Runze Zhan

Epitaxial growth of multiwall carbon nanotube from stainless steel substrate and effect on electrical conduction and field emission.

The epitaxial growth of carbon nanotubes (CNTs) is an important subject of research. Recent attention has been paid to finding new strategies for the controlled growth of single-wall CNTs with a defined chirality. In addition, many potential applications require multiwall CNTs (MWCNTs) to grow vertically from the substrate and the interface property is crucial. Here, we report for the first time that MWCNTs can grow directly from the surface of a substrate by epitaxy, based on the experimental study of individual multiwall carbon nanotubes on a large-area stainless steel substrate, which is a very useful system for electrical and mechanical applications. In particular, evidence is given of the lattice matching between the MWCNT and the lattice of a hexagonal Cr2O3: (Fe, Mn) film formed on the surface of the substrate. Furthermore, a method is developed to increase the density of the MWCNTs; a mechanism of simultaneous top and bottom growth is proposed. The resultant significantly improved electrical transport and field emission properties are also presented, showing the Ohmic contact for electrical conduction and high performance in resisting the catastrophic cold-cathode vacuum breakdown of the CNTs.

In Situ Characterization of the Local Work Function along Individual Free Standing Nanowire by Electrostatic Deflection

In situ characterization of the work function of quasi one dimensional nanomaterials is essential for exploring their applications. Here we proposed to use the electrostatic deflection induced by work function difference between nanoprobe and nanowire for in situ measuring the local work function along a free standing nanowire. The physical mechanism for the measurement was discussed in details and a parabolic relationship between the deflection and the potential difference was derived. As a demonstration, measurement of the local work functions on the tip and the sidewall of a ZnO nanowire with Au catalyst at its end and a LaB6 nanowire have been achieved with good accuracy.

Thermal-enhanced field emission from CuO nanowires due to defect-induced localized states

The temperature dependence of the field emission properties of CuO nanowires was studied from 163 to 453 K. Large current increases were observed with increasing temperature, which cannot be explained by band to band excitation or emission from the valence band. Two distinct sections were observed from the Arrhenius plot. Activation energies of 100 meV for the high-temperature range (273 to 453 K) and 26.4 meV for the low-temperature range (163 to 273 K) were obtained. Phonon-assisted and defect-assisted thermal field emission mechanisms from p-type CuO NWs were proposed to explain the observed phenomena in the two temperature ranges, which relate to the defect-induced localized states. Numerical simulation using the proposed mechanism was carried out and a good fit with the experimental results was achieved. The results suggest that defect-induced localized states play an important role in field emission from nanowires.

In situ study of graphene crystallinity effect on field electron emission characteristics

Crystallinity and field electron emission characteristics of few-layer graphene (FLG) have been investigated synchronously by using in situ transmission electron microscope (TEM) to reveal their relationship. The crystallinity of a single FLG sheet is modified from polycrystalline to amorphous by TEM electron beam irradiation. In the meantime, the field electron emission measurement shows that the degradation of crystallinity has a negative effect on the field electron emission characteristics. This can be attributed to the violently decline of electrical conductivity of FLG. The results indicate that crystallinity is a key factor to the field electron emission of FLG, and thus, conditions leading to the degradation of crystallinity of FLG should be avoided.

Subgap State Engineering Using Nitrogen Incorporation to Improve Reliability of Amorphous InGaZnO Thin-Film Transistors in Various Stressing Conditions

Instability of amorphous InGaZnO thin-film transistors (a-IGZO TFTs) remains an obstacle for commercialization. Here, we systematically discuss the effect of nitrogen incorporation on a-IGZO TFT stability and developed Ar/O2/N2 atmosphere to improve the stability under stressing in different conditions. Based on X-ray photoelectron spectrometer results, it is revealed that the positive gate bias stress (PGBS) stability is significantly improved due to microscopically passivated metal-oxygen bonds. Yet, the negative gate bias and light stress (NBLS) stability is seriously deteriorated with heavily nitrogen incorporation probably due to the bandgap narrowing effect. By optimizing a mixed O2/N2 atmosphere, the subgap states are finely tuned to afford optimal performance and stability. The developed IGZO TFTs exhibit mobility (12.67 cm2/Vs), small shift of threshold voltage under PGBS (reduced by 64% as compared with the pristine a-IGZO TFTs), and good negative gate bias stability and with NBLS stability as well.