Yafei Zhang

Covalent sidewall functionalization of single-walled carbon nanotubes: a?photoreduction approach

Covalent sidewall functionalization of single-walled carbon nanotubes (SWNTs) via photoreduction of aromatic ketones by alcohols is reported for the first time. Irradiation of benzophenone, benzhydrol and SWNTs in benzene resulted in covalent attachment of benzhydrol to the sidewalls of the SWNTs. A variety of tools were used to characterize the functionalized SWNTs. Raman scattering, UV-visible and near-IR spectroscopy confirm the covalent nature of the sidewall functionalization. Attenuated total reflection (ATR) FTIR and NMR provided evidence for attachment of benzhydrol onto the sidewalls of nanotubes. Thermogravimetric analysis (TGA) showed that the degree of functionalization was about one benzhydrol in 52 sidewall carbons. A long-chain hydrocarbon marker (n-C(18)H(35)) was also grafted onto the functional groups by esterification reaction for high-resolution TEM (HRTEM) visualization.

Alignment characterization of single-wall carbon nanotubes by Raman scattering

A novel method for identifying the Raman modes of single-wall carbon nanotubes (SWNT) based on the symmetry of the vibration modes has been studied. The Raman intensity of each vibration mode varies with polarization direction, and the relationship can be expressed as analytical functions. This method avoids troublesome numerical calculation and easily gives clear relations between Raman intensity and polarization direction. In this way, one can distinguish each Raman-active mode of SWNT through the polarized Raman spectrum.

Review on Optimization Methods of Carbon Nanotube Field-Effect Transistors

Carbon nanotube field-effect transistors (CNTFETs) have been considered as a replacement for, or complement to, future semiconductor devices due to high mobility, low defect structure, and intrinsic nanometer scale of carbon nano- tubes (CNTs). The great superiority in performance for CNTFETs vis-a-vis state-of-the-art silicon devices has attracted an intense research effort to explore their application viability. Since the first CNTFET was fabricated, CNTFETs have expe- rienced great advances at the device structure as well as device performance. Various methods had been attempted to op- timize the devices. These methods can mainly be divided into four aspects: (1) Decrease the contact resistance between CNTs and metal electrodes; (2) Increase the tuning efficiency of gate voltage to CNT channels; (3) Shorten the CNT channel length; (4) Adopt the optimized device structure. This review will briefly summarize these methods and describe the device performances achieved with these methods. Representative researches and updated progress on the optimiza- tion methods of CNTFETs will be introduced. From the review, the advances in CNTFETs can be also learned in the rough.

The effect of transverse wave vector and magnetic fields on resonant tunneling times in double-barrier structures

The effect of transverse wave vector and magnetic fields on resonant tunneling times in double-barrier structures, which is significant but has been frequently omitted in previous theoretical methods, has been reported in this paper. The analytical expressions of the longitudinal energies of quasibound levels (LEQBL) and the lifetimes of quasibound levels (LQBL) in symmetrical double-barrier (SDB) structures have been derived as a function of transverse wave vector and longitudinal magnetic fields perpendicular to interfaces. Based on our derived analytical expressions, the LEQBL and LQBL dependence upon transverse wave vector and longitudinal magnetic fields has been explored numerically for a SDB structure. Model calculations show that the LEQBL decrease monotonically and the LQBL shorten with increasing transverse wave vector, and each original LEQBL splits to a series of sub-LEQBL which shift nearly linearly toward the well bottom and the lifetimes of quasibound level series (LQBLS) shorten with incre...