One-pot synthesis of Mn3O4-decorated GaN nanowires for drastic changes in magnetic and gas-sensing properties

Abstract

Composite nanowires consisting of GaN and Mn3O4 were prepared via a one-step method, wherein a mixture of GaN and Mn powders was thermally heated under flowing ammonia gas at 900 degrees C. Scanning electron microscopy indicated that the nanowire diameter increased with increasing growth temperature. The growth mechanism of composite nanowires at 900 degrees C is mainly related to a vapor-solid or base-growth process, whereas the 700 degrees C-grown product corresponded to pure GaN nanowires synthesized by means of a tip-growth vapor-liquid-solid process. With pure GaN nanowires exhibiting weak ferromagnetism at 5 K, the ferromagnetic behavior was significantly enhanced by employing the GaN/Mn3O4 composite nanowires. We suggest that the Mn3O4 shell plays a role in enhancing the ferromagnetic behavior of composite nanowires. Room-temperature sensing of H-2 gas revealed that the addition of Mn3O4 shell turned the n-type sensing characteristic of the pure GaN nanowires into the p-type one. The conversion is related to the p-type nature of the Mn3O4 phase, which provides the continuous path of hole currents. The significant enhancement of sensing behavior by employing the GaN/Mn3O4 composite nanowires is due to not only the relatively small volume of the Mn3O4 structures but also the presence of p-type Mn3O4/n-type GaN heterojunctions.