Vacuum Thermal Evaporation Method Research Articles

Facile fabrication of Au-Ag alloy nanoparticles/Ag nanowires SERS substrates with bimetallic synergistic effect for ultra-sensitive detection of crystal violet and alkali blue 6B

The bimetallic nanostructure of Au and Ag can integrate two distinct properties into a novel substrate compared to single metal nanostructures. This work presents a rapid and sensitive surface-enhanced Raman scattering (SERS) substrate for detecting illegal food additives and dyes of crystal violet (CV) and alkali blue 6B (AB 6B). Au-Ag alloy nanoparticles/Ag nanowires (Au-Ag ANPs/Ag NWs) were prepared by solid-state ionics method and vacuum thermal evaporation method at 5μA direct current electric field (DCEF), the molar ratio of Au to Ag was 1:18.34. Many 40 nm-140 nm nanoparticles regularly existed on the surface of Ag NWs with the diameters from 80 nm to 150 nm. The fractal dimension of Au-Ag ANPs/Ag NWs is 1.69 due to macroscopic dendritic structures. Compared with single Ag NWs, the prepared Au-Ag ANPs/Ag NWs substrates show superior SERS performance because of higher surface roughness, the SERS active of Ag NWs and bimetallic synergistic effect caused by Au-Ag ANPs, so the limit of detections (LOD) of Au-Ag ANPs/Ag NWs SERS substrates toward detection of CV and AB 6B were as low as 10-16mol/L and 10-9mol/L, respectively. These results indicate that Au-Ag ANPs/Ag NWs substrates can be used for rapid and sensitive detection of CV and AB 6B and have great development potential for detection of illegal food additives and hazardous substances in the fields of environmental monitoring and food safety.

Influence of the distance between evaporation source and substrate on formation of lead telluride (PbTe) nanostructures by vacuum thermal evaporation method

Lead telluride nanostructures were obtained on silicon substrates by thermal evaporation in vacuum. Growth occurred at three different distances between the evaporation source and the substrate. The distances between the evaporator and the evaporation source were 5 cm; 7.5 cm and 10 cm. Structural characteristics were studied using XRD, SEM, EDX, AFM analyses. These methods provided information about the crystal structure, morphology, microstructure and elemental composition of the material. X-ray diffraction analysis showed that thin films of lead telluride obtained by thermal evaporation in vacuum have a cubic crystal structure. This experimental work was carried out to determine the effect of distance on the structure of lead telluride (PbTe). During the experiment, the optimal modes for the formation of lead telluride (PbTe) nanostructures were determined, which was equal to d = 10 cm. It was found that lead telluride (PbTe) nanostructures are formed at this distance.

Study the Effect of Copper Oxide Nanorods Enhanced by Silver Nanoparticles on the Highly Sensitive Gas Sensor

In this paper, ammonia (NH3) gas sensitivity was enhanced by the development of highly dense copper oxide (CuO) nanorods on glass substrates. The layer of copper (Cu) was deposited using a vacuum thermal evaporation method. The grown layer of Cu was sequentially inserted into an oxidation furnace at (400 °C) for (120 min) under atmospheric pressure to produce copper oxide (CuO) nanorods. Silver (Ag) nanoparticles- deposited copper oxide nanoparticles were successfully enhanced via a photo assisted spray pyrolysis technique. A metal-semiconductor-metal (MSM) NH3 gas sensor with aluminum (Al) contact electrodes was fabricated on CuO nanorods. The structure of the crystal as well as the morphology of the CuO nanorods were evaluated with field-emission scanning electron microscopy (FE-SEM), X-ray diffraction, and UV-visible spectroscopy respectively. In order to create a high-performing MSM NH3 gas sensor, silver nanoparticles (NPs) were sprayed by the photo-assisted spray pyrolysis technique on the CuO nanorods, which are produced via the vacuum thermal evaporation method. The results showed that the modified CuO nanorods by Ag nanoparticles demonstrated great sensitivity to NH3 gas might be much improved, and the sensitivity rises from (376.4 to 700 %) , fast response and recovery times about (10.4 and 9.5 s) respectively to NH3 gas.

Study of the Effect of Thin Layer Thickness on the Structural Properties of Copper Phthalocyanine (CuPc) Films Prepared by Vacuum Thermal Evaporation Method

Study of the Effect of Thin Layer Thickness on the Structural Properties of Copper Phthalocyanine (CuPc) Films Prepared by Vacuum Thermal Evaporation Method

Stable, self-biased Cs2AgBiBr6 thin-film based photodetector by three-step vapor-deposition

A lead-free, pure phase double perovskite Cs2AgBiBr6 thin film (TF) is fabricated on an ITO glass plate through a three-step sequential vacuum thermal evaporation method followed by annealing. X-ray diffraction (XRD) analysis of the synthesized material revealed a cubic phase with a lattice constant of α = 11.26 Å. The TF exhibits UV and visible absorption with a bandgap estimated at 2.31 eV (303 K) and a red shift of 0.04 eV (363 K). The optical absorption spectrum is simulated using the modified band anti-crossing (BAC) model, determining the Cs2AgBiBr6 TF's theoretical relative refractive index (r.i.) as 2.10 (303 K) and 1.90 (363 K). Furthermore, a photodetector based on Ag/Cs2AgBiBr6/ITO/glass architecture was fabricated, showcasing excellent stability and self-powered photodetection properties under continuous illumination across a wide temperature range of 303–373 K. The device demonstrates a fast temporal response (13/9 ms), a responsivity of ∼1.0 × 10−4 A/W, and a detectivity of ∼2.5 × 107 Jones. Light sensitivity measurements reveal that the device is twice as sensitive at 373 K compared to room temperature, with negligible (1%) degradation in light sensitivity after 60 days of storage under normal ambient conditions.

Organic heterostructures based on thermal evaporated phthalocyanine and porphyrin as mixed (ZnPc:TPyP) or stacked (ZnPc/TPyP) films

A metallic phthalocyanine (zinc phthalocyanine - ZnPc) and a non-metallic porphyrin (10,15,20-tetra(4-pyridyl)21H,23H-porphyne -TPyP) were used to deposit mixed and stacked organic thin films by vacuum thermal evaporation method. The obtained layers were analyzed in a comparative manner from optical, structural, morphological and electrical point of view. The ultraviolet-visible spectra of the deposited layers showed that both organic components have absorption bands in the visible part of the solar spectrum, which means that the acceptor TPyP also contributes to absorption together with the donor. The photoluminescence spectra revealed only the emission bands associated to the porphyrin, especially in the single and stacked layers, while a quenching effect of the photoluminescence was noted in the mixed ones. The X-ray diffraction showed that the prepared layers are in general amorphous. The constituent materials in the single layers and the ratio between the two organic components in the mixed layers affect the morphology of the deposited films as was emphasized by scanning electron microscopy and atomic force microscopy analysis. The current density-voltage characteristics plotted under illumination revealed that the highest short-circuit current value was achieved in the case of the structure based on the layer showing the lowest roughness and thickness emphasizing the significant role played by these parameters of the layers considered for possible applications in the optoelectronic device area.

High storage and operational stability self-powered UV photodetector based on p-CuI/n-GaN heterojunction prepared by thermal evaporation method

Self-powered ultraviolet (UV) photodetectors play an important role in environmental monitoring, aerospace and other fields because of the advantage of effective light response without an external power supply. Herein, a p-CuI/n-GaN heterojunction UV photodetector with self-powered function is constructed by vacuum thermal evaporation method. At 365 nm UV irradiation, the photodetector has an on/off ratio of 7536, a large photocurrent (∼35 mA) and a fast response time (rise/decay time of 10.46/10.35 ms) at zero bias. There was no significant decrease in photocurrent during the 100 on/off cycles of the continuous test, and the photocurrent of the photodetector can maintain 93.17% of the initial value after continuous operation for 15 h without bias voltage. The rise in ambient temperature exhibits a negative effect on the UV photodetector, but when it is naturally cooled from 80℃ to room temperature (RT), the photocurrent can restore to 95% of the original level. Furthermore, the photodetector maintains superior stability even after being stored in air for 3 months of without package. This work not only proves the controllable preparation strategy of CuI thin films, but also provides an efficient structure for self-powered UV photodetectors with high operational and storage stability.

SnSe Nanosheet Array on Carbon Cloth as a High-Capacity Anode for Sodium-Ion Batteries.

Binder-free electrodes offer a great opportunity for developing high-performance sodium-ion batteries (SIBs) aiming at the application in energy storage devices. Tin selenide (SnSe) is considered to be a promising anode material for SIBs owing to its high theoretical capacity (780 mA h g-1). In this work, a SnSe nanosheet array (SnSe NS) on a carbon cloth is prepared using a vacuum thermal evaporation method. The as-prepared SnSe NS electrode does not have metal current collectors, binders, or any conductive additives. In comparison with the electrode of SnSe blocky particles (SnSe BP), the SnSe NS electrode delivers a higher initial charge capacity of 713 mA h g-1 at a current density of 0.1C and maintains a higher charge capacity of 410 mA h g-1 after 50 cycles. Furthermore, the electrochemical behaviors of the SnSe NS electrode are determined via pseudocapacitance and electrochemical impedance spectroscopy measurements, indicating a faster kinetic process of the SnSe NS electrode compared to that of the SnSe BP. Operando X-ray diffraction measurements prove that the SnSe NS exhibits better phase reversibility than the SnSe BP. After the cycles, the SnSe NS electrode still maintains its particular structure. This work provides a feasible method to prepare SnSe nanostructures with high capacity and improved sodium ion diffusion ability.

Ultrathin metal Ni layer on ZnO/TiO2 photoelectrodes with excellent photoeletrochemical performance in multiple electrolyte solutions

It is well known that the oxygen vacancy (Ovac) as the electron-donor dopant in semiconductor can increase the electron-holes separation in photoeletrochemical (PEC) water splitting. Furthermore, the metal Ni can promote the hydrogen evolution reaction (HER) on the surface of semiconductor. In this paper, the ZnO/TiO2 photoelectrodes with rich Ovac was synthesized by electrostatic adsorption through using ZIF-8 as the precursor. Then the ultrathin Ni layer with about 7 nm was deposited on the surface of ZnO/TiO2 (Ni/ZnO/TiO2) by vacuum thermal evaporation method. The Ni/ZnO/TiO2 photoelectrodes showed the highest photocurrent than ZnO/TiO2, Ni/ TiO2 and pure TiO2 photoelectrodes. The durability of Ni/ZnO/TiO2 photoelectrodes was keeping for 10 h in multiple electrolyte solutions under AM 1.5 G illumination and the photocurrent decline can be ignored. The UV–vis absorption spectra demonstrated that the ultrathin Ni layer showed plasma with ZnO/TiO2 for enhancing the water splitting performance. Furthermore, the ultrathin Ni layer enhanced the photogenerated charges transfer for improving the PEC performance. This work provides a new method for ultrathin metal Ni layer with Ovac semiconductor photoelectrode to improve the PEC performance in multiple electrolyte solutions.

The Performance of V2O5:Ag Nanoparticles as Thin Film and Bulk Pellet Sensor for NO2 and NH3 Detection

A comparison of gas sensing performance of V2O5:Ag nanoparticles as thin film and as bulk pellet toward NO2 and NH3 is presented. V2O5:Ag nanoparticles thin films were deposited by vacuum thermal evaporation method on glass substrates while the pellets were prepared by powder technology. XRD patterns of thin film and pellet were polycrystalline with an orthorhombic structure. The value of average grain size is about 60 nm. The morphological properties of the samples have been distinguished by atomic force microscopy (AFM) and field effect scanning electron microscopy (FESEM) which indicated that the films showed homogeneous surfaces morphology and contained pores between the grains. Sensing results showed a various response to NO2 and NH3 gases. It was found that the sensitivity of thin films sensor is superior to that of the pellets sensor.

Centimeter level high surface roughness copper / silver nanoheterostructures for highly sensitive SERS detection

A novel method for centimeter level high surface roughness copper nanoparticles (CuNPs)/silver nanowires (AgNWs) heterostructures prepared by vacuum thermal evaporation method and solid-state ionics method under 6 ​μA direct current electric field (DCEF) using fast ionic conductor KAg4I5 was developed. The fractal dimension of the CuNPs/AgNWs heterostructures was calculated by grid-coverage method and the surface-enhanced Raman scattering (SERS) performance was detected by melamine aqueous solution as probe molecules. The results indicate that the macroscopic dendritic CuNPs/AgNWs heterostructures arranged neatly near cathode with the longest length of 6.3 ​cm were prepared, the diameters of CuNPs/AgNWs heterostructures ranged from 40 to 100 ​nm and many regularly arranged CuNPs with the diameter from 10 to 30 ​nm lie in the prepared nanoheterostructures, which lead to the CuNPs/AgNWs heterostructures have high surface roughness. The molar ratio of Ag:Cu is 11.87:1 and the fractal dimension of CuNPs/AgNWs heterostructures was 1.64 which means that there were more dentritic nanoheterostructures. The limiting concentration of melamine for the prepared high surface roughness CuNPs/AgNWs heterostructures SERS substrates is 10−16 ​mol/L, which is far below the strictest safety limits required of melamine in US and China. The EF for R6G/CuNPs/AgNWs heterostructures is estimated to be 4.82 ​× ​1012. These results indicate that the prepared CuNPs/AgNWs heterostructures with facile material synthesis, high surface roughness, low detection concentration and simple detection procedure has promising and strong application prospect for SERS detection in food safety.

Effect of Cu distribution on thermoelectric properties of evaporated Cu2−xSe films with various Ag contents

Cu2Se is one kind of popular thermoelectric materials due to its performance of the phonon glass-electron crystal. However, the poor thermal stability limits its application. Regulating the distribution of the Cu+ by elemental dopant is a general method to solve the stability and to improve the thermoelectric performance. In this study, the Ag-doped β-Cu2−xSe films were prepared by vacuum thermal evaporation method. The Cu+ distribution on the octahedral 32(f) sites in the Cu2Se crystal is tuned by the Ag content. It found that when the Ag content is 1.0%, the Cu+ and Ag+ contents in the 32(f) sites reach the maximum. In this case, the power factor of the film is 1750 μW·m−1·K−2 at 530 K. As the Ag content rises, the second phase of CuAgSe appears. This results in the decrease of the power factor. It shows that controlling the distribution of the Cu+ by the Ag dopant is conducive to improve the thermoelectric properties of the β-Cu2−xSe films.

Increasing charge transfer of SERS by the combination of amorphous Al2O3-Al thin film and ZnO nanorods decorated with Ag nanoparticles for trace detection of metronidazole.

In this work, we study the charge transfer improvement by the combination of two semiconductors of SERS. The energy levels of the semiconductor, when combined, become intermediate energy levels that support the charge transfer from the HOMO to the LUMO level, amplifying the Raman signal of the organic molecules. The SERS substrates of Ag/a-Al2O3-Al/ZnO nanorods with high sensitivity are prepared for detecting dye rhodamine 6G (R6G) and metronidazole (MNZ) standard. The highly ordered vertically grown ZnO nanorods (NRs) are first developed on a glass substrate by a wet chemical bath deposition method. Then, ZnO NRs are covered with an amorphous oxidized aluminum thin film by a vacuum thermal evaporation method to produce a platform with a large surface area and high charge transfer performance. Finally, silver nanoparticles (NPs) are decorated onto this platform to form an active SERS substrate. The structure, surface morphology, optical properties, and elements in the sample are investigated by Raman spectroscopy, X-ray diffractometry, field-emission scanning electron microscopy (FE-SEM), ultraviolet-visible spectroscopy (UV-vis), reflectance spectroscopy, and energy dispersion X-ray spectroscopy (EDS). Rhodamine 6G is used as a reagent to evaluate the SERS substrates with an analytical enhancement factor (EF) of ∼1.85 × 1010 at the limit of detection (LOD) of 10-11 M. These SERS substrates are used to detect metronidazole standard at a LOD of 0.01 ppm and an EF of 2.2 × 106. The SERS substrate exhibits high sensitivity and stability for promising wide application in chemical, biomedical, and pharmaceutical detection.

Tailoring the physical and optical properties of Sn-doped In2S3 thin films obtained using VTE technique

In this study, indium sulfide (In2S3) thin films doped with tin (Sn) were prepared and deposited using the Vacuum Thermal Evaporation (VTE) method with different proportions of Sn (0, 2, 4 and 6%). 0.2 g of In2S3 powder was evaporated in vacuum onto a glass substrate (2,5 cm × 1 cm) under 1.7 × 10−5 mbar. Structural, morphological, optical, and elemental composition properties of obtained thin films have been investigated. X-ray diffraction analysis shows well-crystallized films according to the cubic β-In2S3 phase. The films become almost amorphous when tin exceeds 4% (also confirmed by the FTIR results). Raman Spectroscopy shows the main mode at 326 cm−1. Both the SEM and the AFM photographs exhibit that all films are covered without cracks and pinholes. XPS results verifies the diffusion of dopant into the In2S3 thin films and shows two principal peaks of the binding energies of In and S located at 448 eV and 456 eV respectively. Optical analysis revealed that the transmission is achieved 75–80% in visible and 85–95% in the near-IR region. The optical band gap varied from 2.84 eV to 2.62 eV with adding tin until 6%. The optical parameters, single oscillator energy (E0), dispersion energy (Ed), and high-frequency dielectric constant (ε∞) are also determined via the Wemple-DiDomenico Model. This study reflects the prospect of tailoring the properties and integrating Sn-doped In2S3 nanocomposites as thin-film layers in future solar cells.

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

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.

Preparation and thermoelectric properties of layered Bi<sub>1–<i>x</i></sub>Sb<sub><i>x</i></sub>Se nanocrystalline films

<sec>BiSe is found to be a promising near-room-temperature thermoelectric material with higher performance than traditional Bi<sub>2</sub>Se<sub>3</sub> due to its ultra-low intrinsic lattice thermal conductivity. In this work, N-type BiSe nanocrystalline thin films with (00l) preferred orientation are first prepared via vacuum thermal evaporation method, and Bi<sub>1–<i>x</i></sub>Sb<i><sub>x</sub></i>Se nanocrystalline films with different doping concentrations are obtained by Sb co-evaporation. The phases, morphologies, chemical compositions and valences, lattical vibrations, and electrical properties of these films are characterized. It is found that the Sb dopant successfully enters into the crystal lattice and replaces the Bi site of Bi<sub>2</sub>Se<sub>3</sub> quintuple layers and Bi<sub>2</sub> bilayers without selectivity, and the difference of gold properties between Sb atom and Bi atoms leads the carrier concentration to sharply decrease and the Seebeck coefficient in doped BiSe to increase. Meanwhile,</sec><sec>the sizes of nanocrystals in the films decrease and the denser layered structure is formed due to the Sb doping, which is conducive to the carrier transport in the samples, and the in-plane carrier mobility of the films effectively increases from 13.6 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> (BiSe) to 19.3 cm<sup>2</sup>·V<sup>–1</sup>·s<sup>–1</sup> (Bi<sub>0.65</sub>Sb<sub>0.35</sub>Se). The maximum room-temperature power factor of 2.18 μW·cm<sup>–1</sup>·K<sup>–2</sup> is obtained in Bi<sub>0.76</sub>Sb<sub>0.24</sub>Se, which is higher than that in undoped BiSe. The results of this work indicate that the BiSe-based thin films have potential applications in room temperature thermoelectric thin film devices.</sec>

Enhanced Electrochromic Properties of Nanostructured WO3 Film by Combination of Chemical and Physical Methods

WO3 films are the most widely used electrochromic functional layers. It is known that WO3 films prepared by pure chemical method generally possess novel nanostructures, but the adhesion between WO3 films and substrates is weak. However, WO3 films prepared by pure physical method usually show relatively dense morphology, which limits their electrochromic properties. In order to break through these bottlenecks and further improve their electrochromic properties, this work first prepared nanostructured WO3 powder by chemical method, and then using this powder as the evaporation source, nanostructured WO3 films were fabricated by vacuum thermal evaporation method. Properties of nanostructured WO3 films were systematically compared with those of ordinary WO3 films. It turned out that the nanostructured WO3 film exhibited better cyclic stability and memory effect, and also the optical modulation rate was 14% higher than that of the ordinary WO3 film. More importantly, the nanostructured WO3 film showed better adhesion with the ITO substrates. These results demonstrate that a combination of chemical and physical methods is an effective preparation method to improve the electrochromic properties of WO3 films.

Experimental studies and new theoretical modeling on the properties of In2S3 thin films

Indium sulfide (In2S3) is a material extensively used as an alternative buffer layer to that of cadmium sulphide (CdS) for thin film photovoltaic applications. In this work, In2S3 thin films were obtained over SiO2 glass with various substrate temperatures (Ts) using the vacuum thermal evaporation method. The effect of Ts which varies from 25 °C to 300 °C on structural, optical and morphological homestead are reported and discussed here. Our deposited In2S3 films are typified via X-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM) and UV–Vis–NIR spectroscopy. XRD analysis reveals the amorphous nature of all samples. AFM graphics reveals that the deposited layers are smooth along relatively high surface roughness. The UV–Vis–NIR spectra show a high transmittance for all samples ranging from 75% to 90%, over the region extending from the UV–Vis to the near-infrared. The evaluated optical band gap energy showed a decrease from 2.60 eV to 2.12 eV with increasing Ts, which might be attributed to the presence of high concentration of defects, in the compound band structure. These experimental data were confirmed by theoretical predictions obtained by transfer matrix method (TMM) simulations.

Modeling of diffusion motion of In nanoparticles in a CdTe crystal during laser-induced doping

In order to solve the problem of the ohmic contact between the crystal surface and the metal electrode in the manufacturing process of the X/γ-ray detector, this paper uses a laser to probe the doping process of In/CdTe crystals in different media. In this experiment, the Traveling Heater Method (THM) is used to obtain CdTe(111) crystals that meet the requirements (ρ >109Ω∙cm). In and Au materials are respectively coated on the surface of the crystal sample by the vacuum thermal evaporation method to obtain the crystal sample meeting the requirements. The high-resistance p-type CdTe crystal of a relatively thick In film is irradiated with nanosecond laser pulses, the In film is used as an n-type doping source and as an electrode after laser irradiation.