Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.     

Characteristics of vinyl iodide microwave plasma etching of GaAs/AlGaAs and InP/InGaAs heterostructures

Vinyl iodide (C₂H₃I) microwave discharges with additions of H₂ and Ar are found to provide faster etch rates than conventional CH₄/H₂/Ar discharges for InP, InGaAs, GaAs, and AlGaAs. This is a result of the relatively high volatilities of indium, gallium, and aluminum iodide species. The etched features are smooth and anisotropic over a wide range of do self-biases (–150 to –350 V), process pressures (1–20mTorr), and microwave powers (150–500 W). The polymer that forms on the mask during the plasma exposure can be readily removed in O₂ discharges. Electron spectroscopy for chemical analysis (ESCA) showed that the etched surfaces are slightly deficient in the group V elements under most conditions, but changes to the optical properties of the semiconductors are minimal. No defects are visible by transmission electron microscopy (TEM) in GaAs or InP samples etched at dc biases –250 V.     

Plasma etching of III–V semiconductors in BCl3 chemistries: Part I: GaAs and related compounds

BCl₃/Ar discharges provide rapid, smooth pattern transfer in GaAs, AlGaAs, GaP, and GaSb over a wide range of plasma conditions. At high BCl₃-to-Ar ratio there is significant surface roughening on GaSb, which is correlated with the presence of B- and Cl-containing residues detected by Auger electron spectroscopy. BCl₃/N₂ discharges provide similar etch rates to BCl₃/Ar, but when used with photoresist masks lead to rough morphologies on the semiconductor materials due to enhanced dissociation and redeposition of the resist. Etch rates with electron cyclotron resonance discharges are up to two orders of magnitude higher than for rf-only conditions.     

Plasma etching of III–V semiconductors in BCl3 chemistries: Part II: InP and related compounds

BCl₃/Ar and BCl₃/N₂ plasma chemistries were compared for patterning of InP, InAs, InSb, InGaAs, InGaAsP, and AlInAs. Under electron cyclotron resonance conditions etch rates in excess of 1 μm/min can be achieved at room temperature with low additional rf chuck power (150 W). The etch rates are similar for both chemistries, with smoother surface morphologies for BCl₃/Ar. However, the surfaces are still approximately an order of magnitude rougher (as quantified by atomic force microscopy) than those obtained under the same conditions with Cl₂/Ar. InP surfaces etched at high BCl₃-to-Ar ratios have measurable concentrations of boron-and chlorine-containing residues.     

Photon correlation spectroscopy: X rays versus visible light

We have performed combined dynamic light scattering (DLS) and dynamic x-ray scattering (DXS) experiments on dense colloidal suspensions. The intermediate scattering functions obtained with these two techniques are compared directly. In the case of optically index matched samples, the comparison demonstrates that DXS yields accurate and reliable results. It is shown that the hydrodynamic interaction H(q) can be determined experimentally, without taking recourse to any theoretical model, by combining DXS and DLS. The combination of the two methods probes the dynamics over more than one decade in scattering vector. Experiments on optically opaque samples, where DLS fails, demonstrate the necessity to use x rays in these systems.