Thermal Behavior of a Multi-layered Thin Slab Carrying Periodic Signals Under the Effect of the Dual-Phase-Lag Heat Conduction Model

The thermal behavior of a two–layered thin slab carrying periodic signals under the effect of the dual-phase-lag heat conduction model is investigated. Two types of periodic signals are considered, a periodic heating source and a periodic imposed temperature at the boundary. The deviations among the predictions of the classical diffusion model, the wave mode, and the dual-phase-lag model are investigated. Analytical closed-form solutions are obtained for the temperature distribution within the slab. The effect of the angular frequency, thickness of the plate, dimensionless thermal relaxation time, dimensionless phase-lag in temperature gradient, thermal conductivity, and thermal diffusivity on the temperature distribution of the slab was studied. It is found that the deviations among the three models increase as the frequency of the signals increases and as the thickness of the plate decreases. It is found that the use of the dual-phase-lag heat conduction model is necessary when the metal film thickness is of order 10^–6 m and the angular frequency of the signals is of order 10¹²rad · s^–1.     

Deposition and heat treatment of CuAlNi shape memory thin films

CuAlNi thin films were fabricated by magnetron sputtering process. After heat treatment, the thin films presented a shape memory effect. Calowear method was used to measure the thickness of the thin films. SEM, XRD and TEM were used to characterize the thin films. The phase transformation in the thin films was examined by DSC. The deposition rate increased with increasing sputtering power and decreased with increasing Ar pressure. Compared to the composition of the target, both the content of Al and the content of Ni increased a little. The sputtering conditions had little influence on the content of Ni. The content of Al varied slightly with sputtering power, while decreased with increasing Ar pressure. The deposited thin films were columnar. The grain size was very fine. The phases were α‐Cu and α₂. After heat treatment at 800 ^oC/ 60 min + 300 ^oC/ 60 min in vacuum, CuAlNi shape memory thin films were obtained. The phase in the heat‐treated thin films was β₁’ martensite. Martensite transformation was observed and a two‐way shape memory effect could be shown.     

Improved electrochromical properties of sol-gel WO3 thin films by doping gold nanocrystals

In this investigation, the effect of gold nanocrystals on the electrochromical properties of sol-gel Au doped WO₃ thin films has been studied. The Au-WO₃ thin films were dip-coated on both glass and indium tin oxide coated conducting glass substrates with various gold concentrations of 0, 3.2 and 6.4 mol%. Optical properties of the samples were studied by UV-visible spectrophotometry in a range of 300-1100 nm. The optical density spectra of the films showed the formation of gold nanoparticles in the films. The optical bandgap energy of Au-WO₃ films decreased with increasing the Au concentration. Crystalline structure of the doped films was investigated by X-ray diffractometry, which indicated formation of gold nanocrystals in amorphous WO₃ thin films. X-ray photoelectron spectroscopy (XPS) was used to study the surface chemical composition of the samples. XPS analysis indicated the presence of gold in metallic state and the formation of stoichiometric WO₃. The electrochromic properties of the Au-WO₃ samples were also characterized using lithium-based electrolyte. It was found that doping of Au nanocrystals in WO₃ thin films improved the coloration time of the layer. In addition, it was shown that variation of Au concentration led to color change in the colored state of the Au-WO₃ thin films.     

Linear-Defect-Induced Thermal Instability in YBCO Thin Films in Microwave Fields

An induced heat instability proposed to explain the difference between microwave properties of YBCO single crystals and thin films at temperatures just below T _c. Extended strain fields near out-of-plane edge dislocations are initial discontinuities for the instability development. We have shown theoretically and have confirmed experimentally that a single dislocation can not have a strong effect on the microwave surface resistance R _s. Dislocation arrays, which were observed experimentally, can induce the thermal instability if edge dislocations in the arrays are spaced closer than the heat relaxation length. Ordered dislocation structures provide much higher local temperature perturbation than randomly distributed dislocations.     

Characteristics of n-Cd0.9 Zn0.1S/p-CdTe heterojunctions

CdTe thin films were prepared by thermal evaporation under a vacuum of 10⁻⁶ Torr and with a deposition rate of about 60 nm/min. X-ray diffraction studies of the as-deposited films revealed polycrystalline films with cubic structure. The effect of heat treatment with or without CdCl₂ enhances the grain size and improves the crystallinity of the films. Moreover, the activation energy decreases upon heat treatment with or without CdCl₂ for CdTe thin films. The optical spectra of CdTe films show interference oscillations indicating the good optical quality of these films. The calculated energy gap decreases with or without CdCl₂ treatments. The current-voltage and capacitance-voltage characteristics for dark and illuminated three junction cells are measured. By analysing these measurements the different junction parameters are obtained and the effect of CdCl₂ treatment on the performance of the heterojunctions is investigated.     

Study of electrical and optical properties of Cd1 − x Zn x S thin films

Thin films of Cd_0.9Zn_0.1S and CdS were prepared by thermal evaporation under vacuum of 10^–6 Torr and with deposition rate of 60 nm/min. X ray diffraction studies confirm the hexagonal structure of both CdS and Cd_0.9Zn_0.1S films. The effect of heat treatments with or without CdCl₂ enhances the grain size growth and improves the crystalline of the films. Moreover, the activation energy is decreased by heat treatment with or without CdCl₂ for all thin films. The optical absorption coefficient of Cd_0.9Zn_0.1S thin films were determined from measured transmittance and reflectance in the wavelength range of 300 to 2500 nm. The optical absorption spectra reveal the existence of direct energy gap for these films. It was found that the optical energy gap decreases upon annealing or CdCl₂ treatments.     

Solitary waves in saturated films of superfluid 4He

It is shown that there should exist in saturated films of superfluid ⁴He at low temperature a nonlinear surface wave described by the Korteweg-de Vries equation. The effect of surface tension makes the solitary wave cold, in contrast to very thin films discussed in a preceding paper. An electrostatic method is proposed to generate cold solitary waves. The asymptotic behavior can be found theoretically by the inverse scattering method. Estimates of parameters imply the possibility of observing each solitary wave separately.     

Formation and dissolution of copper-based nanoparticles in SiO2 sol-gel film using heat treatment and/or UV light exposure

We report in this paper, results on the formation and dissolution of Cu-based nanoparticles in sol-gel SiO₂ thin films using heat treatment and UV light exposure, respectively. Using UV-vis-NIR spectroscopy, we have shown that Cu₂O nanoparticles can be generated by controlling the aging of the sol prior to film deposition while the Cu⁰ nanoparticles can be synthesized using a heat treatment in H₂ atmosphere at 550 °C for 6 h. It has been also demonstrated that irradiation with an UV pulsed (Q-switched Nd:YAG) or continuous black ray UV lamp can dissolve these Cu-based nanoparticles with controlled, spatial selectivity. The mechanism of the dissolution process was found to be mainly thermal. Finally, we report a new analytical technique for detecting/confirming the presence of low densities of Cu nanoparticles in the films, based on a relative heat flow measurement of such films using a micro-thermal analyzer (e.g., TA Instruments μTA model 2990).     

Improving the performance of the cryogenic heat pipe-target system for the COSY-TOF experiment

Very lightweight, thin liquid hydrogen/deuterium heat pipe-target systems are used in the Time Of Flight (TOF) spectrometer at the COSY accelerator facility. The proton beam impinges upon LH₂/LD₂ targets thereby heating the target. The stability of the liquid targets depends on the thermal capacity of the whole system, the energy losses from the proton beam and heat losses from the surrounding of the heat pipe-target system. The radiation heat load has been reduced by a factor of 4.5 by reducing the length of the gas tube from 180 cm (long tube) to 40 cm (short tube). Furthermore, the 40 cm long gas tube was coated with a thin polished gold layer, thereby reducing the heat load by an additional factor 22. The thermal capacity is improved by reducing the mass of the gas tube from 23 g to 5 g. The cool down time of the 7 mm diameter gold coated heat pipe with the gold coated 40 cm gas tube is reduced by 12 min.     

Thin-Film Thermophysical Property Characterization by Scanning Laser Thermoelectric Microscope

This work presents a scanning laser-based thermal diffusivity measurement technique for thin films as well as for bulk materials. In this technique, a modulated laser beam is focused through a transparent substrate onto the film–substrate interface. The generated thermal wave is detected using a fast-responding thermocouple formed between the sample surface and the tip of a sharp probe. By scanning the laser beam around the thermocouple, the amplitude and phase distributions of the thermal wave are obtained with micrometer resolution. The thermal diffusivity of the film is determined by fitting the obtained phase signal with a three-dimensional heat conduction model. Experimental results are presented for a 150-nm gold film evaporated on a glass substrate.     

Thermal Effusivity Determination of Metallic Films of Nanometric Thickness by the Electrical Micropulse Method

The thermal effusivity of gold, aluminum, and copper thin films of nanometric thickness (20 nm to 200 nm) was investigated in terms of the films’ thickness. The metallic thin films were deposited onto glass substrates by thermal evaporation, and the thermal effusivity was estimated by using experimental parameters such as the specific heat, thermal conductivity, and thermal diffusivity values obtained at room conditions. The specific heat, thermal conductivity, and thermal diffusivity values of the metallic thin films are determined with a methodology based on the behavior of the thermal profiles of the films when electrical pulses of few microseconds are applied at room conditions. For all the investigated materials, the thermal effusivity decreases with decreased thickness. The thermal effusivity values estimated by the presented methodology are consistent with other reported values obtained under vacuum conditions and more elaborated methodologies.     

Diffusion in Au-Ni thin films

The objective of this work was to determine experimentally the values of the surface diffusion parameters of Au-Ni thin films obtained by vacuum evaporation and by sputter deposition. Thin film diffusion couples with an edge-to-edge interface arrangement were employed in order to define the surface diffusion mechanisms better. Experimental results show that the frequency factor (diffusion constant) for evaporated films (1.5×10^-8 cm² sec^-1) is higher than that for sputtered films (1.1×10^-8 cm² sec^-1) and bulk material (bulk diffusion data). The values obtained for the thermal activation energy in evaporated films were one order of magnitude less than those obtained for bulk material. Sputtered thin films were found to have an activation energy over 20% higher than that for evaporated films. This discrepancy apparently occurs because of partial incorporation of sputtered atoms into the glass substrate. Measurements of thin film adhesion showed the same effect.Examination of the structural characteristics of the specimens showed that both sputtered and evaporated films 300 Å and more in thickness become completely microscopically continuous. Some variations in grain size were also observed. Sputtered films were found to have crystallite grains twice as large as those in films prepared by evaporation. Microphotographs showed that for films 300 Å thick the “evaporation-condensation” effect occurs in the overlapping zone.     

Impedance spectroscopic investigation of the effect of thin azo-calix[4]arene film type on the cation sensitivity of the gold electrodes

In this work, we report the impedance spectroscopic investigation of the effect of the thin film type on the selectivity of gold/azo-calix[4]arene electrodes. For this purpose, two C1 and C3 azo-calix[4]arene derivative molecules, used as thin films, are deposited by spin-coating process on the gold surface. These thin films were first studied using contact angle measurements. This revealed a less hydrophobic character for C3 thin film, which has been attributed to the presence of hydroxyl groups at the lower rim.The sensitivity study, by Electrochemical Impedance Spectroscopy (EIS), towards Cu²⁺ and Eu³⁺ cations, has showed that the C3 thin film is more sensitive and selective towards Eu³⁺ than C1. This best performance is due to the presence of two ester groups acting as clips and leading to more complexation stability.The EIS results were modeled by an appropriate equivalent circuit for the aim of elucidating electrical properties of thin films. This modeling has exposed that C3 thin film presents lower ionic conductivity and limited diffusion phenomenon at the interface.     

Preparation of CdTe films by electrodeposition

Single-phase CdTe thin films have been prepared by depositing sequentially a layer of tellurium and a layer of cadmium on a molybdenum substrate followed by a short thermal treatment. Deposition of tellurium films was done in an aqueous solution containing TeO₂ at a current density of ≈ 1 mA/cm². An aqueous solution containing cadmium sulfate was used for cadmium deposition with a current density of ≈1 mA/cm². Solution temperature was ≈ 95°C for tellurium film deposition and was 50°C for cadmium deposition. It was found that after a heat treatment at ≈ 370°C for 10 min the deposited Te/Cd layers were converted to CdTe thin films with a cubic structure. Compositional uniformity of the films was also investigated by electron probe microanalysis.     

Epitaxial growth of thin gold films onto pure and doped NaCl and KCl substrates

The influence of impurities such as calcium, strontium or silver ions present in the substrates on the structural growth features of continuous gold thin films, vacuum evaporated at constant deposition rates onto NaCl and KCl substrates heated in the temperature range from 90 to 300 °C, was studied by transmission electron microscopy and transmission electron diffraction. The epitaxial growth of gold thin films is inhibited by the presence of 5 × 10^-1 mol.% strontium or calcium ions in the KCl and NaCl substrates. The presence of 1.7 × 10^-1 mol.% silver ions in the NaCl substrates enhances the epitaxial growth of the gold thin films even at a substrate temperature of 120 °C. An enhancement of the gold thin film epitaxial growth is also obtained with NaCl-2 × 10^-2mol.%Ag-5 × 10^-1mol.%Ca and NaCl-1.7 × 10^-1mol.%Ag-5 × 10^-1mol.%Ca substrates.     

Effects of Heat Treatment on the Microstructure and Optical Properties of Sputtered GeO2 Thin Films

Microstructure and composition significantly influence the physical properties of thin films. Therefore, these can be adapted to enhance the functionality of thin films for practical applications. Herein, the anomalous microstructural evolution of sputtered GeO₂ thin films based on postdepositional heat treatments is reported. Temperature-dependent microstructural variations are investigated systematically via a combinatorial postdepositional heat treatment employing a natural thermal gradient in a tube furnace. Heat treatment under an oxidizing atmosphere results in a transition from the amorphous phase to the quartz phase, and subsequent heat treatments under a reducing atmosphere cause H₂O-incorporated chemical reactions. Hence, these conditions create unique microstructural features and yield optical transmittance variations in the GeO₂ thin films. The phase transition induces the formation of spherulitic hexagonal GeO₂ crystallites, and further increase in the temperature promotes the agglomeration of crystallites in the amorphous matrix. The incorporation of H₂O results in the growth of the microstructure, and the chemical reduction to Ge metal begins to generate small granules from the boundary of the microstructures. The experimental results and proposed mechanisms presented herein for the microstructural and compositional changes serve as references for designing the physical properties of thin films.     

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.     

Effect of chopping on the properties of bismuth oxide thin films

Nanocrystalline bismuth oxide thin films have been deposited by thermal oxidation, in air, of vacuum evaporated chopped bismuth thin films. The optical properties and adhesion have been studied. The oxidation temperature and duration were varied. As revealed by structural investigations, polycrystalline and multiphase bismuth oxide thin films were obtained. At all oxidation temperatures, monoclinic Bi₂O₃ is predominant. The films showed high transmittance in the visible range of spectrum. The direct band gap of the films obtained was between 2.78 eV and 3.04 eV. The refractive index observed is in the range 1.934 to 2.096. The adhesion of films was in the range 215 × 10² to 470 × 10² kgF/cm². The values are strongly influenced by the heat treatment characteristics. It was observed that chopping helps in improving the adhesion and increasing refractive index, packing density and band gap of bismuth oxide thin films. These bismuth oxide films can have potential use in optical waveguides.     

Thermal Conductivity and Interfacial Thermal Resistance: Measurements of Thermally Oxidized SiO2 Films on a Silicon Wafer Using a Thermo-Reflectance Technique

This article describes the development of a method to measure the normal-to-plane thermal conductivity of a very thin electrically insulating film on a substrate. In this method, a metal film, which is deposited on the thin insulating films, is Joule heated periodically, and the ac-temperature response at the center of the metal film surface is measured by a thermo-reflectance technique. The one-dimensional thermal conduction equation of the metal/film/substrate system was solved analytically, and a simple approximate equation was derived. The thermal conductivities of the thermally oxidized SiO₂ films obtained in this study agreed with those of VAMAS TWA23 within ± 4%. In this study, an attempt was made to estimate the interfacial thermal resistance between the thermally oxidized SiO₂ film and the silicon wafer. The difference between the apparent thermal resistances of the thermally oxidized SiO₂ film with the gold film deposited by two different methods was examined. It was concluded that rf-sputtering produces a significant thermal resistance ((20 ± 4.5) × 10⁻⁹ m²·K·W⁻¹) between the gold film and the thermally oxidized SiO₂ film, but evaporation provides no significant interfacial thermal resistance (less than ± 4.5 × 10⁻⁹ m²·K·W⁻¹). The apparent interfacial thermal resistances between the thermally oxidized SiO₂ film and the silicon wafer were found to scatter significantly (± 9 × 10⁻⁹ m²·K·W⁻¹) around a very small thermal resistance (less than ± 4.5 × 10⁻⁹ m²·K·W⁻¹).     

Characteristics of germanium thin film thermometers for use at low temperatures

Germanium, thin films to be used as resistance thermometers have been tested at liquid helium temperature. Germanium is deposited in vacuum on insulated substrates and then silver is deposited onto the germanium films as ohmic contacts. Thermometers with desired resistances and suitable sensitivities can be easily fabricated by choosing proper deposition conditions. These thermometers have a quick response time and can be used to measure rapidly changing surface temperatures.The film resistance can be expressed as a function of temperature by a simple correlation, log R = C₀ + C₁ log T, between 4.2 K and 20 K. The sensitivity is approximately 20 Ω/K^?1 at 4.2 K. After 50 thermal cycles, the resistance at liquid helium temperature increased slightly, but is reproducible to within 0.8%. An estimated heat capacity of the germanium film is 2 × 10^?8 J K^?1, and a thermal relaxation time is of the order of 10^?12 s at 4.2 K.A stainless steel ribbon with the thermometers deposited on its surfaces is heated by a direct current in a liquid helium pool, and the surface temperature is measured. Large temperature oscillations due to occasional liquid solid contacts are observed.