Control of power law scaling in the growth of silicon nanocolumn pseudo-regular arrays deposited by glancing angle deposition

Abstract

Nanocolumn pseudo-regular arrays of silicon with controlled aspect ratio and porosity are fabricated by electron-beam evaporation using the glancing angle deposition (GLAD) method with vapour impinging at oblique incidence onto rapidly rotating substrates. The width W at positions y along the height of one individual column scales with y following a power law dependence W approximately y(p). We demonstrate that the scaling exponent value, p, can be modified from 0.6 to 0.3 by varying the vapour incidence angle from 75 degrees to a glancing 89 degrees from the substrate normal. This exponent is an important morphological factor for thin films, as it determines the morphological correlation length, nanocolumn profile, size, and spacing. The nanocolumn mean diameter can be varied between 12 and 40 nm, while the intercolumnar spacing can be adjusted between 37 and 85 nm via changing the incidence angle. The growth mechanism and film morphology are explored in detail.

Theoretical and experimental characterization of TiO2 thin films deposited at oblique angles

“…As expected [29], column thickness grows as  ~ d p , ranging the value of the growth exponent, p, between p = 0.16  0.02 for  = 60º and p = 0.64  0.02 for  = 85º.…”

“…Other expressions relating  and  have been proposed in the literature aiming at a general description of the film growth, although such relationships depend on the film chemical composition and deposition conditions, and require some fitting parameters whose physical meaning is, in most of the cases, unclear [26]. In addition to this debate, there is also great interest in understanding the relation between the average column thickness, , and the height, d. This accounts for the widening of the columns as their length increases: a phenomenon that has been reported in the literature and is responsible for a strong dependence of film properties on the film thickness [27][28][29].…”

Anisotropic Bruggeman effective medium approaches for slanted columnar thin films

“…In general, void fraction values between 70% and 80% are also in agreement with general porosity trends for samples deposited at such glancing angles 11 . Unfortunately, no data for accurate direct comparison exist in the literature since either the method does not work for very large pore sizes (gas adsorption isotherm analysis) 10 or values have been determined by top-view SEM image analysis of vertically grown columnar thin films 6,7 .…”

Developing 1D nanostructure arrays for future nanophotonics

“…8b) that transforms the growing interface from two dimensions to a fractal 2+ dimension. This result is explained by chaotic growth mechanics that are intrinsic to film deposition at these glancing deposition angles, and produce power-law scaling in the morphological structure [39,40,46,47]. While these scaling effects do place constraints on what morphological structures are possible with this technique, they also provide unique benefits.…”

“…These techniques have been demonstrated to allow fabrication of single-material optical interference coatings [35], broadband antireflection coatings [36], and other photonic crystals [37,38]. While fractal scaling effects have been found to limit the utility of these films for some applications [39,40], these atomic-scale architectures appear to be uniquely functional three-dimensional (3-D) organized materials [41][42][43][44].…”