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Fabrication of indium nanopillars

Indium and its compounds have many important applications in the field of nanotechnology. For example, it has been demonstrated that indium phosphide (InP) and indium arsenide-phosphide (InAsP) nanowires can be used as highly polarized photoluminescence and infrared photo detection devices. Vertical field-effect transistors have also been constructed with indium oxide (In2O3) nanowires.


Indium nanopillars are fabricated on silicon substrates coated with electron beam evaporated chromium/gold bi-layer. A gold seed layer is selected as the cathode in subsequent electroplating steps while the chromium film is used to promote adhesion between gold and silicon substrate.

Following deposition of the seed layer, polymethylmethacrylate (PMMA) diluted in anisole is spun on the substrates and then cured to form the final resist layer. These PMMA thin films are then patterned by using the electron beam lithography techniques to produce holes in the resist. The resists are exposed to electron beam and developed using a mixture of methylisobutylketone and isopropyl alcohol (IPA). After the PMMA templates are produced, it is subjected to oxygen plasma descum process to reduce pillar tapering caused by electron beam lithography and also to promote homogenous electroplating.

After patterning the PMMA films, indium is electroplated into the template structures by using a two electrode configuration system and a commercially available indium sulfamate solution. This sulfamate bath is maintained at ambient temperature and mechanically stirred during the deposition process. High-purity indium metal slab is used as a soluble anode while the conductive gold seed layer underneath the patterned PMMA resist act as the cathode.The plating process is followed by galvanostatic electroplating to produce a thin indium seed layer which promots homogenous filling of the patterned features and increases the final yield of indium pillars. After plating, they are rinsed in de-ionized water and the PMMA is removed using a commercial photo resist stripper to get indium nanopillars.

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