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21.
The adsorption of DNA molecules on mica surface and the following desorption of DNA molecules at ethanol-mica interface were studied using atomic force microscopy. By changing DNA concentration, different morphologies on mica surface have been observed. A very uniform and orderly monolayer of DNA molecules was constructed on the mica surface with a DNA concentration of 30 ng/μL. When the samples were immersed into ethanol for about 15 min, various desorption degree of DNA from mica (0-99%) was achieved. It was found that with the increase of DNA concentration, the desorption degree of DNA from the mica at ethanol-mica interface decreased. And when the uniform and orderly DNA monolayers were formed on the mica surface, almost no DNA molecule desorbed from the mica surface in this process. The results indicated that the uniform and orderly DNA monolayer is one of the most stable DNA structures formed on the mica surface. In addition, we have studied the structure change of DNA molecules after desorbed from the mica surface with atomic force microscopy, and found that the desorption might be ascribed to the ethanol-induced DNA condensation. 相似文献
22.
S.M. Driver 《Surface science》2007,601(2):510-517
We have used a novel fibre-optic low-energy electron diffraction (FO-LEED) instrument, capable of low flux measurements that minimise electron beam damage to surface overlayers, to study methanethiolate (CH3-S-) structural phases formed on Cu{1 1 1} at temperatures between 110 and 300 K. Three structural phases were seen: a (√3 × √3)R30° phase that forms at 110-140 K; a (4 × 4) phase which was observed transiently at 110 K; and a pseudo-{1 0 0} reconstructed phase which forms at room temperature. We discuss these in the context of previous studies of this system, and demonstrate the ability of the FO-LEED instrument to record high-quality LEED patterns and intensity data from a strongly beam-sensitive surface. 相似文献
23.
A.R. Khan 《Surface science》2007,601(6):1635-1641
We have studied the direct and indirect abstraction of D adatoms by H on the Si(1 0 0) surfaces by employing a pulsed H-beam. Desorptions of HD molecules is found to occur promptly as a result of direct abstraction at the beam on-cycles. In contrast, we find that D2 desorption induced by adsorption of H atoms, i.e., the so-called adsorption-induced desorption (AID), occurs even at the beam off-cycles. The D2 rate curves measured with the pulsed-H beam are decomposed into four components characterized with the reaction lifetimes of ?0.005, 0.06 ± 0.01, 0.8 ± 0.1, and 30 ± 5 s. We propose that the fastest and the second fastest AID channels are related to the thermodynamical instability of (1 × 1) dihydride domains locally formed on the (3 × 1) monodeuteride/dideuteride domains. The 0.8 s AID channel is attributed to the desorption occurring at the stage when (3 × 1) monodeuteride/dideuteride domains are built up upon H adsorption onto the (2 × 1) monohydride surface. The 30 s AID path is attributed to the thermal desorption accompanied by the shrinkage of the (3 × 1) domains which were excessively formed during the beam on-cycles on the (2 × 1) monohydride surface. Atomistic mechanisms are proposed for these three AID pathways. 相似文献
24.
B. Vincent R. Loo W. VandervorstG. Brammertz M. Caymax 《Journal of Crystal Growth》2010,312(19):2671-2676
Dichlorosilane (DCS), silane and trisilane have been investigated as Si precursors for low temperature (<700 °C) Si reduced pressure chemical vapor deposition. DCS and silane are limited to growth temperatures higher than 600–650 and 500 °C, respectively. At lower temperatures, absence of either Cl or H desorption from the surface impedes Si growth with acceptable growth rate (>5 Å/min). Trisilane permits the growth of Si at lower temperatures below 350 °C due to a specific growth mechanism enhancing H desorption. Layers grown at temperatures lower than 500 °C are defective, irrespective of the carrier gas, pressure and precursor flow used. 相似文献
25.
LI Zhong WANG Hongjuan XI Hongxia XU Kefeng WEN Jun Research Institute of Chemical Engineering South China University of Technology Guangzhou 《Chinese Journal of Reactive Polymers》2001,(2)
1. INTRODUCTION In some cities of China, cancer and breath system diseases caused by the pollution of volatile organic compounds (VOCs) have been obviously increasing. The VOCs includes BTEX (benzene, toluene, ethylbenzene, and xylene), aldehydes, cresol, phenol, acetic acid, polynuclear aromatic hydrocarbons (PAHs), which have long-term human health implications. Emission of the VOCs has threatened the health of people seriously [1,2]. The pollution of the VOCs mostly hails from… 相似文献
26.
27.
4 new model, phase equilibrium-kinetics model (PEKM), for estimation of diffusioncoefficient was proposed in this paper. Kinetic experiments of phenol desorption on NKAII resin inthe presence and the absence of ultrasound were separately conducted, and diffusion coefficients ofphenol within an adsorbent particle were estimated by means of proposed PEKM and classicsimplified model. Results show that the use of ultrasound not only changes the phase equilibriumstate of NKAll resin/phenol/water system which had been equilibrium at normal condition, but alsoenhances diffusion of phenol within the resin. The diffusion coefficient of phenol in the resin in thefield of ultrasound increases in an order of magnitude in comparison with the diffusion coefficientdetermined under no ultrasound Experimental results also indicated that the diffusion coefficientsestimated by PEKM were more accurate than that estimated by the classic simplified model. 相似文献
28.
Jeong-Young Ji 《Surface science》2007,601(7):1768-1774
PH3 adsorption on Si(1 1 1)-7 × 7 was studied after various exposures between 0.3 and 60 L at room temperature by means of scanning tunneling microscopy (STM). PH3-, PH2-, H-reacted, and unreacted adatoms can be identified by analyzing empty-state STM images at different sample biases. PHx-reacted rest-atoms can be observed in empty-state STM images if neighboring adatoms are hydrogen terminated. Most of the PH3 adsorbs dissociatively on the surface, generating H- and PH2-adsorbed rest-atom and adatom sites. Dangling-bonds at rest-atom sites are more reactive than adatom sites and the faulted half of the 7 × 7 unit cell is more reactive than the unfaulted half. Center adatoms are overwhelmingly preferred over corner adatoms for PH2 adsorption. The saturation P coverage is ∼0.18 ML. Annealing of PH3-reacted 7 × 7 surfaces at 900 K generates disordered, partially P-covered surfaces, but dosing PH3 at 900 K forms P/Si(1 1 1)- surfaces. Si deposition at 510 K leaves disordered clusters on the surface, which cannot be reordered by annealing up to 800 K. However, annealing above 900 K recreates P/Si(1 1 1)- surfaces. Surface morphologies formed by sequential rapid thermal annealing are also presented. 相似文献
29.
《Comptes Rendus Chimie》2015,18(1):88-99
The performance of a microporous activated carbon prepared chemically from olive stones for removing Cu(II), Cd(II) and Pb(II) from single and binary aqueous solutions was investigated via the batch technique. The activated carbon sample was characterized using N2 adsorption–desorption isotherms, SEM, XRD, FTIR, and Boehm titration. The effect of initial pH and contact time were studied. Adsorption kinetic rates were found to be fast and kinetic experimental data fitted very well the pseudo-second-order equation. The adsorption isotherms fit the Redlich–Peterson model very well and maximum adsorption amounts of single metal ions solutions follow the trend Pb(II) > Cd(II) > Cu(II). The adsorption behavior of binary solution systems shows a relatively high affinity to Cu(II) at the activated carbon surface of the mixture with Cd(II) or Pb(II). An antagonistic competitive adsorption phenomenon was observed. Desorption experiments indicated that about 59.5% of Cu(II) and 23% of Cd(II) were desorbed using a diluted sulfuric acid solution. 相似文献
30.
We compare vibrational, translational and rotational excitations of CO molecules desorbed by electron impact, and the yield of oxygen and carbon atoms from electron-induced fragmentation of CO molecules for: (1) CO monolayers on bare transition metals [Ru(001) and Pt(111)]; (2) CO monolayers coadsorbed with well-ordered oxygen atoms; (3) weakly bound CO monolayers on epitaxially grown silver films; and (4) CO monolayers decoupled from the metallic substrate by mono-atomic xenon spacer layers. For all but the last system, we find CO molecules which are vibrationally extremely hot. This is explained by the excitation of strongly antibonding multi-electron states which are quenched in the vicinity of the metal surface before enough translational energy is acquired by the nuclei to complete dissociation. For CO/Xe/Ag(111), vibrationally hot CO molecules are missing among the desorbing particles, whereas strong fragment signals persist. Because of the isolating Xe layer, the substrate-adsorbate coupling is too weak to terminate the dissociation reaction which is induced by the electron impact before the rupture of the molecular bond. 相似文献