Confinement Effects in Nanoscale Anodic Alumina Structures on Silicon
- PDF / 970,450 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 48 Downloads / 265 Views
U11.5.1
Confinement Effects in Nanoscale Anodic Alumina Structures on Silicon Patrick J. Griffin1, Robert W. Carpick1,2 and Donald S. Stone1,3 1 Materials Science Program 2 Engineering Physics Department 3 Materials Science and Engineering Department University of Wisconsin-Madison Madison, WI 53706, U.S.A. ABSTRACT Anodic aluminum oxide (AAO) has long been considered a viable material for templated growth of nanomaterials for electronic, magnetic and optical applications due to the ability to form self-organized, high aspect-ratio nanochannels. More recently these porous materials have been incorporated with silicon to create a template for nanostructured materials on a semiconducting substrate. However, there has been no investigation into how pore growth is affected by confining the pre-anodized aluminum dimensions to the nanometer scale. We have used electron beam lithography to pattern 200 nm thick aluminum structures on Si with lateral features ranging from 100 nm to several microns in size. Structures consisting of 1 – 10 individual pores 10 – 15 nm in diameter are routinely fabricated. Confinement effects in the narrowest features assist in pore ordering in the porous structures without the use of prepatterning or a two step anodization. INTRODUCTION Anodic aluminum oxide membranes and films were first discovered in the 1940's by Keller and Edwards.1 Until the last decade the AAOs saw interest primarily as filtration devices. More recently the AAOs have seen an increased amount of interest due to the recent activity in nanoscience and technology. The membranes provide highly ordered nanoporous arrays as a means for relatively simple and inexpensive methods of templating, scaffolding and patterning a wide range of materials for potential uses in electronic, magnetic and optical applications.2-5 Porous alumina is formed via an electrochemical process. Under the proper conditions the pores order themselves into a close-packed formation. The ordering has been attributed as a reaction to the mechanical stress that exists upon the conversion of aluminum to aluminum oxide and the subsequent volume expansion.6 This highly ordered pore configuration is achieved on bulk Al through a lengthy two-step anodization producing membranes up to 200 µm thick with ordered domains up to several microns in lateral size. For the silicon integrated AAO films the aluminum thickness is limited due to the metal deposition process. This was problematic as the established method of achieving well-ordered porous films requires at least tens of microns of Al and therefore cannot be applied on Si. Recently significant progress has been made in finding alternate methods to creating ordered porous films. By pre-patterning the aluminum via several different methods including a mechanical imprinting process3,7, focused ion beam milling8 and holographic patterning9 highly ordered porous films have been fabricated. Previously during AAO fabrication the oxides have been prepared with bulk lateral dimensions. In an effort to create discrete, addr
Data Loading...
