Mechanisms of ion-beam-enhanced diffusion in amorphous silicon

We have investigated ion-beam-enhanced diffusion of Au in undoped and B doped amorphous Si. The diffusion coefficients depend linearly on ion flux and exibit an Arrhenius-like temperature dependence with an activation energy of 0.37 eV in the temperature range 200–350° C. Moreover the diffusivity is enhanced by a factor of 5 by B-doping at a concentration of 1×10²⁰ atoms/cm³. A similar enhancement is observed in thermal diffusion of Au which has an activation energy of 1.5 eV. On the basis of these results a model for the ion-beam-enhanced diffusion of Au is proposed where the high density of defects present in amorphous Si act as traps for the fast moving interstitial Au atoms. The effectiveness of this trapping process can be changed by the high concentration of mobile defects generated by the beam and also by a change in the charge state of the traps induced by the presence of B.     

Shape recognition of alkylammonium ions by 1,3-bridged calix[5]arene crown-6 ethers: endo- vs exo-cavity complexation

A series of tri-O-substituted 1,3-bridged calix[5]arene crown-6 ethers bearing alkyl, arylalkyl, alkoxyalkyl, and alkoxycarbonylmethyl residues at the lower rim and either (t)()Bu or H substituents at the upper rim have been synthesized. (1)H NMR studies have shown that p-tert-butylcalix[5]crowns, irrespective of the size and nature of their lower rim pendant groups, adopt preorganized conelike conformations, whereas p-H-calix[5]crowns with bulky substituents preferentially exist in solution as partial cone conformers (C(1) symmetry). Calix[5]crown derivatives behave as mono- or ditopic receptors for isomeric butylammonium ions, forming endo-cavity (inside the calixarene cup) and/or exo-cavity (at the crown ether moiety) 1:1 complexes according to the shape of the guest. These two binding modes can be clearly distinguished and monitored by (1)H NMR titration experiments.     

Vanadium disulfide: Metal substitution and lithium intercalation

The preparation and physical properties of the layered VS₂, M_yV_1?yS₂ (M = Fe or Cr), and their lithium intercalation adducts are described. These compounds were prepared by oxidative delithiation of LiM_yV_1?yS₂ with iodine. Crystallographic distortions present in Li_xVS₂ (0.25 ? x ? 0.6) are suppressed by Fe or Cr substitution for V. The electrochemical sluggishness of Li/Li⁺/VS₂ cells is reduced by the substitution.     

Measurement of the generalized polarizabilities of the proton in virtual Compton scattering at Q2=0.92 and 1.76 GeV2

We report a virtual Compton scattering study of the proton at low c.m. energies. We have determined the structure functions P(LL)-P(TT)/epsilon and P(LT), and the electric and magnetic generalized polarizabilities (GPs) alpha(E)(Q2) and beta(M)(Q2) at momentum transfer Q(2)=0.92 and 1.76 GeV2. The electric GP shows a strong falloff with Q2, and its global behavior does not follow a simple dipole form. The magnetic GP shows a rise and then a falloff; this can be interpreted as the dominance of a long-distance diamagnetic pion cloud at low Q2, compensated at higher Q2 by a paramagnetic contribution from piN intermediate states.     

The influence of hydrogen and nitrogen on the formation of Si nanoclusters embedded in sub-stoichiometric silicon oxide layers

This work reports the study concerning the influence of the preparation conditions on the structure of silicon rich oxide (SRO) deposited by PECVD method by which the structural properties of the film are strictly related. In particular we investigated the role of reactant gases N₂O and SiH₄ on the total Si concentration, Si excess concentration, Si clustered concentration and size of nanoclusters formed by high annealing temperature. We payed particular attention on the role of the hydrogen and nitrogen during the Si agglomeration.The presence of hydrogen atoms on the as-deposited specimen, confirmed by the Si–H bonds peak on the FTIR analysis, has been directly correlated to the silicon excess concentration in the layer. The silicon, oxygen and nitrogen atomic density has been calculated from RBS analysis. These information were coupled to the ones obtained using methodology based on electron energy loss spectroscopy combined with energy filtered images, which allowed us to quantify the clustered silicon concentration in annealed sub-stoichiometric silicon oxide layers (SiO_x). We have verified that the nitrogen dissolved in the layer inhibits the Si excess clustering so that the efficiency of silicon agglomeration process decreases as the nitrogen content increases.     

A Far Infrared Super Radiant FEL

The basic physics, results of 3–D simulations, and relevant parameters for the design of a far infrared FEL, which operates in the SASE superradiant short bunch regime, are presented. It is shown that a quite interesting device can be easily developed, with rather new features, producing coherent laser pulses with ～10 psec duration and around 7 MW peak power.     

On the correlation between SILC and hole fluence throughout the oxide

Stress-induced leakage current (SILC) has been recognized as a topic of concern in flash memory reliability. It is a reliable failure mechanism, occurring long before oxide breakdown and, hence, limiting oxide lifetime[1]. The physical origin and mechanisms of SILC have not yet been clearly understood and several points open to discussion remain. In this work the role of oxide hole fluence in producing the SILC is discussed. An universal power law of SILC generation kinetics is proposed versus the hole fluence throughout the oxide. The experimental results are theoretically validated by modeling the measured quantum-yield by the contributions of both anode hole injection and electron valence band injection mechanisms.     

Ligth from silicon [LED]

This paper discusses the current efforts to develop an electrically powered silicon laser for the fabrication of light emitting diodes (LED). Researchers have been pushing two strategies in their quest to get light out of silicon. One scheme is based on a curious effect called quantum confinement, which reduces silicon's momentum problem and increases the probability that injected electrons will produce photons. The other scheme sidesteps silicon's bandgap problems by having another material, embedded within the silicon device, emit the light. This paper proposes a combination of both techniques to produce light emitters that operate at room temperature with a controllable tradeoff between high efficiency and long lifetime. A key advantage of this approach is that the color of the light emitted depends on the rare-earth ions used. Unfortunately, this approach produces low light output because the maximum output power is limited by how densely the device can be packed with rare-earth ions. Nevertheless, researchers are confident that, within a few years, an electrically driven silicon laser will become a reality.