Control over Pore Positions in Anodised Aluminium Oxide Films via Scratching the Surface of Pure Aluminium
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0921-T07-02
Control over Pore Positions in Anodised Aluminium Oxide Films via Scratching the Surface of Pure Aluminium Darren J. LeClere, Brian Derby, and George E. Thompson School of Materials, University of Manchester, Grosvenor St., Manchester, M1 7HS, United Kingdom ABSTRACT Anodised aluminium oxide films have several applications in nanotechnology due to the ability to control the dimensions and ordering of the pores. Several techniques have been developed which allow for accurate control over the ordering of pore arrays. Examples of such techniques are the “Two-Step” method, and embossing with optical gratings or micro-machined Si templates. It will be demonstrated that it is possible to control the position of the pores using a nanoindenting device that has scratched the aluminium surface before anodising. The interpore distances accomplished via this technique were 200nm and 400nm by anodising in 0.3M (COOH)2 at 80V and 0.1M H3PO4 at 160V respectively. Hexagonal and square arrays were created by scratching the aluminium with a series of crosshatched lines. INTRODUCTION When anodising, imperfections on the surface of aluminium produce a non-uniform distribution of current which aids in pore formation[1]. The ability to nucleate pores has been used to order the pores of anodised aluminium oxide (AAO), which has been widely researched over the past decade due to its application to photonic crystals[2] and magnetic storage devices[3]. Several methods have been used to achieve long range ordering with varying degrees of success. These methods include: the “Two-Step” method[4], embossing with a master stamp[2, 5] or optical grating[6], and nanoindenting[7]. The research presented here concentrates on the outcome of scratching the Al surface using the tip of a TriboScope® (Hysitron, Minneapolis, MN, USA) prior to anodising. The higher current within the scratch aids in oxide film formation which implies a faster pore initiation. The pores outside a scratch do not form as fast as the pores inside a scratch. Therefore pores within a scratch distribute themselves in relation to each other, evenly spacing themselves within the scratch. A grid pattern of intersecting lines should therefore produce an ordered array of pores over the surface. EXPERIMENTAL DETAILS The TriboScope® is normally used for characterising the mechanical properties of a material by forcing the tip into the surface which is known as nanoindenting. For nanoindentation the TriboScope® is mounted onto an Explorer AFM (Veeco, Santa Barbra, CA, USA), replacing the tip of the AFM. The depth that the TriboScope® penetrates into the surface depends on the value given to the setpoint within the software. The setpoint was adjusted so that the surface of the material was slightly indented, after which the tip was moved along the surface to produce scratches of a predetermined depth. These scratches were used to nucleate pore growth in precisely defined positions.
The scratches were straight lines that travelled from one side of a designated area to the oth
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