Mass Fractionation and Energy Distribution of Sputtered Monatomic Positive Ions

Secondary ion yields in sputtering depend significantly on the mass of the emitted species. Ionization as observed by secondary ion mass spectrometry is characterized by isotope fractionation; the yield of an isotope ion of mass Mi being proportional to M-, where a varies with the emitted species, its kinetic energy Ek, and the matrix. By means of SIMS, isotope ratios have been measured for ions at energies up to ca 120 eV in different metallic matrices. For singly charged positive monatomic ions, a has been found to range between O and ca 4. While a may drop steeply at low or moderate Ek, at higher energies the gradient decreases and usually becomes positive. To some extent the trends of a are complementary to those of the energy dependence of elemental ion yields. In the present work, the main tendencies are surveyed for pure element matrices as well as for several elements sputtered from a given metallic matrix. It is attempted to correlate a with the energy distributions of ionic yields. Isotope effects appear inherent in all three basic mechanisms of ion emission, i.e., in sputter yield, ionization, and charge survival

Secondary Ion Mass Spectrometry Studies of Isotope Effect in Diffusion

The mass effect of diffusion is of interest in connection with interactions between defects and impurities and with the mechanisms of atomic displacements in the condensed states. The delineation entails the precise measurement of the isotope ratio as function of tracer concentration, varying within several orders of magnitude along the diffusion profile. The measurement by SIMS (secondary ion mass spectrometry), using stable isotopes, has proved to possess advantages compared to familiar techniques with radiotracers. However, the aims require the utmost counting economy and optimal precision available in SIMS, including the control of the mass fractionation and of some features peculiar to cyclic profiling. Very good results have been obtained for the isotope effect at relatively deep profiling, where step scan analysis can be effected. For more shallow profiles, requiring head-on sputtering, more serious artifacts are encountered and the error margins have hitherto been relatively high. The paper discusses salient experimental points of the determination by SIMS of the isotope effect at different diffusion geometry, and briefly reviews the hitherto obtained results

Black Silicon with high density and high aspect ratio nanowhiskers

Physical properties of black Silicon (b-Si) formed on Si wafers by reactive ion etching in chlorine plasma are reported in an attempt to clarify the formation mechanism and the origin of the observed optical and electrical phenomena which are promising for a variety of applications. The b-Si consisting of high density and high aspect ratio sub-micron length whiskers or pillars with tip diameters of well under 3 nm exhibits strong photoluminescence (PL) both in visible and infrared, which are interpreted in conjunction with defects, confinement effects and near band-edge emission. Structural analysis indicate that the whiskers are all crystalline and encapsulated by a thin Si oxide layer. Infrared vibrational spectrum of Si-O-Si bondings in terms of transverse-optic (TO) and longitudinal-optic (LO) phonons indicates that disorder induced LO-TO optical mode coupling can be an effective tool in assessing structural quality of the b-Si. The same phonons are likely coupled to electrons in visible region PL transitions. Field emission properties of these nanoscopic features are demonstrated indicating the influence of the tip shape on the emission. Overall properties are discussed in terms of surface morphology of the nano whiskers

Vertical single nanowire devices based on conducting polymers.

A simple scheme for single conducting polymer nanowire fabrication and device integration is presented. We discuss a combined top-down and bottom-up approach for the sequential, precise manufacture of vertical polyaniline nanowires. The method is scalable and can be applied on rigid as well as on flexible substrates. The kinetics of the template-confined growth is presented and discussed. We further study the electrical behavior of single vertical polyaniline nanowires and address the fabrication of crossbar latches using a criss-cross arrangement of electrodes. The as-synthesized polyaniline nanowires display electric conductivities reaching values as high as 0.4 S cm−1

Adjustment of self-heating in long superconducting thin film NbN microbridges

The self-heating in long superconducting microbridges made from thin NbN films deposited on top of high silicon mesa structures was studied by analyzing the hysteresis current density jH. We observed a more than twofold decrease of jH with increase in the ratio of the height of the Si mesa, h, to the width of the microbridge, W, from 0 to 24. We describe our experimental results using one-dimensional thermal balance equations taking into account disordered matter in our thin NbN films and limitations imposed on the phonon mean free path by the width of the Si mesa. In the framework of this model we obtain a good agreement between theory and experiment over a wide temperature range from 4.2 K up to the critical temperature TC for all h=W ratios

Planar Double-Gate SOI MOS devices by wafer bonding over pre-patterned cavities

In this paper, a novel method for the fabrication of planar double-gate (DG) MOS devices is presented. Successfully fabricated single-gate and DG MOSFET devices on the same wafer have been fully characterized and their electrical performances compared. The planar DG devices were fabricated using wafer bonding over pre-patterned cavities. Preliminary electrical characterization results show that the built planar DG devices exhibit the expected theoretical performances. We will also show the flexibility of this method in fabricating other devices besides planar DG and the possibility of changing the various materials used for the buried insulator layer. It is demonstrated that this fabrication method is a very promising and viable method for future technology application in fabricating novel devices

Dominating behaviour of the donor-acceptor pair emission in mass-transport GaN

A comprehensive study of the donor-acceptor pair (DAP) luminescence band in mass-transport grown GaN in wide ranges of temperature and excitation conditions was performed. Based on spatially resolved micro-photoluminescence, secondary ion mass spectroscopy, Raman scattering and positron annihilation spectroscopy results, as well as on a kinetic analysis of the emission intensities, we propose an acceptor like complex, creating a state as a semiclassical potential well near the valence band bottom due to the tensile strain caused by the empty clusters to be responsible for the dominating behaviour of the DAP emission.2 page(s