Study of Thermal Properties of Graphene-Based Structures Using the Force Constant Method

The thermal properties of graphene-based materials are theoretically investigated. The fourth-nearest neighbor force constant method for phonon properties is used in conjunction with both the Landauer ballistic and the non-equilibrium Green's function techniques for transport. Ballistic phonon transport is investigated for different structures including graphene, graphene antidot lattices, and graphene nanoribbons. We demonstrate that this particular methodology is suitable for robust and efficient investigation of phonon transport in graphene-based devices. This methodology is especially useful for investigations of thermoelectric and heat transport applications.Comment: 23 pages, 9 figures, 1 tabl

Anomalous Heat Conduction and Anomalous Diffusion in Low Dimensional Nanoscale Systems

Thermal transport is an important energy transfer process in nature. Phonon is the major energy carrier for heat in semiconductor and dielectric materials. In analogy to Ohm's law for electrical conductivity, Fourier's law is a fundamental rule of heat transfer in solids. It states that the thermal conductivity is independent of sample scale and geometry. Although Fourier's law has received great success in describing macroscopic thermal transport in the past two hundreds years, its validity in low dimensional systems is still an open question. Here we give a brief review of the recent developments in experimental, theoretical and numerical studies of heat transport in low dimensional systems, include lattice models, nanowires, nanotubes and graphenes. We will demonstrate that the phonon transports in low dimensional systems super-diffusively, which leads to a size dependent thermal conductivity. In other words, Fourier's law is breakdown in low dimensional structures

Comparative Study of Antimony Doping Effects on the Performance of Solution-Processed ZIO and ZTO Field-Effect Transistors

ZnO-based oxide films are emerging as high-performance semiconductors for field-effect transistors (FETs) in optoelectronics. Carrier mobility and stability in these FETs are improved by introducing indium (In) and gallium (Ga) cations, respectively. However, the strong trade-off between the mobility and stability, which come from In or Ga incorporation, still limits the widespread use of metal oxide FETs in ultrahigh pixel density and device area-independent flat panel applications. We demonstrated that the incorporation of antimony (Sb) cations in amorphous zinc indium oxide (ZIO) simultaneously enhanced the field-effect mobility (��FET) and electrical stability of the resulting Sb-doped ZIO FETs. The rationale for the unexpected synergic effect was related to the unique electron configuration of Sb5+ ([Kr]4d105s05p0). However, the benefit of Sb doping was not observed in the zinc tin oxide (ZTO) system. All the Sb-doped ZTO FETs suffered from a reduction in ��FET and a deterioration of gate bias stress stability with an increase in Sb loading. This can be attributed to the formation of heterogeneous defects due to Sb-induced phase separation and the creation of Sb3+ induced acceptor-like trap states. ? 2017 American Chemical Society.113sciescopu

A stereo PIV measurement of a model ship wake in a towing tank with uncertainty assessment

Detailed information of the flow around a ship is essential for designing the hull because it is related to the propeller performance, maneuverability, and vibration. Thus, lots of experimental and computational researches have been executed to measure or analyze the stern flow of vessels. In this paper, the newly installed underwater SPIV system in Seoul National University Towing Tank is introduced with its measurement results and estimated uncertainty. The SPIV system was installed on the towing carriage which runs along side rails of the towing tank. With the underwater SPIV system, the uniform flow, made by running the towing carriage without a model, was firstly measured to investigate the uncertainty assessment. Uniform flow measurement results for each direction of the coordinate system were analyzed to estimate the random error and systematic error, following the ASME test uncertainty. The reference speed for the longitudinal and transverse uniform flow measurement was set to 1.0m/s and 1.5m/s, which is general towing speed range of model ships in the towing tank. In the uniform flow measurement results, the systematic error, the difference of ensemble-averaged speed and reference speed from the encoder of the towing carriage, was below 1.5% of the towing speed and the random error, derived from the standard deviation of the ensemble-averaged speed, was 4% of the reference speed. After the uncertainty assessment, the nominal wake, the flow on the propeller location with absence of the propeller, was measured and results were compared with experiment results with 5-holes Pitot tube from other towing tank. The model ship was KVLCC2, of which hull design and dimension are open to public. The scale of the model ship was 1/100, and the Froude number was 0.142 in the design speed. SPIV results showed good agreement with existing results and have advantages such as depiction of turbulence properties and reduction of the experiment-operating time