Xue Zeng-Quan

Growth of Silicon Nanowires by Heating Si Substrate

Amorphous silicon nanowires were prepared by heating an Si substrate at high temperatures using an Ni (or Au) catalyst. The nanowires have a diameter of 10-40 nm and a length of up to several tens of micrometres. Unlike the well-known vapour-liquid-solid mechanism, a solid-liquid-solid mechanism appeared to control the nanowire growth. The heating process had a strong influence on the growth of silicon nanowires. It was found that ambient gas was necessary to grow nanowires. This method can be used to prepare other kinds of nanowires.

Field emission from an array of free-standing metallic nanowires

Arrays of single crystalline gold nanowires were synthesized electrochemically in porous polycarbonate membranes. The polycarbonate membrane was then removed to obtain free-standing nanowires for field emission measurements. The turn-on electric field strength for field emission is found to be lower than 2V/µm. The actual electric field that extracted electrons out of the gold nanowires is estimated to be about 103 times higher than the field directly expected in the model of a parallel plate condenser. The availability of the field emission is therefore attributed to the strong electric field at the tips resulting from small curvature radius of the gold nanowires.

Electrical Phenomena of C60-Tetracyanoquinodimethane Thin Films

The electrical properties of C60-tetracyanoquinodimethane (TCNQ) thin films fabricated by using an ionized-cluster-beam method in a high vacuum system were investigated. The films were characterized by transmission electron microscopy (TEM) and electronic spectroscopy. The spectroscopic results evidenced the formation of the charge-transfer complex system in C60-TCNQ thin films and the TEM results revealed the microstructure of the films. The film thickness is of about 100 nm. The electromotive intensity at the transition point is a few 107 V/m. The possible mechanism of the electrical phenomena of the films is discussed in the paper.

Investigation of the growth process of Si nanowires using the vapour-liquid-solid mechanism

Silicon nanowires have been grown by the thermal decomposition of silane via the vapour-liquid-solid (VLS) mechanism. Three different stages of VLS growth (eutectic alloy formation, crystal nucleation and unidirectional growth) were studied separately using a scanning electron microscope and a high-resolution transmission electron microscope. Very short silicon nanowires prepared under particular conditions provide direct evidence of the VLS mechanism on a nanometre scale. Our results will be very helpful for the controllable synthesis of Si nanowires.

Single wall carbon nanotubes and their electrical properties

Single-wall carbon nanotubes (SWCNTs) were synthesized and purified. A water colloid of SWCNTs was prepared and used to assemble SWCNTs onto a gold film surface. Scanning tunneling microscopy (STM) images showed that short SWCNTs stood on gold film surfaces. Using STM tips made of SWCNTs, a crystal grain image of a gold thin film and an atomic resolution image of highly oriented pyrolytic graphite were successfully obtained. The electrical properties of short SWCNTs, which stood on the surface of gold film, were measured using STM. That SWCNTs stand on gold thin films is a promising technique for studying structures and properties of carbon nanotubes, as well as assembling and fabricating high-intensity coherent electron sources, field emission flat panel display, tips for scanning probe microscopes, new nanoelectronic devices, etc.

Structure and Electrical Properties of Gold Nanowires Grown with Electrochemical Deposition

The effect of Al substitution for Fe on the structure, magnetostriction, anisotropy and spin reorientation of a series Of Tb-0.3 Dy-0.7 (Fe1-xAlx)(1.95) alloys (x = 0, 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35) at room temperature has been investigated. It was found that all the compositions of Tb-0.3 Dy-0.7 (Fe1-xAlx)(1.95) substantially retained the MgCu2-type C-15 cubic Laves phase structure and the lattice constant increases with increasing x. The substitution of Al increases slightly the magnetostriction in low magnetic field ( H less than or equal to 40kA.m(-1)) when x 0.15. The intrinsic magnetostriction lambda(111) decreases sharply also with incresasing x. The Mossbauer spectra show that for 0 less than or equal to x 0.15. The measurements of relative susceptibility indicate that the temperature of spin reorientation decreases with increasing x.

Initial Growth of Thin Films with Low Nucleus Density and Linear Lateral Growth Rate on a Substrate Surface

Based on corrected rate equations, the kinetics is revealed for the initial growth of thin films with a low nucleus density and a linear lateral growth rate on a substrate surface. In this case, the mobility and coalescence terms in the rate equations are neglected, and the coverage term takes a dominant role. All the calculated results are in agreement with experimental data. These results introduce a new scaling in the case of dominant coverage, which is different from the those in the case of coalescence or mobility in a dominant role.

Observation of MWCNTs with low-energy electron point source microscope

The low-energy electron point source (LEEPS) microscope, which creates enlarged projection images with low-energy field emission electron beams, can be used to observe the projection image of nano-scale samples and to characterize the coherence of the field emission beam. In this paper we report the design and test operation performance of a home-made LEEPS microscope. Multi-walled carbon nanotubes (MWCNTs) synthesized by the CVD method were observed by LEEPS microscope using a conventional tungsten tip, and projection images with the magnification of up to 104 was obtained. The resolution of the acquired images is ~10 nm. A higher resolution and a larger magnification can be expected when the AC magnetic field inside the equipment is shielded and the vibration of the instrument reduced.

Field-ion microscopy observation of single-walled carbon nanotubes

Field-ion microscopy (FIM), a tool for surface analysis with atomic resolution, has been employed to observe the end structure of single-walled carbon nanotubes (SWCNTs). FIM images revealed the existence of open SWCNT ends. Amorphous carbon atoms were also observed to occur around SWCNTs and traditional field evaporation failed to remove them. Heat treatment was found to be efficacious in altering the end structures of SWCNT bundles. Carbon and oxygen atoms released from heated tungsten filament are believed to be responsible for the decoration imposed on the SWCNT ends.

Coherent field emission from a multi-walled carbon nanotube with two open-ended branches

Interference fringes are obtained in a field-emission microscopy (FEM) study of a multi-walled carbon nanotube (MWCNT) with two open-ended branches. The FEM pattern, which is composed of three parallel streaks, can be interpreted by using classical Youngs double-slit interference with the ends of the two MWCNT branches treated as two secondary sources of the electron wave. The origin of the coherency of the electron beams from the two branches is discussed on the basis of the quantitative analysis of the FEM pattern. The result suggests a new approach to obtaining a coherent electron source.