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Electron emission measurements were conducted on individual carbon nanotubes. The nanotubes had a closed end and their surfaces were thoroughly cleaned. It is shown conclusively that individual carbon nanotube electron emitters indeed exhibit Fowler–Nordheim behavior and have a work function of 5.1±0.1eV for the nanotubes under investigation, which had diameters of 1.4 and 4.9nm.

We report an alternative way of preparing high-quality single-wall carbon nanotubes (SWCNTs). Using a triple-layer thin film of Al/Fe/Mo (with Fe as a catalyst) on an oxidized Si substrate, the sample is exposed to a single short burst (5 s) of acetylene at 1000 °C. This produced a high yield of very well graphitized SWCNTs, as confirmed by transmission electron microscopy and Raman spectroscopy. We believe that the high temperature is responsible for the high crystallinity/straightness of the nanotubes, and the rapid growth process allows us to achieve a clean amorphous carbon (a-C) free deposition which is important for SWCNT device fabrication. The absence of a-C is confirmed by Auger electron spectroscopy, Raman spectroscopy, and electrical measurements.

Field electron emission behavior of individual multiwalled carbon nanotubes (MWNTs), that are elements of a vertically aligned array grown on a Si wafer, were analyzed with a scanning anode field emission microscope. The electron emission of each MWNT followed the conventional Fowler–Nordheim field emission mechanism after their apexes were freed from the erratic adsorption species using a conditioning process at room temperature. The conditioning process led to stable emission currents and reduced their variations ΔI/I to less than 30% between different MWNTs of the array. This opens the possibility for using MWNTs in an array as independent electron sources for massively parallel microguns.

Electron emission from vertically aligned carbon nanotubes grown by plasma enhanced chemical vapor deposition has been measured using a parallel plate anode and a 1 μm tungsten probe. The field emission characteristics were measured as a function of the nanotube diameter, length, and areal density. It was found that less densely populated “short and stubby” nanotubes with diameters of 200 nm and heights of 0.7 μm showed the best emission characteristics with a threshold voltage of 2 V/μm and saturation emission current density of 10 mA/cm2. A triple junction between nanotube, substrate, and vacuum is proposed to explain our results.

In order to utilize the unique properties of carbon nanotubes in microelectronic devices, it is necessary to develop a technology which enables high yield, uniform, and preferential growth of perfectly aligned nanotubes. We demonstrate such a technology by using plasma-enhanced chemical-vapor deposition (PECVD) of carbon nanotubes. By patterning the nickel catalyst, we have deposited uniform arrays of nanotubes and single free-standing aligned nanotubes at precise locations. In the PECVD process, however, detrimental amorphous carbon (a-C) is also deposited over regions of the substrate surface where the catalyst is absent. Here, we show, using depth-resolved Auger electron spectroscopy, that by employing a suitable deposition (acetylene, C2H2) to etching (ammonia, NH3) gas ratio, it is possible to obtain nanotube growth without the presence of a-C on the substrate surface.

A model of the graphene growth mechanism of chemical vapor deposition on platinum is proposed and verified by experiments. Surface catalysis and carbon segregation occur, respectively, at high and low temperatures in the process, representing the so-called balance and segregation regimes. Catalysis leads to self-limiting formation of large area monolayer graphene, whereas segregation results in multilayers, which evidently "grow from below." By controlling kinetic factors, dominantly monolayer graphene whose high quality has been confirmed by quantum Hall measurement can be deposited on platinum with hydrogen-rich environment, quench cooling, tiny but continuous methane flow and about 1000°C growth temperature.

An improved technique for transferring large area graphene grown by chemical vapor deposition on copper is presented. It is based on mechanical separation of the graphene/copper by H2 bubbles during H2O electrolysis, which only takes a few tens of seconds while leaving the copper cathode intact. A semi-rigid plastic frame in combination with thin polymer layer span on graphene gives a convenient way of handling- and avoiding wrinkles and holes in graphene. Optical and electrical characterizations prove the graphene quality is better than that obtained by traditional wet etching transfer. This technique appears to be highly reproducible and cost efficient.

We demonstrate time-resolved terahertz transmission ellipsometry of vertically aligned multi-walled carbon nanotubes. The angle-resolved transmission measurements reveal anisotropic characteristics of the terahertz electrodynamics in multi-walled carbon nanotubes. The anisotropy is, however, unexpectedly weak: the ratio of the tube-axis conductivity to the transverse conductivity, σz/σxy≅2.3, is nearly constant over the broad spectral range of 0.4–1.6 THz. The relatively weak anisotropy and the strong transverse electrical conduction indicate that THz fields readily induce electron transport between adjacent shells within multi-walled carbon nanotubes.

A noncatalytic chemical vapor deposition mechanism is proposed, where high precursor concentration, long deposition time, high temperature, and flat substrate are needed to grow large-area nanocrystalline graphene using hydrocarbon pyrolysis. The graphene is scalable, uniform, and with controlled thickness. It can be deposited on virtually any nonmetallic substrate that withstands ∼1000 °C. For typical examples, graphene grown directly on quartz and sapphire shows transmittance and conductivity similar to exfoliated or metal-catalyzed graphene, as evidenced by transmission spectroscopy and transport measurements. Raman spectroscopy confirms the sp 2-C structure. The model and results demonstrate a promising transfer-free technique for transparent electrode production.

Large-area uniform carbon films with graphene-like properties are synthesized by chemical vapor deposition directly on Si3N4/Si at 1000 degrees C without metal catalysts. The as deposited films are atomically thin and wrinkle- and pinhole-free. The film thickness can be controlled by modifying the growth conditions. Raman spectroscopy confirms the sp(2) graphitic structures. The films show ohmic behavior with a sheet resistance of similar to 2.3-10.5 k Omega/square at room temperature. An electric field effect of similar to 2-10% (V-G=-20 V) is observed. The growth is explained by the self-assembly of carbon clusters from hydrocarbon pyrolysis. The scalable and transfer-free technique favors the application of graphene as transparent electrodes.

Highly transparent zinc oxide (ZnO) nanowire networks have been used as the active material in thin film transistors (TFTs) and complementary inverter devices. A systematic study on a range of networks of variable density and TFT channel length was performed. ZnO nanowire networks provide a less lithographically intense alternative to individual nanowire devices, are always semiconducting, and yield significantly higher mobilites than those achieved from currently used amorphous Si and organic TFTs. These results suggest that ZnO nanowire networks could be ideal for inexpensive large area electronics.

Vertically aligned carbon nanotubes (VA-CNTs) filled with Pd–Co nanocomposites on an Si substrate have been synthesized by microwave plasma-enhanced chemical vapor deposition. It was confirmed that adjacent Pd–Co nanocomposites in the VA-CNTs were compositionally separated. Most CNTs contained Co pillars on top; however, Pd pillars were rarely present. The strong magnetic induction from an individual Co pillar was revealed by electron holography. The simultaneous phenomenon of the demixing by plasma hydrogen irradiation and the preferential encapsulation into CNTs realized the unique Pd–Co nanocomposites.

We demonstrate the use of nanoimprint lithography as an alternative low-cost fabrication route for the production of ordered arrays of individual carbon nanotube field emitters. A high emission site density of 4×105cm−2 was observed and is well within the specification of the cathode for a field emission display. The measured field enhancement values from the geometry of the nanotubes were in reasonable agreement with the values obtained through electrical measurements. We also show that the distribution of the field enhancement factor is Gaussian, indicative of the presence of well ordered arrays of carbon nanotube field emitters.

The subthreshold slope, transconductance, threshold voltage, and hysteresis of a carbon nanotube field-effect transistor (CNT FET) were examined as its configuration was changed from bottom-gate exposed channel, bottom-gate covered channel to top-gate FET. An individual single wall CNT was grown by chemical vapor deposition and its gate configuration was changed while determining its transistor characteristics to ensure that the measurements were not a function of different chirality or diameter CNTs. The bottom-gate exposed CNT FET utilized 900nm SiO2 as the gate insulator. This CNT FET was then covered with TiO2 to form the bottom-gate covered channel CNT FET. Finally, the top-gate CNT FET was fabricated and the device utilized TiO2 (κ∼80, equivalent oxide thickness=0.25nm) as the gate insulator. Of the three configurations investigated, the top-gate device exhibited best subthreshold slope (67–70mV∕dec), highest transconductance (1.3μS), and negligible hysteresis in terms of threshold voltage shift.

We demonstrate the fabrication and operation of a carbon nanotube (CNT) based Schottky diode by using a Pd contact (high-work-function metal) and an Al contact (low-work-function metal) at the two ends of a single-wall CNT. We show that it is possible to tune the rectification current-voltage (I-V) characteristics of the CNT through the use of a back gate. In contrast to standard back gate field-effect transistors (FET) using same-metal source drain contacts, the asymmetrically contacted CNT operates as a directionally dependent CNT FET when gated. While measuring at source-drain reverse bias, the device displays semiconducting characteristics whereas at forward bias, the device is nonsemiconducting.

Remarkably stable and low noise field-emission electron sources have been obtained using individual carbon nanotubes. The maximum current fluctuation observed over 1h was merely 0.5% and the emission frequency spectrum exhibited 1∕f behavior over a bandwidth of 0.1–25Hz, above which the shot-noise limit was reached. The average noise percentage was determined to be 0.08% (i.e., a signal-to-noise ratio of 1250) for seven CNT emitters operated at several current levels. The influence of the vacuum level was also investigated.