Huijuan Chen

Fabrication of Carbon Nanoscrolls from Monolayer Graphene

A simple way of synthesizing carbon nanotube (CNT)/graphene (GN) nanoscroll core/shell nanostructures is demonstrated using molecular dynamics (MD) simulations. The simulations show that GN sheets can fully self-scroll onto CNTs when the CNT radius is larger than a threshold of about 10 A, forming a stable core/shell structure. Increasing the length of the GN sheet results in multilayered carbon nanoscroll (CNS) shells that exhibit a tubular structure similar to that of multiwall CNTs. The distances between the CNT and the GN wall or adjacent GN walls are about 3.4 A. It is found that the van der Waals force plays an important role in the formation of the CNT/GN nanoscroll core/shell-composite nanostructures. However, the chirality of the CNT and the GN sheet does not affect the self-scrolling process, which thus provides a simple way of controlling the chirality and physical properties of the resulting core/shell structure. It is expected that this preparation method of CNT/GN nanoscroll core/shell composites will lead to further development of a broad new class of carbon/carbon core/shell composites with enhanced properties and even introduce new functionalities to composite materials.

The core/shell composite nanowires produced by self-scrolling carbon nanotubes onto copper nanowires.

We demonstrated a novel method to produce core/shell composite nanowires (NWs) by self-scrolling carbon nanotubes (CNTs) onto copper NWs via forced-field-based molecular dynamic (MD) simulations. When large diameter CNTs are placed beside the copper NWs, the CNTs approach the NWs, collapse, and self-scroll onto the NWs, resulting in coaxial core/shell composite NWs. It is found that the van der Waals force plays an important role in the formation of the composite NWs. The expected outcome of this novel method is to determine various strategies on how to produce composite NWs. Coaxial core/shell composite NWs represent an important class of nanoscale building blocks with substantial potential for exploring new concepts and functional materials.

Photovoltaic characteristics of Pd doped amorphous carbon film/SiO2/Si

The Pd doped amorphous carbon (a-C:Pd) films were deposited on n-Si substrates with or without a native SiO2 layer using magnetron sputtering. The photovoltaic characteristics of the a-C:Pd/SiO2/Si and a-C:Pd/Si junctions were studied. It is found that under light illumination of 15 mW/cm2 at room temperature, the a-C:Pd/SiO2/Si solar cell fabricated at 350 °C has a high power conversion efficiency of 4.7%, which is much better than the a-C/Si junctions reported before. The enhanced conversion efficiency is ascribed to the Pd doping and the increase in sp2-bonded carbon clusters in the carbon film caused by the high temperature deposition.

Room-temperature high-sensitivity detection of ammonia gas using the capacitance of carbon/silicon heterojunctions

Ammonia (NH3) sensors based on carbon/silicon (C/Si) heterojunctions are demonstrated at room temperature (RT). Upon exposure to NH3 molecules (0.2 ml l−1) at RT, the interface capacitance of C/Si junction increases dramatically, to about 230%. The results show that C/Si junctions have high NH3 gas sensitivity, rapid response and high recovery speed at RT. This phenomenon can be attributed to the change of the potential barrier width of the junction, which is caused by the adsorption of NH3 gas molecules. The C/Si junctions can greatly amplify the detection sensitivity of the nano-sized carbon so that the C/Si junctions act as excellent RT gas sensors.

Ethanol gas sensitivity of carbon nanotip arrays/n-Si heterojunctions at room temperature

Carbon nanotip arrays were grown from silicon substrates via direct current magnetron sputtering at room temperature RT. The simple carbon nanotip arrays/n-Si C /Si heterojunctions were used to detect ethanol gas at RT. The results show that the C /Si junctions have high ethanol gas sensitivity, rapid response, and high recovery speed at RT. Upon exposure to ethanol gas 0.64 g /l at RT, the resistance of the junction decreases by 35% at a given positive voltage of 8 V. Moreover, the interface capacitance of the junction at 5 kHz can increase by about 40% rapidly when exposed to ethanol gas. The phenomena should be attributed to the change in the Fermi level of the carbon film caused by adsorbing electrons from ethanol molecules. The study shows that the C /Si junctions have potential application as ethanol gas sensors.