Inelastic light scattering spectra of Bi2Se3 and Sb2Te3 single crystals have been measured over the temperature range from 5 K to 300 K. The temperature dependence of dominant A 2 1g phonons shows similar behavior in both materials. The temperature dependence of the peak position and linewidth is analyzed considering the anharmonic decay of optical phonons and the material thermal expansion. This work suggests that Raman spectroscopy can be used for thermometry in Bi2Se3-and Sb2Te3-based devices in a wide temperature range.Recently, much attention has been paid to the study of Bi 2 Se 3 , Sb 2 Te 3 and other layered stoichiometric compounds, as a promising playground for the realization of a new class of quantum matter, topological insulators [1]. A topological insulator has a "conventional" energy gap in the bulk and gapless Dirac-like states on the surface, which are protected against any time-invariant perturbations such as crystal imperfections [2][3][4]. These topologically protected surface states hold great promise for a broad range of potential applications, including field effect transistors [5][6][7], infrared-THz detectors [8,9], and magnetic field sensors [10,11]. It is essential to understand the dynamics of phonons in these materials, particularly the phonon-phonon and electron-phonon interactions, in order to achieve the best device performance. While the room-temperature Raman characterizations of optical phonons in Bi 2 Se 3 and Sb 2 Te 3 have been well documented in the literature [12,13], accurate measurements of the temperature dependence are still lacking. In this Letter, we present a Raman spectroscopy study of Bi 2 Se 3 and Sb 2 Te 3 crystals in the temperature range between 5 K and 300 K. We uncover a characteristic temperature dependence of the phonon peak position and linewidth, and interpret it in the context of thermal expansion and three-phonon anharmonic decay. The observed linear dependence in the elevated temperature range (80-300 K) allows for applications using Raman spectroscopy as thermometry in Bi 2 Se 3 -and Sb 2 Te 3 -based devices.The Bi 2 Se 3 and Sb 2 Te 3 single crystals studied in this work were synthesized at the University of California -Riverside, Purdue University, and the Sandia National Laboratories. Electronic transport characterization revealed that the as-grown crystals were naturally doped, with bulk carrier density in the range of 10 18 -10 19 cm −3 . The typical onset magnetic field for observing

Lattice constant of Bi 2 Se 3 and Sb 2 Te 3 crystals is determined by X-ray powder diffraction measurement in a wide temperature range. Linear thermal expansion coefficients (α) of the crystals are extracted, and considerable anisotropy between α and α ⊥ is observed. The low temperature values of α can be fit well by the Debye model, while an anomalous behavior at above 150 K is evidenced and explained. Grüneisen parameters of the materials are also estimated at room temperature.Recently, much attention has been given to an intriguing class of materials, the so-called topological insulators (TIs). This type of material exhibits a band gap in the bulk, but gapless states on the edge or surface, which are protected by topological order and cannot be analogized to conventional semiconductors or insulators 1,2 . Bi 2 Se 3 , Bi 2 Te 3 and Sb 2 Te 3 are among the most interested compounds of three-dimensional TIs, owing to their robust and simple surface states 3 . Although these compounds were under extensive studies in 1950s and 1960s as excellent thermoelectric materials, some basic physical properties still remain unexplored. In this letter, we present the measurements of the temperature dependent linear thermal expansion coefficients of Bi 2 Se 3 and Sb 2 Te 3 crystals using X-ray powder diffraction (XRD). Thermal expansion is the tendency of materials to change in size and shape as they heat and cool. It is essential to device design and engineering, as the induced strain could cause the deformation of the device and affect its phonon dynamics. Indeed, our recent Raman spectroscopy study of TIs has uncovered significant contributions in the temperature dependent phonon frequency shifts from the thermal expansion of the materials 4 . In addition, the knowledge of thermal expansion coefficients is necessary for the directional growth of TI crystals and the understanding of the high thermoelectric efficiency 5 .Large grain polycrystalline Bi 2 Se 3 materials (single crystal grain size >1 mm) were synthesized at Sandia National Laboratories. First, Bi 2 Se 3 pieces (99.999%, from VWR international, LLC.) were placed in an evacuated (<10 −7 Torr) quartz ampoule and melted at 800 • C for 16 hours. The melt was then cooled at 10 • C/h to 550 • C, held for 3 days at this temperature, and finally allowed to furnace cool to room temperature. Single crystals of Sb 2 Te 3 were grown by Bridgman method at Purdue University. Stoichiometric amount of high purity antimony and tellurium (99.999%) was deoxidized and purified by multiple vacuum distillations under dynamic vacuum of <10 −7 Torr, and then heated up to 900 • C.This was followed by a slow cool down under a controlled pressure to minimize tellurium defects. Afterwards, the crystals were grown at a speed of 0.5-1.5 mm/h with a linear temperature gradient set to 5 • C/cm. Bi 2 Se 3 and Sb 2 Te 3 crystals have similar rhombohedral structure with five atoms in the trigonal primitive cell. A straightforward way to visualize the structure is to use a hexagonal lattice with th...

No abstract

Plants and plant-derived materials play an extremely important role in pest management programs. Essential oil from wood chips of Himalayan Cedar, Cedrus deodara (Roxburgh) Don (Pinales: Pinaceae), was obtained by hydrodistillation and fractionated to pentane and acetonitrile from which himachalenes and atlantones enriched fractions were isolated. A total of forty compounds were identified from these fractions using GC and GC-MS analyses. Essential oils and fractions were evaluated for insecticidal activities against second instars of the diamondback moth, Plutella xylostella L. (Lepidoptera: Yponomeutidae), using a leaf dip method. All samples showed promising larvicidal activity against larvae of P. xylostella. The pentane fraction was the most toxic with a LC50 value of 287 µg/ml. The himachalenes enriched fraction was more toxic (LC50 = 362 µg/ml) than the atlantones enriched fraction (LC50 = 365 µg/ml). LC50 of crude oil was 425 µg/ml and acetonitrile fraction was LC50 = 815 µg/ml. The major constituents, himachalenes and atlantones, likely accounted for the insecticidal action. Present bioassay results revealed the potential for essential oil and different constituents of C. deodara as botanical larvicides for their use in pest management.