H.D. Hochheimer

Frontiers of high pressure research II: application of high pressure to low-dimensional novel electronic materials

Contributors. Preface. Acknowledgements. Evangelos Anastassakis (1938-2000). Material Synthesis at High Pressures. Stabilization of Unusual Oxidation States of Transition Metals in Oxygen Lattices: Correlations with the Induced Electronic Phenomena G. Demazeau. Synthesis and Properties of Low dimensional F-Element Chalocogenide Compounds P.K. Dorhout, C.R. Evenson, IV. Synthesis and High-Pressure Behavior of C6N9H3*HCl: A graphitic material with a two-dimensional C-N network G.H. Wolf, et al. Plasma Polymerization of Thin Films Using Aniline and p-Xylene Precursors A. Dumitru, et al. Pressure-Induced Phase Transitions. Compressibility, Pressure-Induced Amorphisation and Thermal Collapse of Zeolites G.N. Greaves. Pressure-induced H-transfers in the networks of hydrogen bonds A. Katrusiak. The Light Elements at High Pressure, in Layered Form, and in Combination N.W. Ashcroft. Pressure-induced Phase Transitions in GaSe-, TlGaSe2- and CdGa2S4-type Crystals K.R. Allakhverdiev. Influence of Pressure on the Physical Properties of Chain TlSe-type Crystals K.R. Allakhverdiev, S.S. Ellialtiogammalu. Impendance Spectroscopy at Super High Pressures A.N. Babushkin, et al. Optical Properties of A2CuCl4 Layer Perovskites under Pressure: Structural Correlations F. Rodriguez, et al. The Effect of Pressure-Induced Collapse of Correlation and Hunds Rules on Structure and Electronic Properties of Transition-Metal Compounds M. Paz-Pasternak, et al. Pressure Tuning of Condensation and Ordering of Charge-Transfer Strings H. Cailleau, et al. From Ferroelectric to Quantum Paraelectric: Ktal-xNbxO3(KTN), a Model System G.A.Samara. Molecular Solids Under High Pressures. Quartz like phases in CO2 at very high pressure from ab initio simulations R. Ahuja, et al. Progress in Experimental Studies of Insulator-Metal Transitions at Multimegabar Pressures R.J. Hemley, et al. Solid Oxygen as Low dimensional System by Spectroscopic Studies A. Brodyanski, et al. Evolution of Rotational Spectrum in Solid Hydrogen with Pressure: Implications for Conversion and other Properties M.A. Strzhemechny. An Influence of the Pressure on Metastability of the HCP Phase of Solid Nitrogen B. Kuchta, et al. Semiconductors, 2-D Impurity States, Quantum Dots. X-ray Study of Strain Relaxation in Heteroepitaxial Layers of Semiconductors Annealed under High Hydrostatic Pressure J. Bak-Misiuk. Application of High Temperature-Pressure Treatment for Investigation of Defect Creation in Basic Materials of Modern Micro-electronics: Czochralski Silicon and Solicon Containing Films A. Misiuk. Pressure-induced Phase Transformations in Semiconductors under Contact Loading V. Domnich, Y. Gogotsi. Far-Infrared Spectroscopy of Quasi-2D Impurity States in Semiconductor Nanostructures under High Hydrostatic Pressure B.A. Weinstein, et al. Probing the Effects of Three-Dimensional Confinement on the Electronic Structure of InP under Hydrostatic Pressure C.S. Menoni, et al. Pressure Studies in InGaN/GaN Quantum Wells D. Patel, et al. Superconductivity. What High Pressure Studies Have Taught Us about High-Temperature Superconductivity J.S. Schilling. Anisotropic Low-Dimensional Superconductors Close to an Electronic Topological Transition G.G.N. Angilella, et al. Pressure-Induced Superconducting Phase Separation in Oxygen-Doped La2-xSrxCuO4+&dg

High pressure Brillouin scattering and energy dispersive X-ray diffraction study of (NH4)2ZnCl4

Abstract We have performed a high pressure Brillouin scattering and energy dispersive X-ray diffraction study on (NH 4 ) 2 ZnCl 4 in the temperature range from room temperature to 150°C. At ambient pressure three phase transitions occur in this temperature range. Of special interest are the phase transitions at 91°C and 133°C because an incommensurate phase has been detected in this temperature range. We compare the results of our high pressure Brillouin scattering study with the ones obtained from other studies of the elastic constants. Our results for the anomaly in C 33 observed at the commensurate–incommensurate transition at 133°C at ambient pressure contradict the results of the other Brillouin scattering studies but agree well with the results of an ultrasonic study. This result seems to indicate that critical fluctuations of the order parameter at the phase transition are reduced by pressure. Values of the calculated adiabatic bulk modulus, B S , and the experimentally determined isothermal bulk modulus, B T , for various materials of the A 2 BX 4 family, are compiled and discussed.

High-pressure low-temperature electrical properties of polypyrrole doped with p-toluenesulfonate

The electrical properties of polypyrrole doped with p-toluenesulfonate are investigated at temperatures from 300 to 1.2 K and pressures up to 2 GPa. A linear temperature dependence of the thermopower below 150 K supports the intrinsic metallic nature of the samples. The electrical conductivity shows the crossover from nearest-neighbour hopping to variable range hopping at low temperatures. Application of pressure results in a remarkable decrease of the localization strength of the charge carriers and a weaker temperature dependence of the conductivity.

High pressure angle-dispersive Brillouin spectroscopy: A technique for determining acoustic velocities and attenuations in liquids and solids

We report the combination of a high-pressure sample chamber and a stable, nonscanning, angle-dispersive Fabry–Perot interferometer allowing the rapid measurement of inelastic light scattering from acoustic phonon modes in solid and liquid samples at high pressure. The primary components of the apparatus are a (i) narrow frequency gas ion laser, (ii) a solid or air-spaced etalon, (iii) a multichannel charge coupled device detector, and (iv) a large volume, high-pressure cell. The fundamental principle of this spectrometer is based on the angular dispersion of light through an etalon, whereupon the multiple-order frequency dispersed spectrum can be acquired with an array detector. Typical acquisition times are less than 1 s using low to moderate laser power.

HIGH-PRESSURE BRILLOUIN SCATTERING STUDY OF DENSE ARGON AND NITROGEN

We have measured the Brillouin shift as a function of hydrostatic pressure in dense argon and nitrogen at different constant temperatures. We show that for argon there is a linear relation between the index of refraction and the reduced density. A comparison of the sound velocities determined ultrasonically and from our Brillouin data shows a negative velocity dispersion. This is in agreement with theoretical predictions and measurements of the temperature dependence of the sound velocity along the vapor‐pressure equilibrium curve using Brillouin scattering. The fact that the negative velocity dispersion increase with pressure at constant temperature is smaller at lower temperatures is, however, puzzling and cannot be explained within the framework of the above‐mentioned theoretical model.

Mesopiezoresistive effects in double-barrier resonant tunneling structures

This letter reports a mesopiezoresistive effect in a double-barrier resonant tunneling (DBRT) structure. In a DBRT system, an external mechanical stress causes a tensile strain, and the strain, in turn, affects the resonant tunneling and thereby the resistance. Theoretical analysis was carried out on an AlAs∕GaAs∕AlAs DBRT structure under in-plane uniaxial tensile stresses. The results show that the tunneling current and resistance of a DBRT structure change significantly with external stress-induced tensile strains. The results also show that the resistance-strain response can be tuned effectively by the external voltage. The effect has potential applications in miniature electromechanical devices.

Main techniques used in high pressure research with some selected examples

Abstract Various high pressure techniques are introduced, and their advantages in connection with certain measurement techniques are discussed. Selected examples of light scattering, energy dispersive X-ray diffraction, and absorption measurements are presented.

High pressure study of the antiferromagnetic state of chromium alloys

Abstract We have studied the pressure dependence of the Neel temperature (TN) in Cr-Si, Cr-Ge, and Cr-Sn alloys. In all alloys we have found a transition to the commensurate antiferromagnetic spin density wave state above a certain threshold concentration (1·35at.% Si, 0·6at. % Ge, and >2 at.% Sn). On the basis of a two-band nesting model this behaviour can be understood only if the group IV elements act as electron donors to the d band of Cr, as is found for transition metal additions.

Pressure-induced phonon softening and structural phase transitions in Cs2MoS4

Abstract We report the results of a Raman study on Cs 2 MoS 4 under hydrostatic pressures up to 12 GPa. Two successive phase transitions are observed at 8.0 and 9.7 GPa, respectively. A low frequency phonon mode with a negative pressure shift is seen in the low pressure phase. The results are discussed within the framework of structural phase transitions driven by a soft phonon.

High Pressure Conductivity Study of Template Synthesized Polypyrrole: Observation of a Crossover from Three to One Dimensional Variable Range Hopping.

Abstract We have studied thin films of thin and thick wall template synthesized polypyrrole microtubules. We observe a crossover from three- to one-dimensional variable range hopping in our samples at low temperatures. Our results clearly indicate that the geometry of the microtubules has an influence on the conductivity. The transition temperature from three- to one-dimensional variable range hopping shifts to lower temperatures when high pressure is applied. The results are discussed on the basis of the geometry of the microtubules.