Substrate For Film Deposition Research Articles

Influence of substrate stress on in-plane and out-of-plane ferroelectric properties of PZT films

Solution-deposited ferroelectric films often are under mechanical stress due to the difference in thermal expansion coefficients between films and substrate materials. Knowledge of how stress changes the ferroelectric response under different actuation conditions is essential when selecting a substrate for film deposition. Here, a comparative study of the ferroelectric properties of lead zirconate titanate thin films on transparent fused silica glass and sapphire substrates is presented. Sapphire exerts a compressive in-plane stress on the film, favoring an out-of-plane domain orientation, while fused silica causes tensile in-plane stress and a predominantly in-plane domain configuration. As expected, the out-of-plane polarization is high under in-plane compressive stress but reduced by a factor of nearly 4 by in-plane tensile stress. In contrast, the in-plane polarization shows an unexpectedly weak stress dependence. It is larger by only about 10% under tensile stress compared to compressive stress. Permittivity increases when the major domain orientation does not coincide with the electric field. The observations are explained based on a model taking into account the crystallographic structure of the film.

Characterization of N, F Co-Doped Mixed-Anion TiO2 Thin Films Prepared By Reactive Pulsed Laser Deposition for Visible-Light Responsive Photocatalyst

Introduction The study of water splitting by photocatalyst as the method of directly producing hydrogen from water has been reported in 1972, well-known as “Honda-Fuzishima effect”. Conventional TiO2 material can produce hydrogen under only ultraviolet light and the its production rate is still low. In order to use TiO2 under visible light, the anion doping is one of the effective solution. In this study, photocatalytic N, F-doped TiO2 thin film was synthesized by the responsible pulsed laser deposition(PLD) technique. Nitridation and fluoridation of TiO2 were simultaneously conducted with PLD under O2/N2/NF3 gas. Experimental TiO2 thin film was prepared by pulsed laser deposition (PLD). A Nd:YAG laser operating at a wavelength of 532 nm was focused on a sintered TiO2 target. We used a chamber which can be evacuated to a base pressure of 5.0 x 10-4 Pa by means of a turbo-molecular pump. When depositing TiO2 thin film, the total pressure of the mixed gas was fixed to 5 Pa. FTO (Fluorine doped tin oxide) was used as the glass substrate for film deposition. The substrate temperature was changed from room temperature to 400℃. The target (φ10) was produced by sintering the Rutile TiO2 powder at 1000℃ for 12h in air. Structural analysis of TiO2 is carried out by XRD (X-ray diffiraction) and XAFS (X-ray Absorption Spectroscopy). Especially, the product identification was observed by XRD with parallel beam method at SPring-8 BL02B2. An incident angle of X-ray is 0.1o and wavelength of X-ray is 0.7Å. Measurement of the absorption edge of Ti K was carried out by XAFS with electron yield method. In addition, for defining of the flatband level and bandgap carried out by UV-vis and AC impedance measurement. Photoelectrochemical measurements were conducted in an aqueous Na2SO4 solution (0.1 M, pH=9) using a potentiostat (Hokuto Denko HSV-110) connected to the photocatalyst-deposited FTO glass as a working electrode an Ag/AgCl reference electrode (in saturated KCl aqueous solution), and Pt wire as a counter electrode. The solution was purged with Ar gas for 30 min. To measure photocurrent responses, intermittent visible light (420 < λ < 800 nm) was applied to the working electrode with a Xe lamp (300 W, output current: 20 A). Result & Discussion Fig. 1 shows that XRD results under various gas atmosphere. In the case of under the O2 atmosphere, Anatase/Rutile TiO2 composition was observed. Under the N2 atmosphere, TiN was observed and under the NF3 atmosphere, Anatase TiO2 was observed. Under the N2 and N2/NF3 atmosphere, FTO substrate was decomposed. Under the O2/N2/NF3 atmosphere, the decomposition of the substrate was suppressed while the compounds derived from Ti couldn’t be observed. These results indicated that O2 gas was necessary for depositing TiO2 by suppressing of substrate as well as supplementation of the oxygen defects. Fig. 2 shows that the visible light response as a function of the photocurrent and voltage. By switching Xe lamp on/off per 3 second, the increase and decrease of current density was observed over 0.4 µA cm-2. The photocurrent response under visible light was observed for the atmosphere of O2/N2/NF3 and O2/N2 while that of O2/NF3 was not. In addition, the photocurrent was larger for the materials prepared under O2/N2/NF3 than O2/N2. UV-vis diffuse reflectance spectrum indicated that N, F-doped TiO2 showed a wide absorption band in visible region in contrast to a narrow one of N-doped TiO2. This extended absorption band of N, F-doped TiO2 in the visible region allowed the materials to improve the efficiency of the catalytic reactions such as water oxidation. Conclusion It is necessary that O2 gas to suppress substrate decomposition and compensate oxygen defect. PLD performed under O2/N2/NF3 mixed gas could successfully incorporated N3- and F- into TiO2 matrix. The visible light response of co-doping of N3- and F- was better than N3- single doping. It was subjected to the UV-vis measurement, the N3-, F- co-doped TiO2 thin film has wide absorption band of a visible light, which was considered to have led to a visible light absorption. Reference 1) A. Nakada et al., J.Mater. Chem. A, 2017, 5, 11710-11719. 2) K. Maeda et al., J. Phys. Chem. C, 2007, 111 (49), 18264–18270. Figure 1

Biocompatible Nanocoatings of Fluorinated Polyphosphazenes through Aqueous Assembly.

Nonionic fluorinated polyphosphazenes, such as poly[bis(trifluoroethoxy)phosphazene] (PTFEP), display superb biocompatibility, yet their deposition to surfaces has been limited to solution casting from organic solvents or thermal molding. Herein, hydrophobic coatings of fluorinated polyphosphazenes are demonstrated through controlled deposition of ionic fluorinated polyphosphazenes (iFPs) from aqueous solutions using the layer-by-layer (LbL) technique. Specifically, the assemblies included poly[(carboxylatophenoxy)(trifluoroethoxy)phosphazenes] with varied content of fluorine atoms as iFPs (or poly[bis(carboxyphenoxy)phosphazene] (PCPP) as a control nonfluorinated polyphosphazene) and a variety of polycations. Hydrophobic interactions largely contributed to the formation of LbL films of iFPs with polycations, leading to linear growth and extremely low water uptake. Hydrophobicity-enhanced ionic pairing within iFP/BPEI assemblies gave rise to large-amplitude oscillations in surface wettability as a function of capping layer, which were the largest for the most fluorinated iFP, while control PCPP/polycation systems remained hydrophilic regardless of the film top layer. Neutron reflectometry (NR) studies indicated superior layering and persistence of such layering in salt solution for iFP/BPEI films as compared to control PCPP/polycation systems. Hydrophobicity of iFP-capped LbL coatings could be further enhanced by using a highly porous polyester surgical felt rather than planar substrates for film deposition. Importantly, iFP/polycation coatings displayed biocompatibility which was similar to or superior to that of solution-cast coatings of a clinically validated material (PTFEP), as demonstrated by the hemolysis of the whole blood and protein adsorption studies.

Wet-cleaning of MgO(001): Modification of surface chemistry and effects on thin film growth investigated by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy

The effect of the wet-cleaning process using solvents and detergent on the surface chemistry of MgO(001) substrate for film deposition was investigated. Six different wet-cleaning processes using solvent and detergent were compared. The effect on film growth was studied by the example system ScN. The surface chemistry of the cleaned surface was studied by x-ray photoelectron spectroscopy and the film/substrate interface after film growth was investigated by time-of-flight secondary ion mass spectroscopy. The surface composition is dependent on the wet-cleaning process. Sonication in a detergent before the solvents yield a pure oxide surface compared to hydroxide/carbonate contaminated surface for all the other processes. An annealing step is efficient for the removal of carbon contamination as well as most of the hydroxide or carbonates. The study of the film/substrate interface revealed that the wet-cleaning process significantly affects the final interface and film quality. The substrate cleaned with detergent followed by solvent cleaning exhibited the cleanest surface of the substrate before annealing, after annealing, in addition to the sharpest film/substrate interface.

Effects of Sn and Zn Seed Layers on the Electrical Characteristics of Pd/ZnO Thin-Film Schottky Diodes Grown on n-Si Substrates

The effects of Sn and Zn seed layers on the rectifying characteristics of Pd/ZnO thin-film Schottky diodes fabricated on n-Si substrates by the thermal evaporation method have been investigated in this letter. The field emission scanning electron microscopy images show the changes in the surface morphology of the ZnO thin film from nanocrystalline to nanoparticle, and nanocrystalline to nanowires structures when the substrates for film deposition are changed from the bare n-Si to Sn seed layer-coated n-Si and from bare n-Si to Zn seed layer-coated n-Si substrates, respectively. Furthermore, a dramatic enhancement in the rectification ratio of Pd/ZnO Schottky diodes is observed from a nominal value of 1.13 × 10 2 at ±2 V (for the device grown on the bare n-Si substrates) to a large value of 8.85 × 10 2 for the device grown on Sn seed layer coated n-Si substrates and to a value of 7.564 × 10 3 for the Zn seed layer coated device. The effects of the seed layers on the series resistance, ideality factor, and barrier height of the Pd/ZnO thin-film Schottky devices are also investigated for the first time in this letter.

Bifunctional electroactive nanostructured membranes

The advent of techniques based upon the spontaneous assembly of different materials with control over molecular architecture has afforded the fabrication of composite thin films for many nanotechnological applications. The layer-by-layer technique (LbL), in particular, has largely been used in the molecular level processing of nanohybrid systems in the form of multilayers, owing to its low cost and experimental simplicity. In this study we describe the fabrication of a novel, bifunctional film containing platinum nanoparticles/polyamidoamine (PAMAM) dendrimers. Pt nanoparticles were chemically synthesized/stabilized in the presence of PAMAM dendrimers and incorporated in LbL films in conjunction with nickel tetrasulfonated phthalocyanine (NiTsPc). A metallophthalocyanine was chosen because of its well-defined redox activity. Indium tin oxide (ITO)-covered glass plates were used as substrates for film deposition. The nanocomposites displayed high electrocatalytic activity toward dopamine and hydrogen peroxide molecules, two compounds with dissimilar chemical properties.

Growth of Pyrochlore Bi2Ti2O7 Epitaxial Films and Their Electrical Characterization

Epitaxial growth condition of Bi2Ti2O7 films on the substrates having rutile-structure was investigated. TiO2 single crystals and the conductive epitaxial IrO2layers having same rutile-structure were used as substrates for film deposition. Strongly (111)-oriented Bi2Ti2O7 films were confirmed to be deposited on (110) TiO2 substrates by XRD θ-2θ scans, but obvious orientations were not detected on (100), (001) and (110) TiO2 substrates. The epitaxial growths of Bi2Ti2O7 films were confirmed on (100), (001) and (110) TiO2 substrates, where two variants were observed on (100) and (110) TiO2 substrates. The epitaxial relationships were confirmed as follows; (14 14 19)Bi2Ti2O7//(100)TiO2, (112)Bi2Ti2O7//(101)TiO2, and (111)Bi2Ti2O7//(110)TiO2. Same epitaxial growth was confirmed only on (110)IrO2//(110)TiO2 substrate, but not on (101)IrO2//(012)Al2O3 and (100)IrO2//(100)TiO2 substrates. The dielectric constant and loss tangent at 1 kHz were 130 and 2%, respectively for the 130 nm-thick epitaxial Bi2Ti2O7 film grown on (110)IrO2//(110)TiO2 substrate.

Measurement of the permeability of thin films

A system has been developed to directly measure the flow of inert gases through an arbitrary thin film. The system employs a porous aluminum silicate ceramic as the substrate for film deposition, a flow control apparatus to hold the substrate under vacuum and allow a helium gas pressure differential to be established across the substrate, and a helium leak detector to measure the flow of helium through the substrate/film combination. This allows calculation of the permeability of the film. The permeability of plasma enhanced chemical vapor deposited diamondlike carbon films and sputter deposited silicon nitride, and nickel films were measured. A thermally grown silicon dioxide film was also tested.

Monte Carlo simulations of plume evolution from laser ablation of graphite and barium titanate

Evolution of laser ablation products from graphite and barium titanate targets has been simulated using a Monte Carlo method, assuming elastic collisions. The calculated species arrival times and intensities, at a hypothetical detection plane, compare favorably with those obtained experimentally by time-resolved mass spectrometric sampling of the expanded vapor plumes. As such experiments are difficult to perform, the simulation method should prove useful for unstudied systems in defining the spatial and temporal distributions of species arriving for example, at a film deposition substrate.

The preparation of substrates for film deposition using glow discharge techniques

The preparation of substrates for film deposition using glow discharge techniques

The preparation of substrates for film deposition using glow discharge techniques

Substrates for film deposition can be cleaned and/or modified in a variety of ways by various sputtering techniques, but this can be done controllably only by careful attention to all of the possible effects that can occur. In this review the known effects are summarised. Some of the system configurations that can be used are described. The physical and chemical sputtering effects are emphasised. These include rates of material removal and recontamination, backscattering, redeposition, trenching, faceting, cone formation, formation of altered surface layers, dissociation of compounds, diffusion, sublimation, ion implantation, crystallographic damage and radiation damage.

Ultrahigh vacuum low temperature stage for i n s i t u film deposition and characterization

An apparatus which combines a liquid 4He Dewar with an ultrahigh vacuum system used for LEED or AES surface analysis and ultrathin film deposition is described. A linear motion bellows seal allows the substrate for film deposition to be moved out of the radition shields, which makes ion bombardment cleaning possible. A He gas heat exchanger between the substrate holder and He reservoir provides a wide variation of temperatures. In situ measurements of superconducting transition temperatures below 2 K have been made with this apparatus.