U.S. patent application number 12/407512 was filed with the patent office on 2009-09-17 for method for the preparation of nanostructures and nanowires.
This patent application is currently assigned to ISTANBUL TEKNIK UNIVERSITESI. Invention is credited to Mustafa Urgen, Yasin Yesil.
Application Number | 20090229989 12/407512 |
Document ID | / |
Family ID | 37943909 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090229989 |
Kind Code |
A1 |
Urgen; Mustafa ; et
al. |
September 17, 2009 |
METHOD FOR THE PREPARATION OF NANOSTRUCTURES AND NANOWIRES
Abstract
A process for producing porous nanostructures suitable for the
manufacture of nanowires and processes for manufacturing of the
nanowires by using said nanostructure are disclosed. The process
for obtaining the nanostructure of the invention comprises the
steps of cleaning and polishing the surface of an aluminum metal
substrate, forming a porous oxide layer bearing nanoholes on said
aluminum substrate, immersing the porous structure into a basic
zincate solution for etching the bottoms and walls of the nanoholes
and depositing a thin and substantially pure Zn film extending from
the bottom of the nanoholes through the aluminum substrate.
Nanowires can be fabricated by the step of utilizing so obtained
etched nanostructure as an electrode and subjecting the same to a
metal electro-deposition operation.
Inventors: |
Urgen; Mustafa; (Istanbul,
TR) ; Yesil; Yasin; (Istanbul, TR) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
ISTANBUL TEKNIK
UNIVERSITESI
Istanbul
TR
|
Family ID: |
37943909 |
Appl. No.: |
12/407512 |
Filed: |
March 19, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP2006/066660 |
Sep 22, 2006 |
|
|
|
12407512 |
|
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Current U.S.
Class: |
205/150 ;
977/762 |
Current CPC
Class: |
C23F 1/36 20130101; C25D
1/04 20130101; C25D 11/20 20130101; B82Y 30/00 20130101 |
Class at
Publication: |
205/150 ;
977/762 |
International
Class: |
C25D 5/00 20060101
C25D005/00; C25D 11/02 20060101 C25D011/02 |
Claims
1. A process for manufacturing of nanowires comprising the steps
of; cleaning and polishing the surface of an aluminum metal
substrate, and then forming a porous oxide layer bearing nanoholes
on the aluminum substrate, immersing the porous structure into a
basic zincate solution for etching the bottoms and walls of the
nanoholes and depositing a Zn film from inner walls of the pores
through the aluminum substrate, wherein said solution comprising
Zn(OH).sub.2 and a strong base selected from the group consisting
of NaOH, KOH, Ba(OH).sub.2, Ca(OH).sub.2, LiOH, RbOH, CsOH and
Sr(OH).sub.2, and utilizing the etched nanostructure as an
electrode and subjecting the same to a metal electro-deposition
process.
2. A process according to claim 1, wherein the porous oxide layer
is formed by means of two anodization steps for providing regular
arrays of nanoholes.
3. A process for producing a porous nanostructure according to
claim 2 wherein said anodization steps are carried out in the
presence of an acidic electrolytic solution selected from the group
consisting of aqueous sulfuric acid, oxalic acid, phosphoric acid
and chromic acid solutions.
4. A process according to claim 3 wherein concentration of said
acidic solution varies in the range of 1% to 50%, more preferably
3% to 15% (v/v).
5. A process for producing a porous nanostructure according to
claim 1 wherein the Zn(OH).sub.2/strong base ratio in the zincate
solution varies in the range of 0.1 to 1.8, more preferably in the
range of 0.4 to 0.8 by weight.
6. A process according to claim 1 wherein the metal deposited
within the pores of the nanostructure is selected from the group
consisting of Ni, Fe and Co.
7. A process according to claim 1, wherein the electro-deposition
is carried out in a current density ranging from 0.1 to 20
A/dm.sup.2, more preferably 0.2 to 2 A/dm.sup.2.
8. A process according to claim 1, wherein the electro-deposition
step is carried out in the presence of an electrolytic solution
comprising NiSO.sub.4 and a weak acid selected from the group
consisting of H.sub.3BO.sub.3, H.sub.3PO.sub.4, CH.sub.3COOH, HF,
CH.sub.3COCOOH and C.sub.5H.sub.5NCOOH.
9. A process for producing nanowires according to claim 8, wherein
the ratio of NiSO.sub.4/weak acid varies in the range of 1 to 50,
more preferably 5 to 8 (w/w).
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates to an improved method for
producing nanostructures bearing regular arrays of pores, and
method of electrochemical metal or alloy deposition within said
pores in order to form nano scale patterns and nanowires. The
present invention is characterized by the principle of etching pore
walls and bottoms by using a unique solution and making the same
electro-conductive by forming a Zn film extending from inner walls
of the pores through the substrate layer. The solution of the
invention enables to provide the metal deposition with simplified
and efficient electrolytic plating processes.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] Nanostructures, which consist of a porous alumina oxide film
on a substantially pure substrate are conventionally produced
according to a number of well known methods such as electrochemical
anodization of aluminum or various lithographic techniques. Also a
number of methods have been developed in the past years for
providing the regularity of the pores within the oxidized alumina
layer which is formed after the pre-treatment of the conductive or
semi-conductive substrate. For the purpose of obtaining nanowire
and nanopatterned functional surfaces, porous material as described
above is subjected to the electrochemical deposition of certain
metals within said pores. So obtained structures have wide
applications in electronics, optics, photocatalysis, catalysis,
photovoltaics, magnetics and superconductivity.
[0003] Oxide films can be formed with the traditional techniques
such as electrolytic or non-electrolytic processes, sol-gel or
chemical vapor deposition. Said pores on the aluminum oxide films
produced by anodization are mostly desired to be regular arrays in
the form of hexagonal honeycomb structure, and said oxide layer is
constituted by a barrier layer and a porous layer. The porous layer
is widely used for the production of nanowires and nanopatterned
surfaces, and has a particular importance with respect to the
nanostructure applications for use as a pattern. Various acidic
solutions such as sulfuric acid, oxalic acid, phosphoric acid and
chromic acid are used in the state of the art for the formation of
nanoholes.
[0004] Formation of nanowires within each nanohole is carried out
for instance by way of removing the substrate and barrier layers
from the aforementioned porous structure and attaching the same to
an electrode for electrochemical deposition of a definite metal
inside the nanoholes. This is because the barrier layer is not
substantially conductive for carrying out the conventional
electrochemical applications. Such an application has been
disclosed with U.S. Pat. No. 6,139,713 (Masuda et al.), wherein
aluminum and barrier layers are removed for obtaining solely
anodized alumina film having through holes. Accordingly, aluminum
plate is selectively etched by using a saturated solution of
corrosive sublimate (HgCl.sub.2) or a saturated methanol solution
of Br.sub.2 to remove aluminum. Next, the barrier layer is removed
using phosphoric acid or the like in order to obtain a through hole
membrane. Said membrane can be used not only as a filter but also
as a starting structure to be used to manufacture a regular
structure of a metal or semiconductor such as nanowires. The
process provides an effective way to obtain a nanostructure for use
as a filter, however the process is rather complicated to operate
and is not cost effective in terms of obtaining nano scale wires
within the apertures of the nanoholes.
[0005] On the other hand, formation of a porous layer on any
substrate may also be conducted by support of the mechanical ways
such as nano-imprinting techniques in which a mold of
recess/projection structures is directly pressed onto the surface
of an object in order to obtain regular projections having holes in
dimensions of nanometers. This lithographic technique can be used
for later on manufacturing of nanostructures such as integrated
circuits and microdevices as disclosed for instance in U.S. Pat.
No. 5,772,905 (Chou). However, it is well known in the art that
such lithographic applications damage the nanostructure in an
undesired way and change the structural properties of the material
making the same relatively unsuitable for many applications such as
nanowires production.
[0006] Moreover, U.S. Pat. No. 5,747,180 (Miller et al.) discloses
a method for manufacturing nanostructures and depositing certain
metals within said structures in order to form quantum wires.
According to an embodiment of the disclosure, preferred
nanostructures are fabricated by way of selecting a semiconducting
substrate, depositing a layer of metal on the substrate,
electro-polishing the layer of metal so as to form pits therein,
anodizing the metal layer so as to convert substantially all of the
metal layer to an oxide layer containing pores, and depositing
material in the pores. In order to form semiconductor compounds
like CdS and ZnS in the pores, anodized aluminum is immersed into a
solution of CdSO.sub.4 and ZnSO.sub.4 wherein the cation Cd.sup.2+
or Zn.sup.2+ reacts with S.sup.2-. The porous structure including
the semiconductor compounds in the pore bottoms is not suitable for
using the whole structure as an electrode for manufacturing the
nanowires with any method of electrochemical treatment.
[0007] Further references indicating the well known fashion of
etching either the substrate and barrier layers, as for instance EP
1378487, or etching of the pores have also been available in the
art, however, a method comprising the basic idea of etching of the
pore bottoms in order to penetrate through the aluminum oxide layer
and reach the electro-conductive aluminum metal layer by means of
an etchant solution which forms a film of an electro-conductive
metal have never been proposed in the art.
[0008] In light of the prior art references cited herein as well as
the unwritten practice of the technical field, the need for
eliminating those problems mentioned above still exists. The
present invention solves the problems mentioned above by an
improved method of electrolytic deposition of metals or alloys
within a porous structure. Said electrolytic way of deposition
comprises the steps of anodizing a metal substrate in order to form
a porous oxide layer, etching the pore bottoms with the unique
zincate solution of the invention in order to obtain a thin zinc
film in the inner wall and bottom portions of the nanoholes and
making the same electro-conductive, utilizing the whole structure
as an electrode and conducting the electrochemical deposition of
certain metals, preferably nickel within said pores. The
electrolytic process disclosed with the present invention does not
require removal of the substrate and barrier layers for the
electrochemical treatment since the pore bottoms of the oxide layer
reaches the electro-conductive substrate and enables to use the
whole structure as an electrode with a novel and inventive
approach. Zincate solution of the present invention can also be
used for electroless deposition of metals or alloys within the
porous structure for obtaining nanowires or nanopatterned
functional surfaces. The methods hereby presented provides a
practical, cost effective and easy to implement way of fabricating
nanowires as would readily be appreciated for those skilled in the
art.
[0009] Further details and preferred embodiments of the invention
with reference to the drawings are given in the following detailed
description.
OBJECTS OF THE INVENTION
[0010] The present invention relates mainly to a method of
obtaining a porous nanostructure suitable for use in fabrication of
nanowires and a method of manufacturing nanowires and nanopatterned
functional surfaces using said nanostructure.
[0011] A first object of the present invention is to provide a
method for the production of a nanostructure suitable for
manufacturing nanowires and nanopatterned functional surfaces,
wherein the need for removal of the aluminum substrate and aluminum
oxide layers for the electrochemical treatment is eliminated by
means of etching the pore bottoms and making these portions
electro-conductive.
[0012] Another object of the present invention is to provide a
method for producing a nanostructure wherein pore bottoms are made
electro-conductive with a unique etchant solution which forms a
film of a pure metal extending from said pores through the
electro-conductive layer.
[0013] A further object of the present invention is to provide a
method for the fabrication of the nanowires and nanopatterned
functional surfaces, wherein a unique etchant solution etches the
inner walls and bottoms of the pores to reach the
electro-conductive layer and accumulates therein, consequently
eliminates the need for separate steps of etching of pore bottoms,
deposition of a metal film and pore enlargement.
BRIEF DESCRIPTION OF THE FIGURES
[0014] FIG. 1 shows an ideal honeycomb like hexagonal porous
structure formed after the anodization of a metal substrate;
[0015] FIG. 2-a, 2-b and 2-c are the SEM micrographs of the surface
of a metal sheet polished with acid, thermal treatment and a
combination of the thermal treatment and electro-polishing
respectively;
[0016] FIG. 3 is a schematic view of an aluminum structure showing
the movement of ions during the anodization procedure in order to
form a porous oxide layer;
[0017] FIG. 4-a, 4-b and 4-c are the SEM micrographs of the surface
of a metal sheet anodized in the presence of sulfuric acid, oxalic
acid, phosphoric acid respectively;
[0018] FIG. 5 shows a cross sectional view of an ideal porous
structure wherein aluminum substrate layer and aluminum oxide layer
are explicitly shown;
[0019] FIG. 6 is a cross sectional view of the porous oxide layer
wherein the pore bottoms are etched by using the unique solution of
the present invention;
[0020] FIG. 7-a and 7-b are the SEM micrographs of the surface of
the nanostructure treated with the unique zincate solution of the
invention for durations of 60 s and 30 respectively;
[0021] FIG. 7-c is the SEM micrograph of the surface of the
nanostructure prior to the treatment with the zincate solution of
the invention;
[0022] FIG. 8-a and 8-b are the SEM micrographs of the surface and
cross section of a nanostructure anodized in the presence of a
sulfuric acid electrolytic solution;
[0023] FIG. 9-a and 9-b are the SEM micrographs of the surface and
cross section of a nanostructure anodized in the presence of an
oxalic acid electrolytic solution; and
[0024] FIG. 10-a and 10-b are the SEM micrographs of the nanowires
formed in 2 A/dm.sup.2 and 0.2 A/dm.sup.2 current density values
respectively.
[0025] FIG. 11-a and 11-b are the SEM micrographs of the nanowires
formed within the porous nanostructures which are treated with the
zincate solution for 30 s. and 60 s. respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention is directed to the cost effective and
uncomplicated production of the nanowires as well as the production
of the nanostructures in which such nanowires are formed by way of
the electrochemical deposition of a desired metal. In a preferred
embodiment of the present invention, the metal deposited within the
pores for the formation of the nanowires or nanopatterned
functional surfaces is nickel, however, one skilled in the art may
appreciate that said metal can also be any metal, alloy or compound
suitable for use in the nano scale implementations such as Fe and
Co or mixture thereof.
[0027] During the course of the anodization of an aluminum
substrate, an oxide layer, namely a barrier layer is formed on the
outer surface. If the electrolytic solution of the anodization
process is capable of dissolving the barrier oxide layer, a porous
layer forms on the outer surface with regular or irregular porosity
due to the local dissolution of the oxide layer. Porous layer is
mostly desired to have regular arrays of nanoholes such as a
honeycomb like hexagonal structure as shown in FIG. 1.
[0028] According to the present invention, a nanostructure suitable
for use as a pattern in manufacturing of nanowires is produced with
a process comprising the general steps of; [0029] polishing an
aluminum substrate which is substantially pure and suitable for
nano implementations wherein said polishing step is conducted by a
chemical treatment or thermal treatment procedure or
electro-polishing or combination thereof, [0030] anodizing the
aluminum substrate in the presence of an acidic electrolyte and
dissolving the so formed porous layer in the presence of an acidic
electrolyte such as sulfuric acid, oxalic acid or phosphoric acid,
[0031] applying a second anodization step in order to form the
desired porous layer having hexagonal arrays of nanoholes, [0032]
immersing the porous structure into a zincate solution for etching
the bottoms and inner walls of the nanoholes and depositing a thin
Zn film on all contact surfaces of the nanostructure. Thereby, said
structure is made suitable for electrochemical deposition of
various materials within the porous structure for obtaining
nanowires and/or nanopatterned functional surfaces.
[0033] The process described above can be further continued with an
additional step of electrochemical deposition of a metal or alloy
in order to obtain said nanowires and/or nanopatterned functional
surfaces. The zincate solution of the invention provides certain
advantages for both electrolytic and non-electrolytic deposition
procedures as per described in detail below. The nanostructure
produced according to the steps of the given process is an
alternative way over the prior art particularly for eliminating the
need for the removal of the substrate and barrier layers prior to
the electro-deposition of metals or alloys in an electrolytic
deposition procedure.
[0034] Such an electrolytic process enables to utilize the whole
structure as an electrode since pore bottoms are made
electro-conductive with substantially a pure Zn film.
[0035] Accordingly, deposition of a metal or alloy through the
nanoholes of the porous layer can be conducted by an additional
deposition step wherein the whole structure mentioned above is
utilized as the cathode of electro-deposition system. According to
a preferred embodiment of the invention, electrolytic solution of
this electro-deposition step can be a mixture of NiSO.sub.4 and
H.sub.3BO.sub.3 in any proportion and the metal deposited through
the nanoholes can be Ni, Fe or Co.
[0036] Surface polishing of the aluminum substrate as per mentioned
in the first step of the process given above has a particular
importance for the successful formation of a uniform porous layer
in the form of regular arrays of nanoholes. Chemical treatment of
the metal substrate surface can be conducted for example by
sequential treatment steps of NaOH and HNO.sub.3. Thermal treatment
is another way of pre-treatment of the substrate to be anodized. In
such a procedure, substrate is immersed into oil and cleaned with
an appropriate acid. Then said metal substrate is subjected to a
heat treatment at a temperature around 450-550.degree. C. in the
presence of an inert gas atmosphere after which the grain size
extends and becomes homogenous through the substrate structure.
Electro-polishing is relatively an advanced way of surface
polishing which is mostly preferred in sensitive nano
implementations rather than the previous methods or it is conducted
in combination with the previous methods. Exemplary SEM analysis
results of the treatment techniques given above are shown in FIGS.
2-a, 2-b and 2-c, wherein FIG. 2-a shows the surface of a metal
sheet cleaned with acid, FIG. 2-b shows the surface of a metal
sheet subjected to the thermal treatment and FIG. 2-c shows the
surface of a metal sheet subjected to thermal treatment and
electro-polishing. Apparently, the metal surface treated with a
combination of thermal and electro-polishing treatment steps
provides better surface properties with improved smoothness.
[0037] Anodization of the metal as per mentioned in the second and
third steps of the process given above is conducted for the purpose
of obtaining an oxide layer which is constituted by a barrier layer
and a porous layer having regular arrays of nanoholes. Two step
anodization process provides the ideal hexagonal porous structure
as per described by Masuda, H. and Fukuda, K., 1995. Ordered Metal
Nanohole Arrays Made by a Two-Step Replication of Honeycomb
Structures of Anodic Alumina, Science, 268, 1466-1468.
[0038] During the anodization steps mentioned above, an oxide layer
consisting of a barrier layer and a porous layer grows up in the
presence of an acidic aqueous solution according to the following
general oxidation reaction. Also the ion movement through the
structure is schematically shown in FIG. 3;
2Al+3H.sub.2O.fwdarw.Al.sub.2O.sub.3+3H.sub.2 (I)
[0039] The oxidation reactions of the anode belonging to the
general reaction of (I) are given below;
2Al.sup.+3+3OH.sup.-.fwdarw.Al.sub.2O.sub.3+3H.sup.+ (II)
2Al.sup.+3+3O.sup.2-.fwdarw.Al.sub.2O.sub.3 (III)
[0040] If the electrolyte is not capable of dissolving said oxide
layer, barrier layer forms without the porous layer. Therefore, the
electrolytic solution chosen for the formation of the nanoholes
within a porous layer has particular importance for obtaining a
nanostructure suitable for the nanowire production. The acidic
solution is preferred to dissolve the oxide layer substantially
slower than the formation rate of the metal oxide and is also
preferred to provide the local dissolution of the oxide layer in
order to form the nanoholes in accordance with the present
invention. Said electrolytic solution may comprise the well known
acids such as sulfuric acid, oxalic acid, phosphoric acid and
chromic acid. FIG. 4-a shows the porous structure formed in the
presence of sulfuric acid, FIG. 4-b shows the porous structure
formed in the presence of oxalic acid and FIG. 4-c shows the porous
structure formed in the presence of phosphoric acid. Apparently,
maximum pore size is obtained with phosphoric acid and narrower
pores are obtained in the presence of sulfuric acid. Acidic
electrolyte selection can be made depending on the desired size of
the nanowires. A cross sectional view of an ideal porous structure
is given in FIG. 5.
[0041] Porous structure of the previous anodization treatment steps
is immersed into the unique zincate solution of the present
invention as per described in the fourth step of the process given
above. Unique zincate solution of the invention preferably
comprises Zn(OH).sub.4.sup.2- in combination with any strong base
such as NaOH, KOH, Ba(OH).sub.2, Ca(OH).sub.2, LiOH, RbOH, CsOH and
Sr(OH).sub.2. The strong base in the solution behaves as an
electron donor for the formation of the non-ionic Zn film in the
pore bottoms. Sequential reaction mechanism of the film formation
is given below; [0042] Anodic reaction;
[0042] Al.sup.0+3OH.sup.-.fwdarw.Al(OH).sub.3+3e.sup.- [0043]
Cathodic reaction;
[0043] Zn(OH).sub.4.sup.2-+3OH.sup.-.fwdarw.Zn.sup.2++4OH.sup.-
Zn.sup.2++2e.sup.-.fwdarw.Zn.sup.0 [0044] Overall reaction for the
zincating process;
[0044] 2Al+6OH.sup.-+3Zn.sup.2+.fwdarw.3Zn+2Al(OH).sub.3
[0045] One of the inventive features of the present invention
appears in the use of said solution which simultaneously etches the
pore walls of the nanoholes and forms substantially a pure metallic
Zn film in the pore bottoms, thereby provides excellent
electro-conductivity between said pores and the aluminum substrate.
The porous layer in which the pore bottoms are etched with the
above mentioned solution is schematically shown in FIG. 6. Time
duration of the zincate solution treatment is one of the parameters
directly affecting the pore size of the nanoholes. FIG. 7-a shows
the nanostructure after 60 seconds of zincate solution bath, FIG.
7-b shows the nanostructure after 30 seconds of zincate solution
bath and FIG. 7-c shows the nanostructure prior to the zincate
solution bath treatment. Consequently, a nanostructure suitable for
easy fabrication of nanowires is obtained right after the above
mentioned pore widening procedure and formation of the Zn film in
the pore bottoms.
[0046] Electrochemical deposition of any desired metal through the
nanoholes for manufacturing nanowires is traditionally conducted by
way of first removing the substrate and barrier layers and
obtaining the porous layer alone, then attaching the porous layer
to a conductive metal for carrying out the electro-deposition step
as per discussed in the background of the invention. According to
another inventive feature of the invention, etching the pore
bottoms and the barrier layer through the conductive aluminum
substrate and filling so formed apertures with substantially a pure
Zn film makes the porous layer highly electro-conductive and
eliminates the need for removing said substrate and barrier layers
in order to apply the electrochemical treatment of the nanowire
production.
[0047] Electrolytic solution of the anodization for the formation
of an oxide layer can be an acidic aqueous solution containing 1%
to 50% of an acid selected from the group consisting of sulfuric
acid, oxalic acid, phosphoric acid and chromic acid. A 3% to 15%
acidic (v/v) solution is preferred. Applied voltage through the
electrochemical treatment may vary in the range of 5 V to 100 V
depending on the electrolytic solution and the desired thickness of
the oxide layer. A voltage ranging from 20 V to 60 V is generally
preferred.
[0048] The zincate solution to which the samples of the invention
are immersed, comprises Zn(OH).sub.2 and a strong base such as
NaOH, KOH, Ba(OH).sub.2, Ca(OH).sub.2, LiOH, RbOH, CsOH and
Sr(OH).sub.2. NaOH is particularly preferred. Zn(OH).sub.2/Base
ratio may vary 0.1 to 1.8 (by weight) in said zincate solution
bath, however, said ratio is preferably kept in the range of 0.4 to
0.8 by weight.
[0049] Electro-deposition of metals within the conductive porous
nanostructure of the present invention can be carried out in the
presence of a bath solution consisting of NiSO.sub.4 and a weak
acid such as H.sub.3BO.sub.3, H.sub.3PO.sub.4, CH.sub.3COOH, HF,
CH.sub.3COCOOH and C.sub.5H.sub.5NCOOH. H.sub.3BO.sub.3 is
particularly preferred. Weight ratio of NiSO.sub.4/weak acid may
vary in the range of 1 to 50, however, said ratio varies more
preferably in the range of 5 to 8. Ni, Fe or Co can well be
deposited within the nanoholes of the porous nanostructure by means
of the anodization step of the process disclosed above. Applied
current density values may vary in the range of 0.1 to 20
A/dm.sup.2, more preferably 0.2 to 2 A/dm.sup.2 during the metal
deposition.
[0050] Further advantages and best mode of carrying out the present
invention are apparent and more recognizable to those skilled in
the art in light of the following examples.
Example 1
Preparation of the Oxidized Nanostructure Suitable for Metal
Electro-Deposition
[0051] Aluminum sheets having the size of 7.times.4 cm and
thickness of 0.5 mm were used as the substrates during the
experimental procedure. The substrates used for this purpose were
supplied from Assan Aluminyum San. A.S.-Istanbul Turkiye, as 1050
series aluminum sheets which have the following specific
composition;
TABLE-US-00001 Al Fe Si Cu Mg Mn Zn V Ti Others 99.5 0.4 0.25 0.05
0.05 0.05 0.05 0.05 0.03 0.03 min max max max max max max max max
max
[0052] Aluminum sheets are subjected to the cleaning steps prior to
the anodization procedure. Sheets are immersed into a 40 g/L NaOH
solution at 55.degree. C. for 2 minutes and then washed with
purified water. Samples are polished by way of immersing the same
into a 15% (by volume) HNO.sub.3 solution for 30 seconds and washed
again with distilled water. Anodization experiments were conducted
twice with a 72V-12 A DC source in a double walled cooling bath
wherein the temperature was controlled with a thermostat having
.+-.0.5.degree. C. sensitivity. The current passing through the
circuitry was measured with a GANZ HDA-2 apparatus which has the
measurement range of 60 mA-6 A. Separate sheets of aluminum were
anodized in sulfuric acid and oxalic acid electrolytic solutions in
various voltage values and number of pores in unit area have been
observed. Results were as follows;
TABLE-US-00002 Number of Voltage nanoholes/cm.sup.2 Size of the
Electrolyte (V) (.times.10.sup.9) Nanoholes (nm) 15% (w/w) Sulfuric
20 52 10-13 Acid solution at 18.degree. C. 3% (w/w) Oxalic Acid 60
6 30-35 solution at 18.degree. C.
[0053] FIG. 8-a and 8-b shows the surface and cross sectional SEM
view of the nanostructure respectively, which is obtained with the
anodization procedure in the presence of sulfuric acid solution.
Also FIG. 9-a and 9-b shows the surface and cross sectional SEM
view of the nanostructure respectively, which is obtained with the
anodization procedure in the presence of oxalic acid solution.
[0054] After the anodization of the aluminum sheets the sample
anodized in the presence of oxalic acid gave the larger pore size
compared to the sulfuric acid. Larger pore size provides more
tolerance to the pore enlargement as well as to etching the pore
bottoms during the zincate solution treatment. Therefore, the
aluminum structure anodized in the oxalic acid solution was chosen
for the zincate solution treatment in the next step. Anodized
sample was immersed into a zincate solution consisting of 354 g/L
Zn(OH).sub.2 and 525 g/L NaOH for 30 and 60 seconds. Pore size of
the nanostructure varied as follows;
TABLE-US-00003 Time duration of Pore Size Level the Immersion (sn)
(nm) 1 0 30-35 2 30 60-65 3 60 95-100
[0055] Inner walls and bottoms of the nanoholes are etched during
the zincate treatment wherein etching of the pore bottoms for
making the same electro-conductive and also enlargement of the pore
diameters were conducted simultaneously within this single step. A
thin Zn film extending through the aluminum substrate layer forms
in the pores after which the nanostructure becomes suitable to be
utilized in the further steps of metal deposition for manufacturing
nanowires.
Example 2
Metal Electro-Deposition and Manufacturing of Nanowires
[0056] The porous nanostructure which was made electronically
conductive for 60 seconds in the previous example was subjected to
an electrolytic metal deposition step wherein said structure was
utilized as the cathode and Ni was utilized as the anode electrode.
Electrolytic solution bath was containing 300 g/L NiSO.sub.4 and 45
g/L H.sub.3BO.sub.3 and said solution was heated to 50.degree. C.
before starting the electrolytic process. Two pieces of
nanostructure sheets were used in the process in order to observe
the amount of metal deposition depending on the current density.
One of the pieces was subjected to 2 A/dm.sup.3 and the other one
was subjected to 0.2 A/dm.sup.2 current densities for this purpose.
Pieces were washed right after the electrolytic process and
analyzed with Scanning Electron Microscope. Results are shown in
FIGS. 10-a and 10-b wherein the nanowires formed in 2 A/dm.sup.2
current density and the nanowires formed in 0.2 A/dm.sup.2 current
density are shown respectively.
[0057] Apparently, the basic zincate solution mentioned herein is
the key element of the present invention since it initially etches
the inner surfaces of the pores and then forms the crucial Zn film
extending from the inner walls of the nanoholes through the
substrate layer. Said film of Zn makes the pores electro-conductive
for electrolytic metal deposition. In other words, the zincate
solution of the present invention provides effective metal
deposition in electrolytic deposition processes. The nanostructure
obtained as in Example 1 can be subjected to an electrolytic
deposition procedure with a quite simplified way as in Example 2
for manufacturing nanowires.
[0058] It is easy for the skilled person to recognize that such
deposition processes can be used not only for manufacturing of
nanowires but also for manufacturing a wide variety of
nanopatterned functional surfaces and devices suitable for use for
instance in electronics, optics, photocatalysis, catalysis,
photovoltaics, magnetics and superconductivity. It is also apparent
for the skilled person to carry out the invention without the
anodization step of the process for pore formation; instead the
porous layer can also be formed by means of the well known
techniques, for instance lithographic methods.
[0059] Appended claims provided herewith disclose the subject
matter of the invention. The examples and illustrative figures do
not limit invention in any way.
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