Pulsed Electron Beam Ablation Research Articles

Chemical Structure of EVA Films Obtained by Pulsed Electron Beam and Pulse Laser Ablation.

Poly(ethylene-co-vinyl acetate) (EVA) films were deposited for the first time using physical methods. The chemical structure of the films obtained using two techniques, pulsed electron beam deposition (PED) and pulsed laser deposition (PLD), was studied by attenuated total reflection Fourier infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Whilst significant molecular degradation of the EVA films was observed for the PLD method, the original macromolecular structure was only partially degraded when the PED technique was used, emphasizing the superiority of the PED method over PLD for structurally complex polymers such as EVA. Optical and scanning electron microscopic observations revealed compact and smooth EVA films deposited by pulsed electron beam ablation as opposed to heterogeneous films with many different sized particulates obtained by PLD.

Influence of pulse repetition rate on the growth of cobalt-doped ZnO thin films by pulsed electron beam ablation

Abstract

Effect of post-annealing on the properties of Co-doped ZnO thin films deposited by channel-spark ablation

In this study, we report on the effect of post-annealing treatment on the structure and morphology of Co-doped ZnO (CZO) thin film nano-composites deposited on Si (100) by channel-spark pulsed electron beam ablation (PEBA) from a single target, CoxZn1-xO (x = 0.20). The as-grown CZO films have been deposited within the temperature range 350 °C–450 °C, at electron beam acceleration voltages of 15 kV and 16 kV, and a beam frequency of 4 Hz. The films have been subjected to thermal annealing at either 400 °C or 600 °C for one hour. The effect of post-growth annealing on film properties has been discussed in terms of surface morphology, chemical composition, chemical state, and crystal structure. Experimental results show that, overall, post-annealing treatment significantly affects the structural and morphological properties of the films. Films annealed at 400 °C have higher average particle size and degree of crystallinity of ZnO hexagonal wurtzite structure relatively to the films annealed at 600 °C. Films annealed at 400 °C exhibit larger content in hexagonal close-packed (hcp) metallic Co (Co°) compared to the films annealed at 600 °C and to as-grown films. Both x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) indicate that enhanced growth of Coо is achieved at the annealing temperature of 400° C.

Co‐doped ZnO thin films grown by pulsed electron beam ablation as model nano‐catalysts in fischer‐tropsch synthesis

A single‐step deposition of cobalt‐doped zinc oxide (Co‐ZnO) thin film nano‐composites on three different crystalline substrates, viz., Al2O3 (c‐sapphire), silicon (100) (Si), and SiO2 (quartz) is reported, using pulsed electron beam ablation (PEBA). The results indicate that the type of substrate has no effect on Co‐ZnO films stoichiometry, morphology, microstructure, and film thickness. The findings show the presence of hexagonal close‐packed metallic Co whose content increases in the films deposited on Al2O3 and Si substrates relatively to SiO2 substrate. The potential of the films as model nano‐catalysts has been evaluated in the context of the Fischer‐Tropsch (FT) process. Fuel fractions, which have been observed in FT liquid products, are rich in diesel and waxes. Specifically, Co‐ZnO/Al2O3 nano‐catalyst shows a selectivity of ∼4%, 31%, and 65% towards gasoline, diesel, and waxes, respectively, while Co‐ZnO/SiO2 nano‐catalyst shows a selectivity of ∼12%, 51%, and 37%, for gasoline, diesel, and waxes, respectively. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3332–3340, 2018

Modelling of pulsed electron beam induced graphite ablation: Sublimation versus melting

Pulsed electron beam ablation (PEBA) has recently emerged as a very promising technique for the deposition of thin films with superior properties. Interaction of the pulsed electron beam with the target material is a complex process, which consists of heating, phase transition, and erosion of a small portion from the target surface. Ablation can be significantly affected by the nature of thermal phenomena taking place at the target surface, with subsequent bearing on the properties, stoichiometry and structure of deposited thin films. A two stage, one-dimensional heat conduction model is presented to describe two different thermal phenomena accounting for interaction of a graphite target with a polyenergetic electron beam. In the first instance, the thermal phenomena are comprised of heating, melting and vaporization of the target surface, while in the second instance the thermal phenomena are described in terms of heating and sublimation of the graphite surface. In this work, the electron beam delivers intense electron pulses of ∼100 ns with energies up to 16 keV and an electric current of ∼400 A to a graphite target. The temperature distribution, surface recession velocity, ablated mass per unit area, and ablation depth for the graphite target are numerically simulated by the finite element method for each case. Based on calculation findings and available experimental data, ablation appears to occur mainly in the regime of melting and vaporization from the surface.

Influence of Co loading on structural and morphological properties of Co-doped ZnO thin films grown by pulsed electron beam ablation

We report on the effect of cobalt loading in the target material on the properties of thin film nanocomposites of Co-doped zinc oxide (CZO) Zn1-xCoxO. The films have been deposited by pulsed electron beam ablation (PEBA) at 450°C on pre-annealed (1100°C) c-sapphire and Si (100) substrates. The experimental results, based on scanning electron and atomic force microscopies (SEM, AFM), indicate that Co doping significantly affects the morphology of the films. X-ray diffraction (XRD) measurements reveal that the films on both substrates exhibit a prominent ZnO hexagonal wurtzite structure for x = 0.05, whereas higher Co loading (x = 0.1, 0.2) results in a strong deformation of ZnO wurtzite lattice and in a higher content of hexagonal close-packed (hcp) metallic Co in CZO films. X-ray photoelectron spectroscopy (XPS) data confirm the presence of non-oxidized metallic Co (Co°) in the deposited films. Both XRD and XPS results indicate an increase in Co° content in the films as Co loading in the target is increased.

Effect of temperature and discharge voltage on the properties of Co-doped ZnO thin films deposited by pulsed electron beam ablation

Cobalt-doped ZnO (CZO) thin films have been deposited from CoxZn1-xO (x=0.20) target on Si (100) substrate by pulsed electron beam ablation (PEBA). The effects of process temperature (350°C–800°C) and electron beam acceleration voltage (15kV, 16kV) on the deposited films have been assessed. The films have been prepared at constant beam pulse frequency (2Hz) and Argon background pressure (∼3mTorr). The structure and surface morphology of CZO films have been investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). As per SEM data, the results show that the films consist of Co rich nano-sized globules (∼20nm–300nm). Energy dispersive x-ray (EDX) measurements reveal that Co content in the films seems to be unaffected by accelerating voltage while it increases with temperature in the range 350°C–450°C. At higher deposition temperatures (600°C & 800°C), the films exhibit faceted particles and are relatively rough. The films deposited at 800°C consist of a predominantly Co phase. X-ray photoelectron spectroscopy (XPS) data confirm the presence of metallic cobalt in the films, whose content increases with temperature but is practically unaffected by beam voltage. X-ray diffraction (XRD) analysis confirms the presence of herxagonal close-packed (hcp) metallic cobalt in the films.

Modeling of Plasma Expansion during Pulsed Electron Beam Ablation of Graphite

ABSTRACTPulsed electron beam ablation (PEBA) has proven to be a promising and powerful technique for the growth of high quality thin films. Pulsed electron beam film deposition consists of many physical processes including target material heating, target ablation, plasma plume expansion, and film growth on a substrate. Plasma plume expansion into a vacuum or an ambient gas is a fundamental issue in PEBA as the quality of thin films deposited onto the substrate depends on the composition, energy and density of particles ejected from the target. In the present study, gas-dynamics equations are solved to investigate plasma expansion induced by interaction of a nanosecond electron beam pulse (∼100 ns) with a graphite target in an argon atmosphere at reduced pressure. The spatio-temporal profiles of the temperature, pressure, velocity, and density of the plasma plume are numerically simulated for a beam efficiency of 0.6 and accelerating voltage of 15 kV. The preliminary results show a rich variety of behaviors. The model is validated by comparing some of the obtained simulation results with experimental data available in the literature.

Modeling of beam-target interaction during pulsed electron beam ablation of graphite: Case of melting

A one-dimensional thermal model based on a two-stage heat conduction equation is employed to investigate the ablation of graphite target during nanosecond pulsed electron beam ablation. This comprehensive model accounts for the complex physical phenomena comprised of target heating, melting and vaporization upon irradiation with a polyenergetic electron beam. Melting and vaporization effects induced during ablation are taken into account by introducing moving phase boundaries. Phase transition induced during ablation is considered through the temperature dependent thermodynamic properties of graphite. The effect of electron beam efficiency, power density, and accelerating voltage on ablation is analyzed. For an electron beam operating at an accelerating voltage of 15kV and efficiency of 0.6, the model findings show that the target surface temperature can reach up to 7500K at the end of the pulse. The surface begins to melt within 25ns from the pulse start. For the same process conditions, the estimated ablation depth and ablated mass per unit area are about 0.60μm and 1.05μg/mm2, respectively. Model results indicate that ablation takes place primarily in the regime of normal vaporization from the surface. The results obtained at an accelerating voltage of 15kV and efficiency factor of 0.6 are satisfactorily in good accordance with available experimental data in the literature.

Deposition of Cobalt Doped Zinc Oxide Thin Film Nano-Composites Via Pulsed Electron Beam Ablation

AbstractThis study reports on the preparation of cobalt doped zinc oxide (Co:ZnO) films via pulsed electron beam ablation (PEBA) from a single target containing 20 w% Co on sapphire (0001) and silicon (100) substrates. The films have been deposited at various temperatures (350оC, 400оC, 450оC) and pulse frequencies (2 Hz, 4 Hz), under a background argon (Ar) pressure of about 3 mtorr, and an accelerating voltage of 14 kV. The surface morphology has been examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). According to SEM analysis, the films consist of nano-globules whose size is in the range of 80-178 nm. Energy dispersive x-ray spectroscopy (EDX) reveals that deposition is congruent and the prepared films contain ∼20±5 w% cobalt. It has been found that the nano-globules in the deposited films are cobalt-rich zones containing ∼70 w% Co. From x-ray photoelectron spectroscopy (XPS) analysis, Co 2p3/2 peaks indicate that the deposited films contain CoO (binding energy = 780.5 eV) as well as metallic Co (binding energy = 778.1-778.5 eV). X-ray diffraction (XRD) analysis supports the presence of metallic Co hcp phase (2ϴ = 44.47° and 47.43°) in the films.

Nanocrystalline diamond films prepared by pulsed electron beam ablation on different substrates

Abstract

Accelerating voltage effect on the ablation process during pulsed electron deposition

In this study, we have analyzed the effect of electron beam accelerating voltage on the maximum temperature of a graphite target during pulsed electron beam ablation (PEBA). To this end, a two stage, one dimensional thermal model is used. The target is subjected to an electron pulse with accelerating voltages of 10, 13, 15, 17 and 18 kV. The surface temperature, vaporization front velocity, ablated depth, and ablation rate are estimated from the solution of the model. Simulation results have shown that target surface temperature is not proportional to the accelerating voltage. It has been found that the surface temperature increases with the accelerating voltage from 10 kV to 15 kV, and reaches a maximum value (7500 K) at 15 kV. After 15 kV, the temperature decreases with increasing accelerating voltage. Similar trends have been observed in the vaporization front velocity, ablated depth and ablation rate, with maximum values (75 m/s, 2.1 μm, and 4 μg/mm2) at 15 kV. The calculation results are in good agreement with relevant experimental data from the literature.

Hydrogen-Free Deposition of Nanocrystalline Diamond by Channel-Spark Electron Beam Ablation

We report on the preparation of hydrogen-free nanocrystalline diamond films by pulsed electron beam ablation (channel-spark) from a single target on silicon and stainless steel substrates and under different process conditions. The films have been grown from highly ordered pyrolytic graphite at room temperature in an argon atmosphere under a pressure of 0.6 Pa. This study aims at elucidating the influence of the accelerating voltage (13, 14.5, and 16 kV) and electron beam pulse repetition rate (5 and 8 Hz) on film morphology, grain size, carbon-carbon sp3 content, and crystalline fraction. The films have been characterized using visible-reflectance spectroscopy, visible-Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The correlations between measurement data and film properties are examined and discussed.

Deposition of iron pyrite via pulsed electron ablation

Pulsed electron beam ablation is a relatively novel deposition technique with some unique advantages, such as ease for scale-up and low operating cost. In this work, we report on the preparation of iron pyrite (FeS2) on 1.5-cm2 glass substrates through the pulsed electron beam ablation of a single synthetic target. The 40–120-nm-thin films were deposited at a substrate temperature ranging from room temperature to 250 ∘C and under a background argon atmosphere of 3.5 mTorr. Different characterization techniques have been used to analyze the deposited films, such as grazing-angle x-ray diffraction (XRD), X-ray photon spectroscopy (XPS), visible Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and visible optical reflectance spectroscopy. The findings show that iron pyrite can be obtained at high temperature in association with other phases.

Photoluminescence in silicon/silicon oxide films produced by the Pulsed Electron Beam Ablation technique

In this work we report studies of the photoluminescence emission in samples based on Si/SiOx films deposited by the Pulsed Electron Beam Ablation (PEBA) technique. The samples were prepared at room temperature using targets with different Si/SiO2 concentrations. The samples were characterized using X-ray Absorption Edge Spectroscopy (XANES) at the Si―K edge, Raman spectroscopy, Photoluminescence (PL) and X-ray Photoelectron Spectroscopy (XPS). The concentration of a-Si and nc-Si in the film was dependent on the silicon concentration in the target. It was also observed that the PL is strongly dependent on the structural amorphous/crystalline arrangement.

Compositional analysis of lead telluride films deposited via pulsed electron-beam ablation

Pulsed electron deposition (PED) is a novel thin film growth technique with unique advantages for industrial-scale manufacturing. Previously, no investigations into local deviations in stoichiometry have been carried out. The authors report the first analysis of large-scale compositional variations in thin films deposited via PED. Ablated lead telluride (PbTe) was deposited at various target-substrate distances on 5cm2 substrates. Rutherford backscattering was employed to systematically analyze compositional variation at different positions within the deposition. Stoichiometry is reported as a function of both distance and angular displacement. Deposition rates for the center of the ablated plume are reported. The authors show PED to be capable of uniform deposition over areas of moderate (0.5–1cm2) size, with an enrichment of heavier elements in the center of the film. The results are explained within the context of expanding plasma behavior.

Preparation of nanometer thin films with intense pulsed electron beam ablation

Physical processes of films deposition and the interactions between beam and target by pseudospark electron beam deposition (PED), similar to pulse laser beam deposition (PLD) have been presented in this paper. The nanometer thin films with similar ingredients as target materials are available through the interaction of intense pulsed electron beam and target to cause rapid melting, evaporations, ablation of target materials, and then nucleation crystallization on the surface of low temperature substrate. The intense interactions between beam and target affect the mass transfer processes, deposition rate, composition and space distribution of target materials, which influence and determine the components, structure and performance of films. The surface morphology, components and microstructure of nanometer thin films prepared by PED ablation have been investigated with high resolution electron microscopy (HREM), X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Due to high power density of the electron beams (10 9 W/cm 2), the rapid ablation on the surface of solid target has been obtained. Experimental results show that, by using PED ablation preparation, a variety of multilayered films with the oxides of multiple elements and refractory metal multilayered films are promising.

Parameters that control pulsed electron beam ablation of materials and film deposition processes

Conditions for ablation of materials and film deposition were analyzed for a pulsed (∼100 ns) electron beam produced by a channel-spark source. For dielectric materials, we found the existence of an optimal source voltage related to the saturation of the pulse current. Our analysis indicates a larger ablated mass, smaller optimal deposition rates (∼0.25 Å/pulse), and a larger optimal target to substrate distance relative to pulsed laser deposition process.

Deposition of YBa 2Cu 3O 7−x thin films by channel-spark pulsed electron beam ablation

A novel technique, channel-spark pulsed electron (YBCO) beam ablation, was applied to deposit high quality c-axis oriented YBa 2Cu 3O 7− x thin films with T c0 around 88 K. The apparatus, which is extremely compact, simple and inexpensive, is described. The electron beam power density and the efficiency of channel-spark ablation were studied. The effects of the beam and some processing parameters on T c of YBCO films fabricated on SrTiO 3 (100) substrates are reported.

Schlieren diagnostics of pulsed electron beam ablation of polymethyl-methacrylate

The investigation of the interaction of pulsed electron beams with PMMA (polymethylmethacrylate) targets is reported. The electron beam of some 10−8 s in duration is produced in a pulsed low-pressure gas discharge. The beam power density of up to 108 W/cm2 leads to a surface plasma formation similar to that of the pulsed laser ablation process. The propagation of the ablated material and the shock wave inside the PMMA target are observed by means of Schlieren diagnostics. An electron density gradient of over 3×1019 cm−4 has been observed in the expanding plasma up to 1.5 μs after the plasma formation. During the early stage of expansion, the expansion velocity of the plasma plume as determined by the steep electron density gradient is around 105 cm/s. The pressure behind the shock front inside the PMMA target as determined from the shock velocity exceeds 0.3 Gpa.