| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Monday Sessions |
| Session TF-MoE |
| Session: | Nanostructured Surfaces & Thin Films I |
| Presenter: | Kedar Manandhar, U.S. Naval Research Laboratory, USA |
| Authors: | K. Manandhar, U.S. Naval Research Laboratory, USA J.A. Wollmershauser, U.S. Naval Research Laboratory, USA B.N. Feigelson, U.S. Naval Research Laboratory, USA |
| Correspondent: | Click to Email |
Powders with particle size ≤100 nm typically posses unique physical, chemical, opto-electronic, mechanical and catalytic properties compared to bigger size particle powder and their bulk counterpart and are increasingly being used in commercial systems. However a path to exploit these size specific properties of nano-powders is not always straight forward since they are often in danger of being deteriorated from the environments in which they are intended to be used. To enable these powders to withstand working environments, the surface of powders are commonly engineered via coating with films of thickness varying few monolayer to thousands of monolayers. For many cases a continuous ultrathin shell is desired. In the applications where a continuous ultrathin films is desired, understandings about growth mode, in the early stage of growth is very important since it defines how the material is arranged on the surface.
When it comes to the need of a thin metal-oxide film as protective layer or active surface, aluminum oxide is the material of choice for at least two reasons, (i) ALD chemistry of alumina from trimethylaluminium/ water is well studied (ii) relative easiness of forming a continuous film with alumina. To understand film morphology of alumina in the early stage of growth, we selected tungsten powder as substrate because this substrate/ film material combination eases for core-shell analysis by transmission electron microscopy (TEM) as TEM micrographs show a high contrast between core and shell for easy and more accurate determine of films thickness ranging from ultrathin to thin[1]. Alumina films resulting from 1 to 20 ALD cycles were grown on W-nanopowders with an average particle size of 50 nm using rotary reactor ALD. The results for alumina deposition at ~110 ֩C demonstrated stoichiometric and continuous but non-uniformly thick films in the beginning with varying growth per cycle (GPC) as a function of number of cycles. The as prepared samples were investigated with x-ray photoelectron spectroscopy , scanning and transmission electron microscopy. Film surface morphology and GPC as a function of ALD cycle for early stage growth will be presented and discussed.
1. Manandhar, K., et al., Growth per cycle of alumina atomic layer deposition on nano- and micro-powders. Journal of Vacuum Science & Technology A, 2016. 34(2): p. 021519.
Work is supported by NRL Base Program and DARPA