The oblique angle configuration has emerged as an invaluable tool for the deposition of nanostructured thin films. This review develops an up to date description of its principles, including the atomistic mechanisms governing film growth and nanostructuration possibilities, as well as a comprehensive description of the applications benefiting from its incorporation in actual devices. In contrast with other reviews on the subject, the electron beam assisted evaporation technique is analyzed along with other methods operating at oblique angles, including, among others, magnetron sputtering and pulsed laser or ion beam-assisted deposition techniques. To account for the existing differences between deposition in vacuum or in the presence of a plasma, mechanistic simulations are critically revised, discussing well-established paradigms such as the tangent or cosine rules, and proposing new models that explain the growth of tilted porous nanostructures. In the second part, we present an extensive description of applications wherein oblique-angle-deposited thin films are of relevance. From there, we proceed by considering the requirements of a large number of functional devices in which these films are currently being utilized (e.g., solar cells, Li batteries, electrochromic glasses, biomaterials, sensors, etc.), and subsequently describe how and why these nanostructured materials meet with these needs.Peer reviewe

Transparent thin film electrodes made of vertically aligned nanocolumns of TiO₂ with well-controlled oblique angles were grown by physical vapor deposition at glancing incidence (PVD-GLAD). For an electrode thickness of 500 nm, we report a 40% variation on solar cell efficiency (from 0.6% to 1.04%) when the deposition angle was modified between 60° and 85°. Transparent thicker films with higher surface area deposited at the optimal angle of 70° were grown with a zigzag morphology which confers high mechanical strength to the thin films. Using this topology, the application of an electrode thickness of 3 µm in a DSC resulted in a power conversion efficiency of 2.78% maintaining electrode transparency.

$\mathrm{Si}{\mathrm{O}}_x$ thin films with different stoichiometries from $\mathrm{Si}{\mathrm{O}}_{1.3}$ to $\mathrm{Si}{\mathrm{O}}_{1.8}$ have been prepared by evaporation of silicon monoxide in vacuum or under well-controlled partial pressures of oxygen $(P<{10}^{-6}\text{Torr})$ . These thin films have been characterized by x-ray photoemission and x-ray-absorption spectroscopies, this latter at the Si $K$ and $L_{2,3}$ absorption edges. It has been found that the films prepared in vacuum consists of a mixture of ${\mathrm{Si}}^{3+}$ and ${\mathrm{Si}}^{+}$ species that progressively convert into ${\mathrm{Si}}^{4+}$ as the partial pressure of oxygen during preparation increases. From this spectroscopic analysis, information has been gained about the energy distribution of both the full and empty states of, respectively, the valence and conduction bands of $\mathrm{Si}{\mathrm{O}}_x$ as a function of the $\mathrm{O}∕\mathrm{Si}$ ratio. The characterization of these films by reflection electron energy-loss spectroscopy (REELS) has provided further evidences about their electronic structure (band gap and electronic states) as a function of the oxygen content. The determination of the plasmon energies by REELS has also shown that the films prepared by evaporation in vacuum consist of a single phase which is characterized by a density $\left(1.7\mathrm{g}{\mathrm{cm}}^{-3}\right)$ lower than that of $\mathrm{Si}{\mathrm{O}}_2$ (i.e., $2.2\mathrm{g}{\mathrm{cm}}^{-3}$ ) or Si (i.e., $2.4\mathrm{g}{\mathrm{cm}}^{-3}$ ). The optical properties ($\mathbf{n}$ and $\mathbf{k}$ ) of the films as a function of the $\mathrm{O}∕\mathrm{Si}$ content have been deduced from the analysis of REELS spectra in the energy range from $4\text{to}20\mathrm{eV}$ . It has been also shown that the $\mathrm{O}∕\mathrm{Si}$ ratio in the films and several spectroscopic parameters such as the Auger parameter or the energy of bulk plasmons present a linear relationship and that this linear dependence can be used for a rapid characterization of $\mathrm{Si}{\mathrm{O}}_x$ materials. By contrast, the band-gap energy changes differently with the $\mathrm{O}∕\mathrm{Si}$ ratio, following a smooth linear increase from about $3.8\mathrm{eV}$ for $\mathrm{Si}{\mathrm{O}}_{1.3}$ to ca. $5.0\mathrm{eV}$ for $\mathrm{Si}{\mathrm{O}}_{1.7}$ and a jump up to $8.7\mathrm{eV}$ for $\mathrm{Si}{\mathrm{O}}_2$ . These results indicate that the random-bonding model does not apply to thin films prepared by evaporation under our experimental conditions. Other distributions of ${\mathrm{Si}}^{n+}$ states can be induced if the films are excited with an external source such as heat or photon irradiation. In this case the electronic properties vary and the previous linear correlations as a function of the oxygen content do not hold any longer.