Gallium vacancy related defects in silicon doped GaAs grown at low temperatures

ABSTRACTThe lattice site of H/D atoms in silicon doped with B and 111In atoms is investigated using the ion channeling and perturbed γγ angular correlation (PAC) technique. The results indicate that at 295 K the antibonding site is occupied by H/D and that this site is easily transformed into a near tetrahedral site under the influence of an analyzing ion beam. Based on PAC results, the population of a second site, possibly a bond-center site, is expected at low temperatures.

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Optical Properties of Novel Vibronic Bands in Electron-Irradiated Tin Doped Silicon

MRS Proceedings ◽

10.1557/proc-163-261 ◽

1989 ◽

Vol 163 ◽

Author(s):

J. H. Svensson ◽

B. Monemar ◽

B. G. Svensson

Keyword(s):

Optical Properties ◽

Low Temperatures ◽

Excited Electronic State ◽

Electronic States ◽

Optical Excitation ◽

Electronic Transitions ◽

Vibrational States ◽

Doped Silicon ◽

Silicon Doped ◽

Excitation Conditions

AbstractThe optical absorption of two new electronic transitions in silicon doped with tin has been investigated. At low temperatures two no-phonon lines are observed at 2755.3 and 4112.2 cm-1, each with strong coupling to a single quasi-localized vibration in the excited electronic state. These vibrations have quantum energies of 69.6 and 70.2 cm-1, respectively. At higher temperatures coupling to thermally excited vibrational states in the ground electronic states is observed for both lines. The transition with the no-phonon line at 4112.2 cm-1 has been studied in detail and is found to be well described using the adiabatic and Condon approximations. The optical properties of the two transitions are found to be quite similar. Moreover the relative intensities of the two lines are found to be dependent on the optical excitation conditions.

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Interpretation of irradiation-induced changes in electron diffractograms and images of extinction contours at low temperatures

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100111458 ◽

1984 ◽

Vol 42 ◽

pp. 268-269

Author(s):

E. Knapek ◽

H. Formanek ◽

G. Lefranc ◽

I. Dietrich

Keyword(s):

Low Temperatures ◽

Carbon Films ◽

Organic Crystals ◽

Wide Spread ◽

Lens System ◽

Preparation Conditions ◽

Thin Carbon ◽

Electron Diffractograms ◽

Diffraction Patterns ◽

Induced Changes

A few years ago results on cryoprotection of L-valine were reported, where the values of the critical fluence De i.e, the electron exposure which decreases the intensity of the diffraction reflections by a factor e, amounted to the order of 2000 + 1000 e/nm2. In the meantime a discrepancy arose, since several groups published De values between 100 e/nm2 and 1200 e/nm2 /1 - 4/. This disagreement and particularly the wide spread of the results induced us to investigate more thoroughly the behaviour of organic crystals at very low temperatures during electron irradiation.For this purpose large L-valine crystals with homogenuous thickness were deposited on holey carbon films, thin carbon films or Au-coated holey carbon films. These specimens were cooled down to nearly liquid helium temperature in an electron microscope with a superconducting lens system and irradiated with 200 keU-electrons. The progress of radiation damage under different preparation conditions has been observed with series of electron diffraction patterns and direct images of extinction contours.

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Radiation Damage of Support Films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100096862 ◽

1981 ◽

Vol 39 ◽

pp. 28-29

Author(s):

H.A. Cohen ◽

W. Chiu

Keyword(s):

Transfer Function ◽

Low Temperatures ◽

Carbon Support ◽

Contrast Transfer Function ◽

Electron Dose ◽

Imaging Parameters ◽

Negative Stain ◽

Phase Corrections ◽

Two Parameters ◽

Medium Dose

The goal of imaging the finest detail possible in biological specimens leads to contradictory requirements for the choice of an electron dose. The dose should be as low as possible to minimize object damage, yet as high as possible to optimize image statistics. For specimens that are protected by low temperatures or for which the low resolution associated with negative stain is acceptable, the first condition may be partially relaxed, allowing the use of (for example) 6 to 10 e/Å2. However, this medium dose is marginal for obtaining the contrast transfer function (CTF) of the microscope, which is necessary to allow phase corrections to the image. We have explored two parameters that affect the CTF under medium dose conditions.Figure 1 displays the CTF for carbon (C, row 1) and triafol plus carbon (T+C, row 2). For any column, the images to which the CTF correspond were from a carbon covered hole (C) and the adjacent triafol plus carbon support film (T+C), both recorded on the same micrograph; therefore the imaging parameters of defocus, illumination angle, and electron statistics were identical.

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In situ Tensile Experiments at Low Temperatures on Niobium Single Crystals by H.V.E.M.

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113913 ◽

1975 ◽

Vol 33 ◽

pp. 58-59

Author(s):

F. H. Louchet ◽

L. P. Kubin

Keyword(s):

Electron Microscope ◽

Transition Temperature ◽

Low Temperature ◽

Slip System ◽

Low Temperatures ◽

Tensile Axis ◽

Image Intensifier ◽

Screw Dislocations ◽

Source Operation

Experiments have been carried out on the 3 MeV electron microscope in Toulouse. The low temperature straining holder has been previously described Images given by an image intensifier are recorded on magnetic tape.The microtensile niobium samples are cut in a plane with the two operative slip directions [111] and lying in the foil plane. The tensile axis is near [011].Our results concern:- The transition temperature of niobium near 220 K: at this temperature and below an increasing difference appears between the mobilities of the screw and edge portions of dislocations loops. Source operation and interactions between screw dislocations of different slip system have been recorded.

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Ultrastructure of the soil fungus, Geomyces pannorus

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100113573 ◽

1984 ◽

Vol 42 ◽

pp. 738-739

Author(s):

J. A. Traquair ◽

E. G. Kokko

Keyword(s):

Electron Microscopy ◽

Scanning Electron Microscopy ◽

Fine Structure ◽

Low Temperatures ◽

Soil Fungus ◽

Organic Soils ◽

Anatomical Studies ◽

Transmission Electron ◽

Electron Microscopical ◽

Scanning Electron

With the advent of improved dehydration techniques, scanning electron microscopy has become routine in anatomical studies of fungi. Fine structure of hyphae and spore surfaces has been illustrated for many hyphomycetes, and yet, the ultrastructure of the ubiquitous soil fungus, Geomyces pannorus (Link) Sigler & Carmichael has been neglected. This presentation shows that scanning and transmission electron microscopical data must be correlated in resolving septal structure and conidial release in G. pannorus.Although it is reported to be cellulolytic but not keratinolytic, G. pannorus is found on human skin, animals, birds, mushrooms, dung, roots, and frozen meat in addition to various organic soils. In fact, it readily adapts to growth at low temperatures.

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Structure and Orientation of As Precipitates in LT-MBE Grown GaAs

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100088816 ◽

1991 ◽

Vol 49 ◽

pp. 900-901 ◽

Cited By ~ 1

Author(s):

Alain Claverie ◽

Zuzanna Liliental-Weber

Keyword(s):

Transport Properties ◽

Layer Thickness ◽

Growth Temperature ◽

Low Temperatures ◽

Lattice Parameter ◽

Crystalline Quality ◽

Insulating Properties ◽

Lt Gaas

GaAs layers grown by MBE at low temperatures (in the 200°C range, LT-GaAs) have been reported to have very interesting electronic and transport properties. Previous studies have shown that, before annealing, the crystalline quality of the layers is related to the growth temperature. Lowering the temperature or increasing the layer thickness generally results in some columnar polycrystalline growth. For the best “temperature-thickness” combinations, the layers may be very As rich (up to 1.25%) resulting in an up to 0.15% increase of the lattice parameter, consistent with the excess As. Only after annealing are the technologically important semi-insulating properties of these layers observed. When annealed in As atmosphere at about 600°C a decrease of the lattice parameter to the substrate value is observed. TEM studies show formation of precipitates which are supposed to be As related since the average As concentration remains almost unchanged upon annealing.

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