Indium tin oxide nanowhisker morphology control by vapour–liquid–solid glancing angle deposition

Abstract

A new growth technique for indium tin oxide nanowhiskers with increased control over feature size and spacing is reported. The technique is based on a unique combination of self-catalysed vapour-liquid-solid (VLS) growth and glancing angle deposition (GLAD). This VLS-GLAD technique provides enhanced control over nanowhisker morphology as the effect of typical VLS growth parameters (e.g. flux rate, temperature) is amplified at large deposition angles characteristic of GLAD. Spatial modulation of the collimated growth flux controls trunk width, number and orientation of branches, and overall nanowhisker density. Here we report the influence of growth conditions (including deposition angle, flux rate, nominal pitch and substrate temperature) on nanowhisker morphology, with specific focus on the effect of large deposition angles. Sheet resistance and transmission of the films were measured to characterize their performance as transparent conductive oxides. Hybrid nanostructured films grown in this study include high surface area nanowhiskers protruding from a conductive film, ideal for transparent conductive electrode applications.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

“…5.1(A)-(C)), (ii) nanostructures with a tapered nanocolumn profile over a critical length obtained by deposition with a carrier nitrogen flux (Fig. 5.1(D)-(H)), and (iii) nanowhiskers and hierarchical, multi-branched tree-shaped nanostructures obtained by sequential application of VLS-OAD [133,134,137,331] (see Section 3.1 and Fig. 5.2 for a more detailed description of the singular branched nanostructures created using this method).…”

“…For example, by keeping the substrate at typical VLS growth temperatures, crystalline Ge nanowhiskers with a nanostructure determined by the angle of material flux have been obtained [132]. Fancy ITO (indium tin oxide) 2D-branched nanostructures have also been fabricated by combining VLS and OAD while azimuthally rotating the substrate [133][134][135][136][137]. In this case, liquid indium-tin alloy droplets act as both the catalyst and the initial nuclei for branch formation.…”

Nanocolumnar growth of thin films deposited at oblique angles: Beyond the tangent rule

“…[1][2][3] This anisotropy combined with their high open porosity [4][5][6][7] are essential for other applications such as Bragg reflectors with tunable optical response, 8 templates for nanocomposite films, [9][10][11][12] broad band antireflection coatings, 13,14 optical microresonators, 15 light emitting diodes, 16 photovoltaic cells, 17 advanced plasmon photocatalysis, 18,19 microfluidic sensors, 20 transparent conductive electrodes 21 and many others. In this technique, a given material is sublimated in a vacuum reactor, either thermally or assisted by an electron beam, yielding vapor species that follow straight trajectories in a "line of sight" configuration with respect to the substrate, and giving rise to thin films with well-defined tilted nanocolumnar structures.…”

Tuning the reactivity of nanostructured indium tin oxide electrodes toward chemisorption

“…This latter technique allows for preparation of nanostructured ITO films which shape, porosity and thickness that can be easily controlled and tuned during the deposition step. 3,7,16 To characterize the surface reactivity of these nanostructured ITO electrodes towards organophosphorous compounds,…”