Strain modification in coherent Ge and SixGe1–x epitaxial films by ion-assisted molecular beam epitaxy

We have observed large changes in Ge and SixGe1–x layer strain during concurrent molecular beam epitaxial growth and low-energy bombardment. Layers are uniformly strained, coherent with the substrate, and contain no dislocations, suggesting that misfit strain is accommodated by free volume changes associated with injection of ion bombardment induced point defects. The dependence of layer strain on ion energy, ion-atom flux ratio, and temperature is consistent with the presence of a uniform dispersion of point defects at high concentration. Implications for distinguishing ion-surface interactions from ion-bulk interactions are discussed

Self-consistent determination of the perpendicular strain profile of implanted Si by analysis of x-ray rocking curves

Results of a determination of strain perpendicular to the surface and of the damage in (100) Si single crystals irradiated by 250-keV Ar+ ions at 77 K are presented. Double-crystal x-ray diffraction and dynamical x-ray diffraction theory are used. Trial strain and damage distributions were guided by transmission electron microscope observations and Monte Carlo simulation of ion energy deposition. The perpendicular strain and damage profiles, determined after sequentially removing thin layers of Ar+-implanted Si, were shown to be self-consistent, proving the uniqueness of the deconvolution. Agreement between calculated and experimental rocking curves is obtained with strain and damage distributions which closely follow the shape of the trim simulations from the maximum damage to the end of the ion range but fall off more rapidly than the simulation curve near the surface. Comparison of the trim simulation and the strain profile of Ar+-implanted Si reveals the importance of annealing during and after implantation and the role of complex defects in the final residual strain distribution

Dynamical Properties of a Growing Surface on a Random Substrate

The dynamics of the discrete Gaussian model for the surface of a crystal deposited on a disordered substrate is investigated by Monte Carlo simulations. The mobility of the growing surface was studied as a function of a small driving force $F$ and temperature $T$. A continuous transition is found from high-temperature phase characterized by linear response to a low-temperature phase with nonlinear, temperature dependent response. In the simulated regime of driving force the numerical results are in general agreement with recent dynamic renormalization group predictions.Comment: 10 pages, latex, 3 figures, to appear in Phys. Rev. E (RC

Near-Equilibrium Dynamics of Crystalline Interfaces with Long-Range Interactions in 1+1 Dimensional Systems

The dynamics of a one-dimensional crystalline interface model with long-range interactions is investigated. In the absence of randomness, the linear response mobility decreases to zero when the temperature approaches the roughening transition from above, in contrast to a finite jump at the critical point in the Kosterlitz-Thouless (KT) transition. In the presence of substrate disorder, there exists a phase transition into a low-temperature pinning phase with a continuously varying dynamic exponent $z>1$. The expressions for the non-linear response mobility of a crystalline interface in both cases are also derived.Comment: 14 Pages, Revtex3.0, accepted to be published in Phys. Rev. E Rapid Communicatio

Toward Identifying the Unassociated Gamma-ray Source 1FGL J1311.7-3429 with X-ray and Optical Observations

We present deep optical and X-ray follow-up observations of the bright unassociated Fermi-LAT gammaray source 1FGL J1311.7-3429. The source was already known as an unidentified EGRET source (3EG J1314-3431, EGR J1314-3417), hence its nature has remained uncertain for the past two decades. For the putative counterpart, we detected a quasi-sinusoidal optical modulation of delta_m\sim2 mag with a period of ~1.5 hr in the Rc, r' and g' bands. Moreover, we found that the amplitude of the modulation and peak intensity changed by > 1 mag and 0.5 mag respectively, over our total six nights of observations from 2012 March and May. Combined with Swif t UVOT data, the optical-UV spectrum is consistent with a blackbody temperature, kT \sim1 eV, and the emission volume radius Rbb\sim 1.5x10^4 km. In contrast, deep Suzaku observations conducted in 2009 and 2011 revealed strong X-ray flares with a lightcurve characterized with a power spectrum density of P(f) propto f^(-2) but the folded X-ray light curves suggest an orbital modulation also in X-rays. Together with the non-detection of a radio counterpart, and significant curved spectrum and non-detection of variability in gamma-rays, the source may be the second radio-quiet gamma-ray emitting milli-second pulsar candidate after 1FGL J2339.7-0531, although the origin of flaring X-ray and optical variability remains an open question.Comment: 8 pages, 10 figures, to appear in the Astrophysical Journal (ApJ

Influence of substrate temperature on lattice strain field and phase transition in MeV oxygen ion implanted GaAs crystals

A detailed study of the influence of substrate temperature on the radiation-induced lattice strain field and crystalline-to-amorphous (c-a) phase transition in MeV oxygen ion implanted GaAs crystals has been made using channeling Rutherford backscattering spectroscopy, secondary ion mass spectrometry, and the x-ray rocking curve technique. A comparison has been made between the cases of room temperature (RT) and low temperature (LT) (about 100 K) implantation. A strong in situ dynamic annealing process is found in RT implantation at a moderate beam current, resulting in a uniform positive strain field in the implanted layer. LT implantation introduces a freeze-in effect which impedes the recombination and diffusion of initial radiation-created lattice damage and defects, and in turn drives more efficiently the c-a transition as well as strain saturation and relaxation. The results are interpreted with a spike damage model in which the defect production process is described in terms of the competition between defect generation by nuclear spikes and defects diffusion and recombination stimulated by electronic spikes. It is also suggested that the excess population of vacancies and their complexes is responsible for lattice spacing expansion in ion-implanted GaAs crystals