Vacuum Evaporation Method Research Articles

Stable resistive switching characteristics from highly ordered Cu/TiO2/Ti nanopore array membrane memristors

This article focuses on the fabrication of highly ordered Cu/TiO2/Ti nanopore array membrane memristors by using two-step anodization and vacuumevaporation methods and exploration the effects of oxidation parameters such as anodization voltage and electrolyte temperature on device performance. The performance test results show that this novel ordered TiO2 nanopore array membrane structure can effectivelyregulate the distribution of the local electric fieldthatrestrictsthe growth path of the conductive filaments (CFs), which thereby greatly improves the stability and yield of the devices. In addition, it is found that through adjusting the process parameters, such as anodization voltage and electrolyte temperature, the lateral (pore diameter) and longitudinal (pore depth) dimensions of the TiO2 nanopores can be regulated for further optimizing device performance. These exciting results demonstrate that the highly ordered TiO2 nanopore array structure can offer atangible effectiveness and controllability for improving the stability of memristors, suggesting the strategy seems to have an important scientific significance and application value.

The electric memory properties of azo-chalcone derivatives based on different film forming processes

The azo chalcone derivative 3-(4-(dimethylamino)phenyl)diazenyl)phenyl)-1- (2-nitrophenyl)prop-2-en-1-one (AZOC-2N) was designed and synthesized. The active layer was prepared by solution spin coating and vacuum evaporation methods, respectively. The accumulation of molecular film was studied by AFM and crystalline structure. It was found that the device had a non-volatile binary write once read many (WORM) memory performance and device in which form by vacuum evaporation with a higher threshold voltage -2.1 V. Finally, the electrical memory performance of the device is analysed by theoretical calculation simulation.

Magnetic and magnetocaloric properties in amorphous CexNi1-x thin films (0.12 ≤ x ≤ 0.43)

We investigate the influence of Ce substitution on the magnetic and magnetocaloric properties in CexNi1-x amorphous alloys with x = 0.12, 0.34 and 0.43, synthesized using ultrahigh vacuum evaporation method. The Ni magnetic moment decreases from 0.033µB, 0.0087µB to 0.002µB when Ce content increases from 0.12, 0.34 to 0.43. The same trend was found for Curie temperature TC which decreases from 40 K, 12 K to 2 K. The magnetic behavior and the magnetic transition were analyzed using Landau theory around the transition temperature. The magnetic transition nature is of a second order from ferromagnetic to paramagnetic state. Good agreement was found between the magnetic entropy (−ΔSM) values estimated by Landau theory and those obtained using classical Maxwell relation.

Dielectric, magnetic, and microwave absorbing properties of Ag-plated terapod-like ZnO whiskers

Thin thickness, lightweight, wideband and high absorption intensity are highly desirable properties for the next-generation electromagnetic wave absorbing materials. This study investigates the dielectric, magnetic, and microwave absorbing properties of terapod-like ZnO whisker (ZnOW) modified by Ag nanocrystals (Ag-ZnOW), synthesized by vacuum evaporation method. The complex permittivity and permeability were measured at a microwave frequency range of 2–18 GHz. Ag nanocrystals plated on the surface of whiskers enhance the magnetic loss of ZnOW. The Ag-ZnOW possesses much broader bandwith of absorbing peak than that of unplated ZnOW. The maximum reflectivity (R) is about −30.27 dB at 11.40 GHz and the corresponding bandwidth below −10 dB is more than 5.25 GHz with a matching thickness of 3.0 mm. The calculated results show that the peak of R shifts to lower frequency region with the increase of thickness, and the Ag-ZnOW is an excellent candidate for designing lightweight and multipurpose microwave absorbers.

Ammonia gas sensing response of gamma-irradiated CdTe thin films

In this work, cadmium telluride (CdTe) thin films of thickness 250 nm are deposited on the glass substrate using the thermal vacuum evaporation (TVE) method. The as-deposited CdTe thin films are then exposed to three different doses of gamma rays (50, 100 and 150 kGy) from 60Co source at Inter University Accelerator Centre, New Delhi, India. The structural, morphological, electrical and gas sensing properties of as-prepared and gamma-irradiated thin films are investigated using grazing incidence X-ray diffraction (G-XRD), Field emission scanning electron microscopy (FESEM) and two-probes set up connected with current-voltage (I–V) source meter, respectively. The assessment of adsorption and desorption rate of pristine and gamma-irradiated films is studied using Brunauer –Emmett-Teller (BET) analysis. After irradiation, the XRD pattern indicates the polycrystalline nature of thin films along with the retention of cubic structure with a minor decrease in the crystallite size at the highest gamma dose. From FESEM, relevant changes in the surface morphology of thermally deposited CdTe thin films have been observed after irradiation. Moreover, the films after irradiation were found to be highly conductive up to the dose of 100 kGy as depicted from electrical studies. The gamma irradiated films are further proposed for gas sensing applications. For the highest concentration of ammonia (36.02 ppm), the maximum sensitivity of the as-deposited film is found to be (14.59%) which is higher than the sensitivity at a maximum gamma dose of 150 kGy (10.28%) for the same concentration of gas which shows that process of gamma irradiation deteriorates the sensing performance of CdTe thin films.

Unique phonon modes of a CH3NH3PbBr3 hybrid perovskite film without the influence of defect structures: an attempt toward a novel THz-based application

The exploration of new physical properties for various THz-based applications, such as THz-wave sensing, modulation, and imaging devices, is a key challenge in the research on organic–inorganic hybrid perovskite materials. These THz-based applications require satisfactory, sensitive, and stable absorption properties with values between 0.5 and 3 THz. To achieve these properties, candidate materials should possess a purified structure that induces regular and fixed phonon modes without any defects or impurities. CH3NH3PbBr3, an organic–inorganic hybrid perovskite thin film produced by a sequential vacuum evaporation method on a flexible PET substrate, was investigated in this study. Although the thin film contains only molecular defects related to CH3NH2 incorporated into the perovskite structure, our THz-wave absorption measurement and first-principles simulation confirmed that these molecular defects do not influence the three phonon modes originating from the transverse vibration (0.8 THz), the longitudinal optical vibrations (1.4 THz) of the Pb–Br–Pb bonds, and the optical Br vibration (2.0 THz). After spin-casting an ultrathin PTAA polymer protective layer (5 nm) on the hybrid perovskite thin film, it was additionally observed that there was no significant effect on the phonon modes. Thus, this novel flexible organic–inorganic hybrid perovskite material is a potential candidate for THz-based applications.

Stable Luminescent Radicals and Radical-Based LEDs with Doublet Emission

Radical-based light-emitting diodes are an innovative type of organic light-emitting diodes (OLEDs), which adopt luminescent radicals as emitters, aiming at improving the external quantum efficienc...

Effect of Rapid Thermal Annealing on Thermal Evaporated CdSe Thin Film for Solar Cell Application

Cadmium Selenide (CdSe) thin films have been deposited on a cleaned glass substrate by thermal vacuum evaporation method under the pressure of 10-5 torr. These CdSe thin films were also kept into a quart glass tube for rapid thermal annealing at 60 and 120 second using a 500 W halogen lamp for crystalline the structure. These thin films were characterized for structural, optical and thermo-electrical properties. The optical studies have been done using UV-VIS-NIR, shows that the transition of the deposited film is found to be a direct band gap of 1.74, 1.70 and 1.67 eV for asdeposited, 60 sec and 120 sec annealed thin films respectively. It was also found that absorbance has increased and transmission decreased with increasing annealing time, the change in the extinction coefficient with energy (hν) has been also measured. The Thermoelectric power (TEP) studies confirm the n-type nature of CdSe thin films but as well as annealing time increased the hole concentration increased resultant n-nature of CdSe thin film changing toward p-type nature, the Seebeck coefficient for different annealing time at as-deposited (RT), 60 seconds and 120 seconds have observed 549, 949 and 1031 μV/K respectively. The SEM result shows that with increasing annealing time the grain size and roughness of surface are increased. X-ray diffraction (XRD) studies indicate that the film is like a cubic crystal structure with average crystalline size (D) was measured using Scherrer formula and it is 16.44 nm.

Structural and optical properties of lead iodide nanostructure synthesized by vacuum evaporation method

Structural and optical properties were studied as a function of films thickness for thermally evaporation PbI2 films. X-ray diffraction analysis confirmed that PbI2 films are polycrystalline having hexagonal structure. The optical absorption data indicate an allowed direct transmission with optical energy gap varies continuously from (2.15eV - 2.33 eV). The energy gap shows thickness dependence, which can be explained qualitatively by a thickness dependence of grain size through the decrease of the grain boundary barrier height with grain size. The low fluctuation in energy gap indicates that the grain size is quite small, which is finding in agreement with AFM results.

Fermi-Level Pinning Mechanism in MoS2 Field-Effect Transistors Developed by Thermionic Emission Theory

Molybdenum disulfide (MoS2) field-effect transistors (FETs) with four different metallic electrodes (Au,Ag,Al,Cu) of drain-source were fabricated by mechanical exfoliation and vacuum evaporation methods. The mobilities of the devices were (Au) 21.01, (Ag) 23.15, (Al) 5.35 and (Cu) 40.52 cm2/Vs, respectively. Unpredictably, the on-state currents of four devices were of the same order of magnitude with no obvious difference. For clarifying this phenomenon, we calculated the Schottky barrier height (SBH) of the four metal–semiconductor contacts by thermionic emission theory and confirmed the existence of Fermi-level pinning (FLP). We suppose the FLP may be caused by surface states of the semiconductor produced from crystal defects.

Structural and optical properties of lead iodide nanostructure synthesized by vacuum evaporation method

Structural and optical properties were studied as a function of films thickness for thermally evaporation PbI2 films. X-ray diffraction analysis confirmed that PbI2 films are polycrystalline having hexagonal structure. The optical absorption data indicate an allowed direct transmission with optical energy gap varies continuously from (2.15eV - 2.33 eV). The energy gap shows thickness dependence, which can be explained qualitatively by a thickness dependence of grain size through the decrease of the grain boundary barrier height with grain size. The low fluctuation in energy gap indicates that the grain size is quite small, which is finding in agreement with AFM results.

Strong Linear Correlation between CH3NH2 Molecular Defect and THz-Wave Absorption in CH3NH3PbI3 Hybrid Perovskite Thin Film.

To control the density of a CH3NH2 molecular defect, which strongly contributed to a significant THz-wave absorption property in the CH3NH3PbI3 hybrid perovskite thin film formed by the sequential vacuum evaporation method, we performed post-annealing processes with various temperatures and times. In the thin film after post-annealing at 110 °C for 45 min, the density of the CH3NH2 molecular defect was minimized, and CH3NH3I and PbI2 disappeared in the thin film after the post-annealing process at 150 °C for 30 min. However, the density of the CH3NH2 molecular defect increased. Moreover, the THz-wave absorption property for each thin film was obtained using a THz time-domain spectroscopy to understand the correlation between the density of a molecular defect and the THz-wave oscillation strength at 1.6 THz, which originated in the molecular defect-incorporated hybrid perovskite structure. There is a strong linear correlation between the oscillator strength of a significant THz-wave absorption at 1.6 THz and the CH3NH2 molecular defect density.

Effect of Thickness on Structural, Morphological, and Optical Properties of Copper (Cu) Doped Zinc Selenide (ZnSe) Thin Films by Vacuum Evaporation Method

Effect of thickness on structural, optical and morphological properties of 2% copper (Cu) doped zinc selenide (ZnSe) thin films, grown onto chemically and ultrasonically cleaned glass substrate by thermal evaporation method in high vacuum (~10-6 Torr) were studied. Films of 100, 200, 300 and 400 nm thickness were prepared at 200℃ substrate temperature where annealing temperature and annealing time was fixed at 100℃ and 1 hour respectively. The X-ray diffraction (XRD) exhibited polycrystalline nature indicating the zinc-blende structure with a preferential orientation along the (111) plane of cubic phase. The grain size was found to be 19.27 nm. Dislocation density and microstrain were also found as 2.691 × 10-3 nm-2 and 1.85 × 10-3 respectively. Atomic Force Microscopy (AFM) study confirmed the growth of grains and their distribution over the entire surface of the films. All the films were characterized optically by UV-VIS-NIR spectrophotometer in the photon wavelength ranging from 300 to 1000 nm. The optical transmittance and reflectance were utilized to compute the absorption coefficient, extinction coefficient and band gap energy of the films. The calculated band gap energy was found to increase (2.99 to 3.94 ev) with varying thickness. The maximum transmittance was found to be 87.65% for the 400 nm film.
 Journal of Bangladesh Academy of Sciences, Vol. 43, No. 2, 159-168, 2019

Investigation on the Rapid Annealing of Ti-Au Composite Electrode on n-Type (111) CdZnTe Crystals

In this paper, the ohmic properties of Ti, Al, and Ti-Au composite electrodes on n-type (111) CdZnTe crystal deposited by vacuum evaporation method were first analyzed, and then the rapid annealing of Ti-Au electrode under Ar atmosphere with different temperature and time was explored. The ohmic property and barrier height were evaluated by current–voltage (I–V) and capacitance-voltage (C–V) measurements, and the adhesion strength of various electrodess to CdZnTe was compared. The Ti-Au electrode on CdZnTe showed the lowest leakage current and barrier height, and the highest adhesion strength among the three kinds of electrodes on (111) CdZnTe crystals. The rapid annealing of Ti-Au electrode under Ar atmosphere was proved to improve its ohmic property and adhesion strength, and the optimal annealing temperature and time were found to be 423 K and 6 min, respectively. The barrier height of the Ti-Au/CdZnTe electrode is 0.801 eV through rapid annealing for 6 min at 423 K annealing temperature, and the adhesion is 1225 MPa, which increases by 50% compared with that without rapid annealing.

Characterization of ZnO Thin Film/p-Si Fabricated by Vacuum Evaporation Method for Solar Cell Applications

Characterization of ZnO Thin Film/p-Si Fabricated by Vacuum Evaporation Method for Solar Cell Applications

Structural, optical and photoelectrochemical properties of phase pure SnS and SnS2 thin films prepared by vacuum evaporation method

Two-dimensional (2D) layered semiconducting materials, such as MoS2, SnS2 and SnS, have received remarkable consideration due to their thickness dependent properties and potential applications. In this study, SnS and SnS2 thin films were grown using a simple method of thermal evaporation and their possible application in photoelectrochemical splitting of water reaction have been investigated. X-ray diffraction, Scanning electron microscopy, Raman spectroscopy, and UV–Vis spectroscopy techniques results show the presence of SnS and SnS2 pure phases with orthorhombic and hexagonal crystal structure, having band gap values of 1.8 eV and 2.75 eV, respectively. The photoelectrochemical response of as grown SnS and SnS2 thin films was investigated and the results showed the photoanodic behaviour for SnS2 films with photocurrent density of 1 mA cm−2 and photocathodic nature for SnS with photocurrent density of 0.4 mA cm−2 at 0.95 V vs. Ag/AgCl. The above obtained properties of SnS and SnS2 opens a pathway for using these films for SnS–SnS2 heterojunctions for further improving the photoelectrochemical response.

Fabrication of novel CuAgZnSnSe4–Cu2ZnSnSe4thin film solar cells by the vacuum evaporation method

The heterojunction solar cells based on the glass/X/CAZTSe/CZTSe/Ag structure (X = Al, Cu, Ag, FTO, and AZO) were fabricated by the vacuum evaporation method. The heterojunction solar cells showed poor efficiency.

Исследование свойств нанопорошка фторида кальция после облучения наносекундным электронным пучком

Mesoporous CaF2 nanopowders with specific surface area up to 91.5 m2/g have been produced using by electron beam evaporation method in vacuum. The effect of nanosecond e-beam irradiation in air on magnetic and texture properties this nanopowders has been studied. The irradiation influence on the specific surface area and magnetization of CaF2 nanopowder has been discovered for the first time.

Effect of Annealing Temperature on Thermally Evaporated Lithium Fluoride Thin Films

Abstract Lithium fluoride thin films were successfully deposited on glass substrates using a well known vacuum evaporation method by means of resistive heating at (10-3Torr). These thin films were then annealed for 350°C, 400°C and 450°C respectively. The annealed thin films were characterized for structural surface morphological and optical properties; the annealing temperature strongly affects the properties of LiF thin films the crystallite size was found to increase with respect to increase in annealing temperature. The increase in annealing temperature also affects the optical properties of the LiF thin films show improved transmittance with respect to increase in annealing temperature, the refractive index increases whereas optical band decreases with increase in annealing temperature.

High‐Performance NO2 Sensors Based on Ultrathin Heterogeneous Interface Layers

AbstractGas sensors based on different interface layers are prepared by vacuum evaporation method. In comparison with the microscope images of films on different interface layer, zinc phthalocyanine (ZnPc) films exhibit good continuity on the heterogeneous interface of p‐sexiphenyl/α‐sexithiophene (p‐6P/α‐6T). Under the optimal conditions of ZnPc films, ZnPc film sensors with high performance are obtained based on ultrathin heterogenous interface layers. The responsivity is up to 2271% at 3 ppm NO2 gas and the sensitivity is 570% ppm−1. The minimum detection limit of sensors is lower than 500 ppb and the responsivity is 157% to 500 ppb NO2 gas. The high performance of sensors is attributed to the ultrathin heterogeneous interface layer. The island‐like p‐6P domains at the bottom provide the precursor for the growth of α‐6T layer while the α‐6T molecules fill the interval of p‐6P islands, as a result, a continuous interface for the growth of ZnPc molecules came into being. In addition, the ZnPc and α‐6T films have high electrical characteristics. The results are favorable for the adsorption and desorption of NO2 gas molecules. The ultrathin heterogeneous interface layer provides a feasible research evidence for the further research and development of ultrathin and flexible electronic devices.