Nanostructured Material, Production Process and Use Thereof

Abstract

The present document provides details of a nanostructured material defined by an anodized alumina having a nanostructure with transverse pores that pass through and connect longitudinal pores grown on an aluminum substrate. This document also describes the process for producing said nanostructured material and the possible use thereof as a template or mould for obtaining nanostructures formed by nanowires, which are generated in the cavities or pores of the aforementioned nanostructure of the nanomaterial of the invention. Likewise, this document details the use of the nanostructured anodized alumina material as a mould for producing nanostructures.

Claims

1-26. (canceled)

27. A nanostructured material comprising a substrate, which in turn comprises alumina, wherein at least one longitudinal pore is disposed on the substrate, whose longitudinal axis is essentially perpendicular to said substrate, wherefrom nanostructured material emerges, and at least one transverse pore whose longitudinal axis is essentially perpendicular to the longitudinal axis of the longitudinal pore.

28. The nanostructured material of claim 27, wherein at least one of the longitudinal pore and the transverse pore has an essentially circular cross-section or an elliptical cross-section, wherein: a circular cross-section of the longitudinal pore has a diameter comprised between 6 nm and 450 nm, a circular cross-section of the transverse pore has a diameter of 100 nm, and an ellipse of the cross-section of the transverse pore comprises: a first axis having a perpendicular direction to the longitudinal axis of the longitudinal pore, and a second axis aligned in a parallel direction to the aforementioned longitudinal axis of the longitudinal pore, wherein at least one of the axes of the elliptical cross-section is less than 100 nm in size.

29. The nanostructured material of claim 27, comprising a plurality of transverse pores defined with their longitudinal axes parallel therebetween and defining at least one plane parallel to the substrate.

30. The nanostructured material of claim 27, comprising at least two transverse pore planes, wherein said planes are parallel therebetween.

31. The nanostructured material of claim 27, comprising a plurality of longitudinal and transverse pores, defining a three-dimensional pore lattice wherein the longitudinal pores are perpendicular to the substrate and the transverse pores are perpendicular to the longitudinal pores, passing through the latter and orthogonally crossing the respective longitudinal axes of the pores.

32. A process for obtaining an anodized nanostructured material, the process comprising: preparing a substrate that comprises Al, carrying out an anodizing process on a surface of the substrate, wherein said anodizing process comprises pulse anodizing, which in turn comprises: pulse mild anodizing stages with fixed potential, and current-limited pulse hard anodizing stages, growing at least one nanostructured anodized material layer on the substrate as a consequence of the preceding step, said layer corresponding to the anodized nanostructured material, and carrying out a chemical attack to reveal the transverse pores.

33. The process of claim 32 wherein the preparation step comprises: at least one cleaning of the substrate, electrochemical polishing, previous anodizing and chemical attack.

34. The process of claim 32 wherein the fixed potential of the mild anodizing pulses is comprised between 20-30 V and the current of the hard anodizing pulses has a maximum limit value of 60 mA with a fixed potential with a maximum value of 35 V during maximum duration of 5 seconds.

35. The process of claim 32 wherein the anodizing process is performed at a temperature below 25° C.

36. The process of claim 32 further comprising agitating the substrate during the anodizing process, homogenising the nanostructured anodized material layer during its growth on the substrate.

37. The process of claim 32 further comprising performing a chemical attack on the alumina layer with 5% by weight of phosphoric acid for a time comprised between 16 minutes and 21.5 minutes at a temperature comprised between 30° C. and 35° C. for the purpose of generating pores by means of dissolution of alumina regions formed during current-limited pulse hard anodizing.

38. The process of claim 32 further comprising milling the alumina layer to a thickness of 200 microns.

39. A nanostructured material, obtainable by means of the process of claim 32.

40. A three dimensional nanostructure obtainable by filling the pores of a nanostructured material comprising a substrate, which in turn comprises alumina, wherein at least one longitudinal pore is disposed on the substrate, whose longitudinal axis is essentially perpendicular to said substrate, wherefrom nanostructured material emerges, and at least one transverse pore whose longitudinal axis is essentially perpendicular to the longitudinal axis of the longitudinal pore.

41. Three-dimensional lattices of interconnected Bi2Te3 nanowires obtainable by filling the pores of a nanostructured material comprising a substrate, which in turn comprises alumina, wherein at least one longitudinal pore is disposed on the substrate, whose longitudinal axis is essentially perpendicular to said substrate, wherefrom nanostructured material emerges, and at least one transverse pore whose longitudinal axis is essentially perpendicular to the longitudinal axis of the longitudinal pore.

42. Three-dimensional polymer nanowire lattices interconnected obtainable by filling the pores of a nanostructured material comprising a substrate, which in turn comprises alumina, wherein at least one longitudinal pore is disposed on the substrate, whose longitudinal axis is essentially perpendicular to said substrate, wherefrom nanostructured material emerges, and at least one transverse pore whose longitudinal axis is essentially perpendicular to the longitudinal axis of the longitudinal pore.

Description

DESCRIPTION OF THE DRAWINGS

[0052] In order to complement the description being made and with the object of helping to better understand the characteristics of the invention, in accordance with a preferred embodiment thereof, said description is accompanied, as an integral part thereof, by a set of drawings where, in an illustrative and non-limiting manner, the following has been represented:

[0053] FIG. 1. Shows a diagram showing a film of material of the invention on aluminum, said film comprising longitudinal pores perpendicular to the anodized alumina layer and transverse pore planes parallel to the surface of the anodized alumina that interconnect the longitudinal pores in the perpendicular direction thereto.

[0054] FIG. 2. Shows a diagram of the internal three-dimensional lattice of the invention showing the arrangement of longitudinal pores and transverse pore planes that interconnect them. The transverse pores interconnect the longitudinal pores through the first neighbours.

[0055] FIGS. 3a, 3b. FIG. 3a shows a scanning electron microscopy micrograph of a cross section corresponding to a film of anodized alumina in which the existence of longitudinal pores and transverse pore planes that interconnect the longitudinal pores can be. The distance between longitudinal pores is 65 nm and the distance between transverse pore planes is 320 nm. FIG. 3b shows a scanning electron microscopy micrograph corresponding to a higher magnification of the cross-section of (A), where the longitudinal pore diameter is 40 nm and the cross-section of the transverse pores is elliptical with at least one of its minor axes of 20 nm is aligned in the perpendicular direction to the longitudinal pores and a major axis of 35 nm aligned in the parallel direction to the longitudinal pores.

[0056] FIGS. 4a-4c. Shows scanning electron microscopy micrographs corresponding to a cross section of various films of the invention showing different distances between the transverse pore planes with a periodicity between the set of transverse pore planes. In FIG. 4a, the distance between the transverse pore planes is 500 nm, in FIG. 4b, the distance is 320 nm and in FIG. 4c, 150 nm. The scale bars incorporated to the figures correspond to length of 500 nm.

[0057] FIG. 5 shows photographs of the film of the invention following the procedure described in the present invention, taken at different angles of incidence of light and showing interference colours.

[0058] FIG. 6 shows a scanning electron microscopy micrograph of a cross-section of a film of the invention wherein the transverse pores have aperiodic distance.

[0059] FIGS. 7a and 7b. Show photographs of three-dimensional periodic lattices of conjugated polymer nanowires embedded in films of the invention taken upon exposure to black light. The conjugated polymers infiltrated in the anodized alumina films referred to were in FIG. 7a: PCDTBT, PFO-DTBT, P3EAT and PPV. FIG. 7b: the infiltrated polymer is PVDF-TrFE. The scale bars represent a length of 1 cm.

[0060] FIG. 8 shows a scanning electron microscopy micrograph corresponding to a cross-section of a three-dimensional periodic lattice of polystyrene nanowires. The scale bar of the internal image represents a length of 1 cm.

[0061] FIG. 9 shows a scanning electron microscopy micrograph corresponding to a cross-section of a three-dimensional periodic lattice of Bi.sub.2Te.sub.3 nanowires.

[0062] FIG. 10 shows a graph showing the optical properties of the material of the invention. Said graph shows a correlation between transmittance and wavelength for an alumina represented with a dark line and the material of the invention, three-dimensional alumina, represented with a lighter line.

PREFERRED EMBODIMENT OF THE INVENTION

[0063] As a practical embodiment of the invention, but not limited thereto, following is a description of various examples of embodiment of the three-dimensional nanostructured material (1) of one of the aspects of the invention that is shown in FIGS. 1 and 2 using anodizing electrolytic processes, that implement the main concepts object of this invention in a simple manner.

EXAMPLE 1

[0064] Relates to a porous alumina film—nanostructured material (1) of the invention—on a substrate (4), said film having at least one longitudinal pore (2), preferably several longitudinal pores (2) that emerge from said substrate (4) and having respective longitudinal axes essentially perpendicular to the substrate (4) and which are connected by at least one transverse pore (3), preferably various longitudinal axes (3) defined in periodically spaced planes, as can be observed in FIGS. 4a-4c, although in other possible embodiments, as can be observed in FIG. 6, the transverse pores (3) may be defined in planes having aperiodic distances therebetween, as will be seen in subsequent example.

[0065] An aluminum wafer 1.6 cm diameter was firstly subjected to a cleaning process using acetone, water, isopropanol and ethanol sequentially. Next, the dean aluminum wafer was subjected to an electrochemical polishing process in an electrolyte composed of HClO.sub.4:EtOH (1:3) at 20 V for 3 minutes. After the electrochemical polishing process, the wafer was subjected to a first anodizing reaction at a voltage of V.sub.AB, V 25, to form aluminum oxide film called alumina. This alumina layer was removed by dissolution in a mixture of phosphoric acid at 7% by weight and chromic oxide at 1.8% by weight for 24 hours at 25° C.

[0066] After removing the first layer of alumina formed, the silicon wafer was subjected to a second anodizing process using pulse anodizing, which consisted of applying a constant voltage of 25 V for 180 s and a pulse at a nominal voltage of 32 V for 2 s. The second pulse anodizing process produced a growth of anodic alumina. This second anodizing process was maintained until the thickness of said layer was 20 μm.

[0067] In a process subsequent to the growth of the anodic alumina layer by pulse anodizing, the alumina layer formed is subjected to a chemical attack process using H.sub.3PO.sub.4 at 5% by weight at a temperature of 30° C. for 18 minutes.

[0068] The resulting anodic alumina film whose microstructure is shown in FIG. 3a is characterized by having longitudinal pores (2) and transverse planes pores (3) resulting in the nanostructured material (1). The longitudinal pores (2) are characterised in that they have a hexagonal arrangement, a distance of 65 nm between first neighbours and a cross-section of 40 nm. Transverse pores (3) are characterised in that they have an elliptical section with an axis aligned parallel to the 35 nm longitudinal pores (2) and an axis aligned on the 25 nm transverse pore plane (3) (see FIG. 3b). Transverse pore planes (3) may have a periodic distance of approximately 320 nm (see FIG. 3a).

[0069] In another preferred embodiment of example 1, the application time of the pulse anodizing process was maintained until reaching an anodized alumina film thickness of 200 μm. The anodized alumina film thus obtained has the same characteristics described above relating to the dimensions and the arrangement of the longitudinal pores (2) and transverse pores (3).

[0070] In another preferred embodiment of Example 1 in the second anodizing process using pulse anodizing during the application of a constant voltage of 25 V between pulses at a nominal voltage of 32 V for 2 s, it was varied so that longer times between pulses increased the distance between the transverse pore planes (3) and shorter times decreased said distance. The distance between transverse pore planes (3) can be proportional to the time of application of the constant voltage between current-limited anodizing pulses.

[0071] The nanostructured material (1) of the invention, and therefore the anodic alumina film, may exhibit a colour that is variable depending on the angle of incidence of light forming an interference colour.

EXAMPLE 2

Porous Alumina Film with Longitudinal Pores (2) Connected to Aperiodically Spaced Transverse Pore Planes (3)

[0072] The porous alumina material of Example 1 was processed following the process described in said Example No. 1, which was repeated during the pulse anodizing process modifying the application time at a constant voltage of 25 V between the current-limited anodizing pulses at a nominal voltage of 32 V. The resulting alumina film is characterised as shown in FIG. 6 in that it has transverse pore planes (3) are aperiodically spaced.

EXAMPLE 3

Porous Alumina Film with Longitudinal Pores (2) Connected to Transverse Pore Planes (3) Filled with Polymeric Material which is Shown in FIGS. 7a and 7b

[0073] The porous alumina material of Example 1 was processed following the process described in said Example No. 1 and the three-dimensional pore lattice was filled following a process of infiltration of polymeric compounds, PFO-DTBT, P3EAT and PPV. In order to fill the porous alumina with longitudinal pores (2) and transverse pores (3) with these polymers, the following solutions were prepared: PCDTBT 4 g/L in chloroform, PFO-DTBT 4 g/L in chloroform, P3EAT 4 g/L in chloroform and PPV 4 g/L in tetrahydrofuran. Next, the anodized alumina films with three-dimensional porosity were immersed in each of the solutions for 10 minutes. The anodized alumina films with three-dimensional porosity were extracted and the solvent contained in their pores was left to dry in ambient conditions.

[0074] The nanostructured material (1) and therefore, the porous alumina film with longitudinal pores (2) connected to transverse pore planes (3) filled with these polymeric materials may have luminescent properties that vary depending on the polymer used.

[0075] In another preferred embodiment of Example 3, the nanostructured porous alumina material (1) of Example 1 was processed following the process described in said Example 1 and the three-dimensional pore lattice was filled following a process of infiltration with polymeric compound of P(VDF-TrFE). In order to fill the nanostructured anodized alumina material (1) with three-dimensional porosity with this polymer, the following solution was prepared: P(VDF-TrFE) 5% by weight of dimethylformamide. Next, the AAO3D was immersed in the solution for 10 minutes. The anodized alumina film with three-dimensional porosity was extracted and the solvent contained in its pores was left to dry in ambient conditions. The porous alumina film with longitudinal pores (2) connected to transverse pore planes (3) filled with said polymeric materials has the advantage of having possess ferroelectric properties besides luminescent properties that also change with the angle of incidence of light.

EXAMPLE 4

Process for Obtaining Three-Dimensional Polymer Nanowire Lattices Interconnected as Shown in FIG. 8

[0076] The nanostructured porous alumina material (1) Example 1 was processed following the process described in said Example 1 and the three-dimensional pore lattice (2, 3) was filled with polystyrene following a process of in situ polymerisation. The styrene was polymerised within the three-dimensional alumina using AIBN as a primer in an atmosphere of N.sub.2 for 1 hour. Subsequently, the nanostructured anodized alumina material (1) was selectively dissolved in a solution of 10 M NaOH for 60 minutes. As a result, a polypropylene nanowire lattice connected by transverse planes of polystyrene wires that connect the longitudinal wires through their first neighbours was obtained.

EXAMPLE 5

Process for Obtaining Three-Dimensional Lattices of Interconnected Bi.SUB.2.Te.SUB.3 .Nanowires Shown in FIG. 9

[0077] The three-dimensional nanostructured porous alumina material (1) of Example 1 was processed following the process described in said Example 1 and the three-dimensional pore lattice (2, 3) was filled with Bi2Te3, following an electrochemical deposition process. To this send, a metallic layer was deposited on one of the 3D alumina surfaces that served as an electrode. This deposited electrode was used as a cathode of an electrochemical cell. The growth of Bi.sub.2Te.sub.3 inside the three-dimensional porous lattice in the anodic alumina was carried out by means of electrodeposition in a triple-electrode electrochemical cell for 8 hours. The conditions of the pulses were: 20 mV for 0.1 s and 0 mA/cm.sup.2 for 0.1 s. The three-dimensional porous anodic alumina film thus obtained and filled by electrochemical deposition of Bi.sub.2Te.sub.3 is characterised in that it is green as opposed to the colour of the compound Bi.sub.2Te.sub.3, which is dark grey.

[0078] As a result, a lattice of Bi.sub.2Te.sub.3 nanowires was obtained. An X-ray diffraction assay confirmed the crystalline structure of Bi.sub.2Te.sub.3. This crystalline phase is characterised in that it has a semiconductor response that confers thermoelectric properties, therefore it can be used in power generation devices.