Throughput enhancement technique for MAPPER maskless lithography

A stable LaB6 nanoneedle field-emission electron source for atomic resolution imaging with a transmission electron microscope

A theoretical study has been made of the electromagnetic radiation arising from pulsed electron beams. The study assumes an electron beam which has a well‐organized spatial structure determined by a fixed trajectory in a magnetic field and on/off pulsing governed by the electron source. From this model the electromagnetic radiation is determined by adding coherently the radiation from each individual electron in the helical stream. The radiation per unit frequency interval is determined, as well as the radiation per unit solid angle, as a function of both propagation and ray angles, electron beam pulse width and separation, total number of pulses, and beam current. As expected for a coherent process, it is found that the radiated power varies at the square of the beam current. The relatively high efficiency of the beam in producing electromagnetic radiation is illustrated by consideration, among others, of a 1‐keV, 100‐mA beam used in recent experiments on the space shuttle. For these parameters the total radiated power per steradian is calculated at selected angles to be greater than 1% of the total beam power carried as electron kinetic energy. These results provide a useful theoretical basis for planning future electron beam experiments in space plasmas.

Computer aided simulations of high current small energy electron beam channels

The electron source generating density modulated electron beam (a train of electron beam pulses) at high frequency directly from the cathode surface has attracted significant interest since they could be used in a wide variety of vacuum electronics devices, such as compact microwave sources [1-4], ultrafast electron microscopy [5], or electron beam lithography [6]. In particular, bunching the electron beam at the cathode surface can not only dramatically reduce dimensions and weight through the elimination of the pre-modulation circuit, but can also provide extremely high efficiency and improve power in electron beam devices due to coherence effects. The high-frequency modulation of the gate potential of field emitter arrays (FEAs) has been proposed and studied for microwave tube applications [1]. However, challenges resulting from parasitic capacitances have still remained [7]. An alternative is producing electron bunches by optical means. The emission current from p-type semiconductor field emitter arrays, unlike metals, is limited by the supply of minority carriers (electrons) in the depletion region in the high field, and is, therefore, highly sensitive to the additional supply of photoexcited carriers. Several studies have revealed the transient photoresponse of p-type Si-FEAs was limited by diffusion of photogenerated electrons outside the surface depletion region in the tip [8-10]. To generate a high frequency modulated electron beam, we need to design the emitter structure which eliminates photoexcitation of carriers outside the depletion region. In this paper, we descuss the photoresponse of volcano-structured p-type Si-FEAs fabricated by etch-back technique, where the gate metal effectively prevents photoexitation of carriers outside the depletion region, under laser light illumination. Our Si-FEA devices tested here consist of 100 emitter tips, a gate aperture of less than a half micrometer in diameter and insulating layer of 200 nm thickness, as shown in Fig.1. In a proof-of-principle experiment, the FEA device was optically modulated from the front side. Figure 2 shows the typical current-voltage characteristics of our FEA device with and without laser pulse illumination of a wavelength of 405-nm. This result clearly suggests our device is a highly sensitive photocathode. In the dark, the emission current saturation by limitation in supply of electrons at high voltages is clearly displayed and the irradiation enhanced the emission current. Figure 3 shows the response of optically modulated emission current from our FEA device and a reference commercial photodetector. The rise and fall times of each pulse response are 5 ns, respectively. These values are similar to the minimum rise time of the current-voltage conversion amplifier used in this experiment, so the measured rise and fall times are determined by the response time of the current amplifier and the real rise and fall times of photoresponse in the device are at least less than 5 ns. A delayed slow response in the falling phase is not included in the component of the transient signal. Although optimization of the FEA structure is underway, it is experimentally demonstrated that the FEA photocathode is a structure suitable for minimizing the photogeneration of electrons outside the depletion layer, giving a high-speed modulated electron beam [11].

Electron linear accelerator applications involving the generation of hard X-rays frequently require accurate knowledge of the electron beam parameters. We developed a beam stop device which houses a tungsten Bremsstrahlung target and enables the electron beam current, energy and position to be monitored. The beam stop consisted of four plates. The first was a removable aluminium (Al) transmission plate. Then followed the tungsten target. Behind the target there were four Al quadrant plates for beam position measurement. The last plate was a thick Al back-stop block. Currents from the four quadrants and the back-stop were measured and the beam lateral position, energy and current were calculated. The beam stop device was optimised using Monte-Carlo simulation, manufactured (including custom-made electronics and software) in our laboratory and tested at the ARPANSA (Australian Radiation Protection and Nuclear Safety Agency) linear accelerator in Melbourne. The electron beam energy was determined with a precision of 60 keV at beam energies between 11 and 21 MeV and the lateral beam position was controlled with a precision of 200 mum. The relative changes of the beam current were monitored as well.

Summary form only given. One of the main advantages of the plasma cathode electron guns is its ability to produce electron beam under the higher operation pressure up to fore-pump pressure range. Present work is devoted to plasma electron guns that were designed especially to generate narrow focusing electron beams under the high pressure. To produce narrow focusing beam two contradictory requirements should be satisfied. From the one hand the plasma emission area must be as small as possible to realize beam focusing and to prevent plasma penetration from discharge gap to accelerating one. From the other hand to reach necessary total beam current the emission area has to be increased. One of the reasonable ways to solve the problem is to enhance plasma density just near plasma surface in emission area. Two different versions of the plasma guns were investigated. First one has the following electrode configuration: hollow cathode, flat anode with emission hole and accelerating electrode with special configuration. Recently this electrode configuration was already introduced for generation of cylindrical electron beam. Experiments showed strong beam current dependence on discharge gap geometry such as hollow cathode diameter and distance between cathode and anode. Under the 50 mtorr gas pressure electron beam current of 0.1 A DC with energy up to 12 keV were reached. Under the lower pressure of 30 mtorr it was possible to increase high voltage up to 17 kV. With magnet focusing system applied the beam diameter, measured by rotating probe at 20 cm distance far from extractor, was as small as 1 mm. Another version was based on reflected (PIG) discharge with hollow cathode. This gun was used in pulsed mode of operation (100 mus, 2-500 pps). With acceleration voltage of 50 kV it produces 150 mA of the beam current, with the beam diameter of smaller than 1 mm under 0.1-1 torr gas pressure in work chamber (after two gas-dynamic windows). Main application fields for such plasma electron guns are surface treatments including electron beam heating, welding, cladding, evaporations as well as plasma chemistry

A free electron laser comprising: an electron source (21), a linear accelerator (22), an undulator (26), electron beam optics and a deceleration unit (28'). The electron source is operable to produce a bunched electron beam. The linear accelerator arranged to impart energy to electrons in the bunched electron beam produced by the electron source. The undulator is operable to produce a periodic magnetic field and is arranged so as to guide the bunched electron beam along a periodic path about a central axis of the undulator such that they interact with radiation in the undulator, stimulating emission of coherent radiation. The electron beam optics is arranged to direct the bunched electron beam back into the linear accelerator after it leaves the undulator so as to extract energy from electrons in the bunched electron beam. The deceleration unit is arranged to extract energy from electrons in the bunched electron beam after it has left the undulator. The deceleration unit comprises one or more resonant cavities (33), and an energy dissipation mechanism. The bunched electron beam is directed through the one or more resonant cavities so as to excite one or more resonant standing wave modes therein.

Development of alloy-film coated dispenser cathode for terahertz vacuum electron devices application

The results of the study on the formation of transverse dimensions of an electron beam by a magnetron gun with a secondary emission cathode in the voltage range of 25..90 kV are presented. Investigations of the formation of electron beams in electron sources with cold metal cathodes operating in the secondary emission regime are carried out. The electron source is a magnetron gun. The principle of operation of such gun s is based on the reverse bombardment of the cathode by electrons returned by the magnetic field, the formation of an electron cloud near the cathode a nd the formation of a beam in crossed electric and magnetic fields. Their main difference from thermionic guns is the large current density from a unit of the cathode’s cross-sectional area ~ 50 A/cm² and a long service life. Therefore, the search and investigation of electron sources with a long service life is an urgent task. On the basis of a magnetron gun with a secondary-emission cathode, an electron accelerator is created in which an axial electron beam is used to irradiate metal targets and the inner cylindrical surface with a radial electron beam. The article presents the experimental data and the results of modeling calculations on the formation and control of the electron beam distribution by a magnetron gun with a secondary-emission cathode in motion in a solenoidal magnetic field. The dependence of the formation of the radial dimensions of the electron beam on the amplitude and gradient of the solenoidal magnetic field in the gun, which grows or falls in the channel of the beam transport, is studied. The results of numerical simulation of the motion of a tubular electron beam in a magnetic field of a solenoid are presented. Based on the motion model of the electron beam, the characteristics of the resultant electron beam are considered. It is shown that the diameter of the beam can be adjusted by varying the control magnetic field. The results of numerical modeling on the motion of a tubular electron flux in a magnetic field of a solenoid are given. The possibility of controlling the transverse dimensions of the beam is studied.

In this paper, we present the research results on focusing and transport of an intense (up to 100 A) nonrelativistic (up to 20 kV) pulsed electron beam using an axially symmetric device with a high-current plasma lens configuration. The electron source is based on electron extraction from the plasma of a hollow-anode vacuum arc discharge. The arc is initiated by a dielectric surface flashover. The emission hole is covered with a fine mesh grid. The beam is extracted and accelerated in a diode-type electro-optical system formed between the grid surface and an open anode plasma boundary. The anode plasma is produced in an electron beam transport channel through residual gas ionization by beam electrons and a plasma lens discharge. The plasma lens configuration of crossed electric and magnetic fields provides an attractive means to obtain a stable low-pressure plasma discharge. This geometry allows the compression of the electron beam in diameter from 6 to 1 cm with more than 100- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm A}/{\rm cm}^{2}$</tex></formula> beam current density at the collector.

Interface control: A modified rooting technique for enhancing field emission from multiwall carbon nanotube based bulk emitters

The main features of additive electron beam process control system using filler wire and modern trends in design of process control systems are considered. The main way to control heat power generated in liquid metal bath during building-up welding is proven regulation of electron beam current by varying bias voltage of the electron gun. Technological advantages of pulse beam current control method in comparison with continuous one are confirmed. Specific features and process limitations of the method are shown. The method of tuning the accelerating voltage and beam current is proposed, which provides regulatory quality indicators that meet the requirements of electron beam technology.

Lateral-type polysilicon field emission triode, consisting of two symmetric gate tips aligned by an angle of 70/spl deg/ with respect to the sharp cathode tips was fabricated by using local oxidation of polysilicon (LOCOS) process. The fabricated device has the electrical characteristics of a low turn-on voltage of 13 V and the emission anode current of 150 /spl mu/A/50tips at V/sub AC/ = 50 V and V/sub GC/ = open. After high field activation treatment, the turn-on voltage was down to 2 V and the emission current increased up to 525 /spl mu/A/50tips at V/sub AC/ = 50 V and V/sub GC/ = open. Furthermore, the emission current versus gate biases indicated a dramatic change of emission currents from gate tip-end resulting in an interesting operational behavior.

Summary form only given. In most fast wave and slow wave vacuum electron devices dispenser cathodes, which are made of porous tungsten impregnated with barium calcium aluminate, are used as the electron source. A very necessary process called activation must occur that results in barium uniformly covering the surface and remaining there for a sufficient time to provide a lowered work function. The key to this is the formation of a dipole of barium over oxygen over the metal substrate from which the electrons are pulled. A fully activated surface must have every available site occupied by the barium-oxygen dipole. This not only provides the lowest work function but also assures a constant and uniform source of electrons during the life of the device. The chemical reactions that take place and the processes required to remove the unwanted species from the surface are described.

Recent experimental observations1 of collective ion acceleration produced when an intense relativistic electron beam was iniected into a low pressure neutral gas have firmly established a threshold beam current for the process which was predicted by Olson2; for this geometry ion acceleration does not occur unless the electron beam current (I) exceeds the space-charge limiting current (Il). In this paper we report additional observations of ion acceleration obtained in two series of experiments. In the first series, the guide tube and diode were configured to provide a large ratio of injected beam current to space charge limiting current, and drift tube endplate effects were examined. When the separation between the anode and tube endplate become less than the drift tube diameter the efficiency of the collective acceleration process is strongly reduced. In the second series of experiments the scaling of accelerated ion energy with electron beam kinetic energy was investigated using two electron beam machines which differ in stored energy by a factor of approximately 20. Using the larger machine proton energies in excess of 16.5 MeV have been attained. In addition, we also present an expression for the optimum pressure for ion acceleration in the drifting beam neutral gas geometry.