Electron microscopy studies of plasma-polymerized organosilicon thin films

Plasma-polymerized thin films of hexamethylcyclotrisilazane were pyrolysed in vacuum and studied by transmission electron microscopy. Examination of the polymer film after various durations of pyrolysis revealed significant changes in their surface structure and a distinct difference in the thermal stability powder and film phases. The number of powder particles in the surface layer and their size increased with pyrolysis time. The observations showed that powder particles embedded in the film matrix were gradually exposed in the surface layer owing to a decrease in the film thickness during pyrolysis. Good agreement was obtained between the experimental and theoretical distribution curves of particle size. The identical properties of powder particles exposed in the surface of the pyrolysed film and those taken from the interelectrode region indicates that they are primarily formed in the gas phase.     

Pyrosol deposition of fluorine-doped tin dioxide thin films

Fluorine-doped tin dioxide (SnO₂F) films were deposited from a tin tetrachloride solution in methanol utilizing a pyrosol deposition process. It is shown from thermodynamic calculations that the atmosphere during deposition is oxygen-rich and also suggested that chlorine and hydrogen chloride, which are produced during the deposition reaction, influence crystal growth. Detailed electrical, optical and structural properties of the material with respect to varying film thickness and substrate temperature are presented and discussed. Resistivity of the films deposited at 450 °C decreased from 6×10^–4 to 2×10^–4 cm, while the mobility increased from 14 to 45 cm²V^–1s^–1, respectively, when the film thickness was varied from 100 to 1650 nm. The carrier concentration was relatively unchanged for film thicknesses higher than 200 nm. Optimized SnO₂F films (600 nm) having a resistivity of 6×10^–4 cm, a carrier mobility of 20 cm²V^–1s^–1, a carrier concentration of 8×10²⁰ cm^–3 and a transmittance in excess of 80% are quite suitable as electrodes for amorphous silicon solar cells.     

Synthesis and characterization of ferromagnetic cobalt-doped tin dioxide thin films

Co-doped SnO₂ thin films are grown on sapphire (0001) substrates at 600 °C by the technique of dual-beam pulsed laser deposition. The prepared films show preferred orientation in the [100] direction of the rutile structure of SnO₂. Nonequilibrium film growth process results in doping Co into SnO₂ much above the thermal equilibrium limit. A Film with 3% of Co is ferromagnetic at room temperature with a remanent magnetization of ∼ 26% and a coercivity of ∼ 9.0 mT. As Co doping content x increases, the optical band gap absorption edge (E₀) of the Co-doped SnO₂ thin films initially shows a redshift at low x up to x = 0.12 and then increases at the higher x, which are attributed to the sp-d exchange interactions and alloying effects, respectively.     

Dopant effects in sprayed tin oxide films

The effects of donor impurities such as antimony, fluorine and antimony plus fluorine on the structural, electrical and optical properties of tin oxide films prepared by spray pyrolysis have been studied. The dopant concentration in the films, as determined by Auger analysis, is less than that in the solution. The mobility of free carriers in doped tin oxide films is found to depend on the nature and the concentration of the dopant. Fluorine doping of tin oxide films results in the highest conductivity and the highest optical transmission in the visible region.     

Electron back-scattered diffraction of crystallized vanadium dioxide thin films on amorphous silicon dioxide

Crystalline films and isolated particles of vanadium dioxide (VO₂) were obtained through solid phase crystallization of amorphous vanadium oxide thin films sputtered on silicon dioxide. Electron back-scattered diffraction (EBSD) was used to study the crystals obtained in the thin films, to differentiate them from different vanadium oxide stoichiometries that may have formed during the annealing process, and to study their phase and orientation. EBSD showed that the crystallization process yielded crystalline vanadium dioxide thin films, semi-continuous thin films, and films of isolated particles, and did not show evidence of other vanadium oxide stoichiometries present. Indexing of the crystals for the orientation study was performed using EBSD patterns for the tetragonal phase of vanadium dioxide, since it was observed that EBSD patterns for the monoclinic and tetragonal phases of vanadium dioxide are not distinguishable by computer automated indexing. Using the EBSD patterns for the tetragonal phase of vanadium dioxide, orientation maps showed that all VO₂ crystals that were measurable (approximately the thickness of the film) had a preferred orientation with the c-axis of the tetragonal phase parallel to the plane of the specimen.     

Peculiarities of nitrogen dioxide detection with sprayed undoped and indium-doped zinc oxide thin films

Nitrogen dioxide (NO₂) sensors based on sprayed zinc oxide (ZnO) thin films have been prepared. The effect of the film thickness and the In-doping on the sensor performance (sensor response and resistance) is analyzed. By adding 3 wt.% of indium nitrate to the spraying solution it is possible to enhance the film-gas response to 5 ppm of NO₂ at 275 °C. At the same time the film resistance is sensibly reduced. The film crystallographic structure, morphology and additive content are studied by means of X-ray Diffraction, Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy and Atomic Force Microscopy. The possible sensitization mechanism is discussed.     

Effect of solvent ratio on the properties of highly oriented sprayed fluorine-doped tin oxide thin films

Transparent conducting thin films of F:SnO₂ have been deposited onto preheated glass substrates by a spray pyrolysis technique using pentahydrate stannic chloride (SnCl₄·5H₂O) and ammonium fluoride (NH₄F) as precursors and mixture of water and propane-2-ol as solvent. The concentration of SnCl₄·5H₂O and NH₄F is kept fixed and the ratio of water and propane-2-ol solvent in the spraying solution is varied. A fine spray of the source solution using air as a carrier gas has grown films of thickness up to 995 nm. Optical absorption, X-ray diffraction, Van der Pauw technique for measurement of a sheet resistance and Hall effect measurements at room temperature for determination of carrier density and conductivity have been used. The as-deposited films are of polycrystalline SnO₂ with a tetragonal crystal structure and are preferentially having orientation along the (200) direction with texture coefficient as high as 6.16. The average grain size for the as-deposited sample is found to be of the order of 44 nm. The films have moderate optical transmission (up to 70–85% at 550 nm). The figure of merit (ϕ) values vary from 1.95 · 10^− 3 to 35.68 · 10^− 3 Ω^− 1. The films are heavily doped, degenerate and exhibit n-type electrical conductivity. The lowest sheet resistance (R_s) for the optimized sample is 5.1 Ω. The films have a resistivity of 5.43 · 10^− 4 Ω cm and mobility around 7.38 cm² V^− 1 s^− 1.     

Electron and Atomic Force Microscopy studies of photocatalytic titanium dioxide thin films deposited by DC magnetron sputtering

Titanium dioxide thin films were deposited on glass substrates and on fluorine doped tin oxides at room temperature by DC magnetron sputtering at different working gas pressures and were evaluated using photocatalytic degradation of an organic compound. The structural properties of the films were studied by electron microscopy techniques and Atomic Force Microscopy. Numerous structural defects were detected for samples deposited at 16 mTorr and it was associated with the highest photo-degradation rate. Also small band gap shift in titanium dioxide films was detected for different gas pressures. These behaviors are related with structural details derived from the synthesis conditions and the influence of structural defects on the photocatalytic activity is discussed.     

XRD and SEM studies of reactively deposited tin oxide thin films

Stoichiometric polycrystalline tin oxide thin films were deposited by the reactive evaporation of tin and the SnO₂ formation was found to be strongly dependent on the deposition parameters. The preferred orientation of the SnO₂ films deposited on different substrates was varying due to the dislocation defects arising during the thin film formation. The X-ray diffraction (XRD) studies identified a tetragonal structure while the scanning electron microscopic (SEM) studies revealed a polycrystalline surface for the SnO₂ films reactively deposited.     

Microstructure of vacuum-deposited tin thin films

Tin thin films of equal thickness were vacuum deposited on NaCl substrates at different deposition rates both in high vacuum (2×10^–5 Torr) and poor vacuum (1×10^–3 Torr). These films were examined by electron microscopy and the grain size and density in the films were determined. It was found that both in poor and high vacuum, as the deposition rate was increased the grain size decreased and grain density increased. However, the deposition rate must be increased by an order of magnitude in order to observe large changes in the grain size and density. It was also observed that the films prepared in poor vacuum, especially at low deposition rates, consist of islands with jagged edges. These observations have been interpreted on the basis of nucleation theory and the effect of adsorbed/chemisorbed gases on island growth in these films.     

Nano-particle thin films of tin oxides

Nano-particle thin films of tin oxides were deposited on SiO₂ substrates by using radio frequency (RF) magnetron sputtering with various substrate temperatures, sputtering powers and oxygen partial pressures. The tin oxides thin films were then investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). XPS data suggested that the deposited tin oxides thin films are almost made up of half of SnO₂ and half of SnO. The oxygen partial pressure nearly does not affect the chemical stoichiometry of the thin films in our deposition conditions. SEM results showed that the tin oxides thin films were formed by nano-particles with size of about 60 nm. Sputtering power has a strong influence on the particle size of the thin films. Increase of sputtering power will enlarge the size of the particles.     

Scanning probe microscopy studies of isocyanide functionalized polyaniline thin films

The technique of scanning probe microscopy was used to study the nanometer-scale morphological changes in isocyanide functionalized polyaniline films due to protonation in aqueous HCl, as well as exposure to Ir⁺ cations in CH₂Cl₂ solution. Electropolymerized isocyanide functionalized aniline films exhibited a highly oriented fibrous structure, with individual strands averaging 25 Å in diameter. Upon protonation, the fibrous structure was lost, with the material reorganizing into oriented, elongated bundles of average diameter 200 Å. Ir⁺ exposed unprotonated films exhibited an oriented, interlocking bundle structure, resulting from Ir⁺ incorporation into the film matrix. The diameter of these bundles averaged 400 Å.     

Electron microscopy of geometrically confined copper thin films after rapid lateral solidification

We have used transmission electron microscopy and scanning electron microscopy to study the microstructure in polycrystalline 200 nm thick copper thin films that are geometrically confined between transparent amorphous silicon oxide layers after single pulse laser melting and rapid lateral solidification (RLS). The microstructure consisted predominantly of directionally solidified grains with an in-plane columnar structure and dimensions of up to 22 μm long and about 1 μm wide. A <100> preferred orientation in the vicinity of the average growth direction in the thin film plane has been identified for these high aspect ratio columnar grains produced by RLS in this Cu thin film12.     

Electron microscopy reveals structure and morphology of one molecule thin organic films

Transmission electron microscopy was used to determine the structure of molecular films of self-assembled monolayers of pentathiophene derivatives supported on various electron transparent substrates. Despite the extreme beam sensitivity of the monolayers, structural crystallographic maps were obtained that revealed the nanoscale structure of the film. The image resolution is determined by the minimum beam diameter that the radiation hardness of the monolayer can support, which in our case is about 90 nm for a beam current of 5 × 10(6) e(-)/s. Electron diffraction patterns were collected while scanning a parallel electron beam over the film. These maps contain uncompromised information of the size, symmetry and orientation of the unit cell, orientation and structure of the domains, degree of crystallinity, and their variation on the micrometer scale, which are crucial to understand the electrical transport properties of the organic films. This information allowed us to track small changes in the unit cell size driven by the chemical modification of the support film.     

Sputter deposition of semicrystalline tin dioxide films

Tin dioxide is emerging as an important material for use in copper indium gallium diselenide based solar cells. Amorphous tin dioxide may be used as a glass overlayer for covering the entire device and protecting it against water permeation. Tin dioxide is also a viable semiconductor candidate to replace the wide band gap zinc oxide window layer to improve the long-term device reliability. The film properties required by these two applications are different. Amorphous films have superior water permeation resistance while polycrystalline films generally have better charge carrier transport properties. Thus, it is important to understand how to tune the structure of tin dioxide films between amorphous and polycrystalline. Using X-ray diffraction (XRD) and Hall-effect measurements, we have studied the structure and electrical properties of tin dioxide films deposited by magnetron sputtering as a function of deposition temperature, sputtering power, feed gas composition and film thickness. Films deposited at room temperature are semicrystalline with nanometer size SnO₂ crystals embedded in an amorphous matrix. Film crystallinity increases with deposition temperature. When the films are crystalline, the X-ray diffraction intensity pattern is different than that of the powder diffraction pattern indicating that the films are textured with (101) and (211) directions oriented parallel to the surface normal. This texturing is observed on a variety of substrates including soda-lime glass (SLG), Mo-coated soda-lime glass and (100) silicon. Addition of oxygen to the sputtering gas, argon, increases the crystallinity and changes the orientation of the tin dioxide grains: (110) XRD intensity increases relative to the (101) and (211) diffraction peaks and this effect is observed both on Mo-coated SLG and (100) silicon wafers. Films with resistivities ranging between 8 mΩ cm and 800 mΩ cm could be deposited. The films are n-type with carrier concentrations in the 3 × 10¹⁸ cm^− 3 to 3 × 10²⁰ cm^− 3 range. Carrier concentration decreases when the oxygen concentration in the feed gas is above 5%. Electron mobilities range from 1 to 7 cm²/V s and increase with increasing film thickness, oxygen addition to the feed gas and film crystallinity. Electron mobilities in the 1-3 cm²/V s range can be obtained even in semicrystalline films. Initial deposition rates range from 4 nm/min at low sputtering power to 11 nm/min at higher powers. However, deposition rate decreases with deposition time by as much as 30%.     

Thickness-dependent properties of sprayed iridium oxide thin films

Iridium oxide thin films with variable thickness were deposited by spray pyrolysis technique (SPT), onto the amorphous glass substrates kept at 350 °C. The volume of iridium chloride solution was varied to obtain iridium oxide thin films with thickness ranging from 700 to 2250 Å. The effect of film thickness on structural and electrical properties was studied. The X-ray diffraction (XRD) studies revealed that the as-deposited samples were amorphous and those annealed at 600 °C for 3 h in milieu of air were polycrystalline IrO₂. The crystallinity of Ir-oxide films ameliorate with film thickness thereby preferred orientation along (1 1 0) remains unchanged. The infrared spectroscopic results show Ir–O and Ir–O₂ bands. The room temperature electrical resistivity (ρ_RT) of these films decreases with increase in film thickness. The p-type semiconductor to metallic transition was observed at 600 °C.     

The optical properties of sprayed CdS thin films

In the study presented in this paper we attempted to interpret the reflectance and the transmittance of sprayed CdS films. Assuming a model based on multilayer film theory we showed that sprayed CdS film is a combination of multilayer stacks of crystallites and gaseous inclusions.