Quantification of porosity and deposition rate of nanoporous films grown by oblique-angle deposition

Abstract

We propose an analytic model that accurately predicts the porosity and deposition rate of nanoporous films grown by oblique-angle deposition. The model employs a single fitting parameter and takes into account geometrical factors as well as surface diffusion. We have determined the porosity and deposition rate from the measured refractive index and thickness of SiO2 and indium tin oxide nanoporous films deposited at various incident angles. Comparison of experimental data with the model reveals excellent agreement. The theoretical model allows for the predictive control of refractive index, porosity, and deposition rate for a wide range of deposition angles and materials.

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

“…Continuum approaches, which are based on the fact that the geometrical features of the film (i.e., the nanocolumns) are much larger than the typical size of an atom [42,266,267], have been also explored. For instance, Poxson et al [228] developed an analytic model that takes into account geometrical factors as well as surface diffusion. This model accurately predicted the porosity and deposition rate of thin films using a single input parameter related to the cross-sectional area of the nanocolumns, the volume of material and the thickness of the film.…”

“…Furthermore, the competitive growth that gives rise to a tilted columnar nanostructure is directly dependent on the angle at which the vapor species arrives [228]. The connection between the value of a and the tilt angle of the columns, b, is of outmost importance to controlling the film's properties [39,41,44], and has been roughly described by means of the heuristic tangent rule [11] (Eq.…”

“…For example, the porosity of a Cu OAD thin film is qualitatively related to its deposition rate and the wetting ability of copper on a silicon substrate, in such a way that the initially formed nuclei control the posterior evolution of the thin film's microstructure and therefore also the final porosity of the film [143]. Modeling the OAD thin film microstructure and growth by Monte Carlo (MC) simulation and other numerical methods has been carried out to better understand the evolution of porosity as a function of the deposition angle [93,228], with Suzuki et al [62] deducing that evaporated OAD thin films should present a maximum surface area at an evaporation angle of 70°. Interestingly, experiments exploring different adsorptions from the liquid phase have confirmed a maximum surface adsorption capacity at this ''magic deposition angle" [63,[229][230][231].…”

Opto-electronic properties of TiO2nanohelices with embedded HC(NH2)2PbI3perovskite solar cells

“…The porosity of the three types of TiO 2 helices was therefore expected to be similar, since the porosity of the nanocolumns grown using oblique-angle deposition depended on the angle of incident vapor ux (substrate-tilt angle). 31 Such high porosity values conrmed the presence of a high density of pores, into which the perovskite could easily penetrate during the two-step dipping procedure. 32 The microstructural evolution of helical TiO 2 by thermal annealing has been described in a previous paper.…”

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.…”