Formation of capped nano-pillars

Abstract

A method of forming capped nano-pillars on a substrate includes forming a template on the substrate, the template defining nano-pores having a first width. The nano-pores are partially filled to define nano-pillar stem portions of a first thickness corresponding to the first width. The nano-pores are re-shaped to define re-shaped nano-pore sections having a second width different than the first width. The re-shaped nano-pore sections are at least partially filled to define nano-pillar cap portions of a second thickness corresponding to the second width. The method further includes removing the template.

What is claimed is: 
     
         1 . A method of forming capped nano-pillars on a substrate, the method comprising:
 forming a template on the substrate, the template defining nano-pores having a first width;   partially filling the nano-pores to define nano-pillar stem portions of a first thickness corresponding to the first width;   re-shaping the nano-pores to define re-shaped nano-pore sections having a second width different than the first width;   at least partially filling the re-shaped nano-pore sections to define nano-pillar cap portions of a second thickness corresponding to the second width; and   removing the template.   
     
     
         2 . The method of  claim 1 , wherein partially filling the nano-pores includes:
 forming a layer of a first oxidizable material; and   anodizing the layer of first oxidizable material to grow oxide from the first oxidizable material into the nano-pores.   
     
     
         3 . The method of  claim 2 , wherein re-shaping the nano-pores includes selectively etching the nano-pores to broaden unfilled regions of the nano-pores. 
     
     
         4 . The method of  claim 3 , wherein at least partially filling the re-shaped nano-pore sections includes further anodizing the first oxidizable material to grow oxide into the re-shaped sections. 
     
     
         5 . The method of  claim 1 , wherein forming a template includes:
 forming a layer of a second oxidizable material; and   anodizing the layer of second oxidizable material to define the nano-pores.   
     
     
         6 . The method of  claim 5  wherein the layer of the second oxidizable material is disposed beneath the template, and wherein the method further comprises forming the nano-pillar cap portions by further anodizing the layer of the second oxidizable material, to grow oxide into the re-shaped nano-pore sections. 
     
     
         7 . The method of  claim 1  wherein, after removing the template, a nano-structure array is formed on the substrate, and wherein:
 the nano-structure array includes a plurality of the capped nano-pillars having columnar stem portions; 
 the first thickness is different than the second thickness; and 
 each of the stem portions and the cap portions consists of an oxide of a refractory metal or alloy. 
 
     
     
         8 . The method of  claim 7 , wherein the first thickness is substantially uniform along a height of the stem portions, and the second thickness is substantially uniform along a height of the cap portions. 
     
     
         9 . The method of  claim 8 , wherein the second thickness is greater than the first thickness. 
     
     
         10 . The method of  claim 9 , wherein the stem portions have a first height and the cap portions have a second height, the first height being greater than the second height. 
     
     
         11 . The method of  claim 9 , wherein the stem portions have a first height and the cap portions have a second height, the first height being less than the second height. 
     
     
         12 . A method of forming capped nano-pillars on a substrate, the method comprising:
 depositing a first oxidizable material onto the substrate;   depositing a second oxidizable material onto the first oxidizable material;   anodizing the second oxidizable material to form a porous oxide having nano-pores that extend through the porous oxide to expose portions of the first oxidizable material;   anodizing the first oxidizable material so as to partially fill the nano-pores in the porous oxide with an oxide of the first oxidizable material;   broadening unfilled sections of the nano-pores by selective etching; and   further anodizing the first oxidizable material so as to at least partially fill broadened sections of the nano-pores with the oxide of the first oxidizable material; and   further removing porous oxide by selective etching, thereby yielding an array of capped nano-pillars on the substrate.   
     
     
         13 . The method of  claim 12 , wherein anodizing the first oxidizable material comprises anodizing the first oxidizable material with a first voltage corresponding to a target nano-pillar stem portion height. 
     
     
         14 . The method of  claim 12 , wherein further anodizing the first oxidizable material comprises anodizing the first oxidizable material with a second voltage corresponding to a target nano-pillar cap portion height. 
     
     
         15 . The method of  claim 12 , wherein broadening unfilled sections of the nano-pores comprises etching of the substrate in an etchant solution configured to etch the porous oxide at a substantially higher etch rate than the oxide of the first oxidizable material.