Pulsed Electron Deposition Technique Research Articles

Growth of multiferroic γ-BaFe2O4 thin films by Pulsed Electron Deposition technique

Multiferroic materials have attracted significant attention due to their potential to revolutionize logic and memory devices by reducing energy consumption or increasing information density. Barium monoferrite (γ-BaFe2O4 or BaFeO) is a promising lead- and bismuth-free multiferroic material with a stuffed tridymite-like structure, exhibiting both ferroelectricity and antiferromagnetism at room temperature. BaFeO thin films with engineered grain orientation, composition, elastic strain, and magnetic interlayer couplings could open new avenues for novel devices. However, synthesizing the stoichiometric "1–2–4" phase in the BaO-Fe2O3 system remains a challenge. This study focuses on the deposition of pure and crystalline γ-BaFe2O4 thin films using the Pulsed Electron Deposition (PED) method. An analysis of the plasma plume revealed that two main mechanisms govern the dynamics of BaFeO deposition: a congruent ablation process occurring far from thermodynamic equilibrium and an incongruent low-energy evaporation process. The regions of the film with maximized ablative/evaporative ratios are free from the secondary Ba2Fe2O5 phase, suggesting that the thermal evaporative contribution is the primary factor responsible for the out-of-stoichiometry composition. The influence of the substrate type on the structural properties of BaFeO films was also evaluated. It was confirmed that (h00)-oriented BaFeO tends to grow on amorphous quartz and polycrystalline Pt-coated quartz in the 700–800°C temperature range. Conversely, the growth on SiO2/Si leads to the preferential grain orientation along the (0k0) and (0kl) directions by increasing the temperature. These findings demonstrate the potential of PED for producing high-quality γ-BaFe2O4 polycrystalline thin films. A fully heteroepitaxial (h00)-BaFeO/(111)-MgO system was even achieved by depositing on a single-crystal MgO substrate. This unprecedented result paves the way for utilizing such thin films in multiferroic applications, where phase purity, structural orientation, and defect-free structures can be exploited to enhance the magnetoelectric properties of the device.

Preparation of epitaxial BiFeO3 thin films on Si(001) substrates by pulsed electron deposition

To achieve the epitaxial thin films deposition, it is necessary to use properly oriented substrates, with or without buffer layers, matching the lattice parameters of the epitaxial thin film we want to grow. In this work, the deposition of epitaxial Bi2SiO5(200) and BiFeO3(001) thin films on Si(001) substrates by pulsed electron deposition (PED) technique is reported without special substrate preparation. The deposition of epitaxial BSO(200) and T-BFO(001) directly onto Si(001) substrates during a single target deposition process is relevant and presents enormous potential to reduce costs and improve practicality, interface quality and BFO integration efficiency with Si(001) substrates.

Exploring Cu-Doping for Performance Improvement in Sb2Se3 Photovoltaic Solar Cells.

Copper-doped antimony selenide (Cu-doped Sb2Se3) thin films were deposited as absorber layers in photovoltaic solar cells using the low-temperature pulsed electron deposition (LT-PED) technique, starting from Sb2Se3 targets where part of the Sb was replaced with Cu. From a crystalline point of view, the best results were achieved for thin films with about Sb1.75Cu0.25Se3 composition. In order to compare the results with those previously obtained on undoped thin films, Cu-doped Sb2Se3 films were deposited both on Mo- and Fluorine-doped Tin Oxide (FTO) substrates, which have different influences on the film crystallization and grain orientation. From the current-voltage analysis it was determined that the introduction of Cu in the Sb2Se3 absorber enhanced the open circuit voltage (VOC) up to remarkable values higher than 500 mV, while the free carrier density became two orders of magnitude higher than in pure Sb2Se3-based solar cells.

Effect of Au thin film thickness and surface nanoparticles morphologies on the optical band gap and photoluminescence of ZnO thin films deposited by pulsed electron deposition technique

Effect of Au thin film thickness and surface nanoparticles morphologies on the optical band gap and photoluminescence of ZnO thin films deposited by pulsed electron deposition technique

Role of the substrates in the ribbon orientation of Sb2Se3 films grown by Low-Temperature Pulsed Electron Deposition

Antimony selenide (Sb2Se3) is a p-type semiconductor, considered as an excellent photovoltaic absorber for its high absorption coefficient in the visible region and a nearly optimal band-gap for single-junction solar cells. The simple binary composition, together with non-toxic and earth-abundant constituents make this material very promising toward industrial production of low-cost thin-film solar cells. Theoretical calculations and experimental data have confirmed that Sb2Se3 exhibits strong anisotropic optoelectronic properties, due to the presence of infinite covalent (Sb4Se6)n ribbons along the (001) direction, whereas weak van der Waals interactions occur between ribbons. In such anisotropic materials, electronic transport is strongly affected by crystal structure: when ribbons are aligned perpendicularly to the solar cell surface, a better collection of photogenerated current occurs, leading to larger photovoltaic conversion efficiencies.In order to understand the alignment mechanisms of ribbons, Sb2Se3 thin films were grown by Low-Temperature Pulsed Electron Deposition (LT-PED) technique at different temperatures (from 200 °C to 400 °C) on a variety of substrates, such as glass, molybdenum, CdS, Fluorine-doped Tin Oxide (FTO) and nanostructured ZnO. The structural and morphological characterization of the Sb2Se3 films, performed by out-of-plane and in-plane X-Ray Diffraction and micro-Raman spectroscopy, demonstrated that ribbon alignment along the surface normal is strongly dependent on the used substrate. The comparison between solar cells grown in substrate configuration on Mo and FTO, clearly demonstrates the influence of ribbon orientation on short-circuit current.

The Pulsed Electron Deposition Technique for Biomedical Applications: A Review

The “pulsed electron deposition” (PED) technique, in which a solid target material is ablated by a fast, high-energy electron beam, was initially developed two decades ago for the deposition of thin films of metal oxides for photovoltaics, spintronics, memories, and superconductivity, and dielectric polymer layers. Recently, PED has been proposed for use in the biomedical field for the fabrication of hard and soft coatings. The first biomedical application was the deposition of low wear zirconium oxide coatings on the bearing components in total joint replacement. Since then, several works have reported the manufacturing and characterization of coatings of hydroxyapatite, calcium phosphate substituted (CaP), biogenic CaP, bioglass, and antibacterial coatings on both hard (metallic or ceramic) and soft (plastic or elastomeric) substrates. Due to the growing interest in PED, the current maturity of the technology and the low cost compared to other commonly used physical vapor deposition techniques, the purpose of this work was to review the principles of operation, the main applications, and the future perspectives of PED technology in medicine.

Gas Sensing Properties of In₂O₃ Nano-Films Obtained by Low Temperature Pulsed Electron Deposition Technique on Alumina Substrates.

Nanostructured Indium(III) oxide (In2O3) films deposited by low temperature pulsed electron deposition (LPED) technique on customized alumina printed circuit boards have been manufactured and characterized as gas sensing devices. Their electrical properties have monitored directly during deposition to optimize their sensing performance. Experimental results with oxidizing (NO2) as well as reducing (CO) gases in both air and inert gas carriers are discussed and modeled.

Equivalent Circuit Model for Cu(In,Ga)Se2 Solar Cells Operating at Different Temperatures and Irradiance

The modeling of photovoltaic cells is an essential step in the analysis of the performances and characterization of PV systems. This paper proposes an experimental study of the dependence of the five parameters of the one-diode model on atmospheric conditions, i.e., irradiance and temperature in the case of thin-film solar cells. The extraction of the five parameters was performed starting from two sets of experimental data obtained from Cu(In,Ga)Se2 solar cells fabricated by the low-temperature pulsed electron deposition technique. A reduced form approach of the one-diode model has been adopted, leading to an accurate identification of the cell. It was possible to elaborate suitable relations describing the behavior of the parameters as functions of the environmental conditions. This allowed accurately predicting the trends of the parameters from a pair of curves, instead of a whole set of measurements. The developed model describing the dependence on irradiance and temperature was validated by means of a large set of experimental measurements on several Cu(In,Ga)Se2 (CIGS) devices built with the same technological process.

Epitaxial graphene thermistor for cryogenic temperatures

The thermal responsivity of monolayer epitaxial graphene grown on the Si-face surface of semi-insulating SiC substrate is investigated as a function of temperature below 300 K. The measurements showed that adsorption/desorption of atmospheric adsorbates can randomly modify the electrical characteristics of graphene which is indeed undesirable for consistent temperature sensing operations. Therefore, in order to avoid the interaction between graphene layer and adsorbates, the grown graphene layer is encapsulated with a thin SiO2 film deposited by Pulsed Electron Deposition technique. Temperature dependent resistance measurement of encapsulated graphene exhibited a clear thermistor type behavior with negative temperature coefficient resistance character. Both the sensitivity and transient thermal responsivity of the SiO2/graphene/SiC sample were found to be enhanced greatly especially for the temperatures lower than 225 K. The experimentally obtained results suggest that SiO2 encapsulated epitaxial graphene on SiC can be used readily as an energy efficient and stable temperature sensing element in cryogenic applications.

Structural Characterization of La1-xSrxCoO3 Thin Films Deposited by Pulsed Electron Deposition Method

The aim of the presented research was to investigate the influence of strontium dopant on the structure and composition of La1−xSrxCoO3 (x = 0, 0.1, 0.2) perovskite thin films. Pure and Sr doped LaCoO3 thin films were grown by pulsed electron deposition technique on crystalline epi-polished Si/MgO substrates. Numerous analytical techniques (scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction) were applied to characterize their phase/chemical composition, structure and surface morphology. X-ray diffraction analysis showed the presence of pure LaCoO3 perovskite phase in the undoped thin film. For Sr doped thin films La0.8Sr0.2CoO3 (x = 0.2), La0.9Sr0.1CoO3 (x = 0.1) small contents of La2 O3 and LaSrCoO4 phases were noticed. The crystallite sizes, calculated from the Williamson–Hall plots, were about 18 nm for all analyzed films. According to scanning electron microscopy/atomic force microscopy observations, obtained thin films were free from defects and cracks. Atomic force microscopy (tapping mode) analysis revealed the differences in the shape and quantity of surface crystallites for all thin films as a result of Sr doping and different deposition parameters. Atomic force microscopy technique also allowed measurement of roughness parameters for analyzed samples. X-ray photoelectron spectroscopy analyses of chemical states of elements of thin films showed that their chemical state was stable across the film thickness and even at the interface with the MgO substrate. X-ray photoelectron spectroscopy analysis also allowed to evaluate chemical states and atomic concentration of La, Co, and Sr elements within cross-sections of deposited thin films.

Joule heating-assisted growth of Cu(In,Ga)Se2 solar cells

We report on the development of an unconventional method for heating a Mo-coated substrate during the deposition of a Cu(In,Ga)Se2 (CIGS) layer by the pulsed electron deposition technique, to be used as absorber in thin film solar cells. This method is based on the application of a DC electrical power directly through the Mo back contact of the cell, converting electrical energy into heat by Joule effect. Since the current flows only on the superficial metal-coated region of the substrate, a localized heating of the surface can be achieved, thus limiting the heat losses. Due to the very efficient heat transfer to the thin Mo layer, a very little electrical power density (few W/cm2) is enough to achieve the required deposition temperature on the Mo surface, much lower compared to the traditional resistor- or lamp-based external heaters. The morphological and electrical properties of Joule-heated samples have been compared to those of CIGS films heated by a conventional external heater. As far as the structure concerns, a remarkable difference is revealed by Scanning Electron Microscopy analysis, indicating a significant enlargement of the CIGS grains size on Joule-heated samples. On the contrary, Capacitance-Voltage and Current-Voltage measurements evidence similar electrical features: both types of heated samples have a net free carrier concentration ≈5 × 1015 cm−3, resulting in a similar photovoltaic conversion efficiency (≈15%). The main recombination path, deduced from the dependence of VOC on the temperature, results to be the Shockley-Read-Hall mechanism in both types of the absorber layer. These results indicate that the Joule effect could be adopted as a feasible, low cost alternative heating method for growing high quality CIGS layers.

Low-temperature growth of single-crystal Cu(In,Ga)Se2 films by pulsed electron deposition technique

High quality epitaxial crystalline Cu(In,Ga)Se2 (CIGS) films were grown on n-type (100)—Germanium (Ge) substrates using pulsed electron deposition (PED) technique at a remarkably low substrate temperature of 300°C, thanks to the high-energy of adatoms arriving to the substrate. The crystalline quality was confirmed by X-ray diffraction techniques and from Transmission Electron Microscopy and the only defects found were twin boundaries along the (112) direction in these CIGS films; surprisingly neither misfit dislocations nor Kinkerdall voids were observed. A 100meV optical band located below the band edge was observed by Photoluminescence technique. Current–voltage and capacitance–voltage measurements confirm an intrinsic p-type conductivity of CIGS films, with a free carrier concentration of ≈3.5×1016cm−3. These characteristics of crystalline CIGS films are crucial for a variety of potential applications, such as more efficient absorber layers in single-junction and as an integral component of multi-junction thin-film solar cells.

Focused ion beam fabrication and magneto-electrical transport properties of La0.67Ca0.33MnO3 nanobridge

La0.67Ca0.33MnO3 particle films with an average particle size of ~150 nm were grown on single-crystal silicon substrate using pulsed electron deposition technique and then focused ion beam was introduced to fabricate nanobridge in size of 300 × 900 nm on the particle film. The magneto-transport properties of both samples were studied. For the film, there is only one resistance peak at 182 K in temperature-dependent resistance (R–T) curves, which is far lower than ferromagnetic–paramagnetic transition temperature (TC) of 250 K. When compared to the film, double peaks were observed in both R–T curves and magnetoresistance dependent on temperature (MR–T) curves of the nanobridge, one peak is at 186 K, which is very close to metal–insulator transition temperature (TP) of film, the other one is at 250 K, which is close to the TC of film, and these two peaks caused separately by grain and grain boundary (GB), which demonstrated that the electrical transport behavior of grain was separated from that of GB.

Infrared conductivity of PED-grown (La,Ba)SnO3 thin films

We have synthesized La-doped BaSnO3 thin films on SrTiO3 substrates by using the pulsed electron deposition technique. By performing reflection/transmission measurements on the films and a Drude model analysis of the data, we determined the carrier density n = 6.7 × 1019 cm−3 and the room-temperature mobility µ = 17 cm2V−1s−1 of the conducting electrons. The standard Drude optical conductivity of the films demonstrates that the electron correlation effect is minimal in the present transparent conducting oxide material.

Dynamics of evaporation from CuGaSe2 targets in pulsed electron deposition technique

The evaporation mechanisms from a solid target in pulsed electron deposition (PED) technique have been investigated by analysing the chemical composition and the thickness distribution of CuGaSe2 (CGS) films grown at different discharge voltages on glass substrates. The behaviour of the plasma plume generated from the target can be described by a linear combination of two coexisting processes: incongruent thermal evaporation and congruent ablation, which exhibit different weights depending on the PED voltage. The first component arises from the thermodynamic liquid-to-vapour transition involving the very first layers of the target surface, while the second one is due to the subsurface target penetration of the pulsed e-beam. The chemical composition of the thermally evaporated cloud, according to the CuGaSe2 phase diagram, exhibits an incongruent Cu depletion during the solid-to-gas phase transition with respect to the target, thus forming the ordered vacancy compound CuGa3Se5, while the sublimation of ablated species is perfectly stoichiometric. The thermally evaporated plasma follows a typical surface source spatial distribution, while the expansion of the ablation products exhibit a forward-peaked angular behaviour proportional to cos pθ (4 < p < 7). The incongruent component becomes negligible by enhancing the discharge voltage, where the e-beam is able to more deeply penetrate the target, and the electron power density exceeds the threshold ablation value of 1 × 108 W cm−2. The proposed mechanism for PED process is compared to other models describing the plume generation in pulsed high-energy-induced growth technique. This study represents a remarkable result to better understand and control the PED process.

Role of substrate temperature on the structural, morphological and optical properties of CuGaSe2 thin films grown by Pulsed Electron Deposition technique

CuGaSe2 (CGS) thin films were grown on uncoated and Mo-coated soda lime glass by Pulsed Electron Deposition (PED) technique at substrate temperatures comprised between 25°C and 475°C. X-ray diffraction analysis reveals that CGS samples exhibit a noteworthy crystal quality even at low growth temperature, Tg=100°C, whereas the out-of-plane preferential orientation of CGS chalcopyrite phase switches from <220> to <112> by increasing the substrate temperature. Annealing treatments seem to enhance the crystallinity of the film and to release the residual strain energy. Visible/near-infrared absorbance spectra show a monotonic decrease of CGS optical bandgap (from 1.75 to 1.65eV) by enhancing the substrate temperature. Yet the morphology of CGS films strongly depends on Tg, which promotes the formation of larger columnar grains perpendicular to the growth plane. Grain dimensions of ~2μm are achieved when CGS films are grown at high temperature (>400°C) on Mo-coated glass. The results indicate that PED is a promising growth technique for achieving good-quality CGS that can be useful as absorber layers in thin film solar cells.

Pulsed Electron Deposition (PED) - a Novel Tool for Growth of Thin Films

Pulsed Electron Deposition (PED) is a novel technique that can be applied for growing high quality thin films. In this technique, we used an electron beam with a focused diameter of about 1 mm, the energy up to 15 kV, the frequency of 1-10 Hz, the pulse width of 100 ns and the total current of 1.5 kA generated in a discharge system. A remarkable advantage of this technique is the low deviation in composition from bulk to film. By using the PED technique the transparent coducting ZnO and Cu(InGa)Se\(_{2 }\) films were prepared. The effect of some deposition conditions on the properties of film has been examined and discussed. For Cu(InGa)Se\(_{2 }\), the best film was obtained at the discharge voltage of 12 kV and substrate temperature of 400\(^\circ\)C, while for ZnO, the best film was grown at the oxygen pressure of 1.3 Pa and at 400(^\circ\)C.

Fabrication and Surface Morphology of YBCO Superconducting Thin films on STO Buffered Si Substrates

ABSTRACTPulsed Electron Deposition (PED) is an attractive alternative to Pulsed Laser Deposition (PLD) for growing high temperature superconductor thin films because of its relatively low cost. In this study, YBa2Cu3O7-δ(YBCO) thin film has been fabricated on silicon substrates by Pulsed Electron Deposition technique. SrTiO3 (STO) as a buffer layer has been grown between Si substrate and YBCO superconducting layer. The crystalline structures of STO/Si and YBCO/STO/Si films have been investigated by x-ray diffraction (XRD). The surface morphology and microstructure of YBCO/STO/Si thin film have been characterized with atomic force microscope (AFM) and scanning electron microscope (SEM). From the θ-2θ XRD analysis of YBCO thin films, (00l) diffraction peaks are obtained indicating they have a poor c-axis oriented structure. SEM analysis shows that the surfaces of films are crack-free, but they have some particulates. On AFM images, the droplets are clearly observed leading to a roughly surface.

Transport properties of LCMO granular films deposited by the pulsed electron deposition technique

By finely controlling the deposition parameters in the pulsed electron deposition process, granular La2/3Ca1/3MnO3 (LCMO) film was grown on silicon substrates. The substrate temperature, ambient pressure in the deposition chamber and acceleration potential for the electron beam were all found to affect the grain size of the film, resulting in different morphologies of the samples. Transport properties of the obtained granular films, especially the magnetoresistance (MR), were studied. Prominent low-field MR was observed in all samples, indicating the forming of grain boundaries in the sample. The low-field MR show great sensitive to the morphology evolution, which reaches the highest value of about 40% for the sample with the grain size of about 250 nm. More interestingly, positive-MR (p-MR) was also detected above 300 K when low magnetic field applying, whereas it disappeared with higher magnetic field applied up to 1.5 and 2 Tesla. Instead of the spinpolarized tunneling process being commonly regarded as a responsible reason, lattice mismatch between LCMO film and silicon substrate appears to be the origin of the p-MR

Preparation of polytetrafluoroethylene by pulsed electron ablation: Deposition and wettability aspects

Polytetrafluoroethylene (PTFE) has been prepared by pulsed electron deposition technique on glass and silicon substrates. Deposition of the thin films has been carried out in the temperature range from room temperature to 300 °C, pressure range from 133.32 × 10 −3 Pa to 799.93 × 10 −3 Pa, and discharge voltages between 10 kV and 16 kV. Argon or nitrogen has been used as a background gas during the deposition of the films. Attenuated Total Reflection Fourier Transform Infrared spectroscopy shows absorption peaks in the films at 644 cm −1, 1154 cm −1 and 1210 cm −1 consistent with those of PTFE target material. Atomic force microscopy and spectroscopic reflectometry reveal the clustered nature of the films and other morphological characteristics. Surface wettability of the films, expressed via the contact angle, has been measured via static angle goniometry. PTFE films increase the contact angle from about 32° (bare glass) and 43° (bare silicon) to up to 90° and 110° for PTFE-coated glass and silicon substrates, respectively. The contact angle decreases with an increase in both pressure and temperature, while it increases then decreases as the discharge voltage increases.