Persistent Oscillations of X-ray Speckles: Pt (001) Step Flow

TL;DR

This study uses coherent x-ray scattering to observe persistent oscillations in speckle patterns from Pt (001) surfaces, revealing step-flow dynamics at high temperatures and demonstrating a new method for real-time surface monitoring.

Contribution

It introduces a novel application of speckle autocorrelation to detect and analyze surface step-flow oscillations in real-time using coherent x-ray scattering.

Findings

Oscillatory speckle autocorrelations observed at high temperatures.

Surface dynamics due to step-flow motion identified.

Method demonstrates potential for real-time surface evolution monitoring.

Abstract

We have performed coherent x-ray scattering experiments on the hexagonally reconstructed Pt (001) surface to study the temperature-dependent surface dynamics. By correlating speckle patterns collected at the (001) anti-Bragg position we are able to measure surface dynamics when the averaged incoherent x-ray scattering appears static. In the temperature range above the rotational epitaxy transition and below the roughening transition (1750 K - 1830 K), we have observed well-defined oscillatory autocorrelations of speckles that persist for tens of minutes, in addition to the expected thermal decorrelation. The observed oscillations indicate surface dynamics due to "step-flow" motion. This is shown with a simple model in which the phase of the scattered x-rays from the steps within the illumination area is retained in the coherent x-ray scattering. This demonstrates a possibility that x-ray speckles can be used to monitor the real-space real-time evolution of surfaces in addition to the traditional decorrelation measurements.