WO2008029416A1

WO2008029416A1 - A metal nanowire based device for obtaining gas discharge in air at low voltage less than 100v at atmospheric pressure.

Info

Publication number: WO2008029416A1
Application number: PCT/IN2006/000354
Authority: WO
Inventors: Javed Mazher; Shankar Ghosh; Pushan Ayyub
Original assignee: Tata Institute Of Fundamental Research (Tifr)
Priority date: 2006-09-08
Filing date: 2006-09-08
Publication date: 2008-03-13

Abstract

A metal nanowire-based device for obtaining gas discharge in air at low voltage less than 100V at atmospheric pressure involving metal Nanowires embedded in an alumina (Al2O3) template; a silver top electrode and a bottom electrode separated from the front of the template; and means to apply DC Voltage across the said electrodes for obtaining the gas discharge at low Voltage.The metal nanowire based electrode and devices would favour low voltage self-sustaining gas discharge wherein the value of self-sustaining discharge (continuous discharge current) achieved is in the range of 100 nanoamps to 100 microamps. The invention avoids the limitations of high operating voltages usually required in many modern devices such as spark plugs in automobiles (petrol / gasoline) engines, melting and welding of metals, decomposition of hydro-carbons and industrial effluent gases and also in various types of light sources and plasma display panels.

Description

FIELD OF THE INVENTION

The present invention relates to low voltage gas discharge and, in particular, to provision of selective metal nanowire based electrodes adapted to reduce breakdown voltage in air at atmospheric pressure from about 750V. to even lower than 10V. Advantageously, the metal nanowire based electrode and devices obtained thereof in accordance with the invention is directed to favour low voltage self-sustaining gas discharge wherein the value of self-sustaining discharge (continuous discharge current) achieved is in the range of 100 nA to lOOμA. The invention would thus favour large scale application and use of metal nanowire based electrodes and devices obtained thereof in spark discharge processes and avoid the limitations of high operating voltages usually required in many modern devices such as spark plugs in automobiles (petrol / gasoline) engines, melting and welding of metals, decomposition of hydro-carbons and industrial effluent gases and also in various types of light sources such as neon lamps, mercury vapour lamps, xenon flash lamps and plasma display panels.

BACKGROUND ART

It is well known that when an electrical potential is applied across a pair of electrodes separated by a gas column, a sudden increase in current occurs when the applied voltage between the cathode and the anode exceeds a certain threshold known as the breakdown voltage. The electrical breakdown can manifest itself as a momentary electrostatic discharge (similar to a lightening strike) or can take the form of continuous arc discharge. At voltages smaller than the breakdown voltage, a gas such as air acts as an insulator. At this stage, a very small current flows due to ionization of the gas by cosmic rays or radioactive sources or caused by electrons emitted by photoelectric or thermionic process. At the breakdown voltage, the gas gets ionized (and hence starts conducting electricity) by collision with a cascade of electrons, which gets formed at this voltage. This process is commonly known as "spark discharge". The breakdown voltage (say, V_B) depends on the nature and pressure of the gas and on the shape and separation of the electrodes. For dry air at atmospheric pressure, V_B is about 3OkV / cm. However, the variation of V_B with spark gap is not linear for small gaps. Thus, it is generally found that in the parallel electrode geometry, it is not possible to reduce the breakdown voltage below 380V.

It is well known that spark discharge process is extensively used in many modern day devices, such as spark plugs in automobiles (petrol / gasoline) engines, melting and welding of metals, decomposition of hydro-carbons and industrial effluent gases and in various types of light sources including neon lamps, mercury vapour lamps, xenon flash lamps and plasma display panels.

The automotive spark plug is an electrical device that fits into the cylinder heads of internal combustion engine and ignites the compressed petrol - air mixture by means of^" an electrical spark. Spark plugs have an insulated central electrode, which is separated by a spark gap to a grounded terminal on the base of the plug. The centra! electrode is connected by a heavily insulated wire to an ignition coil placed outside, which generates a few kilovolts to drive each spark. This ionizes the gas in the spark channel and raises its temperature to thousands of degrees, causing a small explosion that drives the piston of the engine.

Gas discharge lamps are based on the fact that a gas emits light of a characteristic colour when an electric current passes through it. Neon lamps are tubes filled with gas at 5-15 torr pressure, which emits a bright light when a voltage of 1-5 kV is applied across electrodes on either end of the tube. Some discharge lamps such as mercury vapour and sodium vapour lamps operate at a relatively higher pressure of 1-2 atmosphere. In addition, a gas discharge tube is at the heart of many types of gas lasers, such as the He-Ne, Ar-ion and Kr-ion lasers.

Flat panel plasma display panels (PDP) are fast becoming popular because they provide a screen as wide as the largest cathode ray tube but are much thinner (about 15cm) and lighter. Each pixel in the PDP is composed of three phosphor- coated sub-pixel cells (red, green and blue). Each such cell is a tiny bulb containing a gas (Xe or Ne) and is addressed by transparent conducting electrodes. To activate any of these PDP cells, a pulsed DC plasma is created by applying voltage pulses of about 200-250V over a few nanoseconds. Ozonization of oxygen is another very useful application of gas discharge. There are large numbers of patents on efficient methods to generate ozone from oxygen by using glow discharge, spark discharge, corona discharge or their variants.

All these methods require the application of high voltages (typically 5-25 kilo volts) and in many cases the electrodes require to be cooled.

The operating voltages of all devices based on the gas discharge process are thus quite high (few hundred volts to tens of kilovolts) because, as mentioned earlier, the breakdown fields required for electrical discharge in a gas at atmospheric pressure are very large, of the order of about a few kV per mm.

It would be clearly apparent from the above that such large breakdown fields required for electrical discharge in a gas at atmospheric pressure require the generation of quite high operating voltage which is on one hand technically complex and on the other hand is necessarily cost extensive. Thus, while devices based on gas discharge process are well known, the application and use of such devices is found to be limited due to such complexities and cost constraints in generating the required high operating voltages for such devices.

Attempts have previously been made to lower the break down voltage for more favourable application of gas discharge processes. Further, it is recognized and made known to the art that the breakdown voltage between a point such as a wire or needle and a plane is less than that between two planes at the same separation. This has been discussed in details in the classical text book entitled "Fundamental processes and electrical discharge in gases by L.B.Loeb (John Wiley, New York, 1939 at p485) and "Electrical breakdown in gases" by J. M. Meek and J. D. Craggs (Oxford, 1953 at p. 321). However, these studies dealt with macroscopic tips with a tip diameter of 0.5 to 1.0 mm. and hence the breakdown voltage was still found to be in the kilovolt range.

Using finer tips therefore has expectedly led to smaller values of V_B. Thus, in

"N.Spyrou, R. Pepyrous, N. Soulem and B. Held, J. Physics D: Appl. Physics, 28 (1995) 701" it has been reported V_B=550V for a tip radius of 0.1mm and tip- surface separation of a^' few mm. However, such measurements were made at low pressure of 0.1 - 1.9mbar.

More recently, with the advent of methods of reproducibly creating different types of nano-structured solids, further attempts to bring down the breakdown voltage by using a carbon nanotube (CNT) array as one of the electrodes has been reported. In 2000, Rosen et al (Applied Physics Lett. 76 (2000) 1668) disclosed a V_B(min) = 448V with gap spacing of lmm. In 2003, Ajayan et al

(A.Modi, N.Koratkar, E.Lass, B.Wei and P.M.Ajayan, Nature 424 (2003) 171) disclosed V_B(min) = 346V with gap spacing of 0.15mm. In 2006, Yong et al

(Sensors and actuators A 128 (2006) 278) disclosed V_B(min) = 128V with gap spacing of 0.09mm.

It would be apparent that while such attempts involving state of art CNT based discharge devices have also been made available to the art, the breakdown voltage achieved was still of few hundred volts to tens of kilo volts and the need to further reduce the breakdown voltages for effective and wide scale application and use of electrical discharge in a gas for variety of end use/applications and devices involving such gas discharge operation in a simple and cost-effective manner is yet to be attained.

OBJECTS OF THE INVENTION

It is thus the basic object of the present invention to provide for lowering of breakdown voltage for gas discharge in atmospheric pressure from about 750 V (measured using plane metallic electrodes) to lower than 100V, preferably 10V, and to thereby favour wide scale and cost effective application and use of gas discharge devices at low voltage.

A further object of the present invention is directed to a metallic nanowire based electrode adapted to reduce the breakdown voltage in air at atmospheric pressure from about 750V to even lower than 10V with the value self-sustained (continuous) discharge current in the range of 100 nA to 100 μA. Another object of the present invention is directed to avoid the limitations of the afore discussed prevailing state of the art in achieving low breakdown voltages in discharge devices operating in air and thereby facilitate user-friendly, beneficial and advantageous use / application of such low voltage operable gas discharge devices.

A further object of the present invention is directed to selective metallic nanowire based electrode and discharge devices obtained thereof which would be adapted to favour achieving low operative voltage gas discharge.

A further object of the present invention is directed to lowering the operating voltages in devices based on gas discharge processes, which would achieve enormously lower power expenditure and operating cost in addition to providing for longer operating life for the corresponding device.

A further object of the present invention is directed to metallic nanowire based electrode and gas discharge devices which would favour significant lowering of the breakdown voltages in air to a level that can be supplied by commercial dry cells.

A further object of the present invention is directed to selective metallic nanowire based electrodes and gas discharge devices which would enable strong, highly non-linear electric fields leading to the formation of ionization regions in the proximity of the electrodes and thereby favour achieving the gas discharge at much lower voltages than in conventional electrodes.

A further object of the present invention is directed to the development of metal nanowire based electrodes adapted to reduce the breakdown voltage in air at atmospheric pressure from 750V to lower than 100V, preferably even lower than 10V by way of selective sharpening of tips of metal nanowires for further reduction in the breakdown voltage.

Another object of the present invention is directed to achieving selective optimum nanowire diameter, which could favour significant lowering of discharge voltage and thereby provide for a safe and user friendly provision of gas discharge operated devices and utilities.

SUMMARY OF THE INVENTION

Thus according to the basic aspect of the present invention there is provided an electrode adapted to reduce the breakdown voltage for gas discharge in air to less than 100V at atmospheric pressure comprising :

a metal nanowire based electrode with sharpened tip adapted to provide for strong highly nonlinear electric field which forms ionization regions in the proximity of the electrodes.

In accordance with a preferred aspect of the present invention there is provided an electrode adapted to reduce the breakdown voltage for gas discharge in air to less than 10V at atmospheric pressure comprising:

a Copper nanowire (Cu-NW) based electrode with sharpened tip adapted to provide for strong highly nonlinear electric field which forms ionization regions in the proximity of the electrodes.

In accordance with yet another preferred aspect of the present invention there is provided an electrode adapted to reduce the breakdown voltage for gas discharge in air to less than 100V at atmospheric pressure comprising :

a Nickel nanowire (Ni-NW) based electrode with sharpened tip adapted to to provide for strong highly nonlinear electric field which forms ionization regions in the proximity of the electrodes.

Importantly, the electrode tips are sharpened to the level of a few atoms. As also disclosed above the said metal nanowire based electrodes are selected from Copper or Nickel nanowire (Cu-NW)/(Ni-NW) based electrode which is adapted to achieve a self-sustained (continuous) discharge current in the range of 10OnA to lOOμA. In accordance with another aspect of the invention the said nanowire diameter is preferably in the range of 250nm to 20nm, more preferably about 200 nm for discharge at reasonably low voltage of about 50V.

Preferably, the electrode should be about 200nm diameter adapted for continuous electrical discharge up to at least 220 hours at a stretch.

Importantly, the electrode comprises a parallel array of said nanowires embedded in an insulating matrix. The said insulating matrix comprises alumina material. In particular, the electrode system comprises a porous anodic alumina (Al₂O₃) disk with a uniform distribution of 200nm diameter and 60 micrometer long parallel pores wherein the metal nanowires preferably copper nanowires are electrolytically grown from an aqueous solution of copper sulphate, boric acid, thiourea and saccharine.

Importantly, the above disclosed metal nanowire electrodes adapted for reduced breakdown voltage at atmospheric pressure are provided with sharp metallic tips which result in strong, highly nonlinear electric field. These electric fields lead to the formation of ionization regions in the proximity of the electrodes formed by the nanowires and leads to the occurrence of gas discharge at much lower voltages than in conventional electrodes.

In accordance with the preferred aspect there is disclosed the provision of parallel array of metal nanowires preferably selected from Cu-NW and Ni-NW.

Also, in accordance with another aspect of the invention it is found that the metal nanowires adapted for reduced operating voltage is approximately 20 to 250 nm, preferably 200 nanometer (nm) in diameter and 20 to 50 micrometer, preferably 40 micrometer in length.

In accordance with another aspect of the present invention there is provided a metal nanowire-based device for obtaining gas discharge in air at low voltage less than 100V at atmospheric pressure comprising metal Nanowires embedded in an alumina (AI₂O₃) template ;

top electrode evaporated on the back of the alumina template while the bottom electrode is provided separated from the front of the template; and means to apply DC Voltage across the said electrodes for obtaining the gas discharge at low Voltage.

In accordance with a preferred aspect of the present invention there is provided a metal nanowire-based device for obtaining gas discharge in air at low voltage less than 10V at atmospheric pressure comprising

Copper (Cu-NW) Nanowires embedded in an alumina (AI₂O₃) template; top electrode evaporated on the back of the alumina template while the bottom electrode is provided separated from the front of the template; and means to apply DC Voltage across the said electrodes for obtaining the gas discharge at low Voltage.

Preferably, in the said metal nanowire-based device the said metal nanowire comprises selectively a Copper nanowire (Cu-NW) or Nickel nanowire (Ni-NW) with sharpened tips adapted to provide for strong highly nonlinear electric field which form ionization regions in the proximity of the electrodes. Importantly, the said Copper nanowire (Cu-NW) or Nickel nanowire (Ni-NW) based electrode is adapted to achieve a self-sustained (continuous) discharge current in the range of 100 nA to 100 μA.

In accordance with a preferred aspect of the device on said metal nanowire- based device the said copper nanowire diameter is in the range of 250nm to 20nm preferably about 200 nm for discharge at reasonably low voltage of about 50V. Advantageously, the metal nanowire-based device of the invention is adapted for continuous electrical discharges up to at least 220 hours at a stretch. Moreover, in the metal nanowire-based device the said bottom electrode is separated by a spacer preferably 50-100 micrometer from the front of the template.

Advantageously, in accordance with an aspect of the invention, in the metal nanowire-based device the said Copper nanowires are provided grown within the pores of a porous anodic alumina matrix. Importantly, also said Copper nanowire (Cu-NW) or Nickel nanowire (Ni-NW) are provided with sharpened tips obtained by repeated discharge cycles causing said sharpening of the tips of the metal nanowires to favour further reduction in the breakage down voltage.

The electrode and the metal nanowire based device of the invention thus provides for a method of reducing the breakdown voltage in air at atmospheric pressure to lower than 10V with the value of self-sustained (continuous) discharge current in the range of 100 nA to 100 μA comprising carrying out the self-sustaining gas discharge using the said electrode / metal nanowire-based device.

In accordance with the above further aspect of the present invention there is disclosed a metal nanowire based device for self-sustaining gas discharge in air at very low voltages below 100V, preferably even below 10V, which would avoid the limitation of high operating voltages of known devices based on gas discharge process. In particular, the device of the invention involving the metal nanowire array as an electrode would avoid a need for very large breakdown field required for electrical discharge in a gas at atmospheric pressure. Importantly, by way of such substantial lowering of the operating field, the device of the invention would favour enormously lower power expenditure and operating cost in addition to achieving much longer operating life vis-a-vis the presently available system requiring high operating voltages.

As clearly apparent from the above, the present invention and in particular the metal nanowire based electrodes and device for self-sustained gas discharge in air at low voltage involving the same would favour reducing the breakdown voltage in air down to a level that can be supplied by commercial dry cells. Thus, the metallic nanowire selectively used in the present system involving tips sharpened to the level of few atoms would favour producing higher localized electrical field near the tip which in turn would significantly lower the breakdown voltage in air in the self-sustaining gas discharge in the device of the invention.

The details of the invention, its object and advantages are explained hereunder in greater detail in relation to non-limiting exemplary illustration as per the following accompanying figure:-

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES

Figure 1 is a schematic diagram of an embodiment of the metal nanowire-based device for obtaining gas discharge at low voltage in accordance with the present invention;

Figure 2 illustrates the current voltage characteristics of a device involving plane parallel electrodes and that of the device of the invention with 200 nm copper nanowire based electrodes;

Figure 3 is a scanning electron micrograph of the copper nanowire samples grown within the pores of a porous anodic alumina matrix in according with the invention;

Figure 4 is a current voltage characteristic of a device based on 350 nm copper nanowire electrode;

Figure 5 is a current voltage characteristic of a device based on 40nm copper nanowire electrode;

Figure 6 is a current voltage characteristics of a device based on a 200nm nickel nanowire electrode;

Figure 7 shows the variation of the breakdown current as a function of ambient air pressure. DETAILED DESCRIPTION OF THE FIGURES:

Reference is first invited to accompanying figure 1 which illustrates the metal nanowire based device in accordance with the invention of obtaining gas discharge at low voltage. As shown in the figure the nanowires (1) are embedded in an alumina (AI₂O₃) template (2). The top electrode (3) is evaporated on the back of the alumina template, while the bottom electrode (4) is separated by a spacer (5) preferably 50-100 micrometers from the front of the template. A DC voltage is applied across the electrodes (3,4) and the circuit current is obtained by measuring the voltage drop across a load resistance (R_L) .

Advantageously, as apparent from the above in the embodiment of the device of figure 1, a commercial (Whatman Anodisk) porous anodic alumina (AI₂O₃) template with a uniform distribution of 200nm diameter and 60 micrometer long parallel pores has been used. A metallic (silver) electrode (3) was evaporated on one side of the template and the copper nanowire were electrolytically grown within the pores from an aqueous solution of copper sulphate, boric acid, thiourea and saccharine. Preferably, the said top evaporated silver electrode is further electroplated on top with a copper layer to add rigidity and favour electrical contact. The alumina material thus provides an insulating matrix for a uniform, parallel array of Cu-NWs.

A suitable DC voltage is applied between the back plate of the Cu-NW cathode and a plane copper plate (anode) separated by about 50-100 micrometer by an alumina spacer in a parallel plate geometry. The breakdown voltage was obtained by measuring the current (I) as a function of the applied voltage (V). The onset of gas discharge is indicated by a sharp increase in current over a comparatively narrow voltage range.

Reference is now invited to figure 2 which clearly illustrates that while the breakdown voltage (V_B) is about 750V for a device with plane parallel copper plate (right hand curve), V_B get reduced to less than 10V (left hand curve) when one of the copper plates is replaced by a copper nanowire electrode as described above. Importantly, when the voltage was first applied to the nanowire-based sensor, the observed value of V_B was found to be between 200V and 300V. On repeated cycling, V_B gets systematically reduced to its final value of about 5-lOV. Reference is invited to figure 3, which illustrates the observation using a scanning electron microscope, which shows the effect that repeated voltage cycling helps to sharpen the tips of the nanowire and further enhance local electrical field near the tip. The as-prepared, unsharpened nanorod tip is shown at the top, while the sharpened tips (obtained repeated cycling) is shown below.

It would be apparent from the above illustration that the 200 nm diameter copper nanowire arrays are found to be very effective in reducing the value of V_B. In order to further ascertain the range of NW diameter over which it remains effective further trials with templates of different pore sizes so as to yield NW arrays with average rod diameter of 40 nm and 350nm respectively were carried out.

Figure 4 shows that the copper nanowire (CuNWs) with 350nm diameter did not exhibit electrical discharge below 400V and was therefore found not useful for the present purposes.

Figure 5 illustrates that 40nm diameter Cu NWs achieved reasonable properties but the breakdown voltage could not usually be pushed down below 50V. This is possibly because these nanowires are too thin and get easily destroyed during discharge. Thus a diameter of 200nm was found to be optimum for the purposes of the present invention.

Further trials were repeated with Ni nanowires of 200nm diameter and the results / data obtained are shown in figure 6. It would be clearly apparent that like CuNWs, NiNWs also showed good discharge properties though minimum observed breakdown voltage was found to be somewhat higher (about 50V). Thus, it was found that the desired effect of reduced minimum voltage involving metal nanowires was not limited to copper nanowires only but was also applicable for Ni Nanowires. Moreover, in order to obtain an estimate of the operational life of the nanowire based discharge device of the invention, a typical Cu-NW device (200nm diameter) was operated under constant voltage (50V) mode for over 220 hours. During the entire period of operation the current remained in the 50-100 micro amp range, indicating that the device did not show any degradation in properties during this period. In particular, the operating voltage in the degradation study as above was deliberately chosen to be much higher than the breakdown voltage of about 10V since sample damage, if any, would be higher at higher voltages.

Importantly, the sudden increase in current in the nanowire based devices is indeed due to electrical breakdown and not due to field emission. This is proven by the fact that at a fixed bias voltage (30V) above V_B, the discharge current is seen to decrease with decreasing pressure (shown in figure 7). Had the process been due to field emission, the current would have increased with decreasing pressure.

It would be thus clearly apparent from the above that by selectively using metal nano rod based electrode preferably copper /nickel nano rod based electrode, it is possible to reduce the breakdown voltage in air at atmospheric pressure from about 750V to even lower than 10V. The invention involving metal nanowire based electrode with sharp tip makes advantageous use of nanoscale properties and is based on a parallel array of metal nanowires with sharp metallic tips adapted to provide strong, highly non-linear electric field for the formation of ionization regions in the vicinity of the sharpened tips of the nanowire electrodes and lead to the occurrence of gas discharge at much lower voltages than in conventional electrode. The invention as above is thus expected to have significant influence on cost and energy savings in a variety of devices based on electrical discharge in gases.

Claims

WE CLAIM:

I; An electrode adapted to reduce the breakdown voltage for gas discharge in air to less than 100V at atmospheric pressure comprising:

a metal nanowire based electrode with sharpened tip adapted to provide for strong highly nonlinear electric field which form ionization regions in the proximity of the electrodes.

2. An electrode adapted to reduce the breakdown voltage for gas discharge in air to less than 10V at atmospheric pressure comprising :

a Copper (Cu-NW) nanowire based electrode with sharpened tips adapted to provide for strong highly nonlinear electric field which forms ionization regions in the proximity of the electrodes.

3. An electrode adapted to reduce the breakdown voltage for gas discharge in air to less than 100V at atmospheric pressure comprising :

a Nickel nanowire (Ni-NW) based electrode with sharpened tips adapted to provide for strong highly nonlinear electric field which forms ionization regions in the proximity of the electrodes.

4. An electrode as claimed in any one of claims 1 to 3 wherein the electrode tips are sharpened to the level of a few atoms.

5. An electrode as claimed in any one of claims 1 to 3 wherein the said metal nanowire based electrode selected from copper or nickel nanowire (Cu- NW)/(Ni-NW) based electrode is adapted to achieve a self-sustained

(continuous) discharge current in the range of 100 nanoamps to 100 microamps.

6. An electrode as claimed in any one of claims 1 to 3 wherein the said nanowire diameter is preferably in the range of 250nm to 20nm, more preferably close to 200 nm for discharge at a reasonably low voltage of about 50V.

7. An electrode as claimed in any one of claims 1 to 3 comprising 200nm diameter metal nanowires adapted for continuous electrical discharges up to at least 220 hours at a stretch.

8. An electrode as claimed in any one of claims 1 to 3 comprising a parallel array of said nanowires embedded in an insulating matrix.

9. An electrode as claimed in claim 8 wherein the said insulating matrix comprises of alumina material.

10. An electrode as claimed in claim 9 comprising a porous anodic alumina (Al₂O₃) disk having long parallel pores of uniform diameter wherein the metal nanowires preferably copper nanowires are electrolytically grown from an aqueous solution of copper sulphate, boric acid, thiourea and saccharine.

11. A metal nanowire-based device for obtaining gas discharge in air at low voltage less than 100V at atmospheric pressure comprising

metal Nanowires embedded in an alumina (Al₂O₃) template ;

12. A metal nanowire-based device for obtaining gas discharge in air at low voltage less than 100V at atmospheric pressure comprising metal Nanowires embedded in an alumina (AI₂O₃) template ; top electrode comprising evaporated silver on the back of the alumina template while the bottom electrode is provided separated from the front of the template; and means to apply DC Voltage across the said electrodes for obtaining the gas discharge at low Voltage.

13. A metal nanowire-based device for obtaining gas discharge in air at low voltage less than 10V at atmospheric pressure comprising Copper Nanowires (Cu-NW) embedded in an alumina (Al₂O₃) template; top electrode evaporated on the back of the alumina template while the bottom electrode is provided separated from the front of the template; and means to apply DC Voltage across the said electrodes for obtaining the gas discharge at low Voltage.

14. A metal nanowire-based device for obtaining gas discharge in air at low voltage less than 10V at atmospheric pressure as claimed in anyone of claims 11 to 13 wherein said top electrode comprises evaporated silver further electroplated on top with a copper layer.

15. A metal nanowire-based device as claimed in any one of claims 11 or 13 wherein said

metal nanowire comprises selectively a copper nanowire (Cu-NW) or

Nickle nanowire (Ni-NW) with sharpened tips adapted to provide for strong highly nonlinear electric field which produces ionization regions in the proximity of the electrodes.

16. A metal nanowire-based device as claimed in any one of claims 11 to 13 wherein the said copper nanowire (Cu-NW) or Nickel nanowire (Ni-NW) based electrode is adapted to achieve a self-sustained (continuous) discharge current in the range of 100 nanoamps to 100 microamps.

17. A metal nanowire-based device as claimed in any one of claims 11 to 13wherein the said copper nanowire diameter is in the range of 250nm to 20nm, preferably about 200 nm for discharge at reasonably low voltage of about 50V.

18. A metal ηanowire-based device as claimed in any one of claims 11 to 13 adapted for continuous electrical discharge up to at least 220 hours at a stretch.

19. A metal nanowire-based device as claimed in any one of claims 11 to 13 wherein said bottom electrode is separated by a spacer preferably 50-100 micrometer from the front of the template.

20. A metal nanowire-based device as claimed in any one of claims 11 to 13 wherein the said copper nanowires are provided grown within the pores of a porous anodic alumina matrix.

21. A metal nanowire-based device as claimed in any one of claims 11 to 12 wherein said Copper nanowire (Cu-NW) or Nickel nanowire (Ni-NW) are provided with sharpened tips obtained by repeated discharge cycles causing said sharpening of the tips of the metal nanowires to favour further reduction in the breakage voltage.

22. A method of reducing the breakdown voltage in air at atmospheric pressure to lower than 10V with the value of self-sustained (continuous) discharge current in the range of 100 nanoamps to 100 microamps comprising carrying out the self-sustaining gas discharge using the electrode as claimed in any one of claims 1 to 10.

23. A method of reducing the breakdown voltage in air at atmospheric pressure to lower than 10V with the value of self-sustained (continuous) discharge current in the range of 100 nanoamps to 100 microamps comprising carrying out the self-sustaining gas discharge using the metal nanowire-based device as claimed in any one of claims 11 to 21.

24. An electrode and a metal nanowire-based device adapted to reduce the breakdown voltage in air to less than 10V at atmospheric pressure substantially as herein described and illustrated with reference to the accompanying figures.