Effect of substrate temperature on HWCVD deposited a-SiC:H film

Hydrogenated amorphous silicon carbon (a-SiC:H) films were deposited using pure SiH₄ and C₂H₂ without hydrogen dilution by hot wire chemical vapor deposition (HWCVD) technique. The photoluminescence, optical, and structural properties of these films were systematically studied as a function of substrate temperature (T_s). a-SiC:H films deposited at lower substrate temperature (T_s) show degradation in their structural, optical and network properties. The hydrogen content (C_H) in the films was found to be increased with decrease of T_s studied. Photoluminescence spectra shift to higher energy and less FWHM at high T_s. Raman spectroscopic analysis showed that structural disorder increases with decrease in the T_s.     

Revisiting the B-factor variation in a-SiC:H deposited by HWCVD

In order to understand material properties in a better way, it is always desirable to come up with new variables that might be related to the film properties. The B-parameter is such a variable, which relates to the quality of a-SiC:H films both in terms of electronic and optical properties. B (scaling factor) is essentially the slope of the straight-line part of the (E)^1/2–E (Tauc plot). Due to dependence on a large number of parameters and no detailed research, many previous authors have surmised that B has an ambiguous correlation with carbon content. We have made an attempt to establish the relation between the B-parameter as a quality-indicating factor of a-SiC:H films in both carbon- and silicon-rich material. For this we studied a-SiC:H films deposited by the HWCVD method with broad deposition parameters of substrate temperature (T_s), filament temperature (T_F) and C₂H₂ fraction. Our results indicate that the B-parameter varies considerably with process conditions such as T_F, total gas pressure and carbon content. An attempt is made to correlate the B-parameter with an opto-electronic parameter, such as the mobility edge, which has relevance to the device-quality aspects of a-SiC:H films prepared by HWCVD.     

The effect of composition on the bond structure and refractive index of silicon nitride deposited by HWCVD and PECVD

Silicon nitride (SiN_x) is a material with many applications and can be deposited with various deposition techniques. Series of SiN_x films were deposited with HWCVD, RF PECVD, MW PECVD and LF PECVD. The atomic densities are quantified using RBS and ERD. The influence of the atomic densities on the Si-N and Si-Si bond structure is studied. The density of N-N bonds is found to be negligible. New Si-N FTIR proportionality factors are determined which increase with increasing N/Si ratio from 1.2 · 10¹⁹ cm^− 1 for Si rich films (N/Si = 0.2) to 2.4 · 10¹⁹ cm^− 1 for N rich films (N/Si = 1.5). The peak position of the Si-H stretching mode in the FTIR spectrum is discussed using the chemical induction model. It is shown that especially for Si-rich films the hydrogen content affects the Si-H peak position. The influence of the composition on the refractive index of the films is discussed on the basis of the Lorentz-Lorenz equation and the Kramers-Kronig relation. The decreasing refractive index with increasing N/Si ratio is primarily caused by an increase of the band gap.     

Photoluminescence properties of TiO2: Eu3 + thin films deposited on different substrates

Strong photoluminescence of Eu^3 + due to intra 4f transitions are obtained from amorphous xerogel TiO₂: Eu^3 + films prepared by sol–gel method and treated at a low temperature of 100 °C. The films are deposited on four different substrates: Si, Al, AAO (anodic alumina oxide) and porous silicon. We find that the luminescence intensity on AAO substrate increased 4 times comparing with that of Si or Al, and luminescence intensity decreases obviously on porous silicon substrate. Energy transfer mechanism from TiO₂ host to Eu^3 + is deduced through analysis of photoluminescence and photoluminescence excitation spectrum. Concentration quenching of Eu^3 + does not appear even at high atomic concentration of 7.69%.     

Characterisation of oxidised erbium films deposited on Si(1 0 0) substrates

Thin Er-oxide films were prepared by oxidation of pure Er films grown on glass and Si (p) substrates. The oxide films were characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD), and optical absorption spectroscopy. The XRD analysis of the as-prepared oxide film and the vacuum-annealed film demonstrates the formation of Er₂O₃ phase with about 4.6% of ErO phase, which totally transforms into Er₂O₃ phase under annealing at 600 °C in dry oxygen. Therefore, the phase-structural changes in the prepared Er-oxide films because of the annealing and the long-time storage in vacuum were studied. The constructed Al/Er-oxide/Si MOS devices were characterised by measuring gate-voltage dependence of their capacitance and ac conductance, from which the surface states density (D_it) of insulator/semiconductor interfacial charges and the density of fixed charges in the oxide, were determined, which were within the device-grade range. The ac-electrical conduction and dielectric properties of the of the Er oxide–silicon structure were studied at room temperature. The data of ac conductivity measurements were found to follow the correlated barrier-hopping (CBH) model and the model's parameters were calculated, while the Kramers–Kronig (KK) relations explain the high-frequency dependence of the capacitance.     

Simulated body fluid (SBF) adsorption onto a-SiC:H thin films deposited by hot wire chemical vapor deposition (HWCVD)

Hydrogen amorphous silicon carbon (a-SiC:H) film deposited by the Hot Wire Chemical Vapor Deposition (HWCVD) technique on silicon substrates were soaked in simulated body fluid (SBF). Characterization of the film with different soaking durations in SBF was carried out by Fourier Transform Infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and contact angle measurements. It was found that the relative amounts of carbon in the a-SiC:H film surface decreases with increase in soaking period. XPS results showed the adsorption of Ca and Mg on the a-SiC:H surface. This indicates the formation of negatively charged surface possibly due to formation of silanol groups or dissolution of carbon to SBF confirming the bioactivity of the material. Contact angle decreased from 74° to 65° during 30 days of soaking in the body fluid. Present study is an attempt to observe the interaction of a-SiC:H film prepared by HWCVD technique with the body environment for its future suitability as artificial heart valve and stent coating materials.     

Characterization of microstructural changes in an Al-6.8 wt.% Mg alloy by electrical resistivity measurements

Microstructural changes in an AlMg6.8 alloy after different thermo mechanical (TMT) and sensitization treatments were investigated by electrical resistivity measurements. The electrical resistivity was most affected by the content of Mg solute atoms in the α-Al matrix, due to β-phase precipitation, while contribution of the dislocation density to the resistivity of the AlMg6.8 alloy was less pronounced. The amount and distribution of the β-phase precipitated during sensitization were found to be strongly affected by the microstructure developed under the previously applied TMTs, i.e. by the dislocation density and the primary β-phase particles in the dual (α + β) phase structure. During sensitization of the specimens with a recovered/recrystallized dual (α + β) phase structure, precipitation of randomly distributed, globular β-phase particles occurred. Sensitization of cold deformed and recrystallized single α-Al structures induced β-phase precipitation in the form of a continuous layer along the shear bands/grain boundaries.     

Phosphorous and boron doping of nc-Si:H thin films deposited on plastic substrates at 150 °C by Hot-Wire Chemical Vapor Deposition

Gas-phase phosphorous and boron doping of hydrogenated nanocrystalline thin films deposited by HWCVD at a substrate temperature of 150 °C on flexible-plastic (polyethylene naphthalate, polyimide) and rigid-glass substrates is reported. The influence of the substrate, hydrogen dilution, dopant concentration and film thickness on the structural and electrical properties of the films was investigated. The dark conductivity of B- and P-doped films (σ_d = 2.8 S/cm and 4.7 S/cm, respectively) deposited on plastic was found to be somewhat higher than that found in similar films deposited on glass. n- and p-type films with thickness below ∼ 50 nm have values of crystalline fraction, activation energy and dark conductivity typical of doped hydrogenated amorphous silicon. This effect is observed both on glass and on plastic substrates.     

Study on spray deposited Ni-doped CuO nanostructured thin films: microstructural and optical behavior

Journal of Materials Science: Materials in Electronics - In this study, CuO and Ni-doped CuO thin films are deposited on glass substrates at 400 °C by the spray pyrolysis as easy,...     

Ultraviolet–green photoluminescence of β-Ga2O3 films deposited on MgAl6O10 (1 0 0) substrate

β-Ga₂O₃ films were grown on double-side polished MgAl₆O₁₀ (1 0 0) substrate by metal organic chemical vapor deposition (MOCVD) at 600, 650 and 700 °C. The refractive index dispersive behaviors of Ga₂O₃ films have the typical shape of the normal dispersion curve. Photoluminescence (PL) spectra measured at room temperature revealed that all the films exhibited intense ultraviolet (UV)–green emission from 300 to 650 nm. A minor deep UV emission around 275 nm (∼4.51 eV) was observed for the sample prepared at 700 °C. The intensity of the emission increased markedly when measured at low temperature. The corresponding PL mechanisms were discussed in detail and a schematic diagram was proposed.     

Ageing effect on microstructural and mechanical properties of mullite-ZrO2-TiO2 composites

The microstructural and mechanical properties of mullite-zirconia composites with TiO₂ (0.25 and 1.0 mol) additions have been studied, after ageing the samples over a wide temperature range (1000 to 1500° C) for long periods of time (100 to 200 h). In the sample with 0.25 mol TiO₂ addition, changes in mullite composition and in the solid state compatibility at temperatures below 1450° C were detected. In the sample containing 1 mol TiO₂, decomposition of Al₂TiO₅ occurs atT1200° C. Both compositions exhibit no increment in zirconia average grain size during ageing and, concomitantly, there is no strength degradation until higher temperatures (>1400° C) are reached, which become more drastic when Al₂Ti₅ is present.     

ITO substrate resistivity effect on the properties of CuInSe<Subscript>2</Subscript> deposited using two-electrode system

The purpose of this work is to deposit the CuInSe₂ films on the ITO substrate by electrodeposition technique using a simplified two electrodes system and to investigate the effect of ITO sheet resistance on the fundamental properties of the resulting films. The as deposited films were annealed under argon atmosphere at 300 °C during 30 min. The structural, morphological and electrical properties were characterized respectively by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrical resistivity measurements. The optical band gap of samples was estimated using the optical absorption technique. After annealing, the XRD spectra show diffraction peaks corresponding to the single-phase chalcopyrite CuInSe₂ with (112) as main reflection. The SEM images reveal a homogeneous surface and the estimated grain size was calculated from Scherrer’s Equation with (112) peak lay in the range of 165–272 Å. The band gap, E _g, is a decreasing function with the ITO sheet resistance.     

A comparative study of Co thin film deposited on GaAs (1 0 0) and glass substrates

The structural, magnetic and transport properties of Co/GaAs (1 0 0) and Co/glass thin films have been investigated. The structural measurements reveal the crystalline nature of Co thin film grown on GaAs, while microcrystalline nature in case of glass substrate. The film grown on GaAs shows higher coercivity (49.0 G), lower saturation magnetization (3.65 × 10⁻⁴) and resistivity (8 μΩ cm) values as compared to that on glass substrate (22 G, 4.77 × 10⁻⁴ and 18 μΩ cm). The grazing incidence X-ray reflectivity and photoemission spectroscopy results show the interaction between Co and GaAs at the interface, while the Co layer grown on glass remains unaffected. These observed results are discussed and interpreted in terms of different growth morphologies and structures of as grown Co thin film on both substrates.     

Chemical synthesis and microstructural analysis of superconducting YBa2Cu3O7-δ ink deposited by drop-on-demand ink-jet printing on silver substrates

The basis for the development of computer controlled printing techniques for YBa₂Cu₃O_7-δ (YBCO) coated conductors is discussed in detail. This method of continuous deposition of YBCO material potentially enables non-vacuum formation of complex multi-layer superconducting patterns on silver substrates. Sol–ink processes were used to print single droplets of YBCO on polycrystalline silver substrates under varying printing conditions. Droplet sizes were controlled from a range of 300 μm–1200 μm. The formation and the stability of the sol–ink with respect to pH and concentration has been studied and discussed herein. For optimum results, the pH of the ink had to regulated to 6.5. Printing and substrate parameters that alter solid–liquid interface properties were also investigated such as ink concentration and surface roughness, the best results produced were with an ink concentration of 0.025 M on a polished silver surface. In order to control the flow properties of the sol media dynamic viscosities were determined. Characterisation by X-Ray Diffraction, Differential Thermal Analysis, Thermal Gravitometry and Scanning Electron Microscopy was used to examine the sol–ink samples, whilst AC susceptibility was used to assess the superconductivity of the printed samples where they were discovered to have a characteristic T _c of ∼83 K.     

Influence of filament-to-substrate distance on the spectroscopic,structural and optical properties of silicon carbide thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition (HWCVD) technique from pure silane and methane gas mixture. The effect of filament distance to the substrate on the structural and optical properties of the films was investigated. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman scattering spectroscopy and UV–Vis–NIR spectroscopy were carried out to characterize SiC films. XRD patterns of the films indicated that the film deposited under highest filament-to-substrate distance were amorphous in structure, while the decrease in distance led to formation and subsequent enhancement of crystallinity. The Si–C bond density in the film structure obtained from FTIR data, showed significant increment with transition from amorphous to nano-crystalline structure. However, it remained almost unchanged with further improvement in crystalline volume fraction. From Raman data it was observed that the presence of amorphous silicon phase and sp ² bonded carbon clusters increased with the decrease in distance. This reflected in deterioration of structural order and narrowing the optical band gap of SiC films. It was found that filament-to-substrate distance is a key parameter in HWCVD system which influences on the reactions kinetics as well as structural and optical properties of the deposited films.     

Electrochemical performance and microstructural evolution of laser deposited Al‐Sn coating in acidic environment

Outstanding performance of materials is one of the requirements of modifying the existing materials in order to meet a global demand necessary in technology innovation. Direct laser metal deposition technique due to excellent properties has replaced conventional techniques in modifying the surface of materials. The interplay between melting, fusion and optimised laser parameters are very important factors to be considered when using laser metal deposition technique. ASTM A29 steel property was enhanced through this technique by Al‐Sn reinforcements. A 3‐kW continuous wave ytterbium laser system was employed by this process. This research investigated the microstructure and corrosion properties of fabricated laser metal deposited ASTM A29 steel. The resulting microstructure and content of the inconsequential elements in the coatings fabricated were studied to obtain the results achieved. Observation of the microstructure showed typical phase of acicular α′‐martensite attributed to rapid cooling of the molten pool. The electrochemical behaviour was investigated in 1 M HCl solution at 27 °C via potentiodynamic polarization technique. The fabricated coatings had corrosion rate of 0.03435 mm/yr, current density of 3.95 ? 10^?6 A/cm², and polarization resistance of 7093.4 Ω ? cm². While the control had corrosion rate of 16.308 mm/yr and polarization resistance of 8.0631 Ω ? cm².     

Maintaining Cu metal integrity on low-k IMDs with a nanometer thick a-SiC:H film obtained by HWCVD

Hydrogenated amorphous silicon carbon (a-SiC:H) ultra thin films obtained by Hot wire chemical vapor deposition (HWCVD) have been shown to act as efficient diffusion barriers for copper on inter metal dielectric (IMD) layers which are of great significance for ultra-large scale integration (ULSI) circuits. In this work, we have studied the influence of the a-SiC:H barrier layer obtained by HWCVD which has implications towards issues related to the resistance to electromigration of Cu in the low dielectric (low-k) hydrogen silsesquioxane (HSQ) film. The presence of the ultra thin a-SiC:H film maintains the integrity of the Cu metal not only by suppressing Cu diffusion but also by increasing its crystallinity, which would have implications with respect to the mean time to failure (MTF) arising from metal electromigration. Though, we demonstrate this aspect on the low-k (HSQ)/Cu system, this should yield similar benefits for other low-k dielectric materials too.     

On the synthesis and dielectric studies of (1 − x)Bi(Mg1 / 2Zr1 / 2)O3 − xPbTiO3 piezoelectric ceramic system

Scandium free piezoelectric ceramics of the composition (1 − x)Bi(Mg_1 / 2Zr_1 / 2)O₃ − xPbTiO₃ (BMZ − xPT) were fabricated by the solid state reaction method. Dielectric and structural properties were measured and phase diagram was constructed from the temperature dependent dielectric and impedance data. The morphotropic phase boundary (MPB) was found to be located in the range 0.55 < x < 0.60 with paraelectric–ferroelectric phase transition temperature, T_C (∼ 280 °C). The ceramics near the MPB showed high room temperature dielectric constant (∼ 1387). The room temperature values of the remanent polarization (P_r) and coercive filed (E_C), were ∼ 29 μC/cm² and ∼ 23 kV/cm, respectively.