It was found that the diameter distribution of single-walled carbon nanotubes (SWNTs) grown by the chemical vapor deposition (CVD) method could be controlled by the carbon feeding rate at the growth stage. A unified hypothesis on the relationship between nanoparticle size, growth condition, growth temperature, and diameter of the resulting nanotubes was developed and used to explain the relationship. It was shown that the diameters of SWNTs can be controlled even when highly polydisperse nanoparticles were used as catalyst. Such control enabled us to synthesize uniform small-diameter SWNTs at low carbon feeding rates. Additionally, understanding of the important role of the carbon feeding rate can be used to explain the cause of low growth efficiency in most CVD processes. It would also help us to design methods to improve the growth efficiency of CVD growth of nanotubes.

Semiconducting-only single-walled carbon nanotube (SWNT) network field effect transistors (FETs) have been fabricated by selectively reacting all the metallic SWNTs in the devices with diazonium reagents in a controlled manner. We have shown that the concentration of diazonium reagents used is crucial for selectively eliminating metallic SWNTs and keeping semiconducting ones intact. Excessive amounts of diazonium reagents can indiscriminately react with both metallic and semiconducting SWNTs and thus degrade the performance of the devices. This new technique will facilitate the process of fabrication of high-performance SWNT-based electronic devices.

Single-walled carbon nanotube field-effect transistors were fabricated using solid electrolyte (PEO plus LiClO 4 ) as gating materials. The SWNT FETs demonstrated strong gate-channel coupling with improved device characteristics compared with back-gated devices. More importantly, the nanotubes can be easily doped using different concentrations of electron acceptor mixed in the polymer materials. The transport type of the devices can be easily controlled through doping.Discovered in the early 1990s, 1,2 single-walled carbon nanotubes(SWNTs) are attractive materials for many research fields. Using them in molecular-scale electronic devices is one of the most commonly proposed applications. 3 From both theoretical expectations 4 and experimental results, 5,6 SWNTs have been divided into two groups: metallic or semiconducting. Semiconducting SWNTs are of special interest because they are promising in producing semiconducting devices that rival devices made by traditional Si technology. In this report, we focus on the fabrication of field-effect transistors (FET), a core component for logic circuit fabrication, 7 with SWNTs.In early work on nanotube FETs, a back-gating structure, which used the underlying highly doped Si substrate as the gate electrode, was often used because of its ease of fabrication, 8 but device performance was the trade off for such ease. To improve the FET performance, more complex structures and more expensive materials have been used in making nanotube FETs. For example, Appenzeller et al. 9 used HfO 2 as the insulating layer; Javey et al. 10 used ZrO 2 , which has a very high dielectric constant, to constructed SWNT logic gates. They all succeeded in improving device performance greatly; however, the materials are expensive, and the fabrication processes are time-consuming. Meanwhile, the traditional FET structure of having a dielectric material between the gate and conducting channel was not abandoned in this work.Here we introduce a new idea of using low-cost materials and easy processing procedures to fabricate nanotube FET devices with good device performance. This idea is motivated by the work done by Kruger et al. 11 and Rosenblatt et al.,12 where salty water was used as a gate material and gatechannel coupling was enhanced by orders of magnitude. However, although the device performance is very good, the use of a liquid in devices presented practical problems in real electronic devices. Here, we demonstrate that the replacement of salty water with a polymeric solid electrolyte material can achieve similarly good device performance and avoid the problem of using a liquid in the devices. More importantly, the addition of different chemicals at controlled concentrations to the solid electrolytes enables us to control the device behavior. P-type, n-type, and ambipolar transistor devices can be controllably produced using the method.Solid electrolytes (SEs), which are under intensive study as electrolytes in dry batteries, are formed by dissolving salts in polymers instead of water. 13 Thei...

Single Walled carbon nanotubes (SWNTs) were grown directly on flat substrates using chemical vapor deposition (CVD) method with carbon monoxide and hydrogen mixture as feeding gas. Comparing with other CVD methods, this new approach yields higher efficiency and more reproducible results in obtaining high quality SWNTs separated as individual nanotubes on substrates. Such samples can be used to fabricate nanodevices directly with no further purification or dispersion. Important factors that affect the nanotube growth and possible mechanisms are also discussed.Since their discovery, single-walled carbon nanotubes (SWNTs) have been heavily studied owing to their outstanding physical and chemical properties. 1 They are widely considered as ideal candidates for interconnections and active components in nanoscale electronic devices. Recent research has demonstrated SWNT-based nanodevices, such as quantum wires, 2 field-effect transistors, 3-5 field emitters, 6 etc. Until recently, most of the SWNT-based devices used materials synthesized by either the laser ablation method 7 or the arc method, 8 where the as-grown samples have to be purified and suspended in solvent before deposition on surfaces for device fabrication. The processes of purification and suspending nanotubes in solvent involve the use of highly oxidative chemicals and ultrasonication that are known to create defects on nanotubes and alter their electronic properties. For nanoscale electronics, defect-free SWNTs on surfaces are especially desirable. An alternative and successful way to fabricate nanotube devices is to use nanotubes grown directly on surfaces to avoid the undesired purification steps. However, up to now, surface growth of SWNTs has been limited to chemical vapor decomposition (CVD) of methane on metal nanoparticles supported on surfaces. [9][10][11][12] The growth conditions are critical for the preparation of nanotubes with high purity and efficiency. Here we report an improved CVD method for the growth of SWNTs on surfaces using monodispersed Fe/Mo nanoparticles as the catalyst and a mixture of carbon monoxide (CO) and hydrogen (H 2 ) as feed gas. In contrast to CVD of methane, 9-12 this method allows higher efficiency for nanotube growth and easier control of the growth conditions, thus offering more reproducible results.In our experiments, the catalysts are monodispersed Fe/ Mo nanoparticles (4.2 nm) prepared according to reference 13. The nanoparticles can be dissolved in nonpolar solvents such as hexane. They were deposited on the substrate by slow evaporation of the solution. The substrate was then annealed in air at 700°C for 10 min to remove the organic coating on the particles formed during their preparation steps. 13 Si/SiO 2 substrates were purchased from MEMC Electronic Materials with 500 nm SiO 2 layer. Alumina (sapphire A plane) and magnesium oxide substrates (Superconductive Components, Inc.) were also used. To grow nanotubes, we used a two-furnace setup (Figure 1). The substrates were loaded into the second furnac...

Monodisperse Au@CdS core–shell nanostructured hybrids are synthesized and used as an ideal model to investigate the mechanism of photocatalytic hydrogen generation. Au nanoparticle cores act as the hole scavengers, which evidently improves both catalytic activity and catalytic stability of the Au@CdS core–shell nanostructures toward hydrogen production under visible light irradiation. Hot electron transfer from Au to CdS is also observed to be an ineffective way to improve hydrogen evolution.