  Unsteady simulations of horizontal ribbon growth of silicon were performed
that included both Marangoni and buoyancy effects. A chaotic flow was observed
dominated by strong Marangoni-driven jets emerging near the local temperature
minima on the free surface. This oscillatory flow caused the vertical position
of the leading edge of the sheet to fluctuate, resulting in corrugations on the
top surface of the ribbon. Additionally, larger amplitude and wavelength
nonuniformities appeared on the bottom of the sheet resulting in a sheet with
varying thickness. Lastly, the unsteady flow caused temporal variations in
growth rate, which when converted to distance using the pull speed, matched the
wavelengths observed on the top surface. All three of these phenomena have been
observed experimentally: The median of the surface wavelengths and amplitudes
decreased with increasing temperature sensitivity of surface tension and had
wavelengths on the same order as experiments for a sensitivity corresponding to
uncontaminated silicon. Oscillations in growth rate have been observed using
passive antimony demarcation and thickness variations have been measured after
sheet removal. These results indicate that the chaotic flow makes producing
thin uniform sheets using HRG challenging.
