Tiny imperfections cause big changes in nanopatterned materials

While modelling random sequential adsorption (RSA), Clarkson University researchers made an interesting discovery: even the tiniest imperfection in the position of the lattice landing can have dramatic impacts on the density of the permanently formed deposit.

This finding could have significant impact for constructing nanopatterned materials in electronic, magnetic or optical devices.

With the advent of nanotechnology, not only can we deposit tiny particles, but the target surfaces or substrates can be tailored to control the resulting structures.

The pattern of the target surface must be precise, in order to achieve high perfection and high coverage in the pattern of deposited particles. To examine this, the researchers compared RSA on three types of surfaces: a continuous (non-patterned) lattice, a precisely patterned surface and a surface with small imprecisions in the pattern. The researchers found that very small imprecisions can make RSA proceed as if the surface is continuous. The consequence is that the deposition process is less efficient and the ultimate coverage is much lower.

In the process of RSA, a continuous surface is covered slowly with a larger fraction of the area remaining uncovered than a precisely lattice-patterned surface. In the past when surfaces on which microscopic particles were deposited were naturally flat (continuous) or had a lattice structure, the importance of small imprecisions had not been recognised.

The researchers explained their analysis in the Journal of Chemical Physics, from AIP Publishing.

Vladimir Privman at Clarkson University has been involved in studying aspects of such systems since 2007; however, this study, conducted with graduate student Han Yan, was the first to consider the imprecision in the surface lattice-site localisation, rather than in the particle size uniformity.

Initially suggested by computer modelling, their results were later derived by analytical model considerations, which are novel for the research field of RSA.

“The greatest difficulty was to understand and accept the initial numerical finding that suggested results that seemed counterintuitive,” Privman explained. “Once accepted, we could actually confirm the initial findings, as well as generalise and systematise them by analytical arguments.”

Pre-patterned substrates have been studied for applications ranging from electronics to optics, to sensors, and to directed crystal growth. The reported results suggest that efforts at precise fixed positioning and object-sizing in nanomanufacturing might be counterproductive if done as part of forming structures by RSA, under practically irreversible conditions. A certain degree of relaxation, to allow objects to ‘wiggle their way’ into matching positions, may actually be more effective in improving both the density and rate of formation of the desired dense structures, Privman said.

This work has implications that the team is preparing to explore.

“Now that we have realised that not only particle non-uniformity, but also substrate-pattern imprecision have substantial effects on the dynamics of the RSA process, we will begin studying various systems and patterning geometries, expanding beyond our original model,” Privman said.

The article is available here.