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.     

Inductively Coupled Plasma Etching in ICl- and IBr-Based Chemistries. Part I: GaAs, GaSb, and AlGaAs

High-density plasma etching of GaAs, GaSb, and AlGaAs was performed inICl/Ar and IBr/Ar chemistries using an Inductively Coupled Plasma (ICP)source. GaSb and AlGaAs showed maxima in their etch rates for both plamachemistries as a function of interhalogen percentage, while GaAs showedincreased etch rates with plasma composition in both chemistries. Etchrates of all materials increased substantially with increasing rf chuckpower, but rapidly decreased with chamber pressure. Selectivities >10 forGaAs and GaSb over AlGaAs were obtained in both chemistries. The etchedsurfaces of GaAs showed smooth morphology, which were somewhat better withICl/Ar than with IBr/Ar discharge. Auger Electron Spectroscopy analysisrevealed equirate of removal of group III and V components or thecorresponding etch products, maintaining the stoichiometry of the etchedsurface.     

Dry etching characteristics of III–V semiconductors in microwave BCl3 discharges

Electron cyclotron resonance (ECR) BCl₃ discharges with additional rf biasing of the sample position have been used to etch a variety of III–V semiconductors. GaAs and Al_xGa_1–xAs (x = 0–1) etch at equal rates in BCl₃ or BCl₃/Ar discharges, whereas SF₆ addition produces high selectivities for etching GaAs over AlGaAs. These selectivities are in excess of 600 for dc biases of –150 V, and fall to 6 for biases of –300 V. If the dc biases are kept to – 100 V, there is no measurable degradation of the optical properties of the GaAs and AlGaAs. The AlF₃ formed on the AlGaAs surface during exposure to BCl₃/SF₆ plasmas can be removed by sequential rinsing in dilute NH₄OH and water. In-based materials (InP, InAs, InSb, InGaAs) etch at slow rates with relatively rough morphologies in BCl₃ plasmas.     

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.     

Inductively Coupled Plasma and Electron Cyclotron Resonance Plasma Etching of an InGaAlP Compound Semiconductor System

Current and future generations of sophisticated compound semiconductor devices require the ability for submicron scale patterning. The situation is being complicated because some of the new devices are based on a wider diversity of materials to be etched. Conventional RIE (reactive ion etching) has been prevalent across the industry so far, but has limitations for materials with high bond strengths or multiple elements. In this article, we suggest high-density plasmas such as ECR (electron cyclotron resonance) and ICP (inductively coupled plasma), for the etching of ternary compound semiconductors (InGaP, AlInP, AlGaP) that are employed for electronic devices such as heterojunction bipolar transistors (HBTs) or high electron mobility transistors (HEMTs), and photonic devices such as light-emitting diodes (LEDs) and lasers. Operating at lower pressure, high-density plasma sources are expected to meet target goals determined in terms of etch rate, surface morphology, surface stoichiometry, selectivity, etc. The etching mechanisms that are described in this article can also be applied to other III-V (GaAs-based, InP-based) as well as III-Nitride, because the InGaAlP system shares many of the same properties.     

Detection of CO using bulk ZnO Schottky rectifiers

Bulk Pt/ZnO Schottky rectifiers show gas sensitivities for CO of 4% and 8%, respectively, at 150 °C for 1 and 10% CO in N₂. The current or voltage changes are time dependent, with an activation energy of 40.7 kJmol^-1. Over a limited range of partial pressures of CO (P_CO) in the ambient gas, the on-state resistance R of the sensor at fixed bias voltage decreased according to R=(R_O+A(P_CO)^0.5)^-1, where A is a constant and R_O is the resistance in N₂. Since these devices are also sensitive to H₂ and C₂H₄, the ZnO rectifiers appear promising for a range of gas-sensing applications. PACS 81.05.Dz; 73.61.Ga; 72.80.Ey     

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.     

Spin waves in the (π,0) magnetically ordered iron chalcogenide Fe1.05Te

We use neutron scattering to show that spin waves in the iron chalcogenide Fe(1.05)Te display novel dispersion clearly different from both the first principles density functional calculations and recent observations in the related iron pnictide CaFe(2)As(2). By fitting to a Heisenberg Hamiltonian, we find that although the nearest-neighbor exchange couplings in the two systems are quite different, their next-nearest-neighbor (NNN) couplings are similar. This suggests that superconductivity in the pnictides and chalcogenides share a common magnetic origin that is intimately associated with the NNN magnetic coupling between the irons.