Electron Beam Apparatus Research Articles

Structural, Optical, Electric and Magnetic Characteristics of (In1-xGdx)2O3 Films for Optoelectronics.

After (In1-xGdx)2O3 powder with a wide x range of 0 to 10 at.% was chemically produced, (In1-xGdx)2O3 thin films were evaporated under ultra-vacuum using an electron beam apparatus. We investigated the influence of the Gd doping concentration on the magnetic, optical, electrical, and structural properties of the resultant In2O3 deposits. The produced Gd-doped In2O3 films have a cubic In2O3 structure without a secondary phase, as shown by the X-ray diffraction results. Additionally, the chemical analysis revealed that the films are nearly stoichiometric. A three-layer model reproduced the spectroscopic ellipsometer readings to determine the optical parameters and energy gap. The Egopt changed toward the lower wavelength with growing the Gd doping in (In1-xGdx)2O3 films. The Egopt in the (In1-xGdx)2O3 films was observed to increase from 3.22 to 3.45 eV when the Gd concentration climbed. Both carrier concentration and hall mobility were found during the Hall effect studies. It was possible to construct the heterojunction of Ni (Al)/n-(In1-xGdx)2O3/p-Si/Al. At voltages between -2 and 2 volts, investigations into the dark (cutting-edge-voltage) characteristics of the produced heterojunctions were made. The oxygen vacancies and cationic defects in the lattice caused by the uncompensated cationic charges resulted in significant magnetism and ferromagnetic behavior in the undoped In2O3 films. The (In1-xGdx)2O3 films, however, displayed faint ferromagnetism. The ferromagnetism seen in the (In1-xGdx)2O3 films was caused by oxygen vacancies formed during the vacuum film production process. Metal cations created ferromagnetic exchange interactions by snatching free electrons in oxygen.

New magnetized electron beam apparatus and measurement of total electron scattering cross section of N2O at intermediate energy region

SynopsisA new electron scattering apparatus is developed based on concepts from the positron system built by Surko et al. In an electron-version of the system, the electron beam is provided by a cathode and the rest of the system is correspondingly modified to a simpler system. The system was tested with argon to verify its operation. N2O is important in atmosphere and plasma, and in the intermediate energy region, there are two previous results which are in disagreement. We present here a result for the total electron cross section of N2O.

Measurement of total electron scattering cross-section of N2O at intermediate energy region using a new magnetized electron beam apparatus

A new electron scattering apparatus is developed based on concepts from the positron system built by Surko et al (1988). In an electron version of the system, the electron beam is provided by a cathode and the rest of the system is correspondingly modified to a simpler system. The system was tested by measuring electron scattering from argon to verify its operation. N2O is important in the atmosphere and plasma processes, and in the intermediate energy region from 5 eV to 50 eV, there are two previous results for the electron scattering total cross-section which are in disagreement. We present here a new measurement for the total electron cross-section of N2O, helping to resolve this disagreement.

Tungsten Surface Morphology Control and Its Thermal Fatigue Behavior Under Cyclic Heat Loading

Thermal fatigue behavior under various cyclic heat loading is an important concern for tungsten as armor material in fusion devices. Surface morphology controlling experiments have been performed on polycrystalline tungsten using an ECR plasma system and cyclic heat loading tests have been conducted upon the polished and modified samples using an electron beam apparatus. The results indicate that the surface topography has little effect on the characteristics of damage caused by the cycle plastic deformation during the cyclic heat loading. The micro-cracks and extrusions form in some grains after suffered 300 cyclic heat loading, which are aligned in different directions for varying grains. In addition, the modified specimens with both different triangular pyramid and homogeneous nanostructures were fabricated by dry etching under different conditions. The cross-section of damage regions were analyzed and a set of schematic diagram was presented to explain the mechanism for the formation of micro-cracks and extrusions under cyclic heat loading.

Time Series Artificial Neural Network Approach for Prediction of Optical Lens Properties

Well-designed electrostatic cylindrical lenses are commonly used to control charged particles in atomic and molecular physics instruments such as electron guns and electron microscopes. The most commonly used of these, three-element electrostatic lenses are capable of keeping magnification constant for definite image position. The correct determination of focal and aberration characteristics of these lenses is very important for experimental studies. In this study, motions of electrons in three-element electrostatic cylindrical lenses have been investigated with nonlinear autoregressive exogenous based time series artificial neural network technique. The spherical and chromatic aberrations which aect the beam are also predicted with time series artificial neural network technique. This method is a mathematical model that emulates the biological neural networks. The basic working principle of time series artificial neural network technique is training of network with the known data and then prediction of the unknown data. Simulation results from SIMION 8.1 ray-tracing program are used as training and test data set. According to the results obtained from time series artificial neural network technique technique, a considerably agreement is found between simulation and artificial neural network technique prediction results. The study shows that such an artificial neural network model which has time advantage can be applicable to various electron and ion beam apparatus.

Polymerization of room-temperature ionic liquid monomers by electron beam irradiation with the aim of fabricating three-dimensional micropolymer/nanopolymer structures.

A novel method for fabricating microsized and nanosized polymer structures from a room-temperature ionic liquid (RTIL) on a Si substrate was developed by the patterned irradiation of an electron beam (EB). An extremely low vapor pressure of the RTIL, 1-allyl-3-ethylimidazolium bis((trifluoromethane)sulfonyl)amide, allows it to be introduced into the high-vacuum chamber of an electron beam apparatus to conduct a radiation-induced polymerization in the nanoregion. We prepared various three-dimensional (3D) micro/nanopolymer structures having high aspect ratios of up to 5 with a resolution of sub-100 nm. In addition, the effects of the irradiation dose and beam current on the physicochemical properties of the deposited polymers were investigated by recording the FT-IR spectra and Young's modulus. Interestingly, the overall shapes of the obtained structures were different from those prepared in our recent study using a focused ion beam (FIB) even if the samples were irradiated in a similar manner. This may be due to the different transmission between the two types of beams as discussed on the basis of the theoretical calculations of the quantum beam trajectories. Perceptions obtained in this study provide facile preparation procedures for the micro/nanostructures.

Influence of diode gap distance on space charge effects in field emission

Under intense electric field, the electrons emitted from the cathode by field emission have strong space charge effects, so the space charge limited current of a diode is an important parameter in the design of many intense electron beam apparatus, such as the high power microwave source devices. The field emission current density depends on cathode material and electric field at the cathode surface, while the space charge limited current density is a function of applied voltage and diode gap distance. To investigate the influence of the diode gap distance on space charge effect in field emission, in the paper we build a model of a planar vacuum diode operating with a field emission cathode. The time evolutions of the electric field at the cathode surface with various diode gap distance and applied voltage are studied using the particle-in-cell method, and the steady value of the electric field at the cathode surface is obtained. The electric field at the cathode surface first oscillates and finally reaches a steady state. At a given applied electric field, the longer the diode gap distance, the higher the absolute value of the electric field at the cathode surface is, and it takes more time to reach the steady state for longer diode gap distance; the distribution of the electric field in the diode gap region is steeper for shorter diode gap distance after the electric field at the cathode surface has reached a steady state.

Effect of electron beam irradiation on the properties of ethylene‐(vinyl acetate) copolymer/natural rubber/organoclay nanocomposites

AbstractThe effects of electron beam (EB) irradiation on the morphology, crosslink density, and tensile properties of EVA/SMR L (Standard Malaysian Rubber)/organoclay nanocomposites prepared by a melt‐blending technique were investigated. All the samples were irradiated by using a 3.0‐MeV EB apparatus with doses ranging from 50 to 200 kGy. Organoclay loading was varied from 0 to 10 phr (parts by weight per hundred parts of resin). X‐ray diffraction results and transmission electron microscopy images proved that the dispersion of organoclay in the nanocomposites was slightly improved by EB irradiation. The gel fraction yield for the nanocomposites increased with irradiation dose but decreased with organoclay loading. However, at 200 kGy, the gel fraction yield was almost the same at all organoclay loadings. Tensile strength and stress at 100% elongation increased proportionally with the irradiation dose. Elongation at break of the nanocomposites increased up to 100 kGy but then decreased at higher irradiation doses. The intercalation and exfoliation of the organoclay, the barrier effect, and the Hofmann degradation of the modification agent are the three major factors leading to the improvement of the properties of the irradiated nanocomposites. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers

Low-energy electron attachment to chloroform (CHCl3) molecules: A joint experimental and theoretical study

Results from a joint experimental and theoretical study of electron attachment to chloroform (CHCl3) molecules in the gas phase are reported. In an electron swarm study involving a pulsed Townsend technique with equal gas and electron temperatures, accurate attachment rate coefficients were determined over the temperature range 295–373K; they show an Arrhenius-type rise with increasing temperature, corresponding to an activation energy of 0.11(1)eV. In a high resolution electron beam experiment involving two versions of the laser photoelectron attachment method, the relative cross section for Cl− formation from CHCl3 over the energy range 0.001–1.25eV at the gas temperature TG=300K was measured. It exhibits clear downward cusp structure at the threshold for excitation of one quantum of the vibrational symmetric deformation mode ν3, indicating that this mode is active in the primary attachment process. With reference to our thermal attachment rate coefficient k(T=300K)=3.9(2)×10−9cm3s−1, a new highly resolved absolute attachment cross section for TG=300K was determined. This cross section is extended to higher energies by measurements, carried out with a pulsed electron beam apparatus which also provided new data for the distinctly weaker fragment anions HCl2− and CCl2−. The resulting total absolute cross section for anion formation is used to calculate the dependence of the attachment rate coefficient k(Te;TG) on electron temperature Te over the range 50–15000K at the fixed gas temperature TG=300K. In addition, we report the dependence of the relative cross section for Cl− formation on gas temperature (TG=310–435K). For comparison with the experimental data, R-matrix calculations have been carried out for the dominant anion channel Cl−. The results recover the main experimental observations and predict the dependence of the DEA cross section on the initial vibrational level ν3 and on the vibrational temperature. Our results are compared with those of previous electron beam and electron swarm experiments.

Electron-impact ionization of SiCl3 using an improved crossed fast-neutral-beam - electron-beam apparatus

The fast-neutral-beam technique is a versatile approach to the determination of absolute cross sections for electron-impact ionization of atoms, stable molecules as well as free radicals and metastable species. A fast neutral beam of the species under study is prepared by charge-transfer neutralization of a mass-selected ion beam and the species are subsequently ionized by an electron beam. Mass- and energy-dispersive selection separates singly from multiply charged ions and parent from fragment ions and allows the determination of partial ionization cross sections. Here we describe some major improvements that were made recently to the fast-beam apparatus that has been used extensively for ionization cross section measurements for the past 15 years in our group. Experiments using well-established ionization cross sections in conjunction with extensive ion trajectory simulations were carried out to test the satisfactory performance of the modified fast-neutral-beam apparatus. We also report absolute partial cross sections for the formation of various singly charged positive ions produced by electron impact on SiCl3 for impact energies from threshold to 200 eV in the modified fast-beam apparatus.

Improvement of the wear resistance of titanium alloyed with boron nitride by electron beam irradiation

Surface alloying of commercially pure titanium was carried out with an electron beam (EB) apparatus using a boron nitride powder which was previously deposited on its surface by Atmospheric Plasma Spraying (APS) in order to produce a composite layer with high wear resistance. Electron beam surface alloying is an important surface engineering routine that involves melting of a pre-deposited layer or concomitantly added alloying elements/compounds with a part of the underlying substrate by direct energy electron beam irradiation to form an alloyed zone characterized by a novel microstructure and composition. The present study is concerned with the influences of EB-remelting process on the wear resistance of the alloyed titanium material. The microstructure, corrosion resistance and phase analysis were also examined. Scanning electron microscopy (SEM), light microscopy (LM) and X-ray Diffraction (XRD) were performed to characterize the phase modification and morphology after the EB treatment. The sliding wear as well as the hardness of the remelted material was significantly improved (in comparison with pure Ti) through this alloying technique. The corrosion behaviour of the modified surfaces was compared with that of Ti in order to demonstrate that its initial good corrosion resistance is not strongly influenced due to surface alloying.

Two-axis-of-rotation drive system in electron-beam lithography apparatus for nanotechnology applications

A two-axis-of-rotation drive system has been developed that enables electron-beam lithography (EBL) to be applied to three-dimensional (3D) nanofabrication. It is built on a pallet that can be loaded into the EBL apparatus, and rotates a sample while the e-beam writes on it. It has a positional accuracy of a few milliradians. In addition, a height-measurement system has also been developed. This helps to focus the e-beam on the surface of a rotating or non-planar sample, and enables fine patterns to be formed on such samples. These systems allow samples to be exposed to the e-beam from various directions, resulting in 3D fabrication with a high degree of freedom. A demonstration carried out on a polymethylmethacrylate sphere resulted in the formation of pillars with various shapes and about 100 nm in diameter.

Some approaches to producing microporous materials and coatings by EB PVD

Techniques to produce bulk microporous structures as well as coatings, are examined in metal and ceramic systems based on the role of second source additives to the main component during their simultaneous evaporation and condensation in an electron beam apparatus. An arbitrary grouping of additives is proposed to differentiate the extent of their interaction in the vapor and solid phases of the main component. Additives are chosen from components that essentially do not interact (group 1), that are essentially removed (group 2), and those that react and are accompanied by the creation and removal of gaseous products during formation of the main condensate phase (group 3). These additives are shown to have a marked influence on the vapor solid interface shape and the dimensions of the deposited columnar crystals, their boundary zones and their internal porous structure. The chemical nature and content of the additives to the vapor phase opens up a broad spectrum of possibilities for construction of stable porous materials with micron and sub-micron size pores and large percentages (30–40%) of voids. Three characteristic shapes of microporous structures were distinguished within columnar and dendritic crystallites containing additives: gaps between dense and porous columns, micropores inside columnar cells and interdendritic (branch) porosity.

In-Situ Study of the Oxide Mediated Epitaxy of CoSi2 on Si

AbstractOxide Mediated Epitaxy (OME) shows promise as a method to form good quality, thin epitaxial CoSi2 films on most Si surfaces. We have performed an in-situ study of the OME of CoSi2, on the Si (001) surface. Our work was carried out with our specially modified ultra-high vacuum transmission electron microscope (UHV TEM) SHEBA (Surface High Energy Electron Beam Apparatus). With SHEBA we were able to monitor the diffraction pattern and therefore the phase formation throughout the anneal. Our results confirm the suppression of intermediate phases during CoSi2 formation in the OME process. We also see a difference in the as deposited Co film when the oxide coated silicon surface is used rather than a clean substrate. From combined imaging and diffraction studies we will shed some light on the mechanism behind the success of OME.

A new surface science in situ transmission and reflection electron microscope

We describe an ultrahigh vacuum instrument for transmission electron microscopy and reflection electron microscopy for the study of surfaces and thin film growth. The focus of previous experiments was on the high spatial resolution (<3 Å) generally associated with microscopy, at the cost of controlled growth and characterization. We have taken a different approach. It has been shown that most experiments using diffraction and diffraction contrast imaging can be performed well at poorer resolution (∼20 Å), including the imaging of monatomic steps and monolayer coverages. The instrument is designed for best control of growth and vacuum, with sacrifices in optical resolution, which is theoretically ∼2 nm. The instrument is called SHEBA (surface high-energy electron beam apparatus). We can examine a ∼1 cm2 sample in both transmission electron microscopy and reflection electron microscopy, in situ with well-controlled molecular beam epitaxy (MBE) growth capabilities, well characterized vacuum, and surface characterization by Auger spectroscopy and low-energy electron diffraction. Preliminary experiments of cobalt on silicon have shown MBE growth rates ranging from 1.5 monolayers per hour to 18.3 monolayers per hour depending on the temperature of the evaporation source. Using SHEBA for a reactive MBE experiment has provided the first direct evidence of the formation of aluminum nitride by nitridation of basal plane sapphire. The most serious design problems were stray magnetic fields and mechanical vibrations. These have been overcome and allow a spatial resolution of <10 nm. The instrument is expected to be very valuable in studies of film growth.

Electron attachment to thermally excited trichlorotrifluoroethane (1, 1, 2-)

Electron attachment to trichlorotrifluoroethane (1, 1, 2-) was investigated in buffer gases of and Ar using a high-temperature electron swarm apparatus. The negative ion intensity was also measured as a function of electron energy using an electron beam apparatus. The electron attachment rate constant, , was measured in the mean electron energy range, , 0.043 to 4.7 eV and over a temperature, T, range 300 to 700 K in the electron swarm experiments. The electron attachment rate constant was found to first increase slightly with increasing temperature and subsequently decrease for K. Our room-temperature electron beam study showed that 1, 1, 2- attaches electrons predominantly via dissociative negative ion states and revealed that the electron attachment cross section exhibits three main peaks: one at eV producing , a second one at eV due to and a third one at eV also producing . The electron attachment cross sections obtained using an electron swarm-unfolding technique show that the peak at eV observed in the electron beam study is actually composed of three peaks; one at eV and two more at higher electron energies but below 1.5 eV.

Improvement of the accuracy of 3-D electron trajectory calculations using both the finite element method and the boundary element method

A new simulation method is presented to improve the accuracy of 3-D electron trajectory calculations with the space charge effect, using both the finite element method and boundary element method to calculate the electric field and the magnetic field. In this method, the magnetic potential is first calculated by the finite element method, then calculated again by the boundary element method, and finally the magnetic field is calculated at the nodes and interpolated in the finite elements. Next, the electric field is calculated in the same manner used for the magnetic field. This method was specifically designed for the electron focusing system of an electron beam apparatus.

Modifications of a JEOL 2000EX TEM for insSitu surface studies

We have modified a JEOL 2000EX Transmission Electron Microscope (TEM) to allow in-situ ultra-high vacuum (UHV) surface science experiments as well as transmission electron diffraction and imaging. Our goal is to support research in the areas of in-situ film growth, oxidation, and etching on semiconducter surfaces and, hence, gain fundamental insight of the structural components involved with these processes. The large volume chamber needed for such experiments limits the resolution to about 30 Å, primarily due to electron optics. Figure 1 shows the standard JEOL 2000EX TEM. The UHV chamber in figure 2 replaces the specimen area of the TEM, as shown in figure 3. The chamber is outfitted with Low Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES), Residual Gas Analyzer (RGA), gas dosing, and evaporation sources. Reflection Electron Microscopy (REM) is also possible. This instrument is referred to as SHEBA (Surface High-energy Electron Beam Apparatus).The UHV chamber measures 800 mm in diameter and 400 mm in height. JEOL provided adapter flanges for the column.

Electron-impact excitation of the Rb 7 (2)S1/2, 8 (2)S1/2, 5 (2)D3/2, and 6 (2)D3/2 states.

Electron-impact cross sections for excitation of the 7 $^{2}$${\mathit{S}}_{1/2}$, 8 $^{2}$${\mathit{S}}_{1/2}$, 5 $^{2}$${\mathit{D}}_{3/2}$, and 6 $^{2}$${\mathit{D}}_{3/2}$ states of rubidium have been measured from threshold to 1000 eV. The optical-excitation-function method has been employed in a crossed atom- and electron-beam apparatus. Relative, total (cascade including) experimental cross sections are made absolute by comparison with the known total cross section of the Rb D1 line. Total excitation cross sections are compared with theoretical calculations employing first Born approximation and theoretical branching ratios. Born cross sections for the 7 $^{2}$${\mathit{S}}_{1/2}$ and 8 $^{2}$${\mathit{S}}_{1/2}$ states are obtained from the literature, while Born cross sections for the 5 $^{2}$${\mathit{D}}_{3/2}$, 6 $^{2}$${\mathit{D}}_{3/2}$, and all cascading states are calculated in this paper. At high energies, the measured total $^{2}$${\mathit{D}}_{3/2}$ state cross sections show 1/E behavior and converge to first Born theory; for Eg100 eV, experiment and theory agree within 6.7% for 5 $^{2}$${\mathit{D}}_{3/2}$ and within 3.7% for 6 $^{2}$${\mathit{D}}_{3/2}$. The total cross sections for the $^{2}$${\mathit{S}}_{1/2}$ states do not converge to Born theory even at 1000 eV, and it is shown that this cannot be attributed to cascading. At low energies, $^{2}$${\mathit{S}}_{1/2}$ and $^{2}$${\mathit{D}}_{3/2}$ state total excitation cross sections have similar shapes with sharply peaked maxima at about 0.9 eV above threshold. After cascading is corrected using first Born theory, estimated experimental cross sections for direct excitation of higher fine-structure states of rubidium are given.

Cathodoluminescence of semiconductors at 200 eV?

Brillson and Vitturo have recently reviewed the application of low energy (300 - 3000 eV) cathodoluminescence (CL) to surface studies of various semiconductors. In principle, the resulting electron penetration (40 - 1500 Å) at these energies should make it possible to differentiate near surface from bulk phenomena. The above authors demonstrated that deep level spectral features could be correlated with changes in the electronic structure of the surface as a result of metallization, laser annealing and thermal desorption. However, the experimental configuration used in the above studies was a room temperature, UHV-based, glancing incidence electron beam apparatus, i.e., no imaging capabilities. A future development in this area would be measurements performed in a regular SEM at cryogenic temperatures. The luminescence efficiency of GaAs greatly increases at low temperatures, and therefore, this would be beneficial to CL signal detection. We also require a better understanding of the factors which may limit progress in this matter. For example, the role of surface recombination velocity, the properties of luminescence dead layers and cross-over voltage phenomena are important to such an investigation. We report on progress in addressing some of these questions.