Sun Lianfeng

Synthesizing graphenes directly on SiO2/Si in open environments by a dual flame method

In this work, a simple, productive and low cost method is reported for synthesizing few-layer graphenes directly on SiO2/Si substrates. Films of nickel with different thicknesses (25–700 nm) are thermally deposited on SiO2/Si substrates as catalyst. The substrates with nickel films are treated by lighting cotton and alcohol blast burners in sequence and then cooling down quickly. The dual flames last only several minutes. After growth, few-layer graphenes can be found on the upper surface of nickel and at the interfaces between the nickel and the SiO2/Si, which are confirmed by Raman spectroscopy. Few-layer graphenes can be directly obtained on the SiO2/Si substrate after etching off nickel, without further transfer process. Scanning Raman mapping and transmission electron microscopy indicate that the graphenes are uniform, continuous and of high quality. The dependence of the quality of graphenes on the thickness of nickel have been studied and discussed.

Dynamic surface wettability of three-dimensional graphene foam

In this work, three-dimensional graphene foams (GFs) are synthesized and characterized by scanning electron microscope (SEM) and Raman spectroscopy. The SEM images indicate that after the growth of graphene, the graphene covers the surface of nickel (Ni) foam uniformly. Raman spectra show that the percentages of monolayer, bilayer, trilayer, and multilayer graphenes are ~ 58%, ~ 32%, ~ 8%, and ~ 2%, respectively. The contact angle (CA) (~ 12°) of water droplet (3 μL) on GF is found to be larger than that on Ni foam (~ 107°), indicating that graphenes have changed the surface wettability of the Ni foam. Meanwhile, the dynamic characteristics of CA of water droplet on GF are different from those on Ni foam. The mechanisms for different behaviors are discussed, which are attributed to volatilization and seepage of water droplets.

AuPd catalytic nanoparticle size effect on the formation of amorphous silicon nanowires

Amorphous silicon (a-Si) nanowires have been prepared on SiO2/Si substrates by AuPd nanoparticles / silane reaction method. Field-emission scanning electron microscopy and transmission electron microscopy were used to characterize the samples. The typical a-Si nanowires we obtained are of a uniform diameter about 20 nm and length up to several micrometers. The growth mechanism of the nanowires seems to be the vapor-liquid-solid mechanism. The catalytic particle size effect on the formation of the nanowires and the cause of forming amorphous state Si nanowires are discussed.

Giant magnetic moment at open ends of multiwalled carbon nanotubes

(Received 14 October 2014; revised manuscript received 6 November 2014; published online 9 December 2014) The attractions of cantilevers made of multiwalled carbon nanotubes (MWNTs) and secured on one end are studied in the non-uniform magnetic field of a permanent magnet. Under an optical microscope, the positions and the corresponding deflections of the original cantilevers (with iron catalytic nanoparticles at the free end) and corresponding cut-off cantilevers (the free ends consisting of open ends of MWNTs) are studied. Both kinds of CNT cantilevers are found to be attracted by the magnet, and the point of application of force is proven to be at the tip of the cantilever. By measuring and comparing deflections between these two kinds of cantilevers, the magnetic moment at the open ends of the CNTs can be quantified. Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes, it is called giant magnetic moment, and its possible mechanisms are proposed and discussed.

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.

Water-assisted highly enhanced crystallographic etching of graphene by iron catalysts

We report the assisted role of water vapor in crystallographic cutting of graphene via iron catalysts in reduced atmosphere. Without water, graphene can be tailored with smooth trenches composed of straight lines with angles of 60? or 120? between two adjacent trenches. After the addition of water, new chacteristics are found: such as almost no iron particles can be detected along the trenches; each trench becomes longer and lots of graphene nanoribbons can be generated. The underlying mechanism is proposed and discussed, which is attributed to stimulating and lengthening of the catalytic activity of iron particles by water vapor.

AuPd catalytic nanoparticle size effect on the formation of amorphous silicon nanowiresProject supported in part by the National Natural Science Foundation of China (Grant No. 19834080) and by the Laboratory of Advanced Materials, Tsinghua University, Beijing, China.

Amorphous silicon (a-Si) nanowires have been prepared on SiO2/Si substrates by AuPd nanoparticles / silane reaction method. Field-emission scanning electron microscopy and transmission electron microscopy were used to characterize the samples. The typical a-Si nanowires we obtained are of a uniform diameter about 20 nm and length up to several micrometers. The growth mechanism of the nanowires seems to be the vapor-liquid-solid mechanism. The catalytic particle size effect on the formation of the nanowires and the cause of forming amorphous state Si nanowires are discussed.

Structure and morphology of carbon nanotubes grown on zeolite-supported catalysts by chemical vapor deposition

The zeolite-supported catalysts were prepared in nickel and cobalt nitrate aqueous solutions by ion exchange method. After reducing these substrates by hydrogen, we grew carbon nanotubes on them by chemical vapor deposition under different conditions. The results reveal that nickel/zeolite, cobalt/zeolite and nickel+cobalt/zeolite have different optimal conditions. When nickel+cobalt/zeolite was used as the catalyst, we can get straight carbon nanotubes. The Raman spectrum of the straight nanotubes shows they have fewer defects. We propose a growth mechanism for the growth of these nanotubes.