Carbon Nanotube Electron Source Research Articles

Coherent ultrafast photoemission from a single quantized state of a one-dimensional emitter.

Femtosecond laser-driven photoemission source provides an unprecedented femtosecond-resolved electron probe not only for atomic-scale ultrafast characterization but also for free-electron radiation sources. However, for conventional metallic electron source, intense lasers may induce a considerable broadening of emitting energy level, which results in large energy spread (>600 milli-electron volts) and thus limits the spatiotemporal resolution of electron probe. Here, we demonstrate the coherent ultrafast photoemission from a single quantized energy level of a carbon nanotube. Its one-dimensional body can provide a sharp quantized electronic excited state, while its zero-dimensional tip can provide a quantized energy level act as a narrow photoemission channel. Coherent resonant tunneling electron emission is evidenced by a negative differential resistance effect and a field-driven Stark splitting effect. The estimated energy spread is ~57 milli-electron volts, which suggests that the proposed carbon nanotube electron source may promote electron probe simultaneously with subangstrom spatial resolution and femtosecond temporal resolution.

Patterning of Silicon Substrate with Self-Assembled Monolayers Using Vertically Aligned Carbon Nanotube Electron Sources.

We introduce a novel patterning technique based on e-beam lithography using vertically aligned carbon nanotube (VACNT) emitters with self-assembled monolayers (SAMs). A 20 μm line width of silicon wafer patterning was successfully demonstrated using octadecyl trichlorosilane (OTS) as a photoresist. To investigate surface modification by the irradiated electrons from the emitters, both contact angle measurement and energy dispersive X-ray (EDX) analysis were conducted. The patterning mechanism of the electron beam irradiated on OTS-coated substrate by our cold cathode electron beam (C-beam) was demonstrated by the analyzed results. The effect of current density and exposure time on the OTS patterning was studied and optimized for the Si wafer patterning in terms of the electronic properties of the VACNTs. The authors expect the new technique to contribute to the diverse applications to microelectromechanical (MEMS) technologies owing to the advantages of facile operation and precise dose control capability based on field electron emission current from the VACNT emitter arrays.

A Cylindrical Triode Ultrahigh Vacuum Ionization Gauge with a Carbon Nanotube Cathode.

In this study, a cylindrical triode ultrahigh vacuum ionization gauge with a screen-printed carbon nanotube (CNT) electron source was developed, and its metrological performance in different gases was systematically investigated using an ultrahigh vacuum system. The resulting ionization gauge with a CNT cathode responded linearly to nitrogen, argon, and air pressures in the range from ~4.0 ± 1.0 × 10−7 to 6 × 10−4 Pa, which is the first reported CNT emitter-based ionization gauge whose lower limit of pressure measurement is lower than its hot cathode counterpart. In addition, the sensitivities of this novel gauge were ~0.05 Pa−1 for nitrogen, ~0.06 Pa−1 for argon, and ~0.04 Pa−1 for air, respectively. The trend of sensitivity with anode voltage, obtained by the experimental method, was roughly consistent with that gained through theoretical simulation. The advantages of the present sensor (including low power consumption for electron emissions, invisible to infrared light radiation and thermal radiation, high stability, etc.) mean that it has potential applications in space exploration.

Field Emission Damage Modes of Carbon Nanotube Spindt Cathode Arrays

The field electron emission of carbon nanotubes has been heavily studied over the past two decades for various applications, including display technologies and spacecraft propulsion. However, a commercializable, lightweight and internally gated electron source has yet to be realized. Electrical shorting of the gate to the substrate from arcing between electrodes is a common and problematic failure mode for Spindt-type carbon nanotube electron sources, causing catastrophic damage and severely limiting their manufacturability. Other types of damage and degradation include physical damage to the carbon nanotubes and their disconnection from the substrate. This work explores field emission damage and its effects on failure in a uniquely designed Spindt-type carbon nanotube cathode. Eighty samples are fabricated and characterized for field emission performance. Analysis of the tested samples reveals three distinct types of damage to the emission pits.

Development of a compact FE-SEM and X-ray microscope with a carbon nanotube electron source

A carbon nanotube (CNT) possesses various benefits as a field electron emitter. Multi-walled CNT (MWNT) have exhibited high brightness and the field emission (FE) current is stable even under poor high-vacuum condition of 10−6 – 10−7 Pa without ion pumping. In this study, we have experimentally manufactured a compact composite field emission scanning electron microscope (FE-SEM) and X-ray microscope (XRM) with a single isolated MWNT electron source. An electron beam from a MWNT was focussed and accelerated by a Butler electrostatic lens. Stable SEM images were observed at a Butler voltage Vbut = 1.5 kV and accelerating voltage Vacc ≃ 15 kV with a focussed probe current Ifoc = 61 pA. The spatial resolution of the SEM, which was estimated from 80 – 20 % edge profile of polystyrene latex spheres, was about 9 nm. XRM images were acquired by 30-min exposure at Vbut = 1.5 kV and Vacc ≃ 17 kV. A spatial resolution of about 200 nm was obtained for XRM. The present results prove the high performance of the compact FE-SEM and XRM using a single isolated MWNT electron source at 10–7 Pa.

Parametrically Optimized Carbon Nanotube-Coated Cold Cathode Spindt Arrays.

Here, we investigate, through parametrically optimized macroscale simulations, the field electron emission from arrays of carbon nanotube (CNT)-coated Spindts towards the development of an emerging class of novel vacuum electron devices. The present study builds on empirical data gleaned from our recent experimental findings on the room temperature electron emission from large area CNT electron sources. We determine the field emission current of the present microstructures directly using particle in cell (PIC) software and present a new CNT cold cathode array variant which has been geometrically optimized to provide maximal emission current density, with current densities of up to 11.5 A/cm2 at low operational electric fields of 5.0 V/μm.

Simulation and Optimization of a Carbon Nanotube Electron Source

AbstractThis paper deals with an optimization of a field-emission structure concept based on vertically aligned carbon nanotubes (CNT). A design concept for a fabrication method for a gate structure based on electron beam lithography is reviewed in the first part of the paper. A single carbon nanotube is grown by the PECVD method inside the gate structure. Calculations and simulations that help determine gate structure proportions in order to obtain the best possible electron reduced brightness and to predict the cathode's electric behavior are also essential parts of this study.

Carbon Nanotube Electron Sources: From Electron Beams to Energy Conversion and Optophononics

Carbon nanotubes have a host of properties that make them excellent candidates for electron emitters. A significant amount of research has been conducted on nanotube-based field-emitters over the past two decades, and they have been investigated for devices ranging from flat-panel displays to vacuum tubes and electron microscopes. Other electron emission mechanisms from carbon nanotubes, such as photoemission, secondary emission, and thermionic emission, have also been studied, although to a lesser degree than field-emission. This paper presents an overview of the topic, with emphasis on these less-explored mechanisms, although field-emission is also discussed. We will see that not only is electron emission from nanotubes promising for electron-source applications, but also its study could reveal unusual phenomena and open the door to new devices that are not directly related to electron beams.

Oxygen plasma resurrection of triode type carbon nanotube field emission cathodes

Abstract The field electron emission of carbon nanotubes has been heavily studied over the past two decades for various applications, such as in display technologies, microwave amplifiers, and spacecraft propulsion. However, a commercializable lightweight and internally gated electron source has yet to be realized. Electrical shorting of the gate to the substrate is a common and problematic failure mode for Spindt type carbon nanotube electron sources, severely limiting their manufacturability. This work explores the novel use of an oxygen plasma etch to reverse this shorting. Plasma treatments on CNTs are commonly used to improve FE performance, but no work presents the use of a plasma etch to reverse shorting. The oxygen plasma etch is shown to be a simple and highly effective method to reverse shorting and increase yield of open circuit Spindt type CNT electron sources by over 70%.

Making carbon nanotube electron sources of defined lengths and with closed caps

A method is reported to make an electron source consisting of an individual multi-walledcarbon nanotube (MWNT) mounted on a tungsten support tip, and cut to length usinglocalized electron beam irradiation in a scanning electron microscope. The apex of the MWNTwas transformed into a closed cap with at least one fullerene-like layer via an annealingprocess involving simultaneous heating and the extraction of an emission current of ∼ 1 mA. The electron emission occurred at localized emission sites. The electron emissionshowed Fowler–Nordheim behavior, was highly stable with time, and exhibited a lowenergy spread. The structure of the caps of two MWNTs was studied with transmissionelectron microscopy before and after the cap closure.

First-principles study of quantum tunneling from nanostructures: Current in a single-walled carbon nanotube electron source

We present a first-principles calculation of the emission current in a single-walled carbon nanotube electron source. We have employed the nonequilibrium Green's function and Fisher-Lee's transmission formulation to describe electronic transport through the system. The simulation results reproduce the trends observed in experimental data closely and, in particular, the current saturation and deviation from the Fowler-Nordheim behavior. The proposed numerical approach is useful whenever a region of vacuum is present in the system Hamiltonian.

A carbon nanotube field emission cathode with high current density and long-termstability

Carbon nanotube (CNT) field emitters are now being evaluated for a wide range of vacuumelectronic applications. However, problems including short lifetime at high current density,instability under high voltage, poor emission uniformity, and pixel-to-pixel inconsistencyare still major obstacles for device applications. We developed an electrophoretic process tofabricate composite CNT films with controlled nanotube orientation and surface density,and enhanced adhesion. The cathodes have significantly enhanced macroscopic fieldemission current density and long-term stability under high operating voltages. Theapplication of this CNT electron source for high-resolution x-ray imaging is demonstrated.

삼극형 CNT 전자원에 대한 신뢰성 평가

삼극형(triode type) 전자 방출원을 프린팅된 CNT(Carbon Nanotube) 에미터를 이용하여 제작하였다. 후면노광(Back Exposure)방법으로 CNT 에미터의 높이를 균일하게 하고, 나노 Ag를 첨가하여 CNT와 전극 사이의 접착력 및 전기전도성을 높임으로써 고전압, 고전류 구동 시 신뢰성을 확보하였다. 게이트 높이가 에미터 길이에 비해 비교적 높은 매크로 게이트 구조를 사용하여 누설 전류가 적고 안정적인 구동이 가능하였다. 제작된 삼극형 전자 방출원은 DC 전압이 인가된 상태에서 일정시간동안 전계방출 전류를 측정하여 신뢰성을 평가하였다. 가열 배기 에이징(Aging) 과정을 거친 경우 약 12 시간동안 안정적인 전계방출 특성을 보였다. 이 때 게이트 누설전류는 약 10 % 미만이었다. The electron emission source of triode type has been fabricated using CNT paste. The nano Ag particle and photosensitive polymers were added to the CNT paste. The surface roughness of the CNT emitter was uniform by the back exposure method. The added nano Ag particle improves the adhesion and the electric conductance with small variation in the CNTs and between electrode. After the aging with heat-exhausting, the reliability of the triode CNT electron source was secured in the high voltage and current operation for 12 hours. At this time, the gate leakage current was about 10 % less than.

An empirical study of dynamic properties of an individual carbon nanotube electron source system

In this paper we present an empirical study of some dynamic properties of an individual carbon nanotube (CNT) field emission electron source system. We propose a circuit model that represents the CNT cathode to anode diode as a capacitor in parallel with a voltage-controlled variable resistor. The transient response of the CNT electron source system to the falling edge of a voltage step input was evaluated. For input voltages below the threshold voltage for field emission, the nanotube loop is effectively open and the circuit response is consistent with a discharging capacitor. On the other hand, for input voltages above field emission threshold, the nanotube loop conducts and now the capacitor discharges to a certain extent through the nanotube loop as well. Field emission current versus voltage data also shows that the resistance across the CNT cathode to anode diode varies as a function of applied voltage. Below turn-on voltage, the diode behaves as an open circuit (4 TΩ at the ammeter noise floor). Above turn-on voltage, resistance falls exponentially, as expected from the Fowler–Nordheim equation for cold field emission current. Experimental current–voltage data is presented for a simple emitter array consisting of two CNTs with equal lengths. Despite the similarity in their lengths the turn-on voltages of the nanotubes varied significantly, viz. 26 V versus 109 V. This large difference in the turn-on voltages can be attributed to tip imperfections. For advanced array applications such as high-throughput parallel e-beam lithography, in which precise dose control is necessary, the diode circuit model will be useful for controlling individually addressed nanotubes to account for dissimilar field emission properties. The model may also be applied to optimize the design of a SEM incorporating a single CNT electron source.

High-current-density field emission display fabricated from single-walled carbon nanotube electron sources

Single-walled carbon nanotubes can be used as electron sources in the process of field emission, and have great potential for practical application of the field emission display (FED) panels with large screen size. We fabricated a FED using the single-walled carbon nanotubes (SWNTs) as the cathode by the screen-printing process. Test showed that the SWNTs emitters exhibit excellent macroscopic emission properties. It has low turn-on voltage (2.7 V/μm) and high brightness, with a high current density of good uniformity and stability. It was observed that the field emission qualitatively follows the conventional Fowler–Nordheim (F–N) theory, and aging treatment played an important role in improving the image uniformity and stability. Compared to other complicated processes, the simple fabrication using screen-printing process seems to be advantageous for practical application.

MiniSEM with Carbon Nanotube Electron Source and Electrostatic Lens

MiniSEM with Carbon Nanotube Electron Source and Electrostatic Lens

Evaluation of Decomposition Treatment for Halogenized Compounds Using by Acceleration of Electrons from Carbon Nanotubes

A novel decomposition treatment for halogenized compounds using a carbon nanotube (CNT) electron source has been proposed. It is observed that a high concentration of chlorophenol can be significantly decreased by using a CNT electron source. The concentration is reduced to less than 1/1000 after only a few minutes of treatment. The input energy for 1 g of chlorophenol is 46 J when the injection power is 0.5 W. The input energy is only 1/161 times lesser than that for the treatment for barrier discharge. The proposed treatment using CNTs has a high efficiency because the input energy is provided only by the accelerated electrons.

Low noise and stable emission from carbon nanotube electron sources

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.

Optical Performance of Carbon-Nanotube Electron Sources

The figure of merit for the electron optical performance of carbon-nanotube (CNT) electron sources is presented. This figure is given by the relation between the reduced brightness and the energy spread in the region of stable emission. It is shown experimentally that a CNT electron source exhibits a highly stable emission process that follows the Fowler-Nordheim theory for field emission, fixing the relationship among the energy spread, the current, and the radius. The performance of the CNT emitter under realistic operating conditions is compared with state-of-the-art electron point sources. It is demonstrated that the reduced brightness is a function of the tunneling parameter, a measure of the energy spread at low temperatures, only, independent of the geometry of the emitter.

59.1: Invited Paper: National FED Project in Japan

Japanese government has started a three-year project on carbon nanotube (CNT) FED in 2003. The feasibility of uniform CNT electron source both by chemical vapor deposition (CVD) method and printing method has been proved. The high-temperature CVD extended the applicability to fine pitch of 0.2mm. The emitter fabricated by low-temperature CVD proved to be driven with low voltage. The printing method employs a new etching process of silicone-ladder polymer insulator combined with laser irradiation surface-treatment. A spacer-free glass panel structure and a new sealing material applicable under low temperature have been sucessfully applied to test panels.