Effect of plasma carrier gas on the moisture barrier properties of plasma-enhanced chemical vapor deposited (PECVD) polyorganosiloxane thin film

Abstract

A polyorganosiloxane thin film was deposited on an optically transparent poly(ethylene 2,6-naphthalate) (PEN) film using plasma-enhanced chemical vapor deposition (PECVD) at room temperature to improve the moisture barrier property of the PEN film. In the PECVD process, hexamethyldisiloxane (HMDSO) was used as the monomer. Argon or oxygen and their mixture gases were used as the plasma carrier gas. Poly(HMDSO) thin film was successfully deposited through plasma-induced radical polymerization reaction on the surface of PEN film. It was observed that the mixture ratio of argon-oxygen carrier gas significantly affected the surface and the moisture barrier properties of the resulting poly(HMDSO) film. Chemical structures of the poly(HMDSO) were confirmed using FT-IR analysis. Surface properties of the poly(HMDSO) thin film were investigated by water contact angle measurement and atomic force microscopy (AFM). Water vapor transmission rate (WVTR) value was obtained by an electrical calcium test (Ca test) at 85?°C and 85% relative humidity condition. It was confirmed that the poly(HMDSO) thin film exhibited excellent water vapor barrier capability. WVTR value of the PEN film coated with poly(HMDSO) deposited with a mixture of argon and oxygen (Ar: O₂ = 2: 8) was 5.09?g/m²-day, which is much lower than 18.4?g/m²-day of a bare PEN film.     

Quantification of Polymer Fouling on Heat Transfer Surfaces During Synthesis

During the synthesis and processing of polymers, a significant amount of polymer may be deposited on the heat transfer surfaces. This deposit is unwanted and is usually named fouling. This study deals with the fouling behavior of a vinyl acetate/vinyl ester copolymer during emulsion polymerization and compares this to fouling of an already reacted vinyl acetate/ethylene copolymer dispersion. Besides the state of polymerization, also the influence of the wall temperature is investigated. The experiments are performed on cooled and heated surfaces. The deposition process is quantified by the mass‐based fouling resistance, the height of the fouling layer, and the surface coverage using a digital microscope. It is found that the state of polymerization and the temperature gradient between wall and bulk exert a strong influence on the fouling behavior, especially on the structure of the fouling layer.     

Effect of iron doping on the hydrophobicity of titanium dioxide film: experiment and simulation

In this study, we carried out experiments and molecular dynamics simulations to identify the effect of Fe doping on the hydrophobicity of a titanium dioxide film. TiO₂ and Fe-doped TiO₂ films were fabricated in situ by atomic layer deposition without annealing. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterise the crystal structure and elemental composition. Iron doping resulted in the TiO₂ becoming more hydrophobic at a macroscopic level, as estimated by atomic force microscopy observations and static contact angle measurements. Furthermore, the effect of iron doping on the structure and kinetics of water molecules on the exterior of TiO₂ were studied by molecular dynamics simulations. On the basis of the XPS results, the Fe-TiO₂ surface matrix has a Ti:Fe ratio of 36:5. In addition, the density distribution of oxygen and hydrogen atoms indicate that interfacial water molecules enter the Fe-TiO₂ film more easily and hydrogen atoms in the water molecules are oriented upward at the interface. The self-diffusion coefficients indicate that iron doping makes the TiO₂ more hydrophobic, which is consistent with the macroscopic test results.     

Photochemistry in the Low-Temperature Processing of Metal Oxide Thin Films by Solution Methods

Photochemistry has emerged in the last few years as a powerful tool for the low-temperature processing of metal oxide thin films prepared by solution methods. Today, its implementation into the fabrication procedure makes possible the integration of amorphous semiconductors or functional crystalline oxides into flexible electronic systems at temperatures below 350 °C. In this review, the effects of UV irradiation at the different stages of the chemical solution deposition of metal oxide thin films are presented. These stages include from the synthesis of the precursor solution to the formation of the amorphous metal-oxygen network in the film and its subsequent crystallization into the oxide phase. Photochemical reactions that can be induced in both the solution deposited layer and the irradiation atmosphere are first described, highlighting the role of the potential reactive chemical species formed in the system under irradiation, such as free radicals or oxidizing compounds. Then, the photochemical effects of continuous UV light on the film are shown, focusing on the decomposition of the metal precursors, the condensation and densification of the metal-oxygen network, and the nucleation and growth of the crystalline oxide. All these processes are demonstrated to advance the formation and crystallization of the metal oxide thin film to an earlier stage, which is ultimately translated into a lower temperature range of fabrication. The reduced energy consumption of the process upon decreasing the processing temperature, and the prospect of using light instead of heat in the synthesis of inorganic materials, make photochemistry as a promising technique for a sustainable future ever more needed in our life.     

Dual Metastability in Electroless Plating: Complex Inertness Enabling the Deposition of Composition-Tunable Platinum Copper Alloy Nanostructures

Autocatalytic deposition represents a facile, versatile, and scalable wet-chemical tool for nanofabrication. However, the intricate component interplay in plating baths containing multiple metal species impedes alloy deposition. We resolved this challenge in the bimetallic copper-platinum system by exploiting the kinetic stability of platinum complexes, which allows adjusting their ligand sphere and thus reactivity independently from the present copper ions in a preceding, thermally activated ligand exchange step. By using metastable Pt^IV precursors of varying degrees of complexation, copper-platinum alloys of adjustable atomic ratio were plated from solutions of identical composition and concentration, but differing local coordination environment. Due to its excellent conformity and nanoscale homogeneity, the reaction is compatible with ambitious 3D substrate morphologies, as demonstrated in the template-assisted fabrication of nanotubes with high aspect ratio. The ability to generate additional synthetic degrees of freedom by decoupling the metal complex speciation from the solution composition is of large interest for redox-chemical synthesis techniques, such as electrodeposition or nanoparticle colloid production.     

Fabrication of in situ alkali doped flexible CIGSSe solar cells by using aqueous spray deposition

Flexible Cu(In,Ga)(S,Se)₂ (CIGSSe) solar cells were fabricated on stainless steel foil by using aqueous spray deposition method. Since stainless steel foil is used, external alkali doping is necessary to passivate defects in CIGSSe absorber. We investigated effects of (Na, K) co-doping and selenization temperature on solar cell performance. With co-doping of Na and K, defect states were passivated significantly and highest power conversion efficiency (PCE) was obtained. However, at higher K concentration of more than 0.5%, different growth mode of CIGSSe was observed and deep defect states were developed, decreasing PCE. In addition, selenization temperature effects were studied by varying selenization temperatures. With higher selenization temperature, defect passivation for the CIGSSe absorber was more apparent, which facilitated increase of open circuit voltage. However, short circuit current was observed to be decreased at higher selenization temperature of 570 °C. This work demonstrates in-situ alkali co-doping into CIGSSe absorber with simple and low-cost spray deposition in an air environment.     

低温制备微晶硅薄膜生长机制的研究

采用热丝化学气相沉积技术制备了一系列处于不同生长阶段的薄膜样品，用原子力显微镜系 统地研究生长在单晶硅衬底和玻璃衬底上薄膜表面形貌的演化.按照分形理论分析得到：在 玻璃衬底上的硅薄膜以零扩散随机生长模式生长；而在单晶硅衬底上，薄膜早期以有限扩散 生长模式生长，当膜厚超过某一临界厚度时转变为零扩散随机生长模式.岛面密度与膜厚的 依赖关系表明，在临界厚度时硅衬底和玻璃衬底上的岛面密度均出现了极大值.Raman谱的测 量证实，玻璃衬底上薄膜临界厚度与非晶/微晶相变之间存在密切的关系.不同的衬底材料直 接影响反应 关键词： 生长机制 微晶硅薄膜 表面形貌 热丝化学气相沉积     

Optical properties and electronic transitions of SnO2 thin films by reflection electron energy loss spectroscopy

Optical properties of SnO₂ thin films in the 4–60 eV energy range are determined by reflection electron energy loss spectroscopy. Bulk and surface electron loss functions, real and imaginary parts of the dielectric function, refraction index, extinction and absorption coefficients are obtained from the analysis of the electron energy loss spectra. Electronic transitions are identified through the interpretation of the optical data. The samples (250–500 nm thick) were produced by ion beam-induced chemical vapor deposition. It is found that the compacity of the SnO₂ thin films affects their optical properties and therefore the relative intensity of the observed electronic transitions. The advantages of this method to determine optical properties of thin films are discussed. Inelastic mean free paths (6.2, 17 and 41 Å for electrons traveling in SnO₂ with kinetic energies of 300, 800 and 2000 eV, respectively) are obtained from the corresponding inelastic electron scattering cross-sections.     

Excimer laser ablation of thin titanium oxide films on glass

Thin titanium dioxide films are deposited on glass substrates by magnetron sputter deposition. They are irradiated in air, by means of a KrF excimer laser. The ablation rate is measured as a function of the laser fluence per pulse, F, and of the number of pulses, N. Above a fluence threshold, the films are partially ablated. The ablated thickness does not vary linearly with N. This is the signature of a negative feedback between the film thickness and the ablation rate. The origin of this negative feedback is shown to be due to either thermal or electronic effects, or both. At high F, the film detachs from the substrate.