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J Haines - One of the best experts on this subject based on the ideXlab platform.

  • a neutron diffraction study of the thermal stability of the α quartz type structure in Germanium Dioxide
    Journal of Solid State Chemistry, 2002
    Co-Authors: J Haines, Olivier Cambon, Etienne Philippot, Laurent Chapon, S Hull
    Abstract:

    The structure of the α-quartz-type form of Germanium Dioxide was refined at room temperature and up to 1344 K by the Rietveld method using time-of-flight neutron powder diffraction data. The intertetrahedral bridging angle θ and the tilt angle δ exhibit thermal stabilities that are among the highest observed in α-quartz homeotypes. The temperature dependence of these angles is found to be a function of the structural distortion in these materials. Structure–property relationships predict that due to its highly distorted structure, Germanium Dioxide is potentially a high-performance piezoelectric material. The high stability of the above structural parameters as a function of temperature infers that the corresponding piezoelectric properties should also be retained under these conditions. At the present time, problems related to phase stability and crystal growth need to be resolved before the α-quartz-type form of ger-manium Dioxide can be used as a piezoelectric material.

  • structural evolution of rutile type and cacl 2 type Germanium Dioxide at high pressure
    Pacific Rim Conference on Multimedia, 2000
    Co-Authors: J Haines, Jeanmichel Leger, Christian Chateau, Altair Soria Pereira
    Abstract:

    Germanium Dioxide was found to undergo a transition from the tetragonal rutile-type to the orthorhombic CaCl2-type phase above 25 GPa. The detailed structural evolution of both phases at high pressure in a diamond anvil cell has been investigated by Rietveld refinement using angle-dispersive, X-ray powder-diffraction data. The square of the spontaneous strain (a−b)/(a+b) in the orthorhombic phase was found to be a linear function of pressure and no discontinuities in the cell constants and volume were observed, indicating that the transition is second-order and proper ferroelastic. Compression of the GeO6 octahedra was found to be anisotropic, with the apical Ge-O distances decreasing to a greater extent than the equatorial distances and becoming shorter than the latter above 7 GPa. Above this pressure, the GeO6 octahedron exhibits the common type of tetragonal distortion predicted by a simple ionic model and observed for most rutile-type structures such as those of the heavier group-14 Dioxides and the metal difluorides. Above the phase transition, the columns of edge-sharing octahedra tilt about their two fold axes parallel to c and the rotation angle reaches 10.2(5)° by 36(1) GPa so as to yield a hexagonal close-packed oxygen sublattice. The compressibility increases at the phase change as is expected for a second-order transition at which an additional compression mechanism becomes available.

  • ferroelastic phase transition in rutile type Germanium Dioxide at high pressure
    Physical Review B, 1998
    Co-Authors: J Haines, Jeanmichel Leger, Christian Chateau, Roberto Bini, Lorenzo Ulivi
    Abstract:

    Rutile-type ${\mathrm{GeO}}_{2}$ was found to undergo a proper ferroelastic transition at 26.7(2) GPa from Raman spectroscopic measurements. The ${B}_{1g}$ optic mode softens up to this pressure and then becomes a hard ${A}_{g}$ mode. The square of these mode frequencies varies linearly with pressure in accordance with the soft-mode theory of second-order phase transitions. The present results have enabled a systematic relationship between the square of the soft-mode frequency at ambient pressure and the critical pressure in the homologous series ${\mathrm{SiO}}_{2},$ ${\mathrm{GeO}}_{2},$ and ${\mathrm{SnO}}_{2}$ to be identified.

Aftanas Galík - One of the best experts on this subject based on the ideXlab platform.

Seiji Samukawa - One of the best experts on this subject based on the ideXlab platform.

  • formation of thin Germanium Dioxide film with a high quality interface using a direct neutral beam oxidation process
    Japanese Journal of Applied Physics, 2012
    Co-Authors: Akira Wada, R Zhang, Shinichi Takagi, Seiji Samukawa
    Abstract:

    A damage-free and low-temperature neutral beam oxidation (NBO) process is used to directly form a thin Germanium Dioxide (GeO2) film. A GeO2 film with only a small amount of suboxide is formed even at a low substrate temperature of 300 °C because of the extremely low-activation-energy oxidation owing to bombardment with 5-eV-energy oxygen neutral beams. We combined the NBO process with hydrogen radical native oxide removal treatment to form high-quality GeO2 films, and our fabricated Al2O3/GeO2/Ge gate stack has an extremely low interface state density (Dit) of less than 1×1011 cm-2 eV-1.

  • thin Germanium Dioxide film with a high quality interface formed in a direct neutral beam oxidation process
    European Solid-State Device Research Conference, 2012
    Co-Authors: Akira Wada, Seiji Samukawa, R Zhang, Shinichi Takagi
    Abstract:

    Germanium Dioxide (GeO 2 ) thin film with a high-quality interface was directly formed by using a damage-free and low-temperature neutral beam oxidation (NBO) process. GeO 2 film with little suboxide could be formed even at a low substrate temperature of 300°C because of the extremely low activation energy (E a ) oxidation resulting from bombardment with energetic oxygen neutral-beams of 5 eV. A high-quality GeO 2 /Ge interface with an low interface state density (D it ) of less than 1 × 1011 cm−2eV−1 was created by combining the NBO process with a hydrogen (H) radical native oxide removal treatment.

  • high quality Germanium Dioxide thin films with low interface state density using a direct neutral beam oxidation process
    Applied Physics Letters, 2012
    Co-Authors: Akira Wada, R Zhang, Shinichi Takagi, Seiji Samukawa
    Abstract:

    High-quality Germanium Dioxide (GeO2) as a gate oxide is in high demand for use in future high mobility Ge-channel field-effect transistors. GeO2 thin films were directly formed by using a damage-free and low-temperature process of neutral beam oxidation (NBO) after treatment with hydrogen (H) radicals. GeO2 thin films (equivalent oxide thickness (EOT) = 1.7 nm) with a high-quality interface and an extremely low interface state density (<1 × 1011 cm−2 eV−1) could be formed even at low temperature (300 °C) by combining the H radical treatment, which resulted in the removal of native oxides, with the NBO process we developed.

Yasuo Ohishi - One of the best experts on this subject based on the ideXlab platform.

  • phase transition between thecacl2 type andα pbo2 type structures of Germanium Dioxide
    Physical Review B, 2003
    Co-Authors: Shigeaki Ono, Taku Tsuchiya, Kei Hirose, Yasuo Ohishi
    Abstract:

    Observations of the phase transition between the CaCl 2 -type (Pnnm) and α-PbO 2 -type (Pbcn) structures of Germanium Dioxide (GeO 2 ) were carried out using quench and in situ x-ray diffraction methods in a laser-heated diamond anvil cell (LHDAC). First-principle theoretical simulations were also performed to complement the experimental results. The experiments showed that the transition had a positive dP/dT dependence. The phase boundary between the CaCl 2 -type and α-PbO 2 -type structures in the temperature range 1500-2400 K was determined to be P (GPa)= (53′3)+(0.011′0.005)(T-1800) (K) based on the equation of state of platinum and the ruby scale. The positive slope of the transition is consistent with the known phase boundary between the CaCl 2 -type and α-PbO 2 -type structures of tin Dioxide (SnO 2 ) as Germanium Dioxide analog and theoretical simulation results. However, our results do not agree with the slope of the phase boundary of silica (SiO 2 ), which has been reported to have a negative slope.

  • high pressure form of pyrite type Germanium Dioxide
    Physical Review B, 2003
    Co-Authors: Shigeaki Ono, Taku Tsuchiya, Kei Hirose, Yasuo Ohishi
    Abstract:

    Structural phase transitions of Germanium Dioxide $({\mathrm{GeO}}_{2})$ have been investigated at pressures up to 120 GPa, which was heated to a temperature above 2000 K, using a laser-heated diamond anvil cell technique. A phase transition between ${\mathrm{CaCl}}_{2}$-type and $\ensuremath{\alpha}\ensuremath{-}{\mathrm{PbO}}_{2}$-type phases was observed at about 50 GPa. At pressures higher than 90 GPa, we also observed the occurrence of a new high-pressure phase of pyrite-type (modified-fluorite type) structure $(Pa3\ifmmode\bar\else\textasciimacron\fi{})$ that is denser than other known ${\mathrm{GeO}}_{2}$ phases. Our results were consistent with the high-pressure transition sequence of tin Dioxide $({\mathrm{SnO}}_{2})$ as analog of ${\mathrm{GeO}}_{2}.$ The new structure of the ${\mathrm{GeO}}_{2}$ high-pressure phase may be that of high-pressure silica $({\mathrm{SiO}}_{2})$ phase predicted by the theoretical investigations.

Shigeaki Ono - One of the best experts on this subject based on the ideXlab platform.

  • structural refinements of high pressure phases in Germanium Dioxide
    Acta Crystallographica Section B-structural Science, 2003
    Co-Authors: Koichi Shiraki, Taku Tsuchiya, Shigeaki Ono
    Abstract:

    Recently, there has been substantial interest in the new high-pressure polymorphs of GeO2 synthesized in the laboratory. Previous investigators reported the synthesis of `CaCl2-type', `α-PbO2-type' and `pyrite-type (modified-fluorite-type)' GeO2 at pressures of 30–130 GPa in laser-heated diamond anvil cells. In order to provide definitive information about the new high-pressure polymorphs, we performed Rietveld refinements of the structures. The structure refinements confirm that two of these high-pressure phases do have the α-PbO2-type and pyrite-type (modified-fluorite-type) structures.

  • phase transition between thecacl2 type andα pbo2 type structures of Germanium Dioxide
    Physical Review B, 2003
    Co-Authors: Shigeaki Ono, Taku Tsuchiya, Kei Hirose, Yasuo Ohishi
    Abstract:

    Observations of the phase transition between the CaCl 2 -type (Pnnm) and α-PbO 2 -type (Pbcn) structures of Germanium Dioxide (GeO 2 ) were carried out using quench and in situ x-ray diffraction methods in a laser-heated diamond anvil cell (LHDAC). First-principle theoretical simulations were also performed to complement the experimental results. The experiments showed that the transition had a positive dP/dT dependence. The phase boundary between the CaCl 2 -type and α-PbO 2 -type structures in the temperature range 1500-2400 K was determined to be P (GPa)= (53′3)+(0.011′0.005)(T-1800) (K) based on the equation of state of platinum and the ruby scale. The positive slope of the transition is consistent with the known phase boundary between the CaCl 2 -type and α-PbO 2 -type structures of tin Dioxide (SnO 2 ) as Germanium Dioxide analog and theoretical simulation results. However, our results do not agree with the slope of the phase boundary of silica (SiO 2 ), which has been reported to have a negative slope.

  • high pressure form of pyrite type Germanium Dioxide
    Physical Review B, 2003
    Co-Authors: Shigeaki Ono, Taku Tsuchiya, Kei Hirose, Yasuo Ohishi
    Abstract:

    Structural phase transitions of Germanium Dioxide $({\mathrm{GeO}}_{2})$ have been investigated at pressures up to 120 GPa, which was heated to a temperature above 2000 K, using a laser-heated diamond anvil cell technique. A phase transition between ${\mathrm{CaCl}}_{2}$-type and $\ensuremath{\alpha}\ensuremath{-}{\mathrm{PbO}}_{2}$-type phases was observed at about 50 GPa. At pressures higher than 90 GPa, we also observed the occurrence of a new high-pressure phase of pyrite-type (modified-fluorite type) structure $(Pa3\ifmmode\bar\else\textasciimacron\fi{})$ that is denser than other known ${\mathrm{GeO}}_{2}$ phases. Our results were consistent with the high-pressure transition sequence of tin Dioxide $({\mathrm{SnO}}_{2})$ as analog of ${\mathrm{GeO}}_{2}.$ The new structure of the ${\mathrm{GeO}}_{2}$ high-pressure phase may be that of high-pressure silica $({\mathrm{SiO}}_{2})$ phase predicted by the theoretical investigations.