Field Emission Investigations Research Articles

The Field Emission Characteristics of a Unit Pixel of a 7 × 7 Array Oxidized Porous Polysilicon Field Emitter

We fabricated oxidized porous polysilicon (OPPS) field emitters and investigated their field emission characteristics using a Ti/Pt multi-layer electrode of different thicknesses and OPPS emitters, which were patterned in a 7 × 7 array. Each unit pixel of the 7 × 7 array OPPS on the field emitter, with a structure of Pt/OPPS/n-type Si, was in operation and their field emission characteristics were investigated using a thermal oxidation process with a Ti/Pt multi-layer electrode. A non-doped polysilicon layer 1.75 µm is deposited on a heavily doped n-type silicon wafer and anodized in a solution of HF (50%):ethanol in a 1:1 ratio. The Ti/Pt multi-layer electrodes were formed with different thicknesses using a DC sputter. The achieved higher emission efficiency of the Ti/Pt electrode, with thickness of 2 nm/7 nm was 1.57% at Vps = 20 V. The investigated field emission characteristics of the unit pixel also demonstrated good uniformity.

Sb-doped SnO 2 wire: Highly stable field emitter

Field emission investigations of a single Sb-doped SnO 2 wire synthesized by thermal evaporation have been carried out in conventional field emission geometry under ultrahigh vacuum. An onset field required to draw a current of 1 nA has been reproducibly observed to be 9.5×10 3 V/μm. A current density of 5.88×10 3 A/cm 2 has been drawn with an applied field of 2×10 4 V/μm. The Fowler–Nordheim plot, obtained from the current–voltage ( I– V) measurements, shows linear nature in accordance with the quantum mechanical tunneling phenomenon. The field enhancement factor has been estimated to be 26,500 cm −1, indicating that the emission is from the nanometric features of the Sb-doped SnO 2 wire. The current–time ( I– t) measurement shows high current stability without severe deviations from the initial set value of 1 μA.

Field emission investigations of RuO 2-doped SnO 2 wires

Field emission studies of a bunch and a single isolated RuO 2:SnO 2 wire have been performed. A current density of 5.73 × 10 4 A/cm 2 is drawn from the single wire emitter at an applied field of 8.46 × 10 4 V/μm. Nonlinearity in the Fowler–Nordheim (F–N) plot has been observed and explained on the basis of electron emission from both the conduction and the valence bands of the semiconductor. The current stability recorded at the preset value of 1.5 μA is observed to be good. Overall the high emission current density, good stability and mechanically robust nature of the RuO 2:SnO 2 wires offer advantages as field emitters for many potential applications.

Imogolite as an electron emitter and a water sensor

We investigated field emission (FE) properties of imogolite including the turn-on field and lifetime stability. Imogolite is an excellent electron emitter with a turn-on field of approximately 2.5–3.5 V/μm. A lifetime test revealed that imogolite protects itself during FE under exposure to O2 gas. We also measured the current–voltage characteristics of the imogolite as a function of the amount of water adsorbed on the surface. The results suggested that the electrode-containing imogolite device could be a useful water sensor in a nanoscale environment.

Stable multiwalled carbon nanotube electron emitter operating in low vacuum

AbstractWe have investigated field emission (FE) properties of an individual multiwalled carbon nanotube (CNT) under low‐vacuum regions around 10−3 Pa. Current versus voltage characteristics of the present CNT emitters were found to be explicable on the basis of the Fowler–Nordheim (F–N) formalism. Time trace of the FE current exhibited more than 30% fluctuation about the mean value, and the lifetime was less than 5 h. Scanning electron microscopy (SEM) observation elucidated that the lengths of the CNTs were reduced after prolonged field emission, plausibly because of local heating induced by the large current density at the apex. To prolong the lifetime, we attempted a type of feedback system by inserting a high ohmic resistance between the electron emitter and the power supply. As a result, the current fluctuation decreased from ∼30% to 2% at 0.1 µA, and the lifetime increased from 5 to 50 h. Finally, an SEM was equipped with both the emitter systems, with and without resistance, which were designed for the CNT field emitter. The SEM images taken by using the emitter with resistance showed consistently brighter appearance, whereas those taken without the resistance exhibited fluctuations in the image brightness. Copyright © 2006 John Wiley & Sons, Ltd.

Investigation of Field Emission and Photoemission Properties of High-Purity Single-Walled Carbon Nanotubes Synthesized by Hydrogen Arc Discharge

Single-walled carbon nanotubes (SWCNTs) were directly synthesized by a hydrogen arc-discharge method by using only Fe catalyst. The synthesized carbon materials indicated high-purity SWCNTs without amorphous carbon materials from SEM observation. The SWCNTs had diameters of 1.5-2.0 nm from TEM and Raman observation. After a simple purification, TGA indicated that SWCNTs had a purity of ca. 90.1 wt %. Field emission from the SWCNT emitters which were fabricated by using a spray method was measured by a diode structure. The vertically aligned SWCNT emitters showed the low turn-on voltage of 0.86 V/microm and a high emission-current density of 3 mA/cm2 at an applied field of about 3 V/microm. From a Fowler-Nordheim plot, the vertically aligned SWCNT revealed a high field enhancement factor of 2.35 x 10(4). The photoemission measurements, excited by a photon energy of 360 eV, showed significantly delocalized graphite-pi states at the purified SWCNTs. Here, we investigated that the field-emission properties of SWCNTs would be attributed to the high electronic density of states near Fermi energy, including the delocalized graphite-pi states.

Field emission current saturation of aligned carbon nanotube—Effect of density and aspect ratio

The investigation of field emission (FE) properties of carbon nanotube film reveals a strong dependency on the density and its aspect ratio. Nonlinearity in the Fowler-Nordheim (F–N) plot has been explained in terms of change in work function of carbon due to heating during FE. A characteristic knee in the F-N plot, separates the linear region from the nonlinear region. Iknee value turns out to be a basic parameter to define the FE process. It has been shown that an optimum density and length of the nanotubes have high efficiency of field emission. An explanation has been given for the phenomena responsible for efficient field emission in short nanotubes.

Influence of nanocrystalline structure on work function of tungsten

The field emission investigations of nanocrystalline (NC) tungsten have revealed the essential difference in energy distribution of field-emitted electrons from NC tungsten as compared to the coarse-grained one. The measurement by the electron beam retarding potential technique also showed the reduction in work function of NC tungsten. The revealed features are explained using two phase model for NC metal.

Electron emission and work function—Past, present and future

The history of electron emission is reviewed from a standpoint of the work function and the applications. For years, in the field of thermionic emission, a great deal of efforts have been devoted to search for low work function materials with a high melting temperature, while the reduction of the local change in time of the work function rather than the work function itself has been the main issue of field emission investigations. High brightness and long life are the central targets of the emission material investigations for the scientific instrument application, while high current density and low power consumption are the guiding principles for the display application. In both fields, field emission has recently become dominant in research and development. In all above cases, the main issue in the future research works will be to analyze the work function in atomic level and thereby to understand the mechanism of the work function reduction by atom adsorption, the change in time of the local work function leading to the current fluctuation, and the relationship between microscopic and macroscopic work functions. Our attempt is discussed, where the work function in atomic level is measured by utilizing the STM technique and it is made clear how far the work function in atomic level extends its influence over the neighboring sites. As a result, a simple relationship is established between microscopic and macroscopic work functions.

53.2: Characteristics of Field Emission from Printed Carbon Nanotubes by Physical Surface Treatments

We investigated field emission properties modify surface morphology of printed CNTs and align CNTs vertically by physical surface treatments such as roller and tapping, also suggest that surface treatment apply to the once electric field keeping method for increase the number of emission sites in the printed CNT cathode.

Ion beam effects on dust grains

Our experimental set-up allows us to keep a single dust grain trapped in a high-vacuum chamber for hours or days and to affect it by electron or ion beams. It apparently makes possible to study each particular charging process separately but, as our results have shown, the influence of emissions from the surfaces surrounding the experimental space cannot be neglected in interpretation of results.The paper is devoted to experimental and theoretical investigations of ion field emission from spherical non-conducting monodisperse melamine resin grains with diameters of 2.35(m∼1×10-14kg), 4.97, and 9.78μm that were exposed by the ion beam with energies ranging from 0.3 to 5keV. We present the methodology of the determination of different charging currents as well as the determination of a grain size. These quantities are then used for estimation of equilibrium potentials. Results obtained using He ions show that ion field emission from the investigated grains can be recorded at field intensities of the order of 109V/m and strongly depends on a history of the grain charging.

Field emission current technique for investigating the energy gap in BCS‐like superconductors

AbstractThis paper considers the ‘current techniques’ for field emission investigations of the parameters of BCS‐like superconductors, which are based on observing the change in field emission current upon the superconducting‐to‐normal (or reverse) phase transition. Based on the results obtained, it has been shown that the field emission current density in the superconducting state is greater than that in the normal state everywhere over the temperature range. Comparison of the expressions obtained with available experimental results has shown that they are in good qualitative and quantitative agreement. Calculating the width of the superconducting gap with the use of the experimental data and the expressions derived in presented paper, we have obtained a value very closely approaching the tabulated one. Copyright © 2004 John Wiley & Sons, Ltd.

Emissions From Nonconducting Negatively Charged Dust Grains

Dust grains immersed into a low-temperature plasma are charged negatively because the electron attachment dominates other charging processes. However, increasing energy of impinging electrons leads to the increase of the yield of secondary emission. When this yield exceeds unity, the grain becomes charged positively. Previous laboratory experiments with electron beams have shown that the surface potential of large grains follows roughly an energy dependence of the secondary emission yield. It means that the grain potential reaches its maximum for hundreds of electronvolts of electron energy and then decreases. Model calculations reveal that the decrease of the grain potential with the electron energy can lead to the reversal of charge sign in a certain range of grain diameters. After this reversal, the grain is charged to the negative potential close to the beam energy. We use of this effect for investigations of electron field emission from nonconducting spheres (glass and melamine formaldehyde resin) with the diameter 4-11 /spl mu/m for glass and 5 and 10 /spl mu/m for resin. Single grains were trapped in a Paul trap and bombarded by the electron beam. The beam energy was changed in a range of 0.3-10 keV. The experimental results confirm the aforementioned expectations and an analysis of these results has shown that: 1) the effective work function for electron field emission from charged nonconducting materials (glass and melamine resin) could be as low as 2 eV, but it can be close to 5 eV as expected for insulating materials. The difference is connected with the charging history. 2) The effect of field dependent secondary emission limits the attainable negative potential.

Self-assembly of carbon nanohelices: Characteristics and field electron emission properties

We report the synthesis of self-assembled carbon nanohelices on iron needles using microwave plasma assisted chemical vapor deposition. The catalytic growth can be explained by the vapor–liquid–solid theory. Their morphologies and microstructures are investigated by scanning electron microscopy, high-resolution transmission electron microscopy, nanobeam diffraction, and Raman spectroscopy. The field-emission investigations show a rather low turn-on electrical field and high emission current.

Low macroscopic field electron emission from surface of plasma sprayed and laser engraved TiO 2, Al 2O 3+13TiO 2 and Al 2O 3+40TiO 2 coatings

The paper deals with investigation of electron field emission from plasma sprayed and laser engraved TiO 2 and Al 2O 3–TiO 2 coatings of two compositions (13 and 40 wt.% of TiO 2). The coatings were plasma sprayed onto aluminum rolls coated initially with Ni20Cr alloy. Their technology included also grinding and polishing prior to CO 2 laser treatment. The treatment was similar to that applied for anilox rolls manufacturing and allowed a production of three different patterns with the lines densities of 60, 100 and 200 cm −1 and depths of approximately 80, 50 and 10 μm correspondingly. The patterns were engraved under angle of 60° that results in a honeycomb geometry of cells. Measurements of emission current under macroscopic electric field up to 150 V/μm for all the samples were carried out. The SEM observations of engraved coating morphology were made in order to find the electron emission spots and XRD analysis allowed to identify the crystal phases present in the coatings. A tentative explanation of a field emission mechanism basing onto Fowler–Nordheim (FN) model is also presented.

Enhanced electron emission from carbon nanotubes through density control using in situ plasma treatment of catalyst metal

We controlled the density of carbon nanotubes (CNTs) through in situ NH3 plasma pretreatment and investigated field emission properties with the density variation. Ni catalytic layer was transformed into small nanoparticles with NH3 plasma pretreatment time and power. As NH3 plasma pretreatment time was increased, the growth rate of grown CNTs was gradually decreased. Also, the density of CNTs reduced from 2×109 to 8×106/cm2 with an increase in NH3 plasma pretreatment time from 10 to 30 min for the Ni layer of 10 Å. With a decrease in the density of CNTs, the emission current density was increased and turn on electric field was decreased. We obtained large and uniform emission current (about 9 mA/emission area of 0.49 cm2) from CNTs film with the density of 8×106/cm2.

Electrical and field emission investigation of individual carbon nanotubes from plasma enhanced chemical vapour deposition

Plasma enhanced chemical vapour deposition (PECVD) is a controlled technique for the production of vertically aligned multiwall carbon nanotubes for field emission applications. In this paper, we investigate the electrical properties of individual carbon nanotubes which is important for designing field emission devices. PECVD nanotubes exhibit a room temperature resistance of 1–10 kΩ/μm length (resistivity 10 −6 to 10 −5 Ω m) and have a maximum current carrying capability of 0.2–2 mA (current density 10 7–10 8 A/cm 2). The field emission characteristics show that the field enhancement of the structures is strongly related to the geometry (height/radius) of the structures and maximum emission currents of ∼10 μA were obtained. The failure of nanotubes under field emission is also discussed.

322 プラズマ CVD 法によるアモルファス炭素膜の合成と電気的特性の評価

In this study, we investigated electrical properties of amorphous carbon (a-C : H) films fabricated by plasma CVD. First, photovoltaic cells consisting of Au/ a-C : H films / n-Si (p-Si) /In-Ga films were fabricated with changing deposition condition. Deposition of a-C"H films were performed using methane as a source gas. Nitrogen and tri-methyl boron (TMB) were also used as the doping gases. Under the light illumination (Xe are lamp at 100mW/cm^2), this cell shows photovoltaic behavior with short circuit current of 0.3mA/cm^2,open circuit voltage of 0.3V and energy conversion efficiency of 0.023%. Secondly, we investigated field emission from a-C : H on ITO films. The film shows field emission at the surface potential barrier of 4∿4.5eV.

Field-emission characteristics of carbon nanotubes and their applications in photonic devices

Based upon the field-emission investigation of carbon nanotubes, several prototype devices have been suggested that operate with low swing voltages with sufficiently high current densities. Characteristics that allow improved current stability and long operating lifetime as electrical and opto-electronic devices are presented. The aim of this paper is to illustrate the useful characteristics of carbon nanotubes and their possible applications.

Carbon Buckypaper field emission investigations

We investigated Carbon Buckypaper with respect to field emission properties, especially long-term field emission stability and under well-defined stress conditions. The Carbon Buckypaper field emitters showed a threshold field strength of about 1 V μm −1 for an emission current of 1 nA. Field emission current densities of more than 10 mA cm −2 are measured for higher applied field strengths. The main focus of our current investigations is the interaction of field emission and vacuum conditions. In this contribution reproducible stress tests with controlled micro-discharges are presented. At higher emission current densities of about 100 mA cm −2 increased ionization and even luminescence out of the emission zone appears before the micro-discharges start. After arcing with micro-discharges the Carbon Buckypaper field emission has lower emission current density and lower variation range. However, the contribution demonstrates the advantages of Carbon Buckypaper as a large array electron field emitter for cold cathode applications.