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The formation of self-organized Si nanostructures induced by Mo seeding during normal incidence Ar+ ion bombardment at room temperature is reported. Silicon surfaces without Mo seeding develop only power-law roughness during 1000eV ion bombardment at normal incidence, in agreement with scaling theory expectations of surface roughening. However, supplying Mo atoms to the surface during ion bombardment seeds the development of highly correlated, nanoscale structures (“dots”) that are typically 3nm high with a spatial wavelength of approximately 30nm. With time, these saturate and further surface roughening is dominated by the growth of long-wavelength corrugations.

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A free relativistic electron in an electromagnetic field is a pure case of a light-matter interaction. In the laboratory environment, this interaction can be realized by colliding laser pulses with electron beams produced from particle accelerators. The process of single photon absorption and reemission by the electron, so-called linear Thomson scattering, results in radiation that is Doppler shifted into the x-ray and gamma-ray regions. At elevated laser intensity, nonlinear effects should come into play when the transverse motion of the electrons induced by the laser beam is relativistic. In the present experiment, we achieved this condition and characterized the second harmonic of Thomson x-ray scattering using the counterpropagation of a 60 MeV electron beam and a subterawatt CO2 laser beam.