Influence of Sn<Superscript>4+</Superscript> on Structural and DC Electrical Resistivity of Ni-Zn Ferrite Thick Films

Among the soft ferrites, Ni-Zn ferrite is one of the most versatile ceramic materials because of their important electrical and magnetic properties. These properties were improved by substituting Sn⁴⁺ in Ni-Zn ferrites with chemical composition of Ni _x Zn_1+y?x Fe_2?2y Sn _y O₄ (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0; y = 0.1, 0.2). To achieve homogenous ferrite powder at lower sintering temperature and smaller duration in nano-size form, the oxalate co-precipitation method was preferred as compared to other physical and chemical methods. Using this powder, ferrite thick films (FTFs) were prepared by the screen printing technique because of its low cost and easy use. To study structural behavior, the FTFs were characterized by different techniques. The x-ray diffraction and thermo-gravimetric and differential thermal analysis studies show the formation of cubic spinel structure and ferrite phase formation, respectively. There is no remarkable trend observed in lattice constants for the Sn⁴⁺ (y = 0.1)- and Sn⁴⁺ (y = 0.2)-substituted Ni-Zn ferrites. The bond lengths as well as ionic radii on the A-site of Ni-Zn-Sn ferrites were found to decrease with increasing nickel content. The bond length and ionic radii on the B-sites remained almost constant for Sn⁴⁺ (y = 0.1, 0.2)-substituted Ni-Zn ferrites. The energy dispersive x-ray analysis confirms the elemental analysis of FTFs. The Fourier transform infrared spectra show two major absorption bands near 400 cm^?1 and 600 cm^?1 corresponding to octahedral and tetrahedral sites, respectively, which also confirms the formation of the ferrites. The field emission scanning electron microscopy images shows that the particles are highly porous in nature and located in loosely packed agglomerates. The average particle size of the FTFs lies in the range 20–60 nm. Direct current (DC) resistivity of Ni-Zn-Sn FTFs shows the semiconductor nature. The DC resistivity of Ni-Zn-Sn_0.2FTFs is lower than Ni-Zn-Sn_0.1 FTFs. The DC resistivity is found to decrease with the increase in Ni²⁺ content up to x = 0.6. It increases thereafter for a further increase in Ni²⁺ content up to x = 1.0, and a similar trend is observed for the variations of activation energy with Ni²⁺ content.     

Effective masses and evidence for alloy disorder effects in GaxIn1−xAsyP1−y investigated by shallow donor photoconductivity

An investigation is reported of shallow donor photoconductivity for four compositions in the alloy series Ga_xIn_1−xAs_yP_1−y (y = 0.22, 0.56, 0.83, 1.0). The sample peak mobilities exceed 1.5 m² V⁻¹ s⁻¹. A linear effective mass variation through the alloy range is found to be most consistent with the experimental data. This is at variance with the predictions of K.P theory: possible reasons for this are discussed.     

Energy bandgap and lattice constant contours of II–VI quaternary alloys

Energy bandgap and lattice constant contours of A_1?x B_x C_1?y D_y and AB_1?x?y C_x D_y II-VI quaternary alloys were calculated by the interpolation method using ternary alloy parameters. Three interpolation methods were applied to A_1?x B_x C_1?y D_y alloy systems. The maximum energy differences between the three methods, which occur near the center of the composition plane, are 0.14, 0.24, and 0.33 eV for (ZnCd)(SSe), (ZnCd)(SeTe), and (ZnCd)(STe) alloy systems, respectively. The calculated results are compared with two sources of experimental data and were fitted within 0.23 eV for all the three methods. For AB_1?x?y C_x D_y alloy systems the calculated results based on two interpolation methods agreed very well within 0.03 eV.     

Measured compositions and laser emission wavelengths of GaXIn1−XAsyP1−y lpe layers lattice-matched TO InP Substrates

The alloy compositions of Ga_XIn_1−XAs_yP_1−y LPE layers lattice-matched to InP substrates have been determined by electron microprobe analysis. The composition data are well repre-sented by x = 0.40y + 0.067y². The emission wavelengths of lattice-matched Ga_XIn_1−XAs_yP_1−y/InP double-heterostructure diode lasers have been measured at 300 and 80 K. The photon energies for laser emission at 300 K are given by hΝ(eV) = 1.307 − 0. 60y + 0.03y². The emission energies at 80 K are 57 meV higher. This work was sponsored by the Department of the Air Force.     

Thermodynamic and Transport Study of Electron- and Hole-Doped MGa3 Single Crystals (M = Fe,Co)

FeGa₃ and related compounds have been subjects of recent investigation for their interesting thermoelectric, electronic, and magnetic behaviors. Here, single crystals of FeGa_3?y Ge _y were grown by the self-flux technique with effective y = 0, 0.09(1), 0.11(1), and 0.17(1) in order to investigate the evolution of the diamagnetic semiconducting compound FeGa₃ into a ferromagnetic metal, which occurs through the electron doping and band structure modifications that result from substitution of Ge for Ga. Heat capacity and magnetization measurements reveal non-Fermi liquid behavior in the vicinity of the transition from a paramagnetic to ferromagnetic ground state, suggesting the presence of a ferromagnetic quantum critical point (FMQCP). We also present the first results of hole doping in this system by the growth of FeGa_3?y Zn _y single crystals, and electron- and hole doping of the related compound CoGa₃ by CoGa_3?y Ge _y and CoGa_3?y Zn _y crystal growths, aiming to search for further routes to band structure and charge carrier tuning, thermoelectric optimization, and quantum criticality in this family of compounds. The ability to tune the charge carrier type warrants further investigation of the MGa₃ system’s thermoelectric properties above room temperature.     

Heteroepitaxial silicon-carbide nitride films with different carbon sources on silicon substrates prepared by rapid-thermal chemical-vapor deposition

Cubic crystalline silicon-carbon nitride (Si_1−x−yC_xN_y) films have been grown successfully using various carbon sources by rapid-thermal chemical-vapor deposition (RTCVD). The characteristics of the Si_1−x−yC_xN_y films grown with SiH₃CH₃, C₂H₄, and C₃H₈ are examined and compared by x-ray photoelectron spectroscopy (XPS) spectra, scanning electron microscopy (SEM) images, and transmission electron microscopy (TEM) patterns. The XPS spectra show that the differences of chemical composition and chemical-bonding state are co-related to the C bonding type of the different carbon source. The SEM images and TEM analysis indicate that the better Si_1−x−yC_xN_y film can be obtained using C₃H₈ gas as the carbon source. In addition, correlations between the growing stages to the microstructure of the cubic-crystalline Si_1−x−yC_xN_y films have been illustrated in detail.     

Incorporation of group V elements in Gaxin1−xAsyP1−y grown by gas source molecular beam epitaxy

A simple growth model has been successfully developed for the determination of the As to P incorporation ratio, i.e., mole fraction y, in growing Ga_xIn_1−xAs_yP_1−y quaternary alloys by gas source molecular beam epitaxy. The model covers the whole composition range with only two fitting parameters, k_In and k_Ga, whose physical meanings are the product of As to P desorption time constant ratio and incorporation rate constant ratio for InAs_yP_1−y and GaAs_yP_1−y, respectively. The best fitting values of k_In and k_Ga from our experimental results are 28 and 3, respectively, at a growth temperature of 480°C. The temperature dependency of the parameters were also studied. The activation energies of k_In and k_Ga are +30 and −330 meV, respectively. The significant differences between the parameters may be due to the different bond energies of binary alloys.     

Band anticrossing in highly mismatched group II-VI semiconductor alloys

We have successfully synthesized highly mismatched Cd_1−yMn_yO_xTe_1−x alloys by high-dose implantation of O ions into Cd_1−yMn_yTe crystals. In crystals with y>0.02, incorporation of O causes a large decrease in the bandgap. The bandgap reduction increases with y; the largest value observed is 190 meV in O⁺-implanted Cd_0.38Mn_0.62Te. The results are consistent with the band anticrossing (BAC) model, which predicts that a repulsive interaction between localized states of O located above the conduction-band edge and the extended states of the conduction band causes the bandgap reduction. A best fit of the measured bandgap energies of the O-ion-synthesized Cd_1−yMn_yO_xTe_1−x alloys using the BAC model for y<0.55 suggests an activation efficiency of only ∼5% for implanted O in Cd_1−yMn_yTe.     

Stoichiometry control of some II–VI ternary solid solutions during sublimation growth

A useful method is presented to control the stoichiometric composition y in Cd_1+y(S_xSe_1−x) and Zn_1+y(S_xSe_1−x) systems. The stoichiometry y is controlled through vapor growth process by regulating the sum of chalcogen partial pressures P_ps (=P_S2+P_Se2), and by keeping the pressure ratio P_r (=P_S2/P_Se2) constant in each growth experiment. The electrical properties of the grown crystal change obviously depending on P_ps and it is confirmed that the deviation y from stoichiometric composition y is effectively controlled without changing the composition x. The applicability of this method to other II–VI solid solutions is presented.     

Optoelectronic properties of cubic BxInyGa1−x−yN alloys matched to GaN for designing quantum well Lasers: First-principles study within mBJ exchange potential

A Full-Potential Linearized Augmented Plane Wave calculation within density functional theory is performed to investigate the electronic and optical properties of cubic B_xIn_yGa_1−x−yN alloys matched to GaN with low-Boron content (x≤0.187). The exchange-correlation potential is treated by the local density approximation (LDA) to calculate the structural properties. The band structure and density of states of these compounds are well predicted by modified Becke–Johnson (mBJ) exchange potential compared to LDA and generalized gradient approximation (GGA). Also, the optical properties are calculated by the mBJ exchange potential. The computed structural parameters are found to be in good agreement with experimental and theoretical data. The B_xIn_yGa_1−x−yN alloy is expected to be lattice matched to GaN substrate for (x=0.125, y=0.187). The incorporation of B and In into GaN substrate allows the reduction of the band gap energy. The real and imaginary parts of the dielectric function, refractive index, reflectivity and absorption coefficient are discussed on the basis on the energy band structure and the calculated density of states. The optical properties of B_xIn_yGa_1−x−yN depend on the incorporated Boron content (with y=0.187). This means that B_xIn_yGa_1−x−yN could constitute an active layer in single quantum well for the design of high-efficiency solar cells and optoelectronic devices as Laser Diodes operating in the UV spectral region.     

Band gap and optical properties of the CdxHg1 − x − y ZnyTe alloys in ultraviolet and visible spectral regions

Optical properties of the Cd_xHg_{1 ? x ? y} Zn_yTe semiconductor alloy are examined in ultraviolet, visible, and infrared spectral regions. The relations are obtained, which make it possible to estimate the _x and _y composition of this material by the position of singular points E ₀ and E ₁ in the optical spectra. Theoretical and experimental results in the composition regions 0.09 < x < 0.22 and 0.02 < y < 0.17 agree well.     

Transparent and Flexible Mn1−x−y(CexLay)O2−δ Ultrathin-Film Device for Highly-Stable Pseudocapacitance Application

Control over the fabrication of state-of-the-art portable pseudocapacitors with the desired transparency, mechanical flexibility, capacitance, and durability is challenging, but if resolved will have fundamental implications. Here, defect-rich Mn_1−x−y(Ce_xLa_y)O_2−δ ultrathin films with controllable thicknesses (5–627 nm) and transmittance (≈29–100%) are fabricated via an electrochemical chronoamperometric deposition using a aqueous precursor derived from end-of-life nickel-metal hydride batteries. Due to percolation impacts on the optoelectronic properties of ultrathin films, a representative Mn_1−x−y(Ce_xLa_y)O_2−δ film with 86% transmittance exhibits an outstanding areal capacitance of 3.4 mF cm⁻², mainly attributed to the intercalation/de-intercalation of anionic O²⁻ through the atomic tunnels of the stratified Mn_1−x−y(Ce_xLa_y)O_2−δ crystallites. Furthermore, the Mn_1−x−y(Ce_xLa_y)O_2−δ thin-film device exhibits excellent capacitance retention of ≈90% after 16 000 cycles. Such stability is associated with intervalence charge transfer occurring among interstitial Ce/La cations and Mn oxidation states within the Mn_1−x−y(Ce_xLa_y)O_2−δ structure. The energy and power densities of the transparent flexible Mn_1−x−y(Ce_xLa_y)O_2−δ full-cell pseudocapacitor device, is measured to be 0.088 μWh cm⁻² and 843 µW cm⁻², respectively. These values show insignificant changes under vigorous twisting and bending to 45–180° confirming these value-added materials are intriguing alternatives for size-sensitive energy storage devices.     

Nickel silicidation techniques for strained Si1?xGex, Si1?x?yGexCy, and Si1?yCy alloys material-device applications

A nickel silicide process for Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy materials compatible with Si technology has been developed. Low-resistivity-phase (12–20 μΘ cm) nickel silicides have been obtained for these alloys with different low sheet-resistance temperature windows. The study shows that thin (15–18 nm) silicide layers with high crystalline quality, smooth silicide surface, and smooth interface between silicide and the underlying material are achievable. The technique could be used to combine the benefits of Ni silicide and Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloys. The technique is promising for Si or Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy-based metal-oxide semiconductor, field-effect transistors (MOSFETs) or other device applications.     

Crystallophysical properties of the In1 ? yGayAs1 ? xNx/GaAs heterostructures

Some properties of the In_{1 − y} Ga _y As_{1 − x} N _x unordered alloys and physical prerequisites of their use in science and technology are considered. The results of studying the intermolecular interaction in the systems under study and the features of their application to the In_{1 − y} Ga _y As_{1 − x} N _x /GaAs functional hetero-structures are presented.     

Valence-band offsets in strained SiGeSn/Si layers with different tin contents

Admittance spectroscopy is used to study hole states in Si_0.7–y Ge_0.3Sn _y /Si quantum wells in the tin content range y = 0.04–0.1. It is found that the hole binding energy increases with tin content. The hole size-quantization energies in structures containing a pseudomorphic Si_0.7–y Ge_0.3Sn _y layer in the Si matrix are determined using the 6-band kp method. The valence-band offset at the Si_0.7–y Ge_0.3Sn _y heterointerface is determined by combining the numerical calculation results and experimental data. It is found that the dependence of the experimental values of the valence-band offsets between pseudomorphic Si_0.7–y Ge_0.3Sn _y layers and Si on the tin content is described by the expression ΔE _V ^exp = (0.21 ± 0.01) + (3.35 ± 7.8 × 10^–4)y eV.     

Heterogeneous AgxCdyS-AgCd Nanoparticles with Chiral Bias for Enhanced Photocatalytic Efficiency

Stereoselective catalysis is common in living systems mediated by natural nanoenzymes. However, few artificial nanomaterials are developed for enantioselective and stereoselective catalysis. In this study, Ag_xCd_yS-AgCd nanoparticles (NPs) with specific heterojunctions, strong chiral optical activities, and excellent enantioselective catalytic ability are constructed. Similar to photosensitive enzymes, Ag_xCd_yS-AgCd NPs stabilized with l -/d -penicillamine (l -/d -Ag_xCd_yS-AgCd NPs) can serve as photocatalysts, which show the highest catalytic efficiency toward the photodegradation of methyl blue compared with that of Ag₂S and CdS NPs and lead to 50% enhancement of photoconversion efficiency of Cr⁶⁺ to Cr³⁺ as well. Moreover, attributed to the higher chiral preference between l -Ag_xCd_yS-AgCd NPs and l -Tartaric acid (l -TA), d -Ag_xCd_yS-AgCd NPs and d -Tartaric acid (d -TA), the photoreduction efficiency of Cr⁶⁺ to Cr³⁺ mediated by l -Ag_xCd_yS-AgCd NPs with l -TA, and d -Ag_xCd_yS-AgCd NPs with d -TA samples is enhanced as high as 30% compared with the samples of l -Ag_xCd_yS-AgCd NPs with d -TA, and d -Ag_xCd_yS-AgCd NPs with L-TA. This study establishes a versatile way to construct enantioselective inorganic catalysts for biocatalysis, biomedicine, and other applications.     

HgCdZnTe quaternary materials for lattice-matched two-color detectors

As the number of bands and the complexity of HgCdTe multicolor structures increases, it is desirable to minimize the lattice mismatch at growth interfaces within the device structure in order to reduce or eliminate mismatch dislocations at these interfaces and potential threading dislocations that can degrade device performance. To achieve this we are investigating the use of Hg_1−x−yCd_xZn_yTe quaternary alloys which have an independently tunable lattice constant and bandgap. Lattice matching in Hg_1−x−yCd_xZn_yTe structures can be achieved using small additions of Zn (y<0.015) to HgCdTe ternary alloys. We have investigated some of the basic properties of Hg_1−x−yCd_xZn_yTe materials with x≈0.31 and 0≤y≤0.015. The quaternary layers were grown on (112)CdZnTe substrates using MBE and the amount of Zn in the layers was determined from calibrated SIMS measurements. As expected, the lattice constant decreased and the bandgap increased as Zn was added to HgCdTe to form Hg_1−x−yCd_xZn_yTe. Hall-effect results for both n-type (In) and p-type (As) Hg_1−x−yCd_xZn_yTe layers were very similar to HgCdTe control samples. We have also utilized x-ray rocking curve measurements with (246) asymmetric reflections as a novel sensitive technique to determine the correct amount of Zn needed to achieve lattice matching at an interface. MWIR/LWIR n-p-n two-color triple-layer heterojunction structures were grown to evaluate the effects of minimizing the lattice mismatch between the widest bandgap p-type collector layer, using Hg_1−x−yCd_xZn_yTe, and the HgCdTe MWIR and LWIR collector layers and compared to structures that did not incorporate the quaternary. Sequential mode two-color detectors were fabricated using a 256 × 256, 30 μm unit cell design. There were several interesting findings. Macro defects predominantly affected the LWIR band (Band 2) operability and had little effect on the MWIR band (Band 1). The incorporation of Hg_1−x−yCd_xZn_yTe p-type collector layers had little effect on MWIR detector performance, but overall the LWIR performance was generally better. These initial detector results indicate that the use of Hg_1−x−yCd_xZn_yTe alloys in multicolor detector structures are potentially promising and should be pursued further.     

Model-based analytical FOE determination

An analytical procedure for the estimation of the focus of expansion (FOE) location is introduced. The method is applied to a vector field which has been obtained from the analysis of the relative translational movement of a rigid body with respect to the acquiring camera (monocular system). A polynomial model is fitted to the vector field; the order and shape of the model are determined by the kinetic analysis of the Euclidean camera centered coordinate system in which the camera is moving, and some hypothesis concerning the approximation of the inverse of the depth function 1/Z(x, y). Two basic properties of complex differentiation theory are applied, assuming that each vector of the optic flow is a real-valued complex function of the form v(x, y)=v_x(x, y)+iv_y(x, y). These properties provide the set of points for which both components of the vector field v_x(x, y) and v_y(x, y) are harmonic and, as a subset, the set of points for which both components are zero. The use of perspective projection states that the FOE is the locus where v_x(x, y)=0=v_y(x, y) and, therefore, where the conditions stated by both properties meet.     

Characterization of various alloying metal oxide nanoparticles embedded in HfOxNy as charge trapping nodes in nonvolatile memory devices

This work compares Co_xMo_yO, Co_xFe_yO and Fe_xMo_yO alloying metal oxide nanoparticles (AMONs) that were individually embedded in HfO_xN_y high-k dielectric as charge trapping nodes. They were formed by chemical vapor deposition using Co/Mo, Co/Fe and Fe/Mo acetate, respectively, calcined and reduced in Ar/NH₃ ambient. The effects of various pre-treatments on Co_xMo_yO, Co_xFe_yO and Fe_xMo_yO AMONs preparation were investigated. The results indicate that the larger charge trap density, larger memory window and better programming characteristics of Co_xMo_yO AMONs are attributable to their higher surface density and smaller diameter. The average collected charge in each Co_xMo_yO AMON is the smallest among three AMONs, revealing that a local leakage path is associated with the least charge loss. The main mechanism that governs the programming characteristics involves the trapping of holes.     

Determination of the composition of multicomponent chalcogenide semiconductors by X-ray fluorescence analysis

The composition of As _x (Ge _y Se_{1 ? y} )_{1 ? x} glassy alloys is quantitatively determined by measuring the X-ray fluorescence spectrum of a Ge_0.2As_0.4Se_0.4 reference alloy. The atomic fractions of arsenic, germanium, and selenium are calculated from the X-ray fluorescence spectra and the x _RFA = f(x) and y _RFA = f(y) dependences are plotted. These dependences make it possible to determine the composition of the glasses with an accuracy of ±0.0005 for x and y. This procedure is effective for finding the concentration of the tin impurity in Pb_{1 ? x} Sn _x Se crystalline solid solutions. However, it is impossible to determine the content of tellurium in Te _x (As _y Se_{1 ? y} )_{1 ? x} glassy alloys because the alloy components have significantly different X-ray fluorescence characteristics.