Elena Stolyarova

High-resolution scanning tunneling microscopy imaging of mesoscopic graphene sheets on an insulating surface

We present scanning tunneling microscopy (STM) images of single-layer graphene crystals examined under ultrahigh vacuum conditions. The samples, with lateral dimensions on the micrometer scale, were prepared on a silicon dioxide surface by direct exfoliation of crystalline graphite. The single-layer films were identified by using Raman spectroscopy. Topographic images of single-layer samples display the honeycomb structure expected for the full hexagonal symmetry of an isolated graphene monolayer. The absence of observable defects in the STM images is indicative of the high quality of these films. Crystals composed of a few layers of graphene also were examined. They exhibited dramatically different STM topography, displaying the reduced threefold symmetry characteristic of the surface of bulk graphite.

Proton and ion beams generated with picosecond CO2 laser pulses

I-TW, 6-ps, circularly polarized CO(2) laser pulses focused onto thin Al foils are used to drive ion acceleration. The spectra of ions and protons generated in the direction normal to the rear surface, detected with a compact magnet spectrometer with CR39, reveals a broad proton high-energy peak at similar to 1 MeV. This observation conforms to the theoretical predictions that circularly polarized laser pulses are less efficient than linearly polarized pulses in driving ion acceleration via the Target Normal Sheath Acceleration (TNSA) mechanism. Instead, there is evidence that the circularly polarized laser may provide direct ponderomotive acceleration of ions and protons. We report also the first application of the BNL proton source in nano-science. Irradiation of graphite and graphene films produced local defects and membranes for variety of applications.

Proton and Ion Acceleration by an Ultrafast TW CO 2 Laser: Proof-of-Principle Experiments

Results on proton acceleration by an ultrashort TW CO2 laser interacting with Al foils show proton energy spectra substantially different from those obtained with solid-state lasers, due to the lasers different wavelength and polarization.