Method for assembling nano objects

Abstract

A method for the self assembly of a macroscopic structure with a pre-formed nano object is provided. The method includes processing a nano object to a desired aspect ratio and chemical functionality and mixing the processed nano object with a solvent to form a suspension. Upon formation of the suspension, a substrate is inserted into the suspension. By evaporation of the solvent, changing the pH value of the suspension, or changing the temperature of the suspension, the nano objects within the suspension deposit onto the substrate in an orientational order. In addition, a seed crystal may be used in place of the substrate thereby forming single-crystals and free-standing membranes of the nano-objects.

1 . A method for assembling nano objects onto a macroscopic structure, the method comprising:
 (a) processing nano objects to a desired aspect ratio and chemical functionality;   (b) admixing the processed nano objects with a solvent to form a suspension, the suspension having a concentration, a temperature and a pH level;   (c) submersing a substrate into the suspension; and   (d) changing the concentration to control deposition of the nano objects onto the substrate, thereby assembling the macroscopic structure onto the substrate.   
     
     
         2 . The method of  claim 1 , wherein the nano objects comprise single wall carbon nanotubes (SWNTs) or single wall carbon nanotube bundles. 
     
     
         3 . The method of  claim 1 , wherein the nano objects comprise multi wall carbon nanotubes (MWNTs). 
     
     
         4 . The method of  claim 1 , wherein the nano objects comprise a mixture of single wall carbon nanotubes (SWNTs) and multi wall carbon nanotubes (MWNTs). 
     
     
         5 . The method of  claim 2 , wherein the operation of processing the nano objects further comprises:
 (e) synthesizing the carbon nanotubes;   (f) purifying the carbon nanotubes; and   (g) modifying both a length of the carbon nano tubes and at least one chemical property of the carbon nano tubes.   
     
     
         6 . The method of  claim 2 , wherein the operation of processing the nano objects further comprises:
 (e) synthesizing the SWNTs by a process selected from the group consisting of laser ablation, arc discharge, chemical vapor deposition, and pyrolysis;   (f) purifying the SWNTs by selective oxidation and/or filtration; and   (g) reducing an aspect ratio of the SWNTs by sonication in acid or mechanical cutting.   
     
     
         7 . The method of  claim 2 , wherein the operation of processing the nano objects further comprises:
 (e) synthesizing the SWNTs by a process selected from the group consisting of laser ablation, arc discharge, chemical vapor deposition, and pyrolysis;   (f) purifying the SWNTs by selective oxidation and/or filtration; and   (g) chemically modifying the SWNTs.   
     
     
         8 . The method of  claim 6 , wherein a length of the processed SWNTs is in a range between about 0.1 micron and about 10 microns. 
     
     
         9 . The method of  claim 2 , wherein the solvent is selected from the group consisting of water, alcohol, and combinations thereof. 
     
     
         10 . The method of  claim 9 , wherein the concentration of the suspension of carbon nanotubes in water is in a range between about 0.01 grams of carbon nanotube per liter of water and about 10.0 grams of carbon nanotube per liter of water. 
     
     
         11 . The method of  claim 2 , wherein the substrate comprises a hydrophilic region and a hydrophobic region such that the SWNTs deposit on the hydrophilic region of the substrate. 
     
     
         12 . The method of  claim 11 , wherein the substrate comprises hydrophilic glass patterned with a hydrophobic material. 
     
     
         13 . The method of  claim 12 , wherein the hydrophobic material is selected from the group consisting of a polystyrene, a photoresist, a mono-layer of hydrophobic functional groups, and combinations thereof. 
     
     
         14 . The method of  claim 1 , wherein the method further comprises patterning a surface of the substrate such that the substrate surface comprises a first region and a second region where the first region has an affinity to the nano objects and the second region has no affinity to the nano objects, where changing the concentration of the suspension deposits the nano objects on the first region of the substrate surface. 
     
     
         15 . The method of  claim 1 , wherein the substrate has a planar configuration. 
     
     
         16 . The method of  claim 1 , wherein the substrate has a curved configuration. 
     
     
         17 . The method of  claim 1 , wherein the operation of changing the concentration of the suspension further comprises changing the concentration of the suspension by gradual evaporation of the solvent such that the nano objects deposit on the substrate along an air/liquid/substrate triple line of the substrate. 
     
     
         18 . The method of  claim 17 , wherein the operation of submersing the substrate into the suspension further comprises submerging the substrate into the suspension in a vertical orientation relative to the suspension. 
     
     
         19 . The method of  claim 18 , wherein longitudinal axes of the nano objects align in a direction of the air/liquid/substrate triple line. 
     
     
         20 . The method of  claim 1 , further comprising:
 (e) removing the substrate from the suspension;   (f) depositing a second material onto the nano objects assembled on the substrate; and   (g) repeating operations (c) through (e) thereby forming a multi layer structure.   
     
     
         21 . The method of  claim 20 , wherein the second material is selected from the group consisting of a metal, a semiconductor, a polymer, an inorganic material, an organic material, a biological material, and combinations thereof. 
     
     
         22 . A multilayer structure prepared by the method of  claim 20 . 
     
     
         23 . The multilayer structure of  claim 22 , wherein the multi layer structure is selected from the group consisting of an electrode, an electrolyte for a battery, and a fuel cell. 
     
     
         24 . The multilayer structure of  claim 22 , wherein the multi-layer structure is selected from the group consisting of a capacitor, a super-capacitor, an electronic device, and a sensor. 
     
     
         25 . A method for assembling pre-formed nano objects into a macroscopic structure, the method comprising:
 (a) processing the nano objects, wherein the processing of the nano object comprises:
 (i) synthesizing the pre-formed nano objects, where the pre-formed nano objects are single wall carbon nanotube (SWNT) bundles; 
 (ii) purifying the SWNT bundles by reflux in a hydrogen peroxide solution and filtering the SWNT bundles; and 
 (iii) cutting the purified SWNT bundles by reacting the SWNTs with HNO 3  and/or H 2 SO 4 , and with ultra-sonication; 
   (b) forming a suspension by admixture of the nano objects with a solution;   (c) inserting a substrate into the suspension; and   (d) gradually removing the substrate from the suspension during which the nano objects from the suspension deposit on the surface of the substrate.   
     
     
         26 . The method of  claim 25 , wherein the substrate comprises a material selected from the group consisting of glass, quartz, aluminum, chromium, tin, and silicon or any other substrate with a hydrophilic coating on a surface of the substrate. 
     
     
         27 . The method of  claim 25 , the substrate further comprising a hydrophobic coating, the hydrophilic coating and the hydrophobic coating forming a pattern on the substrate wherein the processed pre-formed nano objects form onto the substrate at the hydrophilic coating thereby forming a pattern corresponding to the pattern formed by the hydrophilic coating and the hydrophobic coating. 
     
     
         28 . A method for assembling pre-formed nano objects into a macroscopic structure, the method comprising:
 (a) processing the nano objects;   (b) forming a suspension by admixture of the nano objects with a solution;   (c) inserting a substrate into the suspension; and   (d) gradually removing the substrate from the suspension during which the nano objects from the suspension deposit on the surface of the substrate, wherein the nano objects form on an air/liquid/substrate triple line of the substrate.   
     
     
         29 . A method for assembling nano objects into a free-standing macroscopic structure, the method comprising:
 (a) processing the nano objects such that the nano objects disperse or dissolve in a solvent;   (b) admixing the processed nano objects with the solvent to form a stable suspension or a solution in a container that does not attract the processed nano objects;   (c) submersing a seed-crystal into the suspension; and   (d) changing a concentration of the suspension to bring the suspension into super-saturation such that the processed nano objects assemble into a free-standing macroscopic structure.   
     
     
         30 . The method of  claim 29 , wherein the nano objects assemble into the macroscopic structure around the seed crystal such that a structure of the macroscopic structure is the same as a structure of the seed crystal. 
     
     
         31 . The method of  claim 29 , wherein a thickness of the freestanding macroscopic structure is in a range between about 1 nanometer to about 10 microns. 
     
     
         32 . The method of  claim 29 , wherein an area of the free-standing macroscopic structure is in a range between about 1 micron×1 micron and about 10 cm×10 cm. 
     
     
         33 . The method of  claim 29 , wherein the nano objects are selected from the group consisting of single wall carbon nanotubes and multi wall carbon nanotubes. 
     
     
         34 . The method of  claim 29 , wherein the nano objects comprise nanowires/nanorods, and wherein the nanowires/nanorods comprise at least one material selected from the group consisting of carbon, silicon, germanium, oxygen, boron, nitrogen, sulfur, phosphorus, and metal. 
     
     
         35 . A free-standing macroscopic structure assembled by the method of  claim 29 . 
     
     
         36 . A method for fabricating electron field emission cathodes by self-assembly of pre-formed nano objects, the method comprising:
 (a) processing the nano objects such that the nano objects disperse or dissolve in a solvent;   (b) admixing the processed nano objects with the solvent to form a suspension;   (c) submersing a substrate into the suspension; and   (d) changing a concentration of the suspension to assemble the processed nano objects on certain regions of the substrate surface thereby fabricating the electron field emission cathode,   wherein the substrate comprises a region A and a region B where the region A attracts the processed nano objects and the region B does not attract the processed nano objects where the nano objects deposit on the region A upon changing the concentration of the suspension.   
     
     
         37 . The method of  claim 36 , wherein the nano objects comprise carbon nanotubes. 
     
     
         38 . The method of  claim 36 , wherein a smallest lateral dimension of the region A is at least about 100 nm. 
     
     
         39 . The method of  claim 36 , wherein the substrate comprises hydrophilic glass. 
     
     
         40 . The method of  claim 39 , further comprising coating the substrate with a region of a hydrophobic polymer such that the region of the hydrophobic polymer forms the region B and an uncoated region of the substrate forms the region A. 
     
     
         41 . The method of  claim 40 , further comprising removing the region of the hydrophobic polymer after deposition of the nano objects. 
     
     
         42 . The method of  claim 40 , wherein the hydrophobic polymer is removed by washing in a solvent selected from the group consisting of acetone, methanol, ethanol, buffered hydrofluoric acid, and combinations thereof. 
     
     
         43 . The method of  claim 36 , wherein the process further comprises annealing the substrate deposited with the nano-objects at a temperature in a range between about 100° C. and about 500° C. in a vacuum. 
     
     
         44 . The method of  claim 36 , wherein the nano objects are single wall carbon nanotube bundles with an aspect ratio larger than about 10 and a bundle length in a range between about 300 nm and about 1 micron. 
     
     
         45 . The method of  claim 36 , wherein the field emission cathode has a threshold electrical field in a range between about 1 V/micron and about 5V/micron for an emission current density of about 1 mA/cm 2 . 
     
     
         46 . A field emission cathode fabricated by the method of  claim 36 . 
     
     
         47 . A method for assembling nano objects onto a macroscopic structure, the method comprising:
 (a) processing nano objects to a desired aspect ratio and chemical functionality;   (b) admixing the processed nano objects with a solvent to form a suspension, the suspension having a concentration, a temperature and a pH level; and   (c) coating the suspension onto a substrate thereby assembling the macroscopic structure onto the substrate.   
     
     
         48 . The method of  claim 47 , wherein the operation of coating the suspension onto a substrate further comprises a coating procedure selected from the group consisting of spin coating, spraying, and electrophoresis. 
     
     
         49 . The method for assembling nano objects onto a macroscopic structure as recited in  claim 47 , wherein the substrate has a first region and a second region where the first region attracts the nano objects and the second region does not attract nano objects.