Small-angle X-ray scattering from GaN nanowires on Si(111): facet truncation rods, facet roughness, and Porod's law

TL;DR

This study investigates small-angle X-ray scattering from GaN nanowires on Si(111), revealing how facet orientation and roughness influence scattering behavior, deviating from classical Porod's law, with experimental and simulation insights.

Contribution

It provides a combined experimental and Monte Carlo simulation analysis of how facet orientation and roughness affect X-ray scattering in GaN nanowires.

Findings

Scattering intensity varies with facet orientation and is maximized along facet normals.

Large wave vector scattering deviates from Porod's law, indicating complex surface effects.

Surface roughness significantly reduces scattering intensity at high wave vectors.

Abstract

Small-angle X-ray scattering from GaN nanowires grown on Si(111) is studied experimentally and modeled by means of Monte Carlo simulations. It is shown that the scattering intensity at large wave vectors does not follow Porod's law $I(q)\propto q^{-4}$. The intensity depends on the orientation of the side facets with respect to the incident X-ray beam. It is maximum when the scattering vector is directed along a facet normal, as a reminiscence of the surface truncation rod scattering. At large wave vectors $q$, the scattering intensity is found to be decreased by surface roughness. A root mean square roughness of 0.9~nm, which is the height of just 3--4 atomic steps per micron long facet, already gives rise to a strong intensity reduction.