Electron Beam Evaporation Technique Research Articles

Tuning the bandgap and photoluminescence properties of Ge/Al2O3 multilayer thin films using annealing and ion beam irradiation

Abstract The present work reports high energy ion beam irradiation induced modifications in Ge/Al2O3 multilayers (MLs). Ge and Al2O3 multilayer thin films were deposited using the electron beam evaporation technique. Afterward, the as-deposited films were annealed using Rapid thermal annealing (RTA) at different temperatures ranging from 500 to 800°C under high vacuum. At a constant fluence of 5×1012 ions /cm2, the annealed films were subjected to irradiation with 80 MeV Ag ions. X-ray diffraction patterns show the crystalline nature of films that were annealed above 500°C, and the increase in crystallite size of Ge nanocrystals from 4.5 to 5.7 nm is observed for annealed samples. After Ag ion irradiation, the crystallinity of the films deteriorates. The crystallinity and optical bandgap are found to vary with Ag ion irradiation. The band gap of annealed films decreased from 1.1 to 0.97 eV with increase in crystallite size. The band gap of irradiated samples increased than that of pristine films. In addition, photoluminescence (PL) measurements were carried out to investigate the luminescence characteristics of annealed and irradiated multilayer films, and a wide emission band in the visible region was observed. The basic mechanism for tailoring the optical band gap and PL emission using RTA and ion irradiation is discussed.


Bipolar resistive switching behavior of bilayer β-Ga2O3/WO3 thin film memristor device

This article investigates the bipolar resistive switching behavior of bilayer Au/β-Ga2O3/WO3 thin film (TF)/Ag heterostructure memristor device deposited using an electron beam evaporation technique. The purity of the deposited sample was confirmed by the XRD and FESEM with EDS characterizations. The root mean square roughness(RRMS) of single layer WO3 TF and heterolayer of Ga2O3/WO3 TF were obtained from the AFM analysis as 4.56 nm and 2.20 nm, respectively. The presence of more oxygen vacancies in WO3 sample was also confirmed by the XPS analysis. The optical measurement of the sample also revealed a bandgap of ∼ 4.35 eV for β-Ga2O3 TF and ∼ 3.66 eV for WO3 TF. Moreover, the bilayer Au/β-Ga2O3/WO3 TF/Ag heterostructure memristor device demonstrated bipolar resistive switching behavior with a good resistance ratio of ∼ 182, an endurance of 300 cycles, and a data retention of 103 s at room temperature. The device also yielded a low SET power of 1.17 mW (at 1.74 mA, +0.67 V) and a low RESET power of 2.50 mW (at 7.16 mA, – 0.35 V). The logarithmic current-voltage (I-V) relationship revealed that the switching behavior of the memristor device is mainly dominated by Ohmic conduction in LRS as well as Child’s square law, TCLC and Ohmic conductions in HRS. With the above parameters, the Au/β-Ga2O3/WO3 TF/Ag memristor device has the potential for future RRAM applications.

Design and fabrication of highly efficient antireflective coating in MWIR on germanium using ion-assisted e-beam deposition

We present the design, fabrication, and characterization of a multilayer anti-reflective (AR) coating on a Germanium (Ge) substrate for mid-wavelength infrared (MWIR) applications using the ion-assisted electron-beam evaporation (IAPVD) technique. The AR coating structure comprises five layers of thin films, alternating between low (nL) and high (nH) refractive index materials, specifically silicon dioxide (SiO2) and Ge. The total thickness of the multilayer structure is maintained below 2 μm. The design was meticulously optimized for the 3.6–4.9 μm MWIR range using OptiLayer software, achieving an impressive average transmission of 99.492 % and an average reflectance of merely 0.508 % over a broadband spectral width of 1300 nm. Following the fabrication process using the IAPVD technique, the empirical results demonstrated an average transmission of 98.56 % and a reflectance value of 0.177 % within the 3.6–4.9 μm range. A strong correlation was observed between the simulated and the fabricated results, with a deviation of only 0.331 % on the reflectance value, proving the accuracy and reliability of the design and fabrication process. This work introduces a highly efficient solution for AR coatings on Ge surfaces, enhancing the performance of electro-optical applications in the MWIR region. To the best of our knowledge, the newly designed Ge/SiO2 multilayer structure and the results achieved have not been previously documented in the literature, and offer substantial improvements in transmission efficiency and reflectance reduction for Ge-based optical systems.

Dark-field microscopy studies of single silicon nanoparticles fabricated by e-beam evaporation technique: effect of thermal annealing, polarization of light and deposition parameters.

Herein, we report the dark-field microscopic studies on single silicon nanoparticles (SiNPs) fabricated using different deposition parameters in the electron beam (e-beam) evaporation technique. The morphology of the fabricated SiNPs is studied using the Atomic Force Microscope. Later, for the first time, the effect of thermal annealing and deposition parameters (i.e., beam current and deposition time) on the far-field scattering images and spectra of single SiNPs is studied using a transmission-mode dark-field optical microscope to estimate the wavelength locations and full-width at half maxima of the optical resonances of single SiNPs. Finally, the role of polarization of incident light on the optical resonances of single SiNPs is also studied by recording their scattering images and spectra.&#xD.

Effect of substrates on the structural, surface chemical state, and optical properties of Ga-doped Al2O3 thin films

We report the stabilization of Ga-doped Al2O3 (GaAlO) thin films into rhombohedral structure (R 3‾ c space group). We used the target material of composition A11.5Ga0.5O3 (bulk) to deposit the films on Alumina (0001) and p-type Si (100) substrates by using the electron beam evaporation technique. X-ray diffraction pattern confirmed the formation of polycrystalline rhombohedral structure for the as-grown films on Alumina substrate, whereas the films grown on Si substrate showed amorphous structure. The post-heat treatment of as-grown films at 550 °C stabilized rhombohedral structure in all the films, irrespective of the substrates. X-ray photoelectron spectra confirmed modification in surface chemical state of the films depending on nature of the substrates. Optical bandgap of the GaAlO films was stabilized in the range of 3.44 eV–4.04 eV, which is substantially reduced in comparison to corundum structured α-Al2O3 having optical band gap in the range of 8–9 eV and α-Ga2O3 having optical band gap of 4.5–5.5 eV. The defect-induced electronic states and substrate induced interfacial diffusion contributed additional energy gap in the range of 1.50–2.92 eV for GaAlO films grown on Si substrate. The development of highly crystalline corundum structured α-(Al, Ga)2O3 alloyed thin films and engineering their band gap energy in a wide range (1.5–4 eV) is useful for applications of semiconductor metal oxides in high power and medium frequency opto-electronic devices.

Tailoring of structural and optical properties of GeOx thin films using 100 MeV Si ions

In the present work, the effects of 100 MeV Si ions on the structural and optical properties of GeOx thin films have been investigated. Thin films of Germanium oxide (GeOx) were deposited onto silicon substrates using electron beam evaporation technique. Subsequently, 100 MeV Si7+ ions were used to irradiate as-deposited films at different fluences ranging from 5 × 1012 to 2 × 1013 ions/cm2. As-deposited films are amorphous as evident from XRD and Raman results. After irradiation with a fluence of 5 × 1012 ions/cm2 the films show partial crystallization. The strong photoluminescence (PL) exhibited from as-deposited and irradiated films is in ultraviolet (UV) and blue region. The blue shift was observed in PL bands after ion beam irradiation. PL band intensity was found to vary with irradiation fluence. The possible mechanism of variation in the PL emission from GeOx thin films with Si ion irradiation has been studied.

E-beam synthesized fast-switching TiO2/SnO2 type-II heterostructure photodetector

A fast-switching TiO2/SnO2 heterostructure thin-film (TF) photodetector synthesized by electron beam evaporation technique is analyzed in this study. The substrate utilized is n-type silicon (Si), while gold (Au) is employed as the top electrode. To assess sample morphology and confirm elemental composition, field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDS), and chemical mapping were conducted. Structural characteristics were determined using X-ray diffraction (XRD) analysis. The XRD analysis confirmed the presence of various phases of TiO2 (anatase and rutile) and SnO2 (rutile). UV-Vis spectroscopy revealed multiple absorption peaks, at 447 nm, 495 nm, 560 nm, and 673 nm, within the visible spectrum. The device demonstrates high detectivity (D∗) of 1.737×109 Jones and a low noise equivalent power (NEP) of 0.765×10−10W. Evaluation of the device’s switching response through current-time characteristic (I-T) analysis indicates rapid switching with a rise time and fall time of 0.33 s and 0.36 s, respectively.

Synthesis and characterization of Co3O4 spinel nanowall: understanding the growth mechanism and properties

Formation of spinel tricobalt tetraoxide (Co3O4) nanostructures through a controlled thermal oxidation process is discussed here. Thin films of high purity cobalt (Co) were deposited on glass/quartz substrates using an electron beam (E-beam) evaporation technique. Thermal oxidation of the as-deposited Co thin films was carried out at various oxidation temperatures (400 °C to 600 °C) for different durations (5 h to 15 h) to grow various oxide nanostructures. Different surface characterizations techniques were used to investigate the structure, chemistry and electronic properties of the as-grown cobalt oxide nanostructures. x-ray diffraction analysis revealed the presence of the CoO phase along with the Co3O4 phases at relatively lower oxidation temperature. However, the Co3O4 phase becomes more predominant for longer oxidation durations at higher oxidation temperatures. Field emission scanning electron microscopy analysis showed a surface morphological transition from nanowalls to nanograins with an increase in the oxidation temperature. The surface electrical conductivity of the oxidized Co films is also increased for higher oxidation temperature and/or duration mainly due to the oxide phase purity and larger particle sizes. Ultraviolet–visible spectroscopy indicated two distinct optical energy bandgaps, which effectively decreased with an increase in the oxidation temperature and duration. Raman spectroscopy identified five different Raman-active modes corresponding to the Co3O4 phase, with the F2g mode dominating at higher temperatures. All these findings provide clear insights into the structural, electrical, chemical and optical properties of cobalt oxide thin films. Moreover, it provides a mechanism on how to grow 2D nanowalls morphology of Co3O4 films which can further be used in energy, sensor or catalytic applications.

Fabrication of 197Au-backed Silicon target for In-beam Gamma-ray spectroscopy experiment

The fabrication of stable 197Au-backed natural Si targets with a thickness ranging from ∼ 400 μg/cm2 to ∼ 1.1 mg/cm2 using an electron beam evaporation technique is discussed. In one of the attempts, a graphite sheet was used as an evaporation source, which proves to be an efficient method in terms of minimal wastage of source material. Characterizations of the fabricated targets using various technique revealed that the targets were uniform in thickness and had negligible contamination. The optimization of evaporation parameters in the present work enhances the potential for future fabrication of isotopically enriched Si targets.

Performance of normally off hydrogen-terminated diamond field-effect transistor with Al2O3/CeB6 gate materials

In this work, we demonstrate a hydrogen-terminated diamond (H-diamond) field-effect transistor (FET) with Al2O3/CeB6 gate materials. The CeB6 and Al2O3 films have been deposited by electron beam evaporation technique, sequentially. For the 4/8/12/15 μm gate length (LG) devices, the whole devices demonstrate distinct p-type normally off characteristics, and all the threshold voltage are negative; all the absolute values of leakage current density are 10−4 A/cm2 at a VGS of −11 V, exhibiting a relatively low leakage current density compared with CeB6 FETs, and this further demonstrates the feasibility of the introduction of Al2O3 to reduce the leakage current density; the maximum drain–source current density is −114.6, −96.0, −80.9, and −73.7 mA/mm, which may be benefited from the well-protected channel. For the 12 μm LG devices, the saturation carrier mobility is 593.6 cm2/V s, demonstrating a good channel transport characteristic. This work may provide a promising strategy for the application of normally off H-diamond FETs significantly.

Exotic Topological Magnetic States in Thin Co/Pd Ferromagnetic Films

AbstractThin ferromagnet/heavy metal multilayer films are considered as prospective media for a magnetic recording and Co/Pd films are a good example of such materials. In this work, the magnetic properties and micromagnetic structure of Co/Pd multilayer films are studied with different bilayer thicknesses ([Co(0.3 × t nm)/Pd(0.5 × t nm)]10), but with the same ratio Co versus Pd. Transmission electron microscope and X‐ray diffraction studies allow authors to suppose that the investigated films are highly mixed alloys. Magnetic force microscopy and Lorentz transmission electron microscopy showed the presence of various micromagnetic features in the films. Along with skyrmions that are well‐known magnetic topological artifacts some new features are revealed, which are interpreted as 360° domain walls, skyrmioniums and the combination of the above two. It is found that the type and density of micromagnetic features strongly depend on the bilayer thickness parameter (t). The effect is associated with the peculiarities of interfacial magnetic interactions in the samples with highly mixed interfaces. The tooling coefficient represents a useful tool of the electron beam evaporation technique enabling wide manipulation of micromagnetic particles, in particular, skyrmioniums that are currently considered a prospective media for current driven magnetic recording.

Mid-infrared tunable absorber based on an Ag/SiO2/VO2/Ag/VO2 multilayer structure and its molecular sensing capability.

We present a design of middle-infrared modulation absorbers based on vanadium dioxide (VO2). By using the electron beam evaporation technique, the Ag/SiO2/VO2/Ag/VO2 multilayer structure can achieve double band strong absorption in the mid-infrared, and dynamically adjust the absorption performance through VO2. The simulation results demonstrate a remarkable absorption rate of 91.8% and 98.9% at 9.09 µm and 10.25 µm, respectively. The high absorption is elucidated by analyzing the field strength distribution in each layer. Meanwhile, based on the phase change characteristics of VO2, the absorber has exceptional thermal regulation, with a remarkable 78% heat regulation range in the mid-infrared band. The size altering of the absorbing layer is effective in enhancing and optimizing the structure's absorption performance. The structure is used to characterize probe molecules of CV and R6 G by mid-infrared spectroscopy, which illustrates an impressive limit of detection (LOD) of 10-7 M for both substances. These results provide valuable insights for designing future high-performance tunable optical devices.

Continuously variable Fourier filters fabricated using varying angle glancing angle deposition for chip-scale spectroscopy.

Low-cost spectroscopy has received a great deal of attention in recent years in applications such as food inspection, disease detection, and manufacturing. Current spectroscopic systems rely on multiple optical components, making them mechanically fragile systems. In our previous work, we demonstrated the use of Fourier filtering using thin dielectric films. The sampling effect from the cavity resonances can be used to decompose a signal into its Fourier components. Although the thin films were deposited directly on the face of the detectors, filters of varying thicknesses were needed, which required multiple lithographic processes. To overcome this challenge, in this work, we use a continuously variable filters deposited by a single-step electron-beam evaporation technique. We demonstrate a novel, to our knowledge, method that utilizes the glancing angle deposition technique with a continuously varying angle in order to produce tens of variable Fourier filters in a single deposition run. To prove this technique, we deposit this variable filter on a 38-channel linear detector and show the results from this device.

Improved field electron emission behavior of ultrathin lanthanum hexaboride-coated copper oxide nanowires

A simple approach dealing with thermal oxidation at atmospheric pressure was used to synthesize copper oxide nanowires (CuO-NWs) on copper substrate. The vertically oriented CuO-NWs were used for further subjected to deposition of ultrathin layer (∼20[Formula: see text]nm) of lanthanum hexaboride (LaB[Formula: see text] using the electron beam evaporation technique. The observation of the characteristic vibrational mode of LaB6 in the Raman spectrum of LaB6-coated CuO-NWs (LaB6@CuO-NWs) revealed the existence of LaB6 in the deposited sample. Furthermore, confirmation of LaB6 coating on CuO-NWs was corroborated by X-ray photoelectron spectroscopy (XPS) analysis. The field electron emission (FEE) characteristics of pristine CuO-NWs and LaB6@CuO-NWs were investigated in a planer diode geometry at a base pressure of [Formula: see text][Formula: see text]mbar. The values of turn-on and threshold fields (defined at emission current density of 1 and 10[Formula: see text][Formula: see text]A/cm2, respectively) were found to be 5.4[Formula: see text]V/[Formula: see text]m and 1.6[Formula: see text]V/[Formula: see text]m (for pristine CuO-NWs emitter) and 6.75, and 2.85[Formula: see text]V/[Formula: see text]m (for LaB6@CuO-NWs emitter). Interestingly, a noticeably large emission current density of [Formula: see text][Formula: see text][Formula: see text]A/cm2 has been extracted from the LaB6@CuO-NWs emitter at a relatively lower applied field of 5.8[Formula: see text]V/[Formula: see text]m. The Fowler–Nordheim (FN) plots of both the emitters showed nonlinear behavior, indicative of their semiconductive nature. Furthermore, both the emitters showed relatively stable emission behavior tested at a pre-set value of 1[Formula: see text][Formula: see text]A more than 3[Formula: see text]h. The enhanced FEE behavior of LaB6@CuO-NWs emitter is attributed to the modulation of electronic properties due to LaB6-CuO interface-induced effects. Although the promising FEE behavior of LaB6@CuO-NWs emitter warrants its potential for practical applications, further improvement can be achieved via fabricating an array emitter due to CuO NWS and optimizing the thickness of LaB6 coating.

Room-Temperature O3 Detection: Zero-Bias Sensors Based on ZnO Thin Films

ZnO thin films with a thickness of 300 nm were deposited on Si and Al2O3 substrates using an electron beam evaporation technique with the aim of testing them as low cost and low power consumption gas sensors for ozone (O3). Scanning electron microscopy and atomic force microscopy were used to characterize the film surface morphology and quantify the roughness and grain size, recognized as the primary parameters influencing the gas sensitivity due to their direct impact on the effective sensing area. The crystalline structure and elemental composition were studied through Raman spectroscopy and X-ray photoelectron spectroscopy. Gas tests were conducted at room temperature and zero-bias voltage to assess the sensitivity and response as a function of time of the films to O3 pollutant. The results indicate that the films deposited on Al2O3 exhibit promising characteristics, such as high sensitivity and a very short response time (<2 s) to the gas concentration. Additionally, it was observed that the films display pronounced degradation effects after a significant exposure to O3.

High‐Quality NiFe Thin Films on Oxide/Non‐Oxide Platforms via Pulsed Laser Deposition at Room Temperature

AbstractSoft ferromagnetic permalloy (NiFe) thin films are promising for applications in spintronic devices because of their constituent electrical and magnetic properties. Electron beam evaporation and sputtering techniques have been used to deposit NiFe thin films. For in situ stacking of NiFe with functional complex oxides, the pulsed laser deposition (PLD) method is highly desirable. However, the growth of high‐quality NiFe (and non‐oxide thin films in general) by PLD remains a formidable task. Here, high‐quality NiFe thin films of various thicknesses on oxide/non‐oxide substrates with desirable magnetic properties by PLD at room temperature are reported. The magnetic properties are found to be strongly dependent on the laser fluence of the deposition process. The laser fluence of 4 J cm−2 produces the highest magnetization of ≈547 emu cc−1. The small coercivity (few Oersted) and sharp ferromagnetic switching behavior indicate uniaxial anisotropy with an easy axis along the in‐plane direction. In addition, thickness‐dependent magnetodynamics characterizations are studied via ferromagnetic resonance. These results offer significant insight into the PLD‐based development of thin metal magnetic films.

Exploration of annealing effect on physical properties of Indium oxide films for gas sensors

In the present work, an influence of annealing on physical properties of Indium oxide (In2O3) thin films is investigated for H2S gas sensing applications. The In2O3 films of thickness 450 nm are grown employing physical vapor deposition based electron beam evaporation technique followed by annealing at different temperatures viz. 250 °C, 325 °C and 400 °C for 1 h. XRD analysis indicated crystallization of annealed films in cubic phase having (222) predominant reflection where crystallite size of all the In2O3 layers is tuned in range of 17–26 nm. Optical analysis unveiled higher transmittance in ultraviolet and visible regions whereas absorbance of films is fluctuated with thermal annealing. The 2D AFM images of In2O3 films indicated distribution of nano-spherical grains and these In2O3 films also indicated Ohmic nature where resistivity is detected to be enhanced with annealing. Optimized In2O3 films based gas sensors showed gas response of 0.85 and sensor response of 15.38 % towards toxic H2S gas.

Controllable growth of wafer-scale PdS and PdS2 nanofilms via chemical vapor deposition combined with an electron beam evaporation technique

Palladium (Pd)-based sulfides have triggered extensive interest due to their unique properties and potential applications in the fields of electronics and optoelectronics. However, the synthesis of large-scale uniform PdS and PdS2 nanofilms (NFs) remains an enormous challenge. In this work, 2-inch wafer-scale PdS and PdS2 NFs with excellent stability can be controllably prepared via chemical vapor deposition combined with electron beam evaporation technique. The thickness of the pre-deposited Pd film and the sulfurization temperature are critical for the precise synthesis of PdS and PdS2 NFs. A corresponding growth mechanism has been proposed based on our experimental results and Gibbs free energy calculations. The electrical transport properties of PdS and PdS2 NFs were explored by conductive atomic force microscopy. Our findings have achieved the controllable growth of PdS and PdS2 NFs, which may provide a pathway to facilitate PdS and PdS2 based applications for next-generation high performance optoelectronic devices.

Tailoring oxygen disparity induced luminescence of Dy3+ incorporated WO3 thin films

Pure and Dy doped WO3 thin films have been prepared by the physical vapor deposition method of electron beam evaporation technique under a pressure of 1 × 10−5 mbar. Films start out amorphous and become crystalline when they are annealed at 350 °C. The diffraction peaks of the X-ray diffractogram are associated with mixed triclinic and monoclinic phases which is determined by performing Rietveld analysis and confirmed by Raman spectroscopy. X-ray photoelectron spectra of the prepared WO3 thin films confirm the presence of six valent tungsten (W+6) and trivalent Dysprosium (Dy+3) in the samples. The even and homogeneous distribution of the particles is visible in SEM pictures of the prepared WO3 thin films. The energy band gap values show a significant decrease on annealing and fall more with Dy doping as a result of the emergence of intermediate states. The annealed films have superior transmittance compared to the non-annealed films which are in amorphous state The prepared thin films' PL emission spectra at 410 nm excitation wavelength exhibit blue, green, and yellowish green emissions as a result of optical band-to-band transitions of oxygen vacancies. Due to the existence of defects like oxygen vacancies, strain, etc., amorphous system, or non-annealed films, have shown better photoluminescence at higher rare earth ion concentration than crystalline system, or annealed films. After annealing the thin films, the overall colour hue of the emitted light can be shown to change from cold white to warm white using the Commission International de l'Eclairage (CIE) diagram. These findings imply that numerous lighting applications can make use of the prepared thin films. According to magnetic experiments, Ferromagnetism (FM) increases with Dy doping due to disparity in oxygen vacancies which is consistent with the results of the Pl experiment. The BMP model was used to discuss these results. The magnetic parameters derived from the fitted data are in good accord with the literature, and the experimental results suit the BMP model well.

Tunable granularity of superconducting Pb films on substrates with different thermal conductivity

Among various ways to tune the granularity in superconducting films, the effect of substrate thermal conductivity has rarely been considered. Here, as an effort to further study the effect of granularity on superconducting properties, superconducting Pb films with different granularity and morphology were grown on substrates with different thermal conductivity by using low temperature electron beam evaporation technique. Despite the similar lattice mismatch ratio, the granularity of Pb films changes monotonically with the substrate thermal conductivity. With decreasing the grain size, the upper critical field of Pb films increases, and Pb films tend to feature flux avalanche at low magnetic fields. Further analysis suggests that, the pinning mechanism gradually evolves from mixed δTc+δl to δl pinning. Our results further enrich the way to tune granularity of superconducting films, and open up a promising perspective for studying the pinning mechanism of granular superconductors and provide favorable conditions for potential applications of manipulative vortex pinning by adjusting the granularity of superconducting films.