Quench-induced defects in silicon doped with group III acceptor impurities: Generation and annealing

The formation and annealing of quench-induced defects in Czochralski silicon have been studied using IR spectroscopy and Hall effect measurements. The results demonstrate that the behavior of quench-induced defects in Si〈Al〉 differs markedly from that in silicon doped with other Group III acceptor impurities: B, Ga, and In. The elastic fields created in Si by the Ga and In dopants, as well as by the isovalent impurity Sn, increase the density and annealing temperature of quench-induced defects. The highest density of quench-induced defects in Si〈Al〉 was observed at 1100°C.     

The interaction of linear and ring forms of DNA molecules with nanodiamonds synthesized by detonation

Nanodiamonds synthesized by detonation have been found not to immobilize the ring form of pUC19 plasmid DNA. Linear pUC19 molecules with blunt ends, prepared by restriction of the initial ring form of pUC19 DNA, and linear 0.25-10?kb DNA fragments are adsorbed on nanodiamonds. The amount of adsorbed linear DNA molecules depends on the size of the molecules and the size of the nanodiamond clusters.     

Influence of hydrogen bonds on the colloidal and fluorescent properties of detonation nanodiamonds in water,methanol and ethanol

This paper presents the results of research of influence of hydrogen bonds with different strength on fluorescence and colloidal properties of detonation nanodiamonds with surface carboxylic groups in the solvents. It is established that the colloidal properties of detonation nanodiamonds are almost independent on hydrogen bonds strength in water, methanol and ethanol. The fluorescent properties of detonation nanodiamonds are dependent on the type of solvent: the more intensive fluorescent properties correspond to weaker hydrogen bonds in solvents.     

Raman and XRD studies of Ge nanocrystals in alumina films grown by RF-magnetron sputtering

Germanium (Ge) nanocrystals (NCs) embedded in alumina thin films were produced by deposition on fused silica and silicon (111) substrates using radio-frequency (RF) magnetron sputtering. The films were characterised by both Raman and X-ray diffraction (XRD) spectroscopy. The deposition conditions were optimised in order to obtain crystalline Ge nanoparticles. In as-deposited films, the typical NC size was ∼3 nm as estimated by means of X-ray diffraction. Raman spectra taken from as-deposited films revealed both amorphous and crystalline semiconductor phases. Annealing was performed in order to improve the crystallinity of the semiconductor phase in the films. After a 1 h annealing at 800 °C the mean NC size estimated from the XRD data and Raman spectra increased to ∼6.5 nm. An increase in the crystallinity of the Ge phase was also confirmed by the Raman spectroscopy data.     

Creep of polycrystalline alumina,pure and doped with transition metal impurities

Grain size effects were used to evaluate the relative contributions of aluminium lattice and oxygen grain boundary diffusion to the high temperature (1350 to 1550° C) steady state creep of polycrystalline alumina, pure and doped with transition metal impurities (Cr, Fe). Divalent iron in solid solution was found to enhance both aluminium lattice and oxygen grain-boundary diffusion. Large concentrations of divalent iron led to viscous Coble creep which was rate-limited entirely by oxygen grain-boundary diffusion. Nabarro-Herring creep which was rate-limited by aluminium lattice diffusion was observed in pure and chromium-doped material. Chromium additions had no effect on diffusional creep rates but significantly depressed non-viscous creep modes of deformation. Creep deformation maps were constructed at various iron dopant concentrations to illustrate the relative contributions of aluminium grain boundary, aluminium lattice, and oxygen grain-boundary diffusion to the diffusional creep of polycrystalline alumina.     

Improved characterization of polycrystalline silicon film,by resonant Raman scattering

In this article, we report the results showing the usefulness of resonant Raman scattering to study polycrystalline silicon films, in complement to conventional Raman spectrometry. In addition to a strong enhancement of the Raman signal of crystalline silicon, the low probing depth of the UV light used in such experiments allows one to investigate very thin films and more generally near-surface regions.     

Raman spectra of biological samples: A study of preprocessing methods

In this study preprocessing of Raman spectra of different biological samples has been studied, and their effect on the ability to extract robust and quantitative information has been evaluated. Four data sets of Raman spectra were chosen in order to cover different aspects of biological Raman spectra, and the samples constituted salmon oils, juice samples, salmon meat, and mixtures of fat, protein, and water. A range of frequently used preprocessing methods, as well as combinations of different methods, was evaluated. Different aspects of regression results obtained from partial least squares regression (PLSR) were used as indicators for comparing the effect of different preprocessing methods. The results, as expected, suggest that baseline correction methods should be performed in advance of normalization methods. By performing total intensity normalization after adequate baseline correction, robust calibration models were obtained for all data sets. Combination methods like standard normal variate (SNV), multiplicative signal correction (MSC), and extended multiplicative signal correction (EMSC) in their basic form were not able to handle the baseline features present in several of the data sets, and these methods thus provide no additional benefits compared to the approach of baseline correction in advance of total intensity normalization. EMSC provides additional possibilities that require further investigation.     

Raman scattering study of molten alkali-metal molybdates ricn in MoO3

Raman scattering spectroscopy has been used to study the melting behavior and structure of Mo-O complexes alkali-metal molybdates rich in MoO₃: Li₄Mo₅O₁₇, K₂Mo₃O₁₀, and M₂Mo₄O₁₃ (M = Li, Na, K). The complex structure of the anion motif in these molybdates, made up of edge-sharing [MoO₆] octahedra, transforms on melting into short chains of [MoO₄] tetrahedra. We discuss the general trends in the variation of the chain structure of the anion motif in melts across the series of alkali-metal molybdates as the MoO₃ concentration increases from mono- to tetramolybdate compositions.     

Raman scattering study of the phonon dispersion in twisted bilayer graphene

Bilayer graphene with a twist angle θ between the layers generates a superlattice structure known as a Moiré pattern. This superlattice provides a θ-dependent q wavevector that activates phonons in the interior of the Brillouin zone. Here we show that this superlattice-induced Raman scattering can be used to probe the phonon dispersion in twisted bilayer graphene (tBLG). The effect reported here is different from the widely studied double-resonance in graphene-related materials in many aspects, and despite the absence of stacking order in tBLG, layer breathing vibrations (namely ZO’ phonons) are observed.      

Low-temperature radiation-stimulated gettering of impurities and defects in silicon by layers of porous silicon

Experimental results are presented for the low-temperature gettering of impurities and defects in semiconductor silicon wafers by layers of porous silicon followed by argon ion irradiation. It is shown that the gettering effect is caused by the simplest mobile point defects (vacancies) and elastic waves.     

Study of rotons in superfluid4He by Raman scattering

There is a long standing disagreement between neutron and Raman scattering from rotons in superfluid⁴He near T. In neutron scattering the linewidth becomes very large and the roton signal seems to disappear at T. A substantially smaller linewidth is observed with Raman scattering and the roton signal is present even at T. We have interpreted this difference (J. Low Temp. Phys. 93, 879 (1993)) as due to a modulation of the roton energy by a fluctuating local superfluid velocity due to proliferation of vorticity as T is approached. This gives rise to an extra contribution to the roton linewidth in neutron scattering but not in Raman scattering in which two rotons with almost opposite momenta are excited. We propose a test of this explanation with evanescent field Raman scattering. It has been suggested (A. Kuklov, A. Bulatov and J.L. Birman, Phys. Rev. Lett. 72, 3855 (1994)) that in such a measurement the scattering by a single roton should be measurable. In this case the presence of a fluctuating local superfluid velocity should show up as in neutron scattering and corroborate our proposal.     

Raman scattering study of molten alkali-metal molybdates and tungstates rich in basic oxides

Structural transformations of alkali-metal (Li, K, and Na) mono- and dimolybdates and tungstates have been studied by Raman scattering spectroscopy from room temperature to above their melting point. The structure of the Mo-O and W-O complexes in the form of isolated [MoO₄] and [WO₄] tetrahedra in crystalline monomolybdates and monotungstates has been shown to persist in the molten state. At the same time, the mixed anion motif made up of tetrahedra and octahedra in dimolybdate and tungstate crystals transforms on melting into complexes made up of two corner-sharing tetrahedra. We have identified the internal vibrational modes of such complexes in molten alkali-metal dimolybdates and ditungstates. Using rapid quenching of K₂O · 2MoO₃ and K₂O · 2WO₃ melts, we have obtained transparent glasses whose Raman spectra suggest that they have the same anion motif as the corresponding melts.     

Observation of Raman scattering by cloud droplets in the atmosphere

In a recent field campaign, the NASA Goddard Space Flight Center scanning Raman lidar measured, in the water vapor channel, Raman scattering from low-level clouds well in excess of 100% relative humidity. The excess scattering has been interpreted to be spontaneous Raman scattering by liquid water in the cloud droplets. A review of research on Raman scattering by microspheres indicates that the technique may provide a remote method to observe cloud liquid water. The clouds studied appear, from Mie scattering, to have two distinct layers with only the upper layer showing significant Raman scattering from liquid water in the droplets.     

Probing the nature of defects in graphene by Raman spectroscopy

Raman spectroscopy is able to probe disorder in graphene through defect-activated peaks. It is of great interest to link these features to the nature of disorder. Here we present a detailed analysis of the Raman spectra of graphene containing different type of defects. We found that the intensity ratio of the D and D' peak is maximum (～13) for sp(3)-defects, it decreases for vacancy-like defects (～7), and it reaches a minimum for boundaries in graphite (～3.5). This makes Raman Spectroscopy a powerful tool to fully characterize graphene.     

New features of the Mott-Hubbard insulator gap of parent HTS compounds found by resonance Raman scattering and UV-excited ordinary Raman scattering

Optical absorption at the insulating gap in the parent phase of cuprate superconductors shows a broad exciton-like peak near 1.7 eV, followed by a gradual decrease in absorption persisting 1 eV above the gap. By using ultraviolet laser lines to excite Raman spectra, we have found a Raman peak 0.2 eV below the first absorption peak in insulating cuprates. The Raman peak is much narrower than the absorption peak and hasA _2g symmetry. We assign it to an exciton consisting of a hole transition from Cu to a linear combination of Cud _xy and nearest neighbor Op orbitals. We have also studied the resonance Raman profile for two-magnon Raman scattering in the same samples. We find a sharp resonance feature at about 2.7 eV, and little Raman intensity for photon energies at the 1.7 eV absorption peak. The state created at the peak must therefore be an inappropriate intermediate state for the double spin-flip Raman process.     

Characterization of sprayed CuInS2 films by XRD and Raman spectroscopy measurements

We studied CuInS₂ (CIS) film growth using two deposition methods, which were high electrostatic field assisted ultrasonic spray (HEFAUS) deposition and sulfurization of Cu-In metallic film. The sprayed-films were grown with chalcopyrite ordering and Cu-Au ordering mixed. In order to obtain higher quality CIS films, post-sulfurization was carried out for sprayed-films. The post-sulfurization induced improvement of crystallinity and enhancement of chalcopyrite ordering. However, it was observed that Cu-Au ordering still coexisted in the CIS film after post-sulfurization. With the same sulfurization condition, sulfurization was done to transform Cu-In metallic film into CIS film. The sulfurized metallic film was turned out to be formed as CIS film with higher crystallinity and better chalcopyrite ordering than sulfurized sprayed-films. All fabricated films were characterized by X-ray diffraction, Raman scattering, scanning electron microscope and energy dispersive X-ray analysis measurements.     

Raman scattering and photoluminescence study of porous silicon formed on n-type silicon

We report Raman scattering and photoluminescence studies on porous silicon film formed on n-type silicon. The Raman spectra over the sample surface exhibit considerable variation whereas the photoluminescence spectra are practically identical. Our results indicate that, well inside the film surface, it consists of spherical nanocrystals of typical diameter ≈ 100Å, while on the edge these nanocrystals are ? 300Å. We further observe that there is no correlation between the photoluminescence peak position and the nanocrystal diameter. This suggests that the origin of the photoluminescence is due to radiative recombination between defect states in the bulk as well as on the surface of the nanocrystal.     

Structure of oxide gels and glasses by infrared and Raman scattering

Optically clear monolithic gels and fine gel powders have been synthesized using various alkoxide hydrolysis reactions. The gels have been characterized using various methods to determine their structures. (X-ray diffraction, DTA, TGA, DSC, IR and Raman spectroscopies). The spectra and the nature of gels depend on the solvent and the hydrolysis conditions (rate, pH, etc.). The use of acetone as solvent allows reduction of the hydrolysis time, from weeks to hours. If the hydrolysis of aluminium sec-butoxide is too rapid, at high pH, crystalline bayerite Al(OH)₃ is formed. Regular hydrolysis leads to amorphous optically clear gel with sometimes boehmite (or diaspore) traces. Formation of the (porous) glass (300 to 600°C) and also of the γ-alumina does not modify the Raman spectra strongly whereas large modifications are observed on IR spectra with the evolution of protonic species. The structure of alumina gel and glass is of the spinel type. The α-alumina phase grows above 1200 to 1250°C (above 1050°C if boehmite traces are present).