Transmission Fourier-transform infrared (FTIR) spectroscopy has been used to monitor laser-induced degradation of the photoluminescence (PL) intensity of porous Si. It is observed that the release of hydrogen from silicon hydride surface species coincides with a decrease in the PL intensity and oxidation of the porous Si. The as-anodized PL characteristics can be recovered, with a slight blue shift, by a brief immersion in hydrofluoric acid.

Laser-induced degradation of the photoluminescence intensity of porous silicon

Short, intense laser pulses can thermally desorb hydrogen and other gases from the near surface (∼1 μm) of solids. This can be used, with some advantages, to study the trapping mechanisms, whether physical or chemical, the diffusion, and the surface recombination of these gases. By assuming a laser pulse with a Gaussian time profile, these successive steps are modeled with a finite difference code by using realistic temperature‐ and concentration‐dependent material parameters. We show explicit results for the magnitude of the desorption puff as a function of the laser energy and for the depth profiles of the remaining gas under various assumptions for the detrapping mechanism, the diffusion coefficient, and the surface recombination coefficient. The results demonstrate that in spite of the poorer control on temperature, compared to isochronal or ramp anneals, the rate‐limiting process can be identified and the activation energies determined.

Modeling of pulsed-laser-induced gas detrapping, chemical reactions, diffusion, and desorption

Laser desorption study of deuterium implanted in beryllium

Effect of lithium wall conditioning on deuterium in-vessel retention in the TdeV tokamak

The behavior of H‐ion‐implanted c‐Si was investigated at temperatures up to the melting point, on the 10−8 s time scale, using pulsed‐laser annealing in conjunction with quantitative analysis of the released gas. Laser reflectivity, scanning electron microscopy, and surface profilometry were also used to characterize implantation and annealing effects. Computational kinetic modeling of H release as a function of laser energy is applied to the interpretation of the data. The desorption of H implanted at 1 or 2 keV takes place at ≥1000 K, without extensive surface deformation, and can be fitted by detrapping with an activation energy (≊2 eV) that slowly decreases with the H/Si ratio in the range 4%–27%; contrary to expectation, no limitation by diffusion is observed. Implanted at 5 or 10 keV and H/Si≥20%, H is released at ≥550 K by blister rupture. In spite of the differences between the results for low and high implantation energies, a unified picture emerges, involving a layer with a high‐temperature H mo...

Desorption and other effects of pulsed‐laser annealing of hydrogen‐implanted silicon

An apparatus and an experimental procedure, mainly designed to investigate the thermodynamics and kinetics of hydrogen evolution in materials, are described. Employing a 30 ns ruby laser pulse as a heat source, this method probes H behavior at higher temperatures and on a much shorter time scale than classic thermal desorption. Precise calibration techniques for the laser fluence and the desorption yield have been developed. The absolute calibration agrees well with a measurement of the H content by elastic recoil detection. Particular attention has been paid to lateral uniformization of the laser intensity, to allow valid one‐dimensional modeling of laser heating and H evolution, and extraction of the activation energies and kinetic factors. As an example, a cursory study of intrinsic H in Be is presented. The method is also applicable to other volatile dopants.

A method of pulsed‐laser desorption of hydrogen

We have conducted an experimental and theoretical study of the desorption, by 25 ns ruby laser pulses, of hydrogen implanted at ∼25 at. % concentration in c‐Si. The evolution of the hydrogen depth profile was monitored by elastic recoil detection. The implantation or laser‐induced damage was observed by optical microscopy. The heat and hydrogen transport were modeled with a finite‐difference code. Desorption sets in at a very sharp threshold of (0.50±0.05) J/cm2 as a function of the laser energy fluence, corresponding to a peak temperature of ∼1000 K, and to minimal laser damage. The rate limiting process is detrapping with an activation energy of 1.2–1.5 eV, and an effective diffusion energy ≤0.1 eV.

B. Terreault

Papers

A method of pulsed‐laser desorption of hydrogen

Laser desorption for hydrogen quantitative analysis: Study by a nuclear method of the laser‐induced hydrogen mobility