A new bottom-up methodology to produce silicon layers with a closed porosity nanostructure and reduced refractive index

Abstract

A new approach is presented to produce amorphous porous silicon coatings (a-pSi) with closed porosity by magnetron sputtering of a silicon target. It is shown how the use of He as the process gas at moderated power (50-150 W RF) promotes the formation of closed nanometric pores during the growth of the silicon films. The use of oblique-angle deposition demonstrates the possibility of aligning and orientating the pores in one direction. The control of the deposition power allows the control of the pore size distribution. The films have been characterized by a variety of techniques, including scanning and transmission electron microscopy, electron energy loss spectroscopy, Rutherford back scattering and x-ray photoelectron spectroscopy, showing the incorporation of He into the films (most probably inside the closed pores) and limited surface oxidation of the silicon coating. The ellipsometry measurements show a significant decrease in the refractive index of porous coatings (n(500 nm) = 3.75) in comparison to dense coatings (n(500 nm) = 4.75). The capability of the method to prepare coatings with a tailored refractive index is therefore demonstrated. The versatility of the methodology is shown in this paper by preparing intrinsic or doped silicon and also depositing (under DC or RF discharge) a-pSi films on a variety of substrates, including flexible materials, with good chemical and mechanical stability. The fabrication of multilayers of silicon films of controlled refractive index in a simple (one-target chamber) deposition methodology is also presented.

Porous amorphous silicon film anodes for high-capacity and stable all-solid-state lithium batteries

“…1a, b). By contrast, He was used as the sputtering gas for the preparation of porous films; according to the previous studies 16,17 , it is known that He can be incorporated in the amorphous Si films during deposition and thus He bubbles are formed due to the extremely low solubility of He in metals. The resulting films exhibited (Fig.…”

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

“…Some examples of this approach include: (i) antireflection and self-cleaning coatings for III-V multi-junction solar cells made of OAD layers of gold grown on nanocone arrays fabricated by plasma etching borosilicate glass [366], (ii) magnetron sputtered Ti x Sn 1Àx O 2 films prepared on top of a seed layer of polystyrene spheres [367,368], (iii) HfO 2 films [369] combined with amorphous porous silicon with closed porosity [370], and (iv) sculptured TiO 2 films [371].…”

Supported Co catalysts prepared as thin films by magnetron sputtering for sodium borohydride and ammonia borane hydrolysis

“…[21][22][23][24][25] Magnetron sputtering is a PVD technique that allows the deposition of thin films with precise controlled thickness over a wide variety of substrates due to the low deposition temperature of the process. It can be easily scaled to industrial processes and is a low cost process without the need of precursors avoiding emissions of toxic by- This technique has proven before to be a versatile tool to prepare nanostructured and porous materials in our group [26][27][28]. To our knowledge, magnetron sputtering has not been reported as preparation technique for supported Co catalysts for sodium borohydride or ammonia borane hydrolysis before [29].…”