Piezoelectric composite nanofibers, nanotubes, nanojunctions and nanotrees

Abstract

Piezoelectric nanostructures, including nanofibers, nanotubes, nanojunctions and nanotrees, may be made of piezoelectric materials alone, or as composites of piezoelectric materials and electrically-conductive materials. Homogeneous or composite nanofibers and nanotubes may be fabricated by electrospinning. Homogeneous or composite nanotubes, nanojunctions and nanotrees may be fabricated by template-assisted processes in which colloidal suspensions and/or modified sol-gels of the desired materials are deposited sequentially into the pores of a template. The electrospinning or template-assisted fabrication methods may employ a modified sol-gel process for obtaining a perovskite phase in the piezoelectric material at a low annealing temperature.

1 . A method of preparing a nanoscale piezoelectric structure, comprising the steps of:
 providing a template having a pore extending therethrough, said pore having an interior surface;   depositing a precursor material into said pore such that said precursor material remains in said pore in direct or indirect contact with said interior surface, said precursor material being a material that is transformable to a piezoelectric material upon heating; and   heating said precursor material, whereby said precursor material is transformed into a piezoelectric material.   
   
   
       2 . The method of  claim 1 , wherein said depositing step comprising the step of forming a layer of said precursor material on said interior surface. 
   
   
       3 . The method of  claim 2 , comprising the further steps of solidifying said layer of said precursor material, and depositing a second material onto said precursor material, wherein said second material comprises either a material that is electrically-conductive in a solid form or a material that is transformable into a piezoelectric material upon heating. 
   
   
       4 . The method of  claim 1 , comprising a further step of depositing another material into said pore, thereby forming a layer of said another material on said interior surface, said another material including a material that is electrically-conductive in a solid form, wherein said step of depositing said another material is performed before said step of depositing said precursor material, and said step of depositing said another material includes the step of depositing said precursor material onto said another material. 
   
   
       5 . The method of  claim 4 , further comprising the step of if said layer of said first material is not a solid layer, then solidifying said another material before said step of depositing said precursor material. 
   
   
       6 . The method of  claim 2 , comprising the further step of dissolving at least a portion of said template, whereby at least a portion of said piezoelectric material is exposed. 
   
   
       7 . The method of  claim 6 , comprising the further step of depositing an electrically-conductive material on said at least a portion of said piezoelectric material. 
   
   
       8 . The method of  claim 1 , wherein said pore is a branched pore. 
   
   
       9 . The method of  claim 8 , wherein said branched pore includes branches having further branches extending therefrom. 
   
   
       10 . The method of  claim 1 , wherein said precursor material comprises lead zirconate titanate, and said heating step includes the step of maintaining said material at a temperature of about 650° C. until at least a portion of said lead zirconate titanate is transformed into crystals having a perovskite structure. 
   
   
       11 . The method of  claim 1 , wherein said precursor material further includes at least one organic liquid, and said heating step includes the further step removing substantially all of said at least one organic liquid from said precursor material before said maintaining step. 
   
   
       12 . The method of  claim 1 , wherein said precursor material comprises lead zirconate titanate, poly(vinyl pyrrolodine) and an alcohol, and said heating step includes the steps of maintaining said precursor material at 380° C. for at least 5 minutes, then maintaining said material at a temperature of about 650° C. for at least about one hour. 
   
   
       13 . The method of  claim 1 , wherein said precursor material is a fluid in the form of a sol-gel or a nanocolloidal suspension. 
   
   
       14 . The method of  claim 13 , wherein said pore has an opening through a side of said template and another opening through another side of said template, and said depositing step includes the steps of placing a portion of said precursor material onto said opening and applying a vacuum to said pore at said another opening, thereby drawing a portion of said precursor material into said pore. 
   
   
       15 . The method of  claim 3 , wherein said material that is conductive in its solid form comprises indium titanium oxide. 
   
   
       16 . The method of  claim 7 , comprising the further step of depositing a dielectric material on at least a portion of said electrically-conductive material and said at least a portion of said piezoelectrical material. 
   
   
       17 . The method of  claim 1 , wherein said template comprises an anodized aluminum oxide. 
   
   
       18 . A method of preparing a nanoscale piezoelectric structure, comprising the steps of:
 providing a template having a pore extending therethrough, said pore having an interior surface;   depositing a first material into said pore, thereby forming a layer of said first material on said interior surface of said pore, said layer having an exposed surface facing away from said interior surface of said pore;   depositing a second material into said pore, thereby forming a layer of said second material on said exposed surface, wherein at least one of said first and second materials is a material that is transformable to a piezoelectric material upon heating; and   heating said first and second materials, whereby said at least one of said materials is transformed into a piezoelectric material.   
   
   
       19 . A method of fabricating piezoelectric fibers having nanoscale diameters, comprising the steps of:
 providing an electrospinning apparatus comprising a hollow, electrically-conductive needle having an end with an opening having a micron-scale diameter, an opposite end with another opening, a high-resistance substrate opposed to said opening, and a voltage means for providing a high voltage across said needle and said substrate;   selecting a precursor material comprising lead zirconate titanate, poly(vinyl pyrrolodine) and an alcohol, said precursor material being a sol-gel of said lead zirconate titanate;   providing said precursor material to said another opening of said needle at a controlled rate while providing a high voltage across said needle and said substrate, so as to spin a fiber therefrom;   collecting said fiber on said substrate; and   heating said fiber at a temperature of about 80° C. for about 5 minutes, then heating said fiber at a temperature of about 380° C. for about 5 minutes, then maintaining said fiber at a temperature of about 650° C. for about 1 hour, thereby transforming at least a portion of said lead zirconate titanate into crystals having a perovskite structure.   
   
   
       20 . An article, comprising a nanoscale piezoelectric structure including a branched structure having a stem with a plurality of branches extending therefrom and a further plurality of branches extending from at least one of said plurality of branches, wherein said stem, said at least one of said plurality of branches and at least one of said further plurality of branches comprises a piezoelectric material.