Thin Hydrocarbon Research Articles

Static SIMS: A Study of Damage Using Polymers

As a result of work to establish the surface potential of insulators accurately in a quadrupole static SIMS system of high sensitivity, we have been able to study the effects of increasing dose-related damage on the intensities of the mass spectral peaks in the two archetypal bulk polymers PET and PTFE, as well as thin hydrocarbon contamination layers, with high accuracy. It is shown that the intensities follow very well-defined functions which give damage cross-sections whose values reflect the fragmentation behaviour of the polymers. The effects reflect the number of bonds to be broken to liberate the fragment, the internal complexity of that fragment and the typical damage zone of the ion impact. These concepts show that a static SIMS limit of below 3×1015 ions m-2 exists for changes of <10% in the intensities of the most easily damaged species but that some larger fragments may require a dose of 2×1017 ions m-2 to maximize their intensity! This work has three main conclusions. Firstly, by defining a figure of merit factor,F, equal to the ratio of the absolute intensity of a peak to the fractional rate of change of that peak with the ion dose, it is possible to define the optimal beam parameters for static SIMS measurements. The higher the value ofF, the more the intensity per unit of onset of damage. The highestFvalues occur at higher beam energies and, in general, xenon gives greater efficiency than argon. Secondly, the development of damage may be described by simple bond breaking. Thirdly, a study of the damage process gives quite detailed structural bonding information not directly available from the traditional static SIMS spectrum.

Mass density and hydrogen content of diamondlike carbon as related to the preparation by plasma-enhanced chemical vapor deposition

Combined neutron and x-ray reflectometry was used to determine mass density and hydrogen content for thin (less than 3000 Å) diamondlike hydrocarbon films on polished Si (100) substrates. The introduction of ‘‘twin’’ neutron reflectometry improved the accuracy of the measurements. Mass densities in the range of 1.60–1.84 g/cm3 and hydrogen contents of 31–36 at. % were determined together with the nucleus densities of hydrogen and carbon. A series of diamondlike carbon films prepared by plasma-enhanced chemical vapor deposition was investigated to analyze the effect of depositing films at different flow rates of methane precursor gas. The mass density was found to increase with flow in the range of 1–8 standard cm3/min (sccm). For higher flows the mass density was constant. The hydrogen content did not depend on the rate of flow in the interval of 2–30 sccm. Finally, results of the mass density measured in a simpler way, using a scanning electron microscope and a profilometer, were compared to the results obtained by neutron and x-ray reflectometry.

パルス化RF放電によるプラズマ重合アセチレン超薄膜の生成モデル

Plasma polymerization by using a pulsed rf discharge was performed for preparation of ultra thin organic film. The discharge capacitively coupled was initiated in a box-type reactor at an uniform flow of an acetylene/argon mixture gas. 2-10 nm scale ultra thin hydrocarbon film was deposited on a silicon wafer. The surface topography of the film examined by AFM appears to be pinhole free. The distribution of thickness measured by an elipsometer suggested the reaction in gas phase is significant. Therefore, the theoretical calculation was performed by using a model of radical reaction in the gas phase, and the obtained equations were fitted well to the results of experiments.

Ellipsometry and X-ray Reflectivity Studies on Monolayers of Phosphatidylethanolamine and Phosphatidylcholine in Contact with n-Dodecane, n-Hexadecane, and Bicyclohexyl

Monolayers of the phospholipids 1,2-dipalmitoylphosphatidylethanolamine (DPPE) and 1,2-dipalmitoylphosphatidylcholine (DPPC) are studied at the water/air interface in contact with n-hexadecane, n-dodecane, and bicyclohexyl by null ellipsometry and X-ray reflectivity along the isotherms. From recent diffraction data we derive refractive indices nx and nz to calculate the thickness of the mixed films in the condensed phase by ellipsometry. The thickness is compared with the results from X-ray reflectivity measurements. Both methods reveal that the mixed lipid/hydrocarbon film is not covered by a thin hydrocarbon film as known from short chain alcanes like hexane. The incorporation of the hydrocarbon affects the film thickness by reducing the tilt angle of the lipids. This way DPPC, which due to the large head group does not exhibit a non tilted condensed phase at the water/air interface at all, enlarges its value for nz at the expense of nx, yielding a condensed mixed phase with zero tilt angle. The resulting value for the thickness of the tail region from both methods is always smaller than 21 Å, showing that penetration is strictly limited to the monolayer region.

Thin Hydrocarbon and Water Films on Bare and Methylated Silica: Vapor Adsorption, Wettability, Adhesion, and Surface Forces

The vapor adsorption of different n-alkanes, cyclohexane, toluene, and water on bare and methylated pyrogenic silica (Aerosil OX-50) has been studied gravimetrically. Linear adsorption isotherms of the n-alkanes and of cyclohexane on both substrates are found up to high relative vapor pressures; the same holds true for toluene on methylated silica. The linearity of the isotherms indicates relatively weak lateral interactions. On bare silica, the adsorption, expressed in mol/m 2 , of the n-alkanes studied (C7-C9) is independent of chain length. The adsorption strongly increases after the coverage, corresponding to a monolayer of alkanes oriented perpendicular to the surface has been reached. Methylation of the silica is found to decrease the adsorption of all the adsorptives studied. On methylated silica the octane isotherm lies below the coverage of a monolayer parallel to the surface until just before saturation. From the adsorption data, surface pressure isotherms are constructed, and the work of adhesion is obtained. The work of adhesion reveals that the Lifshits-van der Waals part of the silica surface tension is reduced from 44 mJ/m 2 for bare (pyrogenic) silica to 30 mJ/m 2 for methylated silica. The adsorption data are also converted to disjoining pressure isotherms. At small film thicknesses, the disjoining pressure can be described by an exponential short-range interaction

Suppression of AlSb oxidation with hydrocarbon passivation layer induced by MeV-He+ irradiation

A very thin hydrocarbon coating layer of at most a few monolayers induced by the electronic scattering of MeV-He+ ion-beam irradiation effectively and completely suppresses oxidation of the compound semiconductor AlSb, which is liable to be oxidized by mere exposure to air, because of the coating layer’s hydrophobic property. Of the many kinds of hydrocarbons, alkyl and phenyl groups are particularly effective for oxidation suppression. The AlSb oxidation mechanism and oxidation suppression mechanism are discussed.

Energetically and Pressure Driven Liquid-Solid Transitions in Molecularly Thin Hydrocarbon Films

ABSTRACTIn this study we used molecular dynamics simulations to investigate the structural changes in nanoscopically thin n-octane films confined between smooth solid surfaces as a result of a) increasing solid-methylene unit affinity and b) increasing pressure. Increasing solid-methylene unit energetic affinity resulted in the solidification of the film at a critical value. A similar transition is observed at a critical value of pressure. Bulk n-octane was a liquid in both cases. The transition was signaled by an abrupt increase in the intermolecular order and was facilitated by a precipitous extension of the octane molecules, which adopted almost fully extended configurations. A discontinuous jump in the film density at the critical values of solid affinity and pressure was evident. The characteristics of the transitions showed that it was a mild first order transition from a highly ordered liquid to a poorly organized solid.

On the structure of thin hydrocarbon films

We compare reported compositions of a-C:H films in a ternary phase diagram. It is assumed that the films comprised three phases: sp3 hybridized carbon, sp2 hybridized carbon and hydrogen. The data are found to split into two well-separated groups. This separation depends on the method used to measure the sp3/sp2 ratio. We conclude from the comparison of NMR and infrared data that infrared analysis does not provide a quantitative measure of the sp3/sp2 ratio.

Influence of the ion energy on the growth and structure of thin hydrocarbon films

Noncrystalline hydrocarbon films were deposited from methane plasmas in an electron-cyclotron-resonance plasma reactor. The films were characterized by infrared spectroscopy and high-energy ion-beam analysis. Film properties were investigated as a function of the energy of ions impinging on the surface of the growing film. The ion energy was varied by applying a dc bias to the sample in the range from 30 to 200 eV. The ion energy was measured with a retarding field analyzer under identical experimental conditions. An abrupt change was found in the sp3/sp2 ratio in the energy interval from 80 to 120 eV. Other film properties such as the refractive index, density, and hydrogen-to-carbon ratio exhibit a more or less monotonic dependence on the ion energy. The results are compared with published data on hydrocarbon films. An analytical model was developed to describe the energy dependence of the hydrogen fraction in the films. It is based on the assumption that displacement of hydrogen atoms is the dominating mechanism that controls the hydrogen fraction in hydrocarbon films. The results are also discussed on the basis of the fully constrained network model.

TIME DEPENDENT FORMATION OF SULFIDIC FILMS ON COPPER SUBSTRATES WHEN EXPOSED TO HYDROCARBONS CONTAINING ELEMENTAL SULFUR

ABSTRACT Hydrocarbon fuels containing elemental sulfur can cause copper and copper alloy components of a fuel delivery system to severely corrode. Experiments were undertaken to study the composition, thickness and rate of growth of films formed in sulfur containing fuels. The time dependent growth of these films was studied using Auger electron spectroscopy in combination with standard ion sputtering techniques. Initially, the thickness of the films increased rapidly, but slowed after longer exposures. This behavior was shown to obey the parabolic law that is used to describe oxide film growth in air. The relative amount of sulfur in a layer directly beneath a thin hydrocarbon overlayer was found to increase with exposure of copper to the fuel. For long exposures this layer appeared to be predominantly CuS with Cu2-xS and then Cu2S below it, while the film was composed of predominantly Cu2S after short exposures to the hydrocarbon. X-ray photoelectron spectroscopy supported this conclusion.

THE INTRA-LATROBE PLAY : A CASE HISTORY FROM THE BASKER/MANTA BLOCK (VIC/P19), GIPPSLAND BASIN

In 1981 Shell and its co-venturers were the successful applicants for gazettal block V80-3, now permit VIC/P19, on the north-eastern margin of the Gippsland Basin where, subsequently, 10 exploration wells were drilled. At the time of the award, the offshore Gippsland Basin had been explored for some 20 years, and the conventional 'Top Latrobe' play even then was considered to be largely exhausted although a few small traps of doubtful economic viability remained untested. Thus, from the outset, exploration in VIC/P19 also emphasised the intra-Latrobe play. While the existence of the intra-Latrobe play has long been recognised, its extent and limiting parameters are less well documented.Recent exploration results in the southern part of VIC/P19 indicate that the main phase (peak) of generation and expulsion of hydrocarbons from intra- Latrobe source rocks occurs at depths of 4 to 5 km for oil and 5 to 6 km for gas. Large-scale vertical migration of hydrocarbons (up to 2 km or more) is probably occurring in many parts of the central Gippsland Basin and has charged faulted intra- Latrobe traps, such as found at Basker-1 and Manta-1. These accumulations are characterised by multiple stacked reservoirs (fluvial and alluvial sandstones) and thin hydrocarbon columns. However, similar adjacent traps are dry, despite the presence of equivalent reservoirs (e.g. Basker South-I and Chimaera-I), probably due to inadequate lateral fault seals. Lateral sealing may occur along the fault plane itself or by favourable juxtaposition of lithologies, both cases being demonstrated in the Manta accumulation. The petrology and reservoir characteristics of Latrobe Group sandstones vary considerably, depending largely on sedimentary facies. Sands of fluvial or alluvial origin are generally inferior to those deposited in shoreline environments. An effective intra-Latrobe reservoir 'floor' lies at around 4 km burial depth for both fluvial and alluvial sandstones.

Solid hydrocarbon aerosols produced in simulated Uranian and Neptunian stratospheres.

Optical constants n and k are measured for thin hydrocarbon films produced from charged particles (RF plasma) irradiation of (1) 100% CH4; (2) 7% CH4, 93% H2; (3) 0.5% CH4, 99.5% H2; (4) 0.0002% CH4, 99.3% H2 (with impurities); and (5) 3 to 25% CH4, 25% He, remainder H2--all at submillibar pressures. In all experiments, yellow to deep brown-red solid products are synthesized which are hypothesized to be, at least in part, the unidentified visible and near-UV chromophores in the stratospheres of Uranus and Neptune. Results for experiments 2, 3, and 4 are in good mutual accord, but are significantly different from experiments 1 and 5. He in the precursor gases affects the product composition. Typical solid products for experiments 5 show, at 0.55 micrometer wavelength, n = 1.60 +/- 0.05, 3 x 10(-2) > or = k > or = 3 x 10(-3), and [C/H] approximately equal to 0.7. These results are, for n and k respectively, consistent with and in excellent agreement with those derived from high phase angle Voyager 2 photometry of Uranus (Pollack et al., this issue). Aerosols produced directly from the atmosphere by precipitating magnetospheric charged particles may be competitive with those produced by UV and charged particle irradiation of simple hydrocarbon condensates. The optical and chemical properties of aerosols in the Uranian and Neptunian atmospheres may evolve toward higher values of n and k and higher carbon content as the particles sediment through changing radiation and thermal environments.

Saturation effects in the phonon reflection at a quartz-liquid helium interface

The reflection coefficient of longitudinal 25-GHz phonons at a quartz-liquid 4He interface was measured for various phonon intensities. For thoroughly cleaned quartz surfaces a reflection coefficient of 1 independent of the incident intensity was found. When the sample was covered with a thin hydrocarbon film, however, the reflection coefficient dropped by typically 5–10% when the phonon intensity was low. At high intensities this extra phonon loss disappeared, suggesting the saturation of the inelastic processes at the quartzhelium interface.

Energetics of permeation of thin lipid membranes by ions

The energy of an ion in a thin hydrocarbon membrane relative to its energy in a bulk aqueous phase is considered in terms of the electrostatic and surface components that may be expected to be involved. Except when diffusion activation energies are large compared to partition free energies, the latter will control permeation rate and the state of an ion having the lowest partition energy will be critical for its permeability. This minimum is found when an ion is surrounded with a thin layer of water. All ions of the same charge will tend to be at their lowest state in a sphere of water of the same size. It is concluded, therefore, that all ions of a given charge will have about the same permeability in lipid membranes.

Electron range studies in solid hydrocarbon films at 77 K

Low energy (E &amp;lt;2 eV) photoelectron transmission data have been obtained for thin hydrocarbon films at 77°K as a function of film thickness, which has been varied in steps of 10–70 Å. The photocurrent data approximate exponential attenuation which yield low energy range values which vary from 7 (n-nonane) to 82 Å (neopentane) for very thin films (t &amp;lt;100 Å) and 30 (n-hexane) to 138 Å (neopentane) for thicker films. The origin and interpretation of the exponential distribution as well as the Gaussian distribution which is usually employed, are discussed in terms of Fermi-Age and diffusion models. Two scattering models are discussed as a means of interpreting the two diffusion lengths and the apparent √2 factor between them.

A theoretical study of hydrocarbon adsorption on water surfaces using Lifshitz theory

We compute the chemical potential (disjoining pressure) given by Lifshitz theory for thin liquid hydrocarbon films on an aqueous substrate. The microwave, infrared, optical and ultraviolet frequency regimes are analyzed in detail, and the positive and negative contributions to the chemical potential are identified. For pentane, hexane, and heptane on pure water the total chemical potential is negative, and these films wet the substrate. For octane and dodecane on pure water the chemical potential is positive in the non-retarded regime, and these films do not wet the substrate, although octane lies close to the critical point. Experiments confirm these results. If sufficient NaC1 is dissolved in the water, our calculations predict that both octane and dodecane will form wetting films.

Low‐Energy Electron Irradiation of Thin Paraffin Hydrocarbon Films

Low‐energy photoelectrons are excited through thin paraffin hydrocarbon films at 77°K. The photocurrent is measured as a function of film thickness which is increased in steps of 20–80Aå. The attenuation length or range for electrons of approximately 1 eV initial energy is 65Aå for 3‐methylpentane, 59Aå for hexane, and 55Aå for nonane. The mean free paths determined from Baraff Theory are of the order of 12Aå.

Fluid Film Interferometry in Lubrication Studies

INTERFEROMETRY has been used in both surface chemical investigations1 and lubrication studies2 to measure the thickness of thin hydrocarbon films. Until now experiments have suffered from the disadvantage of being restricted to films thicker than a quarter of a wavelength and this has meant that films of less than about 900 A thick could not be investigated. Fig. 1A shows the general arrangement of the apparatus used by Gohar and Cameron2 in their studies of the elastohydrodynamic lubrication of a hard steel ball. Partial reflexion occurred at the diamond (or high refractive index glass) to oil interface because of the difference in refractive indices. Better fringe definition can be obtained by the use of optical crown glass (µ≃1.5) which has been vacuum coated3 with a quarter wavelength film of titanium dioxide, as is shown in Fig. 1B. The interference pattern gives a direct measure of the lubricant film contours under diverse conditions.