Surface Desorption Research Articles

Formation and Temperature Effect of InN Nanodots by PA-MBE via Droplet Epitaxy Technique.

In this report, self-organized indium nitride nanodots have been grown on Si (111) by droplet epitaxy method and their density can reach as high as 2.83 × 1011 cm−2 for the growth at low temperature of 250 °C. Based on the in situ reflection high-energy electron diffraction, the surface condition, indium droplets, and the formation of InN nanodots are identified during the epitaxy. The X-ray photoelectron spectroscopy and photoluminescence measurements have shown the formation of InN nanodots as well. The growth mechanism of InN nanodots could be described via the characterizations of indium droplets and InN nanodots using scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The density of the InN nanodots was less than that of the In droplets due to the surface diffusion and desorption of atoms during the nitridation and annealing process. The average size and density of InN nanodots can be controlled by the substrate temperatures during the growth. For the growth at lower temperature, we obtained the higher density and smaller average size of InN nanodots. To minimize the total surface energy, the coarsening and some preferred orientations of InN nanodots were observed for the growth at high temperature.

Plasma Catalytic Synthesis of Ammonia Using Functionalized-Carbon Coatings in an Atmospheric-Pressure Non-equilibrium Discharge

We investigate the synthesis of ammonia in a non-equilibrium atmospheric-pressure plasma using functionalized-nanodiamond and diamond-like-carbon coatings on α-Al2O3 spheres as catalysts. Oxygenated nanodiamonds were found to increase the production yield of ammonia, while hydrogenated nanodiamonds decreased the yield. Neither type of nanodiamond affected the plasma properties significantly. Using diffuse-reflectance FT-IR and XPS, the role of different functional groups on the catalyst surface was investigated. Evidence is presented that the carbonyl group is associated with an efficient surface adsorption and desorption of hydrogen in ammonia synthesis on the surface of the nanodiamonds, and an increased production of ammonia. Conformal diamond-like-carbon coatings, deposited by plasma-enhanced chemical vapour deposition, led to a plasma with a higher electron density, and increased the production of ammonia.

First-principles study of water desorption from montmorillonite surface.

Knowledge about water desorption is important to give a full picture of water diffusion in montmorillonites (MMT), which is a driving factor in MMT swelling. The desorption paths and energetics of water molecules from the surface of MMT with trapped Li(+), Na(+) or K(+) counterions were studied using periodic density functional theory calculations. Two paths--surface and vacuum desorption--were designed for water desorption starting from a stationary structure in which water bonds with both the counterion and the MMT surface. Surface desorption is energetically more favorable than vacuum desorption due to water-surface hydrogen bonds that help stabilize the intermediate structure of water released from the counterion. The energy barriers of water desorption are in the order of Li(+) > Na(+) > K(+), which can be attributed to the short ionic radius of Li(+), which favors strong binding with the water molecule. The temperature dependence of water adsorption and desorption rates were compared based on the computed activation energies. Our calculations reveal that the water desorption on the MMT surface has a different mechanism from water adsorption, which results from surface effects favoring stabilization of water conformers during the desorption process.

Unconventional resource's production under desorption-induced effects

Abstract Thousands of horizontal wells are drilled into the shale formations across the U.S. and hydrocarbon production is substantially increased during past years. This fact is accredited to advances obtained in hydraulic fracturing and pad drilling technologies. The contribution of shale rock surface desorption to production is widely accepted and confirmed by laboratory and field evidences. Nevertheless, the subsequent changes in porosity and permeability due to desorption combined with hydraulic fracture closures caused by increased net effective rock stress state, have not been captured in current shale modeling and simulation. Hence, it is essential to investigate the effects of induced permeability, porosity, and stress by desorption on ultimate hydrocarbon recovery. We have developed a numerical model to study the effect of changes in porosity, permeability and compaction on four major U.S. shale formations considering their Langmuir isotherm desorption behavior. These resources include; Marcellus, New Albany, Barnett and Haynesville Shales. First, we introduced a model that is a physical transport of single-phase gas flow in shale porous rock. Later, the governing equations are implemented into a one-dimensional numerical model and solved using a fully implicit solution method. It is found that the natural gas production is substantially affected by desorption-induced porosity/permeability changes and geomechancis. This paper provides valuable insights into accurate modeling of unconventional reservoirs that is more significant when an even small correction to the future production prediction can enormously contribute to the U.S. economy.

Thermodynamic Complexing of Monocyclopentadienylferrum (II) Intercalates with Double-Walled Carbon Nanotubes.

By employing the methods of molecular mechanics, semi-empirical quantum-chemical РМ3 and Monte-Carlo, the positioning of monocyclopentadienylferrum (II) molecules in double-walled (5,5)@(10,10) carbon nanotubes (CNT) depending on their concentration and temperature has been studied. The molecules have been found out to form stable bonds with CNT walls, with a tendency between intercalate stability and the CNT structure. The temperature growth (over ~500 K) causes gradual bond ruining followed by extrusion of interwall intercalate. Further temperature increase up to 600–700 K is characterised with intercalate external surface desorption, stabilising the whole system and keeping the interwall intercalate only. The CNT’s UV-spectrum (5,5)@(10,10) depending on the intercalate concentration and association constant of the “double-walled CNT–intercalate” system have been calculated. A combination of unique optical, electrical and magnetic behaviour of cyclopentadienyl complexes with their ability to form high-stable intercalate with CNT opens a prospect of their applying in nanotechnology.

“Guest‐host” intercalate of double‐walled carbon nanotube with tricarbonyl (cyclopentadienyl)manganese

The positioning of tricarbonyl(cyclopentadienyl)manganese molecules in double‐walled (5.5)@(10.10) carbon nanotubes depending on their concentration and temperature was studied using the methods of molecular dynamics, semi‐empirical quantum‐chemical parameterized model number 3 and Monte‐Carlo. The molecules were found to form stable bonds with the carbon nanotubes walls, with a tendency between intercalate stability and the carbon nanotubes structure. A temperature increase (above ˜460 K) causes gradual bond ruining followed by extrusion of interwall intercalate. Further temperature increase up to 600–750 K is characterised with intercalate external surface desorption, stabilising the whole system and keeping the interwall intercalate only. Double‐walled carbon nanotubes UV‐spectra depending on the intercalate concentration and association constant of the “double‐walled carbon nanotubes‐intercalate” system were calculated. A combination of unique optical, electrical and magnetic behaviour of cyclopentadienyl complexes with their ability to form high‐stable intercalate with carbon nanotubes opens a prospect of their application in nanotechnology.

Surface nitrogen functionality for the enhanced field emission of free-standing few-layer graphene nanowalls

The effects of nitrogen functionalization on the field emission properties of vertically aligned few-layer graphene (FLG) nanowall thin films are investigated. Lowered work function and enhanced electron emission property are observed after ammonia plasma treatment. The turn-on field (defined at 10 μAcm−2) is found to be decreased from 6.5 to 4.6 Vμm−1. Additionally, more stable emission with fluctuation less than 5% is obtained after surface N-functionalization. The electron configuration of nitrogen in FLG edge is proposed to be amine (C–NH2) terminal configuration. Nitrogen doping could significantly increases the π density states near the Fermi level. The maximum upward shift of EF is determined to be ∼0.23 eV by low-energy XPS measurements, which mainly accounts for the lower turn-on electric field. Meanwhile, nitrogen functionalization would minimize surface desorption and accounts for more uniform work function distribution. Finally, the nonlinear characteristics of Fowler–Nordheim plots could be understood by thermionic-field emission process.

Thermal stability and microstructure of catalytic alumina composite support with lanthanum species

Lanthanum (La) modified γ-alumina composite was examined for application toward thermostable catalytic support at elevated temperature. La added alumina was prepared through an aqueous process using lanthanum (III) nitrate and then characterized by surface area measurement, X-ray powder diffraction (XRD), differential thermal analysis (DTA), scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoemission spectroscopy (XPS) and surface desorption of CO2. It was found that the properties depended on the La content and heat treatment temperatures. The characterization of the surface, structural and chemical properties of La-Al2O3 showed the existence of a strong interaction between the La species and alumina via formation of new phase and modified surface in Al2O3 samples. LaAlO3 nanoparticle formed among alumina particles by the solid phase reaction of Al2O3 and La2O3. The increase of the surface basicity of La modified alumina was demonstrated using CO2 temperature programmed desorption experiments. The controlled surface interaction between La oxide and alumina provide the unique surface and structural properties of the resulting mixed oxides as catalysts and catalytic supports.

Lateral resolution of desorption nanoelectrospray: a nanospray tip without nebulizing gas as a source of primary charged droplets.

Desorption nanoelectrospray (nanoDESI) was described in 2007 and it represents a miniaturized version of desorption electrospray without the assistance of the nebulizing gas. Compared to DESI, a nanoelectrospray tip (2 ± 1 μm I.D.) generates primary charged droplets of smaller sizes and lower spray liquid flow rates. This is the first report on utilization of nanoDESI for mass spectrometry imaging (MSI). Its new coupling with a Q-TOF instrument allowed faster mass spectra acquisition (4 Hz) essential for MSI of fine surface details. To evaluate nanoDESI potential for mass spectrometry imaging, etched glass substrates with Rhodamine B patterns of different dimensions were prepared. The Rhodamine B lines were analysed in 1D scanning mode and their width was determined experimentally by nanoDESI measurement. The experimental data revealed that the lateral resolution of nanoDESI is close to 30 μm along the x-axis (orthogonal to the inlet). 2D scanning mode confirmed good resolution along both axes as dye squares with dimensions about 60 μm × 60 μm were easily distinguished. The low flow rate of the spray liquid reduced undesirable analyte washing effects, which allowed repeated scanning analysis of the surface. The presented results demonstrate the applicability of nanoDESI for high surface resolution mass spectrometry imaging.

Method for Improving Spatial Resolution of Liquid-assisted Surface Desorption Atmospheric Pressure Chemical Ionization Mass Spectrometry

Abstract Liquid-assisted surface desorption atmospheric pressure chemical ionization source (LA-DAPCI) technique shows good potential in complex matrix mass spectrometry imaging. Due to primary ions and high density charged droplets of solvent generated by corona discharge, analytes on sample surface are extracted and ionized efficiently. However, direct application of the DAPCI ionization for mass spectrometry imaging of complex matrix analytes usually tends to be challenging because of low spatial resolution. To resolve this problem, several ion source parameters and experiment conditions were optimized in the present work, including ion source configuration, chemical composition of the extraction solvent, geometry parameters, solvent flow rate and pressure of nebulizing gas. The results presented here confirmed that the spatial resolution of LA-DAPCI was improved (from (441 ± 14) μm to (58 ± 7) μm). The proposed LA-DAPCI-MS/MS method was successfully used to profile the distribution of Rhodamine 6G with a limit of detection of 0.01 ng cm −2

Tritium release from Li4SiO4 ceramic pebbles in high magnetic field

The behavior of tritium release from Li4SiO4 ceramic pebbles in high magnetic field (MF) was investigated by temperature programmed desorption (TPD). Two batches of Li4SiO4 pebbles produced by wet method were used as the experimental samples, one batch with an average pebble diameter of 0.8mm (the SMALL samples), and the other 1.2mm (the BIG samples). A superconducting magnet was applied to generate MF up to 7T in the sample area during annealing. For both batches of samples, the tritium release curves within and without MF showed very similar characteristics, indicating that the effect of high MF on tritium release behavior is not significant. The tritium release peaks for the BIG samples were observed at much lower temperatures than that for the SMALL samples, even though the grain sizes of the BIG samples are much bigger than that of the SMALL samples. It is considered that surface desorption process dominates the overall tritium release behavior in this work, which probably weakened the MF effect.

Modeling of kinetically limited growth rate for solution-synthesized germanium nanocrystals

Solution synthesis is a common method for preparing semiconductor nanocrystals (NCs). For such solution synthesis, many investigations have considered diffusion-limited growth, in which the diffusion of reactants through the boundary layer (BL) limits the NC growth rate. These studies often model the growth rate with a diffusion BL thickness much larger than the NC size and with unphysically low diffusion constants on the order of 10−12 cm2 s−1. In this work, we have examined the growth of Ge NCs synthesized by injecting Ge amide precursors into a solution of 1-octadecene, oleylamine, and hexadecylamine. We have previously established this low-temperature, low-pressure synthesis route. The resulting Ge growth rate compares well with our model, in which we consider both BL diffusion and surface kinetics of Ge precursors and organic ligand adsorbates. Our modeling results suggest that the NC growth is limited not by diffusion, but by the surface adsorption and desorption kinetics. The BL thickness in the stirred reaction vessel is calculated to be on the same order of magnitude as the crystal radius; therefore, the surface kinetics cannot be ignored. Furthermore, the synthesis temperature is near 300 °C, where the Ge monomer diffusion coefficient within the growth solution is substantially increased and estimated to be on the order of 10−5 cm2 s−1. These considerations agree well with our experimentally measured growth rate and strongly suggest that the NC size evolution is controlled primarily by the surface kinetics.

Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces

The desorption kinetics of molecular hydrogen (H2) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H2 desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH2/3), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H2 desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H2 evolved from subsurface states and 450 °C exposure leading to more H2 desorption from surface SiHx species. Additional surface desorption states were observed, which were attributed to H2 desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H2 desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen.

Advancements in Copper Interconnect Technology: The Effect of Sulfuric Acid on the Adsorption & Desorption of an Advanced MLI Suppressor

In the last five years the size of the copper plated interconnect features for the logic and memory market has dropped below 30nm. This decrease in size has forced plating chemistries to operate on copper seed that is often times either non continuous or has morphology that requires special tuning of the additives to create the bottom up phenomenon. In the past, the traditional path of development led to the continued optimization of the organics additives (accelerators, suppressors, levelers) to help generate the void free fill in the plated interconnects while mostly fixing the inorganic concentrations. A new approach to additive development is to optimize the organic additives in different electrolyte concentrations. Traditionally, the copper chemical vendors were focused on the traditional 40g/L Cu2+, 10g/L sulfuric acid, 50ppm electrolyte formulation. However, optimization of electrolytes can allow for a decrease in defectivity across the wafer. This change in electrolyte formulation has sparked a new set of chemistry development at MLI to tune the organic chemistry to the electrolyte concentrations and also expand the understanding of the effect of electrolyte on the organic additives. The current set of work aims at showing how acid affects the adsorption and desorption of a new advanced MLI suppressor. This work starts with a basic understanding of how acid affects the plating bath with no suppressor present and then expands to show how this new suppressor is affected by the acid changes. A surface adsorption and desorption model is then hypothesized based on the electrochemical signal. The figure below outlines a typical adsorption result where an applied current of 10mA/cm2 is run while solution over the electrode is transitioned from one containing the electrolyte only to one containing the electrolyte and the MLI suppressor. The two plots in the graph show the difference in the adsorption rate as a function of acid concentration. One will note that the higher acid concentration shows a stronger steady state suppression and also a slower adsorption rate. Experiments similar to these will be disclosed and the adsorption / desorption model discussed. Figure 1

Thermal degradation of Poly(methyl methacrylate) with a 1.064 μm Nd:YAG laser in a buoyant flow

The laser radiative oxidative decomposition of poly(methyl methacrylate) (PMMA) and the evolved decomposition products in the gas-phase are investigated using imaging Fourier transform infrared spectroscopy (IFTS). The spatial and temporal evolution of the gas plume in air was investigated with adequate spatial (0.81 mm2 per pixel) and spectral resolutions (2 cm−1). Surfaces of black PMMA samples were irradiated from 4 to 22 W/cm2 with a cw 1.064 μm Nd:YAG laser. Strong spectral emission of methyl methacrylate (MMA) was observed in the infrared. Spatial maps of plume temperature and MMA column density were obtained from modeling the observed spectra by assuming a homogeneous single-plume radiative transfer model (RTM). A spectral model was used to compute the gas emissivity from an experimentally measured, interpolated and extrapolated MMA absorption coefficient database. In addition, the spectral radiance from the irradiated PMMA surface was fitted with Planck's distribution to obtain temporal and spatial surface temperature profiles. The peak signal-to-noise exceeded 50:1, allowing plume temperature and MMA column density determinations with low statistical errors. Laser irradiated PMMA reached a steady surface temperature of 613.9 ± 0.8 K and a peak gas-phase temperature of 700 ± 19 K at 22 W/cm2. The reported statistical uncertainties for all the results are defined as the half-width of the 95% confidence interval and do not include systematic errors associated with the assumption of a homogeneous plume or the effects of turbulence. As laser intensity increased, gas temperature decreased at the surface-boundary layer. A simplified thermal analysis was developed to understand the wavelength dependent surface heating rates from using both CO2 and Nd:YAG lasers. An Arrhenius plot of MMA formation at the surface for a single pixel was compared with established kinetics models. At surface temperatures of 450–600 K, an effective activation energy of 30.83 ± 8.29 kJ/mol was obtained, consistent with surface desorption of the monomer.

Direct analysis of micro area on tooth surface by surface desorption atmospheric pressure chemical ionization mass spectrometry

A novel analytical platform based on a nanoliter needle for sampling and surface desorption atmospheric pressure chemistry ionization mass spectrometry(SDAPCI-MS) for analysis was developed for the direct,fast and micro-area analysis of different parts of a human tooth,including cavity,cavity edge,tooth cusp and tooth sulcus.The results showed that the mass spectra from the four sampling spots on the same tooth were different,and that SDAPCI-MS detected lactic acid,pyruvic acid,phenylacetic acid and propanoic acid were confirmed using tandem mass spectrometry(MS/MS).Principal component analysis(PCA) of the mass spectral data successfully differentiated the different sampling spots,levels of tooth decay and levels of gum disease.Therefore,our nano-SDAPCI-MS approach provides a promising way for micro-area analysis with fast,minimal pretreatment sampling,enabling rapid,simple and reliable surface MS investigation.

Dissolved amino acids in oceanic basaltic basement fluids

The oceanic basaltic basement contains the largest aquifer on Earth and potentially plays an important role in the global carbon cycle as a net sink for dissolved organic carbon (DOC). However, few details of the organic matter cycling in the subsurface are known because great water depths and thick sediments typically hinder direct access to this environment. In an effort to examine the role of water–rock–microorganism interaction on organic matter cycling in the oceanic basaltic crust, basement fluid samples collected from three borehole observatories installed on the eastern flank of the Juan de Fuca Ridge were analyzed for dissolved amino acids. Our data show that dissolved free amino acids (1–13nM) and dissolved hydrolyzable amino acids (43–89nM) are present in the basement. The amino acid concentrations in the ridge-flank basement fluids are at the low end of all submarine hydrothermal fluids reported in the literature and are similar to those in deep seawater. Amino acids in recharging deep seawater, in situ amino acid production, and diffusional input from overlying sediments are potential sources of amino acids in the basement fluids. Thermodynamic modeling shows that amino acid synthesis in the basement can be sustained by energy supplied from inorganic substrates via chemolithotrophic metabolisms. Furthermore, an analysis of amino acid concentrations and compositions in basement fluids support the notion that heterotrophic activity is ongoing. Similarly, the enrichment of acidic amino acids and depletion of hydrophobic ones relative to sedimentary particulate organic matter suggests that surface sorption and desorption also alters amino acids in the basaltic basement. In summary, although the oceanic basement aquifer is a net sink for deep seawater DOC, similar amino acid concentrations in basement aquifer and deep seawater suggest that DOC is preferentially removed in the basement over dissolved amino acids. Our data also suggest that organic carbon cycling occurs in the oceanic basaltic basement, where an active subsurface biosphere is likely responsible for amino acid synthesis and degradation.

Characterisation and potential migration of silver nanoparticles from commercially available polymeric food contact materials

The potential for consumer exposure to nano-components in food contact materials (FCMs) is dependent on the migration of nanomaterials into food. Therefore, characterising the physico-chemical properties and potential for migration of constituents is an important step in assessing the safety of FCMs. A number of commercially available food storage products, purchased domestically within the United States and internationally, that claim to contain nanosilver were evaluated. The products were made of polyethylene, polypropylene and polyphenylene ether sulfone and all contained silver (0.001–36 mg kg–1 of polymer). Silver migration was measured under various conditions, including using 3% acetic acid and water as food simulants. Low concentrations (sub-ppb levels) of silver were detected in the migration studies generally following a trend characterised by a surface desorption phenomenon, where the majority of the silver migration occurred in the first of three consecutive exposures. Silver nanoparticles were not detected in food simulants, suggesting that the silver migration may be due solely to ionic silver released into solution from oxidation of the silver nanoparticle surface. The absence of detectable silver nanoparticles was consistent with expectations from a physico-chemical view point. For the products tested, current USFDA guidance for evaluating migration from FCMs was applicable.

ELECTROCHEMICAL REDUCTION OF BENZYL CHLORIDE ON SILVER, GRAPHITE AND SILVER/GRAPHITE POWDER MACROELECTRODES

Benzyl chloride reduction was studied in a powder macroelectrode (PME) made of silver, graphite or silver/graphite mixtures (1:3, 1:1 and 3:1) in absence of solvent, or using a very low amount of DMF as solvent (PhCH2Cl/DMF 3:1). A 0.1molL−1 KCl aqueous solution was used as anolyte. A competitive hydrogenation and dimerization process was observed, affording the respective toluene and bibenzyl products. The well-known electrocatalytic effect of silver on reduction of the CCl bond was confirmed by a significant positive shift of the benzyl chloride reduction potential in comparison with pure graphite powder. The products distribution was analysed after linear sweep voltammetries at low scan rate (0.1mVs−1), indicating high yields of bibenzyl produced on Ag/graphite-PME. Pure graphite-PME was not selective towards dimer formation. The best results for bibenzyl production occurred at more positive potentials, in the presence of silver. A small amount of solvent (DMF) play an important role on the electrode surface desorption and diffusion of intermediary species.

Aging effects on the stability of nitrogen-doped and un-doped InGaZnO thin-film transistors

The long-term electrical reliability/stability measurements, including negative bias stress and aging over 10 months of nitrogen-doped (N-doped) and un-doped amorphous InGaZnO thin-film transistors (a-IGZO TFTs) were investigated. Aged un-doped a-IGZO TFT exhibits larger threshold voltage shift (ΔVth) of 2.43V and turn on voltage shift (ΔVon) of 5.37V due to combination of the surface desorption of oxygen atoms and moisture adsorption. The noticeable decrease in ΔVth (0.93V) and ΔVon (0.81V) of in-situ nitrogen doped a-IGZO TFT indicates the surface interaction is prevented due to effective passivation of inactive oxygen׳s in the channel. After 10 months aging time, the ΔVth (~2.66V) and ΔVon (~4.62V) of un-doped devices were observed under the negative gate bias stress, which is comparable to ~0.83V and ~0.85V in nitrogen doped a-IGZO devices, respectively. The perspectives reported here shall be useful in fabricating passivation-free oxide based semiconductor TFTs for device operation in stable ambient conditions.