Thermal Evaporation Method Research Articles

An evolution to Bismuth dopant concentration on properties of CdSe films for solar cell appliances

The deliberated introduction of dopant to the crystalline host lattice is a promising approach towards the adjustment of physical properties. The present work deals with the influence of Bi dopant concentration on crystallographic, optical, topographical and electrical features of CdSe films for absorber layer applications to solar cells. Herein, the deposition of undoped and Bi doped CdSe films having 1%, 3% and 5% Bi dopant concentration is carried out via resistive heating thermal evaporation method. The crystallographic patterns reveal to the polycrystalline nature of films with occurrence of major reflection along (111) plane of cubic CdSe system where the intensity of this peak is substantially altered with Bi dopant. The crystallite size and strain of the CdSe films are appeared in range of 32–53 nm and 3.01 × 10−3–5.06 × 10−3, respectively upon changing the Bi doping. Optical study indicates the manifestation of strong absorption in visible region of spectra and fluctuation in absorbance of CdSe films with change in Bi dopant concentration. The optical band gap of undoped and Bi doped CdSe films is obtained in 1.61–1.69 eV range. Electrical assessment of films points towards creation of Ohmic contacts where the conductivity of films is improved at 1% Bi doping and decreased at higher doping. All the films show spherical shaped grains with variable density where the grain size obtained from AFM analysis is varied from 24 nm to 40 nm with Bi dopant concentration. Hence, the concentration of trivalent Bi dopant plays a pivotal role in modulation of properties of CdSe films for absorber layer appliances.

Hydrogenation and annealing impact on Si/CdTe junction for solar energy application

In the present research work, author has deposited CdTe thin film on N-type Si substrate, by a thermal evaporation method. The Hind High vacuum system had used, under the pressure of 10−5 torr, and investigated the effect of hydrogenation and annealing on Si/CdTe junction. The current-voltage (I–V) characteristics of the Si/CdTe junction have obtained using Keithley power supply. The I–V characteristics have found change with hydrogenation and annealing. The Scanning electron micrograph (SEM) image of the Si/CdTe junction indicates that the CdTe layer deposited on the substrate has regular and crystalline in structure. The change in I–V characteristics with both Hydrogenation and Annealing make it useful in hydrogen and light sensing device.

Insight into electronic structure and optical properties of ZnTPP thin films for energy conversion applications: Experimental and computational study

Theoretical and experimental study of the electronic structure and optical characteristics of Zinc (II) 5,10,15,20-tetraphenyl 21 H, 23 H-porphine (ZnTPP) was reported. The ground state molecular geometry, Frontier molecular orbitals, vibrational frequency, and total energy of ZnTPP were determined using density functional theory (DFT) calculations. Homogenous ZnTPP thin films were grown on glass and fused quartz substrates using the thermal evaporation method. The ZnTPP thin film structure was described experimentally using FTIR, XRD, AFM and UV-Vis. spectroscopy. XRD results illustrate the polycrystalline structure of ZnTPP powder, whereas the pristine ZnTPP thin films have amorphous nature. The AFM results revealed that the pristine ZnTPP film has uniform elliptical crystallites dispersed throughout the whole surface. Optical parameters of the ZnTPP films were obtained from the absorbance spectra. The absorption coefficient and band gap values showed that ZnTPP can be employed in optoelectronic devices. The experimental findings are in good accord with theoretical ones. A hybrid solar cell was prepared by growing a thin film of ZnTPP on p-silicon single crystal wafers. The photovoltaic performance of the prepared solar cell were estimated as JSC = 1.556 mA/cm2, VOC = 0.366 V, FF = 0.274 and η = 3.12 %.

Structural, optical and DFT studies of disodium phthalocyanine thin films for optoelectronic devices applications

Theoretical and experimental investigations have been carried out on the structural and optical properties of disodium phthalocyanine (Na2Pc) thin films prepared using the thermal evaporation method. The optimized geometry structure, vibrational bands and HOMO-LUMO gap were predicted by density functional theory (DFT) computations. FTIR and XRD techniques were utilized to analyze the structural characteristics of Na2Pc thin films. XRD exhibited that the Na2Pc powder has α-polycrystalline nature with a triclinic structure, whereas the Na2Pc thin films have an amorphous structure. The optical properties of different thicknesses films were studied in the wavelength range of 200–2500 nm using the UV–Vis-NIR spectrophotometer. The absorption coefficient of the Na2Pc molecules showed four absorption bands in the UV–Vis region. The types of optical transitions were determined by applying the energy band model as an indirect allowed transition. The onset gap, optical gap and Urbach energy were estimated to be 1.31, 2.25 and 0.41 eV, respectively. The results of absorption coefficient and energy gap showed that the Na2Pc thin films can be utilized in optoelectronic device applications. The absorption index, k, and refractive index, n, were determined and found to be independent of the film thickness. The dispersion parameters have been evaluated according to a single oscillator model in the non-absorbing region of the spectrum.

Study of the structural and optical properties of thallium gallium disulfide (TlGaS2) thin films grown via thermal evaporation

Thallium gallium disulfide (TlGaS2) belonging to layered structured semiconducting family has been a significant compound due to its outstanding characteristics. Its layered characteristics take attention for two-dimensional (2D) material research area and thus TlGaS2 is known as promising layered compound to develop 2D materials for optoelectronic devices. To the best of our knowledge, the present work is the first one investigating TlGaS2 thin films grown by thermal evaporation method. The current study focused into the structural, morphological, and optical characteristics of thermally evaporated TlGaS2 thin films. X-ray diffraction pattern of the films exhibited one peak around 36.10° which was associated with (−422) plane of the monoclinic crystalline structure. The atomic compositional ratio of Tl:Ga:S was found to be suitable for the chemical formula of TlGaS2. Scanning electron microscopy images showed uniformly and narrowly deposited nanoparticles with sizes varying between 100 and 200 nm. Room temperature transmission measurements were recorded to obtain the bandgap energy of the evaporated thin films. Tauc analyses indicated direct band gap energy of 2.60 eV. Finally, Urbach energy was obtained as 95 meV. The results of the present paper would provide valuable insight to 2D material technology to understand the potential device applications of the TlGaS2.

Formation of Gallium Nanoparticles by Thermal Evaporation Method in an Argon Atmosphere

Formation of Gallium Nanoparticles by Thermal Evaporation Method in an Argon Atmosphere

Tellurium Nanostructures Obtained by Thermal Evaporation Method

Tellurium Nanostructures Obtained by Thermal Evaporation Method

Comparison of optical properties of CdS thin films synthesized by spray pyrolysis and thermal evaporation method

Comparison of optical properties of CdS thin films synthesized by spray pyrolysis and thermal evaporation method

Synthesis, Characterization, and Antibacterial Activity of Ag–TiO2–Fe Composite Thin Films

Ag–TiO2–Fe composite thin films with different Ag contents are deposited onto a glass substrate by a thermal evaporation method. TiO2, TiO2–Fe, and Ag–TiO2–Fe thin films are characterized by X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV–vis–NIR spectroscopy, and photoluminescence (PL) to study the relation between their structural, morphological, optical, and luminescent properties with their antibacterial activities. XRD and Raman measurements show the formation of the anatase phase with increasing silver content in Ag–TiO2–Fe composite thin films. SEM images show the presence of silver in the metallic form. Optical measurements display a redshift in the optical absorption edge of TiO2–Fe and Ag–TiO2–Fe composite films with a decrease in the energy bandgap compared to pure TiO2. The antibacterial activity of the films against Escherichia coli is investigated both in the dark and under UV light. It is found that Ag plays a major role on the antibacterial efficiency in the dark. Ag–TiO2–Fe composite thin films exhibit a synergistic antibacterial effect under UV light, resulting an excellent antibacterial coating.

Thermally grown indium (In) thin-film for creating ohmic contact and In-bumps for HgCdTe-based IR detectors

Indium (In) thin films over the mercury cadmium telluride (HgCdTe) substrate were grown employing the thermal evaporation method. Various techniques, namely X-ray diffraction, scanning electron microscopy (SEM), energy dispersive X-ray, atomic force microscopy, and current-voltage (I-V) were employed to investigate the developed films. The tetragonal phase (bcc lattice) of the In films was recognized with a maximum growth along with preferred orientation (101). The desired elemental composition and purity of In were realized. Uniform, dense and non-porous In film with low roughness was achieved. The films with desired features (film height, particle size, and minimum grain boundaries) were realized by SEM analysis. The optimized indium films were further used to fabricate In bumps/n-HgCdTe structure and Transfer length method (TLM) structure (with a configuration of In/n/p-HgCdTe). The thermally grown indium-bumps having the microstructural properties (desired film height & particle size, bumps with uniform dia and height, etc.) were established. In metal contacts exhibited ohmic behavior with a specific contact resistance ρc = 5.96 × 10−4 Ω∙cm2. Thus, In could be applied as the most appropriate material for creating the ohmic n-contact and indium-bumps in HgCdTe-based IR detectors.

N-Si/p-Sb2Se3 structure based simple solar cell device

Sb2Se3 is a p-type semiconductor that has been widely used as an absorber layer in thin film solar cells. For this study, Sb2Se3 was made using the solid-state reaction route, and thin films were deposited by the thermal evaporation method at room temperature and annealed at various temperatures. The crystallinity of Sb2Se3 thin films improved after annealing. The material and thin films were characterized by XRD, Raman, SEM, and UV–Vis spectroscopy to study their structural and optical properties. A simple device structure that can be made using a thermal evaporation system is proposed. We have accomplished simulation work based on Sb2Se3/c-Si hetero-junction photovoltaic cells using SCAPS-1D. In the simulation, experimental data of Sb2Se3, including its band gap, thickness, and absorption coefficient, have been introduced. The simulation is used to extract the parameters, such as back contact work function, electron affinity, and the thickness of the p-Sb2Se3 layer and n-Si layer, which is also varied and optimized to improve the device's performance. p-Sb2Se3 with a band gap of 1.64 eV showed a maximum efficiency of 12.75% at the optimized conditions. As n-Si is commercially available, this simple device structure can have multiple local applications. It can be considered a reliable method for predicting photovoltaic performance for future studies, such as improving the efficiency of Sb2Se3 solar cells or trying out a new tandem solar cell structure using Sb2Se3.

Investigating the potential of AgZnO thin film composites for waste heat recovery using Seebeck data

In this paper, we have demonstrated the thermoelectric properties of Silver Zinc oxide (AgZnO) composite grown by thermal evaporation method. A mixture of Silver and Zinc powders with 1:4 ratio was evaporated on silicon substrate using a vacuum tube furnace. The grown composites were subjected to post growth annealing process at various temperatures ranging from 500 to 800 °C in a programmable muffle furnace. XRD data proved that the crystallinity of the annealed samples was improved because more and more oxygen atoms were able to fill the oxygen vacancy type defects in the host crystal of AgZnO. The observed structural behavior was also verified by Raman spectroscopy measurements. Seebeck measurements revealed a remarkable enhancement in the values of Seebeck coefficient (303–711 μV/°C) and electrical conductivity (17–176 S/cm) with annealing temperature. The high annealing temperature may cause an enhancement in the mobility of Ag atoms which resulted in the increase of Seebeck coefficient and electrical conductivity simultaneously.

High-performance self-powered UV photodetector based on CuI/CsCu2I3/GaN heterojunction

Self-powered ultraviolet (UV) photodetectors have far-reaching applications in the nanoelectronics. In this work, nontoxic copper halide perovskite CsCu2I3 thin films were grown by vacuum thermal evaporation method on n-GaN substrates. The p-CuI/CsCu2I3/n-GaN heterojunction photodetectors exhibit obvious sensitivity and self-powered characteristics in the ultraviolet (∼365 nm) narrowband. The device exhibits excellent reproducibility and a high on/off ratio of 97,886 under zero bias voltage. Furthermore, under UV illumination, the responsivity, specific detectivity, and external quantum efficiency reach 71.7 mA/W, 3.3 × 1012 Jones, and 26.1% at 0 V bias, respectively. The result provides a new strategy to design a highly integrated monolithic device for self-powered detection

High-Performance Surface-Enhanced Raman Scattering Substrates Based on the ZnO/Ag Core-Satellite Nanostructures.

Recently, hierarchical hybrid structures based on the combination of semiconductor micro/nanostructures and noble metal nanoparticles have become a hot research topic in the area of surface-enhanced Raman scattering (SERS). In this work, two core-satellite nanostructures of metal oxide/metal nanoparticles were successfully introduced into SERS substrates, assembling monodispersed small silver nanoparticles (Ag NPs) on large polydispersed ZnO nanospheres (p-ZnO NSs) or monodispersed ZnO nanospheres (m-ZnO NSs) core. The p-ZnO NSs and m-ZnO NSs were synthesized by the pyrolysis method without any template. The Ag NPs were prepared by the thermal evaporation method without any annealing process. An ultralow limit of detection (LOD) of 1 × 10−13 M was achieved in the two core-satellite nanostructures with Rhodamine 6G (R6G) as the probe molecule. Compared with the silicon (Si)/Ag NPs substrate, the two core-satellite nanostructures of Si/p-ZnO NSs/Ag NPs and Si/m-ZnO NSs/Ag NPs substrates have higher enhancement factors (EF) of 2.6 × 108 and 2.5 × 108 for R6G as the probe molecule due to the enhanced electromagnetic field. The two core-satellite nanostructures have great application potential in the low-cost massive production of large-area SERS substrates due to their excellent SERS effect and simple preparation process without any template.

Room temperature NO2 sensing performance of a-C-decorated TeO2 nanowires

TeO2 is a semiconducting metal oxide that is not popular for sensing studies due to its poor sensing performance in its pristine form. To enhance its sensing performance, we deposited amorphous carbon (a-C) on its surface. We first synthesized TeO2 nanowires using a thermal evaporation method, and then we deposited an a-C layer on them by a simple procedure using a flame carbon vapor deposition technique. We showed that the a-C-decorated sensor had a lower optimized sensing temperature (26 °C) relative to the pristine TeO2 sensor (50 °C) and presented a higher sensitivity to NO2 gas. The maximum responses to NO2 (10 ppm) were 1.918 and 1.468 for a-C-decorated and pristine TeO2 nanowires, respectively. Furthermore, the a-C-decorated sensor indicated outstanding selectivity toward NO2. The high performance of a-C-decorated sensor was results of its higher surface area created by the bumpy carbon layer on the surface of TeO2 nanowires as well as the electronic sensitization due to the a-C layer. We also confirmed NO2 sensing behaviors of bare and a-C-decorated TeO2 nanowires using density functional theory (DFT) calculations, where calculated binding energies between NO2 and the sensing layer were stronger for NO2 and a-C-decorated TeO2 nanowire gas sensor relative to pristine gas sensors. The present approach for enhancing the sensing of TeO2 nanowires can be extended to other sensor systems as a simple, inexpensive strategy to improve sensor performance.

Salts of Lanthanide(III) Hexafluoroacetylacetonates [Ln = Sm(III), Eu(III) and Tb(III)] with Dipyridylammonium cations: Synthesis, characterization, photophysical properties and OLED fabrication

A series of tetrakis lanthanide complexes with the general formula [Ln(hfaa)4]-(DpaH)+ [Ln = (Sm-1), (Eu-1) and (Tb-1)], hfaa = hexafluroacetylacetonate and Dpa −2,2′-dipyridylamine] has been synthesized by the reaction of LnCl3, hfaa and Dpa in the presence of ammonia solution (25%). The complexes have been characterized by analytical and spectroscopic methods. The solution molecular structure of the complexes was elucidated by one- and two-dimensional NMR spectroscopy which shows that the DpaH+ cation retains a close interaction with the lanthanide anion in solution. The crystal structure of Eu-1, determined by single crystal X-ray diffraction, confirms this intermolecular interaction in the solid-state through a N–H⋯O hydrogen bond of 2.187 Å. In the [Eu(hfaa)4]- anion the EuO8 coordination polyhedron has a distorted triangular dodecahedron geometry with approximate D2d-symmetry around the metal centre. Photophysical, thermal, and electroluminescent properties of the complexes have been investigated. The Sm-1 and Eu-1 complexes displayed efficient typical red emission with a sizeable photoluminescence quantum yield (PLQY) while Tb-1 displayed near-white light emission. The complexes have been used as dopants to fabricate single- and double-emitting layer (EML) OLEDs through the thermal evaporation method. At the optimum doping concentration, double-EML Eu-1 based device displayed orange electroluminescence (EL) with a brightness (B) of 417 cd/m2 and very low Vturn-on = 3.4 V. Interestingly, the Sm-1 based single-EML device exhibited pure red emission with the Commission internationale de l'éclairage [(CIE)x,y = 0.613, 0.321], which is rare. The Sm-1 based device performance [B = 145 cd/m2, current efficiency (ηc) = 0.35 cd/A, power efficiency (ηp) = 0.15 lm/W with an external quantum efficiency (EQE) = 0.3% and Vturn-on = 7.1 V] surpassed that of the only reported Sm-based single red-OLED (R-OLED).

Fully Vacuum-Free Fabrication of Bi-Directional Polymer Light-Emitting Diodes Based on a Hybrid Lamination Top Electrode

This study investigates a hybrid lamination electrode based on a silver nanowire and a conductive polymer for the top electrode of bi-directional polymer light-emitting diodes (PLEDs). Through a vacuum-free hot-press lamination step, the proposed hybrid electrode employed a complete and concrete electrical contact with the underlying emissive polymer layer. In addition, by inserting a hole injecting poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) layer to increase the level of work function, the bi-directional PLED device with a laminated top electrode showed a more competitive device performance such as an operating voltage, a current efficiency, and a total external quantum efficiency compared to the counterpart device with a multilayered electrode of MoO3/Ag/MoO3 by the vacuum thermal evaporation method. An analysis carried out on the angular characteristics of bi-directional PLEDs including the variation of color coordinates and change in luminance values according to emission angles confirmed that the hybrid lamination electrode provided a more uniform angular distribution regardless of the direction of emission without any optical micro-cavity effect. Detailed optical and electrical analyses were also performed to evaluate the compatibility of the hybrid lamination electrode for the low-cost fabrication of efficient PLEDs.

Temperature-Dependent n-p-n Switching and Highly Selective Room-Temperature n-SnSe2/p-SnO/n-SnSe Heterojunction-Based NO2 Gas Sensor.

Many toxic gases are mixed into the atmosphere because of increased air pollution. An efficient gas sensor is required to detect these poisonous gases with its ultrasensitive ability. We employed the thermal evaporation method to deposit an n-SnSe2/p-SnO/n-SnSe heterojunction and observed a temperature-dependent n-p-n switching NO2 gas sensor with high selectivity working at room temperature (RT). The structural and morphological properties of the material were studied using the characterization techniques such as XRD, SEM, Raman spectroscopy, XPS, and HRTEM, respectively. At RT, the device response was 256% for 5 ppm NO2. The response/recovery times were 34 s/272 s, respectively. The calculated limit of detection (LOD) was ∼115 ppb with a 38% response. The device response was better with NO2 gas than with SO2, NO, H2S, CO, H2, and NH3. The mechanism of temperature-dependent n-p-n switching, fast response, recovery, and selective detection of NO2 at RT has been discussed on the basis of physisorption and charge transfer. Thus, this work will add a new dimension to 2D materials as selective gas detectors at room temperature.

Analysis of temperature dependent current-voltage characteristics of Sn/p-GaTe/In Schottky diode

In present study, Sn/p-GaTe/In Schottky diode is fabricated using thermal evaporation method. The current–voltage (I–V) measurements of Sn/p-GaTe/In diode are carried out in the temperature range of 40–300 K with the steps of 10 K under dark conditions. While the ideality factor takes values between 1.03 and 1.24 at 300–180 K temperature range, it has values between 1.30 and 5.18 at 170–40 K temperature range. It is observed that the values of ideality factor and series resistance (RS) decrease with increasing temperature. The barrier height increases due to barrier inhomogeneity with increasing temperature since the current prefers to flow through the lowest barrier height with decreasing temperature. The temperature dependence of the inhomogeneous barrier height exhibites a double-Gaussian distribution. The mean barrier height and standard deviation values calculated from the barrier height versus 1/2 kT curve are 0.68 eV and 88.9 meV for the distribution-1 (D1) and 0.36 eV and 42.2 meV for the distribution-2 (D2), respectively. The Richardson constant (A*) value is calculated to be 41.7 for D1 and 55.0 A/K2cm2 for D2 from modified Richardson plot, respectively. These values are very close to the theoretical value of 55.8 A/K2cm2 for the p-GaTe semiconductor.

Experimental investigation of frosting behavior on superhydrophobic copper surface prepared by thermal evaporation Method

An experimental study is proposed to analyze the frosting behavior of ice on a superhydrophobic surface. Ice accumulation can result in performance problems and safety concerns for transmission lines, marine and offshore structures, refrigeration, cryogenics, wind turbines, and heat-exchangers. Wetting properties are important for ice formation on surfaces from the liquid phase, where the water repellency of the surfaces could enhance their anti-icing effect. Such surfaces will be prepared by using a nanotextured coating. A thermal evaporation system will be proposed for nanocoating on a copper surface. The prepared surface produces a contact angle of 162° ± 2°. The Low Bond Asymmetric Drop Shape analysis is used to measure the contact angle using imageJ software. The heat-transfer performance of an evaporator is affected by frost formation. In this work, the heat-transfer coefficient of the surface will be estimated in the defrosting process. The effect of hydrophobicity and superhydrophobicity of surfaces, surface chemistry, morphology, and roughness scale will be studied on the defrosting process. In particular, wetting characteristics of the superhydrophobic surfaces revealed defrosting performance. The experiments will be performed in controlled environmental conditions. The anti-icing properties of superhydrophobic surfaces with different topography but similar chemistry are studied.