Estimation of ionic conductivity of CuI through tarnishing studies of copper in iodine atmosphere

The conductivity values of isolated CuI crystal has been reported by a large number of investigators. But the conductivity be-haviour of a growing CuI film on copper has not been explored yet. An attempt has been made in this investigation to provide ionic conductivity values of growing CuI films from the kinetics studies of the film growth process. The conductivity value has been found to be proportional to the square of the partial pressure of iodine in the thinner film range while it is approximately proportional to the square root of the partial pressure in the thicker range. Estimation has been based on the fundamental parabolic equation of Wagner relating the rate constant and conductivity. An analysis of the experimental results indicate that the conductivity value of the growing CuI is of higher magnitude for thicker films than that for the thinner ones.     

Crystallization of amorphous antimony films on silver films

The crystallization process in amorphous antimony films 70–330 Å thick evaporated onto silver films 10–150 Å thick which have previously been evaporated onto glass is directly observed through an optical microscope. The conditions under which the crystallization process in the amorphous antimony films is observed are found to be severely limited by the preparation conditions of the silver films. The crystallization can only be observed on silver films thinner than 30–40 Å which have previously been exposed to oxygen or nitrogen gas. The crystallization thickness of amorphous antimony films on these substrates is estimated to be 123-75 Å as the substrate temperature varies from 20 to 80 °C and the activation energy for crystallization to be 0.23-0.30 eV as the film thickness varies from infinity to 200 Å.     

Electrical conduction mechanism in solution grown thin polyvinylchloride (PVC) films

The electrical transport behaviour of thin polyvinylchloride (PVC) films deposited by the solution growth technique has been investigated. The current transport in PVC films of 2500 Å thickness at temperatures below 250 K is ascribed to hopping mechanisms. The weak temperature dependence of the conductivity is attributed to interchain hopping, whereas the strong temperature dependence is attributed to the trap hopping process. The conductivity of PVC films is increased on doping with iodine. This is interpreted on the basis of the formation of charge transfer complexes in the film. The activation energy for conduction increases from 0.7 to 1.22 eV at 315 K and decreases from 2.2 to 0.8 eV at 375 K on doping PVC films with iodine (0.7 g of iodine per 100 ml PVC solution). At high (≧5 × 10⁴ V cm^-1) fields and at higher (≧350 K) temperatures, the observed conduction behaviour can be described by the Schottky emission mechanism. The height of the Schottky barrier is found to depend on the type of the metal electrode and the direction of the current. The barrier height decreases with increasing iodine concentration in the PVC films.     

Thermal conductivity of copper films

The thermal conductivity of thin films of copper (400–8000 Å) has been measured in the temperature range 100–500 K. It decreases with decreasing film thickness. An electrical-thermal transport analogy has been used to calculate the size-dependent thermal conductivity of the thin copper films. The decrease of the thermal conductivity with thickness is attributed partly to the scattering of the conduction electrons from the film surfaces and partly to the scattering by lattice impurities and frozen-in structural defects in the films. The variation of the thermal conductivity with temperature agrees with the variation for bulk copper. The Lorentz ratio has been determined and is found to vary from 2.4 × 10^-8 to $\text{2.0 × 10}{}^{-8}\text{W}\text{Ω/}\text{deg}{}^2$ for film thicknesses ranging from 400 to 8000 Å.     

Dependence of the longitudinal strain coefficient of resistivity of silver films on thickness and grain size diameter

A grain boundary model modified by including the Fuchs size effect has been used to derive a general expression for the longitudinal strain coefficient of resistivity of continuous polycrystalline silver films, of thickness greater than the intrinsic mean free path, in terms of the grain size diameter and the film thickness. It has been found that the longitudinal strain coefficient of film resistivity has zero value for very small grain size and attains the bulk value when the grain size and the film thickness are very large. It has also been found that a threshold value of the grain size diameter exists, below which the film thickness has practically no effect on the strain coefficient of film resistivity. However, for grain size diameters greater than the threshold value, thicker films have values of the strain coefficient or resistivity higher than those for thinner films.     

In situ electrical conductivity and the amorphous-crystalline transition in vacuum deposited thin films of Se80Te20 alloy

The electrical conductivity of thin films of Se₈₀Te₂₀ polycrystalline alloy vacuum-deposited at room temperature on glass substrates has been studied duringin situ heating and cooling cycles. From the electron diffraction of as-grown films it is seen that the studied films are amorphous at room temperature. The electrical conductivity and electron diffraction studies showed that the as-grown amorphous thin films undergo an amorphous-crystalline transition in the temperature range 340 to 360 K. Upon cooling, the films appear to undergo a crystalline crystalline transition around the same temperatures. There does not appear to be any dependence of the amorphous-crystalline transition temperature on the thickness of the films. However, high-resistance films (thinner films) have a well-defined transition temperature while the low-resistance films (thicker films) have a broader transition. The electrical conductivity of polycrystalline Se₈₀Te₂₀ films above 360 K appears to be an exponential function of reciprocal temperature.     

Epitaxial growth of the Au/C/Ag system in ultrahigh vacuum

Carbon layers were evaporated onto silver single crystals (that had been previously exposed to air) at room temperature in an ultrahigh vacuum (UHV), and a gold film was subsequently evaporated onto the specimens without change of temperature. The gold films were examined by transmission electron microscopy to determine whether or not epitaxy had occurred. Three cases were observed: complete epitaxy when the average carbon film thickness was 1 Å or less; completely disordered structures for amorphous films 3 Å thick or more; and a partially oriented structure in the intermediate range. The fact that epitaxy is destroyed before the coalescence stage of the carbon film is reached suggests that the carbon islands block the mobility of the nuclei that are growing epitaxially; there is no need for carbon to cover the silver crystal completely for epitaxy to be destroyed. The experimental results obtained also indicate that not only is direct contact between substrate and evaporated film necessary for epitaxy but that the substrate surface must be “suitably” contaminated.     

The variation in electrical resistance with temperature for Bi/Ag bilayer films

The variation in the electrical resistance of vacuum-evaporated Bi/Ag bilayers with different layer thicknesses was studied as a function of temperature. A silver overlayer 50 Å thick increased the variation in R_T/R with temperature of the bismuth film (R_T is the resistance of the film at temperature T and R the resistance at room temperature). It increased the resistance of the film and made the temperature coefficient of resistance at room temperature more negative. In addition, the resistance minimum was shifted to higher temperatures. The variation in resistance with temperature is explained on the basis of the Kaidanov and Regal model. When the total thickness of the bilayer film was kept constant (approximately 1000 Å), the variation in resistance on annealing was dependent on the thickness of the silver layer. The rapid rise in resistance above 100 °C observed in films with silver layers between 100 and 600 Å thick is explained on the basis of diffusion at the interface and aggregation of the silver film on the surface. By controlling the thickness of the layers it is possible to keep the variation in resistance with temperature of the film to a minimum.     

Structure of chemically deposited polycrystalline-silicon films

The influence of the deposition conditions on the structure of chemically deposited, polycrystalline-silicon films has been examined. The films were deposited primarily onto oxidized silicon wafers by the thermal decomposition of silane over temperature and thickness ranges of 650°–1200°C and 0.6–15 microm, respectively. After an initial induction period, which exhibits an activation energy of about 1.0 eV, island-type nucleation was observed for deposition temperatures of 850° and 1025°C; however, no islands could be resolved for a deposition temperature of 650°C. Although {110}- and {111}-texture are both important in the thinner films, {110}-texture becomes dominant over most of the temperature range as the film thickness increases. The {100}-texture is important in thicker films deposited at higher temperatures. Transmission electron microscopy indicated that the grain size increases with increasing film thickness and deposition temperature, ranging from less than 0.05 microm to more than 1 microm in the films studied. An investigation of the influence of the initial stages of deposition on the development of the texture indicated that the highly twinned {110}-grains, once nucleated, grow most rapidly. An anomalous, low-temperature structure, the effect of the reactant gas, and the influence of the substrate have been briefly investigated.     

Epitaxial growth on MgO on (001) surfaces of silver single-crystal film substrates

The epitaxial growth of evaporated MgO films (<25–4000 Å) on smooth (001) surfaces of silver single-crystal film substrates at a temperature inthe range 25°–200°C has been studied by reflection high energy electron diffraction. At substrate temperatures below 150°C, MgO is oriented with its (111) plane parallel to the surface of the substrate. The (111) orientation is fibrous. At 150°C a major fraction of the deposit is oriented in parallel and at 200°C only the parallel orientation is observed. The deposit initially grows as oriented three-dimensional nuclei. As the film thickness increases to 500 Å, randomly oriented MgO is simultaneously formed at the surface. With further increase in thickness the degree of epitaxial orientation decreases and at 1000 Å a small amount of one- degree (111) orientation appears at the surface. At 4000 Å the surface orientation becomes one-degree (111); the (111) orientation is interpreted as a final growth orientation.     

Experimental determination of the thermal conductivity of thin films

Two techniques have been developed to determine experimentally the thermal conductivity of thin solid films of thickness 500 Å or more at low and high temperatures. The first technique is a steady state and is suitable for measurements above room temperature. The method enables the thermal conductivity of eight film specimens to be measured simultaneously. The second technique is a transient one (an adaptation of Ioffe's method for bulk materials) and is suitable for measurements in the temperature range 100–260 K. The two techniques have been used to make measurements of thin films of copper and various crystalline and amorphous semiconductors. The values of the thermal conductivity for thick copper films by both techniques agree quite well with the bulk values.     

Studies of structural transformations and electrical behaviour of FeSe films

The formation of FeSe alloy films as a result of the co-deposition of Se and Fe thin films has been studied. It has been found that the as-grown FeSe film corresponds to a cubic phase with a = 5.37±0.05 Å. The effect of annealing on this FeSe phase has been investigated. At annealing temperatures ranging between 150° and 200°C, the cubic phase transforms to a hexagonal phase (a = 4.00±0.05 Å, c = 5.88±0.05 Å) which resembles one of the known bulk phases of FeSe. On further annealing in the temperature range 250°–300°C, the hexagonal phase transforms to a tetragonal phase with a = 4.18±0.05 Å, c = 4.73±0.05 Å. All the transformations have been found to be irreversible. The electrical behaviour of the FeSe films at various temperatures has also been studied. Evidence for the phase transformations is provided by the nature of the variation of the electrical resistivity with temperature.     

Chemical bath deposition of SnS thin films on ZnS and CdS substrates

We illustrate that Tin sulfide (SnS) thin films of 110–500 nm in thickness may be deposited on ZnS and CdS substrates to simulate the requirement in developing window-buffer/SnS solar cells in the superstrate configuration. In the chemical bath deposition reported here, tin chloride and thiosulfate are the major constituents and the deposition is made at 25 °C. In a single deposition, film thickness of 110–170 nm is achieved and in two more successive depositions, the film thickness is 450–500 nm. The thicker films are composed of vertically stacked flakes, 100 nm across and 10–20 nm in thickness. The Sn/S elemental ratio is ~1 for the films 110–170 nm in thickness, but it slightly increases for thicker films. The crystalline structure is orthorhombic, similar to the mineral herzenbergite, and with crystallite diameters 13 nm (110–170 films) and 16 nm (450–500 nm films). The Raman bands at 94, 172 and 218 cm^?1 further confirm the SnS composition of the films. The optical band gap of SnS is 1.4–1.5 eV for the thinner films, but is 1.28–1.39 eV for the thicker films, the decrease being ascribed to the increase in the crystallite diameter. Uniform pin-hole free SnS thin films were successfully grown on two different substrates and can be applied in solar cell structures.     

银纳米线-聚对苯二甲酸乙二醇酯透明导电胶膜

以银纳米线作为导电填料,以聚对苯二甲酸乙二醇酯(PET)为柔性衬底,采用平板热压机通过热压方式制备了银纳米线-PET透明导电胶膜。研究了银纳米线-PET导电胶膜的耐弯曲性能、电学性能以及透光性。结果表明,所制备的银纳米线-PET导电胶膜透光率达到80%以上,表面电阻率达到1×10^-3Ω·cm。银纳米线-PET导电胶膜经过500次的弯曲循环后电阻率未下降。随着银纳米线溶液浓度的增加,银纳米线-PET导电胶膜透光性下降,表面电阻率增加。     

非织造基磁控溅射纳米银薄膜导电性能的研究

在室温条件下采用射频磁控溅射在丙纶(PP)、聚乳酸(PLA)熔喷非织造布表面生长纳米银(Ag)薄膜,并且用等离子体预处理样品进行对比。采用扫描电子显微镜(SEM)对其形貌进行表征,采用四探针测试仪对所制备的纳米薄膜的导电性能进行表征。研究溅射时间、孔隙率及孔径分布和等离子处理对非织造基纳米银薄膜的导电性能的影响。实验表明:随着反应溅射时间的增加,薄膜的方块电阻值下降,导电性能增加;孔径大小也影响薄膜的导电性能,随着孔径的增大,薄膜的导电性能降低;等离子体处理对织物表面进行刻蚀,增加了纤维的比表面积,提高了纤维的润湿性能,改善了织物的导电性能。     

The effect of oxygen and hydrogen contamination on the electrical resistivity of rare earth metal films

The effect of air and hydrogen contamination on the electrical resistivity of Er, Ho, Dy, Tb, Gd and Yb films was studied. The resistivity of the films increases almost discontinuously as soon as air is admitted into the vacuum chamber. After this sudden increase, the change becomes slow and the resistivity attains a constant value for thicker films (> 200 Å). For very thin films (<100 Å) the resistivity increases rapidly after the initial jump and very soon attains a very high value owing to the complete oxidation of the film. When hydrogen is admitted into the system, the resistivity of the films increases as for air contamination, but after a few minutes the resistivity starts to decrease except for Yb films. The increase in the resistivity for Er, Ho, Dy, Tb and Gd films is due to the interstitial solution of hydrogen in these metals (α phase); however, the decrease in ? after the initial increase is due to the formation of high conductivity f.c.c. dihydride. In the case of Yb the resistivity does not decrease because YbH₂ has a higher resistivity than pure Yb. For thin erbium films (about 200 Å) at a hydrogen pressure of several torrs the resistivity rises again after reaching a minimum value. This increase is thought to be due to the interstitial solution of hydrogen in the metallic conductor ErH₂. The investigation supports an earlier suggestion of the authors that the dihydride phase present in rare earth metal films (except Yb and Eu) made in ordinary vacuum may decrease the resistivity of these films below their bulk value.     

Dielectric behaviour of dysprosium oxide films

The dielectric properties of vacuum-deposited dysprosium oxide films have been studied in the audio-frequency range (10²–10⁴ Hz) at various temperatures (78–373 K). The dielectric constant (6.7) was independent of film thickness for thicker films (d > 1000 Å). The capacitance was dependent both on temperature and frequency, but became constant for all frequencies at low temperature. Tan δ showed a frequency minimum and its variation with frequency and temperature was in agreement with the model proposed earlier by Goswami and Goswami. The breakdown field (≌10⁶ V cm^-1) followed the Forlani-Minnaja relation. The activation energy and the refractive index of these films were also measured.     

Deposition of diamond like carbon (DLC) and C-N films using ion beam assisted deposition (IBAD) technique and evaluation of their properties

Diamond like carbon films and C-N films were prepared using ion beam assisted deposition technique (IBAD). Tribological properties were studied by subjecting DLC coated films to the accelerated wear tests. These tests indicated a significant improvement in the mechanical surface properties of glass by DLC coating. Better wear features were obtained for thinner DLC coating as compared to the thicker ones. We also studied the optical properties and obtained a band gap of 1·4 eV for these films. An attempt was made to prepare C₃N₄ films by using IBAD. We observed variation in the nitrogen incorporation in the film with the substrate temperature.     

Influence of deposition conditions and substrate structure on the structure of sputtered tellurium films

A study has been made of the growth of tellurium films sputtered onto four substrate materials (cover glass, spinel, quartz and alumina), unheated as well as heated to 100°, 150°, 200° and 250°C. It was found that the structure of the substrate exerted no measurable influence on the structure of the films. However, sputtering conditions do influence the preferred orientation. Tellurium films sputtered onto unheated substrates have a preferred orientation of the (100) type (i.e. with the (100) planes parallel to the substrate). Those on heated substrates show a preferred orientation of the (101) type. Furthermore, thickness is an important factor. Tellurium films with thickness less than 6000 Å have a (100)-type preferred orientation, but thicker films have a (101) orientation. All the observations can be explained in terms of recrystallization taking place during deposition due to heating of the film.     

Properties of polycrystalline silicon films prepared from fluorinated precursors

Polycrystalline silicon films have been prepared at low temperature on glass substrate from fluorinated precursors by PECVD technique varying the hydrogen dilution and gas flow rate. Undoped film with dark-conductivity 1.05×10⁻² S cm⁻¹ has been obtained. For n-type poly-Si film the highest conductivity achieved is 2.8 S cm⁻¹. Grain size observed from SEM varies from 4 to 6 μm for undoped and 2 to 3 μm for phosphorous doped films. The main crystalline peak is 〈111〉 whereas the crystallite size calculated from XRD is 350 Å. The optical absorptions and hydrogen contents in the films deposited under different conditions have been studied. Growth kinetics are dominated by the precursors SiF_nH_m (m+n≤3) and concentrations of F and H on the growth surface.