Nanomaterial for Sensors Science & Technology Objective(s): To use the aligned nanotube array as sensor for monitoring gas flow rate To fabricate nano-size gas sensors using semiconducting oxide nanobelts Design principles: Nanotechnology Z.L. Wang, Georgia Tech Collaborations: Government – NASA, Oak Ridge National Lab URETI – Peter Heskerth Proposed Approach: Sensor for gas flow rate: Step 1: Synthesizing aligned nanotube arrays Step 2: Building the set up for field emission measurement under flowing gas environment Step 3: Testing the device for engine applications Oxide Nanobelt for Gas Sensors Step 1: Synthesizing oxid nanobelts (ZnO) Step 2: Build the electrodes using e-beam lithography Step 3: Testing the device for gas sensor NASA Relevance/Impact: In-situ real time monitoring of gas flow at a very confined region for providing better control on engine working condition In-situ, real time monitoring of residual gas at high temperature with high selectivity Gold electrodes (50 nm thick) ZnO nano- ribbon (w=285nm, h=110nm) SiO 2 (~120n thick)

Proposed Approach: Synthesis of Nanotubes Furnace Ar View window To pump CH 4 - Deposit Fe/Ni catalyst particles onto a ceramic substrate; - Grown carbon nanotubes by decomposition of CH 4 at high temperature; - Control temperature and gas flow rate to optimize the alignment. Z.L. Wang, Georgia Tech

-Emission current is a measure of the distance between the tips of the carbon nanotubes and counter electrode; -The emission current drops if the nanotubes are bent by flowing gas; -Monitoring the emission current can quantitatively determine the gas flow rate Proposed Approach- Testing the Sensor Z.L. Wang, Georgia Tech

Furnace Ar View window Oxide powders alumina substrate To pump Thermal couple Alumina tube Ar Proposed Approach- Synthesis of Oxide Nanobelts -Place oxide powder as the source material in the crucible; -Thermal vaporization of the oxide followed by a deposition at the low temperature region results in the growth of nanobelts; -Control temperature and gas flow rate to optimize the morphology. Z.L. Wang, Georgia Tech

Two-probe measurements of electric conductance of a single nanowire under different temperature and gas partial pressure. Nanowire Insulator substrate Electrode Proposed Approach- Building Gas Sensors - The electric conductance of the nanobelt depends on the type and amount of molecules adsorbed on its surface - Using the semiconductive oxide nanobelts, nanosensors using individual nanobelt will be built. Z.L. Wang, Georgia Tech