Simple fabrication of high density quantum dot arrays using anodic aluminum oxide mask
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Simple fabrication of high density quantum dot arrays using anodic aluminum oxide mask
Joon-ho Sung, Heesung Moon, Jae Ho Bahng1, Ja-Yong Koo1 and Bongsoo Kim* Department of Chemistry and School of Molecular Science – BK21, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, Korea 1 Korea Research Institute of Standards and Science (KRISS), Daejeon 305-340, Korea
ABSTRACT
We fabricated quantum dot arrays using anodic alumina mask. We grew an alumina template on Si wafers by two-step anodization. The porous alumina template thus grown is used as a mask for metal deposition. After thermal evaporation and removal of the mask, we fabricated the quantum dot arrarys on a Si substrate. Using this template-assisted method we obtained a high density array of quantum dots in a large scale. These quantum dots have a narrow size distribution which can be easily controlled by a pore widening of templates from 20 to 60 nm.
INTRODUCTION
Template method offers a promising method to fabricate nanomaterials. Recently, selfordered nano-pore materials get increasing attention as templates for nanostructures, such as magnetic, electronic, and optoelectronic devices [1]. Nanoporous anodic alumina, which is formed by anodization of aluminum in appropriate acid solution, is a typical example of a naturally occurring ordered structure [2]. Under appropriate conditions large area ordered pore arrays with hexagonally arranged packing have been reported by Masuda et al. [3]. The pore diameters which can be controlled in the range of ten to several hundred nanometers make porous anodic alumina an ideal template for fabricating ordered arrays of nanostructured materials [4]. Considering the engineering process and cost, anodic aluminum oxide (AAO) template can provide very simple and inexpensive method compared to other techniques. Recently, AAO has been fabricated directly on an aluminum film coated on silicon wafer for device applications [5]. In this case AAO can be used as a nano-fabrication mask to transfer the hexagonal pore array
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into various substrates and thus fabricated structures can directly adopt the silicon industrial technique [6]. We first prepared AAO template on a silicon wafer and then fabricated high density quantum dot arrays, which can be used for a variety of device applications.
EXPERIMENTAL DETAILS
The experimental details on porous alumina fabrication can be found elsewhere [1-6]. In figure 1, a schematic of the fabrication of a quantum dot array is shown. An aluminum film which is ~ 600 nm thick was deposited by an electron beam evaporator on a Si wafer. In order to obtain a smooth surface, the film was electropolished in the mixed solution of perchloric acid and ethanol (1:4) under 15 V for 30 seconds. We performed two-step anodization because it can provide more ordered pore arrays than just one step anodization. The first anodization was carried out in a 0.3 M oxalic acid solution at 4℃ with an applied voltage of 60 V for proper duration depending on the areas of
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