Electron Beam Evaporation System Research Articles

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.

Optimization of diamond sensor for trace detection of SARS-CoV-2 N-protein using Au nanoparticles

In this study, Au nanoparticles were introduced to functionalize hydrogen-terminated diamond (H-diamond) to optimize surface modification and improve the performance of diamond sensor for trace detection of SARS-CoV-2 N-protein. The Au nanoparticles were obtained by an electron beam evaporation system and annealing. Atom force microscope and scanning electron microscope were utilized to characterize the structure, morphology, and distribution of fabricated Au nanoparticles. The concentration of SARS-CoV-2 N-protein was determined by the investigation of transfer characteristics of a diamond solution gate field effect transistor. Sensitivity of this sensor was obtained as 27.43 mV/lg (N-protein concentration), which was higher than a regular H-diamond sensor. In addition, it had a wider linear detection range of 10−15–10−5 mg/ml and a lower limit of detection of 10−15 mg/ml. Accordingly, the detection performance of diamond sensor has been greatly improved due to the functionalization of Au nanoparticles.

Investigation of omnidirectional transmittance related to ITO nanorods orientation for optical applications

Indium-doped tin oxide (ITO) nanorods thin films were fabricated on silicon (100) wafer and commercial thin film coated glass (ITO-G) substrates via ion-assisted electron-beam evaporation system with inclinable and rotatable substrate setup. The thickness was controlled in the range of 100–400 nm through the QCM monitoring. With the fixed substrate's tilted angle at 85°, the film's structures were respectively observed as the slant and vertical nanorods corresponding to the substrate's rotation speed of 0 and 30 rpm by the field-emission scanning electron microscope (FE-SEM). The grazing-incident X-ray diffraction (GIXRD) and photoelectron spectroscopy (PES) were used to analyze the crystallinity and atomic composition of the ITO nanorods films. It was observed that the films were amorphous and non-significant of composition variation relative to the change of the film's-controlled thickness and structure. The optical transmittance in omnidirectional (omni-T) of p- and s-polarized light was determined through the variable-angle UV-VIS-NIR spectrophotometer. We found the different profiles of the omni-T with the change of film's structure and thickness which could be explained through the generated birefringence of the films. In addition, the different results of the p- and s-polarized were also discussed.

Performance of hydrogen-terminated diamond MOSFET with LaB6/Al2O3 bilayer dielectric

A diamond-based field effect transistor with LaB6/Al2O3 bilayer has been fabricated. Al2O3 and LaB6 layer were deposited by atomic-layer-deposition and electron beam evaporation system, respectively. The LaB6/Al2O3 bilayer shows a high dielectric constant (29.8). The leakage current density of LaB6/Al2O3 diamond metal-insulator-semiconductor field effect transistor keeps lower than 1 × 10−6 A cm−2 when the gate bias changed from 5 V to −5 V. This device operates in a p-type depletion mode, whose maximum drain-source current, threshold voltage, maximum transconductance, effective mobility and sheet hole density are determined to be −73.8 mA·mm−1, 2.2 V, 10.4 mS·mm−1,128 cm2·V−1·s−1, and 3.2 × 1013 cm−2, respectively.

Growth and characterization of ZnO/MgZnO thin film hetero structures on p-Si for visible light detectors

ZnO- and MgZnO-based single- and double-layer heterostructures have been grown using an electron-beam evaporation system. Structural, morphological, optical and electrical characteristics were elaborated for all the configurations. Using x-ray diffraction, it was inferred that a hexagonal wurtzite structure is maintained for both ZnO and MgZnO with fairly good crystallinity. Field emission scanning electron microscopy (FESEM) images showed the homogeneous distribution of particles in ZnO and MgZnO throughout the films. Both atomic force microscopy and FESEM images exhibit a larger size for ZnO particles. The UV emission for ZnO at ∼371 nm and MgZnO at ∼359 nm was anticipated from photoluminescence spectra. The visible photoconductive properties of all the different configurations were studied in the dark and under the illumination of a white light source. The highest responsivities measured for the ZnO/MgZnO/Si structure were 0.242 A W−1 and 0.164 A W−1 for as deposited and annealed at 400 °C, respectively. These results show the suitability of bilayer photo detectors for visible light detection.

Forward bending of silicon nanowires induced by strain distribution in asymmetric growth

The flexibility and quasi-one-dimensional nature of nanowires offer wide-ranging possibilities for novel heterostructure design and strain engineering. In this work, we realized controllably bent Si nanowires by using asymmetric growth with electron beam evaporation system. It is demonstrated that the degree of arc-bending depends on the deposition angle and deposition thickness. The forward bending of the Si nanowires is due to the lattice mismatch and thermal mismatch between Si and the metallic materials such as Cr and Ti, which can be generally utilized to control the shape and internal strain of Si nanowires, with potential applications for fabricating desired nano-devices.

Internal Stress Prediction and Measurement of Mid-Infrared Multilayer Thin Films.

We present an experimental method for evaluating interfacial force per width and predicting internal stress in mid-infrared band-pass filters (MIR-BPF). The interfacial force per width between the two kinds of thin-film materials was obtained by experimental measurement values, and the residual stress of the multilayer thin films was predicted by the modified Ennos formula. A dual electron beam evaporation system combined with ion-assisted deposition was used to fabricate mid-infrared band-pass filters. The interfacial forces per width for Ge/SiO2 and SiO2/Ge were 124.9 N/m and 127.6 N/m, respectively. The difference between the measured stress and predicted stress in the 23-layer MIR-BPF was below 0.059 GPa. The residual stresses of the four-layer film, as well as the 20-layer and 23-layer mid-infrared band-pass filter, were predicted by adding the interface stress to the modified Ennos formula. In the four-layer film, the difference between the predicted value and the measured stress of the HL (high–low refractive index) and LH (low–high refractive index) stacks were −0.384 GPa for (HL)2 and −0.436 GPa for (LH)2, respectively. The predicted stress and the measured stress of the 20-layer mid-infrared filter were −0.316 GPa and −0.250 GPa. The predicted stress and the measured stress of the 23-layer mid-infrared filter were −0.257 GPa and −0.198 GPa, respectively.

Experimental investigation and comparative analysis of electron beam evaporated ZnO/MgxZn1-xO/CdxZn1-xO thin films for photodiode applications

— This work reports the growth optimization and analysis of ZnO, Mg x Zn 1-x O, and Cd x Zn 1-x O thin films on silicon substrate using an electron beam evaporation system. The crystal phase purity, surface morphology, optical and electrical properties of deposited ZnO, Mg x Zn 1-x O, and Cd x Zn 1-x O thin films were studied. X-ray diffraction (XRD) spectra revealed that the deposited films were polycrystalline in nature with preferred (002) crystal orientation. Field emission scanning electron microscope study showed a dense-packed grained structure with an exact symmetrical distribution. The root-mean-square roughness of 3.03 nm was perceived by atomic force microscopy measurement for Mg x Zn 1-x O thin-film, indicating good morphology of the deposited film. Photoluminescence measurement demonstrated a near-band-edge emission peak around 363 nm for ZnO thin film. The energy band gap obtained for ZnO, Mg x Zn 1-x O, and Cd x Zn 1-x O were 3.36 eV, 3.86 eV, and 2.89 eV, respectively, as measured by Ultraviolet–Visible spectroscopy. The higher amount of photocurrent was detected in illumination condition compared to dark condition with responsivity 0.54 AW -1 for ZnO films, making it suitable for photodiodes applications. • The growth and characterization of ZnO, Mg x Zn 1−x O, and Cd x Zn 1−x O on a silicon substrate using an electron beam evaporation technique is presented. • From IV characteristics measured in dark and under illumination, it was inferred that ZnO based alloys are sensitive to light and can be utilized for fabricating photodiodes.

Nonlinear and low-loss tantalum pentoxide based micro-ring resonator by ion-assisted electron-beam deposition

Tantalum pentoxide (Ta2O5) is a promising material for optical waveguide applications of photonics integration due to its excellent linear and nonlinear optical properties, such as high refractive index, large bandgap, and high nonlinearity. The quality of thin film deposition will then be critical for realizing optical waveguide devices and modules. In this work, an ion-assisted electron-beam evaporation system has been used to deposit such thin film. As low as 0.73 nm thickness roughness has been demonstrated in a 700 nm thick film, indicating it as a candidate for fabricating a low-loss waveguide. An optical waveguide-based ring resonator was made for examining the optical waveguide performance. Through the flat surface morphology, a low propagation loss of 1.4 dB/cm with an unloaded quality factor of 3 × 105 ring resonance has been realized. The nonlinear index of refraction (n2) in as-deposited Ta2O5 film was found to be in an order of magnitude of 10−14 cm2/W, which was also confirmed by both Z-scan technique and all-optical modulation technique. By such high bandgap properties, a nonlinear absorption threshold of few TW/cm2 was also observed for the first time. The measured device performances are comparable to the state-of-the-art results from up-to-date counterparts.

Reduction of interface state density in coaxial TiO2/Ge nanowire assembly-based heterostructure and superior photodetection

This paper compares the advantages of a catalyst-free vertically aligned coaxial titanium dioxide nanowire/germanium nanowire (TiO2-NW/Ge-NW) heterostructure compared to basic germanium nanowire (Ge-NW) on silicon (Si) substrate. Both were fabricated using the glancing angle deposition (GLAD) technique integrated into an electron beam evaporation system. The study is focussed on the successful suppression of native germanium oxide (GeO2) as well as the reduction of interface state density (Dit) by incorporating TiO2-NW. X-ray diffraction (XRD) patterns confirm the successful growth of rutile phase TiO2-NW in the coaxial TiO2-NW/Ge-NW assembly at room temperature. The crystal size analysis was carried out using the Scherrer equation and it confirmed the decrease in crystal size of GeO2 in the coaxial TiO2-NW/Ge-NW assembly. FEGSEM reveals the growth of vertically oriented NWs. Capacitance and conduction voltage data were used to extract the interface state density (Dit). The presence of TiO2 reduced the interface defect in the TiO2-NW/Ge-NW heterostructure compared to the bare Ge-NW sample. The optical absorption study showed that TiO2-NW/Ge-NW samples exhibited enhancement in the UV region primarily due to the presence of TiO2. The electrical characterization of Ag/TiO2-NW/Ge-NW/Si and Ag/Ge-NW/Si revealed a low dark current of −1.056 × 10−7 A/cm2 for Ag/TiO2-NW/Ge-NW/Si compared to −8.39 × 10−7 A/cm2 for Ag/Ge-NW/Si. Ag/TiO2-NW/Ge-NW/Si exhibited a superior rectification ratio, increased detectivity, and enhanced noise equivalent power compared to the Ag/Ge-NW/Si device. The TiO2-NW/Ge-NW heterostructure exhibited a fast temporal response with rise and fall times of ∼0.047 s and ∼0.037 s, respectively.

Effect of 1 MeV electron irradiation on TiO2/Al2O3/MgF2 anti-reflective coating for GaInP/InGaAs/Ge triple junction solar cells

Abstract In this study, a high performance TiO 2 / Al 2 O 3 / MgF 2 multilayer anti-reflective (AR) coating, with an average reflectivity of 6.36% in spectral range of 300–1800 nm, applied on GaInP/GaAs/Ge triple-junction solar cell was designed by Essential Macleod Program (EMP) software. Based on the simulation results, TiO 2 , Al 2 O 3 , MgF 2 single layer and TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating samples were grown by Electron Beam Evaporation (EBE) system for 1 MeV electron beam irradiation experiment. The overall reflectivity of TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating is decreased with the increase of electron irradiation fluence due to the change of reflectivity of each AR layer caused by the refractive index changes. This result indicates that the TiO 2 / Al 2 O 3 / MgF 2 multilayer AR coating can improve the triple junction solar cell radiation resistance by achieving favorable permeability in the broadband solar spectrum, especially in 750–900 nm region where the main degradation spectral window for triple junction solar cell.

ZnO-Ge MULTILAYER THIN FILM STRUCTURES DEPOSITED BY THERMAL EVAPORATION TECHNIQUE

Zinc oxide and germanium multilayer films have been deposited on glass substrate using electron beam evaporation and resistive heating system, respectively, for alternate layers. The structural optical and electrical parameters have been investigated for the deposited films. The layer formation was confirmed by employing Rutherford back-scattering technique. Optical properties exhibit quantum confinement effect by showing the separate band gaps for ZnO and Ge. Electrical conductivity increases due to combined effect of all six layers (six alternate layers of Ge and ZnO).

Thickness-Dependent Resistive Switching Behavior of KCu7S₄/CuxO/Au Device.

We report the fabrication of KCu7S₄/CuxO/Au devices with interfacial CuxO layers of different thicknesses through the spontaneous oxidation of Cu film during deposition. Deposition was conducted with an electron-beam evaporation system under the deposition rate and the chamber pressure of 0.1 Å s-1 and 9.8×10-3 Pa, respectively. X-ray diffraction and X-ray photoelectron spectroscopy characterizations reveal that the interfacial CuxO layers mostly comprise Cu₂O and CuO. Electrical characterization reveals that the devices exhibit remarkably thickness-dependent resistive switching behavior. After undergoing an electroforming process under a high compliant current of 1000 μA, the KCu7S₄/16 nm CuxO/Au device exhibits stable bipolar resistive switching behavior with the set voltage of 0.58 V and reset voltage of -0.21 V, whereas the KCu7S₄/32 nm CuxO/Au device only shows a hysteresis loop in the forward voltage regime. These findings are ascribed to the existence of high-insulation CuO, which is difficult to be softly broken down. Therefore, the depositional condition of Cu film and the thickness of the interfacial layer should be appropriately controlled for the effective performance of devices with Cu electrodes. The results may also provide guidance for the improvement of the performance and stability of Cu-based nonvolatile memory devices.

Effect of Annealing on the Structural and Electrical Properties of GLAD Synthesized Vertical Aligned WO3 Nanowire

This paper reports the fabrication of catalyst-free vertically aligned tungsten oxide (WO3) nanowire (NW) on Si substrate through glancing angle deposition technique incorporated in an electron beam evaporation system. The fabricated samples were annealed at 500 °C to study the effect on the structural properties. The average crystallite size increased from 67.51 to 76.24 nm after annealing. Also, the lattice strain and dislocation density were found to be decreased at 500 °C. A significant improvement on the surface morphology was observed for the annealed sample. Au electrode was used to fabricate the Au/WO3 NWs/Si structure and the electrical parameters were measured for both the as deposited and annealed sample. The annealed sample showed higher sensitivity toward the light by surface adsorption–desorption process as compared to as deposited WO3 NW. The responsivity, external quantum efficiency, and detectivity of the as deposited sample were 9.66 A/W, 3.33 × 103%, and 5.94 × 1012, respectively, which significantly enhanced to 50.95 A/W, 1.75 × 104%, and 1.05 × 1013 Jones, respectively, after annealing at a bias of 3 V. The rise time and fall time were calculated to be 1.33 and 0.94 s, respectively, at 3 V applied bias voltage, which is superior to the state of art of WO3-based photodetectors. Thus, the fabricated sample can be a potential candidate for photodetector application.

The Preparation of Fe3O4 Thin Film and Its Electrochemical Characterization for Li-Ion Battery

In this study, the Fe3O4 thin film was prepared as anode materials to simultaneously provide higher reversible Li+ capacity compared to 2D materials with high cycle properties for lithium ion batteries. Nano-crystalline Fe3O4 thin film has been prepared by using an electron beam evaporation system followed by heat treatment. Electrochemical measurement showed that the as-fabricated Fe3O4 thin film showed the conventional charge–discharge voltage profiles of magnetite and good cycle performance. The initial reversible capacity of Fe3O4 thin film was maintained during the 100 cycles with no capacity fading in a potential range of 0.005–3.0 V (vs. Li+/Li).

Annealing effect of E-beam evaporated TiO2 films and their performance in perovskite solar cells

Titanium dioxide (TiO2) films have been deposited on indium-doped tin oxide (ITO) glass substrate by electron-beam evaporation (EBE) system at room temperature (RT, 25 °C). After that, prepared TiO2 films are annealed at different temperatures of 150, 250, 350, 400, 450 and 500 °C. The novelty of this work is to investigate the effect of annealing temperature on the photovoltaic performances of perovskite solar cell (PeSC) with these annealed TiO2/ITO structures. For the fabrication of PeSC, perovskite (PRV) layer has been fabricated on TiO2 films by two-steps method. The TiO2 film prepared at RT shows the amorphous structure with the compact surface and Ti3+ state. Interestingly, crystallinity and porosity of the TiO2 films increase with the increase of annealing temperature. The TiO2 films annealed at 500 °C have shown high crystallinity with Ti4+ state and mixed phases (anatase and rutile). The grain boundary becomes visible, the size and porosity of TiO2 films increase with the increase of annealing temperature. The PeSC with TiO2 films prepared at RT shows the highest photoelectric conversion efficiency (PCE) of 6.15% with maximum photocurrent (14.37 mA/cm2) than the other PeSCs with annealed TiO2 films. The PCE, photocurrent and fill factor of PeSC decrease but the photovoltage increases with increase in annealing temperature, which may be caused by carrier leakage between PRV layer and ITO substrate, high series and low shunt resistances, and also the enhanced sheet resistance of ITO substrate.

Giant Magnetoresistance in NiO/Co/Cu/Co/Ti spin valve fabricated by EBPVD

In this paper, glass/NiO/Co/Cu/Co/Ti magnetic multilayers were deposited by electron beam evaporation system. A magnetic field of a few tens Oe was applied during the deposition of some of the layers in order to pin the magnetic moments of the ferromagnetic layer to the adjacent antiferromagnetic layer. The thickness of NiO layer is 140 nm and Co/Cu/Co/Ti layers thickness is 15 nm. The dc 4-point probe technique was used to measure the magnetoresistance (MR) of the prepared samples while the magnetic field was applied in the film plane and in the current direction. The giant magnetoresistance values up to 12% and 8% achieved respectively in samples deposited in presence and absence of magnetic field.

Investigation of optical characteristics of the evaporated Ta2O5 thin films based on ellipsometry and spectroscopy

The tantalum oxide (Ta2O5) thin films were prepared by the ion-assisted electron-beam evaporation system. With the fixed film thickness at 200 nm, the deposition conditions were performed based on oxygen flow rate the ion assistance during the film deposition. The prepared thin films were characterized by spectroscopic ellipsometry in order to determine their physical and optical properties. From the ellipsometric measurements, the physical structures of the thin films and the optical dispersions were constructed, and then analyzed for the results of film thickness and optical constants. The thin films were also measured by the UV-Vis-NIR spectrophotometry for the optical transmission. The measured transmission was analyzed with the Swanepoel method, whose results also yielded the thickness and the refractive index. Finally, the thin films were examined by the scanning electron microscopy (SEM) in order to observe physical microstructures. This study explored the physical and optical analyses based on the spectroscopic ellipsometry and the spectrophotometry, with the confirmations from the SEM micrographs. The results from the analyses would be compared and thoroughly discussed.

Investigation of high-temperature charge transport mechanism in Al–Gd2O3–Al-based metal–insulator–metal (MIM) structure

In this paper, the charge conduction mechanism at high temperature in Al–Gd2O3 (MIM) structure has been investigated by performing temperature-dependent current–voltage measurements in the temperature range 280–390 K. MIM structure is realized by electron beam evaporation system where thin films of Gd2O3 (40, 60 and 80 nm) and Al metal on both sides of dielectric film were deposited on glass substrate. The possibility of different transport mechanisms has been testified by plotting various graphs. The nonlinear behavior of LnV versus LnI and V 1/2 versus LnV/I graphs ruled out the possibility of space-charge-limited conduction (SCLC) and Poole–Frenkel mechanism in Al–Gd2O3–Al MIM structure. The straight lines LnI–V 1/2 graphs at various temperatures confirmed that Schottky emission is the dominant transport mechanism in Al–Gd2O3–Al structure. The calculated values of field barrier lowering coefficient at different measurement temperatures were in good agreement with the theoretical prediction confirming conduction is via Schottky emission. The field-dependent Ln(I/T 2) versus 1000/T plots were obeyed a linear relationship according to Schottky emission theory. Furthermore, the dielectric thickness dependence room-temperature current–voltage characteristics of Al–Gd2O3–Al MIM structure were showed strong dependence of current on dielectric film thickness according to Schottky emission theory of conduction current.

Effect of Grazing Angle Cross-Ion Irradiation on Ag Thin Films.

Apart from the spherical shape, control over other shapes is a technical challenge in synthesis approaches of nanostructures. Here, we studied the effect of grazing angle cross-irradiation Ag thin films for the nanostructures evolution from a top-down approach. Ag thin films of different thicknesses were deposited on Si (100) and glass substrates by electron beam evaporation system and subsequently irradiated at grazing angle ions by 80 keV Ar+ in two steps (to induce effectively a cross-ion irradiation). Pristine films exhibited dense and uniform distribution of Ag nanoparticles with their characteristic surface plasmon resonance-induced absorption peak around 420 nm. When the film surfaces were treated with cross-grazing angle irradiation of Ar ions with varying effective fluences from 0.5 × 1017 ions/cm2 to 2.0 × 1017 ions/cm2, it was found that fluence values governed the competition of sputtering and sputter re-deposition of Ag. As a result, lower irradiation fluence favoured the formation of cone-like nanostructures, whereas high fluence values demonstrated dominant sputtering. Fluence-dependent modification of surface features was studied through the Fourier transform infrared spectroscopy and the Rutherford backscattering spectroscopy. Theoretical justifications for the underlying mechanisms are presented to justify the experimental results.