Study Of Film Growth Research Articles

Study of Anodic Film Growth on GaAs and Bi2Te3 by in situ Photoacoustic Technique

Anodic film growth on GaAs and Bi2Te3 during the anodization process was observed with an in situ photoacoustic technique. It was shown that the time dependence of the normalized change in the photoacoustic signal reflects the anodic film growth on GaAs and Bi2Te3. The photoacoustic technique is complementary to the differential reflectance technique; the measured quantity is a change in transmittance of the electrolyte-anodic film-substrate system for the former case and a change in reflectance of the three phase system for the latter case. Experimental results obtained in the photoacoustic measurements are discussed in relation to those previously obtained in the differential reflectance and in situ ellipsometry measurements.

Anodic Film Growth on Titanium at Temperatures from 200° to 257°C

An electrochemical study of anodic film growth on titanium in oxygenated at temperatures from 200° to 257°C and at constant potential, below the evolution potential is presented. At constant applied potential, it is assumed that the voltage drop across the oxide is constant and the field , where is the film thickness. The results are interpreted in terms of a rate expression derived by Dignam (20–22) and assume the effective field, , assisting the ionic conduction process is the local field, for , where is the dielectric constant of the oxide and δ is a geometric factor having a value the order of unity.

Photometric Ellipsometer for the Study of Film Growth in the Very Early Stages

Photometric Ellipsometer for the Study of Film Growth in the Very Early Stages

Zircaloy oxide thickness measurement by ellipsometry

Ellipsometry can be used to measure the thickness of Zircaloy oxide to 5 μm at a measuring wavelength of 3.39 μ to an accuracy of about 10%. If we assume that the extinction coefficient remains relatively constant between 3 and 10 μm wavelength, thicknesses of up to 15 μm should be measurable at the latter wavelength. In addition to thickness measurements, ellipsometry could be used effectively for in situ kinetic point-by-point studies of Zircaloy oxide film growth in closed systems involving a variety of experimental conditions so long as the ambient medium in the system allows reflection from the specimen. Automation of the ellipsometer would make it possible to measure rapid changes in film thickness.

UHV Transmission and Reflection Electron Microscopies for Surface Studies

This paper reviews recent results of surface structure studies of mono-layer levels done in our group with use of an UHV electron microscope (EM) of 10-8∿10-10Torr, which was originally designed for in-situ thin film growth studies [1]. Our techniques of UHV EM and of in-situ deposition and clean surface preparation were applied to studies of microtopographies of surfaces, in which previous surface researches mainly done by LEED, AES and RHEED are lacking. Some efforts to get topographic informations were done with use of AES and RHEED in scanning mode [2] but their resolutions were much poorer than that of conventional EM. We observed surfaces in two modes, transmission (TEM) and reflection (REM). TEM had been considered to be insensitive to details in depth direction in contrast to its high resolving power in lateral directions. Recent reports, however, showed that atomic steps stand out both in bright and dark field images with appreciable contrast due to diffraction extinction effects [3]. The REM method is based on the fact that RHEED is sensitive to surface structures [4]. The previous REM works, however, did not succeeded in observing clean surfaces on account of poor vacuum of the microscope and lack of preparation techniques of specimens with clean surfaces [5].

A qualitative ellipsometric-electrochemical approach to the study of film growth under organic coatings

A study was made to determine if qualitative ellipsometry could be used together with electrochemical pH and potential measurements as a technique for the study of metal substrates protected by transparent organic coatings. The objective was to gain a deeper understanding of the mechanisms governing the corrosion protective actions of paints on metal surfaces. Computer modeling and experiments with collodion coatings on iron substrates indicated that changes in the ellipsometric parameter Δ could, for the most part, be safely interpreted as thickness alterations in the substrate oxide film. Experiments with the Fe-collodion system in dilute chloride solutions exhibited three sequential stages of activity, two of which could be interpreted in terms of corrosion mechanisms using the optical and electrochemical measurements. Chromate ion as a corrosion inhibitor in coatings was also studied using this technique, and was shown to have significant effects upon the development of the subcoating processes.

A qualitative ellipsometric-electrochemical approach to the study of film growth under organic coatings

Abstract A study was made to determine if qualitative ellipsometry could be used together with electrochemical pH and potential measurements as a technique for the study of metal substrates protected by transparent organic coatings. The objective was to gain a deeper understanding of the mechanisms governing the corrosion protective actions of paints on metal surfaces. Computer modeling and experiments with collodion coatings on iron substrates indicated that changes in the ellipsometric parameter Δ could, for the most part, be safely interpreted as thickness alterations in the substrate oxide film. Experiments with the Fe-collodion system in dilute chloride solutions exhibited three sequential stages of activity, two of which could be interpreted in terms of corrosion mechanisms using the optical and electrochemical measurements. Chromate ion as a corrosion inhibitor in coatings was also studied using this technique, and was shown to have significant effects upon the development of the subcoating processes.

Temperature Study of Oxide Film Growth at Platinum Anodes in H 2 SO 4 Solutions

The growth of anodic oxide films at platinum in sulfuric acid solution was studied at different temperatures using galvanostatic transients. The activation energy and preexponential factor for the rate of growth were evaluated. In the plane in which the rate‐determining step occurs the surface density of ions, or ion pairs participating in the growth process, is about 1015 cm−2. This is close to the density of atoms in the surface of the metal. The analysis appears to support the process at the metal/oxide interface being the rate‐determining step. However, the same value for N is compatible with, the field‐assisted place exchange process as the rate‐determining step at the metal/ oxide interface or within the oxide phase. Because the growth follows the same rate equation from the very early stages of oxide formation, the process at the metal/oxide interface seems to be the rate‐determining step.

Simultaneous RHEED / AES study of Si film growth on Si(111) and sapphire (11̄02) surfaces

Epitaxial growth of Si thin films deposited on the Si(111)-7 × 7 and sapphire (11̄02)-2 × 1 substrate surfaces are studied by using a new combined system at substrate temperatures ranging from 30 to 1100°C. The role of simultaneous measurement of chemical composition of the surface by Auger electron spectroscopy and residual gas analysis by quadrupole mass spectrometry during observation of RHEED patterns is illustrated. The 7×7 structure of the Si(111) fades with increasing thickness of deposited film. The integral order spots corresponding to the Si bulk structure become streaky and change into broad spots after a film of 150 Å thickness is deposited at a substrate temperature of 800°C. The fact that partially ionized vapor deposition (PIVD) prefers epitxial growth is also demonstrated, whereas the ion concentration ratio and ion energy are only 0.5% and 100 eV respectively. The RHEED pattern corresponding to the 2 × 1 structure of atomically clean sapphire (11̄02) surface disappears after deposition of up to 10 Å at a substrate temperature of 30°C. However, it remains unchanged, at least for films of thickness up to 100 Å, when deposition is made at a substrate temperature of 1100°C, and the mass peaks of m e 27(Al +) and 44(SiO +) increase markedly. A postulated reaction mechanism between Al 2O 3 and impinging Si is discussed.

In situ oxygen conditioning of (001) MgO thin film substrates for film growth studies by electron microscopy

It was found that the in situ treatment of (001) single-crystal films of MgO (prepared by epitaxial growth from the vapor phase) at high temperatures with a jet of oxygen will produce a surface that is almost equivalent, for epitaxial studies, to surfaces with the same orientation prepared by vacuum cleavage of bulk single crystals. The effectiveness of the process is demonstrated by its impact on the epitaxy of silver.

Surface study by UHV electron microscope

Recent advances of UHV techniques, LEED, RHEED and AES, arose a surge of interest on the surface of solids. These techniques reveal structures and chemical compositions at the mono-atomic or mono-molecular level. All of them, however, are devoid of detailed topographic informations, although some efforts to introduce the scanning techniques have been done[l]. Transmission electron microscopy of high resolution should play a complementary role to these techniques. No attempt, however, has been done previously to use it to such a purpose. This was because it was difficult to get and keep clean surfaces in the poor vacuum at 1x10-5Torr level of the conventional electron microscope.The present paper reports observations of surface phenomena of one or two atomic layer level using a UHV JEM 100B electron microscope (10-8-10-10Torr), recently developed for insitu thin film growth studies[2]. Atomically flat (111) surfaces of Ag, Pd, Au and Cu were prepared by in- situ deposition at 150-350°C on M0S2, graphite and MgO. Air Cleaved thin films of MoS2 and graphite were preheated to 800°C to get clean surfaces[3].

UHV In-Situ Electron Microscopy of thin Film Growth

An ultra-high vacuum (UHV) electron microscope was constructed for special purpose of in-situ studies of thin film growth and some experimental results have already been published (1). Here, recent results are described.1. Au/graphite (nucleation and growth mode). Growths of Au in a dendritic shape at 150°C were observed on graphite. The dendritic morphology was said to be characteristic of the Au growth on UHV cleaved graphite (2). We cleaned an air cleaved surface by heating in UHV EM (10-8 torr) for 20 minutes prior to the Au deposition. The dendritic shape growth in Fig. 1, therefore, indicates that the graphite surface became clean with the present heat treatment and that the in-situ studies were done under clean conditions.

Energy loss spectroscopy of sulphide films on Mo (100)

Energy loss spectroscopy has revealed features on clean Mo(100) due to bulk and surface plasmons, surface state emission, core-conduction band transitions, and multiple losses. On random adsorption of H 2S at room temperature new peaks appear which are associated with chemisorption bonds. Spectra from epitaxially grown MoS 2 on Mo(100) are in broad agreement with those from bulk MoS 2. The results complement other studies of sulphide film growth using low energy electron diffraction and Auger spectroscopy.

Autocollimation-type ellipsometer for monitoring film growth through a single window

Three autocollimation-type ellipsometers (ACE) are proposed for in situ study or monitoring of film growth through a single window of a vacuum chamber. An example of the monitoring is given; the growth process of a Corning 7059 glass film is monitored during rf sputtering using one of the ACE that is able to monitor directly the thickness of a transparent film.

Experimental studies of metal film nucleation and growth on amorphous substrates

Experimental studies of metal film nucleation and growth on amorphous substrates

A study of barrier film growth on aluminium in solutions of film-promoting and aggressive ions using secondary ion mass spectrometry☆

A study of barrier film growth on aluminium in solutions of film-promoting and aggressive ions using secondary ion mass spectrometry☆

A study of barrier film growth on aluminium in solutions of film-promoting and aggressive ions using secondary ion mass spectrometry

A Cameca Ion Analyser has been used to examine barrier-type anodic films grown on aluminium in neutral phosphate, chromate or phosphate/chromate solutions and in phosphate and chromate solutions containing relatively small amounts of chloride ion. Barrier layers grow at relatively high current efficiencies in phosphate solution, and are characterized by a rather wide phosphorus-containing layer adjacent to the oxide/solution interface. In chromate solutions, barrier layers grow at relatively low current efficiencies and contain little, if any, chromium resulting from the film growth process itself. Barrier layers grown in chromate-phosphate mixtures are generally typical of those grown in pure phosphate solutions, even at quite high chromate/phosphate concentration ratios. The presence of chloride ions in either phosphate or chromate solutions lowers the current efficiency of barrier film growth, and is associated with pitting of the aluminium substrate at the bases of flaws in the growing film, resulting in lateral undermining of the film. The results are explained in terms of a model for film development, involving growth partly by ionic migration and partly by a dissolution/precipitation process.

Oxidation study of iron by Mössbauer conversion electron and γ-ray scattering

57Fe Mössbauer conversion electron and 14.4 keV γ-ray back-scattering have been applied to study the surface of oxidized iron samples. While γ-ray scattering explores a surface depth of about 10–20 μm, conversion electron spectra are indicative for the state of the Fe ion in the outermost surface layer up to about 3000 Å thick. Several oxide phases, like haematite, magnetite and wüstite, could be identified in the various oxide layers by their Mössbauer parameters. It is shown that the electron scattering technique is sensitive enough to allow a phase analysis and a kinetic study of oxide film growth at 500°C in an early stage, i.e. for oxidation times of the order of minutes, even if natural iron samples are used. Some examples demonstrate that due to the different depth-selectiveness of electron and γ-ray scattering spectra the combination of both techniques can give information about the type of oxide phases which are present in different surface depths.

Kinetic study of silver iodide film growth on silver at low temperatures (30-73° C)

Studies on tarnishing of silver in iodine atmosphere both for thinner (<6000A) and thicker (5500 to 30000A) silver iodide film formation in the temperature and pressure ranges of 30° to 73°C and 0.019 to 1.241 mm Hg, respectively, show the validity of a parabolic growth law. While the rate constant value for the thinner halide film range has been found to be proportional top 1.5 I2 the same for the thicker film growth follows a modified √pI2 relation. These unusual pressure dependences suggest a situation of non-attainment of steady state conditions at the phase boundaries of the films. An activation energy value of 6.3 ± 1.5 kcal mole-1 in the above temperature range atp I2 = 0.039 mm Hg is in accord with that obtained by analyzing others’ data, thereby supporting the hole diffusion controlled process of Wagner. The presence of moisture in the atmosphere has been found to reduce the rate of iodination. Comparison of tarnishing behavior between annealed and cold deformed silver samples demonstrates a reduction in rate of iodination with percentage cold work.

Kinetic Study of Thin Film Growth on Silver in Bromine Vapour at Low Temperatures (35°–70°c)

AbstractThe tarnishing of silver in bromine vapour in the temperature range 35°–70°c, at bromine pressures between 25·3–404 Nm−2 (0·19–3·03 mm Hg)followed a cubic rate law. This has not been reported so far for this system. The mechanism proposed by Mott to account for a cubic growth law seems to apply to the present work. This may be because of the relatively small thickness of the film (≶ 1600A) and the persistence of the electrical field throughout the layer. An activation energy of ∼37·6 kJ mole−1 in the above temperature range supports the hypothesis that the creation of positive holes at the outer interface is the rate-determining factor. The direct proportionality between the rate constant and the partial pressure of the bromine suggests that a steady state condition is not attained at the phase boundaries because of the thinness of the bromide film.