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Few-layered gallium selenide (GaSe) is obtained by using the mechanical exfoliation method, and its properties are characterized by photoluminescence and Raman spectroscopy. The pressure-dependent phonon scatterings of bulk, few-layered, oxidized few-layered GaSe are characterized up to 30 GPa by using a diamond anvil cell with inert argon used as the pressure transmission medium. All the GaSe samples processed a phase transition around 28 GPa. A new vibration mode at 250 cm−1 is found in oxidized few-layered GaSe by Raman spectra, which is indexed as the Raman vibration mode of α-Se. [ABSTRACT FROM AUTHOR]

As is well known, the basic intrinsic properties of materials can be significant for their practical applications. In this work, the room-temperature absorption, transmittance, reflectance spectra, and relative photoelectricities parameters of the Mg4Ta2O9 crystals are demonstrated. Meanwhile, the polarized Raman spectra of Mg4Ta2O9 crystals are also described. The room-temperature photoluminescence (PL) and the temperature-dependent PL for Mg4Ta2O9 crystals are obtained. Significantly, we observe a phonon-participated PL process in Mg4Ta2O9. [ABSTRACT FROM AUTHOR]

Abstract: Recently, the superconductivity in phosphine (PH3) has been discovered with the superconducting transition temperature Tc up to 203 GPa by using high pressure resistance measurements. However, the structural information of PH3 under high pressure remains elusive. Motivated by this, in this work, the behavior of PH3 under high pressure has been investigated by Raman spectroscopy at 298 K. The Raman spectra varied with pressure increasing, accompanying with the change of the sample color, which first became yellow, then red, and finally opaque. In the pressure range of 8.53–18.36 GPa, the decomposition of PH3 was observed, and the main decomposition products were P2H4 and element hydrogen (H2). Upon compression to higher pressure, the Raman signal of hydrogen vibration was observed to become stronger, indicating that PH3 or P2H4 further decomposed into element phosphorus and hydrogen. The original PH3 did not form again upon decomposition to ambient pressure. P2H4 and other decomposition products of compressed phosphine were considered as main products of the high temperature superconducting phase reported in experiment. [ABSTRACT FROM AUTHOR]

Single wall carbon nanotubes with a diameter distribution from 1.30 to 1.55 nm filled with perylene molecules were synthesized via a vapor-phase encapsulation method. The perylene molecules formed short-chain nanoribbon analogs inside the tubes by polymerization. The polymerization of perylene molecules is found to be dependent on the annealing temperature and thus the length of the formed nanoribbons. High-pressure transformation of the formed hybrid nanostructure has been studied by means of Raman spectroscopy combined with theoretical simulation. It is found that the encapsulated nanoribbon analogs can act as a probe for identifying the structural transitions of the host nanotubes. In comparison to empty carbon nanotube, filling with nanoribbon analogs into the nanotubes decreases the collapse pressure of the nanotubes, which can be explained in terms of their inhomogeneous interactions between the fillers and carbon nanotubes. Our theoretical calculation gives further insight into the experimental observations. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Layered transition-metal dichalcogenides (TMDs) have recently attracted intense scientific and engineering interest because of their unique semiconducting and opto-electronic properties. We investigated the pressure-induced structural phase transition of layered semiconductor molybdenum disulfide (MoS2) using Raman spectroscopy and studied its metallization using infrared (IR) spectroscopy under both non-hydrostatic and quasi-hydrostatic conditions. Under quasi-hydrostatic and non-hydrostatic conditions, we found that the structural phase transition from 2 Hc stacking to 2 Ha stacking starts at approximately 16 and 21 GPa, respectively, and finishes at ∼35 and ∼41 GPa, respectively. Furthermore, the structural phase transition was followed by a semiconductor-to-metal (S-M) electronic transition. The pressure point of metallization under quasi-hydrostatic conditions is ∼5 GPa lower than that under non-hydrostatic conditions. [ABSTRACT FROM AUTHOR]

Abstract: Pressure engineering is considered as a novel strategy to modulate the properties of transition metal dichalcogenide materials. Here, through photoluminescence (PL) and Raman measurements, we investigate the electronic band structure variation and lattice vibrational dynamics of monolayer tungsten diselenide (WSe2) under pressure. As the pressure increases, the energy of the direct Κ→Κ interband transition increases, whereas that of the indirect Λ→Κ interband transition decreases, leading to a significant transition from direct to indirect band gap at 3.8 GPa. With the increase of pressure, the intensity of the direct Κ→Κ interband transition constantly decreases and finally vanishes around 12.2 GPa. Moreover, a remarkable transition between A′ and LA(M) modes under pressure has been determined by virtue of Raman spectra variations, which indicate a pressure‐induced lattice disorder. This work provides a deep understanding of the intrinsic variation of WSe2 under pressure, which effectively facilitates the development of device applications. [ABSTRACT FROM AUTHOR]

Raman spectroscopy of the one-dimensional atomic or molecular chains, which are the attractive building blocks of advanced nanoscale materials, is crucial in understanding the physical properties of the one-dimensional atomic or molecular chains. Here, we introduce the bromine into the one-dimensional channels of AlPO4-5 single crystals through a physical vapor diffusion method. Raman spectroscopy indicates that the confined bromine structures mainly exist as (Br2)n chains, individual Br2 molecules, and a small amount of Br3− chains inside the channels of AlPO4-5 single crystals. Polarized Raman spectra demonstrate that the bromine molecular chains are approximately parallel to the channel direction of AlPO4-5 single crystals. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The first high pressure study of solid hydrazinium monochloride has been performed by in situ Raman spectroscopy and synchrotron X-ray diffraction (XRD) experiments in diamond anvil cell (DAC) up to 39.5 and 24.6 GPa, respectively. The structure of phase I at room temperature is confirmed to be space group C2/ c by the Raman spectral analysis and Rietveld refinement of the XRD pattern. A structural transition from phase I to II is observed at 7.3 GPa. Pressure-induced position variation of hydrogen atoms in NH3+ unit during the phase transition is attributed to the formation of N-H...Cl hydrogen-bonds, which play a vital role in the stability and subsequent structural changes of this high energetic material under pressure. This inference is proved from the abnormal pressure shifts and obvious Fermi resonance in NH stretching mode of N2H5+ ion in the Raman experiment. Finally, a further transition from phase II to III accompanied with a slight internal distortion in the N2H5+ ions occurs above 19.8 GPa, and phase III persists up to 39.5 GPa. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Raman spectra of single-walled carbon nanotubes (SWNTs) with diameter distribution of 0.6-1.6 nm have been studied under high pressure. We focused on the dependence of radial R-band frequency (associated with the radial breathing mode, RBM) on pressure, d ωRBM/d P, and studied the effect of experimental factors on the structural changes of nanotubes under pressure. We found that the nanotube diameter and the pressure transmission medium (PTM) strongly affect the d ωRBM/d P dependence of a nanotube in the experiments with PTMs, while the nanotube diameter and the intertube interactions between the tube walls play a dominant role on the upshift of RBMs for nanotubes without a PTM. These results are in line with the theoretical predictions that PTMs have a strong effect on the pressure-induced shift in the R-bands of SWNTs. In addition, we found that the collapse of nanotubes and their reversibility depend not only on diameter and pressure environment but also on the sample quality. This could explain that there have been different results reported by different groups even for nanotubes with the same diameter distribution. [ABSTRACT FROM AUTHOR]

High-pressure Raman measurements on single-wall carbon nanotubes (SWNTs) have been carried out in a diamond anvil cell by using two wavelength lasers: 830 and 514.5 nm. Irrespective of using a pressure transmitting medium (PTM) or not, we found that nanotubes undergo similar transformations under pressure. The pressure-induced changes in Raman signals at around 2 and 5 GPa are attributed to the nanotube cross-section transitions from circle to ellipse and then to a flattened shape, respectively. Especially with pressure increasing up to 15-17 GPa, we observed that the third transition takes place in both the Raman wavenumber and the linewidth of G-band. We propose explanations that the interlinked configuration with sp3 bonds forms in the bundles of SWNTs under pressure, which was the cause for the occurrence of those Raman anomalies, similar to the structural-phase transition of graphite above 14 GPa. Our TEM observations and Raman measurements on the decompressed samples support this transition picture. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We studied the coating of C60 nanorods with nickel by electroless plating method and investigated their magnetic properties. The morphology and structure of the nickel layer coated on C60 nanorods were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Raman spectroscopy. The coated nickel is in the form of nano-sized crystals and becomes a continuous layer as reaction time increases. The hysteresis loop shows a super paramagnetic characteristic similar to that of nanometer-sized nickel particle. These results suggest that the average size of nickel particles on C60 rods is below 10 nm. Our study has shown that electroless plating is an efficient and simple method for coating C60 nanorods with nickel. [ABSTRACT FROM AUTHOR]

C60 nanosheets with thicknesses in the nanometer range were synthesized by a simple method. Compared to bulk C60, the lattice of the nanosheets is expanded by about 0.4%. In situ Raman spectroscopy and energy-dispersive x-ray diffraction under high pressures have been employed to study the structure of the nanosheets. The studies indicate that the bulk modulus of the C60 nanosheets is significantly larger than that of bulk C60. The C60 cages in nanosheets can persist at pressures over 30 GPa, 3 GPa higher than for bulk C60. These results suggest that C60 crystals in even small size will be a potential candidate of superhard materials. [ABSTRACT FROM AUTHOR]

A systematic computational study on the crystal structure of n-diamond has been performed using first-principle methods. A novel carbon allotrope with hexagonal symmetry R32 space group has been predicted. We name it as HR-carbon. HR-carbon composed of lonsdaleite layers and unique C3 isosceles triangle rings, is stable over graphite phase above 14.2 GPa. The simulated x-ray diffraction pattern, Raman, and energy-loss near-edge spectrum can match the experimental results very well, indicating that HR-carbon is a likely candidate structure for n-diamond. HR-carbon has an incompressible atomic arrangement because of unique C3 isosceles triangle rings. The hardness and bulk modulus of HR-carbon are calculated to be 80 GPa and 427 GPa, respectively, which are comparable to those of diamond. C3 isosceles triangle rings are very important for the stability and hardness of HR-carbon. [ABSTRACT FROM AUTHOR]

We present an experimental study of a new hybrid material where nitrogen is encapsulated in the channels of porous zeolite AlPO4-5 (AFI) single crystals by a high-pressure method. The high-pressure behavior of nitrogen confined inside the AFI nano-channels is then investigated by Raman spectroscopy up to 44 GPa. Under pressure, the Raman modes of confined nitrogen show behaviors different from those of the bulk nitrogen. After the return to atmospheric pressure, it is demonstrated that non-gaseous nitrogen can be effectively stabilized by being confined inside the intact AFI sample. This result provides new insight into nitrogen capture and storage technologies. [ABSTRACT FROM AUTHOR]

We studied the behavior of solvated and desolvated C60 crystals under pressure by in situ Raman spectroscopy. The pressure-induced bonding change and structural transformation of C60s are similar in the two samples, both undergoing deformation and amorphization. Nevertheless, the high pressure phases of solvated C60 can indent diamond anvils while that of desolvated C60s cannot. Further experiments suggest that the solvents in the solvated C60 act as both spacers and bridges by forming covalent bonds with neighbors in 3D network at high pressure, and thus, a fraction of fullerenes may preserve the periodic arrangement in spite of their amorphization. [ABSTRACT FROM AUTHOR]

We have performed in situ low-temperature Raman spectroscopy studies on iodine molecules confined in the one-dimensional (1D) round channels of AlPO 4 -5 (AFI) crystals. Polarized Raman measurements show that the Raman intensity of individual iodine molecules parallel to channel axis (termed lying molecules) increases more than that of iodine molecules perpendicular to channel axis (termed standing molecules) upon cooling temperature down to −196 °C. This suggests that an orientation transformation of individual iodine molecules has occurred to increase the population of iodine molecules lying along channel axis as temperature decreases. Consequently, the corresponding Raman mode shows a redshift due to the enhancement of intermolecular interaction. This low-temperature induced orientation transformation is observed to recover when heated back to room temperature, indicating that orientation of iodine molecules confined in this porous medium can be modulated reversibly at a molecular level by cooling temperature down. [ABSTRACT FROM AUTHOR]

Highlights: [•] High pressure study of graphene nanoplates is carried out by Raman spectroscopy. [•] The transition pressure for graphene nanoplates is found to be lower than that for graphite. [•] The reasons for the reduction of transition pressure for graphene nanoplates are discussed. [Copyright &y& Elsevier]

Abstract: High pressure behaviors of nanoporous anatase TiO2 were studied using in situ Raman spectroscopy up to 37GPa. The nanoporous anatase phase starts to transform into the baddeleyite phase with poor crystallinity at ∼15.2GPa, and the baddeleyite phase coexists with anatase phase up to 18.4GPa. The baddeleyite form transforms into an amorphous phase above 20.5GPa. Upon decompression, the amorphous phase recovers to the baddeleyite phase and then transforms to the α-PbO2 phase. The phase transition from the baddeleyite phase to the amorphous form is reversible. The poor crystalline baddeleyite phase acts as an intermediate state in the amorphization process. The phase transitions of the nanoporous anatase TiO2 are obviously different from the pressure-induced amorphization in the anatase TiO2 nanoparticles. These results indicate that the porous microstructure plays important roles in the high pressure phase transitions of the nanoporous anatase TiO2. [Copyright &y& Elsevier]

Abstract: The high quality boron-doped diamond (BDD) film electrodes deposited on titanium (Ti) substrate have been prepared by a microwave plasma-assisted chemical vapor deposition (MP-CVD) method. The products consist of high quality dense grains characterized by Raman spectroscopy and scanning electron microscopy (SEM) employed. The BDD electrodes have wide electrochemical window (approximate 4.0V) and low background current (near zero) and the oxidation peak of phenol appears before the discharge of water, examined by cyclic voltammetry and linear sweep voltammetry. Compared with the fluorine-doped lead dioxide anodes (Ti/F-PbO2), the Ti/BDD anodes showed higher current efficiency and lower power consumption with degradation of low concentration phenol. The experimental results demonstrated that the BDD electrode on the Ti substrate possesses the excellent electrocatalytic activity in dilute solution. [Copyright &y& Elsevier]

Abstract: C60 nanotubes have been synthesized by a solution–solution method. After degassing in a dynamic vacuum, the C60 nanotubes doped with alkali metals by means of vapor evaporation method. Different temperatures have been studied to evaporate the alkali metals for the doping experiments. Raman spectrum was further employed to analyze the doping concentration of the obtained samples. It was found that all three alkali metals (Li, Na and K) used can be efficiently doped into the C60 nanotubes, forming A x C60 nanotubes. The doping concentration of Li, Na changed from low to high level, depending on the experiment temperatures, while K doping always gave saturated doping. The melt points, the ionic sizes and vapor pressures of alkali metals were thought to affect the final doping results. [Copyright &y& Elsevier]

Abstract: C60 rods with nano- and submicrometer dimensions were polymerized at 4.5GPa and 973K. Raman spectroscopy showed that the material transformed into a rhombohedral polymeric structure under high pressure and high temperature (HPHT) conditions. The HPHT polymerized samples keep the original rod shape. The position dependence of photoluminescence (PL) spectra have been studied on the rhombohedral polymer C60 rods at room temperature. The intensity of the 1.74eV peak from the rhombohedral phase varies systematically between the edge of and the middle of the rod. Our results indicate that the 1.74eV peak originates from surface defects. [Copyright &y& Elsevier]

Abstract: The effect of a new bimetallic catalyst Ho/Ni for synthesis of single-walled carbon nanotubes (SWNTs) by arc discharge has been studied. Long ribbons consisting of roughly-aligned SWNT bundles were obtained by a modified arc discharge apparatus. Ribbon lengths can reach as much as 20cm. Both elements Ho and Ni play important roles in the synthesis of SWNTs with high yield and purity. Changes in the Ho and Ni concentration in the catalyst hardly affect the diameter distribution of SWNTs, but the yield and purity of SWNTs are very sensitive to the concentration. An optimal range of Ho/Ni compositions for synthesis of SWNTs with relatively high purity and yield is given. [Copyright &y& Elsevier]