The effect of grain boundaries inside the individual ZnO nanowires in gas sensing.

We present the gas sensing characteristics of the individual ZnO nanowires with single-crystalline and multiple grain boundaries (GBs) fabricated using bottom-up and top-down approaches, respectively. The sensor response of the individual ZnO nanowires with the multiple GBs was enhanced approximately three times as compared to that of single-crystalline ZnO nanowires due to well-known GB modulations. However, the response and recovery times of the individual ZnO nanowires with multiple GBs were much slower than those of the single-crystalline ZnO nanowire, indicating the presence of oxygen diffusion resistance to GBs due to the relatively fast surface kinetic reaction. Simplified kinetic diffusion modeling and experimental results could quantify the significant diffusion resistance of gas molecules into the GBs of the individual ZnO nanowires.

The synthesis of single PdAu bimetallic nanowire: feasibility study for hydrogen sensing.

Single PdAu bimetallic nanowires have been synthesized via the sequential processes of electrochemical deposition and dielectrophoresis (DEP). In the first step, Pd/Au grains on predefined Au electrodes were grown by electrochemical deposition and could assist effectively the formation of a single PdAu nanowire with a good directionality by the subsequent DEP process. The synthesized PdAu nanowires have an average of approximately 10 at.% of Pd, a good resistance of a few hundred Omega, diameters of 300 nm on average and lengths of up to 15 microm. Based on the single PdAu nanowire, hydrogen detection was demonstrated in the range from 100 to 2500 ppm.