E1(A) electronic band gap in wurtzite InAs nanowires studied by resonant Raman scattering

We report on resonant Raman experiments carried out on wurtzite InAs nanowires. Resonant conditions have been obtained by tuning either the excitation energy or the band gap through external high pressure at fixed excitation energy. A complete azimuthal study of the Raman spectra with two laser excitation lines (2.41 and 1.92 eV) has also been performed on a single wire. The measured E2 H mode resonance indicates that the E1(A) gap is about 2.4 eV, which is considerably reduced with respect to the zinc-blende InAs E1 gap. These findings confirm recent theoretical calculations of crystal phase induced bandstructure modifications. © 2013 American Chemical Society

Complete thermoelectric benchmarking of individual InSb nanowires using combined micro-Raman and electric transport analysis

Nanowires (NWs) are ideal nanostructures for exploring the effects of low dimensionality and thermal conductivity suppression on thermoelectric behavior. However, it is challenging to accurately measure temperature gradients and heat flow in such systems. Here, using a combination of spatially resolved Raman spectroscopy and transport measurements, we determine all the thermoelectric properties of single Se-doped InSb NWs and quantify the figure of merit ZT. The measured laser-induced heating in the NWs and associated electrical response are well described by a 1D heat equation model. Our method allows the determination of the thermal contact resistances at the source and drain electrodes of the NW, which are negligible in our system. The measured thermoelectric parameters of InSb NWs agree well with those obtained based on field-effect transistor Seebeck measurements

Pressure tuning of the optical properties of GaAs nanowires

The tuning of the optical and electronic properties of semiconductor nanowires can be achieved by crystal phase engineering. Zinc-blende and diamond semiconductors exhibit pressure-induced structural transitions as well as a strong pressure dependence of the band gaps. When reduced to nanoscale dimensions, new phenomena may appear. We demonstrate the tuning of the optical properties of GaAs nanowires and the induction of a phase transition by applying an external pressure. The dependence of the E-0 gap on the applied pressure was measured, and a direct-to-indirect transition was found. Resonant Raman scattering was obtained by pressure tuning of the E-0 and the E-0 + Delta(so) gaps with respect to the excitation energy. The resonances of the longitudinal optical modes L0 and 2L0 indicate the presence of electron-phonon Frohlich interactions. These measurements show for the first time a variation of ionicity in GaAs when in nanowire form. Furthermore, the dependence of the lattice constant on applied pressure was estimated. Finally, we found a clear indication of a structural transition above 16 GP

DEVELOPMENT OF PROCESS AND IMPROVEMENT OF SYSTEMS FAILING TO RUN TRUE FOR DRILLING OF SECOND SHAFTS OF WELLS BY BOTTOM ENGINES

There the problem about the correction of heavy emergenicies by the cutting and by the drilling of second shaft in the non-cased wells. The purpose is to develop the new technical-and-production approaches for the rise of quality of drilling process of second shaft at the great depthes and in the hard rocks. The design method of profile of second shafts, which was based on the relationship of milling speed of shaft, which was based on the relationship of milling speed of shaft wall and of failure speed of bottom as well as the method, which was based on the keeping of constant of forse failing to run true on the bit during the formation process of new shaft have been offered. The drilling manner of second shaft without the pre-working of bench, the cutting bit have been developed. The improved cutting bit the drilling of second shafts has been introduced. The preliminary tests of cutting bit give the positive results. The application field is the drilling of second shafts at the correction of emergencies in the deep wellsAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio

Valence band splitting in wurtzite InGaAs nanoneedles studied by photoluminescence excitation spectroscopy

We use low-temperature microphotoluminescence and photoluminescence excitation spectroscopy to measure the valence band parameters of single wurtzite InGaAs nanoneedles. The effective indium composition is measured by means of polarization-dependent Raman spectroscopy. We find that the heavy-hole and light-hole splitting is ∼95 meV at 10 K and the Stokes shift is in the range of 35–55 meV. These findings provide important insight in the band structure of wurtzite InGaAs that could be used for future bandgap engineering

Surface-directed molecular assembly of pentacene on aromatic organophosphonate self-assembled monolayers explored by polarized Raman spectroscopy

Organophosphonate self-assembled monolayers (SAMPs) fabricated on SiO 2 surfaces can influence crystallization of vapor-deposited pentacene and thus can affect device performance of pentacene-based organic thin film transistors. Polarized Raman spectroscopy is demonstrated to be an effective technique to determine the degree of anisotropy in pentacene thin films deposited on three structurally different, aromatic SAMPs grown on silicon oxide dielectrics. Vibrational characterization of pentacene molecules in these films reveals that the molecular orientation of adjacent crystalline grains is strongly correlated on the SAMP-modified dielectric surface, which results in enhanced interconnectivity between the crystallite domains, well beyond the size of a single grain. It is found that vibrational coupling interactions, relaxation energies, and grain size boundaries in pentacene thin films vary with the choice of SAMP. This information clearly shows that molecular assembly of pentacene thin films can be modulated by controlling the SAMP-modified dielectric surface, with potentially beneficial effects on the optimization of electron transfer rates

Assessing the thermoelectric properties of single InSb nanowires: the role of thermal contact resistance

The peculiar shape and dimensions of nanowires ( NWs ) have opened the way to their exploitation in thermoelectric applications. In general, the parameters entering into the thermoelectric fi gure of merit are strongly interdependent, which makes it dif fi cult to realize an optimal thermoelectric material. In NWs, instead, the power factor can be increased and the thermal conductivity reduced, thus boosting the thermoelectric ef fi ciency compared to bulk materials. However, the assessment of all the thermoelectric properties of a NW is experimentally very challenging. Here, we focus on InSb NWs, which have proved to be promising thermoelectric materials. The fi gure of merit is accurately determined by using a novel method based on a combination of Raman spectroscopy and electrical measurements. Remarkably, this type of experiment provides a powerful approach allowing us to neglect the role played by thermal contact resistance. Furthermore, we compare the thermal conductivity determined by this novel method to the one determined on the same sample by the thermal bridge method. In this latter approach, the thermal contact resistance is a non-negligible parameter, especially in NWs with large diameters. We provide experimental evidence of the crucial role played by thermal contact resistance in the assessment of the thermal properties of nanostructures, using two different measurement methods of the thermal conductivity