Showing papers on "Evaporation (deposition) published in 2021"

Flexible, biocompatible and highly conductive MXene-graphene oxide film for smart actuator and humidity sensor

Abstract: The evaporation of water occurs ubiquitously on earth. Hence, smart materials that can directly convert signals generated via water stimulation into mechanical motion have attracted wide attention. However, it is still a challenge to develop novel functional materials with fast response, large scale deformation, and long-term stability for moisture-gradient actuators. Here, a flexible, conductive, layer-structured homogenous Ti3C2TX MXene-graphene oxide (MGO) film-based moisture-driven actuator and humidity sensor were fabricated. The oxygen groups and d-spacing could be effectively adjusted by MXene/GO composition ratio, thereby tuning the actuation performance. MGO3 (MXene/GO = 3) displayed a large bending angle, and reversible deformation. And the bending speed of MGO3 is up to 32°s−1. Furthermore, MGO3 actuation displayed long-term stability via suppression of MXene oxidation by the introduction of GO and showed good cycling stability. MGO3 actuators are constructed, which could mimic the blooming of flower, lifting and carrying objects, and be used as a non-contact control switch. In addition, MGO3 showed a linear sensitive response to humidity and excellent biocompatibility which make it suitable for respiratory monitoring. This work demonstrated that flexible, biocompatibility and conductive MGO films have broad application prospects in the fields of smart actuators, sensing devices, and biology and health care.

High efficiency solar desalination and dye retention of plasmonic/reduced graphene oxide based copper oxide nanocomposites

Abstract: Water desalination via solar-driven interfacial evaporation is one of the most essential technologies to limit the problem of global freshwater scarcity. Searching for a highly efficient, stable, eco-friendly, and cost-effective solar-absorber material that can collect the full solar spectrum is critically important for solar steam generation. This study reports the development of a new solar thermal evaporation system based on plasmonic copper oxide/reduced graphene oxide (rGO). The silver nanoparticles in the composite exhibit a very strong solar absorption. Also, rGO and CuO nanoparticles offer excellent thermal absorptivity. Polyurethane was used as the support and as a thermal insulator. Moreover, filter paper was used for fast water delivery to the surface of the solar absorber. Ag/CuO-rGO nanocomposite is manifested to be one of the most efficient solar-absorbers reported to date for solar desalination which exhibits an average 2.6 kg m−2 h−1 evaporation rate with solar thermal efficiency up to 92.5% under 1 sun irradiation. Furthermore, the composite has excellent stability and durability as it displays stable evaporation rates for more than 10 repeated cycles in use, with no significant decrease in the activity. Besides, the successful removal of various organic dyes from contaminated water is also revealed, resulting in the production of clean condensed freshwater. Finally, this work commences a new avenue of synthesizing cost-effective thermal absorbers based on metal oxides.

Magnetically Driven 3D Cellulose Film for Improved Energy Efficiency in Solar Evaporation

Abstract: The architecture of cellulose nanomaterials is definitized by random deposition and cannot change in response to shifting application requirements Herein, we present a magnetic field-controlled ce

Tellurium Single-Crystal Arrays by Low-Temperature Evaporation and Crystallization.

Abstract: Thermally evaporated tellurium possesses an intriguing crystallization behavior, where an amorphous to crystalline phase transition happens at near-ambient temperature. However, a comprehensive understanding and delicate control of the crystallization process for the evaporated Te films is lacking. Here, the kinetics and dynamics of the crystallization of thermally evaporated Te films is visualized and modeled. Low-temperature processing of highly crystalline tellurium films with large grain size and preferred out-of-plane orientation ((100) plane parallel to the surface) is demonstrated by controlling the crystallization process. Tellurium single crystals with a lateral dimension of up to 6 µm are realized on various substrates including glass and plastic. Field-effect transistors based on 5 °C crystallized Te single grains (6-nm-thick) exhibit an average effective hole mobility of ≈100 cm2 V-1 s-1 , and on/off current ratio of ≈3 × 104 .

β-Ga2O3 on Si (001) grown by plasma-assisted MBE with γ-Al2O3 (111) buffer layer: Structural characterization

Abstract: β-Ga2O3 was deposited in thin film form by plasma-assisted molecular beam epitaxy at 670 °C and 630 °C onto a γ-Al2O3 (111) buffer layer grown at 840 °C by e-beam evaporation on a clean Si (001) surface. The β-Ga2O3 film was 66 nm thick, stoichiometric, and strongly textured, as determined by x-ray reflectivity, x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, x-ray diffraction, and transmission electron microscopy, with three basal growth planes (201), (101), and {310}, including one twin variant {310}. The observed basal growth planes correspond to the close-packing planes of the distorted face-centered cubic oxygen sublattice of β-Ga2O3. Local structural ordering can be thought to occur due to a continuation of the oxygen sublattice from the γ-alumina buffer layer into the β-gallia film. Each β-Ga2O3 growth plane further gives rise to 12 symmetry-derived rotational in-plane variants, resulting in a total of 48 domain variants. Atomistic models of possible gallia–alumina interfaces are presented.

Effect of Energy and Temperature on Tetrahedral Amorphous Carbon Coatings Deposited by Filtered Laser-Arc.

Abstract: In this study, both the plasma process of filtered laser-arc evaporation and the resulting properties of tetrahedral amorphous carbon coatings are investigated. The energy distribution of the plasma species and the arc spot dynamics during the arc evaporation are described. Different ta-C coatings are synthesized by varying the bias pulse time and temperature during deposition. An increase in hardness was observed with the increased overlapping of the bias and arc pulse times. External heating resulted in a significant loss of hardness. A strong discrepancy between the in-plane properties and the properties in the film normal direction was detected specifically for a medium temperature of 120 °C during deposition. Investigations using electron microscopy revealed that this strong anisotropy can be explained by the formation of nanocrystalline graphite areas and their orientation toward the film’s normal direction. This novel coating type differs from standard amorphous a-C and ta-C coatings and offers new possibilities for superior mechanical behavior due to its combination of a high hardness and low in-plane Young’s Modulus.

Investigation of AgGaSe2 as a Wide Gap Solar Cell Absorber

Abstract: The compound AgGaSe2 has received limited attention as a potential wide gap solar cell material for tandem applications, despite its suitable band gap This study aims to investigate the potential of this material by deposition of thin films by co-evaporation and production of solar cell devices Since AgGaSe2 has a very low tolerance to off-stoichiometry, reference materials of possible secondary phases in the Ag2Se-Ga2Se3 system were also produced Based on these samples, it was concluded that X-ray diffraction is suited to distinguish the phases in this material system An attempt to use Raman spectroscopy to identify secondary phases was less successful Devices were produced using absorbers containing the secondary phases likely formed during co-evaporation When grown under slightly Ag-rich conditions, the Ag9GaSe6 secondary phase was present along with AgGaSe2, which resulted in devices being shunted under illumination When absorbers were grown under Ag-deficient conditions, the AgGa5Se8 secondary phase was observed, making the device behavior dependent on the processing route Deposition with a three-stage evaporation (Ag-poor, Ag-rich, and Ag-poor) resulted in AgGa5Se8 layers at both front and back surfaces, leading to charge carrier blocking in devices Deposition of the absorber with a one-stage process, on the other hand, caused the formation of AgGa5Se8 locally extended through the entire film, but no continuous layer was found As a consequence, these devices were not blocking and achieved an efficiency of up to 58%, which is the highest reported to date for AgGaSe2 solar cells

Pulsed Laser Deposition of Cs2AgBiBr6: from Mechanochemically Synthesized Powders to Dry, Single-Step Deposition.

Abstract: Cs2AgBiBr6 has been proposed as a promising lead-free and stable double perovskite alternative to hybrid and lead-based perovskites. However, the low solubility of precursors during wet synthesis, or the distinct volatility of components during evaporation, results in complex multistep synthesis approaches, hampering the widespread employment of Cs2AgBiBr6 films. Here, we present pulsed laser deposition of Cs2AgBiBr6 films as a dry, single-step and single-source deposition approach for high-quality film formation. Cs2AgBiBr6 powders were prepared by mechanochemical synthesis and pressed into a solid target maintaining phase purity. Controlled laser ablation of the double perovskite target in vacuum and a substrate temperature of 200 °C results in the formation of highly crystalline Cs2AgBiBr6 films. We discuss the importance of deposition pressure to achieve stoichiometric transfer and of substrate temperature during PLD growth to obtain high-quality Cs2AgBiBr6 films with grain sizes > 200 nm. This work demonstrates the potential of PLD, an established technique in the semiconductor industry, to deposit complex halide perovskite materials while being compatible with optoelectronic device fabrication, such as UV and X-ray detectors.

Two Birds One Stone: Facile and Controllable Synthesis of the Ag Quantum Dots/Reduced Graphene Oxide Composite with Significantly Improved Solar Evaporation Efficiency and Bactericidal Performance.

Abstract: Interfacial solar evaporation (ISE) is an environmentally friendly and promising water treatment strategy. However, the bactericidal performance of an ISE system during the evaporation process is usually ignored, which may result in potential water safety hazards. In this study, a facile method is presented for the controllable synthesis of Ag quantum dots (QDs)/rGO to simultaneously achieve efficient solar evaporation and evaporated water disinfection. The size of the Ag nanoparticles (NPs) rather than the loading amount is the factor that considerably affects the solar evaporation efficiency and the bactericidal performance. Under 1 sun of irradiation (1 kW·m2), the evaporation rate and solar evaporation efficiency of Ag QDs/rGO are as high as 2.11 kg·m2·h-1 and 94.0%, respectively. Based on E. coli and S. aureus, the bactericidal activity of Ag QDs/rGO in the evaporation process is qualitatively and quantitatively characterized; no bacteria could be detected in the evaporated water. Furthermore, various water samples, including acidic water, alkaline water, dye water, and seawater, are selected to verify the solar evaporation performance of Ag QDs/rGO. When considering complex water samples, the as-prepared material maintains a high evaporation efficiency and an excellent purification effect, indicating attractive potential for various practical applications.

Li-Zn Overlayer to Facilitate Uniform Lithium Deposition for Lithium Metal Batteries.

Abstract: The highly reactive nature and rough surface of Li foil can lead to the uncontrollable formation of Li dendrites when employed as an anode in a lithium metal battery. Thus, it could be of great practical utility to create uniform, electrochemically stable, and "lithiophilic" surfaces to realize homogeneous deposition of Li. Herein, a LiZn alloy layer is deposited on the surface of Li foil by e-beam evaporation. The idea is to introduce a uniform alloy surface to increase the active area and make use of the Zn sites to induce homogeneous nucleation of Li. The results show that the alloy film protected the Li metal anode, allowing for a longer cycling life with a lower deposition overpotential over a pure-Li metal anode in symmetric Li cells. Furthermore, full cells pairing the modified lithium anode with a LiFePO4 cathode showed an incremental increase in Coulombic efficiency compared with pure-Li. The concept of using only an alloy modifying layer by an in-situ e-beam deposition synthesis method offers a potential method for enabling lithium metal anodes for next-generation lithium batteries.

Sodium doping of solution-processed amine-thiol based CIGS solar cells by thermal evaporation of NaCl

Abstract: Poor crystallinity, high degree of porosity and rough surfaces are the main drawbacks of solution-processed CIGS absorbers resulting in lower power conversion efficiencies when compared to vacuum-based CIGS solar cells. Therefore, promoting absorber grain growth is key to further improve solution-based solar cell performance. The effect of alkali elements such as Na in CIGS absorbers is generally recognised to have beneficial effects not only on the absorber opto-electronic properties but also on the grain growth. In this work, thermal evaporation of a thin layer of NaCl prior to selenisation resulted in absorbers with significantly larger CIGS grains than previously seen with Na diffusing directly from the from soda-lime glass substrate. NaCl is non-toxic, abundant and readily available compound that has not been typically used as an evaporation source, but rather as an additive into CIGS precursor solution. The effect of Na on these solution-processed CIGS devices was primarily observed in the spectacular morphological changes leading to improved carrier collection and minority carrier lifetimes, but less on the absorber doping. Transmission electron microscopy (TEM) revealed voids forming around large CIGS grains upon NaCl addition and these had a negative effect on inter-grain carrier transport. Nonetheless, the resulting device performance doubled from 5% to 10% with addition of Na using this doping approach; however, a compromise between the optimum grain growth and optimum electronic properties had to be made. This study demonstrates a novel, simple and effective Na-doping strategy for CIGS absorbers and reveals the current limitations of the Na-doping in solution-processed atmospherically deposited cells.

Fabrication of Chiral M13 Bacteriophage Film by Evaporation-Induced Self-Assembly.

Abstract: Biomacromolecules are likely to undergo self-assembly and show specific collective behavior concentrated in the medium. Although the assembly procedures have been studied for unraveling their mysteries, there are few cases to directly demonstrate the collective behavior and phase transition process in dynamic systems. In the contribution, the drying process of M13 droplet is investigated, and can be successfully simulated by a doctor blade coating method. The morphologies in the deposited film are measured by atomic force microscopy and the liquid crystal phase development is captured in real time using polarized optical microscope. Collective behaviors near the contact line are characterized by the shape of meniscus curve and particle movement velocity. With considering rheological properties and flow, the resultant chiral film is used to align gold nanorods, and this approach can suggest a way to use M13 bacteriophage as a scaffold for the multi-functional chiral structures.

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

Abstract: 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.

Modeling and the main stages of spin coating process: A review

Abstract: Spin coating is a technique employed for the deposition of uniform thin films of organic materials in the range of micrometer to nanometer on flat substrates. Typically, a small amount of coating material generally as a liquid is dropped over the substrate center, which is either static or spinning at low speed. The substrate is then rotated at the desired speed and the coating material has been spread by centrifugal force. A device that is used for spin coating is termed a spin coater or just a spinner. The substrate continued to spin and the fluid spins off the boundaries of the substrate until the film is reached the required thickness. The thickness and the characteristics of coated layer (film) are depending on the number of rotations per minute (rpm) and the time of rotation. Therefore, a mathematical model is obtained to clarify the prevalent method controlling thin film fabrication. Viscosity and the concentration of (solution) spin coating material are also affecting the thickness of the substrate. This article reviews spin coating techniques including stages in the coating process such as deposition, spin-up, stable fluid outflow (spin-off), and evaporation. Additionally, the main affecting factors on the film thickness in the coating process are reviewed.

Thickness and annealing evolution to physical properties of e-beam evaporated ZnTe thin films as a rear contact for CdTe solar cells

Abstract: The CdTe solar cell engineering is still lacking maximum achievable power conversion efficiency as predicted based upon the detailed balance. In device development, each constituent layer plays important role and to reduce open-circuit voltage loss, the reduction of back surface recombination is a promising approach. It could be made by introducing a wide-band gap ZnTe layer between the absorber CdTe layer and metal contact which can solve the issue of the Schottky barrier at the interface. The ZnTe layers also need optimization to the physical properties to implicate in CdTe-based device and therefore, the present work reports annealing and thickness evolution to ZnTe films to seek their feasibility as rear contact material where 200 nm and 300 nm thin ZnTe films are developed employing e-beam evaporation and subsequently annealed at 100 °C, 200 °C and 300 °C in air ambient followed by characterizations by amicable tools for exploration of relevant physical properties. Findings demonstrate that the film thickness and annealing temperature have considerably affected the physical properties of the developed films and the 200 nm ZnTe thin films annealed at 100 °C may be implicated as rear contact material in CdTe solar cell devices.

Evaporation Effect on Thickness Distribution for Spin-Coated Films on Rectangular and Circular Substrates

Abstract: Spin-coating is widely applied in the field of thin-film fabrication due to its simplicity and high film uniformity. To prepare thin films on rectangular substrates by spin-coating, the simulation and experimental methods were used to study the characteristics of the film thickness in this work. The two-phase flow simulations of spin-coating on a rectangular substrate and circular substrate were carried out with the volume of fluid (VOF) method. The simulation results showed that the airflow field and the substrate geometry had little effect on the evolution of spin-coated film thickness. However, in the experimental results, there was a significant difference in the thickness of the spin-coated film on the rectangular substrate and the circular substrate. According to further study, the solvent evaporation that was neglected in the simulation was the dominant factor of the differences. In addition, it was concluded that the non-uniform evaporation caused by the surface tension and edge accumulation in the later spin-coating stage was the main reason for the film accumulation of the windward area on the rectangular substrate. This work is useful to obtain a deeper understanding of the thin-film formation mechanism of spin-coating.