M. Behar

Distributions of light ions and foil destruction after irradiation of organic polymers

It is found that light ions (6Li, 10B) distribute neither according to their calculated range nor to their nuclear damage distributions but according to their ionization distributions after implantation into organic polymers. Also, the profile of chemical destruction after low dose light ion implantation (typically 1012–1014 ions/cm2) into organic foils obeys the ionization distribution rather than the range or nuclear damage distributions. After annealing, or at higher implanted doses, a slight shift of the implantation or destruction profiles towards the nuclear damage distribution is found. The reason for this implantation behavior may be partly understood in terms of diffusion and subsequent recombination with the created radicals. Li and B distributions in carbon (which may be regarded as the final product of polymer destruction) show a shape which can be described by range profiles with subsequent diffusion and trapping at homogeneously distributed defects. In contrast to light ions, implanted heavy...

Range parameters study of medium-heavy ions implanted into light substrates

Abstract Carbon films were implanted with Cs, Xe, Sn, Rb, Kr, Ga and Cu and boron films with Bi, Pb, Au, Yb, Cs and Rb ions in an energy range of 10 to 300 keV. Range parameters were determined using the Rutherford backscattering technique. The experimental results are 20–40% higher than the theoretical predictions by Ziegler, Biersack and Littmark. Good agreement is achieved only when inelastic effects are included in the nuclear stopping regime. These features are also observed when previously published range parameter data for medium-heavy ions implanted into Be films are analyzed.

Ion beam synthesis of cubic FeSi2

Cubic FeSi2 precipitates were synthesized in Si (100) by room‐temperature Fe ion implantation followed by Si 500 keV ion beam induced epitaxial crystallization at 320 °C. High resolution electron microscopy and Rutherford backscattering/channeling techniques show that the cubic precipitates occur in both aligned (A) and twinned (B) types with a lattice parameter very similar to that of the Si (100) matrix.

Synthesis of GaN by N ion implantation in GaAs (001)

Both the hexagonal and cubic GaN phases were synthesized in GaAs (001) by 50 keV N ion implantation at 380 °C and subsequent furnace annealing at 850–950 °C for 10 min–2 h. For a fluence of 1.5×1017 cm−2, transmission electron microscopy revealed that cubic GaN epitaxially crystallizes as precipitates in the GaAs matrix. A cubic‐to‐hexagonal GaN phase transition was observed for extended thermal anneals. By increasing the N fluence to 3×1017 cm−2, a continuous buried layer of randomly oriented hexagonal‐GaN nanocrystals was produced.

Ion beam induced carbon clusters in polymers

Abstract It is thought that the formation of carbon precipitates (or carbon enriched zones) during ion irradiation of polymers is responsible for the observed optical blackening as well as for the onset of electronic conductivity. The latter is explained as the result of an electronic hopping mechanism between the conducting carbon (enriched) zones. Rough estimations from electronic condition theory indicate typical cluster sizes of 10 to 50 nm diameter and surface-to-surface distances of 0.1 to 20 nm. The existence of these carbon precipitates in polymers has never been proven directly. Therefore, we used neutron scattering to verify them in 50 MeV boron implanted mylar foils. As neutron scattering is sensitive to essentially hydrogen atoms in the polymers, the carbon precipitates show up as hydrogen depleted zones. Indeed, neutron scattering data suggest the formation of small globular particles. Their dimensions (radius 6 to 7 nm) and mutual distance (around 13 nm) agree with previous predictions. The particle population seems to be quite homogeneous in size. The number density of these particles decreases with increasing deposited ion energy density. Simultaneously, larger objects with a sharp surface are observed. Their number density increases with increasing transferred ion energy, as judged from the increase of total surface area. We interpret these objects as clusters of the above described globular carbon precipitates.

Range profiles of implanted Bi and Au in amorphous silicon

Abstract The Rutherford backscattering technique is used to measure the depth profiles for 10 to 390 keV 209Bi and 15 to 390 keV 197Au implanted in amorphized silicon wafers. The obtained projected ranges and projected range stragglings are compared with previous data and with recent universal range-energy calculations. Whereas good agreement is found between the experimental and theoretical range predictions for Bi, the measurements for Au yield, at low energies, ranges longer than predicted. The discrepancy between measured Au and Bi ranges is ascribed to the Z1-range oscillation.

Electronic stopping power of 〈100〉 axial-channelled He ions in Si crystals

Abstract Measurements of the electronic stopping power of He2+ ions along the 〈100〉 direction in Si crystal with energies ranging between 200 keV and 4.5 MeV are presented. The Rutherford backscattering technique has been used with SIMOX samples consisting of a Si single-crystal layer on top of a buried layer of 500 nm SiO2 built into a Si 〈100〉 wafer.

Cluster coarsening and luminescence emission intensity of Ge nanoclusters in SiO2 layers

SiO2 layers 180 nm thick are implanted with 120 keV Ge+ ions at a fluence of 1.2×1016 cm−2. The distribution and coarsening evolution of Ge nanoclusters are characterized by Rutherford backscattering spectrometry and transmission electron microscopy and the results are correlated with photoluminescence measurements as a function of the annealing temperatures in the 400 °C⩽T⩽900 °C range. At 400 °C we observe a monomodal array of clusters characterized by a mean diameter 〈φ〉=2.2 nm which increases to 〈φ〉=5.6 nm at 900 °C. This coarsening evolution occurs concomitantly with a small change of the total cluster–matrix interface area and an increase of the Ge content trapped in observable nanoclusters. However, at 900 °C a significant fraction of up to about 20% of the Ge content still remains distributed in the matrix around the nanoparticles. The results are discussed in terms of possible atomic mechanisms involved in the coarsening behavior that lead to the formation of the oxygen deficiency luminescence ce...

Non-regular depth profiles of light ions implanted into organic polymer films

Abstract 3 He and 10 B implantation profiles in several polymers are examined by means of a NRA technique with thermal neutrons. 200 keV 10 B ions were implanted into different kinds of polymers. In all the cases, it is found that the resulting depth profiles have a nonregular shape. A fraction which depends on the target material distributes along a tail directed towards the surface. Due to the nonregularity of the depth profiles, we present only the most probable ranges and the full width half maxima of the distributions. These results are compared with the Ziegler, Biersack and Littmark prediction. On the other hand, 3 He implanted into Mylar is found to be mobile at room temperature, as after ten days no trace of the implanted material is found in the substrate.

Range profiles of 10 to 390 keV ions (29 ≦ Z1 ≦ 83) implanted into amorphous silicon☆

Abstract Our recent range profile measurements for a series of elements (29 ≦ Z1 ≦ 83) implanted from 10 to 390 keV in amorphous silicon are compared with the Biersack-Ziegler (BZ) calculations. While the theoretical predictions are in good agreement with the experimental ranges at implantation energies larger than 70 keV, the results for several elements at lower energies are strongly underestimated by the calculations. These differences are ascribed to the Z1-range oscillation effect. In the present work we perform range calculations simulating a decrease of the elastic interaction at low energies. This approach is phenomenologically related to modifications of the charge distribution during the collisions. The results obtained show a better agreement between the calculations and the great majority of the existing low energy experimental ranges in silicon substrates.