L.J. Mitchell

Formation of Carbon‐based Nanocrystal using Low Energy Carbon Ion Implantation into Silica

Carbon‐based nanocrystals, formed in silica by low‐energy carbon implantation and subsequent thermal annealing, have been previously reported, but ambiguities as to the equilibrium morphology and its relationship to the source of photo luminescence. In our study, silica samples were implanted with 2.0×1017 atoms/cm2 C− ions at energies of 8.5 keV, 40 keV and 70 keV. Samples were annealed for 15, 30, 60, 120, 240 minutes at 1100° C in a forming gas (4%H2+96%Ar). Rutherford backscattering (RBS), particle induced x‐ray emission (PIXE), and photoluminescence (PL) were used to characterize the nanocrystals formed by these conditions. The resulting photoluminescence analysis indicated that the size distribution of the nanocrystals could be tailored to yield a broad spectral output between 2.0–2.8 eV by controlling the formation parameters. Also a few notable factors, such as liberation of oxygen in the silica during implantation, as well as uptake of ambient oxygen in the annealing furnace, will be shown to pla...

Depth Profiles of Mg, Si, and Zn Implants in GaN by Trace Element Accelerator Mass Spectrometry

GaN is one of the most promising electronic materials for applications requiring high-power, high frequencies, or high-temperatures as well as opto-electronics in the blue to ultraviolet spectral region. We have recently measured depth profiles of Mg, Si, and Zn implants in GaN substrates by the TEAMS particle counting method for both matrix and trace elements, using a gas ionization chamber. Trace Element Accelerator Mass Spectrometry (TEAMS) is a combination of Secondary Ion Mass Spectrometry (SIMS) and Accelerator Mass Spectrometry (AMS) to measure trace elements at ppb levels. Negative ions from a SIMS like source are injected into a tandem accelerator. Molecular interferences inherent with the SIMS method are eliminated in the TEAMS method. Negative ion currents are extremely low with GaN as neither gallium nor nitrogen readily forms negative ions making the depth profile measurements more difficult. The energies of the measured ions are in the range of 4-8 MeV. A careful selection of mass/charge ratios of the detected ions combined with energy-loss behavior of the ions in the ionization chamber eliminated molecular interferences.