The properties of artificially grown thin films are often strongly a ected by the dynamic relationships between surface growth processes and subsurface structure. Coherent mixing of X-ray signals promises to provide an approach to better understand such processes. Here, we demonstrate the continuously variable mixing of surface and bulk scattering signals during realtime studies of sputter deposition of a-Si and a-WSi2 films by controlling the X-ray penetration and escape depths in coherent grazing-incidence small-angle X-ray scattering. Under conditions where the X-ray signal comes from both the growth surface and the thin film bulk, oscillations in temporal correlations arise from coherent interference between scattering from stationary bulk features and from the advancing surface. We also observe evidence that elongated bulk features propagate upwards at the same velocity as the surface. Furthermore, a highly surface-sensitive mode is demonstrated that can access the surface dynamics independently of the subsurface structure.A key objective for understanding surface dynamics during thin film growth is the ability to monitor nanometre-scale surface fluctuation dynamics in real time 1-3 . These fluctuations of roughness and density occur on timescales that rarely exceed a few seconds, and take place in environments that are inaccessible to most high spatial resolution probes. For example, scanning probe microscopy is widely used to study interfacial reactivity in non-vacuum environments 4 , but is limited by its inability to probe surfaces in real time during deposition; electron microscopy is mainly limited to high-vacuum environments and low magnetic fields 5,6 . X-rays have the potential to overcome these challenges owing to their highly penetrating nature and sensitivity to nanometrescale features. Observation of subsurface structures in real time during film growth appears to be even more challenging, and has rarely been attempted 7 . Bulk signals are sometimes observed as unwanted background in grazing-incidence surface X-ray scattering experiments, but there have been few attempts to quantitatively understand the features responsible for such signals 8,9 .The interaction of surfaces with nanometre-scale buried defects and the formation of bulk defects at a growing surface are integral to many industrial processes. For example, misfit dislocations nucleate at free surfaces and buried interfaces in strained-layer epitaxial growth of layers for photonic devices 10 ; motion and ordering of oxygen vacancies in complex oxide materials for ferroelectric memory depend on the surface conditions during growth 11-13 ; and voids in electrochemically deposited layers used for interconnects in electronic circuits are introduced by surface processes during deposition 14 .The use of X-ray scattering techniques to probe in situ realtime processes has largely been restricted to well-ordered crystalline structures and to statistical averages of disorder, owing to limitations in the spectral brightness of X-ray sources. A fu...

Detailed quantitative measurement of surface dynamics during thin film growth is a major experimental challenge. Here X--ray Photon Correlation Spectroscopy with coherent hard X--rays is used in a Grazing--Incidence Small--Angle X--ray Scattering (i.e. Co--GISAXS) geometry as a new tool to investigate nanoscale surface dynamics during sputter deposition of a--Si and a--WSi2 thin films. For both films, kinetic roughening during surface growth reaches a dynamic steady state at late times in which the intensity autocorrelation function g2(q,t) becomes stationary. The g2(q,t) functions exhibit compressed exponential behavior at all wavenumbers studied.The overall dynamics are complex, but the most surface sensitive sections of the structure factor and correlation time exhibit power law behaviors consistent with dynamical scaling.

The authors have investigated the early stages of indium island formation and growth by vapor phase deposition on room temperature sapphire using real-time grazing incidence small angle x-ray scattering (GISAXS), followed by ex-situ atomic force microscopy and scanning electron microscopy. The results are consistent with the formation and coalescence of hemispherical islands, as described by Family and Meakin. Monte Carlo simulations of systems of coalescing islands were used to supplement and quantify the results of GISAXS, and a good agreement is seen between the data and the simulations.

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We used the Coherent Grazing Incidence Small Angle X-Ray Scattering (Co-GISAXS) technique to study the average kinetics and nanoscale dynamics during early-stage a-WSi2 sputter deposition. The kinetic and dynamic properties are examined as a function of pressure, which is known to be a critical factor in determining final surface roughness. Surface growth kinetics and dynamics are characterized by time parameters extracted from the height-height structure factor and correlation functions. The roughness at a given length scale reaches a maximum before relaxing down to a steady state. The lateral length scale dependence and pressure dependence are then compared among measured kinetics and dynamics time parameters. Surfaces grown at lower pressures are smoother, leading to longer correlation times. The time to reach a dynamic steady state and a kinetic steady state show contrasting pressure dependence. A dynamic steady state is reached earlier than the kinetic steady state at high pressure. A more random deposition direction and lower kinetic energy at higher pressures can explain these phenomena, along with the hypothesis that larger nanoclusters form in vapor before arriving at the surface. A continuum model is applied to simulate the overall behavior with mixed success.