School of Physics - Research Publications
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ItemP2 dimer implantation in silicon:: A molecular dynamics study(ELSEVIER SCIENCE BV, 2006-10)
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ItemRoom-temperature coherent coupling of single spins in diamond(NATURE PUBLISHING GROUP, 2006-06)
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ItemDiamond nanocrystals formed by direct implantation of fused silica with carbon(AMER INST PHYSICS, 2001-09-15)We report synthesis of diamond nanocrystals directly from carbon atoms embedded into fused silica by ion implantation followed by thermal annealing. The production of the diamond nanocrystals and other carbon phases is investigated as a function of ion dose, annealing time, and annealing environment. We observe that the diamond nanocrystals are formed only when the samples are annealed in forming gas (4% H in Ar). Transmission electron microscopy studies show that the nanocrystals range in size from 5 to 40 nm, depending on dose, and are embedded at a depth of only 140 nm below the implanted surface, whereas the original implantation depth was 1450 nm. The bonding in these nanocrystals depends strongly on cluster size, with the smaller clusters predominantly aggregating into cubic diamond structure. The larger clusters, on the other hand, consist of other forms of carbon such as i-carbon and n-diamond and tend to be more defective. This leads to a model for the formation of these clusters which is based on the size dependent stability of the hydrogen-terminated diamond phase compared to other forms of carbon. Additional studies using visible and ultraviolet Raman Spectroscopy, optical absorption, and electron energy loss spectroscopy reveal that most samples contain a mixture of sp2 and sp3 hybridized carbon phases.
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ItemEmergence and decay of turbulence in stirred atomic Bose-Einstein condensates.(American Physical Society (APS), 2005-09-30)We show that "weak" elliptical deformation of an atomic Bose-Einstein condensate rotating at close to the quadrupole instability frequency leads to turbulence with a Kolmogorov energy spectrum. The turbulent state is produced by energy transfer to condensate fragments that are ejected by the quadrupole instability. This energy transfer is driven by breaking the twofold rotational symmetry of the condensate. Subsequently, vortex-sound interactions damp the turbulent state leading to the crystallization of a vortex lattice.
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ItemControlled vortex-sound interactions in atomic Bose-Einstein condensates.(American Physical Society (APS), 2004-04-23)The low temperature dynamics of a vortex in a trapped quasi-two-dimensional Bose-Einstein condensate are studied quantitatively. Precession of an off-centered vortex in a dimple trap, embedded in a weaker harmonic trap, leads to the emission of sound in a dipolar radiation pattern. Sound emission and reabsorption can be controlled by varying the depth of the dimple. In a shallow dimple, the power emitted is proportional to the vortex acceleration-squared over the precession frequency, whereas for a deep dimple, periodic sound reabsorption stabilizes the vortex against radiation-induced decay.
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ItemKinetics of arsenic-enhanced solid phase epitaxy in silicon(AMER INST PHYSICS, 2004-04-15)The kinetics of intrinsic and arsenic-enhanced solid phase epitaxy (SPE) have been measured in buried amorphous Si (a-Si) layers in which crystallization occurs free from the rate retarding effects of hydrogen. Surface a-Si layers, where H infiltration can occur during crystallization, have also been studied. A single 1.45×1016 As/cm2 implant at 1200 keV was used to form an As concentration profile with a peak concentration of 3×1020 As/cm3 centered at 8000 Å beneath the crystal surface, allowing many different enhanced SPE rates to be examined simultaneously. The SPE rate through this profile and its intrinsic counterpart were measured using time-resolved reflectivity. The effects of hydrogen on the SPE rate can be determined by a comparison between the buried and surface a-Si layers. For the surface a-Si layers, it was found that the As-enhanced SPE rate versus depth curve is offset with respect to the concentration profile. We attribute this offset to the H infiltration in the case of the surface a-Si layer.