Energetic Surface Research Articles

On the nature of the energetic surface heterogeneity in ion adsorption at a water oxide interface: the behavior of potentiometric, electrokinetic, and radiometric data

On the nature of the energetic surface heterogeneity in ion adsorption at a water oxide interface: the behavior of potentiometric, electrokinetic, and radiometric data

Synthesis of ultrafine particles by surface discharge-induced plasma chemical process (SPCP) and its application

A comparison was made between the present surface discharged-induced plasma chemical process (SPCP) approach to chemical vapor deposition (CVD) and another type of cold plasma CVD using a silent glow discharge (GPCP). In the GPCP CVD system, two coaxial cylindrical electrodes are used in combination with two coaxial quartz tubes spaced at a small gap to generate silent discharge in the gap. In the SPCP CVD system, a ceramic-made electrode assembly is used, and a high frequency and a high voltage are applied to form an energetic and stable surface discharge. Both of the methods can produce ultrafine particles of silicone dioxide and titanium dioxide under room temperature and atmospheric pressure. However, SPCP CVD has a great advantage over GPCP CVD in that it permits further electrostatic processing in the same reaction region. For example, a very peculiar ceramic membrane could be produced with SPCP CVD by depositing electrostatically the ultrafine particles on a ceramic substrate and sintering the deposited layer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Monolayer adsorption on heterogeneous solid surfaces: a density functional approach

A density functional type theory for strictly two-dimensional films adsorbed on geometrically flat, but energetically heterogeneous surfaces is presented. Model calculations are carried out for a monolayer adsorbed film of hard spheres. The obtained results indicate that, in contrast to previous assumptions, the role of the topography may be even more important than the role of global energetic surface heterogeneity.

Late Quaternary sedimentation and sea level changes on the inner Scotian Shelf

The inner Scotian Shelf off the Eastern Shore of Nova Scotia forms an irregular surface that extends some 25–30 km seaward of the present coastline to water depths of about 100 m where it drops off into Emerald Basin. The distribution of Late Quaternary deposits is highly variable both along and across the shelf. These sediments preserve a record of Late Wisconsinan glaciation, ice recession, and late- and post-glacial changes of relative sea level. Glaciomarine deposits occur in a valley complex extending seaward from Halifax Harbour. East of Halifax, we observe a three-part zonation across the inner shelf. The innermost zone extends to water depths of about 50 m. It is characterized by acoustic basement (Meguma Group metasediments), either outcropping or overlain by acoustically unstratified deposits, interpreted as glacial diamict, and by a unit interpreted as stratified outwash. These units are overlain by stratified valleyfill deposits representing Holocene lacustrine and estuarine facies, which have been sampled in a number of cores. Much of the inner shelf is covered by a thin veneer of sand and gravel, generally less than 1 m thick. Further seaward, the sea floor is an erosional unconformity that truncates acoustic units interpreted as glacial diamict and stratified drift. The stratified estuarine deposits found in the inner zone appear to be absent here, but thin patches of transgressive lag deposits occur throughout the area. The outer part of the inner shelf is dominated by outcrop of acoustic basement, with very limited surficial sediment cover. This zone of rugged outcrop occupies half or more of the inner shelf width over much of the study area. The extensive outcrop is attributed to a combination of glacial and/or glaciofluvial erosion, limited recessional deposition, and reworking of any remaining sediment cover by energetic long-period surface gravity waves under lower postglacial sea levels. Seaward of the outcrop zone, there is a transitional area between the inner shelf and Emerald Basin. This zone is characterized by high relief, with exposures of acoustic basement rising up to 60 m above intervening depressions. The depressions are partially filled by stratified glaciomarine and marine deposits up to 55 m thick. Lateral transitions between stratified and unstratified facies along a morainal ridge in northern Emerald Basin suggest the presence of a partially grounded floating ice margin in this area. Late-glacial relative sea level changes remain poorly defined. Several lines of evidence suggest high relative sea level early in the process of glacial recession from the inner shelf, followed by a rapid drop resulting from glacio-isostatic rebound. Samples of estuarine and salt-marsh deposits collected in cores from the inner part of the inner shelf provide evidence of Holocene marine transgression from below −40 m at 11,000 years BP, continuing to the present.

The nature of catalytic sites on lanthanum and neodymium oxides for dehydration/dehydrogenation of ethanol

The multi-pathway (dehydration/dehydrogenation) conversion of ethanol has been used to investigate the nature and behavior of catalytically active sites on lanthanum and neodymium sesquioxides. Catalytic reaction data, coupled with infrared spectroscopic characterizations of adsorbed species, indicate that at least two different types of catalytically active sites are generated on activated La 2O 3 and Nd 2O 3 surfaces that are prepared by thermal dehydration of the corresponding trihydroxides. One kind of site (designated Type I) is much less numerous than the other (Type II), but is more strongly basic and has a much higher initial activity for alcohol dehydration, via a probable ethoxide intermediate, at 300–400°C. The parallel alcohol dehydrogenation pathway, on the other hand, occurs only on Type II sites, which also have moderate dehydration activity. The resulting aldehyde product readsorbs exclusively on the more strongly basic Type I sites, where it undergoes a series of secondary condensation reactions that cause a decrease in the overall rate of alcohol dehydration. The comparative behavioral features of the two kinds of sites may be due to differing surface environments, with Type I sites being in structurally more defective and/or more energetic surface locations than are Type II sites. Increases in pretreatment temperature of the oxides cause thermally induced transformations of Type I sites into Type II sites by a surface annealing or restructuring process, with corresponding modifications in the observed catalytic behaviors for the two alcohol conversion pathways.

The variation in, and correlation of, the energetic potential and surface areas of powders with degree of uniaxial compaction stress

Particulate solids of different sizes, shapes, surface area and hardness were characterized in terms of surface area, surface energy and intraparticulate porosity before and after uniaxial compaction over the stress range 0–250 MPa using low temperature (77K) nitrogen adsorption. Prepared compacts of microfine cellulose (Elcema P050), microcrystalline cellulose (Avicel PH101), dicalcium phosphate dihydrate, magnesium trisilicate and titanium dioxide were diametrally fractured to elucidate the physico-mechanical behaviour of the coherent compacts and to assess the nature of the particleparticle bond. Surface adsorption potentials and a dimensionless bonding factor were correlated with the unaxial compact stress to form coherent compacts for a range of plastic, elastic and fragmentary materials. There is, with the above materials, a linear relationship between the natural logarithm of the diametrally fracture stress and compact voidage.

Further comments on the preparation of mixed organic layers chemically bonded on silicon dioxide : Adsorption of modifiers from strongly adsorbed solvents

When cyclohexane was used to dilute mixtures of R 1R 2R 3-(dimethylamino)silanes, the adsorption isotherms relating the composition of the resulting monolayer of organosiloxy substituents with that of the mixture used for treatment were of the Freundlich type. This was an impressive check on the energetic surface heterogeneity of hydrated silicon dioxide samples as the most important factor governing the chemical modification of that surface. Therefore, in seeking an explanation of the origin of the non-Freundlich isotherms when pyridine and 1,2-dimethoxyethane were used to dilute the modifiers, attention was focused on the more subtle nature of the surface energetic heterogeneity. In this way a satisfactory explanation of the origin of the non-Freundlich adsorption isotherms was obtained.

Process monitoring of a-C:H plasma deposition

The deposition process of amorphous hydrogenated carbon (a-C:H) in a 13.56 MHz hydrocarbon glow discharge system is investigated. Mass spectrometry was used to measure the relative abundance of the different ionic species. While there is a strong dependence of the mass spectra on the type of hydrocarbon gas (e.g., benzene, hexane, methane), the film properties are independent of the precursor. Spatially resolved spectroscopy of the optical emission was applied to study the interaction between energetic ions and substrate surface. Strong emission from small fragments, such as C, C2, and CH in the vicinity of the negatively self-biased cathode shows the importance of impact-induced fragmentation and explains the independence of film properties of the hydrocarbon process gas. With an electrically heated Langmuir probe we measured the potential, the density and the electron temperature of the plasma. In situ determination of the properties of the growing film, such as refractive index, thickness, absorption, and optical gap, was achieved by recording the reflectivity of the substrate during deposition.

Theory of charge exchange in the scattering of molecular ions from simple metals.

A description of the charge exchange between energetic diatomic molecular ions and metal surfaces is presented, which includes in a semiclassical way the coupling between the available exit channels. Explicit results for resonant electron capture during the scattering of ${\mathrm{H}}_{2}$${\mathrm{}}^{+}$ from Al(110) are given. For low incident energies, capture to both the X ${}^{1}$${\ensuremath{\Sigma}}_{g}^{+}$ and b ${}^{3}$${\ensuremath{\Sigma}}_{u}^{+}$ states occurs on the incident portion of the trajectory. Capture to the singlet state predominates for molecule-axis orientations nearly parallel to the surface, and to the triplet state for near-normal orientations. The axis-orientation dependence of the triplet occupation probability and the dissociation-fragment relative kinetic-energy distribution are calculated, as is the vibrational population distribution of the singlet ground state.

Electroinitiated polymerization of 2-ethylhexylacrylate on carbon fibers

The electroinitiated polymerization of 2-ethylhexylacrylate in dimethylformamide in the presence of tetrabutylammoniumiodide was investigated at 288–314 K, with graphitized monofibers being used as a cathode. Electron microscopy showed that the surface of a carbon fiber is characterized by considerable microheterogeneity. The fiber interaction with the propagating polymer chain was supposed to be different due to the energetic microheterogeneity of the fiber surface. This has been proved by micrographs of carbon fiber samples after electrolysis. The local excrescences of poly (2-ethylhexylacrylate) could not be separated after prolonged acetone extraction of the samples. They were conventionally referred to as a grafted polymer. It is inferred that the energetic surface microheterogeneities have a considerable effect on the grafting process regardless of the nature of the reactive centers. The use of carbon monofibers as a cathode does not substantially affect the mechanism of the 2-ethylhexylacrylate electroinitiated bulk polymerization. It is shown that the solution polymerization of 2-ethylhexylacrylate in dimethylformamide occurs according to an anionic mechanism and leads to oligomer formation. The experimental rate constants of the electroinitiated polymerization of 2-ethylhexyl-acrylate, depending on current density and temperature, as well as the total activation energy were determined.

Numerical Method for Two-Dimensional Vlasov Equilibrium as a Nonlinear Boundary Value Problem

A computational method for analyzing axially symmetric Vlasov equilibrium as nonlinear boundary value problem is presented. The method consists of combined use of shooting method and Newton's method. Equilibrium distribution function is expressed in terms of constants (or quasi-constants) of motion and parameters representing temperature anisotropy and magnetic trapping. Charge and current density calculated are substituted into Maxwell equations which reduce to coupled equations for magnetic flux function and electrostatic potential. These equations are solved by shooting method from two opposite boundaries on which the values are determined by Newton's iteration scheme such that solution are smoothly connected inside plasma. Some techniques are introduced to remove singularities on symmetry axis and to determine boundary values on vacuum surface. The method is applied to bumpy cylinder with hot electrons and surface plasma and to thermal barrier with sloshing ions, energetic and warm electrons and surface plasma, assuming periodicity along symmetry axis.

Adsorption and excess fission XE: Adsorption of XE on vacuum crushed minerals

We report the results of Xe adsorption studies at low partial pressures of Xe (∼2×10−13 atm) for a terrestrial labradorite and lunar anorthosite 15415 which were crushed under high vacuum. The creation of fresh surfaces resulted in a distribution of surface adsorption potentials, with the most energetic, but least abundant, fractions of the surface dominating adsorption behavior at lower temperatures. Atmospheric exposure tends to eliminate the most energetic surface fractions. For sample 15415, surfaces with an adsorption potential as great as 13.7 kcal/mole were created, but these constituted only about 10−6 of the surface area. Observation of the adsorption behavior of this sample over a period of days revealed the gradual disappearance of the most energetic fractions of the surface, probably because of site competition effects caused by sorption of active gases in our high vacuum manifold. Our results consist of values of the Henry constants of Xe adsorption at various temperatures. We have used extrapolations based upon these data to evaluate the possible role of adsorption in the excess fission Xe effect observed in lunar highland gas‐rich breccias, for a model in which excess fission Xe is concentrated by adsorption while diffusing through the regolith. Our experimental results, and estimations of the sorptive properties of the in situ regolith based on the time scale of lunar surface Rn emanations, indicate that adsorption falls about five orders of magnitude short of accounting for the effect. We also infer that the adsorption characteristics of our vacuum‐crushed lunar sample are reasonable analogs to those of in situ lunar soil, so that the failure of adsorption to account for excess fission Xe cannot be attributed to significant differences in sorptive behavior of these materials.

Entrainment by bottom currents in Lake Erie

Previous studies of the central basin of Lake Erie have indicated, on the basis lakewide budgets of heat and dissolved oxygen, that the thickness of the hypolimnion and the interaction of the hypolimnion with the overlying fluid are important factors governing the dissolved oxygen concentration in the near‐bottom water. Data collected during an intensive field program in 1979 contain an example of an event during which both the thickness and temperature of the hypolimnion increase due to an erosion of the thermocline from below. This thickening of the hypolimnion requires two conditions. First, the thermocline region, or metalimnion, must be thick enough so that the effects of the energetic surface mixing processes are confined to the upper portion of the thermocline. And second, the currents in the thin hypolimnion must be strong enough to entrain overlying metalimnion water down into the hypolimnion. An analysis of the current meter data suggests the source of turbulent energy driving the mixing is shearing stresses at the bottom. During the entrainment event, the contribution to bottom dissolved oxygen supply is about 10% of the daily demand.

Adsorption of surfactants on mineral oxide surfaces from aqueous solutions: I: Isomerically pure anionic surfactants

Adsorption isotherms for three isomerically pure alkylbenzene sulfonates were measured on alumina and kaolinite from aqueous solutions. A patchwise adsorption model, which incorporates bilayer adsorption, lateral interactions, and two-dimensional phase transitions, is developed and shown to describe the observed isotherms below the CMC. As expected, Henry's Law describes the adsorption at sufficiently low surfactant concentrations. In this region, only unassociated, first-layer, surfactant molecules are present on the surface and at least the terminal 10th through the 12th carbons in the alkyl chain interact strongly with the surface, in addition to the charged head-surface electrostatic attraction. The adsorption increases rapidly beyond a certain concentration. At this concentration, hemimicelles resulting from lateral interaction between adsorbed surfactants first appear on the most energetic surface patches. At still higher concentrations, successively less energetic patches are sites for two-dimensional phase transitions forming hemimicelles. The environment for methylene groups in the hemimicelle is more favorable than that in a micelle. Above the CMC, adsorption is independent of concentration. This indicates that micelles do not adsorb significantly and that the pseudo-phase separation model is a good approximation for these systems.

Conformational analysis of double‐helical polynucleotides

AbstractThe intramolecular interaction energy of the regular double‐helical polynucleotide as a function of variables that determine the mutual position of base pairs and sugar pucker was calculated using atom–atom potentials. The calculations showed the existence of two valley‐like regions with minimal values on the energetic surface. One of them corresponds to the A family of nucleic acids, the other to the B family. The points that correspond to the models constructed by means of x‐ray data are placed in a conformational space near the lines that describe the position of the bottom of the valleys.

Investigation of energetic surface state distributions at real surfaces of silicon after treatment with HF and H2O using large-signal photovoltage pulses

It is shown that the field-modulated large-signal photovoltage offers definite methodological advantages in comparison to other methods more frequently used for the determination of surface state distribution. Apparatus and sample preparations are described. The distribution of fast states in the forbidden gap at real silicon surfaces was studied after treatment in HF and rinsing in H2O up to times in excess of 100 h. Whilst for short rinsing times minimum concentrations of 3*1012 states cm-2 eV-1 were found, prolonged rinsing led to an 'intrinsic' distribution where the concentration in the minimum was lower by a factor of ten. The results are compared with those recently obtained at thermally oxidised silicon. A meaningful separation of surface states into three groups of different physical origin is possible both for real and for oxidised silicon surfaces. Fluoridation as a probable cause of extrinsic surface states, model descriptions of intrinsic states and, finally, certain aspects concerning semiconductor device technology are discussed.

Adsorption of Freon 113

Comparative adsorption data for Freon 113 (1,1,2 trichloro-1,2,2 trifluoroethane) and krypton on Graphon, presented in the preceding paper, showed that the adsorption behavior for krypton, measured at 104–120 K, and Freon 113, measured at 250–370 K, were very similar over the entire pressure range studied. The Freon 113 molecule was shown to adsorb with approximately 2.5 times the molecular area of krypton and to orient with its dipole axis perpendicular to the Graphon surface. Additional adsorption data gathered here indicate that the similar inert behavior of krypton and Freon 113 is also shown on heterogeneous energetic surfaces — anatase, silicon and water covered silica. Surface pressures (π) calculated for Freon 113 on surfaces exhibiting low heats of adsorption are approximately equal to the liquid surface tension, while for surfaces with high heats of adsorption, π can be twice as large.

The nature of active sites on catalytic alumina: Information from site poisoning by sulfur-containing molecules

The natures of low-temperature (<100 °C) catalytic sites on activated alumina have been examined by selective poisoning studies, using various sulfur-containing molecules. Hydrogen sulfide and methyl mercaptan are effective poisons, at 25 °C, for sites on alumina that catalyze double-bond migration and cis/trans rotation in olefins, but have virtually no effect on sites that promote deuterium exchange reactions of olefins and aromatics. Sulfur dioxide, on the other hand, affects neither type of site at 25 °C, but is “lethal” to both types when absorded at 400 °C. The results have been correlated with those of previous infrared, EPR, and selective poisoning studies. Olefin isomerization sites on alumina have a surface density of ≈5 × 10 13/cm 2 and consist of certain exposed Al 3+ ions at the surface, but may require the presence of adjacent O 2− ions. Deuterium exchange sites are much less numerous (0.3–0.8 × 10 13/cm 2) and are associated with a very small fraction of highly energetic surface O 2− ions. At 25 °C, the two types of sites apparently operate simultaneously but independently of each other.

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF 2 underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.

On the energetic heterogeneity of clean evaporated nickel films studied by means of the place change between adsorbed isotopic CO molecules

The adsorption of C 12O 16, C 13O 16, and C 12O 18 was used to study the energetic surface heterogeneity of evaporated Ni films. The isotopic gases were adsorbed one after the other and the gas phase was analyzed mass spectrometrically. If the gases were adsorbed at 77 °K, the equilibrium between gas phase and adsorption phase was obtained between 90 ° and 195 °K. The temperature at which the equilibrium is reached is lowest for the molecules adsorbed at high coverages and highest for the molecules adsorbed on the clean film indicating differences in adsorption energies of the film surface concerning the adsorption of CO. If the successive adsorption of the three isotopic gases took place at 273 °K, no difference in the behavior of the isotopic gases could be observed, indicating that the mobility of the adsorbed molecules is large enough to overshadow the influence of surface heterogeneity. An isotopic exchange between the atoms of the adsorbed molecules could not be observed.