Dry deposition and desorption of toxic gases to and from snow surfaces

A model describing toxic gas deposition to and desorption from a snow surface is presented. The model is based on the assumption that the deposition is caused by an adsorption of the toxic gas to small amounts of liquid water, which exist in the snow at temperatures equal to or below 0°C. It includes molecular diffusion in the snow, partition between gas and solution by use of Henry's law, drainage flow in melting snow and decomposition of agent. The interface to the atmosphere is defined by the flux to and from the surface with help of the aerodynamic resistance and the resistance in the viscous sub-layer. Deposition velocities to snow for some air pollutants are reviewed. The model is compared with sarin experiments in a test chamber, which verifies two main features of the model—primarily decreasing deposition with time and decreasing deposition with decreasing temperature. The model shows that the accumulation of sarin in the top layer of snow could be high enough to give lethal or severe injuries to people if the snow was used as drinking water. However, there is a tendency of the model to give too low deposition (too high surface resistance). Possible reasons for this observation are discussed.     

The desorption of condensed noble gases and gas mixtures from cryogenic surfaces

In accelerators, operating at liquid-helium temperature, cold surfaces are exposed to intense synchrotron radiation and bombardment by energetic electrons and ions. Molecular desorption yield and secondary electron yield can strongly influence the performance of the accelerator. In order to predict the gas density during the operation, the knowledge of electron-induced desorption yields of condensed gases and of its variation with the gas coverage is necessary. Desorption yields under electron impact of various noble gases and gas mixtures condensed on a copper surface cooled at 4.2 K have been measured.     

Surface tension of liquid inert gases

The surface tension of liquid inert gases, including ³He and ⁴He helium isotopes, has been calculated using a method based on determining the work that must be done to remove an atom from the liquid surface. This approach provides quite satisfactory agreement with the available experimental data. Calculations of the surface tension in liquid helium also take into account the quantum zero-point oscillations of atoms. The role of the dimensional effect in the surface tension for nanodroplets is discussed.     

High-numerical-aperture effects in photoresist

Two-beam and three-beam vector interference in thin photoresist films is used to illustrate the striking differences between s -polarized and p-polarized high-numerical-aperture illumination. Both simulations and experiments are performed for several cases, including undyed photoresist on silicon, dyed photoresist on silicon, and the addition of an antireflective layer between the photoresist and the silicon. A 0.85 numerical-aperture system is examined. The major differences between s- and p-polarized illumination include elliptical versus rectangular features and lower contrast for p-polarized images.     

Carbon based conductive photoresist

A conductive photoresist for photolithographic application was studied here. The negative near-UV sensitive epoxy-based photoresist was used as a polymer matrix and conductive carbon black was used as functional filler. DC electrical resistivity of composite as a function of filler concentration has a well-known S-shape. After UV-exposure the resistivity of the composite decreases for almost five orders of magnitude, mostly at percolation threshold (approx. 0.6 vol.%). This effect can be attributed to the fully cross-linked polymer structure formed during UV-exposure of the composite. The resistivity of prepared samples also depend on the state of dispersion of the functional filler obtained using different dispersing additives. Composites with better dispersed particles have lower resistivities. This effect remained below one order of magnitude and decreased after UV-exposure. The composites with carbon black concentration of up to 1.1 vol.% are suitable for spin-coating and photolithography.     

Thermal desorption of hydrogen from graphane

The process of hydrogen desorption from graphane (graphene sheet saturated by hydrogen adsorbed from both sides) has been studied using the method of molecular dynamics. The temperature dependences of the time of desorption onset for various hydrogen coverages on graphene are calculated and the corresponding activation energies in the Arrhenius equation are determined. It is established that graphane exhibits a rather high thermal stability that makes possible its use in two-dimensional electronics even at room temperature. For the same reason, graphane can hardly be considered as a promising hydrogen storage material for fuel cells.     

Dynamic holographic gratings with photoresist

The theoretical development of dynamic holographic gratings with piezoelectric crystals is presented. A thin layer of photoresist is applied over the surface of the piezoelectric crystal. A holographic grating was recorded over the photoresist-piezo device in such a way that when it is activated the changes in its dimensions produce a geometrical change in the grooves of the grating. Hence the initial diffraction pattern created may be dynamically modified.     

Surface scanning analysis of planar arrays of analytes with desorption electrospray ionization-mass spectrometry

The analysis of analytes deposited on, separated on, or otherwise distributed about a planar surface using desorption electrospray ionization mass spectrometry in a surface scanning sampling mode was investigated. The physical regions of the surface-impacting solvent/gas jet desorption/ionization plume were described. Under the conditions typical for desorption electrospray ionization used here, the impact plume formed an elliptical desorption/ionization region on the surface. Most effective desorption/ionization was obtained from a smaller elliptical area within the larger impact region that was centered on a point on-axis from the sprayer tip to the surface. Maximum signal from a given amount of material on a surface was observed with proper plume and sample alignment when the diameter of the sample spot was less than the diameter of the central high-efficiency desorption/ionization region of the impact plume. Solvent and gas flow out of this high-efficiency desorption/ionization region was found to limit analyte accessibility to this region via a "washing effect" when analytes were on smooth surfaces or on surfaces for which the analyte had little affinity. As such, the direction of surface scanning and scan speed during an analysis was found to be important for maximizing signal levels and signal reproducibility on particular surface types. Overall, the results presented illustrate means to improve analysis of sample spots on various types of surfaces using desorption electrospray ionization mass spectrometry in a surface scanning mode.     

Slow desorption of volatile organic compounds from soil: evidence of desorption step limitations.

Transient adsorption and desorption of 1,2 dichloroethane and toluene on dry Yolo silt loam soil were studied by continuously measuring the composition of the effluent from a soil-packed chromatography column with a mass spectrometer. After obtaining complete breakthrough at approximately 30% relative saturation of one chemical in nitrogen, pure nitrogen feed was initiated and maintained for several hours. Of the material adsorbed at breakthrough, 9.7% of the 1,2 dichloroethane and 14.2% of the toluene were highly resistant to desorption and remained sorbed on the soil even after 5 h of nitrogen flow. When a second chemical with a higher adsorption affinity was introduced into the soil column (water following toluene or toluene following 1,2 dichloroethane), the majority of the first chemical was quickly desorbed and began leaving the soil column before breakthrough of the second chemical. Conversely, when a second chemical with a smaller adsorption affinity was introduced into the soil column, only a small amount of the first chemical was displaced and began leaving the soil column after breakthrough of the second chemical. The results of this study indicate that the desorption step itself may be the rate-limiting step for sorbate which remains after prolonged exposure to sorbate-free gas.     

Developed profile of holographically exposed photoresist gratings

A simulation of the profile of holographically recorded structures in photoresists is performed. In addition to its simplicity this simulation can be used to take into account the effects that arise from exposure, photosensitization, development, and resolution of positive photoresists. We analyzed the effects of isotropy of wet development, nonlinearity of the photoresist response curve, background light, and standing waves produced by reflection at the film-substrate interface by using this simulation, and the results agree with the experimentally recorded profiles.     

Interferometric fabrication of modulated submicrometer gratings in photoresist

Interferometric recording is applied to the fabrication of modulated submicrometer gratings in photoresist.High diffraction efficiency requires optimized recording conditions, which are obtained by the use of an on-axis continuous surface-relief grating for the generation of the object beam. The optimized phase function is copied into the resist layer by means of a self-aligned two-step recording process with an intermediate copy in a volume photopolymer hologram. As a result, we demonstrate high carrier frequency surface-relief off-axis fan-out gratings for illumination in transmission with visible light.     

用于MEMS结构的光刻胶牺牲层接触平坦化技术

实验研究一种新颖的光刻胶牺牲层的接触平坦化(contact planarization)技术,应用于MEMS结构制作.实验研究了温度与光刻胶流动性的关系,以及牺牲层厚度、施加压力和温度、MEMS结构密度等因素对平坦化效果的影响,在优化条件下,牺牲层的起伏台阶从2μm减小到20～40nm.与化学机械抛光技术相比,接触平坦化无明显凹陷(Dishing)效应,无衬底损伤,同时呈现出良好的局部和总体均匀性.     

Regeneration of pyrolyzed photoresist film by heat treatment

A simple, time-, and cost-effective procedure is described for regenerating film-modified or deactivated pyrolyzed photoresist film (PPF) surfaces. Heating for 30 min at 545 ± 25 °C in argon at a flow rate of 1 L min(-1) removes covalently bound thin organic films, attached via electrografting from aryldiazonium salt solutions. The heat-treated surfaces exhibit improved electrochemical characteristics compared to those prior to modification and can be reused for solution-based electrochemical measurements and for electrografting. The same treatment reactivates PPF electrodes that have been deactivated by exposure to adsorbates from air or solution. X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and water contact angle measurements establish that the regeneration procedure does not lead to significant changes in oxygen content, roughness, or hydrophobicity of PPF surfaces. XPS measurements also confirm the complete removal of covalently attached organic films after heat treatment but reveal a specific interaction between grafted nitrophenyl films and PPF which results in a small amount of N incorporation in the surface.