The effect of amorphous intermediate layers on the epitaxial growth of gold evaporated onto silver single crystals

Amorphous layers of carbon and silicon monoxide have been evaporated onto silver substrates at temperatures of 150°, 270° and 400°C. Gold was subsequently evaporated onto the specimens without changing the temperature. The gold films were examined by electron microscopy in order to determine whether or not epitaxy had occurred. Three “phases” were observed: complete epitaxy for amorphous films less than 4 Å (carbon) or 5 Å (silicon monoxide); completely disordered structures for amorphous films greater than 10 Å (carbon) or 11 Å (silicon monoxide); and a partially oriented structure (partial epitaxy) for intermediate thicknesses.     

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.     

Fiber texture and surface composition of evaporated gold films on quartz

The fiber texture, surface composition and homogeneity of polycrystalline films of gold 300–2000 Å thick evaporated onto quartz in the pressure range from 1.5 × 10⁻² to 2 × 10⁻⁷ Pa were investigated by means of X-ray diffraction, electron microscopy, Auger electron spectroscopy and gas sorption experiments. No qualitative differences are observed between the films characterized here and previous results reported for glass substrates: a (111) fiber orientation is observed and is enhanced as the substrate temperature, during or after the deposition, is increased. The percentage of gold present at the surface and the surface homogeneity are more sensitive to the cleaning and outgassing procedure than to the actual pressure during deposition. The uniformity of the quartz substrate has little influence on the surface homogeneity of the gold film.     

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.     

The microstructure and orientation of silver on NaCl: The influence of surface conditions

Silver films up to 1000 Å thick (coalescence stage and continuous films) were evaporated onto vacuum-cleaved NaCl at constant temperature and constant deposition rate but under various vacuum conditions (ultrahigh vacuum (UHV), high vacuum (oil pumped and ion pumped), a partial pressure of contaminant (10^-10–10^-6 Torr) etc.). The films were characterized by low energy electron diffraction, Auger electron spectroscopy, transmission electron microscopy and transmission electron diffraction to determine their orientation, microstructure and cleanliness. The UHV-grown films were always polycrystalline. In contrast with previous observations, however, an increase in the partial pressure of H₂O alone did not improve the epitaxy. Hence the influence of other materials such as O₂, H₂O + O₂, hydrocarbons etc. was investigated. In addition, films were grown in UHV after pre-irradiation of the substrate with electrons and prenucleation at room temperature. If the prenucleated silver clusters were small and if their orientation was improved by annealing, continuous films were perfectly epitaxial even when the deposition of silver was carried out at room temperature after prenucleation. This indicates a post-nucleation mechanism of epitaxy.     

Influence of substrate temperature and film thickness on the structure of reactively evaporated In2O3 films

Indium oxide films 25–550 Å thick were reactively evaporated at an oxygen pressure of about 0.27 Pa and at a substrate temperature between room temperature and 400°C. The dependence of the structure of the films on the substrate temperature and on the film thickness was studied using transmission electron microscopy and electron diffraction. It was found that thick films (about 550 Å) were amorphous at room temperature, partially crystallized at 50–125°C and crystalline at 150–400°C. The crystallinity of the films deposited at 150–250°C also depended markedly on the film thickness. Very thin films about 25 Å thick were quasi-amorphous, but with increasing film thickness the amorphous phase transformed into a crystalline phase.The thermal transformation of the amorphous films after deposition was also studied. Amorphous films about 550 Å thick deposited at room temperature and 100°C crystallized at 230°C and 210°C respectively.     

Author index

There are conflicting reports in the literature as to whether epitaxial films can be grown over intermediate thin continuous carbon layers. A series of experiments was carried out on the NaClAu system in which the effect of intermediate carbon films on the epitaxy of the gold was studied. For a very limited thickness range of carbon intermediate layers, good epitaxial gold films were formed. The corresponding carbon films were stripped, and examination in the electron microscope showed that the films were continuous and free from holes greater than 10 Å in diameter. A model based on “pseudomorphic islands” in the carbon film is proposed to account for the observations.     

The epitaxial growth of germanium and silicon on an Ag(111) film on a mica substrate

With the aim of finding a method of obtaining self-supporting single-crystal films of silicon for solar cells we studied the epitaxial growth of silicon and germanium prepared by evaporation in ultrahigh vacuum onto an Ag(111) film evaporated in situ onto a mica substrate cleaved in air. The films were examined mainly by reflection high energy electron diffraction. Silicon and germanium films 50–200 Å thick were composed of crystallites with two main orientations relative to the substrate and unoriented crystallites in varying proportions depending on the substrate temperature T_s and the previous heat treatment temperature T_H of the mica. Nearly single-crystal films of silicon could be obtained for T_s = 350 °C and T_H = 250 °C. The sticking coefficient for silicon on silver was found to decrease almost to zero for T_s = 420 °C with T_H = 250 °C. No single-crystal films of germanium were obtained.     

TiC coatings deposited onto carbon and molybdenum surfaces by electron beam evaporation

TiC coatings were deposited onto graphite and molybdenum substrates by an electron beam evaporation method. A titanium film 1000–10000 Å thick was evaporated onto the graphite substrate which was then heated at 1000 °C for 5 min to form the TiC film by an interdiffusion process. In the case of the molybdenum substrate, a double-layer film consisting of titanium and carbon (Ti/C/Mo) was prepared by evaporation and the subsequent heat treatment was performed at 700 °C or at 1000 °C for 5 min. The properties of the coatings were examined by various surface analysis techniques including Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and Rutherford backscattering (RBS). The atomic ratio of carbon to titanium in these coatings was found to be 0.9. The in-depth profiles obtained by XPS examination showed that the coating prepared at 700 °C had a carbon layer between the TiC layer and the molybdenum substrate, while that prepared at 1000 °C had an Mo₂C layer between the coating and the substrate.     

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.     

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.     

Investigation of germanium films and GeSi interface structure by transmission electron microscopy

The structure of germanium films (d≌0.3 μm) evaporated onto a silicon substrate and the GeSi interface have been investigated by transmission electron microscopy (TEM). Ge was evaporated in a vacuum of approximately 10^?6 Torr onto (111) Si. Epitaxial growth was observed at substrate temperatures T_s>500°C. The films grown at T_s = 520°–600°C (low temperature epitaxy) were characterized by a high density of stacking faults (SF), microtwin lamellae and dislocations which lay normal to the film surface. In this case the interface dislocations were regular and the dislocation density was equal to (3–4)×10¹⁰ cm^?2. At T_s = 700°–850°C (high temperature epitaxy) few stacking faults were discovered. Dislocations in the interior of the film formed three-dimensional networks as a result of interactions of different slip systems and dislocation climb. The formation of misfit dislocations was apparent at the interface. The region T_s = 630°–700°C is an intermediate region.     

Zinc phthalocyanine — Influence of substrate temperature, film thickness, and kind of substrate on the morphology

Zinc phthalocyanine (ZnPc), C₃₂H₁₆N₈Zn, is a planar organic molecule having numerous optical and electrical applications in organic electronics. This work investigates the influence of various deposition parameters on the morphology of vapour thermal evaporated ZnPc films. For this purpose, ZnPc is deposited at different substrate temperatures up to 90 °C and film thickness up to 50 nm onto various substrates. The morphology of this ZnPc layers is characterised by X-ray diffraction (XRD), X-ray reflectivity (XRR) and atomic force microscopy (AFM) methods. XRD measurements show that all ZnPc films are crystalline in a triclinic (α-ZnPc) or monoclinic (γ-ZnPc) phase, independent from the kind of substrate, layer thickness, or substrate temperature. The ZnPc powder, the starting product for the thermally evaporated ZnPc films, is present in the stable monoclinic β-phase. Thus, the stacking of the ZnPc molecules changes completely during deposition. The crystallite size perpendicular to the substrate determined by XRD microstructure analysis is in the range of the layer thickness while the lateral size, obtained by AFM, is increasing with substrate temperature and film thickness. AFM and XRR show an increase of the layer roughness for thicker ZnPc layers and higher substrate temperatures during film deposition. The strain in the ZnPc films decreases for higher substrate temperatures due to enhanced thermal relaxation and for thicker ZnPc films due to lower surface tension.     

Quantum size effect in thin Cd3As2 films

An investigation has been carried out of the resistivity ?, Hall coefficient R_H and Hall mobility μ_H as functions of film thickness for vacuum-evaporated thin Cd₃As₂ films. The films were evaporated in a vacuum of 10^?5 torr onto mica substrates heated to a temperature t_s of about 160 °C at a rate of deposition v of about 40 Å s^?1. The thicknesses of the films were in the range 0.02–0.2 μm. An oscillating character of the resistivity and the carrier mobility was observed for thicknesses of 0.03–0.1 μm. No distinct oscillations of the Hall coefficient were found. The analysis of the results obtained was performed on the basis of theories of the quantum size effect (QSE). The period of the oscillations measured from the experimental data was about 100 Å, which is in good agreement with the calculated value of about 80 Å.     

Studies of the Ti-W/Au metallization on aluminum

The temperature stability of a composite film structure of 1500 Å of Ti_0.3W_0.7 and 3000 Å of gold r.f. sputtered sequentially onto an evaporated aluminum film 9000 Å thick on silicon was investigated by Auger depth profile analysis. Annealing of this structure at 300 °C for 6 min is shown to result in extensive intermixing. This phenomenon appears to proceed via hillock growth in the aluminum and a grain boundary diffusion mechanism involving the Ti-W. Thorough characterization of the Ti-W by transmission electron microscopy, helium ion backscattering spectrometry and deuterium activation analysis suggests that the Ti-W is of reasonable purity. These data indicate that Ti_0.3W_0.7 exhibits marginal diffusion barrier properties when deposited in a relatively pure state. In addition, it is shown that the barrier properties improve by orders of magnitude when Ti-W is sputtered in N₂-Ar. Thus it appears that optimum diffusion barrier properties are present only when Ti-W is deposited in a relatively impure state.     

Structure and growth mechanisms in thin epitaxial PbTe films

Thin (100–1500 Å) epitaxial PbTe films evaporated in a vacuum on the (100) plane of a single crystal of NaCl were investigated. The films were deposited using both the conventional evaporating system and the hot-wall system. The structure of the films was studied by transmission electron microscopy. The films were obtained at substrate temperatures ranging from 20 to 360°C and all had single crystal structures with the (100) plane parallel to the substrate.Intensive nucleation was observed on surface defects. The influence of the substrate temperature on the character of the nucleation process was studied. In addition, the shape, size and density of the crystallites and their dependence on the substrate temperature were examined. The number of defects and the degree of crystalline perfection of the films depend on the temperatures of the substrate and the hot wall. The films obtained in the hot-wall system were more homogeneous with depth and were less defective than those obtained in the conventional system. From the temperature dependence of the density of nuclei under saturation conditions the activation energy E for the nucleation process was found to be 0.30±0.05 eV.     

Effect of angle of incidence during deposition on Ti-Pd-Au conductor film adhesion

The influence of a number of the preparation conditions on the adhesive properties of the Ti-Pd-Au metallization on Ta₂N film resistors was investigated. Test samples consisted of a filament-evaporated conductor film on an unpatterned Ta₂N film on glass, sapphire and Al₂O₃ ceramic substrates. The adhesive properties of the Ti-Pd-Au films were examined as a function of the angle of incidence at which the Ti and Pd atoms were deposited. In addition the adhesive properties were examined after heat treatment in air and after electroplating gold. Transmission electron microscopy and density measurements established that at higher angles of incidence (&#62;60°) Ti and Pd films became increasingly porous and that adhesion at the Ti-Pd interface degraded rapidly upon exposure to air. Both evaporated and plated Au layers appear to offer little protection for films evaporated under these conditions. Good adhesion was found to be independent of the substrate material and of the method used for gold deposition when the Ti-Pd films were evaporated at angles of incidence of 48° or less.     

From nanorings to nanodots by patterning with block copolymers

We demonstrate three different transfer patterns that can be achieved by use of a surface reconstructed block copolymer film where metal is evaporated onto the surface of the film, providing the contrast. Thin films of diblock copolymers having cylindrical microdomains oriented normal to the surface with long-range lateral order were used. Solvent reconstruction of the film, followed by a glancing angle metal evaporation and thermal annealing, led to three different decorations of the films with gold. These films were used as masks for pattern transfer of pores, columns, and rings to underlying substrate with high fidelity.     

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.     

Electrochemical processing of high-T c Bi(Pb)-Sr-Ca-CuO thin films

Superconducting thin films of Bi(Pb)-Sr-Ca-CuO system were prepared by depositing the film onto silver substrate by d.c. electrodeposition technique with dimethyl sulphoxide bath in order to examine the effect of Pb addition to the BSCCO system. The films were deposited at the potential of -0.8 V vs saturated calomel electrode (SCE) onto the silver substrate. The different preparative parameters such as deposition potential, deposition time were studied and optimized. These films were then oxidized electro-chemically at room temperature in an alkaline (1 N KOH) solution, and also at 600°C temperature in an oxygen atmosphere. The films showed the superconducting behaviour, with T_c values ranging between 85 K and 96 K, respectively.