Generation and recovery of strain in (28)Si-implanted pseudomorphic GeSi films on Si(100)

Effects of ion implantation of 320 keV Si-28 at room temperature in pseudomorphic metastable GexSi1-x (x almost-equal-to 0.04, 0.09, 0.13) layers approximately 170 nm thick grown on Si(100) wafers were characterized by x-ray double-crystal diffractometry and MeV He-4 channeling spectrometry. The damage induced by implantation produces additional compressive strain in the GexSi1-x layers, superimposed on the intrinsic compressive strain of the heterostructures. This strain rises with the dose proportionally for doses below several times 10(14) Si-28/cm2. Furthermore, for a given dose, the strain increases with the Ge content in the layer. Upon thermal processing, the damage anneals out and the strain recovers to the value before implantation. Amorphized samples (doses of greater than 2 x 10(15) Si-28/cm2) regrow poorly

Defect production in Si(100) by 19F, 28Si, 40Ar, and 131Xe implantation at room temperature

We used x-ray double-crystal diffractometry and MeV 4He channeling spectrometry to study quantitatively the damage produced in Si(100) at room temperature by 230-keV 19F, 230-keV 28Si, 250-keV 40Ar, or 570-keV 131Xe implantation. The measured defect concentration and the perpendicular strain have the same depth profile, and both are depleted near the surface compared to the Frenkel pair concentration calculated from computer simulation. The perpendicular strain is proportional to the defect concentration with a coefficient of B~0.01 common to all implanted species. The maximum value of the perpendicular strain and of the defect concentration rises nonlinearly with the dose for all species. The damage produced by different implanted species depends on the dose in approximately the same way save for a scaling factor of the dose. In the regime of low damage, the strain and the defect concentration rise linearly with increasing dose. The slope of this rise with dose increases with the square of the Frenkel pairs produced per unit dose of incident ions, as calculated from computer simulations. This fact means that stable defects produced by room-temperature implantation in Si(100) cannot be predicted by a linear cascade model

Defects production and annealing in self-implanted Si

230-keV 28Si ions were implantated into Si(100) at room temperature with doses from 1014 to 1015/cm2. The samples were analyzed by x-ray double crystal diffractometry and 2-MeV 4He ion channeling spectrometry. The implanted layer has a parallel lattice spacing equal to that of the unimplanted substrate. The perpendicular lattice spacing is larger than that of the unimplanted substrate and is proportional to the defect concentration extracted from the channeling measurement. Both the perpendicular lattice spacing and the defect concentration increase nonlinearly with ion dose. The defect concentration initially increases slowly with dose until a critical value (~15%, at 4×1014/cm2), then rises rapidly, and finally a continuous amorphous layer forms. The initial sluggish increase of the damage is due to the considerable recombination of point defects at room temperature. The rapid growth of the defect concentration is attributed to the reduction of the threshold energy for atomic displacement in a predamaged crystal. The amorphization is envisioned as a cooperative process initiated by a spontaneous collapse of heavily damaged crystalline regions. The annealing behavior of the damaged layer reveals various stages of defect recovery, indicating that the damage consists of a hierarchy of various defect structures of vacancy and interstitial aggregates

Damage production and annealing in 28Si-implanted CoSi2/Sim(111) heterostructures

The damage in epitaxial CoSi2 films 500 nm thick grown on Si(111) produced by room-temperature implantation of 150 keV 28Si were investigated by 2-MeV 4He channeling spectrometry, double-crystal x-ray diffractometry, and electrical resistivity measurements. The damage in the films can be categorized into two types. In lightly (heavily) damaged CoSi2 the damage is in the form of point-like (extended) defects. The resistivity of lightly damaged CoSi2 films rises with the dose of implantation. Electrical defects correlate well with structural ones in lightly damaged films. The resistivity of heavily damaged films flattens off while the structural defects continue to rise with the dose, so that resistivity no longer correlates with structural defects. Upon thermal annealing, lightly damaged films can fully recover structurally and electrically, whereas heavily damaged films do so only electrically. A residual structural damage remains even after annealing at 800 °C for 60 min

Isovector spin-singlet (T=1, S=0) and isoscalar spin-triplet (T=0, S=1) pairing interactions and spin-isospin response

We review several experimental and theoretical advances that emphasise common aspects of the study of T=1 and T=0 pairing correlations in nuclei. We first discuss several empirical evidences of the special role played by the T=1 pairing interaction. In particular, we show the peculiar features of the nuclear pairing interaction in the low density regime, and possible outcomes such as the BCS-BEC crossover in nuclear matter and, in an analogous way, in loosely bound nuclei. We then move to the competition between T=1 and T=0 pairing correlations. The effect of such competition on the low-lying spectra is studied in N=Z odd-odd nuclei by using a three-body model; it is shown that the inversion of the 0+ and 1+ states near the ground state, and the strong magnetic dipole transitions between them, can be considered as a clear manifestation of strong T=0 pairing correlations in these nuclei. The effect of T=0 pairing correlations is also quite evident if one studies charge-changing transitions. The Gamow-Teller (GT) states in N=Z+2 nuclei are studied here by using self-consistent HFB+QRPA calculations in which the T=0 pairing interaction is taken into account. Strong GT states are found, near the ground state of daughter nuclei; these are compared with available experimental data from charge-exchange reactions, and such comparison can pinpoint the value of the strength of the T=0 interaction. Pair transfer reactions are eventually discussed: while two-neutron transfer has been long proposed as a tool to measure the T=1 superfluidity in the nuclear ground states, the study of deuteron transfer is still in its infancy, despite its potential interest in revealing effects coming from both T=1 and T=0 interactions.Comment: Paper submitted to Physica Scripta for inclusion in the Focus Issue entitled "Focus Issue on Nuclear Structure: Celebrating the 75 Nobel Prize" (by A. Bohr and B.R. Mottelson). arXiv admin note: text overlap with arXiv:nucl-th/0512021 by other author

Is perpendicular magnetic anisotropy essential to all-optical ultrafast spin reversal in ferromagnets?

All-optical spin reversal presents a new opportunity for spin manipulations, free of a magnetic field. Most of all-optical-spin-reversal ferromagnets are found to have a perpendicular magnetic anisotropy (PMA), but it has been unknown whether PMA is necessary for the spin reversal. Here we theoretically investigate magnetic thin films with either PMA or in-plane magnetic anisotropy (IMA). Our results show that the spin reversal in IMA systems is possible, but only with a longer laser pulse and within a narrow laser parameter region. The spin reversal does not show a strong helicity dependence where the left- and right-circularly polarized light lead to the identical results. By contrast, the spin reversal in PMA systems is robust, provided both the spin angular momentum and laser field are strong enough while the magnetic anisotropy itself is not too strong. This explains why experimentally the majority of all-optical spin-reversal samples are found to have strong PMA and why spins in Fe nanoparticles only cant out of plane. It is the laser-induced spin-orbit torque that plays a key role in the spin reversal. Surprisingly, the same spin-orbit torque results in laser-induced spin rectification in spin-mixed configuration, a prediction that can be tested experimentally. Our results clearly point out that PMA is essential to the spin reversal, though there is an opportunity for in-plane spin reversal.Comment: 20 pages, 4 figures and one tabl

SU(3) Family Gauge Symmetry and the Axion

We analyze the structure of a recently proposed effective field theory (EFT) for the generation of quark and lepton mass ratios and mixing angles, based on the spontaneous breaking of an SU(3) family gauge symmetry at a high scale F. We classify the Yukawa operators necessary to seed the masses, making use of the continuous global symmetries that they preserve. One global U(1), in addition to baryon number and electroweak hypercharge, remains unbroken after the inclusion of all operators required by standard-model-fermion phenomenology. An associated vacuum symmetry insures the vanishing of the first-family quark and charged-lepton masses in the absence of the family gauge interaction. If this U(1) symmetry is taken to be exact in the EFT, broken explicitly by only the QCD-induced anomaly, and if the breaking scale F is taken to lie in the range 10 to 9 - 10 to 12 GeV, then the associated Nambu-Goldstone boson is a potential QCD axion.Comment: References added and clarifications in Vacuum Structure sectio