Electron Beam Deposition Technique Research Articles

Investigation of the optical properties of Pb1-xCdxTe films using spectroscopic ellipsometry

Using spectroscopic ellipsometry, we studied the optical properties of four Pb1-xCdxTe (0 ≤ x ≤ 0.20) films. The Pb1-xCdxTe films, deposited on silicon substrates using an electron-beam deposition technique, show a rock-salt structure, with their lattice constants decreasing as a function of Cd concentration. Ellipsometry measurements, which covered a wide spectral range between 0.1 eV to 4.1 eV, determined the index of refraction and the extinction coefficient of the films. As the Cd concentration increases from 0 % to 20 % in the Pb1-xCdxTe films, the index of refraction decreases by ∼10 %, across the entire energy range. Similarly, there seems to be a decrease in the extinction coefficient with the increase of Cd concentration. An oscillator model, depicting the optical functions of each Pb1-xCdxTe film, allowed us to obtain the band gap of each film which blue-shifts as the Cd concentration is increased. Besides the fundamental band gap, we recovered the higher-order electronic transitions that occur in the Brillouin zone of the Pb1-xCdxTe lattice.

Rubber-like PTFE Thin Coatings Deposited by Pulsed Electron Beam Deposition (PED) Method.

PTFE coatings were manufactured using the pulsed electron beam deposition (PED) technique and deposited on Si substrates. The deposition was carried out at constant parameters: temperature 24 °C, discharge voltages 12 kV, and 5000 electron pulses with a pulse frequency of 5 Hz. Nitrogen was used as the background gas. The gas pressure varied from 3 to 11 mTorr. The coating adhesion was evaluated using micro scratch testing and the residual scratch morphology was characterized by atomic force microscopy. Detailed studies of the chemical and physical structure were conducted using infrared spectroscopy and X-ray diffraction. These analyses were then correlated with the mechanical response of the coatings observed during the scratch tests. Drawing upon a review of the literature concerning energetic beam interactions with PTFE material, hypotheses were posed to explain why only specific conditions of the PED process yielded PTFE coatings with rubber-like properties.

Improvements of multifunctional spintronic and optoelectronic applications of nanostructured Eu-doped ZnS thin films through magnetic and linear, nonlinear optical investigations

This study describes the spintronic and optoelectronic improvements upon Eu substitution in Zn atomic site of the nanostructure ZnS thin films. The electron beam deposition technique has been used to deposit a series of Zn1-xEuxS thin films on a glass substrate with different Eu dopants (x = 0, 0.01, 0.03, 0.05, and 0.08). The nanostructure nature of the Eu-doped ZnS thin film has been confirmed from structural and morphology studies performed by the X-ray diffraction (XRD) and atomic force microscope (AFM) measurements. XRD investigations further show a hexagonal-type structure with no detectable extra phases with the lattice parameter c increasing, while a decrease linearly with increasing Eu-dopant in the ZnS hosted lattice. The microstructures analysis reveals a reduction in the mean crystallite size and increasing in the lattice strain of the films with rising Eu doping. The Fourier transform infrared spectra display the existence of chemical bonds in the thin films whereas photoluminescence reveals near-band edge emission. The linear optical parameters were obtained from the analysis of the transmission data measured by the spectrophotometer technique. The results reveal that the band gap energy (EgOpt) reduces by raising ohe Eu doping ratio, which is ascribed to the structural deformation (strain and/or defects) confirmed from structural analysis, density of localized states and PL measurements. The index of refraction n was calculated using the Swanepoel method. The values were found to increase as the level of Eu doping grows, which is associated with the rise in polarizability. Wemple and DiDomenico's (WDD) model was utilized to compute the dispersive and oscillator energies (Eo, and Ed), the nonlinear absorption coefficient βc, nonlinear refractive index n2, and nonlinear optical susceptibility χ3. The results demonstrate that the adjustability of EgOpt , Eo, and Ed of ZnS: Eu films is conducted to improve the nonlinear optical characteristics, providing it well-suited for optoelectronic device implementations. On the other hand, ZnS doped with Eu film displays inherent ferromagnetic properties at room temperature, as evidenced by the results of the magnetic investigation. This finding could be attributed to the presence of sulphur defects (vacancies), as supported by photoluminescence (PL) measurements, which lead to the creation of the bound magnetic polaron. These discoveries indicate the potential of utilizing Eu-doped ZnS film in the effective development of spintronic devices.

Illumination-Dependent I-V Characteristics of MgF2/Al Multilayered Photodetector

The demand for highly efficient and sensitive photodetectors has driven extensive research in the field of optoelectronics. In this study, a novel photodetector utilizing a multilayered structure based on MgF2/Al/Si is presented. The heterostructure device was fabricated using the electron beam deposition technique, and their structural, and electrical properties were thoroughly characterized. The optoelectronic properties were explained based on the thermionic emission (TE) theory under different light intensities. Additionally, a comprehensive study was established to explore the diode electronic parameters, such as the ideality factor (n), potential barrier height (Φ0), and series resistance (Rs), using the methods proposed by Cheung and Nord. The photocurrent shows an increase with higher illumination intensity, indicating efficient generation of electron-hole pairs within the device. Additionally, the photo-transient time measured under an irradiance level of approximately 1000 W m−2 exhibits a fast detection of light. Furthermore, the MgF2 photodetector showed remarkable stability, offering long-term reliability for practical applications. Overall, this research offers valuable perspectives on the potential of MgF2 as a competent substance for the development of highly efficient and sensitive photodetectors for various optoelectronic applications.

Advancement of Reverse Electrowetting-on-Dielectric With Flexible Electrodes for Bias-Free Energy- Harvesting Applications

Energy harvesting with the utilization of the reverse electrowetting-on-dielectric (REWOD) phenomenon is a unique method of generating energy by implementing electrolyte impingement using mechanical modulation. The goal of wearable motion sensors that are self-powered has been undermined by the prior REWOD research’s emphasis on planar electrodes, which are not flexible and require high voltage bias to improve output power. In this paper, REWOD-based energy harvesting is implemented using two sets of dissimilar flexible electrodes. The electron-beam physical vapor deposition (EBPVD) technique is utilized to coat materials on polyimide sheet. In the first planar REWOD experiment, mechanical energy was harvested through electrolyte impingement via 2 mm electrode displacement between the top and bottom electrodes. In a second REWOD experiment, the electrodes underwent a flexing test with electrolyte encapsulated between the electrodes. The planar experiment resulted in the maximum power density value of 0.002 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the proposed flexing REWOD test measurement with electrolyte encapsulated between both electrodes resulted in 0.05 μW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of power density which is ≈ 25 times higher than the value generated using the conventional REWOD setup.

Novel Hydrophobic Ultrafiltration Membranes for Treatment of Oil-Contaminated Wastewater

Cutting fluids are the main source of oily wastewater in the metalworking industry. This study deals with the development of antifouling composite hydrophobic membranes for treatment of oily wastewater. The novelty of this study is that a low energy electron-beam deposition technique was applied for a polysulfone (PSf) membrane with a molecular-weight cut-off of 300 kDa, which is promising for use in the treatment of oil-contaminated wastewater, by using polytetrafluoroethylene (PTFE) as target materials. The effect of the thickness of the PTFE layer (45, 660, and 1350 nm) on the structure, composition, and hydrophilicity of membranes was investigated using scanning electron microscopy, water contact angle (WCA) measurements, atomic force microscopy, and FTIR-spectroscopy. The separation and antifouling performance of the reference and modified membranes were evaluated during ultrafiltration of cutting fluid emulsions. It was found that the increase in the PTFE layer thickness results in the significant increase in WCA (from 56° up to 110-123° for the reference and modified membranes respectively) and decrease in surface roughness. It was found that cutting fluid emulsion flux of modified membranes was similar to the flux of the reference PSf-membrane (7.5-12.4 L·m-2·h-1 at 6 bar) while cutting fluid rejection (RCF) of modified membranes increased compared to the reference membrane (RCF = 58.4-93.3% for modified and RCF = 13% for the reference PSf membrane). It was established that despite the similar flux of cutting fluid emulsion, modified membranes demonstrate 5-6.5 times higher flux recovery ratio (FRR) compared to the reference membrane. The developed hydrophobic membranes were found to be highly efficient in oily wastewater treatment.

High performance laser-driven flyers based on a refractory metamaterial perfect absorber.

Laser-driven flyers (LDFs), which can drive metal particles to ultra-high speeds by feeding high-power laser, have been widely used in many fields, such as ignition, space debris simulation, and dynamic high-pressure physics. However, the low energy-utilization efficiency of the ablating layer hinders the development of LDF devices towards low power consumption and miniaturization. Herein, we design and experimentally demonstrate a high-performance LDF based on the refractory metamaterial perfect absorber (RMPA). The RMPA consists by a layer of TiN nano-triangular array, a dielectric layer and a layer of TiN thin film, and is realized by combing the vacuum electron beam deposition and colloid-sphere self-assembled techniques. RMPA can greatly improve the absorptivity of the ablating layer to about 95%, which is comparable to the metal absorbers, but obviously larger than that of the normal Al foil (∼10%). This high-performance RMPA brings a maximum electron temperature of ∼7500 K at ∼0.5 µs and a maximum electron density of ∼1.04 × 1016 cm-3 at ∼1 µs, which are higher than that the LDFs based on normal Al foil and metal absorbers due to the robust structure of RMPA under high-temperature. The final speed of the RMPA-improved LDFs reaches to about 1920 m/s measured by the photonic Doppler velocimetry system, which is about 1.32 times larger than the Ag and Au absorber-improved LDFs, and about 1.74times larger than the normal Al foil LDFs under the same condition. This highest speed unambiguously brings a deepest hole on the Teflon slab surface during the impact experiments. The electromagnetic properties of RMPA, transient speed and accelerated speed, transient electron temperature and density have been systematically investigated in this work.

Structural, surface morphological and dielectric studies of FeGe alloys grown using electron beam deposition

FeGe alloys were accumulated on the Si substrates using the electron beam deposition technique. XRD technique was used to analyze the dependence of the crystal and phase of FeGe alloys. By applying Scherrer’s method, the theoretically calculated crystallite dimension comparisons were performed. Depending on the concentration of increasing Ge, the size of the crystalline increases from 44.8 to 51.8 nm. The morphology and grain size changes of the alloys were compared with SEM in terms of their surface distribution. Dielectric properties, tangent loss, and AC conductivity (σ ac) were demonstrated depending on the frequency.

Deconvoluting Photoelectrochemical Activity in Monoclinic–Scheelite BiVO4 Facet Selected Thin Films

Crystal facet engineering is one of the promising strategies to tune the band edge positions and surface electrochemistry of a material, which are essential to improve photoelectrochemical (PEC) water splitting. Materials with low-crystal symmetry structures demonstrate facet-dependent properties due to asymmetric coordination, and facet engineering can modulate PEC properties. In this regard, different facets [e.g., (002), (121), and (040)] of the monoclinic–scheelite polymorph of BiVO4 (low-crystal symmetry structure) have been grown by controlling the thickness (deposition time) of thin films [22 nm (10 s) to 265 nm (50 s)] by the electron beam deposition technique. X-ray diffraction and high-resolution transmission electron microscopy analysis suggest the presence of different exposed planes that display different EC and PEC activity. PEC water splitting measurements suggest that the 110 nm/30 s thin-film sample, that is, the (040) facet, has the highest current density, that is, 0.29 mA/cm2 (under light) and 0.068 mA/cm2 (under dark) at 1.8 V versus RHE. However, the applied bias photon to current efficiencies (ABPEs) of both the thin films, that is, (040)/30 s and (121)/40 s facets, are nearly equal, whereas (121)/40 s has enhanced electrical and solar power-to-hydrogen (ESPH) conversion efficiencies compared to the (040)/30 s facet sample. Band edge positions computed via density functional simulations of exposed surfaces suggest that different facets have different band edge positions, thereby offering different driving forces to perform oxygen evolution reaction (OER). The relation between efficiency (ABPE and ESPH) and driving force suggests that the enhanced PEC performance of the (040) facet of BiVO4 is due to the increased driving force to perform OER, whereas the improved efficiency of (121)/40 s can be due to enhanced surface catalytic activity. The highest catalytic activity of the (040)/30 s sample is due to low electron–hole recombination in the bulk and maximum charge injection at the surface.

Osteogenic potential evaluation of biotin combined with magnesium-doped hydroxyapatite sustained-release film

Biotin is one of the water-soluble B-complex group of vitamins. Recent studies have found that the relative protein expression of BMP2, BSP and OPG in MC3T3-E1 cells is prominent after 14 days of co-culture with biotin film, especially for BMP2. It is also found that the rapid degradation of biotin film in vivo limits its application value. In this work, magnesium-doped hydroxyapatite (MgHA) film can form a porous network structure as a biological sustained-release film. Therefore, the multilayer (MgHA|biotin|MgHA|biotin) film was prepared by pulsed laser assisted electron beam deposition technique. The morphology, structure and properties of biotin film and multilayer film were analyzed and characterized. Also, the osteogenic effect of biotin film and multilayer film was evaluated after implantation into the femoral bone marrow cavity of SD rats. The results of micro-CT scan and 3D reconstruction showed that there were a large number of trabecular bones around the multilayer film, which was superior to biotin film in osteogenesis. Hematoxylin-eosin staining showed cancellous bone structure and intact bone marrow structure around the multilayer film, and the newly formed bone became lamellar. Masson-trichromatic staining revealed abundant osteoid and braided bone formation around the multilayer film. In conclusion, MgHA sustained release film can realize the continuous release of bioactive drugs, which provides a new route to accelerate the repair of bone defects.

Sub-femtogram sensing by engineering evanescent field on a single serially grafted waveguide

The intensity of the evanescent field (EF) is vital for the sensitivity and limit of detection (LoD) of optical fiber or waveguide EF sensors. The fusion of ultra-highly sensitivity, simplicity, and cost effectiveness is still a major research field of sensing system despite the advances achieved during the last decades. In this study, we engineered EF by coating a high-refractive-index layer on a polymer waveguide that was serially grafted onto optical fibers. The simulation results show that the proportion of EF intensity can be significantly increased by 2–3 orders of magnitude compared with that of the non-coated waveguide. As a proof-of-concept, we fabricated Ta2O5 coated optical fiber-waveguide-fiber (OFWF) sensors via laser-induced waveguide self-writing and electron beam deposition techniques. The absorbance- and fluorescence-based sensing properties of the coated OFWF were investigated by spectral measurement of rhodamine B aqueous solutions. Owing to large EF ratio and high adsorption capacity of the sensor, we achieved a spectral sensing LoD of 9.5 × 10−16 g/ml with absolute mass of 0.4–0.5 fg.

Multi-layer MgF2/ITO coatings for electromagnetic interference shielding

Indium tin oxide (ITO) coatings have been found useful for diverse applications including electromagnetic interference (EMI) shielding for defense and aerospace purposes, solar cells, gas sensors, etc. However, the reliability, adhesion, transmittance and control of conductivity are some issues that need to be discussed for EMI shielding. Composite multi-layer coating of magnesium di-fluoride (MgF2) and ITO have been deposited on soda lime glass substrate using electron beam (e-beam) deposition technique at a substrate temperature of 350 °C and annealed in the temperature range of 200–500 °C for 1 h under vacuum. The deposited coatings have been characterized for structural, optical and electrical properties. The deposited coatings were crystalline with a crystallite size in the range of 20–30 nm for ITO and 15–20 nm for MgF2 coatings. The coating thickness of ITO and MgF2 determined by Rutherford backscattering technique were found to be 95 nm and 12 nm, respectively. The maximum transmittance in the visible range is ~92% for as-deposited and annealed multi-layer coatings. The band gap has been found in the range of 3.95–4.02 eV, which is suitable for EMI shielding effectiveness. Raman spectroscopy confirms quantum confinement in MgF2/ITO coatings. The electrical conductivity of as-deposited MgF2/ITO coating has been found to be 200 (Ω-cm)−1 which increased to a value of 1.002 x 103 (Ω-cm)−1 for the sample annealed at 500 °C under vacuum. The multi-layer coating annealed at 500 °C show good EMI shielding effectiveness of 50.4 dB without scarifying the transmittance.

Broadband wide-angle multilayer absorber based on a broadband omnidirectional optical Tamm state.

Recently, broadband optical Tamm states (OTSs) in heterostructures composed of highly lossy metal layers and all-dielectric one-dimensional (1D) photonic crystals (PhCs) have been utilized to realize broadband absorption. However, as the incident angle increases, the broadband OTSs in such heterostructures shift towards shorter wavelengths along the PBGs in all-dielectric 1D PhCs, which strongly limits the bandwidths of wide-angle absorption. In this paper, we realize a broadband omnidirectional OTS in a heterostructure composed of a Cr layer and a 1D PhC containing layered hyperbolic metamaterials with an angle-insensitive photonic band gap. Assisted by the broadband omnidirectional OTS, broadband wide-angle absorption can be achieved. High absorptance (A > 0.85) can be remained when the wavelength ranges from 1612 nm to 2335 nm and the incident angle ranges from 0° to 70°. The bandwidth of wide-angle absorption (0°-70°) reaches 723 nm. The designed absorber is a lithography-free 1D structure, which can be easily fabricated under the current magnetron sputtering or electron-beam vacuum deposition technique. This broadband, wide-angle, and lithography-free absorber would possess potential applications in the design of photodetectors, solar thermophotovoltaic devices, gas analyzers, and cloaking devices.

Enhancement of multifunctional optoelectronic and spintronic applications of nanostructured Cr-doped SnO2 thin films by conducting microstructural, optical, and magnetic measurements

A chemical synthesis method was used to produce Cr-doped SnO2 nanoparticles. By using the TEM technique, the nanocrystalline nature of the Sn1-xCrxO2 (0.0 ≤ x ≤ 0.1) nanopowder was confirmed. With different Cr concentrations, the electron beam deposition technique was used to deposit a series of Sn1-xCrxO2 nanocrystalline thin films on a silica substrate. X-ray diffraction (XRD), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and vibrating sample magnetometry (VSM) techniques were used to examine the physical properties of the deposited films. The nanocrystalline nature of the Sn1-xCrxO2 (0.0 ≤ x ≤ 0.1) thin film was confirmed by XRD and AFM morphology measurements. The XRD spectrum of the Sn1-xCrxO2 nanocrystalline film demonstrated a tetragonal crystal structure with no detectable extra phases. The optical measurements showed that as the Cr content increases, the direct optical energy gap Eg decreases without any sign of solubility limit up to x ≤ 0.1. The decrease in Eg is attributed to the sp-d exchange interaction. Also, the spectral behavior of the refractive index dispersion of the Cr-doped SnO2 indicates that as the Cr dopant increases, the refractive index of the deposited film also increases, which is attributed to the increase in the polarizability. Moreover, as the Cr content raises the atomic number, the density of the deposited film increases from 1.43 × 1022 cm−3 for SnO2 to 1.57 × 1022 cm−3 for Sn0·9Cr0·1O2. Further, the behavior of the refractive index dispersion of the deposited film was revealed using a single oscillator model proposed by Wemple-DiDomenico (WDD). Our calculations revealed that as the Cr concentration increases, the value of oscillator energy Eo decreases owing to the decrease in Eg, whereas the value of dispersion energy Ed increases because of the chemical structural changes such as the lattice parameters. Finally, the magnetic studies revealed that incorporating a small fraction of Cr into SnO2 produces room temperature ferromagnetism in the film, which is gradually suppressed by a further increase in Cr doping. These findings indicate that the Cr-doped SnO2 film can be recommended for optoelectronic and spintronic device applications.

Tailoring the physical properties of titania thin films with post deposition air and vacuum annealing

The present article carefully reports the influence of post deposition annealing on photophysical properties of titania (TiO 2 ) thin films, which are developed employing the electron-beam deposition technique. The pristine films are annealed at 100 °C, 200 °C, 300 °C in air and vacuum conditions followed by the investigation of photophysical properties employing several characterization tools viz. XRD, SEM, AFM, EDS, PL, UV Vis. spectrophotometer and source meter. The films showed amorphous nature, whereas Ti and O peaks in the EDS pattern are evident for TiO 2 films deposition. The increase in annealing temperature resulted into an increment in the transmittance (except for 100 °C) of air annealed films, whereas transmittance is decreased for vacuum annealed films. The obtained higher transmittance is suitable for TiO 2 thin films to implicate as buffer layer for solar cell devices where the band gap is observed in a range of 3.06–3.13 eV for air annealed and 2.57–3.05 eV for vacuum annealed films. The electrical conductance of films is enhanced up to 200 °C during annealing possibly due to the removal of traps present in titania thin films. AFM analysis of air annealed films demonstrates a decrement in surface roughness and grain size. Room temperature photoluminescence spectra exhibited strong peaks at 400 nm and 621 nm corresponding to the band edge and Ti 2+ , Ti 3+ , Ti 4+ surface state emissions, respectively. The higher transmittance, lower surface roughness, and ohmic nature of 300 °C air annealed films might attract kind attention for photoanode and optical window or buffer layer applications in dye-sensitized and Cd-based solar cells and charge transport layers in organic and perovskite solar cells. • An impact of air and vacuum annealing on properties of titania films is studied. • The structural analysis reveals the amorphous nature of pristine and annealed films. • Higher transmittance is observed for 300 °C air annealed titania films. • All the titania films showed conspicuous ohmic nature along with lower roughness. • The titania films air annealed at 300 °C may be applied as window or buffer layer.

Multi-layer Laser Mirrors for Optical Sensors Deposited by Electron Beam Deposition and Ion Assisted Electron Beam Deposition

High reflectivity and low loss mirrors are very much essential for state-of art sensors like Ring Laser Gyroscopes widely used for navigation of moving platforms. Surface scattering is the main source of loss for the Laser mirrors of high reflectivity. Surface scattering also lead to coupling of back reflected light leading to dead band of optical sensors at low input rotation. Super polished glass substrates have been prepared from low expansion glass ceramic material. Surface roughness is achieved about 3-5Å (RMS value) for the ceramic glass substrates prior to thin film coating. The substrates are deposited with 41 alternative layers of SiO2 and Ta2O5 of Quarter-Wave optical thickness with Electron Beam Deposition (EBD) technique. Ion beam Assisted Electron Beam Deposition (IAEBD) is used for another batch of substrates to coat identical stack of layers on glass substrates of the same surface quality. The key process parameters of both the coating processes are presented. The optical constants of the films are evaluated with spectroscopic Ellipsometer from 400nm to 1600nm. Total Integrated Scattering is estimated from the achieved surface finishing of mirrors deposited. The multi-layer coatings are characterized with UV-Vis-IR Spectrophotometer and Cavity Ring Down(CRD) loss meter. The quantitative optical loss of the mirrors is measured at 45o angle of incidence with CRD loss meter. The merits of ion assisted EB process over simple EB coating processes are evaluated against optical constants of thin films and performances of mirrors. Fitness of the processes for realizing Laser mirrors for optical sensors at 632.8nm is evaluated.

Binder-Free, Thin-Film Ceramic-Coated Separators for Improved Safety of Lithium-Ion Batteries.

Separators play a crucial role in ensuring the safety of lithium-ion batteries (LIBs). Commercial polyolefin-based separators such as polyethylene (PE) still possess serious safety risks under abuse conditions because of their poor thermal stability. In this work, a novel type of binder-free, thin ceramic-coated separators with superior safety characteristics is demonstrated. A thin layer of alumina (Al2O3) is coated on commercial PE separators using the electron-beam physical vapor deposition (EB-PVD) technique. Scanning electron microscopy (SEM), contact angle, impedance spectroscopy, and adhesion test techniques were employed to evaluate structure–property correlations. When compared to commercial slurry-coated separators, the EB-PVD-coated separators display (i) higher thermal stability, (ii) stronger ceramic–polymer adhesion, and (iii) competitive electrochemical performance of full LIB cells. Thermal stability, in terms of improved shutdown and breakdown characteristics of the separator, was studied using the in situ impedance technique up to 190 °C. In addition, the improved adhesion of the ceramic layer deposited on the PE separator was studied following the tape adhesion strength test. We prove that the thin (binder-free) ceramic layer coated by EB-PVD is far more effective in improving separator safety than those made using the conventional thick slurry coating.

Spectroscopic ellipsometry and morphological studies of nanocrystalline NiO and NiO/ITO thin films deposited by e-beams technique

The current article reported a new data on the structural, surface morphology and optical properties of multi-thickness nanocrystalline NiO/glass substrate and NiO/ITO/glass substrate semiconductor thin films prepared by electron beam deposition technique. Structural investigation shows that the as-deposited multi-thickness NiO films deposited on a glass substrate crystallize in the form of cubic NaCl type structure. However, ITO thin film has a cubic type structure. Besides, the increase in the crystallite size was observed with increasing the thickness of NiO film, this behavior was confirmed by AFM micrographs. In the spectral range 280 nm–1800 nm, the optical properties of the NiO/glass substrate and NiO/ITO/glass substrate thin films have been investigated using spectroscopic ellipsometry (SE) technique. For NiO/glass substrate sample, the SE results providing direct energy E g d i r ≈ 3.954 eV, indirect energy E g i n d i r ≈ 2.855eV and phonon energy of order 200 meV. In addition, the analysis of the refractive index dispersion gives the atomic number density to be N f i j = 2.213 x 10 22 c m − 3 . On the other hand, for the NiO (410 nm)/ITO (99 nm)/glass substrate thin film sample, a reduction in the direct transition energy to E g d i r ≈ 3.24eV and also in the factor N f i j to 1.6 x 10 22 c m − 3 was observed. Additionally, the values of the oscillator parameters were calculated for NiO/glass substrate and NiO/ITO/glass substrate thin films using the Wemple-DiDomenico single oscillator model (WDD). Finally, it was found that the values of Urbach energy for NiO/glass substrate and NiO (410 nm)/ITO (99 nm)/glass substrate are very small relative to the energy gap values which indicates that the region of localized sates is very narrow compared to the width of the energy gap. • The D/nm of NiO film increase from 16.86 to 22.75nm and for NiO/ITO from 15 to 26nm with increasing thickness from 75 to 410nm. • Good correlation between the increase in D/nm and reduction of dislocation density (δ) is found. • SE provides E g d i r ≈ 3.954 eV, E g i n d i r ≈ 2.855eV and E phon 200meV. For NiO/glass film a reduction in E g d i r to 3.24eV for the NiO(410nm)/ITO (99 nm)/glass. • The refractive index of NiO film is independent of the film thickness and atomic number density is found to be N f i j = 2.213 x 10 22 c m − 3 • The values of E o = 6.828eV, E d = 19.3eV for NiO film and E o = 4.56eV, E d = 15.1eV for (410 nm)/ITO (99nm)/glass substrate film are found.

Ultrasensitive yttrium modified tin oxide thin film based sub-ppb level NO2 detector

Considering the adverse effect of rising air pollution on environment and human health, highly selective and trace level sensors are needed. Herein, yttrium (Y) incorporated tin oxide (SnO2) thin film gas sensors have been developed for sub-ppb level detection of NO2 at room-temperature. The undoped and Y-doped (1, 3 and 5 wt%) thin films have been prepared via electron beam deposition technique. The XPS studies confirmed the substitution of Sn with Y in SnO2 lattice. The morphological and structural characterizations reveal smooth and crystalline thin films, while Raman and PL spectroscopic studies confirm the presence and growth of oxygen vacancies (OVs), specifically in-plane OVs, in doped samples. Moreover, narrowing of electron absorption spectra in doped samples implied the formation of mid-gap states in energy bandgap of SnO2 leading to enhanced electron transfer. The 3 wt% Y-doped SnO2 sensor exhibited excellent sensing response with high selectivity towards NO2 in 15–240 ppb range. The sensors also showed high stability and repeatability along with humidity insensitivity. Notably, the sensor was observed to be highly sensitive to 0.6 ppb NO2 exhibiting a 26 % response along with response/recovery time of 4/2 min. The improved sensing characteristics have been ascribed to reduced crystallite size, elevated in-plane OVs, enhanced charge transfer and increased specific surface area due to Y integration.

Thickness-Dependent Optical Nonlinearities of Nanometer-Thick Sb2Te3 Thin Films: Implications for Mode-Locking and Super-resolved Direct Laser Writing

2D materials are currently very promising candidates for various photonic applications. Optimizing their optical nonlinearities requires a thorough adjustment of several properties including the film thickness. In thiswork thin Sb2Te3layers with different thicknesses (ranging from 2.5 nm to 50 nm)are prepared by the electron beam deposition technique, then they are properly annealed in order to achieve significant third order nonlinearities. The film structure and morphology are extensively studied by means of X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and Energy-dispersive X-Ray spectroscopy. The presence of nanocrystals with sizes highly dependingon the film thickness has beenobserved.Optical studies are carried out by Vis-NIR spectrophotometric studies. Finally, a thickness dependent study of the ultrafast third order nonlinear optical properties of the Sb2Te3thin films is performed. This study is carried out by means of the Z-scan technique, employing 400 fs laser pulses at 1030 nm. The observed optical nonlinearities are veryhigh, comparedwith those of state-of-the-art nonlinear optical materials. Moreover they are highly dependent on the thickness of the layers. The findings demonstrate the importance of a fine adjustment of the Sb2Te3thickness in order to enhance its nonlinear optical efficiency.They are expected tobe of significant importance for mode-locking of laser systems and super-resolved direct laser writing.