Artykuły w czasopismach: „Temperature dependent Raman measurements”

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Yumigeta, Kentaro, Yashika Attarde, Jan Kopaczek, Mohammed Y. Sayyad, Yuxia Shen, Mark Blei, Seyed Tohid Rajaei Moosavy, Ying Qin, Renee Sailus i Sefaattin Tongay. "The phononic and charge density wave behavior of entire rare-earth tritelluride series with chemical pressure and temperature". APL Materials 10, nr 11 (1.11.2022): 111112. http://dx.doi.org/10.1063/5.0110395.

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Here, we present comprehensive phononic and charge density wave properties (CDW) of rare-earth van der Waals tritellurides through temperature dependent angle-resolved Raman spectroscopy measurements. All the possible rare-earth tritellurides (RTe3) ranging from R = La–Nd, Sm, Gd–Tm were synthesized through a chemical vapor transport technique to achieve high quality crystals with excellent CDW characteristics. Raman spectroscopy studies successfully identify the emergence of the CDW state and transition temperature (TCDW), which offers a non-destructive method to identify their CDW response with micron spatial resolution. Temperature dependent Raman measurements further correlate how the atomic mass of metal cations and the resulting chemical pressure influence its CDW properties and offer detailed insight into the strength of CDW amplitude mode-phonon coupling during the CDW transition. Angle-resolved Raman measurements offer the first insights into the CDW-phonon symmetry interplay by monitoring the change in the symmetry of phonon mode across the CDW transition. Overall results introduce the library of RTe3 CDW materials and establish their characteristics through the non-destructive angle-resolved Raman spectroscopy technique.

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Sagitova, E. A., P. Donfack, K. A. Prokhorov, S. M. Kuznetsov, M. A. Guseva, V. A. Gerasin, G. Yu Nikolaeva i A. Materny. "Sensitive temperature-dependent phase resolution of polyethylene-clay nanocomposites". Laser Physics 32, nr 8 (15.06.2022): 084009. http://dx.doi.org/10.1088/1555-6611/ac7334.

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Abstract With the help of spectroscopic and differential scanning calorimetry (DSC) techniques, we have studied conformational and phase reorganizations as function of temperature in intercalated polymer-clay nanocomposites based on low-, middle-, and high-density polyethylene (PE) matrices. We show that Raman spectroscopy is sensitive to structural changes appearing during heating at much lower temperatures (about 47 °C) in comparison to DSC measurements. In fact, in the melting region where DSC traces show endotherms, Raman spectra reveal dramatic changes in the phase and conformational compositions of PE and PE-matrices within PE-clay nanocomposites. Noteworthy, the structural reorganization pathway, through which the semicrystalline nanocomposites transform into a melt state, depends primarily on the PE density and weakly on the filler (nanoclay). Moreover, the temperature-dependent crystallinity degree and the total amount of trans-conformers of the PE system are determined, and the evidence for the formation of intermediate crystal-like phase during heating is shown.

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Unger, Miriam, Harumi Sato, Yukihiro Ozaki, Dieter Fischer i Heinz W. Siesler. "Temperature-Dependent Fourier Transform Infrared Spectroscopy and Raman Mapping Spectroscopy of Phase-Separation in a Poly(3-hydroxybutyrate)–Poly(l-Lactic Acid) Blend". Applied Spectroscopy 67, nr 2 (luty 2013): 141–48. http://dx.doi.org/10.1366/12-06712.

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Variable-temperature Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopic mapping measurements were applied to study the phase separation of a poly(3-hydroxybutyrate) (PHB)–poly(l-lactic acid) (PLA) (50:50 wt.%) polymer-blend film as a function of temperature between 25 and 175 °C. Because of the better band separation compared with the fundamental absorptions, the first overtones of the v(C=O) bands of PHB and PLA were used to evaluate the temperature-dependent FT-IR images as PLA–PHB and PHB–PLA band-ratio contour plots, respectively. From the visualization of the band-ratio FT-IR images, it could be derived that even beyond the melting point of PLA (145 °C), the lateral position and the geometry of the PHB-rich and PLA-rich phases were retained up to 165 °C. Furthermore, the FT-IR images derived during and after the melting of PHB (174 °C) provided an interesting insight into the homogenization process of the polymer melt. By exploiting its higher lateral resolution, valuable additional information became available from the Raman mapping measurements. Based on the Raman data, the scenario of phase-separated PHB-rich and PLA-rich domains of about 50 iμ size, based on the FT-IR imaging measurements, had to be revised. Instead, the originally interpreted PHB-rich and PLA-rich domains are actually clusters of much smaller grains. Additionally, the Raman images measured in the same temperature interval revealed that the clusters of small PHB-rich grain structures aggregated as a function of temperature increase. These investigations prove that FT-IR and Raman imaging in combination with variable-temperature measurements can provide new (and so far unavailable) insights into structural phenomena of phase-separated polymer blends.

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Miao, Peng, Jie Wu, Yunchen Du, Yanchun Sun i Ping Xu. "Phase transition induced Raman enhancement on vanadium dioxide (VO2) nanosheets". Journal of Materials Chemistry C 6, nr 40 (2018): 10855–60. http://dx.doi.org/10.1039/c8tc04269a.

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Crystal symmetry matters: with the increase in the crystal symmetry from VO₂(B) to VO₂(M) and to VO₂(R), a dramatic decline in Raman enhancement on VO₂ nanosheets is revealed through temperature-dependent Raman measurements.

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Shvets, Petr, Ksenia Maksimova i Alexander Goikhman. "Raman Spectroscopy of V4O7 Films". Coatings 12, nr 3 (22.02.2022): 291. http://dx.doi.org/10.3390/coatings12030291.

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A thin film of vanadium oxide Magnéli phase V4O7 was produced using cathodic arc sputtering. X-ray diffraction, Rutherford backscattering spectrometry and Raman investigations confirmed the formation of this phase. The Raman spectrum of V4O7 differs considerably from the spectrum of another Magnéli oxide, V3O5, showing that Raman spectroscopy is an excellent tool for distinguishing between these two phases. Temperature-dependent Raman measurements revealed a significant change of the spectra near the V4O7 metal–insulator phase transition.

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Holloway, Simon, Hugo Ricketts i Geraint Vaughan. "Boundary layer temperature measurements of a noctual urban boundary layer". EPJ Web of Conferences 176 (2018): 06004. http://dx.doi.org/10.1051/epjconf/201817606004.

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A low-power lidar system based in Manchester, United Kingdom has been developed to measure temperature profiles in the nocturnal urban boundary layer. The lidar transmitter uses a 355nm diode-pumped solid state Nd:YAG laser and two narrow-band interference filters in the receiver filter out rotational Raman lines that are dependent on temperature. The spectral response of the lidar is calibrated using a monochromator. Temperature profiles measured by the system are calibrated by comparison to co-located radiosondes.

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Gogolin, Mathias, M. Mangir Murshed, Lkhamsuren Bayarjargal, Detlef Klimm i Thorsten M. Gesing. "Thermal anomalies and phase transitions in Pb₂Sc₂Si₂O₉ and Pb₂In₂Si₂O₉". Zeitschrift für Kristallographie - Crystalline Materials 236, nr 11-12 (19.10.2021): 283–92. http://dx.doi.org/10.1515/zkri-2021-2046.

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Abstract Pb2Sc2Si2O9 and Pb2In2Si2O9, respectively, the scandium and indium containing structural analogues of the mineral kentrolite are grown by spontaneous crystallization from a PbO flux. The corresponding polycrystalline powder samples are synthesized by conventional solid-state approach. The compounds are thoroughly characterized using temperature-dependent single crystal and powder X-ray diffraction, heat capacity measurements, second harmonic generation experiments and Raman spectroscopy. At ambient conditions, both compounds crystallize in the non-centrosymmetric Pna21 space group and undergo phase transitions to the centrosymmetric Pbcn space group at elevated temperatures. The Pbcn into Pna21 phase transitions are complemented by the signals of the temperature-dependent second harmonic generation. The specific heat capacity exhibits distinct cusp, supporting the λ-type second-order phase transition. The temperature dependency of some selective Raman modes further complements the findings, showing softening and hardening of the phonons across the phase transitions.

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Pan, Xiaoguang, Tianwen Yang, Hangxin Bai, Jiangbo Peng, Lujie Li, Fangli Jing, Hailong Qiu, Hongjun Liu i Zhanggui Hu. "Controllable Synthesis and Charge Density Wave Phase Transitions of Two-Dimensional 1T-TaS2 Crystals". Nanomaterials 13, nr 11 (5.06.2023): 1806. http://dx.doi.org/10.3390/nano13111806.

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1T-TaS2 has attracted much attention recently due to its abundant charge density wave phases. In this work, high-quality two-dimensional 1T-TaS2 crystals were successfully synthesized by a chemical vapor deposition method with controllable layer numbers, confirmed by the structural characterization. Based on the as-grown samples, their thickness-dependency nearly commensurate charge density wave/commensurate charge density wave phase transitions was revealed by the combination of the temperature-dependent resistance measurements and Raman spectra. The phase transition temperature increased with increasing thickness, but no apparent phase transition was found on the 2~3 nm thick crystals from temperature-dependent Raman spectra. The transition hysteresis loops due to temperature-dependent resistance changes of 1T-TaS2 can be used for memory devices and oscillators, making 1T-TaS2 a promising material for various electronic applications.

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Hagemann, H., J. Mareda, C. Chiancone i H. Bill. "Conformational studies of 2-butanol using temperature-dependent Raman measurements and MM3 calculations". Journal of Molecular Structure 410-411 (czerwiec 1997): 357–60. http://dx.doi.org/10.1016/s0022-2860(96)09584-1.

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Felhi, Houda, Mourad Smari, Saber Mansouri, Jalel Massoudi i Essebti Dhahri. "Deciphering the Structural Characterization, Hirshfeld Surface Analysis, Raman Studies, and Temperature-Dependent Magnetodielectric Properties of BiMn2O5". Magnetochemistry 7, nr 5 (16.05.2021): 68. http://dx.doi.org/10.3390/magnetochemistry7050068.

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We investigate the structural, Hirshfeld surface, magnetic, and magnetodielectric properties of BiMn2O5. The sample can be indexed with an orthorhombic phase associated with space group Pbam, with crystallographic parameters a = 7.54946 Å, b = 8.54962 Å and c = 5.753627 Å. The Hirshfeld surface analysis, associated with 2D fingerprint plots, was used to visualize and explore the significant intermolecular interactions in the crystal structure quantitatively. The Raman spectra, measured from 6 to 300 K in a frequency range between 250 and 750 cm−1, exhibit good agreement between the SHELL model calculations and the experimental measurement of the proximity of the phonon frequencies for our sample. Furthermore, magnetic measurements show that BiMn2O5 becomes antiferromagnetic below the Néel temperature (TN)—the temperature above which an antiferromagnetic material becomes paramagnetic (TN = 31 K). The relaxation at intermediate temperatures (200–300 K) can be attributed to the polar jump process at two charge transfer sites between the Mn3+ and Mn4+ ions, which, in combination with the special arrangement of the Mn3+/Mn4+ ions, is likely to produce the strong intrinsic magnetodielectric effect (MD) in the same temperature range.

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Mitsai, Evgeniy, i Aleksandr A. Kuchmizhak. "Non-Invasive Temperature-Feedback SERS with all-Dielectric Resonant Nanostructures". Defect and Diffusion Forum 386 (wrzesień 2018): 196–200. http://dx.doi.org/10.4028/www.scientific.net/ddf.386.196.

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All-dielectric resonant micro-and nanostructures emerge as a promising platform, which can complement the metal-based counterparts in routine biosensing measurements based on surface-enhanced Raman scattering (SERS). However, lack of in-situ temperature control limits performance of nanostructures for precise SERS-based applications. Here, we present an approach for SERS measurement with simultaneous temperature control and employ Raman spectroscopy to mapping of temperature-dependent Raman signal distribution. We attest a chemically inert black silicon (b-Si) substrate for a non-invasive (chemically non-perturbing) SERS identification of the molecular fingerprints at low concentrations. Additional studies of the slow daylight-driven para-aminothiophenol (PATP)-to-4,4'-dimercaptoazobenzene (DMAB) catalytic conversion in the aqueous methanol solution loaded with colloidal silver nanoparticles confirm the non-invasive SERS performance of the all-dielectric crystalline b-Si substrate. Proposed SERS substrates can be fabricated using easy-to-implement scalable technology of plasma etching making such inexpensive all-dielectric substrates promising for routine SERS applications, where the temperature-feedback and the noninvasiveness are of mandatory importance.

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Adam, Mariana. "Notes on Temperature-Dependent Lidar Equations". Journal of Atmospheric and Oceanic Technology 26, nr 6 (1.06.2009): 1021–39. http://dx.doi.org/10.1175/2008jtecha1206.1.

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Abstract The temperature dependence of molecular backscatter coefficients must be taken into account when narrowband interference filters are used in lidar measurements. Thus, the spectral backscatter differential cross section of the molecules involved in the backscattering of the radiation has to be calculated or measured and the interference filter transmission efficiency must be known. The present paper is intended to describe in an easily reproducible manner the procedure involved in calculating the temperature-dependent functions introduced in the lidar equations, including the computation of the differential cross sections for air, nitrogen, and water vapor. The temperature-dependent functions are computed for the Howard University Raman lidar (HURL). The interference filter efficiencies are given by the manufacturer. Error estimates in water vapor mixing ratio and aerosol backscatter ratio involved when temperature-dependent functions are omitted are given for measurements taken with HURL. For the data analyzed, it is found that errors in estimating the water vapor mixing ratio are up to ∼6% while in estimating the aerosol backscattering ratio the errors are up to ∼1.3% in the planetary boundary layer and ∼2.2% in cirrus clouds. Theoretical computations are performed to determine temperature-dependent functions for nitrogen, water vapor, and their ratio, using simulated Gaussian-shaped filters. The goal is to find the optimum combination of different filters that will determine the ratio profiles of the temperature-dependent functions that are either the closest to unity or the least variable. The analyses reveal that quite constant profiles can be obtained for several combinations of the filters.

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Krylov, Alexander, Svetlana Krylova, Svitlana Kopyl, Aleksandr Krylov, Ferid Salehli, Pavel Zelenovskiy, Alexander Vtyurin i Andrei Kholkin. "Raman Spectra of Diphenylalanine Microtubes: Polarisation and Temperature Effects". Crystals 10, nr 3 (20.03.2020): 224. http://dx.doi.org/10.3390/cryst10030224.

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Diphenylalanine microtubes have remarkable physical properties that allow one to use them in electronics. In this work, we measured polarised temperature-dependent Raman spectra in self-assembled diphenylalanine microtubes grown from the solution. We observed the anomalous temperature behaviour of the Raman lines. Their temperature changes were minimal, which required a significant improvement in the resolution and stability of Raman measurements. The anomalies in the behaviour of the spectra at about 178 K, 235 K, 255 K, 278 K, 296 K, 398 K and 412 K were observed. The structural phase transition at 398 K is irreversible. This transition is associated with the release of water molecules from nanochannels. The irreversible phase transition has a temperature range of about 10 K.

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Alpers, M., R. Eixmann, C. Fricke-Begemann, M. Gerding i J. Höffner. "Temperature lidar measurements from 1 to 105 km altitude using resonance, Rayleigh, and Rotational Raman scattering". Atmospheric Chemistry and Physics Discussions 4, nr 1 (6.02.2004): 923–38. http://dx.doi.org/10.5194/acpd-4-923-2004.

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Abstract. For the first time, three different temperature lidar methods are combined to obtain time-resolved complete temperature profiles with high altitude resolution over an altitude range from the planetary boundary layer up to the lower thermosphere (about 1–105 km). The Leibniz-Institute of Atmospheric Physics (IAP) at Kühlungsborn, Germany (54° N, 12° E) operates two lidar instruments, using three different temperature measurement methods, optimized for three altitude ranges: (1) Probing the spectral Doppler broadening of the potassium D1 resonance lines with a tunable narrow-band laser emitter allows the determination of atmospheric temperature profiles at the metal layer altitudes (80–105 km). (2) Between about 20 and 90 km, temperatures were calculated from Rayleigh backscattering on air molecules, where the upper start values for the calculation algorithm were taken from the potassium lidar results. Correction methods have been applied to account for, e.g. Rayleigh extinction or Mie scattering of aerosols below about 32 km. (3) At altitudes below about 25 km, backscattering on the Rotational Raman lines is strong enough to obtain temperatures by measuring the temperature dependent spectral shape of the Rotational Raman spectrum. This method works well down to about 1 km. The instrumental configuration of the IAP lidars was optimized for a 3–6 km overlap of the temperature profiles at the method transition altitudes. First night-long measurements show clear wave structures propagating from the lower stratosphere up to the lower thermosphere in most of the nights.

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Alpers, M., R. Eixmann, C. Fricke-Begemann, M. Gerding i J. Höffner. "Temperature lidar measurements from 1 to 105 km altitude using resonance, Rayleigh, and Rotational Raman scattering". Atmospheric Chemistry and Physics 4, nr 3 (24.05.2004): 793–800. http://dx.doi.org/10.5194/acp-4-793-2004.

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Abstract. For the first time, three different temperature lidar methods are combined to obtain time-resolved complete temperature profiles with high altitude resolution over an altitude range from the planetary boundary layer up to the lower thermosphere (about 1–105 km). The Leibniz-Institute of Atmospheric Physics (IAP) at Kühlungsborn, Germany (54° N, 12° E) operates two lidar instruments, using three different temperature measurement methods, optimized for three altitude ranges: (1) Probing the spectral Doppler broadening of the potassium D1 resonance lines with a tunable narrow-band laser allows atmospheric temperature profiles to be determined at metal layer altitudes (80–105 km). (2) Between about 20 and 90 km, temperatures were calculated from Rayleigh backscattering by air molecules, where the upper start values for the calculation algorithm were taken from the potassium lidar results. Correction methods have been applied to account for, e.g. Rayleigh extinction or Mie scattering of aerosols below about 32 km. (3) At altitudes below about 25 km, backscattering in the Rotational Raman lines is strong enough to obtain temperatures by measuring the temperature dependent spectral shape of the Rotational Raman spectrum. This method works well down to about 1 km. The instrumental configurations of the IAP lidars were optimized for a 3–6 km overlap of the temperature profiles at the method transition altitudes. We present two night-long measurements with clear wave structures propagating from the lower stratosphere up to the lower thermosphere.

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LEVICHEV, S., A. CHAHBOUN, A. G. ROLO, O. CONDE i M. J. M. GOMES. "THERMAL STABILITY OF ENERGY-EMISSION FROM CdTe NANOCRYSTALS EMBEDDED IN SiO2 THIN FILMS". Modern Physics Letters B 24, nr 29 (20.11.2010): 2837–43. http://dx.doi.org/10.1142/s0217984910025206.

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CdTe -doped SiO 2 thin films were produced by RF magnetron co-sputtering technique. Presence of CdTe nanocrystals inside the silica matrix was confirmed by Raman spectroscopy and grazing incidence X-ray diffraction. The samples demonstrate size dependent photoluminescence. Temperature dependent photoluminescence measurements were carried out in the temperature range 15–295 K and revealed energy-emission thermal stability. This feature can be usefully applied in a production of light-emitting diodes with wavelength stability in a wide temperature range.

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Rassat, Scot D., i E. James Davis. "Temperature Measurement of Single Levitated Microparticles Using Stokes/Anti-Stokes Raman Intensity Ratios". Applied Spectroscopy 48, nr 12 (grudzień 1994): 1498–505. http://dx.doi.org/10.1366/0003702944027921.

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A method has been developed to determine the temperature of single microparticles levitated in an electrodynamic balance. Particle temperatures were ascertained from the measured intensities of the Stokes and anti-Stokes Raman spectra. Temperatures near ambient were obtained for titanium dioxide and calcium nitrate microparticles with the use of a Raman-based calibration of the optical system to correct for wavelength-dependent effects. Higher temperatures were also measured with the use of a carbon dioxide infrared laser to electromagnetically heat the particle. In an effort to minimize particle instabilities caused by the heating beam, the Gaussian intensity profile of the beam was modified with an axicon beam expander to produce a doughnut-like intensity distribution. The temperature measurement technique and quantitative Raman composition analysis were applied to study dehydration of a calcium nitrate tetrahydrate particle.

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Gim, Dong-Hyeon, Yeahan Sur, Yoon Han Lee, Jeong Hyuk Lee, Soonjae Moon, Yoon Seok Oh i Kee Hoon Kim. "Pressure-Dependent Structure of BaZrO3 Crystals as Determined by Raman Spectroscopy". Materials 15, nr 12 (17.06.2022): 4286. http://dx.doi.org/10.3390/ma15124286.

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The structure of dielectric perovskite BaZrO3, long known to be cubic at room temperature without any structural phase transition with variation in temperature, has been recently disputed to have different ground state structures with lower symmetries involving octahedra rotation. Pressure-dependent Raman scattering measurements can identify the hierarchy of energetically-adjacent polymorphs, helping in turn to understand its ground state structure at atmospheric pressure. Here, the Raman scattering spectra of high-quality BaZrO3 single crystals grown by the optical floating zone method are investigated in a pressure range from 1 atm to 42 GPa. First, based on the analyses of the infrared and Raman spectra measured at atmospheric pressure, it was found that all the observed vibrational modes could be assigned according to the cubic Pm3¯m structure. In addition, by applying pressure, two structural phase transitions were found at 8.4 and 19.2 GPa, one from the cubic to the rhombohedral R3¯c phase and the other from the rhombohedral to the tetragonal I4/mcm phase. Based on the two pressure-induced structural phase transitions, the true ground state structure of BaZrO3 at room temperature and ambient pressure was corroborated to be cubic while the rhombohedral phase was the closest second.

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Li, Lianfu, Xin Zhang, Zhendong Luan, Zengfeng Du, Shichuan Xi, Bing Wang, Chao Lian i Jun Yan. "A New Approach to Measuring the Temperature of Fluids Reaching 300 ℃ and 2 mol/kg NaCl Based on the Raman Shift of Water". Applied Spectroscopy 72, nr 11 (16.07.2018): 1621–31. http://dx.doi.org/10.1177/0003702818776662.

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The OH stretching band of water is very sensitive to temperature and salinity for the existence of hydrogen bonds between H2O molecules. In this study, the OH stretching band was deconvoluted into two Gaussian peaks, with peak 1 at approximately 3450 cm−1 and peak 2 at approximately 3200 cm−1. The positions of peaks 1 and 2 both shifted to higher wavenumbers with increasing temperature from 50 ℃ to 300 ℃. The effects of salinity in the range of 0–2 mol/kg NaCl on the OH stretching band were also studied. Linearity for the relationship between Raman shift of peak 1 and temperature increased as the salt concentration increased from 0 to 2 mol/kg, while peak 2 displayed an opposing trend. Two temperature calibration models were developed based on the temperature-dependent changes in the Raman frequency shifts of peaks 1 and 2 (precision of 0.9 ℃ and 1.0 ℃, respectively). The calibration models for temperature were successfully applied to determining the temperatures of deep-sea hydrothermal fluids in the Okinawa Trough hydrothermal field. The degree of mixing of hydrothermal fluids and ambient seawater during in situ Raman measurements was estimated by the difference in temperatures determined through these calibration models and those measured through thermocouple sensors.

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Peschke, Irma, Lars Robben, Christof Köhler, Thomas Frauenheim, Josef-Christian Buhl i Thorsten M. Gesing. "Crystal structure and temperature-dependent properties of Na2H4Ga2GeO8 – a novel gallogermanate". Zeitschrift für Naturforschung B 75, nr 9-10 (26.11.2020): 805–13. http://dx.doi.org/10.1515/znb-2020-0159.

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AbstractSynthesis, crystal structure and temperature-dependent behavior of Na2H4Ga2GeO8 are reported. This novel gallogermanate crystallizes in space group I41/acd with room-temperature powder diffraction lattice parameters of a = 1298.05(1) pm and c = 870.66(1) pm. The structure consists of MO4 (M = Ga, Ge) tetrahedra in four-ring chains, which are connected by two different (left- and right-handed) helical chains of NaO6 octahedra. Protons coordinating the oxygen atoms of the GaO4 tetrahedra not linked to germanium atoms ensure the charge balance. Structure solution and refinement are based on single crystal X-ray diffraction measurements. Proton positions are estimated using a combined approach of DFT calculations and NMR, FTIR and Raman spectroscopic techniques. The thermal expansion was examined in the range between T = 20(2) K and the compound’s decomposition temperature at 568(5) K, in which no phase transition could be observed, and Debye temperatures of 266(11) and 1566(65) K were determined for the volume expansion.

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Shrestha, S., C. S. Chang, S. Lee, N. L. Kothalawala, D. Y. Kim, M. Minola, J. Kim i A. Seo. "Raman spectroscopic characterizations of graphene on oxide substrates for remote epitaxy". Journal of Applied Physics 133, nr 10 (14.03.2023): 105301. http://dx.doi.org/10.1063/5.0143083.

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Graphene layers placed on SrTiO3 single-crystal substrates, i.e., templates for remote epitaxy of functional oxide membranes, were investigated using temperature-dependent confocal Raman spectroscopy. This approach successfully resolved distinct Raman modes of graphene that are often untraceable in conventional measurements with non-confocal optics due to the strong Raman scattering background of SrTiO3. Information on defects and strain states was obtained for a few graphene/SrTiO3 samples that were synthesized by different techniques. This confocal Raman spectroscopic approach can shed light on the investigation of not only this graphene/SrTiO3 system but also various two-dimensional layered materials whose Raman modes interfere with their substrates.

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Liu, Yanli, Xifeng Yang, Dunjun Chen, Hai Lu, Rong Zhang i Youdou Zheng. "Determination of Temperature-Dependent Stress State in Thin AlGaN Layer of AlGaN/GaN HEMT Heterostructures by Near-Resonant Raman Scattering". Advances in Condensed Matter Physics 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/918428.

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The temperature-dependent stress state in the AlGaN barrier layer of AlGaN/GaN heterostructure grown on sapphire substrate was investigated by ultraviolet (UV) near-resonant Raman scattering. Strong scattering peak resulting from the A1(LO) phonon mode of AlGaN is observed under near-resonance condition, which allows for the accurate measurement of Raman shifts with temperature. The temperature-dependent stress in the AlGaN layer determined by the resonance Raman spectra is consistent with the theoretical calculation result, taking lattice mismatch and thermal mismatch into account together. This good agreement indicates that the UV near-resonant Raman scattering can be a direct and effective method to characterize the stress state in thin AlGaN barrier layer of AlGaN/GaN HEMT heterostructures.

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Suriani, Abu Bakar, Salina Muhamad, Puteri Sarah Mohamad Saad, Syazwan Afif Mohd Zobir, Roslan Md Nor, Yosri Mohd Siran, Syahril Anuar M. Rejab i in. "The Effect of Precursor Vaporization Temperature on the Growth of Vertically Aligned Carbon Nanotubes Using Palm Oil". Defect and Diffusion Forum 312-315 (kwiecień 2011): 906–11. http://dx.doi.org/10.4028/www.scientific.net/ddf.312-315.906.

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Carbon nanotubes (CNTs) were fabricated from palm oil using the thermal chemical vapor deposition technique utilizing a two furnace system. The effect of precursor vaporization temperature of the first furnace, in the range of 300-600°C was systematically studied with the synthesis temperature (second furnace) fixed at 750°C for a total time of 30 min. The samples were characterized using field emission scanning electron microscopy and micro-Raman spectroscopy. CNTs of various packing densities and diameters were synthesized with the varying precursor vaporization temperature. Based on micro-Raman measurements nanotube defect level and the presence of SWCNT were dependent on the vaporization temperature. Vertically aligned CNTs (VACNTs) were found to grow within the vaporization temperature range of 400-500°C, with well graphitized and higher yield obtained at 450°C with excellent lateral alignment, uniform nanotubes diameter (~15 nm), orientation and distribution within the CNT bundles. At vaporization temperatures of 300-350°C and 500-600°C, lower growth rate, bigger nanotubes diameter and higher ID/IG ratio were observed which indicated lower nanotubes quality that produced at both temperature ranges.

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Dobrynin, Danil, Zhiheng Song i Alexander Fridman. "Synthesis of Highly Energetic PolyNitrogen by Nanosecond-Pulsed Plasma in Liquid Nitrogen". Materials 14, nr 15 (31.07.2021): 4292. http://dx.doi.org/10.3390/ma14154292.

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We report on an experimental study of nanosecond-pulsed plasma treatment of liquid nitrogen demonstrating synthesis of a highly energetic nitrogen material. Raman, FTIR analysis of gas phase products of decomposition, and the material explosion characteristics suggest synthesis of polymeric (amorphous) nitrogen compound which is stable at ambient pressure up to temperatures of about −150 °C. Addition of adsorbents with relatively large characteristic pore sizes (>5 nm) allows marginally improved recovery of the material as determined by temperature-dependent Raman measurements. By analyzing the shock wave propagation resulting from the explosions, we estimated the energy density of the material to be 13.3 ± 3.5 kJ/g, close to the previously predicted value for amorphous polymeric nitrogen.

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Hubert, D., F. Leblanc i P. Gaimard. "Current state-of-the-art for the measurement of non-Maxwellian plasma parameters with the EISCAT UHF Facility". Annales Geophysicae 14, nr 12 (31.12.1996): 1506–12. http://dx.doi.org/10.1007/s00585-996-1506-4.

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Abstract. New results on the information that can be extracted from simulated non-Maxwellian incoherent radar spectra are presented. The cases of a pure ionosphere and of a composite ionosphere typical of a given altitude of the auroral F region are considered. In the case of a pure ionosphere of NO+ or O+ ions it has been shown that the electron temperature and the electron density can be derived from a Maxwellian analysis of radar spectra measured at aspect angles of 0° or 21° respectively; the ion temperature and ion temperature anisotropy can be derived from a non- constraining model such as the 1D Raman fitting of a complementary measurement made at an aspect angle larger than 0° for the NO+ ions, or at an aspect angle larger than 21° for the O+ ions. Moreover with such measurements at large aspect angles, the shape of the velocity ion distribution functions can simultaneously be inferred. The case of a composite ionosphere of atomic O+ and molecular NO+ ions is a difficult challenge which requires simultaneously a complementary measurement of the electron temperature to provide the ion composition and the electron density from the incoherent radar spectra at a specific aspect angle of 21°; hence, a model dependent routine is necessary to derive the ion temperatures and ion temperature anisotropies. In the case where the electron temperature is not given, a routine which depends on ion distribution models is required first: the better the ion distribution models are, the more accurately derived the plasma parameters will be. In both cases of a composite ionosphere, the 1D Raman fitting can be used to keep a check on the validity of the results provided by the ion distribution model dependent routine.

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Shukla, R., Keka R. Chakraborty, B. P. Mandal, S. D. Kaushik, M. D. Mukadam, G. Lawes, R. Naik i in. "Synthesis, Characterization and Exploration of Multiferroic Properties in Nano-Crystalline Tb1−x YxMnO3 (0 ≤ x ≤ 0.4)". Journal of Nanoscience and Nanotechnology 16, nr 4 (1.04.2016): 4094–99. http://dx.doi.org/10.1166/jnn.2016.11102.

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We report the synthesis and electric properties of nano-crystalline Tb1−xYxMnO3 (x = 0, 0.1, 0.2, 0.3 and 0.4) compounds prepared by gel-combustion method. These samples were characterized by a number of techniques including X-ray diffraction (XRD), Raman spectroscopy, specific-heat measurement, neutron diffraction, and magnetic field dependent pyrocurrent measurement. All the samples crystallize in the orthorhombic structure with space group Pnma at room temperature. Anomalies were observed in low temperature specific-heat measurement corresponding to magnetic and electric phase transitions. The magnetic phase transitions occurred at ∼35, ∼22–28 and ∼7 K for all the samples. Signatures of coupling between magnetic and electric order parameters were revealed by pyrocurrent measurements carried out in presence of magnetic fields.

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Seabrook, Brian C., Andreas Ellmauthaler, Michel LeBlanc, Mikko Jaaskelainen, John L. Maida i Glenn A. Wilson. "Comparison of Raman, Brillouin, and Rayleigh Distributed Temperature Measurements in High-Rate Wells". Petrophysics – The SPWLA Journal of Formation Evaluation and Reservoir Description 63, nr 6 (1.12.2022): 685–99. http://dx.doi.org/10.30632/pjv63n6-2022a8.

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With the maturity of and demand for fiber-optic sensing technology growing steadily over the last few years across multiple basins, operators are seeking fiber-optic sensing solutions that address the technology challenges associated with the life-of-field monitoring of subsea developments. Single-ended distributed temperature sensing (DTS) measurements have been acquired for decades now, typically using Raman optical time-domain reflectometry (OTDR) on multimode fiber. However, for topside interrogation of subsea completions, Raman DTS performs poorly. This is due to the available optical power budget and the potential wavelength dependency of optical attenuation across multiple connectors and splices comprising the optical subsea infrastructure. Any wavelength-dependent attenuation as the signals pass through connectors, splices, and optical feedthrough systems will generate step changes in the measured Raman DTS temperature profile. Brillouin OTDR can provide a DTS alternative that overcomes these challenges and operates on single-mode fiber. Brillouin OTDR operates with a large dynamic range to measure a wavelength (frequency) shift of the Stokes/anti-Stokes components that is proportional to both strain and temperature. Since downhole cables are manufactured with optical fibers suspended in a gel and with appropriate extra fiber length (EFL), any fiber strain relaxes, and the Brillouin wavelength shift is an absolute temperature measurement. An additional alternative is also explored here. We typically associate coherent Rayleigh OTDR with distributed acoustic sensing (DAS) on single-mode fibers, but low frequencies also contain a relative temperature dependence. The low-pass filtering of DAS data can then be used as a form of Rayleigh DTS with appropriate data processing. In this paper, we report on a comparison of Raman, Brillouin, and Rayleigh DTS simultaneously acquired in the same high-rate producer and injector wells. We validate that, with appropriate cable design, Brillouin DTS can be simultaneously operated on the same single-mode fiber with DAS and can deliver absolute temperature measurements suitable for production analysis. We also use a laboratory experiment to show that Rayleigh DTS provides an accurate measure of temperature changes comparable in precision to a traditional thermocouple. We conclude with a discussion about the implementation of this DAS-DTS solution for sensing subsea completions.

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Faqir, M., A. Manoi, T. Mrotzek, S. Knippscheer, M. Massiot, M. Buchta, H. Blanck, S. Rochette, O. Vendier i M. Kuball. "New GaN Power-Electronics Packaging Solutions: A Thermal Analysis Using Raman Thermography". Journal of Microelectronics and Electronic Packaging 8, nr 3 (1.07.2011): 110–13. http://dx.doi.org/10.4071/imaps.297.

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Raman thermography measurements were performed on AlGaN/GaN multifinger high electron mobility transistors (HEMTs) to determine their channel temperature at various power levels. The devices were mounted on both silver diamond composite and CuW baseplates, in order to benchmark the thermal performance of novel diamond composite baseplates compared with traditional materials. We illustrate that AlGaN/GaN HEMT devices mounted on silver diamond composite baseplates show peak temperatures that are 50% lower than the peak temperatures exhibited by devices mounted on traditional CuW baseplates. This is a dramatic improvement in terms of heat extraction as a basis to enable longer device lifetimes and better performance. In addition, time-resolved Raman thermography measurements were carried out to obtain the thermal dynamics of devices on the silver-diamond baseplate and on heat diffusion during pulsed device operation. This time-dependent information is of great importance for reliability and failure analyses, as pulsed operation of a HEMT is a typical device operation condition. Finite-element thermal simulations were performed for comparison with experimental results, and good agreement with the experimental data was obtained.

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Micovic, Dragana, Maja Pagnacco, Predrag Bankovic, Jelena Maletaskic, Branko Matovic, Veljko Djokic i Marija Stojmenovic. "The influence of short thermal treatment on structure, morphology and optical properties of Er and Pr doped ceria pigments: Comparative study". Processing and Application of Ceramics 13, nr 3 (2019): 310–21. http://dx.doi.org/10.2298/pac1903310m.

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Potential non-toxic pink and red ceramic pigments based on CeO2 were successfully synthesized by selfpropagating room temperaturemethod and thermally treated at 600, 900 and 1200?C for 15min. The structure, morphology and optical properties, as well as thermal stability of Ce1-xErxO2-? and Ce1-xPrxO2-?(x = 0.05) were examined. Single-phase composition of all obtained CeO2 pigments was confirmed using XRPD method and Raman spectroscopy and it was not dependent on temperature. The mechanism of structural behaviour was thoroughly examined using Raman and FTIR spectroscopy. Nanometric dimensions of the crystallites of all pigments were confirmed using XRPD, TEM and FE-SEM analysis. Colour properties were dependent on the temperature treatment, and their position in the chromaticity diagram was studied using UV/VIS spectrophotometry. Colour efficiency measurements were supplemented by colorimetric analysis. It is proved that all samples are thermally stable in the investigated temperature range (up to 1200?C), and their potential application as environmentally friendly pigments of desired colour is confirmed.

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Zhang, Shuping, Hong Yang, Lianshan Wang, Hongjuan Cheng, Haixia Lu, Yanlian Yang, Lingyu Wan i in. "Structural, Surface and Optical Studies of m- and c-Face AlN Crystals Grown by Physical Vapor Transport Method". Materials 16, nr 5 (25.02.2023): 1925. http://dx.doi.org/10.3390/ma16051925.

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Bulk aluminum nitride (AlN) crystals with different polarities were grown by physical vapor transport (PVT). The structural, surface, and optical properties of m-plane and c-plane AlN crystals were comparatively studied by using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Temperature-dependent Raman measurements showed that the Raman shift and the full width at half maximum (FWHM) of the E2 (high) phonon mode of the m-plane AlN crystal were larger than those of the c-plane AlN crystal, which would be correlated with the residual stress and defects in the AlN samples, respectively. Moreover, the phonon lifetime of the Raman-active modes largely decayed and its line width gradually broadened with the increase in temperature. The phonon lifetime of the Raman TO-phonon mode was changed less than that of the LO-phonon mode with temperature in the two crystals. It should be noted that the influence of inhomogeneous impurity phonon scattering on the phonon lifetime and the contribution to the Raman shift came from thermal expansion at a higher temperature. In addition, the trend of stress with increasing 1000/temperature was similar for the two AlN samples. As the temperature increased from 80 K to ~870 K, there was a temperature at which the biaxial stress of the samples transformed from compressive to tensile stress, while their certain temperature was different.

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Faqir, M., A. Manoi, T. Mrotzek, S. Knippscheer, M. Massiot, M. Buchta, H. Blanck, S. Rochette, O. Vendier i M. Kuball. "New GaN Power-Electronics Packaging Solutions: A Thermal Analysis using Raman Thermography". International Symposium on Microelectronics 2010, nr 1 (1.01.2010): 000446–49. http://dx.doi.org/10.4071/isom-2010-wa3-paper3.

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Raman thermography measurements were performed on AlGaN/GaN multi-finger high electron mobility transistors (HEMTs) to determine their channel temperature at various power levels. The devices were mounted on both silver diamond composite and CuW base plates, in order to benchmark the thermal performance of novel diamond composite base plates compared to traditional materials. We illustrate that AlGaN/GaN HEMT devices mounted on silver diamond composite base plates show peak temperatures which are 50% lower than the peak temperatures exhibited by devices mounted on traditional CuW base plates. This is a dramatic improvement in terms of heat extraction, as basis to enabling longer device life-times and better performances. In addition, time-resolved Raman thermography measurements were carrier out to obtain thermal dynamics of devices on the silver-diamond base plate and on heat diffusion during pulsed device operation. This time-dependent information is of great importance for reliability and failure analyses, as pulsed operation of a HEMT is a typically device operation condition. Finite-element thermal simulations were performed for comparison with the experimental results, and good agreement with the experimental data was obtained.

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32

Solonenko, Dmytro, Agnė Žukauskaitė, Julian Pilz, Mohssen Moridi i Sarah Risquez. "Raman Spectroscopy and Spectral Signatures of AlScN/Al2O3". Micromachines 13, nr 11 (11.11.2022): 1961. http://dx.doi.org/10.3390/mi13111961.

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III-V solid solutions are sensitive to growth conditions due to their stochastic nature. The highly crystalline thin films require a profound understanding of the material properties and reliable means of their determination. In this work, we have investigated the Raman spectral fingerprint of Al1−xScxN thin films with Sc concentrations x = 0, 0.14, 0.17, 0.23, 0.32, and 0.41, grown on Al2O3(0001) substrates. The spectra show softening and broadening of the modes related to the dominant wurtzite phase with increasing Sc content, in agreement with the corresponding XRD results. We investigated the primary scattering mechanism responsible for the immense modes’ linewidths by comparing the average grain sizes to the phonon correlation length, indicating that alloying augments the point defect density. The low-frequency Raman bands were attributed to the confined spherical acoustic modes in the co-forming ScN nanoparticles. Temperature-dependent Raman measurements enabled the temperature coefficient of the E2(high) mode to be determined for all Sc concentrations for the precise temperature monitoring in AlScN-based devices.

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33

Pei, Woye, Zhiren Xiong, Yingjia Liu, Xingguang Wu, Zheng Vitto Han, Siwen Zhao i Tongyao Zhang. "An Optical Spectroscopic Study of Air-Degradation of van der Waals Magnetic Semiconductor Cr2Ge2Te6". Magnetochemistry 9, nr 4 (10.04.2023): 104. http://dx.doi.org/10.3390/magnetochemistry9040104.

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Two-dimensional (2D) magnetic semiconductors exhibit unique combination of electronic and magnetic properties, holding great promise in potential applications such as spintronics and magneto-optics. However, many of them are air-sensitive, and their properties can be significantly altered upon exposure to air. Here, we showed an optical spectroscopic investigation of the effects of air-degradation on few-layered van der Waals (vdW) magnetic semiconductor Cr2Ge2Te6. It was found that although the partially degraded few-layered Cr2Ge2Te6 showed a significant Raman redshift and a split of Eg peak at room temperature, the magneto-optic Kerr hysteresis loop can remain largely unchanged below the Curie temperature. Temperature-dependent Raman measurements further revealed characteristic blueshifts of phonon energy, which were associated with the ferromagnetic phase transition in partially degraded Cr2Ge2Te6, in agreement with Kerr measurements. Our results provide an optical spectroscopic insight into the air-instability of 2D magnetic semiconductors, and contribute to a better understanding of the relationship between phonon modes and long-range spin order at the presence of defects in ultra-thin vdW magnetic semiconductors.

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He, Lei, Zhen Yin, Ming-Sheng Zhang, Ze-Xiang Shen i Hui-Fen Chen. "Vibrational Spectroscopic Analysis of Ferroelectric Liquid Crystal MBOPDOB". Applied Spectroscopy 52, nr 6 (czerwiec 1998): 847–50. http://dx.doi.org/10.1366/0003702981944373.

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Raman spectra of ferroelectric liquid crystal (FLC) D-4-(2-methylbutoxy) phenyl 4-decyloxybenzoate (MBOPDOB) are recorded. All the vibrational modes are assigned, and their vibrational characteristics are studied. It is found that the s-cis and the s-trans conformers of the ester group coexist in the crystal phase at room temperature. By temperature-dependent measurements, the line shape changes due to the transition of the ester group conformation near the crystal-Sm C phase transition point are examined.

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35

Cheng, J. G., J. S. Zhou i Y. Uwatoko. "Temperature-Pressure Phase Diagram and Possible Pressure-Driven New Electronic Phase in the Polar Metal LiOsO₃". ECS Journal of Solid State Science and Technology 11, nr 2 (1.02.2022): 023008. http://dx.doi.org/10.1149/2162-8777/ac5472.

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LiOsO3 is a strongly correlated metal that undergoes a nonpolar to polar transition at the critical temperature (T s) of 140 K. Complementary to previous studies of structure, Raman, and resistivity under high pressure (P), here we map out a complete pressure evolution of T s(P) via high-pressure resistance measurements up to 18.5 GPa by using a low-temperature multianvil apparatus. Our results show that T s(P) first increases linearly with pressure at a large slope as reported and then levels off gradually at pressures above 10 GPa when approaching room temperature (295 K). Interestingly, we find that the resistance R(T) of LiOsO3 at 18.5 GPa in the polar R3c phase exhibits a distinct temperature profile in comparison with those at lower pressures, signaling the possible occurrence of pressure-driven new electronic phase. The critical pressure for this transition is determined to be P c ≈ 16.8(1) GPa based on the pressure-dependent resistance measurement at room temperature.

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36

Sundaray, Bibekananda, V. Jagadeesh Babu, V. Subramanian i T. S. Natarajan. "Preparation and Characterization of Electrospun Fibers of Poly(methyl methacrylate) - Single Walled Carbon Nanotube Nanocomposites". Journal of Engineered Fibers and Fabrics 3, nr 4 (grudzień 2008): 155892500800300. http://dx.doi.org/10.1177/155892500800300405.

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Electrospinning is a versatile method of preparing polymer nanocmposite fibers. Electrospun nanocomposite fibers of poly(methyl methacrylate) and single walled carbon nanotubes were prepared. The fibers were characterized by SEM, TEM, TGA and Raman spectroscopy. These fibers show dramatic improvement in the electrical conductivity compared to the polymer. The temperature dependent electrical resistance measurements show a one dimensional variable range hopping model (1–D VRH) type of conduction mechanism operating in these types of systems.

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Bu, Ian Yi Yu. "Aluminium Induced Crystallization of Amorphous Silicon via Solution Derived Catalyst". Applied Mechanics and Materials 481 (grudzień 2013): 3–6. http://dx.doi.org/10.4028/www.scientific.net/amm.481.3.

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In this paper, aluminum induced crystallization (AIC) was studied by examining the effect of using solution derived AlCl3 catalyst. Such catalyst preparation method offers possibility of low-cost, non-vacuum solution process and allows examination of the role of alumina on the AIC process. The deposited AIC films were examined by using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Raman spectroscopy, X-ray diffraction (XRD) and four probe measurements. It was found that AIC process is highly dependent on annealing temperature and can occur at annealing temperatures above 500°C through Al2O3 formation. Based on the presented data, a possible growth model is proposed to clarify AIC mechanism.

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Simon, Nataline, Olivier Bour, Nicolas Lavenant, Gilles Porel, Benoît Nauleau, Behzad Pouladi i Laurent Longuevergne. "A Comparison of Different Methods to Estimate the Effective Spatial Resolution of FO-DTS Measurements Achieved during Sandbox Experiments". Sensors 20, nr 2 (20.01.2020): 570. http://dx.doi.org/10.3390/s20020570.

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For many environmental applications, the interpretation of fiber-optic Raman distributed temperature sensing (FO-DTS) measurements is strongly dependent on the spatial resolution of measurements, especially when the objective is to detect temperature variations over small scales. Here, we propose to compare three different and complementary methods to estimate, in practice, the “effective” spatial resolution of DTS measurements: The classical “90% step change” method, the correlation length estimated from experimental semivariograms, and the derivative method. The three methods were applied using FO-DTS measurements achieved during sandbox experiments using two DTS units having different spatial resolutions. Results show that the value of the spatial resolution estimated using a step change depends on both the effective spatial resolution of the DTS unit and on heat conduction induced by the high thermal conductivity of the cable. The correlation length method provides an estimate much closer to the value provided by the manufacturers, representative of the effective spatial resolutions along cable sections where temperature gradients are small or negligible. Thirdly, the application of the derivative method allows for verifying the representativeness of DTS measurements all along the cable, by localizing sections where measurements are representative of the effective temperature. We finally show that DTS measurements could be validated in sandbox experiments, when using devices with finer spatial resolution.

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Das, Sayantani, Md Sariful Sheikh, Rajesh Mukherjee, Alo Dutta i T. P. Sinha. "Size-Dependent Structural, Optical and Vibrational Properties of ZnTe Nanoparticle". International Journal of Nanoscience 19, nr 05 (12.03.2020): 1950038. http://dx.doi.org/10.1142/s0219581x19500388.

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ZnTe semiconductor nanoparticles have been prepared by soft chemical route using mercaptoethanol as capping agent to arrest the agglomeration. The structural investigations performed by X-ray diffraction technique show that the prepared samples have cubic structure. Average crystallite sizes of the prepared nanomaterial are estimated by Debye–Scherrer’s equation. The particle size of the synthesized material is estimated by transmission electron microscope (TEM). UV-visible absorption spectra gives the idea of the band gap of the sample using Tauc plot. The Raman spectroscopy measurements are performed to know the different vibrational modes of ZnTe. The impedance spectroscopy is applied to investigate the room temperature dielectric relaxation of the prepared samples in the frequency range from 100[Formula: see text]Hz to 1.1[Formula: see text]MHz.

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Ahabboud, M., T. Lamcharfi, F. Abdi, N. Hadi, F. Z. Ajyaje i M. Haddad. "Effect of Cu Doping on Structural and Dielectric Properties of Pb1-xCux(Zr0.52Ti0.48)O3(PCxZT) (0 ≤ x ≤ 0.2) Ceramics Prepared by Sol-Gel Method". Asian Journal of Chemistry 33, nr 3 (2021): 665–70. http://dx.doi.org/10.14233/ajchem.2021.23052.

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In present work, the structural and dielectric properties of Pb1-xCuxZr0.52Ti0.48O3 (PCxZT) ceramics where x = 0. 0.025, 0.05, 0.075, 0.10, 0.15 and 0.20 were studied. Powder of the compositions (PCxZT) was obtained by sol-gel route, the powders were calcined at 700 ºC for 4 h and sintered at 1100 ºC for 4 h. X-ray diffraction analysis and Raman spectroscopy suggest the formation of mixed-phase of tetragonal and rhombohedral structure which was confirmed by Rietveld refinement. Dielectric measurements of the compounds were studied as a function of temperature (from room temperature to 420 ºC at different frequencies) and as a function of frequency (from 100 Hz to 2 MHz at different temperatures). The temperature variation of the real permittivity gives evidence of the ferroelectric phase transition as well as of the resonance behaviour also observed in the dielectric permittivity frequency-dependent variation.

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41

Varma, Meera, Markus Krottenmüller, H. K. Poswal i C. A. Kuntscher. "Pressure-Induced Structural Phase Transitions in the Chromium Spinel LiInCr4O8 with Breathing Pyrochlore Lattice". Crystals 13, nr 2 (18.01.2023): 170. http://dx.doi.org/10.3390/cryst13020170.

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This study reports high-pressure structural and spectroscopic studies on polycrystalline cubic chromium spinel compound LiInCr4O8. According to pressure-dependent X-ray diffraction measurements, three structural phase transitions occur at ∼14 GPa, ∼19 GPa, and ∼36 GPa. The first high-pressure phase is indexed to the low-temperature tetragonal phase of the system which coexists with the ambient phase before transforming to the second high-pressure phase at ∼19 GPa. The pressure-dependent Raman and infrared spectroscopic measurements show a blue-shift of the phonon modes and the crystal field excitations and an increase in the bandgap under compression. During pressure release, the sample reverts to its ambient cubic phase, even after undergoing multiple structural transitions at high pressures. The experimental findings are compared to the results of first principles based structural and phonon calculations.

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42

Ivanda, Mile, M. Buljan, U. V. Desnica, K. Furić, D. Ristić, G. C. Righini i Maurizio Ferrari. "Low Frequency Coherent Raman Scattering of Spherical Acoustical Vibrations of Three-Dimensional Self-Organized Germanium Nanocrystals". Advances in Science and Technology 55 (wrzesień 2008): 127–31. http://dx.doi.org/10.4028/www.scientific.net/ast.55.127.

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The Ge+SiO2 and SiO2 alternating multilayers are prepared by the magnetron sputtering of germanium and silica targets. By controlling the substrate temperature and by subsequent thermal annealing, the self-organized germanium quantum dots in 3D rombohedral (R 3 m) superlattice are produced. The polarized low-frequency Raman scattering measurements shows the coherent effects on the symmetric and quadrupolar spheroidal vibrations of Ge nanocrystals. It has been shown that the coherence effects are dependent on degree of Ge-ordering in the superlattice.

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43

Díaz-Reyes, J., Miguel Galvan-Arellano i R. Peña-Sierra. "Concentration-Dependent Photoluminescence and Raman of p-Type GaAs Grown in a Metallic-Arsenic-Based-MOCVD System". Materials Science Forum 587-588 (czerwiec 2008): 283–87. http://dx.doi.org/10.4028/www.scientific.net/msf.587-588.283.

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This work presents the optical and structural characterization of p-type GaAs epilayers. The gallium precursor was the organometallic compound trimethylgallium (TMG). The influence of the doping in the optical and structural properties of the GaAs layers has been studied by photoluminescence (PL) and Raman dispersion measurements. The range of analyzed hole concentration was from 1017 to 1019 cm-3 as measured by the Hall-van der Pauw method. For carrying out doping p-type, it was necessary to modify the hydrogen activity in the growth atmosphere with the control of a H2+N2 mixture, which was used like transporting gas. The photoluminescence response and Raman dispersion of the layers are strongly dependence of the growth temperature, which were investigated based on the hole concentration. The PL response of the layers shows two radiative transitions, band-to-band and band-to-C-acceptor at low hole concentration and disappears at high concentrations. Raman scattering spectra show LO mode at 270 cm-1 for low doped samples and a LO-like mode at 290 cm-1 produced by the phonon-holeplasmon coupling for high doped samples.

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Hong, Meiling, Lidong Dai, Heping Li, Haiying Hu, Kaixiang Liu, Linfei Yang i Chang Pu. "Structural Phase Transition and Metallization of Nanocrystalline Rutile Investigated by High-Pressure Raman Spectroscopy and Electrical Conductivity". Minerals 9, nr 7 (18.07.2019): 441. http://dx.doi.org/10.3390/min9070441.

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We investigate the structural, vibrational, and electrical transport properties of nanocrystalline rutile and its high-pressure polymorphs by Raman spectroscopy, and AC complex impedance spectroscopy in conjunction with the high-resolution transmission electron microscopy (HRTEM) up to ~25.0 GPa using the diamond anvil cell (DAC). Experimental results indicate that the structural phase transition and metallization for nanocrystalline rutile occurred with increasing pressure up to ~12.3 and ~14.5 GPa, respectively. The structural phase transition of sample at ~12.3 GPa is confirmed as a baddeleyite phase, which is verified by six new Raman characteristic peaks. The metallization of the baddeleyite phase is manifested by the temperature-dependent electrical conductivity measurements at ~14.5 GPa. However, upon decompression, the structural phase transition from the metallic baddeleyite to columbite phases at ~7.2 GPa is characterized by the inflexion point of the pressure coefficient and the pressure-dependent electrical conductivity. The recovered columbite phase is always retained to the atmospheric condition, which belongs to an irreversible phase transformation.

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Shende, Chetan, Stuart Farquharson, Duncan Farquharson i Carl Brouillette. "Measurements of Bicarbonate in Water Containing Ocean-Level Sulfate Using a Simple Multi-Pass Optical Raman System". Oceans 2, nr 2 (6.04.2021): 330–36. http://dx.doi.org/10.3390/oceans2020019.

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The concentration of dissolved inorganic carbon in the oceans at depths of a few meters to thousands of meters is a critical parameter for understanding global warming. The concentration is both pH dependent and depth dependent. Current analysis that employs pH meters must account for several other parameters, such as salinity, temperature, pressure, and the dissolved carbon’s form, carbon dioxide, bicarbonate, or carbonate. Recently, Raman spectroscopy has been used to measure these forms directly in water at ~1000 ppm, which is unfortunately insufficient for typical ocean concentrations, such as ~115 ppm bicarbonate near the surface. Here, we employed a simple multi-pass optical system, a flat mirror to reflect the laser back through the sample, and a concave mirror opposite the entrance slit that effectively doubled the laser power and the collected Raman photons, respectively. This multi-pass optical Raman system with a 1.5 W, 532 nm laser was used to measure 30 ppm bicarbonate in water that contained 2650 ppm sulfate to simulate ocean water, a bicarbonate concentration well below that near the ocean surface. Furthermore, spectral analysis employed the bicarbonate C=O symmetric stretch at 1360 cm−1 instead of the C–OH stretch at 1015 cm−1 to avoid the intense, overlapping sulfate SO4 symmetric stretch at 985 cm−1. The calculated standard deviation of ~5 ppm for the described approach suggests that accurate measurement of bicarbonate in situ is possible, which has been, heretofore, either calculated based on pH or measured in a lab.

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Chauhan, Himanshu, Rohit Kumar i G. D. Varma. "Study of anisotropy in the superconducting properties of FeTe_0.55Se_0.45 single crystal grown by the self-flux method". Superconductor Science and Technology 35, nr 4 (14.02.2022): 045003. http://dx.doi.org/10.1088/1361-6668/ac504d.

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Abstract We report anisotropy in the superconducting properties of FeTe0.55Se0.45 bulk single crystal synthesized via the self-flux method. We have performed magnetotransport, magnetic and heat capacity measurements on single crystals of same batch. The grown crystals have also been characterized by XRD, XPS and Raman measurements. The superconductivity at T C ∼ 14 K has been affirmed by the temperature-dependent resistivity, magnetic, and specific heat measurements. The anisotropy in the upper critical field (H C2), coherence length (ξ), and critical current density (J C) have been studied from the magnetotransport and magnetic measurements, respectively, under applied magnetic fields of 0–12 T along the ab-plane and c-axis. The critical current density has been estimated by Bean’s critical state model at different magnetic fields (J C(H)) and temperatures (J C(T)) measured for H‖ab-plane and H‖c axis. The anisotropic behaviour has also been observed for J C(H). The presence of ‘peak effect’ or fishtail characteristic has been noticed in M–H loops for H‖c only, which shows a shift towards the lower fields with increasing temperature. The nature of the pinning mechanisms in the sample has been determined by the normalized pinning force density using the Dew Hughes scaling rule, and the analysis of experimental data indicates the presence of δl-pinning in the sample. The temperature-dependent electronic specific heat has been fitted with the exponential law and the evaluated coupling constant 2Δ0/kBTc is ∼3.42 which is close to the universal BCS value of 3.53. The observed low value of residual Sommerfeld coefficient γ r e s ≈ 4.59 mJ mol−1 K2 indicates good quality of the grown single crystal.

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Lin, Der-Yuh, Hung-Pin Hsu, Chi-Feng Tsai, Cheng-Wen Wang i Yu-Tai Shih. "Temperature Dependent Excitonic Transition Energy and Enhanced Electron-Phonon Coupling in Layered Ternary SnS2-xSex Semiconductors with Fully Tunable Stoichiometry". Molecules 26, nr 8 (10.04.2021): 2184. http://dx.doi.org/10.3390/molecules26082184.

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In this study, a series of SnS2-xSex (0 ≤ x ≤ 2) layered semiconductors were grown by the chemical–vapor transport method. The crystal structural and material phase of SnS2-xSex layered van der Waals crystals was characterized by X-ray diffraction measurements and Raman spectroscopy. The temperature dependence of the spectral features in the vicinity of the direct band edge excitonic transitions of the layered SnS2-xSex compounds was measured in the temperature range of 20–300 K using the piezoreflectance (PzR) technique. The near band-edge excitonic transition energies of SnS2-xSex were determined from a detailed line-shape fit of the PzR spectra. The PzR characterization has shown that the excitonic transitions were continuously tunable with the ratio of S and Se. The parameters that describe the temperature variation of the energies of the excitonic transitions are evaluated and discussed.

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Petersen, Hilke, Lars Robben i Thorsten M. Gesing. "On the nature of the phase transitions of aluminosilicate perrhenate sodalite". Zeitschrift für Kristallographie - Crystalline Materials 235, nr 6-7 (28.07.2020): 213–23. http://dx.doi.org/10.1515/zkri-2020-0027.

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AbstractThe temperature-dependent structure-property relationships of the aluminosilicate perrhenate sodalite |Na8(ReO4)2|[AlSiO4]6 (ReO4-SOD) were analysed via powder X-ray diffraction (PXRD), Raman spectroscopy and heat capacity measurements. ReO4-SOD shows two phase transitions in the investigated temperature range (13 K < T < 1480 K). The first one at 218.6(1) K is correlated to the transition of dynamically ordered $P\overline{4}3n$ (> 218.6(1 K) to a statically disordered (<218.6(1) K) SOD template in $P\overline{4}3n$. The loss of the dynamics of the template anion during cooling causes an increase of disorder, indicated by an unusual intensity decrease of the 011-reflection and an increase of the Re-O2 bond length with decreasing temperature. Additionally, Raman spectroscopy shows a distortion of the ReO4 anion. Upon heating the thermal expansion of the sodalite cage originated in the tilt-mechanism causes the second phase transition at 442(1) K resulting in a symmetry-increase from $P\overline{4}3n$ to $Pm\overline{3}n$, the structure with the sodalites full framework expansion. Noteworthy is the high decomposition temperature of 1320(10) K.

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Sugie, Ryuichi, Kenichi Kosaka, Hirofumi Seki, Hideki Hashimoto i Masanobu Yoshikawa. "Measurement of temperature-dependent stress in copper-filled silicon vias using polarized Raman spectroscopy". Journal of Applied Physics 114, nr 23 (21.12.2013): 233503. http://dx.doi.org/10.1063/1.4848115.

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Kim, Seul-Ki, Eun Young Jung i Myung-Hyun Lee. "Defect-Induced Luminescence Quenching of 4H-SiC Single Crystal Grown by PVT Method through a Control of Incorporated Impurity Concentration". Compounds 2, nr 1 (2.03.2022): 68–79. http://dx.doi.org/10.3390/compounds2010006.

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The structural defect effect of impurities on silicon carbide (SiC) was studied to determine the luminescence properties with temperature-dependent photoluminescence (PL) measurements. Single 4H-SiC crystals were fabricated using three different 3C-SiC starting materials and the physical vapor transport method at a high temperature and 100 Pa in an argon atmosphere. The correlation between the impurity levels and the optical and fluorescent properties was confirmed using Raman spectroscopy, X-ray diffraction, inductively coupled plasma atomic emission spectroscopy (ICP-OES), UV-Vis-NIR spectrophotometry, and PL measurements. The PL intensity was observed in all three single 4H-SiC crystals, with the highest intensities at low temperatures. Two prominent PL emission peaks at 420 and 580 nm were observed at temperatures below 50 K. These emission peaks originated from the impurity concentration due to the incorporation of N, Al, and B in the single 4H-SiC crystals and were supported by ICP-OES. The emission peaks at 420 and 580 nm occurred due to donor–acceptor-pair recombination through the incorporated concentrations of nitrogen, boron, and aluminum in the single 4H-SiC crystals. The results of the present work provide evidence based on the low-temperature PL that the mechanism of PL emission in single 4H-SiC crystals is mainly related to the transitions due to defect concentration.

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