The physics of zero-gradient stepped surfaces

On normal flat surfaces of a single crystal, there are a large number of steps which could be a single atomic layer or multilayers in height. These steps are usually found in groups of the same sign, i.e., stepping down (-sign) in one area, but stepping up (+ sign) in a neighbouring area. This way, the macroscopic flatness of the surface is maintained. In order to study how steps interact with one another, a commonly adopted method is to make vicinal surfaces, which are surfaces created by cutting a crystal with a miscut angle in relation to a principal crystal direction. Vicinal surfaces consist of a high density of steps where the distance between neighbouring steps depends on the miscut angle. All steps on a vicinal surface follows the same sign, and thus step-step interaction involves steps of the same type.In order to study how different types of steps interact, one needs to place different types of steps close together, ideally with nanometre separations. Such kind of surfaces do not exist in nature because of steps of opposite signs tend to annihilate under thermal equilibrium to give rise to an atomically flat surface. However, zero-gradient stepped surfaces (ZGSS), where a - step always follows a + step, can be produced using surface atomic manipulation in combination with self-organisation. The proposed research follows our recent discovery of ZGSS on the (111) surface of gold where closely spaced, finger-like stripes of a few nanometres wide are created. Manufacturing at the nanometre scale inevitably involves the fabrication of structures that are not at their thermal equilibrium, structures that are formed under kinetic constraints and are meta-stable. A detailed understanding of fabricated nanostructures such as the ZGSS is of great importance en route to the realisation of many nanoscale devices. Our preliminary findings from the (111) surface of gold unveiled a number of interesting features of the very first ZGSS. This serves as a promising starting point for a systematic investigation of complex step structures on metal surfaces and of the effect of those steps in nanostructure fabrication. We therefore propose to initiate a research programme on the structure and function of zero-gradient stepped surfaces.