Patent Application
20170307561
This application claims the benefit of priority of Singapore patent application No. 10201407136R, filed 31 Oct. 2014, the content of it being hereby incorporated by reference in its entirety for all purposes.
Various embodiments relate to a method of forming an indium oxide nanowire including copper-based dopants, an indium oxide nanowire including copper-based dopants, a method of forming a plurality of nanowires including metal phthalocyanine, a nanowire arrangement and gas sensors.
Detection and monitoring of atmospheric gases and hazardous molecular species are of critical importance for a wide range of work places, for example, from petrochemical companies, shipyards to wastewater treatment plants, underground car parks and for defence and safety aspects. Gas sensors have an estimated market of USD 1.50 billion in 2012. Existing gas sensors in the market are generally based on bulky technologies with several different operation mechanisms, including electrochemical sensors, catalytic sensors, semiconductor sensors and infrared light sensors. Although the bulky sensors are acceptable for gas sensing in their respective fields, there remains a strong demand for improved sensors, with better performances, lower form factor, and lower costs. As such, there is a need for sensors that are compact, slim, light-weight and handy.
According to an embodiment, a method of forming an indium oxide nanowire including copper-based dopants is provided. The method may include providing an indium-based precursor material and a copper-based dopant precursor material, and performing a thermal evaporation process to vapourise the indium-based precursor material and the copper-based dopant precursor material to form an indium oxide nanowire comprising copper-based dopants on a substrate.
According to an embodiment, an indium oxide nanowire including copper-based dopants is provided.
According to an embodiment, a gas sensor is provided. The gas sensor may include at least one indium oxide nanowire including copper-based dopants, and at least one electrode electrically coupled to the at least one indium oxide nanowire.
According to an embodiment, a method of forming a plurality of nanowires including metal phthalocyanine is provided. The method may include providing a solution including a metal phthalocyanine, spin-coating the solution onto a substrate to form a film including the metal phthalocyanine on the substrate, and controlling a heat treatment performed on the film so as to form a plurality of nanowires from the film, the plurality of nanowires comprising the metal phthalocyanine.
According to an embodiment, a nanowire arrangement is provided. The nanowire arrangement may include a substrate, and a film on the substrate, the film including a plurality of metal phthalocyanine nanowires.
According to an embodiment, a gas sensor is provided. The gas sensor may include a film including a plurality of metal phthalocyanine nanowires, and at least one electrode electrically coupled to the plurality of metal phthalocyanine nanowires.
In the drawings, like reference characters generally refer to like parts throughout the different views. The drawings are not necessarily to scale, emphasis instead generally being placed upon illustrating the principles of the invention. In the following description, various embodiments of the invention are described with reference to the following drawings, in which:
The following detailed description refers to the accompanying drawings that show, by way of illustration, specific details and embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.
Embodiments described in the context of one of the methods or devices are analogously valid for the other methods or devices. Similarly, embodiments described in the context of a method are analogously valid for a device, and vice versa.
Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and/or combinations and/or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.
In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.
In the context of various embodiments, the phrase “at least substantially” may include “exactly” and a reasonable variance.
In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance.
As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
As used herein, the phrase of the form of “at least one of A or B” may include A or B or both A and B. Correspondingly, the phrase of the form of “at least one of A or B or C”, or including further listed items, may include any and all combinations of one or more of the associated listed items.
Various embodiments provide miniaturization of sensors based on nanowires and granular network.
Various embodiments may provide nanowire gas sensors that are highly sensitive (detection limit<1 ppm), selective (with engineered materials/structures for targeted gases), fast response (achieving<1 s response), with low power consumption (10−8-10−6 W) and remarkable stability (intrinsic stability of nanomaterials).
Various embodiments may provide nanowire sensors that may allow efficient shrinking of product sizes, from the existing bulky sensors to a slim sensor card size. Various embodiments may further provide a highly integrated portable nanowire sensor card that is promising for commercialization in view of the broad market needs, with improved performances, enhanced portability, slim and compact design, and lower costs.
At 102, an indium (In)-based precursor material and a copper (Cu)-based dopant precursor material are provided.
At 104, a thermal evaporation process is performed to vapourise the indium-based precursor material and the copper-based dopant precursor material to form an indium oxide (In2O3) nanowire including copper (Cu)-based dopants on a substrate (e.g., a silicon (Si) substrate). This may mean that the indium oxide nanowire may be doped with copper-based dopants, or in other words, the indium oxide nanowire may be copper-doped.
In various embodiments, at 104, the indium-based precursor material and the copper-based dopant precursor material may be heated to generate respective vapours therefrom, where the respective vapours may be deposited on the substrate to form an indium oxide nanowire including copper-based dopants on the substrate. The respective vapours generated from the indium-based precursor material and the copper-based dopant precursor material may interact or react with each other prior to deposition on the substrate or prior to forming the indium oxide nanowire including the copper-based dopants.
In various embodiments, the indium-based precursor material and the copper-based dopant precursor material may be provided in or into a quartz tube, e.g., towards a sealed end of the quartz tube. A substrate may also be provided in the quartz tube, e.g., towards an open end of the quartz tube. The open end and the sealed end of the quartz tube may be opposite ends. At 104, the thermal evaporation process may be performed in a furnace, for example, a (horizontal) tube furnace. This may mean that the quartz tube having the indium-based precursor material, the copper-based dopant precursor material and the substrate may be positioned in the (tube) furnace.
In the context of various embodiments, the thermal evaporation process may be a vapour deposition process, e.g., a chemical vapour deposition (CVD) process.
In the context of various embodiments, the term “precursor material” may mean a starting material.
In various embodiments, the indium-based precursor material and the copper-based dopant precursor material may be provided at a molar ratio between about 3:1 and about 20:1, for example, between about 3:1 and about 10:1, between about 3:1 and about 5:1, between about 5:1 and about 20:1, or between about 5:1 and about 10:1, e.g., about 10:1. This may mean that the molar ratio of indium-based precursor material: copper-based dopant precursor material may be in a range of about 3:1 to about 20:1
In various embodiments, at 104, the thermal evaporation process may be performed at a (predetermined) temperature between about 700° C. and about 1000° C., for example, between about 700° C. and about 900° C., between about 700° C. and about 800° C., or between about 800° C. and about 1000° C., e.g., about 875° C. As a non-limiting example, the central temperature of the (tube) furnace (or the temperature at the central part of the (tube) furnace, for example, where the indium-based precursor material and the copper-based dopant precursor material may be positioned), may be increased at a ramping rate of about 15° C./min from room temperature (e.g., about 25° C.) to the (predetermined) temperature (e.g., about 875° C.).
In various embodiments, at 104, the thermal evaporation process may be performed for a (predetermined) duration of between about 10 minutes and about 300 minutes, for example, between about 10 minutes and about 200 minutes, between about 10 minutes and about 100 minutes, between about 10 minutes and about 50 minutes, between about 100 minutes and about 300 minutes, or between about 100 minutes and about 200 minutes, e.g., about 60 minutes. This may mean that the (predetermined) temperature may be maintained for the (predetermined) duration.
In various embodiments, at 104, the substrate may be maintained at a (predetermined) temperature between about 400° C. and about 500° C. during the thermal evaporation process, for example, between about 400° C. and about 450° C. or between about 450° C. and about 500° C. As a non-limiting example, while the central temperature of the (tube) furnace (or the temperature at the central part of the (tube) furnace, for example, where the indium-based precursor material and the copper-based dopant precursor material may be positioned), may be at a (predetermined) temperature between about 700° C. and about 1000° C., the substrate may be positioned at a portion of the (tube) furnace where the temperature may be at about 400° C.-500° C.
In various embodiments, at 104, the thermal evaporation process may be performed in an at least substantially vacuum environment. The thermal evaporation process may be performed at a (vacuum) pressure of between about 0.01 mbar and about 5 mbar, for example, between about 0.01 mbar and about 3 mbar, between about 0.01 mbar and about 1 mbar, between about 0.01 mbar and about 0.1 mbar, between about 0.1 mbar and about 5 mbar, between about 1 mbar and about 5 mbar, or between about 0.1 mbar and about 1 mbar. For example, the tube furnace where the thermal evaporation process may be carried out may be sealed and vacuumed to a predetermined (vacuum) pressure, for example, between about 0.01 mbar and about 5 mbar, e.g., a pressure of about 0.01 mbar.
In various embodiments, the method may further include mixing the indium-based precursor material with the copper-based dopant precursor material.
In various embodiments, a carbon-based material may be mixed with the mixture of the indium-based precursor material and the copper-based dopant precursor material. The carbon-based material may be provided at a 1:1 molar ratio with the mixture of the indium-based precursor material and the copper-based dopant precursor material. The carbon-based material may be carbon black. The carbon-based material or the carbon black may be provided to assist in the carbothermal reaction or combustion of the reaction.
In various embodiments, the method may further include introducing an inert gas during the thermal evaporation process. The inert gas may carry or flow the respective vapours corresponding to the indium-based precursor material and the copper-based dopant precursor material resulting from the thermal evaporation process. In this way, the inert gas may act as a carrier gas. In various embodiments, the inert gas may include at least one of argon (Ar) or nitrogen (N2), optionally with presence of oxygen (O2) included with the inert gas. For example, while optional, it may be preferable to include O2 to tailor the stoichiometry of In2O3. The introduction of oxygen may reduce oxygen deficient sites in the In2O3 nanowires.
In various embodiments, the ratio of the inert gas to oxygen may be in the range of about 100:1 to about 5:1, for example, between about 50:1 and about 5:1, between about 10:1 and about 5:1, between about 100:1 and about 50:1, or between about 50:1 and about 20:1.
In various embodiments, the inert gas (and the oxygen gas) may be introduced at a flow rate of between about 1 sccm and about 1000 sccm, for example, between about 1 sccm and about 500 sccm, between about 1 sccm and about 100 sccm, between about 1 sccm and about 50 sccm, between about 50 sccm and about 1000 sccm, or between about 50 sccm and about 100 sccm, e.g., about 50 sccm.
In the context of various embodiments, the indium-based precursor material may include at least one of indium oxide, indium trichloride(s), indium nitrate(s), indium acetate, indium sulfide, indium sulfate or indium hydroxide(s), for example, an indium oxide (In2O3)-based precursor material, e.g., indium oxide (In2O3) powder.
In the context of various embodiments, the copper-based dopant precursor material may include at least one of copper oxide, cuprous oxide, cupric oxide, cupric chloride, copper oxychloride, cuprous chloride, cupric nitrate, copper nahpthenate, copper acetate or copper sulphate, for example, copper oxide (CuO) powder.
In various embodiments, the method may further include coating the substrate with a metal. The metal may act as a catalyst for the formation of the indium oxide nanowire including the copper-based dopants. The metal or the catalyst may include at least one of gold (Au) silver (Ag), nickel (Ni), platinum (Pt), palladium (Pd), zinc (Zn), molybdenum (Mo), tin (Sn), manganese (Mn), germanium (Ge), or bismuth (Bi). However, it should be appreciated that other metal or material may be used as the catalyst.
In various embodiments, the copper-based dopants 114 may include copper dopant atoms 114. It should be appreciated that in various embodiments, in addition to the copper-based dopants 114 or in the alternative, other dopants such as tin (Sn), iron (Fe), cobalt (Co), magnesium (Mg), aluminum (Al), zinc (Zn), germanium (Ge), bismuth (Bi), lead (Pb), platinum (Pt), palladium (Pd), arsenic (As), selenium (Se), or gallium (Ga), may also be employed.
In various embodiments, a diameter, d, of the indium oxide nanowire 112 may be between about 50 nm and about 300 nm, for example, between about 50 nm and about 150 nm, between about 50 nm and about 100 nm, between about 100 nm and about 150 nm, between about 70 nm and about 120 nm, or between 150 nm and about 300 nm.
In various embodiments, a length, 1 g, of the indium oxide nanowire 112 may be between about 0.5 μm and about 10 μm, for example, between about 0.5 μm and about 5 μm, between about 0.5 μm and about 2 μm, between about 1 μm and about 10 μm, between about 5 μm and about 10 μm, or between about 2 μm and about 5 μm.
The at least one electrode 126 may serve as an electrical contact for the at least one indium oxide nanowire 122. The at least one electrode 126 may be provided on or over the at least one indium oxide nanowire 122.
In various embodiments, the at least one indium oxide nanowire 122 including the copper-based dopants 124 may act as a gas sensing element. This may mean that the at least one indium oxide nanowire 122 including the copper-based dopants 124 may be used for sensing gas. As a non-limiting example, at least one parameter (e.g., conductivity or resistivity) of the at least one indium oxide nanowire 122 may change in response to a gas interacting with the at least one indium oxide nanowire 122. The gas may contact the at least one indium oxide nanowire 122. For example, molecules of the gas may be adsorbed in or on the at least one indium oxide nanowire 122.
In various embodiments, the gas sensor 120 may further include a substrate 128 (shown as a dashed box, not in scale relative to the nanowire 122), wherein the at least one indium oxide nanowire 122 may be arranged on the substrate 128. The substrate 128 may include silicon (Si). In various embodiments, the substrate may include or consist of a dielectric (for example, silicon dioxide, oxynitride(s), nitride(s), rare earth oxide(s), or transition metal oxide(s)) deposited on a semiconductor material such as silicon (Si), germanium (Ge), or silicon on insulator (SOI). In various embodiments, for low temperature processes, the substrate 128 may be or may include a polymeric substrate such as polyester, polyethylene terephthalate, polycarbonate, polyimide, or polyether ether ketone.
In various embodiments, the gas sensor 120 may include a single indium oxide nanowire 122 including the copper-based dopants 124.
In various embodiments, the gas sensor 120 may include a plurality of indium oxide nanowires 122, each indium oxide nanowire 122 of the plurality of indium oxide nanowires 122 including the copper-based dopants 124. This may mean that each indium oxide nanowire 122 may be copper-doped. The plurality or array of indium oxide nanowires 122 may define a nanowire network.
In various embodiments, the plurality of indium oxide nanowires 122 may be spaced apart from each other.
In various embodiments, the nanowires 122 may be core-shell nanowires, or nanowires with one or more particulates, or nanowires with one or more chemical coatings.
In various embodiments, adjacent indium oxide nanowires 122 of the plurality of indium oxide nanowires 122 may be in contact with each other. In this way, the adjacent indium oxide nanowires 122 may define an interface, e.g., a nanowire-nanowire interface.
In various embodiments, the plurality of indium oxide nanowires 122 may be at least substantially parallel to each other.
In various embodiments, the gas sensor 120 may include two electrodes (one of which may be electrode 126) electrically coupled to the at least one indium oxide nanowire 122, wherein the two electrodes may be arranged spaced apart from each other. The two electrodes may be provided on opposite ends of the at least one indium oxide nanowire 122. In various embodiments, the two electrodes may, for example, define source and drain electrodes respectively. In this way, the indium oxide nanowire 122 and the two electrodes may define a nanowire transistor based on transistor configuration (e.g., the gas sensor 120 may be a transistor type gas sensor). This may mean that the gas sensor 120 may be a copper-doped indium oxide nanowire transistor (e.g., field effect transistor, FET)-based gas sensor.
In various embodiments, the at least one electrode 126 may include a metal. The at least one electrode may include at least one of titanium (Ti) or gold (Au).
In various embodiments, the gas sensor 120 may further include a display. The display may be a touch display or a touch screen display, meaning that the display (or screen) may be responsive to the touch of a user.
In various embodiments, the gas sensor 120 may further include an audio output means (e.g., for outputting an alarm). For example, an alarm may be provided or activated when an amount of a predetermined gas sensed by the gas sensor 120 exceeds a predetermined threshold level.
In various embodiments, the gas sensor 120 may further include a power source (e.g., a battery such as a lithium battery). The power source may be a rechargeable power source.
In various embodiments, the gas sensor 120 may be a portable gas sensor.
In various embodiments, the gas sensor 120 may be a card-sized gas sensor. This may mean that the gas sensor 120 may be configured or arranged in the form or size of a card (e.g., a credit card).
In the context of various embodiments, the gas sensor 120 may be a resistor type sensor. The resistivity of the at least one indium oxide nanowire 122 may be modulated in response to an interaction of the at least one indium oxide nanowire 122 with a gas which the gas sensor 120 may be exposed to and which may be sensitive to.
In the context of various embodiments, the gas sensor 120 may be employed to sense (or detect) gases including but not limited to methane (CH4), carbon monoxide (CO), oxygen (O2), nitrogen dioxide (NO2), hydrogen sulfide (H2S), and ammonia (NH3), and volatile organic compounds (VOCs) including but not limited to isobutylene, perchloroethylene, formaldehyde, benzene, methylene chloride etc.
Various embodiments may also provide a device including at least one indium oxide (In2O3) nanowire including copper (Cu)-based dopants, and at least one electrode electrically coupled to the at least one indium oxide nanowire. The elements or components of the device may be as described in the context of the gas sensor 120.
In the context of various embodiments, the term “copper-based dopants” refer to copper-based doping members or copper-based impurities or copper-based doping atoms that may be present. This may mean that the term “copper-based dopants” may include dopants or doping atoms which may be of the same (copper-based) species.
At 132, a solution including a metal phthalocyanine is provided.
At 134, the solution is spin-coated onto a substrate to form a film including the metal phthalocyanine on the substrate.
At 136, a heat treatment performed on the film may be controlled so as to form a plurality of nanowires from the film, the plurality of nanowires including (or consisting of) the metal phthalocyanine. This may mean performing a heat treatment on the film and controlling the heat treatment, for example, in terms of at least one associated parameter such as temperature and/or duration of the heat treatment, so as to enable formation of the plurality of nanowires including the metal phthalocyanine (or plurality of metal phthalocyanine nanowires).
The plurality of metal phthalocyanine nanowires that may be formed may originate from the film.
The plurality of metal phthalocyanine nanowires may be formed on the substrate. The substrate may be heated, for example, to a predetermined temperature, to form the plurality of metal phthalocyanine nanowires on the substrate.
In various embodiments, at 134, spin-coating the solution onto the substrate may be carried out at room temperature (e.g., 25° C.). Spin-coating the solution onto the substrate may be carried out in air (e.g., ambient atmosphere or environment).
In various embodiments, at 134, the solution may be spin-coated onto the substrate at a (spin) rate or spin speed of between about 100 rpm and about 5000 rpm, for example, between about 100 rpm and about 2500 rpm, between about 100 rpm and about 1000 rpm, between about 2500 rpm and about 5000 rpm, between about 500 rpm and about 2500 rpm, e.g., about 2500 rpm. The term “rpm” means revolutions per minute.
In various embodiments, at 134, the solution may be spin-coated onto the substrate for a duration of between about 5 seconds and about 300 seconds, for example, between about 5 seconds and about 100 seconds, between about 5 seconds and about 30 seconds, between about 30 seconds and about 300 seconds, between about 100 seconds and about 300 seconds, or between about 50 seconds and about 100 seconds, e.g., about 30 seconds.
In various embodiments, at 136, the heat treatment may be performed in air (e.g., ambient atmosphere or environment).
In various embodiments, at 136, controlling a heat treatment performed on the film may include performing the heat treatment at a temperature of between about 50° C. and about 200° C., for example, between about 50° C. and about 150° C., between about 50° C. and about 100° C., or between about 100° C. and about 200° C.
In various embodiments, at 136, controlling a heat treatment performed on the film may include performing the heat treatment for a duration of at least 10 minutes (i.e., ≧10 minutes), for example, ≧20 minutes, ≧30 minutes, ≧40 minutes, ≧50 minutes or ≧60 minutes.
In various embodiments, at 136, controlling a heat treatment performed on the film may include performing the heat treatment at a temperature of about 100° C. for a duration of about 10 minutes. Subsequently, or thereafter, the heat treatment may be further performed at a temperature of about 140° C. for a duration of about 60 minutes. This may mean that the heat treatment may include 2 stages or processes, for example, at a temperature of about 100° C. for a duration of about 10 minutes, and following that, at a temperature of about 140° C. for a duration of about 60 minutes.
In various embodiments, the method may further include stirring the solution. The solution may be stirred at a (stiffing) rate of between about 100 rpm and about 2000 rpm, for example, between about 100 rpm and about 1000 rpm, between about 100 rpm and about 500 rpm, between about 400 rpm and about 2000 rpm, between about 400 rpm and about 1000 rpm, or between about 1000 rpm and about 2000 rpm, e.g., about 400 rpm.
In various embodiments, at 132, a precursor material including the metal phthalocyanine (e.g., a metal phthalocyanine powder) may be dissolved in at least one solvent to provide the solution. The at least one solvent may include (a mixture of) chlorobenzene and trifluoroacetic acid.
In various embodiments, a concentration of the metal phthalocyanine in the solution may be between about 0.01 wt % and about 20 wt %, for example, between about 0.01 wt % and about 10 wt %, between about 0.01 wt % and about 5 wt %, between about 0.01 wt % and about 1 wt %, between about 0.01 wt % and about 0.5 wt %, between about 0.5 wt % and about 20 wt %, between about 1 wt % and about 20 wt %, or between about 0.5 wt % and about 5 wt %, e.g., about 0.5 wt %.
In various embodiments, the method may further include forming at least one electrode on the substrate prior to spin-coating the solution onto the substrate. This may mean that the solution may be spin-coated onto the at least one electrode. In this way, at least part of the film may be formed on the at least one electrode. The at least one electrode may include at least one of titanium (Ti) or gold (Au).
In various embodiments, a metal layer may be formed on the substrate, and the metal layer may be patterned (e.g., by lithography) to form the at least one electrode.
In various embodiments, at 136, controlling the heat treatment performed on the film may include heating the at least one electrode, for example, based on the parameters (e.g., temperature and/or duration) associated with the heat treatment as described above.
In various embodiments, the plurality of nanowires may be comprised in the film.
In various embodiments, a thickness of the film may be between about 50 nm and about 1000 nm, for example between about 50 nm and about 500 nm, between about 50 nm and about 200 nm, between about 200 nm and about 1000 nm, between about 100 nm and about 500 nm, e.g., about 200 nm.
In the context of various embodiments, the substrate may include a polymer substrate or a plastic substrate or a glass substrate. The substrate may be flexible, meaning that the substrate may be made of a flexible material.
In the context of various embodiments, the metal phthalocyanine may include (or consists of) copper phthalocyanine (CuPc). This may mean that each metal phthalocyanine nanowire of the plurality of metal phthalocyanine nanowires may include (or consist of) copper phthalocyanine (CuPc). In the context of various embodiments, other metals such as at least one of nickel (Ni), iron (Fe), zinc (Zn), magnesium (Mg), or cobalt (Co) may also be employed to form the metal phthalocyanine, e.g., nickel phthalocyanine, iron phthalocyanine, zinc phthalocyanine, magnesium phthalocyanine or cobalt phthalocyanine.
The film 144 may include the metal phthalocyanine of the plurality of metal phthalocyanine nanowires 146.
In various embodiments, the plurality of metal phthalocyanine nanowires 146 may include or consist of the metal phthalocyanine.
In various embodiments, the plurality of metal phthalocyanine nanowires 146 may be interconnected to each other (or intertwined with each other).
In various embodiments, a thickness of the film 144 may be between about 50 nm and about 1000 nm, for example, between about 50 nm and about 500 nm, between about 50 nm and about 200 nm, between about 200 nm and about 1000 nm, or between about 50 nm and about 500 nm, e.g., about 200 nm.
In various embodiments, the film 144 may be spin-coated on the substrate 142, meaning a spin-coated film.
In the context of various embodiments, the substrate 142 may include a polymer substrate or a plastic substrate or a glass substrate. The substrate may be flexible, meaning that the substrate may be made of a flexible material.
In the context of various embodiments, the plurality of metal phthalocyanine nanowires 146 may include (or consist of) copper phthalocyanine (CuPc). This may mean that each metal phthalocyanine nanowire 146 of the plurality of metal phthalocyanine nanowires 146 may include (or consist of) copper phthalocyanine (CuPc). In the context of various embodiments, other metals such as at least one of nickel (Ni), iron (Fe), zinc (Zn), magnesium (Mg), or cobalt (Co) may also be employed to form the plurality of metal phthalocyanine nanowires 146, e.g., each metal phthalocyanine nanowire 146 may include (or consist of) nickel phthalocyanine, iron phthalocyanine, zinc phthalocyanine, magnesium phthalocyanine or cobalt phthalocyanine.
In the context of various embodiments, an aspect ratio of each metal phthalocyanine nanowire 146 of the plurality of metal phthalocyanine nanowires 146 may be between about 5 and about 100, for example, between about 5 and about 50, between about 5 and about 20, between about 5 and about 10, between about 20 and about 100, between about 10 and about 50.
In the context of various embodiments, a diameter of each metal phthalocyanine nanowire 146 of the plurality of metal phthalocyanine nanowires 146 may be between about 50 nm and about 150 nm, for example, between about 50 nm and about 100 nm, between about 100 nm and about 150 nm, or between about 70 nm and about 120 nm.
In the context of various embodiments, a length of each metal phthalocyanine nanowire 146 of the plurality of metal phthalocyanine nanowires 146 may be between about 50 nm (0.05 μm) and about 20 μm, for example, between about 50 nm and about 10 μm, between about 50 nm and about 5 μm, between about 50 nm and about 1 μm, between about 1 μm and about 20 μm, between about 1 μm and about 10 μm, or between about 10 μm and about 20 μm.
In other words, a gas sensor 150 may be provided, having a film 154 with a plurality of metal phthalocyanine nanowires 156 comprised in the film 154. This may mean that the gas sensor 150 may be a nanowire gas sensor. The plurality of metal phthalocyanine nanowires 156 may include or consist of the metal phthalocyanine. The plurality of metal phthalocyanine nanowires 156 may form a metal phthalocyanine nanowire network. The film 154 may include the metal phthalocyanine of the plurality of metal phthalocyanine nanowires 156. In various embodiments, the plurality of metal phthalocyanine nanowires 156 may be as described in the context of the plurality of metal phthalocyanine nanowires 146.
The gas sensor 150 may further include at least one electrode 158 electrically coupled to the plurality of metal phthalocyanine nanowires 156. The at least one electrode 158 may serve as an electrical contact for the plurality of metal phthalocyanine nanowires 156. The at least one electrode 158 may be provided below the plurality of metal phthalocyanine nanowires 156. The at least one electrode 158 may be electrically coupled to the film 154.
In various embodiments, the plurality of metal phthalocyanine nanowires 156 may act as gas sensing elements. This may mean that the plurality of metal phthalocyanine nanowires 156 may be used for sensing gas. As a non-limiting example, at least one parameter (e.g., conductivity or resistivity) of the plurality of metal phthalocyanine nanowires 156 or of each metal phthalocyanine nanowire 156 may change in response to a gas interacting with the plurality of metal phthalocyanine nanowires 156. The gas may contact the plurality of metal phthalocyanine nanowires 156. For example, molecules of the gas may be adsorbed in or on the plurality of metal phthalocyanine nanowires 156.
The gas sensor 150 may include a substrate 152 (shown as a dashed box, not in scale relative to the film 154), the film 154 being formed on the substrate. The plurality of metal phthalocyanine nanowires 156 may be formed or arranged on the substrate 152.
In various embodiments, the film 154 may be spin-coated on the substrate 152, meaning a spin-coated film.
In the context of various embodiments, the substrate 152 may include a polymer substrate or a plastic substrate or a glass substrate. The substrate may be flexible, meaning that the substrate may be made of a flexible material.
In various embodiments, a thickness of the film 154 may be between about 20 nm and about 1000 nm, for example between about 20 nm and about 500 nm, between about 20 nm and about 200 nm, between about 200 nm and about 1000 nm, between about 100 nm and about 500 nm, or between about 50 nm and about 500 nm, e.g., about 200 nm.
In various embodiments, the plurality of metal phthalocyanine nanowires 156 may be interconnected to each other (or intertwined with each other).
In the context of various embodiments, an aspect ratio of each metal phthalocyanine nanowire 156 of the plurality of metal phthalocyanine nanowires 156 may be between about 5 and about 100, for example, between about 5 and about 50, between about 5 and about 20, between about 5 and about 10, between about 20 and about 100, between about 10 and about 50.
In the context of various embodiments, a diameter of each metal phthalocyanine nanowire 156 of the plurality of metal phthalocyanine nanowires 156 may be between about 50 nm and about 150 nm, for example, between about 50 nm and about 100 nm, between about 100 nm and about 150 nm, or between about 70 nm and about 120 nm.
In the context of various embodiments, a length of each metal phthalocyanine nanowire 156 of the plurality of metal phthalocyanine nanowires 156 may be between about 50 nm (0.05 μm) and about 20 μm, for example, between about 50 nm and about 10 μm, between about 50 nm and about 5 μm, between about 50 nm and about 1 μm, between about 1 μm and about 20 μm, between about 1 μm and about 10 μm, or between about 10 μm and about 20 μm.
In the context of various embodiments, the plurality of metal phthalocyanine nanowires 156 may include (or consist of) copper phthalocyanine (CuPc). This may mean that each metal phthalocyanine nanowire 156 of the plurality of metal phthalocyanine nanowires 156 may include (or consist of) copper phthalocyanine (CuPc). In the context of various embodiments, other metals such as at least one of nickel (Ni), iron (Fe), zinc (Zn), magnesium (Mg), or cobalt (Co) may also be employed to form the plurality of metal phthalocyanine nanowires 156, e.g., each metal phthalocyanine nanowire 156 may include (or consist of) nickel phthalocyanine, iron phthalocyanine, zinc phthalocyanine, magnesium phthalocyanine or cobalt phthalocyanine.
In various embodiments, the at least one electrode 158 may include a metal. The at least one electrode may include at least one of titanium (Ti) or gold (Au).
In various embodiments, the gas sensor 150 may further include a display. The display may be a touch display or a touch screen display, meaning that the display (or screen) may be responsive to the touch of a user.
In various embodiments, the gas sensor 150 may further include an audio output means (e.g., for outputting an alarm). For example, an alarm may be provided or activated when an amount of a predetermined gas sensed by the gas sensor 150 exceeds a predetermined threshold level.
In various embodiments, the gas sensor 150 may further include a power source (e.g., a battery such as a lithium battery). The power source may be a rechargeable power source.
In various embodiments, the gas sensor 150 may be a portable gas sensor.
In various embodiments, the gas sensor 150 may be a card-sized gas sensor. This may mean that the gas sensor 150 may be configured or arranged in the form or size of a card (e.g., a credit card).
In the context of various embodiments, the gas sensor 150 may be a resistor type sensor. The resistivity of the plurality of metal phthalocyanine nanowires 156 or of each metal phthalocyanine nanowire 156 may be modulated in response to an interaction of the plurality of metal phthalocyanine nanowires 156 with a gas which the gas sensor 150 may be exposed to and which may be sensitive to.
In the context of various embodiments, the gas sensor 150 may be employed to sense (or detect) gases including but not limited to methane (CH4), carbon monoxide (CO), oxygen (O2), nitrogen dioxide (NO2), hydrogen sulfide (H2S), and ammonia (NH3), and volatile organic compounds (VOCs) including but not limited to isobutylene.
Various embodiments may also provide a device having a film including a plurality of metal phthalocyanine nanowires, and at least one electrode electrically coupled to the plurality of metal phthalocyanine nanowires. The elements or components of the device may be as described in the context of the gas sensor 150.
In the context of various embodiments, the term “nanowire” may mean a nanostructure extending, for example, in a longitudinal direction, with at least one dimension in the order of nanometers, and may be used interchangeably with the terms “nanorod”, “nanopillar”, “nanocolumn”, “nanotube” and the likes.
While the methods described above are illustrated and described as a series of steps or events, it will be appreciated that any ordering of such steps or events are not to be interpreted in a limiting sense. For example, some steps may occur in different orders and/or concurently with other steps or events apart from those illustrated and/or described herein. In addition, not all illustrated steps may be required to implement one or more aspects or embodiments described herein. Also, one or more of the steps depicted herein may be carried out in one or more separate acts and/or phases.
There may be several target gases (CH4, CO, O2, H2S, with >80% share of gas sensor market) or NH3, and other toxic and hazardous species, volatile organic compounds (VOCs) such as isobutylene that may be of key interests. The microscale sensors in accordance with various embodiments may be based on nanowires as the sensing elements. A scanning electron microscope (SEM) image 200 of synthesized indium oxide (In2O3) nanowires 202 is shown in
Doping of nanowires may play an important role in sensing performance For example, copper-indium oxide (Cu—In2O3) nanowires (NWs) may display enhanced sensor response with improved response and recovery time compared to undoped In2O3 nanowires-field effect transistors (NW-FETs) for carbon monoxide (CO) sensing operated at room temperature.
Doping in metal oxide NW may cause defects such as oxygen vacancies, metal interstitials, surface defects, etc. These defects may act as preferential adsorption sites for gas molecules and thus may play a vital role in the sensing of gas (e.g., CO gas) at room temperature by enhancing adsorption. Enhanced adsorptions of gas molecules may change the electrical conductivity and hence the position of a Fermi level in the band gap of oxide semiconductors. The modulation of Schottky barrier height (SBH) after the exposure of testing gas molecules may equally contribute to the electrical response of nano-sensors. For example, the higher the SBH changes after the exposure, the faster the sensor response may be.
In various embodiments, the copper-doped indium oxide (Cu doped In2O3) nanowires may be synthesized via the following method:—
The nanowires may be configured in a device having a network of nanowires based on resistive modulation or a single nanowire transistor based on transistor configuration (for example, as shown in
When the nanowire device 400 is exposed to a certain gas, e.g., carbon monoxide (CO) 408, the gas molecules 408 contacting the nanowire surface may exchange electrons with the nanowire 402, that is, undergoing chemical reactions (e.g., oxidation of CO 408 to CO2 410), and thus the current levels in the device 400 may change. Consequently, the presence of certain gases may be reflected on the external monitoring system via current differences.
Sensitivity may be the lower limit of the gas concentrations that a sensor may detect. A high sensitivity may be required to monitor the contents of hazardous gases and alert the users. However, existing gas sensors may not detect gas concentrations down to few ppm levels, due to an intrinsic limit of bulk technologies. For example, the detection limit of CO gas may be as high as 30 ppm (TGS2442, Figaro Engineering Inc., Japan). A typical response behaviour of commercial CO sensor response and reset time may be about 200 seconds and about 600 seconds, respectively. In contrast, the CO gas sensor based on nanowires, in accordance with various embodiments, may show a significantly faster responsive behavior, with response/reset time of about 20/50 seconds, respectively.
The In2O3 nanowire network device of various embodiments may be used for two-terminal sensors detection of methane (CH4) gas, which may exhibit a significantly fast response and reset time as shown in the plot 660 of
The underlying mechanism may be that conductance of the nanowire network device may be determined by the nanowire-nanowire interface. The intrinsic depletion layer on the nanowire surface may construct Schottky barrier-like conduction barriers in the network. The barrier may be rapidly modulated when exposed to gases, thus leading to a fast responsive behavior. The mechanism may be readily adopted to achieve fast response in other nanowire network gas sensors.
Testing conditions and the results obtained may be as shown in Table I.
The CH4 concentration may be about 2.5 vol %. Testing may be performed at room temperature of about 25° C. and no heating may be required. The In2O3 nanowires may respond to the CH4 gas with a response time of about 47 s and a reset time of about 0.8 s. Industrial testing is typically done using combustion wire (platinum (Pt) wire) to catalytically burn the CH4 at a high temperature and hence enable efficient detection. The testing using the device/sensor of various embodiments may be performed at room temperature in air. That is, the sensors may be exposed in air before introducing the CH4 gas. The current change may be induced by the change of oxygen environment instead of any reactions with CH4, since CH4 is rather inert at room temperature.
In various embodiments, methods to tune the sensitivity and selectivity may include the doping of nanowires, surface functionalization, alloying of nanowires and nanoparticles decorations onto the nanowires or core-shell nanostructures.
Various embodiments may provide a polymer nanowire network, e.g., phthalocyanine (e.g., copper phthalocyanine; CuPc), polypyrrole and polyaniline, which may also be used to establish gas sensing performance
Instead of using the complex evaporation setup or the vapor phase deposition process to form CuPc, which may require a high temperature up to 500° C. or above, an exemplary spin coating method, as explained below, may be used in various embodiments:—
Compared to the thick film CuPc device, a thin film 200 nm device may show a higher sensitivity. However,no significant improvement to the change in conductivity with increasing concentration of NO2 gas may be observed, as shown in the sensitivity versus time plots 860, 870, 880 of
The response and the recovery time of the thin film device may be significantly faster than those of the thick film device at about 5 s. This may be due to a higher number of defects found on the thin film of the device, where the thin film may be lesser condensed (e.g., as compared to the thick film device). Therefore, any addition of charge carrier may contribute to a larger change in conductivity as compared to a thicker film with already a better conductivity.
Based on the successful fabrication and testing of key sensing component, the components may be integrated with other functional components into a portable sensor card.
While the invention has been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10201407136R | Oct 2014 | SG | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SG2015/050425 | 11/2/2015 | WO | 00 |
