ES2334195B1 - PROCEDURE FOR DISSOLVING THE ALUMINUM OXIDE BARRIER IN SITU IN THE POROUS ALUMINUM MANUFACTURING PROCEDURE. - Google Patents

Abstract

Procedure for dissolving the aluminum oxide barrier layer in situ in the process of manufacturing porous alumina.

The present invention describes a process to prepare a nanostructure comprising a substrate of aluminum and in contact with it a layer of porous alumina characterized in that the barrier layer inside The pores have been removed: (i) obtaining an alumina layer porous by anodizing an aluminum substrate and (ii) decrease of the value of the current intensity of the system until it stabilizes

Description

Procedure for dissolving the aluminum oxide barrier layer in situ in the process of manufacturing porous alumina.

Field of the Invention

The present invention fits within the field of porous alumina nanostructures obtained from an aluminum substrate by anodic oxidation. Plus specifically, the invention relates to a new process that allows to eliminate or reduce the barrier layer that is shape inside the pores of the porous alumina, as well as to the nanostructure obtained by this procedure. This Porous nanostructure is useful as a functional material as well as mold in the manufacture of other uni- and nanostructures two-dimensional

Background of the invention

Aluminum anodization for the production of porous alumina is a process widely used both industrially and in the laboratory. During the second half of the last century, great efforts were made to improve the manufacturing process of porous alumina membranes [F. Keller, et. al ., J. Electrochem. Soc., 100 (1953) 411]. Since Masuda et al., Science , 268 (1995) 1466 presented the process of manufacturing porous alumina in two steps, a large number of research groups have studied the process and new ways of producing porous alumina membranes have seen the light [Nielsch, K. et. al., Appl. Phys. Lett ., 79 (2001) 1360-1362]. The studies that have been carried out over the last few years have made it possible to relate the technical characteristics of these membranes with the working parameters used (type of acid, anodizing voltage, temperature, anodizing time, etc.) [Che , G. et. al., Nature , 393 (1998) 346; Du, Y. et. al., Appl. Phys. Lett ., 74 (1999) 20; and Marsal, LF et. al ., Phys. Stat. Sol. (C) 4, No. 6, 1918-1922 (2007)]. Therefore, at present, it is possible to adapt the technical characteristics of these membranes (pore diameter, membrane thickness, etc.) to the requirements that require subsequent applications.

The structure of porous alumina produced at starting from the anodic oxidation of aluminum substrates comprises open pores at the top and whose bottom is covered by a barrier layer (Fig.). The thickness of this barrier layer is directly related to the voltage used during the anodizing process. From a point functional view, get to open these pores without peel off the aluminum metal substrate from the alumina layer Porous is an interesting goal, since that would open a wide range of possibilities to use such material for example as a mask to transfer nanostructures type nanowires ("nanowires"), nanotubes ("nanotubes") or nanpoints ("nanodots") or nanopillars ("nanopillars") on various conductive substrates such as metals, polymers, ceramics etc. metallic or semi-metallic substrates (aluminum, titanium, platinum, silicon, etc.).

They are known in the state of the art double anodized aluminum procedures, and the problem that raises the low conductivity of the barrier layer of the pores For example, said barrier layer makes it difficult the electrodeposition of a metal in the pores.

To solve this problem they have proposed various electrochemical and chemical methods, as well as procedures  which combine both methods, to reduce or eliminate said layer.

Sander, MS et al . Adv. Matter (2002), 14, No.9, May3 describes the use of APO membranes produced by standard type anodization on silver substrates to produce Bi2 Te3 nanowires. The fact that it is an anodization of aluminum on silver substrates implies that it is considerably less than its corresponding thickness in the case of aluminum substrates. Therefore, it is possible to open the pores of the alumina by its lower part by immersing the samples in aqueous solution of HNO 3 (1M) for 1 or 2 hours. Regarding the method, it should be said that if the exposure time of the alumina to the acid is excessive or its concentration is not adequate, the total dissolution of the oxide or the partial or total collapse of the alumina structure can occur as consequence of its weakening. In addition, both surface roughness and pore diameter will increase, which may restrict the use of these membranes in those cases where certain surface properties or pore diameters are required.

O. Rabin et al . Adv. Funct. Mater. (2003), 13, No.8, describes the use of APO membranes produced by standard type anodization on silicon substrates with a platinum adhesive layer to produce Bi2 Te3 nanowires. Therefore, the thickness of the barrier layer is also much lower than in the case of aluminum substrates. The opening of the pores is carried out by means of a cathodic polarization in neutral KCl solution (0.5M) with a voltage of -2.25 V.

Zhao, X. et. al . Journal of The Electrochemical Society, 154 (10) C553-C557 (2007) describes APO membranes produced by standard type anodization on aluminum substrates. To achieve the opening of the pores at the bottom, the anodization ends with a stepped reduction of the voltage to produce microcracks in the barrier layer. Finally, to dissolve it in its entirety, a cathodic polarization (-5 V) in neutral KCl solution (0.5M) is applied.

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As for these last two methods you should comment that, as the authors state, there is a high probability of partial or total dissolution of the membrane as well as a fracture thereof as a result of the generation of tensions by hydrogen production in the oxide-substrate interface. In addition, if later the sample is not cleaned profusely, it can remain contaminated with traces of salt inside the pores.

M. Tian et al . Nano Letters (2005), Vol. 5, No. 4, 697-703 describes the use of APO membranes produced by standard type anodizing on aluminum substrates and silicon substrates with an adhesive layer of titanium and silicon oxide to produce nanowires of Au. The barrier layer is perforated using a voltage inversion (-5 V) in the same electrolyte used during anodization. In the case of silicon substrates with adhesive layers, the technique manages to open the pores at the bottom without the detachment of the alumina from the substrate, however, in the case of aluminum substrates, in which the Thickness of the barrier layer is greater, the alumina membrane undergoes a "detach" or extraction when a large amount of fissures and gaps are generated in the substrate-alumina interface. On the other hand, the technique used is not a valid technique when the substrate is aluminum, since the detachment of the substrate membrane occurs as a result of the generation of hydrogen at the interface as well as the appearance of many cracks that mechanically weaken the membrane and that can cause the total fracture of the membrane.

Nielsch, K et. al ., Adv. Mater . (2000) 12, No. 8 describes the use of APO membranes produced by standard type anodizing on aluminum substrates to produce nickel nanowires, but since it does not achieve the total opening of the pores, an AC mode electrodeposition is necessarily used . Once the standard anodization is finished, chemical wetting of the pores is applied to the sample ("chemical pore widening"), thus reducing the thickness of the barrier layer isotropically, and then a stepped profile is applied decreasing of 2 steps to reduce the thickness of the same up to ten nanometers. Finally, the applied method only manages to reduce the thickness of the barrier layer to a few tens of nanometers, so the electrodeposition must be carried out in AC mode. This is because the barrier layer acts as a screen and prevents the attraction of the metal cations towards the bottom of the pores. In addition, by means of this technique the fabricated metal nanowires do not remain adhered to the metal substrate, so when the oxide membrane is removed they are entrained with it.

From the foregoing it follows that the techniques employed in the state of the art to reduce or eliminate the barrier layer of the pores bottom of the ordered porous alumina produced by anodization have been applied only to the standard type of anodization. The thickness of the barrier layer in the porous alumina produced by the standard type of anodization is considerably less than the corresponding "fast" type thickness, since the anodizing voltage is also lower. Therefore, it is much easier to eliminate or reduce it. In addition, in the case of aluminum anodizations carried out on other types of substrates (titanium, silicon, etc.), the thickness of the aforementioned barrier-layer is also reduced with respect to the thickness obtained on aluminum substrates. In some of these methods even the (APO) layer is separated from the aluminum layer [Tian, M. et al . Letters (2005), Vol.5, No.4, 697-703], and, in general, most of these methods lead to APO with defective pores that then negatively impact the ends of the 1D and 2D nanostructures obtained using the APO as a mask.

Therefore, in view of the above, follow there is a need in the state of the art to provide an alternative and simple procedure to obtain from a aluminum substrate, a porous alumina nanostructure, of whose nanopores has reduced or eliminated the barrier layer of aluminum oxide, which exceeds Some of the disadvantages mentioned.

Brief description of the figures

Figure 1: alumina cross section porous produced by anodizing a substrate of aluminum.

Figure 2: cell scheme electrochemistry.

Figure 3: Scheme of the manufacturing process of ordered porous alumina (APO).

Figure 4: versus current density curve at the time during the porous alumina manufacturing process ordered (APO).

Figure 5: reduction of the thickness of the alumina barrier layer by steps decreasing current intensity.

Figure 6: cross section scheme of porous alumina during the process of removing the barrier layer of the bottom of the pores.

Figure 7: ESEM images of porous alumina ordered on the aluminum substrate.

Figure 8: ESEM images of porous alumina ordered from the top.

Figure 9: ESEM images of metallic nanowires (a) Nickel and (b) Cobalt on an aluminum substrate.

Figure 10: XRD analysis of Ni nanowires and Co.

Figure 11: represents the removal of thickness of the alumina barrier layer according to the Example of the request.

Description of the invention

The present invention relates in one aspect to a method for preparing a nanostructure comprising a aluminum substrate and in contact with it an alumina layer porous characterized because the barrier layer of inside the pores has been removed or reduced, which comprises the following stages:

(i) obtaining a porous alumina layer by anodizing an aluminum substrate in an electrochemical cell until the current density value stabilizes;

(ii) decrease in the intensity value of current until it stabilizes again; and optionally the repetition of step (ii) until the barrier layer inside the pores is reduced or eliminates

The aluminum substrate used in the anodization can be in principle in any way, and dimensions, such as, for example, an aluminum foil. He aluminum has, in a particular embodiment, a purity of 99.999%

In the context of the present invention the aluminum substrate term should not be construed as meaning limited to a single layer of aluminum. On the contrary the substrate of aluminum used in the present invention may further comprise At least another layer of another material. Thus, in one embodiment particular the aluminum substrate comprises a first layer of aluminum and a second layer, which has been deposited in contact with it, and comprising a conductive material different from aluminum.

The conductive material can be in principle any material with which there is electrical contact. With Only illustrative character may be cited, among others, a conductive polymer that meets the wettability requirement, such such as PH3T, PDMS or PMMA, a metal such as Ag, Au, Pt, You; a semiconductor material like Si or Ge, or, a ceramic conductive such as SiC, SnO2, ZrO2 or MoSi2, as well as mixtures of these elements and materials.

The aluminum substrate is generally subjected to a conventional pretreatment comprising an annealing step and an electropolishing stage to reduce its surface roughness and homogenize the crystalline phases before anodizing (see Example).

The step (i) of the process of the invention refers to the anodization of the aluminum substrate, which appears schematized in Figure 1, in which a substrate of aluminum (Al) before and after anodizing, in which obtains a layer of porous alumina oxide (Al 2 O 3) on The aluminum substrate. Figure 1 shows the flow of Al 3+ cations, and O 2- anions.

The structure of porous aluminum oxide obtained in step (i) can be messy, like the one that results of an anodizing stage and is represented in the part top of Figure 3 A, or it can be ordered porous alumina (APO), resulting from a two-stage anodizing procedure as shown in the lower part of Fig. 3 C.

This two-stage anodizing procedure appears schematically in Fig. 3, where A is the substrate of aluminum with the alumina layer after the first step of anodization A top view is shown in which they are appreciated the messy pores. B represents the aluminum substrate from which porous alumina has been removed, and C represents the substrate of aluminum after the second anodizing step. Top view Shows the ordering of the pores. The two step procedure understand the stages of

a) anodizing an aluminum substrate in a electrochemical cell to obtain an alumina layer messy

b) interruption of anodization and elimination of the disordered porous alumina layer obtained in a); Y

c) substrate re-anodization of aluminum obtained in b) to obtain the APO.

An ESEM image (electron microscope of environmental scan) of the APO seen from the top is shown in Fig. 8, in which the ordering of the pores in hexagonal cells.

The anodizing methods for obtaining APO are well known as mentioned in the Background as well such as the working conditions to which the anodization that can be selected based on the desired characteristics have porous alumina. One of the Advantages of the process of the invention is that anodization It can be both standard and fast. In this sense in a particular embodiment of the process of the invention the Anodizing the aluminum substrate is performed according to one of the following working conditions:

- phosphoric acid in a concentration between 5 and 10% by weight and at a voltage between 140 and 195 V;

- sulfuric acid in a concentration between 5 and 10% by weight and at a voltage between 18 and 70 V; or

- oxalic acid in a concentration included between 0.1 and 0.5 M and at a voltage between 40 and 180 V.

The electrochemical cell for carrying out the process of the invention is a conventional cell like the one shown schematically in Figure 2, and in which the basic parts thereof are shown: the ammeter (A), the voltmeter (V), the positive anode-pole A , which is the aluminum substrate, in which the interface between metal and the solution ( Im-s ) is indicated a negative cathode-pole C , which in a particular embodiment is a cable of platinum, and where the interface ( Im-s ) is indicated a power supply (- +) and an electrolyte (S).

After a certain time of anodization, the system reaches a stationary stage, and the system response (current density) stabilizes, tending asymptotically towards a certain more or less constant value as shown in Figure 4, which depends on the type of anodization used and the other work parameters mentioned above. In this point, the system is in electrochemical equilibrium and the alumina dissolution rate at the interface electrolyte-alumina (v1) equals speed of its formation at the interface alumina-aluminum (v2), so the thickness of the barrier layer located at the bottom of the pore it remains constant during its growth. In Figure 4 the voltage in volts V (V) is represented on an ordinate axis, on the other axis of ordinates the current density J (mA / cm2), in abscissa the time in seconds; the straight V line represents the applied voltage or potential difference; J1 represents the current density or response during the first anodizing step, and J2 represents the current density or response during the second step of the anodization.

Step (ii) of the process of the invention it consists of disturbing the system, by decreasing the value of the current intensity, which implies that a speed difference between (v1) and (v2), resulting in greater alumina dissolution rate at the interface electrolyte-alumina (v1) that the speed of formation of it at the interface alumina-aluminum (v2). Figure 6 shows in D an equilibrium situation in which v1 = v2, in E it represents the situation in which v1> v2, and finally in F the situation final after chemical widening of pores as discussed more down.

Disturbing the system remains evidenced in the response of the system (voltage), which suffers a  progressive decrease until the system itself has elapsed certain time, counteracts this disturbance and reaches again asymptotically a new equilibrium value. This process of represented in Figure 5 where V (V) represents the voltage applied, J the current density or response, and t (s) the time. In the context of the present invention the system is considered reaches electrochemical equilibrium when the difference between two Consecutive voltage measurements is less than 0.01V, the period between measures of 1 s.

The decrease in the intensity value of current that is carried out in step (ii) is comprised between one third and two thirds of the intensity value of current immediately before the disturbance.

The result of successively disturbing the equilibrium state reached by the system after each disturbance, reducing the value of the current intensity as indicated above, can be observed in Fig. 5. After each disturbance the system responds counteracting this disturbance and tending its response towards A new state of balance.

The person skilled in the art can therefore optionally repeat step (ii) as many times as you consider reach the thickness of the desired barrier layer, because each of the equilibrium states (voltage) corresponds to a thickness of the aforementioned barrier-layer according to the 1.3 nm / V ratio.

Step (ii) has the advantage that, not excessively modifies the diameter of the pores, since the solution alumina occurs mostly at the bottom of the pores, where the flow of electrochemical species is greater for existing greater exchange surface, and not in the walls of the same (Fig. 6).

In a preferred embodiment of the invention stages (i) and (ii) take place in the same electrochemical cell  and in the same electrolyte, which simplifies the procedure compared to others in the state of the art and represents a saving in costs and time

In a preferred embodiment of the procedure of the invention, this further comprises a step (iii) of chemical widening of the pores by wet route. This stage can be carried out in a conventional manner by a person skilled in the art in the presence of an inorganic acid, with stirring and at temperature conventional. In a more preferred embodiment this stage is performed at 35 ° C.

The chemical widening gets an opening homogeneous pore base of porous alumina without need for it to be extracted from the aluminum substrate, such and as shown in Figure 6 F, and in the image of Fig. 7, and allows to remove the thin layer of thick residual alumina typically between 2-3 nm that can remain at the bottom of the pores after stage (ii). This residue is mainly due to the presence of micro-crimes on the surface of the aluminum substrate after electropolishing,  which implies that the thickness of the barrier layer located between the substrate and aluminum oxide is not homogeneous. Having in counts the approximate speed of alumina dissolution of 2 nm / min can easily determine the immersion time in the acid depending on the desired pore enlargement.

In a particular embodiment of the invention the step (iii) comprises immersion of the nanostructure obtained in step (ii) in 5% by weight phosphoric acid during 10 minutes and with constant agitation at 300 r.p.m. In other particular embodiment 1M nitric acid is used.

The process of the invention presents numerous advantages with respect to the procedures of the state of The technique. In this sense, it can be used for any thickness of the barrier layer and, therefore, is applicable to porous alumina and ordered porous alumina produced by anodization standard type and "fast" type. The procedure is simple and economic, since it is carried out on the same electrolyte in the that the anodization is performed, and the obtained nanostructure is free of chemical contamination. It is also significantly reduced the operation time, with respect to other procedures, because additional stages such as "pore widening" of pore), "membrane detach" and "metallic sputtering" (deposition of a metallic contact in one of the membrane surfaces.) are not necessary.

Another advantage of the procedure is that neither surface roughness or pore size is modified, what which allows to adapt the technical characteristics of the Nanostructures obtained at further applications.

In another aspect the present invention relates to a nanostructure obtained by the procedure of the invention.

In the process of the invention the layer of Porous alumina remains on the aluminum substrate, without separate, so it is possible to use this nanostructure as Effective template in various applications. In this regard, due that the pores are open at the bottom, just as shown in Fig. 7, it is possible to perform for example a electrodeposition in DC mode and obtain other 1D nanostructures and 2D, such as nanowires, nanotubes, nanpoints and nanopillars, of various materials such as polymers, ceramics, or metals among others. Later you are second 1D and 2D nanostructures remain on the aluminum substrate Once the aluminum oxide has been removed.

Therefore in another aspect the invention is refers to the use of the nanostructure obtained through the process of the invention in the preparation of a second 1D and 2D nanostructure.

In a particular embodiment of the invention, the use refers to the use of the nanostructure of the invention as a mask to transfer a second 1D and 2D nanostructure on said nanostructure. Examples of these second Nanostructures are nanowires, nanotubes, nanpoints and nanopilars. These second nanostructures remain, well on the own aluminum substrate, either on the first aluminum layer of item that in turn is on another substrate, or on the substrate directly comprising a conductive material. In a preferred embodiment the second nanostructure is on the substrate as the aluminum layer is so thin that it oxidizes completely. As defined above, said substrate it can be a metal, a semiconductor, a conductive polymer, a conductive ceramics or mixtures thereof.

In a particular embodiment they are obtained Ni nanowires and in another particular embodiment are obtained Co. nanowires Thus, Fig. 9 shows the ESEM images of metallic nanowires of: (a) nickel and (b) cobalt obtained by DC electrodeposition on the aluminum substrates and using porous alumina as a mask ("template"). The images of Figures 7, 8 and 9 were obtained with an ESEM device FEI Quanta 600.

Figure 10 shows the Diffraction analysis X-ray (XRD) of said metal nanowires of Ni and Co manufactured. The analysis was carried out with a team X-ray diffractometer Broker AXS model D8 Discover.

In another particular embodiment the employment is refers to the use of the nanostructure of the invention, as a mask in the manufacture by replica of a membrane of a material different from aluminum such as polymers. To do this prepares a second nanostructure on the aluminum substrate; to then the porous alumina used as a mask is removed; be pour a precursor of a polymer onto the generated structure, which polymerizes and finally separates the metal structure from the polymer being transferred the shape of the nanostructure original of the invention to the polymer matrix.

Below are examples illustrative of the invention set forth for a better understanding of the invention and in no case should be considered a Limitation of its scope.

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Examples Example 1 Procedure for obtaining a nanostructure according to the invention

It started from a commercial aluminum substrate (Goodfellow Cambridge Ltd.), 99.999% pure, and dimensions (5X5 cm and 250 µm thick).

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1.1 Sample pretreatment 1.1.1 Annealing

The aluminum substrate was subjected to a first cleaning with distilled water and was dried in an oven at 100 ° C. This was then annealed in an electric oven in an atmosphere of nitrogen at 400 ° C for 3 hours. The temperature profile that Followed the sample was as follows:

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Initial section (of temperature ambient at 400ºC with a ramp of 1ºC / minute)

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Intermediate section (at one constant temperature of 400 ° C for 3 hours)

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Final section (natural descent until the ambient temperature is reached again)

After finishing the annealing phase the substrate extracted from the oven washed with acetone in an ultrasonic bath for 2 minutes Subsequently, it was rinsed with distilled water and dried (carefully to avoid bending) with a stream of air. Finally, the 5X5 cm substrate was cut into pieces of 2.5X2.5 cm to fit its size to the cell window electrochemistry in which the anodization was carried out.

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1.1.2 Electropolishing

Once the sample was cut, it was subjected to a electropolishing process The parameters used were the following:

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Dissolution (Ethanol mixture: HClO4 (v: v))

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Temperature (5ºC)

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Agitation (300 r.p.m.)

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Voltage (20V)

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Time (2 minutes)

Finally, the sample was submerged in water distilled in an ultrasonic bath for 5 minutes and dried in a stream of air to make sure that its surface was completely free of possible remains of the solution used for electropolishing.

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1.2 Anodization 1.2.1 First step

The sample was placed in the electrochemical cell and The first step of the anodization was carried out.

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Solution (oxalic acid 0.3 M)

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Cathode (platinum in filament of 5cm approximately)

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Agitation (300 r.p.m.)

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Voltage (40V)

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Time (30 minutes)

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Temperature (10ºC)

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1.2.2 Removal of the alumina layer

Once the first step of the anodizing, the sample was immersed in a solution suitable for remove the oxide layer formed.

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Dissolution (acid mixture phosphoric (0.4 M) and chromic acid (0.2 M))

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Temperature (70ºC)

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Agitation (300 r.p.m.)

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Time (30 minutes)

To make sure that the above layer had completely removed its conductivity was checked with a voltmeter.

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1.2.3 Second step

Under the same parameters set forth in the first step was carried out the second step of the anodization, Except the time that was 4 hours.

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1.3. Reduction / elimination of the barrier layer 1.3.1. Staggered reduction of the intensity of stream

Without extracting the sample from the cell anodization, the last recorded value of the current intensity (which was approximately 3 mA). Saying value was taken as a reference point to perform the reduction / elimination of the pore bottom barrier layer with a process in CC mode. A multiplier factor of 0.5 was chosen, and the current intensity value was reduced so staggered until the voltage value reached 2 V approximately (as can be seen in the example, in this case the second step was 30 minutes).

This stage was performed in the following terms:

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Solution (oxalic acid 0.3 M)

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Cathode (platinum in filament of 5 cm approximately)

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Agitation (300 r.p.m.)

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Initial Intensity (3 mA)

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Time of each step (4 minutes)

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Temperature (10ºC)

Figure 11 represents this stage, from the end of the second step, until the reduction corresponding to the voltage of about 2 V.

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1.3.2. Widening of the pores and elimination of the possible traces of the barrier layer of the bottom of the pores

The sample was taken from the cell of anodizing, rinsed with distilled water, and dipped:

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Dissolution (5% phosphoric acid in weigh)

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Temperature (35ºC)

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Agitation (300 r.p.m.)

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Time (between 20 and 30 minutes)

Claims (12)

1. Procedure for preparing a nanostructure comprising an aluminum substrate and in contact therewith a porous alumina layer characterized in that the barrier layer inside the pores has been removed or reduced comprising the following steps: (i) obtaining a porous alumina layer by anodizing an aluminum substrate in an electrochemical cell until the current density value stabilizes; (ii) decrease in the intensity value of current until it stabilizes again; and optionally, repetition of step (ii) until the barrier layer inside the pores is reduced or eliminates 2. Method according to claim 1 in the that the aluminum substrate comprises: a layer comprising a material other than conductive aluminum and an aluminum layer deposited on said layer. 3. Method according to claim 1, which it also comprises a stage (iii) of chemical widening of the wet pores. 4. Procedure according to any of the claims 1 to 3, wherein in step (ii) the decrease of the value of the current intensity is between a third and two thirds of the current intensity value previous. 5. Procedure according to any of the claims 1 or 4, wherein steps (i) and (ii) take place  in the same electrochemical cell and in the same electrolyte. 6. Procedure according to any of the claims 1 or 5, wherein in step (i) a messy porous alumina layer. 7. Procedure according to any of the claims 1 or 5, wherein in step (i) a porous alumina layer sorted by a method that understands: a) anodizing an aluminum substrate in a electrochemical cell; b) interruption of anodization and elimination of the disordered porous alumina layer obtained in a); c) anodization of the aluminum substrate obtained in b). 8. Procedure according to any of the claims 1, 5, 6 or 7 wherein the substrate anodization Aluminum is performed in one of the following conditions of job: - phosphoric acid present in a concentration between 5 and 10% by weight and at a voltage between 140 and 195 V; - in sulfuric acid present in a concentration between 5 and 10% by weight and at a voltage comprised between 18 and 70 V; or - in oxalic acid at a concentration between 0.1 and 0.5 M and at a voltage between 40 and
180 V. 9. Nanostructure obtained by the procedure according to any of claims 1 to 8. 10. Use of the nanostructure according to claim 9, in the preparation of a second nanostructure 11. Use according to claim 10 wherein this is used as a mask to transfer a second One-dimensional nanostructure selected from among nanowires, nanotubes, nanpoints and nanopillars on said nanostructure. 12. Use according to claim 10 wherein this is used as a mask in the manufacture by replica of a membrane of a polymeric material.