Practical applications of thin films nanostructured by shadowing growth

Abstract

Abstract. Even prior to the recent advent of advanced top-down processes, shadowing growth by oblique angle deposition (OAD) has long been providing self-assembled nanostructures over much larger areas for much lower costs. In the past two decades, significant progress has been made in the development of well-controlled three-dimensional nanomorphologies such as zigzags and helixes. Much effort has been put into theoretical and numerical understanding of the growth mechanism to improve morphology. Many researchers in academia have been investigating useful properties of nanocolumnar thin films in their laboratories. However, most companies seem hesitant to introduce OAD techniques into the factory, owing to the prejudice that the OAD thin films are neither durable nor reproducible. The progress in OAD technology for practical applications is reviewed and discussed.

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

“…At present, this use of templates in the OAD of thin films has transcended pure scientific interest, and is now developed for advanced technological applications. For example, mass-produced metal wire grid polarizers are being fabricated via the OAD deposition of antireflection FeSi and SiO 2 layers on previously deposited aluminum columnar arrays [87,114,115]. Other emerging applications in biomedical areas [107,116,110,117], or for controlling the wetting properties of substrates [102,118], also rely on the use of patterned surfaces rather than the direct OAD of thin films (see Section 5.5).…”

“…Nevertheless, in a systematic investigation of the OAD of magnetic metals and alloys (Co, Ni, Fe), Hara et al [51][52][53][54][55][56] showed that although the aforementioned relation between temperature and deposition rate was generally maintained, other effects besides diffusion must be involved to explain unexpected deviations in the growth tendencies and the appearance of more complex morphological patterns. For a large variety of metals and oxides deposited by DC magnetron sputtering, Deniz et al [49] determined the nanostructuration Cross sectional SEM images of (a) zig-zag nanocolumns obtained by back and forth azimuthal turning of the substrate [63], (b) spiral nanocolumns obtained by continuous azimuthal rotation (i.e., dynamic OAD) [87], (c) zig-zag plus spiral nanocolumns (author's unpublished results), (d) nanocolumns with width modulation obtained by azimuthal rotation and back and forth polar angle tilting [87], and (e) vertical nanocolumns obtained by rapid azimuthal rotation at two different rates [65]. above which ad-atom surface diffusion becomes dominant over surface shadowing, thereby preventing the formation of a typical OAD nanocolumnar morphology. For metals, this temperature threshold has been tentatively established at around 0:33T f , while for oxides the value is approximately 0:5T f .…”

“…Expanding on this simple approach, the use of substrates with a well-defined lithographic pattern opens up a range of new and unexpected possibilities for the nano-structuring of OAD thin films. To this end, patterned substrates consisting of well-ordered nano-structured array patterns or seed layers have been prepared through a variety of lithographic methods, laser writing, embossing or other top-down fabrication methods [24,87,[98][99][100][101][102][103][104][105][106][107][108][109]. Among these, the use of colloidal lithography (i.e., OAD on a substrate pre-coated with packed nanospheres of different materials) has gained much popularity over the last few years thanks largely to its simplicity [110][111][112][113].…”

Electrochemical characterization of nanostructured Ag:TiN thin films produced by glancing angle deposition on polyurethane substrates for bio-electrode applications

“…In recent years, the extensive dissemination of their works in leading scientific journals demonstrates the strong interest generated by nanostructured thin films prepared with this method. Moreover, the growing interest of the GLAD technique shown by many researchers coming from academia and industry [31][32][33][34][35][36][37][38] is due to the possibility to tailor even further the majority of the properties of most thin film systems, which can be of major interest in the fields of photonics, mechanics, catalysis or biology. Thus, GLAD thin films, prepared by either evaporation or magnetron sputtering are becoming an attractive strategy to obtain a wide variety of architectures and sculptured materials at the micro-and nanoscale.…”

Annealing effect on the photoelectrochemical and photocatalytic performance of TiO2 nanorod arrays

“…35 The porous structure was formed during the deposition process due to the self-shadowing effects and the limited mobility of the deposited atoms. 36 The pore size of the TiO 2 NRAs becomes lager with increase in gaps between nanorods by annealing at 300 C which can contributed to the shrink during the annealing process. Further increasing annealing temperature, the morphology of TiO 2 NRAs does not change much as shown in Fig.…”