Strain-controlled growth of nanowires within thin-film cracks

Abstract

There is continued interest in finding quicker and simpler ways to fabricate nanowires, even though research groups have been investigating possibilities for the past decade. There are two reasons for this interest: first, nanowires have unusual properties-for example, they show quantum-mechanical confinement effects, they have a very high surface-to-volume ratio, enabling them to be used as sensors, and they have the ability to connect to individual molecules. Second, no simple method has yet been found to fabricate nanowires over large areas in arbitrary material combinations. Here we describe an approach to the generation of well-defined nanowire network structures on almost any solid material, up to macroscopic sample sizes. We form the nanowires within cracks in a thin film. Such cracks have a number of properties that make them attractive as templates for nanowire formation: they are straight, scalable down to nanometre size, and can be aligned (by using microstructure to give crack alignment via strain). We demonstrate the production of nanowires with diameter <16 nm, both singly and as networks; we have also produced aligned patterns of nanowires, and nanowires with individual contacts.

Cracking-assisted photolithography for mixed-scale patterning and nanofluidic applications

“…However, the nanolithography and/or the combination of the two multi-scale lithography techniques show weaknesses in throughput and cost caused by the direct-writing-based nanofabrication processes and scale-up or scale-down lithography processes in series 2,3 . Cracks are considered material failures and have never been welcome in micro/ nanofabrication processes, but active manipulation of cracking phenomena made it possible to produce various micro and nanoscale patterns, showing remarkable potential for a novel unconventional patterning technique [4][5][6][7][8][9][10][11][12][13][14] . However, the crackingbased micro and nanopatterns show several weaknesses and limitations: only one-dimensional (1D) or limited 2D patterns because of the direction of applied stresses [4][5][6][7][8][9] and the crystallinity of a substrate 11 , respectively; the insufficient controllability of the geometric dimension (for example, width, depth and length) of cracks/patterns caused by the incapability of manipulating the stress strength [6][7][8][10][11][12][13][14] ; low success rates in patterning because of unwanted crack formation 4,9,11 ; low throughput in fabrication because of sequential and multiple fabrication processes 11,14 ; incompatibility with other microfabrication processes [5][6][7]10 and low reproducibility by micromoulding and/or soft lithography [10]…”

Quasi-one-dimensional thermal breakage

“…Yet for p = 0 both Z n /p 2 and Ω n /p 2 are still well posed in (8) and (11). The assumpton p = 0 simply means that breakages are forbidden, p being the Boltzmann factor for a rupture.…”

“…Such systems can now be manipulated at a molecular level and engineered to a desired specification using patterned substrates as templates [1][2][3][7][8][9][10]. As a result, there is a growing theoretical appreciation for subtle phenomena activated or suppressed by thermal fluctuations in individual systems: e.g.…”

“…As a result, there is a growing theoretical appreciation for subtle phenomena activated or suppressed by thermal fluctuations in individual systems: e.g. bubble opening and DNA denaturation under external load, nanoisland to nano-wire transitions in Stranski-Krastanov growth, local narrowing in nano-wires, local collapse in nano-tubes, selection of growth direction in vapor deposition, or nano-dot to nano-ring transition in droplet epitaxy [2,3,7,8,[11][12][13][14][15][16][17][18][19][20].…”

“…These methods imply horizontal growth into patterned nano-channels obtained by strain-controlled cracking of the substrate [7,8], or other means [3].…”