Spiral growth, two-dimensional nucleation, and the Ehrlich-Schwoebel effect

TL;DR

This paper explores how step edge barriers influence spiral growth and mound formation in crystal growth, revealing that such barriers cause spiral hillocks to resemble wedding cakes, confirmed through experiments on Pt(111).

Contribution

It demonstrates that step edge barriers lead to unique spiral morphologies that mimic two-dimensional nucleation structures, expanding understanding of crystal growth dynamics.

Findings

Step edge barriers cause spiral hillocks to develop steep, wedding cake-like profiles.

Experimental verification on Pt(111) confirms coexistence of spiral and nucleation growth forms.

Unconventional spiral shapes are linked to interlayer transport barriers.

Abstract

Frank's prediction of the spiral growth mode in 1949 defined a pivotal moment in the history of crystal growth. In recent decades the topic has received less attention, and instead we have seen a resurrection of two-dimensional nucleation theory in the context of growth experiments on defect-free homoepitaxial thin films. In particular, the key role of interlayer transport controlled by step edge barriers of the Ehrlich-Schwoebel type in shaping the morphology of multilayer films has been increasingly recognized. After a brief review of the classical theory, this paper reports on a recent study of spiral growth in the presence of step edge barriers. Our key observation is that step edge barriers lead to unconventionally shaped spiral hillocks that display the same characteristic ever-steepening height profiles as wedding cakes formed during growth by two-dimensional nucleation. This prediction was verified experimentally by inducing screw dislocations through ion bombardment of the Pt(111) surface, thus creating a homoepitaxial growth system on which spiral hillocks and wedding cakes coexist.