Triple phase boundary induced self-catalyzed growth of Ge–graphite core–shell nanowires: field electron emission and surface wettability

Abstract

We report a simple method to fabricate Ge–graphite core–shell nanowires on a large scale using a CVD (Chemical Vapor Deposition) system free of catalyst and complicated precursors, which demonstrates interesting V–L–S (vapor–liquid–solid) boundary induced self-catalyzed growth. The novel catalyst-free VLS (vapor liquid solid) mechanism is expected to be generalized for the design of other 1D (one dimensional) metal–graphite hybrids in a controlled manner, based on the fact that tunable shell thickness was achieved on Ge–graphite and a 1D Cu–graphite core–shell was realized in the same way. The Ge–graphite core–shell nanowires deliver very good field emission properties with a threshold field of about 5.33 V μm⁻¹ and a turn-on field of 2.58 V μm⁻¹. The surface wetting measurement confirms the superhydrophobicity of the sample with a WCA (Water Contact Angle) of about 150.8° ± 2°, which decreased to 84.7° after 300 °C (3 h) treatment under vacuum (10⁻³ Torr). Moreover, the wettability behavior is robust against 365 nm UV (ultraviolet) radiation with the WCA unchanged, indicating stable superhydrophobicity in a UV-rich environment. We hope that this study contributes to the design of 1D metal–graphite nanostructures with the aim to explore more novel functionalities.