WO2010028712A1

WO2010028712A1 - Capillarity-assisted, mask-less, nano-/micro-scale spray deposition of particle based functional 0d to 3d micro- and nanostructures on flat or curved substrates with or without added electrocapillarity effect

Info

Publication number: WO2010028712A1
Application number: PCT/EP2009/004818
Authority: WO
Inventors: Niklas Schirmer; Dimos Poulikakos; Timo Schwamb
Original assignee: ETH Zürich
Priority date: 2008-09-11
Filing date: 2009-07-03
Publication date: 2010-03-18

Abstract

The invention pertains to a method for the production of ID, 2D and/or 3D depositions (37, 38) from a nano-particle loaded liquid (34, 35) by means of a capillary (2) for holding the liquid with a backside section (16) and a smaller diameter tip section (15) located below said backside section (16), wherein the inner diameter the essentially cylindrical tubular part of the tip section (15) is in the range of 50nm - lμm, wherein the capillary (2) is provided with an outer electrode (5) on the outside of or integrated into the wall of the capillary (2) but isolated with respect of the liquid in the capillary (2) and wherein there is a counter electrode (1) in or on a substrate, including the steps of: i) keeping the outer electrode (5) and the counter electrode (6) on an essentially equal potential; ii) establishing a potential difference between the outer electrode (5) and the counter electrode (6) leading to the ejection of a drop (13) or stream from the tip (3) of the tip section (15) of the capillary (2); iii) movement of the opening (32) of the tip section (15) along a pathway as a function of time, wherein said nano-particles are non-charged.

Description

SPECIFICATION

TITLE

Capillarity-assisted, mask-less, nano-/micro-scale spray deposition of particle based functional OD to 3D micro- and nanostructures on flat or curved substrates with or without added electrocapillarity effect

TECHNICAL FIELD

The herein-presented novel methods concern capillarity-assisted, mask-less, nano- /micro-scale spray deposition of particle based functional OD to 3D micro- and nanostructures on flat or curved substrates with or without added electrocapillarity effect.

BACKGROUND OF THE INVENTION

The controlled and spatially resolved deposition of pigmented liquids onto surfaces is of interest in a large variety of fields, in particular in the field of printing, conductor track generation for micro devices and in the field of biological and/or chemical testing and substance/sample handling.

According to the state-of-the-art if small quantities of a liquid such as an ink are to be transferred from an ejection device (typically a liquid nozzle or the like) located above the surface of the substrate (e.g. a piece of paper) in a highly spatially resolved manner, the propulsion of the liquid for the generation of a jet of liquid out of the nozzle (e.g. in the form of small droplets) can either be effected mechanically, as in the case of inkjet printing by using a piezo-element, thermally, by using a thermally activated nozzle as in the case of bubble-jet-printing.

In addition, the application of a liquid, which in this case needs to be loaded with electrolytes or with charged particles in general, by means of electro-spraying is possible. In this case an electric potential difference between the liquid nozzle and the substrate to which the liquid is to be applied is established, and due to the charged nature of the liquid, the liquid is, so to speak, attracted electrostatically by the surface of the substrate leading to deposition on the surface of the substrate. EP 1477230 discloses an ultrafine fluid jet apparatus comprising a substrate arranged near a distal end of an ultrafine-diameter nozzle to which a solution is supplied, and an optional- waveform voltage is applied to the solution in the nozzle to eject an ultrafme- diameter fluid droplet onto a surface of the substrate; wherein an electric field intensity near the distal end of the nozzle according to a diameter reduction of the nozzle is sufficiently larger than an electric field acting between the nozzle and the substrate; and wherein Maxwell stress and an electrowetting effect being utilized, a conductance is decreased by a reduction in the nozzle diameter or the like, and controllability of an ejection rate by a voltage is improved; and wherein landing accuracy is exponentially improved by moderation of evaporation by a charged droplet and acceleration of the droplet by an electric field. All of these methods are developed and used in many applications, but have their limits regarding the spatial resolution, i.e. in particular the possible minimal droplet size, which can be applied to a surface. Furthermore, for many of these methods specific fluids are required (e.g. fluids with charged particles), or the methods critically rely on the spacing between substrate and nozzle and the like, which imposes limitations and problems. This is one of the aspects where the present invention proposes significant improvements.

SUMMARY OF THE INVENTION

The aim of the first aspect of the present invention is to provide an improved method for the drop wise deposition of a liquid in particular onto a surface. Generally speaking this aspect includes a dielectrophoresis-based triggering mechanism which serves as volumetric control of the liquid deposition.

Specifically, a method for the production of ID, 2D and/or 3D depositions from a nano- particle loaded liquid by means of a capillary for holding -the liquid with a backside section and a smaller diameter tip section located below said backside section (below meaning directly or indirectly adjacent to the backside section and in the direction of a substrate), wherein the inner diameter of the tip section (normally essentially cylindrical tubular oval or rectangular) sufficiently large for the particles to easily pass through (typically 10-1000 times, preferably 50-500 times, larger than the average particle size, normally in the range of 50nm - lμm) , is proposed, wherein the capillary is provided with an outer electrode on the outside of or integrated into the wall of the capillary but isolated with respect of the liquid in the capillary and wherein there is a counter electrode in or on a substrate. The proposed method includes the following steps: i) keeping the outer electrode and the counter electrode on an essentially equal potential; ii) establishing a potential difference between the outer electrode and the counter electrode leading to the ejection of a drop (normally for the generation of dots) or stream (normally for the generation of three-dimensional coherent structures such as wires) from the tip of the tip section of the capillary; iii) preferably movement of the opening of the tip section along a pathway as a function of time. Preferably said nano-particles are non-charged. According to a first embodiment, the potential difference in this process is adjusted such that the electrical field between the tip and the substrate is in the range of 6-15 kV/mm. This electrical field can for example be applied over an extended period of time e.g. for the generation of three-dimensional structures (wires) or it can be applied intermittently (pulsed application of voltage) for the generation of individual dots or for the intermittent deposition to a three-dimensional structure. If no electrical field is present between the tip and the substrate (tip and substrate on the same potential), essentially no liquid will be ejected. alternatively speaking according to a further preferred embodiment, the electrical field gradient at the tip is preferably in the range of gradE²=0.5-5*E25 V²/m². According to a further preferred embodiment, the conductivity of the nano-particles, alone or including (mono)layers thereon, is larger than the conductivity of the liquid. This condition makes sure that the particles provided in the liquid experience a sufficient force (dielectrophoretic force) to be expelled out of the capillary together with the liquid to form drops or a stream. An alternative criterion to achieve this can be formulated that the real part of the Clausius-Mossotti factor of the nano-particle loaded liquid (for a more detailed definition of this factor see specific description given below) for a given DC electrical field is larger than zero. Yet another alternative criterion to achieve this is that the liquid is essentially non-polar, i.e. that it has a dipole moment of less than 5 ^• 10^~30 Cm, preferably of less than 1 ^■ 10^~30 Cm, more preferably of less than 0.1 ^■ 10^" Cm. Put differently, according to a preferred embodiment the electronegativity of the liquid is essentially zero. Possible preferred systems are carbohydrate solvents such as liquid alcanes, preferably tetradecane.

In order to make sure that indeed the particles may draw a sufficient amount of solvent with them when exiting the tape, the concentration of the nano-particles in the liquid is preferably in the range of 0.1-10 Vol.-%, preferably in the range of 0.5-5 Vol.-%. This holds true in particular for the generation of nano-wires. In case of dot-production also lower concentrations down to 0.01 Vol-% are possible.

According to a further embodiment of the invention, the average particle size (typically d50 per volume) of the nano-particles is in the range of 1-50 run, preferably in the range of 2-20nm, most preferably in the range of 3-7 nm. Also larger particles are possible if the tip opening is correspondingly adapted. Preferably the particle size distribution is narrow and the width of the corresponding distribution (sigma) is less than 10%, preferably less than 5% of the average value.

According to a further preferred embodiment, the inner diameter of the tip is in the range of 100-lOOOnm, preferably in the range of 150-500nm. Alternatively speaking, the pipette opening diameter is at least one order of magnitude bigger than the average particle diameter.

The substrate and/or the deposited material/particles can be globally or locally heated, preferably by using a preferably focused laser beam, for in-situ drying, carrier liquid evaporation and/or annealing of the deposited material/particles and/or by electron beam for a subsequent modification of the three-dimensional shape of the generated structures.

Normally the liquid fills the tip section of the capillary as well as the backside section.

The liquid can be filled into the capillary either from the tip or via the backside.

Preferentially the nano particle loaded liquid is loaded with, preferably at least partially metallic, nanoparticles (e.g. gold particles, ZnO-particles, silicon-based particles and the like) with an average diameter in the range of 1-100 nm, preferably in the range of 1-10 nm, most preferably in the range of 3-7 nm.

The aim of a second aspect of the present invention is to provide an improved method for the drop wise deposition of a liquid in particular onto a surface. Generally speaking this aspect includes a triggering mechanism based on the electrowetting effect, which serves as volumetric control of the liquid deposition. The present invention therefore in a second aspect proposes a method for the spray or drop wise deposition of a liquid or colloid in particular onto a surface. The liquid in this method is held or introduced into the process in a capillary with a backside section and a tip section located below said backside section (below meaning directly or indirectly adjacent to the backside section and further away in the direction of a substrate). The capillary is of essentially tubular structure, it may have a circular cross-section, it may however also have a oval, cocoon shaped or angular i.e. polygonal cross-section such as square, rectangular triangular and the like. The ratio of the cross-sectional area of the backside section to the cross- sectional area of the tip section is preferably in the range of 100- 10⁶. Furthermore, the backside section (preferably only the backside section) is provided with an outer electrode on the outside of or integrated into the wall of the capillary and with a central electrode in the cavity of the capillary, wherein the liquid fills the tip section of the capillary as well as the backside section at least to a height such that the central electrode penetrates at least partially into the liquid. Typically the inner electrode and the outer electrode as well as the meniscus of the liquid must be located at the same height of the device. The proposed method now specifically includes the following steps: i) keeping the outer electrode and the central electrode at an essentially equal potential; ii) establishing a potential difference, typically in the range of 10-1000 V

(depending on the materials used and that dimensions of the device), between the outer electrode and the central electrode within a very brief timespan of typically below 200 ms leading to the ejection of a drop from the tip opening of the tip section of the capillary. Without being bound to any theoretical explanation, it is believed that the mechanism of ejection as proposed above, which as a matter of fact allows the production of extremely small liquid droplets as previously not achievable using methods according to the state- of-the-art, relies on the so-called electrowetting or electrocapillarity effect. The effect as such it is known in the state-of-the-art, and it essentially is the effect that if an electric potential is established between an electrode immersed into a liquid and an electrode behind a dielectric substrate which is in contact with the liquid, the contact angles of the liquid on the surface will have the tendency to change. This is usually leading to a spreading of the liquid, if the liquid is lying as a droplet on the surface. The new finding is now that if an analogous situation is produced by holding a liquid in a hollow cylinder with a top opening and a bottom opening, by having a first electrode surrounding this cylinder and a second electrode immersing into the liquid from the top, and if the liquid meniscus is located in the region where the first and the second electrode so to speak are adjacent to each other (in a surrounding manner) like a capacity, upon the application of a rapidly changing voltage between the two electrodes the meniscus of the liquid will change shape and leads to a very highly controllable ejection of a liquid droplet out of the bottom opening of the device for each voltage pulse applied to the pair of electrodes. The different size of the two openings of the capillary thereby seems to be one of the important elements for the droplet generation. In other words, the small electrowetting effect in the wide top part of the capillary seems to cause a large fluid motion in the narrow bottom or tip part of the capillary from thereby causing the droplet expulsion.

Using this method, droplets with a volume as low as 65* 10^"21 m³ (65 attoliter) or even as low as 65* 10^"24 m³ (65 zeptoliter) or with a diameter as low as 500 nm or even as low as 50 nm are possible. As indicated above, typically the potential difference to be established within a small timespan is in the range of 10-1000 V or preferably in the range of 100-800 V. The actual basis for the determination of the necessary voltage difference is essentially determined the geometry and the materials used, so normally specifically by the thickness and the dielectric strength of the wall in the system. The decisive relationship in this context seems to be given by the Young-Lippman- equation, which for a droplet on a flat surface with a certain thickness establishes a functional relationship of the change in contact angle as a function of the applied voltage, and which is given as follows:

Wherein ε is the permittivity of the wall, ε₀ is the dielectric constant, U is the applied voltage, d is the thickness of the wall, σi_g is the surface tension between the liquid and the gaseous phase above the liquid, <9₀ is the contact angle without application of an electric field (U=O), and 3 is the contact angle with application of the electric field U. For a given wall thickness, surface tension between the liquid and the gaseous phase, and a given permittivity of the wall, the voltage U is preferably chosen such that the difference in contact angle between no application of the electric field and application of an electric field (the difference being defined as

) is larger than 1°, preferably larger than 5°, more preferably larger than 10°.

According to a first preferred embodiment of the first aspect of the proposed invention, the potential difference is established within a timespan of below 100 ms, preferably within a timespan of below 50 ms, most preferably within a timespan of below 10 ms. Operation frequencies can therefore go up to the kHz range, even up to several tens of kHz. The quick rise of the voltage according to the present view seems to be important and again without being bound to any theoretical explanation it seems that the so-called pinned-contact, i.e. the temporal reluctance of the meniscus to change the point of contact between the liquid and the surface with which it is in contact, may be of importance, and this pinned-contact effect in particular plays in situations where there is a rapid change of the potential.

According to a still further preferred embodiment of this first aspect of the invention, the capillary at least in the backside section, and preferably also in the tip section (it is particularly preferred that the backside section and the tip section made of one single material and a one-piece), consists of a dielectric material, preferably of glass or of a polymer-based material. Preferentially, in the backside section (and preferably only in this section) the outer electrode is provided as a striped or circumferential outer electrode attached to or at least located closely surrounding the outer surface of the capillary. If a striped outer electrode is used (axial stripes) these stripes of electrode material on the dielectric wall material (preferably at least two, more preferably at least four, most preferably at least five or six such stripes) are preferably equally distributed around the circumference of the wall of the capillary, and they preferably have a central symmetry (point symmetry) with respect to the main axis of the capillary. Further preferably the outer electrode may be provided as an electrically conducting, preferably metallic, more preferably noble metal based, coating on the outer surface of the capillary. The coating may either be produced by vapour deposition or by applying a corresponding paste or another kind of metal or more generally electrode material deposition. A further preferred embodiment of the second aspect of the invention is characterised in that the central electrode is provided as an electrically conducting, preferably metallic, wire, essentially centrally extending into the cavity of the backside section from a backside (opening) of the capillary. Typically the terminal end of the central electrode is located in a transition region between the backside section and the tip section, and it is further preferred that the terminal end of this wire is contacting the inner surface of the transition region. This allows having a mechanical fixing of the tip of the electrode and allows avoiding movement of the tip of the electrode in particular when applying rapidly changing voltages between the two electrodes. However, for transport of liquid from the backside region to the tip side region there should be channels between the tip and the surface of this transition region in order not to block and seal the backside region from the tip side region. The wire preferably has a diameter in the range of 0.1 μm - 3 mm, normally in the range of 3-30 μm, more preferably in the range of 7 - 15 μm. It may for example be a cylindrical wire (polygonal or oval cross-section all shapes or however also possible) and such a wire may be a platinum-based wire. Preferentially the inner diameter of the opening of the tip section is in the range of lOOnm - 200μm, preferably in the range of 300 nm - 100 μm. The wall thickness in the tip region is preferentially in the same range, i.e. in the range of lOOnm — 200μm, preferably in the range of 300 nm - 100 μm. As mentioned above, according to the theoretical background of electrowetting, the necessary potential needed to alter the contact angle sufficiently is a function of the thickness of the dielectric ("wall"), and vice versa.

Further preferably the backside section has a diameter in the range of 400-1500 μm, preferably in the range of 600-1000 μm. According to a further preferred embodiment, the tip section, and/or the backside section and/or a transition region between the backside section and the tip section have an essentially circular cross-section. The structure may for example be made as described to the below starting from a cylindrical glass tube which, under the influence of heat, is drawn in the tip section to form the very thin tip section. According to a further preferred embodiment of the second aspect of the invention, the ratio of the cross-sectional area of the backside section to the cross-sectional area of the tip section is in the range of 1000- 10⁵.

Preferentially furthermore, the ratio of diameter of the backside section to the diameter of the tip section can be in the range of 10- 1000, in particular for circular cross-sections thereof.

Preferably, a voltage source can be connected to the two electrodes which preferably applies the potential difference in the form of a single pulse causing one droplet to eject. A certain pulse pattern or pulse sequence may lead to certain printing patterns e.g. in combination with a distinct xy-stage movement. In the case of a pulse sequence or pulse pattern (for example sequence of essentially rectangular pulses), the average period of the preferably (but not necessarily) periodic pulse sequence can be in the range of 0.01 — 30 kHz, more preferably in the range of 0.1-10 kHz. This allows the very rapid deposition of individual dots if concomitantly either the substrate is moved and/or the capillary is moved, in any case if the substrate is moved relative to the capillary. Quite generally, a further preferred embodiment of the proposed method is characterised in that the capillary is moved relative to the substrate for the individual deposition of individual droplets on to the surface at different specific locations. Movement can take place in x,y directions but also perpendicular to the plane of the substrate, so along z. The delta z between substrate and nozzle does essentially not affect the droplet ejection mechanism. This is in contrast to e.g. the electrospraying process and therefore opens new possibilities in particular in respect of application of liquid to non-flat surfaces (curved, irregular, structured surface topologies).

According to a still further preferred embodiment of this first aspect of the invention, the liquid is a particle loaded and/or pigmented liquid. It can for example be a nano particle loaded liquid, more preferably a nano particle loaded liquid loaded with metallic (or at least metal based) nanoparticles. Also possible for example silica based nanoparticles or other types of particles with sizes in the nano range. Generally the nanoparticles can have an average diameter in the range of 1-100 nm, preferably in the range of 1-10 nm. The particles should be significantly (typically about 100 times) smaller than the smallest opening of the pipette tip to avoid clogging. The actual carrier liquid can be any type of solvent or other liquid (for example water, toluene, tetradecane, or another polarisable liquid). Where no particles (the concept particle in a liquid including suspensions, emulsions, sols, colloids and the like) are present in the liquid, the liquid is preferably an electrolyte, more preferably it is loaded with electrolytes such that the conductivity of the liquid is above than or equal to 4 or 5 μS/m, preferably above than or equal to 100 μS/m. Also if the liquid is loaded with particles it may be an electrolyte. The present invention furthermore relates to a device for carrying out the method as described above. It therefore relates to a device for the drop wise deposition of a liquid in particular onto a surface (which may be flat or curved), in particular using a method as described above. The device is including a capillary for holding the liquid with a backside section and a tip section located below said backside section, wherein the ratio of the cross-sectional area of the backside section to the cross-sectional area of the tip section is in the range of 100- 10 . Wherein the backside section is provided with an outer electrode on the outside of or integrated into the wall of the capillary and with a central electrode in the cavity of the capillary, wherein the central electrode penetrates the backside section such that its tip is located in a transition region between the backside section and the tip section. Generally it is preferred that the device has rotational symmetry, i.e. that the capillary in particular in the backside section has a circular cross-section, that the central electrode is essentially located on the axis of the capillary, and that the outer electrode is an annular electrode also with circular cross- section aligned along the same axis. According to a first preferred embodiment, the capillary, at least in the backside section is made from glass (or from another dielectric material), wherein preferably the capillary is made from an essentially cylindrical glass tube for example with an inner diameter in the range of 400-1500 μm which has been drawn in a tip region under formation of the tip section such that the inner diameter of the opening of the tip of the tip section is for example in the range of lOOnm — 200μm, preferably in the range of 300 nm - 100 μm. It should be noted that the capillary may have multiple tip openings and/or multiple backside openings

Furthermore the present invention relates to a printer or printing head (generally meaning a device for depositing a liquid including at least one of the devices as outlined above), including means for moving a substrate as a function of time in accordance with a programmed or programmable motion scheme and/or means for moving the at least one device at a function of time in accordance with a programmed or programmable motion scheme relative to the substrate, and with at least one voltage source for the establishment of the potential difference in the device and with a controller for controlling the motion of the substrate and/or of the device as well as for controlling the potential difference applied by the voltage source. Such a printing head may include an array of devices making use of the above method of droplet deposition. A still further aspect of the invention relates to the use of a method as described above, preferably with the aid of the device as described above, for the printing of images, signs, conductor, insulator or semiconductor tracks, for the deposition of samples, in particular of chemical and/or biological samples or test solutions. The proposed method may also be used for the creation of three dimensional structures such as wires or the like on flat or curved substrates.

A third aspect of the present invention, also generally in the context of liquid deposition using very thin capillaries, but being rather separate, and not necessarily linked to the above method, pertains to a method for the production of ID, 2D and/or 3D depositions from a liquid by means of a capillary for holding the liquid. The capillary has a backside section and a smaller diameter tip section located below said backside section and the inner diameter of the opening of the tip section and of an essentially cylindrical tubular part of the tip section is preferably in the range of lOOnm - lμm. The proposed method includes the following steps: i) filling the tip section, preferably only the essentially cylindrical tubular part thereof with a nano-particle loaded liquid; ii) movement of the opening of the tip section (relative to a substrate) along a pathway (including movement in all three spatial directions) as a function of time preferably essentially without further external influence on the liquid and/or the capillary under concomitant release of liquid from the tip of the capillary. To initiate this spraying mechanism, variable cross section microchannels (exemplified by micropipettes) are filled by capillary forces or externally applied back-pressure or other mechanisms from a reservoir with nano-particle solutions. Once the filling is completed and the pipette tip is removed from the liquid reservoir, the spraying process is initiated and is maintained, without being bound to any theoretical explanation, most likely by at least one or the combination of a) The capillary pressure difference along the variable cross section channel which forces the solution to leave the pipette at its smallest opening; b) Vaporization of the meniscus at the smallest channel opening on a pinned contact line and therewith accelerated particle transport to the tip (same effect as in coffee stain problem) and also beyond the contact line; c) The breakup of a meniscus at the pipette tip due to an instability in the sudden removal of the pipette tip out of the liquid reservoir. d) Disjoining pressure effects in particular at the upper meniscus e) Thermal activation of the liquid: The ejection of the liquid is depending on the heating of the pipette, preferably heating locally the region of the upper meniscus. Once, the liquid is heated up after been sucked up by he capillary, the surface tension of the liquid decreases due to an increase in temperature. Moreover, a reduction of surface tension leads to reduction of capillary pressure and therewith an ejection of the liquid.

The above-mentioned thermal activation of the liquid can be used for controlling the liquid ejection method. As typically the surface tension increases with decreasing temperature, and as the higher the surface tension the higher the rising of the liquid in the capillary due to capillary forces, the filling of the capillary preferably takes place at as low as possible a temperature. It is also possible to essentially freeze the liquid in the capillary as soon as it is filled sufficiently. The actual spraying process can then be initiated/enhanced/supported by heating the capillary, essentially the liquid in the meniscus region) e.g. by (laser) irradiation, electrically by activating microheaters on the capillary as needed or the like. The spraying process can thus be controlled by a control of the temperature of the liquid in the capillary (in particular in the upper meniscus region). The spraying can be reduced or even stopped by reducing the temperature, and it can be triggered/enhanced by increasing the temperature, and it can be varied as a function of time by a corresponding variation of the temperature as a function of time.

A possible temperature control scheme is for example given in that during the filling of the capillary a temperature is chosen which is just above the melting temperature of the liquid, so typically 1-15K above the melting temperature of the liquid. For stopping ejection of the liquid the temperature in the capillary is adjusted to be in the range of the melting temperature, so not more than 5K or IK above the melting temperature. The main factor for the triggering is normally the relative temperature difference to the initial filling temperature. Once it is higher, the spraying starts. Once it is constant or lower, the spraying can be stopped. For initiating ejection of the liquid from the tip of the capillary a temperature is chosen above the melting temperature or above the initial temperature during filling of the capillary and below the evaporation temperature of the liquid, so typically in a window 5, 10 or 15K above the melting temperature of the liquid and at least IK or 5K below the evaporation temperature.

Another approach for the temperature control is to use an optical fibre integrated at or attached to the back of the capillary and to heat the area of the meniscus as desired, controlling its intensity and also controlling its temperature temporally with pulses. If the nanoparticles in the liquid absorb the selected laser wavelength, very little power is needed to reduce the surface tension, and sometimes only care has to be taken not to vaporize the liquid on top.

According to one embodiment of this method therefore, the method is carried out in that during step i) and/or ii) the temperature of the liquid is controlled to vary as a function of time, preferably in the above-mentioned sense. According to a first preferred embodiment of this method according to the third aspect of the invention, the liquid is a pigmented liquid, preferably a nano particle loaded liquid, more preferably a nano particle loaded liquid loaded with at (preferably least partially metallic) nanoparticles with an average diameter in the range of 1-100 nm, preferably in the range of 1-10 nm, most preferably in the range of 3-7 nm. According to a second preferred embodiment of this method within step i) the tip section is filled by dipping the tip opening into a liquid and allowing the liquid to mount in the tip section either by capillary forces or by applying under pressure in the backside section, preferably mounting not beyond the tubular region of the tip section. According to a third preferred embodiment of this method the substrate and/or the deposited material/particles is globally or locally heated, preferably by using a preferably focused laser beam, for in-situ drying, carrier liquid evaporation and/or annealing of the deposited material/particles.

ID, 2D and/or 3D deposition preferably in the form of dots, lines and/or patterns and/or structures on shaped surfaces inclusive of non flat surfaces, as obtainable or as obtained by using a method as described above (first, second aspect as well as third aspect), in particular preferably in the form of conductor, semiconductor or insulator tracks and/or nano-scale wires but also in the form of patterns, signs, text, graphics and the like in particular based on a nano material.

Further embodiments of the present invention are outlined in the dependent claims. To summarise: The presented methods allow the direct spray deposition and 3- dimensional growth of nano-particle formations also on curved substrates to all spatial directions independent from gravity and surface structure. The concept has been proven by experiments with glass micropipettes and is applicable for integration into large scale industrial processes. In a 2D-regime similar tasks as in inkjet printing but with much higher resolution and less liquid content can be fulfilled. The 3D-growth mechanism goes far beyond classical ink-jetting methods and provides new opportunities in the emerging field of 3D bottom-up rapid prototyping, wiring technology, and manufacturing of porous structures. Further, the invention includes a triggering mechanism based on the electrowetting effect, which serves as volumetric control of the liquid deposition. SHORT DESCRIPTION OF THE FIGURES

In the accompanying drawings preferred embodiments of the invention are shown in which:

Figure 1 is a schematic of the electrowetting liquid deposition and the device used, wherein in a) on the left side the situation before the application of a potential difference and on the right side the situation during application of a potential difference is shown, and in b) a detailed view of the transition region between the thin tip end region and the wide backside end region is shown;

Figure 2 a) is a schematic of the capillary filling (a) and spraying of two- dimensional (b) and three dimensional (c) structures in an experimental setup; and b) is a schematic of the dielectrophoresis-based liquid deposition and the device used, wherein in on the left side the situation before the application of a potential difference and on the right side the situation during application of a potential difference is shown;

Figure 3 SEM image of sprayed gold lines, with a magnification on the right side; Figure 4 Intersection of sprayed dots and submicrometer gold lines, with a magnification on the left side;

Figure 5 Gold nanoparticle dots intersection;

Figure 6 Gold Nanorod sprayed on SiN substrate (estimated length: 10 -15 μm);

Figure 7 Branched and bent Gold wires (diameter: 300nm, estimated length 15 μm) in a) and b), respectively;

Figure 8 Nano-wires with multiple branches; and

Figure 9 shows the controlled fabrication of gold nanowires, wherein inset (a) illustrates a schematic of the experimental setup; an electric potential is applied on the substrate inducing an electric field between the insulated nozzle and the substrate; graph (b) shows the inverse linear relationship between the global electric field and the wire diameters, and (c)-(f) SEM images of Au wires with diameters between 200 - 800 run;

Figure 10 shows SEM images of an array of Au wires grown on a Si substrate with a nozzle inclination of 75°. The length of the wires is between 5 μm (lower row) and 18 μm (upper row). Right: Looping of Au wire grown on Pd electrode before (b) and after (c) treatment with a targeted electron beam, (d) Close-up of a nanowire loop with wire diameter -350 ran;

Figure 11 shows an illustration of the micromanipulation with the nozzle (a-c), wherein inset (d) shows the SEM image of a vertical wire (diameter: 500 nm, length: 15 μm) grown on a palladium electrode embedded in a SiO₂ dielectric layer; mechanical manipulation bends the wire and bridges the gap towards a second Pd-electrode (e); and Figure 12 single Au droplets deposited on a surface using the method according to figure 2 under the formation of a pattern.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Extracapillary Control of Liquid Deposition:

A first aspect of the invention is the control of liquid deposition by electrocapillary forces. Modulation of an electrical field applied on the microchannel enables a controlled deposition of various amounts of liquid and the triggering of the process. The main contribution to this effect seems to be related to electrowetting phenomena (i.e.: the change of the contact angle between liquid and surface under the influence of an electric field).

For the technical realization (see figure 1) we have coated the outside of a glass pipette 2 with a conductive layer 5, preferably based on gold. Whilst the outside metal coating serves as one electrode 5, the second electrode 6 is a metal wire (platinum wire, diameter 10 micro meter) that is connected to the liquid 11 itself from the upper aperture 4 of the pipette capillary.

Once the voltage is switched on between the outer electrode 5 and the central electrode 6 by means of the voltage source 7, the wiring 8, 9 and the switch 10, the liquid 11 in the channel will decrease its contact angle (on the same pinned contact line) with the wall which induces an impulse into the liquid to eject a droplet 13 out of the nozzle 3 as is indicated in figure 1 a) on the right side.

The glass pipette used for making the capillary as given above has an outer diameter of 1.5 mm, and an inner diameter of 0.86 mm. The glass pipette is drawn after heating in the tip region leading to a very thin tip region with the dimension is as specified generally above. Between a backside region 16 and a tip region 15 there is provided a transition region 17 which conically converges (see in particular figure 1 b). Mechanical stabilisation of the central electrode 6 in its tip region it is advisable to shift this electrode as far as possible into their cavity from the top opening such that in certain circumferential regions the tip 19 of the central electrode 6 abuts with the inner surface of this transition region 17. In order to still have a sufficient flow and communication between the liquid in the tip region 15 and in the backside region 16, there must however be channels or openings or communication pathways in between. As one can see, normally the outer electrode 5 has essentially the same extension towards the tip of the device as the inner electrode 6.

As a nano particle loaded liquid which can be used in this first and second but also in the third method as described further below, a liquid as available from ULVAC Technologies Inc. of the type: AuITeH with a metal content (wt%): 60-70 and the solvent: n-Tetradecane with a curing temperature: 300°C x 30 min can be used. It is found that the pulsed high voltage fields (100 - 1000 V) applied on microchannels enables the dropwise purging of liquid and can further be used as the triggering mechanism for liquid deposition, also in the spraying mechanism given in more detail as the third aspect of the invention below. In contrast to mechanical droplet generation out of channels, such as piezo- or thermally driven ink-jet printing, the droplet size is not mainly decided by the channel diameter, but can rather exactly be controlled by the length of the electric pulse. Nanoparticle (Colloid) Spray:

The basic idea of this third aspect of the invention is the capillarity-driven, mask-less nano-/micro-scale spray deposition, with or without added electrocapillarity effect, of plane or 3D nanoparticle structures on flat and curved substrates by immediate (pre- deposition) evaporation of their suspending liquid (nanoparticle colloid) as schematically illustrated in figure 2a.

To initiate this spraying mechanism, variable cross section microchannels (exemplified by micropipettes 31 essentially of the same type as illustrated and described in connection with figure 1 just not necessarily equipped with the electrodes) are filled by capillary forces (see a) or externally applied back-pressure or fields from a reservoir 34 with nano-particle solutions. Once, the filling is completed and the pipette tip 32 is removed from the liquid reservoir 34, the spraying process starts and is maintained by the combination of a) The capillary pressure difference along the variable cross section channel which forces the solution to leave the pipette at its smallest opening. b) Vaporization of the meniscus at the smallest channel opening on a pinned contact line and therewith accelerated particle transport to the tip and also beyond the contact line (same effect as in coffee stain problem), c) The breakup of a meniscus at the pipette tip due to an instability in the sudden removal of the pipette tip out of the liquid reservoir.

For opening diameters of a few micrometers or smaller, well into the submicrometer range, we have observed that a stable meniscus at the end of the capillary does not develop, and hence, the particle solution leaves the pipette immediately in a spraying mode. On the other hand, once a meniscus is formed, the liquid flow is interrupted and the spraying does not occur as observed for larger capillary regimes. Generally therefore if the spraying process is to be initiated immediately after filling as illustrated in a, care should be taken that no meniscus forms in the frontside region.

Further, colloid diameters in the range of less than ten nanometers and typically low surface tension of the transporting liquid, allow for rapid evaporation of the liquid phase during the spraying process which enables therewith a direct deposition and assembly of individual particles. The invented spraying method according to the first and second as well as to the third aspect can be used for "writing" of zero- to three- dimensional patterns and structures. Dots, lines and patterns can be written on arbitrarily shaped surfaces (also non flat), from nanoparticles of many different materials and combinations thereof. For example, 3D-writing of singular and branched "wires" perpendicular to the surface is realized by rapid evaporation and controlled movement of either the surface or the pipette.

All colloidal suspensions containing suspended solid metallic, semi-conducting or non- metallic particles can in principle be used in this particle deposition method as long as the liquid phase of the medium has a sufficiently high evaporation rate in its environment. Global or local heating of the substrate continuous or transient, e.g. by focused laser beam enables an in-situ annealing of the deposited particles. Heat introduction into the deposition region will influence the evaporation rate of the colloid liquid phase, as well as the particle to particle interaction (sintering etc) and can serve as a deposition rate control mechanism. Figure 2b shows such a process which is controlled by using the potential difference between the substrate 1 and an electrode 5 which is circumferential to the capillary 2 or is embedded in the isolating (glass) wall thereof. The effect here is also dielectrophoresis-based. The electrode 5 is isolated with respect to the liquid 11 contained in the capillary 2. The potential between the substrate surface 1 and this outer electrode 5 is controlled by a voltage source 7 and/or a switch 10 provided in the wiring 9 or 8. The electrode 5 in this case may extend to the tip opening 3 and it may also be provided only in the region of the tip opening 3.

In the situation illustrated on the left side the potential difference between substrate 1 and electrode 5 is essentially zero, so that there is no electrostatic field gradient between the tip 3 and the surface 1 and correspondingly no expulsion of the liquid 11. In the situation shown in the middle the switch 10 is closed so that a potential difference between the electrode 5 and the substrate is established leading to an inhomogeneous electrostatic field distribution around the tip 3 and correspondingly to an expulsion of the liquid 11 in the form of droplets 13 as illustrated in this middle figure or in the form of a continuous stream (e.g. for the formation of three-dimensional structures such as wires) as illustrated on the right side, as shall be illustrated in more detail further below. In the following the vertical growth of conductive gold nanowires in ambient atmosphere through on-demand dielectrophoretically guided deposition of nanoparticle- laden colloids is demonstrated. Accelerated by dielectrophoresis, rapidly evaporating colloidal droplets leave a capillary nozzle (diameter 500 nm) and are guided through an inhomogeneous electrostatic field. The nanoparticles in the colloidal droplets combine under the action of van-der-Waals attraction forces on the substrate to form highly flexible vertical nanowires with easily controllable lengths and diameters, herein in the range of 150-800 nm. After bending to bridge an electrode pair and after annealing at 300°C, the sample gold nanowires demonstrate excellent electrical conductivity considering their size.

The emerging field of nanoscale structuring and MEMS-fabrication is dominated by photolithographic methods, such as etching and lift-off technologies, or contact printing with PDMS-plates. These methods are appropriate for batch processing, typically affecting entire wafers or chips, while direct printing such as inkjet deposition or electro hydrodynamic jet printing has gained much attention in micro- and nanofabrication as an alternative approach over wafer based manufacturing. The feasibility of printing colloidal suspensions (nano-inks) on planar surfaces has been demonstrated employing either non-contact Taylor cone jets or fountain pen assisted by direct laser-annealing hot plate substrate heating or microwave annealing. All these deposition techniques are focused on two-dimensional or quasi-two dimensional layer-based systems, leaving the unrestricted third space dimension unexploited.

The contribution given in the following describes a process for in-situ non-contact, free form wire or column growth, applicable to a host of substrate materials and without the need of complicated clean-room or vacuum conditions. The setup consists of a nanometer sized printing nozzle as for example illustrated in figure 2 b, and a three-axis piezo-electric stepper motor (e.g. Nanomotion HR4 with a precision of 100 run). The print head nozzle is manufactured out of a borosilicate capillary tube (outer diameter 1.8 mm, inner diameter 1.2 mm), which is pulled in a ZEITZ DMZ-Puller into a micropipette with an orifice diameter of 500 nm. The outer wall of the micropipette is covered with a conductive gold layer deposited by physical vapour deposition (Edwards E306). The capillary is filled from the back-end with a few microliters of sterically stabilized gold nanoparticle suspension (ULVAC AuTeHl) with a mean particle size of 3-7 nm, suspended in non-polar n-tetradecane (C14H30). Also filling as illustrated in figure 2 a) via the front side is possible. For the deposition process, an electrostatic DC voltage (± 0.3-1.0 kV, Keithley 2410 voltage source) is applied to the substrate with the print head nozzle electrically insulated and thus serving as floating electrode. The printing process is visualized by a CCD camera with microscope optics. Zeta-Potential measurements (Malvern Zetasizer Nano S) of the suspension reveal no significant particle charge (ζ=0.14 mV). However, the nanoparticles are polarizable and are therefore expected to react to a non-uniform external electric field, thus resulting in dielectrophoresis (DEP). The electric field gradients at the capillary tip end cause particle acceleration in the suspension towards the very tip of the nozzle, where the electric field gradients are strongest, and ultimately result in the on-demand droplet release of the colloid. Unlike classical electrospraying for liquid deposition, where charged particles are guided through a static electric field, without being bound to any theoretical explanation, the driving mechanism of the present method is the dielectrophoretic force acting on the uncharged, but polarizable particles. The velocity of a spherical particle with diameter d suspended in a medium of permittivity ε_m and dynamic viscosity η is given by v_DEP = d²ε_m Rer/_CiU lv|E|² / (677) , with Ref/_CM 1 representing the real-part of the Clausius-Mossotti factor for the DEP. Its value for the given DC-field is (σ_p - σ_m) I (σ_p + 2σ_m) « 1 , where σ is the electrical conductivity of the particle p and the medium m respectively. For gold nanoparticles suspended in non-conductive tetradecane, a particle attraction towards the substrate, for positive as well as for negative applied voltages is hence expected. Numerical simulations of the electric field gradient V|E| , not shown here for brevity, and assuming the particle velocity v_DEP to be approximately the same as the velocity of the colloidal suspension, suggest Weber numbers in the range 10 < We < 15 , typical for drop-on-demand breakup. The present method also takes advantage of the large surface-to-volume ratios of the ejected small liquid elements resulting in high evaporation rates of the colloids. Due to the very rapid evaporation of the carrier liquid, once ejected, the nanoparticles pile up on the substrate forming wire structures attracted by van-der-Waals forces. As will be illustrated further below, it is also possible to deposit minute droplets in a two- dimensional pattern.

In case of the generation of wire structures, as the released particles propagate along the highest electric field gradient at the shortest distance between substrate and nozzle opening, the growth direction of the wire is controlled by the nozzle position. Once a deposition site is created on the surface, the growth of wires with arbitrary curvatures is therefore possible. The initiation of the deposition process, the wire diameter, and the wire length, are controlled by adjusting the global electric field between the nozzle and the substrate either by modifying the applied voltage or adjusting the nozzle-to-substrate distance. Switching off the potential immediately stops the spraying process.

Printing on dielectric materials and arbitrarily shaped surfaces is achieved by placing a back electrode underneath the printing substrate or by using the substrate as the electrode if possible. In case of using electrode behind the printing substrate this adds an additional capacitance to the system and the electrostatic field has to be adjusted according to the dielectric strength of the material. Furthermore, the limited influence of gravity due to the small length scales involved, allows the deposition to be performed up-side-down, in the direction opposite to gravity.

The evaporation rate of bulk C₁₄H₃₀ at ambient conditions is slow and prevents clogging at the pipette opening. However, once ejected as a spray of colloidal droplets, the high surface-to-volume ratio ensures a very rapid evaporation of the carrier liquid. The capillary pressure difference in the conical pipette guarantees that the very tip of the pipette remains constantly filled with liquid. This enables a continuous free-form wire printing process. The exact spraying conditions are investigated and characterized in the voltage range between 300 and 800 V on a highly p-doped Si substrate. Assuming a parallel plate capacitor between nozzle and substrate, the global average electric field intensity is obtained by E = V Ih , where V is the voltage applied to the substrate and h is the distance between the nozzle and substrate. The local electric field intensity is typically strongest at the nozzle opening and is responsible for dielectrophoretic movement of the particles. However, a steady-state global electric field is advantageous for stable wire growth with a well-defined diameter.

In order to investigate the correlation between the diameter of the deposited structures and the electric field, the applied voltage is stepwise decreased while keeping the nozzle-substrate distance constant. The experiment reveals an inverse linear correlation for an electric field from 6 to 14 kV/mm, resulting in wire diameters of 150-800 nm (see FIG. 9). Taking the nozzle aperture of approx. 500 nm into account, the wide range of wire diameters indicates that the colloidal jet develops through various ejection modes. For a global electric field lower than ~6 kV/mm the deposition stops, whereas an electric field higher than ~13 kV/mm results in an uncontrolled liquid flushing. Wires of various lengths up to 20 μm and aspect ratios as high as 100:1 are readily grown by the described method. To demonstrate the wire growth of different lengths, a 5x5 array of nanowires is fabricated on a silicon chip and is depicted as a top view SEM image in FIG. 10a. Taking the nozzle inclination of 75° for the wire deposition into account, the wire lengths are calculated to be in the range of ~5μm (lower row) and ~18 μm (upper row).

In order to assess the electrical conductivity of the grown Au-wires, micro fabricated palladium electrodes, embedded in Si/SiO₂ structures, and with gaps of 1-2 μm created between them, are used. Gold-nanowires are built on the rim of one electrode by directing the nozzle towards the electrode and applying an electric field (see FIG. 1 Ia). As soon as the nanoparticle spray is released, a wire is grown to the desired height (10 μm) at the electrode edge (see FIG. l ib). Using the same nozzle as an electrostatic micromanipulator, the free standing, but highly flexible wire is then bent towards the second electrode by electrostatic attraction (applied voltage ~10V). Once the wire has touched the surface of the electrode it adheres to it permanently through surface forces. Alternatively, the wire can be bent by a focused electron beam. A global electron beam, used in scanning electron microscopy for large-scale imaging, causes an alignment of the wire structure along the beam direction. By concentrating the energy input on a specific part of the wire, however, immediate local deformations can result in bent or loop-like structures (FIG. lOb-d). A careful use of both, the aligning and bending characteristics of the electron beam therefore provides an alternative approach to deform the vertically grown Au wires.

Electric transport measurements on gold nanowires are performed directly after deposition and after an annealing step. Measurements in the voltage range between -10 mV and 10 mV reveal a linear current- voltage behaviour and an electrical resistivity of 0.1 Ωm after depostion. An annealing process in a furnace for 45 min at 300°C causes sintering of the nanoparticles and decreases the electrical resistivity down to 8.8* 10^"7 Ωm. The measured resistivity is found to be in excellent agreement to that of sintered Au-nanoparticle lines, and the conductivity is only one order of magnitude lower than that of bulk gold. The same process can be used for the generation of two-dimensional structures, so for example for the deposition of small droplet points e.g. for the generation of a pixelated image structure. An example of such a structure is illustrated in figure 12. Extremely small droplets can be deposited with a very high accuracy as concerns the coordinates of deposition. This allows the generation of security features e.g. by the formation of micro-print images which can only be visualised by using magnification means. Fingerprinting by using the spatial distribution of such points is possible. Also possible is the micro deposition of specific fingerprint materials which can only be detected using specific equipment. Combinations of spatial distributions with using particular materials for the deposition as fingerprints, such fingerprints can be for example given by deposition of materials of different electrical properties so read out of the fingerprint is possible using (spatially resolved) micro-capacitive and/or micro-inductive measurements techniques. Also possible is the generation of minute electrical and/or resonance circuits of dimensions hitherto unavailable using known deposition techniques.

In conclusion, this part demonstrates a novel, controllable, atmospheric environment method for the in-situ free form growth of vertical nanowire and pillar structures or minute two-dimensional patterns on arbitrarily shaped substrates. The structure growth is independent of the surface properties of the substrate, but is strongly dependent and therefore controllable by the external electric field, causing DC-dielectrophoretic particle movement in the nozzle and ultimately the dropwise ejection of the colloid. Contact and non-contact manipulation methods are employed to deform the highly flexible nanostructures to bridge two electrodes and enable electrical transport measurements. The results reveal a high electrical conductivity of the deposited structures, close to bulk gold, considering the size of the structures. Applications (for all aspects of the invention): In the 2D regime, the proposed method can fulfil all tasks of particle deposition in the manner of a nano-/micro-scale paint-brush system and can be employed for the production of thin films, lines and dots of arbitrary particle composition. The 3D growth mechanism can be applied for the creation of free standing wires (both straight and branched) which can for example be employed for nano-antennas of short wavelengths, growth of forest structures for adhesive effects such as the gecko-effect, nano-heat fins and other similar applications of individually surface mounted nano- wires or can be ,,harvested" for integration in MEMS/NEMS devices. Arbitrary compositions of nanoparticles as the solute in the precursor liquid pave the way for controlled metal-metal, metal-semi-conducting or metal-polymeric alloy compositions. Especially due to the reduced annealing temperature of metallic nanoparticles, this method offers a brought range of application of composite materials as in transistors, solar photovoltaic cells, organic light emitting diodes (OLEDs), quantum dots and further electronic devices.

In the bio and life science sector our method can for example be used to generate structures or scaffolds for tissue and bone regeneration, micro and nano meshes for skin repair, and solid drug composition of various substances of content. Wiring and cabling of thin and flexible film solar cells can be fulfilled by the presented technology. This is especially promising for composite materials in which low annealing temperatures of the nanoparticles can avoid critical peak stresses in the manufacturing process. Additionally, the method allows for the production of various doped materials and therefore enables the bottom-up formation of nanosolar cells. Generally, the electro wetting based and/or dielectrophoresis-based triggering mechanism can be used for any application that requires a volume controlled liquid deposition process. Proof of concept

The feasibility of the herein-presented spray deposition method for suspended Au nano- particles (diameter: 3-7 nm) in an n-tetradecane based liquid (gold nano-ink) has been demonstrated.

Several pipettes with conical shaped capillaries have been produced out of borosilicate-capillary tubes with a commercial pulling machine (Zeitz DMZ- UNIVERSAL-PULLER). The larger the tapering angle and the smaller the opening diameter of the capillary, the better the spraying performs. Spraying occurs instantaneously after leaving the liquid reservoir, and has been observed for pipettes with opening diameters of less than 10 μm.

- Linear, curved and branched 3D electrically conductive Au- wires have been grown with diameters of less than 300 nm and lengths up to 20 μm. The shape of the wires follows the movement of the pipette since the sprayed particles agglomerate at the nearest available surface structure. After annealing at 300°C the wires showed high electric conductivities.

Electrically conductive 2D patterns have been written by the herein-described mechanism. The minimum line-width produced was 300 nm, and the line width can be controlled by either the filling state of the pipette or the distance between the pipette nozzle and the substrate The spraying mechanism and the growth of 3D-structures have been carried out in all spatial directions, evidentially without limitation by gravitational forces. The emptying process of the pipette has been documented by video taping with a CCD camera, and under an optical microscope. - The spraying process was triggered by electrical fields and externally applied pressure.

- The triggering of liquid deposition by electro-capillary forces has been successfully demonstrated for capillaries of various diameters (500nm - 100 μm) and for applied voltages of 100-lOOOV. Advantages:

The main advantage and the novelty of these bottom-up deposition methods (the method according to the first aspect, according to the second as well as the method according to the third aspect) is the contact-less direct writing of patterns, lines and the like as well as of OD to 3D-structures by in-situ growth on arbitrarily shaped surfaces. Using this method, for example nano-wires and interconnects can be deposited on any desired surface by direct and maskless writing. The method enables new pathways in cabling and wiring technology for individual 3D micro- and nano-chip designs beyond traditional wire bonding technologies.

The method also enables the manufacturing of submicron features of a wide palette of devices using nanoparticle deposition and without requiring high temperatures. Thermal energy input and pressurized or under-pressurized environments are possible if so desired for property improvement of the generated structures, but the method was also successively demonstrated at room temperature and pressure environments, also beyond clean-room conditions. The writing process is not limited by gravitational forces since it is governed by surface force regimes.

Bond numbers have been calculated in the range of ~10^~7. This independence from gravity enables the method to write in any applicable spatial direction. Furthermore, the method is not limited to flat surface structures as in traditional wafer based chip designs, but allows for writing on arbitrary surface structures.

As an example, the lengths of the produced nano-wires can be controlled by the amount of liquid sucked into the pipette, either by simple capillary principles or by externally applied variations (for example partial vacuum) The invented method is not limited to the single use of pulled glass pipettes. It is rather open to be integrated into a printing head consisting of arrays of conically shaped microchannels for a controlled multi-scale and/or multimaterial deposition of nano-particle sprays.

Electrowetting as a mean of liquid movement in micro and nanochannels has yet been employed for various applications (e.g. lab on a chip), however, to our knowledge, it has never been utilized as a means of droplet generation out of channels in printing on demand and at the same time as triggering mechanism for deposition processes. Hence, the here-in presented droplet generation mechanism is a novel electrically controlled method besides the usage of piezo-crystals such as in demand ink-jet printing. Furthermore, in contrast to the well-established method of "electrospraying" our method does not necessarily require the substrate to serve as a counter-electrode, and the deposited liquid is uncharged. Summary:

The herein-presented novel methods allow the direct spray deposition and 3- dimensional growth of nano-particle formations also on curved substrates to all spatial directions independent from gravity and surface structure. The concept has been proven by experiments with glass micropipettes and is applicable for integration into large scale industrial processes. In a 2D-regime similar tasks as in inkjet printing can be fulfilled, however, the 3D-growth mechanism goes far beyond classical ink-jetting methods and provides new opportunities in the emerging field of 3D bottom-up rapid prototyping, wiring technology, and manufacturing of porous structures. Further, this invention includes a triggering mechanism based on the electrowetting effect or on a dielectrophoresis-based effect, which serves as volumetric control of the liquid deposition.

This method can be used for any controlled 2D and 3D nano particle deposition. It provides a valuable method for wiring problems which become more and more important in 3D chip designs. It is useful for chip industry, printing industry, chemical and pharmaceutical industry, energy industry etc. LIST OF REFERENCE NUMERALS

1 surface

2 pipette/capillary

3 tip opening of 2 4 backside opening of 2

5 circumferential electrode

6 central electrode

7 voltage source

8 wiring of 7 to 6 9 wiring of 7 to 9

10 switch

11 liquid

12 meniscus of 11

13 ejected droplet 14 meniscus under applied voltage

15 thinned region of 2

16 wide region of 2

17 transition region between 15 and 16

18 tip end of 5 19 tip end of 6

20 channel/opening

31 pipette

32 tip opening of 31

33 backside opening of 31 34 liquid/nanoparticle solution

35 liquid ascended in 31

36 stream of liquid out of 32

37 layer of liquid/solid formed on 1

38 wire/columnar structure formed by 36

Claims

CLAIMS 1. Method for the production of ID, 2D and/or 3D depositions (37, 38) from a nano-particle loaded liquid (34, 35) by means of a capillary (2) for holding the liquid with a backside section (16) and a smaller diameter tip section (15) located below said backside section (16), wherein the inner diameter of the essentially cylindrical tubular part of the tip section (15) is in the range of 50nm

- lμm, wherein the capillary (2) is provided with an outer electrode (5) on the outside of or integrated into the wall of the capillary (2) but isolated with respect of the liquid in the capillary (2) and wherein there is a counter electrode (1) in or on a substrate, including the steps of: i) keeping the outer electrode (5) and the counter electrode (6) on an essentially equal potential; ii) establishing a potential difference between the outer electrode (5) and the counter electrode (6) leading to the ejection of a drop (13) or stream from the tip

(3) of the tip section (15) of the capillary (2); iii) movement of the opening (32) of the tip section (15) along a pathway as a function of time, wherein said nano-particles are non-charged.

2. Method according to claim 1, wherein the potential difference is adjusted such that the electrical field between the tip (3) and the substrate (1) is in the range of

6-15 kV/mm.

3. Method according to any of the preceding claims, wherein the conductivity of the nano-particles, alone or including (mono)layers thereon, is larger than the conductivity of the liquid.

4. Method according to any of the preceding claims, wherein the real part of the Clausius-Mosotti factor of the nano-particle loaded liquid (34, 35) for a given DC electrical field is larger than zero.

5. Method according to any of the preceding claims, wherein the liquid has a dipole moment of less than 5 ^• 10^"30 Cm, preferably of less than 1 ^• 10^~30 Cm, more preferably of less than 0.1 ^• 10^"30 Cm, wherein particularly preferably the solvent is a liquid alcane, preferably tetradecane.

6. Method according to any of the preceding claims, wherein the concentration of the nano-particles in the liquid is in the range of 0.1-10 Vol.-%, preferably in the range of 0.5-5 Vol.-%.

7. Method according to any of the preceding claims, wherein the average particle size of the nano-particles is in the range of 1-50 run, preferably in the range of 2- 20nm, most preferably in the range of 3-7 run.

8. Method according to any of the preceding claims, wherein the inner diameter of the tip is in the range of 100-lOOOnm, preferably in the range of 150-500nm.

9. Method according to any of the preceding claims, wherein the electrical field gradient at the tip is preferably in the range of gradE²=0.5-5*E25 V²/m².

10. Method according to any of the preceding claims, wherein the substrate (1) and/or the deposited material/particles is globally or locally heated, preferably by using a preferably focused laser beam, for in-situ drying, carrier liquid evaporation and/or annealing of the deposited material/particles.

11. Method according to any of the preceding claims, wherein the liquid fills the tip section (15) of the capillary (2) as well as the backside section (16).

12. Method according to any of the preceding claims, wherein the nano particle loaded liquid is loaded with, preferably at least partially metallic, nanoparticles with an average diameter in the range of 1-100 nm, preferably in the range of 1-

10 nm, most preferably in the range of 3-7 nm.

14. Method for the drop wise deposition of a liquid (11) in particular onto a surface (1), wherein the liquid is held in a capillary (2) with a backside section (16) and a tip section (15) located below said backside section (16), wherein the ratio of the cross-sectional area of the backside section (16) to the cross-sectional area of the tip section (15) is in the range of 100- 10 , wherein the backside section (16) is provided with an outer electrode (5) on the outside of or integrated into the wall of the capillary (2) and with a central electrode (6) in the cavity of the capillary (2), wherein the liquid fills the tip section (15) of the capillary (2) as well as the backside section (16) at least to a height such that the central electrode (6) penetrates into the liquid (1 1), including the steps of i) keeping the outer electrode (5) and the central electrode (6) on an essentially equal potential; ii) establishing a potential difference between the outer electrode (5) and the central electrode (6) within a timespan of below 200 ms leading to the ejection of a drop (13) from the tip (3) of the tip section (15) of the capillary (2).

15. Method according to any of the preceding claims, wherein the potential difference is in the range of 10-1000 V depending on the thickness and dielectric strength of the wall.

16. Method according to claim 1 and claim 14, wherein the potential difference is established within a timespan of below 200 ms, preferentially below 100 ms, preferably within a timespan of below 50 ms, most preferably within a timespan of below 10 ms.

17. Method according to any of the preceding claims, wherein the capillary at least in the backside section (16), and preferably also in the tip section (15), consists of a dielectric material, preferably of glass or of a polymer-based material, and wherein in the backside section (16) the outer electrode (5) is provided as a circumferential outer electrode attached to the outer surface of the capillary (2), wherein preferably the outer electrode (5) is provided as an electrically conducting, preferably metallic, or preferably noble metal based, coating on the outer surface of the capillary (2).

18. Method according to any of the preceding claims, wherein a central electrode (6) is provided as an electrically conducting, preferably metallic, wire, essentially centrally extending into the cavity of the backside section (16) from a backside opening (4) of the capillary (2), and wherein the terminal end (19) of the central electrode (6) is located in a transition region (17) between the backside section

(16) and the tip section (15), and wherein preferably the terminal end (19) is contacting the inner surface of the transition region (17), and wherein preferably the wire has a diameter in the range of 0.1 μm - 3 mm, preferably in the range of 3-30 μm, more preferably in the range of 7 - 15 μm, and wherein further preferably the preferably cylindrical wire is a platinum-based wire.

19. Method according to any of the preceding claims, wherein the inner diameter of the opening of the tip of the tip section (15) is in the range of lOOnm — 200μm, preferably in the range of 300 nm - 100 μm, and wherein preferably a wall thickness in the tip section (15) is in the same range and wherein further preferably the backside section (16) has a diameter in the range of 400-1500 μm, preferably in the range of 600-1000 μm, and wherein further preferably the tip section (15), and/or the backside section (16) and/or a transition region (17) between the backside section (16) and the tip section (15) have a preferably essentially circular cross-section.

20. Method according to any of the preceding claims, wherein the ratio of the cross- sectional area of the backside section (16) to the cross-sectional area of the tip section (15) is in the range of 1000- 10⁵, and/or wherein the ratio of diameter of the backside section (16) to the diameter of the tip section (15) is in the range of 10- 1000, in particular for circular cross-sections thereof.

21. Method according to any of the preceding claims, wherein a voltage source (7) connected to the two electrodes (5, 6) applies the potential difference in the form of a single pulse for single droplet generation, or of a pulse sequence or pulse pattern in particular for multiple droplet generation, wherein the average period of the preferably periodic pulse sequence and the corresponding droplet generation is in the range of 0.01 - 30 kHz, more preferably in the range of 0.1- 10 kHz.

22. Method according to any of the preceding claims, wherein the liquid (11) is a particle loaded and/or pigmented liquid, preferably a nano particle loaded liquid, more preferably a nano particle loaded liquid loaded with metallic nanoparticles with an average diameter in the range of 1-100 nm, preferably in the range of 1- 10 nm.

23. Device for the drop wise deposition of a liquid (11) in particular onto a surface (1), preferably for use in a method according to any of the preceding claims, including a capillary (2) for holding the liquid with a backside section (16) and a tip section (15) located below said backside section (16), wherein the ratio of the cross-sectional area of the backside section (16) to the cross-sectional area of the tip section (15) is in the range of 100- 10⁶ or wherein the inner diameter the essentially cylindrical tubular part of the tip section (15) is in the range of 50nm - lμm, wherein at least the backside section (16) is provided with an outer electrode (5) on the outside of or integrated into the wall of the capillary (2) and/or with a central electrode (6) in the cavity of the capillary (2) and/or with a counter electrode (1) in or on a substrate, wherein the central electrode (6) penetrates the backside section (16) such that its tip (19) is located in a transition region (17) between the backside section (16) and the tip section (15).

24. Device according to claim 23, wherein the capillary, at least in the backside section (16) is made from glass or another dielectric material, wherein preferably the capillary is made from an essentially cylindrical glass tube with an inner diameter in the range of 400-1500 μm which has been drawn in a tip region under formation of the tip section (15) such that the inner diameter of the opening of the tip of the tip section (15) is in the range of lOOnm - 200μm, preferably in the range of 300 run - 100 μm.

25. Printer or printing head with at least one device or an array of devices according to any of the preceding claims, preferably including means for moving a substrate (1) as a function of time in accordance to a preprogrammed motion scheme and/or means for moving at least one device as a function of time in accordance to a preprogrammed motion scheme relative to the substrate (1), and with at least one voltage source (7) for the establishment of the potential difference in the device and with a controller for controlling the motion of the substrate (1) and/or of the device as well as for controlling the potential difference applied by the voltage source (7).

26. Use of a method according to one of the claims 1-22, preferably with the aid of the device according to any of claims 23-25, for the printing of images, signs, conductor, semiconductor or insulator tracks, for the deposition of samples, in particular of chemical and/or biological samples or test solutions and/or for the generation of three-dimensional structures preferably in the form of wires.

27. Method for the production of ID, 2D and/or 3D depositions (37, 38) from a liquid (34, 35) by means of a capillary (2) for holding the liquid with a backside section (16) and a smaller diameter tip section (15) located below said backside section (16), wherein the inner diameter of the opening (32) of the tip section (15) and of an essentially cylindrical tubular part of the tip section (15) is in the range of lOOnm - lμm, including the steps of: i) filling the tip section (15), preferably only the essentially cylindrical tubular part thereof with a nano-particle loaded liquid (35); ii) movement of the opening (32) of the tip section (15) along a pathway at the function of time preferably essentially without further external influence on the liquid (35) and/or the capillary (2), wherein preferably the liquid (11) is a pigmented liquid, preferably a nano particle loaded liquid, more preferably a nano particle loaded liquid loaded with at least partially metallic nanoparticles with an average diameter in the range of 1-100 run, preferably in the range of 1-10 nm, most preferably in the range of 3- 7 nm and/or wherein preferably within step i) the tip section (15) is filled by dipping the tip opening (32) into a liquid (34) and allowing the liquid to mount in the tip section either by capillary forces or by applying under pressure in the backside section (16) , preferably mounting not beyond the tubular region of the tip section (15) and/or wherein preferably the substrate (1) and/or the deposited material/particles is globally or locally heated, preferably by using a preferably focused laser beam, for in-situ drying, carrier liquid evaporation and/or annealing of the deposited material/particles.

28. ID, 2D and/or 3D deposition (37, 38) preferably in the form of dots, lines and/or patterns and/or 3D structures on shaped surfaces inclusive of non flat surfaces, as obtainable or as obtained by using a method according to any of claims 1-22 or 26 or 27, in particular preferably in the form of conductor, semiconductor or insulator tracks and/or nano-scale wires.

29. Security features using a method according to any of the preceding claims 1-22, preferably in the form of a micro-print.