Probing orbital ordering in LaVO3_{3} epitaxial films by Raman scattering

Single crystals of Mott-Hubbard insulator LaVO3 exhibit spin and orbital ordering along with a structural change below ≈140 K. The occurrence of orbital ordering in epitaxial LaVO3films has, however, been little investigated. By temperature-dependent Raman scatteringspectroscopy, we probed and evidenced the transition to orbital ordering in epitaxial LaVO3film samples fabricated by pulsed-laser deposition. This opens up the possibility to explore the influence of different epitaxial strain (compressive vs. tensile) and of epitaxy-induced distortions of oxygen octahedra on the orbital ordering, in epitaxial perovskite vanadate films

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

Phonon Raman spectra of colloidal CdTe nanocrystals: effect of size, non-stoichiometry and ligand exchange

Resonant Raman study reveals the noticeable effect of the ligand exchange on the nanocrystal (NC) surface onto the phonon spectra of colloidal CdTe NC of different size and composition. The oleic acid ligand exchange for pyridine ones was found to change noticeably the position and width of the longitudinal optical (LO) phonon mode, as well as its intensity ratio to overtones. The broad shoulder above the LO peak frequency was enhanced and sharpened after pyridine treatment, as well as with decreasing NC size. The low-frequency mode around 100 cm-1 which is commonly related with the disorder-activated acoustical phonons appears in smaller NCs but is not enhanced after pyridine treatment. Surprisingly, the feature at low-frequency shoulder of the LO peak, commonly assigned to the surface optical phonon mode, was not sensitive to ligand exchange and concomitant close packing of the NCs. An increased structural disorder on the NC surface, strain and modified electron-phonon coupling is discussed as the possible reason of the observed changes in the phonon spectrum of ligand-exchanged CdTe NCs

Thermal conductivity and phonon anharmonicity of chemical vapor transport grown and mineral–FeS₂ single crystals: An optothermal Raman study

In this work, thermal conductivity and anharmonic properties of chemical vapor transport (CVT)-grown pyrite-FeS2 and mineral single crystals have been investigated and compared. It has been shown that optothermal Raman technique is able to capture the large thermal conductivity difference between the CVT and mineral samples at low temperatures. This difference is attributed to point defects such as sulfur vacancies or impurity doping of CVT-grown FeS2 crystals. Balkanski–Klemens model analysis of the samples has shown that three-phonon scattering of Ag and Eg modes and the lattice thermal expansion are the dominant anharmonic contributors while four-phonon scattering is negligible in pyrite-FeS2. Thus, thermal conductivity of materials that is difficult to measure by conventional methods (i.e., flash method) can be measured in their most native form by using optothermal Raman spectroscopy (RS) without rigorous sample preparation. © 2022 The Authors. Journal of Raman Spectroscopy published by John Wiley & Sons Ltd

Strained silicon on wafer level by wafer bonding: materials processing, strain measurements and strain relaxation

peer reviewedDifferent methods to introduce strain in thin silicon device layers are presented. Uniaxial strain is introduced in CMOS devices by process-induced stressors allowing the local generation of tensile or compressive strain in the channel region of MOSFETs. Biaxial strain is introduced by growing thin silicon layer on SiGe buffer and transferring it to an oxidized silicon substrates. The latter forms strained silicon on insulator (SSOI) wafer characterized by tensile strain only. Future CMOS device technologies require the combination of the global strain of SSOI substrates with local stressors to increase the device performance

Structural stability and thermoelectric performance of high quality synthetic and natural pyrites (FeS₂)

Synthetic bulk and natural pyrite from the hydrothermal mine in Schonbrunn (Saxony, Germany) are confirmed to be stoichiometric FeS2 compounds and stable (for thermoelectric applications) up to similar to 600 K by combined thermal, chemical, spectroscopic and X-ray diffraction analyses. Natural pyrite with a small amount (<0.6 wt%) of well-defined transition metal carbonates revealed characteristics of a nondegenerate semiconductor and is suitable as a model system for the investigation of thermoelectric performance. In the temperature range 50-600 K both natural and synthetic high quality bulk FeS2 samples show electrical resistivity and Seebeck coefficients varying within 220-5 x 10(-3) omega m and 4 - (-450) mu V K-1, respectively. The large thermal conductivity (similar to 40 W m(-1) K-1 at 300 K) is exclusively due to phononic contribution, showing a well pronounced maximum centered at similar to 75 K for natural pyrite (grain size <= 5 mm). It becomes almost completely suppressed in the sintered bulk samples due to the increase of point defect concentration and additional scattering on the grain boundaries (grain size <= 100 mu m). The thermoelectric performance of pure pyrite with ZT similar to 10(-6) at 600 K is indeed by a factor of similar to 1000 worse than those reported earlier for some minerals and synthetic samples

Improving thermoelectric performance of indium thiospinel by Se- and Te-substitution

A structural and thermoelectric study of the polycrystalline Se- and Te-substituted In2.67S4thiospinels was performed. The obtained In2.67S4−xSex(0 ≤x≤ 0.5) and In2.67S4−yTey(0 ≤y≤ 0.15) samples were single phase and the solubility limits of Se and Te were not reached. A comprehensive phase analysis based on powder X-ray diffraction and Raman spectroscopy, as well as Rietveld refinements, confirmed that Se/Te-incorporation into the structure of binary β-In2.67S4(x= 0) favors the formation of the cubic α-modification forx&gt; 0.15 andy≥ 0.05. Moreover, both cubic and tetragonal phases were shown to coexist in the In2.67S3.9Se0.1specimen. The Se/Te-for-S substitution strongly influenced electronic transport properties, leading to an increase of the charge carrier concentration and thus, a reduction of the electrical resistivity and Seebeck coefficient. A decrease of charge carrier mobility, observed previously upon the stabilization of the α-phase, was partially counterbalanced by a reduction of effective electron mass, as revealed by the electronic structure calculations. This resulted in the enhancement of the power factor PF &gt; 10−4W m−1K−2above RT for In2.67S3.9Se0.1and In2.67S3.5Se0.5thiospinels in comparison to pristine In2.67S4. Combination of such an effect with the decreased thermal conductivity (i.e., &lt; 1.5 W m−1K−1above RT) led to the improvement of the thermoelectric figure of merit by factor of 2.5 in In2.67S3.5Se0.5 © The Royal Society of Chemistry 2021