P.F.P. Fichtner

Effect of helium ion implantation and annealing on the relaxation behavior of pseudomorphic Si1−xGex buffer layers on Si (100) substrates

The influence of He implantation and annealing on the relaxation of Si0.7Ge0.3 layers on Si (100) substrates is investigated. Proper choice of the implantation energy results in a narrow defect band ≈100 nm underneath the substrate/epilayer interface. During annealing at 700–1000 °C, He-filled bubbles are created, which act as sources for misfit dislocations. Efficient annihilation of the threading dislocations is theoretically predicted, if a certain He bubble density with respect to the buffer layer thickness is maintained. The variation of the implantation dose and the annealing conditions changes density and size of spherical He bubbles, resulting in characteristic differences of the dislocation structure. Si1−xGex layers with Ge fractions up to 30 at. % relax the initial strain by 70% at an implantation dose of 2×1016 cm−2 and an annealing temperature as low as 850 °C. Simultaneously, a low threading dislocation density of 107 cm−2 is achieved. The strain relaxation mechanism in the presence of He fi...

OVERPRESSURIZED BUBBLES VERSUS VOIDS FORMED IN HELIUM IMPLANTED AND ANNEALED SILICON

The formation of helium induced cavities in silicon is studied as a function of implant energy (10 and 40 keV) and dose (1×1015, 1×1016, and 5×1016 cm−2). Specimens are analyzed after annealing (800 °C, 10 min) by transmission electron microscopy (TEM) and elastic recoil detection (ERD). Cavity nucleation and growth phenomena are discussed in terms of three different regimes depending on the implanted He content. For the low (1×1015 cm−2) and high (5×1016 cm−2) doses our results are consistent with the information in the literature. However, at the medium dose (1×1016 cm−2), contrary to the gas release calculations which predict the formation of empty cavities, ERD analysis shows that a measurable fraction of the implanted He is still present in the annealed samples. In this case TEM analyses reveal that the cavities are surrounded by a strong strain field contrast and dislocation loops are generated. The results obtained are discussed on the basis of an alternative nucleation and growth behavior that all...

Ruthenium dioxide nanoparticles in ionic liquids: synthesis, characterization and catalytic properties in hydrogenation of olefins and arenes

A reacao de NaBH 4 com RuCl 3 dissolvido no liquido ionico 1-n-butil-3-metilimidazolio hexafluorfosfato (BMI.PF 6 ) e um metodo simples e reprodutivel para a sintese de nanoparticulas de RuO 2 estaveis com distribuicao estreita e diâmetro da particula entre 2-3 nm. As nanoparticulas de RuO 2 foram caracterizadas por XRD, XPS, EDS e TEM. Estas nanoparticulas mostraram alta atividade catalitica tanto na catalise heterogenea quanto na hidrogenacao bifasica liquido-liquido de olefinas e arenos sob condicoes moderadas de reacao. Experimentos de envenenamento com Hg(0) e CS 2 , e analises de XRD e TEM de particulas isoladas apos a catalise indicaram a formacao de nanoparticulas de Ru(0). As nanoparticulas podem ser reutilizadas em condicoes de catalise heterogenea ate 10 vezes na hidrogenacao de 1-hexeno rendendo um numero total de ciclos cataliticos de 175.000 para atomos de Ru expostos. The reaction of NaBH 4 with RuCl 3 dissolved in 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMI.PF 6 ) ionic liquid is a simple and reproducible method for the synthesis of stable RuO 2 nanoparticles with a narrow size distribution within 2-3 nm. RuO 2 nanoparticles were characterized by XRD, XPS, EDS and TEM. These nanoparticles showed high catalytic activity either in the solventless or liquid-liquid biphasic hydrogenation of olefins and arenes under mild reaction conditions. Hg(0) and CS 2 poisoning experiments and XRD and TEM analysis of particles isolated after catalysis indicated the formation of Ru(0) nanoparticles. The nanoparticles could be re-used in solventless conditions up to 10 times in the hydrogenation of 1-hexene yielding a total turnover number for exposed Ru atoms of 175,000.

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.

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.

Role of dipolar interactions in a system of Ni nanoparticles studied by magnetic susceptibility measurements

The role of dipolar interactions among Ni nanoparticles (NP) embedded in an amorphous SiO2/C matrix with different concentrations has been studied performing ac magnetic susceptibility Chi_ac measurements. For very diluted samples, with Ni concentrations < 4 wt % Ni or very weak dipolar interactions, the data are well described by the Neel-Arrhenius law. Increasing Ni concentration to values up to 12.8 wt % Ni results in changes in the Neel-Arrhenius behavior, the dipolar interactions become important, and need to be considered to describe the magnetic response of the NPs system. We have found no evidence of a spin-glasslike behavior in our Ni NP systems even when dipolar interactions are clearly present.

Nanoporous SiO2/Si thin layers produced by ion track etching: Dependence on the ion energy and criterion for etchability

Vitreous SiO2 thin films thermally grown onto Si wafers were bombarded by Au ions with energies from 0.005 to 11.1 MeV/u and by ions at constant velocity (0.1 MeV/u A197u, T130e, A75s, S32, and F19). Subsequent chemical etching produced conical holes in the films with apertures from a few tens to ∼150 nm. The diameter and the cone angle of the holes were determined as a function of energy loss of the ions. Preferential track etching requires a critical electronic stopping power Seth∼2 keV/nm, independent of the value of the nuclear stopping. However, homogeneous etching, characterized by small cone opening angles and narrow distributions of pore sizes and associated with a continuous trail of critical damage, is only reached for Se>4 keV/nm. The evolution of the etched-track dimensions as a function of specific energy (or electronic stopping force) can be described by the inelastic thermal spike model, assuming that the etchable track results from the quenching of a zone which contains sufficient energy f...

Implanted boron depth profiles in the az111 photoresist

The isotope 10B has been implanted into the photoresist AZ111 in the 30–150 keV energy range. The corresponding depth profiles have been analyzed using the 10B(n,α)7Li reaction. At 60 keV, the profile changes from a regular shape to one with an additional tail directed towards the surface. Despite the nonregular shape of the ion distributions, it is possible to extract the characteristic range parameters such as projected range Rp, most probable range R, and full width at half‐maximum. Good agreement is found between the experimental results and the calculations by Ziegler, Biersack, and Littmark (ZBL). It is also shown that the tail distribution follows closely the ZBL calculated ionization profiles. A tentative explanation of this behavior is given.