Controllable Fabrication of GeSi Nanowires in Diameter of About 10 nm Using the Top-Down Approach

Ordered GeSi nanowires with a ～ 10nm cross section are fabricated utilizing top-down and Ge condensation techniques. In transmission electron microscopy measurements, the obtained GeSi nanowires exhibit a single-crystal structure and a smooth Ge/SiO2 interface. Due to the linear relationship between the cross-section area and the initial pattern size under the self-limited oxidation condition, the cross-section size of GeSi nanowires can be precisely controlled. The Raman spectra reveal a high Ge fraction （up to 97%） and a biaxial strain of the GeSi nanowires. This top-down technique is promising for fabrication of high-performance GeSi nanowire based optoelectronic devices.

Diameter-Controlled Growth of Carbon Nanotubes Through Pyrolysis of Acetylene Using Rare Earth Alloy as Catalyst in Hydrogen

High-purity carbon nanotubes(CNTs)were synthesized in hydrogen ambience by CVD method by (using) rare earth alloy MlM_(5-1.35)(CoAlMn)_(1.35) as catalyst, acetylene as carbon source. The influence of hydrogen flow rate on the diameter, shape, purity, graphitization degree and output of carbon nanotubes was systematically studied by scanning selectronic microscopy(SEM), transmission electron microscopy(TEM), X-ray diffraction(XRD)and Raman technique. The results indicate that the size of MlM alloy particles changed from μm order into nm order during the process of hydrogen reduction. While no introducing hydrogen in the reaction of acetylene and catalyst, CNTs can also be synthesized on the catalyst. The CNTs are short and thick with average diameter of about 97.8 nm, and the wall of CNTs is also thick and rough. With increasing of hydrogen flow rate, the diameter of CNTs first decrease and then increase, while the output, purity, and graphitization degree first increase and then decrease. The optimized conditions are: CNTs reach its narrowest size with diameter of 49.1 nm when hydrogen flow rate is 50 ml·min^(-1). The purity, graphitization degree, and output of CNTs reach highest and largest when hydrogren flow rate is 75 ml·min^(-1). It has the most uniform tube size of 97.38 nm when hydrogen flow rate is 100 (ml·min^(-1).)

Study on Diameter Controlled Growth of Carbon Nanotubes by LaAl_(1-x)Fe_xO_3 Catalysts

A series of LaAl 1-xFe xO 3 catalysts prepared with lanthanum nitrate, aluminium nitrate and iron nitrate was investigated in catalytical syntheses of carbon nanotubes with high yields and purity. The properties of carbon nanotubes prepared by the method of CVD(chemical vapor deposition) with n-hexane as the carbon resource were studied and it was shown that the diameter of carbon nanotubes can be controlled by the molar ratio of iron to aluminum in the catalysts and that the diameter of carbon nanotubes changes a little with the decrease of the iron content in the catalysts. From the TEM pictures of carbon nanotubes, it can be found that the LaAl 1-xFe xO 3 catalysts have a significant influence on the wall thickness of the carbon nanotubes, whereas they have little influence on the inner diameter of the carbon nanotubes.

Controlling the Diameter of Single-Walled Carbon Nanotubes by Improving the Dispersion of the Uniform Catalyst Nanoparticles on Substrate

To have uniform nanoparticles individually dispersed on substrate before single-walled carbon nanotubes(SWNTs)growth at high temperature is the key for controlling the diameter of the SWNTs.In this letter,a facile approach to control the diameter and distribution of the SWNTs by improving the dispersion of the uniform Fe/Mo nanoparticles on silicon wafers with silica layer chemically modified by 1,1,1,3,3,3-hexamethyldisilazane under different conditions is reported.It is found that the dispersion of the catalyst nanoparticles on Si wafer surface can be improved greatly from hydrophilic to hydrophobic,and the diameter and distribution of the SWNTs depend strongly on the dispersion of the catalyst on the substrate surface.Well dispersion of the catalyst results in relatively smaller diameter and narrower distribution of the SWNTs due to the decrease of aggregation and enhancement of dispersion of the catalyst nanoparticles before growth.It is also found that the diameter of the superlong aligned SWNTs is smaller with more narrow distribution than that of random nanotubes.