Gozde Ozaydin

Real-time x-ray studies of Mo-seeded Si nanodot formation during ion bombardment

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.

Effects of Mo seeding on the formation of Si nanodots during low-energy ion bombardment

Effects of seed atoms on the formation of nanodots on silicon surfaces during normal incidence Ar+ ion bombardment at room temperature are studied with real-time grazing-incidence small-angle x-ray scattering (GISAXS), real-time wafer curvature stress measurements and ex situ atomic force microscopy. Although Si surfaces remain smooth during bombardment at room temperature, when a small amount of Mo atoms is supplied to the surface during ion bombardment, the development of correlated structures (“dots”) is observed. Stress measurements show that initially a compressive stress develops during bombardment, likely due to amorphization of the surface and insertion of argon. However, seeding causes a larger tensile stress to develop with further bombardment, possibly due to the formation of higher density regions around the Mo seed atoms on the surface. Detailed fits of the GISAXS evolution during nanostructure growth show that the instability is larger than predicted by the Bradley-Harper theory of curvature...

Wavelength tunability of ion-bombardment-induced ripples on sapphire

A study of ripple formation on sapphire surfaces by 300-2000 eV Ar{sup +} ion bombardment is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering and ex-situ atomic force microscopy is performed in order to study the wavelength of ripples formed on sapphire (0001) surfaces. We find that the wavelength can be varied over a remarkably wide range -- nearly two orders of magnitude -- by changing the ion incidence angle. Within the linear theory regime, the ion induced viscous flow smoothing mechanism explains the general trends of the ripple wavelength at low temperature and incidence angles larger than 30{sup o}. In this model, relaxation is confined to a few nm thick damaged surface layer. The behavior at high temperature suggests relaxation by surface diffusion. However, strong smoothing is inferred from the observed ripple wavelength near normal incidence, which is not consistent with either surface diffusion or viscous flow relaxation.

Transition behavior of surface morphology evolution of Si(100) during low-energy normal-incidence Ar+ ion bombardment

The temperature dependence of the surface morphology evolution during 1000 eV Ar+ ion bombardment of Si(100) surfaces at normal incidence is studied in real time. At room temperature the surface is amorphized by the ion bombardment but remains smooth. Calculations suggest this may be due to ion impact induced lateral mass redistribution. However, at the fluxes used here, surface roughening occurs above 400 °C, and in the range of 400 °C to 500 °C a transition region from amorphous to crystalline surface is observed. Above 500 °C, the surface remains crystalline and the growing corrugations exhibit dynamic scaling with power law growth in amplitude and characteristic length scale. This behavior is characteristic of instabilities driven by surface diffusion processes.

Real-time x-ray studies of gallium adsorption and desorption

Real-time grazing-incidence small-angle x-ray scattering has been employed to study the adsorption and desorption of Ga on c-plane sapphire and Ga-polar GaN surfaces. Formation of self-organized liquid Ga nanodroplets has been observed on sapphire during Ga exposure from an effusion cell at high flux. Subsequent to the Ga deposition, the nanodroplets were nitridated in situ by a nitrogen plasma source, which converted the droplets into GaN nanodots. In addition to the droplet studies, at lower Ga flux, the adsorption and desorption of Ga have been studied in the predroplet regime. For identical processing conditions, significantly different Ga adsorption∕desorption rates were observed on sapphire and GaN surfaces.