[0001] The present application claims priority from Australian Provisional Patent Application No. 2018904703, the entire disclosure of which is incorporated herein by reference.

Technical Field

[0002] The present invention relates to a method of manufacturing a

nanostructure on a surface.

Background of Invention

[0003] Methods of nanofabrication and patterning have myriad applications such as photonics for optical sensors and optical computers; and nanofluidics for rapid genomics and molecular sensors.

[0004] Nanopores have many applications from advanced chemical separations to the sequencing of single stranded DNA. Many of the more exciting applications are limited by the need to generate single pores with controllable pore size and

dimension. Current nanopore technologies utilize elastomer films which do not lend themselves to controlled surface modification and often are difficult to fabricate reliably at dimensions less than ~20 nm. Another example uses transmembrane pore-forming proteins that are embedded in lipid membranes so as to create porous surfaces. These membranes, however, suffer from poor stability and limited shelf life.

[0005] Photonics requires defect-free nanopatterns over large surface areas and this can generally only be achieved through complex, multistage processes. Often the nanochannels are too large (> 50 nm) to be useful in nanofluidics and, again, complex, multi-step processes are typically required to achieve true molecule scale dimensions.

[0006] One drawback to conventional nanofabrication techniques such as scanning probe lithography is that these techniques are generally only applicable to certain materials, such as polymer films. Such polymer substrates generally have limited functional properties such as low refractive index, poor thermal stability, mechanical weakness, lack of semiconductor properties, a tendency to swell on contact with moisture and the fact that many polymers are chemically inert so do not lend themselves to further functionalisation.

[0007] Focused ion beam techniques are applicable to a wider range of materials. Nevertheless, these methods generally require expensive equipment such as high energy lasers and vacuum systems as well as highly trained personnel, necessitating the use of multi-million-dollar nanofabrication facilities. This leads to high fabrication costs and, often, poor reproducibility. Furthermore, it is often difficult to achieve good resolution at the nanoscale for many materials.

[0008] One conventional nanofabrication technique is scanning tunnelling microscopy (STM). STM nanolithography techniques typically use exogenous electric fields and tunnelling currents between a conductive tip and (coated or uncoated) electrode surfaces. In other words, a driving potential is required between two external electrodes or when the substrate is itself an electrode. STM lithography is driven by electrochemical reactions induced and controlled by the tunnelling current and applied voltage gradient between tip and substrate. Electrons supplied by the tunnelling current and driven from tip to substrate by the applied voltage trigger electrochemical oxidation/reduction reactions. These electrochemical reactions can, for example, oxidize or reduce the substrate surface, convert base

metals/semiconductors to oxides (via the anodic reduction of water), or decompose gaseous or dissolved chemical compounds. Etching may be achieved by using the tunnelling current as an electron beam. In this case, the high energy of the electrons accelerated by the voltage ablate the substrate similarly to conventional electron beam lithography. This‘field-emission’ etching typically must be conducted under vacuum and so cannot be performed in a liquid environment.

[0009] In these STM methods, the tip and the substrate being patterned have to be connected in a circuit and the deposition/etching reactions are the product of externally generated voltages and electrical currents. Without an external power supply to generate the voltage gradient and flow of electrons between the substrate and tip, no deposition, etching, or chemical reactions can take place. Flence, these methods are limited in the types of substrate to which they are applicable and often require expensive fabrication facilities. [0010] There is therefore an ongoing need for methods of nanofabrication, which at least partially address one or more of the above-mentioned short-comings or provide a useful alternative.

[0011] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

Summary of Invention

[0012] In a first aspect the invention provides a method of manufacturing a nanostructure on a first surface, wherein the first surface has a first electrochemical surface potential, said method comprising introducing a second surface having a second electrochemical surface potential, and bringing the two surfaces together in an electrolyte solution to generate a bridging interfacial electrical field, thereby altering the solubility at the first surface to allow formation of a nanostructure at the first surface, wherein there is no externally applied voltage bias between the first surface and the second surface. In other words, no current being externally driven between the first surface and the second surface. This method can be applied to a wide range of classes of materials. Furthermore, this method does not require the use of multi- million-dollar nanofabrication facilities but can be performed in a standard laboratory.

[0013] In a further aspect of the invention the solubility at the first surface is sufficiently altered to allow dissolution of one or both surfaces into the solution to form a nanostructure. This method allows for the construction of nanostructures on a broad range of materials and can be used to form nanopores and nanopits, nanochannels and nanopatterns.

[0014] In a further aspect of the invention, the electrolyte solution further comprises an additional dissolved species and wherein the solubility at the first surface is sufficiently altered to allow precipitation from the solution onto the first surface to form a nanostructure. In a still further aspect, the rate of dissolution at the first surface is sufficiently enhanced to create a local region of oversaturation which allows precipitation of the dissolved species onto the first surface to form a

nanoparticle, and repeating this process to form a nanostructure. In alternate further aspect, the rate of dissolution at the first surface is sufficiently suppressed to allow precipitation from the solution onto the first surface to form a nanoparticle, and repeating this process to form a nanostructure. This method allows for the true additive manufacture of structures at the nanoscale. Furthermore, this method can be performed in a standard laboratory and does not require the use of multi-million-dollar nanofabrication facilities.

[0015] In preferred embodiments of the invention, the second surface is a patterned surface, preferably a gold film or gold coated silicon. Using a patterned surface in this way, it is possible to imprint onto the first surface to create patterned architectures at the nanoscale.

[0016] In other preferred embodiments of the invention, the second surface comprises a probe tip, preferably an atomic force microscopy (AFM) tip selected from the group consisting of a gold coated AFM tip, an alumina coated AFM tip, a silicon carbide AFM tip, a diamond coated AFM tip, a nickel AFM tip, a nickel oxide AFM tip, an iron oxide AFM tip, a chrome AFM tip, a chrome oxide AFM tip, a silica AFM tip and a cerium oxide AFM tip. Using atomic force microscopy (AFM) techniques allows the methods to be performed in standard laboratories using a range of materials.

[0017] Further preferred embodiments of the invention provide methods which further comprise the step of scanning the second surface tip along the first surface to form a nanochannel in the first surface. This allows the user to etch patterns at the nanoscale into a wide variety of surfaces.

[0018] In preferred embodiments of the invention, the surfaces are brought together with oscillating pressure. Preferably, the change in pressure (DR) ranges from 1 MPa to 1 GPa. More preferably, the change in pressure (DR) is around 100 MPa. Further preferred aspects of the invention provide methods wherein the rate of oscillation is in the range of 1 -1000 kHz, preferably in the range of 20-100 kHz, most preferably around 35 kFIz. Oscillating the pressure provides an increase in the rate of change in the solubility, increasing the rate of dissolution or precipitation as needed.

[0019] In preferred embodiments of the invention, the first surface is preferably selected from the list consisting of silicon, silicon dioxide (silica), silicon-germanium, silicon nitride, silicon carbide, germanium, gallium nitride, gallium arsenide, cadmium zinc telluride (CzT), lll-V compound semiconductors (preferably gallium nitride, gallium arsenide, indium nitride, aluminium nitride, indium phosphide), aluminium oxide (alumina), titanium dioxide, cadmium sulfide, diamond (preferably boron-doped diamond, nitrogen-doped diamond and phosphorus-doped diamond), lithium niobate (LiNbCb), silver, copper and aluminium, preferably wherein the first surface is silica or alumina. The wide range of surfaces to which these methods can be applied is one of the advantages of the invention.

[0020] In further preferred embodiments of the invention, the second surface is an electrode and the second surface potential is controllable with a potentiostat and a counter electrode. This allows the user greater control over the bridging interfacial electrical field between the surfaces.

[0021] A further aspect of the invention provides a method where the interfacial distance between the first surface and the second surface is in the range of 0.1 -20 nm, preferably less than 1 nm.

[0022] In other preferred embodiments of the invention, the electrolyte solution preferably comprises an electrolyte where the cation is selected from the Group I and Group II metals, preferably selected from the list consisting of lithium, sodium, potassium, magnesium, calcium and strontium; and where the anion is preferably selected from the list consisting of fluoride, chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate, and combinations thereof. Preferably, the electrolyte solution is selected from the group consisting of aqueous calcium chloride, aqueous sodium chloride and aqueous magnesium sulfate.

[0023] In other preferred embodiments of the invention, the additional dissolved species is selected from the group consisting of silicon dioxide, orthosilicic acid (Si(OH)4), aluminium oxide, aluminium hydroxide, sodium tetrahydroxyaluminate (NaAI(OH)4), sodium aluminate (NaAIC ), aluminium chloride, gold chloride, silver chloride, sodium silicates (such as sodium meta silicate, Na2Si03; sodium

orthosilicate, Na4Si04; and/or sodium pyrosilicate, NaeS^O), and mixtures thereof. This additional dissolved species can allow for precipitation onto the first surface.

[0024] In certain preferred embodiments of the invention, the electrolyte solution comprises calcium chloride and the concentration of the electrolyte solution is between 1 and 100 mM, preferably between 20 and 40 mM, more preferably around 30 mM.

[0025] In some preferred embodiments of the invention, the first surface is silica and the pH of the electrolyte solution is between pH 2 and 6, preferably around pH 3- 4. In some other preferred embodiments of the invention, the first surface is alumina and the pH of the electrolyte solution is between pH 8 and 12, preferably around pH 9.5-10.5.

[0026] A further aspect of the invention provides a nanostructure manufactured by the method of any one of the previous claims.

[0027] Where the terms“comprise”,“comprises” and“comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0028] As used herein, the terms“first”,“second”,“third” etc. in relation to various features of the disclosed devices are arbitrarily assigned and are merely intended to differentiate between two or more such features that the device may incorporate in various embodiments. The terms do not of themselves indicate any particular orientation or sequence. Moreover, it is to be understood that the presence of a“first” feature does not imply that a“second” feature is present, the presence of a“second” feature does not imply that a“first” feature is present, etc.

[0029] Further aspects of the invention appear below in the detailed description of the invention.

Brief Description of Drawings

[0030] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0031] Figure 1 is a simplified mechanism schematic of the principle underlying the present invention. [0032] Figure 2 is a simplified schematic of a nanopore fabrication process in accordance with the present invention.

[0033] Figure 3 is a simplified schematic of a nano imprinting press process in accordance with the present invention. [0034] Figure 4 is a simplified schematic of a nanochannel etching process in accordance with the present invention.

[0035] Figure 5 is a simplified schematic of a nanoscale additive manufacturing process in accordance with the present invention.

[0036] Figure 6 is an AFM image of four pits etched in silica using a gold coated AFM tip.

[0037] Figure 7 is a set of four pit dissolution experiments showing the effect of varying the pH on pits etched in silica using a gold coated AFM tip.

[0038] Figure 8 is a three-dimensional rendering of the pits from Scan # 2 in Figure 7. [0039] Figure 9 shows a topographic line scan of the dissolved trenches from a pit dissolution experiment where the dissolution voltage is varied using an aluminium coated AFM tip.

[0040] Figure 10 shows a topographic line scan of the dissolved trenches from a pit dissolution experiment where the dissolution time is varied using an aluminium coated AFM tip.

[0041] Figure 11 is an AFM image of a nanochannel pattern etched into a fused silica substrate using a gold coated AFM tip.

[0042] Figure 12 is an AFM image of a nanochannel pattern etched into a fused silica substrate using a gold coated AFM tip. [0043] Figure 13 is a diagram of an interdigitated gold electrode which illustrates the pattern of the electrode used to print onto a fused silica surface. [0044] Figure 14 is an AFM image showing the channels generated in a fused silica surface after being pressed against an interdigitated gold electrode similar to the one shown in Figure 13.

[0045] Figure 15 is an SEM showing the structure of a gold-coated‘black Si’ substrate.

[0046] Figure 16 is an AFM image showing the dissolution pits generated in a silica surface after being pressed against the black Si substrate shown in Figure 15.

[0047] Figure 17 is an AFM image of an arrangement of silica nanoparticles deposited onto a crystalline quartz substrate (z-cut) using a gold coated AFM tip.

[0048] Figure 18 is an AFM image of an arrangement of nanoparticles deposited onto a fused silica substrate using a gold coated AFM tip.

[0049] Figure 19 is an AFM image showing an arrangement of nanoparticle deposits of S1O2 deposited on a sapphire wafer produced using a gold coated AFM tip.

[0050] Figure 20 is an AFM image showing the dissolution of a gallium nitride thin film on sapphire surface using a conductive diamond coated AFM tip.

[0051] Figure 21 is a plot showing the effect of the frequency of oscillation on dissolution rates while etching with a boron doped conductive diamond coated AFM tip on a fused silica substrate.

[0052] Figure 22 is a plot showing the effect of the pH and intrinsic dissolution rate on dissolution rate compared with the dissolution rate achieved while etching with a gold coated AFM tip on a fused silica substrate.

[0053] Figure 23 is a plot showing the effect of the potential on dissolution rates while etching with a boron doped conductive diamond coated AFM tip on a fused silica substrate.

[0054] Figure 24 shows a topographic line scan of the dissolved trenches from a pit dissolution experiment where the potential is varied using a boron doped conductive diamond coated AFM tip on a fused silica substrate. [0055] Figure 25 is an AFM image showing a trench pattern etched into a Si substrate using a boron doped conductive diamond coated AFM tip.

[0056] Figure 26 is an AFM image showing a series of nanoholes etched into a silica substrate using a boron doped conductive diamond coated AFM tip.

Detailed Description

[0057] The present invention relates to methods of manufacturing a nanostructure on a surface. The present invention also relates to nanostructures manufactured by the methods of the present invention.

Pressure Solution

[0058] Without being bound by theory, it is proposed that the electrochemical mechanism underlying the present invention is a‘pressure solution’ like process. ‘Pressure Solution’ is a well-described phenomenon in geology but remains almost completely unknown outside this field. Pressure solution is an important process in the diagenesis of sedimentary rock (the process by which sand and other sediments is transformed into sand-stones) and determines such things as the porosity of rock (and whether an oil/gas field can be developed), the slip frequency of earthquake faults, the liberation and accumulation of gold in quartz veins, and the transport of ground water within aquifers.

[0059] In geology, the term‘pressure solution’ refers to the apparent enhanced solubility of certain minerals (e.g. silica, CaCCb) resulting in highly‘flattened’ grain boundaries lacking any residual stress indicating plastic flow. Historically, pressure solution has been attributed to high inter-grain contact stresses (i.e. lithostatic pressure) reducing the chemical potential energy for the dissolution reaction.

Flowever, this traditional explanation fails to explain the most curious feature of pressure solution which is that pressure solution is overwhelmingly observed at the interface between two different minerals.

[0060] It has recently been found that pressure solution is in fact an

electrochemical interaction between dissimilarly charged surfaces. Previously described laboratory experiments performed in surface forces apparatus (SFA) allowed the pressure solution process between quartz (or amorphous silica) and mica to be observed and studied in real time at geological length and time scales. It was shown that the enhancement of the silica dissolution rate was much higher than can be attributed to a purely‘pressure’ effect (experiments were run at just 2-3 atms of contact pressure). Follow up experiments indicated that the dissolution enhancement exhibited characteristics of an electrochemical phenomenon with the dissolution reaction driven by the strength of a bridging interfacial electric field which develops when two dissimilarly charged surfaces are pressed together. The bridging interfacial electric field is generated by the potential gradient between the dissimilarly charged surfaces in close proximity, i.e. less than two Debye lengths. Further follow up experiments found that pressure solution is a general phenomenon (not specific to mica or silica/quartz surfaces) and that only a difference in surface potential was required to drive this process. Replacing the mica surface with a gold electrode whose surface potential could be controlled using a potentiostat, it was found that the dissolution rate of silica could be controlled by simply augmenting the electrode potential. Surprisingly, it was found that the relationship between the electrode potential and the dissolution rate obeyed the well know Butler-Volmer equation for electrochemical corrosion despite nothing in the system undergoing a change in oxidation state. An implication of this relationship is that‘pressure solution’ can work in two directions and can enhance or suppress dissolution depending upon the electrochemical difference between the surfaces in contact which determine the orientation and magnitude of the bridging interfacial electric field. [G. W. Greene, K. Kristiansen, E. E. Meyer, J. R. Boles, J. N. Israelachvili, Geochimica Et

Cosmochimica Acta 2009, 73, 2862; K. Kristiansen, M. Valtiner, G. W. Greene, J. R. Boles, J. N. Israelachvili, Geochimica Et Cosmochimica Acta 2011 , 75, 6882; E. E. Meyer, G. W. Greene, N. A. Alcantar, J. N. Israelachvili, J. R. Boles, J Geophys Res- Sol Ea 2006, 111]

[0061] The inventors have now surprisingly found that this phenomenon can be applied at the nanoscale to produce nanostructures and nanopatterned surfaces on a wide variety of materials.

[0062] Electrochemical Pressure Solution [0063] Figure 1 illustrates the general principle of the present invention. When two surfaces are bought close together in an electrolyte solution so that two surfaces are less than two Debye lengths apart and their Debye lengths overlap, if the two surfaces have a different electrical potential, then a bridging interfacial electrical field is generated. This bridging interfacial electrical field can then change the local solubility between the two surfaces. This change in the solubility can allow either dissolution of one or both surfaces into the solution as shown in Scenario 1 and Scenario 3. Scenario 2 illustrates that when the difference in electrical potential between the two surfaces is relatively small, for example if the two surfaces are made of a similar material, then there is minimal bridging interfacial electrical field observed and this allows the local rate of solubility to change resulting in precipitation onto one of the surfaces rather than dissolution. As used herein, the term“bridging interfacial electrical field” refers to a continuous electrical field that spans the distance between the surfaces, originating at one surface and terminating at the other.

[0064] The present invention differs from previously described lithographic techniques such as scanning tunnelling microscopy (STM) lithography where a driving potential is required between two external electrodes or when the substrate is itself an electrode. As previously explained, STM techniques typically rely on electrochemical reactions driven and controlled by a tunnelling current and applied voltage gradient between substrate and tip. The electrons supplied by the tunnelling current and driven from tip to substrate by the applied voltage trigger electrochemical

oxidation/reduction reactions. These reactions are used to etch or deposit upon the surface of the substrate.

[0065] The present invention, however, does not involve an externally supplied current between the first surface and the second surface. Pressure solution is driven by a naturally occurring electrical field which changes when dissimilarly charged surfaces are pressed together in a liquid medium (such as water). The chemical reactions that occur at the surface are not a product of the electric field or a tunnelling current. The effect of the electrical field is the localized augmentation of the rates of chemical reactions that are already occurring at the surface. The pressure solution process either speeds the reaction rate up or slows the reaction down where the surfaces are in close proximity. [0066] Consequently, the surface being etched or deposited on is not electrically connected to the opposing surface through a circuit. Using the pressure solution of the present invention, etching is achieved without an externally applied voltage gradient between the first surface and the second surface used to drive the removal of material through etching or the deposition of material through precipitation. In the present invention, there is no externally applied voltage bias between the first surface and the second surface, and no current being externally driven between the first surface and the second surface. The methods of the present invention can thus be used with a wide range of insulating, conducting, and semi-conducting substrates.

[0067] In some embodiments of the present invention, the pressure solution effect on chemical reaction rates can be controlled or modified externally, by connecting the second surface (such as an AFM tip or master patterned surface) through a circuit to an external counter electrode which is not directly involved in the pressure solution effect. The counter electrode allows the surface potential of the second surface to be changed, which in turn changes the gradient in surface potential with the first surface and so alters the magnitude of the bridging interfacial electric field and the pressure solution effect on surface chemical reactions. Any current flowing between the second surface and the counter electrode simply maintains a constant potential and is not involved with any chemical reactions occurring at the first surface. The first surface is not electrically connected to the second surface via any electrical circuit. There is therefore no tunnelling current flowing between the first surface and the second surface.

[0068] This electrochemical pressure solution method of the present invention can be used to create a wide variety of nanostructures such as nanopits and nanopores, nanochannels, imprinted and printed architectures.

[0069] As used herein, the term‘nanostructure’ generally refers to a structure having at least one dimension on the nanoscopic scale (or nanoscale), generally taken to be between 1 and 100 nanometres (nm). The methods of the present invention are particularly suitable for manufacturing nanostructures selected from the group comprising a nanopit, a nanopore, a nanochannel, a nanopattern and an arrangement of nanoparticles although the scope of the invention is not limited to these structures. In some preferred embodiments, the nanostructure is selected from the group comprising a nanopit, a nanopore, a nanochannel, a nanopattern and an arrangement of nanoparticles. While the methods of the present invention are particularly suitable for the manufacture of structures at the nanoscale, it will be appreciated that the methods of the present invention can be applied to structures of larger dimensions.

[0070] Herein, where the prefix 'nano-' is used in reference to something other than a unit of measure, it generally refers to something having at least one dimension on a scale of nanometres, usually between 1 and 100 nanometres (nm) in size.

Hence, as used herein, the term‘nanopit’ generally refers to a pit or blind hole of nanoscale size and the term‘nanopore’ generally refers to a pore or open hole of nanoscale size. As used herein, the term‘nanochannel’ generally refers to a channel or trench of nanoscale size. As used herein, the term‘nanoparticle’ generally refers to a particle of nanoscale size, usually between 1 and 100 nanometres (nm) in size, with a surrounding interfacial layer. As used herein, the term‘nanopattern’ generally refers to a pattern having at least one dimension on the nanoscale.

[0071] Various further embodiments of the invention will now be described with reference to Figures 2 to 5.

[0072] In one embodiment, the methods of the present invention can be used to manufacture nanopits and nanopores, as Figure 2 illustrates. In this exemplary embodiment of the present invention, the first surface is a thin silica film deposited on top of a silicon wafer and the second surface is a probe tip. The probe tip can be held against the silica surface where it penetrates into the silica film by greatly enhancing the dissolution rate of silica underneath the probe resulting in a nanopit with the same geometry as the penetrating probe. If the probe tip is held in contact with the silica surface for sufficient time for the probe to penetrate to the bottom of the silica film, the probe tip will encounter the underlying silicon surface where the tip-silicon surface potential gradient is insufficiently large to result in enhanced dissolution of the silicon which effectively halts further penetration of the tip. Repeating this step results in an array of nanopits of uniform size. The silicon wafer can then be back-etched resulting in a free-standing silica film containing a nanopore or an array of nanopores. The diameter of the nanopore or array of nanopores will be similar to the diameter of the probe tip used to dissolve the original nanopit or array of nanopits. It is also possible to generate trenches and channels by creating a series of nanopits in close proximity to one another.

[0073] In another embodiment, the methods of the present invention can be used to manufacture or“imprint” nanopatterns, as Figure 3 illustrates. In this exemplary embodiment of the present invention, the first surface is a silica surface and the second surface is a patterned surface, for example a patterned gold film. The patterned surface can be pressed against the silica surface resulting in dissolution under the second surface, leading to a duplicate pattern imprinted in the first surface. This imprinting process can be used to create a wide range of nanostructures.

[0074] In another embodiment, the methods of the present invention can be used to manufacture nanochannels, as Figure 4 illustrates. In this exemplary embodiment of the present invention, the first surface is a silica surface and the second surface is the probe tip. The tip can be scanned across the surface resulting in nanochannels. The channel depth can be increased with additional scans.

[0075] In another embodiment, the methods of the present invention can be used to manufacture arrangements of nanoparticles, as Figure 5 illustrates. In this exemplary embodiment of the present invention, the first surface is a silica surface and the second surface is the probe tip. When the electrolyte comprises an additional dissolved species, in this case Si(OH)4, then rapid dissolution under the tip will result in a local region of oversaturation that leads to nucleation and precipitation of the dissolved species. Tapping the tip on the first surface allows nanoparticles to be deposited rapidly and controllably. It is possible to deposit additional nanoparticles on top of already deposited nanoparticles in order to build up three-dimensional structures. This additive manufacturing or“printing” of nanoparticles can be used to create a wide range of nanostructures. In an alternate exemplary embodiment of the present invention, the first surface is a silica surface and the second surface is the probe tip which has been chemically modified to provide a surface potential that is more closely matched with that of silica. This generates a bridging interfacial electric field which suppresses dissolution of the first surface and if there is an additional dissolved species present in the electrolyte, in this case orthosilicic acid (Si(OH)4), then the bridging interfacial electric field under the tip will result in nucleation and precipitation of a nanoparticle of the dissolved species, in this case a silica nanoparticle. Tapping the tip on the first surface allows nanoparticles to be deposited rapidly and controllably. It is possible to deposit additional nanoparticles on top of already deposited nanoparticles in order to build up three-dimensional structures.

This additive manufacturing of nanoparticles can be used to create a wide range of nanostructures. In some embodiments of the present invention, the nanoparticles being deposited will be the same material as the first surface. In other embodiments, the nanoparticles being deposited will be a different material to the first surface.

[0076] A further embodiment of the invention can combine the subtractive and additive manufacturing methods of the present invention by switching between dissolution etching and nanoparticle deposition. In this exemplary embodiment of the present invention, the first surface is a silica surface and the second surface is the probe tip. The probe tip is used to generate nanopits and nanochannels. By switching the surface potential of the AFM tip, it can then be used to generate and deposit nanoparticles. Thus, it is possible to switch between dissolution etching mode and nanoparticle deposition.

[0077] Suitable electrolyte solutions for use with the present invention comprise any electrolyte solution, particularly aqueous solutions. Particularly suitable electrolyte solutions include aqueous solutions of those where the cation is selected from the Group I and Group II metals, preferably selected from the list comprising lithium, sodium, potassium, magnesium, calcium and strontium; and where the anion is preferably selected from the list comprising fluoride, chloride, bromide, iodide, nitrate, sulfate, phosphate, carbonate, and combinations thereof. In one preferred embodiment of the present invention, the electrolyte solution is aqueous calcium chloride. In another preferred embodiment of the present invention, the electrolyte solution is aqueous sodium chloride. In another preferred embodiment of the present invention, the electrolyte solution is aqueous magnesium sulfate.

[0078] It is a preferred feature of the present invention that the electrolyte solution comprises an additional dissolved species. In some preferred embodiments, the additional dissolved species is a similar material to the first surface material. For example, if the first surface is silica, then it is a preferred feature of the present invention that the electrolyte solution further comprises silicon dioxide and/or orthosilicic acid (Si(OH)4) in solution. Flence, in preferred embodiments of the invention, the electrolyte solution further comprises an additional dissolved species selected from the group comprising silicon dioxide, orthosilicic acid (Si(OH)4), aluminium oxide, aluminium hydroxide, sodium tetrahydroxyaluminate (NaAI(OH)4), sodium aluminate (NaAIC ), aluminium chloride, gold chloride, silver chloride, sodium silicates (such as sodium meta silicate, Na2Si03; sodium orthosilicate, Na4Si04;

and/or sodium pyrosilicate, NaeS^O), and mixtures thereof.

[0079] As the skilled person will be aware, the Debye length is the thickness of the diffuse layer in the electrostatic double layer surrounding a surface in solution. It represents the distance from the compact layer of ions adsorbed onto the surface to the point where the effect of the surface is felt by the ions. The Debye length is dependent on the concentration of the electrolyte. The extent of the double layer decreases with increase in electrolyte concentration due to the shielding of charge at the solid-solution interface. Hence, as the concentration of electrolyte is increased, the Debye length decreases. As the present invention works by inducing a bridging interfacial electric field between two dissimilarly charged surfaces, the interfacial distance will be less than 2 Debye lengths. It is preferable that the concentration of the electrolyte solution be sufficient to provide a Debye length of less than around 100 nm, which in turn provides an interfacial distance of less than around 200 nm. In some preferred embodiments, the interfacial distance between the first surface and the second surface is in the range of around 0.1 -20 nm, more preferably in the range of around 0.1 -10 nm, preferably less than around 1 nm. In some preferred

embodiments of the present invention, the concentration of the electrolyte solution is sufficient to provide a Debye length of between about 0.1 and 10 nm. For example, the interfacial distance between the first surface and the second surface may be in the range of around 0.1 -200 nm, 0.1 -190 nm, 0.1 -180 nm, 0.1 -170 nm, 0.1 -160 nm, 0.1 -150 nm, 0.1 -140 nm, 0.1 -130 nm, 0.1 -120 nm, 0.1 -1 10 nm, 0.1 -100 nm, 0.1 -90 nm, 0.1 -80 nm, 0.1 -70 nm, 0.1 -60 nm, 0.1 -50 nm, 0.1 -40 nm, 0.1 -30 nm, preferably around 0.1 -20 nm, more preferably around 0.1 -10 nm. For example, the interfacial distance may be less than around 10 nm, less than around 9 nm, less than around 8 nm, less than around 7 nm, less than around 6 nm, less than around 5 nm, less than around 4 nm, less than around 3 nm, less than around 2 nm, preferably less than around 1 nm, for example around 0.1 -1 nm. For example, the concentration of the electrolyte solution may be sufficient to provide a Debye length of between about 0.1 - 100 nm, 0.1 -90 nm, 0.1 -80 nm, 0.1 -70 nm, 0.1 -60 nm, 0.1 -50 nm, 0.1 -40 nm, 0.1-30 nm, 0.1 -20 nm, preferably around 0.1 -10 nm. As the skilled person will appreciate, the charge gradient across the Debye length is dependent on the pH of the electrolyte solution. Therefore, the skilled person will preferably select the pH which is sufficient to provide a Debye length of between 0.1 and 100 nm. For example, in some embodiments, the pH of the electrolyte solution will be sufficient to provide a Debye length of between about 0.1 -100 nm, 0.1 -90 nm, 0.1-80 nm, 0.1 -70 nm, 0.1 -60 nm, 0.1 -50 nm, 0.1 -40 nm, 0.1 -30 nm, 0.1 -20 nm, more preferably around 0.1 -10 nm. For the purpose of describing this invention, any combination of concentration and pH that is capable of imparting a Debye length of between about 0.1 and 100 nm shall be deemed suitable to achieve the change in solubility sought by this invention. For example, in some embodiments, the combination of concentration and pH of the electrolyte solution is sufficient to provide a Debye length of between about 0.1 -100 nm, 0.1 -90 nm, 0.1 -80 nm, 0.1 -70 nm, 0.1 -60 nm, 0.1 -50 nm, 0.1 -40 nm, 0.1 -30 nm, 0.1 -20 nm, preferably around 0.1 -10 nm.

[0080] As the skilled person will be aware, the surface potential, Y, of each surface is related to its surface charge. As the present invention works by inducing a bridging interfacial electric field between two dissimilarly charged surfaces, the methods of the present invention are suitable for manufacturing nanostructures on a wide variety of surfaces. It will be appreciated that any material suitable for chemical mechanical planarization is suitable for use with the present invention. Particularly, surfaces suitable for use with the present invention include semiconductors, insulators and metals. In some preferred embodiments of the present invention, the first surface is selected from the list comprising silicon, silicon dioxide (silica), silicon-germanium, silicon nitride, silicon carbide, germanium, gallium nitride, gallium arsenide, cadmium zinc telluride (CzT), lll-V compound semiconductors (preferably gallium nitride, gallium arsenide, indium nitride, aluminium nitride, indium phosphide), aluminium oxide (alumina), titanium dioxide, cadmium sulfide, diamond (particularly diamond doped with impurities such as boron, phosphorus and nitrogen), lithium niobate (LiNbCb), silver, copper and aluminium. In one preferred embodiment of the present invention, the first surface comprises silica. In another preferred embodiment of the present invention, the first surface comprises alumina. In some preferred

embodiments of the present invention, the second surface is selected from the list comprising silicon, silicon dioxide (silica), silicon-germanium, silicon nitride, silicon carbide, germanium, gallium nitride, gallium arsenide, cadmium zinc telluride (CzT), lll-V compound semiconductors (preferably gallium nitride, gallium arsenide, indium nitride, aluminium nitride, indium phosphide), aluminium oxide (alumina), titanium dioxide, cadmium sulfide, diamond (particularly diamond doped with impurities such as boron, phosphorus and nitrogen), lithium niobate (LiNbCb), nickel, nickel oxide, chrome, chrome oxide, iron, iron oxide, cerium oxide, gold, silver, copper and aluminium.

[0081] In some preferred embodiments of the present invention, the second surface comprises a patterned surface. Preferably, the patterned surface is a gold film or a gold coated silica surface.

[0082] In other preferred embodiments of the present invention, the second surface comprises a probe tip. Preferably the tip is an atomic force microscopy (AFM) tip. More preferably, the probe tip is selected from the group comprising a gold coated AFM tip, an aluminium coated AFM tip, an alumina coated AFM tip, a silicon carbide AFM tip, a diamond coated AFM tip, a nickel AFM tip, a nickel oxide AFM tip, an iron oxide AFM tip, a chrome AFM tip, a chrome oxide AFM tip, a silica AFM tip and a cerium oxide AFM tip. Most preferably, the probe tip is selected from the group comprising a gold coated AFM tip, an aluminium coated AFM tip, an alumina coated AFM tip, a silicon carbide AFM tip and a diamond coated AFM tip. The skilled person will appreciate that coated surfaces generally have a layer of oxide at the outermost coating surface as most substances will oxidise on contact with air or water. This is particularly true of metals such as aluminium. For example, an aluminium coated surface will generally have a layer of alumina at the outermost surface as aluminium oxidises readily on contact with air.

[0083] In some preferred embodiments of the invention, the method further comprises the step of scanning the second surface tip along the first surface to form a nanochannel in the first surface. This allows the surface tip to form channel in the first surface to create patterns and architectures at the nanoscale. It is also possible to raster scan the second surface tip across the first surface to create patterns and architectures at the nanoscale. [0084] The ability to control the difference in surface potential between the two surfaces and in turn the bridging interfacial electrical field is a useful preferred feature of the present invention. Hence, in some preferred embodiments of the present invention, the second surface is an electrode and the second surface potential (4 ) is controllable with a potentiostat and counter electrode. This allows the operator to control the difference in surface potential (DY) between the two surfaces.

[0085] It is also possible to modify the difference in surface potential (DY) between the two surfaces by chemically modifying one of the surfaces. For example, reacting a silica surface with 5-(triethoxysilyl)pentanoic acid can chemically modify the surface with a covalently grafted, self-assembled monolayer of 5- (triethoxysilyl)pentanoic acid. Likewise, reacting a gold surface with 6- mercaptohexanoic acid can provide a self-assembled monolayer of 6- mercaptohexanoic acid. The modification of the surface with either 5- (triethoxysilyl)pentanoic acid or 6-mercaptohexanoic acid will result in a surface with a surface potential which is more closely matched with that of silica at pH 3.3 thereby generating a bridging interfacial electrical field which suppresses dissolution of silica thus triggering precipitation. For the purpose of describing this invention, any method of chemically modifying the surface that is capable of imparting a change in surface potential shall be deemed suitable for use with the present invention.

[0086] The skilled person will appreciate that increasing the temperature of the manufacturing methods can assist with rate enhancement and thus the methods of the present invention can be performed at any suitable temperature. In some preferred embodiments, the temperature at which the methods of the present invention are performed is room temperature.

[0087] In preferred embodiments of the present invention, the first surface and second surface are brought together with oscillating pressure. This oscillating pressure results in an oscillating electrical field. This can provide a rate enhancement of up to 10 ⁶ times. Preferably, the change in pressure (DR) ranges from around 1 MPa to 1 GPa. More preferably, the change in pressure (DR) is around 100 MPa.

For example, the change in pressure (DR) may be around 1 MPa to 1 GPa, 1 MPa to 900 MPa. 1 MPa to 800 MPa. 1 MPa to 700 MPa. 1 MPa to 600 MPa. 1 MPa to 500 MPa. 1 MPa to 400 MPa. 1 MPa to 300 MPa. 1 MPa to 200 MPa. 1 MPa to 150 MPa, preferably around 100 MPa. For example, the change in pressure (DR) may be around 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, 80 MPa, 90 MPa, 100 MPa, 110 MPa, 120 MPa, 130 MPa, 140 MPa, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa, 200 MPa, and preferably around 100 MPa. In preferred embodiments the rate of oscillation is in the range of around 1-1000 kHz, more preferably in the range of around 20-100 kHz, most preferably around 35 kHz. For example, the rate of oscillation may be in the range of around 1-950 kHz, 1-900 kHz, 1-850 kHz, 1-800 kHz, 1-750 kHz, 1-700 kHz, 1-650 kHz, 1-600 kHz, 1-550 kHz, 1- 500 kHz, 1-490 kHz, 1-480 kHz, 1-470 kHz, 1-460 kHz, 1-450 kHz, 1-440 kHz, 1-430 kHz, 1-420 kHz, 1-410 kHz, 1-400 kHz, 1-390 kHz, 1-380 kHz, 1-370 kHz, 1-360 kHz, 1-350 kHz, 1-340 kHz, 1-330 kHz, 1-320 kHz, 1-310 kHz, 1-300 kHz, 1-290 kHz, 1- 280 kHz, 1-270 kHz, 1-260 kHz, 1-250 kHz, 1-240 kHz, 1-230 kHz, 1-220 kHz, 1-210 kHz, 1-200 kHz, 1-190 kHz, 1-180 kHz, 1-170 kHz, 1-160 kHz, 1-150 kHz, 1-140 kHz, 1-130 kHz, 1-120 kHz, 1-110 kHz, 1-100 kHz, 1-90 kHz, 1-80 kHz, 1-70 kHz, 1-60 kHz, 1-50 kHz, 1-40 kHz, 1-30 kHz, 1-20 kHz, 1-10 kHz, preferably around 20-100 kHz. For example, the rate of oscillation may be in the range of around 20-90 kHz, 20-80 kHz, 20-70 kHz, 20-60 kHz, 20-50 kHz, 20-40 kHz, 20-30 kHz, 30-100 kHz, 40- 100 kHz, 50-100 kHz, 60-100 kHz, 70-100 kHz, 80-100 kHz, or 90-100 kHz. For example, the rate of oscillation may around 20 kHz, around 25 kHz, around 30 kHz, around 35 kHz, around 40 kHz, around 45 kHz, around 50 kHz, around 55 kHz, around 60 kHz, around 65 kHz, around 70 kHz, around 75 kHz, around 80 kHz, around 85 kHz, around 90 kHz, around 95 kHz, around 100 kHz, most preferably around 35 kHz.

[0088] As the skilled person will appreciate, the pressure is a function of the force applied by the second surface to the first surface. Hence, the change in pressure (DR) is directly proportional to the change in force (AF). Therefore, in preferred embodiments of the present invention, the first surface and second surface are brought together with oscillating force sufficient to provide pressures that are in line with those outlined above. This can provide a rate enhancement of up to 10 ⁶ times.

In preferred embodiments, the rate of oscillation is in the range of around 1-1000 kHz, more preferably in the range of around 20-100 kHz, most preferably around 35 kHz. For example, the rate of oscillation may be in the range of around 1-950 kHz, 1-900 kHz, 1-850 kHz, 1-800 kHz, 1-750 kHz, 1-700 kHz, 1-650 kHz, 1-600 kHz, 1-550 kHz, 1 -500 kHz, 1-490 kHz, 1 -480 kHz, 1 -470 kHz, 1 -460 kHz, 1 -450 kHz, 1 -440 kHz, 1 - 430 kHz, 1 -420 kHz, 1 -410 kHz, 1 -400 kHz, 1-390 kHz, 1 -380 kHz, 1 -370 kHz, 1 -360 kHz, 1 -350 kHz, 1 -340 kHz, 1 -330 kHz, 1 -320 kHz, 1 -310 kHz, 1 -300 kHz, 1 -290 kHz, 1 -280 kHz, 1-270 kHz, 1 -260 kHz, 1 -250 kHz, 1 -240 kHz, 1 -230 kHz, 1 -220 kHz, 1 - 210 kHz, 1 -200 kHz, 1 -190 kHz, 1 -180 kHz, 1-170 kHz, 1 -160 kHz, 1 -150 kHz, 1 -140 kHz, 1 -130 kHz, 1 -120 kHz, 1 -110 kHz, 1 -100 kHz, 1 -90 kHz, 1-80 kHz, 1 -70 kHz, 1 - 60 kHz, 1 -50 kHz, 1 -40 kHz, 1 -30 kHz, 1 -20 kHz, 1 -10 kHz, preferably around 1 -100 kHz. For example, the rate of oscillation may be in the range of around 20-90 kHz, 20-80 kHz, 20-70 kHz, 20-60 kHz, 20-50 kHz, 20-40 kHz, 20-30 kHz, 30-100 kHz, 40- 100 kHz, 50-100 kHz, 60-100 kHz, 70-100 kHz, 80-100 kHz, or 90-100 kHz. For example, the rate of oscillation may be around 20 kHz, around 25 kHz, around 30 kHz, around 35 kHz, around 40 kHz, around 45 kHz, around 50 kHz, around 55 kHz, around 60 kHz, around 65 kHz, around 70 kHz, around 75 kHz, around 80 kHz, around 85 kHz, around 90 kHz, around 95 kHz, around 100 kHz, most preferably around 35 kHz.

[0089] In one preferred embodiment, the electrolyte solution comprises calcium chloride and the concentration of the electrolyte solution is between 1 and 100 mM, preferably between 20 and 40 mM, more preferably around 30 mM.

[0090] In some further preferred embodiments of the invention, the first surface is silica and the pH of the electrolyte solution is between pH 2 and 6, preferably around pH 3-4.

[0091] In some further preferred embodiments of the invention, the first surface is alumina and the pH of the electrolyte solution is between pH 8 and 12, preferably around pH 9.5-10.5.

[0092] In one embodiment, the present invention provides a nanostructure manufactured by the methods of the invention. This nanostructure is preferably selected from the group comprising a nanopit, a nanopore, a nanochannel, an imprinted nanopattern and an arrangement of printed nanoparticles although the scope of the invention is not limited to these structures.

[0093] A further aspect of the invention relates to a method of manufacturing a nanostructure on a first surface, wherein the first surface has a first electrochemical surface potential, said method comprising introducing a second surface having a second electrochemical surface potential and bringing the two surfaces together in an electrolyte solution to generate a bridging interfacial electrical field thereby altering the solubility at the first surface to allow either (i) dissolution of one or both surfaces into the solution; and/or (ii) precipitation from the solution onto the first surface; to form a nanostructure, wherein there is no externally applied voltage bias between the first surface and the second surface, and there is no current being externally driven between the first surface and the second surface.

[0094] A further aspect of the invention relates to a method of manufacturing a nanostructure, said method comprising immersing a first surface having a first surface potential in an electrolyte solution; introducing a second surface having a second surface potential and bringing the two surfaces together to generate a bridging interfacial electrical field whereby the rate of dissolution at the first surface is sufficiently enhanced to allow dissolution of one or both surfaces into the solution to form a nanostructure, wherein there is no externally applied voltage bias between the first surface and the second surface.

[0095] A further aspect of the invention relates to a method of manufacturing a nanostructure through the controlled precipitation of nanoparticles, said method comprising immersing a first surface having a first surface potential in an electrolyte solution; introducing a second surface having a second surface potential and bringing the two surfaces together to generate a bridging interfacial electrical field whereby the rate of precipitation at the first surface is sufficiently enhanced to allow precipitation onto the first surface to form a nanoparticle, and repeating this process to form a nanostructure, wherein there is no externally applied voltage bias between the first surface and the second surface.

[0096] The invention is further described with reference to the following examples. It will be appreciated that the invention as claimed is not intended to be limited in any way by these examples. Examples

[0097] Example 1

[0098] A 10 mm x 10 mm square fused quartz (silica) plate was rinsed in clean absolute ethanol before being cleaned in a BioForce UV-Ozone cleaner plus for 15 minutes. After cleaning, the quartz plate was immediately submerged in an aqueous 30 mM solution of CaCte at pH 3.3 that had been passed through a 0.22pm cellulose acetate syringe filter. The pH of the CaCte solution was adjusted via titration with concentrated HCI.

[0099] Experiments were performed using a JPK Nanowizard Sense AFM fitted with a Bruker NCHV cantilever chip (Si, Nominal spring constant 40 N/m) that had been coated on the sample (i.e. tip) side with a ~5 nm thick gold film on top of a ~5 thick chrome adhesion under-layer. Before the experiment, the AFM cantilever was calibrated by measuring the force-distance curve between the AFM tip and a standard microscope slide in air and fitting the linear region of the retraction curve (i.e. the spring compliance) to obtain the inverse optical lever sensitivity (invOLS) for the cantilever. Using the air invOLS, the cantilever spring constant was then determined using the termal method. A petri dish containing the cleaned fused quartz plate in 30 mM CaCl2 solution at pH 3.3 was placed under the AFM scanning head and the invOLS in CaCte solution was again measured using the same procedure described above. The CaCte invOLS and air spring constant were used for the determination of tip-surface forces.

[0100] The creation of dissolution pits was accomplished by simply approaching the gold coated AFM cantilever tip toward the fused quartz surface until the deflection in the cantilever registered a pre-determined 'set-point' force and held at the same position for a pre-determined 'dwell' time. During the dissolution of pits, an additional oscillation in the set-point force (above and below the mean set-point force) was applied externally by driving the AFM piezo position up and down at a fixed

frequency.

[0101] The experiment described above was performed to create the series of pits shown in Figure 6 (from left-to-right) using a pre-determined (mean) set-point of 500 nN, 2000 nN, 5000 nN, and 8000 nN respectively. For all the dissolution pits, the set- point force was oscillated ± 100 nN around the mean set-point at a frequency of 60 kHz for a dwell time of 30s for each of the 4 dissolution pits shown.

[0102] The geometry of the dissolution pit retains the geometry of the AFM tip. Analysis of the pit geometry (i.e. hole cross-section) indicates that the far right pit in Figure 6 must have a depth of 792 nm.

[0103] Example 2

[0104] Cleaning of the fused quartz substrate and AFM cantilever preparation and calibration was the same as used for Example 1.

[0105] A 3 x 3 grid of dissolution pits were dissolved in silica in 30 mM CaC solutions of varying pHs using a dwell time of 30 seconds, a mean set-point of 2500 nN with no externally applied oscillation in the set-point force. The experiment described was performed to create the four sets of 3 x 3 grids of pits shown in Figure 7. As the pH is increased from 2 to 6.5, the size and depths of the dissolution pits also increases. This observation conforms well with the relative effects of pH on the surface potentials of gold oxide [Langmuir 2011 , 27, 6026-6030] and silica [K.

Kristiansen et al. / Geochimica et Cosmochimica Acta 75 (2011) 6882-6892] where the potential gradient is expected to become larger as the pH increases within this range.

[0106] A parallel control experiment was performed using an uncoated Si AFM tip (with a native Si02 surface layer) under the same experimental conditions. No pit formation or dissolution of any kind was observed. The symmetry between the Si AFM tip and the fused silica substrate surface chemistries results in no surface potential gradient when pressed together.

[0107] Example 3

[0108] A Si AFM cantilever with a nominal spring constant of 40 N/m was coated on the sample side with a 5nm thick chromium adhesion underlayer followed by a second 5 nm thick layer of aluminium. The aluminium surface, which contains a thin aluminium oxide expected to have a surface potential within the range of 60-100 mV at pH 3. The Al coated AFM tip was used to dissolve a series of‘trenches’ into a fused silica surface in 30 mM CaC at pH 3.3. The trench was formed by the dissolution of adjacent side-by-side‘pits.’ This procedure was performed to obtain a more accurate measurement of the pit depth upon subsequent scanning of the dissolved features by facilitating the entry of the AFM tip into the feature. Each individual pit forming the trench was dissolved at a contact time of 15 seconds and at different contact forces for each trench of ~4400 nN (5V detector voltage), 6160 nN (7V), 7920 nN (9V), and 9680 (11 V). A topographic line scan of the dissolved trenches is also plotted in Figure 9 showing the relationship between the contact force (i.e. pressure) and the dissolution depth. A large increase, approximately 1 order of magnitude, in the trench depth was observed as the contact force was increased from 4400 nN to 6160 nN with a subsequent decrease in depth at higher contact forces. This decrease in depth at higher contact forces is attributed to the decrease in the amount of water between the surfaces due to pressure induced‘partial dehydration’ of the silica-A Cb interfacial region.

[0109] Again, no trench formation or dissolution of any kind was observed in the parallel control experiments performed using an uncoated Si AFM tip (with a native S1O2 surface layer) under the same experimental conditions. The symmetry between the Si AFM tip and the fused silica substrate surface chemistries results in no surface potential gradient when pressed together.

[0110] Example 4

[0111] A second series of dissolution trenches were formed in fused silica following the same experimental parameter as described in Example 3. In this experiment, however, the contact force was held constant at 6160 nN (7V detector voltage) and the contact time was varied. In Figure 10, the topographic line trace of the post-dissolution image is also plotted indicating a quasi-linear relationship between the contact time and the trench depth.

[0112] Example 5

[0113] Fused silica substrates were cleaned as described in Example 1.

[0114] A gold coated AFM tip (prepared as described in Example 1 ) was brought into contact with a fused silica surface in a 30 mM CaCh solution at pH 3.3 in a JPK nanowizard sense. The AFM tip was pressed against the silica surface to a set-point force of 500 nN. The AFM tip was scanned across the surface in a star pattern at a rate of 0.1 pm/s while simultaneously applying a 60 kFIz sinusoidal oscillation in the set-point force of ±100 nN around the mean set-point (500 nN). After etching the first star pattern, a second square trench was etched into the surface using the same processing conditions. The square was created by scanning 512 parallel lines, 2.5 urn in length, and spaced 4.9 nm apart. Both the star shaped channel and the central trench were etched to a uniform depth of approximately 2 nm. The results of this experiment are shown in Figure 11.

[0115] Example 6

[0116] Using the same conditions used to etch the pattern in Example 5, a spiral pattern consisting of a 2 nm deep channel was etched into fused silica. The spiral pattern in Figure 12 shows an unbroken channel of uniform depth spanning a total length exceeding 100 pm.

[0117] Example 7

[0118] Fused silica substrates were cleaned as described in Example 1.

[0119] An interdigitated gold electrode (Abtech Scientific; Catalogue #IME 2050.5 M-Au-U) containing a parallel array of 20 pm wide gold digits spaced 20 pm apart and 5 mm long was rinsed with clean absolute ethanol and cleaned with a UV-Ozone cleaner for 15 minutes. A drop of 50 mM CaC solution at pH 3.5 was placed on top of the electrode pattern and the fused quartz plate was placed atop of the electrode. The electrode and quartz plate were pressed together using an acrylic c-clamp which tightened to a light‘finger-tight’ pressure. Unfortunately, this set-up does not allow the real pressure between the electrode and quartz to be known. The c-clamp assembly, was then submerged in a larger volume of 50 mM CaCh solution and removed after 8 hours revealing the negative imprint of the inter-digitated pattern of the electrode, as shown in Figure 14.

[0120] Example 8 [0121] Same procedure as used for Example 7 only the experiment was

performed in 30 mM CaCte solution at pH 3.3. The Black Si substrate shown in Figure 15 was coated with a 5 nm thick gold film a top of a 5 nm thick chromium adhesion under-layer. The time in contact to produce the imprint pattern in Figure 16 was 6 hours.

[0122] Example 9

[0123] Crystalline silica substrates (single crystal z-cut) were cleaned as described in Example 1.

[0124] AFM tip was coated with gold as described in Example 1.

[0125] The AFM tip was further modified with a self-assembled monolayer of 6- Mercaptohexanoic acid by soaking the cantilever for 4 hours in a 1 mg/ml solution of 6-Mercaptohexanoic acid in methanol followed by rinsing in Dl water. The

modification of the AFM tip with 6-Mercaptohexanoic acid will result in a surface with a surface potential which is more similar to that of silica at pH 3.3 thereby reducing the electric field strength which enhances precipitation rather than dissolution of silica.

[0126] In a solution of 30 mM CaCte at pH 3.3 containing an addition 5 ppm concentration of dissolved Si(OH)4, the modified AFM tip was brought into close proximity (estimated separation ~ 1 nm) to a crystalline silica surface using the non- contact‘tapping’ mode of the AFM control software. By scanning the surface in tapping mode under an applied driving oscillation of 1V which oscillates the position of the AFM tip up and down (and thus the separation distance between the tip and surface), nanoparticles of precipitated S1O2 were deposited within the scan region. A second smaller square region of S1O2 nanoparticles was then deposited on top of the first deposited layer of nanoparticles by again scanning the region under the same conditions demonstrating multi-layer deposition. The results of this experiment are shown in Figure 17.

[0127] Example 10

[0128] Fused silica substrates were cleaned as described in Example 1.

[0129] AFM tip was coated with gold as described in Example 1. [0130] A gold coated AFM tip was brought into contact with a fused silica surface in a solution of 30 mM CaCh at pH 3.3 with an additional 150 ppm concentration of dissolved Si(OH)4. Although these solution conditions enhance dissolution, the very rapid rate at which the S1O2 dissolves creates a localized condition in the vicinity of the AFM-silica interface where the solution becomes oversaturated. This local oversaturation of dissolved Si(OH)4 triggers the precipitation of S1O2 in this region which can also be used to create patterns.

[0131] To create the above pattern consisting of a larger square with a 4x4 grid of deposited S1O2, the gold coated AFM tip was brought into momentary contact with the fused silica surface at each point in the pattern for 10 ms at a contact set-point force of 500 nN. The results of this experiment are shown in Figure 18.

[0132] Example 11

[0133] Single Crystal sapphire (c-plane (0001 )) was cleaned as described in Example 1 for fused silica.

[0134] AFM tip was coated with gold as described in Example 1.

[0135] A gold coated AFM tip was brought into contact with a sapphire wafer in a solution of 30 mM CaC at pH 3.3 with an additional 150 ppm concentration of dissolved Si(OH)4. At these solution conditions, both the gold and sapphire surfaces are positively charged and believed to possess similar surface potentials (as determined by published zeta potential measurements).

[0136] To create a pattern consisting of a line of large deposits of S1O2 on the sapphire, the gold coated AFM tip was pressed against the sapphire for 30 s at a contact set-point force of 2000 nN. The results of this experiment are shown in Figure 19.

[0137] Example 12

[0138] A CVD deposited thin film of GaN on sapphire (purchased from MTI Corporation, Richmond CA USA) was cleaned as described in Example 1 for fused quartz. [0139] A boron doped conductive diamond coated AFM tip ((AD-40-SS;

purchased from Bruker, Billerica MA USA) with a nominal spring constant of 40 N/m was cleaned in a BioForce UV-ozone cleaner for 10 minutes. This UV-ozone treatment terminates the diamond surface with Oxygen resulting in a slight negative surface charge at acidic phis based on published values of zeta potential

measurements [Chakrapani, V. et.al / Science 2007, 318(5855), pp. 1424-1430]

[0140] A conductive diamond coated AFM tip was brought into contact with the GaN surface in a solution of 30 mM CaCte at pH 3.3. At these solution conditions, the conductive diamond AFM tip is negatively charged and the GaN is expected to have a positive charge based on published values of the zeta potential [Mandal S. et al. /

ACS Omega 2017, 2(10), pp. 7275-7280] The difference in the surface potentials leads to conditions which enhance the dissolution of the GaN.

[0141] To create a pattern consisting of a line of 5 dissolution pits in the GaN, the conductive diamond coated AFM tip was pressed against the GaN for 120 s at a mean contact set-point force of 2000 nN with an additional sinusoidal oscillation of +/- 500 nN above and below the mean set-point force at a frequency of 30 kHz. The results of this experiment are shown in Figure 20.

[0142] Example 13

[0143] Fused silica substrates were cleaned as described in Example 1.

[0144] A boron doped conductive diamond coated AFM probe (AD-40-SS;

purchased from Bruker, Billerica MA USA) was cleaned as described in Example 12.

[0145] The following experiments were performed using‘force modulation mode’ in which the AFM tip is pressed against a surface to a specified mean set-point force and the force is oscillated sinusoidally by a fixed frequency and amplitude above and below the mean set-point force. Using AFM force modulation mode, the conductive diamond AFM cantilever was pressed against a fused silica substrate at a mean set- point force of 2000 nN and oscillated at an amplitude of ±375 nN and different frequencies between 0-300 kHz. To determine the dissolution rate at each frequency tested, a series of 1 x 5 grids of‘pits’ were dissolved into the fused silica by pressing the AFM tip against the fused silica surface for 60s and oscillating the pressure at the frequency being tested under the force modulation mode conditions described above. In these experiments, the frequency was increased in 10 kHz increments up to 300 kHz. Frequencies in the range of 100-150 kHz were not tested due to these frequencies falling within the natural resonance frequency of the cantilever. The dissolution rates were calculated from the dissolution time, pit volume, and pit surface area determined from analysis of the AFM images of the realized pits. The results of these experiments are shown in Figure 21 which shows a maximum dissolution rate achieved by oscillating the pressure at 30 kHz with progressively diminishing dissolution rate maxima occurring at 70 kHz, 100 kHz, 180 kHz which closely align with overtone frequencies of 35 kHz.

[0146] Example 14

[0147] Fused silica substrates were cleaned as described in Example 1.

[0148] AFM tip was coated with gold as described in Example 1.

[0149] A series of 1 x 10 grids of dissolution pits was dissolved into the fused silica substrate by pressing the gold coated AFM tip against the fused silica in force modulation mode using a dwell time of 60 seconds, a mean set-point of 4400 nN, and a sinusoidal oscillation in the set-point force of 30 kHz and an amplitude of ± 220 nN above and below the mean set-point in solutions of 30 mM CaCte at pHs 2.0, 3.2, 4.4, and 5.5. The dissolution rates were calculated from the dissolution time, pit volume, and pit surface area determined from analysis of the AFM images of the realized pits.

[0150] The intrinsic dissolution rate of silica nanoparticles (average particle diameter of 400 nm) was experimentally measured by soaking the nanoparticles in solutions of 30 mM CaCte at pH 2.05, pH 3.1 , pH 4.1 , and pH 5.6 for two weeks at room temperature in air-tight plastic vials. The concentration of dissolved Si(OH)4 was assayed using a colorimetric method described in [Yang, H. et al. / Analytical Methods, 7(13), pp.5462-5467] at various time points over the two week period (roughly every 24-48 hr). The dissolution rate at each time point was determined from the change in concentration of Si(OH)4 with time. The intrinsic dissolution rate which corresponds with the dissolution rate of the silica nanoparticles when there is not additional dissolved Si(OH)4 in the solution was determined by fitting a plot of the dissolution rate as a function of time and extrapolating the fitting curve to time t = 0. [0151] These experiments, the results of which are shown in Figure 22, found that pressure solution resulting from the pressing and oscillating of the gold AFM tip against the fused silica surface resulted in an enhancement in the dissolution rate across all phis of approximately 10 ¹¹ when compared with the experimentally measured intrinsic dissolution rate. In addition, just as the intrinsic dissolution rate of silica was found to increase by approximately 1 order of magnitude as the pH was increased from pH 2.05 to 5.6, the pressure solution enhanced dissolution rate was also found to increase by nearly the same amount.

[0152] Example 15

[0153] Fused silica substrates were cleaned as described in Example 1.

[0154] A boron doped conductive diamond coated AFM probe (AD-40-SS;

purchased from Bruker, Billerica MA USA) was cleaned as described in Example 12.

[0155] The conductive diamond AFM probe was connected as the working electrode in a 3-electrode electrochemical cell using a coil of Pt wire as the counter electrode and Ag/AgCI as the reference electrode. Using a potentiostat, the surface potential on the conductive diamond probe working electrode can be manually controlled by exchanging a current between the working electrode and the Pt counter electrode. When using this 3-electrode electrochemical cell, when the AFM probe working electrode is pressed against a fused silica surface, the fused silica surface remains outside of the electrical circuit of the cell. In other words, the electrochemical cell does not result in an externally driven current or exogenous electric field between the conductive diamond AFM probe working electrode and substrate surface. In experiments using the 3-electrode cell, the bridging interfacial electric field between the conductive diamond AFM probe working electrode and the fused silica is generated by the pressure forcing the two surfaces into close proximity causing the electrostatic double layers between the surfaces to overlap. The strength of the resulting electric field is determined by both the pressure (i.e. the gap distance between the surfaces) and the absolute difference between the surface potentials of the conductive diamond AFM probe working electrode and the fused silica substrate. Since the surface potential of the fused silica surface is determined by the electrolyte and remains a fixed value, applying different surface potentials to the conductive diamond AFM probe working electrode through the 3-electrode electrochemical cell can thus be used to change the surface potential difference between the working electrode and the fused silica resulting in different dissolution rates.

[0156] The conductive diamond probe working electrode was submerged in a solution of 30 mM CaCte at pH 3 (adjusted with addition of HCI). The resonance frequencies of the cantilever were measured using a frequency sweep from 10 kHz to 350 kHz. For scanning in tapping mode, the piezo driving frequency was tuned to a cantilever resonance frequency peak located at approximately 100 kHz which was close to one of the harmonic frequencies previously determined in Example 13 to enhance the pressure solution effect in silica. Using a piezo driving amplitude of 20 nm, a series of 1 pm x 1 pm square trenches were etched into a fused silica substrate at different applied potentials on the conductive diamond AFM probe working electrode.

[0157] Etching of the trenches was performed by scanning a series of 512 parallel and equally spaced 1 pm lines using the AFM‘tapping mode’ at a set-point of 17 nm and a tip velocity of 2 pm/s. When AFM tapping mode is performed in liquid, the tip of the AFM probe makes intermittent‘contact’ with the substrate surface at roughly the same frequency as the piezo driving frequency (i.e. ~ 100 kHz) which results in an oscillating interfacial electric field strength which further enhances the pressure solution effect.

[0158] As observed in Figure 23, varying the potential of the conductive diamond AFM probe working electrode from -350 mV to 500 mV resulted in a changing silica dissolution rate demonstrating the ability to augment the dissolution rate through the control of the working electrode potential.

[0159] Example 16

[0160] Fused silica substrates were cleaned as described in Example 1.

[0161] A boron doped conductive diamond coated AFM probe (AD-40-SS;

purchased from Bruker, Billerica MA USA) was cleaned as described in Example 12. [0162] A conductive diamond AFM probe was assembled into a 3-electrode electrochemical cell as described in Example 15.

[0163] The piezo driving frequency was tuned to the AFM cantilever frequency as described in Example 15.

[0164] In 30 mM CaC I2 electrolyte at pH 3 using AFM tapping mode with a piezo driving amplitude of 20 nm, a set-point amplitude of 17 nm, and a tip velocity of 2 pm/s, a 1 pm wide trench was etched while simultaneously changing the potential on the AFM probe working electrode from -350 mV to 350 mV in a constant linear ramp. The trench shown in Figure 24 was etched starting from the left hand side of the trench moving to the right. Varying the potential on the AFM probe working electrode resulted in a gradual and roughly linear decrease in the dissolution rate resulting in a trench with a linearly sloping floor. As the potential approached 350 mV, eventually the difference between the applied potential on the working electrode and the surface potential on the fused silica became too small for pressure solution induced etching resulting in no observed material removal as the tip was scanned.

[0165] Example 17

[0166] Single crystal Si (110) substrates were cleaned as described in Example 1.

[0167] A boron doped conductive diamond coated AFM probe (AD-40-SS;

purchased from Bruker, Billerica MA USA) was cleaned as described in Example 12.

[0168] The piezo driving frequency was tuned to the AFM cantilever frequency as described in Example 15.

[0169] In 30 mM CaC electrolyte at pH 3 using AFM tapping mode with a piezo driving amplitude of 20 nm, a set-point amplitude of 17 nm, and a tip velocity of 2 pm/s, a 1 pm x 1 pm wide trench was etched into the surface of the silicon wafer. The depth of the trench at the Si wafer surface was measured to be a uniform depth of 0.2-0.3 nm indicating the selective removal of just the oxide (S1O2) layer at the Si wafer surface. Results are shown in Figure 25.

[0170] Example 18 [0171] Single crystal Si (110) substrates were cleaned as described in Example 1.

[0172] A boron doped conductive diamond coated AFM probe (AD-40-SS;

purchased from Bruker, Billerica MA USA) was cleaned as described in Example 12.

[0173] In 30 mM CaC I2 electrolyte at pH 3, 3 sets of 5 holes (arranged as parallel lines) were etched into the Si wafer by pressing the AFM probe against the Si wafer and held at a fixed position and constant force for 60s per hole. The constant force used for each set of 5-hole lines was varied from 1000 nN (top left) to 500 nN (middle) to 250 nN (bottom right) resulting in holes of different sizes and depths. In these experiments, a ring of re-precipitated silica was observed around the rim of the hole. Etching of the Si is believed to occur through the removal of the surface oxide layer of the Si. As this layer is dissolved away, the exposed Si quickly reacts with water to reform the oxide which again is removed by pressure solution. Dissolution of the Si substrate thus proceeds by this continued formation and removal of surface oxide. Results are shown in Figure 26. [0174] Control experiments conducted using the same experimental protocol but using a Si AFM cantilever (resulting in a symmetrical system without any large surface potential gradient) did not result in any observable dissolution of the Si surface.

[0175] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.