Origin and evolution of sculptured thin films

Abstract

Sculptured thin films ͑STFs͒ are a new class of engineered columnar thin films in which their shapes can resemble oblique matchsticks, chevrons, multiple zigzags, S's, C's, helices, and even superhelices. They can have densities as low as 10%-30% of the bulk material and can be made of virtually any material. The origin and evolution of columnar thin films are reviewed in the context of structure zone models in which both thermally induced and ion bombardment-induced adatom mobility effects are considered. Since STFs are prepared under low adatom mobility and oblique angle of vapor incidence conditions, the columns are the result of clustering at the 1-10 nm level, with atomic self-shadowing controlling their growth evolution. The distribution functions of the cluster sizes, shapes, and relative heights are shown to be critical for any quantitative understanding of columnar growth, especially for achieving and maintaining steady state column diameters for oblique incidence where the self-shadowing is anisotropic in the plane of the film.

Tilt angle control of nanocolumns grown by glancing angle sputtering at variable argon pressures

“…[1][2][3][4][5][6] Even though e-beam or resistively heated evaporation sources are commonly used for this purpose due to their high directionality, sputtering has also been used to obtain nanostructured systems by GLAD. [7][8][9][10][11][12][13][14] In this case, the sputtering gas pressure, P g , is obviously a crucial parameter in the formation of the columnar structures, trying to be minimized in order to reduce the number of collisions of the sputtered atoms in the gas phase and therefore to increase the directionality of the sputtered material toward the substrate.…”

Engineering the phase speed of surface-plasmon wave at the planar interface of a metal and a chiral sculptured thin film

“…Let us note that although the bulk refractive indexes of all three oxides are quite close to each other, the coefficients n a0 to m of the three types of CTFs are quite different, as indeed are also their constitutive parameters ǫ a,b,c [15]. These difference arise, in part, due to the dependence of the growth dynamics of a CTF on the evaporant species [13]. As can be gleaned from the predecessor paper [1], just a 2-period thick chiral STF should suffice for the excitation of a surface-plasmon wave; hence, we set L stf = 4Ω with Ω = 200 nm.…”

“…When the substrate is rotated about a normal passing through its centroid at a constant angular velocity of reasonable magnitude, parallel nanohelixes grow instead of parallel nanorods, and a chiral STF is deposited instead of a CTF [12,13]. Although the substrate is nonstationary, the functional relationships connecting ǫ a,b,c and χ to χ v for CTFs would substantially apply for chiral STFs, since the vapor incidence angle χ v remains constant during the deposition of films of either kind.…”

Sculptured thin films: accomplishments and emerging uses

“…Whereas slow substrate-rotation rates result in the growth of arrays of microhelixes or microsprings spaced as close as 20 nm from their nearest neighbors, faster rotation rates yield arrays of increasingly denser pillars [9,10]. Such STFs are essentially photonic bandgap materials in the visible and the infrared regimes.…”

“…For the essentials of the fabrication techniques, the interested reader is enjoined to read the gem of a paper that Young & Kowal wrote [4]. For details of the modern versions of the Young-Kowal technique, reference is made to Lakhtakia & Messier [7], Hodgkinson & Wu [8], Messier et al [9], and Malac & Egerton [10]. The materials that can be deposited as STFs range from insulators to semiconductors to metals, thereby indicating the versatility of STF technology.…”