The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
A new model of low-field electron emission is proposed, presumably applicable for nanostructured materials possessing neither the quality of low work function nor capability of field enhancement at high-aspect-ratio elements. In accordance with the model, hot-electron emission is ultimately driven by thermoelectric phenomena developing near nanosized emission centers. Numerical estimates were performed...
We report on an extended use of the Fowler-Nordheim plot for energetic evaluation of charge transfers in vacuum electronics. First results explained clearly, the transition from field electron emission to plasma discharge is physically conditioned, especially in the case of higher emission currents.
Vacuum arcing (also known as breakdown), is a major limiting factor in various applications such as particle accelerators, fusion reactors etc. Although it is well-established that vacuum arcs appear after intense Field electron Emission (FE), the physical mechanism that leads from FE to the ignition of plasma is not yet understood. A common hypothesis is that intense FE leads to excessive heating...
Strong electric fields are known to create biased adatom migration on metallic surfaces. We present a Kinetic Monte Carlo model that can simulate adatom migration on a tungsten (W) surface in electric fields. We validate our model by using it to calculate the drift velocity of the adatom at different fields and temperature and comparing the results with experimental data from the literature. We obtain...
Hyperspectroscopy consists of spatially-resolved collection of spectra. In order to characterize the performance of electron emitters, in particular thermionic emitters, the thermal characteristics must be known. In this work, we use hyperspectroscopy to map out the blackbody temperature distribution on the surface of an optically-excited source comprised of a carbon nanotube (CNT) forest — a promising...
Nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, is an unconventional field emitter that performs in planar thin film configuration and has turn-on fields on the order of 10 V/ m. To shed more light on fundamental field emission properties of (N)UNCD, we have designed and commissioned a field emission microscope (FEM). The microscope can directly image the field emission site distribution...
We have observed much variety of field emission microscopy (FEM) patterns from C60 molecules, including patterns that are much larger than the geometrical shape of C60 and very similar to those of simple atomic orbitals. It has been reported that C60 possesses unoccupied super atomic molecular orbitals (SAMOs) on the basis of theoretical investigations and experimental observations by means of scanning...
Experimental field emission data from large area field emitters (LAFEs) have been analyzed using a “two-class model”, in which some emitters have a field enhancement factor significantly greater than the remainder. Using parameters derived experimentally, corresponding Fowler-Nordheim plots were theoretically predicted and agree adequately with the “kinked” plots observed experimentally. In the analysis...
Work function measurements are critical both for vacuum electronics and solid state devices. We demonstrate that thermoelectronic generators are suitable not only for energy harvesting, but also for work function measurements. Here, we report on in-situ measurements of single crystal Nb:SrTiO3 and of LaB6 thin films deposited by pulsed laser deposition. These measurements provide a proof of concept...
Nanostructured thermionic energy converters may offer substantial advantages over traditional devices by reducing system complexity and requirements. However, they still face similar fundamental challenges, such as anode collection efficiency and the space charge effect, which have limited their performance to date. Here, we investigate a carbon nanotube-based thermionic converter, demonstrating that...
The cold cathode x-ray source was fabricated by using the point-type CNT film emitter. The CNT x-ray source consists of the CNT point emitter, the metal mesh gate electrode and the tungsten target anode electrode. Those components were mounted in a small vacuum chamber. The fabricated CNT x-ray source shows a high resolution x-ray image at a low anode current and at a low anode voltage compared to...
A control circuit to stabilize the flux of electrons transmitted through an extractor electrode is presented. By controlling the emission current a fluctuation with a standard deviation of 0.015% is observed. However, the achievable stability of the transmitted electron current is limited due to a variation of the extraction grid current ratio showing a standard deviation of 4.33%. By regulating the...
We fabricated field emission electron sources and applied for the glass sealed x-ray tube for medical imaging devices. The x-ray tube consists of an electron beam with a patterned grown CNT emitters with RAP process. Those electron beam shows higher electron emission current and transmittance after glass seal. With the x-ray tube, we success to measure medical image with finger and high resolution...
At present, many vacuum devices based on nanotechnology are widely used. The life time of the device depends mainly on the outgassing rate and the seal leak rate of the device. The leak rate is required to be less than 10−14Pam3/s in some application fields of long-life and high reliability devices. To solve this problem, the ultra-high vacuum leak detection apparatus with the lower limit of 10−16...
Approaches towards high energy THz generation and its use for a new accelerator technology are discussed. Theoretical and experimental results on laser based THz generation, guns, accelerators as well as a proposed compact X-ray source based on those devices are presented.
We describe the implementation and detailed characterization of a laser-triggered field-emitter electron source integrated into a modified transmission electron microscope. Specifically, localized linear photoemission from the front facet of a tip-shaped ZrO/W(100) Schottky emitter is employed, yielding electron pulses with a spectral bandwidth of 0.6 eV and pulse durations down to 200 fs (full-width-at-half-maximum)...
Field emitter is an important cathode to probe atomic structures of large unit-cell crystal samples by electron imaging and diffraction experiments because of the capability to produce high brightness electron beam with a large transverse coherence length. Despite the small energy spread, normally only the near-axis part of the beam is utilized because of the large geometrical angular spread at the...
Needle-like single crystal diamond structures were obtained by combination of the plasma enhanced chemical vapor deposition (CVD) and selective oxidation techniques. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and the intensity of the femtosecond laser focused on the needle. Moreover, a new set-up based...
We present experimental results on laser-induced photoemission from nanotips made of different materials, and we compare photoemission from a metal surface (tungsten) to a dielectric (diamond). Ultrashort laser pulses (15–300 fs) are used to trigger electron emission from nanotips with radii < 100nm under a moderate tip bias. We show how different laser parameters as the repetition rate, the mean...
Ultrafast electron pulses, combined with laser-pump and electron-probe technologies, allow for various forms of ultrafast microscopy and spectroscopy to elucidate otherwise challenging to observe physical and chemical transitions. However, the pursuit of simultaneous ultimate spatial and temporal resolution has been largely subdued by the low monochromaticity of the electron pulses and their poor...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.