AVS 45th International Symposium
    Nanometer-scale Science and Technology Division Thursday Sessions
       Session NS-ThM

Paper NS-ThM2
Fabrication and Structuring of Ordered Two-Dimensional Nanopore Arrays in Anodic Alumina

Thursday, November 5, 1998, 8:40 am, Room 321/322/323

Session: Nanoscale Patterning and Modification
Presenter: A.P. Li, Max-Planck-Institute of Microstructure Physics, Germany
Authors: A.P. Li, Max-Planck-Institute of Microstructure Physics, Germany
F. Mueller, Max-Planck-Institute of Microstructure Physics, Germany
A. Birner, Max-Planck-Institute of Microstructure Physics, Germany
K. Nielsch, Max-Planck-Institute of Microstructure Physics, Germany
U.M. Goesele, Max-Planck-Institute of Microstructure Physics, Germany
Correspondent: Click to Email
We will describe the fabrication of nonlithographic nanopore arrays in anodic alumina with areal pore densities in the 6*10@super 8@ - 5*10 @super 10@ cm @super -2@ range, and the lithographic structuring of the arrays for potential applications in photonic crystal. A two-step anodization process was used to oxidize aluminum in oxalic, sulfuric, and phosphoric acid solutions. Self-organized hexagonal pore arrangements were formed in the end of the first anodization process. After removing the irregular upper part, the densely ordered pits in the bottom of anodic layer act as natural masks, and the nanopore arrays were fabricated by the second anodization process. Perfect ordered pore arrays were obtained within domains of a few micrometers, which are separated from neighboring domains with different orientation of the pore lattice by grain boundaries, i.e., the nanopore arrays show polycrystalline structure. The pore distance can be controlled by changing the anodic electrolyte and voltage. The ratio of pore diameter and wall thickness can be adjusted by chemical etching after anodization. The structural characteristics make the ordered porous alumina a potential two-dimensional photonic crystal material for the visible to ultra-violet light range. Although they are polycrystalline, these structures are expected to exhibit interesting photonic crystal properties analogous to electronic properties of polycrystalline semiconductors. For optical transmission measurements, light has to be coupled in perpendicular to the pore arrays and to traverse a well defined number of pore layers. For this purpose we have developed a lateral structuring technique that allows to remove the porous alumina precisely yielding vertical walls. Bars of porous alumina which are 100-400 µm wide, 100-300 µm high and several mm long have been prepared. The achieved samples are well suited to investigate the optical properties of these structures with light traveling perpendicular to the pore arrays.