Electron Beam Current Density Research Articles

Electron Beam Induced Growth of Silver Nanoparticles

An electron beam inducing method for sprouting large quantities of silver nanoparticles on the surface of silver chloride particles is reported. The electron beam driven process was characterized by time-dependent scanning electron microscope (SEM) and energy dispersive spectrum (EDS), allowing for observing several key intermediates in and characteristics of the growth process. Theoretical calculation coupled with experimental observation demonstrated that the growth of silver nanoparticles was mostly related to the current density of electron beam. Decomposition of the silver chloride on the surface of sample was under electron beam irradiation resulted in silver nanoparticles and chlorine. This phenomenon could be useful in developing a novel mechanism for preparation of nanostructures and proposing a reference to avoid image distortion during the characterization of silver compounds under SEM.

Pulsed cathodoluminescence of calcite crystals of various origins

We have studied the luminescence of calcites from phlogopite-calcite veins, marbles, leucogranites, apatite-calcite ores, and carbonatites in the spectral range 300–800 nm under excitation with nanosecond electron pulses at an electron beam current density of ∼10 A/cm2. All of the calcite varieties have a fast emission component, with a broad spectrum in the near-UV and visible spectral regions, whose decay time is comparable to the excitation pulse duration, and a slow emission component, with a peak-emission wavelength of 610–620 nm and decay time of tens of milliseconds. The spectral composition of the emission depends on the nature of the calcite sample. We analyze the evolution of the spectrum after excitation and discuss the luminescence excitation mechanisms and the nature of the emission centers.

Betavoltaic Performance of Radiation-Hardened High-Efficiency Si Space Solar Cells

Long-lived and high-energy-density betavoltaics have a great potential as power supplies for remote and hostile environmental conditions, where volume power density and/or power lifetime are very important considerations. In this paper, we provide new results to aid in the design and optimization of betavoltaics made with Si space solar cells and beta sources. The new results were obtained by using a customized low-energy electron accelerator to characterize the radiation-hardened high-efficiency Si space solar cells while varying the electron beam energy and electron beam current density, i.e., electron beam flux. The betavoltaic conversion efficiency of Si space solar cells increases until 60 keV and then decreases with the increasing electron beam energy. The maximum efficiency (6%) obtained at the electron beam energy of 60 keV suggests that Pm-147 would be a good beta source to make high-efficiency nuclear batteries. The radiation ionization energy is ~ 3.90 eV per electron-hole pair for Si space solar cells. Some radiation damage-induced performance degradation was also observed when the Si space solar cells were exposed to the bombardment of 62-keV electrons with fluence up to 4.92 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">18</sup> betas/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which is equivalent to the radiation from a semi-infinite Pm-147 layer for ~ 2.26 years. The results in this paper suggest that beta-particle entrance window, betavoltaic cells' configuration structure, and device properties such as charge carriers' diffusion length are very important factors to be engineered to improve the conversion efficiency for practical betavoltaics.

Development of electron beam ion source charge breeder for rare isotopes at Californium Rare Isotope Breeder Upgrade

Recently, the Californium Rare Isotope Breeder Upgrade (CARIBU) to the Argonne Tandem Linac Accelerator System (ATLAS) was commissioned and became available for production of rare isotopes. Currently, an electron cyclotron resonance ion source is used as a charge breeder for CARIBU beams. To further increase the intensity and improve the purity of neutron-rich ion beams accelerated by ATLAS, we are developing a high-efficiency charge breeder for CARIBU based on an electron beam ion source (EBIS). The CARIBU EBIS charge breeder will utilize the state-of-the-art EBIS technology recently developed at Brookhaven National Laboratory (BNL). The electron beam current density in the CARIBU EBIS trap will be significantly higher than that in existing operational charge-state breeders based on the EBIS concept. The design of the CARIBU EBIS charge breeder is nearly complete. Long-lead components of the EBIS such as a 6-T superconducting solenoid and an electron gun have been ordered with the delivery schedule in the fall of 2011. Measurements of expected breeding efficiency using the BNL Test EBIS have been performed using a Cs(+) surface ionization ion source for external injection in pulsed mode. In these experiments we have achieved ∼70% injection∕extraction efficiency and breeding efficiency into the most abundant charge state of ∼17%.

Cathodoluminescence of yttrium oxide and yttrium and zinc silicate films

We have studied the cathodoluminescent properties of Y2SiO5:Ce, Zn2SiO4:Ti, Zn2SiO4:Mn, Y2O3:Eu thin films obtained by high-frequency magnetron sputtering. Based on measurements of the luminescence spectra, we have shown that the films can be used as luminophores with blue emission (Y2SiO5:Ce, Zn2SiO4:Ti), green emission (Zn2SiO4:Mn), and red emission (Y2O3:Eu). We have studied the dependences of the luminescence intensity on the energy of the exciting electrons, the electron beam current density, and the exposure time. We hypothesize that the decrease in the luminescence intensity during electron bombardment is connected with formation of new oxide layers as a result of an electron-stimulated surface chemical reaction.

The evolution of a modulated electron beam in a dense plasma barrier

The dynamics of a modulated electron beam in a plasma barrier is studied via computer simulations using the 1D and 2D models for a wide range of parameters, such as initial beam modulation depth, electron beam current density and plasma density profile. The effects of competition between the resonant mode of a beam–plasma system and space charge wave of the beam at the modulation frequency are discussed. The influence of the beam–plasma turbulence mode on the evolution of the modulated beam is studied. The evolution of the velocity distribution function of the modulated beam during its motion in the dense plasma is considered, and the influence of background plasma inhomogeneity on the modulated beam evolution is also studied. For 2D simulation the influence of the beam transversal restriction is discussed. The simulation results are compared with previous laboratory experiments.

Ionizing radiation-stimulated diffusion and desorption of hydrogen from metals

The processes of hydrogen diffusion from a sample depth activated by electrons with an energy of tens of keV are studied. The difference from the known models of electron-stimulated desorption, which consider as a rule electron energies from 0.5 to several keV, is noted. The proposed model is shown to correspond to at least two established experimental facts: the nonlinear dependence of hydrogen isotope desorption on the electron beam current density affecting the sample and the dependence of hydrogen desorption on the irradiation time of the sample.

Measurements of charge state breeding efficiency at BNL test EBIS

Charge breeding of singly charged ions is required to efficiently accelerate rare isotope ion beams for nuclear and astrophysics experiments, and to enhance the accuracy of low-energy Penning trap-assisted spectroscopy. An efficient charge breeder for the Californium Rare Isotope Breeder Upgrade (CARIBU) to the ANL Tandem Linear Accelerator System (ATLAS) facility is being developed using the BNL Test Electron Beam Ion Source (Test EBIS) as a prototype. Parameters of the CARIBU EBIS charge breeder are similar to those of the BNL Test EBIS except the electron beam current will be adjustable in the range from 1 to 2 A. The electron beam current density in the CARIBU EBIS trap will be significantly higher than in existing operational charge state breeders based on the EBIS concept. The charge state breeding efficiency is expected to be about 25% for the isotope ions extracted from the CARIBU. For the success of our EBIS project, it is essential to demonstrate high breeding efficiency at the BNL Test EBIS tuned to the regime close to the parameters of the CARIBU EBIS at ANL. The breeding efficiency optimization and measurements have been successfully carried out using a Cs + surface ionization ion source for externally pulsed injection into the BNL Test EBIS. A Cs + ion beam with a total number of ions of 5×10 8 and optimized pulse length of 70 μs has been injected into the Test EBIS and charge-bred for 5.3 ms for two different electron beam currents – 1 and 1.5 A. In these experiments we have achieved 70% injection/extraction efficiency and breeding efficiency into the most abundant charge state ∼17%.

Study of discharge after electron irradiation in sapphires and polycrystalline alumina

The fraction R of charges undergoing discharge during the time separating two electron pulses is derived from the induced current method developed in a scanning electron microscope. Irradiation is performed via a 10 keV defocused electron beam and low current density. The evolution of R with temperature (in the range 300–663 K) obeys to an Arrhenius type relation. Activation energies connected with the processes involved are deduced. In sapphire, no discernible discharge is observed due to the dominance of deep traps. In silver doped sapphire, R increases sharply from 10% to 70% as the temperature rises from 360 to 420 K, with a corresponding activation energy of 0.51 eV. In contrast, in polycrystalline alumina processed by solid state sintering (grain diameters of 1.7, 2.7, and 4.5 μm) the degree of discharge increases continuously with temperature and grain size. The enhancement with grain size indicates that the sintering conditions influence strongly the efficiency of a gettering effect. The activation energy below 573 K is about 0.12 eV independently of grain size. Above 573 K, a second activation energy of 0.26 eV appears for the smallest grain size sample. The results suggest that discharge may stem from a density of trapping states, associated to grain boundaries in sintered samples, rather than from a single trapping level linked to the doping element as Ag in sapphire.

High-current diode with ferroelectric plasma source-assisted hollow anode

The operation of a ferroelectric plasma source-assisted hollow anode (HA) electron source in a vacuum diode powered by an ∼200 kV and ∼400 ns pulsed generator was studied using time- and space-resolved laser induced fluorescence diagnostics. It was found that the plasma ion “temperature” in the vicinity of the HA output grid increases up to ∼15 eV during the accelerating pulse, which is consistent with a model of the potential screening of the grid by the randomly moving ions [Phys. Plasmas 13, 073506 (2006)]. Also it was shown that the increase in the HA plasma potential up to several kilovolts because of the appearance of a noncompensated ion charge in the HA bulk plasma due to electrons fast extraction, leads to explosive emission centers being generated at the HA grid and to nonuniformity in the cross-sectional electron beam current density. Finally, the plasma prefilled mode of diode operation was studied using a simple one-dimensional model of the plasma erosion and the HA plasma electron heating by energetic ions was considered.

The MSU EBIT at NSCL

The National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU) is constructing ReA3 to reaccelerate rare-isotope beams available from gas stopping of fast radio-nuclides produced by projectile fragmentation to energies of ∼ 0.3-3 MeV/nucleon. Such beams are unavailable worldwide, but are in demand for Coulomb excitation and transfer reaction studies as well as for the study of astrophysical reactions. ReA3 consists of four main components: an electron-beam ion trap (EBIT), an achromatic mass separator, a radio-frequency quadrupole (RFQ) pre-accelerator, and a superconducting radio-frequency linear accelerator (SRF-LINAC). By increasing the charge of ions injected into the RFQ and SRF-LINAC, the EBIT charge breeder is a key component to provide a compact and cost-efficient reaccelerator for short-lived isotopes. The MSU EBIT will be equipped with an electron-gun cathode yielding a few amperes. A unique EBIS-EBIT hybrid magnet configuration, composed of Helmholtz coils and a solenoid, will provide a maximum magnetic field strength of 6 T. The combination of a high-current cathode and strong magnetic field will allow the MSU EBIT to reach high electron-beam current densities of 104 A/cm2. This will make it well suited to rapidly increase the charge state of short-lived isotopes within tens of milliseconds or less. The unique extended magnet configuration will guarantee high-beam acceptance. This publication will present an overview and status of the MSU EBIT.

Electron Beam Sintering of Zirconium Diboride

Electron beam sintering of ultra‐high‐temperature ceramic material of zirconium diboride (ZrB2) was successfully carried out. Scanning electron microscopy images showed that the sintered layer had smooth surface morphology. Significant grain growth was observed by increasing the electron beam current density. More uniform and finer microstructures could be obtained using high beam currents and short dwell times. Chemical composition analysis confirmed that sintering in a vacuum environment could minimize boron loss. X‐ray diffraction results revealed that the sintered layer mainly preserved the crystalline phase from the starting powder.

ZnSe based films characterization by cathodoluminescence

Abstract In this work the cathodoluminescence investigation have been used to study the ZnSe based films. ZnSe, ZnS y Se 1– y and Zn 1− x Mg x S y Se 1− y films were grown by molecular beam epitaxy with different composition measured by electron probe microanalysis. The film band gap structure and defect energy levels were determined by cathodoluminescence intensity measurements. The cathodoluminescence intensity time variation was measured in dependence on electron beam current density and sample temperature for free exciton recombination band at stationary electron beam irradiation. The cathodoluminescence intensity time variation for different samples points to electron traps with different activation energies that are present depending on sample quality. The presence of deep acceptor levels has been established, with activation energies of around 0.02–0.05 eV. The defect levels are probably associated with a lattice defect like Se vacancy or defect complexes.

Controllable melting and flow of β-Sn in flexible amorphous carbon nanotubes

A high-yield of carbon nanotubes filled with β-Sn nanowires has been produced by the thermal pyrolysis of acetylene over SnO 2 catalysts. Electron beam irradiation (EBI) induced melting and flow of Sn in the nanotubes and this could be controlled by changing the electron beam current density. The mass flow rate of the Sn ranged from 0.9 to 8.2 fg/s. The melting of the nanowires is a result of the temperature rise caused by the EBI. Many factors, including temperature variation, charging, and EBI induced deformation of the carbon shells, contribute to the flow of Sn.

Characterization of radiative centers in wide-band-gap materials by local cathodoluminescence by the example of europium-doped YAG

Europium-doped yttrium-aluminum garnet (YAG) samples were studied by local cathodoluminescence. The europium valence in YAG is 3+; an addition of a small amount of zirconium partially converted europium to the divalent state (2+). The local cathodoluminescence method made it possible to detect the presence of both europium valence states. Concentration dependences of the cathodoluminescence intensity and decay time for various spectral lines and bands were studied. The dependence of the cathodoluminescence intensity on the electron beam current density was studied. The results obtained were interpreted within the two-level model of the radiative center. The local cathodoluminescence method potential and the two-level model applicability were demonstrated. An analysis of the spectra allowed for the detection and identification of an unintentional impurity in one of the samples.

Substrate atom enriched carbon nanostructures fabricated by focused electron beaminduced deposition

Carbon nanostructures fabricated using focused electron beam induced deposition (FEBID)in a residual vacuum atmosphere or in the presence of low pressure precursor gas exhibitenrichment with the atoms of the substrate element. Nanostructures having base sizes upto 100 nm and height up to 250 nm with maximum substrate atom enrichment of 50% havebeen fabricated. The size of the structures (nanocones) and the substrate atomenrichment depends on the electron beam current density and irradiation time. Apossible explanation of the phenomenon has been sought on the basis of localtemperature rise and diffusion of the substrate atoms in the nanostructure duringthe growth process. The phenomenon can be used to fabricate dense 2D carbonnanopatterns enriched with a desired element used as the substrate material.

Dehydrogenation of kaersutitic amphibole under electron beam excitation recorded by changes in Fe3+/ Fe: An EMP and SIMS study

We present in situ microanalyses of Fe3+/ΣFe in mantle-derived kaersutites as measured by electron probe microanalysis (EMP) based on the “self absorption induced FeLα peak shift” method. The EMP results are not in agreement with bulk (wet chemistry) data. The heterogeneities revealed for some kaersutite megacrysts, when comparing bulk and EMP Fe3+/ΣFe results, cannot explain the differences with the EMP measurements. It is thus proposed that any EMP overestimation of Fe3+/ΣFe results from a beam-induced dehydrogenation and a subsequent oxidation of Fe2+ to Fe3+ according to the known relation: Fe2+ + OH- = Fe3+ + O2- + 1/2 H2. To demonstrate this phenomenon, H losses were measured by secondary ion mass spectrometry (SIMS) after EMP irradiation at different beam currents on two amphiboles with 1.1 and 1.7 wt% H2O, respectively. In both amphiboles, H losses were observed under high beam currents (240 and 100 nA). No dehydrogenation is observed under lower beam currents for the 1.1 wt% H2O amphibole, but still occurs, down to at least 50 nA, for the amphibole with the greatest H2O contents. Amphiboles with low H2O contents (below ~0.5 H+) are less affected by beam damage. For amphiboles with higher H2O contents, the electron beam current density should be reduced with consideration given to the resulting high statistical errors.

NUMERICAL ANALYSIS OF LASING DYNAMICS IN VOLUME FREE ELECTRON LASER

Nonlinear phenomena originating in volume free electron laser (VFEL) are investigated by methods of mathematical modelling using computer code VOLC. It was demonstrated the possibility of excitation of quasiperiodic oscillations not far from threshold values of electron beam current density and VFEL resonator length. It was investigated sensibility of numerical solution to initial conditions for different VFEL regimes of operation. Parametric maps with respect to electron beam current and detuning from synchronism condition present complicated root to chaos with windows of periodicity in VFEL. Investigation of chaotic lasing dynamics in VFEL is important in the light of experimental development of VFEL in Research Institute for Nuclear Problems.

Low-Energy Electron Beam Direct Writing Equipment

We proposed an electron beam direct writing (EBDW) system capable of high throughput and maskless operation based on a novel concept of using both low-energy electron beam (EB) and character projection (CP) system. We fabricated an EB optical column of low-energy EBDW equipment and obtained a resist pattern. We also investigated the beam blur and line width roughness (LWR) of lines and spaces (L/S) formed on a resist to change various EB current densities and convergence half angles. The obtained results show that a Coulomb interaction effect markedly affects the beam blur in our EB optical column. Thus, we reduce the number of sources caused by LWR and developed photoresists to obtain small LWR L/S patterns for achieving a high throughput.

Evolution of the cathodoluminescence spectral shape and intensity of GaN quantum dots under 10 keV electron beam irradiation

AbstractIn‐situ degradation experiments are performed by means of plan‐view spectral cathodoluminescence experiments on GaN quantum dots. The influence of the electron beam current density J in the range of 1 to 5.5 A/cm2 is specially studied. Whatever is the J value, the CL peak red‐shifts between 11 and 6 meV and its intensity decreases. Morevoer, a modification of the CL shape is observed which depends on the J value. The results are interpreted in terms of interdiffusion and strain relaxation. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)