Vacuum Thermal Evaporation Technique Research Articles

Comprehensive study of nanostructured Bi2Te3 thermoelectric materials - insights from synchrotron radiation XRD, XAFS, and XRF techniques.

In this contribution, a comprehensive study of nanostructured Bi2Te3 (BT) thermoelectric material was performed using a combination of synchrotron radiation-based techniques such as XAFS, and XRF, along with some other laboratory techniques such as XRD, XPS, FESEM, and HRTEM. This study aims to track the change in morphological, compositional, average and local/electronic structures of Bi2Te3 of two different phases; nanostructure (thin film) and nanopowders (NPs). Bi2Te3 nanomaterial was fabricated as pellets using zone melting process in a one step process, while Bi2Te3 thin film was deposited on sodalime glass substrate using a vacuum thermal evaporation technique. Synchrotron radiation-based Bi LIII-edge fluorescence-mode X-ray absorption fine structure (XAFS) technique was performed to probe locally the electronic and fine structures of BT thin film around the Bi atom, while transmission-mode XAFS was used for BT NPs distributed in the PVP matrix. The structural features of the collected Bi LIII XANES spectra of thin film and powder samples of BT are compared with the simulated XANES spectrum of BT calculated using FDMNES code at 5 Å cluster size. Combining different off-line structural characterization techniques (XRD, FESEM, XPS, and HRTEM), along with those of synchrotron radiation-based techniques (XAFS and XRF) is necessary for complementary and supported average crystal, chemical, morphological and local electronic structural analyses for unveiling the variation between Bi2Te3 in the nanostructure/thin film and nanopowder morphology, and then connecting between the structural features and functions of BT in two different morphologies. After that, we measured the Seebeck coefficient and the power factor values for both the BT nanopowder and thin film.

A self-powered p-CuBr/n-Si heterojunction photodetector based on vacuum thermally evaporated high-quality CuBr films

Violet heterojunction photodetectors based on p-CuBr/n-Si are prepared by the vacuum thermal evaporation technique. The photodetectors have a sensitive violet response with self-powered characteristics and excellent imaging capability.

Studying the Structural, Optical and Electrical Properties of ZnO: SnO2 Thin Films as an Application of a Gas Sensor Using Vacuum Thermal Evaporation Technique

In this work, thermal evaporation in vacuum technique was used to prepare the ZnO thin films as pure and doped with SnO2 NPs on glass substrates. The XRD pattern showed the hexagonal structure of ZnO with (002) preferred orientation. The EDX technique was used to investigate the contents of the film elements prepared which consisted of Zn, Sn and O. The concentration of Zn, O and Sn in the nanostructure films was different for all doping ratios. Thickness and morphology surface of the films were calculated from cross section of the surface films (~144 nm) using scanning electron microscopy images. The FE-SEM images confirmed the ZnO nanostructures and modifications of the morphology when adding SnO2. The pure film deposited was dense and structured; while ZnO: SnO2 (1,5 % wt) was a nanostructure. The optical band gap and Transmittance increased with the increase in the doping ratio of SnO2, while the absorption spectrum decreased for the prepared thin films. The prepared films showed different responses to the gas sensing at two different operating temperatures (100, 200 ºC) and the doping ratio increased the sensor value of the gas at an optimum temperature of (200 ºC).

Optical Properties of CuCdS Thin Film Prepared by Vacuum Thermal Evaporation Technique

This study reports on the synthesis and characterizations of copper cadmium sulfide (CuCdS) thin films prepared using the vacuum thermal evaporation technique with copper sulfide and CdS as precursors in a 1:1 molar ratio. The structural properties of the thin films were analyzed using X-ray diffraction (XRD) which revealed that the main composition of the thin film was CdS with the preferred orientation of the (101) plane. The optical properties were examined using UV–Vis spectrophotometry. The photosensitivity of the films was determined using I–V measurements performed with a two-probe technique. The prepared CuCdS thin films have high optical transmittance of 92%.

Effects of Pb nanosheets substrates on the optical and electrical properties CrSe thin films

Herein the effects of lead nanosheets substrates on the optical and electrical properties of chromium selenide thin films were studied. Chromium selenide thin films were grown by vacuum thermal evaporation technique onto glass and 100 nm thick lead nanosheets substrates. The effects of Pb nanosheets on the structural, morphological, compositional, optical and electrical properties was explored. While films grown onto glass substrates showed compositional stoichiometry forming CrSe2 phase those coated onto Pb substrates preferred the growth CrSe phase. Both films were of amorphous structure and exhibited direct and indirect allowed optical transitions. Pb nanosheets enhanced the optical absorption of chromium selenide in the visible and ultraviolet ranges of light. Formation of films onto Pb nanosheets resulted in band gaps and band tails narrowing and decreased the room temperature electrical conductivity () as well. Deep analyses of the variations in the range of 25–340 K showed that the electronic transport is dominated by the thermal excitation and variable range hopping of charge carriers. It was observed that Pb nanosheets increased the average hopping energy and hopping range, decreased the density of localized states near the Fermi level and increased the degree of state disorder. The features of glass/CrSe2 and Pb/CrSe films are promising for using then in optoelectronic technology.

THE STRUCTURAL AND ELECTRICAL PROPERTIES OF NON-STOICHIOMETRIC CADMIUM SELENIDE THIN FILMS

Non-stoichiometric CdxSe100-x (x=10, 20, 30 at. %) alloys were prepared by melt-quenching technique, while thin films of these alloys were prepared by vacuum thermal evaporation technique. The Differential thermal analysis (DTA) results showed that the composition affects the characteristic temperatures, for instance, the glass transition, and peak crystallization temperatures. X-ray diffraction patterns (XRD) of the as-deposited films confirmed its amorphous nature except for films with x=30 at. %. These results were confirmed by scanning electron microscopy (SEM) investigations and correlated to the rigidity percolation threshold of the lattice. Furthermore, XRD patterns indicated that amorphous structures transformed into crystalline structures for annealed thin films at 423 K for 30 minutes. The microstructure parameters (crystal size, microstrain, and dislocation density) of both Se and CdSe phases were calculated for annealed films. The temperature dependence of dark d.c. conductivity of thin films was studied in the temperature range (300-500 K). The electrical measurements results showed two types of conduction mechanisms. Conduction is due to extended state in the temperature range (370-500 K) and variable range hopping in the temperature range (300-370 K). Moreover, in the high temperature range, the results indicate the validity of Meyer-Neldel rule (MNR) in the studied samples.

Effect of copper and silver as a middle layer on the structural, electrical, photocatalytic, and optical properties of ZnS/metal/ZnS films for optoelectronics applications

In this work, we utilized the thermal vacuum evaporation technique to fabricate ZnS single-layer thin films, ZnS/Cu/ZnS (ZCZ), and ZnS/Ag/ZnS (ZAZ) multilayer thin films. The influence of the middle layer of metals like copper and silver on the physical properties of ZnS/metal/ZnS multilayers is investigated. The results of the X-ray investigation demonstrate that the samples are polycrystalline, with a cubic ZnS structure and texture (111) at 2 = 29.1°. The optical investigation using Tauc’s approach yields energy gap values of 3.76 eV, 3.68 eV, and 3.6 eV for ZnS, ZCZ, and ZAZ films, respectively. CO2 gas sensing efficiency of ZnS, ZCZ, and ZAZ films were found to be at different operating temperatures. The optimal temperatures for ZnS, ZCZ, and ZAZ thin films were determined to be 483 K, 693 K, and 693 K, respectively. Under ultraviolet (UV) irradiation, the photocatalytic activity of ZnS, ZCZ, and ZAZ films for the degradation of methylene blue were studied. The results suggest that the metal intermediate layer is significant in improving the photocatalytic capabilities of ZnS films. When compared to ZnS single layer film (degradation efficiency of 15% after 180 min of UV irradiation), ZAZ multilayer film demonstrates the highest photocatalytic activity (degradation efficiency of 50% after 180 min of UV irradiation). The mechanism of the metal middle layer’s improved UV photoactivity is briefly discussed.

Optical and electrical evaluation of a nylon 11-ZnO film incorporation in disodium phthalocyanine heterostructures

Disodium phthalocyanine (Na2Pc) has been considered as promising organic semiconductor for optoelectronic applications, however, Na2Pc-based devices are not being fully studied. To study the Na2Pc as active layer for optoelectronic devices, and also the effect of the incorporation of a nylon 11-ZnO film within the device heterostructure, in this work two heterojunction cells of Ag/Na2Pc + TCNQ/triphenylamine/p-Si/Al and Ag/nylon 11-ZnO/Na2Pc + TCNQ/triphenylamine/p-Si/Al were fabricated by vacuum thermal evaporation technique. The topography of the heterostructures was analyzed by atomic force microscopy. Later, the films that form the heterostructure were optically characterized by Ultraviolet-visible spectroscopy and the optical band gap and the Urbach energy were obtained. The values of the optical gap for the films are between 2.08 and 2.93 eV. The value of Urbach energy is lower for the pristine triphenylamine film, and higher for the film composed of nylon and ZnO. Moreover, the two heterostructures present a strong photoluminescence in the visible region. On other hand, by introducing the nylon 11-ZnO film in the heterostructure shows an important increase of the short circuit current density (Jsc), conductivity and photocurrent values, indicative of a better mobility and more carriers generation. For this heterostructure a mean 79.7% external quantum efficiency and 0.48 mA/cm2 Jsc were obtained. These results indicate that these heterostructures can be used toward organic solar cell applications and remark on the large effect of the nylon 11-ZnO dielectric film addition on their performance.

Annealing temperature effects on monolayer WS2-veiled Ag nanoparticle array for surface catalytic reaction

Plasmonic-WS2 hybrids have attracted widespread interest for plasmon driven catalytic reactions. In this work, a Ag nanoparticles (NPs)/WS2 hybrid was fabricated by utilizing a one-step anodized Al template-assisted vacuum thermal evaporation technique and wet transfer method. To optimize the catalytic performance, the morphological evolution and corresponding changes in the catalytic properties of the Ag NPs/WS2 hybrid at different thermal annealing temperatures were investigated. It was found that the surface-enhanced Raman scattering (SERS) and catalytic activity of the hybrid were optimized by tuning the annealing temperature, with the optimal SERS and catalytic properties observed at 290 °C. These results may open new avenues for improving the efficiency and expanding the research field of plasmon-driven reactions.

Study of the Optical properties for CdS before and after irradiated by CO2 laser for different exposure times

Cadmium sulphide (CdS) thin films were deposited on glass substrates  using thermal vacuum evaporation technique at pressure (10-6) Torr at room temperature  then samples irradiated by CO2 laser of power (1 watt) and wave length (10.6) μm at distance 10 cm from the source during different exposure times (3, 5, 10, 15) sec. The absorbance spectra was recorded using UV-visible spectrophotometer .Optical  properties such as  transmission , reflection ,absorption coefficient (α), optical band gap (Eg), extinction coefficient (K), refractive index (n), and complex  dielectric constants  (er&ei) were evaluated from absorbance spectra. The results shows that the laser irradiation cause  increased in reflectance R, absorption coefficient a, the extinction coefficient K, the refractive index n and the real part and imaginary part of dielectric constant while irradiation cause decrease in the transmittance T and the value of the energy gap Eg.

Effect of Annealing Temperature on the Structure and Optical Properties of CdS:Cu Thin Films Prepard By Thermal Vacuum Evaporation

In this study, we are studying the effect of annealing temperature on
  
 the structure and the optical properties of CdS:Cu thin films which were
 prepared by thermal evaporation technique in vacuum with rate deposition
 (4.1A°/sec) and thickness(=400nm),all these samples have been annealed at
 different annealing temperatures (RT,373,423 and 473 K). The structural
 properties of the films have been studied by using X-ray diffraction. The
 optical measurements indicate that CdS:Cu films have direct optical energy
 gap (E,""), and it decreases from 2.43 eV to 2.37 eV with the increase of
 annealing temperatures (R.T — 473)K. The optical constants refractive
 index (n), extinction coefficient (k),absorption coefficient (a) and dielectric
 constants (€, and €;) were also studied.

Effect of Zn Transition Layer on Properties of Vacuum Deposited Zn-Mg Coating

Zinc coatings have been served as a barrier and a galvanic protection for steel products for over a century. However, with the depletion of zinc resources, it becomes an urgent issue to obtain a new type of zinc coating that uses less zinc and has higher corrosion resistance. In order to develop Zn/ZnMg coatings with better corrosion resistance than traditional galvanized steel and suitable for advanced high strength steel, the vacuum thermal evaporation technique was used to simultaneously deposit Zn/ZnMg coating onto interstitial free steel plates and single-crystal silicon wafers in a high vacuum environment. The microstructure, morphology, adhesion and corrosion resistance behavior of the Zn/ZnMg coating were studied by scratch test, salt spray test and electrochemical method. The results shows that the grain size in the Zn/ZnMg coating tended to increase with the increase of the substrate temperature. After deposited the pure Zn transition layer, the adhesion of the coating has been obviously improved. When the substrate temperature was increased to 200°C, the obtained coating exhibited strong corrosion resistance.

Preparation CdSe thin films by vacuum thermal evaporation and studying the effect of annealing time on structural, electrical and optical properties.

CdSe thin films were deposited on a glass substrate by using vacuum thermal evaporation technique. The deposited films were annealed to 350˚C for (10, 20, 30) minutes respectively. Structural, morphological, optical and electrical properties of the films were studied by using X-ray diffraction (XRD), ultraviolet-visible (UV-Vis) spectroscopy; and Atomic force microscope (AFM). The X-ray diffraction pattern showed that the film has a cubic phase with preferred orientation (111), the grain size was found to be in the range of( 31-46)nm. The UV tests explain that the energy bandgap decrease with increasing of annealing time from 2.43eV to 2.17eV after 20minute annealed.

Opportunities and Challenges for Perovskite Solar Cells Based on Vacuum Thermal Evaporation

AbstractDeveloping an effective scalable fabrication process for perovskite solar cells is urgent to getting perovskite photovoltaic technology market‐ready. Perhaps due to the relatively cost‐effective setup and tunable fabrication processes, the vast majority of research efforts have been dedicated to the development of solution‐based scalable processes. Comparatively, the vacuum thermal evaporation processes have not been studied in‐depth, regardless of their advantages in reproducibility, scalability, extendable applications, safety, and toxicity. Here possible opportunities and challenges are discussed in utilizing the vacuum thermal evaporation technique for mass production of large‐area perovskite solar modules. While this process has technical and economical potential, more research should be warranted.

Optoelectronic performance of [formula omitted]Si/[formula omitted]MgSe heterojunctions as a visible light communication component

Herein magnesium selenide thin films coated onto glass and n−Si substrates are studied and characterized. The films, prepared by the thermal vacuum evaporation technique under a vacuum pressure of 10−5 mbar, are structurally, morphologically, compositionally, optically, and electrically investigated. While films grown onto glass substrates showed the existence of cubic phases of MgSe and MgSe2, films coated onto n−Si substrates contained SiSe2. Replacement of glass substrates by n−Si highly improved the crystallinity of the films. In addition, the optical analyses on the films grown onto n−Si substrates indicated the formation of n−Si/p−MgSe heterojunctions with valence and conduction band offsets of 0.95 eV and 0.40 eV, respectively. MgSe films are coated onto Si substrates and contacted with Ag contacts performed as photosensors suitable for vehicle visible light communications. The asymmetry (rectification ratios), the current responsivity, the noise equivalent power factor, and the detectivity of the devices reached 517, 0.73 A/W, 5.93×10−12W/Hz1/2 and 5.8×1010 Jones, respectively, at 4.3 V.

Characterizations of MoS2 nanosphere fabricated using vacuum thermal evaporation at steady and rapid heating

Two-dimensional MoS2 has been speculated to be the best material to replace graphene due to its peculiar structural-electronic properties. The MoS2 with size smaller than its exciton Bohr radius (ca. 1.61 nm) would favor multi exciton generation upon absorption of photon with sufficient energy, Ephoton ≫ Egap (1.89 eV); which would increase the efficiency of an excitonic solar cell greater than 60%. Despite promising properties of the MoS2, however an excitonic solar cell with high efficiency is yet to be exhibited. In this work, the MoS2 thin films were fabricated using vacuum thermal evaporation technique and characterized. Four objectives have been outlined i.e., to study the effect of heating rate (steady, and rapid) on the (i) morphology, (ii) size, (iii) optoelectronic and (iv) crystal properties of the fabricated thin films. The MoS2 precursor was heated at the rate 2.027 A/s (steady), and 18.75 A/s (rapid), 1.5 × 10−3 Torr, 1.48 A, and 4.58 V. The deposited films later were characterized using Field Emission Scanning Electron Microscope with Energy Dispersive X-ray attachment, photoluminescence spectrometer, UV–vis-NIR spectrometer, and X-ray Diffractometer. The fabricated thin films exhibited nanosphere morphology with different size distributions i.e., wide (steady heating), and narrow (rapid heating). Two hypotheses were made based on the optoelectronic properties i.e., the basic building block of the MoS2 thin film fabricated under steady heating is (i) experiencing stronger quantum confinement effect, and (ii) dominated by nanocrystals which are smaller than that of the rapid heating. Similar energy loss could be expected in both MoS2 thin films i.e., ca. 0.15 to 0.17 eV, indicating the existence of shallow trap states. The MoS2 thin films were dominated by (002), (004), and (106) crystal planes. Therefore, the vacuum thermal evaporation technique would offer materials with unique size, crystal arrangement, and optoelectronic properties upon change of heating rate.

The Impedance Analysis of a Viscoelastic Petalous Structured Stearic Acid Functional Layer Deposited on a QCM.

A functional layer is crucial in a QCM sensor, to immobilize target molecules. The microstructure of the layer determines the sensitivity of the sensor. On the other hand, the microstructure also affects the loading of the sensor. In this study, impedance analysis was used to investigate the relationship between the microstructure and the viscoelastic properties of a petalous stearic acid (SA) functional layer. The SA layer was deposited using a vacuum thermal evaporation technique. Different petalous pillar structures in the elastic layer were generated by varying the deposition time. Analysis showed that the growth of the embedded pillar structures dramatically reduced the conductance and increased the bandwidth. The energy dissipation during the vibration could be related to the interaction between the pillars and the elastic matrix.

Optical, Electrical Properties and Surface Morphology of Thermal Evaporated Zinc Telluride (ZnTe) Thin Films for Photovoltaic Applications

ZnTe bilayer thin films were deposited onto soda-lime glass by a thermal vacuum evaporation technique using the NANO 36 thermal evaporator under a vacuum pressure of 2.9 x 10-5 torr. The optical characteristics of the film were measured using an AVANTEX UV spectrophotometer in the wavelength range from 239.534 nm to 999.495 nm. Also, the electrical characteristics of the thin films were investigated using KEITHLEY four-point probe techniques. The investigation of the optical properties of the thin films as-deposited and annealed at different temperatures showed high transmission in the NIR region with good absorption in the visible and UV regions. The extrapolated band gap energies were 2.60 eV and 3.20 eV for annealed and as-deposited samples, respectively. electrical resistivity decreased as the annealing temperature increases. The images of the film as-deposited and on annealing have a uniform distribution on the glass slides.

Elucidation the effectiveness of acridine orange as light-harvesting layer for photosensing applications: Structural, spectroscopic and electrical investigations

In this research, acridine orange, AO, bio-photosensitive thin films are prepared using vacuum thermal evaporation technique for optoelectronic applications. First, the crystal structure of the deposited films compared to powder is investigated using the XRD technique. Next, the surface morphology of the deposited AO thin film is characterized using the FESEM technique giving rise to a uniform, homogeneous, and granular polycrystalline film. The amplitude and spatial roughness parameters of the film are estimated. Furthermore, the optical properties of the deposited AO thin film are spectrophotometrically characterized in the range from UV to NIR. The recorded absorbance, transmittance, and reflectance showed high UV and visible absorption characteristics with a direct energy gap of ∼2.238 eV. The optical constants, including refractive index and extinction coefficient, are found, and the dispersion behavior is analyzed using the one-oscillator model for estimating the oscillator and dispersion energies. The dielectric function and dielectric relaxation time of AO thin film are interpreted in detail. In addition, an organic/inorganic heterogeneous junction based on Ag/AO/p-Si/Al is fabricated and electrically evaluated using the current-voltage relation. The fabricated heterojunction shows a rectification behavior of ideality factor, barrier height, and rectification ratio ∼2.09, 0.707 eV, and 176, respectively. The charges dynamics mechanism in terms of band diagram and the density of interface states profile are analyzed. Eventually, the photoresponse of the engineered heterojunction is evaluated under the illumination of intensities that varies from 20 mW/cm2 to 100 mW/cm2. The fabricated photosensor showed a high stable performance with responsivity, specific detectivity, linear dynamic range, and ON/OFF ratio of about 68.4 mA/W, 1.11 × 1010 Jones, 69.3 dB, and 108.4, respectively. The photoresponse performance of the present device is considered more efficient and stable than many other organic/inorganic photosensors.

The synthesis and the effect of Cu on optoelectronic qualities of β-In2S3 as a window layer for CIGS thin film solar cells

In this paper, the vacuum thermal evaporation technique was used to investigate β-In2S3 doped with copper (Cu) as window layer thin film for solar cells. The amount of the Cu source was used to be 0–8 % atomic weight compared with In2S3 source. For various Cu doping levels, the characteristics of the thin films were studied utilizing structural, morphological, and optical characterization techniques, as well as dielectric testing. The research included X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Raman spectroscopy, and energy-dispersive X-ray spectroscopy (EDS), Infrared analysis (FTIR), XPS, Ellipsometry and UV-NIR spectroscopy. The measurements demonstrated that the real and imaginary isolation constants were over the wavelength range and successfully estimated the Urbach energy (Eu) and band gap energy. The Urbach energy varied from 1.88 to 2.21 eV. The band gap energy decreases from 2.10 to 1.93 eV for direct transitions. Moreover, based on the measured optical constants (n and k), employing the Wemple-Didomenico model helped uncover the Cauchy coefficients’, the refractive index, the dispersion and the oscillation energies. Therefore, the results presented in this paper show that the use of Cu-In2S3 for perovskite cells offers a high-efficiency alternative in the solar energy field.