J.R. Kaschny

A theoretical investigation of defects in a boron nitride monolayer

We have investigated, using first-principles calculations, the energetic stability and structural properties of antisites, vacancies and substitutional carbon defects in a boron nitride monolayer. We have found that the incorporation of a carbon atom substituting for one boron atom, in an N-rich growth condition, or a nitrogen atom, in a B-rich medium, lowers the formation energy, as compared to antisites and vacancy defects. We also verify that defects, inducing an excess of nitrogen or boron, such as N(B) and B(N), are more stable in its reverse atmosphere, i.e. N(B) is more stable in a B-rich growth medium, while B(N) is more stable in a N-rich condition. In addition we have found that the formation energy of a C(N), in a N-rich medium, and C(B) in a B-rich medium, present formation energies comparable to those of the vacancies, V(N) and V(B), respectively.

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...

Stability and electronic structure of BxNyCz nanotubes

We apply a first-principles method, based on the density functional theory, to calculate the structural stability and electronic properties of BxNyCz nanotubes. We follow the evolution of the electronic and structural properties as a function of the composition, atomic structure and nanotube diameter. The results indicate that nanotubes present a large variety of electronic properties, showing a remarkable dependence on these parameters. The formation energy decreases with the tube diameter, D, and has a strong dependence on the tube stoichiometry. Additionally, the results show that the strain energy of the tubes, relative to the corresponding unstrained sheet material, varies as 1/Dn. For BC2N the classical strain law (n = 2) is clearly obtained. Nevertheless, in the case of BCN, the exact value of n is a matter of discussion.

Nucleation and growth of platelet bubble structures in He implanted silicon

He a ions were implanted into (1 0 0) Si at energies from 30 to 120 keV and fluences from 5 · 10 15 to 1 · 10 16 cm ˇ2 . After implantation, pieces of these samples were subjected to rapid thermal annealing for 600 s at temperatures ranging from 300∞C to 700∞C. The samples were analyzed by Transmission Electron Microscopy (TEM) and by Rutherford Backscattering and channeling spectrometry (RBS/C). The TEM observations were related to the RBS/C measurements and the results discussed in terms of a nucleation model to explain the formation of overpressurized bubbles in He implanted and annealed silicon. ” 1998 Published by Elsevier Science B.V.

Cavities in helium implanted and annealed silicon characterized by spectroscopic ellipsometry

The formation of helium induced cavities in silicon during short-time annealing is analyzed by spectroscopic ellipsometry. Specimens implanted with 40 keV He+ ions to a dose of 5×1016 cm−2 are heat treated at 800 °C for times of 1–1200 s by rapid thermal annealing. Spectroscopic ellipsometry is employed to obtain quantitative information on the cavity volume depth profiles. A newly developed formula is used to model the optical multilayer depth profiles. The cavity volume is found to increase during annealing for about 300 s and to decrease for longer annealing times. Over this characteristic time a marked change in the He loss occurs, which has been reported only recently. Swelling of the helium implanted and annealed silicon is analyzed using an atomic force microscope. Step heights are consistent with the cavity volume per unit area obtained from spectroscopic ellipsometry data analysis. The number density of cavities after annealing for 600 s is calculated to be ≈1.16±0.27×1017 cm−3 and is found to be...

Spatial distribution of defects in ion-implanted and annealed Si: The RP/2 effect

Abstract Gettering of metal impurities in ion-implanted Si occurs midway between the surface and the projected ion range, RP, after annealing at temperatures in the range of 700–1000°C and vanishes at higher temperatures. This phenomenon, called the RP/2 effect, seems to be a common feature of ion-implanted and annealed Si. The gettering ability of the damage at RP/2 is commensurate with or may exceed that of the damage at RP. The defects around RP/2 acting as gettering sites have not yet been identified by other analysis techniques. They are formed after ion implantation in the process of defect evolution during annealing and, probably, consist of small complexes of intrinsic defects (vacancies or/and self-interstitials).

Very large sputtering yields of ion irradiated C60 films

Abstract We show that ion irradiation of thin fullerite (C 60 ) films produces simultaneously sputtering and compactation. In our experiments both effects are separated, and we measure a very large sputtering yield Y = 1.5 × 10 4 C/ion in C 60 irradiated with 25 keV Xe + ions at low fluence between 5 × 10 11 and 10 12 Xe cm −2 . Y decreases to the amorphous carbon sputtering yield of 5 C/ion at 10 15 Xe cm −2 .

Prevention of impurity gettering in the RP/2 region of ion-implanted silicon by defect engineering

Abstract Si + ion implantation into Si under inclined incidence angle was applied to demonstrate that Cu gettering in the region around half of the projected ion range, R P /2, of ion-implanted Si is controlled by the same mechanism working for excess vacancy generation. The obtained results directly relate the appearance of the R P /2 gettering effect to the radiation-induced excess vacancies. Excess vacancies were found to be the source of the dominating gettering sites of Cu at R P /2. Moreover, it is shown that the undesired impurity trapping at R P /2 can be prevented by means of additional Si + implantation into the vacancy-rich region of ion-implanted Si to balance the excess of vacancies. The parameters in order to remove Cu gettering at R P /2 are determined for the additional Si + implantation. If the threshold fluence necessary to remove the Cu gettering at R P /2 is exceeded, the excess vacancies are overcompensated and new interstitial-type dislocation loops form.

Changes in the photoresist inhibitor distribution after ion irradiation and thermal treatment

Abstract Ion irradiation and thermal treatment leads to strong changes in the physical and chemical properties of photoresist materials. Among others modifications it is observed by Rutherford Backscattering that molecules containing sulfur, that is inhibitor molecules and their fragments, tend to segregate close to the surface region. This behavior can be explained by assuming a model where the diffusion process of these molecules is followed by: (a) trapping at radiation-induced defects in the near surface region and (b) chemical reaction with the implanted ion and/or indiffusing oxygen.

On the redistribution of6Li+ ions implanted into polypropylene foils

Abstract6Li+ (150 keV) was implanted into thin polypropylene foils at fluences of 1 x 1013 to 1 x 1014 cm−2. Subsequent neutron depth profiling measurements of the Li distributions revealed considerable deviations from the expected ballistic range profiles. This Li redistribution was simulated by a numerical computer calculation. The best fit between measurements and simulations was obtained by assuming that (i) Li redistributes immediately after its ballistic slowing-down, (ii) the Li mobility is enhanced in the radiation-damaged polymer region, the local diffusion enhancement being controlled by the targets electronic damage, (iii) mobile Li is readily trapped at radiation-induced defects, their density being proportional to the targets electronic damage, (iv) these traps are saturable ones, and (v) Li migration is not restricted to the ion track region, but proceeds also through the neighboring unirradiated bulk, though with slower speed.