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.     

Elastic properties of lanthanum aluminosilicate glasses

The elastic properties of two series of lanthanum aluminosilicate glasses (15La₂O₃-xAl₂O₃-(85−x)SiO₂ and 25La₂O₃-yAl₂O₃-(75−y)SiO₂, where x, y=15, 20, 25, 30, 35 mol%), were obtained by the ultrasonic pulse-echo technique, at room temperature. The correlation of elastic stiffness, the cross-link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of Young’s modulus, bulk modulus, shear modulus and Poisson’s ratio for our glasses are compared with those theoretically calculated values in terms of the Makishima-Mackenzie model.     

Energy of mixing of Al x In y Ga1 ? x ? y N compounds

The energies of mixing of quaternary compounds of the Al _x In _y Ga_{1 − x − y} N system with crystal structures of the zinc-blende type have been calculated using direct numerical simulations within the framework of the valence forced field model. An analytical approximation of the results of numerical calculations is proposed and the parameters of configurational dispersion of the mixing energy are refined, which are necessary for determining the thermodynamic functions of the quaternary compounds under consideration.     

Magnetic and photoconductive properties of the CoxPt1−x-Pt-TiO2 nanocomposite films prepared by reactive sputter-deposition

Co-Pt-Ti-O films were prepared on SiO₂ glass substrate by sputtering of a Co-Pt-Ti composite target in Ar+O₂ atmosphere with the total pressure of 4 Pa and then in situ annealed at an elevated temperature T_a to form the Co_xPt_1−x-TiO₂ films. It is found that the ferromagnetic films grow in the form of fiber-like columnar grain about 10 nm in diameter when sputtered in the pressure ratio of O₂/Ar=1/133 followed by in situ annealing at The films contain Pt and amorphous anatase-type TiO₂ phases besides the ferromagnetic fcc-Co_xPt_1−x phase. Thus, such nanocomposite films show photoconductive properties due to the anatase-type TiO₂ phase as well as ferromagnetic properties due to the Co_xPt_1−x phase.     

Electrical properties of Al2O3 and AlPxOy dielectric layers on InP

Al₂O₃ and AlP_xO_y dielectric layers have been deposited on n-type InP substrates and the electrical properties of the interfaces have been evaluated by current-voltage and capacitance-voltage (C-V) measurements on metal- insulator-semiconductor diodes. Layers were deposited by combining trimethyl- aluminum, oxygen and phosphine in a low pressure chemical vapor deposition reactor in which the oxygen was excited in an r.f. plasma prior to mixing with the reactive gases in the deposition zone. The Al₂O₃ layers were invariably too conductive for meaningful C-V measurements; however, the AlP_xO_y layers not only were of high resistivity (? > 10¹⁶ Ω cm) but also exhibited interfacial properties superior to those of SiO₂ layers on InP. The surface potential could be modulated over the full band gap of InP since the surface density was less than 10¹¹ cm^-2 eV^-1 over much of the band gap.     

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.     

Silicide formation during heat treatment of thin Ni-Pt and Ni-Pd solid-solution films and Pt/Ni bilayers on (111)Si

It is shown that isothermal heat treatment of (Ni-Pt)/Si and Pt/Ni/Si heterostructures leads to the formation of oriented Ni-and Pt-based silicide solid solutions. Owing to the three equivalent azimuth orientations in the basic lattice orientation relationship for the Si-Ni_1?x Pt_xSi system, the resulting silicides have a nanocrystalline substructure. The stability of the substructure is due to the optimal interfacial lattice match and near-special grain-boundary misorientations. The silicide phases Ni_1?x Pt_xSi and Pt_1?y Ni_ySi (or Ni_1?x Pd_xSi and Pd_1?y Ni_ySi) may undergo segregation, having the same lattice orientation. In both systems, the segregation is associated with the predominant Ni diffusion. The second component (Pt) is shown to stabilize the orthorhombic Ni-based silicide and to prevent NiSi₂ formation. Photon processing accelerates diffusion and leads to the formation of phase-pure Ni_1?x Pt_xSi solid solutions.     

Crystallization mechanisms of (In15Sb85)100−xBix phase change recording thin film

The (In₁₅Sb₈₅)_100−xBi_x films (x = 0–18.3) were deposited on nature oxidized Si wafer and glass substrate at room temperature by magnetron co-sputtering of Sb target and InBi composite target. The optical and thermal properties of the films were examined by reflectivity thermal analyzer. Microstructures of the films were analyzed by X-ray diffraction and transmission electron microscope. The crystallization activation energy of the (In₁₅Sb₈₅)_100−xBi_x film (x = 0–18.3) was decreased with increasing Bi content, this indicated that the crystallization speed was improved by doping Bi. The structure of as-deposited (In₁₅Sb₈₅)_100−xBi_x films was amorphous and it would transform to Sb, InSb, Bi, and BiIn₂ coexisting phases after annealing at 250 °C for 30 min.     

XPS analysis of WxCy thin films prepared by sputter deposition

W_xC_y thin films with different compositions were studied in order to correlate their properties with the thin-film composition and chemical bonding of C and W atoms. Three W_xC_y thin films with C concentrations in the range 40-80 at% were deposited on WC-Co substrates by the plasma beam sputtering technique. The composition of the thin films and chemical states of elements were analysed by X-ray photoelectron spectroscopy (XPS) depth profiling. The C and W concentrations in the films were quantified using XPS intensities from a WC-Co substrate with a known composition. The C1s peaks in the high energy resolution XPS spectra of thin films allowed identification of the WC phase and the amorphous carbon phase as a function of the film composition. The results show that the amorphous carbon a-C phase is present in those films with composition x<y. The measured hardness of the films decreases with a decrease of the WC concentration.     

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.     

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.     

Effect of thermal treatments on the structure of MoNxOy thin films

MoN_xO_y films were deposited on steel substrates by dc reactive magnetron sputtering. The depositions were carried out from a pure molybdenum target, varying the flow rate of reactive gases. X-ray diffraction (XRD) results revealed the occurrence of cubic MoN_x and hexagonal (δ-MoN) phases for the films with high nitrogen flow rates. The increase of oxygen content induces the decrease of the grain size of the molybdenum nitride crystallites. The thermal stability of a set of samples was studied in vacuum, for an annealing time of 1 h, for temperatures ranging from 500 to 800 °C in 100 °C steps. The results showed that pure molybdenum nitride films changed their structure from a meta-stable cubic MoN to hexagonal δ-MoN and cubic γ-Mo₂N-type structures with increasing annealing temperatures. The samples with molybdenum nitride films evidenced a good thermal stability, but those with molybdenum oxynitride coatings showed a tendency to detach with the increase of the annealing temperature.     

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.     

First-principles study of structural stabilities,elastic and electronic properties of transition metal monocarbides (TMCs) and mononitrides (TMNs)

The structural stabilities, elastic and electronic properties of 5d transition metal mononitrides (TMNs) XN with (X = Ir, Os, Re, W and Ta) and 5d transition metal monocarbides (TMCs) XC with (X = Ir, Os, Re and Ta) were investigated using the full-potential linear muffin-tin orbital (FP-LMTO) method, in the framework of the density functional theory (DFT) within the local density approximation (LDA) for the exchange correlation functional. The ground state quantities such as the lattice parameter, bulks modulus and its pressure derivatives for the six considered crystal structures, Rock-salt (B1), CsCl (B2), zinc-blend (B3), Wurtzite (B4), NiAs (B8₁) and the tungsten carbides (B_h) are calculated. The elastic constants of TMNs and TMCs compounds in its different stable phases are determined by using the total energy variation with strain technique. The elastic modulus for polycrystalline materials, shear modulus (G), Young's modulus (E), and Poisson's ratio (ν) are calculated. The Debye temperature (θ_D) and sound velocities (v_m) were also derived from the obtained elastic modulus. The analysis of the hardness of the herein studied compounds classifies OsN – (B4 et B8₁), ReN – (B8₁), WN – (B8₁) and OsC – (B8₁) as superhard materials. Our results for the band structure and densities of states (DOS), show that TMNs and TMCs compounds in theirs energetically and mechanically stable phase has metallic characteristic with strong covalent nature Metal–Nonmetal elements.     

Polymorphous Fe/FexOy composites: One-step oxidation preparation,composition control,and static magnetic and electromagnetic characteristics

Polymorphous Fe/Fe_xO_y core–shell and urchin-like composites were synthesized via a facile oxidation process at relatively low temperatures (100–300 °C) in the absence of surfactants or an external magnetic field. The oxidation temperature plays a key role in determining the morphology, crystal size, and composition of the resulting products. The static magnetic and electromagnetic (EM) properties of Fe/Fe_xO_y composites are influenced by their morphology, crystal size, and composition. In this study, excellent soft magnetic properties and enhanced permeability were obtained from core–shell Fe/Fe_xO_y composites with low Fe_xO_y shell contents and low surface anisotropy. In contrast, high coercivity and dielectric performance were exhibited by urchin-like Fe/Fe_xO_y composites with high shape and surface anisotropy. This work provides insights into the absorption mechanism of urchin-like complex absorption materials.     

First-principles study of structural and mechanical properties of AgB2 and AuB2 compounds under pressure

In this work, density functional theory calculations on the structural, mechanical, and lattice dynamical properties of AgB₂ and AuB₂ compounds in AlB₂, OsB₂, and ReB₂ structures are reported. Generalized gradient approximation has been used for modeling exchange-correlation effects. The detailed information is given for the energetically most stable structure for AgB₂ and AuB₂ compounds. Specifically, the lattice parameters, bulk modulus, cohesive energies, elastic constants, shear modulus, Young’s modulus, Poison’s ratio, Debye temperature, sound velocities, and anisotropic factors are studied. The elastic properties are also studied under pressure. The phonon dispersion curves and corresponding phonon density of states are calculated and discussed. Our structural and some other results are in agreement with the available experimental and theoretical data.     

High-frequency magneto-electrical properties of Zn1 − x − yAlxCoyO thin films

The Al doping effects on high-frequency magneto-electric properties of Zn_{1 − x − y}Al_xCo_yO (x = 0-10.65 at.%) thin films were systematically studied. In the current work, the Zn_{1 − x − y}Al_xCo_yO thin films were deposited by magnetron co-sputtering onto quartz substrates. The magneto-impedance spectra of the thin films were measured by an impedance analyzer. Among all the doped films studied, the thin film with 6.03 at.% Al-doping showed the highest ac conductivity and relaxation frequency. To characterize the relaxation mechanism underlying the magneto-electric properties, a Cole-Cole impedance model was applied to analyze the impedance spectra. The analyzed result showed that the magneto-impedance of the Zn_{1 − x − y}Al_xCo_yO is contributed by multiple processes of magnetization dynamics and dielectric relaxation. The results imply that Zn_{1 − x − y}Al_xCo_yO may be applicable for high-frequency magneto-electric devices.     

Phase stabilities of self-organized nc-TiN/a-Si3N4 nanocomposites and of Ti1 − xSixNy solid solutions studied by ab initio calculation and thermodynamic modeling

Bulk properties of stable binary fcc-TiN and hcp(β)-Si₃N₄, hypothetical fcc-SiN and hcp(β)-Ti₃N₄, and ternary Ti_1 − xSi_xN_y phases are calculated by ab initio method. The values of total energies are then used for thermodynamic calculations of the lattice instabilities of hypothetical binary phases of fcc-SiN and hcp-Ti₃N₄, and of the interaction parameters of ternary Ti_1 − xSi_xN_y phases. Based on these data, Gibbs free energy diagrams of the quasi-binary TiN_y-SiN_y system are constructed in order to study the relative phase stability of the metastable ternary fcc- and hcp-Ti_1 − xSi_xN_y phases over the entire range of compositions. The results are supported by the published data from chemical and physical vapor deposition experiments. The constructed Gibbs free energy diagram and phase selection diagram of quasi-binary TiN_y-SiN_y system in fcc structure show that metastable fcc-Ti_1 − xSi_xN coatings should undergo chemically spinodal decomposition into coherent fcc-TiN and fcc-SiN. Due to a high lattice mismatch between fcc-TiN and hcp-Si₃N₄, and to much higher lattice instability of fcc-SiN with respect to stable hcp-Si₃N₄, only about one monolayer of pseudomorphic SiN_y interfacial phase is stable.     

Synthesis and luminescent properties of novel Ba2−xEuxZr2−yHfySi3O12 phosphor

A series of Eu²⁺ activated luminescent materials according to the composition of Ba_2−xEu_xZr_2−yHf_ySi₃O₁₂ were synthesized using a high temperature solid-state reaction method starting from metal oxides and carbonates. Single phase powders were obtained using two annealing steps and boric acid as a flux. Firstly, starting materials were sintered at 1450 °C for 5 h under CO atmosphere and subsequently annealed at 1200 °C for 5 h under N₂/H₂ (95%/5%) gas flow. All samples were characterized by powder X-ray diffraction (XRD) analysis, thermal quenching (TQ), fluorescence lifetime measurements and photoluminescence (PL) techniques. Moreover, emission colour points, luminous efficacies and quantum efficiencies (QE) were calculated and discussed as a function of Eu²⁺ concentration and Zr/Hf ratio of the host lattice.