J.L. Debrun

Direct evidence for the nonassignment to oxygen of the main electron trap in GaAs

From the direct comparison between quantitative atomic oxygen concentration and electronic deep‐energy‐level concentration in GaAs, it is concluded that oxygen is not involved, either directly or as part of a complex defect, in the origin of the main electron trap at EC−0.75 eV.

Investigation of laser sputtering of iron at low fluence using resonance ionization mass spectrometry

Emission of neutral and ionized Fe atoms induced by N2 laser irradiation (λ=337 nm) of iron targets was investigated for laser fluences ranging from the sputtering threshold (a few tens mJ/cm2) up to 320 mJ/cm2. The unique sensitivity of resonance ionization mass spectrometry permitted to identify the laser‐sputtered neutral particles, to study their velocity distribution and excitation state, and to measure the laser‐sputtering yield at a very low emission level (100 Fe atoms removed per laser shot). In this soft ablation mode, it appears that the sputtered atoms carry direct information on the primary mechanisms involved in the laser sputtering of an iron surface. The present study corroborates a thermal process in which the laser beam acts as a pulsed heat source. Energy characteristics of the emitted neutral atoms reflect rather well the thermal state of the surface, the atom temperature increasing from the ambient at threshold to melting and boiling temperatures for growing laser energies.

FT-ICR with laser ablation and AMS combined with X-ray detection, applied to the measurement of long-lived radionuclides from fission or activation: preliminary results

Abstract The measurement of long-lived radionuclides from fission or activation is difficult when isobars are present. Preliminary results are reported here on two methods that can solve the problem in some instances. The first one, FT-ICR with laser ablation, has a very high mass resolution; the second one, AMS combined with X-ray detection, discriminates isobars using characteristic projectile X-rays (“inverse PIXE”).

Irradiation of elements from Z = 44 to Z = 82 with 10-mev protons and application to activation analysis

Abstract The sensitivities for the determination of 19 elements from Z = 44 to Z = 82, by means of 10-MeV proton activation, have been calculated from experimentally measured yields for 51 radioisotopes obtained mainly via (p,n) reactions. For an irradiation of 1 h at a beam current of 1 μA, the sensitivities established experimentally are about 0.02–2 p.p.m. for Ru, Pd, Ag, Cd, Sn, Sb, Te and I, 0.5–100 p.p.m. for In, W, Re, Ir, Pt, Au, Hg, Tl and Pb, and 15–900 p.p m- for Rh and Ba. Experimental results for the non-destructive analysis of these 19 elements in Al, Ag, Au, Co, Dy, Ho, Ir, Nb, Pr, Rh, Si, Ta and Tb, are presented.

Application of AMS and inverse PIXE to the study of radioactive waste management problems

Abstract Some long-lived radionuclides ( 59 Ni, 93 Zr, 93 Mo, 94 Nb, 99 Tc, 107 Pd, 151 Sm) must be measured at levels −3 Bq/g in radioactive wastes. No method is able to achieve this at the moment, except accelerator mass spectrometry (AMS) in the case of 59 Ni, using high energies. In this paper, we show that AMS at low energy (with a 3 MV tandem) is in principle able to measure the radionuclides of interest with the required sensitivity. To overcome the isobaric interferences, which are the limiting factor in AMS, characteristic projectile X-rays are measured (“inverse PIXE”).

Thermodynamic and Experimental Study of the Chemical Vapor Codeposition in the Silicon‐Boron‐Carbon System at 1400 K

The results of a thermodynamic and experimental study of the codeposition of three elements, silicon, boron, and carbon, by a classical chemical vapor deposition technique in a hot-wall reactor are compared. The initial gaseous mixture consisted of methyltrichlorosilane, boron trichloride, and hydrogen. By the thermodynamic approach, the nonstoichiometry of boron carbide was described from B[sub 4]C to B[sub 10]C, and a comparison can be made between accurate thermodynamic calculation and experimental compositions measured at a given position on the substrate. The thickness and composition uniformity was also studied as a function of the inlet gas composition. The codeposits were first obtained on graphite, but the final purpose was to extend the process to composite materials. When fixed conditions of temperature (T = 1400 K) and total pressure (P = 0.395 atm) were employed, the influence of the total gaseous flux was shown to be great, especially in a hot-wall reactor. The total flux can change the deposition results because of either the depletion phenomenon or some departure from equilibrium.

Photoionization cross sections in resonance ionization mass spectrometry of sputtered metal atoms: Applications to material analysis

(1+1) resonant multiphoton ionization of several metal atoms was investigated in the 285–301‐nm‐wavelength range. Fe, Mg, Cr, Ti, and Ni free atoms were produced using Ar+‐ion sputtering of different metal samples in ultrahigh‐vacuum conditions. The photoionization yields, measured as function of the laser fluence, exhibit saturation or near saturation at the highest laser energy density available in the experiment (100 mJ/cm2). From these measurements the ionization cross sections of the intermediate excited states are deduced, assuming saturation of the excitation step. In this way values ranging between 0.7 and 4×10−17 cm2 are obtained. One can take advantage of the relatively large cross sections to detect these sputtered metal atoms by resonance ionization mass spectroscopy with great sensitivity. Some examples are given, demonstrating, on a single‐laser‐shot basis, the real analyses of Mg and Ti atoms in materials at the ppm level.

Resonant ionization of sputtered neutral atoms for trace analysis in high purity materials

Abstract Resonant ionization of sputtered neutral atoms, followed by mass spectrometry, was studied in view of analytical applications. The experimental setup includes a duoplasmatron ion gun and a quadrupole mass spectrometer, operating in a UHV chamber. Photoionization is obtained via two Nd-YAG pumped dye lasers. Matrix effects were measured for metallic alloys, and detection limits determined for the analysis of Mg, Ti, Cr, Fe, Ni and Cu (in Al or Fe) and of P in silicon.

SEARCH FOR THE INFLUENCE OF CHEMICAL EFFECT ON THE STOPPING POWER: THE CASE OF OXIDES

Abstract Influence of possible chemical effects on the stopping power of BeO, Al 2 O 3 , TiO 2 , ZnO, Nb 2 O 5 and Ta 2 O 5 was studied between 0.5 and 0.7 MeV amu −1 for BeO and at ≅2.5 MeV amu −1 for the other oxides. The method of study was the “average stopping power method”. No chemical effect is detected at 2.5 MeV amu −1 . For BeO, energy dependant deviations from Bragg-Kleemans rule are observed.

Quantitative analysis of oxygen in thin epitaxial layers of GaAs by SIMS

Abstract This paper reports the quantitative analysis of oxygen in GaAs epitaxial layers by a CAMECA IMS 300 secondary ion mass spectrometer. It is shown that the residual oxygen pressure of the apparatus (∼1×10 −7 torr) does not affect the analysis. On the basis of standard samples analysed by activation with tritons [ 16 O(T,n) 18 F] the limit of detection of oxygen in GaAs is found to be ∼0.01 ppm.at. Some results on oxygen depth profiling in epitaxial layers are presented.