Research Summary

• 1. Single Walled Nanotube(SWNT) Synthesis:

  SWNTs possess outstanding chemical and physical properties. They have potential applications in many fields ranging from nanoelectronic devices to high strength materials. However, the lack of methods for large-scale and contollable preparation limits fundamental research and application development of this unique material. We are focusing on developing new method that can be contolled by the rational way and also can be scaled up to industry level with reasonable cost. We developed an improved CVD method for preparing SWNTs with high catalyst productivity. The total amount of high quality SWNTs produced is greater than 200% the weight of the catalysts. The materials made using the method are of high quality as characterized by SEM and TEM.
  
  
  

  
  
  
  
  
  
  
  
  
  
  
  
  We are also interested in controlling the diameter of the SWNTs that we synthesized.Recently by using metal containing molecular nanoclusters with identical composition as catalyst, we are able to prepare SWNTs with extremely uniform diameters. The diameter of the resulting SWNTs ranges from 0.7 nm to 1.5 nm, with a standard deviation of 17%.
  
  
  

  
  
  
  
  
  
  
  
  
  
  Another CVD method was recently developed in our group for surface growth of SWNTs. It uses mixture of carbon monoxide and hydrogen as feeding gas and is highly efficient. Comparing to CVD from methane, this method offers a much more consistent result, providing a reliable way for SWNT device fabrication. By this method, millimeter-long and well-aligned single-walled carbon nanotubes (SWNTs) have been produced on silica/silicon surfaces using the carbon monoxide chemical vapor deposition (CO-CVD) method. The orientation of the nanotube arrays can be well-controlled by the gas flow during the growth. The majority of the orientated SWNTs are straight and individual. The length of the nanotubes can be >2 mm for a 10 min growth. Furthermore, multidimensional crossed-networks of SWNT can be easily generated by multistep processes. These results present a great opportunity in the controllable production of organized SWNT arrays for large-scale carbon nanotube-based nanodevice fabrication.
  
  

• 2. AFM "Dip-Pen" Nanolithography

  Scanning probe lithography is a rapidly growing research field, in which atomic force microscope based "dip-pen" nanolithography (DPN) is a simple new technique for creating chemically distinct nanostructures on surfaces in a "direct-write" fashion. Previous works demonstrate the transport of alkanethiols to a gold substrate, resulting in the formation of patterned self-assembled monolayers. We showed that surface-induced reduction of metal ions combined with DPN can be used to create metallic nanostructures on Si surfaces. Au nanostructures with sub-100-nm resolution can be created routinely, showing that the DPN technique is a general method for nanofabrication.
  
  

• 3. Chemical Modification of Single Walled Nanotubes

  Single walled carbon nanotubes have been shown to be highly sensitive gas sensors. However, attaching functional group with selective sensing functions on nanotubes without destroying the intrinsic electronic property of the nanotubes is still challenging. We developed a new method of coating SWNTs with a thin layer of SiO2 using 3-aminopropyltriethoxysilane as coupling layers. The thickness of SiO2 could be controlled at about 1nm. The coating of SiO2 on SWNTs was confirmed by burning the SWNTs in air.
  
  

• 4. Synthesis of Nanowires

  Other than SWNTs, we are also interested in synthesis of nanowires by CVD method. We have discovered a novel method to synthesize well-aligned silicon oxide nanowires with diameter around 13 nm. We also succeeded in preparing tungsten oxide nanowires by a simple oxidation process.