Gas sensor and gas sensor array

1. A gas sensor comprising counter electrodes and a selenium nanowire disposed between the counter electrodes, which sensor shows a change in a photoelectric current I ph associated with adsorption of a gas to the selenium nanowire,

wherein the photoelectric current I ph is generated by irradiation of light on the selenium nanowire with a voltage applied to the counter electrodes,

wherein the selenium nanowire is in a state where light can be irradiated thereon, and

wherein each of the counter electrodes has an inner surface, and an insulating layer is provided on the inner surface of one of the counter electrodes.

2. The gas sensor according to claim 1 , wherein respective wires in the selenium nanowire are bonded with a transparent insulating resin binder.

3. The gas sensor according to claim 1 , wherein at least one of the counter electrodes is a transparent electrode.

4. The gas sensor according to claim 3 , wherein the transparent electrode has an inner surface, and the transparent electrode comprises a transparent insulating layer, as the insulating layer, provided on the inner surface thereof.

5. The gas sensor according to claim 3 , wherein one of the counter electrodes is a transparent electrode and the insulating layer is provided on the inner surface of the transparent electrode, and the other counter electrode comprises a conductive layer provided on the inner surface of the other counter electrode.

6. The gas sensor according to claim 3 , wherein the at least one transparent electrode has an outside surface, the selenium wire has an energy near a bandgap of the selenium wire, and the gas sensor has a light source arranged to irradiate light on the outside surface of the transparent electrode that emits light with energy which is not less than the energy near the bandgap of the selenium nanowire.

7. The gas sensor according to claim 1 , wherein a conductive layer is provided on the inner surface of the other counter electrode.

8. The gas sensor according to claim 1 , wherein the change in the electric current is a change in the electric current intensity.

9. The gas sensor according to claim 1 , wherein the counter electrodes applied with a voltage have an electric field intensity (absolute value) of 3-34 V/mm.

10. A gas sensor comprising counter electrodes and a selenium nanowire disposed between the counter electrodes, which sensor shows a change in a photoelectric current I ph associated with adsorption of a gas to the selenium nanowire,

wherein the photoelectric current I ph is generated by irradiation of light on the selenium nanowire with a voltage applied to the counter electrodes,

wherein the selenium nanowire is in a state where light can be irradiated thereon,

wherein the distal ends of two conductor wires face each other and the distal ends of the two conductor wires form the counter electrodes, and the selenium nanowires are disposed between the tips of the two conductor wires, and

wherein an insulating layer is provided on the tip of one of the two conductor wires.

11. The gas sensor according to claim 10 , wherein the selenium wire has an energy near a bandgap of the selenium wire, and the tips of the two conductor wires are led to face each other at a predetermined portion of a transparent insulating member containing a light source that emits light having energy which is not less than the energy near the bandgap of the selenium nanowire.

12. A gas sensor array comprising a plurality of gas sensors, which are arranged along a gas flow direction of a gas flow path through which a gas to be detected flows,

wherein each of the plurality of gas sensors comprises counter electrodes and a selenium nanowire disposed between the counter electrodes, which sensors show a change in a photoelectric current I ph associated with adsorption of a gas to the selenium nanowire,

wherein the photoelectric current I ph is generated by irradiation of light on the selenium nanowire with a voltage applied to the counter electrodes,

wherein the selenium nanowire is in a state where light can be irradiated thereon, and

wherein each of the counter electrodes has an inner surface, and an insulating layer is provided on the inner surface of one of the counter electrodes.

13. The gas sensor array according to claim 12 , comprising a single electrode arranged such that its axis is parallel to the gas flow direction of the gas flow path through which the gas to be detected flows, wherein the single electrode is a common electrode used as one of two opposing electrodes of individual gas sensors in the plurality of gas sensors.

14. The gas sensor array according to claim 13 , wherein the single electrode is a transparent electrode.

15. The gas sensor array according to claim 12 , wherein the gas to be detected that flows in the gas flow path comes into contact, under a constant voltage, with selenium nanowires of plural gas sensors to generate time-change spectrum of photoelectric current intensity in each gas sensor, and a delay time between different sensors is detected.

16. A gas analysis system comprising the gas sensor array according to claim 12 , and a calculation part for specifying a gas type, specifying a component ratio of a mixed gas or specifying gas components of a mixed gas, which is based on comparison results of an electric output value based on a change in photoelectric current that occurs in each gas sensor when a gas to be detected is flown in a gas flow path while applying a constant voltage to plural gas sensors in the gas sensor array, and numerical values preserved in a database.

17. The gas sensor according to claim 1 , wherein the gas sensor has a ratio {(photoelectric current I ph +base current I b )/base current I b } of 1.5-70, wherein the base current I b is an electric current that flows without irradiating light on the selenium nanowire with a voltage applied to the counter electrodes.

18. The gas sensor according to claim 17 , wherein the ratio {(photoelectric current I ph +base current I b )/base current I b } is 1.8-10.