Local step-flow dynamics in thin film growth with desorption

Desorption of deposited species plays a role in determining the evolution of surface morphology during crystal growth when the desorption time constant is short compared to the time to diffuse to a defect site, step edge or kink. However, experiments to directly test the predictions of these effects are lacking. Novel techniques such as \emph{in-situ} coherent X-ray scattering can provide significant new information. Herein we present X-ray Photon Correlation Spectroscopy (XPCS) measurements during diindenoperylene (DIP) vapor deposition on thermally oxidized silicon surfaces. DIP forms a nearly complete two-dimensional first layer over the range of temperatures studied (40 - 120 $^{\circ}$C), followed by mounded growth during subsequent deposition. Local step flow within mounds was observed, and we find that there was a terrace-length-dependent behavior of the step edge dynamics. This led to unstable growth with rapid roughening ($\beta>0.5$) and deviation from a symmetric error-function-like height profile. At high temperatures, the grooves between the mounds tend to close up leading to nearly flat polycrystalline films. Numerical analysis based on a 1 + 1 dimensional model suggests that terrace-length dependent desorption of deposited ad-molecules is an essential cause of the step dynamics, and it influences the morphology evolution.Comment: 21 pages, 9 figures, and one tabl

Homoepitaxial growth of SrTiO3 by Pulsed Laser Deposition: energetic vs thermal growth

The role of energetic processes in homoepitaxial growth of SrTiO3 (STO) by Pulsed Laser Deposition (PLD) was studied via Real-Time X-ray scattering. Two process were developed, an energetic process and a thermal process. Both processes utilized a background gas of 2 mTorr of O2. The thermal process had an additional 300 mTorr of Helium to act as a buffer gas. Langmuir probe measurements verified the energies of the two process to be between 50-100 electron-volts (eV) and 0.02-0.05 eV respectively. Specular X-ray reflectivity, sensitive to inter-layer transport of material, was the same for both processes. Diffuse scattering, sensitive to the in-plane transport of material, was markedly different. In both processes, lobes of scattering as a function of Qr arise, reaching a maximum intensity at each half layer of growth. The energetic process has a broader peak at a higher Qr. Both data sets collapse to a common curve upon scaling the axes, suggesting a similar island distribution on different length scales