Anharmonic Effects in Ordered Kesterite-Type Cu2ZnSnS4

We performed an in-depth investigation and analysis of the effect of temperature on the Raman-active A-modes of bulk kesterite-type Cu2ZnSnS4 within the 300–460 K temperature range. We acquired the individual contributions to each Raman mode, namely, the thermal expansion and anharmonic interactions terms responsible for the Raman shift and broadening with temperature. Our results indicate that the Raman shift with temperature is dominated by the thermal expansion term, whereas the broadening is mainly governed by three-phonon damping processes in this material. Considering relevant results from the literature, it appears that dimensionality is a key factor in regulating the dominant phonon decay mechanism.

Beyond ultra-high pressure metamorphism: evidence for extremely high pressure conditions during frictional fusion in gigantic landslides using micro-Raman spectroscopy of quartz: the Tsergo Ri (Langtang Himal, Nepal) rockslide

<p>The Tsergo Ri rockslide represents one of the world's biggest rockslides in crystalline rocks (original volume: 10<sup>10</sup> m<sup>3</sup>). The mass movement comprises migmatites, leucogranites, orthogneisses and paragneisses (Weidinger et al. 2014). During mass-wasting, frictionites and microbreccias formed at the base of the rockslide. The frictionite is mainly composed of a glassy matrix containing biotite, quartz, and abundant plagioclase and K-feldspar. Biotite locally shows a transformation to spinel + glass in highly glassy microdomains. Fe-rich layers in the glass indicate melting of biotite-rich layers of the protolith biotite-bearing orthogneiss. Locally, quartz grains are rimmed by a thin layer of SiO<sub>2</sub> glass (lechatelierite).</p><p>Investigations by McMillan et al. (1991) and Kowitz et al. (2013) have shown that shocked quartz shows a shift in the main A1 Raman mode down to lower wavenumbers with increasing pressures. Tropper et al. (2017) and Sanders et al. (2020) found that quartz from the frictionites in the Köfels landslide (Austria) shows a significant shift of up to 4 cm<sup>-1</sup> in the main A1 Raman mode. Therefore micro-Raman spectroscopy was applied to quartz crystals with and without lechatelierite rims in the Tsergo Ri frictionites. Raman maps of quartz grain areas were prepared using a HORIBA Jobin Yvon LabRam HR800 micro-spectrometer equipped with a 30 mW He-Ne laser (633 nm emission).</p><p>Micro-Raman spectroscopy of 'normal' quartz yielded an intense A1 Raman mode at 464 cm<sup>-1</sup>, whereas<sup>  </sup>quartz without lechatelierite rims shows a shift of this band down to 461.5 cm<sup>-1</sup>. The highest shifts down to 460.5 cm<sup>-1</sup> were observed in quartz grains rimmed by lechatelierite. It is also noteworthy that these grains show an internal gradient of Raman shift of up to 3 cm<sup>-1</sup> from the core (463.5 cm<sup>-1</sup>) to the rim (460.5 cm<sup>-1</sup>) to just below the lechatelierite rims. This is an important observation since lechatelierite formation in frictionites from rockslides was considered so far to be a function of temperature only. Because lechatelierite only rims quartz with strongly shifted A1 band numbers, we interpret lechatelierite formation to be driven by both temperature and pressure, at least under frictionite conditions. The completely molten granitic matrix and the breakdown of biotite to spinel + melt indicates minimum temperatures of 900-1000°C. Sanders et al. (2020) showed that the shifted A1 mode of quartz is stable only below 1100°C, thus giving an upper limit of the temperature range. The observed Raman shift of the A1 mode and the presence of lechatelierite strongly suggest that a pressure of possibly >24-26 GPa was attained (cf. McMillan et al. 1991, Kowitz et al. 2013). The data from Köfels and Tsergo Ri provide the first quantitative estimates of peak pressures during frictionite formation, and show that UHP-modified quartz associated with lechatelierite is common in landslides of silica-rich rocks.</p><p> </p><p> </p><p>References:</p><p>Kowitz et al. 2013: Earth and Planetary Science Letters, 384:17</p><p>McMillan et al. 1992: Physics and Chemistry of Minerals, 19:71</p><p>Sanders et al. 2020: EGU2020-4831</p><p>Tropper et al. 2017: Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 163: 89</p><p>Weidinger et al. 2014: Earth and Planetary Science Letters, 389:62</p>

Correlation analysis of vibration modes in physical vapour deposited Bi2Se3 thin films probed by the Raman mapping technique

We propose the evaluation of strain in Bi2Se3 films based on the correlation analysis of in-plane (E2g) and out-of-plane (A21g) Raman mode positions as well as the algorithm of phonon deformation potential calculation for biaxial in-plane strain.

Doping controlled Fano resonance in bilayer 1T′-ReS2: Raman experiments and first-principles theoretical analysis

Fano resonance with electron doping for the in-plane Raman mode near 151 cm−1 in ReS2.

Raman spectroscopy study of manganese oxides: Tunnel structures

Raman spectra were collected for an extensive set of well-characterized tunnel-structure Mn oxide mineral species employing a range of data collection conditions. Using various laser wavelengths, such as 785, 633, and 532 nm at low power levels (30–500 µW), as well as the comprehensive database of standard spectra presented here, it is generally possible to distinguish and identify the various tunnel structure Mn oxide minerals. The Raman mode relative intensities can vary significantly as a function of crystal orientation relative to the incident laser light polarization direction as well as laser light wavelength. Consequently, phase identification success is enhanced when using a standards database that includes multiple spectra collected for different crystal orientations and with different laser light wavelengths. For the hollandite-group minerals, the frequency of the Raman mode near 630 cm–1 shows a strong linear correlation with the fraction of Mn3+ in the octahedral Mn sites. With the comprehensive Raman database of well-characterized Mn oxide standards provided here (and available online as Supplemental Materials1), and use of appropriate data collection conditions, micro-Raman is a powerful tool for identification and characterization of biotic and abiotic Mn oxide phases from diverse natural settings, including on other planets.