Uniaxial structural flexibility of an anisotropic Br adlayer structure on Au(100) electrodes revealed by video-rate STM

Abstract The motion of surface species within a dense layer of coadsorbates, a common case in real-world interface systems, relies on structural flexibility of the coadsorbate phase. Here, we study by video-rate scanning tunneling microscopy the lateral deformability of the pseudo-hexagonal $$c(\sqrt{2}\times 2\sqrt{2})R4{5}^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>c</mml:mi> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:msqrt> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msqrt> <mml:mo>×</mml:mo> <mml:mn>2</mml:mn> <mml:msqrt> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msqrt> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> <mml:mi>R</mml:mi> <mml:mn>4</mml:mn> <mml:msup> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>∘</mml:mo> </mml:mrow> </mml:msup> </mml:math> -Br adlayer on Au(100). It is shown that the structural anisotropy of this adlayer phase allows strongly dynamic, uniaxial distortions via antiphase shifting of Br adsorbate rows along the [010] direction. The observed structural flexibility can be explained by rapid one-dimensional diffusion of fractional vacancies in the Br adlayer. This is supported by density functional theory calculations, which find low diffusion barriers for this process, and allows the adlayer adapting in a highly dynamic way to embedded surface species.