One-dimensional (1D) multiple segment nanostructures that contain heterojunctions between various metals and semiconductors are of great interest due to their fascinating chemistry and size-, shape-, and material-dependent properties. Here we report on the synthesis and electronic characterization of multi - segment nanowire (NW) junctions of Au1-xGex and Ge. The 1D heterostructures are grown with a low - temperature chemical vapor deposition process, assisted by electrodeposited Au NWs inside nanochannels of anodic aluminum oxide template.[1,2] The Au-catalyzed vapor-liquid-solid growth process occurs simultaneously in multiple locations along the nanochannel, which leads to multi-segment Au1-xGex/Ge heterojunctions. The structures of the as-grown hybrid NWs, analyzed by using transmission electron microscopy and energy dispersive X-ray s pectroscopy elemental mapping, show clear compositional modulation with variable modulation period and controllable junction numbers. Remarkably, both GeNW and Au1-xGexNW segments are single crystalline with abrupt interfaces and good crystallographic coherences. The electronic and transport properties of individual NW junctions are measured by using a multi-probe scanning tunneling microscope (STM). The semiconducting nature of Ge segments and the metallic behavior of Au1-xGex segments are examined by scanning tunneling spectroscopy (STS). The transport current-voltage curves across the heterojunctions show a characteristic rectifying behavior, which is discussed in association with the potential barriers at the junction. The high yield of multiple segment NW junctions and the ability to control predictably the properties of a metal-semiconductor can facilitate the applications in nanoelectronics and optoelectronics that harness multiple functionalities of hetero-interfaces.

[1] Li, X. D.; Meng, G. W.; Xu, Q. L.; Kong, M. G.; Zhu, X. G.; Chu, Z. Q.; Li, A. P. Controlled Synthesis of Germanium Nanowires and Nanotubes with Variable Morphologies and Sizes. Nano Lett. 2011, 11, 1704–1709.

[2] Li, X. D.; Meng, G. W.; Qin, S. Y.; Xu, Q. L.; Chu, Z. Q.; Zhu, X. G.; Kong, M. G.; Li, A. P. Nanochannel-Directed Growth of Multi-Segment Nanowire Heterojunctions of Metallic Au1-xGex and Semiconducting Ge. ACS Nano 2012, 6, 831–836.