The morphology and surface structures of silicon nitride films grown on Si(111) by exposing to ammonia at high temperature have been systematically studied using scanning tunneling microscopy. The results showed that flat beta-Si3N4 crystalline films could be obtained at a nitridation temperature of 1075-1275 K. A (4 x 4) reconstruction of beta-Si3N4 (0001) was observed on the nitride film.

Crystalline silicon nitride (Si3N4) thin films have been grown on Si(111) surfaces by exposing the substrate to NH3 at a temperature of greater than or equal to 1075 K. An "8 x 8" electron diffraction pattern was observable even for a relatively thick Si3N4 film. Images of the same surfaces obtained with a scanning tunneling microscope show surface superstructure with a period of 30.7 Angstrom, and a minimum step height of 2.9 Angstrom. These suggest the formation of beta-Si3N4, with Si3N4(0001)parallel to Si(111). The 30.7-Angstrom periodic superstructure is attributed to the 4 x 4 surface reconstruction on Si3N4(0001). [S0163-1829(99)50428-1].

The three-dimensional distribution of 200 keV Hg implanted into Ni at ambient temperature has been reconstructed by means of a modified tomographic reconstruction technique from three Hg depth profiles for different implantation angles. This is possible by describing the geometrical shape of the 3D distribution by a combination of a longitudinal split-Gaussian with a lateral Gaussian function with in total only 3 adjustable parameters. In the presented example, the depth profiles have been obtained by Rutherford backscattering. The variability of the tomographic results without the preselection of such a specific class of 3D curves is demonstrated for another example. The resulting 3D distribution of Hg in Ni is longer than theoretically predicted along the incident beam direction. This is interpreted by radiation enhanced diffusion of the implanted Hg.

The linewidth of laser emission in random-scattering gain media is found to be broadened as the number of scatterers increases. This broadening is attributed to the reduction of amplification by stimulated emission as a result of the shortened total path length traversed by the backscattered light in a highly scattering medium. In addition, the spectral shift of the emission peak is found to depend on the dye concentration and the pumping power.

Recently, laser action was observed in random-scattering1 and biological gain media.2 In this paper, the linewidth of lasing emission from biological and random gain media are shown to be affected by the scattering characteristics of the media. This finding indicates that the linewidth could be used to characterize the optical properties of biomedical tissues for diagnosis.

Simultaneous laser action of a binary-dye mixture in random media was observed. The relative intensity of lasing emissions from donor and acceptor dyes is found to be strongly dependent on the number density of the scatterers in addition to the pumping power and the dye concentrations. The laser action in a binary-dye mixture can potentially be used to determine the scattering characteristics of random media.

A multilayer structure is shown to reflect X-rays over a broad spectrum when the thickness of each layer is random. The bandwidth of the reflection increases when the number of the layer and the fluctuations of the layer thicknesses increase. However, the reflectivity is reduced by the absorption in the layer materials.

In recent years a great deal of theoretical work has been devoted to the description of the interaction of ultrarelativistic electrons and positrons and high energy photons moving along the major directions of crystals.1–9 It was predicted that quantum electrodynamic (QED) effects must be taken into account. In particular, the perfect alignment of photons with a crystal axis was predicted to increase the pair production rate above the Bethe-Heitler (BH) value.

With the frontiers of nuclear physics pushed toward higher and higher energies, an increasing number of small accelerators are being freed for other uses. A description of some of the areas of small accelerator applications will therefore serve a useful purpose. Since the topics are both rich and varied, a reasonably detailed description must be confined to ä selected few. These topics are compositional studies of layered materials, channeling of heavy charged particles., and characteristic radiation of channeled relativistic electrons. All interface closely with nuclear physics and are aspects of particle-solid interactions which is a field receiving increasing attention.

Annals of the New York Academy of SciencesVolume 306, Issue 1 p. 306-321 COLLISIONAL PROCESSES OF HEAVY CHARGED PARTICLES ON LIGHT ATOMS AT INTERMEDIATE ENERGIES Nelson Cue, Nelson Cue Department of Physics State University of New York at Albany Albany, New York 12222Search for more papers by this author Nelson Cue, Nelson Cue Department of Physics State University of New York at Albany Albany, New York 12222Search for more papers by this author First published: March 1978 https://doi.org/10.1111/j.1749-6632.1978.tb25656.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume306, Issue1Short Wavelength MicroscopyMarch 1978Pages 306-321 RelatedInformation