X. W. Zhou

Color Detection Using Chromophore-Nanotube Hybrid Devices

We present a nanoscale color detector based on a single-walled carbon nanotube functionalized with azobenzene chromophores, where the chromophores serve as photoabsorbers and the nanotube as the electronic read-out. By synthesizing chromophores with specific absorption windows in the visible spectrum and anchoring them to the nanotube surface, we demonstrate the controlled detection of visible light of low intensity in narrow ranges of wavelengths. Our measurements suggest that upon photoabsorption, the chromophores isomerize from the ground state trans configuration to the excited state cis configuration, accompanied by a large change in dipole moment, changing the electrostatic environment of the nanotube. All-electron ab initio calculations are used to study the chromophore-nanotube hybrids and show that the chromophores bind strongly to the nanotubes without disturbing the electronic structure of either species. Calculated values of the dipole moments support the notion of dipole changes as the optical detection mechanism.

Towards more accurate molecular dynamics calculation of thermal conductivity: Case study of GaN bulk crystals

Significant differences exist among literature for thermal conductivity of various systems computed using molecular dynamics simulation. In some cases, unphysical results, for example, negative thermal conductivity, have been found. Using GaN as an example case and the direct nonequilibrium method, extensive molecular dynamics simulations and Monte Carlo analysis of the results have been carried out to quantify the uncertainty level of the molecular dynamics methods and to identify the conditions that can yield sufficiently accurate calculations of thermal conductivity. We found that the errors of the calculations are mainly due to the statistical thermal fluctuations. Extrapolating results to the limit of an infinite-size system tend to magnify the errors and occasionally lead to unphysical results. The error in bulk estimates can be reduced by performing longer time averages using properly selected systems over a range of sample lengths. If the errors in the conductivity estimates associated with each of the sample lengths are kept below a certain threshold, the likelihood of obtaining unphysical bulk values becomes insignificant. Using a Monte Carlo approach developed here, we have determined the probability distributions for the bulk thermal conductivities obtained using the direct method. We also have observed a nonlinear effect that can become a source of significant errors. For the extremely accurate results presented here, we predict a [0001] GaN thermal conductivity of

Accuracy of existing atomic potentials for the CdTe semiconductor compound

185text{ }text{W}/text{K}text{ }text{m}

Molecular Dynamics Prediction of Thermal Conductivity of GaN Films and Wires at Realistic Length Scales

at 300 K,

Finite element analysis of an atomistically derived cohesive model for brittle fracture

102text{ }text{W}/text{K}text{ }text{m}

Melt-Growth Dynamics in CdTe Crystals

at 500 K, and

Defect formation dynamics during CdTe overlayer growth

74text{ }text{W}/text{K}text{ }text{m}

High-fidelity simulations of CdTe vapor deposition from a bond-order potential-based molecular dynamics method

at 800 K. Using the insights obtained in the work, we have achieved a corresponding error level (standard deviation) for the bulk (infinite sample length) GaN thermal conductivity of less than

Effects of cutoff functions of Tersoff potentials on molecular dynamics simulations of thermal transport

10text{ }text{W}/text{K}text{ }text{m}

Analytical law for size effects on thermal conductivity of nanostructures

,