Boron Nitride Surface Research Articles

Effects of Excimer Laser Ablation on the Surface of Hexagonal Boron Nitride

AbstractThe laser-induced changes in the hexagonal boron nitride targets that are used in the deposition of pulsed laser-deposited cubic boron nitride films are examined. Although the structure of the hexagonal boron nitride in the irradiated areas is unaltered, the surface morphology changes considerably. Boron-rich spheroids were found to cover the irradiated area. Their origin is consistent with the hydrodynamic sputtering of the hexagonal boron nitride targets, and a liberation of nitrogen atoms to the gas phase.

Atomic force sensors constructed from carbon and quartz fibers

A simple design of force sensors constructed from carbon and fused quartz fibers is presented. The handmade force sensors exhibit characteristics similar to those of cantilevers produced by micromechanic techniques. Atomically resolved force maps of the c surface of graphite and boron nitride and a topographic image of mica have been obtained using an atomic force microscope equipped with a fiber sensor.

Surface precipitation of boron nitride on the surface of stainless steel/boron nitride film

A mixture of type 304 stainless steel and boron nitride was deposited on the surface of type 304 substrate which a r.f. magnetron sputtering method. Scanning Auger electron microscopy and X-ray photoelectron spectroscopy observation showed that boron nitride precipitated on the surface of the deposited film and the precipitated boron nitride uniformly covered the surface after annealing at more than 600 K in high vacuum. Only small carbon and oxygen Auger peaks were observed on the surface of the preciptated boron nitride after the 3.6 ks (= 1 hour) exposure in air indicating that the surface of this film covered with boron nitride was inert to gas adsorption. Therefore, the film of the mixture of stainless steel and boron nitride can be a candidate material for surface modification of vacuum vessels.

Evolution of the collective-mode resonance in small adsorbed sodium clusters.

The optical spectra of small isolated sodium clusters adsorbed on a boron nitride surface have been measured from 3000 to 7500 A\r{} over a range of average cluster size 〈N〉=10 to 300 atoms by change in reflectivity spectroscopy. The spectra are dominated by the dipole resonance of the surface collective mode of the sodium valence electrons, and the resonance frequency shifts from 2.4 eV to near the bulk value of 3.4 eV as cluster size increases. A quantitative comparison of experimental results with the jellium model of sodium clusters is presented.

Model adsorption potentials of rare gases on boron nitride.

Calculations are presented for the interaction of rare-gas atoms (Ar, Kr, Xe) on the (0001) surface of boron nitride. The interaction potential is constructed with use of a damped dipole and a quadrupole attractive part and a repulsive part derived from the effective-medium theory. Only one free parameter has been used to fit the constructed potential to experimental data available. We checked our procedure by calculating the second virial coefficient of the adsorbed atoms interacting with the surface of BN and the interaction potential for the same rare gases on graphite (0001). In both cases we find good agreement with experiments. Finally, we comment on the similarities between rare gases interacting with BN and with graphite and on how our model potential can be applied to other systems.

Radiation damage effects in boron nitride mask membranes subjected to x-ray exposures

The effects of radiation damage with 1 to 3 keV x-rays on hydrogenated boron nitride films prepared by LPCVD have been investigated. It is shown that both the surface and bulk film properties of these materials are modified and may potentially limit the use of this material as a membrane in an x-ray mask structure. Specifically, it is shown that growths will form on exposed boron nitride surfaces irradiated in oxygen-containing ambients; optical transmission of irradiated films will degrade with the cumulative absorbed dose; the tensile stress of an x-ray mask membrane will decrease and introduce pattern distortions depending upon the irradiation dose/flux and exposure geometries. A model to evaluate the observed pattern distortions and a mechanism to explain the observed stress changes of the hydrogenated boron nitride films are proposed.

Benzene adsorption on basal planes of boron nitride; comparison with the benzene-graphite system

A set of adsorption isotherms of benzene on boron nitride have been determined between 198 and 268 K. Just as in the case of the benzene-graphite system, the isotherms do not present the shape of the stepped isotherm. The benzene layer appears more mobile with a weaker adsorption energy on boron nitride than on graphite. The monolayer defined at the point B presents an important negative thermal expansion coefficient. It is proposed that the first layer might be unstable at high coverage and transform into clusters leaving some bare surface of boron nitride. Thus the observed isotherms might be considered as a combination of type I and III according to the Brunauer classification.

Surface segregation of boron in nitrogen-strengthened stainless steel

The characteristic surface segregation of both impurities as well as major alloy constituents in 21Cr–6Ni–9Mn (21–6–9), a nitrogen strengthened austenitic stainless steel, has been studied using scanning Auger microscopy (SAM), x-ray photoelectron spectroscopy (XPS), and sputter Auger techniques. Segregation effects were examined for polycrystalline material heated to temperatures ranging up to 800° C. The SAM results show both a nonuniform spatial distribution of the various segregating species, as well as a strong cosegregation of boron with nitrogen at temperatures above approximately 700° C. Based on a bulk concentration of less than 10 ppm, the resulting surface-to-bulk concentration ratio for boron is greater than approximately 5×104. Both the boron and nitrogen Auger and XPS spectra associated with commercially available boron nitride material are identical to those obtained from the segregated layer on 21–6–9 and indicate that the boron and nitrogen cosegregate to form a boron nitride surface layer. This segregated BN layer, which initially is formed at high temperatures and uniformly covers the surface after one hour of heating, is found to be stable down to room temperature. The observed Auger peak positions are compared with semiempirically calculated values based on the XPS results.

Critical and triple point temperatures of the first adsorbed layer of nitric oxide on graphite, boron nitride and lamellar halides

The two-dimensional critical temperature T c(2D) of the first layer of nitric oxide adsorbed on homogeneous surfaces of graphite, boron nitride, cadmium halides (CdI 2, CdBr 2, CdCl 2) and magnesium bromide has been determined as accurately as possible. A correlation curve between T c(2D) and the adsorbent crystalline parameter is compared to the correlation curve of this parameter with the two-dimensional triple point temperature T t(2D) of the same layer on the above substrates and on those previously investigated by Enault and Larher. It appears from this comparison that T c(2D) is less sensitive than T t(2D) to the nature of the substrate: the difference between the extreme values of T c(2D) is 25 K, whereas it is larger than 70 K for T t(2D). Moreover the lowest values of T c(2D) correspond to the substrates for which the lowest values of T t(2D) have also been observed, namely graphite and boron nitride, both standing out by the smoothness of the adsorption potential of their cleavage faces. Furthermore we are led to reconsider the nature of the less dense phase (α phase) which hitherto has been inferred to be a 2D solid essentially composed of dimers lying flat on the surface.

Some Observation on the Crystal Surfaces of Cubic Boron Nitride

Crystal surfaces of cubic boron nitride synthesized at 55 to 60 k bars an d 1600 to 1800°C and identified by X ray diffraction analysis, has been observed optically. Although cubic boron nitride has similar structure to diamond, it shows somewhat different aspect of crystal growth from diamond. The most dominant crystal face is (111). However it must be emphasized that (110) face prefers to appear more frequently than (100) face in cubic boron nitride in this experimental condition. The crystal growth of cubic boron nitride is by means of plane sheet growth on the (111) face as in diamond and two types of plane sheet growth are observed; one is the growth of various shapes of layers on (111) face and another the growth of triangular pyramids on (111) face.

On physical adsorption: X. Adsorbed monolayers of argon and nitrogen on boron nitride and on a graded series of partially graphitized carbon blacks

Low-pressure adsorption isotherms of argon and nitrogen at 77.8° and 90.1°K. were measured on members of a graded series of a carbon black, which had been partially graphitized in an inert atmosphere at temperatures of 1000, 1500, 2000, and 2700°C. An increasing homogeneity of the surface accompanies graphitization and is reflected in a number of adsorption phenomena, all of which gradually become more pronounced with increasing degree of surface homogeneity: ( a) the two-dimensional van der Waals' equation provides a description of the isotherm over a greater range of surface concentrations; ( b) the two-dimensional critical temperature of the adsorbate increases regularly toward the theoretical value expected of an ideally uniform substrate; ( c) the mobilities of the adsorbed monolayers correspond over an increasingly greater range of surface concentration to that of a two-dimensional gas on a uniform substrate. A sample of boron nitride was also used as adsorbent for monolayers of argon and nitrogen at 77.8 and 90.1°K. A comparison of the results for boron nitride with those for the carbon black series shows that the boron nitride surface would correspond to a carbon black of the present series graphitized at 1800°C.