Three-Dimensional Crystalline, Homogenous, and Hybrid Nanostructures Fabricated by Electric Field Directed Assembly of Nanoelements

Abstract

A variety of homogeneous or layered hybrid nanostructures are fabricated by electric field-directed assembly of nanoelements. The nanoelements and the fabricated nanostructures can be conducting, semi-conducting, or insulating, or any combination thereof. Factors for enhancing the assembly process are identified, including optimization of the electric field and combined dielectrophoretic and electrophoretic forces to drive assembly. The fabrication methods are rapid and scalable. The resulting nano structures have electrical and optical properties that render them highly useful in nanoscale electronics, optics, and biosensors.

What is claimed is: 
     
         1 . A method of fabricating a hybrid nanostructure by electric field directed assembly of nanoelements, the method comprising the steps of:
 providing a nanosubstrate comprising a base layer, a conductive layer deposited onto the base layer, and an insulating layer deposited onto the conductive layer, the insulating layer comprising a via, the via forming a void in the insulating layer and defining a pathway through the insulating layer that exposes the conductive layer;   contacting the nanosubstrate with an aqueous suspension of first nanoelements;   applying an electric field between the conducting layer and an electrode in the suspension for a period of time sufficient for migration of first nanoelements from the suspension into the via and their assembly in the via, wherein the electric field consists of the sum of a DC offset voltage and an AC voltage; and   repeating, after the assembly, the contacting and the applying steps, using an aqueous suspension of second nanoelements different from the first nanoelements, thereby obtaining a hybrid nanostructure.   
     
     
         2 . The method according to  claim 1 , wherein the first and second nanoelements differ in electrical conductivity. 
     
     
         3 . The method according to  claim 2 , wherein the first and/or second nanoelements are electrically conducting, semi-conducting, or insulating. 
     
     
         4 . The method according to  claim 3 , wherein the first nanoelements are conducting and the second nanoelements are semi-conducting or insulating. 
     
     
         5 . The method according to  claim 3 , wherein the first nanoelements are semi-conducting and the second nanoelements are conducting or insulating. 
     
     
         6 . The method according to  claim 3 , wherein the first nanoelements are insulating and the second nanoelements are conducting or semi-conducting. 
     
     
         7 . The method according to  claim 3 , wherein the electric field used to assemble either semi-conducting or insulating nanoelements is greater than the electric field used to assemble conducting nanoelements. 
     
     
         8 . The method according to  claim 3 , wherein the electric field produces a dielectrophoretic force that acts on the nanoelements, and a greater dielectrophoretic force is used to assemble either semi-conducting or insulating nanoelements than the dielectrophoretic force used to assembly conducting nanoelements. 
     
     
         9 . The method according to  claim 1 , wherein the nanosubstrate comprises a plurality of vias, and a plurality of hybrid nanostructures are formed. 
     
     
         10 . The method according to  claim 1 , wherein the period of time for migration and assembly is adjusted to obtain a desired height or configuration of the nanostructure. 
     
     
         11 . The method according to  claim 1 , wherein the nanostructure possesses a geometry selected from the group consisting of nanopillars, nanoboxes and nanorings. 
     
     
         12 . The method according to  claim 1 , wherein the first and/or second nanoelements are selected from the group consisting of nanotubes, nanoparticles, and nanowires. 
     
     
         13 . The method according to  claim 12 , wherein the first and/or second nanoelements are nanoparticles and the nanoparticles are selected from the group consisting of conducting, semiconducting and insulating nanoparticles. 
     
     
         14 . The method according to  claim 12 , wherein the nanoelements are nanotubes and the nanotubes are selected from the group consisting of single-walled metallic nanotubes, single-walled carbon nanotubes, semiconducting single walled carbon nanotubes, and multi-walled carbon-nanotubes. 
     
     
         15 . The method according to  claim 13  wherein the nanoparticles are insulating nanoparticles comprising a polymer. 
     
     
         16 . The method according to  claim 15  wherein the polymer is selected from the group consisting of polystyrene, polystyrene latex, poly(methyl methacrylate, poly(lactic-co-glycolic acid), polycaprolactone, polyethylene glycol (PEG), and functionalized PEG lipids. 
     
     
         17 . The method according to  claim 13  wherein the nanoparticles are semiconducting nanoparticles comprising silicon (Si), gallium arsenide (GaAs), zinc oxide (ZnO), cadmium selenide (CdSe), cadmium selenide-zinc sulfide (CdSe—ZnS), cadmium telluride (Cd—Te), cadmium sulfide (CdS), lead selenide (PbSe), lead telluride (PbTe), or lead sulfide (PbS). 
     
     
         18 . The method of  claim 1  further comprising fusing the first and/or second nanoelements to form a solid mass by either heating the assembled nanoelements or by applying a large DC electric potential. 
     
     
         19 . The method of  claim 1 , wherein the AC voltage is about 12 volts peak to peak (v pp ). 
     
     
         20 . The method of  claim 1 , wherein the AC frequency is from about 10 to about 50 kilohertz. 
     
     
         21 . The method of  claim 1 , wherein the DC offset voltage is about 2 volts and the steady-state current is about 50 μA. 
     
     
         22 . A method of fabricating a nanostructure having a diameter at least about 200 nm by electric field directed assembly of nanoparticles, the method comprising the steps of:
 providing a nanosubstrate comprising a base layer, a conductive layer deposited onto the base layer, and an insulating layer deposited onto the conductive layer, the insulating layer comprising a via having a diameter of at least about 200 nm, the via forming a void in the insulating layer and defining a pathway through the insulating layer that exposes the conductive layer;   contacting the nanosubstrate with an aqueous suspension of the nanoparticles, wherein the nanoparticles have a diameter of about 20-100 nm;   applying an electric field between the conducting layer and an electrode in the suspension for a period of time sufficient for migration of nanoparticles from the suspension into the via and their assembly in the via, wherein the electric field consists of the sum of a DC offset voltage and an AC voltage thereby producing an incomplete nanostructure; and   fusing the assembled nanoparticles by heating the incomplete nanostructure by applying an external heat source or applying a DC voltage between the conducting layer and the electrode, thereby obtaining the nanostructure.   
     
     
         23 . The method of  claim 22 , wherein the nanosubstrate comprises a plurality of vias, and a plurality of nanostructures are formed. 
     
     
         24 . The method according to  claim 22 , wherein the DC voltage is from about 5 V to about 30 V. 
     
     
         25 . The method according to  claim 22 , wherein the temperature is about from about 100° C. to about 400° C. 
     
     
         26 . The method according to  claim 22 , wherein the nanoparticles are gold nanoparticles. 
     
     
         27 . The method according to  claim 22 , wherein the AC voltage is about 12 V pp , and the DC offset voltage is about 2V. 
     
     
         28 . The method according to  claim 22 , wherein the period of time for migration and assembly is adjusted to obtain a desired height or configuration of the nanostructure. 
     
     
         29 . The method according to  claim 22 , wherein the nanoparticles are conducting, semiconducting, or insulating nanoparticles. 
     
     
         30 . The method according to  claim 22 , wherein the nanoparticles are insulating nanoparticles and the period of time for migration and assembly is in the range of about 30-180 seconds. 
     
     
         31 . A hybrid nanostructure comprising a first portion and a second portion, the first and second portions differing in electrical conductivity. 
     
     
         32 . The hybrid nanostructure according to  claim 31 , wherein one of said first and second portions comprises a conducting material and the other comprises a semiconducting or insulating material. 
     
     
         33 . The hybrid nanostructure according to  claim 31 , wherein one of said first and second portions comprises a semiconducting material and the other comprises a conducting or insulating material. 
     
     
         34 . The hybrid nanostructure according to  claim 31 , wherein one of said first and second portions comprises an insulating material and the other comprises a conducting or semiconducting material. 
     
     
         35 . The hybrid nanostructure according to  claim 31 , wherein the nanostructure has a geometry selected from the group consisting of a nanopillar, a nanoring, and a nanobox. 
     
     
         36 . The hybrid nanostructure according to  claim 31 , wherein the diameter of the nanostructure is at least about 200 nm. 
     
     
         37 . A nanostructure array, comprising a plurality of nanostructures according to  claim 31  arranged in an array. 
     
     
         38 . The nanostructure array according to  claim 37 , wherein each nanostructure has a geometry selected from the group consisting of a nanopillar, a nanoring, and a nanobox. 
     
     
         39 . The nanostructure array according to  claim 37 , wherein each nanostructure is a nanopillar comprising a conducting material. 
     
     
         40 . The nanostructure array according to  claim 39 , wherein the nanopillar comprises gold and is polycrystalline. 
     
     
         41 . The nanostructure array according to  claim 40 , wherein the nanopillars further display an electrical resistivity equivalent to electroplated gold and supports plasmon resonance. 
     
     
         42 . A hybrid nanostructure comprising a plurality of nanoelements, produced by electric field directed assembly of the nanoelements comprising the steps of:
 providing a nanosubstrate comprising a base layer, a conductive layer deposited onto the base layer, and an insulating layer deposited onto the conductive layer, the insulating layer comprising a via, the via forming a void in the insulating layer and defining a pathway through the insulating layer that exposes the conductive layer;   contacting the nanosubstrate with an aqueous suspension of first nanoelements;   applying an electric field between the conducting layer and an electrode in the suspension for a period of time for migration and assembly of first nanoelements from the suspension into the via, wherein the electric field consists of the sum of a DC offset voltage and an AC voltage; and   repeating, after the assembly, the contacting and the applying steps, using an aqueous suspension of second nanoelements, thereby obtaining a hybrid nanostructure.   
     
     
         43 . The hybrid nanostructure according to  claim 42 , wherein the period of time for migration and assembly is adjusted to obtain a desired height or configuration of the nanostructure. 
     
     
         44 . The hybrid nanostructure according to  claim 42 , wherein the nanostructure possesses a geometry selected from the group consisting of nanopillars, nanoboxes and nanorings. 
     
     
         45 . The hybrid nanostructure according to  claim 42  wherein the first and/or second nanoelements are selected from the group consisting of nanotubes, nanoparticles, and nanowires. 
     
     
         46 . The hybrid nanostructure according to  claim 45 , wherein the nanoelements are nanoparticles and the nanoparticles are selected from the group consisting of conducting, semiconducting and insulating nanoparticles. 
     
     
         47 . The hybrid nanostructure according to  claim 45  wherein the nanoelements are nanotubes and the nanotubes are selected from the group consisting of single-walled metallic nanotubes, single-walled carbon nanotubes, semiconducting single walled carbon nanotubes, and multi-walled carbon-nanotubes. 
     
     
         48 . A nanostructure having a cross-sectional size of at least about 200 nm, fabricated by electric field directed assembly of nanoparticles, comprising the steps of:
 providing a nanosubstrate comprising a base layer, a conductive layer deposited onto the base layer, and an insulating layer deposited onto the conductive layer, the insulating layer comprising a via having a cross-sectional size of at least about 200 nm, the via forming a void in the insulating layer and defining a pathway through the insulating layer that exposes the conductive layer;   contacting the nanosubstrate with an aqueous suspension of the nanoparticles, wherein the nanoparticles have a diameter of about 20-100 nm;   applying an electric field between the conducting layer and an electrode in the suspension for a period of time sufficient for migration of nanoelements from the suspension into the via and for assembly in the via, wherein the electric field consists of the sum of a DC offset voltage and an AC voltage, thereby producing an incomplete nanostructure; and   fusing the assembled nanoparticles by heating the incomplete nanostructure using an external heat source or applying a DC voltage, thereby obtaining the nanostructure.   
     
     
         49 . The nanostructure according to  claim 48 , wherein the nanosubstrate comprises a plurality of vias, and a plurality of nanostructures are formed. 
     
     
         50 . A method of converting an incomplete nanostructure formed by electric field directed assembly of nanoelements into a complete nanostructure, the incomplete nanostructure comprising unfused nanoelements, the method comprising:
 heating the incomplete nanostructure;   
       whereby the unfused nanoelements are fused to form the complete nanostructure. 
     
     
         51 . The method of  claim 50 , wherein the incomplete nanostructure is heated to about 250° C. 
     
     
         52 . The method of  claim 50 , further comprising:
 applying a DC voltage across the incomplete nanostructure.   
     
     
         53 . The method of  claim 52 , wherein the DC voltage is about 30V. 
     
     
         54 . A method of converting an incomplete nanostructure formed by electric field directed assembly of nanoelements into a complete nanostructure, the incomplete nanostructure comprising unfused nanoelements, the method comprising:
 applying a DC voltage across the incomplete nanostructure;   
       whereby the unfused nanoelements are fused to form the complete nanostructure. 
     
     
         55 . The method of  claim 54 , wherein the DC voltage is about 30V. 
     
     
         56 . The method of  claim 54 , further comprising:
 heating the incomplete nanostructure.   
     
     
         57 . The method of  claim 56 , wherein the incomplete nanostructure is heated to about 250° C. 
     
     
         58 . The method of  claim 1 , wherein the applied electric field attains a magnitude of at least 2 MV/m within the via. 
     
     
         59 . The method of  claim 1 , wherein a higher dielctrophoretic force is applied on the second nanoelements than on the first nanoelements. 
     
     
         60 . The method of  claim 1 , wherein a higher concentration is used for the second nanoelements than for the first nanoelements. 
     
     
         61 . A method of increasing the rate, extent, or completeness of formation of a nanostructure by electric field directed assembly of nanoelements, the method comprising a step selected from the group consisting of:
 increasing the electric field used for assembly;   decreasing the frequency of an AC component of the electric field used for assembly;   increasing a dielectrophoretic force acting on the nanoelements;   increasing an electrophoretic force acting on the nanoelements;   increasing a nanoelement concentration used for assembly;   decreasing a dimension of a via into which the nanoelements are assembled;   decreasing a density of vias into which the nanoelements are assembled; and   increasing a dimension of the nanoelements.   
     
     
         62 . A method of fabricating a homogeneous electrically insulating nanostructure by electric field directed assembly of nanoelements, the method comprising the steps of:
 providing a nanosubstrate comprising a base layer, a conductive layer deposited onto the base layer, and an insulating layer deposited onto the conductive layer, the insulating layer comprising a via, the via forming a void in the insulating layer and defining a pathway through the insulating layer that exposes the conductive layer;   contacting the nanosubstrate with an aqueous suspension of electrically insulating nanoelements; and   applying an electric field between the conducting layer and an electrode    in the suspension for a period of time sufficient for migration of the nanoelements from the suspension into the via and their assembly in the via, wherein the electric field consists of the sum of a DC offset voltage and an AC voltage; thereby obtaining a homogeneous electrically insulating nanostructure.   
     
     
         63 . The method of  claim 62 , wherein the electrically insulating nanoelements comprise an inorganic oxide or an organic polymer. 
     
     
         64 . The method of  claim 63 , wherein the electrically insulating nanoelements are selected from silica, alumina, titania, polystyrene, polystyrene latex, poly(methyl methacrylate, poly(lactic-co-glycolic acid), polycaprolactone, polyethylene glycol (PEG), and functionalized PEG lipids. 
     
     
         65 . A homogeneous electrically insulating nanostructure obtainable by the method of  claim 62 . 
     
     
         66 . The method according to  claim 1  wherein the first and second nanoelements are conducting, and the first and second nanoelements are not the same. 
     
     
         67 . The method according to  claim 1  wherein the first and second nanoelements are insulating, and the first and second nanoelements are not the same. 
     
     
         68 . The method according to  claim 1  wherein the first and second nanoelements are semiconducting, and the first and second nanoelements are not the same. 
     
     
         69 . A nanoantenna comprising an array of hybrid nanostructures fabricated according to  claim 1 . 
     
     
         70 . The nanoantenna according to  claim 69 , wherein the first and second nanoelements differ in electrical conductivity. 
     
     
         71 . The nanoantenna according to  claim 69 , wherein the first and/or second nanoelements are electrically conducting, semi-conducting, or insulating. 
     
     
         70 . The nanoantenna according to  claim 67 , wherein the first nanoelements are conducting and the second nanoelements are semi-conducting or insulating. 
     
     
         71 . The nanoantenna according to  claim 67 , wherein the first nanoelements are semi-conducting and the second nanoelements are conducting or insulating. 
     
     
         72 . The nanoantenna according to  claim 67 , wherein the first nanoelements are insulating and the second nanoelements are conducting or semi-conducting. 
     
     
         73 . The nanoantenna according to  claim 67 , wherein the first and second nanoelements are conducting, and the first and second nanoelements are not the same. 
     
     
         74 . The nanoantenna according to  claim 67 , wherein the first and second nanoelements are insulating, and the first and second nanoelements are not the same. 
     
     
         75 . The nanoantenna according to  claim 67 , wherein the first and second nanoelements are semiconducting, and the first and second nanoelements are not the same. 
     
     
         72 . The nanoantenna according to  claim 69 , wherein the first nanoelements are conducting and the second nanoelements are semi-conducting or insulating. 
     
     
         73 . The nanoantenna according to  claim 69 , wherein the first nanoelements are semi-conducting and the second nanoelements are conducting or insulating. 
     
     
         74 . The nanoantenna according to  claim 69 , wherein the first nanoelements are insulating and the second nanoelements are conducting or semi-conducting. 
     
     
         75 . The nanoantenna according to  claim 69 , wherein the first and second nanoelements are conducting, and the first and second nanoelements are not the same. 
     
     
         76 . The nanoantenna according to  claim 69 , wherein the first and second nanoelements are insulating, and the first and second nanoelements are not the same. 
     
     
         77 . The nanoantenna according to  claim 69 , wherein the first and second nanoelements are semiconducting, and the first and second nanoelements are not the same.