WO2008081182A1

WO2008081182A1 - Methods of adhering particles to a material by heating

Info

Publication number: WO2008081182A1
Application number: PCT/GB2008/000005
Authority: WO
Inventors: Sembukutiarachilage Ravi Silva; Simon John Henley
Original assignee: University Of Surrey
Priority date: 2007-01-02
Filing date: 2008-01-02
Publication date: 2008-07-10
Also published as: TW200844257A; GB0700021D0

Abstract

Adhering particles (108) of a second material to a first material (110), by producing a dispersion of particles (108) of said second material in a medium, the medium being in contact with the first material (110), and adhering particles (108) of said second material to the first material (110) by selectively heating particles (108) of said second material dispersed within the medium. The particles (108) may be heated above their melting or boiling point by, for example, a laser.

Description

METHODS OF ADHERING PARTICLES TO A MATERIAL BY HEATING

FIELD OF THE INVENTION

This invention is directed to the adhesion of particles, such as metal particles, to surfaces of materials, and in particular the adhesion of micro- and nano-particles of metals and other materials to carbon nanotubes.

BACKGROUND TO THE INVENTION

Methods for depositing metals on surfaces are known. Such methods activated by laser light are also known. For example, US 4,340,617 discloses a method for depositing a layer of a surface-compatible material from the fluid phase onto a selected surface of a substrate body in a fluid deposition chamber. A laser is focused on the body surface at a position adjacent the surface. An introduced fluid medium has at least one component which absorbs a portion of the incident laser energy at the selected frequency for effecting photodecomposition or photolysis of the component in the fluid phase, depositing the product(s) of the photolysis process on the substrate surface.

This method requires the photolysis or photodecomposition of the component, which thus requires specific functionality for the material of the component. This technique also necessitates a complex procedure, as the raw material itself cannot simply be deposited on the surface.

US 5,059,449 discloses a method in which a metal track is deposited on a substrate surface by means of a laser beam, from a solution comprising a salt of a noble metal (for example palladium) and ammonia or amine. The method is based on the thermochemical decomposition of, for example, the ammonia under the energy of the laser. The hydrogen produced reduces the palladium ions to palladium metal.

In US 5,260,108, deposits of a metal such as palladium are formed on a substrate by contacting the substrate surface with a solution of the metal, and then exposing the surface through the solution to laser radiation having a wavelength absorbable by the substrate, and a power density effective to release electrons to promote deposition of the metal onto the substrate.

Both of these methods require chemical processes, which again require specific functionality for the metal in question. Also, in such methods the attachment of the metal to the substrate can be weak.

In US 2006/0057502, fine wirings are made by painting a board with a metal dispersion colloid including metal nanoparticles, drying the metal dispersion colloid into a metal- suspension film, irradiating the metal-suspension film with a laser beam, aggregating metal nanoparticles into larger conductive grains, washing the laser-irradiated film, eliminating unirradiated metal nanoparticles, and forming metallic wiring patterns built by the conductive grains on the board.

Here again, the adherence between the metal and the board can be unreliable, as the particles simply drop onto the board.

Methods for depositing materials onto nanotubes have been previously considered. For example, simple mixing of a dispersion of carbon nanotubes (CNTs) and metal nanoparticles has been considered. This method produces weak attachments of the particles to the CNTs, and is inefficient, as many particles remain unattached. As can be seen from Figure 7, which is a transmission electron microscope image of a product of this mixing technique, the particles are also clumped in areas around and along the CNTs, rather than spread out along their lengths.

Yen-Yu Ou et al, "High-density Assembly of Gold Nanoparticles on Multiwalled Carbon Nanotubes ...", J. Phys Chem. B 2006, 110, 2031-2036 discloses a chemical method of attaching gold nanoparticles to CNTs, using a methylamine interlinker.

Again, as this method is chemical based, specific functionality is required for the material to be deposited, and the attachment can be weak. Furthermore, the chemical linkage can affect the contact between the deposited material and the nanotube.

Y. Zhang et al, "Metal coating on suspended carbon nanotubes ...", Chemical Physical Letters 331 (2000), 35-41 , 24 November 2000 discloses coating CNTs with various metals by electron beam evaporation.

This method is complex to implement, as it requires a vacuum for the evaporation. It is therefore also difficult to scale up to practical volumes. Moreover, the CNTs are attached to the micro-grid substrate, which can hamper the processing. The CNTs will also only be decorated or coated on the side(s) exposed, away from the substrate.

SUMMARY OF THE INVENTION The present invention aims to address one or more of these problems and provide improvements upon the known devices and methods. Aspects and embodiments of the invention are set out in the accompanying claims.

In general terms, one embodiment of a first aspect of the invention can provide a method of adhering particles of a second material to a first material, comprising the steps of: producing a dispersion of particles of said second material in a medium, the medium being in contact with the first material; and adhering particles of said second material to the first material by selectively heating particles of said second material dispersed within the medium above their melting point.

Thus, as the particles are heated above their melting point, the adherence to the first material is more secure than in previously considered methods. This method also provides a simple means of applying the particles to the first material, namely heating. Therefore no specific chemical linkage is required.

Alternatively, one embodiment of a second aspect of the invention can provide a method of adhering particles of a second material to a first material, comprising the steps of: producing a dispersion of particles of said second material in a liquid medium, the medium being in contact with the first material; and adhering particles of said second material to the first material by selectively heating particles of said second material dispersed within the liquid medium and by said heating at least modifying the structure of the particles of said second material.

This method also provides simple heating of the particles for adherence to the first material. Furthermore, no vacuum is required, as the particles are heated selectively within the fluid medium, so that oxidisation can be inhibited. This method also enables a better dispersion of the particles on the first material than in previously considered methods, by means of the dispersion in the liquid medium.

It will be apparent to the skilled reader that the first aspect of the invention, concerning ^■ heating the particles above their melting point in a medium, is interrelated to the second aspect, concerning heating the particles in a liquid medium. These aspects may also provide alternative solutions to problems that may be addressed by the other respective aspect.

Preferably, the step of heating particles of said second material divides said particles into a plurality of sub-particles. More preferably, the methods comprise heating particles of the second material beyond their boiling point, thereby at least partially evaporating the particles. The resultant particles or sub-particles are thus smaller and hotter than the original particles, thus increasing their likelihood of good adhesion to the first material.

Suitably, the step of heating imparts a velocity to the particles or sub-particles. Thus the particles impact the first material at speed, providing better adhesion.

Preferably, the step of heating comprises illuminating the particles of the second material with a laser. The laser is able to provide high energy for selectively heating the particles.

In embodiments, the first material comprises at least one nanostructure, such as a nanotube. In one embodiment, the nanostructures are dispersed in the medium. This allows adhesion of particles of the second material to all sides of the nanostructures.

The above aspects and embodiments may be combined to provide further aspects and embodiments of the invention. BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is a diagram illustrating apparatus according to an embodiment of the invention;

Figure 2 is a plan view of part of the apparatus of Figure 1 ;

Figure 3 is diagram illustrating an evaporation process according to an embodiment of the invention;

Figure 4 is a schematic diagram of a product according to an embodiment of the invention;

Figure 5 is diagram illustrating a close-up view of a product according to an embodiment of the invention;

Figure 6 is another diagram illustrating an evaporation process according to an embodiment of the invention;

Figure 7 is a diagram illustrating a product according to a previously considered technique;

Figure 8 is a diagram illustrating a product according to an embodiment of the invention; Figure 9 is a graph illustrating absorbance characteristics of components according to embodiments of the invention;

Figure 10 is another graph illustrating absorbance characteristics of components according to embodiments of the invention; and

Figure 11 is a diagram illustrating another product according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

Figure 1 illustrates a basic apparatus for an embodiment of the invention. A fused silica vessel 100 is used as a container for the components to be processed.

The vessel 100 contains a medium 102 in which are dispersed a first material, in this case nanotubes 110, and particles 108 of a second material. In this embodiment, the medium is a liquid, such as water, and as such is disposed in a layer along the bottom of the vessel.

The vessel in this embodiment is closed above the liquid layer 102, in order to prevent any splashes exiting the vessel.

Here, the nanotubes 110 are carbon nanotubes (CNTs). The sizes of the tubes are generally comparable to the size of the particles of the second material, and generally in the range of 0.2nm to 100 nm in diameter. In this embodiment, the particles are nanoparticles of gold, which absorb the laser energy whilst not reacting readily with the medium.

A laser (not shown) produces laser light 106 which enters the vessel in a direction perpendicular to the layer of liquid medium, and illuminates the medium containing the nanotube and nanoparticle dispersion 102.

The laser, in this embodiment an excimer laser, can be of a variety of chosen wavelengths and powers, and can be timed to a variety of pulse regimens, and the total processing time limited suitably.

For example, the repetition frequency of the pulses is between of the order of 1 Hz and 10MHz.

The laser pulses are extremely short, of the order of nanoseconds, in order to maximise the power to which the nanoparticles, nanotubes and liquid can be exposed without damaging them. However, in this embodiment, the energy of each pulse is limited at least below 10OmJ, and preferably lower, as higher energy per unit area values can damage the nanotubes. The energy per unit area at the liquid medium is of course also governed by the size of the spot to which the laser is focused.

The laser wavelength is chosen as an absorption wavelength, or plasmon resonance wavelength, of the gold nanoparticles. This absorption of the particles, or the particles and solution in combination, will reduce the absorption of the nanotubes, thus protecting them from damage. The plasmon resonance wavelength for gold particles may be between 500nm and 800nm, and this wavelength may be used in this embodiment.

A glass plate 104, which is opaque to the laser, is disposed underneath the silica vessel. This plate could also be formed as a bottom piece of the vessel, or laid inside the bottom of the vessel. In this embodiment, the plate 104 covers at least the area covered by the layer of solvent medium, so that the whole of the medium can be illuminated without any laser light being transmitted through to the lower stage 112.

The stage 112 situated underneath the vessel and glass plate is capable of translation in the x and y directions, in order to allow the laser to be tracked over the entire area of the solvent layer.

Figure 2 is a plan view of part of the apparatus of Figure 1. In this embodiment, the laser light 106 is focused to a spot 202 which can be tracked over the vessel 100, in order to cover the entire area of the solvent layer 102. In this embodiment, the vessel is of similar width to the laser spot 202, and so the only movement required is in the x direction indicated by arrow 200.

Figure 3 is diagram illustrating the evaporation process of this embodiment of the invention. The input laser light 106 illuminates the particles 108, which in this embodiment are nanoparticles, one of which is shown in Figure 3. The nanoparticles absorb the incident laser light, becoming heated. The nanoparticles may be heated beyond their melting point, producing highly malleable particles 300. In some instances the particles 108 may be shattered into smaller particles 302 by the laser energy. In such case, the resultant smaller particles 302 will be ejected at speed. After sufficient heating by the laser, the boiling point of the particles 108 will be reached, and the particles will evaporate, producing atoms of the material, and reducing the size of the parent nanoparticle. These atoms may be briefly ionised. These atoms may coagulate into further small nanoparticles. The sub-particles produced by the heating effect may therefore be atoms, or small clusters of a few atoms.

The sub-particles produced, or the particles heated beyond their melting point, may be assembled into new structures or nanostructures prior to attachment to the first material. For example, the sub-particles may be assembled into larger structures such as nanowires, which are then adhered to the first material, creating a particular composite material. This effect may occur spontaneously on separation of the particles, due to properties of the second material, or it may be encouraged by the heating effect of the laser.

The first material, in this embodiment nanotubes 110, is thus exposed to a flux of metal atoms and hot (smaller) nanoparticles 302, which adhere to the surface of the nanotube. In this embodiment, the adhesion is primarily physical, and any chemical reaction between the particles and the nanotubes may be incidental. Chemical attachment of some sort may be advantageous in other embodiments.

The principal mechanisms for the adhesion are one or other (or both) of: the particles being melted, and hence readily conformed to the shape of the nanotube; or the particles moving at speed after the shattering of the primary particle, and hence meeting the surface of the nanotube at high impact velocities.

The nanotubes are thus decorated by particles and atoms 304 stuck to their surface. These particles 304 may retain a mostly spherical shape, or in cases of high impact or partially melted larger particles, can form flattened globules such as illustrated at 306. Larger deposits may be "grown" as more particles are adhered, and can coagulate with already deposited particles.

Deposited particles may of course receive further doses of laser energy. Such further doses may help to grow larger deposits, or spread the deposits along the nanotube surface, depending on the material used.

Figure 4 is a schematic diagram representing a product of this embodiment of the invention. As can be seen, the particles 304, 306 are adhered to the surface of the nanotube 110.

Figure 5 is a transmission electron microscope image of such a product, showing particles 304, 306 stuck to the surface of the nanotube 110, some of the particles being partially flattened.

Figure 6 is another diagram illustrating the evaporation process according to this embodiment of the invention. As described above, the input laser light 106 evaporates the nanoparticles 300, producing smaller particles 302, which adhere to the nanotube 110. As can be seen in Figure 4, in this embodiment both the upper 400 and lower 402 sides of the nanotube can be decorated. This is due to a number of factors. As the nanoparticles 300 and nanotubes 110 are in dispersion together, this entails that the lower surface 402 is not attached to a substrate. The free movement of the hot flux of particles 302 in any direction allows any surface of any nearby nanotube to be decorated. Typically, the wavelengths of the laser light are greater than the diameters of the nanotubes and the nanoparticles, so there is little (if any) shielding from the laser of any nanoparticles which may be directly below a nanotube. In the above embodiments, the dispersion of nanoparticles could be produced in a number of ways. For example, gold particles could be evaporated by laser from the surface of a solid gold source submerged in the liquid medium. In a known method, gold nanoparticles are photochemically grown by laser irradiation of a tetrachloroaurate complex (Inasawa et al, "Size controlled formation of ^'gold nanoparticles. . . ", Jpn. J. Appl. Phys. Vol. 42 (2003) pp. 6705-6712, part 1 , no.10, October 2003). The dispersion could be produced by chemically decomposing any suitable such gold-containing compound.

The nanotubes may be removed from the medium by, for example, filtering the liquid.

Examples

By way of further illustration of the features of the invention, specific examples will now be described.

Example 1

In this example, the solvent medium used is water, in which are dispersed multiwalled carbon nanotubes (MWCNTs) of diameters between about 2 and about 100nm, and gold nanoparticles of about 10nm .diameter. These sizes are approximate; generally speaking the diameters of the nanotubes and adhered nanoparticles will be comparable.

The laser used is a Lambda Physik LPX 21Oi excimer laser, and the wavelength of light used is 248nm in the ultra-violet range. The laser is pulsed, each pulse lasting approximately 25 nanoseconds. The energy per unit area applied by the laser is 65mJ per square cm. The repetition frequency of the pulses can be chosen to be between 1 Hz and 200Hz. In this example, the energy per pulse is set at 25mJ or lower.

Figure 9 is a graph illustrating absorbance characteristics CNTs alone dispersed in water. The line (i) indicates the absorbance of the CNTs across the wavelengths shown without exposure to the laser. The graph therefore shows that for 5OmJ (iii) and 10OmJ (iv), the absorbance of the CNTs for all wavelengths is low, indicating that most of the CNTs have been destroyed by the high-energy pulses. However, for 25mJ (ii), the absorbance of the CNTs is not greatly affected.

Figure 10 is a graph illustrating absorbance characteristics a dispersion of CNTs and gold nanoparticles in water. Line (v) indicates the absorption spectrum with no incident laser pulse. The graph shows therefore that 25mJ (vi) pulses affect the absorption very slightly, 5OmJ (vii) more so, and 10OmJ again appear to destroy large numbers of the components.

Figure 8 is a transmission electron microscope image of the product of this example. As can be seen.from Figure 8, the distribution of nanoparticles (304, 306) along the CNTs 11 is much more consistent than in the mixing product 5 (Figure 7), and there is much less "clumping", resulting in a reasonably even layer of particles along the surface of the CNTs.

Example 2

In this example, the same conditions were used as in Example 1 , with palladium as the i nanoparticle. Figure 11 is a transmission electron microscope image of the product of this example. Again, the distribution of nanoparticles 304, 306 along the CNTs 11 is more consistent than in the mixing product (Figure 7), with less "clumping".

Applications

The gold decorated CNTs produced in embodiments described above could be used in a variety of applications. For example, gold-decorated CNTs may be applied in fields such as biosensing and plasmonics.

A gold/CNT junction can be used as a biosensor, as it has good electrochemical transduction properties. Some biological groups will bond well to a gold particle adhered to a CNT surface.

As surface plasmon resonance (SPR) occurs in gold nanoparticles at particular visible wavelengths, such visible wavelengths could be readily coupled with gold-decorated CNTs. This effect can be used to enhance photovoltaic efficiency.

Gold-decorated CNTs could be used in large-area substrates for surface enhanced Raman spectroscopy. Such substrates could be used in trace-level chemical sensing or sensing of biological molecules.

Silver-decorated CNTs could also be used for such large-area substrates utilizing the surface-enhanced Raman Effect.

Palladium can be used as the applied metal. Palladium coated CNT mats could be used for hydrogen storage or detection. Large area catalysts may be fabricated, for example, from CNT supported rhodium nanoparticles.

The nanoparticle-CNT junction can be used for a variety of further applications. Field- effect-transistors could be constructed using CNTs decorated with metal in this manner.

Other embodiments

Various other alternative embodiments are available, some with different applications.

For example, for the vessel 100 although fused silica is preferred, as it is transparent to the input laser light, other materials could be used..

The medium 102 is preferably transparent to the laser light, and may be chosen for various properties for different embodiments. For example, a particular liquid may be chosen for aiding dispersion of a particular nanoparticle. Where the particles are nickel, the liquid could be one which does not contain oxygen (or any oxidised compounds). A dispersion agent or surfactant could be added to the medium.

In alternative embodiments, the medium is a gas orplasma in which the particles of the second material are dispersed. In one embodiment, the medium is a vacuum.

Instead of CNTs, silicon or boron nitride nanotubes could be used. The nanotubes may be single walled (SWCNT) or multi-walled (MWCNT). In other embodiments, the material to be decorated could be a microstructure, or another nanostructure, such as a fullerene, or nanowire, or a different type of nanoparticle. In other embodiments, the first material could be a much larger object, which could be disposed at the bottom of the vessel underneath the liquid layer.

The particles could be of metals other than gold, such as palladium, silver, magnesium, rhodium or nickel, or other substances such as semiconductors, or indeed any substance capable of absorbing the laser energy, and not readily reacting with the solution used. Preferred materials absorb different wavelengths of laser light from the nanotubes, thus allowing selective activation of the nanoparticles.

The particles could be larger, for example, on the micro-scale. Such larger particles may be easier to melt, and thus easier to adhere to the nanotubes. The smaller particles will likely move faster (if produced by shattering of a larger particle), but may lose heat more quickly.

In alternative embodiments, either the first or second material could be amorphous (such as a glass) or crystalline.

Where the particles are amorphous (perhaps having some near-crystalline or low quality crystalline properties), the heating may transform the particles or nanoparticles into crystalline material, prior to the adhesion to the first material. Where the particles are crystalline, the sub-particles produced may be more susceptible to assembling into new or larger structures, particularly under influence of the heating effect of the laser.

The laser wavelength could be chosen as one less readily absorbed by the nanotubes or nanostructures and the solution. For particular particles, this absorption of the particles, or the particles and solution in combination will reduce the absorption of the nanotubes, thus protecting them from damage.

The wavelength may be varied between 100nm (UV) and 1 mm (far infra-red). In • particular instances, the wavelength can be set according to the size of the particles, as the absorption wavelengths of the particles can vary with the size.

The stage 112 situated underneath the vessel and glass plate could simply be a rigid base, with no translating stage.

In other embodiments, the vessel could be larger, thus requiring x and y translation, and an x/y scan technique such as a raster scan. Of course, if necessary, the laser itself could be moved, rather than the stage 112.

In one alternative embodiment, the first and second materials are similar types of micro or nanostructure or particle. The materials may be two different types of nanoparticle (such as a gold nanoparticle and a nanoparticle which does not absorb the laser light), or two different types of nanowire, resulting in a composite of the two similar types of material.

In another alternative embodiment, the nanotubes are attached to a substrate. In this case, the decoration process may be more stable. However, the side of the nanotubes attached to the substrate may not be efficiently covered with the particles.

The first material may be modified, for example by texturing or roughening, in order to enhance attachment of the particles of the second material, or to allow^' ordering of the attached particles. In one embodiment, it is the heating effect or impact of the laser pulses which modifies the first material. In an alternative, the first material is cleaned or smoothed, for example by the impact of the laser pulses, in order to aid attachment or ordering. In another alternative, the first material is textured or roughened by application of a suitable abrasive chemical. This chemical may form part of a fluid medium in which the first and/or second material are dispersed.

In other embodiments, a two (or more) stage process is performed, decorating the substrate or nanotube with a first material, and in a second stage, with second material. For example, a first metal could be deposited on a nanotube, the deposition of the first metal allowing an easier or more secure decoration with a second metal or other material.

In other embodiments, the nanotube is at least partially coated. In one embodiment, a nanowire can be created by almost completely coating a CNT with a conducting metal.

Transition metal nanoparticles, such as Nickel, Cobalt or Iron may be attached to a first material for subsequent catalytic growth of CNTs. Similarly Gold nanoparticles may be used for the growth of Silicon nanowires.

In another embodiment, a nanoparticle is deposited on a CNT, and the site at which the nanoparticle is adhered is used for seeding growth of a new CNT. Nickel is particularly suitable for this purpose. For example, a surface could be decorated with an array of nickel dots, each of which is for seeding growth of a CNT.

Ferric metals can also be applied to such nanostructures, giving magnetic effects with various possible applications. For example, a simple method for separation of grown CNTs from a medium could involve decorating them with a ferric metal, and applying a magnetic field. Where the applied nanoparticle is a semiconductor, this applied semiconductor particle could, like gold, exhibit SPR. Therefore the resultant nanostructure could be used for conduction or absorption of particular wavelengths of light into the nanostructure.

Application of different metals to the nanotube or nanostructure will produce different results, as certain metals will adhere to the surface in a generally flat, spread out form, and others will adhere maintaining a largely spherical shape. These alternatives could be used for different applications; for example, a more spread out metal covering may lend itself more easily to production of coated CNTs and nanowires.

It will be appreciated by those skilled in the art that the invention has been described by way of example only, and that a variety of alternative approaches may be adopted without departing from the scope of the invention.

Claims

1. A method of adhering particles of a second material to a first material, comprising the steps of: producing a dispersion of particles of said second material in a medium, the medium being in contact with the first material; and adhering particles of said second material to the first material by selectively heating particles of said second material dispersed within the medium above their melting point.

2. A method of adhering particles of a second material to a first material, comprising the steps of: producing a dispersion of particles of said second material in a liquid medium, the medium being in contact with the first material; and adhering particles of said second material to the first material by: selectively heating particles of said second material dispersed within the liquid medium; and by said heating at least modifying the structure of the particles of said second material.

3. A method according to Claim 2, further comprising heating the particles of the second material in the medium above their melting point.

4. A method according to any preceding claim, wherein the step of heating particles of said second material divides said particles into a plurality of sub-particles.

5. A method according to any preceding claim, further comprising heating particles of the second material beyond their boiling point, thereby at least partially evaporating the particles.

6. A method according to any preceding claim, wherein the step of heating imparts a velocity to the particles or sub-particles.

7. A method according to any preceding claim, wherein the step of heating comprises illuminating the particles of the second material with a laser.

8. A method according to Claim 7, wherein the wavelength of the laser is at an absorption wavelength of the second material, or at a surface plasmon resonance wavelength of the second material.

9. A method according to Claim 7 or Claim 8, wherein the wavelength of the laser is between 100nm and 1mm.

10. A method according to any of the Claims 7 to 9, wherein the wavelength is between 500nm and 800nm.

11. A method according to any of the Claims 7 to 10, further comprising setting the wavelength of the laser according to the size of the particles of the second material.

12. A method according to any of the Claims 7 to 11 , in which the second material has a peak absorption wavelength different from that of the first material.

13. A method according to any of the Claims 7 to 12, in which the illumination of the particles with the laser is carried out in pulses of set duration.

14. A method according to Claim 13, wherein each pulse has a duration of 25 nanoseconds.

15. A method according to Claim 13 or Claim 14, wherein the repetition frequency of the pulses is between 1Hz and 10MHz.

16. A method according to any of the Claims 13 to 15, wherein the energy of each pulse is between 1 to 100 mJ.

17. A method according to Claim 16, wherein the energy of each pulse is 25m J or less.

18. A method according to any preceding claim, wherein the particles of the second material are micro- or nano-particles.

19. A method according to any preceding claim, further comprising modifying a surface of the first material.

20. A method according Claim 19, comprising modifying the surface of the first material using an abrasive chemical.

21. A method according to Claim 19 comprising using a/the laser to modify the surface of the first material.

22. A method according to any preceding claim, wherein the first material comprises at least one nanostructure.

23. A method according to Claim 22, wherein the particles of the second material and the diameter of the at least one nanostructure are comparable in size.

24. A method according to Claim 22 or Claim 23, wherein at least one nanostructure is a nanotube between 0.2nm and 100nm in diameter.

25. A method according to any of the Claims 22 to 24, wherein the nanostructure(s) is/are mounted on a substrate.

26. A method according to any of the Claims 22 to 24, further comprising dispersing the nanostructure(s) in the medium.

27. A method according to any of the Claims 22 to 26, wherein the step of adhering particles of the second material to the nanostructure comprises at least partially coating the nanostructure.

28. A method according to any preceding claim, wherein the first material comprises at least one nanoparticle.

29. A method according to any preceding claim, in which the second material is non- reactive with the medium.

30. A method according to any preceding claim, wherein the second material is a metal.

31. A method according to Claim 29, wherein the metal is nickel, and the medium is a solvent that does not contain oxygen.

32. A method according to any of the Claims 1 to 29, wherein the second material is a semiconductor material.

33. A method according to any preceding claim, wherein the medium is a solvent containing a dispersion agent.

34. A method according to any preceding claim, wherein the medium is transparent to wavelengths of light between 100nm and 1mm. , ■

35. A method according to any preceding claim, wherein the first and/or the second material is amorphous.

36. A method according to any of the Claims 1 to 34, wherein the first and/or the second material is crystalline;

37. A method according to any preceding claim, further comprising: dispersing a third material in the medium; and, after the step of heating the second material, adhering particles of the third material to the first material and/or to the second material adhered to the first material, by heating the particles of the third material within the medium.

38. A method according to any preceding claim, comprising producing the dispersion of particles of the second material in the medium by illuminating a surface of a sample of the second material with, a laser, and evaporating particles from the surface of the sample.

39. A method according to any of the Claims 1 to 37, comprising producing the dispersion of particles of the second material in the medium by chemically decomposing an Au containing compound.

40. A method of seeding a nanostructure, comprising identifying the site of a particle of a second material adhered to a first material according to any preceding claim, and seeding a nanostructure from the site.

41. An apparatus for adhering particles of a second material to a first material, comprising: a container containing a dispersion of particles of the second material in a liquid medium, the medium being in contact with the first material; and means for selectively heating the particles of the second material within the liquid medium, thereby provoking adhesion of particles of the second material to the first material.

42. Apparatus for adhering particles of a second material to a first material, comprising: a container containing a dispersion of particles of the second material in a medium, the medium being in contact with the first material; and means for heating the particles of the second material within the medium above a melting point of the particles, thereby provoking adhesion of particles of the second material to the first material.

43. An apparatus according to Claim 41 or Claim 42, wherein the means for heating comprises a laser.

44. An apparatus according to Claim 43, wherein the laser is an excimer laser.

45. An apparatus according to Claim 43 or Claim 44, further comprising a stage translatable in the x and y directions for providing a scan of the laser over the container.

46. A first material with at least one adhered particle of a second material, produced by a method according to any of the Claims 1 to 39.

47. A first material with at least one adhered particle of a second material according to Claim 46, wherein the first material is a carbon nanostructure, and the second material is a metal nanoparticle.

48. A biosensor formed from the carbon nanostructure with an adhered particle according to Claim 47.

49. A method of adhering particles of a second material to a first material, substantially as hereinbefore described, with reference to the accompanying Figures 1 to 6 and 8 to 11.

50. Apparatus for adhering particles of a second material to a first material, substantially as hereinbefore described, with reference to the accompanying Figures 1 to 6 and 8 to 11.

51. A first material with at least one adhered particle of a second material, substantially as hereinbefore described, with reference to the accompanying Figures 1 to 6 and 8 to 11.