Evidence of transient species occurring in the reduction process of trivalent lanthanides under 2.5 MeV electron irradiation by in situ cathodoluminescence and time-resolved photoluminescence

2009 ◽  
Vol 105 (11) ◽  
pp. 113515 ◽  
Author(s):  
N. Ollier ◽  
B. Boizot ◽  
P. L’henoret ◽  
S. Guillous ◽  
G. Petite
Keyword(s):  
Electron Irradiation ◽  
Reduction Process ◽  
Transient Species ◽  
Time Resolved ◽  
Trivalent Lanthanides ◽  
Time Resolved Photoluminescence

Exciton dynamics in thick GaN MOVPE epilayers deposited on sapphire.

1997 ◽  
Vol 2 ◽  
Author(s):  
J. Allègre ◽  
P. Lefebvre ◽  
J. Camassel ◽  
B. Beaumont ◽  
Pierre Gibart
Keyword(s):  
Layer Thickness ◽  
Buffer Layers ◽  
Rate Equations ◽  
Time Resolved ◽  
Versus Layer ◽  
Level Model ◽  
Shallow Impurities ◽  
Aln Buffer ◽  
Time Resolved Photoluminescence

Time-resolved photoluminescence spectra have been recorded on three GaN epitaxial layers of thickness 2.5 μm, 7 μm and 16 μm, at various temperatures ranging from 8K to 300K. The layers were deposited by MOVPE on (0001) sapphire substrates with standard AlN buffer layers. To achieve good homogeneities, the growth was in-situ monitored by laser reflectometry. All GaN layers showed sharp excitonic peaks in cw PL and three excitonic contributions were seen by reflectivity. The recombination dynamics of excitons depends strongly upon the layer thickness. For the thinnest layer, exponential decays with τ ~ 35 ps have been measured for both XA and XB free excitons. For the thickest layer, the decay becomes biexponential with τ1 ~ 80 ps and τ2 ~ 250 ps. These values are preserved up to room temperature. By solving coupled rate equations in a four-level model, this evolution is interpreted in terms of the reduction of density of both shallow impurities and deep traps, versus layer thickness, roughly following a L−1 law.

PL and FTIR Absorption Study on Porous Silicon in Situ During Etching, in Oxygen Ambient, and After Chemical Oxidation

1992 ◽  
Vol 283 ◽  
Author(s):  
G. Mauckner ◽  
T. Walter ◽  
T. Baier ◽  
K. Thonke ◽  
R. Sauer Abteilung
Keyword(s):  
Defect Density ◽  
Chemical Oxidation ◽  
Laser Exposure ◽  
Porous Si ◽  
Radiative Recombination Rate ◽  
Time Resolved ◽  
Radiative Defect ◽  
Recombination Lifetimes ◽  
Time Resolved Photoluminescence

ABSTRACTSteady state and time-resolved photoluminescence (PL) and Fourier-transform infrared (FTIR) spectroscopy have been performed in situ during etching, on “as prepared” porous Si in air under laser exposure and on chemically oxidized porous Si. We suppose that PLdegradation of “as prepared” porous Si is caused by creating non-radiative defect centers during photooxidation. Chemically oxidized porous Si shows increased PL intensity and longer recombination lifetimes as compared to non-oxidized samples. We conclude, that an oxide layer with low defect density on the inner surface of chemically oxidized porous Si reduces the non-radiative recombination rate.

In-Situ crystallization of nano-wires and dots by electron irradiation in a field-emission TEM/STEM

1995 ◽  
Vol 53 ◽  
pp. 242-243
Author(s):  
M. Libera
Keyword(s):  
Field Emission ◽  
Electron Irradiation ◽  
Atomic Displacement ◽  
High Energy ◽  
Ex Situ ◽  
Time Resolved ◽  
First Results ◽  
Carbon Coated ◽  
Power Radiation

Specimen damage and heating by high-energy electron irradiation can be exploited to affect local specimen composition/temperature to drive phase transformations. Field-emission (FEG) sources are especially prone to inducing damage/heating, because their high brightness provides focused ~1nm FWHM/1.0nA probes. The physics of beam heating and damage are reviewed by Reimer (1,2). Heating is related to energy-loss mechanisms broadly summarized by the Bethe formula for stopping power. Radiation damage can cause atomic displacement, ionization, and bond scission. Displacement increases the point-defect concentration. Composition changes occur when displacements eject atoms from the specimen. This paper outlines first results using focused-probe irradiation in a Philips CM20 FEG TEM/STEM to locally crystallize an amorphous 80nm Ge48Te52 film. Ex-situ annealing leads to spherulitic crystallites. The crystallization kinetics have been studied by time-resolved reflectivity (3) and in-situ hot-stage optical microscopy (4). In-situ TEM annealing was done with a single-tilt hot stage. Films were floated from carbon-coated mica onto Cu grids. In-situ annealing under a parallel (low dose) beam leads to crystallization much like the ex-situ studies except that the crystallite morphology is highly anisotropic due to non-uniform film heating (5).

In situ time-resolved HEROS study of Pt electronic structure during regenerative H2-O2 cycles

2015 ◽  
Vol 2 (1) ◽  
Author(s):  
Jacinto Sá
Keyword(s):  
Electronic Structure ◽  
Energy Resolution ◽  
Time Resolution ◽  
Electronic States ◽  
Reduction Process ◽  
High Energy ◽  
Single Step ◽  
High Energy Resolution ◽  
Time Resolved

AbstractWe report an in situ time-resolved high-energy resolution off-resonant spectroscopy (HEROS) study with unprecedented 100 ms time resolution revealing the unoccupied electronic states of platinum during regenerative oxidation and reduction cycles. The study depicted a slowed oxidation step in comparison with reduction. The oxidation cycle is composed of two characteristic stages, namely adsorption of dissociated oxygen followed by partial oxidation of Pt subsurface. Besides improved temporal resolution of the experiment, the detected reduction process of platinum showed no intermediate features and was completed in a single step within a few seconds.

Study of 3-MeV electron irradiation damage in amorphous silicon with TRMC

2004 ◽  
Vol 808 ◽  
Author(s):  
A. Klaver ◽  
J.M. Warman ◽  
M.P. de Haas ◽  
J.W. Metselaar ◽  
R.A.C.M.M. van Swaaij
Keyword(s):  
Simple Model ◽  
Amorphous Silicon ◽  
Electron Irradiation ◽  
Probe Beam ◽  
Electron Accelerator ◽  
Defect Density ◽  
Irradiation Damage ◽  
Microwave Conductivity ◽  
Time Resolved

ABSTRACTThe effects of 3-MeV electron irradiation on a-Si:H have been studied using Time-Resolved Microwave Conductivity (TRMC). A Van der Graaff electron accelerator is used to generate the probe-beam pulses for the TRMC experiment as well as for the in-situ irradiation of the samples for the degradation of the material. Using several probe-beam pulse doses, TRMC transients were obtained on samples that have been subjected to various radiation fluences. These transients were later analyzed using a simple model based on the Shockley-Read-Hall capture and emission processes. Using these simulations we deduce a relationship between the radiation fluence and the defect density in the material.

scholarly journals Time resolved photoluminescence studies of degradation in GaInP/GaAs/Ge solar cells after 1MeV electron irradiation

AIP Advances ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 085213 ◽  
Author(s):  
Hongliang Guo ◽  
Yiyong Wu ◽  
Jingdong Xiao ◽  
Bin Guo ◽  
Qiang Sun ◽  
...  
Keyword(s):  
Solar Cells ◽  
Electron Irradiation ◽  
Time Resolved ◽  
Photoluminescence Studies ◽  
Time Resolved Photoluminescence

In Situ Diagnostics of Nanomaterial Synthesis by Laser Ablation: Time-resolved Photoluminescence Spectra and Imaging of Gas-Suspended Nanoparticles Deposited for Thin Films

1998 ◽  
Vol 536 ◽  
Author(s):  
D. B. Geohegan ◽  
A. A. Puretzky ◽  
A. Meldrum ◽  
G. Duscher ◽  
S. J. Pennycook
Keyword(s):  
Thin Films ◽  
Laser Ablation ◽  
Rayleigh Scattering ◽  
Silicon Nanoparticles ◽  
Time Resolved ◽  
Nanomaterial Synthesis ◽  
Z Contrast ◽  
Time Resolved Photoluminescence ◽  
Suspended Nanoparticles

AbstractThe dynamics of nanoparticle formation by laser ablation into background gases are revealed by gated-ICCD photography of photoluminescence (PL) and Rayleigh-scattering (RS) from gas-suspended nanoparticles. These techniques, along with gated-spectroscopy of PL from isolated, gassuspended nanoparticles, permit fundamental investigations of nanomaterial growth, doping, and luminescence properties prior to deposition for thin films. Using the time-resolved diagnostics, particles unambiguously formed in the gas phase were collected on TEM grids. Silicon nanoparticles, 1-10 nm in diameter, were deposited following laser ablation into 1-10 TorrAror He. Three in situ PL bands (1.8, 2.6, 3.2 eV) similar to oxidized porous silicon were measured, but with a pronounced vibronic structure. Structureless photoluminescence bands were reproduced in the films (2.1, 2.7, 3.2 eV) only after standared annealing. The ablation of metal zinc into Ar/02 is also reported for the preparation of < 10 nm diameter hexagonal zincite nanocrystals, The particles were analyzed by bright field and Z-contrast TEM and high resolution EELS.

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