Oxygen Tracer Diffusion in Vitreous Silica

Oxygen diffusion in vitreous silica glass is studied using the gas exchange technique. The tracer concentration profiles are consistent with a model based on two mechanisms, one network and the other interstitial. These processes are coupled through limited network–interstitial exchange. Nuclear reaction analysis and secondary ion mass spectrometry techniques are performed and compared. These results are compared to experiments on transport in thin silica films grown on single-crystal silicon.     

Surface tailoring of an ethylene propylene diene elastomeric terpolymer via plasma‐polymerized coating of tetramethyldisiloxane

In the research presented here, we explore the use of a low‐energy plasma to deposit thin silicone polymer films using tetramethyldisiloxane (TMDSO) (H(CH₃)₂? Si? O? Si? (CH₃)₂H) on the surface of an ethylene propylene diene elastomeric terpolymer (EPDM) in order to enhance the surface hydrophobicity, lower the surface energy and improve the degradation/wear characteristics. The processing conditions were varied over a wide range of treatment times and discharge powers to control the physical characteristics, thickness, morphology and chemical structure of the plasma polymer films. Scanning electron microscopy (SEM) shows that pore‐free homogeneous plasma polymer thin films of granular microstructure composed of small grains are formed and that the morphology of the granular structure depends on the plasma processing conditions, such as plasma power and time of deposition. The thicknesses of the coatings were determined using SEM, which confirmed that the thicknesses of the deposited plasma‐polymer films could be precisely controlled by the plasma parameters. The kinetics of plasma‐polymer film deposition were also evaluated. Contact angle measurements of different solvent droplets on the coatings were used to calculate the surface energies of the coatings. These coatings appeared to be hydrophobic and had low surface energies. X‐ray photoelectron spectroscopy (XPS) and photoacoustic Fourier‐transform infrared (PA‐FT‐IR) spectroscopy were used to investigate the detailed chemical structures of the deposited films. The optimum plasma processing conditions to achieve the desired thin plasma polymer coatings are discussed in the light of the chemistry that takes place at the interfaces. Copyright © 2004 Society of Chemical Industry     

Cover Picture: Toward Large‐Scale Alignment of Electrohydrodynamic Patterning of Thin Polymer Films (Adv. Funct. Mater. 15/2006)

By integrating lithography and self‐assembly via electrohydrodynamic instabilities, Russel and co‐workers are able to guide initially flat polymer films to evolve into periodic arrays of pillars over regions much greater in extent than their natural domain sizes, as detailed on p. 1992. Novel structures that involve a combination of linear ridges and pillars are also produced, mainly as as result of the dynamic merging among preformed pillars. To pattern thin polymer films via electrohydrodynamic instabilities, we design and utilize two different kinds of mask patterns to guide pillars into alignment over regions much greater in extent than their natural domain sizes. First, narrow protruding ridges that intersect to form regular patterns on the mask trigger the growth of pillars beneath. Later, square and triangular packings of pillars develop in the regions enclosed by those ridges, preserving the registry from one domain to the next over a much larger area than within individual domains in unpatterned portions of the mask. Second, small square protrusions that are prealigned into a large regular array on the mask guide the formation of square packings of pillars in domains that conform to the mask, forming a large array of pillars. Novel structures involving a combination of linear ridges and pillars are also produced mainly due to the dynamic merging among preformed pillars. Finally, we find vertex symmetry of the mask pattern is necessary for generating and preserving ordered patterns on the polymer film.     

双辊式薄带连铸工艺研究

进行了双辊法薄带连铸的试验研究。阐述了双辊连铸机浇注系统的研究结果、工艺参数对连铸的影响，以及18—8不锈钢薄带坯的凝固组织和冷轧特性，该工作为薄带连铸的中间生产机组的研究奠定了基础。     

Structural and electrical properties of brush plated ZnTe films

Zinc telluride thin films were deposited by the brush plating technique at a potential of −0.90 V (SCE) on conducting glass and titanium substrates at different temperatures in the range 30–90 °C. The films were polycrystalline in nature with peaks corresponding to the cubic phase. Direct band gap of 2.30 eV was observed. XPS studiers indicated the formation of ZnTe. Depth profiling studies indicated a uniform distribution of Zn and Te throughout the entire thickness. EDAX measurements were made on the films and it was found that there was a slight excess of Te. The carrier concentration was found to vary from 10¹⁴–10¹⁵ cm⁻³ with increase of substrate temperature. The mobility was found to vary from 5 to 60 cm² V⁻¹ s⁻¹.     

CFD Simulation of Liquid Film Flow on Inclined Plates

A two‐phase flow CFD model using the volume of fluid (VOF) method is presented for predicting the hydrodynamics of falling film flow on inclined plates, corresponding to the surface texture of structured packing. Using the proposed CFD model the influence of the solid surface microstructure, liquid properties and gas flow rate on the flow behavior was investigated. From the simulated results it was shown that under the condition of no gas flow the liquid flow patterns are dependent on the microstructure of the plates, and proper microstructuring of the solid surface will improve the formation of a continuous liquid film. It was also found that liquid properties, especially surface tension, play an important role in determining the thin‐film pattern. However, there are very different liquid film patterns under the action of gas flow. Thinner liquid films break easily, but thicker liquid films can remain continuous even at higher gas flow rates, which demonstrates that all factors affecting the liquid film thickness will affect the liquid film patterns under conditions of counter‐current two‐phase flow.     

Influence of the deposition atmosphere on the characteristics of Pd–Mg thin films prepared by pulsed laser deposition

Bilayered palladium (30 nm thick)–magnesium (350 nm thick) thin films were prepared using the pulsed laser deposition technique in the presence of various background gases (Ar, He and a mixture He + H₂) under different partial pressures (47 and 27 Pa). According to the deposition atmosphere, the Pd/Mg interface shows either a sharp or an extended transition. The electrochemical hydriding properties and the mechanical stability upon cycling of the Pd/Mg film are greatly improved when an extended «intermixing» zone between the Pd and Mg layers is present. The Pd–Mg films prepared under pure helium fulfill these conditions.