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The scaling of reaction yields in light ion fusion to low reaction energies is important for our understanding of stellar fuel chains and the development of future energy technologies. Experiments become progressively more challenging at lower reaction energies due to the exponential drop of fusion cross sections below the Coulomb barrier. We report on experiments where deuterium-deuterium (D-D) fusion reactions are studied in a pulsed plasma in the glow discharge regime using a benchtop apparatus. We model plasma conditions using particle-in-cell codes. Advantages of this approach are relatively high peak ion currents and current densities (0.1 to several A/cm2) that can be applied to metal wire cathodes for several days. We detect neutrons from D-D reactions with scintillator-based detectors. For palladium targets, we find neutron yields as a function of cathode voltage that are over 100 times higher than yields expected for bare nuclei fusion at ion energies below 2 keV (center of mass frame). A possible explanation is a correction to the ion energy due to an electron screening potential of 1000 ± 250 eV, which increases the probability for tunneling through the repulsive Coulomb barrier. Our compact, robust setup enables parametric studies of this effect at relatively low reaction energies. [ABSTRACT FROM AUTHOR]

We report a systematic study on the structural and electronic properties of Bi2Te3-xSex topological insulator alloy grown by molecular beam epitaxy(MBE). A mixing ratio of Bi2Se3 to Bi2Te3 was controlled by varying the Bi:Te:Se flux ratio. X-ray diffraction and Raman spectroscopy measurements indicate the high crystalline quality for the as-grown Bi2Te3-xSex films. Substitution of Te by Se is also revealed from both analyses. The surfaces of the films exhibit terrace-like quintuple layers and their size of the characteristic triangular terraces decreases monotonically with increasing Se content. However, the triangular terrace structure gradually recovers as the Se content further increases. Most importantly, the angle-resolved photoemission spectroscopy results provide evidence of single-Dirac-cone like surface states in which Bi2Te3-xSex with Se/Te-substitution leads to tunable surface states. Our results demonstrate that by fine-tuned MBEgrowth conditions, Bi2Te3-xSex thin film alloys with tunable topological surface states can be obtained, providing an excellent platform for exploring the novel device applications based on this compound. [ABSTRACT FROM AUTHOR]

The interdigital transducer (IDT)/AlN/conducting layer/diamond structures are investigated in this study to design surface acoustic wave (SAW) devices in the super high frequency band. Simulation results using the finite element method show that a thin conducting layer can effectively increase the coupling coefficient and, thus, broaden the bandwidth of SAW devices. For the Sezawa mode, it is illustrated that using a Ti layer with a layer thickness-to-wavelength ratio of 0.02 the maximum coupling coefficient is 2.546% and the associated SAW phase velocity is 10657 m/s at the AlN films’ thickness-to-wavelength ratio of 0.14. This coupling coefficient is 105% higher than that in the IDT/AlN/diamond structure. The research results can be applied to design SAW devices using diamond based structures in the super high frequency band. [ABSTRACT FROM AUTHOR]

HfO2/SiOx/Si layer structures have been fabricated using atomic layer deposition and subsequently annealed at partial oxygen pressures close to the equilibrium pressure of bulk SiO2. These ultralow oxygen partial pressures at around 10-40 atm have been achieved by a solid state buffer method. An interfacial SiOx layer with an approximate thickness of 1 nm is shown to be part of the equilibrium configuration of HfO2 on Si even at an oxygen activity eight orders of magnitude below the equilibrium pressure of bulk SiO2. Elimination of the silica-rich interfacial layer in any process permitting approach toward thermodynamic equilibrium seems highly improbable. By comparison with the case of pure SiOx on Si, it is shown that HfO2 acts as a “surfactant” to SiOx leading to a smooth film structure, while the pure SiOx on Si exhibits island formation under the same conditions. Furthermore, the oxidation state of Si in SiOx and the silicate composition at the HfO2/SiOx interface can be tailored by the partial oxygen pressure. [ABSTRACT FROM AUTHOR]

The van der Waals-London dispersion (vdW-Ld) spectra are calculated for the [9,3,m] metallic and [6,5,s] semiconducting single wall carbon nanotubes (SWCNTs), graphite, and graphene (a single carbon sheet of the graphite structure) using uniaxial optical properties determined from ab initio band structure calculations. The [9,3,m], exhibiting metallic optical properties in the axial direction versus semiconducting optical properties in the radial direction, highlights the strong anisotropic nature of metallic SWCNTs. Availability of both efficient ab initio local density band structure codes and sufficient computational power has allowed us to calculate the imaginary parts of the frequency dependent dielectric spectra, which are then easily converted to the required vdW-Ld spectra for Hamaker coefficient calculations. The resulting Hamaker coefficients, calculated from the Lifshitz quantum electrodynamic theory, show that neither graphite nor graphene are accurate model materials for estimating the Hamaker coefficients of SWCNTs. Additionally, Hamaker coefficients were calculated between pure radial-radial, radial-axial, and axial-axial components of both SWCNTs. Analysis of these coefficients reveals that the vdW-Ld interactions will depend on both chirality and the particular orientation between neighboring SWCNTs. The minimization of energy, with respect to orientation, predicts that vdW-Ld alignment forces will arise as a result of the anisotropic optical properties of SWCNTs. [ABSTRACT FROM AUTHOR]

Low-temperature (10 K) microcathodoluminescence spectroscopy with a scanning electron microscope has been used to probe shallow and deep levels within the grains of Bi[SUB2]O[SUB3]-doped ZnO powders prepared under different process conditions. These studies reveal strong electronic state variations between the bulk and boundaries of these submicron ZnO grains, including new emissions at ~3.329 eV at grain boundaries attributed to Bi phase segregation and/or the formation of new electrically active defects. The characteristic deep level defect emission at 2.4 eV due to nonstoichiometric point defects varies spatially, appearing much stronger in the grain bulk than at the boundaries. The 3.329 eV emissions become more pronounced with higher doping concentration and annealing temperature, indicating a strong dependence on processing. The strong temperature and composition dependence of these boundary-specific features are consistent with the known influence of process conditions on the varistor properties of ZnO powder. [ABSTRACT FROM AUTHOR]

The stability and composition of Hf[O.sub.2]/Si[O.sub.x] gate oxide stacks in the [P.sub.[O.sub.2]] regime about the coexistence of Si and Si[O.sub.2] as bulk phases are studied. The oxidation state of Si in Si[O.sub.x] and the silicate composition at the Hf[O.sub.2]/Si[O.sub.x] interface is tailored by the partial oxygen pressure.

Presents a study which examined the effects of processing thermal history on the formation and morphology of grain boundary phases and on the composition of BaPb[sub0.75]Bi[sub0.25]O[sub3] (BPB) superconductor. Characteristics of BPB superconductor; Overview of microstructural and microchemical studies on BPB; Implications of the results for cuprate superconductors.

Presents a study that examined the temperature and composition dependence of grain boundary segregation in lanthanum-strontium-copper-oxide polycrystalline superconducting materials. Methodology; Determination of the bulk and grain boundary concentrations of strontium; Correlation between the resistivity and the temperature characteristics of the superconducting samples.