Role In Desorption Research Articles

STM-Induced Desorption and Lithographic Patterning of Cl-Si(100)-(2 × 1).

A scanning tunneling microscope (STM) was used to investigate tip-induced chlorine desorption and lithographic patterning of Cl-terminated Si(100)-(2 × 1) surfaces from 4 to 600 K in ultrahigh vacuum. Until now, STM lithography has exclusively focused on hydrogen-based chemistry for donor device fabrication. As the initial step in developing halogen-based chemistries for STM fabrication of acceptor-based devices, we substituted the hydrogen resist with chlorine. We found that chlorine can be selectively desorbed by the STM tip using both electron and hole injection. Observations show that targeted chlorine was not driven into the surface but desorbed completely as both individual and pairs of atoms. Chlorine depassivation lithography is demonstrated using both field-emission patterning to desorb chlorine from large areas with high efficiency (0.83(1)) and atomic-precision patterning to desorb one to two dimer rows at a time, resulting in 1.5 nm wide lines. Further, varying the experimental parameters for lithography revealed a positive correlation between pattern line widths and both positive sample bias voltage (1.7(2) nm/V) and total electron dose (0.15(2) nm/(mC/cm)), demonstrating that the energy and total number of electrons play a role in desorption from multiple sites.

Multilayer arsenic mobilization and multimetal co-enrichment in the alluvium (Brahmaputra) plains of India: A tale of redox domination along the depth

The study attempts to understand arsenic (As) mobilization in a shallow aquifer with depth variation while focusing on the potential co-occurrence of As with priority metals (zinc and lead), using a pilot scale multilevel groundwater monitoring system (MGWS). Groundwater samples (n = 72) were collected bi-weekly (every 15 days) from the multilevel sampler (4.6, 9.2 and 13.8 m depths), installed at Tezpur, Sonitpur district of Brahmaputra floodplain (BFP), Assam, India, for a period of 1 year (August 2013–July 2014). Both geogenic and anthropogenic influences were found to affect the studied unconfined aquifer. At 4.6 m, weathering dominated due to interaction with CO2 and infiltrating water. Prevalent high pH (7.9–8.6) at all three depths in association with strong oxidizing condition (at 4.6 m) during the drier months seem to play a crucial role in desorption based As release. Multivariate analyses revealed that redox potential (ORP) remains the primary controller of As release at all three depths. With depth, stronger anoxic conditions resulted in the dominance of reductive hydrolysis leading to a co-occurrence scenario of As (max 4.6 μgL−1) with Zn (max 2514 μgL−1) and Pb (max 740 μL−1) with influences of anthropogenic modes of activities like agriculture and dry deposition from a brick kiln. Multi-element enrichment is an emerging concern but the bigger picture would be to understand the peculiarities of individual aquifers, as a generalization can lead to missing a ton of information. In this regard, long-term multilevel monitoring can help in the predictive understanding of the vertical stratification and co-occurrences of multi-metals that can subsequently be applied for water production at the safer depths.

Desorption of low-volatility compounds induced by dynamic friction between microdroplets and an ultrasonically vibrating blade.

Friction plays an important role in desorption and/or ionization of nonvolatile compounds in mass spectrometry, e.g., sonic spray, easy ambient sonic-spray ionization, solvent-assisted inlet ionization, desorption electrospray, etc. In our previous work, desorption of low molecular weight compounds induced by solid/solid dynamic friction was studied. The objective of this work was to investigate desorption of low-volatility compounds induced by liquid/solid friction. Water/methanol (1/1) microdroplets with ∼30 μm in diameter were generated by using a piezoelectric microdroplet generator. They were injected to analytes deposited on the flat surface of a blade vibrating ultrasonically with the frequency of 40 kHz. Neutral molecules desorbed from the blade were ionized by a helium dielectric barrier discharge (DBD), generating strong signals for samples including drugs, explosives, and insecticides. These signals were not detected when either the blade vibrator or the piezoelectric microdroplet generator was off. In contrast, for ionic compounds such as 1-butyl-3-methylimidazolium bis(trifluoro-methylsulfonyl)imide, p-chlorobenzyl pyridinium chloride, and rhodamine B, strong ion signals were obtained when the vibrator and droplet generator were on, but DBD was off. Sub-nanogram limits of detection were attained for low-volatility compounds.

Determination of Cu(II) in water and food samples by Na+-cloisite nanoclay as a new adsorbent: Equilibrium, kinetic and thermodynamic studies

Na+-MMT (sodium montmorillonite) or Na+-cloisite nanoclay as a new adsorbent was employed for the sorption of Cu(II) ions from water and food samples in batch system. Copper ion determination was carried out by applying the solid phase extraction (SPE) method followed by atomic absorption spectroscopy (AAS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). The effects of varying parameters such as initial concentration of metal ions, volume of the standard solutions, eluent and buffer solutions characteristics, amount of adsorbent, contact time, and temperature on the adsorption process, also, the role of desorption and centrifugation time on the desorption step were explored. The effect of the interfering ions on the recovery of copper ions was also examined. This optimized method was applied to a variety of real water and food samples. The adsorption data was correlated with Freundlich, Langmuir, Dubinin–Radushkevich (D–R), and Temkin isotherms. The kinetic data were described with pseudo-first-order, pseudo-second-order and double-exponential models. The adsorption process follows a pseudo-second-order reaction scheme. Calculation of ΔG0, ΔH0 and ΔS0 showed that the nature of Cu(II) ion sorption onto Na+-cloisite nanoclay was exothermic and was favored at lower temperature.

Effects of matrix moisture on gas diffusion and flow in coal

Gas production from coal is a complex process whereby gas, initially adsorbed in the coal matrix, desorbs and diffuses through the matrix into the cleat and eventually flows through the cleat system into a production well or a drainage borehole. Hence, the gas production rate is mainly controlled by the gas diffusivity in the matrix and gas permeability in the cleat system. Moisture in the coal matrix has significant impact on gas adsorption capacity and would also play a key role in desorption and migration of gas. However, how moisture affects gas desorption and diffusion in the coal matrix is still poorly understood. In this work, experimental study is performed to investigate effects of moisture on gas sorption rate for an Australian coal. Coal seam gases, CH 4 and CO 2, are used in the study. The experimental results show that moisture content in the matrix has significant impact on the gas sorption rate and the impact of moisture content on the diffusion rate is stronger for CH 4 than CO 2. Moreover, the impact of moisture on gas diffusivity in pores with different size is different, suggested from the modelling results using the bidisperse approach. Furthermore, moisture in coal matrix would cause coal swelling/shrinkage and mechanical properties change that could impact on coal permeability under reservoir conditions. Experimental measurements of coal matrix swelling and Young’s modulus on the same coal sample show that matrix moisture content has significant impact on those properties and may have significant implications on coalbed methane recovery and CO 2 storage in coal.

NOx Reduction and Desorption Studies Under Electric Discharge Plasma Using a Simulated Gas Mixture: A Case Study on the Effect of Corona Electrodes

In this study, reduction and desorption of oxides of nitrogen (NOx) were conducted using an electrical discharge plasma technique. The study was carried out using a simulated gas mixture to explore the possibility of re-generation of used adsorbents by a nonthermal plasma desorption technique. Three different types of corona electrodes, namely, pipe, helical wire, and straight wire, were used for analyzing their effectiveness in NOx reduction/desorption. The pipe-type corona electrode exhibited a nitric oxide (NO) conversion of 50%, which is 1.5 times that of the straight-wire-type electrode at an energy density of 175 J/L. The helical-wire-type corona electrode exhibited a NOx desorption efficiency almost 4 times that of the pipe-type electrode, indicating the possibility that corona-generated species play a crucial role in desorption.

Dynamics study of the adsorption and diffusion in early growth stage of AlN/α-Al2Ｏ3（0001） films

The research of temperature effect on the surface adsorption and diffusion is an important problem for the initial growth mechanism of AlN/α-Al2Ｏ3（0001） thin films. Using the ab initio molecular dynamics method based on the first principles, the adsorption process, system energy, dynamic track and the diffusion coefficient are calculated at temperatures from 300℃ to 800℃. The results indicate that the adsorption process can be divided into three stages, the physical adsorption, the chemical adsorption and the stable surface growth state. With the temperature increasing, the average diffusivity of the particles at α-Al2Ｏ3（0001） surface is enhanced in the bonding process. The diffusion coefficient of N atom is higher than that of the Al atom, especially in the physical adsorption stage. At higher temperatures （over 700℃）, the role of desorption of the N atom is markedly strengthened, so it is unfavorable to the stable absorption of AlN. The temperature between 500℃ and 700℃ is beneficial to the stable adsorption and the growth of the AlN on α-Al2Ｏ3（0001） surface.

Step line tension and step morphological evolution on the Si(111)(1×1)surface

The temperature dependence of the step line tension on the Si(111) $(1\ifmmode\times\else\texttimes\fi{}1)$ surface is determined from a capillary wave analysis of two-dimensional island edge fluctuations and straight step fluctuations that are observed with low energy electron microscopy. The line tension decreases by nearly 20% with a linear temperature coefficient of $\ensuremath{-}0.14\phantom{\rule{0.3em}{0ex}}\mathrm{meV}∕\mathrm{\AA{}}\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ between 1145 and $1233\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Temporal correlations of step fluctuations exhibit the distinctive signature in the wavelength dependence of the relaxation time of a terrace diffusion-limited mechanism for step motion. We also find that the role of desorption in island decay increases dramatically in the temperature range $(1145--1380\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ that island decay is studied. Consequently, we generalize the current quasistatic model of island decay to take account of desorption. The evaluation of the island decay time with this model referenced to the temperature-dependent line tension accurately determines activation energies that are relevant to mass transport and sublimation.

Forensic analysis of inks by imaging desorption electrospray ionization (DESI) mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) is employed in the forensic analysis of documents. Blue ballpoint pen inks applied to ordinary writing paper are examined under ambient conditions without any prior sample preparation. When coupled to an automated moving stage, two-dimensional molecular images are generated. Proof-of-principle experiments include characterization of a simulated forged number and examination of older written records. This application of DESI has advantages over extractive techniques in terms of speed and sample preservation. The effects of the desorbing solvent composition, in this case a mixture of methanol and water, and of flow rate, are evaluated. Results suggest that the solubility of the analyte (dyes Basic Blue 7, Basic Violet 3 and Solvent Blue 26) plays an important role in desorption from the paper surface.

Desorption Behaviour in Nanostructured MgH<sub>2</sub>-Co

The influence of the Co addition and synthesis route on desorption properties of MgH2 were investigated. Ball milling of MgH2-Co blends was performed under Ar using different milling intensities and different weight ratios. Microstructural and morphological characterization, performed by XRD and SEM, show a huge correlation with thermal stability and hydrogen desorption properties investigated by DSC. A complex desorption behaviour is correlated with the dispersion of the catalytic particles that appears to play a main role in desorption performances. The optimum catalyst concentration was found to be around 10 wt.%, while the optimum value of the ball to powder ratio was 10:1.

Energetic electronic processes on extraterrestrial surfaces

Astronomical bodies without atmospheres are subject to irradiation with energetic photons and particles. The resulting surface alterations are evident in the optical reflectance spectra discernible through remote optical sensing from Earth. Here I review the most important processes initiated by electronic excitations and ionizations by ions. These include electronic desorption or sputtering, chemical reactions, and charge transfer. It is argued that dissociative electron attachment and Auger initiated desorption play a role in desorption of ice mantles on grains in dense interstellar molecular clouds. The paper describes the essentials of laboratory simulations and points out to opportunities for atomic collision physicists to contribute to important astrophysical and planetary problems, including the evolution of galactic matter and the possible extraterrestrial genesis of life.

Role of Desorption in the Growth Process of Molecular Organic Thin Films

Growth studies of ultrahigh vacuum deposited thin films are often carried out ex situ, assuming the total film mass reached at the end of the deposition is preserved in the subsequent stages of film preparation. Many kinetic models commonly adopted to analyze quantitatively the mechanism of growth take into account the role of the deposition rate of molecules on the substrate surface, their diffusion, and their possible desorption. Within this framework, a strong simplification (and approximation) of the model is achieved when considering a regime of complete condensation (i.e., neglecting the possibility of re-evaporation of the deposited molecules, both during the deposition and the postdeposition stages of growth). Here, we demonstrate that, for molecular materials of relatively small organic molecules physisorbed on inert surfaces, this phenomenon may strongly affect not only the surface dynamics during deposition but also the postdeposition stage of thin film preparation. Some examples showing clearly its effects on the surface of single crystals and the thin film phase are reported and discussed. Finally, a quantitative description of desorption is provided by comparing the prediction of thermodynamics for the quaterthiophene/silica system with the experimental observation of the growth dynamics of the film and the results of approximate kinetic models. The thermodynamic model employs the surface free energies of a quaterthiophene crystal, which are evaluated by molecular simulation using a newly developed force field.

Effects of low-molecular-weight organic acids and residence time on desorption of Cu, Cd, and Pb from soils

Effects of low-molecular-weight organic acids (LMWOAs) and residence time on desorption of Cu, Cd, and Pb from two typical Chinese soils were studied. Citric, malic, and acetic acids were chosen as representatives of LMWOAs commonly present in soils. CaCl 2 and NaNO 3 were used in desorption as they were main soil background electrolytes for comparison. Desorption of Cu, Cd, and Pb from both soils followed the descending order: citric acid > malic acid > acetic acid > CaCl 2 > NaNO 3, which was consistent with the order of stability of Cu–, Cd–, and Pb–LMWOAs complexes from large to small and ion exchange ability of Ca 2+ and Na +. Desorption of metals by inorganic salts decreased with increasing desorption solution pH. Whereas desorption of metals by LMWOAs showed different trend in response to pH change due to their different complexing abilities. Malic and acetic acids released less metals at low pH 3.1 compared with citric acid at pH 7, indicating that pH was not the dominant factor governing the release of metals. In addition, all LMWOAs desorbed more metals than inorganic salts, CaCl 2 and NaNO 3. Therefore, organic ligands played a dominant role in desorption of heavy metals. More metals were released from Jiangxi soil than from Heilongjiang soil due to lower soil pH, CEC, organic matter content and manganese oxide of Jiangxi soil. Generally, desorption of metals decreased with increasing residence time of metals in soils.

The Use of Surfactants as Possible Enhancers in Bioremediation of Creosote Contaminated Soil

A study on five nonionic surfactants (Arkopal-N-060, Arkopal-N-080, Arkopal-N-100, Hosaf-541-KS and Tween-80) commercially available in South Africa was carried out to determine their effect on the desorption and degradation of creosote in a soil contaminated with 250 000 mg kg(-1) creosote with a view to developing a cost effective methodology for treating creosote contaminated soils. The surfactants were studied in concentrations of 0.01, 0.1, 0.35, 0.5 and 1.0% (v/v) in liquid cultures. Results from the studies showed that all the surfactants studied were able to enhance the desorption and degradation of creosote to different extents. The enhancement ranged from as little as <10% in 0.1% surfactant to as high as 45% in 0.5% surfactant. The effect on degradation of creosote was more obvious (30-65%) in the different surfactants at different concentrations. Arkopal-N-060 was observed to be the most effective in the desorption and degradation of creosote. The effect of Hosaf-541-KS on the degradation of creosote was found to be comparable with those of Arkopal-N-060, however, its desorption capabilities were much lower than those of Arkopa-N-060. The concentration of the surfactant was found to play a significant role in desorption of creosote. It was observed that surfactant concentrations of 0.35 and 0.5% were the most effective in the desorption of creosote. Above and below these concentrations, the effect of the surfactants was observed to decrease. All surfactants studied were not found to inhibit microbial growth at the concentrations studied.

Gas‐Phase Desorption of Diphenylamine from Porous Silicon

In this work, the desorption of diphenylamine from different five types of porous Si substrates under low vacuum is examined. These substrates include (i) freshly prepared porous Si; (ii) ambient‐oxidized porous Si, and rapidly oxidized porous Si samples processed at the maximum temperatures of (iii) 400°C, (iv) 600°C, and (v) 1180°C. A typical experiment involves the measurement of the rate of desorption as a function of surface morphology, composition, and temperature. These results suggest that desorption from the porous matrix is limited by strong capillary forces and can be overcome by external factors such as temperature. The chemical composition of the porous Si surface also plays a role in desorption and can increase or lower desorption rates. The clearest difference in diphenylamine desorption behavior is detected between the freshly prepared porous Si surface and porous Si samples rapid thermally oxidized at 600 and 1180°C. © 1999 The Electrochemical Society. All rights reserved.

Limiting role of desorption in hydrogen transport across a deposited beryllium film

Hydrogen transport across a deposited beryllium layer has been investigated using the hydrogen permeability and concentration pulse methods. A layer of beryllium was deposited on a prepurified nickel membrane by cathode sputtering in a glow discharge plasma in “especially pure” grade hydrogen. An analysis of the experimental results showed that the main limiting process for hydrogen transport is desorption from the layer rather than diffusion in the bulk of the layer. A mathematical transport model is proposed and used to determine the rate constant of hydrogen desorption from beryllium.

Adsorption and desorption of oxygen on stepped tungsten surfaces

The adsorption and desorption of oxygen on stepped tungsten surfaces with orientations close to the (110) orientation and steps parallel to the most densely packed crystal direction ([111]) is studied with low energy electron diffraction, Auger electron spectroscopy, work function measurements and thermal desorption spectroscopy. With increasing deviation from the (110) orientation, an increasing preference for the formation of the p(2 × 1) domain with the densely packed direction parallel to the steps is noted. The adsorption kinetics does not differ markedly from that on the flat (110) surface, however the desorption behaviour at low coverages ( θ < 0.3) is quite different. The results are interpreted in terms of the dissociation of a mobile precursor at terrace and step sites, the competition between the two domains during their growth and a step-induced premature transition to the complex structure observed on flat (110) surfaces at θ ⋍ 8. The steps are believed to play also a significant role in desorption.

Methoden zur bestimmung der desorptionsgeschwindigkeitskonstante chromatographischer prozesse

Methods for the determination of the desorption—mass-transfer coefficients in chromatographic processes Methods for the determination of desorption—mass-transfer coefficients are discussed. The role of desorption has been investigated from a basic model of chromatography. The role of desorption has been investigated from a basic model of chromatography. Resolution of the equation and calculation of the coefficient is possible by numerical methods. Comparison demonstrated that experimental and calculated curves were in good agreement.