Necklaces of silicon nanowires

Abstract

In an embodiment of the disclosure, a structure is provided which comprises a silicon substrate and a plurality of necklaces of silicon nanowires which are in direct physical contact with a surface of the silicon substrate, wherein the necklaces cover an area of the silicon substrate.

1 . A structure comprising: a silicon substrate and a plurality of necklaces of silicon nanowires which are in direct physical contact with a surface of the silicon substrate, wherein the necklaces cover an area of the silicon substrate. 
     
     
         2 . The structure of  claim 1 , wherein the necklaces of nanowires have an average height of at least about 350 nm. 
     
     
         3 . The structure of  claim 1 , wherein the silicon is monocrystalline. 
     
     
         4 . The structure of  claim 3 , wherein a surface with which the necklaces of nanowires are in direct physical contact has orientation (100). 
     
     
         5 . The structure of  claim 1 , wherein the silicon is multicrystalline. 
     
     
         6 . The structure of  claim 1 , wherein the necklaces of nanowires comprise on average at least about 10 nanowires. 
     
     
         7 . The structure of  claim 1 , wherein the necklaces of nanowires comprise on average no more than about 100 nanowires. 
     
     
         8 . The structure of  claim 1 , further comprising a p-n junction in the silicon substrate, a conducting electrical contact to necklaces of nanowires, and a conducting electrical contract to a surface other than the surface with which necklaces of nanowires are in direct physical contact, such that the structure exhibits photovoltaic behavior when illuminated on a side with which circles of nanowires are in direct physical contact. 
     
     
         9 . The structure of  claim 1 , wherein the standard deviation of the heights of the nanowires in all necklaces collectively is no more than about 30%. 
     
     
         10 . The structure of  claim 1 , wherein the necklaces of nanowires are approximately circular. 
     
     
         11 . The structure of  claim 1 , wherein the necklaces of nanowires follow approximately the shape of a curved line segment having a radius of curvature no greater than a predetermined value at all of its points. 
     
     
         12 . The structure of  claim 11 , wherein the length of the curved line segment is no more than about  5  times the predetermined value. 
     
     
         13 . The structure of  claim 11 , wherein the average distance between two adjacent necklaces of nanowires is no more than about 5 times the predetermined value. 
     
     
         14 . The structure of  claim 1 , further comprising silicon walls joining some or all pairs of adjacent nanowires which form part of at least one necklace. 
     
     
         15 . The structure of  claim 3 , wherein the silicon walls joining nanowires rise approximately to the height of the nanowires. 
     
     
         16 . The structure of  claim 1 , wherein the nanowires are of a density sufficient to result in black silicon. 
     
     
         17 . The structure of  claim 1 , wherein the nanowires are tapered. 
     
     
         18 . The structure of  claim 1 , wherein as a result of the nanowires the index of refraction of the structure varies in a direction perpendicular to the nanowires. 
     
     
         19 . The structure of  claim 1 , wherein the nanowires are on average at an angle to a surface of the silicon substrate to which they are attached. 
     
     
         20 . The structure of  claim 19 , wherein the angle lies between about 10 degrees and about 30 degrees relative to a direction perpendicular to the surface. 
     
     
         21 . A process for etching a silicon-containing substrate to form nanowires, comprising the steps of:
 (a) depositing nanoparticles comprising a first metal on the surface of a silicon-containing substrate,   (b) depositing a layer of a second metal on top of the nanoparticles and silicon in such a way that areas of bare or sparsely covered silicon are produced in the vicinity of the nanoparticles, and   (c) contacting the metallized substrate with an etchant aqueous solution comprising about 2 to about 49 weight percent HF and an oxidizing agent, wherein the process causes etching to occur in areas touched by the nanoparticles and in areas touched by the second metal.   
     
     
         22 . The process of  claim 21 , wherein the first metal comprises silver. 
     
     
         23 . The process of  claim 21 , wherein the second metal comprises silver. 
     
     
         24 . The process of  claim 21 , wherein the first and second metal are substantially identical. 
     
     
         25 . The process of  claim 21 , wherein step (a) of depositing nanoparticles comprises first depositing the first metal in an approximately uniform manner and then causing the metal so deposited to agglomerize. 
     
     
         26 . The process of  claim 25 , wherein agglomerizing is performed at least partly in a sputtering tool. 
     
     
         27 . The process of  claim 25 , wherein agglomerizing results in balls comprising the first metal. 
     
     
         28 . The process of  claim 25 , wherein the step of agglomerizing comprises heating a layer of deposited first metal. 
     
     
         29 . The process of  claim 28 , wherein the heating of the first layer involves subjecting the substrate to temperatures in a range between about 200° C. and about 400° C. 
     
     
         30 . The process of  claim 29 , wherein the heating of the first layer involves subjecting the substrate to temperatures in the range for a time between about 2 and about 10 minutes. 
     
     
         31 . The process of  claim 25 , wherein agglomerizing comprises placing the substrate with a deposited first layer of metal in a solution. 
     
     
         32 . The process of  claim 21 , wherein step (a) of depositing nanoparticles comprises sputtering. 
     
     
         33 . The process of  claim 21 , wherein prior to step (a) a UV-ozone clean process is performed. 
     
     
         34 . The process of  claim 30 , wherein step (a) is initiated no more than about 10 minutes after the UV-ozone clean process. 
     
     
         35 . The process of  claim 21 , wherein the oxidizing agent of step (c) comprises H 2 O 2  or oxygen bubbled through a perforated tube. 
     
     
         36 . The process of  claim 21 , wherein step (a) of depositing nanoparticles comprises a solution based process. 
     
     
         37 . The process of  claim 21 , wherein prior to step (a) a preclean of the surface is performed which alters the surface in such a way so the deposition of metal is altered. 
     
     
         38 . A process for creating a nanosized pattern of a metal on a surface, comprising the steps of depositing the metal, annealing the deposited metal so as to produce a pattern comprising round deposits and elongated deposits with a worm-like shape covering the surface, and employing the nanosized pattern for the formation of other nanostructures by means of additional processing. 
     
     
         39 . A structure comprising: a silicon substrate and a plurality of nanosized potentially curved silicon walls whose bottoms are in direct physical contact with a surface of the silicon substrate, wherein the walls cover an area of the silicon substrate. 
     
     
         40 . The structure of  claim 39 , wherein the walls have an average aspect ratio of at least about 10:1, at least about 20:1, or at least about 40:1. 
     
     
         41 . The structure of  claim 39 , wherein the silicon walls have silicon protrusions along their tops.