Highly ordered arrays of micelles or nanoparticles on a substrate surface and methods for producing the same

Abstract

The invention provides a method for increasing the order of an array of polymeric micelles or of nanoparticles on a substrate surface comprising a) providing an ordered array of micelles or nanoparticles coated with a polymer shell on a substrate surface and b) annealing the array of micelles or nanoparticles by ultrasonication in a liquid medium which is selected from the group comprising H.sub.2O, a polar organic solvent and a mixture of H.sub.2O and a polar organic solvent. In a related aspect, the invention provides the highly ordered arrays of micelles or nanoparticles obtainable by the methods of the invention.

Claims

1. A method for increasing an order of an array of polymeric micelles or of nanoparticles on a substrate surface comprising: a) providing an ordered array of micelles or nanoparticles coated with a polymer shell on a substrate surface, and b) annealing the array of micelles or nanoparticles by ultrasonication in a liquid medium which comprises a C.sub.1-C.sub.10 alkanol or a mixture of H.sub.2O and the C.sub.1-C.sub.10 alkanol, wherein the ultrasonication is effected at a frequency in a range of 20 kHz to 2 MHz, a power input in a range of 5 W/l to 50 W/l, and a temperature in a range from 15° C. to 70° C.

2. The method according to claim 1, wherein the liquid medium consists of ethanol or of a mixture of H.sub.2O and ethanol in a ratio in a range from 2:1 to 0.01:1.

3. The method according to claim 1, wherein the ultrasonication is effected for a time period in a range of 10 to 500 s.

4. The method according to claim 1, wherein the ordered array of micelles is a hexagonal array produced by a block copolymer micellar nanolithography (BCML) technique.

5. The method according to claim 1, wherein the substrate is a member selected from the group consisting of glasses, Si, SiO.sub.2, ZnO, TiO.sub.2, Al.sub.2O.sub.3, C, InP, GaAs, GaP, GaInP, and AlGaAs.

6. The method according to claim 1, wherein the micelles are micelles of a two-block- or multi-block copolymer selected from the group consisting of polystyrene (n)-b-poly (2-vinylpyridine (m), polystyrene (n)-b-poly (4-vinylpyridine (m), and polystyrene (n)-b-poly (ethylene oxide) (m), in which n and m indicate a number of repetition units and are, independently of one another, integers in a range of 10-10,000.

7. The method according to claim 1, wherein the nanoparticles coated with a polymer shell are metals, metal oxides or semiconductors.

8. The method according to claim 1, wherein the micelles are loaded with at least one metal salt.

9. The method according to claim 8, wherein the at least one metal salt is a member selected from the group consisting of salts of Au, Ag, Pd, Pt, In, Fe, Zr, Al, Co, Ni, Ga, Sn, Zn, Ti, Si and Ge.

10. The method according to claim 8, further comprising the following step: c) converting the at least one metal salt in said micelles by an oxidation or reduction treatment into inorganic nanoparticles and optionally partial or complete removal of an organic copolymer of the micelles by a plasma treatment.

11. The method according to claim 1, wherein the ultrasonication treatment results in an at least 10% increase of an order of the array of micelles or nanoparticles as indicated by a corresponding decrease of a standard deviation of a mean intermicelle or interparticle distance.

12. The method according to claim 1, wherein the substrate surface is prestructured with primary structures having mean distances in a range from to 25 nm to 10 μm, and the ordered array of micelles or inorganic nanoparticles is provided in an interspace between the primary structures.

13. The method according to claim 12, wherein the primary structures having mean distances in the range from to 25 nm to 10 μm are formed on the substrate surface by optical lithography, UV lithography, deep-UV lithography, laser lithography, electron-beam lithography or nano-Imprint techniques.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows SEM micrographs of a substrate surface structured with gold nanoparticles (in order to show the order more clearly the individual particles have been masked with white circles): (A) before annealing; B) after annealing

(2) FIG. 2 shows the results of an ultrasound annealing treatment of a micellar array with varying solvent ratios: (A) Increase of the degree of order of the micellar array; (B) Decrease of the standard deviation of the mean distance of the micellar array

(3) FIG. 3 shows the results of an ultrasound annealing treatment of a micellar array with varying solvent ratios and subsequent plasma treatment to obtain a corresponding gold nanoparticle array; (A) Increase of the degree of order of the nanoparticle array; (B) Decrease of the standard deviation of the mean distance of the nanoparticle array

(4) FIG. 4 shows the results of an ultrasound annealing treatment of a micellar array with a solvent ratio ethanol:H.sub.2O=2:1 and varying duration of the annealing treatment: (A) Increase of the degree of order of the micellar array; (B) Decrease of the standard deviation of the mean distance of the micellar array

(5) FIG. 5 shows schematically a specific embodiment of the invention, wherein the array of micelles or nanoparticles is provided in the interspaces of larger primary structures.

(6) The present invention is illustrated in more detail in the following non-limiting examples.

EXAMPLE 1

Preparation of Highly Ordered Arrays of Micelles on a Substrate Surface

(7) Arrays of gold-salt loaded micelles on a glass substrate were prepared by micellar block copolymer nanolithography essentially according to published methods (e.g. EP 1 027 157).

(8) As an initial step, a 5 mg/ml toluene solution of micelles of the diblock copolymer polystyrene-block-polyvinylpyridine (PS-b-P2VP; Mn(PS) 190.000; Mn (P2VP) 55.000; Mw/Mn=1.10) loaded with HAuCl.sub.4 was prepared and stored in a sealed glass vial.

(9) This micellar solution was applied on a glass substrate (24 mm×24 mm) by spin coating (6000 rpm, 1 min) in a spin coater (WS-400B, Laurell Technologies, North Wales, USA) and left drying.

(10) The conditions were adjusted so that a sample with a mean micelle distance of 68-72 nm and a standard deviation of the mean distance value in range of 9-13 nm was obtained. If desired, it is possible to decrease the initial degree of order by adding ultra pure H.sub.2O to the above polymer solution (e.g. 1 vol. %).

(11) The resulting nanostructured sample was placed in a commercial sonifier (Sanorex, Bandelion electronic, Berlin) and immersed in a liquid medium consisting of a mixture of ethanol:H.sub.2O in different ratios at room temperature and sonicated at a frequency of 35 kHz and a power input in the range of 5-50 W/l, preferably 15-30 W/l, for 120 s.

(12) FIG. 2 shows the results of this ultrasound annealing treatment with different solvent ratios. These diagrams were obtained by image processing of corresponding SEM micrographs. The data are derived from 14 measuring points (7 different positions on 2 identically treated samples).

(13) The degree of order as used herein is indicated by the “sixfold bond-orientational order parameter” ψ.sub.6 as defined by D. Nelson and B. I. Halperin in Physical Review B 19.5 (1979), 2457-2484, for a hexagonal array.

(14) ${\psi }_6=.Math.\frac{1}{N_{\mathrm{bonds}}}\underset{j}{.Math.}\underset{k}{.Math.}{e}^{i.Math.6.Math.{\theta }_{\mathrm{jk}}}.Math.$
with N.sub.bonds=number of connections between the central particle of a hexagon and its next neighbors; θ.sub.jk=angle between a central particle and 2 next neighbors in juxtaposition, k=central particle and j=neighbor.

(15) For an ideal structure exclusively consisting of perfect hexagons, the order parameter ψ.sub.6=1.

(16) A high order parameter corresponds to a low standard deviation of the interparticle distance, both values are largely inverse proportional to each other. Thus, for a more simple indication of the order of a nanostructured array, often the standard deviation of the interparticle or intermicelle distance is used herein.

(17) As evident from FIG. 2, a marked increase of the degree of order of the micellar array and a corresponding decrease of the standard deviation of the mean distance of the micellar array is observed in each case. The influence of the specific solvent ratio is rather low.

(18) In order to assess the influence of the duration of the annealing treatment, a micellar array was prepared as indicated above and ultrasonicated for different time periods with an ethanol: H.sub.2O ratio of 2:1.

(19) FIG. 4 shows that a rather short annealing time of about 35-55 s already provides excellent results with respect to the increased degree of order of the micellar array and a corresponding decrease of the standard deviation of the mean distance of the micellar array. Considerable longer annealing times resulted in rather marginal improvements.

EXAMPLE 2

Preparation of Highly Ordered Arrays of Nanoparticles on a Substrate Surface

(20) A micellar array was prepared on a glass substrate and subjected to an ultrasound annealing treatment with varying solvent ratios analogous to Example 1.

(21) The resulting micellar array was subjected to a plasma treatment essentially according to published methods (e.g. EP 027 157). Typically, the substrate was treated with W10 plasma (90 vol. % argon and 10 vol. % hydrogen) at a pressure of 0.4 mbar for 45 minutes and 150 W power input in a PlasmaSystem 100 (PVA TePla, Wettenberg, Germany) device.

(22) In the course of this process, the polymer shell of said micelles was removed and the gold salt contained therein was reduced to elemental gold, whereby a highly ordered array of gold nanoparticles was obtained.

(23) FIG. 3 shows the results of the preceding ultrasound annealing treatment with different solvent ratios. These diagrams were obtained by image processing of corresponding SEM micrographs. The data are derived from 14 measuring points (7 different positions on 2 identically treated samples).

(24) The plasma treatment results in a slightly lower degree of order as compared with the initial micellar array and a corresponding increase of the standard deviation of the mean interparticle distance to about 14.5 nm for the non-annealed sample.

(25) A considerable increase of the degree of order of the nanoparticle array and a corresponding decrease of the standard deviation of the mean distance of the nanoparticle array was observed for each solvent ratio. In this case, however, a strong influence of the specific solvent ratio is evident. Best results were obtained with an ethanol:H.sub.2O ratio of 2:1.