Solid State Physics

Engineering of dispersion of indirect excitons by normal electric and in-plane magnetic fields is proposed to be used for controlling the state of many-exciton system (e.g., coherent state) and its photoluminescence and for producing an inverse population in the excitonic system. The possibility of phonon laser creation on the basis of the latter effect is discussed. Phonon number distribution appears to be a fingerprint of that in exciton system. Numerical estimations for the proposed scheme are made for GaAs/AlGaAs quantum wells. © 2000 MAIK "Nauka/Interperiodica".

The possibility of identifying the provenance of classical marbles and solving related questions, such as the joining fragments problem, via electron spin resonance spectroscopy has been reexamined. The method is based on characterization of the Mn" impurity ubiquitously present in marbles. Six different, although correlated, spectroscopic variables, such as intensity, linewidth, metal hyperfine splitting and others have been measured, together with some petrographic properties, for over 500 samples belonging to 14 different Italian, Greek and Turkish quarrying sites. The work, still in progress, is aimed to establish a marble database including all the historically relevant sites within the Mediterranean basin. The experimental data matrix has been analyzed with the aid of multivariate statistical techniques, primarily linear and quadratic discriminant analysis, and the ability of the method to classify correctly unknown samples has been estimated through standard techniques (resubstitution, jackknife), but also employing control "unknown" samples. The essential result is that, although the all-variables approach may describe the data set very accurately, the predictive power is due to four variables only, which are a suitable combination of spectroscopic and petrographic information. In this way 82.4% of the control samples could be assigned correctly, whereas inclusion of additional variables in the classification rule may result in substantially poorer performance. The conclusion is that ESR spectroscopy, although not providing a complete and general solution for the marble provenance problems, is probably, at the moment, the most developed methodology for identifying marbles. Its results, coupled with artistic historical information, deal correctly with a number of relevant archaeometric problems.

Cu 2 O/ZnO:Al (AZO) and Cu 2 O/ZnO/AZO heterojunctions have been deposited on glass substrates by a unique three-step pulsed laser deposition process. The structural, optical, and electrical properties of the oxide films were investigated before their implementation in the final device. X-ray diffraction analysis indicated that the materials were highly crystallized along the c-axis. All films were highly transparent in the visible region with enhanced electrical properties. Atomic force and scanning electron microscopies showed that the insertion of a ZnO layer between the Cu 2 O and AZO films in the heterojunction enhanced the average grain size and surface roughness. The heterojunctions exhibited remarkable diode behavior and good rectifying character with low leakage current under reverse bias. The presence of the ZnO interlayer film significantly reduced the parasitic and leakage currents across the barrier, improved the quality of the heterostructure, made the energy band between AZO and Cu 2 O layers smoother, and eliminated the possibility of interface recombination, leading to much longer electron lifetime.

The temperature dependence of the static dielectric susceptibility obtained from the experiment on Raman scattering in a deuterated KDP (DKDP) crystal has been described using the cluster approxima tion in terms of the microscopic mean field theory. The optimum values obtained for parameters of the clus ter approximation are in good agreement with experimental data over a wide temperature range. These values are found to be comparable to the estimates previously obtained in describing experimental data on the DKDP crystal.

HgCdTe remains the material of choice for high-performance infrared (IR) detectors due to its tunable direct bandgap energy corresponding to the IR spectral region, and the advancement of HgCdTe materials growth and processing technologies. Accurate knowledge of the HgCdTe optical absorption coefficient is important for IR detector design, layer screening, and device analysis. The spectral response for IR detectors is dependent on optical absorption above the bandgap energy, where much of the study of absorption coefficient in HgCdTe has focused on the bandtail region. In this work, the optical absorption coefficient was studied by theoretical bandstructure calculations and experimental measurements on HgCdTe layers using techniques of IR spectroscopic ellipsometry and IR transmission. The theoretical and experimental results suggest that the absorption coefficient between 600 cm Ϫ1 and 5,000 cm Ϫ1 is related to energy relative to bandgap with a fractional exponent between 0.6 and 1, rather than the previously used expressions relating to a parabolic or hyperbolic bandstructure. The fitting parameters for Hg 1-x Cd x Te with x ϭ 0.22-0.60 are presented to develop a model for the optical absorption coefficient spectra. The calculated detector spectral response using the new and previously reported absorption coefficient models suggests that next generation IR detectors employing multilayer structures with graded compositional profiles will likely benefit from this new model.

This paper reports the further development of the model for the analysis of FTIR transmission spectra from the dual-color Hg 1-x Cd x Te (MCT) structures for the constituent layer thickness and alloy composition. The previously reported model 1 was shown to suffer from excessively high uncertainty in the provided individual layer thickness and low convergence rate for some types of structures, attributed primarily to inaccuracies in the model representation of the MCT dielectric function. Since last report, we have substantially improved the FTIR analysis accuracy by developing a better MCT dielectric function approximation, which is based on the interpolation of the measured spectroscopic ellipsometry (SE) experimental spectral dielectric functions at few discrete alloy compositions. Based on this, the optical model for graded layers was also created and calibrated against the traditional FTIR data reduction technique. The new model was shown to produce the most accurate fits to the experimental FTIR transmission spectra from single-and two-color detector structures, and has demonstrated a better convergence rate. The new model was tested to predict both band cutoff wavelengths for the actual two-color MWIR/LWIR SUMIT detectors. We have demonstrated that the model prediction from as-grown structures was in good agreement with the actual two-color device data, as measured on performance evaluation chips (PECs), thus validating the modeling technique for routine postgrowth wafer screening.

Ceramic samples of the multiferroic perovskite Pb(Fe1-xScx) 2/3 W 1/3 O3 with 0 ≤ x ≤ 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (F m3m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B sites. As the non-magnetic Sc 3+ ions replace the magnetic Fe 3+ cations, the antiferromagnetic state of PbFe 2/3 W 1/3 O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B and B sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1-xScx) 2/3 W 1/3 O3 and possibly also in the undoped PbFe 2/3 W 1/3 O3.

In this paper we initiate a study concerning the influence of demagnetizing energy on conventional amorphous wires’ (CAW) magnetic anisotropy. Normally, if we want to calculate the magnetic anisotropy of CAW we must take into account the magnetoelastic energy as the most influent energy in the expression of magnetic anisotropy. The importance of this energy is determinant in domain walls creation and, consequently, in amorphous material magnetic behavior. There is a critical value of radius/length ratio for which the effects of demagnetizing field, the field depending on wire form, can’t be no more neglected. We have established this ratio. It exhibits a great importance, especially when we wish to avoid these demagnetizing effects and to have a better control of final magnetization. What it counts, undoubtedly, in all applications involving CAW.

In-water quenching technique, which is the preparation procedure of conventional amorphous wires (CAW), induces internal stresses in the material. These stresses, coupled with magnetostriction, give rise to large magnetoelastic anisotropies. Using the calculated distribution of internal stresses, the aim of this work is to evaluate the theoretical distribution of magnetoelastic anisotropies of CAW with positive, negative and nearly zero magnetostriction. The anisotropy constants were calculated as functions of wire dimensions, taking into account that the influence of wire length is neglected. Consequently, we elaborate two simple calculation programs which enable us to calculate the magnetoelastic distribution in every point of wire radius, for any magnetostriction, positive, negative or nearly zero, and any values of parameters and physical quantities involved.

Metallization of high-T c superconductors using low resistivity metal oxides and Cu-Ge alloys has been investigated on high quality pulsed laser deposited epitaxial YBa2Cu3OT_ x (YBCO) films. Epitaxial LaNiO 3 (LNO) thin films have been grown on YBCO films at 700~ using pulsed laser deposition. The specific resistivity of LNO was measured to be 50 p~-cm at 300K which decreases to 19 p~-cm at 100K indicating good metallicity of the LNO films. The contact resistance of LNO-YBCO thin film interface was found to be reasonably low (of the order of 104 ~2-cm 2 at 77K) which suggests that the interface formed between the two films is quite clean and LNO can emerge as a promising metal electrodematerial to YBCO films. A preliminary investigation related to the compatibility of Cu3Ge alloy as a contact metallization material to YBCO films is discussed. The usage of other oxide based low resistivity materials such as SrRuO 3 (SRO) and SrVO 3 (SVO) for metallization ofhigh-T YBCO superconductor films is also discussed.

The classical Hall effect resulting from the impact of external magnetic and electric fields on the non-Markovian dynamics of charge carriers is studied. The dependence of the tangent of the Hall angle on the magnetic field is derived and compared with the experimental data for Zn. The method is proposed to determine experimentally the memory time in a system.

Motivated by recent experimental and theoretical works on silicene and its derived materials and based on the exceptional Lie algebra G2 we propose a new hexagonal symmetry producing the ( √ 3 × √ 3)R30 • superstructure for silicon atoms. The principal hexagonal unit cell contains twelve atoms instead of the usual structure involving only six ones and it is associated with the G2 root system. In this silicon atom configuration appears two hexagons of unequal side length at angle 30 • . This atomic structure can be tessellated to exhibit two superstructures (1 × 1) and ( √ 3 × √ 3)R30 • on the same atomic sheet. To test this double hexagonal structure, we perform a numerical study using Ab-initio calculations based on FPLO9.00-34 code. We observe that the usual silicon electronic properties and the lattice parameters of planar geometry are modified. In particular, the corresponding material becomes a conductor rather than zero gaped semi-conductor arising in single hexagonal structure. Although the calculation is done for silicon atoms, we expect that this structure could be adapted to all two dimensional materials having a single hexagonal flat geometry.

We study the site and bond quantum percolation model on the two-dimensional square lattice using series expansion in the low concentration limit. We calculate series for the averages of P ij r k ij Tij(E), where Tij(E) is the transmission coefficient between sites i and j, for k = 0, 1, . . . , 5 and for several values of the energy E near the center of the band. In the bond case the series are of order p 14 in the concentration p (some of those have been formerly available to order p 10 ) and in the site case of order p 16 . The analysis, using the Dlog-Padé approximation and the techniques known as M1 and M2, shows clear evidence for a delocalization transition (from exponentially localized to extended or power-law-decaying states) at an energy-dependent threshold pq(E) in the range pc < pq(E) < 1, confirming previous results (e.g. pq(0.05) = 0.625 ± 0.025 and 0.740 ± 0.025 for bond and site percolation) but in contrast with the Anderson model. The divergence of the series for different k is characterized by a constant gap exponent, which is identified as the localization length exponent ν from a general scaling assumption. We obtain estimates of ν = 0.57 ± 0.10. These values violate the bound ν ≥ 2/d of Chayes et al.

Product Description Periodically Poled Stoichiometric Lithium Tantalate chips offer a cost effective method for visible and mid-infrared frequency generation. A multi-step lithographic and electric field poling process effects a permanent change in the non-linear properties of Lithium Tantalate. Using quasi-phase matching, with a selection of periods, crystal widths and lengths, PPSLT offers users an alternative to dedicated frequency conversion crystals. Applications • RGB laser generation • IR/Mid-IR laser generation • Visible Light Generation • 1st order or higher order wavelength conversion • Remote Sensing

In the recent years a significant amount of efforts are focused on the development of single-frequency nanosecond and sub-nscompact lasers providing high energy (&gt;1 mJ) and high average power(&gt;1W ) simultaneously. Q-switched, single frequency and si gletransversemode lasers are essential for wide vari ty of applications [1] such as laser-induced breakdown sp ectroscopy, LIDARs, optical communications and lase r trapping or cooling. The spatial dimension of conve ntional solid state Q-switched lasers precludes pro ducing single frequencypulses with sub-nanosecondor few-ns duration. Although the short-cavity, passively Q-s witched microchip lasers allow oscillations in single longi tudinalmode and generation of ~1 ns pulses device s th ir applicability is limited due to the inherent non-sa tur ted losses in the absorber, which impose consid erable limitation over achieving average power levels (~10 0mW) and poor ability for synchronization of the la ser pulses with external elec...

In this work polyvinyl butyral (PVB) was used both as a dispersing agent for carbon nanotubes (CNTs) into ethanol, and as the matrix for composite tapes obtained by the tape casting technology. Heavily entangled commercial CNTs were used, in order to verify the effective polymer dispersing capability and the methodology. The dispersing effect of PVB is probably due to a polymer wrapping effect, and is evident also at low concentration, even if some bundles of CNTs can remain in the suspension. A slurry of PVB containing various percentages of carbon nanotubes was tape cast to obtain composite tapes, whose mechanical properties depends on both the concentration of CNTs and the type of PVB. If the CNTs concentration is too high, undispersed bundles remain, that reduce mechanical properties. If the PVB chain is too short, no significant mechanical properties improvement is observed.

Texas -We study the effects of anisotropy of a dielectric substrate and a metal film on the dispersion relation and range of propagation of surface plasmons. The substrate is considered to be a uniaxial crystal with its axis perpendicular to the metal surface. The dielectric constants of the substrate are ε || (in the plane of propagation) and ε ⊥ (in the perpendicular direction). The metal film is characterized by a complex dielectric tensor with isotropic real negative part ε ′ (ω)and anisotropic positive imaginary part ε ′′ ik (ω). The latter has two different componentsε ′′ || (ω) and ε ′′ ⊥ (ω). Anisotropy of the dissipative part of the dielectric tensor is due to the surface channel of electron scattering, leading to the lower ac conductivity of the thin film in the direction perpendicular to the metal surfaces. We show that the substrate with ε ⊥ > ε || gives rise to larger propagation length of the surface plasmon. Thus from the point of view of efficiency of the plasmonic devices anisotropic negative uniaxial crystals are preferential. In this case the decay length of the plasmon field in the substrate also increases. This decay length is an important characteristic of the sub-wavelength optical resolution.

No presente trabalho, investigamos as propriedades eletronicas e estruturais de nanoestruturas a base de carbono e de elementos metalicos, por primeiros principios, baseados na Teoria do Funcional da Densidade. Dentro dessas nanoestruturas vamos abordar: redes de nanoparticulas de ouro funcionalizadas ou nao depositadas sobre grafeno e sobre bicamadas de grafeno, nanotubos de carbono zig-zag (10,0) comprimido por superficies de ouro ou diamante e hetero-estruturas metalicas Ni/Fe/grafeno. No caso de redes de nanoparticulas sobre grafeno, investigamos as modificacoes nos estados eletronicos do grafeno quando uma rede triangular de nanoparticulas de Au (cobertas ou nao) e depositada sobre uma monocamada de grafeno. Um estudo similar foi feito para nanoparticulas de Au depositadas sobre bicamadas de grafeno para quatro configuracoes de empilhamento possiveis. No caso de nanotubos zig-zag, exploramos a transicao semicondutor-metal do tubo (10,0) induzida por compressao radial de superfi...

Hundred and seventy-five thousand device-hours of operating life at channel temperatures above 200°C is demonstrated on AlGaN/GaN HEMTs fabricated using GaN-ondiamond technology for the first time. No catastrophic failures and no drain-current drift larger than 10% from turning the devices on were recorded throughout this two-year DC test.

X-ray photoemission spectra of Sm~_xRxS ( R = C a , Y, Gd and Th) in the range prior to collapse ("black phase") exhibit only divalent samarium components. The 4f final state energy is found independent of lattice constant, but sensitive to 5d band screening. The fully screened final state 4f55d, 6H, which is also involved in the interconfiguration fluctuation process, is found to reach the Fermi energy in a gradual insulator to metal transition. The results are interpreted to show that the modifications of the band structure which give rise to the phase transition are confined to the 5d level.

Predictions of Electronic and Optical Properties of Cubic InN LASHOUNDA FRANKLIN, HUA JIN, G. L. ZHAO, DIOLA BAGAYOKO, Southern University and A&M College -We present theoretical predictions of electronic, optical, and related properties of cubic indium nitride (c-InN). We utilized a local density functional approximation (LDA) potential and the linear combination of atomic orbitals (LCAO) in our ab-initio, self-consistent calculations that implemented the Bagayoko, Zhao, and Williams (BZW) method. The predicted band gap is 0.65 eV at a theoretical, equilibrium lattice constant of 5.017 Å . We discuss other predictions for the structural and optical properties of c-InN, including the bulk modulus, electron effective masses, and the calculated dielectric function.

We report findings from several ab-initio, self-consistent calculations of electronic and transport properties of wurtzite aluminum nitride (w-AlN). Our calculations utilized a local density approximation (LDA) potential and the linear combination of Gaussian orbitals (LCGO). Unlike some other density functional theory (DFT) calculations, we employed the Bagayoko, Zhao, and Williams' method, enhanced by Ekuma and Franklin (BZW-EF). The BZW-EF method verifiably leads to the minima of the occupied energies; these minima, the low laying unoccupied energies, and related wave functions provide the most variationally and physically valid density functional theory (DFT) description of the ground states of materials under study. With multiple oxidation states of Al (Al 3+ to Al) and the availability of N 3-to N, the BZW-EF method required several sets of self-consistent calculations with different ionic species as input. The binding energy for (Al 3+ & N 3-) as input was 1.5 eV larger in magnitude than those for other input choices; the results discussed here are those from the calculation that led to the absolute minima of the occupied energies with this input. Our calculated, direct band gap for w-AlN, at the Γ point, is 6.28 eV, in excellent agreement with the 6.28 eV experimental value at 5K. We discuss the bands, total and partial densities of states, and calculated, effective masses.

We report high pressure study of CdS using the full-potential linear augmented plane wave (FP-LAPW) method based on density functional theory approach. In this approach, generalized gradient approximation (GGA) and Engel-Vosko generalized gradient approximation (EV-GGA) have been used for the exchange correlation potential in the calculations. The equilibrium lattice constant, electronic band structure, elastic constants, Debye temperature and melting temperature of binary solid CdS have been calculated under ambient and high pressure. Furthermore, the linear optical properties such as dielectric function, absorption, optical conductivity reflectivity, refractive index and energy loss are computed and analyzed in detail within the energy range up to 14 eV. The obtained results are in good agreement with earlier reported experimental and other theoretical results.

We report high pressure study of CdS using the full-potential linear augmented plane wave (FP-LAPW) method based on density functional theory approach. In this approach, generalized gradient approximation (GGA) and Engel- Vosko generalized gradient approximation (EV-GGA) have been used for the exchange correlation potential in the calculations. The equilibrium lattice constant, electronic band structure, elastic constants, Debye temperature and melting temperature of binary solid CdS have been calculated under ambient and high pressure. Furthermore, the linear optical properties such as dielectric function, absorption, optical conductivity reflectivity, refractive index and energy loss are computed and analyzed in detail within the energy range up to 14 eV. The obtained results are in good agreement with earlier reported experimental and other theoretical results.

XVIII dinastia. La storia egiziana comprende 33 dinastie di faraoni comprese nell'arco di circa 3000 anni. La più studiata ed oggetto del maggior numero di ipotesi e discussioni è di gran lunga la XVIII dinastia. Lo è quanto meno per quanto riguarda la sua ultima parte e per tre motivi: 1) La figura del faraone Akhenaton, indagata anche da Freud e Thomas Mann. Ripudiò la religione tradizionale per introdurre il culto tendenzialmente monoteista di Aton, il dio Sole. 2) Il ruolo di sua moglie Nefertiti, conosciuta per il suo splendido busto in gesso, perfettamente conservato ed esposto a Berlino. 3) La figura di Tutankhaton, successore di Akhenaton e poi rinominato Tutankhamon, che salì al trono appena bambino. Fu costretto a rinnegare la religione paterna in favore degli antichi dei. La memoria dei suoi predecessori fu cancellata dai monumenti. La stessa capitale che Akhenaton aveva costruito ex-novo venne completamente rasa al suolo. 4) La tomba di Tutankhamon fu rinvenuta nel 1923 pressoché intatta e ripiena di tesori. Per questo è ritenuta la più grande scoperta archeologica del XX secolo.

The growth of higher manganese silicide (HMS) films on monocrystalline silicon (100) has been investigated. This growth was performed by solid-state reaction. Using electron beam evaporation a single layer of manganese was deposited on a silicon substrate. The samples so prepared were heat treated in a classical furnace under vacuum. A highly textured film was obtained after treatment at 890°C for 18 h. The obtained HMS was identified as Mn 15 Si 26 . The texture relationship is (105) [100] Mn 15 Si 26 i (100) [100] Si. Mn 15 Si 26 has a tetragonal cell; hence, the angle between the c-axis and the normal of the sample surface is 60°. Since this value is far from 0°and 90°, a large transverse thermoelectric effect is expected in these samples. As a consequence the HMS films could be used in anisotropic electromotive force-thermogenerators.

Mg 2 Si thin and ultra-thin films are grown on silicon (Si) substrates by performing heat treatments of Magnesium (Mg) layers deposited on Si (100), using radio frequency (RF)-sputtering and molecular beam epitaxy (MBE) techniques. In order to investigate the effect of annealing parameters on the formation of Mg 2 Si thin films, we conducted heat treatments under vacuum for some samples and in an argon gas atmosphere for others. X-ray diffraction (XRD) analysis of the thin films annealed in both environments confirms the formation of polycrystalline Mg 2 Si. This characterization also reveals that the formation of this compound depends on duration and pressure for the vacuum annealing and on temperature for the argon gas atmosphere annealing. Here, we report that the vacuum annealing is a good choice for Mg 2 Si thin film formation because the low temperature of the process is condusive to silicon technology. Some optimum parameters for obtaining Mg 2 Si thin films are proposed in this paper. Auger electron spectroscopy (AES) characterization technique confirms the formation of Mg 2 Si ultra-thin films at an annealing temperature of 200°C and under an ultra-high vacuum (UHV). In addition, scanning tunneling microscopy (STM) characterization indicates a nanosized grain formation of this compound with average size of approximately 20-40 nm.

for HEMT Devices May Nwe Myint Aye, Than Htike Aung, Win Zaw Hein 1,2,3 Department of Electronic Engineering, Mandalay Technological University Patheingyi 5071, Mandalay Region, Republic of the Union of Myanmar # Department of Electronic Engineering, Technological University (Lashio) Shan State, Republic of the Union of Myanmar. maynwemyintaye2018@gmail.com,thanhtikeaung85@gmail.com,winzawhein2007@gmail.com

This paper presents a study of electron scattering in damascene-processed Cu interconnects. To understand the leading electron-scattering mechanism responsible for the size effect, Cu interconnects with varying physical widths, 80-750 nm, were made, and their resistivity characterized as a function of temperature, ranging from liquid He temperature (4.2 K) to 500 K. The resulting data suggest that surface scattering, contrary to expectations, was not the primary cause of the size effect observed in this investigation. Surface scattering was found to weaken with decreasing line width. Further analysis leads to the conclusion that a substantial fraction of the size effect originates from impurity content scaling inversely with width in these samples.

In this reported work, comparison is made of a passivation treatment of a III-V compound semiconductor using ammonia and ammonium sulphide solution. The treatment is applied on In 0.53 Ga 0.47 As which is chosen for its high mobility especially in high electron mobility transistors. The samples were treated with various parameters such as precursor, vacuum condition and different chemical solutions. Then, samples were deposited with the high k-dielectric Al 2 O 3 (4 nm thickness) using the atomic layer deposition technique. Five different passivation treatments were used to give proper comparison. Native oxide elements and contaminants were inspected at the interface of the oxide layer and the substrate using X-ray photospectrometry in different angles (25°and 70°). The results indicate the effectiveness of some treatments to eliminate the oxide of gallium and arsenic with a slight presence of indium oxide.

Nanotransistor now is one of the most promising fields in nanoelectronic in order to less energy consuming and application to create developed programmable information processors. Most of Computing and communications companies invest hundreds of millions of dollars in research funds every year to develop smaller transistors. Approach: The Junction-less side gate silicon Nano-wire transistor has been fabricated by Atomic Force Microscopy (AFM) and wet etching on p-type Silicon On Insulator (SOI) wafer. Then, we checked the characteristic and conductance trend in this device regarding to semi-classical approach by Semiconductor Probe Analyser (SPA). Results: We observe in characteristic of the device directly proportionality of the negative gate voltage and Source-Drain current. In semi classical approach, negative Gate voltage falling down the energy States of the Nano-wire between the source and the drain. The graph for positive gate voltage plotted as well to check. In other hand, the conductance will be following characteristic due to varying the gate voltage under the different drain-source voltage. Conclusion: The channel energy states are supposed to locate between two electrochemical potentials of the contacts in order to transform the charge. For the p-type channel the transform of the carriers is located in valence band and changing the positive or negative gate voltage, make the valence band energy states out of or in the area between the electrochemical potentials of the contacts causing the current reduced or increased.

We study random XY and (dimerized) XX spin-1/2 quantum spin chains at their quantum phase transition driven by the anisotropy and dimerization, respectively. Using exact expressions for magnetization, correlation functions and energy gap, obtained by the free fermion technique, the critical and off-critical (Griffiths-McCoy) singularities are related to persistence properties of random walks. In this way we determine exactly the decay exponents for surface and bulk transverse and longitudinal correlations, correlation length exponent and dynamical exponent.

A proposed eleven-parameter three-body shell model is used to study the lattice dynamical properties such as phonon dispersion relations along high symmetry directions, phonon density of states, variation of specific heat and Debye characteristic temperature with absolute temperature, elastic constants and related properties for III-V semiconductor AlSb, GaSb and their mixed semiconductor Ga 1-x Al x Sb having zinc-blende structure. We found an overall good agreement with the available experimental and theoretical results available in the literature. Elastic constants • Lattice dynamics • Mixed semiconductor • Phonons B A. K. Kushwaha

We performed measurements of the optical reflectivity in the energy range 0.007-30 eV on the clathrate-VIII type compound α-Eu8Ga16-x Ge30x in order to investigate its electronic band structure. The very low charge carrier concentration as well as ferromagnetic ordering of the divalent Eu ions below 10.5 K characterize the spectra at photon energies below 0.4 eV in accordance with the results of band structure calculations. Disorder induced bound states have been identified to affect the optical conductivity at energies between 10 and 100 meV.

Vanadium-doped forsterite crystal has been studied with X-band electron paramagnetic resonance (EPR) spectroscopy. The sample was grown by the Czochralski technique in an argon atmosphere with 2 vol% of hydrogen. The EPR spectrum of the sample at T = 15 K is predominantly represented by the V 4? ion signals that possess a characteristic eight-line hyperfine structure and are observed close to g = 2. The observation of the two magnetically nonequivalent centers in the angular dependence in the (ab) crystal plane and one center in the (ac) and (bc) planes, combined with the published optical spectroscopy data, unambiguously show that the V 4? ions are located at the silicon lattice site. Principal values of the hyperfine A and g-tensor and magnetic axes orientations of the V 4? centers have been determined. The orientation disorder of the V 4? centers has been found around the crystalline c axis but not in the (ab) crystal plane. The angular variation of the hyperfine component linewidth is described best with a disorder range of ±3.0°. Crystals of the dielectric oxides doped with 3d-ions are often considered as promising laser-active media. Forsterite Mg 2 SiO 4 is among such oxides and it was intensely studied during the last decades [1-5]. Doped with chromium, this material reveals a tuneable-wavelength laser action in the near-infrared (IR) spectral range

A polycrystalline CdTe film has been prepared by thermal evaporation technique on glass substrate at substrate temperature 423 K with 1.0 m thicknesses. The film was heated at various annealing temperature under vacuum (T a = 473, 523 and K). Some of physical properties of prepared films such as structural and optical properties were investigated. The patterns of X-ray diffraction analysis showed that the structure of CdTe powder and all films were polycrystalline and consist of a mixture of cubic and hexagonal phases and preferred orientation at (111) direction. The optical measurements showed that un annealed and annealed CdTe films had direct energy gap (E g ). The E g increased with increasing T a . The refractive index and the real part of dielectric constant for films were observed to decrease with increasing T a , while the extinction and the imaginary part of dielectric were increased. Our result is good candidate for manufacturing optoelectronic device such as solar cells.

Various samples of GexSe1-x system have been prepared for x = 0.05, 0.15 & 0.25 in an evacuated quartz tube. Thin films of GexSe1-x film have been prepared via a thermal evaporation method with 350 ± 5 nm thickness and rate deposition 6 nm/s. The alloy structure and thin films have been examined by X-ray diffraction (XRD). Atomic absorption spectroscopy (AAS) was used to examine the concentration of the composite elements (Ge and Se). The d.c and a.c conductivity of GexSe1-x thin film have been studied as a function of Ge content x and annealing temperature within the range 303-448 K. Our results showed that the dc conductivity σ of thin GexSe1-x films increases with increasing Ge content and decreases with increasing annealing temperature Ta. Electrical activation energy Ea decreases with increasing x values and increases with increasing annealing temperature. The a.c conductivity increases with increasing x values. The exponent s in the relation σa.c ∝ ω s , and which determines the transfer mechanism, decreases with increasing x and Ta. While the electrical a.c activation energy Eω increases with increasing x and Ta and at frequencies f = 10 2 , 10 3 and 10 5 Hz. The relaxation time τ and polarizibility α have been measured from the cole-cole plot for x = 0.05 at Ta = 303, 398 and 448 K, with the finding that the relaxation time and polarizibility decreased with increasing Ta.

for an Invited Paper for the MAR14 Meeting of the American Physical Society Physical foundations and future perspectives of the epitaxial silicene ALESSANDRO MOLLE, CNR-IMM, Laboratorio MDM Silicene, a graphene-like Si monolayer, has been so far a fascinating theoretical hypothesis with no experimental counterpart as due to the natural sp 3 hybridization of Si bonding. Artificially forcing the silicene lattice was firstly made possible in the epitaxial growth of a Si monolayer on Ag(111) substrates . Here it is shown through an in situ scanning tunnelling microscopy investigation [3] that unlike graphene, non-trivial atomistic arrangements (reconstructions) can coexist in multiphase silicene nanosheets as due to the balance between planar and buckled bonding . This structural complexity is kinetic in character as it can be governed by tuning the thermal condition during growth or in a post-growth stage, and it is expected to bring absolutely peculiar physical properties . Silicene is intrinsically limited by its intimate chemical instability. An ad hoc engineered Al 2 O 3 encapsulation is proposed for ex situ investigations such as Raman spectroscopy . Supported by ab initio calculations, the measured Raman spectrum of the silicene phases is consistent with a prevailing a sp 2 hybridization, and it also evidences a reconstruction dependent resonant/non-resonant behavior . To integrate silicene in transistor structures, decoupling from the metallic templates is highly desired. New directions in this respect are outlined which include silicene deposition on cleavable substrates (e.g. Ag(111) films on mica), and the van der Waals growth of Si nanosheets on layered templates (such as MoS 2 layers). Perspectives on the silicene "portability" for a device-oriented exploitation will be discussed.

The chemical coupling of NiO nanostructures with thermally treated multiwall carbon nanotubes (MWCNTs) is not reported as it provides an enhanced dispersion of composite material in water. The dispersion of MWCNTs has been considered a big challenge. For this purpose, we first thermally treated MWCNTs at 1000°C in air for 30 min. Then, thermally treated MWCNTs were chemically coupled with NiO nanostructures by a hydrothermal method. The material characterization in terms of structure, morphology, and composition is well studied by different analytical techniques. The NiO composite (sample 2) with highest weight of MWCNTs had a leaf-like morphology and it exhibits a cubic phase of NiO. Cyclic voltammetry (CV) was used to study the electrochemical activity of prepared composite material towards the oxidation of uric acid in the phosphate buffer solution of pH 7.0. Sample 2 showed a well-behaved anodic peak with enhanced peak current and exhibited a linear range from 0.01 mM to 2.5 mM for uric acid with a low limit of detection 0.001mM. Sample 2 was found to be very selective under the environment of competing interferents such as urea, glucose, lactic acid and ethanol. This sample exhibits significant stability, thus it is a potential protocol for the monitoring of uric acid from real samples. This study provides a low-cost platform for the fabrication of efficient materials for various applications such as batteries, fuel cells and water splitting.

GaAs nanowires (NWs) offer the possibility of decoupling light absorption from charge transport for high-performance photovoltaic (PV) devices. However, it is still an open question as to whether these devices can exceed the Shockley-Queisser efficiency limit for single-junction PV. In this work, single standing GaAs-based nanowire solar cells in both radial and vertical junction configurations is analyzed and compared to a planar thin-film design. By using a self-consistent, electrical-optically coupled 3D simulator, we show the design principles for nanowire and planar solar cells are significantly different; nanowire solar cells are vulnerable to surface and contact recombination, while planar solar cells suffer significant losses due to imperfect backside mirror reflection. Overall, the ultimate efficiency of the GaAs nanowire solar cell with radial and vertical junction is not expected to exceed that of the thin-film design, with both staying below the Shockley-Queisser limit.

Bis-(morpholinodithiato-s,s¢)-Cu-Zn was synthesized as a single solid source precursor and characterized using particle-induced x-ray emission (PIXE), Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). Cu-Zn-S thin film was deposited on sodalime glass substrate using metal organic chemical vapor deposition (MOCVD) technique at temperatures ranging from 360°C to 450°C. The thin films were characterized using Rutherford backscattering spectroscopy (RBS), x-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible spectroscopy and four-point probe technique. PIXE of the precursor confirmed the presence of the expected elements that can lead to deposition of Cu-Zn-S thin film while FTIR confirmed that the organic ligands were attached to the metals. DSC showed that the precursor is thermally stable and can pyrolyze at temperature between 340°C and 460°C. RBS analysis of the films showed that there was no substantial deposition at 360°C while other films showed various stoichiometry and thickness. XRD analysis of the films showed that films deposited at 360°C and 380°C are amorphous, while those deposited between 400°C and 450°C showed peaks, in which the crystal size decreased as the deposition temperature increased. The SEM micrographs showed that the morphology of the films is temperature dependent and as deposition temperature increased larger secondary grains dissociated into smaller grains that are closely packed, without cracks and holes. Optical characterization showed that the films exhibited high transmittance, which fairly increased as the deposition temperature increased. A direct band gap value between 2.49 eV and 2.92 eV was obtained as deposition temperature increased. Urbach energy also increased from 0.87 eV to 1.51 eV, while the steepness parameter decreased as the deposition temperature increased. The electrical characterization showed that the resistivity of the films decreased as the deposition temperature increased while the I-V plot showed a rectifying character.

The generation of discrete breathers in an A 3 B crystal has been modeled by the method of molecular dynamics using Pt 3 Al as an example via the application of random unidirectional momenta, which simulate the action of a particle flux, to atoms. Two possible mechanisms of the excitation of gap discrete breathers with a soft type of nonlinearity have been revealed depending on the energy of particles in a flux. If a particle is able to transfer energy of more than 1.4 eV to the Al atom, a discrete breather can be excited by the only particle. Otherwise, a discrete breather is formed upon numerous particle-Al atom collisions, which are possible only at a sufficiently high density of particles, as each following particle must transfer its momentum to the Al atom before its oscillations provoked by previous particles attenuate.

Using the method of molecular dynamics and taking Ni 3 Al and Pt 3 Al as examples, crystals of the A 3 B composition are considered for the possibility of excitation of soliton-type waves in them. The potentials obtained by the embedded-atom method were used to describe interatomic interactions. It is shown that the harmonic external stimulus can excite waves of the soliton type in a Pt 3 Al crystal, but not in Ni 3 Al. Such compression-expansion waves are generated because of excitation of discrete breathers with soft nonlinearity that cannot exist in a Ni 3 Al crystal near the affected region. The detected waves are capable of propagating to thousands of nanometers along the Pt 3 Al crystal without losses of integrity and speed. The shape of the obtained wave corresponds to the kink solution of the sine-Gordon equation. The aggregate amount of energy transferred by a wave is determined by the number of rows of atoms involved in fluctuations; this may involve dozens and hundreds of electron volts.

We report high quality InGaAs/InP heterojunction bipolar transistors (HBT's) grown by metalorganic chemical deposition (MOCVD) utilizing a wide base structure and exhibiting behavior suggesting good alignment of the electrical and metallurgical junctions. Excellent dc and rf HBT characteristics were obtained with common-emitter dc current gains (P's) up to 1 . 5 ~ 103, small-signal current gains (h,,'s) up to 3.9~103, and unity-gain cut-off frequencies (fT's) up to 15 GHz.