Electron Beam Spot Research Articles

Predictive of Electron Beam Focus Position by Metal Powder Temperature

The equipment for measuring electron beam (EB) focus in electron beam produced by the effect of extremum temperature of powder molten pool caused by the interactive effect of electron beam with metal powder is described. The principle of operation of apparatus and examples of EB characteristics are presented. During electron beam processing, the mechanical analysis of metal powder molten pool temperature following focusing current are studied. As a result, the transferring point of critical energy density described by the peak of metal powder pool temperature can be obtained. Based on the temperature characteristics of critical energy density, the measuring concept of dynamic focal spot of electron beam is put forward in the paper. The method of measuring dynamic focal spot of electron beam will provide a new possibility for 3D scanning prototyping through changing focus position of EB.

The influence of linac spot size on scatter factors

The use of small photon fields in modern radiotherapy requires the determination of total scatter factors Scp or field factors Ω with high precision. Therefore, chamber-dependent correction factors for dose measurements in small fields are necessary. In this study Monte Carlo simulations were used to calculate the field factor Ω and chamber response-related correction factors for four different types of detectors in a clinical 6 MV photon beam for a square field size of 1 cm × 1 cm. As a beam source a Monte Carlo-based model of a Siemens KD linear accelerator was applied. The calculations aimed at the investigation of the influence of electron beam spot size on correction factors for small field dosimetry. The results confirm that accurate Monte Carlo calculations of the field factor Ω can only be carried out when the exact electron spot size is known. On the other hand no dependence of the electron beam spot size on the correction factors for the field size of 1 cm × 1 cm was observed.

Structure and mechanical properties of aluminum alloy/Ag interlayer/steel non-centered electron beam welded joints

Electron beam welding was carried out between aluminum alloy and steel with Ag interlayer. Seam morphology, structure and mechanical properties of the joints were investigated with different action positions of the electron beam spot. The results show that with the increment of the beam offset to the silver side from the interface between silver and steel, the seam morphology was improved, and the porosity in the Ag interlayer vanished. A transition layer mainly composed of Ag 2Al and Al eutectic was formed at the interface between silver and aluminum, and became thin and spiccato as the beam offset increased. When the beam offset was too large, two IMC layers composed of FeAl and FeAl 3 respectively were formed at the interface between steel and Ag interlayer. The optimal beam offset was 0.2 mm, and the maximum tensile strength of the joint was 193 MPa, 88.9% that of the aluminum alloy, and the fracture occurred at the interface between steel and Ag interlayer.

Nanofabrication of photonic crystal-based devices using electron beam spot lithography

This paper reports on photonic crystal-based devices fabricated via the electron beam spot lithography technique. This technique produces uniform, submicron, and nanometer scale periodic holes over large areas in the millimeter range and the write time is a factor of over 120 times faster than the conventional direct-write technique. Generic design guidelines of this technique are established and the patterning of photonic crystal holes’ arrays in the square and hexagonal lattice configurations are investigated. The single spot lithography technique could potentially be useful as a mass fabrication approach, particularly for very large areas of 2D photonic crystal-based devices and possibly for other device fabrication, for a wide range of scientific and technological applications.

Effects of electrons on the shape of nanopores prepared by focused electron beam inducedetching

The fabrication of nanometric pores with controlled size is important for applicationssuch as single molecule detection. We have recently suggested the use of focusedelectron beam induced etching (FEBIE) for the preparation of such nanopores insilicon nitride membranes. The use of a scanning probe microscope as the electronbeam source makes this technique comparably accessible, opening the way towidespread fabrication of nanopores. Since the shape of the nanopores is criticallyimportant for their performance, in this work we focus on its analysis and study thedependence of the nanopore shape on the electron beam acceleration voltage. We showthat the nanopore adopts a funnel-like shape, with a central pore penetratingthe entire membrane, surrounded by an extended shallow-etched region at thetop of the membrane. While the internal nanopore size was found to dependon the electron acceleration voltage, the nanopore edges extended beyond theprimary electron beam spot size due to long-range effects, such as radiolysis anddiffusion. Moreover, the size of the peripheral-etched region was found to be lessdependent on the acceleration voltage. We also found that chemical etching is therate-limiting step of the process and is only slightly dependent on the accelerationvoltage. Furthermore, due to the chemical etch process the chemical compositionof the nanopore rims was found to maintain the bulk membrane composition.

SU‐E‐T‐110: Quantitative Image Based Measurement of Electron Beam Spot Position

Purpose: Develop an image based method to measure electron beam spot position w.r.t the Collimator Axis Of Rotation (CAOR). Methods: Two stainless steel rods, 3 mm in diameter, are mounted in a jig attached to the linac collimator. The rods lay in different planes normal to the CAOR, one at 159 cm SSD and the other at 70 cm SSD, and are offset 10 and 6 cm from the CAOR respectively. Images of both rods are acquired at multiple coll rotations. At each angle the rods project a tangent to an inscribed circle, the centre of which is calculated. The lower rod is very close the plane of the EPID and the centre of its inscribed circle defines the mechanical CAOR. The centre of the inscribed circle calculated from multiple images of the upper rod will be displaced from the CAOR by some distance proportional to the distance the beam source is from the CAOR. Test measurements were performed on an Elekta 6 MV where the In Plane beam spot position was moved a known distance using steering fine and beam spot position was measured.Results: Independent beam spot measurement (Flexmap Image Registration ball bearing) reported the initial beam spot at 0.29 mm from CAOR, moving to 0.91 mm (delta =0.62 mm) with steering. The rod tests showed the initial beam spot to be .31 mm from the CAOR and 1.17 mm from CAOR after adjustment. Note that in our companion paper we report similar values (initial 0.13mm going to 0.92 mm and initial value of 0.09mm going to 0.79) with our two co‐rotational dosimetric beam spot tests Conclusions: A simple method for measuring beam spot position with respect to CAOR is described. It provides its own internal reference and could be incorporated into routine QA using the EPID.Jason Smale is an employee of Elekta Canada

SU‐E‐T‐127: Two Dosimetric Methods of Measuring Linac Beam Spot Position

Purpose: Two dosimetric methods of measuring the electron beam spot position of photon beams w.r.t. the Collimator Axis Of Rotation (CAOR) are described. Methods: Method 1 (SNG test) uses a cylindrical ion chamber (IC) (A1SL) in a phantom mounted on a jig co‐rotational with the collimator making the relationship among the chamber, phantom, jaws and CAOR fixed and independent of collimator angle. A jaw parallel to the IC axis is set to zero and the phantom adjusted so the IC signal is 65% of the open field value. cGy/mu is measured every 30 degrees of collimator rotation. The phantom is then translated normal to the IC axis until the signal is 35%. The shift is recorded to calculate sensitivity (%dose/mm). For a radially symmetric spot centred on CAOR, the IC signal is angularly constant. Deviation from constant indicates a displacement from the CAOR and a shape distortion. The displacement and spot shape are calculated using Fourier analysis and penumbra shape (sensitivity). The 2nd method uses a hard wedge instead of the jaw and sensitivity is obtained from wedge profiles. Test measurements were performed on an Elekta 6 MV: the In Plane beam spot position was measured before and after it was moved by changing bending magnet current (Bending Fine). Results: Independent beam spot measurement (Flexmap Image Registration) showed the initial beam spot, projected back to source, 0.29 mm from CAOR, moving to 0.91 mm (delta=0.62 mm) with steering. The SNG test reported the beam spot moving from 0.13mm to 0.92 mm from CAOR (delta=0.79 mm). The hard wedge test gave an initial position of 0.09 mm off axis and a final position of 0.79 mm (delta=0.7 mm) Conclusions: The methods described provide a quantitative measure of beam spot position, not requiring the user to independently define the CAOR.Jason Smale is an Employee of Elekta Canada

Study on the characteristics of ferroelectric electron emission

Electron emission from ferroelectric cathodes is commonly suggested as an electron source for different applications due to its special characteristics such as high current density, easy treatment and operation. In this experimental research, the electron emission properties of ferroelectric cathodes made of lanthanum-doped lead zirconate–titanate (PLZT) ceramic are studied. The electron beam spot shape was recorded via proximity-imaging techniques.

Electron Emission from Ferroelectric Cathode

The technology of (Pb,La)(Zr,Ti)O3(PLZT) ferroelectric cathode is introduced. Stable emission current and high current density are obtained from it driven by positive high-voltage pulses with a repetition rate of 80 Hz. Proximity-imaging techniques are used to record the electron beam spot shape.

The 3‐D extent of the Io UV footprint on Jupiter

The Io footprint (IFP) is the auroral signature of the electromagnetic interaction between Io and Jupiter's magnetosphere. It consists of several spots followed by an extended tail, which are located close to the feet of the magnetic field lines connecting Io to Jupiter. The size of the main spot is a controversial issue, and previously published values range from ∼400 to ∼8000 km. However, this question is crucial to understand the processes at play, since this quantity is expected to reflect the size of the interaction region at Io. The present study provides estimates of the size of the Io footprint on a much larger image sample than before, paying a particular attention to the differentiation of the spots and to their 3‐D structure. The length of the Main Alfvén Wing (MAW) spot and the length of the trans‐hemispheric electron beam (TEB) spot along the footpath are ∼850 km, while their width perpendicular to the footpath is <200 km. Larger lengths are sometimes observed, but these configurations may be attributed to the overlaps of the different spots. The spot lengths are larger than the projected diameter of Io along unperturbed magnetic field lines, which is consistent with recent simulations. The narrowness of the IFP will need to be carefully accounted for in future studies of its brightness. Additionally, the peak altitudes of the MAW and the TEB spot are as high as 900 and 700 km, respectively, which seem to confirm their different origins.

Effects of Optical Parameters in a Free-Electron Laser Oscillator

We have developed a three-dimensional simulation code to study free-electron laser optical resonator parameters for a proposed far-infrared free-electron laser facility. We have investigated the effects of Rayleigh length, electron beam spot size, power extraction, and waist position by using the modified coupled equations, including a wave equation that is expanded in axisymmetric Gauss–Laguerre modes. The modified coupled equations are also used in the simulation to obtain the effects for fundamental and higher order modes. The optimum value for the oscillator mirror radius of curvature is found, and the effects of Rayleigh length, electron beam spot size, power extraction, and waist position in a free-electron laser oscillator with a short undulator are investigated.

A Novel 270$^{\circ}$ Bent-Axial-Type Electron Gun and Positioning of Its Electron Beam Spot on the Target

In this paper, we propose and evaluate the performance of a practical 270° bent-axial-type electron gun, in which focusing is bidirectional through an axial magnetic field. Such an electron gun has two advantages: (1) a high-voltage cathode assembly placed in a geometrical shadow region of the emerging vapor and (2) a compact electron beam (e-beam) spot with circular symmetry that results in high power density. It is also shown that the position of the e-beam spot on the target is controllable along any direction without compromising the compactness and circular symmetry of the e-beam spot just like a straight-axial-type electron gun, but not typically possible for conventional 270° bent-transverse-type electron guns.

Experimental study of sweep control in e-beam evaporated optical coatings

High performance optical coating requires excellent uniformity of thin-film. Keeping the surface of evaporation material flat is propitious for the stability of vapor plume, and can improve the uniformity of thin-film. Based on the principle of electron beam spot sweep, a pattern controller in domestic coater is designed. For the purpose of even evaporation during auto-sweep, the influence of the depth of material surface in the crucible on the evaporation characteristic is considered. Pre-melting and evaporation experiments are performed on melting material (Ti3O5), subliming material (SiO2), and semi-melting, semi-subliming material (HfO2). The sweeping experimental results show that using the designed sweep controller can make good performance on evaporation and pre-melting for the above materials.

Analyzing indirect secondary electron contrast of unstained bacteriophage T4 based on SEM images and Monte Carlo simulations

The indirect secondary electron contrast (ISEC) condition of the scanning electron microscopy (SEM) produces high contrast detection with minimal damage of unstained biological samples mounted under a thin carbon film. The high contrast image is created by a secondary electron signal produced under the carbon film by a low acceleration voltage. Here, we show that ISEC condition is clearly able to detect unstained bacteriophage T4 under a thin carbon film (10–15 nm) by using high-resolution field emission (FE) SEM. The results show that FE-SEM provides higher resolution than thermionic emission SEM. Furthermore, we investigated the scattered electron area within the carbon film under ISEC conditions using Monte Carlo simulation. The simulations indicated that the image resolution difference is related to the scattering width in the carbon film and the electron beam spot size. Using ISEC conditions on unstained virus samples would produce low electronic damage, because the electron beam does not directly irradiate the sample. In addition to the routine analysis, this method can be utilized for structural analysis of various biological samples like viruses, bacteria, and protein complexes.

Fabrication of a three-dimensional optical vortices phase mask for astronomy by means of electron-beam lithography

In this work, a novel three-dimensional (3D) fabrication process was used to create a series of particular phase masks for astronomical applications. These phase masks, also known as spiral phase plates (SPP), find their application in astronomy for optical vortex coronagraphy in the search of extra solar planets. The 3D profile was directly written on 2.7 mm thick polymethylmethacrylate (PMMA) slide by electron beam lithography (EBL). The effect of electron scattering on topography profile was investigated and the relationship among spatial distribution of electron beam irradiation, spot size and dosage level of irradiation were experimentally characterized. The quality of the fabricated profiles was evaluated using atomic force microscopy (AFM) technique. SPPs were then optically tested by injecting a Gaussian beam and an airy diffraction pattern obtained from a laser source comparing the optical vortices so far obtained with those drawn with numerical simulations.

Optimization of electrostatic lens systems for low-energy scanning microcolumn applications

The optimization of a low-energy scanning microcolumn is proposed by adopting a modified Einzel lens sandwiched between an aligner and a deflector. The modified Einzel lens is composed of four electrodes, and the two center electrodes are specially designed quadrupole lenses having keyhole type rather than circular apertures. The outer electrodes of the Einzel lens having circular apertures are grounded, and the quadrupole lens is operated by applying the quadrupole voltages. The effects of the separated deflector system and the static quadrupole lens were investigated by analyzing the scanning electron beam spot at the target, and the results show that the proposed system can improve the performance of the scanning microcolumn.

An X-ray technique for investigation of the explosive-emission cathode surface

We present the results of pulsed X-ray radiography of an electron beam spot on the anode of a diode employing an explosive-emission cathode. It is demonstrated that this technique can provide objective information on the character of emissive centers on the cathode surface and can be used for preliminary evaluation of the possibility of using a particular explosive-emission cathode type for the formation of desired electron beams in a given diode.

Local charge neutralization using secondary electrons induced by focused electron beam in TOF-SIMS analysis

Local charge neutralization using secondary electrons generated by an electron beam (EB) for SEM was devised and examined. Neutralization with a high-energy EB compared with conventional very low-energy EB requires no pulsing scheme for TOF-MS extraction voltage. Direct irradiation of high-energy EB to the insulating particle was not effective for neutralization. It was shown that the use of secondary electrons induced by EB-irradiation not on the particle directly but on a metal substrate vicinity of the particle. Charge neutralization was found to be effective even when the EB spot was distant (60 μm).

Study on current density distribution of electron beam spots by wave optics theory

The image theory of wave electron optics is used to study the current density distribution of electron beam spots for high-resolution electron optical systems. Using the wave aberration concept and paraxial expansion of charge density, the space charge effect is taken into consideration by modification of paraxial rays and spherical aberration coefficient of the lens. The point spreading function is obtained by Fourier–Bessel transform of the optical transfer function considering the space charge and partial coherence of the electron source.

Improvement of Measurement Method for Luminance Distribution of Electron Beam Spot in Color Display Tubes

A method for measuring the luminance distribution of an electron beam spot was described, which is fundamental to evaluate the resolution of a color display tube. First, to achieve high sensitivity and wide dynamic range identical to those of visual inspection, we proposed the use of an ICCD camera for imaging and two levels of sensitivity. With that method, we were able to measure the luminance distribution of an electron beam spot over a range of currents that extends from the extremely weak cathode current region to large current that correspond to the peak luminance. Specifically, we were able to measure the entire distribution shape from the base to the peak for beam spots in the cathode current range from 20μA to 300μA, while compensating the absolute luminance level. Second, a reconstruction algorithm of entire beam distribution from the shape of the masked part of the beam was also proposed, in which shift error is compensated to reduce the variance in measurement results caused by jitter noise in the conventional image processing method. That algorithm improves the reproducibility of repeated measurements. Specifically, a function for estimating the actual shift from the first-order moment of the image was incorporated into the spot shape reconstruction algorithm, resulting in a reduction of the standard deviation for repeated measurements of the horizontal beam spot diameter at 5% intensity from 0.02 mm to 0.005 mm.