (DCM) occurs when a highly excited electron-hole pair decays by transferring its excess energy to the electrons rather than to the lattice, possibly exciting additional electron-hole pairs. Atomistic electronic structure calculations have shown that DCM can be induced by electron-hole Coulomb interactions, in an impact-ionization-like process whose rate is proportional to the density of biexciton states {rho}{sub XX}. Here we introduce a DCM 'figure of merit' R{sub 2}(E) which is proportional to the ratio between the biexciton density of states {rho}{sub XX} and the single-exciton density of states {rho}{sub x}, restricted to single-exciton and biexciton states that are coupled by Coulomb interactions. Using R{sub 2}(E), we consider GaAs, InAs, InP, GaSb, InSb, CdSe, Ge, Si, and PbSe nanocrystals of different sizes. Although DCM can be affected by both quantum-confinement effects (reflecting the underly electronic structure of the confined dot-interior states) and surface effects, here we are interested to isolate the former. To this end the nanocrystal energy levels are obtained from the corresponding bulk band structure via the truncated crystal approximation. We find that PbSe, Si, GaAs, CdSe, and InP nanocrystals have larger DCM figure of merit than the other nanocrystals. Our calculations suggest that high DCM efficiency requires high degeneracy of the corresponding bulk band-edge states. Interestingly, by considering band structure effects we find that as the dot size increases the DCM critical energy E{sub 0} (the energy at which R{sub 2}(E) becomes {ge}1) is reduced, suggesting improved DCM. However, whether the normalized E{sub 0}/{var_epsilon}{sub g} increases or decreases as the dot size increases depends on dot material.

  17. Device applications and structural and optical properties of Indigo - A biodegradable, low-cost organic semiconductor

    NASA Astrophysics Data System (ADS)

    Wang, Zhengjun; Pisane, Kelly L.; Sierros, Konstantinos; Seehra, Mohindar S.; Korakakis, Dimitris

    2015-03-01

    Currently, memory devices based on organic materials are attracting great attention due to their simplicity in device structure, mechanical flexibility, potential for scalability, low-cost potential, low-power operation, and large capacity for data storage. In a recent paper from our group, Indigo-based nonvolatile organic write-once-read-many-times (WORM) memory device, consisting of a 100nm layer of indigo sandwiched between an indium tin oxide (ITO) cathode and an Al anode, has been reported. This device is found to be at its low resistance state (ON state) and can be switched to high resistance state (OFF state) by applying a positive bias with ON/OFF current ratio of the device being up to 1.02 × e6. A summary of these results along with the structural and optical properties of indigo powder will be reported. Analysis of x-ray diffraction shows a monoclinic structure with lattice parameters a(b)[c] = 0.924(0.577)[0.1222]nm and β =117° . Optical absorption shows a band edge at 1.70 eV with peak of absorption occurring at 1.90 eV. These results will be interpreted in terms of the HOMO-LUMO bands of Indigo.

  18. CaTiO.sub.3 Interfacial template structure on semiconductor-based material and the growth of electroceramic thin-films in the perovskite class

    DOEpatents

    McKee, Rodney Allen; Walker, Frederick Joseph

    1998-01-01

    A structure including a film of a desired perovskite oxide which overlies and is fully commensurate with the material surface of a semiconductor-based substrate and an associated process for constructing the structure involves the build up of an interfacial template film of perovskite between the material surface and the desired perovskite film. The lattice parameters of the material surface and the perovskite of the template film are taken into account so that during the growth of the perovskite template film upon the material surface, the orientation of the perovskite of the template is rotated 45.degree. with respect to the orientation of the underlying material surface and thereby effects a transition in the lattice structure from fcc (of the semiconductor-based material) to the simple cubic lattice structure of perovskite while the fully commensurate periodicity between the perovskite template film and the underlying material surface is maintained. The film-growth techniques of the invention can be used to fabricate solid state electrical components wherein a perovskite film is built up upon a semiconductor-based material and the perovskite film is adapted to exhibit ferroelectric, piezoelectric, pyroelectric, electro-optic or large dielectric properties during use of the component.

  19. Enhancing Crystalline Structural Orders of Polymer Semiconductors for Efficient Charge Transport via Polymer-Matrix-Mediated Molecular Self-Assembly.

    PubMed

    Lei, Yanlian; Deng, Ping; Lin, Ming; Zheng, Xuelin; Zhu, Furong; Ong, Beng S

    2016-08-01

    A facile polymer-matrix-mediated molecular self-assembly of polymer semiconductors into highly crystalline orders for efficient charge transport in organic thin-film transistors is demonstrated. Phenomenal enhancements in field-effect mobility of about one order of magnitude and current on/off ratio of two to three orders of magnitude are realized with polyacrylonitrile-incorporated polymer semiconductor compositions via solution deposition. PMID:27168128

  20. Describing high-dimensional dynamics with low-dimensional piecewise affine models: applications to renewable energy.

    PubMed

    Hirata, Yoshito; Aihara, Kazuyuki

    2012-06-01

    We introduce a low-dimensional description for a high-dimensional system, which is a piecewise affine model whose state space is divided by permutations. We show that the proposed model tends to predict wind speeds and photovoltaic outputs for the time scales from seconds to 100 s better than by global affine models. In addition, computations using the piecewise affine model are much faster than those of usual nonlinear models such as radial basis function models.

  1. First-Principles Study on Dynamic Electron-Transport Property through Low Dimensional System

    NASA Astrophysics Data System (ADS)

    Egami, Yoshiyuki; Hirose, Kikuji

    We present an investigation of electron-transport in a low-dimensional system using a time-dependent first-principles simulator. The response time for the peaks in the transmission curve of a molecular chain system is discussed. Two types of resonant-tunneling channels with different responses to changes in the conformation are observed. It is found that one of the channels plays a minor role in the contribution to the electron transport because of its poor response.

  2. Spin-dependent transport properties of a GaMnAs-based vertical spin metal-oxide-semiconductor field-effect transistor structure

    SciTech Connect

    Kanaki, Toshiki Asahara, Hirokatsu; Ohya, Shinobu Tanaka, Masaaki

    2015-12-14

    We fabricate a vertical spin metal-oxide-semiconductor field-effect transistor (spin-MOSFET) structure, which is composed of an epitaxial single-crystal heterostructure with a ferromagnetic-semiconductor GaMnAs source/drain, and investigate its spin-dependent transport properties. We modulate the drain-source current I{sub DS} by ∼±0.5% with a gate-source voltage of ±10.8 V and also modulate I{sub DS} by up to 60% with changing the magnetization configuration of the GaMnAs source/drain at 3.5 K. The magnetoresistance ratio is more than two orders of magnitude higher than that obtained in the previous studies on spin MOSFETs. Our result shows that a vertical structure is one of the hopeful candidates for spin MOSFET when the device size is reduced to a sub-micron or nanometer scale.

  3. Nonvolatile and tunable switching of lateral photo-voltage triggered by laser and electric pulse in metal dusted metal-oxide-semiconductor structures.

    PubMed

    Zhou, Peiqi; Gan, Zhikai; Huang, Xu; Mei, Chunlian; Huang, Meizhen; Xia, Yuxing; Wang, Hui

    2016-01-01

    Owing to the innate stabilization of built-in potential in p-n junction or metal-oxide-semiconductor structure, the sensitivity and linearity of most lateral photovoltaic effect (LPE) devices is always fixed after fabrication. Here we report a nonvolatile and tunable switching effect of lateral photo-voltage (LPV) in Cu dusted ultrathin metal-oxide-semiconductor structure. With the stimulation of electric pulse and local illumination, the sensitivity and linearity of LPV can be adjusted up and down in a nonvolatile manner. This phenomenon is attributed to a controllable change of the Schottky barrier formed between the metal layer and silicon substrate, including the consequent change of film resistivity. This work may widely improve the performance of existing LPE-based devices and suggest new applications for LPE in other areas. PMID:27535351

  4. Nonvolatile and tunable switching of lateral photo-voltage triggered by laser and electric pulse in metal dusted metal-oxide-semiconductor structures

    PubMed Central

    Zhou, Peiqi; Gan, Zhikai; Huang, Xu; Mei, Chunlian; Huang, Meizhen; Xia, Yuxing; Wang, Hui

    2016-01-01

    Owing to the innate stabilization of built-in potential in p–n junction or metal-oxide-semiconductor structure, the sensitivity and linearity of most lateral photovoltaic effect (LPE) devices is always fixed after fabrication. Here we report a nonvolatile and tunable switching effect of lateral photo-voltage (LPV) in Cu dusted ultrathin metal-oxide-semiconductor structure. With the stimulation of electric pulse and local illumination, the sensitivity and linearity of LPV can be adjusted up and down in a nonvolatile manner. This phenomenon is attributed to a controllable change of the Schottky barrier formed between the metal layer and silicon substrate, including the consequent change of film resistivity. This work may widely improve the performance of existing LPE-based devices and suggest new applications for LPE in other areas. PMID:27535351

  5. Features of the mechanisms of generation and 'Healing' of structural defects in the heavily doped intermetallic semiconductor n-ZrNiSn

    SciTech Connect

    Romaka, V. A.; Hlil, E. K.; Skolozdra, Ya. V.; Rogl, P.; Stadnyk, Yu. V.; Romaka, L. P.; Goryn, A. M.

    2009-09-15

    The crystal structure, density of electron states, and charge-transport characteristics of an intermetallic semiconductor ZrNiSn heavily doped with acceptor impurity Y (N{sub A}{sup Y} {approx} 3.8 x 10{sup 20}-4.8 x 10{sup 21} cm{sup -3}) have been studied in the temperature range T = 80-380 K. Relation between the impurity concentration and the amplitude of a large-scale fluctuation and also the degree of occupation of the potential well of small-scale fluctuation by charge carriers (fine structure) is established. The results are discussed in the context of the Shklovskii-Efros model for a heavily doped and compensated semiconductor.

  6. Nonvolatile and tunable switching of lateral photo-voltage triggered by laser and electric pulse in metal dusted metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Zhou, Peiqi; Gan, Zhikai; Huang, Xu; Mei, Chunlian; Huang, Meizhen; Xia, Yuxing; Wang, Hui

    2016-08-01

    Owing to the innate stabilization of built-in potential in p–n junction or metal-oxide-semiconductor structure, the sensitivity and linearity of most lateral photovoltaic effect (LPE) devices is always fixed after fabrication. Here we report a nonvolatile and tunable switching effect of lateral photo-voltage (LPV) in Cu dusted ultrathin metal-oxide-semiconductor structure. With the stimulation of electric pulse and local illumination, the sensitivity and linearity of LPV can be adjusted up and down in a nonvolatile manner. This phenomenon is attributed to a controllable change of the Schottky barrier formed between the metal layer and silicon substrate, including the consequent change of film resistivity. This work may widely improve the performance of existing LPE-based devices and suggest new applications for LPE in other areas.

  7. Nonvolatile and tunable switching of lateral photo-voltage triggered by laser and electric pulse in metal dusted metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Zhou, Peiqi; Gan, Zhikai; Huang, Xu; Mei, Chunlian; Huang, Meizhen; Xia, Yuxing; Wang, Hui

    2016-08-01

    Owing to the innate stabilization of built-in potential in p-n junction or metal-oxide-semiconductor structure, the sensitivity and linearity of most lateral photovoltaic effect (LPE) devices is always fixed after fabrication. Here we report a nonvolatile and tunable switching effect of lateral photo-voltage (LPV) in Cu dusted ultrathin metal-oxide-semiconductor structure. With the stimulation of electric pulse and local illumination, the sensitivity and linearity of LPV can be adjusted up and down in a nonvolatile manner. This phenomenon is attributed to a controllable change of the Schottky barrier formed between the metal layer and silicon substrate, including the consequent change of film resistivity. This work may widely improve the performance of existing LPE-based devices and suggest new applications for LPE in other areas.

  8. Band structure properties of (BGa)P semiconductors for lattice matched integration on (001) silicon

    SciTech Connect

    Hossain, Nadir; Sweeney, Stephen; Hosea, Jeff; Liebich, Sven; Zimprich, Martin; Volz, Kerstin; Stolz, Wolfgang; Kunert, Bernerdette

    2013-12-04

    We report the band structure properties of (BGa)P layers grown on silicon substrate using metal-organic vapour-phase epitaxy. Using surface photo-voltage spectroscopy we find that both the direct and indirect band gaps of (BGa)P alloys (strained and unstrained) decrease with Boron content. Our experimental results suggest that the band gap of (BGa)P layers up to 6% Boron is large and suitable to be used as cladding and contact layers in GaP-based quantum well heterostructures on silicon substrates.

  9. Long-range p-d exchange interaction in a ferromagnet-semiconductor hybrid structure

    NASA Astrophysics Data System (ADS)

    Korenev, V. L.; Salewski, M.; Akimov, I. A.; Sapega, V. F.; Langer, L.; Kalitukha, I. V.; Debus, J.; Dzhioev, R. I.; Yakovlev, D. R.; Müller, D.; Schröder, C.; Hövel, H.; Karczewski, G.; Wiater, M.; Wojtowicz, T.; Kusrayev, Yu. G.; Bayer, M.

    2016-01-01

    Hybrid structures synthesized from different materials have attracted considerable attention because they may allow not only combination of the functionalities of the individual constituents but also mutual control of their properties. To obtain such a control an interaction between the components needs to be established. For coupling the magnetic properties, an exchange interaction has to be implemented which typically depends on wavefunction overlap and is therefore short-ranged, so that it may be compromised across the hybrid interface. Here we study a hybrid structure consisting of a ferromagnetic Co layer and a semiconducting CdTe quantum well, separated by a thin (Cd, Mg)Te barrier. In contrast to the expected p-d exchange that decreases exponentially with the wavefunction overlap of quantum well holes and magnetic atoms, we find a long-ranged, robust coupling that does not vary with barrier width up to more than 30 nm. We suggest that the resulting spin polarization of acceptor-bound holes is induced by an effective p-d exchange that is mediated by elliptically polarized phonons.

  10. Magnetically-tunable spin-selective positioning of wave functions in asymmetric semiconductor quantum structures

    NASA Astrophysics Data System (ADS)

    Lee, S.; Titova, L. V.; Furdyna, Jacek K.; Dobrowolska, M.

    2000-03-01

    It has been recently reported that the properties of self-organized CdSe quantum dots (QDs) on ZnSe change significantly when they are grown on ZnMnSe spacers separating CdSe form ZnSe.[1] To explore this effect futher, we have prepared a series of samples by depositing one monolayer (ML) of CdSe on ZnMnSe spacer layers of different thickness and different Mn concentration. The system is then capped with ZnSe. The band structure for this geometry results in an asymmetric quantum structure, where the 1 ML thick CdSe acts as a "well" between barriers comprised of ZnSe on side, and ZnMnSe on the other. When a magnetic field is applied, the Zeeman splitting of the band edges in ZnMnSe spacer moves the position of the wave function toward or away from the spacer, depending on spin orientation. Such spin-selective repositioning of the wave functions is fully confirmed by magnetic field dependence of ground state exciton transitions observed in PL. This work was supported by NSF Grant DMR 9705064. [1]C.S. Kim et.al., 9th International conference on II-VI compounds, Kyoto, Nov. 1-5, 1999.

  11. Structural and optical characterization of group III-nitride compound semiconductors

    NASA Astrophysics Data System (ADS)

    Senawiratne, Jayantha

    The structural properties of the group III-nitrides including AlN, Ga 1-xMnxN, GaN:Cu, and InN were investigated by Raman spectroscopy. Absorption and photoluminescence spectroscopy were utilized to study the optical properties in these materials. The analysis of physical vapor transport grown AlN single crystals showed that oxygen, carbon, silicon, and boron are the major impurities in the bulk AlN. The Raman analysis revealed high crystalline quality and well oriented AlN single crystals. The absorption coefficient of AlN single crystals were assessed in the spectral range from deep UV to the FIR. The absorption and photoluminescence analysis indicate that, in addition to oxygen, carbon, boron, and silicon, contribute to the optical properties of bulk AlN crystals. In situ Cu-doped GaN epilayers with Cu concentrations in the range of 2x1016 cm-3 - 5x10 17 cm-3, grown on sapphire substrate by metal organic chemical vapor deposition, were investigated by Raman and photoluminescence (PL) spectroscopy. The Raman study revealed high crystalline GaN:Cu layers with minimal damage to the hexagonal lattice structure due to the Cu incorporation. A strong Cu related emission band at 2.4 eV was assigned to Cu induced optical transitions between deep Cu states and shallow residual donor states. Compensation of Cu states by residual donors and poor activation probability of deep Cu states are responsible for semi-insulating electrical conductivity. Ferromagnetic Ga1-xMnxN epilayers, grown by MOCVD with Mn concentration from x = 0 to x = 1.5, were optically investigated by Raman, PL, and transmission spectroscopy. The Raman studies revealed Mn-related Raman peaks at 300 cm-1, 609 cm-1, and 669 cm -1. Mn-related absorption and emission bands in Ga1-xMn xN were observed at 1.5 eV and 3.0 eV, respectively. The structural properties of InN layers, grown by high pressure-CVD with different free carrier concentrations, were analyzed by Raman spectroscopy. The Raman results show that

  12. SEMICONDUCTOR DEVICES MEMS magnetic field sensor based on silicon bridge structure

    NASA Astrophysics Data System (ADS)

    Guangtao, Du; Xiangdong, Chen; Qibin, Lin; Hui, Li; Huihui, Guo

    2010-10-01

    A MEMS piezoresistive magnetic field sensor based on a silicon bridge structure has been simulated and tested. The sensor consists of a silicon sensitivity diaphragm embedded with a piezoresistive Wheatstone bridge, and a ferromagnetic magnet adhered to the sensitivity diaphragm. When the sensor is subjected to an external magnetic field, the magnetic force bends the silicon sensitivity diaphragm, producing stress and resistors change of the Wheatstone bridge and the output voltage of the sensor. Good agreement is observed between the theory and measurement behavior of the magnetic field sensor. Experimental results demonstrate that the maximum sensitivity and minimum resolution are 48 m V/T and 160 μT, respectively, making this device suitable for strong magnetic field measurement. Research results indicate that the sensor repeatability and dynamic response time are about 0.66% and 150 ms, respectively.

  13. Effects of graphene defect on electronic structures of its interface with organic semiconductor

    SciTech Connect

    Yang, Qing-Dan; Wang, Chundong; Mo, Hin-Wai; Lo, Ming-Fai; Yuen, Muk Fung; Ng, Tsz-Wai E-mail: apcslee@cityu.edu.hk; Zhang, Wen-Jun; Lee, Chun-Sing E-mail: apcslee@cityu.edu.hk; Dou, Wei-Dong; Tsang, Sai-Wing

    2015-03-30

    Electronic structures of copper hexadecafluorophthalocyanine (F{sub 16}CuPc)/graphene with different defect density were studied with ultra-violet photoelectron spectroscopy. We showed that the charge transfer interaction and charge flow direction can be interestingly tuned by controlling the defect density of graphene through time-controlled H{sub 2} plasma treatment. By increasing the treatment time of H{sub 2} plasma from 30 s to 5 min, both the interface surface dipole and the electron transporting barrier at F{sub 16}CuPc/graphene interface are significantly reduced from 0.86 to 0.56 eV and 0.71 to 0.29 eV, respectively. These results suggested that graphene's defect control is a simple approach for tuning electronic properties of organic/graphene interfaces.

  14. Bright and dark excitons in semiconductor carbon nanotubes: insights from electronic structure calculations.

    PubMed

    Kilina, Svetlana; Badaeva, Ekaterina; Piryatinski, Andrei; Tretiak, Sergei; Saxena, Avadh; Bishop, Alan R

    2009-06-01

    We review electronic structure calculations of finite-length semiconducting carbon nanotubes using time-dependent density functional theory (TD-DFT) and the time dependent Hartree-Fock (TD-HF) approach coupled with semi-empirical AM1 and ZINDO Hamiltonians. We specifically focus on the energy splitting, relative ordering, and localization properties of optically active (bright) and optically forbidden (dark) states from the lowest excitonic band of the nanotubes. These excitonic states are very important in competing radiative and non-radiative processes in these systems. Our analysis of excitonic transition density matrices demonstrates that pure DFT functionals overdelocalize excitons making an electron-hole pair unbound; consequently, excitonic features are not presented in this method. In contrast, the pure HF and AM1 calculations overbind excitons, inaccurately predicting the lowest energy state as a bright exciton. Changing the AM1 with the ZINDO Hamiltonian in TD-HF calculations predicts the bright exciton as the second state after the dark one. However, in contrast to AM1 calculations, the diameter dependence of the excitation energies obtained by ZINDO does not follow the experimental trends. Finally, the TD-DFT approach incorporating hybrid functionals with a moderate portion of the long-range HF exchange, such as B3LYP, has the most generality and predictive capacity providing a sufficiently accurate description of excitonic structure in finite-size nanotubes. These methods characterize four important lower exciton bands: the lowest state is dark, the upper band is bright, and the two other dark and nearly degenerate excitons lie in between. Although the calculated energy splittings between the lowest dark and the bright excitons are relatively large ( approximately 0.1 eV), the dense excitonic manifold below the bright exciton allows for fast non-radiative relaxation leading to the rapid population of the lowest dark exciton. This rationalizes the low

  15. Photoinduced superconductivity in semiconductors

    NASA Astrophysics Data System (ADS)

    Goldstein, Garry; Aron, Camille; Chamon, Claudio

    2015-02-01

    We show that optically pumped semiconductors can exhibit superconductivity. We illustrate this phenomenon in the case of a two-band semiconductor tunnel-coupled to broad-band reservoirs and driven by a continuous wave laser. More realistically, we also show that superconductivity can be induced in a two-band semiconductor interacting with a broad-spectrum light source. We furthermore discuss the case of a three-band model in which the middle band replaces the broad-band reservoirs as the source of dissipation. In all three cases, we derive the simple conditions on the band structure, electron-electron interaction, and hybridization to the reservoirs that enable superconductivity. We compute the finite superconducting pairing and argue that the mechanism can be induced through both attractive and repulsive interactions and is robust to high temperatures.

  16. High Spatial Resolution Spectroscopy of Semiconductor Nanostructures

    NASA Astrophysics Data System (ADS)

    Harris, Timothy D.; Gershoni, David; Pfeiffer, Loren N.

    1996-03-01

    Several recent reports employing high spatial resolution have revealed the dominance of exciton localization in the low temperature luminescence of semiconductor quantum structures.^[1-3] Understanding this localization is of critical importance for the reliable studies of low dimensional structures such as quantum wells, quantum wires and quantum dots. We report on low temperature and high spatial resolution photoluminescence and photoluminescence excitation studies of cleaved edge overgrown (CEO) single quantum wires. These samples permit the direct and unambiguous comparison between the optical properties of a (100) oriented quantum well, a (110) oriented quantum well, and the quantum wire which is formed at their intersection. Using low temperature near field optical spectroscopy, and a novel diffraction limited far field apparatus, we determine the carrier diffusion length dependence on pump wavelength and sample temperature in both the 2d systems and the genuinely 1D wire system. We also measure the absorption strength of the 1D system and find it to be a factor of 3 stronger than the absorption of the associated 2D systems.^[2] Using low temperature near field optical spectroscopy, and a novel diffraction limited far field apparatus, we also determine the carrier diffusion length dependence on pump wavelength and sample temperature. ^[1] H. F. Hess, E. Betzig, T. D. Harris, L. N. Pfeiffer, and K. W. West, Science 264, 1740 (1994). ^[2] T. D. Harris, D. Gershoni, R. D. Grober, L. Pfeiffer, K. West, and N. Chand, Appl. Phys. Lett, in press (1996) ^[3] D. Gammon, E. S. Snow, and D. S. Katzer, Appl. Phys. Lett. 67, 2391 (1995)

  17. Research progress on electronic phase separation in low-dimensional perovskite manganite nanostructures

    PubMed Central

    2014-01-01

    Perovskite oxide manganites with a general formula of R1-x AxMnO3 (where R is a trivalent rare-earth element such as La, Pr, Sm, and A is a divalent alkaline-earth element such as Ca, Sr, and Ba) have received much attention due to their unusual electron-transport and magnetic properties, which are indispensable for applications in microelectronic, magnetic, and spintronic devices. Recent advances in the science and technology have resulted in the feature sizes of microelectronic devices based on perovskite manganite oxides down-scaling into nanoscale dimensions. At the nanoscale, low-dimensional perovskite manganite oxide nanostructures display novel physical properties that are different from their bulk and film counterparts. Recently, there is strong experimental evidence to indicate that the low-dimensional perovskite manganite oxide nanostructures are electronically inhomogeneous, consisting of different spatial regions with different electronic orders, a phenomenon that is named as electronic phase separation (EPS). As the geometry sizes of the low-dimensional manganite nanostructures are reduced to the characteristic EPS length scale (typically several tens of nanometers in manganites), the EPS is expected to be strongly modulated, leading to quite dramatic changes in functionality and more emergent phenomena. Therefore, reduced dimensionality opens a door to the new functionalities in perovskite manganite oxides and offers a way to gain new insight into the nature of EPS. During the past few years, much progress has been made in understanding the physical nature of the EPS in low-dimensional perovskite manganite nanostructures both from experimentalists and theorists, which have a profound impact on the oxide nanoelectronics. This nanoreview covers the research progresses of the EPS in low-dimensional perovskite manganite nanostructures such as nanoparticles, nanowires/nanotubes, and nanostructured films and/or patterns. The possible physical origins of the

  18. Performance enhancement of ITO/oxide/semiconductor MOS-structure silicon solar cells with voltage biasing

    NASA Astrophysics Data System (ADS)

    Ho, Wen-Jeng; Huang, Min-Chun; Lee, Yi-Yu; Hou, Zhong-Fu; Liao, Changn-Jyun

    2014-12-01

    In this study, we demonstrate the photovoltaic performance enhancement of a p-n junction silicon solar cell using a transparent-antireflective ITO/oxide film deposited on the spacing of the front-side finger electrodes and with a DC voltage applied on the ITO-electrode. The depletion width of the p-n junction under the ITO-electrode was induced and extended while the absorbed volume and built-in electric field were also increased when the biasing voltage was increased. The photocurrent and conversion efficiency were increased because more photo-carriers are generated in a larger absorbed volume and because the carriers transported and collected more effectively due to higher biasing voltage effects. Compared to a reference solar cell (which was biased at 0 V), a conversion efficiency enhancement of 26.57% (from 12.42% to 15.72%) and short-circuit current density enhancement of 42.43% (from 29.51 to 42.03 mA/cm2) were obtained as the proposed MOS-structure solar cell biased at 2.5 V. In addition, the capacitance-volt (C-V) measurement was also used to examine the mechanism of photovoltaic performance enhancement due to the depletion width being enlarged by applying a DC voltage on an ITO-electrode.

  19. Nanoscale Internal Fields in a Biased Graphene-Insulator-Semiconductor Structure.

    PubMed

    Rangan, Sylvie; Kalyanikar, Malathi; Duan, Junxi; Liu, Gang; Bartynski, Robert Allen; Andrei, Eva Y; Feldman, Leonard; Garfunkel, Eric

    2016-09-01

    Measuring and understanding electric fields in multilayered materials at the nanoscale remains a challenging problem impeding the development of novel devices. At this scale, it is far from obvious that materials can be accurately described by their intrinsic bulk properties, and considerations of the interfaces between layered materials become unavoidable for a complete description of the system's electronic properties. Here, a general approach to the direct measurement of nanoscale internal fields is proposed. Small spot X-ray photoemission was performed on a biased graphene/SiO2/Si structure in order to experimentally determine the potential profile across the system, including discontinuities at the interfaces. Core levels provide a measure of the local potential and are used to reconstruct the potential profile as a function of the depth through the stack. It is found that each interface plays a critical role in establishing the potential across the dielectric, and the origin of the potential discontinuities at each interface is discussed. PMID:27530545

  20. Structural, optical, magnetic and photocatalytic properties of Co doped CuS diluted magnetic semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Sreelekha, N.; Subramanyam, K.; Amaranatha Reddy, D.; Murali, G.; Ramu, S.; Rahul Varma, K.; Vijayalakshmi, R. P.

    2016-08-01

    Pristine and Co doped covellite CuS nanoparticles were synthesized in aqueous solution by facile chemical co-precipitation method with Ethylene Diamine Tetra Acetic Acid (EDTA) as a stabilizing agent. EDAX measurements confirmed the presence of Co in the CuS host lattice. Hexagonal crystal structure of pure and Co doped CuS nanoparticles were authenticated by XRD patterns. TEM images indicated that sphere-shape of nanoparticles through a size ranging from 5 to 8 nm. The optical absorption edge moved to higher energies with increase in Co concentration as indicated by UV-vis spectroscopy. Magnetic measurements revealed that bare CuS sample show sign of diamagnetic character where as in Co doped nanoparticles augmentation of room temperature ferromagnetism was observed with increasing doping precursor concentrations. Photocatalytic performance of the pure and Co doped CuS nanoparticles were assessed by evaluating the degradation rate of rhodamine B solution under sun light irradiation. The 5% Co doped CuS nanoparticles provide evidence for high-quality photocatalytic activity.

  1. Parameters affecting the accuracy of oxide thickness prediction in thin metal-oxide-semiconductor structures

    NASA Astrophysics Data System (ADS)

    Mohaidat, J. M.; Ahmad-Bitar, Riyad N.

    2004-01-01

    On the basis of the solution of the time dependent Schrödinger equation within the framework of the effective mass theory, a complete quantum mechanical electron tunneling through a biased square potential model with abrupt interfaces was deduced. Barriers of 3 eV height and widths up to 140 Å were investigated. Current density-voltage ( J- V) curves were computed for Al/SiO 2/ n+Si structure. The computed J- V curves exhibited oscillations at applied voltages above (Fowler-Nordheim tunneling) and below (direct tunneling) 3 V. For oxide thickness estimation, the position of the oscillation extrema from this quantum mechanical model were fitted to a wave interference formula and showed excellent agreement for oxide layer widths less than 50 Å. However, a systematic deviation appeared for layers larger than 50 Å. We show that the electron energy distribution at the injection layer and the electron effective mass on layers other than the oxide layer are important parameters for accurate oxide thickness estimation.

  2. First principles investigation of electronic structures and hyperfine properties of semiconductors and high-[Tc] superconductors

    SciTech Connect

    Sulaiman, S.B.

    1992-01-01

    The first principles Unrestricted Hartree-Fock Cluster procedure has been applied to investigate the electronic structures and associated hyperfine properties of several categories for solid systems. The first category is concerned with the location and nuclear quadrupole interactions (NQI) of fluorine impurity centers in crystalline silicon (c-Si). The Time Differential Perturbed Angular Distribution experiments show that when excited nuclear static fluorine ([sup 19]F*) is implanted into c-Si, two [sup 19]F* centers are formed characterized by two unique axially symmetric electric field gradients (efg). Models have been examined to determine the stable [sup 19]F* sites in the bulk c-Si. The two models, IB and AB, are also able to explain the experimental [sup 19]F* NQI data in crystalline germanium where two centers with axially symmetric efg are observed. The experimental trends of [sup 19]F* NQI are well reproduced by the investigation using the IB and AB models. The second category of the systems investigated deals with the NQI and magnetic hyperfine interaction of [sup 63]Cu in La[sub 2]CuO[sub 4] and YBa[sub 2]Cu[sub 3]O[sub 6] as well as the NQI of [sup 139]La and [sup 135]Ba in the former and the latter compounds respectively. In the third category, the author investigates the possible stable sites of the Muon Spin Rotation ([mu]SR) probe atom, positive muon ([mu][sup +]) in La[sub 2]CuO[sub 4], and the hyperfine field (H[sub hyp]) at [mu][sup +] site in the antiferromagnetic phase of the system. The most stable [mu][sup +] site is at (0.121a, 0.0, 0.110c) of the tetragonal La[sub 2]CuO[sub 4] unit cell. The value of H[sub hyp] at this site is in reasonable order of magnitude with the observed one.

  3. Structural Characterization and Impedance Spectroscopy of Substituted, Fused-Ring Organic Semiconductors

    NASA Astrophysics Data System (ADS)

    Shaw, Charles Michael

    Organic materials present a number of advantages over silicon that make them ideal candidates for modest performance devices like active matrix backplanes and RFID tags. The work detailed here describes both structural characterization of promising new materials, as well as the adaptation of impedance spectroscopy techniques to the study of organic transistors. Unit cells and solution casting behavior for dioctyl- and didodecyl-pentathienoacene are presented. Dioctyl pentathienoacene has an orthorhombic lattice with parameters a = 1.15 nm, b = 0.43 nm and c = 3.05 nm. Didodecyl pentathienoacene has an monoclinic lattice with parameters gamma = 92.2°, a = 1.10 urn, b = 0.42 nm and c = 3.89 nm. Additionally, thermotropic phase behavior is detailed. Both materials exhibit a "side chain melting" transition---characterized by a dramatic unit cell contraction of more than 20%---and smectic C liquid crystal phases. The side chain melting transition shows similarity to phase transitions elicited by exposing these materials to high energy electron flux. In both cases, disorder in the substitutions results in new phases for these materials. Dioctyl-pentathienoacene also exhibits a unique phase, which is intermediately ordered and shows a threefold increase in critical dose over the as-cast phase. Impedance spectroscopy of triisopropylsilyl pentacene transistors suggests these devices are well fit by a Voigt model equivalent circuit. The gate bias dependent resistor represents the channel conductance and the capacitor represents the drain-gate and source-gate capacitances. This in turn suggests that conduction occurs through delocalized states available in ordered regions, with disordered regions contributing localized, immobile states. Impedance spectroscopy of poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) shows similar behavior. The use of variable temperature impedance spectroscopy is also demonstrated. This technique is used to measure the reduction in trap

  4. Novel monolithic integration scheme for high-speed electroabsorption modulators and semiconductor optical amplifiers using cascaded structure.

    PubMed

    Lin, Fang-Zheng; Wu, Tsu-Hsiu; Chiu, Yi-Jen

    2009-06-01

    A new monolithic integration scheme, namely cascaded-integration (CI), for improving high-speed optical modulation is proposed and demonstrated. High-speed electroabsorption modulators (EAMs) and semiconductor optical amplifiers (SOAs) are taken as the integrated elements of CI. This structure is based on an optical waveguide defined by cascading segmented EAMs with segmented SOAs, while high-impedance transmission lines (HITLs) are used for periodically interconnecting EAMs, forming a distributive optical re-amplification and re-modulation. Therefore, not only the optical modulation can be beneficial from SOA gain, but also high electrical reflection due to EAM low characteristic impedance can be greatly reduced. Two integration schemes, CI and conventional single-section (SS), with same total EAM- and SOA- lengths are fabricated and compared to examine the concept. Same modulation-depth against with EAM bias (up to 5V) as well as SOA injection current (up to 60mA) is found in both structures. In comparison with SS, a < 1dB extra optical-propagation loss in CI is measured due to multi-sections of electrical-isolation regions between EAMs and SOAs, suggesting no significant deterioration in CI on DC optical modulation efficiency. Lower than -12dB of electrical reflection from D.C. to 30GHz is observed in CI, better than -5dB reflection in SS for frequency of above 5GHz. Superior high-speed electrical properties in CI structure can thus lead to higher speed of electrical-to-optical (EO) response, where -3dB bandwidths are >30GHz and 13GHz for CI and SS respectively. Simulation results on electrical and EO response are quite consistent with measurement, confirming that CI can lower the driving power at high-speed regime, while the optical loss is still kept the same level. Taking such distributive advantage (CI) with optical gain, not only higher-speed modulation with high output optical power can be attained, but also the trade-off issue due to impedance mismatch

  5. Development of epitaxial AlxSc1-xN for artificially structured metal/semiconductor superlattice metamaterials

    SciTech Connect

    Sands, Timothy D.; Stach, Eric A.; Saha, Bivas; Saber, Sammy; Naik, Gururaj V.; Boltasseva, Alexandra; Kvam, Eric P.

    2015-02-01

    Epitaxial nitride rocksalt metal/semiconductor superlattices are emerging as a novel class of artificially structured materials that have generated significant interest in recent years for their potential application in plasmonic and thermoelectric devices. Though most nitride metals are rocksalt, nitride semiconductors in general have hexagonal crystal structure. We report rocksalt aluminum scandium nitride (Al,Sc)N alloys as the semiconducting component in epitaxial rocksalt metal/semiconductor superlattices. The AlxSc1-xN alloys when deposited directly on MgO substrates are stabilized in a homogeneous rocksalt (single) phase when x < 0.51. Employing 20 nm TiN as a seed layer on MgO substrates, the homogeneity range for stabilizing the rocksalt phase has been extended to x < 0.82 for a 120 nm film. The rocksalt AlxSc1-xN alloys show moderate direct bandgap bowing with a bowing parameter, B = 1.41 ± 0.19 eV. The direct bandgap of metastable rocksalt AlN is extrapolated to be 4.70 ± 0.20 eV. The tunable lattice parameter, bandgap, dielectric permittivity, and electronic properties of rocksalt AlxSc1-xN alloys enable high quality epitaxial rocksalt metal/AlxSc1-xN superlattices with a wide range of accessible metamaterials properties.

  6. Band structure engineering of semiconductors for enhanced photoelectrochemical water splitting: The case of TiO2

    NASA Astrophysics Data System (ADS)

    Yin, Wan-Jian; Tang, Houwen; Wei, Su-Huai; Al-Jassim, Mowafak M.; Turner, John; Yan, Yanfa

    2010-07-01

    Here, we propose general strategies for the rational design of semiconductors to simultaneously meet all of the requirements for a high-efficiency, solar-driven photoelectrochemical (PEC) water-splitting device. As a case study, we apply our strategies for engineering the popular semiconductor, anatase TiO2 . Previous attempts to modify known semiconductors such as TiO2 have often focused on a particular individual criterion such as band gap, neglecting the possible detrimental consequence to other important criteria. Density-functional theory calculations reveal that with appropriate donor-acceptor coincorporation alloys with anatase TiO2 hold great potential to satisfy all of the criteria for a viable PEC device. We predict that (Mo, 2N) and (W, 2N) are the best donor-acceptor combinations in the low-alloy concentration regime whereas (Nb, N) and (Ta, N) are the best choice of donor-acceptor pairs in the high-alloy concentration regime.

  7. Physics with isotopically controlled semiconductors

    SciTech Connect

    Haller, E. E.

    2010-07-15

    This paper is based on a tutorial presentation at the International Conference on Defects in Semiconductors (ICDS-25) held in Saint Petersburg, Russia in July 2009. The tutorial focused on a review of recent research involving isotopically controlled semiconductors. Studies with isotopically enriched semiconductor structures experienced a dramatic expansion at the end of the Cold War when significant quantities of enriched isotopes of elements forming semiconductors became available for worldwide collaborations. Isotopes of an element differ in nuclear mass, may have different nuclear spins and undergo different nuclear reactions. Among the latter, the capture of thermal neutrons which can lead to neutron transmutation doping, is the most prominent effect for semiconductors. Experimental and theoretical research exploiting the differences in all the properties has been conducted and will be illustrated with selected examples.

  8. Controlling energy transfer processes and engineering luminescence efficiencies with low dimensional doping

    NASA Astrophysics Data System (ADS)

    Yu, Xiaoqiang; Summers, Christopher J.; Park, Wounjhang

    2012-04-01

    Energy transfer between two optical centers has long been used to promote the down- and up-conversion of light. In conventional phosphors, the two centers are distributed uniformly in 3D space and the luminescence efficiency is generally limited by energy transfer to defect states, where the excitation is quenched through non-radiative processes. In this paper, we present a new concept of low-dimensional doping of pairs of optical centers and explore its effect on enhancing the efficiency of down- and up-converted luminescence. The concept takes advantage of the fact that the low-dimensional doping profile significantly reduces the energy transfer rate to unintentional defects, which are naturally distributed in 3D space. The resultant de-coupling between optical centers and defects can lead to a substantial increase in luminescence efficiency. We first present the theoretical framework and apply the theory to well-characterized down- and up-conversion phosphors. For BaMgAl10O17:Eu2+, Mn2+ down-conversion phosphor, a factor of two increase in efficiency is predicted. For Na2Y3F11:Yb3+, Er3+ up-conversion phosphor, low-dimensional doping did not lead to increase in efficiency. This is because the major quenching mechanism is cross-relaxation between Er3+ ions, not energy transfer to defects. In an ideal up-conversion phosphor, where defect quenching is the dominant loss mechanism, similar increases (by a factor of 2-5) are predicted. This work presents a new pathway to engineer luminescent materials and achieve high luminescence efficiencies in up- and down-conversion phosphors.

  9. Analysis of cedar pollen time series: no evidence of low-dimensional chaotic behavior.

    PubMed

    Delaunay, J-J; Konishi, R; Seymour, C

    2006-01-01

    Much of the current interest in pollen time series analysis is motivated by the possibility that pollen series arise from low-dimensional chaotic systems. If this is the case, short-range prediction using nonlinear modeling is justified and would produce high-quality forecasts that could be useful in providing pollen alerts to allergy sufferers. To date, contradictory reports about the characterization of the dynamics of pollen series can be found in the literature. Pollen series have been alternatively described as featuring and not featuring deterministic chaotic behavior. We showed that the choice of test for detection of deterministic chaos in pollen series is difficult because pollen series exhibit [see text] power spectra. This is a characteristic that is also produced by colored noise series, which mimic deterministic chaos in most tests. We proposed to apply the Ikeguchi-Aihara test to properly detect the presence of deterministic chaos in pollen series. We examined the dynamics of cedar (Cryptomeria japonica) hourly pollen series by means of the Ikeguchi-Aihara test and concluded that these pollen series cannot be described as low-dimensional deterministic chaos. Therefore, the application of low-dimensional chaotic deterministic models to the prediction of short-range pollen concentration will not result in high-accuracy pollen forecasts even though these models may provide useful forecasts for certain applications. We believe that our conclusion can be generalized to pollen series from other wind-pollinated plant species, as wind speed, the forcing parameter of the pollen emission and transport, is best described as a nondeterministic series that originates in the high dimensionality of the atmosphere.

  10. Entanglement of strongly interacting low-dimensional fermions in metallic, superfluid, and antiferromagnetic insulating systems

    SciTech Connect

    Franca, V. V.; Capelle, K.

    2006-10-15

    We calculate the entanglement entropy of strongly correlated low-dimensional fermions in metallic, superfluid, and antiferromagnetic insulating phases. The entanglement entropy reflects the degrees of freedom available in each phase for storing and processing information, but is found not to be a state function in the thermodynamic sense. The role of critical points, smooth crossovers, and Hilbert space restrictions in shaping the dependence of the entanglement entropy on the system parameters is illustrated for metallic, insulating, and superfluid systems. The dependence of the spin susceptibility on entanglement in antiferromagnetic insulators is obtained quantitatively. The opening of spin gaps in antiferromagnetic insulators is associated with enhanced entanglement near quantum critical points.

  11. Low-dimensional chaos in magnetospheric activity from AE time series

    NASA Technical Reports Server (NTRS)

    Vassiliadis, D. V.; Sharma, A. S.; Eastman, T. E.; Papadopoulos, K.

    1990-01-01

    The magnetospheric response to the solar-wind input, as represented by the time-series measurements of the auroral electrojet (AE) index, has been examined using phase-space reconstruction techniques. The system was found to behave as a low-dimensional chaotic system with a fractal dimension of 3.6 and has Kolmogorov entropy less than 0.2/min. These indicate that the dynamics of the system can be adequately described by four independent variables, and that the corresponding intrinsic time scale is of the order of 5 min. The relevance of the results to magnetospheric modeling is discussed.

  12. Anderson transition in low-dimensional disordered systems driven by long-range nonrandom hopping.

    PubMed

    Rodríguez, A; Malyshev, V A; Sierra, G; Martín-Delgado, M A; Rodríguez-Laguna, J; Domínguez-Adame, F

    2003-01-17

    The single-parameter scaling hypothesis predicts the absence of delocalized states for noninteracting quasiparticles in low-dimensional disordered systems. We show analytically, using a supersymmetric method combined with a renormalization group analysis, as well as numerically that extended states may occur in the one- and two-dimensional Anderson model with a nonrandom hopping falling off as some power of the distance between sites. The different size scaling of the bare level spacing and the renormalized magnitude of the disorder seen by the quasiparticles finally results in the delocalization of states at one of the band edges of the quasiparticle energy spectrum.

  13. Low-Dimensional Palladium Nanostructures for Fast and Reliable Hydrogen Gas Detection

    PubMed Central

    Noh, Jin-Seo; Lee, Jun Min; Lee, Wooyoung

    2011-01-01

    Palladium (Pd) has received attention as an ideal hydrogen sensor material due to its properties such as high sensitivity and selectivity to hydrogen gas, fast response, and operability at room temperature. Interestingly, various Pd nanostructures that have been realized by recent developments in nanotechnologies are known to show better performance than bulk Pd. This review highlights the characteristic properties, issues, and their possible solutions of hydrogen sensors based on the low-dimensional Pd nanostructures with more emphasis on Pd thin films and Pd nanowires. The finite size effects, relative strengths and weaknesses of the respective Pd nanostructures are discussed in terms of performance, manufacturability, and practical applicability. PMID:22346605

  14. The Structuring of Shared Voluntary Standards in the U.S. Semiconductor Industry: Communicating to Reach Agreement.

    ERIC Educational Resources Information Center

    Browning, Larry D.; Beyer, Janice M.

    1998-01-01

    Contributes to scholarship on organizational communication by tracing how voluntary cooperative standards were developed for the semiconductor industry through reflexive communication processes initiated by the SEMATECH consortium. Analyzes seven pivotal incidents that show how increased communication produced new provinces of meaning, actions,…

  15. First-principles investigation of electronic structure, effective carrier masses, and optical properties of ferromagnetic semiconductor CdCr2S4

    NASA Astrophysics Data System (ADS)

    Xu-Hui, Zhu; Xiang-Rong, Chen; Bang-Gui, Liu

    2016-05-01

    The electronic structures, the effective masses, and optical properties of spinel CdCr2S4 are studied by using the full-potential linearized augmented planewave method and a modified Becke-Johnson exchange functional within the density-functional theory. Most importantly, the effects of the spin-orbit coupling (SOC) on the electronic structures and carrier effective masses are investigated. The calculated band structure shows a direct band gap. The electronic effective mass and the hole effective mass are analytically determined by reproducing the calculated band structures near the BZ center. SOC substantially changes the valence band top and the hole effective masses. In addition, we calculated the corresponding optical properties of the spinel structure CdCr2S4. These should be useful to deeply understand spinel CdCr2S4 as a ferromagnetic semiconductor for possible semiconductor spintronic applications. Project supported by the Joint Fund of the National Natural Science Foundation of China and the China Academy of Engineering Physics (Grant Nos. U1430117 and U1230201).

  16. Structure and dynamics in low-dimensional guest-host systems

    SciTech Connect

    John E. Fischer

    2000-05-01

    This is the final report of the fourth of four three year grants of the same title. The program evolved from an earlier DOE grant on graphite intercalation compounds. Since its inception eight years ago, the focus evolved continuously from conjugated polymers to fullerenes, disordered carbons for Li-ion battery applications, and most recently carbon nanotubes, with side excursion back to GIC's to exploit a recent advance in synthesis of a potentially exciting new phase. The unifying themes are the versatility of carbon in forming novel solids, and the flexibility of intercalation chemistry to provide new materials with potentially useful properties.

  17. Functional Connectivity among Spikes in Low Dimensional Space during Working Memory Task in Rat

    PubMed Central

    Tian, Xin

    2014-01-01

    Working memory (WM) is critically important in cognitive tasks. The functional connectivity has been a powerful tool for understanding the mechanism underlying the information processing during WM tasks. The aim of this study is to investigate how to effectively characterize the dynamic variations of the functional connectivity in low dimensional space among the principal components (PCs) which were extracted from the instantaneous firing rate series. Spikes were obtained from medial prefrontal cortex (mPFC) of rats with implanted microelectrode array and then transformed into continuous series via instantaneous firing rate method. Granger causality method is proposed to study the functional connectivity. Then three scalar metrics were applied to identify the changes of the reduced dimensionality functional network during working memory tasks: functional connectivity (GC), global efficiency (E) and casual density (CD). As a comparison, GC, E and CD were also calculated to describe the functional connectivity in the original space. The results showed that these network characteristics dynamically changed during the correct WM tasks. The measure values increased to maximum, and then decreased both in the original and in the reduced dimensionality. Besides, the feature values of the reduced dimensionality were significantly higher during the WM tasks than they were in the original space. These findings suggested that functional connectivity among the spikes varied dynamically during the WM tasks and could be described effectively in the low dimensional space. PMID:24658291

  18. Low dimensional description of pedestrian-induced oscillation of the Millennium Bridge.

    PubMed

    Abdulrehem, Mahmoud M; Ott, Edward

    2009-03-01

    When it opened to pedestrian traffic in the year 2000, London's Millennium Bridge exhibited an unwanted, large side-to-side oscillation, which was apparently due to a resonance between the stepping frequency of walkers and one of the bridge modes. Models for this event, and similar events on other bridges, have been proposed. The model most directly addressing the synchronization mechanism of individual walkers and the resulting global response of the bridge-pedestrian system is the one developed by Eckhardt et al. [Phys. Rev. E 75, 021110 (2007)]. This model treats individual walkers with a phase oscillator description and is inherently high dimensional with system dimensionality (N+2), where N is the number of walkers. In the present work we use a method proposed by Ott and Antonsen [Chaos 18, 037113 (2008)] to reduce the model of Eckhardt et al. to a low dimensional dynamical system, and we employ this reduced description to study the global dynamics of the bridge/pedestrian interaction. More generally, this treatment serves as an interesting example of the possibility of low dimensional macroscopic behavior in large systems of coupled oscillators.

  19. A low-dimensional deformation model for cancer cells in flow.

    PubMed

    Lee, A M; Berny-Lang, M A; Liao, S; Kanso, E; Kuhn, P; McCarty, O J T; Newton, P K

    2012-08-01

    A low-dimensional parametric deformation model of a cancer cell under shear flow is developed. The model is built around an experiment in which MDA-MB-231 adherent cells are subjected to flow with increasing shear. The cell surface deformation is imaged using differential interference contrast microscopy imaging techniques until the cell releases into the flow. We post-process the time sequence of images using an active shape model from which we obtain the principal components of deformation. These principal components are then used to obtain the parameters in an empirical constitutive equation determining the cell deformations as a function of the fluid normal and shear forces imparted. The cell surface is modeled as a 2D Gaussian interface which can be deformed with three active parameters: H (height), σ(x) (x-width), and σ(y) (y-width). Fluid forces are calculated on the cell surface by discretizing the surface with regularized Stokeslets, and the flow is driven by a stochastically fluctuating pressure gradient. The Stokeslet strengths are obtained so that viscous boundary conditions are enforced on the surface of the cell and the surrounding plate. We show that the low-dimensional model is able to capture the principal deformations of the cell reasonably well and argue that active shape models can be exploited further as a useful tool to bridge the gap between experiments, models, and numerical simulations in this biological setting.

  20. Semiconductor Nanocrystals for Biological Imaging

    SciTech Connect

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

    2005-06-28

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

  1. Structure and optoelectronic properties of spray deposited Mg doped p-CuCrO2 semiconductor oxide thin films

    NASA Astrophysics Data System (ADS)

    Rastogi, A. C.; Lim, S. H.; Desu, S. B.

    2008-07-01

    Transparent p-type Mg doped CuCrO2 wide-band-gap oxide semiconductor thin films were deposited over quartz substrates by chemical spray technique using metallo-organic precursors. Crystalline single phase CuCrO2 delafossite structure was dominant in ≥700 °C argon ambient annealed films but the as-deposited films contained spinel CuCr2O4 mixed phases. X-ray photoelectron Cr 2p spectra show spin-orbit splitting energy ˜9.8 eV consistent with Cr3+ valance state and Cr 2p3/2 resolved peaks show mixed valence state on Cr4+/Cr6+ confirming CuCr0.93Mg0.07O2 compound phase in spray deposited films. The effect of substrate temperature and film thickness on optical, electrical conductivity, and thermoelectric coefficient was investigated. Highly transparent ≥80% CuCr0.93Mg0.07O2 films with direct and indirect optical band gaps of 3.08 and 2.58 eV for 155 nm and 3.14 and 2.79 for 305 nm thin films, respectively, were obtained. Photoluminescence emission bands at 532 and 484 nm interpreted to arise from 3d94s1 and 3d10 Cu+ intraband transitions confirm mixing of Cu 3d, 4s, and 4p with O 2p orbitals necessary for realizing p-type CuCrO2 films. Electrical conductivity of CuCr0.93Mg0.07O2 films ranged 0.6-1 S cm-1 exhibiting activation energies ˜0.11 eV in 300-420 °K and ˜0.23 eV in ≥420 °K regions ascribed to activated conduction and grain boundary trap assisted conduction, respectively. Transparent p-(CuCr1-xMgxO2)/n-(ZnO) heterojunction diodes showing rectifying current-voltage characteristics were fabricated.

  2. Charge carrier dynamics of methylammonium lead iodide: from PbI₂-rich to low-dimensional broadly emitting perovskites.

    PubMed

    Klein, Johannes R; Flender, Oliver; Scholz, Mirko; Oum, Kawon; Lenzer, Thomas

    2016-04-28

    We provide an investigation of the charge carrier dynamics of the (MAI)(x)(PbI2)(1-x) system in the range x = 0.32-0.90 following the recently published "pseudobinary phase-composition processing diagram" of Song et al. (Chem. Mater., 2015, 27, 4612). The dynamics were studied using ultrafast pump-supercontinuum probe spectroscopy over the pump fluence range 2-50 μJ cm(-2), allowing for a wide variation of the initial carrier density. At high MAI excess (x = 0.90), low-dimensional perovskites (LDPs) are formed, and their luminescence spectra are significantly blue-shifted by ca. 50 nm and broadened compared to the 3D perovskite. The shift is due to quantum confinement effects, and the inhomogeneous broadening arises from different low-dimensional structures (predominantly 2D, but presumably also 1D and 0D). Accurate transient carrier temperatures are extracted from the transient absorption spectra. The regimes of carrier-carrier, carrier-optical phonon and acoustic phonon scattering are clearly distinguished. Perovskites with mole fractions x ≤ 0.71 exhibit extremely fast carrier cooling (ca. 300 fs) at low fluence of 2 μJ cm(-2), however cooling slows down significantly at high fluence of 50 μJ cm(-2) due to the "hot phonon effect" (ca. 2.8 ps). A kinetic analysis of the electron-hole recombination dynamics provides second-order recombination rate constants k2 which decrease from 5.3 to 1.5 × 10(-9) cm(3) s(-1) in the range x = 0.32-0.71. In contrast, recombination in the LDPs (x = 0.90) is more than one order of magnitude faster, 6.4 × 10(-8) cm(3) s(-1), which is related to the confined perovskite structure. Recombination in these LDPs should be however still slow enough for their potential application as efficient broadband emitters or solar light-harvesting materials. PMID:26972104

  3. Solution-processed low dimensional nanomaterials with self-assembled polymers for flexible photo-electronic devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Park, Cheolmin

    2015-09-01

    Self assembly driven by complicated but systematic hierarchical interactions offers a qualified alternative for fabricating functional micron or nanometer scale pattern structures that have been potentially useful for various organic and nanotechnological devices. Self assembled nanostructures generated from synthetic polymer systems such as controlled polymer blends, semi-crystalline polymers and block copolymers have gained a great attention not only because of the variety of nanostructures they can evolve but also because of the controllability of these structures by external stimuli. In this presentation, various novel photo-electronic materials and devices are introduced based on the solution-processed low dimensional nanomaterials such as networked carbon nanotubes (CNTs), reduced graphene oxides (rGOs) and 2 dimensional transition metal dichalcogenides (TMDs) with self assembled polymers including field effect transistor, electroluminescent device, non-volatile memory and photodetector. For instance, a nanocomposite of networked CNTs and a fluorescent polymer turned out an efficient field induced electroluminescent layer under alternating current (AC) as a potential candidate for next generation displays and lightings. Furthermore, scalable and simple strategies employed for fabricating rGO as well as TMD nanohybrid films allowed for high performance and mechanically flexible non-volatile resistive polymer memory devices and broad band photo-detectors, respectively.

  4. Artificial atoms on semiconductor surfaces

    PubMed Central

    Tisdale, W. A.; Zhu, X.-Y.

    2011-01-01

    Semiconductor nanocrystals are called artificial atoms because of their atom-like discrete electronic structure resulting from quantum confinement. Artificial atoms can also be assembled into artificial molecules or solids, thus, extending the toolbox for material design. We address the interaction of artificial atoms with bulk semiconductor surfaces. These interfaces are model systems for understanding the coupling between localized and delocalized electronic structures. In many perceived applications, such as nanoelectronics, optoelectronics, and solar energy conversion, interfacing semiconductor nanocrystals to bulk materials is a key ingredient. Here, we apply the well established theories of chemisorption and interfacial electron transfer as conceptual frameworks for understanding the adsorption of semiconductor nanocrystals on surfaces, paying particular attention to instances when the nonadiabatic Marcus picture breaks down. We illustrate these issues using recent examples from our laboratory. PMID:21097704

  5. Dye Sensitization of Semiconductor Particles

    SciTech Connect

    Hartland, G. V.

    2003-01-13

    In this project electron transfer at semiconductor liquid interfaces was examined by ultrafast time-resolved and steady-state optical techniques. The experiments primarily yielded information about the electron transfer from titanium dioxide semiconductor particles to absorbed molecules. The results show that the rate of electron transfer depends on the structure of the molecule, and the crystalline phase of the particle. These results can be qualitatively explained by Marcus theory for electron transfer.

  6. Interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor structure by frequency dependent conductance technique

    NASA Astrophysics Data System (ADS)

    Liao, Xue-Yang; Zhang, Kai; Zeng, Chang; Zheng, Xue-Feng; En, Yun-Fei; Lai, Ping; Hao, Yue

    2014-05-01

    Frequency dependent conductance measurements are implemented to investigate the interface states in Al2O3/AlGaN/GaN metal-oxide-semiconductor (MOS) structures. Two types of device structures, namely, the recessed gate structure (RGS) and the normal gate structure (NGS), are studied in the experiment. Interface trap parameters including trap density Dit, trap time constant τit, and trap state energy ET in both devices have been determined. Furthermore, the obtained results demonstrate that the gate recess process can induce extra traps with shallower energy levels at the Al2O3/AlGaN interface due to the damage on the surface of the AlGaN barrier layer resulting from reactive ion etching (RIE).

  7. Electronic Structure in Thin Film Organic Semiconductors Studied using Soft X-ray Emission and Resonant Inelastic X-ray Scattering

    SciTech Connect

    Zhang,Y.; Downes, J.; Wang, S.; Learmonth, T.; Plucinski, L.; Matsuura, A.; McGuinness, C.; Glans, P.; Bernardis, S.; et al.

    2006-01-01

    The electronic structure of thin films of the organic semiconductors copper and vanadyl (VO) phthalocyanine (Pc) has been measured using resonant soft X-ray emission spectroscopy and resonant inelastic X-ray scattering. For Cu-Pc we report the observation of two discrete states near E{sub F}. This differs from published photoemission results, but is in excellent agreement with density functional calculations. For VO-Pc, the vanadyl species is shown to be highly localized. Both dipole forbidden V 3d to V 3d*, and O 2p to V 3d* charge transfer transitions are observed, and explained in a local molecular orbital model.

  8. Electronic structure near the Fermi level in the ferromagnetic semiconductor GaMnAs studied by ultrafast time-resolved light-induced reflectivity measurements

    NASA Astrophysics Data System (ADS)

    Ishii, Tomoaki; Kawazoe, Tadashi; Hashimoto, Yusuke; Terada, Hiroshi; Muneta, Iriya; Ohtsu, Motoichi; Tanaka, Masaaki; Ohya, Shinobu

    2016-06-01

    Clarification of the electronic structure near the Fermi level is important in understanding the origin of ferromagnetism in the prototypical ferromagnetic semiconductor GaMnAs. Here, we perform ultrafast transient reflectivity spectra measurement, which is a powerful tool for selective detection of absorption edges in GaMnAs. The results show that the Fermi level of GaMnAs exists in the band gap. By using the Kramers-Kronig relation, we find the Mn-induced electronic states around the Fermi level, confirming that the ferromagnetism is stabilized by spin-polarized impurity-band holes.

  9. High-frequency detection of the formation and stabilization of a radiation-induced defect cluster in semiconductor structures

    SciTech Connect

    Puzanov, A. S.; Obolenskiy, S. V. Kozlov, V. A.; Volkova, E. V.; Paveliev, D. G.

    2015-12-15

    The processes of the formation and stabilization of a radiation-induced defect cluster upon the arrival of a fast neutron to the space-charge region of a semiconductor diode are analyzed. The current pulse formed by secondary electrons is calculated and the spectrum of the signal generated by the diode (detector) under the action of an instantaneous neutron flux of the fission spectrum is determined. The possibility of experimental detection of the picosecond radiation-induced transition processes is discussed.

  10. Understanding and Predicting Geomagnetic Dipole Reversals Via Low Dimensional Models and Data Assimilation

    NASA Astrophysics Data System (ADS)

    Morzfeld, M.; Fournier, A.; Hulot, G.

    2014-12-01

    We investigate the geophysical relevance of low-dimensional models of the geomagnetic dipole fieldby comparing these models to the signed relative paleomagnetic intensity over the past 2 Myr.The comparison is done via Bayesian statistics, implemented numerically by Monte Carlo (MC) sampling.We consider several MC schemes, as well as two data sets to show the robustness of our approach with respect to its numerical implementation and to the details of how the data are collected.The data we consider are the Sint-2000 [1] and PADM2M [2] data sets.We consider three stochastic differential equation (SDE) models and one deterministic model. Experiments with synthetic data show that it is feasible that a low dimensional modelcan learn the geophysical state from data of only the dipole field,and reveal the limitations of the low-dimensional models.For example, the G12 model [3] (a deterministic model that generates dipole reversals by crisis induced intermittency)can only match either one of the two important time scales we find in the data. The MC sampling approach also allows usto use the models to make predictions of the dipole field.We assess how reliably dipole reversals can be predictedwith our approach by hind-casting five reversals documented over the past 2 Myr. We find that, besides its limitations, G12 can be used to predict reversals reliably,however only with short lead times and over short horizons. The scalar SDE models on the other hand are not useful for prediction of dipole reversals.References Valet, J.P., Maynadier,L and Guyodo, Y., 2005, Geomagnetic field strength and reversal rate over the past 2 Million years, Nature, 435, 802-805. Ziegler, L.B., Constable, C.G., Johnson, C.L. and Tauxe, L., 2011, PADM2M: a penalized maximum likelihood model of the 0-2 Ma paleomagnetic axial dipole moment, Geophysical Journal International, 184, 1069-1089. Gissinger, C., 2012, A new deterministic model for chaotic reversals, European Physical Journal B, 85:137.

  11. GaN quantum-dots integrated in the gate dielectric of metal-oxide-semiconductor structures for charge-storage applications

    NASA Astrophysics Data System (ADS)

    Dimitrakis, P.; Normand, P.; Bonafos, C.; Papadomanolaki, E.; Iliopoulos, E.

    2013-02-01

    Gallium nitride quantum dots (QDs) were investigated as discrete charge storage nodes embedded in the gate dielectric of metal-oxide-semiconductor (MOS) capacitors. The GaN QDs were formed on top of 3.5 nm-thick SiO2/n-Si(001) substrates by radiofrequency plasma-assisted molecular beam deposition. The MOS structures were studied by transmission electron microscopy. Deposition dose was determined as a critical process parameter to obtain two dimensional arrays of discrete QDs. The memory window width, programming speed, and charge retention time were evaluated for GaN QD devices with different deposition doses. All devices showed enhanced electron trapping leading to significant memory windows. Charge retention measurements, at room temperature, revealed that the sample with the lowest concentration of QDs exhibits a low charge loss with a significant extrapolated programming window after 10 yrs. The present study not only demonstrates GaN QD embedded SiO2 structures fabricated by a fully complementary metal oxide semiconductor compatible method but also points out that these structures are promising for the realization of nanofloating gate non-volatile memory devices.

  12. Order parameter analysis for low-dimensional behaviors of coupled phase-oscillators

    PubMed Central

    Gao, Jian; Xu, Can; Sun, Yuting; Zheng, Zhigang

    2016-01-01

    Coupled phase-oscillators are important models related to synchronization. Recently, Ott-Antonsen(OA) ansatz is developed and used to get low-dimensional collective behaviors in coupled oscillator systems. In this paper, we develop a simple and concise approach based on equations of order parameters, namely, order parameter analysis, with which we point out that OA ansatz is rooted in the dynamical symmetry of order parameters. With our approach the scope of OA ansatz is identified as two conditions, i.e., the limit of infinitely many oscillators and only three nonzero Fourier coefficients of the coupling function. Coinciding with each of the conditions, a distinctive system out of the scope is taken into account and discussed with the order parameter analysis. Two approximation methods are introduced respectively, namely the expectation assumption and the dominating-term assumption. PMID:27443639

  13. Hydrothermal Synthesis and Acetylene Sensing Properties of Variety Low Dimensional Zinc Oxide Nanostructures

    PubMed Central

    Chen, Weigen; Peng, Shudi; Zeng, Wen

    2014-01-01

    Various morphologies of low dimensional ZnO nanostructures, including spheres, rods, sheets, and wires, were successfully synthesized using a simple and facile hydrothermal method assisted with different surfactants. Zinc acetate dihydrate was chosen as the precursors of ZnO nanostructures. We found that polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), glycine, and ethylene glycol (EG) play critical roles in the morphologies and microstructures of the synthesized nanostructures, and a series of possible growth processes were discussed in detail. Gas sensors were fabricated using screen-printing technology, and their sensing properties towards acetylene gas (C2H2), one of the most important arc discharge characteristic gases dissolved in oil-filled power equipments, were systematically measured. The ZnO nanowires based sensor exhibits excellent C2H2 sensing behaviors than those of ZnO nanosheets, nanorods, and nanospheres, indicating a feasible way to develop high-performance C2H2 gas sensor for practical application. PMID:24672324

  14. Order parameter analysis for low-dimensional behaviors of coupled phase-oscillators

    NASA Astrophysics Data System (ADS)

    Gao, Jian; Xu, Can; Sun, Yuting; Zheng, Zhigang

    2016-07-01

    Coupled phase-oscillators are important models related to synchronization. Recently, Ott-Antonsen(OA) ansatz is developed and used to get low-dimensional collective behaviors in coupled oscillator systems. In this paper, we develop a simple and concise approach based on equations of order parameters, namely, order parameter analysis, with which we point out that OA ansatz is rooted in the dynamical symmetry of order parameters. With our approach the scope of OA ansatz is identified as two conditions, i.e., the limit of infinitely many oscillators and only three nonzero Fourier coefficients of the coupling function. Coinciding with each of the conditions, a distinctive system out of the scope is taken into account and discussed with the order parameter analysis. Two approximation methods are introduced respectively, namely the expectation assumption and the dominating-term assumption.

  15. Terahertz spectroscopy of low-dimensional nanomaterials: nonlinear emission and ultrafast electrodynamics

    NASA Astrophysics Data System (ADS)

    Luo, Liang; Wang, Jigang

    2015-08-01

    Nonlinear and non-equilibrium properties of low-dimensional quantum materials are fundamental in nanoscale science yet transformative in nonlinear imaging/photonic technology today. These have been poorly addressed in many nano-materials despite of their well-established equilibrium optical and transport properties. The development of ultrafast terahertz (THz) sources and nonlinear spectroscopy tools facilitates understanding these issues and reveals a wide range of novel nonlinear and quantum phenomena that are not expected in bulk solids or atoms. In this paper, we discuss our recent discoveries in two model photonic and electronic nanostructures to solve two outstanding questions: (1) how to create nonlinear broadband terahertz emitters using deeply subwavelength nanoscale meta-atom resonators? (2) How to access one-dimensional (1D) dark excitons and their non-equilibrium correlated states in single-walled carbon nanotubes (SWMTs)?

  16. Embeddings of low-dimensional strange attractors: topological invariants and degrees of freedom.

    PubMed

    Romanazzi, Nicola; Lefranc, Marc; Gilmore, Robert

    2007-06-01

    When a low-dimensional chaotic attractor is embedded in a three-dimensional space its topological properties are embedding-dependent. We show that there are just three topological properties that depend on the embedding: Parity, global torsion, and knot type. We discuss how they can change with the embedding. Finally, we show that the mechanism that is responsible for creating chaotic behavior is an invariant of all embeddings. These results apply only to chaotic attractors of genus one, which covers the majority of cases in which experimental data have been subjected to topological analysis. This means that the conclusions drawn from previous analyses, for example that the mechanism generating chaotic behavior is a Smale horseshoe mechanism, a reverse horseshoe, a gateau roulé, an S -template branched manifold, etc., are not artifacts of the embedding chosen for the analysis. PMID:17677347

  17. Asymptotic behavior of a low-dimensional model for magnetostriction for periodic input

    NASA Astrophysics Data System (ADS)

    Ekanayake, D. B.; Iyer, R. V.

    2008-02-01

    Models for magnetostrictive actuators need to include rate-independent hysteresis phenomena, magneto-elastic coupling, and eddy current losses that vary nonlinearly with the frequency of the input. In this paper, we study a low-dimensional model for magnetostrictive rod actuators that describes the physical phenomena which are most prominent in the frequency range 0-800 Hz. We show that the solution of the system is asymptotically periodic for bounded, continuous and periodic voltage inputs and with general conditions on a Preisach operator modeling rate-independent hysteresis. The results of this paper are crucial for developing a parameter identification methodology for the model that is addressed in [D.B. Ekanayake, R.V. Iyer, W.P. Dayawansa, Wide band modeling and parameter identification in magnetostrictive actuators, in: Proceedings of IEEE American Control Conference, New York, NY (2007) 4321-4326].

  18. Terahertz Spectroscopy of Low-Dimensional Nanomaterials: Nonlinear Emission and Ultrafast Electrodynamics

    DOE PAGESBeta

    Luo, Liang; Wang, Jigang

    2016-01-01

    Nonlinear and non-equilibrium properties of low-dimensional quantum materials are fundamental in nanoscale science yet transformative in nonlinear imaging/photonic technology today. These have been poorly addressed in many nano-materials despite of their well-established equilibrium optical and transport properties. The development of ultrafast terahertz (THz) sources and nonlinear spectroscopy tools facilitates understanding these issues and reveals a wide range of novel nonlinear and quantum phenomena that are not expected in bulk solids or atoms. In this paper, we discuss our recent discoveries in two model photonic and electronic nanostructures to solve two outstanding questions: (1) how to create nonlinear broadband terahertz emittersmore » using deeply subwavelength nanoscale meta-atom resonators? (2) How to access one-dimensional (1D) dark excitons and their non-equilibrium correlated states in single-walled carbon nanotubes (SWMTs)?« less

  19. Dynamics of low dimensional model for weakly relativistic Zakharov equations for plasmas

    SciTech Connect

    Sahu, Biswajit; Pal, Barnali; Poria, Swarup; Roychoudhury, Rajkumar

    2013-05-15

    In the present paper, the nonlinear interaction between Langmuir waves and ion acoustic waves described by the one-dimensional Zakharov equations (ZEs) for relativistic plasmas are investigated formulating a low dimensional model. Equilibrium points of the model are found and it is shown that the existence and stability conditions of the equilibrium point depend on the relativistic parameter. Computational investigations are carried out to examine the effects of relativistic parameter and other plasma parameters on the dynamics of the model. Power spectrum analysis using fast fourier transform and also construction of first return map confirm that periodic, quasi-periodic, and chaotic type solution exist for both relativistic as well as in non-relativistic case. Existence of supercritical Hopf bifurcation is noted in the system for two critical plasmon numbers.

  20. Order parameter analysis for low-dimensional behaviors of coupled phase-oscillators.

    PubMed

    Gao, Jian; Xu, Can; Sun, Yuting; Zheng, Zhigang

    2016-07-22

    Coupled phase-oscillators are important models related to synchronization. Recently, Ott-Antonsen(OA) ansatz is developed and used to get low-dimensional collective behaviors in coupled oscillator systems. In this paper, we develop a simple and concise approach based on equations of order parameters, namely, order parameter analysis, with which we point out that OA ansatz is rooted in the dynamical symmetry of order parameters. With our approach the scope of OA ansatz is identified as two conditions, i.e., the limit of infinitely many oscillators and only three nonzero Fourier coefficients of the coupling function. Coinciding with each of the conditions, a distinctive system out of the scope is taken into account and discussed with the order parameter analysis. Two approximation methods are introduced respectively, namely the expectation assumption and the dominating-term assumption.

  1. Terahertz Spectroscopy of Low-Dimensional Nanomaterials: Nonlinear Emission and Ultrafast Electrodynamics

    SciTech Connect

    Luo, Liang; Wang, Jigang

    2016-01-01

    Nonlinear and non-equilibrium properties of low-dimensional quantum materials are fundamental in nanoscale science yet transformative in nonlinear imaging/photonic technology today. These have been poorly addressed in many nano-materials despite of their well-established equilibrium optical and transport properties. The development of ultrafast terahertz (THz) sources and nonlinear spectroscopy tools facilitates understanding these issues and reveals a wide range of novel nonlinear and quantum phenomena that are not expected in bulk solids or atoms. In this paper, we discuss our recent discoveries in two model photonic and electronic nanostructures to solve two outstanding questions: (1) how to create nonlinear broadband terahertz emitters using deeply subwavelength nanoscale meta-atom resonators? (2) How to access one-dimensional (1D) dark excitons and their non-equilibrium correlated states in single-walled carbon nanotubes (SWMTs)?

  2. Angle-dependent high magnetic field microwave spectroscopy of low dimensional conductors and superconductors

    NASA Astrophysics Data System (ADS)

    Takahashi, Susumu

    This dissertation presents studies of angle-dependent high-field microwave spectroscopy of low dimensional conductors and superconductors. Over the past 20 years, low dimensional conductors and superconductors have been investigated extensively because of their unusual superconducting, electronic and magnetic ground states. In order to understand these phenomena, it is important to study the topology of the Fermi surface (FS). We employ a novel type of cyclotron resonance to study the FS, the so-called periodic orbit resonance (POR). In Chapter 2, we explain the details of the POR effect using a semiclassical description. An important aspect of this POR effect is that it is applicable not only to a quasi-two-dimensional (Q2D) FS, but also to a quasi-one-dimensional (Q1D) FS. In Chapter 3, our experimental techniques are presented. We outline a rotating cylindrical cavity, which enables angle-dependent cavity perturbation measurements in ultra-high-field magnets, and two-axis rotation capabilities in standard high-field superconducting split-pair magnets. In Chapters 4 and 5, the results of studies of the Q1D conductor (TMTSF) 2ClO4, are shown. Using the POR, we determined the Fermi velocity vF and revealed new information concerning the nature of the so-called Lebed effect in Chapter 4. In Chapter 5, we studied the non-magnetic, impurity effect and its influence on the possible spin-triplet superconductivity in (TMTSF)2ClO4. In Chapter 6, measurements of the POR are performed in the Q2D conductors kappa-(ET)2X [X=Cu(NCS)2 and I3]. In X=I3, POR involving the magnetic breakdown effect was observed for the first time.

  3. Elucidation of the structure-property relationship of p-type organic semiconductors through rapid library construction via a one-pot, Suzuki-Miyaura coupling reaction.

    PubMed

    Fuse, Shinichiro; Matsumura, Keisuke; Wakamiya, Atsushi; Masui, Hisashi; Tanaka, Hiroshi; Yoshikawa, Susumu; Takahashi, Takashi

    2014-09-01

    The elucidation of the structure-property relationship is an important issue in the development of organic electronics. Combinatorial synthesis and the evaluation of systematically modified compounds is a powerful tool in the work of elucidating structure-property relationships. In this manuscript, D-π-A structure, 32 p-type organic semiconductors were rapidly synthesized via a one-pot, Suzuki-Miyaura coupling with subsequent Knoevenagel condensation. Evaluation of the solubility and photovoltaic properties of the prepared compounds revealed that the measured solubility was strongly correlated with the solubility parameter (SP), as reported by Fedors. In addition, the SPs were correlated with the Jsc of thin-film organic solar cells prepared using synthesized compounds. Among the evaluated photovoltaic properties of the solar cells, Jsc and Voc had strong correlations with the photoconversion efficiency (PCE).

  4. Calculating Effect of Point Defects on Optical Absorption Spectra of III-V Semiconductor Superlattices Based on (8x8) k-dot-p Band Structures

    NASA Astrophysics Data System (ADS)

    Huang, Danhong; Iurov, Andrii; Gumbs, Godfrey; Cardimona, David; Krishna, Sanjay

    For a superlattice which is composed of layered zinc-blende structure III-V semiconductor materials, its realistic anisotropic band structures around the Gamma-point are calculated by using the (8x8)k-dot-p method with the inclusion of the self-consistent Hartree potential and the spin-orbit coupling. By including the many-body screening effect, the obtained band structures are further employed to calculate the optical absorption coefficient which is associated with the interband electron transitions. As a result of a reduced quasiparticle lifetime due to scattering with point defects in the system, the self-consistent vertex correction to the optical response function is also calculated with the help of the second-order Born approximation.

  5. Low-dimensional models for the nonlinear vibration analysis of cylindrical shells based on a perturbation procedure and proper orthogonal decomposition

    NASA Astrophysics Data System (ADS)

    Gonçalves, P. B.; Silva, F. M. A.; Del Prado, Z. J. G. N.

    2008-08-01

    In formulating mathematical models for dynamical systems, obtaining a high degree of qualitative correctness (i.e. predictive capability) may not be the only objective. The model must be useful for its intended application, and models of reduced complexity are attractive in many cases where time-consuming numerical procedures are required. This paper discusses the derivation of discrete low-dimensional models for the nonlinear vibration analysis of thin cylindrical shells. In order to understand the peculiarities inherent to this class of structural problems, the nonlinear vibrations and dynamic stability of a circular cylindrical shell subjected to static and dynamic loads are analyzed. This choice is based on the fact that cylindrical shells exhibit a highly nonlinear behavior under both static and dynamic loads. Geometric nonlinearities due to finite-amplitude shell motions are considered by using Donnell's nonlinear shallow-shell theory. A perturbation procedure, validated in previous studies, is used to derive a general expression for the nonlinear vibration modes and the discretized equations of motion are obtained by the Galerkin method using modal expansions for the displacements that satisfy all the relevant boundary and symmetry conditions. Next, the model is analyzed via the Karhunen-Loève expansion to investigate the relative importance of each mode obtained by the perturbation solution on the nonlinear response and total energy of the system. The responses of several low-dimensional models are compared. It is shown that rather low-dimensional but properly selected models can describe with good accuracy the response of the shell up to very large vibration amplitudes.

  6. Semiconductor eutectic solar cell

    NASA Astrophysics Data System (ADS)

    Yue, A. S.; Yu, J. G.

    1986-12-01

    Two-phase semiconducting eutectics are potential device-materials. Of these, the SnSe-SnSe2 eutectic was chosen for studies in detail because it consists of multi-p/n-layers of SnSe and SnSe2 semiconductors. Since plasma frequency has not been detected in its infrared reflectance spectrum up to 40 micrometers of wavelength, it suggests that the SnSe-SnSe2 eutectic is a nondegenerate semiconductor. As-grown SnSe2 single crystals have hexagonal crystallographic structure and show n-type conductivity. Polycrystalline SnSe and SnSe2 films have been successfully prepared in vacuum using a close-space-vapor transport technique.

  7. MBE growth and structural and magnetic properties of (In 1-yAl y) 1-xMn xAs-diluted magnetic semiconductors

    NASA Astrophysics Data System (ADS)

    Lee, W. N.; Chen, Y. F.; Huang, J. H.; Guo, X. J.; Kuo, C. T.; Ku, H. C.

    2006-04-01

    A series of quaternary-diluted magnetic semiconductors, (In 1-yAl y) 1-xMn xAs, have been successfully grown on InP substrates by low-temperature molecular beam epitaxy. The (In 0.52Al 0.48) 1-xMn xAs with x⩽0.11 were grown on a nearly lattice-matched In 0.52Al 0.48As buffer, while the (In 1-yAl y) 1-xMn xAs with a higher Mn content of 0.11< x⩽0.18 were grown on a graded 3-layer In 1-yAl yAs buffer structure. The results of transmission electron microscopy and double-crystal X-ray diffraction reveal that all (In 1-yAl y) 1-xMn xAs epilayers are single crystal with zincblende structure, and the lattice constant increases with increasing the Mn content. The magnetic measurements show that the (In 1-yAl y) 1-xMn xAs semiconductors exhibit a paramagnetic-like state for x⩽0.05 while a ferromagnetic state for x>0.05, and the Curie temperature of ferromagnetic (In 1-yAl y) 1-xMn xAs increases with increasing Mn content.

  8. Handbook of Semiconductor Technology, 2 Volume Set

    NASA Astrophysics Data System (ADS)

    Jackson, Kenneth A.; Schröter, Wolfgang

    2000-09-01

    Semiconductor technology is the basis of today's microelectronics industry with its many impacts on our modern life, i.e. computer and communication technology. This two-volume handbook covers the basics of semiconductor processing technology, which are as essential for the design of new microelectronic devices as the fundamental physics. Volume 1 'Electronic Structure and Properties' covers the structure and properties of semiconductors, with particular emphasis on concepts relevant to semiconductor technology. Volume 2 'Processing of Semiconductors' deals with the enabling materials technology for the electronics industry. World-renowned authors have contributed to this unique treatment of the processing of semiconductors and related technologies. Of interest to physicists and engineers in research and in the electronics industry, this is a valuable reference source and state-of-the-art review by the world's top authors.

  9. Wide band gap semiconductor templates

    DOEpatents

    Arendt, Paul N.; Stan, Liliana; Jia, Quanxi; DePaula, Raymond F.; Usov, Igor O.

    2010-12-14

    The present invention relates to a thin film structure based on an epitaxial (111)-oriented rare earth-Group IVB oxide on the cubic (001) MgO terminated surface and the ion-beam-assisted deposition ("IBAD") techniques that are amendable to be over coated by semiconductors with hexagonal crystal structures. The IBAD magnesium oxide ("MgO") technology, in conjunction with certain template materials, is used to fabricate the desired thin film array. Similarly, IBAD MgO with appropriate template layers can be used for semiconductors with cubic type crystal structures.

  10. Isotopically controlled semiconductors

    SciTech Connect

    Haller, Eugene E.

    2006-06-19

    The following article is an edited transcript based on the Turnbull Lecture given by Eugene E. Haller at the 2005 Materials Research Society Fall Meeting in Boston on November 29, 2005. The David Turnbull Lectureship is awarded to recognize the career of a scientist who has made outstanding contributions to understanding materials phenomena and properties through research, writing, and lecturing, as exemplified by the life work of David Turnbull. Haller was named the 2005 David Turnbull Lecturer for his 'pioneering achievements and leadership in establishing the field of isotopically engineered semiconductors; for outstanding contributions to materials growth, doping and diffusion; and for excellence in lecturing, writing, and fostering international collaborations'. The scientific interest, increased availability, and technological promise of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled semiconductor crystals. This article reviews results obtained with isotopically controlled semiconductor bulk and thin-film heterostructures. Isotopic composition affects several properties such as phonon energies, band structure, and lattice constant in subtle, but, for their physical understanding, significant ways. Large isotope-related effects are observed for thermal conductivity in local vibrational modes of impurities and after neutron transmutation doping. Spectacularly sharp photoluminescence lines have been observed in ultrapure, isotopically enriched silicon crystals. Isotope multilayer structures are especially well suited for simultaneous self- and dopant-diffusion studies. The absence of any chemical, mechanical, or electrical driving forces makes possible the study of an ideal random-walk problem. Isotopically controlled semiconductors may find applications in quantum computing, nanoscience, and spintronics.

  11. Optical waveguide beam splitters based on hybrid metal-dielectric-semiconductor nanostructures

    NASA Astrophysics Data System (ADS)

    Li, Yunyun; Liang, Junwu; Zhang, Qinglin; Zhou, Zidong; Li, Honglai; Fan, Xiaopeng; Wang, Xiaoxia; Fan, Peng; Yang, Yankun; Guo, Pengfei; Zhuang, Xiujuan; Zhu, Xiaoli; Liao, Lei; Pan, Anlian

    2015-11-01

    Miniature integration is desirable for the future photonics circuit. Low-dimensional semiconductor and metal nanostructures is the potential building blocks in compact photonic circuits for their unique electronic and optical properties. In this work, a hybrid metal-dielectric-semiconductor nanostructure is designed and fabricated to realizing a nano-scale optical waveguide beam splitter, which is constructed with the sandwiched structure of a single CdS nanoribbon/HfO2 thin film/Au nanodisk arrays. Micro-optical investigations reveal that the guided light outputting at the terminal end of the CdS ribbon is well separated into several light spots. Numerical simulations further demonstrate that the beam splitting mechanism is attributed to the strong electromagnetic coupling between the Au nanodisks and light guided in the nanoribbon. The number of the split beams (light spots) at the terminal end of the nanoribbon is mainly determined by the number of the Au nanodisk rows, as well as the distance of the blank region between the nanodisks array and the end of the CdS ribbon, owing to the interference between the split beams. These optical beam splitters may find potential applications in high-density integrated photonic circuits and systems.

  12. Stretchable semiconductor elements and stretchable electrical circuits

    DOEpatents

    Rogers, John A.; Khang, Dahl-Young; Menard, Etienne

    2009-07-07

    The invention provides methods and devices for fabricating printable semiconductor elements and assembling printable semiconductor elements onto substrate surfaces. Methods, devices and device components of the present invention are capable of generating a wide range of flexible electronic and optoelectronic devices and arrays of devices on substrates comprising polymeric materials. The present invention also provides stretchable semiconductor structures and stretchable electronic devices capable of good performance in stretched configurations.

  13. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure

    PubMed Central

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-01-01

    The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured. PMID:26596472

  14. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

    SciTech Connect

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-11-24

    In this study, the anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gatecontrol of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.

  15. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

    DOE PAGESBeta

    Oveshnikov, L. N.; Kulbachinskii, V. A.; Davydov, A. B.; Aronzon, B. A.; Rozhansky, I. V.; Averkiev, N. S.; Kugel, K. I.; Tripathi, V.

    2015-11-24

    In this study, the anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gatecontrol of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHEmore » in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured.« less

  16. Berry phase mechanism of the anomalous Hall effect in a disordered two-dimensional magnetic semiconductor structure.

    PubMed

    Oveshnikov, L N; Kulbachinskii, V A; Davydov, A B; Aronzon, B A; Rozhansky, I V; Averkiev, N S; Kugel, K I; Tripathi, V

    2015-01-01

    The anomalous Hall effect (AHE) arises from the interplay of spin-orbit interactions and ferromagnetic order and is a potentially useful probe of electron spin polarization, especially in nanoscale systems where direct measurement is not feasible. While AHE is rather well-understood in metallic ferromagnets, much less is known about the relevance of different physical mechanisms governing AHE in insulators. As ferromagnetic insulators, but not metals, lend themselves to gate-control of electron spin polarization, understanding AHE in the insulating state is valuable from the point of view of spintronic applications. Among the mechanisms proposed in the literature for AHE in insulators, the one related to a geometric (Berry) phase effect has been elusive in past studies. The recent discovery of quantized AHE in magnetically doped topological insulators - essentially a Berry phase effect - provides strong additional motivation to undertake more careful search for geometric phase effects in AHE in the magnetic semiconductors. Here we report our experiments on the temperature and magnetic field dependences of AHE in insulating, strongly-disordered two-dimensional Mn delta-doped semiconductor heterostructures in the hopping regime. In particular, it is shown that at sufficiently low temperatures, the mechanism of AHE related to the Berry phase is favoured. PMID:26596472

  17. Optical-cell model based on the lasing competition of mode structures with different Q-factors in high-power semiconductor lasers

    SciTech Connect

    Podoskin, A. A. Shashkin, I. S.; Slipchenko, S. O.; Pikhtin, N. A.; Tarasov, I. S.

    2015-08-15

    A model describing the operation of a completely optical cell, based on the competition of lasing of Fabry-Perot cavity modes and the high-Q closed mode in high-power semiconductor lasers is proposed. Based on rate equations, the conditions of lasing switching between Fabry-Perot modes for ground and excited lasing levels and the closed mode are considered in the case of increasing internal optical loss under conditions of high current pump levels. The optical-cell operation conditions in the mode of a high-power laser radiation switch (reversible mode-structure switching) and in the mode of a memory cell with bistable irreversible lasing switching between mode structures with various Q-factors are considered.

  18. Magnetically modulated laser-induced resistance effect observed in Metal-Oxide-Semiconductor structure of Cr/SiO(2)/Si.

    PubMed

    Xie, Xin; Liu, Shuai; Huang, Meizhen; Wang, Hui

    2015-09-21

    In this study, we report our finding of laser-induced resistance effect in metal-oxide-semiconductor (MOS) structure of Cr/SiO(2)/Si. Under the irradiation of a laser beam, the effect shows a large linear resistance change ratio of 92% with a spatial sensitivity of 0.79 MΩ/mm. In particular, by the application of an external magnetic field perpendicular to the Cr film, the resistance change ratio is increased to 110%. This effect is attributed to the Lorentz force acting on the photo-generated carriers in the inversion layer of MOS structures. The work suggests an approach for the development of new type magnetically modulated photoelectric devices.

  19. Magnetically modulated laser-induced resistance effect observed in Metal-Oxide-Semiconductor structure of Cr/SiO(2)/Si.

    PubMed

    Xie, Xin; Liu, Shuai; Huang, Meizhen; Wang, Hui

    2015-09-21

    In this study, we report our finding of laser-induced resistance effect in metal-oxide-semiconductor (MOS) structure of Cr/SiO(2)/Si. Under the irradiation of a laser beam, the effect shows a large linear resistance change ratio of 92% with a spatial sensitivity of 0.79 MΩ/mm. In particular, by the application of an external magnetic field perpendicular to the Cr film, the resistance change ratio is increased to 110%. This effect is attributed to the Lorentz force acting on the photo-generated carriers in the inversion layer of MOS structures. The work suggests an approach for the development of new type magnetically modulated photoelectric devices. PMID:26406634

  20. Terahertz radiation from InAlAs and GaAs surface intrinsic-N+ structures and the critical electric fields of semiconductors

    NASA Astrophysics Data System (ADS)

    Hwang, J. S.; Lin, H. C.; Lin, K. I.; Zhang, X. C.

    2005-09-01

    This study examines terahertz radiation from a series of In0.52Al0.48As and GaAs surface-intrinsic-N+ structures (SIN+) with surface-intrinsic layers of various thicknesses. The built-in electric fields in the SIN+ structures are used as the bias. Experimental results indicate that the amplitudes of the THz emission are independent of the built-in electric fields in the emitters when the built-in electric fields exceed the corresponding critical electric fields of the semiconductors. In contrast, the amplitudes of the THz emission are proportional to the thickness of the intrinsic layer and, therefore, the number of photo-excited charged carriers.

  1. Leakage Current Mechanism of InN-Based Metal-Insulator-Semiconductor Structures with Al2O3 as Dielectric Layers

    NASA Astrophysics Data System (ADS)

    Wang, X.; Zhang, G. Z.; Xu, Y.; Gan, X. W.; Chen, C.; Wang, Z.; Wang, Y.; Wang, J. L.; Wang, T.; Wu, H.; Liu, C.

    2016-01-01

    InN-based metal-insulator-semiconductor (MIS) structures were prepared with Al2O3 as the gate oxides. Surface morphologies of InN films are improved with increasing Mg doping concentrations. At high frequencies, the measured capacitance densities deviate from the real ones with turning frequencies inversely proportional to series resistances. An ultralow leakage current density of 1.35 × 10-9 A/cm2 at 1 V is obtained. Fowler-Nordheim tunneling is the main mechanism of the leakage current at high fields, while Schottky emission dominates at low fields. Capacitance densities shift with different biases, indicating that the InN-based MIS structures can serve as potential candidates for MIS field-effect transistors.

  2. Two-dimensional inorganic–organic hybrid semiconductors composed of double-layered ZnS and monoamines with aromatic and heterocyclic aliphatic rings: Syntheses, structures, and properties

    SciTech Connect

    Wang, Sujing; Li, Jing

    2015-04-15

    As an addition to the II–VI based inorganic–organic hybrid semiconductor family, five new two-dimensional (2D) double-layered structures have been synthesized employing monoamines with different aromatic or heterocyclic aliphatic rings. Zn{sub 2}S{sub 2}(bza) (1), Zn{sub 2}S{sub 2}(mbza) (2), Zn{sub 2}S{sub 2}(fbza) (3), Zn{sub 2}S{sub 2}(pca) (4), and Zn{sub 2}S{sub 2}(thfa) (5) (bza=benzylamine, mbza=4-methoxybenzylamine, fbza=4-flurobenzylamine, pca=3-picolylamine, and thfa=tetrahydrofurfurylamine) are prepared by solvothermal reactions and characterized by different analytical methods, including powder X-ray diffraction, optical diffuse reflection, thermogravimetric analysis and photoluminescence spectroscopy. The powder X-ray diffraction patterns show that all five compounds adopt 2D double-layered structures. Optical diffuse reflectance spectra of these compounds suggest that they have notably lower band gaps than those of the similar compounds composed of aliphatic alkyl amines. Their photoluminescence properties and thermal stability are also analyzed. - Graphical abstract: Five new members of two-dimensional double-layered 2D-Zn{sub 2}S{sub 2}(L) (L=Ligand) structures employing monoamines with different aromatic or heterocyclic aliphatic rings have been designed, synthesized, and characterized. - Highlights: • A new sub-family of II-VI based hybrid semiconductors are designed, synthesized, and structurally characterized using amines with aromatic or aliphatic cyclic rings. • These compounds have notably lower band gaps than those made of aliphatic alkyl amines, greatly broadening the range of band gaps of this material family. • They emit strongly with systematically tunable emission intensity and energy.

  3. Temperature dependent junction capacitance-voltage characteristics of Ni embedded TiN/SiO{sub 2}/p-Si metal–insulator–semiconductor structure

    SciTech Connect

    Panda, J.; Nath, T. K.; Chattopadhyay, S.

    2013-12-14

    This work presents the junction capacitance–voltage characteristics of highly textured/epitaxial Ni nanoparticle embedded in TiN matrix (TiN(Ni)) metal-insulator-semiconductor TiN(Ni)/SiO{sub 2}/p-Si (100) heterojunction in the temperature range of 10–300 K. This heterojunction behaves as metal-semiconductor junction with unavoidable leakage through native oxide SiO{sub 2} layer. The clockwise hysteresis loop has been observed in the capacitance-voltage characteristics measured at various frequencies mainly due to presence of trap centers at the TiN(Ni)/SiO{sub 2} interface and these are temperature dependent. The spin-dependent trap charge effect at the interface influences the quadratic nature of the capacitance with magnetic field. The junction magnetocapacitance (JMC) is observed to be dependent on both temperature and frequency. The highest JMC of this heterojunction has been observed at 200 K at higher frequencies (100 kHz–1 MHz). It is found that there is not much effect of band structure modification under magnetic field causing the JMC.

  4. Near-edge band structures and band gaps of Cu-based semiconductors predicted by the modified Becke-Johnson potential plus an on-site Coulomb U

    NASA Astrophysics Data System (ADS)

    Zhang, Yubo; Zhang, Jiawei; Gao, Weiwei; Abtew, Tesfaye A.; Wang, Youwei; Zhang, Peihong; Zhang, Wenqing

    2013-11-01

    Diamond-like Cu-based multinary semiconductors are a rich family of materials that hold promise in a wide range of applications. Unfortunately, accurate theoretical understanding of the electronic properties of these materials is hindered by the involvement of Cu d electrons. Density functional theory (DFT) based calculations using the local density approximation or generalized gradient approximation often give qualitative wrong electronic properties of these materials, especially for narrow-gap systems. The modified Becke-Johnson (mBJ) method has been shown to be a promising alternative to more elaborate theory such as the GW approximation for fast materials screening and predictions. However, straightforward applications of the mBJ method to these materials still encounter significant difficulties because of the insufficient treatment of the localized d electrons. We show that combining the promise of mBJ potential and the spirit of the well-established DFT + U method leads to a much improved description of the electronic structures, including the most challenging narrow-gap systems. A survey of the band gaps of about 20 Cu-based semiconductors calculated using the mBJ + U method shows that the results agree with reliable values to within ±0.2 eV.

  5. Charge-flow structures as polymeric early-warning fire alarm devices. M.S. Thesis; [metal oxide semiconductors

    NASA Technical Reports Server (NTRS)

    Sechen, C. M.; Senturia, S. D.

    1977-01-01

    The charge-flow transistor (CFT) and its applications for fire detection and gas sensing were investigated. The utility of various thin film polymers as possible sensing materials was determined. One polymer, PAPA, showed promise as a relative humidity sensor; two others, PFI and PSB, were found to be particularly suitable for fire detection. The behavior of the charge-flow capacitor, which is basically a parallel-plate capacitor with a polymer-filled gap in the metallic tip electrode, was successfully modeled as an RC transmission line. Prototype charge-flow transistors were fabricated and tested. The effective threshold voltage of this metal oxide semiconductor was found to be dependent on whether surface or bulk conduction in the thin film was dominant. Fire tests with a PFI-coated CFT indicate good sensitivity to smouldering fires.

  6. Theory of operating characteristics of a semiconductor quantum well laser: Inclusion of global electroneutrality in the structure

    NASA Astrophysics Data System (ADS)

    Sokolova, Z. N.; Pikhtin, N. A.; Tarasov, I. S.; Asryan, L. V.

    2016-08-01

    A model for calculating the operating characteristics of semiconductor quantum well (QW) lasers is presented. The model exploits the condition of global electroneutrality, which includes the charge carriers both in the two-dimensional (2D) active region (QW) and bulk waveguide region (optical confinement layer - OCL). The charge of each sign in the OCL is shown to be significantly larger than that in the QW. As a result of this, (i) the global electroneutrality condition reduces to the condition of electroneutrality in the OCL and (ii) the local electroneutrality in the QW can be strongly violated, i.e., the 2D electron and hole densities in the QW can significantly differ from each other.

  7. The impact of the Pb(Zr,Ti)O3-ZnO interface quality on the hysteretic properties of a metal-ferroelectric-semiconductor structure

    NASA Astrophysics Data System (ADS)

    Pintilie, I.; Pasuk, I.; Ibanescu, G. A.; Negrea, R.; Chirila, C.; Vasile, E.; Pintilie, L.

    2012-11-01

    The hysteretic properties of metal-ferroelectric-semiconductor (MFS) structures based on Pb(Zr0.2Ti0.8)O3 (PZT) and ZnO films were studied with respect of the quality of the PZT-ZnO interface. The films were grown by pulsed laser deposition (PLD) on platinized silicon (Pt/Si) substrate and on single crystal, (001) oriented SrTiO3 (STO) substrates. The structural analysis has revealed that the PZT-ZnO stack grown on single crystal STO is epitaxial, while the structure grown on Pt/Si has columnar texture. The temperature change of the capacitance-voltage (C-V) hysteresis direction, from clockwise at low temperatures to counter clockwise at high temperatures, was observed at around 300 K in the case of the MFS structure grown by PLD on Pt/Si substrate. This temperature is lower than the one reported for the case of the PZT-ZnO structure grown by sol-gel on Pt/Si substrate (Pintilie et al., Appl. Phys. Lett. 96, 012903 (2010)). In the fully epitaxial structures the C-V hysteresis is counter clockwise even at 100 K. These findings strongly points out that the quality of the PZT-ZnO interface is essential for having a C-V hysteresis of ferroelectric nature, with negligible influence from the part of the interface states and with a memory window of about 5 V at room temperature.

  8. Enhancement of light depolarization by random ensembles of titania-based low-dimensional nanoparticles

    NASA Astrophysics Data System (ADS)

    Zimnyakov, D. A.; Zdrajevsky, R. A.; Yuvchenko, S. A.; Ushakova, O. V.; Angelsky, O. V.; Yermolenko, S. B.

    2015-02-01

    Depolarization peculiarities of the light scattered by the random ensembles of titania-based low-dimensional nanoparticles are studied during the experiments with aqueous suspensions of potassium polytitanate nanoplatelets and nanoribbons. The obtained experimental results are compared with the theoretical data obtained for the random systems of oblate and prolate flattened ellipsoidal nanoparticles with various values of the shape factor and dielectric function corresponding the parent material (titanium dioxide). The possibility to recover the effective dielectric function from the depolarization ratio spectra using the ellipsoidal shape model is considered. Ellipsoidal approximation is appropriate for both the nanoplatelets and nanoribbons in the spectral region for which the real part of nanoparticles permittivity is sufficiently negative and the near-resonant excitation of longitudinal mode of charge oscillations in nanoparticles occurs. Also, ellipsoidal approximation is appropriate for nanoplatelets in the region of sufficiently po sitive real part of permittivity but gives remarkably underestimated values of the depolarization ratio for nanoribbons in the region. This is presumably caused by considerable difference in the light-induced charge distributions for nanoribbons and prolate flattened ellipsoidal nanoparticles with the decreasing efficiency in longitudinal mode excitation. The recovered values of nanoparticle permittivity exhibit the red shift with respect to the permittivity values of the parent material due to its modification in the course of nanoparticles synthesis.

  9. High Field Magnetization Studies of Low Dimensional Heisenberg S = 1/2 Antiferromagnets

    NASA Astrophysics Data System (ADS)

    Landee, C. P.; Turnbull, M. M.

    1998-03-01

    The magnetization curves of a number of low dimensional S=1/2 Heisenberg antiferromagnets have been determined in fields up to 30 tesla at low temperatures at the National High Magnetic Fields Laboratory. Materials studied include a family of 1D materials, based upon Cu(pyrazine)(NO_3)_2, 2D magnets consisting of pyrazine-bridged copper layers, and several spin ladders with singlet ground states. All of the magnetization data show upward curvature and are well described by T = 0 calculations based upon finite cluster models(Bonner and Fisher, Phys. Rev. A135, 640 (1964); Yang and Mutter, NANL cond-mat/9610092.). Chemical substitution on the pyrazine rings permits the variation of exchange constants by more than 25 percent for the family of well isolated chains. The spin ladder systems consist of ferromagnetic dimers weakly connected by antiferromagnetic intradimer interactions. Field induced transitions are seen at fields of less than one tesla for each of the three compounds.

  10. Spin-phonon coupling and magnetic heat transport in low-dimensional quantum antiferromagnets

    NASA Astrophysics Data System (ADS)

    Prasai, Narayan

    Experimental measurements of heat conduction in the low-dimensional antiferromagnetic compounds CuSb2O6 and BiCu2PO6 are presented for the range 0.5K ≤ T ≤ 390K. Both compounds have magnetic exchange ( J) and Debye (θD) energies that are comparable. This distinguishes the present work from prior studies which have focused on the regime J>>θD Individual crystals were characterized by x-ray diffraction to identify bicrystallinity, twinning and other defects. Thermal conductivity kappa(T) for both the spin-½ chain compound (CuSb2O6) and the spin-½ two-leg ladder compound (BiCu2PO6) imply strong spin-phonon resonant scattering. Model fitting to the lattice component of the heat conductivity was employed to extract a characteristic energy scale for the magnetic excitations. Anisotropy was evident in kappa of both compounds, possibly associated with heat conduction by the spin system. The magnetic mean free path inferred from the data are also presented and compared with those of other low-D spin systems.

  11. A Spatial Division Clustering Method and Low Dimensional Feature Extraction Technique Based Indoor Positioning System

    PubMed Central

    Mo, Yun; Zhang, Zhongzhao; Meng, Weixiao; Ma, Lin; Wang, Yao

    2014-01-01

    Indoor positioning systems based on the fingerprint method are widely used due to the large number of existing devices with a wide range of coverage. However, extensive positioning regions with a massive fingerprint database may cause high computational complexity and error margins, therefore clustering methods are widely applied as a solution. However, traditional clustering methods in positioning systems can only measure the similarity of the Received Signal Strength without being concerned with the continuity of physical coordinates. Besides, outage of access points could result in asymmetric matching problems which severely affect the fine positioning procedure. To solve these issues, in this paper we propose a positioning system based on the Spatial Division Clustering (SDC) method for clustering the fingerprint dataset subject to physical distance constraints. With the Genetic Algorithm and Support Vector Machine techniques, SDC can achieve higher coarse positioning accuracy than traditional clustering algorithms. In terms of fine localization, based on the Kernel Principal Component Analysis method, the proposed positioning system outperforms its counterparts based on other feature extraction methods in low dimensionality. Apart from balancing online matching computational burden, the new positioning system exhibits advantageous performance on radio map clustering, and also shows better robustness and adaptability in the asymmetric matching problem aspect. PMID:24451470

  12. A Low-Dimensional Principal Manifold as the "Attractor Backbone" of a Chaotic Beam System

    NASA Astrophysics Data System (ADS)

    Bollt, Erik M.; Skufca, Joseph D.

    We model an elastic beam subject to a contact load which displaces under a chaotic external forcing, motivated by application of a ship carrying either a crane, or fluids in internal tanks. This model not only has rich dynamics and relevance in its own right, it gives rise to a Partial Differential Equation (PDE) whose solutions are chaotic, with an attractor whose points lie "near" a low-dimensional curve. This form identifies a data-driven dimensionality reduction which encapsulates a Cartesian product, approximately, of a principal manifold, corresponding to spatial regularity, against a temporal complex dynamics of the intrinsic variable of the manifold. The principal manifold element serves to translate the complex information at one site to all other sites on the beam. Although points of the attractor do not lie on the principal manifold, they lie sufficiently close that we describe that manifold as a "backbone" running through the attractor, allowing the manifold to serve as a suitable space to approximate behaviors.

  13. Reduction of optically observed artillery blast wave trajectories using low dimensionality models

    NASA Astrophysics Data System (ADS)

    Steward, Bryan J.; Gross, Kevin C.; Perram, Glen P.

    2011-05-01

    Muzzle blast trajectories from firings of a 152 mm caliber gun howitzer were obtained with high-speed optical imagers and used to assess the fidelity with which low dimensionality models can be used for data reduction. Characteristic flow regions were defined for the blast waves. The near-field region was estimated to extend to 0.98 - 1.25 meters from the muzzle and the far-field region was estimated to begin at 2.61 - 3.31 meters. Blast wave geometries and radial trajectories were collected in the near through far-fields with visible imagers operating at 1,600 Hz. Beyond the near-field the blast waves exhibited a near-spherical geometry in which the major axis of the blast lay along the axis of the gun barrel and measured within 95% of the minor axis. Several blast wave propagation models were applied to the mid and far-field data to determine their ability to reduce the blast wave trajectories to fewer parameters while retaining the ability to distinguish amongst three munitions configurations. A total of 147 firings were observed and used to assess within-configuration variability relative to separation between configurations. Results show that all models perform well, and drag and point blast model parameters additionally provide insight into phenomenology of the blast.

  14. Phases and approximations of baryonic popcorn in a low-dimensional analogue of holographic QCD

    NASA Astrophysics Data System (ADS)

    Elliot-Ripley, Matthew

    2015-07-01

    The Sakai-Sugimoto model is the most pre-eminent model of holographic QCD, in which baryons correspond to topological solitons in a five-dimensional bulk spacetime. Recently it has been shown that a single soliton in this model can be well approximated by a flat-space self-dual Yang-Mills instanton with a small size, although studies of multi-solitons and solitons at finite density are currently beyond numerical computations. A lower-dimensional analogue of the model has also been studied in which the Sakai-Sugimoto soliton is replaced by a baby Skyrmion in three spacetime dimensions with a warped metric. The lower dimensionality of this model means that full numerical field calculations are possible, and static multi-solitons and solitons at finite density were both investigated, in particular the baryonic popcorn phase transitions at high densities. Here we present and investigate an alternative lower-dimensional analogue of the Sakai-Sugimoto model in which the Sakai-Sugimoto soliton is replaced by an O(3)-sigma model instanton in a warped three-dimensional spacetime stabilized by a massive vector meson. A more detailed range of baryonic popcorn phase transitions are found, and the low-dimensional model is used as a testing ground to check the validity of common approximations made in the full five-dimensional model, namely approximating fields using their flat-space equations of motion, and performing a leading order expansion in the metric.

  15. An optoelectronic framework enabled by low-dimensional phase-change films

    NASA Astrophysics Data System (ADS)

    Hosseini, Peiman; Wright, C. David; Bhaskaran, Harish

    2014-07-01

    The development of materials whose refractive index can be optically transformed as desired, such as chalcogenide-based phase-change materials, has revolutionized the media and data storage industries by providing inexpensive, high-speed, portable and reliable platforms able to store vast quantities of data. Phase-change materials switch between two solid states--amorphous and crystalline--in response to a stimulus, such as heat, with an associated change in the physical properties of the material, including optical absorption, electrical conductance and Young's modulus. The initial applications of these materials (particularly the germanium antimony tellurium alloy Ge2Sb2Te5) exploited the reversible change in their optical properties in rewritable optical data storage technologies. More recently, the change in their electrical conductivity has also been extensively studied in the development of non-volatile phase-change memories. Here we show that by combining the optical and electronic property modulation of such materials, display and data visualization applications that go beyond data storage can be created. Using extremely thin phase-change materials and transparent conductors, we demonstrate electrically induced stable colour changes in both reflective and semi-transparent modes. Further, we show how a pixelated approach can be used in displays on both rigid and flexible films. This optoelectronic framework using low-dimensional phase-change materials has many likely applications, such as ultrafast, entirely solid-state displays with nanometre-scale pixels, semi-transparent `smart' glasses, `smart' contact lenses and artificial retina devices.

  16. Low-dimensional recurrent neural network-based Kalman filter for speech enhancement.

    PubMed

    Xia, Youshen; Wang, Jun

    2015-07-01

    This paper proposes a new recurrent neural network-based Kalman filter for speech enhancement, based on a noise-constrained least squares estimate. The parameters of speech signal modeled as autoregressive process are first estimated by using the proposed recurrent neural network and the speech signal is then recovered from Kalman filtering. The proposed recurrent neural network is globally asymptomatically stable to the noise-constrained estimate. Because the noise-constrained estimate has a robust performance against non-Gaussian noise, the proposed recurrent neural network-based speech enhancement algorithm can minimize the estimation error of Kalman filter parameters in non-Gaussian noise. Furthermore, having a low-dimensional model feature, the proposed neural network-based speech enhancement algorithm has a much faster speed than two existing recurrent neural networks-based speech enhancement algorithms. Simulation results show that the proposed recurrent neural network-based speech enhancement algorithm can produce a good performance with fast computation and noise reduction.

  17. Layered semiconductor neutron detectors

    DOEpatents

    Mao, Samuel S; Perry, Dale L

    2013-12-10

    Room temperature operating solid state hand held neutron detectors integrate one or more relatively thin layers of a high neutron interaction cross-section element or materials with semiconductor detectors. The high neutron interaction cross-section element (e.g., Gd, B or Li) or materials comprising at least one high neutron interaction cross-section element can be in the form of unstructured layers or micro- or nano-structured arrays. Such architecture provides high efficiency neutron detector devices by capturing substantially more carriers produced from high energy .alpha.-particles or .gamma.-photons generated by neutron interaction.

  18. Isotopically controlled semiconductors

    SciTech Connect

    Haller, Eugene E.

    2001-12-21

    Semiconductor bulk crystals and multilayer structures with controlled isotopic composition have attracted much scientific and technical interest in the past few years. Isotopic composition affects a large number of physical properties, including phonon energies and lifetimes, bandgaps, the thermal conductivity and expansion coefficient and spin-related effects. Isotope superlattices are ideal media for self-diffusion studies. In combination with neutron transmutation doping, isotope control offers a novel approach to metal-insulator transition studies. Spintronics, quantum computing and nanoparticle science are emerging fields using isotope control.

  19. Prediction of structural and metal-to-semiconductor phase transitions in nanoscale MoS2, WS2, and other transition metal dichalcogenide zigzag ribbons

    NASA Astrophysics Data System (ADS)

    Güller, F.; Llois, A. M.; Goniakowski, J.; Noguera, C.

    2015-02-01

    While MoS2 and WS2 nanostructures gain an increasing importance in a number of recent technological applications, the control of their structure as a function of their size and their environment appears of prominent importance. In the present study which relies on first-principles simulations, we predict the dimerized 1T ' structural phase to be the actual ground state of MoS2, WS2, and MoSe2 zigzag nanoribbons of small width and monolayer thickness. We assign this result to the competition between edge energy—which favors the nonpolar 1T ' edges over the polar 1H edges—and the energy of atoms in the center of the ribbons—which favors the 1H ground state of the infinite monolayers. A metal-to-semiconductor transition accompanies the structural transition. At variance, ZrS2 zigzag ribbons are predicted to display the 1T structure whatever their width. In compounds of major technological importance, such structural and electronic flexibility associated with polarity effects opens the possibility for controlling the ribbon type during synthesis.

  20. Electrical Characteristics of Low-Temperature Polycrystalline Silicon Complementary Metal-Oxide-Semiconductor Thin-Film Transistors with Six-Step Photomask Structure

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Jin; Park, Jae-Hoon; Oh, Kum-Mi; Lee, Seok-Woo; Lee, Kyung-Eon; Shin, Woo-Sup; Jun, Myung-chul; Yang, Yong-Suk; Hwang, Yong-Kee

    2011-06-01

    We propose two types of six-step photomask, complementary metal-oxide-semiconductor (CMOS), thin-film transistor (TFT) PCT device structures in order to simplify their fabrication process compared with that of conventional, low-temperature, polycrystalline silicon (LTPS) CMOS TFT devices. The initial charge transfer characteristics of both types of six-step PCT are equivalent to those of the conventional nine-step PCT. Both types of six-step PCT are comparable to the conventional nine-step mask lightly doped drain (LDD) device in terms of the dc device lifetime of over 10 years at Vds=5 V for line inversion driving, which is the normally recognized duration time for semiconducting devices.

  1. Electrical properties of germanium-based insulator-semiconductor structures with an insulating layer of polynucleotides, and their monomer components on the surface

    SciTech Connect

    Yafyasov, A. M. Bakulev, V. M.; Konorov, P. P.; Bogevolnov, V. V.

    2011-12-15

    It is shown that adsorption of nucleic acid molecules and their monomeric components, i.e., nitrogenous bases, from aqueous solutions results in the formation of an insulating layer on the germanium surface. Comparatively small values of the insulator charge and the surface-state density point to promising applications of nucleotides for both the formation of germanium-based insulator-semiconductor structures with nanoscale insulating layers and low surface-state densities at the phase interface, and for germanium surface passivation. Changes in the electronic properties of the space-charge region of germanium during nucleotide adsorption on its surface can be used as a method for determining the nucleotide molecule concentration in aqueous solutions.

  2. Room-temperature detection of spin accumulation in silicon across Schottky tunnel barriers using a metal-oxide-semiconductor field effect transistor structure (invited)

    NASA Astrophysics Data System (ADS)

    Hamaya, K.; Ando, Y.; Masaki, K.; Maeda, Y.; Fujita, Y.; Yamada, S.; Sawano, K.; Miyao, M.

    2013-05-01

    Using a metal-oxide-semiconductor field effect transistor structure with a high-quality CoFe/n+-Si contact, we systematically study spin injection and spin accumulation in a nondegenerated Si channel with a doping density of ˜4.5 × 1015 cm-3 at room temperature. By applying the gate voltage (VG) to the channel, we obtain sufficient bias currents (IBias) for creating spin accumulation in the channel and observe clear spin-accumulation signals even at room temperature. Whereas the magnitude of the spin signals is enhanced by increasing IBias, it is reduced by increasing VG interestingly. These features can be understood within the framework of the conventional spin diffusion model. As a result, a room-temperature spin injection technique for the nondegenerated Si channel without using insulating tunnel barriers is established, which indicates a technological progress for Si-based spintronic applications with gate electrodes.

  3. Theoretical-physics approach to selected problems in engineering electromagnetics: Evolutionary optimization and low-dimensional nanostructures

    NASA Astrophysics Data System (ADS)

    Mikki, Said M.

    by replacing them with point sources. The QPSO proved powerful in obtaining accurate models for metallic- and dielectric-type antennas. Part II is concerned with the electrodynamics of nano-structures. This emerging field in nanotechnology has attracted the attention recently with great promise for revolutionary changes in the technology of the future. We picked carbon nanotubes as a low-dimensional structure (1D) and studied its electrodynamics extensively. These fascinating structures are expected to play a major role in future electronics and speculations about the possibility of them replacing silicon has already been examined. However, the electrodynamics of nano-structures is very different from the formalism usually understood in engineering electromagnetism. There are many important theoretical consideration that should be taken into account for successful numerical modeling of these devices in the future. We show here that such consideration derives exactly from the proper understanding of electromagnetism in theoretical physics, rather than engineering electromagnetism.

  4. Low-dimensional models for the estimation of anthropogenic CO2 emissions from atmospheric observations

    NASA Astrophysics Data System (ADS)

    van Bloemen Waanders, B.; Ray, J.; McKenna, S. A.; Yadav, V.; Michalak, A. M.

    2011-12-01

    The estimation of anthropogenic fossil fuel emissions using atmospheric observations of CO2 has recently attracted increasing interest due to its relevance to monitoring of CO2 mitigation treaties and programs. To date, techniques to perform large-scale inversions had primarily been developed within the context of understanding biospheric and oceanic fluxes. Such fluxes tend to vary relatively smoothly in space and time, making it possible to use multiGaussian models to parameterize and regularize such inversions, predicated on limited measurements of CO2 concentrations. However, the spatial distribution of anthropogenic emissions is non-stationary and multiscale, and therefore makes the use of multiGaussians models less suitable. Thus, a need exists to identify how anthropogenic emissions may be represented in a low-dimensional manner (i.e., with few parameters), for use in top-down estimation. Certain aspects of the spatial extent of anthropogenic emissions can be represented using easily measurable proxies such as nightlights, population density and GDP; in fact, fossil fuel inventories regularly use them to disaggregate regional emission budgets to finer spatial resolutions. However, such proxies can also be used to construct a priori models for anthropogenic emissions, which can then be updated, with data, through inverse modeling. In this presentation, we compare 3 low-dimensional parameterizations to characterize anthropogenic sources. The models are derived from images of nightlights over the continental USA, but adopt different arguments to achieve their dimensionality reduction. In the first model, we threshold nightlights and fit bivariate Gaussian kernels over clusters to represent emission sources; the emission field is modeled as a weighted sum of the kernels. The second approach models emissions as a weighted superposition of a filtered nightlight-distribution and a multiresolution defect, modeled with Haar wavelet. The nightlight-based methods

  5. Robust low dimensional kernel correlation feature spaces that generalize to unseen datasets

    NASA Astrophysics Data System (ADS)

    Abiantun, Ramzi; Savvides, Marios; Vijayakumar, B. V. K.

    2007-04-01

    In this paper we demonstrate the subspace generalization power of the kernel correlation feature analysis (KCFA) method for extracting a low dimensional subspace that has the ability to represent new unseen datasets. Examining the portability of this algorithm across different datasets is an important practical aspect of real-world face recognition applications where the technology cannot be dataset-dependant. In most face recognition literature, algorithms are demonstrated on datasets by training on one portion of the dataset and testing on the remainder. Generally, the testing subjects' dataset partially or totally overlap the training subjects' dataset however with disjoint images captured from different sessions. Thus, some of the expected facial variations and the people's faces are modeled in the training set. In this paper we describe how we efficiently build a compact feature subspace using kernel correlation filter analysis on the generic training set of the FRGC dataset and use that basis for recognition on a different dataset. The KCFA feature subspace has a total dimension that corresponds to the number of training subjects; we chose to vary this number to include up to all of 222 available in the FRGC generic dataset. We test the built subspace produced by KCFA by projecting other well-known face datasets upon it. We show that this feature subspace has good representation and discrimination to unseen datasets and produces good verification and identification rates compared to other subspace and dimensionality reduction methods such as PCA (when trained on the same FRGC generic dataset). Its efficiency, lower dimensionality and discriminative power make it more practical and powerful than PCA as a robust lower dimensionality reduction method for modeling faces and facial variations.

  6. Low-dimensional attractor for neural activity from local field potentials in optogenetic mice.

    PubMed

    Oprisan, Sorinel A; Lynn, Patrick E; Tompa, Tamas; Lavin, Antonieta

    2015-01-01

    We used optogenetic mice to investigate possible nonlinear responses of the medial prefrontal cortex (mPFC) local network to light stimuli delivered by a 473 nm laser through a fiber optics. Every 2 s, a brief 10 ms light pulse was applied and the local field potentials (LFPs) were recorded with a 10 kHz sampling rate. The experiment was repeated 100 times and we only retained and analyzed data from six animals that showed stable and repeatable response to optical stimulations. The presence of nonlinearity in our data was checked using the null hypothesis that the data were linearly correlated in the temporal domain, but were random otherwise. For each trail, 100 surrogate data sets were generated and both time reversal asymmetry and false nearest neighbor (FNN) were used as discriminating statistics for the null hypothesis. We found that nonlinearity is present in all LFP data. The first 0.5 s of each 2 s LFP recording were dominated by the transient response of the networks. For each trial, we used the last 1.5 s of steady activity to measure the phase resetting induced by the brief 10 ms light stimulus. After correcting the LFPs for the effect of phase resetting, additional preprocessing was carried out using dendrograms to identify "similar" groups among LFP trials. We found that the steady dynamics of mPFC in response to light stimuli could be reconstructed in a three-dimensional phase space with topologically similar "8"-shaped attractors across different animals. Our results also open the possibility of designing a low-dimensional model for optical stimulation of the mPFC local network.

  7. Metastable Phases and Dynamics of Low-Dimensional Strongly-Correlated Atomic Quantum Gases

    NASA Astrophysics Data System (ADS)

    Pielawa, Susanne

    In this thesis we theoretically study low-dimensional, strongly correlated systems of cold atoms, which are not in an equilibrium situation. This is motivated by recent experimental progress, which has made it possible to study quantum many-body physics in a controllable and clean setting; and parameters can be changed during the experiment. In Chapter 2 and 3 we study phases and quantum phase transitions of 'tilted' Mott insulator of bosons. We analyze a variety of lattices and tilt directions in two dimensions: square, decorated square, triangular, and kagome. We show that there are rich possibilities for correlated phases with non-trivial entanglement of pseudospin degrees of freedom encoded in the boson density. For certain configurations three-body interactions are necessary to ensure that the energy of the effective resonant subspace is bounded from below. We find quantum phases with Ising density wave order, with superfluidity transverse to the tilt direction, a quantum liquid state with no broken symmetry. We also find cases for which the resonant subspace is described by effective quantum dimer models. In Chapter 4 we study spin 1/2 chains with a Heisenberg interaction which are coupled in a way that would arise if they are taken off graphene at a zig-zag edge. In Chapter 5 we theoretically analyze interference patterns of parametrically driven one-dimensional cold atomic systems. The parametric driving leads to spatial oscillations in the interference patter, which can be analyzed to obtain the sound velocity of the 1d system, and to probe spin-charge separation.

  8. Anomalous wear-out phenomena of europium-implanted light emitters based on a metal-oxide-semiconductor structure

    SciTech Connect

    Rebohle, L.; Lehmann, J.; Prucnal, S.; Nazarov, A.; Tyagulskii, I.; Tyagulskii, S.; Kanjilal, A.; Voelskow, M.; Grambole, D.; Skorupa, W.; Helm, M.

    2009-12-15

    The anomalous wear-out phenomena of Eu-implanted metal-oxide-semiconductor devices were investigated. It will be shown that in contrast to other rare earth elements the electroluminescence (EL) intensity of Eu-implanted SiO{sub 2} layers can rise under constant current injection before the known EL quenching will start. Under certain circumstances, this rise may amount up to two orders of magnitude. The EL behavior will be correlated with the microstructural and electrical properties of the devices. Transmission electron microscopy and Rutherford backscattering spectroscopy were applied to trace the development of Eu/Eu oxide clusters and the diffusion of Eu to the interfaces of the gate oxide layer. The hydrogen profile within the SiO{sub 2}-SiON interface region was determined by nuclear reaction analysis. Current-voltage characteristics, EL decay times, and the progression of the voltage and the EL spectrum with increasing charge injection were measured to study charge and trapping phenomena in the oxide layer to reveal details of the EL excitation mechanism. A first qualitative model for the anomalous life time behavior is proposed.

  9. Wafer-fused semiconductor radiation detector

    DOEpatents

    Lee, Edwin Y.; James, Ralph B.

    2002-01-01

    Wafer-fused semiconductor radiation detector useful for gamma-ray and x-ray spectrometers and imaging systems. The detector is fabricated using wafer fusion to insert an electrically conductive grid, typically comprising a metal, between two solid semiconductor pieces, one having a cathode (negative electrode) and the other having an anode (positive electrode). The wafer fused semiconductor radiation detector functions like the commonly used Frisch grid radiation detector, in which an electrically conductive grid is inserted in high vacuum between the cathode and the anode. The wafer-fused semiconductor radiation detector can be fabricated using the same or two different semiconductor materials of different sizes and of the same or different thicknesses; and it may utilize a wide range of metals, or other electrically conducting materials, to form the grid, to optimize the detector performance, without being constrained by structural dissimilarity of the individual parts. The wafer-fused detector is basically formed, for example, by etching spaced grooves across one end of one of two pieces of semiconductor materials, partially filling the grooves with a selected electrical conductor which forms a grid electrode, and then fusing the grooved end of the one semiconductor piece to an end of the other semiconductor piece with a cathode and an anode being formed on opposite ends of the semiconductor pieces.

  10. Tunneling versus thermionic emission in one-dimensional semiconductors.

    PubMed

    Appenzeller, J; Radosavljević, M; Knoch, J; Avouris, Ph

    2004-01-30

    This Letter focuses on the role of contacts and the influence of Schottky barriers on the switching in nanotransistors. Specifically, we discuss (i) the mechanism for injection from a three-dimensional metal into a low-dimensional semiconductor, i.e., the competition between thermionic emission and thermally assisted tunneling, (ii) the factors that affect tunneling probability with emphasis on the importance of the effective mass for transistor applications, and (iii) a novel approach that enables determination of barrier presence and its actual height.

  11. Electrical properties of metal-oxide-semiconductor structures with low-energy Ge-implanted and annealed thin gate oxides

    NASA Astrophysics Data System (ADS)

    Kapetanakis, E.; Normand, P.; Holliger, P.

    2008-03-01

    The electrical characteristics of low-energy (3keV) Ge-implanted and, subsequently, thermal annealed SiO2 layers are investigated through capacitance-voltage (C-V ) and conductance-voltage (G-V) measurements of metal-oxide-semiconductor capacitors. Particular emphasis is placed on the properties of such gate oxides for memory applications. Capacitance measurements at flatband voltage before and after the application of constant voltage stress in the accumulation regime indicate that the charge trapping behavior of the devices undergoes a major change after annealing at temperatures higher than 910°C. The latter change is identified as a relocation of Ge atoms mainly toward the upper portion of the oxide with a significant fraction of them leaving the oxide; a finding in harmony with secondary ion mass spectroscopy analysis. The interface trap density (Dit) for the thin (9-12nm) implanted oxides decreases with increasing annealing temperature, approaching at 950°C the Dit levels in the mid-1010eV-1cm-2 range of the nonimplanted samples. At elevated annealing temperatures (>1000°C), the device C-V characteristics are substantially disturbed. In this case, the presence of electrically active Ge atoms at an extended depth in the substrate modifies the intrinsic electrical properties of the n-Si substrate, lending a p-type conductivity character to the device high-frequency C-V curves. Substrate electrical modification is interpreted through a model that takes into account the formation of a SiO2/Ge-rich-Si /n-Si system. The SiO2/Ge-rich-Si interface presents very low Dit levels as revealed by conductance loss characteristics. The present study suggests that a combination of Ge implantation into SiO2 films and thermal annealing may be exploited in damage-free SiGe epitaxial growth technology based on Ge implantation.

  12. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO2 by capacitance voltage measurement on inverted metal oxide semiconductor structure

    NASA Astrophysics Data System (ADS)

    Zhang, Tian; Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-01

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO2. The ncSi thin films with high resistivity (200-400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO2/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 1018-1019 cm-3 despite their high resistivity. The saturation of doping at about 1.4 × 1019 cm-3 and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10-3 cm2/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  13. Determination of active doping in highly resistive boron doped silicon nanocrystals embedded in SiO{sub 2} by capacitance voltage measurement on inverted metal oxide semiconductor structure

    SciTech Connect

    Zhang, Tian Puthen-Veettil, Binesh; Wu, Lingfeng; Jia, Xuguang; Lin, Ziyun; Yang, Terry Chien-Jen; Conibeer, Gavin; Perez-Wurfl, Ivan

    2015-10-21

    We investigate the Capacitance-Voltage (CV) measurement to study the electrically active boron doping in Si nanocrystals (ncSi) embedded in SiO{sub 2}. The ncSi thin films with high resistivity (200–400 Ω cm) can be measured by using an inverted metal oxide semiconductor (MOS) structure (Al/ncSi (B)/SiO{sub 2}/Si). This device structure eliminates the complications from the effects of lateral current flow and the high sheet resistance in standard lateral MOS structures. The characteristic MOS CV curves observed are consistent with the effective p-type doping. The CV modeling method is presented and used to evaluate the electrically active doping concentration. We find that the highly boron doped ncSi films have electrically active doping of 10{sup 18}–10{sup 19 }cm{sup −3} despite their high resistivity. The saturation of doping at about 1.4 × 10{sup 19 }cm{sup −3} and the low doping efficiency less than 5% are observed and discussed. The calculated effective mobility is in the order of 10{sup −3} cm{sup 2}/V s, indicating strong impurity/defect scattering effect that hinders carriers transport.

  14. Materials Science and Technology, Volume 16, Processing of Semiconductors

    NASA Astrophysics Data System (ADS)

    Jackson, Kenneth A.

    1996-09-01

    This self-contained handbook deals with the enabling materials technology for the electronics industry. World renowned authors have contributed to this unique treatment of the processing of semiconductors and related technologies. Contents: Wilkes: Silicon Processing. Mullin: Compound Semiconductor Processing, Kuech/BleLagally/Tischler: Epitaxial Growth. Leuschner/Pawlowski: Photolithography. Griffin: Doping. Turner/Donohoe: Etching Processes in Semiconductor Manufacturing. Chang/Sze: Silicon Device Structures. Lam/Stanchina: Compound Semiconductor Device Structures. Kwong: Silicon Device Processing. Parsey, Jr: Compound Semiconductor Device Processing. Amey: Chip Carriers. Knausenberger/Turlik: Interconnection Systems.

  15. A musculoskeletal model of human locomotion driven by a low dimensional set of impulsive excitation primitives

    PubMed Central

    Sartori, Massimo; Gizzi, Leonardo; Lloyd, David G.; Farina, Dario

    2013-01-01

    Human locomotion has been described as being generated by an impulsive (burst-like) excitation of groups of musculotendon units, with timing dependent on the biomechanical goal of the task. Despite this view being supported by many experimental observations on specific locomotion tasks, it is still unknown if the same impulsive controller (i.e., a low-dimensional set of time-delayed excitastion primitives) can be used as input drive for large musculoskeletal models across different human locomotion tasks. For this purpose, we extracted, with non-negative matrix factorization, five non-negative factors from a large sample of muscle electromyograms in two healthy subjects during four motor tasks. These included walking, running, sidestepping, and crossover cutting maneuvers. The extracted non-negative factors were then averaged and parameterized to obtain task-generic Gaussian-shaped impulsive excitation curves or primitives. These were used to drive a subject-specific musculoskeletal model of the human lower extremity. Results showed that the same set of five impulsive excitation primitives could be used to predict the dynamics of 34 musculotendon units and the resulting hip, knee and ankle joint moments (i.e., NRMSE = 0.18 ± 0.08, and R2 = 0.73 ± 0.22 across all tasks and subjects) without substantial loss of accuracy with respect to using experimental electromyograms (i.e., NRMSE = 0.16 ± 0.07, and R2 = 0.78 ± 0.18 across all tasks and subjects). Results support the hypothesis that biomechanically different motor tasks might share similar neuromuscular control strategies. This might have implications in neurorehabilitation technologies such as human-machine interfaces for the torque-driven, proportional control of powered prostheses and orthoses. In this, device control commands (i.e., predicted joint torque) could be derived without direct experimental data but relying on simple parameterized Gaussian-shaped curves, thus decreasing the input drive complexity

  16. Particle swarm optimization on low dimensional pose manifolds for monocular human pose estimation

    NASA Astrophysics Data System (ADS)

    Brauer, Jürgen; Hübner, Wolfgang; Arens, Michael

    2013-10-01

    Automatic assessment of situations with modern security and surveillance systems requires sophisticated discrimination capabilities. Therefore, action recognition, e.g. in terms of person-person or person-object interactions, is an essential core component of any surveillance system. A subclass of recent action recognition approaches are based on space time volumes, which are generated from trajectories of multiple anatomical landmarks like hands or shoulders. A general prerequisite of these methods is the robust estimation of the body pose, i.e. a simplified body model consisting of several anatomical landmarks. In this paper we address the problem of estimating 3D poses from monocular person image sequences. The first stage of our algorithm is the localization of body parts in the 2D image. For this, a part based object detection method is used, which in previous work has been shown to provide a sufficient basis for person detection and landmark estimation in a single step. The output of this processing step is a probability distribution for each landmark and image indicating possible locations of this landmark in image coordinates. The second stage of our algorithm searches for 3D pose estimates that best t to the 15 landmark probability distributions. For resolving ambiguities introduced by uncertainty in the locations of the landmarks, we perform an optimization within a Particle Swarm Optimization (PSO) framework, where each pose hypothesis is represented by a particle. Since the search in the high-dimensional 3D pose search space needs further guidance to deal with the inherently restricted 2D input information, we propose a new compact representation of motion sequences provided by motion capture databases. Poses of a motion sequence are embedded in a low-dimensional manifold. We represent each motion sequence by a compact representation referred to as pose splines using a small number of supporting point poses. The PSO algorithm can be extended to perform

  17. Unitary lens semiconductor device

    DOEpatents

    Lear, K.L.

    1997-05-27

    A unitary lens semiconductor device and method are disclosed. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors. 9 figs.

  18. Unitary lens semiconductor device

    DOEpatents

    Lear, Kevin L.

    1997-01-01

    A unitary lens semiconductor device and method. The unitary lens semiconductor device is provided with at least one semiconductor layer having a composition varying in the growth direction for unitarily forming one or more lenses in the semiconductor layer. Unitary lens semiconductor devices may be formed as light-processing devices such as microlenses, and as light-active devices such as light-emitting diodes, photodetectors, resonant-cavity light-emitting diodes, vertical-cavity surface-emitting lasers, and resonant cavity photodetectors.

  19. Aqueous Based Semiconductor Nanocrystals.

    PubMed

    Jing, Lihong; Kershaw, Stephen V; Li, Yilin; Huang, Xiaodan; Li, Yingying; Rogach, Andrey L; Gao, Mingyuan

    2016-09-28

    This review summarizes traditional and recent nonconventional, bioinspired, methods for the aqueous synthesis of colloidal semiconductor quantum dots (QDs). The basic chemistry concepts are critically emphasized at the very beginning as these are strongly correlated with the selection of ligands and the optimal formation of aqueous QDs and their more sophisticated structures. The synergies of biomimetic and biosynthetic methods that can combine biospecific reactivity with the robust and strong optical responses of QDs have also resulted in new approaches to the synthesis of the nanoparticles themselves. A related new avenue is the recent extension of QD synthesis to form nanoparticles endowed with chiral optical properties. The optical characteristics of QD materials and their advanced forms such as core/shell heterostructures, alloys, and doped QDs are discussed: from the design considerations of optical band gap tuning, the control and reduction of the impact of surface traps, the consideration of charge carrier processes that affect emission and energy and charge transfer, to the impact and influence of lattice strain. We also describe the considerable progress in some selected QD applications such as in bioimaging and theranostics. The review concludes with future strategies and identification of key challenges that still need to be resolved in reaching very attractive, scalable, yet versatile aqueous syntheses that may widen the scope of commercial applications for semiconductor nanocrystals. PMID:27586892

  20. Optimization of Vertical Double-Diffused Metal-Oxide Semiconductor (VDMOS) Power Transistor Structure for Use in High Frequencies and Medical Devices.

    PubMed

    Farhadi, Rozita; Farhadi, Bita

    2014-01-01

    Power transistors, such as the vertical, double-diffused, metal-oxide semiconductor (VDMOS), are used extensively in the amplifier circuits of medical devices. The aim of this research was to construct a VDMOS power transistor with an optimized structure to enhance the operation of medical devices. First, boron was implanted in silicon by implanting unclamped inductive switching (UIS) and a Faraday shield. The Faraday shield was implanted in order to replace the gate-field parasitic capacitor on the entry part of the device. Also, implanting the UIS was used in order to decrease the effect of parasitic bipolar junction transistor (BJT) of the VDMOS power transistor. The research tool used in this study was Silvaco software. By decreasing the transistor entry resistance in the optimized VDMOS structure, power losses and noise at the entry of the transistor were decreased, and, by increasing the breakdown voltage, the lifetime of the VDMOS transistor lifetime was increased, which resulted in increasing drain flow and decreasing Ron. This consequently resulted in enhancing the operation of high-frequency medical devices that use transistors, such as Radio Frequency (RF) and electrocardiograph machines.