Study of vibrational spectra of lanthanum sulphate nonahydrate at different temperatures in the region from 4000–50 cm−1

Abstract The IR (4000-400 cm-1) and Raman (4000-50 cm-1) spectra of 3-methoxymethylene-2,4-pentanedione [H3C-O-CH=C(COCH3)2] as a liquid and solutes in various solvents of different polarity have been recorded at ambient temperature. Additional IR and Raman spectra were obtained for amorphous and crystalline solid state at low temperature. The vibrational spectra revealed that the compound exists at least in two dominant conformers of different polarity and that the conformer present in the solid phase is less polar. NMR spectra in various solvents at different temperatures were also obtained. The compound can exist in several conformers due to the rotation around O-C= and both =C-C bonds with planar or nonplanar arrangements of heavy atoms. Ab initio MP2 and DFT calculations using a wide scale of basis sets were carried out. According to these calculations six conformational structures of the eight theoretically possible conformational structures with the methoxy group oriented as anti or syn and carbonyl groups oriented as Z or E towards the C=C double bond were obtained at potential energy surface. It has been shown that the conformers with the E orientations of both acetyl groups are not the stable ones. The calculated ab initio MP2 and DFT energies of all found conformers in vacuum suggest the most stable ZEa conformer where Z and E regard to the trans and cis acetyl groups, respectively and a denotes the orientation of the methoxy group. The EZa conformer was calculated as the second most stable one with the energy by at least 10 kJ mol-1 higher. Corrections of the relative energies of single conformers obtained in vacuum on the polar surroundings were done by including the solvent effect into the calculations using IEF Polarizable Continuum Model. Assignments of the vibrational spectra for the studied compound were made with the aid of normal coordinate calculations employing scaled ab initio force field. The scaled ab initio frequencies as well as calculated energies indicate that ZEa is the conformer present in the solid phase.

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Observations oh Nucleation and Growth of Voids in Nickel

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100069065 ◽

1970 ◽

Vol 28 ◽

pp. 414-415

Author(s):

J. L. Brimhall ◽

H. E. Kissinger ◽

B. Mastel

Keyword(s):

High Purity ◽

Growth Stage ◽

Elevated Temperatures ◽

Early Growth ◽

Nucleation And Growth ◽

Pure Nickel ◽

Different Temperatures ◽

Total Fluence ◽

Neutron Exposure ◽

Growth Of Voids

Some information on the size and density of voids that develop in several high purity metals and alloys during irradiation with neutrons at elevated temperatures has been reported as a function of irradiation parameters. An area of particular interest is the nucleation and early growth stage of voids. It is the purpose of this paper to describe the microstructure in high purity nickel after irradiation to a very low but constant neutron exposure at three different temperatures.Annealed specimens of 99-997% pure nickel in the form of foils 75μ thick were irradiated in a capsule to a total fluence of 2.2 × 1019 n/cm2 (E > 1.0 MeV). The capsule consisted of three temperature zones maintained by heaters and monitored by thermocouples at 350, 400, and 450°C, respectively. The temperature was automatically dropped to 60°C while the reactor was down.

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The structure of membranes and membrane proteins embedded in amorphous ice

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100122563 ◽

1992 ◽

Vol 50 (1) ◽

pp. 432-433

Author(s):

Uwe Lücken ◽

Joachim Jäger

Keyword(s):

Phase Transition ◽

Transition Temperature ◽

Membrane Proteins ◽

Phase Transition Temperature ◽

Lipid Vesicles ◽

Freezing Stress ◽

Amorphous Ice ◽

Different Temperatures ◽

Band Pass ◽

Lipid Polymorphism

TEM imaging of frozen-hydrated lipid vesicles has been done by several groups Thermotrophic and lyotrophic polymorphism has been reported. By using image processing, computer simulation and tilt experiments, we tried to learn about the influence of freezing-stress and defocus artifacts on the lipid polymorphism and fine structure of the bilayer profile. We show integrated membrane proteins do modulate the bilayer structure and the morphology of the vesicles.Phase transitions of DMPC vesicles were visualized after freezing under equilibrium conditions at different temperatures in a controlled-environment vitrification system. Below the main phase transition temperature of 24°C (Fig. 1), vesicles show a facetted appearance due to the quasicrystalline areas. A gradual increase in temperature leads to melting processes with different morphology in the bilayer profile. Far above the phase transition temperature the bilayer profile is still present. In the band-pass-filtered images (Fig. 2) no significant change in the width of the bilayer profile is visible.

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Microstructure of sputter deposited Ni-Sb ohmic contacts on GaAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100154226 ◽

1989 ◽

Vol 47 ◽

pp. 450-451

Author(s):

S. Yegnasubramanian ◽

V.C. Kannan ◽

R. Dutto ◽

P.J. Sakach

Keyword(s):

High Performance ◽

Ohmic Contacts ◽

Surface Defects ◽

Pure Metal ◽

Device Fabrication ◽

Native Oxide ◽

Metal Thin Films ◽

Recent Developments ◽

Different Temperatures ◽

Sputter Deposited

Recent developments in the fabrication of high performance GaAs devices impose crucial requirements of low resistance ohmic contacts with excellent contact properties such as, thermal stability, contact resistivity, contact depth, Schottky barrier height etc. The nature of the interface plays an important role in the stability of the contacts due to problems associated with interdiffusion and compound formation at the interface during device fabrication. Contacts of pure metal thin films on GaAs are not desirable due to the presence of the native oxide and surface defects at the interface. Nickel has been used as a contact metal on GaAs and has been found to be reactive at low temperatures. Formation Of Ni2 GaAs at 200 - 350C is reported and is found to grow epitaxially on (001) and on (111) GaAs, but is shown to be unstable at 450C. This paper reports the investigations carried out to understand the microstructure, nature of the interface and composition of sputter deposited and annealed (at different temperatures) Ni-Sb ohmic contacts on GaAs by TEM. Attempts were made to correlate the electrical properties of the films such as the sheet resistance and contact resistance, with the microstructure. The observations are corroborated by Scanning Auger Microprobe (SAM) investigations.

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