Beginning Of Film Growth Research Articles

One-Step Synthesis of TiO2/SiO2-np Nanocomposite Photocatalytic Multilayer Films: Effect of Incorporation Time Sequences of SiO2 Nanoparticles during the TiO2 Film Growth.

In this article, the TiO2/SiO2-np nanocomposite multilayer films were synthesized in a single step by reactive magnetron sputtering combined with a nanoparticle aerosol jet. The SiO2 nanoparticles (SiO2-np) were introduced into a growing TiO2 thin film with different time sequences during deposition for a fixed duration. The SiO2-np acting as impurities are introduced into the TiO2 to willingly disturb its growth and to cause growth defects in order to increase the specific surface area of the photocatalytic film. In reason of the non-photoactive properties of the SiO2 nanoparticles, their introduction allows us to study only the effects induced on the film morphology, microstructure, and photocatalytic properties by their incorporation. The fractographies and topographies reveal strong changes in the morphologies depending on the time sequence of the nanoparticle introduction in the thin films. The introduction of SiO2-np from the beginning of the TiO2 film growth leads to the formation of high and large growth defects resulting in a highly diffusive surface. In addition, XRD analysis shows that the crystallite size tends to decrease as the composite film layer gets closer to the surface. Their photocatalytic performance is obtained by following the degradation of orange G dye under UV-visible irradiation. The photocatalytic performance is not only related to the specific surface area of the catalyst film, and the coverage of the photoactive phase on the surface, but also to the crystal quality of the photoactive phase. Furthermore, the samples exhibit good photostability, maintaining the same activity after four degradation cycles. In the specific case of TiO2/SiO2-np, it is demonstrated that the introduction of the nanoparticles only at the beginning of the film growth is more efficient than a continuous introduction. This result suggests that this original process allows the use of a relevant strategy for the nanoparticle introduction according to the required functionality.

Deposition of rutile TiO2 films by pulsed and high power pulsed magnetron sputtering

Abstract Thin films of titanium dioxide (TiO2) are important high refractive index coatings in optical multilayer stacks. Especially interesting is the rutile crystalline phase of TiO2 films because it's refractive index in the range of 2.6…2.7 is the highest available refractive index of materials being transparent in the visible and near infrared wavelength region. Rutile TiO2 films in optical interference coatings therefore in principle allow achieving the desired optical function with a lower number of layers and a simpler design compared to alternative high index materials. However the crystalline growth of TiO2 layers usually starts with an amorphous start layer of typically 40 nm thickness before going over to an anatase or rutile crystalline structure. The amorphous start layer typically has a refractive index in the range of 2.4…2.5. This significant difference to the index of the rutile film leads to a typical gradient in the refractive index of TiO2 single layers and makes application of TiO2 films in precision optics practically difficult. The paper explores the possibilities of obtaining rutile TiO2 films right from the beginning of film growth by significantly increasing energetic ion bombardment of the growing film and adatom mobility. The influence of a variety of process parameters such as substrate temperature, deposition pressure, magnetic field strength and RF bias is investigated. The main focus of investigations was the comparison of a standard pulse process, a pulsed process with significantly increased pulse current and a pulse process in genuine high power pulsed (HiPIMS) mode. Film deposition was done by stationary sputtering using the double ring magnetron (DRM). Film characterization was carried out by XRD as well as by spectroscopic ellipsometry and photometry. Total optical losses were characterized by cavity-ring-down spectroscopy (CRD) and absorption was measured by laser induced deflection. Results show that in a rather narrow range of process parameters the desired crystalline growth of TiO2 with the rutile phase throughout the film can be obtained. This parameter set includes both the pulsed process with significantly increased pulse current and the genuine HiPIMS mode, but in all cases requires a combination with substrate heating, RF substrate bias and adapted process pressure. A significant reduction of crystallite size and scattering losses was achieved by adding a small amount of silicon dioxide (SiO2) to the film.

Structural evolution of magnetron sputtered shape memory alloy Ni–Ti films

Near equiatomic and Ti-rich Ni–Ti polycrystalline films have been deposited by magnetron co-sputtering using a chamber installed at a synchrotron radiation beamline. The in situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during film processing. The depositions on a 140 nm amorphous SiO 2 buffer layer heated at 520 °C (without applying bias voltage, V b , to the substrate) led to a preferential growth of <100> oriented grains of the Ni–Ti B2 phase from the beginning of film growth until the end of the deposition. Films exhibiting a preferential growth of <110> oriented grains of the Ni–Ti B2 phase from the beginning of the deposition were obtained (without and with a V b of −45 V) by using a TiN coating with a topmost layer formed by <111> oriented grains. Those trends have been observed for the growth of near equiatomic (≈50.0 at.% Ti–Ni) and Ti-rich (≈50.8 at.% Ti–Ni) Ni–Ti films. Additionally, an ion gun had been commissioned, which allows ion bombardment during sputter deposition or post-deposition ion irradiation. In this first series of experiments, a Ni–Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e., avoiding surface oxide formation), thus modifying deliberately the microstructure of the film locally.

Layer-by-layer films from tartrazine dye with bovine serum albumin

We report on the preparation and study of the adsorption process of layer-by-layer films of tartrazine alternated with bovine serum albumin. UV–Vis spectroscopy indicated that the films form J-aggregates of tartrazine. Adsorption kinetics was fitted by the Johnson–Mehl–Avrami equation and surface morphological analyses by atomic force microscopy suggested that the J-aggregates were column-shaped, which was attributed to the column-like symmetry of the tartrazine molecules. The columnar structures that formed probably arose from the juxtaposition of smaller aggregates that were already present at the beginning of film growth.

Growth and electrical conductivity of Gd2O3 doped CeO2 ion conductor electrolyte film on sapphire substrate

Nanocrystalline Gd2O3 doped CeO2 (abbreviated as GDC) ion conductor electrolyte thin films synthesized by reactive magnetron sputtering on (0001) sapphire substrates have been characterized by X-ray diffraction (XRD)，atomic force microscopy (AFM) and AC impedance analysis. The results show that，the f.c.c structured GDC films have strong (111) textures at all the substrate temperatures of our investigation while the surface morphology varied with the temperature. Small, round growth islands transform to large prismatic islands at temperatures from room temperature to 300℃, and the reverse process occurr at temperatures from 400℃ to 700℃. This morphology change characterizing different nucleation mechanisms at the beginning of film growth is probably due to transformation of the surface structure of the (0001) sapphire at different temperatures. The AC impedance complex plane plot of the GDC film is mainly determined by grain boundary resistances. The conductivity activation energy (1.2—1.5eV) calculated by the Arrhenius plot is close to the reported value for the grain boundary conductivity and decreases with rising substrate temperature (Ea300Ea400Ea600). Difference in activation energy and grain size for GDC films causes unequal increasing rates of electrical conductivity at higher temperatures.

SiNx barrier layers deposited at 250°C on a clear polymer substrate

ABSTRACTInterest is widespread in flexible thin-film transistor backplanes made on clear polymer foil, which could be universally employed for a variety of applications. All ultralow process temperatures, plastic compatible thin film transistor (TFT) technologies battle short or long term device instabilities. The quality and stability of amorphous silicon thin-film transistors (a-Si:H TFTs) improves with increasing process temperature. TFT stacks deposited at less than 250°C by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) exhibit higher threshold voltage shifts after gate bias stressing than stacks deposited at ∼300°C in the active matrix liquid-crystal display (AMLCD) industry [1]. Therefore, optically clear plastic (CP) substrates are desired that tolerate high process temperatures. The first step in a-Si:H TFT fabrication on a polymer is the deposition of a planarizing barrier and adhesion layer. For this purpose we have been using silicon nitride (SiNx) grown by PECVD.This paper discusses the substrate preparation and SiNx deposition for the process temperature of 250°C. We study the mechanical strain in the SiNx film on the CP substrate, as a function of RF power. Earlier work has shown that SiNx films deposited at low RF power are under tensile strain, and become increasingly compressed as the deposition power is raised [2]. Additionally, at very high deposition power the substrate is bombarded at the beginning of film growth to achieve good film adhesion. The goal is to identify the correct processing conditions at which the total mismatch strain between the film and the substrate is minimized, to keep the film/substrate composite flat and avoid mechanical fracture as well as peeling due to poor adhesion. Optimal deposition conditions were identified to obtain crack-free SiNx barrier layers. The barrier layers were tested by fabricating a-Si:H TFTs on them at 250°C.

アルミニウムの塗膜密着性に及ぼす水和酸化処理方法の影響

In order to clarify the suitability of aluminum with hydrated oxide film as a base material for painting, the strength of adhesion of epoxy-phenolic resin to aluminum hydrated using several kinds of baths was evaluated by measurement of the peeling strength, and the mechanism of adhesion for each type of treatment was observed by SEM and ESCA.(1) In every method of treatment, resin adhesion rose in the initial induction stage (a), dropped extremely for a time at the beginning of film growth (b), and then rose again depending on the time of treatment (c). The mechanisms were considered to be as follows:(a) The increase in specific surface area depending on the formation of lumps, (b) The decrease in the adhesion of the lumps to the aluminum base depending on the formation of needle-like or petal-like hydrated oxide film, (c) The increase of specific area depending on the growth of petal-like hydrated oxide film having good adhesion to the aluminum base.(2) The films that were treated in waterglass solution after hydration promoted in sodium hypochlorite solution showed better resin adhesion than did films without waterglass treatment. We considered the cause of the increased resin adhesion to be secondary improvement of the surface of the aluminum base depending on the formation of SiO2-film.