Growth peculiarities during vapor–liquid–solid growth of silicon nanowhiskers by electron-beam evaporation

One-dimensional (1D) silicon (Si) nanostructures were grown by electron-beam evaporation catalyzed by gold nanoparticles on silicon substrates following the vapor–liquid–solid growth mechanism. We report three strikingly different growth morphologies of the 1D Si nanostructures and discuss their formation. The morphology of the silicon nanostructures strongly depends on gold layer thickness, annealing temperature before deposition and growth temperature during the deposition. The formation of nanoscale silicon features such as nanobelts, nanowires and nanowhiskers was observed. The nanoscale silicon features were characterized by transmission and scanning electron microscopy using imaging, diffraction and energy-dispersive X-ray spectroscopy, atomic force microscopy and UV micro-Raman spectroscopy. PACS 68.37.Lp; 68.70.+w; 78.30.-j; 81.15.Jj     

Investigation of helium implantation induced blistering in InP

 Four-inch InP wafers were implanted with 100 keV helium ions with a dose of 5×10¹⁶ cm⁻² and subsequently annealed in air in the temperature range of 225-400°C in order to determine the blistering kinetics of these wafers. An Arrhenius plot of the blistering time as a function of reciprocal temperature revealed two different activation energies for the formation of surface blisters in InP. The activation energy was found to be 0.30 eV in the higher temperature regime of 300-400 °C and 0.74 eV in the lower temperature regime of 225-300 °C. The implantation induced damage was analyzed by cross-sectional transmission electron microscopy, which revealed a band of defects extending from 400-700 nm from the surface of InP. The damage band was found to be decorated with a large number of nanovoids having diameters between 2 and 5 nm. These nanovoids served as precursors for the formation of microcracks inside InP upon annealing, which led to the formation of surface blisters.     

Raman spectroscopic characterization of novel carbon‐bonded filter compositions for steel melt filtration

In this work, Raman scattering results on novel carbon‐bonded filter compositions are presented. Such filters are already used for steel melt filtration; however, the potential of this carbon‐bonded Al₂O₃–C system regarding material characteristics and filtration efficiency has not been fully understood yet. In order to investigate thermally induced structural changes of the filter compositions, micro‐Raman spectroscopy was applied. Analyzing the position, intensity, and full width at half maximum of G and D peaks in the Raman spectra, it could be determined that the carbon appears in graphitic form and the graphitic cluster size was estimated. We found an increase of the lateral cluster size L_a with increasing coking temperature. Copyright © 2013 John Wiley & Sons, Ltd.     

Vibrational properties of perfluoropentacene thin film

We have studied the vibrational properties of perfluoropentacene (PFP) thin films on highly oriented pyrolytic graphite (HOPG) substrates by high-resolution electron energy loss spectroscopy (HREELS) and Raman spectroscopy. The HREELS spectra showed slight but clear increase in the vibrational energies with increasing film thickness as well as with decreasing temperature of the multilayer films. In the polarization-dependent Raman spectra of a multilayer film, the depolarization ratios of all detected vibrations with the Ag irreducible representation were found to be larger than 1, indicating that the molecular structure is distorted in the multilayer. Both results suggest that there is a fairly strong intermolecular interaction in PFP multilayer films.     

Structure and orbital ordering of ultrathin LaVO3 probed by atomic resolution electron microscopy and Raman spectroscopy

Orbital ordering has been less investigated in epitaxial thin films, due to the difficulty to evidence directly the occurrence of this phenomenon in thin film samples. Atomic resolution electron microscopy enabled us to observe the structural details of the ultrathin LaVO₃ films. The transition to orbital ordering of epitaxial layers as thin as ≈4 nm was probed by temperature‐dependent Raman scattering spectroscopy of multilayer samples. From the occurrence and temperature dependence of the 700 cm^–1 Raman active mode it can be inferred that the structural phase transition associated with orbital ordering takes place in ultrathin LaVO₃ films at about 130 K.     

Raman spectroscopic investigations of epitaxial BiFeO3 thin films on rare earth scandate substrates

BiFeO₃ epitaxial thin films fabricated by pulsed laser deposition on different scandate substrates were investigated by means of Raman spectroscopy. We observed periodic changes in Raman position, full width at half maximum and intensity for some phonon modes as a function of the azimuthal angle ϕ. Further analysis revealed the possibility to assign the so far controversial discussed Raman modes at low wavenumbers (<250 cm⁻¹) through rotational Raman measurements at different azimuthal angles, which show high sensitivity to the aforementioned parameters. Furthermore, the ferroelectric/ferroelastic domain structure shown by piezo‐response force microscopy investigations of the samples was confirmed. Our results are supported by symmetry‐based calculations including the analysis of Raman scattering geometry as well as the dielectric function of BiFeO₃ in the infrared range. Copyright © 2015 John Wiley & Sons, Ltd.     

High-density-plasma (HDP)-CVD oxide to thermal oxide wafer bonding for strained silicon layer transfer applications

Direct wafer bonding between high-density-plasma chemical vapour deposited (HDP-CVD) oxide and thermal oxide (TO) has been investigated. HDP-CVD oxides, about 230 nm in thickness, were deposited on Si(0 0 1) control wafers and the wafers of interest that contain a thin strained silicon (sSi) layer on a so-called virtual substrate that is composed of relaxed SiGe (∼4 μm thick) on Si(0 0 1) wafers. The surfaces of the as-deposited HDP-CVD oxides on the Si control wafers were smooth with a root-mean-square (RMS) roughness of <1 nm, which is sufficiently smooth for direct wafer bonding. The surfaces of the sSi/SiGe/Si(0 0 1) substrates show an RMS roughness of >2 nm. After HDP-CVD oxide deposition on the sSi/SiGe/Si substrates, the RMS roughness of the oxide surfaces was also found to be the same, i.e., >2 nm. To use these wafers for direct bonding the RMS roughness had to be reduced below 1 nm, which was carried out using a chemo-mechanical polishing (CMP) step. After bonding the HDP-CVD oxides to thermally oxidized handle wafers, the bonded interfaces were mostly bubble- and void-free for the silicon control and the sSi/SiGe/Si(0 0 1) wafers. The bonded wafer pairs were then annealed at higher temperatures up to 800 °C and the bonded interfaces were still found to be almost bubble- and void-free. Thus, HDP-CVD oxide is quite suitable for direct wafer bonding and layer transfer of ultrathin sSi layers on oxidized Si wafers for the fabrication of novel sSOI substrates.     

Spectroscopic ellipsometric characterization of organic films obtained via organic vapor phase deposition

Thin films of Tris(8-hydroxyquinoline)-aluminum(III) (Alq₃) and N,N-Di-[(1-naphthyl)-N,N-diphenyl]-(1,1-biphenyl)-4,4-diamine (-NPD ) were deposited on large-area silicon substrates by means of the recently developed organic vapor phase deposition (OVPD) method. Variable-angle spectroscopic ellipsometry was used to measure the optical constants of OVPD Alq₃ and -NPD layers in the 0.8–5 eV energy range. The absorption onset which defines the lower limit of the optical band gap was found to be at 2.65 eV and 2.9 eV for Alq₃ and -NPD , respectively. Additionally, the thicknesses of the layers as well as the thickness profiles of the organic thin films were determined along the 8 diameter of the wafers. The thickness analysis revealed large-area uniform deposition of the films. PACS 78.20.Ci; 81.70.Fy; 81.15.-z     

Resonant Raman scattering of ZnS,ZnO, and ZnS/ZnO core/shell quantum dots

Resonant Raman scattering by optical phonon modes as well as their overtones was investigated in ZnS and ZnO quantum dots grown by the Langmuir–Blodgett technique. The in situ formation of ZnS/ZnO core/shell quantum dots was monitored by Raman spectroscopy during laser illumination.