Preparation and characterization of LiNiVO4 powder and non-stoichiometric LiNixVyOz films

Inverse spinel type structured oxide, LiNiVO₄, was synthesized by using solid-state method and the crystalline powder was characterized by Rietveld refinement and X-ray photoelectron spectroscopy. Non-stoichiometric lithium nickel vanadate thin films were prepared by physical vapour deposition technique. The amorphous films were characterized by Rutherford back-scattering spectroscopy (RBS), nuclear reaction analysis (NRA), Auger electron spectroscopy (AES), X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analytical methods. Films crystal growth at various temperatures was also studied by XRD and SEM. The HRTEM analysis of sputtered film shows nanocrystalline domains of NiO and LiNiVO₄ phases with characteristic lattice parameters of the host compound and the results correlate well with the XRD data. Electrochemical properties of the films were discussed.     

Structural and optical properties of AlxOy/Pt/AlxOy multilayer absorber

We report on the microstructure and optical properties of Al_xO_y–Pt–Al_xO_y interference-type multilayer films, deposited by electron beam (e-beam) deposition onto corning 1737 glass, silicon (1 1 1) and copper substrates. The structural properties were investigated by Rutherford backscattering spectrometry, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and atomic force microscopy. The optical properties were extracted from specular reflection/transmission, diffuse reflectance and emissometer measurements. The stratification of the coatings consists of a semi-transparent middle Pt layer sandwiched between two layers of Al_xO_y. The top and bottom Al_xO_y layers were non-stoichiometric with no crystalline phases present. The Pt layer is in the fcc crystalline phase with a broad size distribution and spheroidal shape in and between the rims of Al_xO_y. The surface roughness of the stack was found to be comparable to the inter-particle distance. The optical calculations confirm a high solar absorptance of ∼0.94 and a low thermal emittance of ∼0.06 for the multilayer stack, which is attributed not only to the optimized nature of the multilayer interference stacks, but also to the specific surface morphology and texture of the coatings. These optical characteristics validate the spectral selectivity of the Al_xO_y–Pt–Al_xO_y interference-type multilayer stack for use in high temperature solar-thermal applications.     

Optical and electrical H/sub 2/- and NO/sub 2/-sensing properties of Au/In/sub x/O/sub y/N/sub z/ films

In this paper, we describe the optical and electrical gas-sensing properties of In/sub x/O/sub y/N/sub z/ films with an ultrathin gold promoter overlayer. We have fabricated In/sub x/O/sub y/N/sub z/ films with a nanocrystalline porous structure by RF-sputtering in Ar/N/sub 2/ followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In/sub x/O/sub y/N/sub z/ films by dc sputtering and an annealing process. We have investigated the optical H/sub 2/and NO/sub 2/-sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resistance) for these two gases. A combined optical/electrical sensor for H/sub 2//NO/sub 2/ is proposed.     

Fabrication and characterization of NiO/ZnO/ITO p-i-n heterostructure

Transparent oxide semiconductors (TOSs) are promising materials for a variety of optoelectronic applications such as UV detectors. While several TOS-based p-n and p-i-n diodes have been recently reported, the high reverse dark current still poses a major issue. In this work, we report on a NiO/ZnO/ITO p-i-n heterostructure with reduced dark current level suitable for practical applications. Ion beam-assisted e-beam evaporation was used to deposit both p-type NiO and intrinsic ZnO layers, while a conventional sputtering system was used to prepare the ITO layer. Samples with sputtered ZnO layer were also fabricated for comparison. The diodes demonstrated clear rectifying I-V characteristics with a current rectification ratio up to 10⁴ at bias voltages of ± 1 V. The lowest level of reverse dark current (∼ 10 nA/cm² at − 5 V) is observed in samples with ZnO deposited by ion beam-assisted e-beam evaporation. In comparison, diodes with sputtered ZnO layer show two orders of magnitude higher dark current. Analysis of the quasi-static J-V characteristics, including time dependence behavior, shows that the dark current can be attributed to thermal generation of charge carriers via deep defects states in the ZnO layer and charge injection from the contacts. Electrical and optical properties of the TOS films are presented and discussed along with deposition conditions and device performance.     

非晶Tb/Fe/Dy和Fe/Tb/Fe/Dy纳米多层膜磁性能及超磁致伸缩性能(英文)

研究非晶Tb/Fe/Dy(样品A)和Fe/Tb/Fe/Dy(样品B)纳米多层膜超磁致伸缩性能和磁性能.磁滞回线表明样品A的垂直磁各向异性而样品B有面向磁各向异性,样品B比样品A更好的磁性能.样品B有很好的低场超磁致伸缩性能,在外磁场为0.12T情况下样品B的超磁致伸缩性能是样品A的五倍,即从16ppm变为82ppm.     

Effect of Bi/Pb ratio and annealing temperature onTc and formation of high-Tc phase in Bi-Pb-Sr-Ca-Cu-O superconductor

We studied the effect of Bi/Pb ratio and annealing temperature onT _c and formation of the high-T _c ; phase in Bi-Pb-Sr-Ca-Cu-O superconductor by the three-step reaction process. The optimum Bi/Pb ratio is about 1.80.3 and the optimum annealing temperature is about 845–855°C. It is found that a variate high-T _c phase existed at the higher annealing temperature. The zero-resistance temperature of the variate high-T _c phase decreased when the annealing temperature increased, although the phase is isostructural with the 110 K phase.     

Chemical bonds and microstructure in nearly stoichiometric PECVD aSixNyHz

Silicon nitride thin films were prepared by low frequency plasma enhanced chemical vapour deposition in silane, nitrogen and helium mixtures. With different silane flow rates, various thin films with nearly stoichiometric composition but different chemical bonds were prepared with hydrogen content lower than 12%. The films were annealed up to 1100 °C and the hydrogen content was measured by elastic recoil detection analysis and compared to the infrared vibration of hydrogenated modes of silicon and nitrogen atoms. Two kinds of behaviour were observed in the chemical bonding with the annealing temperature: either NH and SiH bonds show a decrease, as is generally reported in the literature, or a strong increase of the SiH one is observed. There is also a dramatic discrepancy between the hydrogen content measured by nuclear technique and by infrared spectroscopy if constant oscillator strengths of the stretching modes of hydrogenated sites are used. As in amorphous silicon, these results confirm the difficulty of deducing the concentration of hydrogen bonded to the silicon atoms in silicon nitride. We suggest that these effects are closely correlated to the local microstructure of the films and specific arrangements around SiH dipoles.     

Properties of composite BxCyNz nanotubes and related heterojunctions

We review the stability and electronic properties of composite B_xC_yN_z nanotubes, including BN-, BC₂N- and B-doped carbon nanotubes. We show in particular that BC₂N systems are driven towards the segregation of pure C and BN sections. The same process of segregation into BC₃ islands is evidenced in the case of B-doped carbon nanotubes. These spontaneous segregation processes lead to the formation of quantum dots or nanotube heterojunctions with potential important technological applications.     

GexNbSe2 and GexNbS2 intercalation compounds

The structures of two intercalation compounds, Ge_∼0.2NbSe₂ and Ge_∼0.3NbS₂ were investigated by single crystal X-ray diffraction and electron microscopy (selected area electron diffraction (SAED), high resolution electron microscopy (HRTEM) and X-ray microanalysis by energy dispersive spectroscopy (XEDS)). Crystal structure determinations of the average structure of the intercalation compounds 2H-Ge_0.217NbSe₂ and 4H-Ge_0.288NbS₂ are reported: the selenide compound crystallizes in the space group P6₃/mmc with a = 3.4560(9) Å and c = 12.966(3) Å and adopts the 2H-NbSe₂ structure-type, while the sulfide compound crystallizes in the P6₃mc space group, with a = 3.3392(9) Å and c = 25.404(7) Å with a structure-type 4H_c-NbS₂ which it is known for TaSe₂. In both structures the germanium atoms are located in the empty octahedral positions of the van der Waals gap between the NbX₂ (X = S, Se) layers. Electron diffraction patterns from several Ge_xNbSe₂ crystal flakes show different superstructures and exhibit diffracted diffuse intensity: weak satellites corresponding to and 2a₀ × 2a₀ superstructures were observed for x ∼ 0.15 (a₀ is the basal lattice parameter of the host structure). For x ∼ 0.25-0.33, the same type of satellite is observed with a stronger intensity. For x ∼ 0.5 only satellites corresponding to the superstructure were present. In the case of Ge_xNbS₂, with 0.10 < x < 0.25, the germanium atoms are ordered in domains with an superstructure. In some crystals disorder along the c-axis has been observed.     

Analysis of phenothiazine and its derivatives using LC/electrochemistry/MS and LC/electrochemistry/fluorescence

The on-line electrochemical conversion of phenothiazine and its derivatives after liquid chromatographic separation has been studied by mass spectrometry and fluorescence spectroscopy. In an electrochemical cell consisting of porous glassy carbon, the phenothiazines are readily converted to oxidized products, which can be detected by on-line fluorescence spectroscopy and mass spectrometry. The method allows rapid investigations on the electrochemical oxidation pathways, as demonstrated for phenothiazine itself. The phenothiazine derivatives are transferred into their strongly fluorescent sulfoxides. Based on this reaction, an LC/electrochemistry/fluorescence method was developed that allows for limits of detection between 5 x 10(-9) and 4 x 10(-8) mol/L and limits of quantification between 2 x 10(-8) and 1 x 10(-7) mol/L for the individual phenothiazines. The linear ranges comprised three decades starting at the limit of quantification.     

Fabrication and electrical properties of Al/phenolsulfonphthalein/n-Si/AuSb structure

The current-voltage (I-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) characteristics of Al/phenolsulfonphthalein (PSP)/n-Si/AuSb structure were investigated at room temperature. A modified Norde's function combined with conventional forward I-V method was used to extract the parameters including barrier height and the series resistance. The barrier height and series resistance obtained from Norde's function were compared with those from Cheung functions, and it was seen that there was a good agreement between the barrier height values from both method. It was also seen that the values of capacitance were almost independent of frequency up to a certain value of frequency, whereas at high frequencies the capacitance decreased quickly. The higher values of capacitance at low frequencies were attributed to the excess capacitance resulting from the interface states in equilibrium with the n-Si that can follow the alternating current (a.c) signal.     

Preparation and investigation of VOx thin films of n- and p-types

In this work we present first results on the synthesis of vanadium oxide semi-transparent conducting thin films of p- and n-types. The films were deposited by thermal evaporation method in vacuum, on: silicon, glass, sapphire, and gold substrates. Temperature of substrate during deposition was set around 250 °C. As deposited films were of a p-type of conductivity. Thermal annealing at 420 °C of as-deposited films in air at atmospheric pressure resulted in a change in the conductivity type.Optical, electrical and thermal properties of the deposited films were studied. The topography of the films was studied using AFM microscope. P-N structures were created using VO_x films on silicon and glass substrates. Electrical measurements had shown a non-linear behaviour of the samples.     

Deflection of wafers and cantilevers with Pt/LNO/PZT/LNO/Pt/Ti/SiO2 multilayered structure

The present paper describes a Pt/LNO/PZT/LNO/Pt/Ti/SiO₂ multilayers deposited on 4-inch Si wafers. We have evaluated the variation of the deflection of the Si wafers with deposition of each of the thin films. The deposition of the multilayers has resulted in downward deflection (center is higher than edge) of the Si wafers. The multilayers have been also deposited onto SOI wafers and fabricated into piezoelectric micro cantilevers through MEMS bulk micromachining. The micro cantilevers have shown the upward deflection. We have characterized the ferroelectric and piezoelectric properties of the PZT thin films through electrical tests of the micro cantilevers. The dielectric constant, saturation polarization, remanent polarization and coercive field were measured to be 1050, 31.3 μC/cm², 9.1 μC/cm² and 21 kV/cm, respectively. The transverse piezoelectric constant, d₃₁, was measured to be − 110 pm/V from the DC response of the micro cantilevers.     

Structure transformations and dielectric properties of PbY1/2Nb1/2O3 and PbHo1/2Nb1/2O3 compounds

The metastable pseudomonoclinic perovskite phases, PbY_1/2Nb_1/2O₃ and PbHo_1/2Nb_1/2O₃ were prepared under conditions of high pressures and temperatures. Investigations of structural parameters, thermal stability and some dielectric properties were carried out. The data were analyzed by comparison with corresponding data of other representatives of the PbB_1/2³⁺Nb_1/2O₃ series. The dependence of unit cell parameters on the B³⁺ rare earth cation radius for the PbB_1/2³⁺Nb_1/2O₃ perovskites was correlated with a change of electronic structure of the rare earth elements, in particular, with the 4f-shell filling.     

Near UV emission and p-type conductivity in Zn1−xLixO and Zn1−xNaxO nanomaterial system

The nanomaterial system Zn_1−xLi_xO and Zn_1−xNa_x  O (0?x?0.15$0?x?0.15$) were synthesized by controlled solid state reaction. XRD analysis showed well formed wurtzite structure of average particle size about 50 nm and change in lattice parameters due to incorporation of group I element in ZnO lattice. SEM exhibited formation of nanorods. Hall effect measurement of Zn_1−xLi_xO and Zn_1−xNa_xO system showed p-type conductivity which varied with concentration of Li and Na. Photoluminescence showed strong emission peak in near UV at 3.11 eV (398 nm) and negligible visible emission. The PL peak positions in Zn_1−xLi_xO and Zn_1−xNa_xO nearly coincide which suggest very similar recombination mechanism in Li and Na doped ZnO nanocrystals. The results hold potential for fabrication of ZnO based near UV LEDs.     

Anomalous Hall Effect in Sn1?x?yMnxEuyTe and Sn1?x?yMnxEryTe Mixed Crystals

The Anomalous Hall Effect (AHE) was investigated in IV–VI ferromagnetic semimagnetic semiconductors of Sn_1–x Mn _x Te codoped with either Eu or Er. The analysis of experimental data is as follows. Hall resistivity and magnetization showed that AHE coefficient R _s depends on temperature and its value decreases with thetemperature increase. We observe that above ferromagnet–paramagnet transition temperature R _s changes sign. We discuss the possible physical mechanisms responsible for observed temperature dependence of R _s , particularly change of the sign.     

High-Tc superconductivity and electronic band structure

We review the main results of the van Hove scenario applied to superconducting cuprates. It is based on the assumption that in these materials, the Fermi level lies near a singularity in the density of states (DOS). This hypothesis has recently been confirmed experimentally. We show that this model explains many properties of the high-T _c superconductors. We show that an anaogous model with a peak in the DOS may also be applied to the superconducting doped fullerenes. A general feature of the model is a very short coherence length.     

Phase Composition and Dielectric Properties of Thin Films Produced by Annealing Sn/Pb/Ti/Si and Pb/Sn/Ti/Si Heterostructures

Sn/Pb/Ti/Si and Pb/Sn/Ti/Si heterostructures were deposited by magnetron sputtering using Ti and Sn solid targets and liquid-phase Pb self-sputtering in the former case and three solid targets in the latter. The heterostructures were then annealed in flowing oxygen at 470–970 K. The major phase in the film produced from the Sn/Pb/Ti/Si heterostructure at 970 K was the Pb(Sn_0.55Ti_0.45)O₃ solid solution with ferroelectric properties. The film prepared from the Pb/Sn/Ti/Si heterostructure consisted of Pb(Sn_0.55Ti_0.45)O₃ and PbTiO₃ and exhibited nonlinear dielectric properties. The coercive field and remanent polarization of the films were determined.     

Preparation and properties of Mn1.5 ? xCuxSb and Mn1.5 ? xZnxSb solid solutions with the B8 structure

Mn_{1.5 − x} Cu _x Sb (x ≤ 0.30) and Mn_{1.5 − x} Zn _x Sb (x ≤ 0.10) solid solutions have been prepared using high-pressure high-temperature processing, and their structural and magnetic properties have been studied. The results of magnetic and M?ssbauer measurements indicate that the interatomic magnetic interactions in the solid solutions are markedly weaker compared to those prepared by direct melting of elemental mixtures.