Liu Li-Feng

Synthesis and characterization of axially periodic Zn2SnO4 dendritic nanostructures

Zn2SnO4 (ZTO) nanowires with a unique dendritic nanostructure were synthesized via a simple one-step thermal evaporation and condensation process. The morphology and microstructure of the ZTO nanodendrite have been investigated by means of field emission scanning electron microscopy (SEM), x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). SEM observation revealed the formation of branched nanostructures and showed that each branch exhibited a unique periodic structure formed by a row of overlaid rhombohedra of ZTO nanocrystals along the axis of the nanobranch. HRTEM studies displayed that the branches grew homoepitaxially as single-crystalline nanowires from the ZTO nanowire backbone. A possible growth model of the branched ZTO nanowires is discussed. To successfully prepare branched structures would provide an opportunity for both fundamental research and practical applications, such as three-dimensional nanoelectronics, and opto-electronic nanodevices.

Structure and electrical characteristics of Nb-doped SrTiO3 substrates

The studies on structure and electrical characteristic of Nb-doped SrTiO3 (SNTO) substrates by XRD, Hall measurements, R-T and SEM, show that the SNTO substrates with the same Nb-doping concentration have different electrical properties because of the nonuniformity of Nb-doping. The uniformly doped high-quality substrates are extremely important for fabricating multilayer structure and devices. In addition, the experimental results also provide us with SEM method to judge the uniformity of conducting material.

Structure, Electrical, and Optical Properties of Nb-doped BaTiO3 Thin Films Grown by Laser Molecular Beam Epitaxy

Structure, electrical, and optical properties of Nb-doped BaTiO3 (Nb:BTO) thin films on MgO substrates grown by laser molecular beam epitaxy with increasing Nb content were investigated. The Nb:BTO thin films with high crystallinity are epitaxially grown on MgO substrates. With more Nb-doped content, the impurity phases are found in Nb:BTO thin films. Hall measurement at room temperature confirms that the charge carriers of the Nb:BTO thin films are n-type. When the Nb-doped content increases, the carrier concentration and carrier mobility increase. Meanwhile the optical transmittance decreases with the increase of the Nb-doping, and the width of the forbidden band in each group is not affected by the presence of Nb in the samples. Raman spectra show that the structural phase transition may occur with the increase of the Nb-doping content, in the meantime more defects and impurities exist in the Nb:BTO thin films.

Electron field emission from single-walled carbon nanotube nonwoven

Field emission from single-walled carbon nanotube (SWNT) nonwoven has been investigated under high vacuum with different vacuum gaps. A low turn-on electric field of 1.05 V/μm is required to reach an emission current density of 10 μA/cm2. An emission current density of 10 mA/cm2 is obtained at an operating electric field of 1.88 V/μm. No current saturation is found even at an emission current of 5 mA. With the vacuum gap increasing from 1 to 10 mm, the turn-on field decreases monotonically from 1.21 to 0.68 V/μm, while the field amplification is augmented. The good field-emission behaviour is ascribed to the combined effects of the intrinsic field emission of SWNT and the waved topography of the nonwoven.

N-Doped LaAlO3/Si(100) Films with High-k, Low-Leakage Current and Good Thermal Stability

High quality amorphous N-doped LaAlO3 (LaAlON) films have been deposited on Si (100) in nitrogen gas by laser molecular beam epitaxy. The chemical nature and physical distribution of N in LaAlON films has been performed by x-ray photoemission spectroscopy. Compared with LaAlO3, a significant improvement in the interfacial quality and leakage current density was obtained by nitrogen additive. At gate voltage +1 V, the leakage current density of the LaAlON film with an equivalent oxide thickness as thin as 2 nm is obtained to be 2.9×10−6 A/cm2, which decreases almost two orders of magnitude from that of LaAlO3 film with the same thickness. Moreover, high-resolution transmission electron microscope analysis show that the LaAlON sample is still amorphous with a very sharp interface between the LaAlON layer and the Si substrate after annealed at 900 degrees C for 60 s.

Seed-mediated growth of gold nanoparticles using self-assembled monolayer of polystyrene microspheres as nanotemplate arrays

Arrays of noble metal nanoparticles show potential applications in (bio-)sensing, optical storage, surface-enhanced spectroscopy, and waveguides. For all such potential devices, controlling the size, morphology, and interparticle spacing of the nanoparticles is very important. Here, we combine seed-mediated growth with nanosphere lithography to study the controllable growth of gold nanoparticles (Au NPs), in which the self-assembly monolayer of polystyrene (PS) on a silicon surface is used to guide the modification of alkanesilanes and the subsequent adsorption of gold seeds; seed-mediated growth is applied to controlling the morphology and size of Au NPs. The size of adsorption region (determining the number of adsorbed gold seeds) is controlled by etching PS microspheres with oxygen plasma or annealing PS microspheres at the glass transition temperature. The size and morphology of the Au NPs are controlled by changing growth conditions. In such a way, we have achieved the dual control of the obtained Au NPs. Preliminary results show that this strategy holds a great promise. This approach can also be extended to a wide range of materials and substrates.

Growth of aligned single-walled carbon nanotubes under ac electric fields through floating catalyst chemical vapour deposition

Through floating catalyst chemical vapour deposition(CVD) method, well-aligned isolated single-walled carbon nanotubes (SWCNTs) and their bundles were deposited on the metal electrodes patterned on the SiO2/Si surface under ac electric fields at relatively low temperature(280 degrees C). It was indicated that SWCNTs were effectively aligned under ac electric fields after they had just grown in the furnace. The time for a SWCNT to be aligned in the electric field and the effect of gas flow were estimated. Polarized Raman scattering was performed to characterize the aligned structure of SWCNTs. This method would be very useful for the controlled fabrication and preparation of SWCNTs in practical applications.

Three-dimensional micro- and nanometre composite aluminium patterns

Three-dimensional micro- and nanometre composite aluminium patterns are constructed on Al substrate by using photolithography, reactive ion etching and anodization. A layer of patterned SiO2 mask is introduced as resist on the surface of Al foil and during anodization the tilted nanopores and remaining Al microstructure are formed underneath the SiO2 mask. The existence of SiO2 mask leads to the deflection of electric field and effect on the transportation of ions, which results in the formation of laterally tilted nanopores, while the nanopores go down directly when being far from the boundaries of SiO2. The vertical and lateral anodization processes proceeding simultaneously construct the Al microstructure under the patterned SiO2 mask.

Nanoscale carbon tubules deposited in anodic aluminium oxide template: a study of soft x-ray transmission

Well-aligned, catalyst-free nanoscale carbon tubules array was prepared by organic compound vapour deposition method using anodic aluminium oxide (AAO) as a template. The experiment of soft x-ray channelling in such carbon tubules array deposited in AAO template was performed at Beijing Synchrotron Radiation Facility. The transmission of x-rays in carbon tubules array with AAO template support was found even higher than that in bare AAO template at high-energy part of energy spectrum though the porous area of the former was smaller than that of the latter. A qualitative explanation is presented to interpret our results.