Beryllium Layer Research Articles

Thermal Diffusion of Buried Beryllium and Silicon Layer in GaAs Doped by Focused Ion Beam Implantation

The diffusion profiles of buried Be and Si doped by focused ion beam (FIB) implantation in GaAs after annealing were investigated. The diffusion coefficients of Be and Si were determined by fitting from the results of computer calculations. The diffusion coefficient of FIB-doped Be was enhanced by excess interstitial Be. Beryllium diffusion profiles expand by annealing with a high dose at 850°C. The concentration-dependent diffusion of Si in GaAs doped using a molecular beam was observed. The diffusion coefficient of Si heavily doped by FIB, however, was undetectably small in contrast with that of Be at 850°C.

Surface relaxation and induced stress accompanying the adsorption of H upon Be(0001)

A series of self-consistent field, molecular orbital cluster calculations has been conducted to ascertain some of the substrate relaxation that would accompany the adsorption of a hydrogen atom by the (0001) surface of beryllium. The total HF energies of clusters of either seven, ten, or fifteen Be atoms, both with and without the adsorbed hydrogen atom, have been determined as functions of the basal plane lattice parameter of the clusters. Comparison of the locations of the minima of these energy functions shows that the adsorbed H atom has the effect of drawing surface Be atoms in with great force towards the perpendicular from the H atom to the surface. There is some indication that this pinching is stronger in the case of a hydrogen atom adsorbed at a bridging site, although the effect is still pronounced for a hydrogen atom adsorbed directly above a beryllium atom. From the predicted relaxation one might infer the possibility of large stresses arising in the surface layer of beryllium (or other metal) when it is exposed to hydrogen. A simple model calculation shows that, in the absence of plastic flow or other deformation, these stresses roughly equal the yield stress of Be metal when the adsorbed H constitutes a few percent of a monolayer. The implications of such stresses in hydrogen damage phenomena are discussed, and various experiments recalled which corroborate the arguments presented.

Work function and loss spectra of beryllium layers adsorbed on tungsten single crystals with (110) and (100) orientations

Work function changes induced by the adsorption of different amounts of beryllium on W(110) and W(100) planes have been measured. At room temperature the work function increases on the (100) plane and decreases on the (110) plane. The effect of the substrate temperature on the work function change is distinctly different for both crystal planes. Both surface and bulk plasmons have been excited within the Be adlayer at coverages less than one monolayer. The loss spectra for Be layers adsorbed on the two crystal faces are distinctly different. An explanation of observed phenomena is proposed.

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X-ray diffraction contrast of inversion twin boundaries in BeO crystals

Inversion twin boundaries in BeO crystals (wurtzite structure) can be studied by X-ray topography. They can be regarded as a special kind of stacking fault. The section topograph images of a twin boundary, lying parallel to the c axis, agree well with the theory for a single stacking fault. From the contrast variation of the images for various reflections, it is concluded that the oxygen sublattice on one side of the twin boundary is displaced from that on the other side by \mid(1/16)[001]\mid so that the oxygen layer parallel to the basal plane on one side is located at the center of the oxygen and beryllium layers on the other side. The image contrast in section topographs is very sensitive to the phase shift due to a fault. The phase shift of a few degrees can be detected easily. This sensitivity leads to an accurate structure determination of the inversion twin boundary.

Preparation of Thin Specimen Films

A FILM of cellulose nitrate or a similar material is laid on a water surface and transferred to a specimen holder. A very thin layer of beryllium or aluminium is then deposited on the film from the vapour phase, after which the cellulose nitrate is dissolved away. Only the metal film then remains, and its lack of visible structure can be checked by photographing in the electron microscope. The durability and resistance of the layer to chemical attack are very high. A matter of great importance in the study of specimens in which completely opaque particles occur on the film is that the metal film readily conducts away absorbed energy. With such particles, however, films of cellulose acetate or similar materials are very easily broken. Beryllium and aluminium films of as little as 20 A. thickness (diameter 100 µ), and also aluminium films 12 A. in thickness, have been prepared by this procedure.

The Detection of Single Positive Ions, Electrons and Photons by a Secondary Electron Multiplier

A secondary electron multiplier tube has been developed and used successfully for counting single positive ions, electrons and photons. This tube has twelve electrodes covered with a thin layer of beryllium. Tests have shown that with 330 volts per stage this tube will multiply the primary current by a factor of ${10}^{5}$. The use of guard ring insulation and electrostatic shielding for the final collecting electrode has reduced the background current to an extremely low value. The last electrode was connected to the grid of the first tube in a linear amplifier. In order to count single positive ions or electrons the tube was waxed to the end of a simple magnetic spectrograph. Ions having energies from 50 to 20,000 electron volts and masses from one to 32 were detected. By increasing the gain of the thermionic amplifier electrons could be counted. With still more gain single photons were counted. The multiplier tube has an extremely low background counting rate. Because a pressure of ${10}^{\ensuremath{-}6}$ mm of Hg is maintained in the counter, it can be connected directly to the vacuum system through which the electrons or positive ions are accelerated. The absence of a thin window between the counter and the vacuum system should be a great advantage in experiments dealing with low energy positive ions or electrons.

Secondary Emission of Beryllium

The secondary electron emission of beryllium films prepared by evaporation in a high vacuum has been studied. As the beryllium is deposited the secondary emission ratio (defined as the ratio of the number of electrons leaving the surface, to the number of primary electrons impinging on it) rises from that of the support metal to a value in the neighborhood of 2.5. The position of the maximum with respect to energy of primary electrons remains near that of the support metal. As the thickness of the layer is increased the ratio falls to less than unity and the voltage of the primary electrons necessary to reach the maximum drops to about 200 volts. Heating the thick beryllium layer to a bright red for a few minutes raises the emission to about 1.6 with the maximum at a primary energy of about 630 volts. Oxidation of the surface increases the emission to about 4.1. Explanations of these effects are discussed and arguments are presented favoring the acceptance of the value of 1.6 as the maximum secondary emission ratio to be expected for pure bulk beryllium.