Electron Emission

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Size of the localized electron emission sites on a closed multiwalled carbon nanotube

Size of the localized electron emission sites on a closed multiwalled carbon nanotube

The distribution of the transverse energy of the trans- mitted electrons limits the resolution of the FEM. We have deconvolved the FEM image with the point spread function as obtained from the transverse energy distribution to increase the spatial resolution of FEM. The field emission energy distribution of the emitted electron beam was de- termined by measuring energy spectra of the nanotube emitters using a hemispherical energy analyzer (VSW Atomtech Ltd.). Figure 4(a) shows the energy spectrum of MWNT 1, obtained at I ¼ 130 nA and U ¼ 470 V. The FEM images and shape of the energy spectrum suggest that the electron emission occurred via field emission. As verification, the current I was measured as a function of U . The plot of lnðI=U 2 Þ versus 1=U was linear, and the field factor ¼ F=U ¼ ð1:7 0:1Þ 10 7 m 1 , indicating that field emission occurred [16] for the MWNT [28]. The current density as a function of energy can be written as [29]
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Electron emission from selected metal surfaces by multiphoton processes

Electron emission from selected metal surfaces by multiphoton processes

The research groiç) headed by Prof. Gyozo Farkas of The Central Research Institute for Sohd State Physics in Hungary has since established itself as the world leaders in this field by pubhshing a number of important papers from 1967 to the present day. Their first paper {Farkas, Ndray & Varga (1967)) was entitled 'Dependence of non-classical electron emission fi*om metals on the direction of polarisation of laser beams'. In this paper the authors described an experiment performed using a passively Q-switched ruby laser (hu=1.786eV, 30ns FWHM pulse width, peak power density = 0.5MWcm'^) incident on a bulk solid silver surface (0=4.8eV). The laser beam was passed through a polarising optic prior to impinging unfocused onto the surface. The target was mounted in a glass bulb under vacuum ( & = 1 0 ® torr) at a glancing angle of 87® to the incoming laser beam.
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The laser assisted field electron emission from carbon nanostructure

The laser assisted field electron emission from carbon nanostructure

Electron emission measurements were performed in a diode configuration with flat cathode and anode elec- trodes. The cathode was composed of NCF film depos- ited on the 20 × 20 mm 2 n-doped Si substrate, which was attached to a glass plate with indium contact layer. The anode consisted of 25 × 25 mm 2 glass plate covered by a transparent indium tin oxide (ITO) layer. The transmittance of the anode was about 80% in the visual wavelength spectral range. The glass plates holding anode and cathode electrodes were glued to each other by a vacuum epoxy glue. The distance between surfaces of NCF (cathode) and ITO (anode) was fixed at 500 μ m by nonconductive spacers. The field emission threshold
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New insights in high energy electron emission and underlying transport physics of nanocrystalline Si

New insights in high energy electron emission and underlying transport physics of nanocrystalline Si

I T IS WIDELY known that high-porosity porous silicon (PS) comprises tree-like network of many nanometer size silicon quantum dots surrounded by thin oxide layer of a few nm (sil- icon nanocrystallites, nanocrystalline silicon: nc-Si). Recently, high-energy electron emission from the PS diode was reported [1], which is schematically illustrated in Fig. 1(a). The silicon substrate is electrochemically treated to form 1 m thick porous silicon region. On top of the surface, 5-nm-thick Au electrode is formed. A positive bias applied to the Au electrode ejects elec- trons from the emitting surface into the vacuum. The emission energy distribution measured from the vacuum level exhibits a peak, which shifts toward higher energy with increasing positive bias [2], [3] as illustrated in Fig. 1(b). The PS diode is a poten- tial candidate for cold cathodes in future flat panel displays due to its low turn-on voltage and high current stability. Therefore, the electron emission from the PS diodes has been intensively
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Electron Emission Spectroscopy Characterization of N-doped Diamond and Si-doped AlGaN

Electron Emission Spectroscopy Characterization of N-doped Diamond and Si-doped AlGaN

The electron emission below the CBM of NEA diamond had been detected previously and used for vacuum level determination. Experimental investigations by Baumann et al. [15] suggested that extended hydrogen or deuterium plasma treatment on diamond surface could strongly influence the emission below the CBM. However, the mechanism of the electron emission below CBM is still controversial. Bandis et al. [16] attributed this feature to the exciton breakup mechanism. Yater et al. [17] proposed that the below CBM electron emission could occur if electrons lose energy under situations of inelastic scattering at the surface/vacuum interface or transitions to low-energy surface states. Ristein et al. [18] attributed it to the defect emission under thermal non-equilibrium. Despite the undetermined origin of the emission below the CBM, from Fig.3.1, it is interesting to note that the vacuum level is near the diamond Fermi level with specifying the vacuum level position with the onset of electron emission. By the definition of semiconductor work function as the energy difference of vacuum level referenced to the Fermi level [4,19], our results indicate zero or negative true work function of N-doped CVD diamond. The barrier to the thermionic emission in this case is then the energy to the CBM and not the vacuum level.
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Enhanced field electron emission properties of hierarchically structured MWCNT based cold cathodes

Enhanced field electron emission properties of hierarchically structured MWCNT based cold cathodes

Hierarchically structured MWCNT (h-MWCNT)-based cold cathodes were successfully achieved by means of a relatively simple and highly effective approach consisting of the appropriate combination of KOH-based pyramidal texturing of Si (100) substrates and PECVD growth of vertically aligned MWCNTs. By controlling the aspect ratio (AR) of the Si pyramids, we were able to tune the field electron emission (FEE) properties of the h-MWCNT cathodes. Indeed, when the AR is increased from 0 (flat Si) to 0.6, not only the emitted current density was found to increase exponentially, but more importantly its associated threshold field (TF) was reduced from 3.52 V/ μ m to reach a value as low as 1.95 V/ μ m. The analysis of the J-E emission curves in the light of the conventional Fowler-Nordheim model revealed the existence of two distinct low-field (LF) and high-field (HF) FEE regimes. In both regimes, the hierarchical structuring was found to increase significantly the associated β LF and β HF field enhancement factors of the h-MWCNT
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Electron Emission of Graphene Diamond Hybrid Films Using Paraffin Wax as Diamond Seeding Source

Electron Emission of Graphene Diamond Hybrid Films Using Paraffin Wax as Diamond Seeding Source

electrons through multiple barriers caused by the pres- ence of different materials [38,39]. The Fowler-Nord- heim plot for graphene-diamond hybrid has two slopes representing electron emission from two different regions. In region 20 < E < 4.5 V/μm the major contribution is due to electrons that are present in the conduction min- ima of graphene-diamond hybrid film and in the other, 4.5 < E < 2.7 V/μm, the major contribution is made by the low occupancy states. An effective field enhancement factor (β) calculated from the slopes of FN plot for

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Filtering of the interstellar dust flow near the heliopause: the importance of secondary electron emission for the grain charging

Filtering of the interstellar dust flow near the heliopause: the importance of secondary electron emission for the grain charging

It is worth noting that interstellar dust grains are electri- cally charged by photoelectron emission, sticking and recom- bination of plasma particles, secondary electron emission, thermionic emission, and field emission (see Draine (1989) for a review). The relative importance of each charging pro- cess depends on the radiation and plasma environment as well as on the size and material composition of the grains. Inter- stellar dust grains enter a zone of increased plasma tempera- ture between the heliopause and the termination shock, which characterizes the transition of the solar wind flow from super- sonic to subsonic (cf. Baranov and Malama, 1993; Pauls and Zank, 1996, 1997; Zank et al., 1996). The high plasma tem- perature in this region (heliosheath) raises the surface charge of grains as a result of the intensive secondary-electron emis- sion induced by energetic electron bombardment (Kimura and Mann, 1998a). We therefore expect that smaller grains are filtered off in the magnetic field near the heliopause be-
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Influence of Deuterium Retention on Secondary Electron Emission from Graphite under Deuterium Plasma Exposure

Influence of Deuterium Retention on Secondary Electron Emission from Graphite under Deuterium Plasma Exposure

The influence of deuterium retention on the electron-impact secondary electron emission (SEE) is studied in isotropic graphite (ETU-10). The ETU-10 surface sheath voltage and its deuterium retention under deuterium plasma exposure were measured simultaneously. Deuterium retention was estimated using in situ nuclear reaction analysis. While deuterium retention increased with decreasing graphite sample temperature, the sheath voltage on the sample surface decreased. The sheath potential variation is considered to be due to the SEE yield variation, which was estimated using the sheath voltage. The estimated SEE yield value increased by approximately 10% as the deuterium retention rose by a factor of two.
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Effect of Electron and/or Ion Nonthermality on Dust Acoustic Wave Propagation in a Complex Plasma in Presence of Positively Charged Dust Grains Generated by Secondary Electron Emission Process

Effect of Electron and/or Ion Nonthermality on Dust Acoustic Wave Propagation in a Complex Plasma in Presence of Positively Charged Dust Grains Generated by Secondary Electron Emission Process

charged positively [27], even during the night hours when the photoelectric emission of electrons from the ice is not operable. The cause of this positive charging may be due to secondary electron emission from charged ice particles. The presence of charged dust modifies the dispersion properties of plasma waves as well as their exci- tation conditions as detailed in references [28]-[30].

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Electron Emission from Low Dimensional Structures.

Electron Emission from Low Dimensional Structures.

depends on the plane potential. Figure 2a illustrates the field above the surface of a cylinder along its perimeter, as a function of angular coordinate. The numerical calculation had been carried out for a cylinder placed between two conducting biased planes representing a back- gate and an anode. For the condition of zero gate voltage, the anode voltage is selected to produce a field below 1 V/μm, which we assume is insufficient for inducing emission from any EMS present at the top of the cathode. When bias in the range of 20 - 30 V is applied at the gate (‘on’ status), the field above the cathode (~ 10 V/μm) is sufficient to produce electron emission from an EMS containing CNTs, for example, while other types of EMS may require different voltage ratios. At the ‘on’ status conditions described above, the field below the cathode is higher than at the top of the cathode, but not high enough to initiate field emission from the cathode metal toward the gate (we assume that a typical macroscopic field required for field emission from metal surfaces is within the range of 25 - 30 V/μm). As it follows from Fig. 2a, the field above the cathode is approximately the same for angular coordinate Θ up to 30 degrees, so that in the ideal case uniform emission from an EMS material deposited within the area restricted by Θ < 30 0
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Effects of Al interlayer coating and thermal treatment on electron emission characteristics of carbon nanotubes deposited by electrophoretic method

Effects of Al interlayer coating and thermal treatment on electron emission characteristics of carbon nanotubes deposited by electrophoretic method

The conical-type CNT-based field emitters were fabri- cated using the EPD method. Substantially, enhanced emission characteristics, such as lower turn-on voltage and higher emission currents, were obtained by ther- mally treating the CNTs. From the FESEM observations as well as from the electrical measurements of emission characteristics, the thermal treatment barely affected the CNTs' surface morphologies and field enhancement fac- tors. The observations of the Raman spectra confirmed that the improved emission characteristics of the ther- mally treated CNTs were ascribed to their higher degrees of crystallinities. In addition, the long-term emission sta- bilities of the CNTs were significantly ameliorated by coat- ing Al interlayers prior to the deposition of CNTs. The CNTs, when deposited on the Al interlayers and thermally treated, exhibited highly stable electron emission beha- viors without any significant degradation of emission cur- rents even after 20 h of operation. The XPS results
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Field Electron Emission from a CNx:H Films Formed on Al Films Using Supermagnetron Plasma CVD

Field Electron Emission from a CNx:H Films Formed on Al Films Using Supermagnetron Plasma CVD

Excellent field electron-emission characteristics of amorphous carbon films have attracted considerable attention due to their promising applicability to cold-cathode materials in future-generation high-performance electronic devices, such as display devices and microelectronics [1]-[4]. Hydrogenated amorphous carbon (a-C:H) and amorphous carbon nitride (a-CN x :H) films are of considerable interest due to their unique properties, such as

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Electron Emission from Metals in Intense Electron Fields

Electron Emission from Metals in Intense Electron Fields

ELECTROH Ei;iISSIO'i! fo'RQl i l 1ETAI JS Di I?i'i'E!YSB ELECri'RIC FIELDS Thcsin by Chas C Lauritsen In Partial Fulfillment of the Requirements for the pegree of Doctor of Philosophy, California Inst[.]

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In Situ, Real-Time Characterization of Silicide Nanostructure Coarsening Dynamics by Photo-Electron Emission Microscopy

In Situ, Real-Time Characterization of Silicide Nanostructure Coarsening Dynamics by Photo-Electron Emission Microscopy

The Duke storage ring OK-4/FEL is capable of generating spontaneous radiation in a broad range from IR to soft X-rays as well as coherent UV and VUV radiation. 27 The storage ring consists of two 34 meter long straight sections and two 180° arcs which form a race-track like shape. The north straight section of the ring houses the RF cavity, diagnostic systems, and synchrotron radiation devices, while the south straight section is dedicated to housing the FEL undulators. The Duke storage ring is capable of being operated between 0.2 and 1.1 GeV and can store a maximum of 64 bunches of electrons. 28 Laser operation requires very precise synchronization between the electron bunch revolution frequency and the optical pulse round trip frequency. This synchronization is accomplished with fine tuning provided by the RF system. The FEL electron supply is generated via a standard thermionic cathode which is heated to a point just below the threshold for thermionic emission. The heated cathode is subjected to a UV laser pulse which stimulates the release of electrons in a narrow energy spread. The electrons are then accelerated to FEL operating energy. A schematic of the Duke FEL storage ring and the PEEM system is shown in Figure 2.12.
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Fabrication, structure, and electron emission of single carbon nanotubes

Fabrication, structure, and electron emission of single carbon nanotubes

carbon fiber is composed of a multi-layer structure. A single carbon nanotube extrudes from the core of the carbon fibers. HRTEM imaging revealed that the carbon layers wrapping the CNT are made of many nanometer-size graphite domains of different orientations, which are connected by amorphous carbon. The HRTEM images also revealed that the nanotubes usually have two shells to more than 20 shells. A diameter distribution has been obtained with a peak at about 6 nm. About 70% of the nanotubes have a diameter less than 10 nm. Due to the high synthesis temperature, the nanotube side-walls have good crystallinity, which will improve the emission lifetime. To achieve a high brightness, the nanotube length needs to be controlled to reduce the thermal vibrations. In this work, we have developed an in-situ cutting technique to control the nanotube length. In a JEM-2010F TEM (operated at 200 KV with a field emission gun), a very fine high energy electron probe (7 Å diameter) was used to cut the MWNTs. We also used the NBD method to determine the atomic structure of MWNT even without HRTEM images. With a small condenser aperture, a fine and parallel electron beam has been formed and used to illuminate the MWNT. The NBD diffraction patterns composed of discrete layer lines were obtained. The atomic structure was determined from the layer line spacings and the scattering intensities. The atomic structure of a five-wall carbon nanotube has been determined and the field emission properties of this nanotube also have been measured.
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Secondary electron emission due to positive ion bombardment

Secondary electron emission due to positive ion bombardment

** Secondary electron ratio is defined in this report as the ratio of the number of electrons emitted frmn the surface of a material to the number of positive ions striking the material.[r]

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Charge Storage and Electron/Light Emission Properties of Silicon Nanocrystals

Charge Storage and Electron/Light Emission Properties of Silicon Nanocrystals

Our nc-Si light emitting device features the electron emission structure based on nc-Si arrays embedded in three-dimensional photonic crystal. Nanocrystalline silicon was fabricated with uniform diameter of 8 nm using pulsed gas plasma CVD method. A high-efficiency visible photo- luminescence was observed for the surface-oxidized nc-Si indicating the quantum confinement effect and quasi-direct recombination [16]. Another key feature of our device is that the dimension of nc-Si can be controlled simply by changing the thermal oxidation time [24]. This is vital to control the electron emission properties, the luminescence wavelength of nc-Si, the refractive index of the structured nc-Si arrays, and therefore to optimize the photonic bandgap properties of the whole device.
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A Review Paper on “Graphene Field Emission for Electron Microscopy”

A Review Paper on “Graphene Field Emission for Electron Microscopy”

For most single-tip point field emitters, the emission current is surface sensitive and the adsorption of any gas molecules will increase the surface work function [15,72]. A high emission current under excessive applied voltage ionizes many gas molecules around the emission surface and eventually triggers a vacuum arc. Therefore, the practical use of cold field emitters in electron microscopes typically requires cathode flashing at regular intervals to remove the residual contaminant molecules. Endo et al. [73] reported that CFE electron sources can be cleaned by in situ Joule heating during the emission process in HV conditions, which is well known as a “conditioning” process in many cold field emission experiments [71,74,75]. For example, during the first and second cycle of voltage ramping up from the graphene flake overlaid on the tungsten probe (Figure 4A), the current-applied voltage characteristic presents a typical conditioning process, which is observed to deviate from the conventional FN plot. The third cycle of electron emission shows a well fitted FN plot with an emission current up to 6 µA. Similar work has been done by other researchers studying the field emission characteristics from reduced graphene oxide (Figure 4B) and carbon nanowalls, and they have obtained high emission current, around several tens of microamperes [71,76].
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Electron optics simulation for designing carbon nanotube based field emission X-ray source

Electron optics simulation for designing carbon nanotube based field emission X-ray source

Current micro-CT scanners are typically comprised of conventional x-ray sources which have limited temporal resolution because of the intrinsic electron emission mechanism. This is a huge limitation for dynamic imaging of small animals where the source needs to be synchronized with the physiological motion of the animal. As can be seen in table (3.1), mouse has 10 time’s faster respiration and cardiac cycle than human beings. This means to capture an image without motion blur it has to be acquired within a very small time frame or very high temporal resolution. Also, high spatial resolution is needed to visualize small anatomical features in the mouse. In addition total dose needs to be small to do longitudinal disease studies. These limitations can be addressed by a CNT based x-ray source with high temporal and spatial resolution and will be discussed in the next section
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