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.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Interfacial microstructure of NiSix/HfO2/SiOx/Si gate stacks

Integration of NiSi_x based fully silicided metal gates with HfO₂ high-k gate dielectrics offers promise for further scaling of complementary metal-oxide- semiconductor devices. A combination of high resolution transmission electron microscopy and small probe electron energy loss spectroscopy (EELS) and energy dispersive X-ray analysis has been applied to study interfacial reactions in the undoped gate stack. NiSi was found to be polycrystalline with the grain size decreasing from top to bottom of NiSi_x film. Ni content varies near the NiSi/HfO_x interface whereby both Ni-rich and monosilicide phases were observed. Spatially non-uniform distribution of oxygen along NiSi_x/HfO₂ interface was observed by dark field Scanning Transmission Electron Microscopy and EELS. Interfacial roughness of NiSi_x/HfO_x was found higher than that of poly-Si/HfO₂, likely due to compositional non-uniformity of NiSi_x. No intermixing between Hf, Ni and Si beyond interfacial roughness was observed.     

Properties of CdxPb1−xTe thin films

Thin films of Cd_xPb_1?xTe have been grown on mica substrates using a flash evaporation technique and isothermal substrate heaters. The Cd concentration of the films was found to increase with decreasing substrate temperature and increasing deposition rates. The Hall coefficient changed from positive to negative with increasing substrate temperature, as did the Seebeck coefficient. Both these changes were associated with an increase in the rate of re-evaporation of Te and an improvement in the crystallinity of the films. Carrier mobilities less than bulk values were obtained; scattering mechanisms are discussed.     

Bibliography of high-Tcsuperconductivity

Bibliography of high-T _c superconductivity     

Synthesis of a new perovskite Pb(Li14Nb34)O3

A high-pressure technique was adopted to obtain perovskite-type $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$. A new perovskite $\text{Pb(Li}{}_{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}\text{Nb}{}_{\mathrm{<mtext>3</mtext><mtext>4</mtext>}}\text{)}\text{O}{}_3$ was characterized to have a cubic symmetry with $\text{a}{}_{\mathrm{<mtext>o</mtext>}}\text{= 4.069}\text{A}\text{?}$; Li and Nb ions in the B-site of perovskite lattice may be in a random arrangement.     

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.     

Effect of pressure onTc in La2-xBaxCuO4 withx=0.125

The superconducting transition temperature,T _c , of La_2–x Ba _x CuO₄ has been measured under high pressure up to 8 GPa.T _c is found to change drastically at the pressure where the structural phase transition takes place. This finding clearly indicates that there exists an intimate relation between the crystal structure and superconductivity.     

t-Model mechanism of high-Tc cuprates

A doublon formalism ofd-p model Hubbard Hamiltonian is studied only with transfer integrals, and without the superexchange term. This gives excellent doping-dependent features ofT _c in high-T _c cuprates.     

Optimization of the thickness of glass/TiO2/Ag/Ti/TiO2/SiON multilayer film

The TiO₂/Ag/Ti/TiO₂/SiON multilayer film was deposited on glass substrate at room temperature using magnetron sputtering method. By varying the thickness of each layer, the optical property was optimized to achieve good selective spectral filtering performance in Vis-NIR region. The multilayer film achieves maximum transmittance of 92.7% at 690 nm, in which the both TiO₂ layers are 33 nm. For good conductivity and transmittance, a 4 nm Ti layer and a 30 nm SiON layer are necessary.     

Crystal growth and characterization of In23PS3

Crystals of $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PS}{}_3$ were grown by chemical vapor transport of the elements from a charge zone maintained at 630°C. and a growth zone at 560°C. The crystals were characterized by chemical, x-ray, and densitometric techniques. $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PS}{}_3$ is structurally related to the M^IIPS₃ thiophosphides. The compound is an insulator and has an optical absorption edge of 3.1(1) e.V.     

Magnetron sputtering of TiOxNy films

This article reports on the characterization and preparation of N-doped titanium dioxide (TiO₂) films by reactive magnetron sputtering from Ti(99.5) targets in a mixture of Ar/O₂/N₂ atmosphere on unheated glass substrates. A dual magnetron system supplied by a dc bipolar pulsed power source was used to sputter the TiO_xN_y films. The amount of N in the TiO_xN_y film ranges from 5 to 40 at%. Its structure was measured using X-ray diffraction (XRD), the optical band gap was calculated from Tauc plots and the decrease of the water contact angle α_ir after the film activation by UV irradiation was investigated as a function of at% of N in the TiO_xN_y film. The yellow-coloured TiO_xN_y films with high (≈8 at%) amount of N exhibited a strong decrease of the band gap E_g down to 2.7 eV. A significant decrease of the water contact angle α_ir after UV irradiation has been observed for 2 μm thick transparent nanocrystalline (anatase+rutile) N-doped TiO₂ films containing less than 6 at% of N.     

Crystal growth and characterization of In23PSe3

Crystals of $\text{In}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}\text{PSe}{}_3$ were grown by chemical vapor transport of the elements. The phase is structurally related to the hyposelenophosphates, M^IIPSe₃, but contains both indium atoms and vacancies on the metal ion sites. The compound shows a high electrical resistivity (>10⁸ ohm-cm) and has an optical absorption edge at 1.9 (1) e.V.     

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.     

Influence of Sm2Ba4CuBiOy phase content on Jc of SmBa2Cu3O7/Sm2Ba4CuBiOy nano-composites

Presence of various nano-scale Y₂Ba₄CuMO_y phase inclusions in YBa₂Cu₃O_7−δ phase matrix are shown to improve magnetic flux pinning over wide range of magnetic fields. We first fabricate single phase of Sm₂Ba₄CuBiO_y (Sm-2411) using a solid-state reaction and then introduced them into SmBCO single grains. Top seeded melt growth (TSMG) has been used to grow SmBCO single grains in air atmosphere. A significant improvement in J_c is observed, over wide magnetic fields, for single grains containing Sm-2411nano-phase inclusions when compared to that of SmBa₂Cu₃O_7−δ/Sm₂BaCuO₅ composites. When compared to YBCO nano-composites, SmBCO composites are shown to exhibit high J_c at medium range of magnetic fields (1–2 T) at 77 K.     

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.     

ab-initio Study of the properties of Ti1−x−ySixAlyN solid solution

We have studied the electronic, structural, and elastic properties of Ti_1−x−ySi_xAl_yN metastable phase, using first principles calculations based on the density functional theory. These calculations provide the lattice parameter, density of states, cohesive energy, formation energy and elastic constants, when Si and Al atoms replace Ti in the TiN lattice. The calculated values of lattice parameters and elastic constants are generally in good agreement with experiments and compare well with other theoretical results. We show that the trend followed by cohesive energy, formation energy, elastic constants is related to the electronic properties and bonding characteristics of these compounds.     

Characterisation of SiOxCyHz thin films deposited by low-temperature PECVD

SiO_xC_yH_z thin films were deposited from hexamethyldisiloxane (HMDSO)/O₂ mixtures in a parallel plate, capacitively coupled, RF plasma reactor. Polyethylene terephthalate (PET), Si(1 0 0) wafers and KBr tablets were chosen as substrates. Effect of HMDSO/O₂ ratio, total treatment pressure and power input on the properties of the deposited films were investigated. The structure and bondings were studied by means of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Wettability characteristics of the deposited thin films were investigated by means of water droplet contact angle measurements. Surface morphology was investigated with atomic force microscopy. Barrier properties of the SiO_xC_yH_z thin films were investigated by measuring the water vapour transmission rate of the coated PET substrates. Correlations between the characteristics of the deposited film and their barrier properties were discussed.