School of Physics - Research Publications

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    Diamond nanocrystals formed by direct implantation of fused silica with carbon
    Orwa, JO ; Prawer, S ; Jamieson, DN ; Peng, JL ; McCallum, JC ; Nugent, KW ; Li, YJ ; Bursill, LA ; Withrow, SP (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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    Kinetics of arsenic-enhanced solid phase epitaxy in silicon
    Johnson, BC ; McCallum, JC (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.
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    Donor activation and damage in Si-SiO2 from low-dose, low-energy ion implantation studied via electrical transport in MOSFETs
    McCamey, DR ; Francis, M ; McCallum, JC ; Hamilton, R ; Greentree, AD ; Clark, RG (IOP PUBLISHING LTD, 2005-05)
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    Defect formation due to the crystallization of deep amorphous volumes formed in silicon by mega electron volt (MeV) ion implantation
    Liu, ACY ; McCallum, JC ; Wong-Leung, J (MATERIALS RESEARCH SOCIETY, 2001-11)
    Solid-phase epitaxy was examined in deep amorphous volumes formed in silicon wafers by multi-energy self-implantation through a mask. Crystallization was effected at elevated temperatures with the amorphous volume being transformed at both lateral and vertical interfaces. Sample topology was mapped using an atomic force microscope. Details of the process were clarified with both plan-view and cross-sectional transmission electron microscopy analyses. Crystallization of the amorphous volumes resulted in the incorporation of a surprisingly large number of dislocations. These arose from a variety of sources. Some of the secondary structures were identified to occur uniquely from the crystallization of volumes in this particular geometry.