C.H. Tsai

Electron field emission properties of pulsed laser deposited carbon films containing carbon nanotubes

Carbon nanotubes (CNTs) were successfully synthesized by using a modified pulsed laser deposition (PLD) process, in which the laser ejected carbon species were directly collected by silicon substrates. A catalyst layer is needed in this process. The morphology of catalyst clusters varies with the heat treatment process which, in turn, alters the morphology and field emission properties of the CNTs pronouncedly. Compared with the conventional laser ablation process, such a modified PLD process is simpler, has better collection efficiently, and has a higher production rate. The CNTs thus obtained exhibit superior field emission electron properties, viz. Je=160 μA/cm2 and E0=1.76 V/μm.

Electron emitters synthesized by selected area deposition of carbon nanotubes on silicon substrates

Abstract We have successfully attained patterned carbon nanotubes grown on two-dimensional Ni arrays of square blocks of various sizes on Si by a microwave-heated chemical vapor deposition process. The Ni blocks are either freestanding or isolated by the silicon dioxide. For patterned carbon nanotube emitters, grown on freestanding Ni blocks, the emission current–density increases with the size of the Ni blocks. To the contrary, patterned carbon nanotube emitters grown on 2 μm by 2 μm Ni blocks isolated by the silicon diode have exhibited an emission behavior as excellent as the un-patterned emitters; both emitters have very low turn-on and threshold fields being at ∼0.1 V/μm and ∼1.50 V/μm, respectively and can emit current density exceeding 120 mA/cm2.

Effect of nickel thickness and microwave power on the growth of carbon nanotubes by microwave-heated chemical vapor deposition

The effect of Ni thickness and microwave power on the growth of carbon nanotubes (CNTs) by microwaveheated chemical vapor deposition is reported. A 5-100-nm-thick nickel layer was deposited with an e-gun in a vacuum of 10-6 Torr. It was found that the diameter and length of CNTs increase with Ni layer thickness. The emission I-V curves clearly show two groups of characteristics marked off at the Ni thickness of 50 nm. The low field emission for those films grown on nickel thickness below 50 nm is consistent with the carbonaceous particles and carbon overlayers observed using SEM. The microwave power that determines the substrate temperature also affects the morphology and emission property of CNT films. A CNT film grown on 80-nm-thick Ni layer at 900 W for 18 min has shown excellent emission characteristics with very low turn-on field of 0.056 V/µm and a high current density of 160 mA/cm2 at 4.5 V/µm, which is comparable to the best field emission samples ever reported.

Nanocarbonaceous materials synthesized by microwave CVD and their characteristics of electron field emission

Electron field emission properties of diamond films synthesized by microwave CVD were examined. B-doping or B/N-co-doping markedly improves electron field emission properties of diamond films. Electron field emission current density increases from (Je)B3N0 = 200 µA/cm2 for B3N0 diamond films, which were doped with 3 sccm B(OCH3)3 to (Je)B3N3 = 1750 µA/cm2 for B3N3 diamond films, which were co-doped with 3 sccm B(OCH3)3 and 3 sccm (NH3)2CO. When diamond films were coated with a thin layer of Fe/Co film and then post-annealed at high enough temperature, electron field emission current density was increased from 20 µA/cm2 to 700 µA/cm2.

Excellent field emission from carbon nanotubes grown by microwave-heated chemical vapor deposition

The growth of carbon nanotubes using a microwave-heated chemical vapor deposition system is reported. The material properties including morphology and emission behavior of carbon nanotubes were studied as a function of the Ni layer thickness, applied microwave power, and substrate types. It was found that the diameter and length of carbon nanotubes increase with the Ni layer thickness. The emission current density versus field characteristics of carbon nanotubes grown at 1000 W for 10 min show clearly two groups of characteristics marked off with the Ni thickness of 50 nm. The microwave power, which determines the resulting substrate temperature, also affects the adhesion, morphology, and emission property of carbon nanotubes. There is essentially no difference in the tube’s appearance for carbon nanotubes grown on different types of Si substrates, while carbon nanotubes grown on glass substrates are smaller and more uniform in diameter. A carbon nanotube emitter, grown at 900 W for 18 min on a p-type Si(100) coated with an 80-nm-thick Ni layer, has shown an excellent emission characteristic with extremely low turn-on and threshold fields, respectively, at 0.056 and 1.50 V/μm.

Electron field emission properties of carbon nanotubes converted from nanodiamonds

The characteristics of nanotubes (nanorods) converted from diamond films were investigated. The microstructures and Raman spectroscopy are markedly altered when the diamond films were coated with a thin layer of Fe/Co films ( 950 °C), which is owing to the formation of carbon nanotubes (nanorods) resulted from the heat treatment. The same phase transform behavior was observed no matter whether the starting materials are diamond nuclei, nanodiamonds, or faceted diamonds. The main reaction is presumably the dissolution and reprecipitation of carbon species in the diamond films through the Fe–Co catalyst layer. The carbon nanotubes (nanorods) derived from faceted diamonds show electron field emission current density 1 order of magnitude larger than those converted from diamond nuclei, that is, (Je)nuclei=320 μA/cm2 and (Je)diamond=3800 μA/cm2, with the turn-on field about the same [(E0)=5.2–7.2 V/μm].

Pre-treatment of Fe(C5H7COO)3 metal-organics for growing carbon nanotubes on silicon substrates

H 2 -plasma treatment on spin-coated Fe(C 7 H 5 COO) 3 , Fe(OR) 3 , imposed marked effect on the morphology of Fe-clusters. The 1200 W H 2 -plasma-treated Fe-catalysts are nanosized (40-80 nm) and uniformly distributed, which results in carbon nanotubes of highest purity and most density populated, exhibiting largest electron field emission capacity (J e = 4500 μA/cm 2 at 6 V/μm applied field). Spin coating of Fe(OR) 3 is thus a simple and inexpensive method for producing catalyst of good quality.