Ion implantation of graphene-toward IC compatible technologies.

Doping of graphene via low energy ion implantation could open possibilities for fabrication of nanometer-scale patterned graphene-based devices as well as for graphene functionalization compatible with large-scale integrated semiconductor technology. Using advanced electron microscopy/spectroscopy methods, we show for the first time directly that graphene can be doped with B and N via ion implantation and that the retention is in good agreement with predictions from calculation-based literature values. Atomic resolution high-angle dark field imaging (HAADF) combined with single-atom electron energy loss (EEL) spectroscopy reveals that for sufficiently low implantation energies ions are predominantly substitutionally incorporated into the graphene lattice with a very small fraction residing in defect-related sites.

Blocking of indium incorporation by antimony in III-V-Sb nanostructures.

The addition of antimony to III-V nanostructures is expected to give greater freedom in bandgap engineering for device applications. One of the main challenges to overcome is the effect of indium and antimony surface segregation. Using several very high resolution analysis techniques we clearly demonstrate blocking of indium incorporation by antimony. Furthermore, indium incorporation resumes when the antimony concentration drops below a critical level. This leads to major differences between nominal and actual structures.

Vacancy clusters, dislocations and brown colouration in diamond.

Following on from the idea that clusters of vacancies are the origin of the featureless absorption and brown colouration in natural diamond, dislocations are shown to exhibit sub-bandgap absorption also. The vacancy cluster idea has arisen from theoretical predictions of π-bonded chains reconstructing the cluster surfaces and has been confirmed by energy loss studies. In contrast, bandgap states at dislocations are observed in brown and colourless diamonds alike, giving rise to weak absorption, which resembles that theoretically predicted from shuffle dislocation segments. This, however, would not account for the degrees of brownness in the diamonds, but it suggests that if such shuffle segments exist, vacancies must have been present and moved to dislocations to create these configurations in the first place. The question arises, what happens to the vast number of vacancy clusters upon high pressure high temperature (HPHT) annealing, which renders the diamonds colourless. Our observations on natural brown diamonds after HPHT treatment suggest that vacancy clusters, trapped in the strain fields of dislocations, grow in size accompanied by a decrease in their numbers; this leads to much reduced optical absorption.

Elemental mapping using the Ga 3d and In 4d transitions in the epsilon2 absorption spectra derived from EELS.

It is proposed that by using the valence-band states in electron energy loss spectroscopy, high-spatial resolution maps of quantitative elemental composition may be acquired with high acquisition rates. Further, it is shown that by using the epsilon(2) spectrum instead of single scattering data, the noise in the observed transitions and associated maps is significantly reduced. The epsilon(2) spectra are derived through a Kramers-Kronig transformation from electron energy loss spectra obtained in a scanning transmission electron microscope. Using transitions that occur in the epsilon(2) absorption spectrum (<40eV), quantitative elemental maps for III-V device structures have been produced. An example is provided using the Ga 3d transition to map a GaInNAs/GaAs laser structure. Weaker transitions such as In 4d have also been used to verify the Ga elemental distribution.