Muhong Wu

Quantum-coupled radial-breathing oscillations in double-walled carbon nanotubes

Van der Waals-coupled materials, ranging from multilayers of graphene and MoS(2) to superlattices of nanoparticles, exhibit rich emerging behaviour owing to quantum coupling between individual nanoscale constituents. Double-walled carbon nanotubes provide a model system for studying such quantum coupling mediated by van der Waals interactions, because each constituent single-walled nanotube can have distinctly different physical structures and electronic properties. Here we systematically investigate quantum-coupled radial-breathing mode oscillations in chirality-defined double-walled nanotubes by combining simultaneous structural, electronic and vibrational characterizations on the same individual nanotubes. We show that these radial-breathing oscillations are collective modes characterized by concerted inner- and outer-wall motions, and determine quantitatively the tube-dependent van der Waals potential governing their vibration frequencies. We also observe strong quantum interference between Raman scattering from the inner- and outer-wall excitation pathways, the relative phase of which reveals chirality-dependent excited-state potential energy surface displacement in different nanotubes.

Wet-Chemistry-Assisted Nanotube-Substitution Reaction for High-Efficiency and Bulk-Quantity Synthesis of Boron- and Nitrogen-Codoped Single-Walled Carbon Nanotubes

We present an innovative wet-chemistry-assisted nanotube-substitution reaction approach for the highly efficient synthesis of boron- and nitrogen-codoped single-walled carbon nanotubes (B(x)C(y)N(z)-SWNTs) in bulk quantities. The as-synthesized ternary system B(x)C(y)N(z)-SWNTs are of high purity and quality and have fairly homogeneous B and N dopant concentrations. Electrical transport measurements on SWNT-network thin-film transistors revealed that the B(x)C(y)N(z)-SWNTs were composed primarily of the semiconducting nanotubes, in contrast to the starting pristine C-SWNTs, which consisted of a heterogeneous mixture of both semiconducting and metallic types.

Synthesis of nitrogen-doped single-walled carbon nanotubes and monitoring of doping by Raman spectroscopy

Nitrogen-doped single-walled carbon nanotubes (CNx-SWNTs) with tunable dopant concentrations were synthesized by chemical vapor deposition (CVD), and their structure and elemental composition were characterized by using transmission electron microscopy (TEM) in combination with electron energy loss spectroscopy (EELS). By comparing the Raman spectra of pristine and doped nanotubes, we observed the doping-induced Raman G band phonon stiffening and 2D band phonon softening, both of which reflect doping-induced renormalization of the electron and phonon energies in the nanotubes and behave as expected in accord with the n-type doping effect. On the basis of first principles calculations of the distribution of delocalized carrier density in both the pristine and doped nanotubes, we show how the n-type doping occurs when nitrogen heteroatoms are substitutionally incorporated into the honeycomb tube-shell carbon lattice.

Ultralong aligned single-walled carbon nanotubes on flexible fluorphlogopite mica for strain sensors

AbstractSingle-walled carbon nanotubes (SWNTs) are expected to be an ideal candidate for making highly efficient strain sensing devices owing to their unique mechanical, electronic, and electromechanical properties. Here we present the use of fluorphlogopite mica (F-mica) as a flexible, high-temperature-bearing and mechanically robust substrate for the direct growth of horizontally aligned ultra-long SWNT arrays by chemical vapor deposition (CVD), which in turn enables the straightforward, facile, and cost-effective fabrication of macro-scale SWNT-array-based strain sensors. Strain sensing tests of the SWNT-array devices demonstrated fairly good strain sensitivity with high ON-state current density.

Removal and Changes of Sediment Organic Matter and Electricity Generation by Sediment Microbial Fuel Cells and Amorphous Ferric Hydroxide

Sediments play an important role in determining the quality of lakes, rivers and oceans as they can act as either a source or sink for pollutants. Once the input pollution is controlled, sediments as a secondary source of pollution can release the accumulated pollutants to overlying water.1 The organic matter content of sediments can also affect the structure of macroinvertebrate assemblages.2 To date, traditional sediments remediation methods include monitored natural recovery, in-situ treatment, and ex-situ treatment.3 The traditional methods are either expensive or not environmentally friendly, so it is crucial to find a cost-effective and environmentally friendly way to solve the contaminated sediments problem. Microbial fuel cell (MFC) technology is considered an environmentally friendly and promising approach for converting wastewater or solid waste into electricity.4–6 Recently, some studies have shown that sediment microbial fuel cell (SMFC) can alter the properties and enhance the removal of organic matter in sediment.7–9 Wang9 developed a three-dimensional floating biocathode to dispose river sediments, and concluded that the sediment organic matter content near the anode was removed by 29 %. Hong7 found that sediment organic matter around the electrodes became more humified, aromatic, and polydispersed, and had a higher average molecular weight, along with its partial degradation and electricity generation compared to that of the original sediment. Sajana10 studied the performance of SMFC by adding cellulose in freshwater and demonstrated effective cellulose degradation from aquaculture pond sediment and maintained the oxidized sediment top layer favourable for aquaculture. Zhou11 improved the SMFC performance by amendment of colloidal iron oxyhydroxide into sediments and concluded that high Fe(II) concentration in pore water of sediments led to high power production. Song12 found that the addition of biomass in appropriate proportions can enhance output power in SMFC. However, mass transfer limitations for electron donors to reach the anode and a low rate of oxygen reduction in cathodes were major limitations for power production.13 In freshwater environments, the maximum power densities in SMFC with felt graphite14 and carbon paper15 as cathode were 4 mW m–2 and 2 mW m–2 respectively. Song13 constructed SMFC with granule activated carbon cathode and stainless steel anode and obtained 3.5 mW m–2 maximum power density, and further increased to 11.2 mW m–2 by adding cellulose. Jiang16 built MFC with graphite fiber brush and enhanced TCOD removal rate from 11.3 % to 19.2 % for raw sludge. Removal and Changes of Sediment Organic Matter and Electricity Generation by Sediment Microbial Fuel Cells and Amorphous Ferric Hydroxide

Measurement of complex optical susceptibility for individual carbon nanotubes by elliptically polarized light excitation

The complex optical susceptibility is the most fundamental parameter characterizing light-matter interactions and determining optical applications in any material. In one-dimensional (1D) materials, all conventional techniques to measure the complex susceptibility become invalid. Here we report a methodology to measure the complex optical susceptibility of individual 1D materials by an elliptical-polarization-based optical homodyne detection. This method is based on the accurate manipulation of interference between incident left- (right-) handed elliptically polarized light and the scattering light, which results in the opposite (same) contribution of the real and imaginary susceptibility in two sets of spectra. We successfully demonstrate its application in determining complex susceptibility of individual chirality-defined carbon nanotubes in a broad optical spectral range (1.6–2.7 eV) and under different environments (suspended and in device). This full characterization of the complex optical responses should accelerate applications of various 1D nanomaterials in future photonic, optoelectronic, photovoltaic, and bio-imaging devices.One-dimensional materials such as carbon nanotubes have many applications, but not all of their properties can be described in the same way as for conventional media. Here, the authors devise a method to measure the complex optical susceptibility in a 1D nanomaterial and demonstrate it for carbon nanotubes.