Morphology control of self-catalyzed germanium nanostructures with graphitic carbon shell

The crystalline germanium nanowires (GeNWs) with a uniform graphitic carbon shell were prepared via a conventional low-pressure chemical vapor deposition method without any external catalyst. The GeNWs grown at low temperature (Tg < 500 degrees C) have a uniform diameter with a large expect ratio of more than 10(3). With increasing the growth temperature (Tg > 500 degrees C), however, the nanowire morphology is dramatically changed into a hybrid structure where highly dense Ge nanoparticles (GeNPs) with a diameter of 5-10 nm are attached onto the Ge nanowires. The nanostructures consist of crystalline Ge-core and very thin graphitic carbon shell. The possible mechanism of anisotropic growth and the control of morphological transition from uniform nanowires to NW/NP hybrid structures are discussed and demonstrated.