Electron Beam Evaporation Technique Research Articles

Influence of temperature on optical properties of electron-beam-evaporated ZnSe thin film

Structural and optical properties of ZnSe thin films grown by electron-beam evaporation technique were reported in the present paper. X-ray diffraction pattern exhibited a single peak around 27° which is well-suited with cubic phase of the films. Energy dispersive X-ray spectroscopy analyses resulted in atomic composition ratio of Zn/Se nearly 1.0 which corresponds to the chemical formula of ZnSe. Transmission experiments were performed at various temperatures in between 10 and 300 K. The analyses of the transmission data showed that direct band gap energy of the ZnSe thin films increases from 2.72 to 2.83 eV as temperature was reduced to 10 K from room temperature. The Varshni and O’Donnell-Chen models giving the temperature-band gap energy relation were used to get various optical parameters of the evaporated thin films. Analyses resulted in absolute zero temperature band gap energy as 2.83 eV, temperature coefficient as −5.8 × 10–4 eV K−1 and average phonon energy as 16 meV. Urbach tail state energies were also calculated using absorption coefficient in the low photon energy region as increasing from 173 meV (300 K) to 181 meV (10 K) with decreasing ambient temperature.

Rare earth-tuned oxygen vacancies in gadolinium-doped tin oxide for selective detection of volatile organic compounds

The gas sensing characteristics of metal oxide-based sensors are found to be influenced by the oxygen vacancies (OVs) that act as selective sites for gas adsorption. To ascertain the effect of OVs on gas sensing properties of tin oxide (SnO2), rare earth (gadolinium)-doped SnO2 thin films have been prepared via electron beam evaporation technique and characterized for structural, optical, and gas sensing properties. Spectroscopic studies revealed the doping dependence of in-plane and sub-bridging OVs that influence the gas interaction properties of Gd-doped SnO2 films. The dominance of sub-bridging OVs leads to enhanced sensing characteristics of 3% Gd-doped SnO2 film towards isopropanol. The gas sensing characteristics of metal oxide-based sensors are found to be influenced by the OVs that act as selective sites for gas adsorption. Among the tested volatile organic compounds (VOCs), the dominance of sub-bridging OVs leads to enhanced sensing characteristics of 3% Gd-doped SnO2 film towards isopropanol.

Multilayer dielectric coated Fabry Perot spectral beam combiner for high power, narrowband, widely tunable laser applications

Spectral beam combination of tunable laser beams demonstrated, using a multilayer dielectric coated single cavity Fabry Perot (FP) filter. A stack of 19 layers using TiO2 and SiO2 was optimally designed and fabricated using an electron beam evaporation technique. This filter was characterized for transmission spectrum, surface morphology and laser induced damage threshold. The sharp transmission spectrum facilitated the spectral combination of closer wavelengths (<10 nm) around 632.8 nm. This filter was utilized as an efficient spectral beam combiner as well as an amplified spontaneous emission (ASE) filter for the transmitting wavelength. This study finds direct application for tunable, multi-wavelength laser-based differential absorption lidar (DIAL) and atmospheric remote sensing applications. The application of this device was successfully demonstrated to spectrally combine high power, tunable copper vapor laser pumped dye laser beams. A mechanism to tune the FP transmission profile along with laser beam tunability was established.

Study of d0 magnetism of BaF2 nanopowder after thermal and radiation exposure

Mesoporous nanocrystal BaF2 nanopowders (NPs) have been obtained with the pulsed electron beam evaporation (PEBE) technique. The transformation of the structure and morphology of BaF2 nanoparticles (NPles) induced by thermal annealing in air at temperatures of 200, 400, and 900 °C has been monitored with the XRD, SEM, and HRTEM methods. The HRTEM analysis has shown the presence of three polymorph phases (cubic, octahedral, and hexagonal) in the unannealed NP. Upon the transition into the nanoscale, diamagnetic (DM) BaF2 (in the volume state) has demonstrated both paramagnetic (PM) and ferromagnetic (FM) responses at room temperature. The thermal analysis (TA) has confirmed the strong adsorption of CO2 while synthesizingthe BaF2 NP via PEBE method and adsorption of different NOx oxides following irradiation of the BaF2 NP (in air by 700 keV electrons) The appearance of the FM contribution in the diamagnetic BaF2 NP after annealing at a temperature of 600–900 °C is likely associated with the achievement of the percolation threshold with an increase of the BaO oxide concentration. This is in agreement with the well-known theoretical predictions of d0 magnetism in N-doped (C-doped) BaO. The appearance and variations of the FM contribution to the BaF2 NP irradiated by 700 keV electrons are likely connected with an increase of the NOx oxide concentration (due to an increase of the time of electron irradiation), which confirms the hypothesis on the appearance of the FM response in solid-state N (C)-BaO solutions. The FM decrease with time is indicative of the surface character of d0 magnetism in the barium fluoride under study.

Influence of Surface Spin Alignment and F-Centers on the Magnetic Behavior of ITO Thin Films

Iron (Fe)-doped indium-tin-oxide thin films were prepared using electron beam evaporation technique. The prepared thin films were characterized by XRD, SEM, EDX, UV-Vis-NIR, and VSM techniques to study their structural, compositional, optical, electrical, and magnetic properties. The XRD studies confirmed the cubic structure of the prepared thin films with crystallite size 26 nm. The morphological studies confirmed the formation of nanorods. The EDX spectra confirmed the presence of elements in the desired ratios. A decrease in optical band gap was observed in the Fe-doped ITO thin films. A broad emission peak at 513 nm was observed in the PL spectra. No change was observed in the emission wavelength with increase of Fe concentration. A weak ferromagnetic nature with an anti-ferromagnetic background was observed in all the Fe-doped ITO thin films. A systematic discussion on observed results was provided in the manuscript.

Structural, Optical and Electrical Properties of Electron Beam Evaporated Tioxny Films as Selective Solar Absorber Coatings

Titanium oxinitride (TiOx Ny ) solar absorber coatings were deposited at different oxygen partial pressures onto Cu, Si and glass substrates using electron beam evaporation technique. XRD diffraction patterns evidenced (111), (200) and (220) orientation of TiNx phase. The preferred orientation of the films changed with oxygen partial pressure. XPS revealed the intensity of both Ti 2P3/2 and Ti 2P1/2 increases as a function of oxygen flow, and also shifted towards higher binding energy, indicating more oxidized state of Ti species than that of TiO2 due to incorporation of nitrogen atoms. Formation of uniformly distributed spherical like particles and an increase in surface roughness of the TiOx Ny films were observed as a function of oxygen partial pressure as depicted from SEM and AFM, respectively. Ellipsometric and resistivity measurements showed a shift from metallic to semiconductor behaviour of the TiOx Ny films as oxygen flow changed. A solar absorptance value of 0.94 in the solar spectrum region and a low thermal emittance value of 0.05 were achieved for the TiOx Ny solar absorber coatings prepared at the oxygen partial pressure of 7.5x10-5 Torr due to both interference and intrinsic absorption. This study confirmed that a single layer of TiOx Ny film can be a good candidate as selective solar absorber.

TiO2 thin films on Au/Ti/SiO2/textured Si substrates as high capacity anode materials for Li-ion batteries

In this paper, we investigate the structural and electrochemical properties of TiO2 thin films deposited on multilayered Au/Ti/SiO2/(100) textured-Si substrates by electron-beam evaporation technique at various substrate temperatures in the range 25 ≤ Ts ≤ 350 °C. Phase-pure and well-crystallized TiO2 thin films grown at Ts = 250 °C exhibit the typical (101) Bragg line of the tetragonal anatase structure with crystallite size of about 30 nm. The surface morphological analysis reveals the uniform growth of prismatic shaped grains (40–120 nm in size) deposited on pyramidal architectures of textured substrates. The electrochemical tests show that TiO2 thin films electrodes deposited at Ts of 250 °C deliver a specific discharge capacity of 74 μAh cm−2 μm−1 at a current density of 1 mA cm−2 with 96% capacity retention after 100 cycles. Hence, the experimental results demonstrate that TiO2 thin films can be used as anodes of planar solid-state Li-ion microbatteries.

Influence of the Pt thickness on the structural and magnetic properties of epitaxial Fe/Pt bilayers

Interface induced phenomena in layered magnetic/non-magnetic structures have led to big discoveries, such as giant magnetoresistance, which has defined the field of spintronics. Interfaces are capable of inducing magnetism even in non-magnetic layers, like platinum. Here, we investigated the static magnetic properties of modified interfaces in Fe/Pt bilayers, deposited on MgO substrates via an electron beam evaporation technique. We show the impact of the thickness reduction of the non-magnetic material, from 18 nm down to 1 nm, on the structural and magnetic properties of the epitaxial Fe/Pt bilayers. Below a platinum thickness of 6 nm a significant increase of the magnetic hardness and a uniaxial anisotropy is observed. We correlate the magnetization reversal with the increase of the elastic strain of the Pt layer, in conjunction with the interfacial Fe/Pt roughness and Pt proximity effect, which is enlarged as the Pt thickness is decreased.

Toward CdCl2 activation on CdSe thin films for absorber layer applications

The polycrystalline thin film solar cells often possess problem of grain boundaries which lower the efficiency of device, but several mechanisms/treatments are available to passivate these grain boundaries and enhance the performance of device concerned. In cadmium-based devices, the passivation could be undertaken by chloride activation where grain boundaries are passivated along with grain growth. In this report, the physical properties of the CdCl2-activated CdSe thin films are optimized. The CdSe thin films of thickness 550 nm are developed on microscopic glass and indium-doped tin oxide glass substrates employing electron beam evaporation technique followed by post-wet chloride treatment and subsequently annealing in air atmospheric condition at temperature of 170 °C, 320 °C and 470 °C. The structural analysis confirmed the polycrystalline nature with cubic phase of the CdSe films which changed into hexagonal at high temperature. The absorbance increases with the activation and optical energy band gap is found to decrease from 2.03 to 1.71 eV. The electrical analysis shows ohmic nature of the pristine and treated films. The surface morphology demonstrates grain growth with treatment, and the energy-dispersive spectroscopy (EDS) patterns indicate the existence of cadmium, selenium and chlorine elements which ensure deposition and chloride activation to the films. The outcomes designate that CdCl2-passivated CdSe films have appropriate candidature as an absorber layer to the solar cell device.

Physical properties of ZnSe thin films: Air and vacuum annealing evolution to buffer layer applications

In order to develop high efficiency solar cell device by replacing conventional hazardous CdS window layer by environmental friendly Zn-based buffer layer, ZnSe thin films of thickness 100 nm were grown on glass and ITO substrates employing electron beam evaporation technique followed by air and vacuum annealing at temperature 100°C, 200°C and 300°C. As-grown and annealed films were subjected to characterization tools like XRD, UV-Vis spectrophotometer, SEM, EDS and source meter. Structural results reveal the amorphous phase, SEM images indicate uniform deposition without pin holes and EDS patterns confirm the deposition. Transmittance is observed to be high in visible region and band gap is found to change with temperature of the treatment and I-V measurements demonstrate ohmic nature. On the basis of optimized results, the films annealed at 200°C in vacuum may be used as buffer layer to develop high efficiency Cd-based and CIGS thin film solar cells.

Magnetic and Structural Properties of Exchange Coupled Heusler Alloy NiO/Co2FeAl Interfaces with n-and p-Type Silicon Substrates

Exchange coupled structures of half metallic ferromagnets, Heusler Alloy (FM), Co2FeAl (CFA) and antiferromagnet (AF), NiO were fabricated by electron beam evaporation technique on n- and p-type Si substrates. These fabricated bilayer structures were further characterized for structural, morphological and magnetic point of views using x-ray diffraction (XRD), atomic/magnetic force microscopy (AFM/MFM) and vibrating sample magnetometer (VSM) techniques. Structural study shows the presence of CFA alloy and NiO phase. Surface morphology shows the granular feature of the top surface with grain size of 200–300 nm due to clustering of smaller grains. Smaller sized magnetic domains have been observed for the structures. Hysteresis behaviour of NiO/CFA/Si structures shows the ferromagnetic behaviour for in-plane orientation with negligible exchange bias whereas a significant exchange bias for out of plane orientation has been observed. The observed result could be understood due to surface roughness and arrangements of spins near the interface of ferromagnetic and anti-ferromagnetic layers.

The effect of temperature and roughness of the substrate surface on the microstructure and adhesion strength of EB-PVD ZrO2-%8wtY2O3 coating

Thermal barrier coatings are of great interest in increasing the working temperature and thus, improving the efficiency of turbine engines. In this study, coating was conducted on nickel-base superalloy substrates using physical vapor deposition process and the electron beam evaporation technique of Yttria-stabilized Zirconia discs. In order to characterize the coatings including microstructure, topography and phase structure, field emission scanning electron microscopy, atomic force microscopy and X-ray diffraction analysis were used, respectively. The scratch test was also used to evaluate the adhesion strength of the coating. It was observed that at the temperature of 470 °C, the coating has no preferential orientation. By increasing the substrate temperature to 750 °C, the intensity of the peak (211) was reduced, while that of the peak (101) was sharply increased, such that at the substrate temperature of 750 °C, the coating had only the preferred orientation (101). Increasing the substrate temperature from 470 °C to 750 °C enhanced the critical force (Lc) from 8.2 N to 25.1 N. Increasing the substrate roughness from 0.55 μm to 3.43 μm enhanced the coating roughness from 0.62 μm to 3.71 μm raised the columnar diameter from 36.98 nm to 120.9 nm and reduced the critical force (Lc) from 18 N to 6.3 N.

Fabrication of the Mn3O4 thin film electrodes by electron beam evaporation for supercapacitor applications

Electron beam evaporation technique has been employed for the fabrication ofMn3O4thin films on various substrates such as Pyrex Glass (PG), Stainless Steel (SS) and Au/Ti/SiO2/(textured) Silicon (ATS). The structural properties of as deposited Mn3O4 films are investigated using XRD, Raman spectroscopy, SEM, EDS and AFM. The optical properties of Mn3O4 films are studied for the films deposited on PG substrates. The electrochemical performance of Mn3O4 films deposited on SS and ATS substrates are examined by Cyclic Voltammetry, Chronopotentiometry and Electrochemical Impedance Spectroscopy. The films grown on PG, SS and ATS substrates are poor crystalline, polycrystalline and crystalline in nature, respectively. The major Raman peak at 654 cm−1 and FTIR absorption peak at 624 cm−1confirm the existence of MnO bonding. The SEM and AFM analysis revealed that the films deposited on PG, SS and ATS substrates covered with non-uniform spherical grains, flakes like grains and well dispersed pyramidal grains, respectively. The optical band gap of the films grown on PG substrates is 2.86 eV. The films deposited on ATS substrates exhibited superior electrochemical properties by offering the high specific capacitance of 754 F g−1 at a specific current of 1 A g−1and good cycling retention (89%) even after 4000 cycles. The specific capacitance and cycling performance are further improved after annealing the films in a controlled oxygen ambience. Prime novelty statementMn3O4 thin film micro electrodes were prepared on Au/Ti/SiO2/Si substrates. Further to improve the structural and morphological features of the films, the films were annealed at different temperatures. The improved electrochemical performance in terms of discharge specific capacitance and cycling stability is correlated with microstructure.

Ohmic Contact of Pt/Au on Hydrogen-Terminated Single Crystal Diamond

In this study, contact properties of platinum/gold (Pt/Au) on the surface of hydrogen-terminated single crystal diamond (H-SCD) were studied with several treatment conditions. The electrodes of Pt (20 nm)/Au (100 nm) were deposited on H-SCD surface by electron beam evaporation technique. Then, the specific contact resistance (ρc) of the as-fabricated sample was measured by the circular transmission line model, which showed good ohmic properties with the value of 5.65 × 10−4 Ω·cm2. To identify the thermal stability of Pt/Au/H-SCD, the sample was annealed in hydrogen ambient from 200 to 700 °C for 20 min at each temperature. As the temperature increased, ρc demonstrated better thermal stability. In addition, the barrier height was evaluated to be −0.67 ± 0.12 eV by X-ray photoelectron spectroscopy (XPS) technique.

Demonstration of tunable Ag morphology from nanocolumns to discrete nanoislands using novel angle constrained glancing angle EB evaporation technique

In glancing angle electron beam evaporation technique, the deposition geometry has been engineered in a novel manner in this work to produce extensive tunablity of Ag morphology. A physical plate (collimator) parallel to the substrate has been suitably placed in order to constrain the angle of incoming deposition vapor flux. The distance between substrate and this collimator as well as the distance between substrate to crucible orifice has been optimized for maximum variation in Ag morphology which resulted in the discussed tunability. SEM images acquired across the sample surface on the best optimized sample show variation of Ag morphology from nearly continuous film to Ag nanocolumns (dia-135 nm) and then to Ag nanoislands of varying size (26–83 nm) with the variation in height from substrate bottom edge. Surface plasmon resonance (SPR) peak of this Ag nanostructure has been found to shift to longer wavelength and to broaden with the increase of thickness across the substrate surface. The estimated band gap values of the Ag nanostructure are non-zero which reveals its dielectric like dispersion behavior. Thickness and optical constants at various locations on the best optimized sample have been estimated through spectroscopic ellipsometry measurements and the obtained results have been validated with measured transmission spectrophotometry spectra. Three different ellipsometry models have been tried to fit the ellipsometry data of such grown ultrathin film consisting of Ag nanoislands/nanocolumns. An effective media consisting of the mixture of bulk Ag, dielectric media represented by Lorentz oscillator and air was found to be the best to describe the disperision behavior of the deposited Ag film. The dielectric like dispersion behavior of Ag ultrathin film has been ascribed to localized surface Plasmon resonance (LSPR) effect of Ag nanoislands in optical wavelength region. Due to the gradual variation of thickness and optical constants across the film, the optimized film exhibits variation in average optical transmittance (600–1000 nm) from 1.1% to 91% across 40 mm distance which demonstrates its potential for application as variable optical transmission attenuator. Finally, this novel deposition flux constrainment technique has been regarded as an effective method for fabrication of tunable Ag nano-morphologies for optical and surface plasmonic applications.

Exploring the functional capabilities of NiTi shape memory alloy thin films deposited using electron beam evaporation technique

The viability of utilizing electron beam evaporation technique for the development of NiTi shape memory alloy (SMA) thin films on kapton polyimide (flexible substrate) has been investigated. The actuation characteristics of the SMA/polyimide structure were evaluated using shape recovery analysis and electrical actuation. The maximum shape recovery ratio of 1.375 was attained with butterfly configuration during shape recovery analysis. The SMA/polyimide stimulated via Joule heating has displayed a maximum displacement of 0.9 mm at 3 V. The surface morphology examined through scanning electron microscope shows the smooth surface without any pores. The thermal stability analyzed using thermogravimetric analysis shows the NiTi SMA thin film can withstand higher temperature above 550 °C without any damage to the SMA/polyimide structure. The stress/strain behavior of the SMA/polyimide structure was analyzed as a function of temperature. The differential scanning calorimetry has showed that the austenite phase transformation temperature lies in the range of 45°C-95 °C. The temperature sweep test performed using dynamic mechanical analyzer recorded a drastic drop in storage modulus in the same phase transformation temperature range as that of DSC. The UV–Vis spectroscopy reveals the NiTi/polyimide structure has high reflective surface in the visible region which aids in the application of reflectors. SMA/polyimide structure can be used as a smart optical mirror in interferometry technique owing to its optical reflectivity.

Experimental studies on nucleate pool boiling heat transfer enhancement for composite nano-structure coated copper heating surface

The present paper is based on experimental studies on nucleate pool boiling heat transfer enhancement of different surfaces using water as a base fluid at atmospheric pressure. The test surfaces for the experiments include untreated, treated, and treated with Aluminum-silver oxide composite thin film surfaces having nano-layer thickness of 180 nm and 260 nm. The thin films are prepared on copper substrate by electron beam evaporation technique. The characterization of the heated surfaces is done by using optical surface profilometer for surface roughness and sessile drop method for contact angle measurement. The experiment is conducted in a closed boiling chamber and the heat flux is varied from 141.524 - 1244.101 kW/m2 in time steps. The enhancement of heat transfer coefficient is found as 22.8%, 17.27% and 11.81% from the 260 nm, 180 nm composite nanostructured coated and treated surfaces respectively compared to plain surface. Enhancement in nanostructured coated surfaces is found higher due to the capillary effect, increased wettability and high active nucleate site density and the increased rate of bubble frequency.

Optical characterization of silicon dioxide thin films prepared by ion-assisted electron beam deposition

A single-layer SiO2 film is deposited using ion-assisted electron beam evaporation technique, and the deposited film is characterized using variable angle spectroscopic ellipsometry, UV–Vis–NIR spectrophotometer, coherence correlation interferometer, and Abbe refractometer as well as image processing techniques to investigate its optical and surface properties. The surface quality of the film in terms of average roughness, kurtosis, skewness, and power spectral density (PSD) is analyzed using interferometer and image processing. The refractive index of the SiO2 film is found to increase from 1.452 to 1.482 at 550 nm with increase in film thickness. This is corroborated by Abbe refractometer findings where the film refractive index is found to be 1.46490 and 1.48226 for a film thickness of 100 and 400 nm, respectively. The SiO2 film also results in reduction in average surface roughness from 35 nm of the uncoated substrate to 0.15 nm of the coated surface. Statistical indicators of surface quality extract from interferometric images such as kurtosis, skewness, and PSD and also exhibit sharp decline in their respective values of the coated surface as compared to the uncoated substrate indicating improvement in the surface quality after coating.

Effect of interfacial modifications on magnetic, morphological and transport properties of CoFe/n-Si thin film structures using ion irradiation

Interfacial structures of ferromagnetic (FM) metal combined with semiconductor (SC) are key step for realizing spintronic devices where spin degree of freedom can also be utilized in addition to the charge of electron. Tailoring of such interfaces (of FM/SC) is known to tune the magnetic, optical, structural and transport properties. Swift heavy ion irradiation (SHI) can be used as a potential tool to tailor the interfaces. In our present work, effect of ion beam irradiation (100 meV Ni+7 ions) on the CoFe/n-Si interfacial structures had been studied. Thin films of CoFe was deposited by electron beam evaporation technique using CoFe metallic alloy on Si substrate. The realized interfacial structure was characterized from structural, morphological and magnetic point of view. The surface exhibits grainy structure with very fine domain (∼50 nm) on the irradiation. Electronic transport study across the interface shows an increase in current on irradiation with significant magnetic field sensitivity and a magnetoresistance of ∼7% has been observed. The observed results of increased magnetization and enhanced magnetic field sensitivity has been understood in the realm of irradiation induced interfacial intermixing across the interfaces. The chemical phases formed and nature of the interface as a result of irradiation was probed by X-ray photoelectron spectroscopy (XPS) study which confirms the formation of various silicide phases along with the metallic phase. The results were also compared with our earlier studies [15–16] on CoFe/n-Si system and found that fluence of 1 × 1011 ions/cm2 seems significant to result in interesting magnetic and transport properties without much damage to interface.

Effect of doping concentration, temperature and magnetic field on magnetic properties of Mn doped ITO nanoparticles and thin films

Manganese substituted indium-tin-oxide (Mn: ITO) nanoparticles (NP) and thin films (TF) were prepared using solid state reaction and electron beam evaporation techniques, respectively and studied the role of doping concentrations, temperature and applied magnetic fields on structural, optical and magnetic properties. The structural, optical and magnetic properties of the prepared NP and TF were studied using X-ray diffractometer, UV–Vis-NIR spectrophotometer and vibrating sample magnetometer, respectively. The Mn: ITO NP and TF exhibited a cubic structure without any secondary phases. The optical band gap of the Mn: ITO NP increased (3.07 eV–3.15 eV) whereas it decreased in Mn: ITO TF (3.9 eV–3.25 eV) with an increase of Mn concentration. The Mn: ITO NP exhibited a clear hysteresis loop at a temperature of 32 K and the strength of magnetization increased with the increase of Mn concentration and it decreased with the increase of temperature. The Mn: ITO NP has shown antiferromagnetic nature at higher applied magnetic fields. The Mn: ITO TF has shown weak ferromagnetic nature at room temperature and the magnetization decreased with the increase of Mn concentration. The magnetic saturation was not observed in these films even at higher applied magnetic fields.