ANODIZED ALUMINUM OXIDE TEMPLATE ENABLED NANOSTRUCTURE FORMATION AND METHOD THEREOF

Abstract

The present invention relates to an anodized aluminum oxide template that is used to grow periodic nanostructure and method of fabrication of the said template. The invention further relates to the fabrication of the respective periodic nanostructures from diverse materials using hydrothermal and/or CVD method for growing the said nanostructure. The AAO template enabled nanostructure comprises of a substrate disposed on the top of the AAO template; seed/s disposed in the nano-channels/nanopores of the AAO; nanostructures that are grown from respective nano-channels to form substantially uniform distribution/near periodic structure.

Description

FIELD OF INVENTION

The present invention relates to an anodized aluminum oxide template that is used to grow periodic nanostructure and method of fabrication of the said template. The invention further relates to the fabrication of the respective periodic nanostructures from diverse materials using hydrothermal and/or CVD method for growing the said nanostructure.

BACKGROUND OF THE INVENTION

The periodic nanostructures find use in the diverse applications is need of the hour in electronics, telecommunication, energy, sensing elements, field emission devices, wave guides, solar cells, LEDs, display, diodes etc. The periodic structure is defined as a structure that is repeated without substantial variation in dimensions and/or distance between the adjacent structures. The nano structures are in diverse forms such as nanowires, nanorods, nanotubes, nano-colloid. Furthermore morphological transformations of the nanorods are in the form of pencil-like, rods, tubular, dot, needle-like, tree-like, ball, Urchin-like, spherical shapes

Conventional methods of creating the periodic nanostructure primarily comprises of use of template. The desired pattern is created on this template using lithography techniques such as electron beam, laser, nano imprint, mask lithography of porous alumina, soft lithography, interference lithography for creating/forming individual openings at desired pitch. It is well established fact that this process is time consuming and therefore very expensive.

Yung-Huang Chang et. al. report Fabrication and Characteristics of Self-Aligned ZnO Nanotube and Nanorod Arrays on Si Substrates by Atomic Layer Deposition.

There are several methods for fabricating nano-rods/nanostructures using AAO template. Following are the details:

• • Electro-deposition of metals inside AAO nano-channels.
  • Direct deposition wherein fluid is forced to enter the AAO nano-channels followed by hardening of the said fluid to convert into solids and form nano-rods.
  • Growing the nano-rods using hydrothermal method from seed layer which is deposited with the help of AAO template.
  • Growing the nano-rods using Chemical Vapor Deposition (CVD) method from seed layer which is deposited with the help of AAO template.

One of the conventional methods uses AAO membrane that is used for gold sputtering to create impression on Silicon substrate. However the membrane is substantially low (of the order of 200 nm) to enable passing through gold particles through the pores of the membrane to reach the Si substrate. The characteristics of the Si substrate (smoothness and crystalline structure) is used in this method. However, it suffers from the drawback that the superthin membrane poses problem in handling leading to limitations of scaling up the process or use of the membrane on a concentrated area (of the order of few micrometer).

In nano imprint technology seed layer is dispersed on the substrate (Si) and further photoresist (adhesive) is placed on the seed layer. An external nano-stamp is fabricated having desired periodic structure in the form of raised/protruding portions. This stamp is pressed on the said photoresist layer to enable nano-indents on the said layer. Etching process is carried out to open the indents for the seed layer that creates periodic arrangement of the seed layer used for growing nano rods.

In yet another method reported in the literature, the nano-stamp is inserted inside the seeds that are adhered on the surface of the nano-stamp. This seed loaded nano-stamp is then pressed on the substrate (such as Si). This results in the transfer of the seeds from the said raised portions of the nano-stamp on the substrate surface creating a periodic arrangement of the seeds. Further, the seeds are processed using methods such as CVD, hydrothermal method for growing nanorods or structures.

In yet another method disclosed in US Patent application number 20060270229 aluminum layer is deposited on the top of the Si wafer. Further the Aluminum is anodized to form AAO. Further the barrier layer is removed to expose Si in the nanochannels of AAO. The desired material is electrodeposited in the nano-channels of AAO from top of the AAO. The Si is the substrate. The AAO is chemically etched to obtain nano-rods that substantially perpendicular to the surface of Si substrate. However this method suffers from limitations that substantially expensive Si substrate is necessary due to its inherent characteristics such as smoothness. This method is not capable of providing crystalline hexagonal geometry of ZnO nano-rods because the said nano-rods are oxidised after formation in the AAO.

The Korean patent application number KR 20060103924 discloses method for fabricating the nano-rod by AAO template and the nano-rod using the method. The AAO is grown on Al. Further, gold is sputtered to form conducting seed layer on the top surface of AAO. Further, the gold layer thickness is increased by electrochemical deposition for enhancing conductivity. The Al is etched chemically followed by etching of barrier layer. The desired material is electrochemically deposited in the opened nano-pores of the AAO. Further, the AAO is etched chemically to form the metallic nano-rods. However, there is limitation of using the thick membrane in this method. The rods are formed using electrochemical deposition that limits use for only metals. The nano-rod length is limited by the membrane thickness. That is the rod length is the function/dependent on the membrane thickness. This method can-not be used for hydrothermal growth or CVD growth of rods.

Muhammad Arif et. al. report method that uses electro-deposition to form rods on the flexible substrate of PDMS. The graphene is used as transparent electrode for connecting nano-rods. However this method suffers from drawback that it is not possible to achieve crystalline structure of the nano-rods because of the use of electrochemical deposition.

US Patent application number 20050276743 discloses method for fabrication of porous metal templates and growth of carbon nanotubes and utilization thereof. The seed for Carbon Nanotube (CNT) is placed inside the nano-channels of AAO and further CNT is grown using CVD. Further, the top of the AAO including grown CNT is attached with electrode. The Al and barrier layer of AAO is etched chemically and CNT is further grown for increasing the length of the tube. However, in this process the tube is grown in two directions. In the first phase the direction for the growth is towards the top surface of the AAO. Further the tube is grown from the bottom surface of the AAO upon removal of the barrier layer. However there is limitation of this method in terms of precisely placing the seed in the nano-channels without attachment with AAO surface

The methods disclosed in the prior art suffer from following drawbacks:

• • Dependence on specific material properties such as smoothness and crystalline structure of substrate for periodic structure formation. For example use of Si.
  • Limitation for using flexible substrate for forming a periodic structure because of dependence on material inherent properties (such as smoothness and crystal structure of the substrate);
  • There is restriction of the use of particular method for the growth of the nanostructures due to material properties of the substrate and temperature considerations
  • Substantial time for formation of the template impedes techno-commercial viability to use large surfaces areas
  • Limitation of using diverse methods for growth of the nano-structures because of the flexibility of selecting appropriate substrate material in accordance with the respective selected method.
  • Limitation of selection of the substrate material due to particular method, for example use of CVD may need high temperatures wherein materials like PDMS can not be used.
  • Interdependence of the nano structure on the material properties of the substrate posing limitations in achieving diversity and/or combinations of the substrate material and nano structure material.
  • Limitation to achieve combinations of the substrate material, nanostructure material and the method of growing the nano-structures.
  • Use of electrochemical deposition is limited to metals only.
  • Lack of formation of the crystalline structure in the methods that use electrochemical deposition
  • Expensive process to enable use of flexible substrate
  • Use of expensive means such as electron beam lithography and/or laser lithography technology for creating/forming template
  • Use of expensive means such as lithography techniques to manufacture template

SUMMARY OF THE INVENTION

The main object of the invention is to provide AAO template assisted substantially uniform nanostructures, method of formation/manufacture of the nanostructures and AAO template thereof.

The main object of the invention is to provide a method for the growth of periodic nanostructures using AAO as a template. Further object of the invention is to provide the AAO template to this effect.

Another object of the invention is to provide a method to form an AAO template.

Yet another object of the invention is to enable substrate disposition for the seeds/nanostructures on the top of the AAO membrane.

Yet another object of the invention is to enable substrate disposition for the seeds and thereby nanostructures on the top of the AAO membrane and yet enable the growth of the nanostructures using AAO as a template.

Yet another object of the invention is to utilize AAO membrane barrier layer side to enable growth of the nanostructure and thereby as a template.

Yet another object of the invention is to integrate the process of seeding for nanostructure growth, substrate disposition and AAO template formation.

Yet another object of the invention is to enable growth of the nanostructures from the barrier layer side of the AAO membrane.

Yet another object of the invention is to enable maintain substantially lower thickness of the AAO template and yet achieve substantially large surface area for formation of the substantially uniform nanostructures.

Yet another object of the invention is to enable growth of the nanostructures from respective nano-channel/nano pore of the AAO membrane to achieve substantially uniform nanostructure near periodic distribution.

Yet another object of the invention is to obviate uncontrolled and undesirable growth of nanostructures from seeds from substrate.

Another object of the invention is to provide a method to selectively orient and direct nanostructure to achieve periodicity using AAO template.

Yet another object of the invention is to utilize AAO nano-channels as a guide to selectively direct the nanostructure to achieve periodicity.

Yet another object of the invention is to obviate use of substantially thick AAO membrane as a template.

Yet another object of the invention is to achieve length of the nanostructure independent of the membrane thickness.

Yet another object of the invention is to use AAO template over substantially large area yet maintaining substantially lower thickness of the template.

Yet another object of the invention is to obviate limitation of the membrane thickness obviating the limitation of the AAO channel thickness consideration.

Yet another object of the invention is to provide a method of fabrication of the AAO template.

Another object of the invention is to provide a method to grow periodic nanostrucuture/s from diverse metal oxides.

Yet another object of the invention is to obviate use of specific material properties such as smoothness and crystalline structure for substrate to achieve periodic structure formation.

Yet another object of the invention to enable use of flexible substrate for the formation of periodic nanostructure.

Yet another object of the invention is to enable use of substrate material to sustain substantially higher temperatures.

Thus in accordance with the present invention the AAO template enabled nanostructure comprises of

• • a substrate disposed on the top of the AAO template;
  • seed/s disposed in the nano-channels/nanopores of the AAO;
  • nanostructures that are grown from respective nano-channels to form substantially uniform distribution/near periodic structure

wherein the method of AAO template assisted substantially uniform nanostructure fabrication comprises steps of:

• • electro polishing of Aluminum substrate (Al) comprising steps of:
    • placing the Al substrate in mixture of perchloric acid and ethanol respectively wherein the ratio in the range of 1:3 to 1:5 by volume wherein purity of ethanol is in the range of 99%-99.9% and that of perchloric acid is in the range of 69-72%;
    • applying potential at a temperature less than 10° C. wherein the potential is in the range of 10 to 20 V;
    • applying potential for 3 to 10 min depending on the surface roughness;
  • first step mild anodization comprising steps of:
    • selecting phosphoric acid as an electrolyte wherein the concentration is in the range of 0.1M to 0.5M
    • applying a potential in the range of 160V to 195V wherein the process time is in the range of 1 to 6 h.
  • chemical etching of the anodized aluminum oxide comprising steps of:
  • etching for the time duration in the range of 5 to 10 minutes in chromic acid and phosphoric acid wherein the temperature is in the range of 65-80° C. wherein phosphoric acid is in the range of 6 wt % to 7 wt % and chromic acid is in the range of 2 wt % to 3 wt %;
  • second step mild anodization comprising steps of repeating the process in the first step anodization wherein hexagonally arranged nanoporous Alumina (AAO) structures are formed with one end blocked with barrier layer wherein process time depends on the membrane thickness, it can range from 5 minutes to 25 minutes.

Optionally hard anodization is used in place of the said mild anodization steps wherein the hard anodization comprises steps of:

• • first step hard anodization comprising steps of:
    • selecting oxalic acid as an electrolyte wherein the concentration is in the range of 0.25M to 0.35M;
    • applying a potential in the range of 35V to 40V for a time duration in the range of 5 to 10 minutes;
    • further increasing the potential gradually in substantially low rate up to the range of 120V to 150V and further maintaining it at the respective voltage for a time duration in the range of 5 to 10 minutes

chemical etching of the anodized aluminum oxide comprising steps of:

etching for the time duration in the range of 5 to 10 minutes in chromic acid and phosphoric acid wherein the temperature is in the range of 65-80° C. wherein phosphoric acid is in the range of 6 wt % to 7 wt % and chromic acid is in the range of 2 wt % to 3 wt %;

second step hard anodization comprising steps of applying voltage in the range of 120V to 150V for 1 to 2 minutes wherein hexagonally arranged nanoporous structures are formed with one end blocked with barrier layer

• • seeding for the growth of nanostructure/s comprising steps of
    • preparation of seed solution and deposition of the said solution on the top surface of the said Alumina (AAO) structure using spin coating,
    • optionally depositing nano-particles on the top surface of the said Alumina (AAO) structure using sputtering process
    • optionally a combination of the said deposition of the solution and deposition of the nanoparticles using respective spin coating and/or sputtering
    • annealing of the Alumina loaded with the said seeds;
  • selection of substrate material depending on the process of growth of the nanostructures wherein the substrate is selected from the materials that withstand substantially high temperatures for the Chemical Vapor Deposition (CVD) process or otherwise for the hydrothermal process;
  • selection of flexible or hard substrate material or combination thereof wherein hard material is selected from glass, thick metal layer and therelike that do not tend to bend under force, a person skilled in art can easily contemplate meaning of the hard material in the context of the substrate in this art wherein the flexible material is selected from Polydimethyl Silexene (PDMS), rubber, polymer based materials, plastics and therelike that tend to bend under force and regain original shape, a person skilled in art can easily contemplate meaning of the flexible material in the context of the substrate in this art
  • removal of Al and barrier layer comprising steps of
  • chemical etching of the Al in cupric chloride (CuCl₂)and hydrochloric acid (HCL) solution wherein the temperature is in the range of 30° C. to 40° C., concentration of CuCl₂ is in the range of 0.2M to 0.25M and that of HCL is in the range of 5.5M to 6.2M wherein the time duration depends on the thickness of Al to be etched optionally saturated mercuric chloride is used for the said chemical etching process and the temperature is in the range of 50 to 60° C.
  • barrier layer (BL) removal by chemical etching comprising steps of placing of AAO in 5 wt % to 6 wt % Phosphoric acid for time duration in the range of 200 to 250 min at a temperature in the range of 32° C. to 33° C.
  • to form an assembly comprising of the substrate that supports the seed loaded AAO which is prepared/ready for growth of the nanostructure from the opened nanopores by virtue of barrier layer removal
  • growth of the nanostructures from the said opened nanopores comprising use of hydrothermal growth or CVD or combination thereof.
  • wherein the process of hydrothermal growth comprises steps of:
    • preparation of a nutrient
    • disposition of the said assembly upside down in the said nutrient in a manner that the substrate is at the top and the AAO pore side (from where the barrier layer was removed) is brought in contact with the said nutrient surface
    • the time and temperature of the said nutrient is arrived at with respect to respective desired nanostructure nature, geometry and length
    • cleaning of the grown nanostructures by Deionized Water (DI water)
    • annealing of the said nanostructures at a temperature that depends on the substrate material temperature withstanding characteristics

to form the AAO template enabled substantially uniform near periodic nanostructures

wherein optional use of the CVD for the growth of the nanostructure comprises steps of selection of carrier and active gas

wherein the carrier gas is selected from a non-reacting gases such as Argon, Nitrogen and the active gas that enables reaction is selected from Oxygen, Carbon dioxide and therelike,

the source that is disposed in the CVD chamber is in the form of powder or gas; it is selected depending on the material of the seed,

optionally the source is a gas itself depending on the nature and material of the nanostructure such as carbon nanotube, zinc oxide, CdS to form the AAO template enabled substantially uniform near periodic nanostructures.

In one of the aspects of the invention the seeding for the growth of nanostructure/s is carried out using spin coating process wherein

• • preparation of seed solution and deposition of the said solution on the top surface of the said Alumina (AAO) structure using spin coating,

optionally depositing nano-particles on the top surface of the said Alumina (AAO) structure using sputtering process

optionally a combination of the said deposition of the solution and deposition of the nanoparticles using respective spin coating and/or sputtering

• • annealing of the Alumina loaded with the said seeds.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of this invention will become apparent in the following detailed description and the preferred embodiments with reference to the accompanying drawings. The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings.

FIG. 1 illustrates schematic of the AAO template assisted nanostructure formation

FIG. 2(a) illustrates the schematic of the seeding

FIG. 2(b) illustrates schematic of the substrate disposition

FIG. 3 illustrates schematic of the Al removal

FIG. 4 illustrates schematic of the boundary layer removal

FIG. 5 illustrates schematic of the AAO assisted nanostructure formation

DESCRIPTION OF THE INVENTION

In the following description, various embodiments will be disclosed. However, it will be apparent to those skilled in the art that the embodiments may be practiced with only some or shall disclosed subject matter. For purposes of explanation, specific numbers, materials, and/or configuration are set forth in order to provide a thorough understanding of the embodiments. However, it will also be apparent to one skilled in the art that the embodiments may be practiced without one or more of the specific details, or with other approaches, materials, components etc. In other instances, well-known structures, materials, and/or operations are not shown and/or described in detail to avoid obscuring the embodiments. Accordingly, in some instances, features are omitted and/or simplified in order to not obscure the disclosed embodiments. Further more, it is understood that the embodiments shown in the Figures are illustrative representation and are not necessarily drawn to scale.

As illustrated in the schematic in FIG. 1, the AAO template enabled nanostructure comprises of

• • a substrate 1 disposed on the top of the AAO template 2;
  • seed/s (indicated as representation by numeral 3) disposed in the nano-channels/nanopores (represented by numeral 4) of the AAO;
  • nanostructures (represented by numeral 5) that are grown from respective nano-channels to form substantially uniform distribution/near periodic structure

The method of AAO template assisted substantially uniform nanostructure fabrication comprises steps of:

electro-polishing of the substrate,

• • combination of hard and mild anodization,
  • seeding for the growth of nanostructure/s
  • substrate disposition
  • removal of Al and barrier layer to open nanopores
  • growth of the nanostructures from the said opened nanopores

The process of electro polishing of Aluminum substrate (Al) comprising steps of:

• • placing the Al substrate in mixture of perchloric acid and ethanol respectively wherein the ratio in the range of 1:3 to 1:5 by volume wherein purity of ethanol is in the range of 99%-99.9% and that of perchloric acid is in the range of 69-72%;
  • applying potential at a temperature less than 10° C. wherein the potential is in the range of 10 to 20 V;
  • applying potential for 3 to 10 min depending on the surface roughness.

First step mild anodization comprising steps of:

• • selecting phosphoric acid as an electrolyte wherein the concentration is in the range of 0.1M to 0.5M
  • applying a potential in the range of 160V to 195V wherein the process time is in the range of 1 to 6 h.

The chemical etching of the anodized aluminum oxide comprising steps of etching for the time duration in the range of 5 to 10 minutes in chromic acid and phosphoric acid wherein the temperature is in the range of 65-80° C. wherein phosphoric acid is in the range of 6 wt % to 7 wt % and chromic acid is in the range of 2 wt % to 3 wt %;

The second step mild anodization comprising steps of repeating the process in the first step anodization wherein hexagonally arranged nanoporous Alumina (AAO) structures are formed with one end blocked with barrier layer wherein process time depends on the membrane thickness, it can range from 5 minutes to 25 minutes.

In one of the embodiments, optionally hard anodization is used in place of the said mild anodization steps wherein the two step hard anodization process comprises steps of:

• • first step hard anodization comprising steps of:
    • selecting oxalic acid as an electrolyte wherein the concentration is in the range of 0.25M to 0.35M;
    • applying a potential in the range of 35V to 40V for a time duration in the range of 5 to 10 minutes;
    • further increasing the potential gradually in substantially low rate up to the range of 120V to 150V and further maintaining it at the respective voltage for a time duration in the range of 5 to 10 minutes.

Chemical etching of the anodized aluminum oxide comprising steps of etching for the time duration in the range of 5 to 10 minutes in chromic acid and phosphoric acid wherein the temperature is in the range of 65-80° C. wherein phosphoric acid is in the range of 6 wt % to 7 wt % and chromic acid is in the range of 2 wt % to 3 wt %.

The second step hard anodization comprising steps of applying voltage in the range of 120V to 150V for 1 to 2 minutes wherein hexagonally arranged nanoporous structures are formed with one end blocked with barrier layer.

The process of seeding for the growth of nanostructure/s comprises steps of:

• • preparation of seed solution and deposition of the said solution on the top surface of the said Alumina (AAO) structure using spin coating.
  • In one of the embodiments nano-particles are deposited on the top surface of the said Alumina (AAO) structure using sputtering process. In another embodiment a combination of the said deposition of the solution and deposition of the nanoparticles using respective spin coating and/or sputtering annealing of the Alumina loaded with the said seeds. FIG. 2(a) represents schematic illustrating disposition of the seeds (representatively indicated by numeral 20) in the AAO structure 21 and Al 22.

The disposition of the substrate comprises steps of selection of substrate material depending on the process of growth of the nanostructures. The schematic of this aspect is illustrated in FIG. 2(b). The substrate 25 is disposed on the top as depicted in this figure. The substrate is selected from the materials that withstand substantially high temperatures for the Chemical Vapor Deposition (CVD) process.

Optionally if the process of hydrothermal growth of the nanostructure is selected a flexible or hard substrate is selected.

In one of the embodiments the hard material is selected from glass, thick metal layer and therelike that do not tend to bend under force, a person skilled in art can easily contemplate meaning of the hard material in the context of the substrate in this art. In another embodiment the flexible material is selected from Polydimethyl Silexene (PDMS), rubber, polymer based materials, plastics and therelike that tend to bend under force and regain original shape, a person skilled in art can easily contemplate meaning of the flexible material in the context of the substrate in this art.

The process of removal of Al and barrier layer comprising steps of chemical etching of the Al in cupric chloride (CuCl₂)and hydrochloric acid (HCL) solution wherein the temperature is in the range of 30° C. to 40° C., concentration of CuCl₂ is in the range of 0.2M to 0.25M and that of HCL is in the range of 5.5M to 6.2M wherein the time duration depends on the thickness of Al to be etched optionally saturated mercuric chloride is used for the said chemical etching process and the temperature is in the range of 50 to 60° C. The result of the barrier layer is depicted in FIG. 3.

The process of barrier layer (BL) removal by chemical etching comprises steps of placing of AAO in 5 wt % to 6 wt % Phosphoric acid for time duration in the range of 200 to 250 min at a temperature in the range of 32° C. to 33° C.

As depicted in FIG. 4, the barrier removal results in the formation of an assembly comprising of the substrate 25 that supports the seeds (represented by numeral 40) loaded AAO which is prepared/ready for growth of the nanostructure from the opened nanopores (represented by numeral 41) by virtue of barrier layer removal.

The process of growth of the nanostructures from the said opened nanopores is effected by use of hydrothermal growth or Chemical Vapour Deposition process.

The process of hydrothermal growth comprises steps of:

• • preparation of a nutrient
  • disposition of the said assembly upside down in the said nutrient in a manner that the substrate is at the top and the AAO pore side (from where the barrier layer was removed) is brought in contact with the said nutrient surface
  • the time and temperature of the said nutrient is arrived at with respect to respective desired nanostructure nature, geometry and length
  • cleaning of the grown nanostructures by Deionized Water (DI water)
  • annealing of the said nanostructures at a temperature that depends on the substrate material temperature withstanding characteristics

to form the AAO template enabled substantially uniform near periodic nanostructures as depicted in FIG. 5 (the numeral 50 represents the nanostructures)

The CVD process for the growth of the nanostructure comprises steps of selection of carrier and active gas

wherein the carrier gas is selected from a non-reacting gases such as Argon, Nitrogen and the active gas that enables reaction is selected from Oxygen, Carbon dioxide and therelike,

The source that is disposed in the CVD chamber is in the form of powder or gas; it is selected depending on the material of the seed,

optionally the source is a gas itself depending on the nature and material of the nanostructure such as carbon nanotube, zinc oxide, CdS cadmium sulphide to form the AAO template enabled substantially uniform near periodic nanostructures.

In one of the embodiments the nanostructure is in the form of nanowires, nanorods, nanotubes, nano-colloid. wherein morphological transformations of the nanorods are in the form of pencil-like, rods, tubular, dot, needle-like, tree-like, ball, Urchin-like, spherical shapes.

In another embodiment the zinc oxide nanostructure is formed.

Claims

1. An anodized aluminum oxide template comprising

a substrate disposed on the top of the AAO template;

seed/s disposed in nanopores of the AAO;

nanostructures that are grown from respective nano-channels/nanopores to form substantially uniform near periodic distribution

2. An anodized aluminum oxide template wherein the method of AAO template assisted substantially uniform nanostructure fabrication comprises steps of:

electro-polishing of the substrate,

combination of hard and/or mild anodization,

seeding for the growth of nanostructure/s

substrate disposition

removal of Al and barrier layer to open nanopores

growth of the nanostructures from the said opened nanopores using hydrothermal and/or chemical vapour deposition process

3. An anodized aluminum oxide template as claimed in claim 2 wherein the process of electro polishing of Aluminum substrate (Al) comprising steps of:

placing the Al substrate in mixture of perchloric acid and ethanol respectively wherein the ratio in the range of 1:3 to 1:5 by volume wherein purity of ethanol is in the range of 99%-99.9% and that of perchloric acid is in the range of 69-72%;

applying potential at a temperature less than 10° C. wherein the potential is in the range of 10 to 20 V;

applying potential for 3 to 10 min depending on the surface roughness.

4. An anodized aluminum oxide template as claimed in claim 2 wherein the process of first step mild anodization comprises steps of:

selecting phosphoric acid as an electrolyte wherein the concentration is in the range of 0.1M to 0.5M

applying a potential in the range of 160V to 195V wherein the process time is in the range of 1 to 6 h.

5. An anodized aluminum oxide template as claimed in claim 4 wherein the chemical etching of the anodized aluminum oxide comprising steps of etching for the time duration in the range of 5 to 10 minutes in chromic acid and phosphoric acid wherein the temperature is in the range of 65-80° C. wherein phosphoric acid is in the range of 6 wt % to 7 wt % and chromic acid is in the range of 2 wt % to 3 wt %.

6. An anodized aluminum oxide template as claimed in claim 2 wherein the second step mild anodization comprising steps of

selecting phosphoric acid as an electrolyte wherein the concentration is in the range of 0.1M to 0.5M

applying a potential in the range of 160V to 195V wherein the process time is in the range of 1 to 6 h

wherein hexagonally arranged nanoporous Alumina (AAO) structures are formed with one end blocked with barrier layer wherein process time depends on the membrane thickness, it can range from 5 minutes to 25 minutes.

7. An anodized aluminum oxide template as claimed in claim 2 wherein two step hard anodization is used.

8. An anodized aluminum oxide template as claimed in claim 7 wherein the first step hard anodization comprises steps of:

selecting oxalic acid as an electrolyte wherein the concentration is in the range of 0.25M to 0.35M;

applying a potential in the range of 35V to 40V for a time duration in the range of 5 to 10 minutes;

further increasing the potential gradually in substantially low rate up to the range of 120V to 150V and further maintaining it at the respective voltage for a time duration in the range of 5 to 10 minutes.

9. An anodized aluminum oxide template as claimed in claim 8 wherein chemical etching of the anodized aluminum oxide comprising steps of etching for the time duration in the range of 5 to 10 minutes in chromic acid and phosphoric acid wherein the temperature is in the range of 65-80° C. wherein phosphoric acid is in the range of 6 wt % to 7 wt % and chromic acid is in the range of 2 wt % to 3 wt %.

10. An anodized aluminum oxide template as claimed in claim 7 wherein second step hard anodization comprising steps of applying voltage in the range of 120V to 150V for 1 to 2 minutes wherein hexagonally arranged nanoporous structures are formed with one end blocked with barrier layer.

11. An anodized aluminum oxide template as claimed in claim 1 wherein the process of seeding for the growth of nanostructure/s comprises steps of:

preparation of seed solution and deposition of the said solution on the top surface of the said Alumina (AAO) structure using spin coating;

deposition of the nano-particles on the top surface of the sand AAO structure

annealing of the Alumina loaded with the seeds.

12. An anodized aluminum oxide template as claimed in claim 11 wherein the nano-particles are deposited on the top surface of the said Alumina (AAO) structure using sputtering process.

13. An anodized aluminum oxide template as claimed in claim 11 wherein the nano-particles are deposited on the top surface of the said Alumina (AAO) structure using spin coating process.

14. An anodized aluminum oxide template as claimed in claim 2 wherein the process of nanostructure growth is selected from Chemical Vapor Deposition (CVD) or hydrothermal process.

15. An anodized aluminum oxide template as claimed in claim 2 wherein the process of disposition of the substrate comprises steps of selection of substrate material depending on the process of growth of the nanostructures wherein the substrate is selected from the materials that withstand substantially high temperatures for the Chemical Vapor Deposition (CVD) process for nanostructure growth.

16. An anodized aluminum oxide template as claimed in claim 2 wherein the substrate is selected from a flexible or hard matter for the hydrothermal nanostructure growth process.

17. An anodized aluminum oxide template as claimed in claim 15 wherein the hard material for the substrate is selected from glass, thick metal layer that do not tend to bend under force,

18. An anodized aluminum oxide template as claimed in claim 16 wherein the the flexible material for the substrate is selected from Polydimethyl Silexene (PDMS), rubber, polymer based materials, plastics and therelike that tend to bend under force and regain original shape.

19. An anodized aluminum oxide template as claimed in claim 2 wherein the process of removal of Al comprises steps of chemical etching of the Al in cupric chloride (CuCl2)and hydrochloric acid (HCL) solution wherein the temperature is in the range of 30° C. to 40° C., concentration of CuCl2 is in the range of 0.2M to 0.25M and that of HCL is in the range of 5.5M to 6.2M wherein the time duration depends on the thickness of Al to be etched optionally saturated mercuric chloride is used for the said chemical etching process and the temperature is in the range of 50 to 60° C.

20. An anodized aluminum oxide template as claimed in claim 2 wherein the process of barrier layer (BL) removal by chemical etching comprises steps of placing of AAO in 5 wt % to 6 wt % Phosphoric acid for time duration in the range of 200 to 250 min at a temperature in the range of 32° C. to 33° C.

21. An anodized aluminum oxide template as claimed in claim 2 wherein the growth of the nanostructures from the said opened nanopores is effected by use of hydrothermal growth and/or Chemical Vapour Deposition (CVD) process.

22. An anodized aluminum oxide template as claimed in claim 21 wherein the process of hydrothermal growth comprises steps of:

preparation of a nutrient;

disposition of the said assembly upside down in the said nutrient in a manner that the substrate is at the top and the AAO pore side from where the barrier layer was removed is brought in contact with the said nutrient surface;

the time and temperature of the said nutrient is arrived at with respect to respective desired nanostructure nature, geometry and length

cleaning of the grown nanostructures by deionized water;

annealing of the said nanostructures at a temperature that depends on the substrate material temperature withstanding characteristics.

to form the AAO template enabled substantially uniform nanostructures.

23. An anodized aluminum oxide template as claimed in claim 21 wherein the chemical vapour deposition process for the growth of nanostructure comprises steps of selection of carrier and active gas

wherein the carrier gas is selected from a non-reacting gases such as Argon, Nitrogen and the active gas that enables reaction is selected from Oxygen, Carbon dioxide and therelike,

the source that is disposed in the CVD chamber is in the form of powder or gas; it is selected depending on the material of the seed,

optionally the source is a gas itself depending on the nature and material of the nanostructure such as carbon nanotube, zinc oxide, CdS cadmium sulphide to form the AAO template enabled substantially uniform nanostructures.

24. A method of AAO template assisted substantially uniform nanostructure fabrication comprises steps of:

electro-polishing of the substrate,

combination of hard and/or mild anodization,

seeding for the growth of nanostructure/s

substrate disposition

removal of Al and barrier layer to open nanopores

growth of the nanostructures from the said opened nanopores using hydrothermal and/or chemical vapour deposition process

wherein the AAO template comprises of

a substrate disposed on the top of the AAO template;

seed/s disposed in nanopores of the AAO;

nanostructures that are grown from respective nano-channels to form substantially uniform distribution/near periodic structure.

25. An anodized aluminum oxide template as claimed in claim 1 wherein the nanostructure is in the form of nanowires, nanorods, nanotubes, nano-colloid. wherein morphological transformations of the nanorods are in the form of pencil-like, rods, tubular, dot, needle-like, tree-like, ball, Urchin-like, spherical shapes.

26. An anodized aluminum oxide template as claimed in claim 2 wherein the zinc oxide nanostructures are formed.