Chemical sensor using semiconducting metal oxide nanowires
Indium oxide nanowires are used for determining information about different chemicals or Biologics. Chemicals are absorbed to the surface of the nanowires, and cause the semiconducting characteristics of the Nanowires to change. These changed characteristics are sensed, and used to determine either the presence of the materials and/or the concentration of the materials. The nanowires may be between 10 and 30 nm in diameter, formed using a comparable size particle of catalyst material. The nanowires may then be used as part of the channel of a field effect transistor, and the field effect transistor is itself characterized.
1. A method, comprising:
forming a vapor of an indium material;
using a carrying gas including oxygen to carry said vapor of the indium material in a furnace;
contacting the vapor of the indium material with a catalyst having a size of 30 nm or less;
using the catalyst to form an In 2 O 3 nanowire of a thickness which is within 20% of the size of the catalyst;
using said nanowire to form a transistor by forming a substrate of silicon with an insulating covering, locating said nanowire on said insulating covering, forming connections to first and second ends of said nanowire as drain and source connections, and using the silicon substrate as a back gate;
characterizing conduction patterns of said transistor; and
using said characterizing to determine whether a material in contact with said nanowire is electron donating or electron removing.
2. A method as in claim 1 , wherein said using the catalyst comprises forming the In 2 O 3 nanowire using a vapor-liquid-solid mechanism in which the catalyst mixed with the indium material is caused to supersaturate and nucleate.
3. A method as in claim 1 , wherein said forming the vapor of the indium material comprises using a laser to evaporate indium from a solid target.
4. A method as in claim 1 , further comprising using said characterizing to determine whether the material is one of an amine group or a Nitro group.
5. A method as in claim 1 , further comprising using said transistor to detect the presence of a species and a concentration of the species.
6. A method as in claim 1 , further comprising characterizing depletion or enrichment of charge carriers on a surface of the In 2 O 3 nanowire to detect specified materials.
7. A method as in claim 1 , further comprising sterilizing the In 2 O 3 nanowire using ultraviolet light.
8. A method as in claim 1 , wherein the In 2 O 3 nanowire has an aspect ratio of at least 100:1 to enhance gate dependence and reduce transconductance of the transistor.
9. A method as in claim 1 , wherein the transistor has a reduction in conductance of at least about five orders of magnitude after the In 2 O 3 nanowire is in contact with the material.
10. A method as in claim 1 , wherein the transistor is capable of detecting 0.5 ppm for NO 2 and 0.02% for NH 3 .