Formation of gaseous and polymer products in a glow discharge in tetrafluoroethylene and hexafluorobenzene

The plasmochemical conversion of tetrafluoroethylene and hexafluorobenzene to the final products of electric discharge synthesis is discussed. Several modes of this process were studied: the synthesis of gaseous products, of a polymer on the surface of the electrodes, and of aerosol particles in the reactor. It was shown that the monomer decomposition rate increases linearly with the discharge current but appears to be pressure-independent. This is indicative of the electron energy distribution function being dependent on the pressure in the reactor. Based on the experimental data, a phenomenological model was developed capable of predicting the consumption of the initial compounds and the formation of the final gaseous and polymer products, including disperse particles. The model predictions were found to be in close agreement with the experimental results.     

真空条件下介质窗表面微波击穿实验

介绍了介质表面真空微波击穿研究实验装置的设计以及介质表面刻凹槽实验。微波源为S波段速调管,中心频率2.86 GHz,脉宽1μs。为确保击穿发生在后端介质样品处,而前端用于和速调管源隔离的陶瓷微波窗不击穿,实验装置采用先分后合的方法,利用两个陶瓷窗,每个陶瓷窗传输总功率的一半。为了抑制三相点带来的效应,采用凹形的圆柱介质,三相点处于电场强度弱的位置,有效消除了三相点的影响。在此实验装置上做了表面刻凹槽实验,初步实验结果表明,与光滑表面击穿阈值相比较,刻凹槽可使功率容量提高2倍以上。     

Diffusion kinetics of gaseous fission products arising under uranium fuel irradiation

A physical mechanism underlying the diffusion migration of gaseous fission products near the triple joints of grain boundaries during nuclear fuel burnout is suggested and mathematically substantiated. The diffusion kinetics is analyzed with regard to the first invariant of the stress tensor for a given structural defect. The results of mathematical simulation are of interest for analysis of nuclear fuel swelling due to the growth of intergranular pores and formation of channels for fission product migration along the grain boundaries.     

Preparation of DNA films for studies under vacuum conditions

Experiments were carried out to determine the optimum conditions required for the preparation of uniform films of supercoiled plasmid DNA to be used in irradiation experiments under high vacuum conditions. Investigations reveal that significant damage to the DNA molecules occurs due to the evacuation process when films were formed from DNA samples in ultra high purity water only. A variety of bases were tested for their possible protective capabilities and sodium hydroxide solution was found to be the most effective in maintaining the supercoiled structure of plasmid DNA during the preparation process. Using a transmission electron microscope we also examined the structure of the DNA films which are formed upon evacuation and how the proposed adducts influence the preparation process. It was found that the addition of bases cause the DNA to aggregate, noting that a base is required for the stability of the DNA molecules. The experimental results presented in this paper show that it may not be possible to perform experiments on so-called pure DNA under vacuum with no stabilizers being added to the sample before the evacuation process.     

金属表面镀高分子膜对真空击穿阈值的影响

探索提高金属表面真空击穿阈值的方法,对脉冲功率技术的发展和应用具有重要意义。在金属表面电子发射理论分析的基础上,采用有限元法计算阴极杆表面电场随二极管电压的变化规律,设计了实验系统,并开展了实验研究。实验对比了在脉宽约30 ns、阴极杆与阳极筒间隙12 mm时,钛合金TC4阴极杆在不同种类高分子膜（膜厚30～60 μm）下真空击穿阈值的变化情况。在表面粗糙度R_z（轮廓最大高度）为0.8 μm的TC4阴极杆表面分别镀环氧树脂膜和丙烯酸膜,实验结果表明,镀丙烯酸膜阴极杆的击穿阈值约505 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约20.6%;在表面粗糙度R_z为0.2 μm的TC4阴极杆表面分别镀聚酰亚胺膜和聚醚醚酮膜,实验结果表明,镀聚酰亚胺膜阴极杆的击穿阈值为584 kV/cm,相对于不镀膜阴极杆,击穿场强提高了约28.1%。因此,在金属表面镀丙烯酸膜、聚酰亚胺膜可以有效提高金属表面的真空击穿阈值。     

Force-extension curves for a single polymer chain under varying solvent conditions

We show that Langevin dynamics can be used to obtain force-extension curves for a single polymer chain under varying solvent conditions. We find that the chains obey Hooke-type and Pincus regime behavior for Theta and good solvents. However, in poor solvents a coil-strand coexistence is observed in the equilibrium state and this leads to a quite different type of deformation behavior.     

Micropore formation by the electrochemical etching of a semiconductor surface under local electrical-breakdown conditions

It is shown that local tunneling breakdown causes selective etching of the surface of a semiconductor electrode. It is shown that the effect of the axially directed etching of micropores in heavily doped semiconductors stops at an anode voltage, when the depletion layer of the inner end face of the pore becomes equal to the depletion layer of the planar surface. In lightly doped semiconductors, lateral etching of pore boundaries is controlled by the initiation of cascade ionization during avalanche breakdown.     

Damage investigations of AR coating under atmospheric and vacuum conditions

The damage characteristics of anti-reflection films exposed to 1064 nm nanosecond laser pulses in vacuum and air were investigated. The laser-induced damage thresholds (LIDT) in vacuum and air environments were compared. The damage morphologies were locally analyzed using optical microscopy and scanning electron microscopy (SEM). The depth of the damage sites in the two environments was analyzed by Alpha2Step 500 m. The differences between the damage observed in the two environments were discussed based on the temperature distribution, absorption and vacuum gaseous composition measurements and gas pressure influence analysis. Increased coupling of the plasma shock wave and adsorbing water in the coating layer may be considered as the primary cause of the low LIDT observed in vacuum.     

Evolution of steel surface composition with heating in vacuum and in air

X-ray photoelectron spectroscopy (XPS) has been used to investigate the changes in surface composition of three steels as they have undergone heating. The steels were mild steel, and two austenitic stainless steels, commonly designated 304 and 316 stainless steels. XPS measurements were made on the untreated samples, and then following heating for 30 min in vacuo and in a 1 × 10⁻⁶ Torr partial pressure of air, at temperatures between 100 °C and 600 °C.Mild steel behaves differently to the two stainless steels under the heating conditions. In mild steel the iron content of the surface increased, with oxygen and carbon decreasing, as a function of increasing temperature. The chemical state of the iron also changed from oxide at low temperatures, to metallic at temperatures above 450 °C.In both stainless steels the amount of iron present in the surface decreased with increasing temperature. The decrease in iron at the surface was accompanied by an increase in the amount of chromium at the steel surface. At temperatures above 450 °C the iron in both 304 and 316 stainless steels showed significant contributions from metallic iron, whilst the chromium present was in an oxide state. In 316 stainless steel heated to 600 °C there was some metallic chromium present in the surface layer.The surfaces heated in air showed the least variation in composition, with the major change being the loss of carbon from the surfaces following heating above 300 °C. There was also a minor increase in the concentration of chromium present on both the stainless steels heated under these conditions. There was also little change in the oxidation state of the iron and chromium present on the surface of these steels. There was some evidence of the thickening of the surface oxides as seen by the loss of the lower binding energy signal in the iron or chromium core level scans.The surfaces heated in vacuum showed a similar trend in the concentration of carbon on the surfaces, however the overall concentration of oxygen decreased throughout the heating of these steels. There were also significant changes in the oxidation state of the iron and chromium on these surfaces with significant amounts or iron and chromium present in the metallic form following heating up to 600 °C.It appears that the carbon contamination on the surfaces plays an important role in the fate of the surface oxide layer for all of the steels heated in a vacuum environment.     

Adsorption of benzene on the fresh steel surface formed by cutting under high vacuum

The adsorption of benzene on a fresh steel surface was carried out in high vacuum at room temperature. The fresh surface was formed by cutting in a high vacuum chamber, and benzene was allowed to adsorb on the surface during cutting. The adsorption and the surface reaction of benzene was monitored with a quadrupole mass spectrometer. It was found that the cut surface was so active that the catalytic decomposition of benzene occured even at room temperature. The adsorption rate and the sticking probability of benzene were estimated. The adsorption rate linearly increased with cutting speed, that is, the formation rate of the fresh steel surface. It was found that the adsorbed amount was under the monolayer level, and that the adsorption activity of toluene on the fresh surface was about two times larger than that of benzene.     

外加磁场下真空沿面闪络特性数值模拟

以单粒子模型和带电粒子运动方程为基础,采用蒙特卡罗方法,编写了真空沿面闪络过程计算程序,研究了外加磁场对真空沿面闪络过程的影响,主要是对二次电子发射及电子束的雪崩运动的影响。研究表明：外加磁场的存在,改变了绝缘体表面电子的运动,进而影响到绝缘体表面电荷的分布,从而在宏观上对绝缘体的耐受电压产生影响;外磁场抑制真空沿面闪络的效果与磁场的空间分布有关,磁场加在阴极附近时产生的效果优于加在阳极附近。     

块状TiO2气凝胶的溶胶-凝胶过程及结构

对块状TiO2气凝胶的溶胶-凝胶过程及结构进行了实验研究,结果发现:增加催化剂的量,凝胶化时间缩短,湿凝胶的透明度降低,强度提高;增加前驱体的量,凝胶化时间缩短,湿凝胶的透明度变化不大,强度提高;增加水量,凝胶化时间先缩短后增加,湿凝胶透明度先减小后增加,强度先增加后减小。利用扫描电镜对超临界干燥法制备的不同催化剂量和密度的块状TiO2气凝胶的结构进行了表征,并对结构与溶胶-凝胶过程之间的联系进行了分析。结果表明:增加催化剂量,由于缩聚反应进行的程度提高,气凝胶粒子粒径较小且总的孔径较大。减小前驱体量,气凝胶粒子粒径增大且结构逐渐疏松。     

Photodegradation of CdSe/ZnS semiconductor nanocrystals in a polymer film in air and under vacuum

We have studied characteristic features of photoinduced processes occurring in CdSe/ZnS semiconductor nanocrystals on prolonged exposure to ultraviolet light in air and under vacuum. Accelerated photodegradation of the nanocrystals in air has been established, associated with photooxidation.     

Fundamental processes of aluminium corrosion studied under ultra high vacuum conditions

Surface sensitive electron spectroscopy was applied to study the fundamental processes of aluminium corrosion. We used metastable induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) for the investigation of the densities of states of surface and bulk, respectively. Furthermore we applied X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition of the top surface layers. All measurements were performed under ultra high vacuum conditions.Al films with thicknesses of 7 nm were investigated. Both the interaction of oxygen and water with these films leads to the formation of an aluminium-oxygen layer, which is partly composed of stoichiometric Al₂O₃. Weak heat treatment at 770 K transforms the surface layer into Al₂O₃ with a thickness of about 2 nm. Further gas offer does not lead to an increase of this thickness, neither for oxygen nor for water. Additional to the oxygen offer, water exposure leads to the formation of OH species in the top aluminium-oxygen layer to a small amount. Weak heat treatment to 770 K removes this species completely. Water exposure leads to a much faster oxide formation than oxygen exposure. We try to give a model for the fundamental corrosion processes on a molecular scale.     

Measuring a colloidal particle's interaction with a flat surface under nonequilibrium conditions

A new and general approach is proposed to analyze the dynamics of a colloidal particle interacting with a nearby wall. This analysis can be used to determine the acting forces even when the system is non-stationary. As an illustration, we use total internal reflection microscopy to investigate the forces acting on a polystyrene sulfate latex particle as it is receding from a charged glass surface. Received 10 October 2002 Published online: 16 April 2003 RID="a" ID="a"Present address: Department of Polymer Physics, BASF Aktiengesellschaft, 67056 Ludwigshafen, Germany RID="b" ID="b"Present address: Arryx. Inc., Chicago, IL 60601, USA     

Method for modifying the structure and elemental composition of the solid surface during a high-voltage vacuum discharge

A new method for modifying the surface of a solid, which makes it possible to change effectively the structure and elemental composition of the surface with a high precision, is developed and tested experimentally. The method is based on the action of the plasma of a pulsed high-voltage vacuum discharge, the ion beam from the plasma, and the electron beam on a solid target. The emission and plasma parameters are observed in a pulsed electric field produced in the diode system to which a pulsed voltage with an amplitude of ～10³–10⁵ V and a duration from 10^?9 to 10^?5 s is applied.     

Deposition of C60 polymer films under various plasma conditions

We studied the deposition of C₆₀ polymer films under different Ar plasma conditions. The films were deposited at a pressure range between 1.3 and 40 Pa, and the input power was varied from 10 to 70 W. The films were investigated by Raman spectroscopy to confirm the C-C valence states of the polymeric phases. C₆₀ polymers were formed under various experimental conditions. However, the depositions resulted in non-uniform films consisting of unpolymerized C₆₀, dimers, linear chains and polymeric planes. Amorphous carbon was found in the films deposited at 13 and 20 Pa (50 W input power) and 13 Pa (70 W).     

Investigation of an unstable diffusion process in isothermal three-component gaseous mixtures under steady conditions

The diffusional transport of a ternary gaseous mixture of helium, Freon-12, and argon is studied under isothermal conditions by a steady-flow method. The experiments were done at atmospheric pressure and a temperature of 298 K. The data are compared with the theory. It is shown that the mass transfer of the components is influenced by convective flows. Zh. Tekh. Fiz. 69, 5–9 (July 1999)     

Direct micropatterning of polymer materials by ice mold

Micropatterning of functional polymer materials by micromolding in capillaries (MIMIC) with ice mold is reported in this paper. Ice mold was selected due to its thaw or sublimation. Thus, the mold can be easily removed. Furthermore, the polymer solution did not react with, swell, or adhere to the ice mold, so the method is suitable for many kinds of materials (such as P3HT, PMMA Alq₃/PVK, PEDOT: PSS, PS, P2VP, etc.). Freestanding polymer microstructures, binary polymer pattern, and microchannels have been fabricated by the use of ice mold freely.