WO2010088726A1

WO2010088726A1 - Fabrication of nanoparticles on solid surfaces

Info

Publication number: WO2010088726A1
Application number: PCT/AU2010/000110
Authority: WO
Inventors: Dusan Losic
Original assignee: University Of South Australia
Priority date: 2009-02-04
Filing date: 2010-02-04
Publication date: 2010-08-12

Abstract

A process for fabrication of an array of metal particles or metal compound particles dispersed on a substrate, the process including providing a solid substrate having a film of the metal or metal compound on a surface thereof and heating the solid substrate for a temperature and time sufficient to convert the film into an array of particles of the metal or metal compound dispersed on the surface.

Description

FABRICATION OF NANOPARTICLES ON SOLID SURFACES

This international patent application claims priority from Australian provisional patent application 2009900405 filed on 4 February 2009, the contents of which are to be taken as incorporated herein by this reference

FIELD OF THE INVENTION

The present invention relates generally to processes for the fabrication of arrays of metal or metal compound nanoparticles on solid surfaces, and to arrays of metal or metal compound nanoparticles formed using the processes. More specifically, the present invention provides processes for template free and wet- chemistry free fabrication of arrays of metal or metal compound nanoparticles on solid surfaces.

BACKGROUND OF THE INVENTION

Large-scale arrays of nanostructures on substrates such as semiconductor or metal nanoparticle arrays have attracted considerable interest due to their unique properties (chemical, optical, electrical and magnetic) and many potential applications in areas such as electronics, optoelectronics, sensing, solar cells, catalysis, high-density storage, and ultra-thin display devices. In the last two decades, the search for efficient and low cost processes for fabricating ordered surface nanostructures with tuneable dimensions and properties has involved interdisciplinary and cross-disciplinary research and development with emerging technologies such as lithographic methods, self-assembly processes and scanning probe techniques.

Nanoparticle arrays are a particularly attractive strategy for engineering nanostructures on surfaces in order to tailor a new generation of nanodevices and "smart" materials. The development and preparation of nanoparticle arrays relies on the controlled assembly of nanoparticles into thin films with predictable and well-defined structural characteristics. To organise the nanoparticles into controlled architectures on surfaces, current technologies are typically based on synthesis of nanoparticles using wet chemistry (solution-based, eg. reductive synthesis), and the adsorption of the nanoparticles on the surface of a solid support from organic or aqueous solution which can be performed in many different ways including adsorption, self-assembly, covalent immobilisation, LB film technique etc. (D. Astruc et al, Chem. Rev. 2004, 104, 293).

The current fabrication methods are cheap and easy to perform but with several disadvantages: the processes are slow (sometimes taking several days), involve many steps, have problems with uncontrolled particle aggregations which requires additional particle modification, the deposition of particles on the surface and their uniformity is hard to control, and fabricated particle arrays on surface are not very stable. To address some of these problems, several methods for direct synthesis of nanoparticles on surfaces have recently been explored including: electrochemical deposition, gas-phase synthesis, and fabrication using porous templates. These methods combine fabrication and assembly of nanoparticles on the surface into one step, but unfortunately some of them require special and very expensive equipment.

There is a need for improved processes for forming arrays of nanoparticles on solid surfaces and/or for processes for forming arrays of nanoparticles on solid surfaces that provide an alternative to existing processes.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.

SUMMARY OF THE INVENTION

The present invention has arisen from research into processes for the fabrication of particle arrays on substrates using a solution-free and template- free method based on solid phase transitions. The processes can be used for fabrication of a large range of metal and metal oxide particles including their alloys.

The present invention provides a process for the fabrication of an array of metal particles or metal compound particles dispersed on a solid substrate. The process includes providing a solid substrate having a film of the metal or metal compound on a surface thereof and heating the solid substrate for a temperature and time sufficient to convert the film into an array of particles of the metal or metal compound dispersed on the surface.

Optionally, the step of providing a solid substrate having a film of the metal or metal compound on a surface thereof may include depositing the film on the surface.

The metal may be: a noble metal, such as gold, silver, platinum, palladium, ruthenium, rhodium, osmium, and iridium; or any other metal that can be deposited as film. The metal compound may be a metal bound or coordinated to a halogen, oxygen, nitrogen, carbon or a combination thereof. Alternatively, the metal compound may be an alloy of a metal with one or more other metals.

The substrate having a metal or metal compound film on a surface thereof may be heated to a temperature of between about 300 °C and about 1500°C. The temperature will usually depend on which metal or metal compound is used. In some cases, temperatures of greater than 2000 °C can be used for some metals.

The process of the present invention allows control of particle size and uniformity. The process can be used to fabricate ordered arrays having uniform sized particles. Alternatively, the process can be used to fabricate ordered arrays having two or more different sized particles.

In comparison with existing wet-chemistry technologies, advantages of the processes of the present invention include: they are simple (very low technical - A -

experience is required), they are easy to use, they are time effective (several hours), they have the ability to be combined with existing microelectronics technologies, they allow for fabrication of large size of particle arrays (standard Si wafer), they can provide superior quality particle arrays with better fixation of particles on surface, superior array robustness, thermal and chemical stability.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 shows schematically the approach for fabrication of metal or metal oxide nanoparticle arrays on solid surface which consist two steps: preparation of thin film and solid phase transition of thin film into nanoparticles.

Figure 2 a), b), c), d), g) and h) is a series of microphotographs of solid substrates formed according to a process of the present invention.

The microphotographs demonstrate the control of metal nanoparticle size by the thickness of the metal film. The microphotographs show the typical surface morphology of metal

(gold) nanoparticle arrays with different diameters fabricated from metal (gold) films of different thickness a) 10 nm, b) 15 nm) c) 20 nm d) 30 nm, f) 40 nm, g) 50 nm h) 60 nm by thermal treatment at

1000°C, whilst h) is a scheme of the process. Silicon wafer was used as the solid.

Figure 3 is a series of microphotographs of solid substrates formed according to a process of the present invention. The microphotographs show the influence of temperature on the transformation of the gold film into gold nanoparticles. The gold film was 57 nm thick. Temperature was applied from a) 600°C, b) 650 °C, c) 700 °C, d) 800 °C, e) 900 °C to f) 1060 °C.

Figure 4 is a series of microphotographs of solid substrates formed according to a process of the present invention. The microphotographs show the improvement in the density and the uniformity of gold nanoparticles obtained by annealing of gold film during thermal vapour deposition (300°C, 4h). The nanoparticles were fabricated by thermal treatment at 1060°C for 2 h.

Figure 5 a), b), and c) is a series of microphotographs of solid substrates formed according to a process of the present invention. Composite nanoparticle arrays of two metals (Au and Ag) were fabricated from double films, gold and silver, followed by their thermal transformation into particles with diameter depends of the thickness of each film, a) Ag and Au gold films fabricated by thermal vapour deposition showing area of Ag film and overlapped Ag and Au film (a mask is used to cover of Ag film during Au deposition), b) Ag nano particles from Ag film, c) Ag and Au binary array of nanoparticles from Au deposited on Ag film. The nanoparticles were fabricated by thermal treatment at 1000°C for 2 h. d) is a scheme of the process used to produce the array shown in c). e)-f) show EDAX graphs confirming the chemical composition (Au or Ag) of single particles on mixed array.

Figure 6 a) to e) is a series of microphotographs of solid substrates formed according to a process of the present invention. Composite nanoparticle arrays of metals (Au) with two different diameters were fabricated by deposition of gold films on array of gold nanoparticles. Gold film (thickness 50 nm) was deposited on gold nanoparticles with four different diameters a) 200 nm, b) 150 nm c) 100 nm and e) < 50 nm. Additional arrays of gold particles with diameters of 500 nm were formed on these arrays from evaporated gold film. Image d) shows two parts of a surface with gold nanoparticles with two diameters. The part without large particles was masked during gold film deposition, f) is a scheme of the process. Figure 7 a) is a microphotograph of a solid substrate formed according to a process of the present invention. Gold /silver alloy nanoparticles were fabricated from deposition of a gold/silver alloy film (thickness of 20 nm) by thermal treatment at 1000°C. Bar scale 500 nm. b) is a scheme of the process, c) shows EDAX graphs confirming the chemical composition (Au/Ag) of single particle.

Figure 8 a), b), and c) is a series of microphotographs of solid substrates formed according to a process of the present invention. Patterned Au nanoparticle arrays were fabricated by masking during deposition of a gold film, a-b) square pattern and c) hexagonal pattern, d) is a scheme of the process.

Figure 9 a), b), and c) is a series of microphotographs of solid substrates formed according to a process of the present invention. Arrays of nanoparticles with size gradient were prepared using a shadow masking technique during gold film deposition, a-b) particle gradient across 100 urn area a) and 10 urn area b) on silicon waver and c) porous alumina, d) is a scheme of the process.

Figure 10 a) to e) is a series of microphotographs of solid substrates formed according to a process of the present invention. The microphotographs demonstrate control of the size and spatial distribution of nanoparticles by surface topography for designing nanostructured surfaces with specific photonic and optical properties. Gold film was deposited on silicon chips with different structural patterns (hexagonal hole and strips, bare Si chips are presented at a), c) and e). b) Gold nanoparticles with small and large diameters were formed on different structures, d) increasing of area of structure on the chip the diameter of particles formed on that area was increased, e) Nanoparticles with two diameters, smaller on the top strip and larger between the strips were created from gold film deposited over these structures, f) is a scheme of the process.

Figure 11 a) to h) is a series of microphotographs of solid substrates formed according to a process of the present invention. Gold nanoparticles were prepared on different solid surfaces, a-b) optically transparent glass (quartz) and sapphire, c-d) diatom silica and f-g) porous alumina membranes.

Figure 12 shows spectra demonstrating the optical properties of nanoparticle arrays formed according to a process of the present invention, a) shows the localised surface plasmonic resonance (LSPR) signal of gold nanoprticle array, b) shows the surface enhanced Raman scattering (SERS) signal from gold nanoparticle film modified with mercaptobenzoic acid.

Figure 13 a) is an SEM image showing the typical shape of gold nanoparticles. B) is an XRD graph showing the polycrystalline surface of gold nanoparticles.

GENERAL DESCRIPTION OF THE INVENTION

Before proceeding to describe the present invention, and embodiments thereof, in more detail, it is important to note that various terms that will be used throughout the specification have meanings that will be well understood by a skilled addressee. However, for ease of reference, some of these terms will now be defined.

The term "noble metal", as used throughout the specification, means a metal that is resistant to corrosion or oxidation. Noble metals include ruthenium, rhodium, palladium, osmium, iridium, platinum, gold, and silver. The term "noble metal compound", as used throughout the specification, means a compound in which a noble metal is bound or coordinated to oxygen, nitrogen, carbon or a combination thereof, a salt of a noble metal, or an alloy of a noble metal with another metal. Suitable salts of these metals include halides, such as palladium chloride and platinum chloride and nitrates such as silver nitrate.

The present invention provides processes for the fabrication of variable sized nanoparticle arrays on solid substrates. Using the processes of the present invention it is possible to fabricate nanoparticles with a range of useful properties including chemical, physical, optical, photonic, electronic, catalytic, magnetic and electrochemical for use in the development of a large range of products and devices.

The process of the present invention, which is shown schematically in Figure 1 , includes providing a solid substrate having a film of the metal or metal compound on a surface thereof and heating the solid substrate for a temperature and time sufficient to convert the film into an array of particles of the metal or metal compound dispersed on the surface.

The substrate may be any suitable material. The material of the substrate may be selected taking in to account the end use of the fabricated array of metal or metal compound particles. For reasons that are explained in more detail later, the melting point of the substrate typically has to be higher than the melting point of metal or metal compound in the film. Examples of suitable substrate materials include silicon, quartz, quartz glass, silica, porous silicon, indium oxide, porous alumina, and other metal or metal oxide substrates. In some embodiments, the substrate is a silica wafer.

Examples of gold nanoparticle arrays formed in accordance with a process of the present invention on transparent surfaces such as quartz glass window, sapphire window, porous alumina membrane and biological surfaces such as diatom silica are shown in Figure 1 1. The fabrication of nanoparticles on optically transparent surfaces is important for applications in the area of optical transduction and for the development of optical sensing/biosensing devices. However, other technically important solid substrates can also be used, including inorganic oxide substrates such as indium oxide, titanium oxide or metal substrates (Ti, Pt, Ge etc). Nanoparticles on metal and conductive or semi conductive surfaces can be used for applications in microelectronics, data storage and electrochemical sensing.

An advantage of the processes of the present invention is that a variety of metals and metal compounds can be used. Suitable metals include copper, zinc, iron, chromium, cobalt, manganese, aluminium, titanium, nickel, and noble metals such as gold, silver, platinum, palladium, ruthenium, rhodium, osmium, and iridium. Other metals from groups I, II, III, IV and V of the periodic table that can be deposited as an ultrathin film can also be used.

In some embodiments, the noble metal is gold. Arrays of gold nanoparticles are commonly used for the detection of chemicals by Raman scattering, localised surface plasmon resonance etc. In some embodiments, the noble metal is silver, which has similar optical properties as gold and can be applied for sensing applications.

Suitable metal compounds include those having a metal bound or coordinated to a halogen, oxygen, nitrogen, carbon or a combination thereof. In some embodiments, the metal compound is a metal oxide. Non-limiting examples of suitable metal oxides are semiconductive oxides, such as ZnO, SnO₂, InO₂, TiO₂, ZrO₂, etc, or magnetic oxides, such as Fe₂O₃.

Suitable metal compounds also include alloys of a metal with one or more other metals. Non-limiting examples of suitable alloys include gold/silver, copper/silver/gold, copper/silver, platinum/palladium, cooper/zinc, cooper/nickel, nickel/silver, aluminium/cooper etc. Any metal alloy can be used provided it can be deposited as an ultrathin film. However, if the difference in melting point of two or more metals in the alloy is too large it is possible that during phase transition the metal with significantly lover melting point may form particles first such that particles of alloy do not form. Generally therefore, it is better to have metals with relatively close melting points.

The metal or metal compound film may be deposited on a surface of the substrate using any of the techniques known for that purpose in the art. For example, the metal or metal compound film may be deposited by any conventional film deposition techniques including thermal (filament) evaporation, sputtering, ion-beam deposition, chemical vapour deposition (CVD, plasma deposition, laser deposition, atomic layer deposition (ALD), electrochemical and electrodeless metal deposition. Each of these techniques has different procedures and conditions for preparation of films.

The growth of the film on the solid substrate will vary depending on a number of factors such as deposition time, temperature, the precursors, the vacuum, pressure, the arrangement of the reactor, and the composition of the substrate including the nature of the material to be deposited. The specific growth temperature may be selected using routine experimentation. There are number of examples of suitable equipment that may be used for deposition of thin films that are commercially available including home made equipment that can be designed for this purpose.

The substrate having a metal or metal compound film on a surface thereof is then treated at a temperature and time sufficient to convert the film into an array of particles of the metal or metal compound dispersed on the surface. Typically, the process is carried out at a temperature between about 300 °C and about 1500°C, but can be carried at higher temperature >2000°C for particular metals such as iridium, ruthenium, rhodium etc that have a higher melting points.

Figure 3 shows SEM images showing the topography of formed structures at several different temperatures. Solid substrates having a gold film (thickness 57 nm) were heated for at least 2 hours at different temperatures, cooled and than characterized by SEM. The thin film formed at 600 °C shows irregular linked structures with no particle formation. At higher temperatures (700 °C -800 °C) these structures were broken into smaller isolated structures with irregular shape. Arrays with particle shape film appeared by treatment of the film at 900 °C, but with a significant population of elongated, rod-like structures. Particle arrays with a full percentage of hexahedral geometry and not rod-like particles were formed above about 1000°C. Thus, higher temperatures that are close to the melting point of metal used in the film are optimal for thin film transition into nanoparticle arrays. Rod-like structures which may have desirable optical properties can be fabricated using temperature of about 850 °C to about 950 °C. The optimal temperatures for fabrication of particle arrays from other metal films such as Ag, Cu, Pt, Pd etc. may be different and may depend of the melting point of the metal and can be determined empirically.

The thickness of the metal or metal compound film can be varied depending on the deposition conditions, such as reaction time. Typically, the thickness of the metal or metal compound film will be in the range of from about several nm to about 100nm. In some embodiments, the thickness of the metal or metal compound film is about 10nm, although that thickness in other embodiments may be about 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm. Figure 2 shows examples of gold nanoparticle arrays on a silicon substrate with different diameters of particles. Gold films with different thickness (10 nm, 15 nm, 20 nm,

30 nm 40 nm 50 nm and 60 nm) were prepared by thermal vapour deposition and then thermally treated at 1050°C for at least 2 hours. The SEM images show that particle size increased with increasing thickness of deposited films.

Table 1 shows an average particle diameters fabricated from gold films with different thickness. Table 1

These results confirm that the thickness of metal film can be used to control the diameter of nanoparticles formed on the surface. The nanoparticles have characteristic multifaceted (close to hexahedral) geometry, instead of their common spherical geometry when fabricated by solution methods.

The average size of the particles produced using the process of the present invention is from about 50 nm to about 1 μm.

SEM images shown in Figures 3 a)-c) indicate a possible mechanism for the thermally induced film-particle fragmentation that leads to conversion of the metal or metal compound film into metal or metal compound particles. Initial formation of micron size and irregular interlinked structures is possibly related to the grain structure of metal films. The sizes of the metal grains in the films are different and, therefore, particles with a quite high distribution of diameters are formed. However, when the metal or metal compound film is annealed (inside the evaporator) after deposition, the uniformity of the particle size is improved. Figure 4 shows fabricated particles from gold films with four different thickness (<10 nm, 12 nm, 15 nm, 20 nm and 25 nm) which confirm fabrication of nanoparticles with small diameters (20 nm -70 nm), high density and significantly improved uniformity of particle size. This fabrication protocol can be particularly attractive for applications where nanoparticle films with small diameters are desired.

The processes of the present invention can be used to form arrays of alloy nanoparticles. Figure 7 shows a gold/silver alloy nanopaticle array formed in accordance with a process of the present invention. The gold/silver alloy nanoparticles were fabricated by depositing a 20 nm thick gold/silver alloy film followed by thermal treatment at 1000°C. The gold/silver alloy is used as initial precursor for deposition of this film. The thermal fragmentation of the film lead to the formation of nanoparticles on the surface and the composition of the array was similar to the composition of the starting film, namely containing equal amounts of Au and Ag. This demonstrates that the process can be used for fabrication of alloy nanoparticles comprising two metals and also that the process can be applied to more complex composites containing three or more metals. In contrast, it is difficult to prepare alloy nanoparticles by wet chemistry methods or other known methods.

The process of the present invention can also be used to fabricate arrays of nanoparticles containing particles of two or more different metals. This may be advantageous for applications when a combination of properties of two or more metals is required or when there is a synergistic effect between the two or more metals. Using the process of the present invention, these arrays can be formed by thermal fragmentation of two overlapped metal films. Figure 5 shows a gold and silver nanoparticle array prepared from a gold film deposited on underlying silver film. The gold film was double the thickness of the silver film and this resulted in the formation of gold particles that were larger than the silver nanoparticles. However, the particles were uniform distributed on the surface. The EDAX graph from single nanoparticles confirmed the chemical composition as being clean gold or silver particles without chemical "mixing" during film fragmentation.

A similar approach can be used to prepare arrays of metal nanoparticles with two metals or one metal but with two different particle dimensions. In this approach, a metal film is evaporated onto a previously formed array of nanoparticles and then the substrate is heat treated to thermally fragment the film. Figure 6 shows a practical demonstration of this process with nanoparticle arrays generated by deposition of gold film on 4 different gold nanoparticle arrays. The images show the formation of four gold particle double arrays with the some large particles but with different smaller particles. Both processes previously discussed (shown in Figures 5 and 6) can be used to make complex nanoparticle composites that consist of three or more metals or the same metal but with three or more diameters of nanoparticles. Therefore, the processes of the present invention provide flexibility for the tuning of the properties of fabricated arrays by the choosing the chemical composition of nanoparticles, their size and the size ratio.

The processes of the present invention can be used to form patterned arrays of particles. Patterned arrays of particles are important for sensing and biosensing applications in which the particles are functionalised with biomolecules (peptides, proteins, DNA, etc) and also in optical detection. Existing technologies that are used to make patterned arrays of nanoparticles are typically based on time consuming and expensive lithographic techniques. The present invention provides simple and inexpensive processes for the fabrication of patterned arrays of nanoparticles.

Figure 8 shows two typical examples with square and hexagonal arrays of patterns. To form patterned arrays, the metal film is formed on a substrate that is masked. Commercially available masks (TEM grids) can be used. After deposition of the metal film over the mask, the substrate is heated to allow thermal fragmentation resulting in the formation of nanoparticles. The size and shape of the patterns, their inter-distance and organisation on the surface are directed by the mask. This process allows for a high degree of flexibility to design desired patterns on the surface. Furthermore, each of the patterned arrays can be functionalised with different bioreceptors and used as multifunctional biosensing devices for biomedical diagnostic (DNA, viruses, cancer, illness etc).

There is a high level of interest in the fabrication of structural and surface-bound chemical gradients that can be used for a range of applications in biology and biotechnology where control of interactions between a surface and cultured eukaryotic cells, bacteria, and viruses is desirable. The processes of the present invention can be used to fabricate nanoparticle arrays with particle size gradients.

Figure 9 shows nanoparticle arrays with particle size gradients formed in accordance with a process of the present invention. Gold nanoparticle arrays having increasing nanoparticle diameter from < 50 nm to > 1 μm over a relatively large area (100 μm) and a relatively small area (10 μm) were fabricated. The process was performed using a "shadow" technique during gold film deposition which provides the deposition film with a gradient in the thickness. Using this process, nanoparticle arrays with gradual changes in the diameter of the particles can be prepared over very large areas of 1 cm to the very small areas of few microns.

It is known that nanoparticles on surfaces show optical and photonic properties that can be used for many applications in optoelectronics and photonics. These properties are highly dependent of the size and inter-particle distance.

Therefore, high reproducibility in fabrication of these structures is required.

Typically, nanoparticle arrays formed using the processes of the present invention that have been described to date have random organisation of particles on the surface and a relatively large distribution of diameters.

To make nanoparticle arrays that are highly ordered and with uniformly sized particles it is possible to direct nanoparticle formation using surface topography. When the metal film is deposited on a surface having particular structural features or surface area, nanoparticles with dimensions relevant to these areas are formed. Figure 10 a-b shows two examples of a silicon chip with the same hexagonal pattern but with different dimensions. Gold film was deposited on silicon chips with different structural patterns (hexagonal holes and strips). After deposition of the gold film with the same thickness on these patterns, nanoparticles with different diameters but with uniform size were formed after heating. These structures are not possible to create using existing technology, such as ion beam or high resolution lithography methods. The present invention also provides a substrate having an array of metal particles or metal compound particles dispersed thereon. The substrate is produced by the process of the present invention.

The optical properties of fabricated substrates having an array of metal particles dispersed thereon were characterized by UV/VIS and Raman spectroscopy. The results are shown in Figure 12. An SPR signal from the gold nanoparticles is observed. This indicates that the substrates can be used for development of SPR biosensing devices. Similarly, enhanced Raman signal (SERS) is also observed on chemically modified gold nanoparticles which confirm that another detection principle can be used for the development of biosensing devices.

The nanoparticles produced by the processes of the present invention have characteristic multifaceted geometry, as shown in Figure 13a. On the basis of the SEM images the particles appear to be hexahedral shaped. The crystal phase, the size and the shape of nanoparticle surfaces are also important parameters for their catalytic properties. XRD results (Figure 13b) confirm the existence of several crystal faces on the surface of the gold nanoparticles.

A substrate formed using a process of the present invention can be used to: a) replace existing nanoparticle platforms used in commercial products or devices that are fabricated by solution-based technologies; and/or b) develop new products and devices by applying these platforms using different nanoparticle materials.

A substrate formed using a process of the present invention may be used in biomedical diagnostics. Gold nanoparticle arrays for the detection of a variety of biomolecules are important for disease diagnosis, drug discovery, and those associated with bioterrorism and warfare. Chip based platforms with gold nanoparticles have been proven to offer several advantages in comparison with existing microarray DNA sequencing technology, protein detection based on fluorophore labelling carriers. For example, the substrates could be used for electrochemical or optical detection of DNA hybridisation or proteins. Substrates formed using a process of the present invention may provide simple, versatile, highly sensitive, selective, portable detection devices based on localised surface plasmon resonance (LSPR) or surface enhanced Raman scattering (SERS) principles which are used for many applications (nucleic acids, proteins, protein markers for cancer and disease detection, biotoxins etc). A substrate formed using a process of the present invention may be used for data storage and catalysis. High density magnetic nanoparticles such as iron, nickel and cobalt may be used as recording and memory devices.

Magnetic storage has played a key role in audio, video and computer development. Present magnetic disk drives are based on longitudinal recording systems where the magnetization of the recorded bit lies in the plane of the disk. The recording media signal-to-noise ratio (SNR) needed for high-density recording is achieved by statistically averaging over a large number of weakly interacting magnetic grains per bit. The process of the present invention could provide high density magnetic nanoparticles on surface as an inexpensive fabrication alternative to existing technologies.

A substrate formed using a process of the present invention may be used in other disciplines which make use of nanodevices, including nanoelectronics, optoelectronics and sensing. These applications require the development of surface nano-patterning techniques to obtain large-scale of nanoparticles on a given substrate such as silicon. Products and devices which employ and have potential to employ nanoparticle arrays include super hard materials, super fast computers, magnetic recording devices, plasmon waveguides, dirt repelling surfaces, new cancer treatments, highly sensitive and selective sensing devices, environmentally friendly fuel cells, solar cells, highly effective catalysis, platform for growth o semi conductive nanowires and carbon nanotubes etc. DESCRIPTION OF EMBODIMENTS

Materials

Silicon wafer, p-type (100), p++ boron doped (from Virginia Semiconductor, USA) was used as the solid substrate in the following examples. However, other substrates including, quartz window, sapphire window, commercial porous alumina membranes (Whatman) and diatom silica (cultured biomaterials) were also used.

Example 1 - Deposition of metal or metal compound film

Metal (gold) film deposition was performed using a thermal evaporator equipped with a quartz crystal monitor able to control the thickness of the film during deposition. A piece of metal (gold, silver or their alloy) was placed in a molybdenum boat inside of the evaporator and used as source of the metal or metal compound for deposition. The boat was connected to a high current power supply which was used to initiate evaporation. Cleaned substrates for film deposition (silicon wafer, or others) were placed on a sample holder inside of the chamber and the chamber was sealed and evacuated to approximately 10-5 Torr. Metal deposition was performed using cold deposition or heated deposition with annealing or without annealing (option of using a heating element during deposition).

Example 2 - Preparation of particle arrays

After deposition of the metal film, the solid substrate having a thin film deposited on a surface thereof was placed in a furnace for the solid phase transition process and heated for minimum of 2 hours at temperature of 600 °C to 11 10⁰C depending on the metal film. In the case of gold, the thermal treatment was performed in air, but the use of vacuum or inert atmosphere (argon) can be required for particular materials. The temperature of 1060°C was used as an optimal temperature for thermal processing of gold film. Temperatures ranging from 300 °C to 1500°C were used in order to investigate the influence of the temperature on the formation of gold nanoparticles. After cooling to room temperature, samples with fabricated nanoparticle arrays were characterized as required using surface characterization techniques such as SEM, EDAX, AFM, XRD, UV/VIS (LSPR) and Raman spectroscopy (SERS) to evaluate their structural and optical properties.

Finally, it will be appreciated that various modifications and variations of the methods and compositions of the invention described herein will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention that are apparent to those skilled in the art are intended to be within the scope of the present invention.

Claims

CLAIMS:

1. A process for fabrication of an array of metal particles or metal compound particles dispersed on a substrate, the process including providing a solid substrate having a film of the metal or metal compound on a surface thereof and heating the solid substrate for a temperature and time sufficient to convert the film into an array of particles of the metal or metal compound dispersed on the surface.

2. A process according to claim 1 , wherein the step of providing a solid substrate having a film of the metal or metal compound on a surface thereof includes depositing the film on the surface.

3. A process according to either claim 1 or claim 2, wherein the metal is a noble metal.

4. A process according to claim 3, wherein the noble metal is selected from one or more of the group consisting of: gold, silver, platinum, palladium, ruthenium, rhodium, osmium, and iridium.

5. A process according to claim 3, wherein the noble metal is gold.

6. A process according to claim 3, wherein the noble metal is silver.

7. A process according to either claim 1 or claim 2, wherein the metal compound includes a metal bound or coordinated to a halogen, oxygen, nitrogen, carbon or a combination thereof.

8. A process according to claim 7, wherein the metal compound is a metal oxide.

9. A process according to either claim 1 or claim 2, wherein the metal compound includes an alloy of a metal with one or more other metals.

10. A process according to any one of claims 7 to 9, wherein the metal is a noble metal.

11. A process according to claim 10, wherein the noble metal is selected from one or more of the group consisting of: gold, silver, platinum, palladium, ruthenium, rhodium, osmium, and iridium.

12. A process according to claim 1 1 , wherein the noble metal is gold.

13. A process according to claim 1 1 , wherein the noble metal is silver.

14. A process according to any one of claims 1 to 13, wherein the average size of the particles is from about 50 nm to about 1 μm.

15. A process according to any one of claims 1 to 14, wherein the substrate is selected from the group consisting of quartz, glass, silica, silicon, and alumina.

16. A process according to claim 15, wherein the substrate is silicon.

17. A process according to any one of claims 1 to 16, wherein the temperature is between about 600 °C and about 1 100°C.

18. A process according to any one of claims 1 to 18, wherein the substrate is patterned.

19. A process for fabrication of an array including metal particles or metal compound particles of a first metal and a second metal dispersed on a substrate, the process including providing a solid substrate having a first film of the first metal or first metal compound on a surface thereof and a second film of the second metal or second metal compound on a surface thereof, and heating the solid substrate for a temperature and time sufficient to convert the film into an array of particles of the first and second metals or first and second metal compounds dispersed on the surface.

20. A process according to claim 19, wherein the thickness of the first film is different to the thickness of the second film.

21. A substrate having an array of metal particles or metal compound particles dispersed thereon produced by the process of any one of claims 1 to 20.

22. A sensing chip having an array of metal particles or metal compound particles dispersed thereon produced by the process of any one of claims 1 to 20.