The transfer of synthesized 2D MoS2 films is important for fundamental and applied research. However, it is problematic to translate the well-established transfer processes for graphene to MoS2 due ...to different growth mechanisms and surface properties. Here we demonstrate a surface-energy-assisted process that can perfectly transfer centimeter-scale monolayer and few-layer MoS2 films from original growth substrates onto arbitrary substrates with no observable wrinkles, cracks, and polymer residues. The unique strategies used in this process include leveraging the penetration of water between hydrophobic MoS2 films and hydrophilic growth substrates to lift off the films and dry transferring the film after the lift off. This is in stark contrast with the previous transfer process for synthesized MoS2 films, which explores the etching of the growth substrate by hot base solutions to lift off the films. Our transfer process can effectively eliminate the mechanical force caused by bubble generations, the attacks from chemical etchants, and the capillary force induced when transferring the film outside solutions as in the previous transfer process, which consists of the major causes for the previous unsatisfactory transfer. Our transfer process also benefits from using polystyrene (PS), instead of poly(methyl methacrylate) (PMMA) that was widely used previously, as the carrier polymer. PS can form more intimate interaction with MoS2 films than PMMA and is important for maintaining the integrity of the film during the transfer process. This surface-energy-assisted approach can be generally applied to the transfer of other 2D materials, such as WS2.
Land surface temperature (LST) has been effectively retrieved from thermal infrared (TIR) satellite measurements under clear-sky conditions. However, TIR satellite data are often severely ...contaminated by clouds, which cause spatiotemporal discontinuities and low retrieval accuracy in the LST products. Several solutions have been proposed to fill the “gaps”; however, a majority of these possess constraints. For example, fusion methods with microwave data suffer from coarse spatial resolution and diverse land cover types while spatial-temporal interpolation methods neglect cloudy cooling effects. We developed a novel method to estimate cloudy-sky LST from polar-orbiting satellite data based on the surface energy balance (SEB) principle. First, the hypothetical clear-sky LST of missing or likely cloud-contaminated pixels was reconstructed by assimilating high-quality satellite retrievals into a time-evolving model built from reanalysis data using a Kalman filter data assimilation algorithm. Second, clear-sky LST was hypothetically corrected by accounting for cloud cooling based on SEB theory. The proposed method was applied to Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) data, and further validated using ground measurements of fourteen sites from SURFRAD, BSRN, and AmeriFlux in 2013. VIIRS LST recovered from cloud gaps exhibited a root mean square error (RMSE) of 3.54 K, a bias of −0.36 K, R2 of 0.94, and sample size (N) of 2411, comparable to the accuracy of clear-sky LST products and cloudy-sky LST estimation from MODIS (RMSE of 3.69 K, bias of −0.45 K, R2 of 0.93, and N of 2398). Thus, the proposed method performs well across different sensors, seasons, and land cover types. The abnormal retrieval values caused by cloud contamination were also corrected in the proposed method. The overall accuracy was better than the downscaled cloudy-sky LST retrieved from passive microwave (PMW) observations and former SEB-based cloudy-sky LST estimation methods. Validation using time-series measurements showed that the all-sky LST time series, including both clear- and cloudy-sky retrievals, can capture realistic variability without sudden abruptions or discontinuities. RMSE values for the all-sky LST varied from 2.54 to 4.15 K at the fourteen sites. Spatially continuous LST maps over the Contiguous United States were compared with corresponding maps from PMW data in the winter and summer of 2018, exhibiting similar spatial patterns but with additional spatial details. Moreover, sensitivity analysis suggested that the reconstruction of clear-sky LST dominantly impacts the accuracy of cloudy-sky LST estimation. The proposed method can be potentially implemented in similar satellite sensors for global real-time production.
•A novel surface energy budget-based method for estimating cloudy-sky LST.•Highly accurate estimations from MODIS and VIIRS based on extensive validation.•Consistency of cloudy-sky LST estimation for different seasons and land covers.•Feasibility for removing cloud contamination and fill the gaps over large regions.
A protocol to produce a silsesquioxane (POSS) with a long alkyl chain coating on natural cotton (CT) fabric is applied. The surface hydroxyl groups of cotton fabric are converted with ...3-mercaptopropyltriethoxysilane (MPTES) to thiol groups. Then the POSS links to the thiol groups by thiol-ene click reactions triggered by UV irradiation to produce POSS-CT or grafted with 1-octadecanethiol (ODT) using one-pot or two-pot modification protocols to generate the ODT-POSS-CT fabrics. The POSS-CT is highly hydrophobic, could absorb 0.96 g hexane/g fabrics when competing with invaded water, and reach 1.12 hexane g/g fabrics when water was absorbed separately. The one-pot modification protocol yielded surfaces with almost constant water contact angle (144o) and perfect wetting by diiodomethane (0o), producing constant dispersive component (50.8 mJ/m2) and polar component (13.6 mJ/m2). The ODT-POSS-CT via two-pot modification leads to water contact angles >143o and diiodomethane contact angle of about 46o, with corresponding dispersive and polar components being 36.1 mJ/m2 and 9.4 mJ/m2, respectively. The complete grafting of ODT onto POSS yields a compact hydrophobic layer with reduced effective surface area for dispersive components, transferring the surface from hydrophobic to omniphobic for both water and diiodomethane.
Anthropogenic heat flux (AHF) is a main contributor to the formation of surface urban heat islands (SUHI). Megacities in particular are facing severe problems due to excessive population growth, ...urban area expansion, human activity, increased energy consumption, and increased anthropogenic heat. In this study, a physical modeling approach based on a triple-source surface energy balance (triple-SEB) model was developed to uncover the effect of AHF on land surface temperature (LST) and surface anthropogenic heat island (SAHI) intensity. For this purpose, satellite imagery along with climatic and meteorological data from 1985 to 2019 were studied for six selected megacities: Los Angeles, Atlanta, Athens, Istanbul, Tehran, and Beijing. First, LST and the fraction of different surface covers were calculated by using a single-channel algorithm and a normalized spectral mixture analysis model, respectively. In the second step, impervious surface cover (ISC) and the urban main boundary area (UMBA) of each city were extracted based on the biophysical composite index and city clustering algorithm, respectively. In the third step, anthropogenic LST (ALST) was modeled using a triple-SEB model. In the fourth step, the ALST and UMBA were used together to model SAHI intensity at different dates. Finally, the relationship between the estimated ALST and ISC, as well as between SAHI and ISC, was examined. Results show that the average value of estimated ALST for the megacities increased from 2.02, 0.55, 0.61, 0.64, 0.58, and 0.72 to 2.99, 1.73, 1.66, 1.19, 2.32, and 2.76 °C, respectively. The coefficient of determination between the mean value of ISC and the estimated ALST for all megacities yielded 0.8, which was higher than that between ISC and satellite-derived LST. Moreover, the SAHI intensity for these megacities was found to have increased to 0.73, 0.92, 0.95, 0.98, 0.95 and 1.32 °C, respectively, which can be predicted by ISC with a coefficient of determination of 0.78, 0.79, 0.79, 0.73, 0.71 and 0.52, respectively. This suggests that the triple-SEB model proposed by this study allowed for independent modeling of AHF's influence on SUHI and a better determination of the effect of ISC on LST and SUHI intensity. This approach facilitated comparative analysis of LST and SAHI for a city at different times as well as SAHIs in different cities with different geographic and climate settings.
•A novel method based on triple-source energy balance model developed for LST•LST due to anthropogenic heat flux used to model surface anthropogenic heat island•SAHI and the effect of ISC on SUHI in five global megacities were investigated.•Better determination and modeling of the effect of ISC on LST and SUHI intensity•New method for comparative analysis of LST and SAHI at different times and cities
The WAter Cycle Multi-mission Observation Strategy – EvapoTranspiration (WACMOS-ET) project has compiled a forcing data set covering the period 2005–2007 that aims to maximize the exploitation of ...European Earth Observations data sets for evapotranspiration (ET) estimation. The data set was used to run four established ET algorithms: the Priestley–Taylor Jet Propulsion Laboratory model (PT-JPL), the Penman–Monteith algorithm from the MODerate resolution Imaging Spectroradiometer (MODIS) evaporation product (PM-MOD), the Surface Energy Balance System (SEBS) and the Global Land Evaporation Amsterdam Model (GLEAM). In addition, in situ meteorological data from 24 FLUXNET towers were used to force the models, with results from both forcing sets compared to tower-based flux observations. Model performance was assessed on several timescales using both sub-daily and daily forcings. The PT-JPL model and GLEAM provide the best performance for both satellite- and tower-based forcing as well as for the considered temporal resolutions. Simulations using the PM-MOD were mostly underestimated, while the SEBS performance was characterized by a systematic overestimation. In general, all four algorithms produce the best results in wet and moderately wet climate regimes. In dry regimes, the correlation and the absolute agreement with the reference tower ET observations were consistently lower. While ET derived with in situ forcing data agrees best with the tower measurements (R2 = 0.67), the agreement of the satellite-based ET estimates is only marginally lower (R2 = 0.58). Results also show similar model performance at daily and sub-daily (3-hourly) resolutions. Overall, our validation experiments against in situ measurements indicate that there is no single best-performing algorithm across all biome and forcing types. An extension of the evaluation to a larger selection of 85 towers (model inputs resampled to a common grid to facilitate global estimates) confirmed the original findings.
Carbon dots (CDs) possess unique optical properties such as tunable photoluminescence (PL) and excitation dependent multicolor emission. The quenching and recovery of the fluorescence of CDs can be ...utilized for detecting analytes. The PL mechanisms of CDs have been discussed in previous articles, but the quenching mechanisms of CDs have not been summarized so far. Quenching mechanisms include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer (PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). Following an introduction, the review (with 88 refs.) first summarizes the various kinds of quenching mechanisms of CDs (including static quenching, dynamic quenching, FRET, PET and IFE), the principles of these quenching mechanisms, and the methods of distinguishing these quenching mechanisms. This is followed by an overview on applications of the various quenching mechanisms in detection and imaging.
Graphical abstract
Schematic representation of the quenching mechanisms of carbon dots (CDs) which include static quenching, dynamic quenching, Förster resonance energy transfer (FRET), photoinduced electron transfer(PET), surface energy transfer (SET), Dexter energy transfer (DET) and inner filter effect (IFE). All these effects can be used to detect and image analytes.
The polymer‐supported wet transfer of chemical vapor deposition‐grown graphene provides high‐quality large‐area graphene on a target substrate. The transfer‐induced defects that result from these ...processes, such as micrometer‐scale folds and cracks, have been regarded as an inevitable problem. Here, the transfer processes are thoroughly examined stage‐by‐stage and it is found that lamination wrinkles, which cause defects in the graphene, are generated as a result of the high contact angles of the trapped transfer medium liquids. Systematic theoretical and experimental studies demonstrate that a liquid droplet with a low surface tension trapped between the polymer/graphene film and the substrate minimizes lamination wrinkles during the transfer process by completely wetting the target substrate, regardless of the surface energy. In connection with these results, a simple and broadly applicable transfer method is developed using an organic liquid with a low surface tension to uniformly transfer high‐quality graphene onto arbitrary substrates, even onto superhydrophobic substrate. The graphene obtained using the proposed organic liquid transfer method displays better electrical and mechanical properties than the graphene transferred by the conventional method using water. This effective and practical transfer method provides an approach to obtaining high‐quality graphene for use in graphene‐based devices.
During transfer of graphene films defects, such as folds and cracks, are generated by wrinkles in the supporting polymer layer. Transfer by a low‐surface tension organic liquid prevents this wrinkle formation, resulting in high‐quality and uniform graphene on arbitrary substrates.
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•Acetic acid treatment introduces micrometer-sized micropits on the sapphire substrate.•The micropits promote the formation of nucleation sites.•The micropits reduce surface energy ...and facilitate the transition to vertical growth mode.•WS2 bilayers and Moiré superlattices were obtained on acid-pretreated substrates.•WS2 bilayers have higher valley polarization and carrier mobility than monolayers.
The bilayer (BL) transition metal dichalcogenides (TMDs), with their elevated carrier mobility and narrowed bandgap, are advantageous for future electronic applications in comparison with their monolayer (ML) counterparts. Here, we introduce a facile and efficient approach for the chemical vapor deposition synthesis of BL WS2. The method involves an acetic acid sonication treatment to modify the substrate surface morphology and the surface energy, which regulates the nucleation processes and shapes the growth mode of WS2 crystals. Further modifications to the growth conditions yield high-quality ML and BL WS2 films. A comparative study confirms the superior valley polarization and higher carrier mobility of BL WS2 compared with its ML counterpart. Additionally, a minor twist angle existed between the upper and lower layers, featuring a Moiré superlattice. This work reveals the role of surface morphology and surface energy in the growth of TMDs. Simultaneously, it offers insights into the controlled preparation of vertically stacked homo- and heterojunctions.
Estimating ecosystem evapotranspiration (ET) is important to understanding the global water cycle and to study land‐atmosphere interactions. We developed a physics constrained machine learning (ML) ...model (hybrid model) to estimate latent heat flux (LE), which conserves the surface energy budget. By comparing model predictions with observations at 82 eddy covariance tower sites, our hybrid model shows similar performance to the pure ML model in terms of mean metrics (e.g., mean absolute percent errors) but, importantly, the hybrid model conserves the surface energy balance, while the pure ML model does not. A second key result is that the hybrid model extrapolates much better than the pure ML model, emphasizing the benefits of combining physics with ML for increased generalizations. The hybrid model allows inferring the structural dependence of ET and surface resistance (rs), and we find that vegetation height and soil moisture are the main regulators of ET and rs.
Plain Language Summary
A physics constrained machine learning model is developed using the FLUXNET2015 Tier 1 data set. This new approach is able to effectively retrieve latent heat flux while constraining energy conservation in the surface energy budget. This hybrid model has better performance in extrapolation than a pure machine learning model.
Key Points
A physics‐constrained machine learning model of evapotranspiration (hybrid model) is developed and trained using the FLUXNET 2015 data set
The evapotranspiration retrieved by the hybrid model is as accurate as pure machine learning model and also conserves surface energy balance
The hybrid model better reproduces extremes and thus better extrapolates compared to the pure machine learning approach
This work presents a comparative study related to the photocatalytic efficiency associated with wettability measurements and organic dye degradation, as well as other relevant properties (i.e., ...corrosion resistance, roughness, wettability, and adhesion to a substrate). The photocatalytic precursors are titanium dioxide nanoparticles (TiOsub.2 NPs) which are dispersed onto a polymeric electrospun fiber matrix by using three different deposition techniques such as electrospraying, spraying, and dip-coating, respectively. In this work, the host electrospun matrix is composed of poly(acrylic acid) fibers crosslinked with cyclodextrin (β-CD), which shows a good chemical affinity and stability with the other deposition techniques which are responsible for incorporating the TiOsub.2 NPs. In order to evaluate the efficacy of each coating, the resultant photocatalytic activity has been monitored by two different tests. Firstly, the reduction in the water contact angle is appreciated, and secondly, the degradation of an organic dye (Rhodamine B) is observed under UV irradiation. In addition, the final roughness, adherence, and pitting corrosion potential have also been controlled in order to determine which solution provides the best combination of properties. Finally, the experimental results clearly indicate that the presence of TiOsub.2 NPs deposited by the three techniques is enough to induce a super hydrophilic behavior after UV irradiation. However, there are notable differences in photocatalytic efficiency on the Rhodamine B as a function of the selected deposition technique.
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