Photodynamics at Low Temperatures, in Time Domain

2019 ◽  
pp. 85-106
Author(s):  
V. Ara Apkarian ◽  
Mika Pettersson
Keyword(s):  
Time Domain ◽  
Low Temperatures

scholarly journals Structural and time-domain peculiarities of the fluorescence excitation spectra of single Mg-TAP in a polymer at low temperatures

2018 ◽  
Vol 190 ◽  
pp. 04019
Author(s):  
Aleksandr Savostianov ◽  
Ivan Eremchev ◽  
Alexei Gorshelev ◽  
Sergei Orlov ◽  
Oleg Korotayev ◽  
...  
Keyword(s):  
Low Temperature ◽  
Spectral Range ◽  
Time Domain ◽  
Low Temperatures ◽  
Single Molecules ◽  
Excitation Spectra ◽  
Fluorescence Excitation ◽  
Zero Phonon Line ◽  
Broad Spectral Range ◽  
Fluorescence Excitation Spectra

The results of low-temperature measurements of spectral trails (temporal evolutions of individual fluorescence excitation spectra) of single molecules Mg-tetraazaporphyrin embedded in polyisobutylene are presented. Spectral trails were recorded in a broad spectral range (up to 4000 GHz) at a temperature 6K. Spectral diffusion in a broad spectral range has been found. Individual spectra of single molecules with a broad peak shifted with respect to zero-phonon line at ~14 – 15 cm-1 were recorded. These broad peaks can be interpreted as the phonon sidebands.

Photocurrent Response In Mg-Doped GaN

1997 ◽  
Vol 482 ◽  
Author(s):  
C. H. Qiu ◽  
J. I Pankove ◽  
I. Akasaki ◽  
H. Amano
Keyword(s):  
Thin Films ◽  
Time Domain ◽  
Low Temperatures ◽  
Room Temperature ◽  
Photocurrent Response ◽  
Defect States ◽  
Maximum Value ◽  
The Time Domain ◽  
Photoconductivity Response ◽  
Mg Doped

AbstractThe photoconductivity response of Mg-doped GaN thin films was studied in the time domain of 50 nanoseconds to a few milliseconds in the temperature range of 100K to 390K. The response time, defined as the time when the photocurrent decreased to half its maximum value, is in the sub-microseconds at room temperature, but increased to a few microseconds at low temperatures. The contact capacitance is suspected for this behavior. Slower decay components due to trapping at defect states were also observed.

Luminescence Decay of the 1.54 μm Emission from Erbium in Silicon

1996 ◽  
Vol 422 ◽  
Author(s):  
J. Hartung ◽  
J. H. Evans ◽  
P. Dawson ◽  
A. P. Sciioles ◽  
T. Taskin ◽  
...  
Keyword(s):  
Time Domain ◽  
Low Temperatures ◽  
Auger Recombination ◽  
Luminescence Decay ◽  
Optically Active ◽  
Excitation Density ◽  
Exponential Behaviour ◽  
The Time Domain ◽  
Nonradiative Processes ◽  
Density Results

AbstractPhotoluminescence of silicon implanted with erbium and oxygen was measured in the time domain focussing on the temperature and excitation density dependence of the intra-4f-shell emission from Er3+. The decay of this luminescence is similar for the different optically active crystal field split Er-centres. At low temperatures the luminescence transients consist of a fast initial non-exponential component followed by slower exponential behaviour. An increase in excitation density results in a higher proportion of the luminescence decaying with the faster decay time. Our results indicate a relation of the fast component to nonradiative processes. Auger recombination is proposed as a possible mechanism.

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

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.

Radiation Damage of Support Films

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.

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

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.

Ultrastructure of the soil fungus, Geomyces pannorus

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.

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

1991 ◽  
Vol 49 ◽  
pp. 900-901 ◽  
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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