Graphite Thin Films Research Articles

Low-temperature thin graphite film thermometers

Thin films of colloidal graphite (typically 1 μm), applied in spray aerosol form, have been tested for use as thermometers below 4 K. These thermometers are easily fabricated, have good low-temperature stability, an estimated heat capacity of 0.25 erg/K cm2 at 3 K, and a thermal relaxation time limited only by the properties of the substrate.

Thin graphite support films for high resolution electron microscopy

A method is described for preparing graphite films down to about 2nm in thickness. First, a suspension of small flakes in ethylene dichloride is prepared by repeated cleavage of a graphite crystal. This is then used to prepare a relatively thin film of graphite which is applied to grids previously coated with a holey carbon film. Fragments of tungsten oxide crystals are placed on the grid which is then exposed in the electron microscope to an electron beam of high intensity. As the result of an apparent reaction between the tungsten oxide and the carbon, the graphite film is etched, thereby producing a film which is both much thinner and cleaner than the original. The thickness of films prepared in this way has been estimated and their characteristics described. A brief account is given of the use of such a film using ferritin as a test object.

Experiments With Thin Single Crystal Graphite Films

The ability to make extremely thin single crystal films could be potentially of great use for high resolution biological and single atom electron microscopy because the substrate noise could be greatly reduced over that obtained with amorphous films. (That is, the number of atoms in any resolution cylinder would not obey a Poisson distribution but would vary in a regular fashion.) This would increase the visibility of atoms and biological particles and would permit imaging with less dose. In addition, very thin films would be useful in minimizing multiple scattering effects in electron energy loss spectra which would be helpful in interpreting EXAFS-like structure near inner shell excitation edges. For these reasons, we have started a program aimed at trying to fabricate very thin (∽20-30 Å) single crystal films.We have begun to grow thin graphite films after the method of Riddle and Siegel (1).

Relativistic excitations of a thin graphite film by inelastic electron scattering in theory and experiment

AbstractRecently Chen and Silcox have published measurements of the inelastic electron scattering by a thin graphite slab. A theory formulated by the author is applied to this experiment. For the calculations the dielectric functions of graphite measured by Zeppenfeld are used. The numerical results and the maxima of the inelastic electron scattering probability are discussed. There is a good agreement between theory and experiment.

Thin Graphite Supporting Films for High Resolution Work

Background noise arising from amorphous carbon supporting films is a crucial problem for high resolution CTEM work, particularly for biological materials. Many people have been trying to overcome this problem, for example, by use of sophisticated image analysis by computers, but without convincingly successful results so far. On the other hand, it is theoretically expected that if we use thin single crystal films the background noise can be completely eliminated. This has been attempted by a few workers (1,2) who used single crystals of BeO or graphite for observing very small metal particles or single atoms. Here we shall report a method of preparing very thin and clean single crystal films of graphite and their properties.Preparation of thin graphite films. Firstly relatively thin graphite films were prepared by repeated cleavage of a graphite crystal between Scotch tapes. Small flakes of cleaved graphite crystal stuck on the tapes were separated in ethylene dichloride.

Bright-Field Images (Ctem) of Phase Objects at High Resolution

We have developed a technique to prepare thin single crystal films of graphite for use as supporting films for high resolution electron microscopy. As we showed elsewhere (1), these films are completely noiseless and therefore can be used in the observation of phase objects by CTEM, such as single atoms or molecules as a means for overcoming the difficulties because of the background noise which appears with amorphous carbon supporting films, even though they are prepared so as to be less than 20Å thick. Since the graphite films are thinned by reaction with WO3 crystals under electron beam irradiation in the microscope, some small crystallites of WC or WC2 are inevitably left on the films as by-products. These particles are usually found to be over 10-20Å diameter but very fine particles are also formed on the film and these can serve as good test objects for studying the image formation of phase objects.

The tribo-chemistry of graphite fluoride studied using X-ray photoelectron spectroscopy

A preliminary investigation involving the application of X-ray photo-electron spectroscopy (XPS) for the study of the degradation, under sliding conditions, of thin graphite fluoride films on steel has been carried out. The results described here show that the technique can provide invaluable information in establishing the mode of failure of the lubricating film.

The optics of spherically stratified graphite grains

Extinction and scattering efficiencies are calculated for spherically stratified graphite spheres using formulae which are valid in the small particle limit. The resulting extinction curve for this model is shown to peak at an ultraviolet wavelengthλ -1=4.8−5μ -1 close to that for the case of the less probable plane stratified model of a graphite sphere. The albedo in the present model is higher than that calculated for the plane stratified case by a factor 1.5–2 in the far ultraviolet. Extinction curves are also obtained for the case of a dielectric sphere surrounded by a thin graphite film, and it is shown that there now is an extinction minimum atλ -1≃4.6μ -1.

Detection of Optical Surface Guided Modes in Thin Graphite Films by High-Energy Electron Scattering

Detection of Optical Surface Guided Modes in Thin Graphite Films by High-Energy Electron Scattering

Detection of Optical Surface Guided Modes in Thin Graphite Films by High-Energy Electron Scattering

Detection of Optical Surface Guided Modes in Thin Graphite Films by High-Energy Electron Scattering

Unusual structural characteristics of a unique thin pyrolytic graphite film

Unusual structural characteristics of a unique thin pyrolytic graphite film

Properties of thin pyrolytic graphite film

Properties of thin pyrolytic graphite film

Thin Pyrolytic Graphite Films for Electron Microscope Substrates

A routine procedure for growing very thin graphite substrate films has been developed. The films are grown pyrolytically in an ultra-high vacuum chamber by exposing (111) epitaxial nickel films to carbon monoxide gas. The nickel serves as a catalyst for the disproportionation of CO through the reaction 2C0 → C + CO2. The nickel catalyst is prepared by evaporation onto artificial mica at 400°C and annealing for 1/2 hour at 600°C in vacuum. Exposure of the annealed nickel to 1 torr CO for 3 hours at 500°C results in the growth of very thin continuous graphite films. The graphite is stripped from its nickel substrate in acid and mounted on holey formvar support films for use as specimen substrates.The graphite films, self-supporting over formvar holes up to five microns in diameter, have been studied by bright and dark field electron microscopy, by electron diffraction, and have been shadowed to reveal their topography and thickness. The films consist of individual crystallites typically a micron across with their basal planes parallel to the surface but oriented in different, apparently random directions about the normal to the basal plane.

Conductivity of CdSe, CdSe-SiO x thin films : I Szczurek et al, Prace PIE, 10 (2/3), 1969, 77–84 ( in Polish)

The experimental apparatus for measurments of sputtering yield of graphite by hydrogen and helium ions was constructed. At present day the operational parformance of the system with a torsion microbalance (sensitivity: 1.5 × 10−7 g/div) has been established.Experimental result is not yet obtained.Modified torsion microbalance is under construction.We have designed the apparatus with vacuum microbalance system for measurements of sputtering yields of graphite sample. As incident ions, H+ and He+ are used, but because B-A gauge type ion source is adopted, ion beam intensity is about order of 10 100 μA/cm2. It can be considered sputtering yield of graphite by light ion with keV energy is not so large, therefore the vacuum microbalance having maximum sensitivity of 5 × 10−9 g has been designed, which is made of quartz bar (diameter of the bar is 0.5 mmϕ and the mean length is 10 cm, the balancer is about 4 g). The balance is installed in UHV chamber. The UHV system could be pumped down to pressure of 10−9 Torr, in order to keep impurity gas pressure as low as possible during sputtering. During sputtering experiment admitted sample gas is pumped with a turbo-molecular pump (70 1/sec), and after sputtering when gas filling is stopped and operation of the balance is started, the UHV system is pumped by an orbitron pump and a Ti sublimation pump to avoid gas adsorption on the sample. We have prepared two kinds of graphite samples, one is a pyloritic graphite plate 2 (5 × 5 mm2, 1 mm in thickness) and the other is a graphite thin film (500 A) sample deposited on gold coated mica plate. These sample plates could be outgassed by electron bombardment.For the graphite film low energy He+ ion scattering technique (ISS) can be applied as well as vacuum microbalance technique. As the thin film is gradually sputtereched by impact ions, the scattering signal intensity ratio I(c)/I(Au) will show a change, i.e. shadowing of gold atom by carbon atom could be measured by as a function of film thickness.

10. Growth of thin single-crystal films of graphite

10. Growth of thin single-crystal films of graphite

Grain Growth of Zirconium Diboride

Hot-pressed zirconium diboride compacts which had four kinds of relative densities were heated in graphite at temperatures ranging from 1400°C to 2500°C. The surfaces of the heated compacts and their textures were examined by X-ray diffraction and optical microscope. Weight and relative density as well as average grain size of each compact were then measured.Through heating at the lower temperatures ZrO2 appeared on the surface of the compacts and then changed to ZrC at the temperatures between 1700°C and 1800°C. Lattice constants of ZrC changed to the normal values from the smaller ones with increasing temperatures. From this fact, it was supposed that ZrN was also formed simultaneously in this temperature range and made solid-solution with ZrC. While oriented graphite layers covered the surfaces of the compacts heated at temperatures above 2400°C, thin films of graphite were observed over the molten surfaces of the compacts heated at 2500°C.Relative density of each compact reached about 0.97 when it was heated at 2500°C for 100 min. Data on grain growth were processed under the application of the following equation:D2-D02=ktm, the value of m being either 0.66-0.78 or about 1 for heating temperatures of 2100°-2300°C or 2400°C. When the compact was heated at 2300°C, grain growth was rapid at the surface layer compared with the inner part and the m reached about 1 at this layer.Grain growth rate constant, k in the above equation increased with the increase in the initial densities of the compacts. But the same temperature dependence was obtained for all the compacts heated at the temperatures between 2100°C and 2300°C. The activation energy in the process of grain growth was calculated to be about 60kcal/mol.

Imperfections in natural graphite

Lattice or surface imperfections in graphite may play an important role as active sites in its oxidation. Thin films of a natural graphite, Madagascar flake, examined by electron microscopy revealed the presence of flat graphite sheets whose basal planes were predominantly normal to the electron beam. Dislocations lying in the basal planes were frequently observed, the estimated mean density being 10 9/cm 2. Graphite has a high incidence of stacking faults. Basal plane dislocations frequently split into partials which bound ribbons of stacking fault, 650–1000 Å wide. If these ribbons of stacking fault occur at the same level in the film they often interact to form stable networks. From measurements of the radius of curvature of dislocation nodes, the stacking fault energy has been estimated to be approximately 0.25 erg/cm 2. Because of the fortuitous relative rotation of graphite sheets, Moiré patterns have been observed with dislocations imaged as extra inserted fringes.

An investigation into sliding bearings suitable for a CO 2-cooled nuclear reactor

In a nuclear reactor a number of mechanisms are required to operate up to about 400/dgC, often in the presence of intense radiation fluxes. Three possible solutions to the problem of making bearings for these mechanisms are discussed; the use of unlubricated metals, of massive graphite, and of thin graphite films on a metal base. Three metals, two nitrided steels and a tool steel, have been found to run well unlubricated, both against themselves and a variety of other steels. Coefficients of friction for unlubricated metals are high, usually in the range 0.3 to 0.8 but tending on occasions towards unity. An electrographite was found which would run satisfactorily in dry CO 2 but the performance in dry air, dry nitrogen and in a vacuum was poor. Thin graphite films have been found to have too unpredictable a life for practical purposes.