Electron Beam Evaporation Research Articles

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.

Low-thermal-budget electrically active thick polysilicon for CMOS-First MEMS-last integration

Low-thermal-budget, electrically active, and thick polysilicon films are necessary for building a microelectromechanical system (MEMS) on top of a complementary metal oxide semiconductor (CMOS). However, the formation of these polysilicon films is a challenge in this field. Herein, for the first time, the development of in situ phosphorus-doped silicon films deposited under ultrahigh-vacuum conditions (~10−9 Torr) using electron-beam evaporation (UHVEE) is reported. This process results in electrically active, fully crystallized, low-stress, smooth, and thick polysilicon films with low thermal budgets. The crystallographic, mechanical, and electrical properties of phosphorus-doped UHVEE polysilicon films are studied. These films are compared with intrinsic and boron-doped UHVEE silicon films. Raman spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and atomic force microscopy (AFM) are used for crystallographic and surface morphological investigations. Wafer curvature, cantilever deflection profile and resonance frequency measurements are employed to study the mechanical properties of the specimens. Moreover, resistivity measurements are conducted to investigate the electrical properties of the films. Highly vertical, high-aspect-ratio micromachining of UHVEE polysilicon has been developed. A comb-drive structure is designed, simulated, fabricated, and characterized as an actuator and inertial sensor comprising 20-μm-thick in situ phosphorus-doped UHVEE films at a temperature less than 500 °C. The results demonstrate for the first time that UHVEE polysilicon uniquely allows the realization of mechanically and electrically functional MEMS devices with low thermal budgets.

Nb2O5 film optical properties and laser-induced damage by phase-change-driven tuning

Niobium oxide (Nb2O5) is widely used in optical and electrical fields because of its high refractive index, wide band gap, high laser-induced damage threshold (LIDT) and high transparency in the ultraviolet to middle-infrared-wavelength range (0.35–7 μm). In this study, Nb2O5 films with different crystalline phases were successfully prepared on BK7 and Si substrates through electron beam evaporation (EB) and post-annealing. Based on the results of X-ray diffraction (XRD) and Raman spectroscopy analysis, the impact of the post-annealing technique on the structure, and optical and physical properties of Nb2O5 films was thoroughly discussed at the molecular level. The crystal phase of an Nb2O5 film and its molecular bonds considerably affect its properties. The Nb2O5(-12 1 2) film prepared in this study exhibited a higher LIDT (17.72 J/cm2) and a higher RMS (0.447 nm) than the corresponding films prepared in previous studies. Following the post-annealing process, the band gap and refractive index of the prepared films were significantly higher than those of the as-deposited film. Thus, this study has significant guiding implications for Nb2O5 film applications and the development costs of the films.

Modeling temperature dependent Ni/β-Ga2O3 Schottky barrier diode interface properties

A TCAD simulator is used to model measured current–voltage characteristics of Ni/β-Ga2O3 Schottky barrier diode (SBD), deposited by E-beam evaporation, at room temperature. A good fit was obtained when the Ni workfunction, Ni/β-Ga2O3 interface traps concentrations and Si-doped β-Ga2O3 surface electron affinity variation were taken into consideration. Temperature dependent J-V characteristics were investigated and a good agreement at low voltage was obtained. However, the simulated current at high voltage (series resistance domain) was higher than measurement while both series resistance (Rs) and on-resistance (Ron) for measurements were higher than their simulations counterparts. In order to overcome this disagreement, the effect of Si-doped β-Ga2O3 surface electron affinity on the SBD at each temperature was studied. This is due to the fact that the electron affinity can be affected by trap levels located above conduction band maximum (CBM) as reported in the literature. The surface electron affinity decreased with increasing temperature because trap levels located above CBM were activated. A better agreement was achieved.

Single atoms and metal nanoclusters anchored to graphene vacancies

Fabricating dispersed single atoms and size-controlled metal nanoclusters remains a difficult challenge due to sintering. Here, we demonstrate that atoms and clusters can be immobilized using atomically clean defect-engineered graphene as the matrix. The graphene is first cleaned of surface contamination with laser heating, after which low-energy Ar irradiation is used to create spatially well-separated vacancies into it. Metal atoms are then evaporated either via thermal or ebeam evaporation onto graphene, where they diffuse until being trapped into a vacancy. The density of embedded structures can be controlled through irradiation dose, and the size of the structures through evaporation time. The resulting structures are confirmed through atomic-resolution scanning transmission electron microscopy and electron energy loss spectroscopy. We demonstrate here incorporation of Al, Ti, Fe, Ag and Au single atoms or nanoclusters, but the method should work equally well for other elements.

Vertical diamond Schottky barrier diodes with curved field plates

Diamond Schottky barrier diodes (SBDs) could theoretically operate at high voltage, high temperature, and high frequency and be potentially used in power electronics. However, the device breaks down prematurely and cannot operate stably at high voltages due to the edge electric field crowding. In this work, a vertical diamond SBD with a curved field plate (CFP) was prepared using a chemical reflow method, inductively coupled plasma etching, and electron-beam evaporation. This structure alleviates the electric field crowding at the edge of the Schottky electrode and results in a breakdown voltage and current density of 380 V and over 3000 A/cm2, respectively. After repetitive measurements, we found that the device can repeatedly breakdown at around 380 V. These results indicate that CFP structure diamond SBDs have great application in high-voltage and high-power electronic devices.

Electrical properties and field emission characteristics of ITO nanorod thin films synthesized by electron beam physical vapor deposition

Electrical properties and field emission characteristics of ITO nanorod thin films synthesized by electron beam physical vapor deposition

Enhancing Adhesion and Reducing Ohmic Contact through Nickel-Silicon Alloy Seed Layer in Electroplating Ni/Cu/Ag.

Due to the lower cost compared to screen-printed silver contacts, the Ni/Cu/Ag contacts formed by plating have been continuously studied as a potential metallization technology for solar cells. To address the adhesion issue of backside grid lines in electroplated n-Tunnel Oxide Passivating Contacts (n-TOPCon) solar cells and reduce ohmic contact, we propose a novel approach of adding a Ni/Si alloy seed layer between the Ni and Si layers. The metal nickel layer is deposited on the backside of the solar cells using electron beam evaporation, and excess nickel is removed by H2SO4:H2O2 etchant under annealing conditions of 300-425 °C to form a seed layer. The adhesion strength increased by more than 0.5 N mm-1 and the contact resistance dropped by 0.5 mΩ cm2 in comparison to the traditional direct plating Ni/Cu/Ag method. This is because the resulting Ni/Si alloy has outstanding electrical conductivity, and the produced Ni/Si alloy has higher adhesion over direct contact between the nickel-silicon interface, as well as enhanced surface roughness. The results showed that at an annealing temperature of 375 °C, the main compound formed was NiSi, with a contact resistance of 1 mΩ cm-2 and a maximum gate line adhesion of 2.7 N mm-1. This method proposes a new technical solution for cost reduction and efficiency improvement of n-TOPCon solar cells.

Investigation of CMAS corrosion resistance for gradient Y2O3 stabilized ZrO2

The threat of calcium‑magnesium-alumina-silicate (CMAS) melt corrosion in thermal barrier coatings (TBCs) is significant at elevated working temperatures. In this study, a gradient Y2O3 stabilized ZrO2 coating (gradient YSZ coating) was designed and prepared by electron beam physical vapor deposition (EB-PVD) and its CMAS corrosion resistance was examined. The CMAS corrosion resistance test on the YSZ pellets highlighted the significance of dissolved Y2O3 and identified the critical Y2O3 content. Compared with the classical 8 wt% Y2O3 stabilized ZrO2 (8YSZ) coating, new crystal phases generated in the gradient YSZ coatings effectively blocked the CMAS melt infiltration for a short time; further, even after a long time, the CMAS melt was primarily distributed in the upper part of the gradient YSZ coating. In addition, the impact of coating microstructure on the CMAS resistance was investigated. The results showed the dense-gradient YSZ coating outperformed the 8YSZ coating on the resistance to CMAS infiltration. Finally, it is demonstrated that the gradient YSZ coating has potential applications against CMAS attacks, providing valuable design guidelines for TBCs with balanced corrosion resistance and promising mechanical properties.

High-reflectivity composite metal substrate for high-power IRLED

Substrate transfer technology is a common way to prepare high-power infrared light emitting diode (IRLED), which seriously affects the photoelectric performance and reliability of LED. In this paper, a preparation technology of LED with composite metal substrate is presented. Based on electroplating and electron beam evaporation, AuGeNi/Au(1)/Au(2)/Cu composite metal substrate with thickness of 70 nm/30 nm/100 nm/45 μm was prepared, and low resistivity of 4.65 × 10−6 Ω⋅cm2 and high reflectance of 91.3 % were obtained. Compared with the original GaAs substrate, the light output power (LOP) of electroluminescence is increased by 89.2 % at the current of 300 mA.

Temperature-Dependent Residual Stresses and Thermal Expansion Coefficient of VO2 Thin Films

This study aims to investigate the thermomechanical properties of vanadium dioxide (VO2) thin films. A VO2 thin film was simultaneously deposited on B270 and H-K9L glass substrates by electron-beam evaporation with ion-assisted deposition. Based on optical interferometric methods, the thermal–mechanical behavior of and thermal stresses in VO2 films can be determined. An improved Twyman–Green interferometer was used to measure the temperature-dependent residual stress variations of VO2 thin films at different temperatures. This study found that the substrate has a great impact on thermal stress, which is mainly caused by the mismatch in the coefficient of thermal expansion (CTE) of the film and the substrate. By using the dual-substrate method, thermal stresses in VO2 thin films from room temperature to 120 °C can be evaluated. The thermal expansion coefficient is 3.21 × 10−5 °C−1, and the biaxial modulus is 517 GPa.

Optical, Electrical, Structural, and Thermo-Mechanical Properties of Undoped and Tungsten-Doped Vanadium Dioxide Thin Films.

The undoped and tungsten (W)-doped vanadium dioxide (VO2) thin films were prepared by electron beam evaporation associated with ion-beam-assisted deposition (IAD). The influence of different W-doped contents (3-5%) on the electrical, optical, structural, and thermo-mechanical properties of VO2 thin films was investigated experimentally. Spectral transmittance results showed that with the increase in W-doped contents, the transmittance in the visible light range (400-750 nm) decreases from 60.2% to 53.9%, and the transmittance in the infrared wavelength range (2.5 μm to 5.5 μm) drops from 55.8% to 15.4%. As the W-doped content increases, the residual stress in the VO2 thin film decreases from -0.276 GPa to -0.238 GPa, but the surface roughness increases. For temperature-dependent spectroscopic measurements, heating the VO2 thin films from 30 °C to 100 °C showed the most significant change in transmittance for the 5% W-doped VO2 thin film. When the heating temperature exceeds 55 °C, the optical transmittance drops significantly, and the visible light transmittance drops by about 11%. Finally, X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to evaluate the microstructure characteristics of VO2 thin films.

The heterointerface characterization of BaF2 or MgF2 on the hydrogenated diamond by X-ray photoelectron spectroscopy

Group-II fluorides (BaF2 and MgF2) insulators are deposited on hydrogenated (C–H) diamonds by E-beam evaporator at room temperature. The bandgaps, chemical bonds and band offsets of fluorides are investigated by the high-resolution X-ray photoelectron spectroscopy (XPS) measurements. The XPS results show bandgap energies of 9.4 ± 0.2 eV for BaF2 and 9.7 ± 0.2 eV for MgF2 by F 1s energy loss spectra. The valence band offsets (ΔEV's) of BaF2/MgF2 on the C–H diamond are determined as 5.2 ± 0.2 and 4.8 ± 0.2 eV, respectively. There are both type II energy band configuration for BaF2 and MgF2 on the C–H diamond with conduction band offsets of 1.3 ± 0.2 eV and 0.6 ± 0.2 eV, respectively. The relatively oxygen-weak or oxygen-free fluoride/C–H diamond interface and large ΔEV suggest that fluorides are an excellent gate dielectric for the C–H diamond field-effect transistors with high hole mobility and low gate leakage.

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.

Point-junction and alkali-assisted surface selenium diffusion: Unveiling a two-step method for enhancing the efficiency of VTD-SnS thin-film solar cells

Surface and interface engineering in thin-film solar cells (TFSCs) is vital for optimizing charge carrier dynamics, reducing recombination, enhancing material properties, and ultimately improving efficiency and overall performance. In this study, e-beam evaporation was used to deposit selenium (Se) onto tin sulfide (SnS) absorber layers with a thickness of 10 nm to 50 nm. The Se layer optimization was validated using various characterization techniques, which confirmed the formation of micro-sized openings via Se droplet deposition. This Se passivation-plus-local opening geometry plays a crucial role in forming point-junctions with the n-type CdS during cell fabrication, presenting a novel approach in state-of-the-art technology. The results revealed a significant enhancement in the conversion efficiency of the SLG/Mo/SnS/Se/CdS/i-ZnO/AZO/Al device to 3.01 % (VOC = 0.326 V, JSC = 20.21 mA cm−2, and FF = 0.45) with 30 nm Se layer deposition. Furthermore, a 30 nm-thick NaF-assisted Se layer was deposited to improve device performance. The diffusion of both Se and Na into the SnS substrate was validated using XRD, SEM, EDS, AFM, and XPS. The power conversion efficiency (PCE) of the SLG/Mo/SnSSe-NaF/CdS/i-ZnO/AZO/Al device was further enhanced to 3.70 % (VOC = 0.340 V, JSC = 22.56 mA cm−2, and FF = 0.48). This enhancement is attributed to the creation of localized junctions via Se surface passivation, and the concurrent SnSSe formation induces band gap tuning and increases the grain size, contributing to additional PCE improvement during Na-assisted Se diffusion.

Spatially selective narrow band and broadband absorption in Ag/SiO2/Ag based trilayer thin films by oblique angle deposition of SiO2 layer

We have experimentally demonstrated spatially selective absorption in Ag-SiO2-Ag based trilayer thin films by tuning the deposition angle of SiO2 layer. These structures generate cavity resonance which can be tuned across the substrate locations due to spatially selective thickness and refractive index of silicon oxide (SiO2) film sandwiched between metallic silver (Ag) mirrors. Spatially selective property of SiO2 film is obtained by oblique angle deposition technique using an electron beam evaporation system. The resonance wavelength of absorption in this trilayer structure shifts across the substrate locations along the direction of oblique deposition. The extent of shift in resonance increases with increase in angle of deposition of SiO2 layer. 4.14 nm mm−1 average shift of resonance wavelength is observed when SiO2 is deposited at 40° whereas 4.76 nm mm−1 average shift is observed when SiO2 is deposited at 60°. We observed that the width of resonance increases with angle of deposition of the cavity layer and ultimately the resonant absorption disappears and becomes broadband when SiO2 is deposited at glancing angle deposition (GLAD) configuration. Our study reveals that there is a suitable range of oblique angle of deposition from 40° to 60° for higher spatial tunability and resonant absorption whereas the absorption becomes broadband for glancing angle deposition.

Development of thermal barrier coating on single crystal superalloy CMSX-4 by two-source evaporation EB-PVD and hot corrosion performance of the coating in a simulated aero-engine environment

Superalloys are crucial in high-temperature applications, particularly in the gas turbine industries. With the development of high-temperature superalloy materials, efforts are still being made to improve the turbine entry temperature (TET), which will ultimately raise the efficiency of gas turbines. In this research, a second-generation single-crystal superalloy CMSX-4 based on nickel was prepared. The surface was coated by thermal barrier coating (TBC) with a bond coat of NiCoCrAlY with vacuum plasma spray (VPS) and a top coat with Yttria Stabilized Zirconia (YSZ) by Electron Beam Physical Vapor Deposition (EB-PVD) with a minimal current of 2.3 A with two sources compared to the conventional high-current that has been currently employed. These CMSX-4 specimens, both the as-cast and TBC coated, were used to test the effects of cyclic oxidation and hot corrosion at 1000 °C, simulating an aircraft engine. Also, a hot corrosion test using salt compositions (Wt%) of 60Na2SO4 - 40NaCl was performed simulating an aviation engine environmental condition. A FE-SEM/EDS analysis was used to examine the surface and cross-section microstructures of oxidized, hot-corroded as-cast, and hot-corroded TBC-coated CMSX-4 and its corrosion products. Using the XRD technique, the phases that were found in the oxidized and hot-corroded samples were identified. The outcome demonstrated that the EB-PVD TBC-coating on CMSX-4 with beam switching technique and a lower electron beam current has adequate protection without any damage to the coatings at 1000 °C.

Optimization of Ion Beam-Assisted Deposition Process for Y<sub>2</sub>O<sub>3</sub> Film to Enhance Plasma Resistance

A ceramic-based plasma etcher window (Lid) requires robust resistance to plasma, especially when exposed to harsh fluorine-based plasma conditions. In this study, a Y<sub>2</sub>O<sub>4</sub> film was deposited using e-beam evaporation with ion beam-assisted deposition (IBAD), and the physical properties of the IBAD-based Y<sub>2</sub>O<sub>4</sub> coating film were thoroughly examined to enhance the mechanical and chemical resistance of the ceramic part, including the Y<sub>2</sub>O<sub>4</sub> film, against etching plasma. The hardness and surface morphology of the IBADbased Y<sub>2</sub>O<sub>4</sub> could be precisely controlled by various deposition processing parameters, such as beam voltage, beam current, and Ar/O2 gas ratio. Following the IBAD deposition of the Y<sub>2</sub>O<sub>4</sub> film, a plasma etching process (Ar/CF<sub>4</sub> mixture gases with 150 W RF power for 60 minutes) was applied to evaluate the plasma resistance of the deposited Y<sub>2</sub>O<sub>4</sub> coating film. The surface morphology characteristics of the Y<sub>2</sub>O<sub>4</sub> films were compared using atomic force microscopy, and their grain size was studied through scanning electron microscopy image analysis. Furthermore, a nanoindenter was used to determine the hardness of the Y<sub>2</sub>O<sub>4</sub> film. These results suggest that optimizing the IBAD coating process requires an in-depth study that fully considers the correlation between deposition processing parameters and physical properties. This optimization can be instrumental for enhancing the durability of the ceramic part.

Performance and Degradation of Electrolyte Supported SOECs with Advanced Thin-Film Gadolinium Doped Ceria Barrier Layers in Long-Term Stack Test

Electrolyte supported Solid Oxide Cells (ESCs) with advanced thin-film Gd-doped ceria diffusion barrier layers between electrolyte and electrodes were assembled and electrochemically investigated in steam electrolysis mode in a so-called “rainbow” stack with 30 repeat units (RUs). The barrier layers were deposited onto the electrolyte supports via electron-beam physical evaporation deposition (EB-PVD) method at 600 °C. In this paper, the investigation mainly focuses on the electrochemical characteristics of RUs containing the EB-PVD thin-film GDC layers. At the initial stage of the SOEC operation, the stack reached a high performance with an electrical efficiency of 99.65% at 75% steam conversion and a total power input of 1.98 kW. A long-term stack test was performed in SOEC mode for over 5000 h and demonstrated a low voltage degradation of approx. +11.3 mV·kh–1 per RU (+0.9% kh–1). The RUs with EB-PVD GDC thin-films revealed similar initial performance and degradation rate to the state-of-the-art cells with screen printed GDC layers.

Photocatalytic degradation of methylene blue by TiO2/Nd2O3 composite thin films

To improve the photocatalytic property of TiO2 thin films, the composite thin films of TiO2/Nd2O3 structure were fabricated by electron-beam physical vapor deposition method, and the photocatalytic property of the fabricated films was experimentally studied in the present work. The XRD and Raman analyses show that the TiO2/Nd2O3 films are mainly hexagonal crystalline phase of Nd2O3. The XPS analysis for the chemical state changes of Ti, O and Nd of the basic elements in the films is confirming the electron flow in the internal electric field which generated in the TiO2/Nd2O3 films. The surface morphology shows the lattice distortion which affects the changes in the energy band structure. Moreover, the formation of n-n homojunctions improved the separation efficiency of electrons and holes, and enhanced the catalytic activity. The photocatalytic performance for the methylene blue target dye shows that the sample with TiO2 thickness of 20–25 nm has better performance, high degradation efficiency and high reaction rate.