Surface Roughness Of Films Research Articles

Biodegradable Active Packaging Material Containing Grape Seed Ethanol Extract and Corn Starch/κ-Carrageenan Composite Film.

An active film composed of corn starch/κ-carrageenan and ethanolic grape seed extract (0, 1, 3, and 5 wt% of GSE on corn starch basis) were successfully prepared using the solvent casting technique. The effects of the different concentrations of ethanolic grape seed extract (GSE) on the physicochemical properties, antioxidant properties, and antibacterial properties of CS/κC films were analyzed. The results showed that the addition of GSE inhibited the recrystallization of starch in the composite film. The glass transition temperature of composite film is 121.65 °C. With the addition of GSE, the surface roughness of the composite film increased, and the cross-section displayed a stratification phenomenon. Meanwhile, when GSE was added to the composite film, the tensile strength of the composite film decreased (3.50 ± 0.27 MPa), the elongation at break increased (36.87 ± 2.08%), and the WVP increased (1.58 ± 0.03 g mm/m2·d· kPa). With the increase of the concentration of GSE in the composite film, the a* value and b* value of the composite film increase, the L* value decreases, and the opacity increases. The lipid oxidation test proved that the composite films containing 1% GSE has a significant inhibitory effect on the oxidation of lard (p < 0.05). The above results indicate that the GSE can be used as a food-grade packaging material and has a good application prospect in the food industry.

Structural, Optical, and Sensing Properties of Nb-Doped ITO Thin Films Deposited by the Sol-Gel Method.

The aim of the present study was the development of Nb-doped ITO thin films for carbon monoxide (CO) sensing applications. The detection of CO is imperious because of its high toxicity, with long-term exposure having a negative impact on human health. Using a feasible sol-gel method, the doped ITO thin films were prepared at room temperature and deposited onto various substrates (Si, SiO2/glass, and glass). The structural, morphological, and optical characterization was performed by the following techniques: X-ray diffractometry (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV/Vis/NIR spectroscopic ellipsometry (SE). The analysis revealed a crystalline structure and a low surface roughness of the doped ITO-based thin films. XTEM analysis (cross-sectional transmission electron microscopy) showed that the film has crystallites of the order of 5-10 nm and relatively large pores (around 3-5 nm in diameter). A transmittance value of 80% in the visible region and an optical band-gap energy of around 3.7 eV were found for dip-coated ITO/Nb films on SiO2/glass and glass supports. The EDX measurements proved the presence of Nb in the ITO film in a molar ratio of 3.7%, close to the intended one (4%). Gas testing measurements were carried out on the ITO undoped and doped thin films deposited on glass substrate. The presence of Nb in the ITO matrix increases the electrical signal and the sensitivity to CO detection, leading to the highest response for 2000 ppm CO concentration at working temperature of 300 °C.

Growth mechanism and characteristics of β-Ga2O3 heteroepitaxailly grown on sapphire by metalorganic chemical vapor deposition

In this study, monoclinic gallium oxide (β-Ga2O3) epilayer was successfully grown on c-plane, (0001), sapphire substrate by metalorganic chemical vapor deposition (MOCVD) with interplaying growth temperature, TEGa flow rate, and growth time. X-ray diffraction 2θ scans show only three narrow diffraction peaks referred to β-Ga2O3(2¯ 01), (4¯ 02), and (6¯ 03) in all epilayers, indicating a superior crystalline quality. Current-voltage (I–V) measurement reveals that these β-Ga2O3 films are insulating and exhibit high resistance in a range of 1012–1014 Ω. The crystallization characteristics of the epilayers can be effectively improved with thickness through increasing TEGa flow rate and growth time, which was evidenced by X-ray rocking curves and I–V measurements. However, the surface roughness of β-Ga2O3 film increases with growth time and TEGa flow rate. When the growth temperature increases above 825 °C, the thickness of β-Ga2O3 film decreases clearly. Furthermore, it can be found that the growth rate decreased as the growth time increasing. The growth mechanism based on first-principles calculation was proposed as that 3D growth induced by the lattice mismatch between β-Ga2O3 and sapphire starts at nucleation stage, and follows up a lateral growth promoting a 2D growth after the thick epilayer being grown. In addition, the complex chemical reaction between TEGa and oxygen precursors was unraveled by density function theory calculation.

Effects of rapid thermal annealing temperature on NO2 gas sensing properties of p-type mixed phase tin oxide thin films

Effects of the rapid thermal annealing (RTA) temperature on the NO2 gas sensing properties of p-type SnOX thin films were investigated. The SnOX thin films were deposited using radio-frequency magnetron sputtering and subjected to RTA at 200 °C, 250 °C, and 300 °C. The deposited SnOX thin films contained both p-type SnO and n-type SnO2 components, but the SnO was the dominant phase. The amount of SnO2 components increased with increasing RTA temperature, but the highest amount of oxygen vacancy (OVac) states was observed in the SnOX thin film annealed at 250 °C. The surface roughness of the SnOX thin film decreased as the RTA temperature increased. The SnOX thin film subjected to RTA at 250 °C exhibited a significantly higher maximum sensing response to NO2 (4.25–10 ppm NO2 at 60 °C) than those of the films treated at 200 °C (1.13) or 300 °C (0.92). The higher response was attributed to the larger amount of SnO2 and OVac in the thin film and large number of defects and cracks on the film surface. The experimental results demonstrated that the post-deposition RTA temperature considerably affects the NO2 sensing properties of the p-type SnOX-based gas sensors.

Green silver nanoparticles functionalised gelatin nanocomposite film for wound healing: Construction and characterization

Wound dressings have progressed from simple to advance by the interdisciplinary approaches of chemical, materials and biological fields to engineer the functional materials that can improve wound healing by reducing bacterial infections on wound site. In the present study, Praecitrullus fistulosus extract was used for the preparation of silver nanoparticles (Ag NPs) via a green synthesis method for wound healing. The synthesized Ag NPs were characterized via Ultraviolet–Visible (UV–Vis) spectroscopy, High-Resolution X-ray Diffractometer (HRXRD), and High-Resolution Transmission Electron Microscopy (HRTEM). The gelatin-Neem extract-nanocomposite films were prepared by incorporating green Ag NPs via solvent casting method. The physico-chemical, morphological, structural, thermal, and biological properties of the nanocomposite (NCP) films were determined in order to check their efficacy for wound healing applications. The NCP films were showing significantly higher water absorption capacity, folding endurance, and porosity as compared to the control gelatin (GLT) film. The observed pH of the NCP film was found to be 5.9, which is suitable for human skin. Antibacterial activity of the NCP films against gram-negative bacteria (Escherichia coli) was higher compared to GLT film. The surface roughness was found to be 22.7 nm for the NCP film containing Ag NPs. The thermal stability of the GLT film was improved after the incorporation of Ag NPs. The high antimicrobial activity, porosity and improved surface roughness of NCP films would favour the adherence, growth and proliferation of seeded cells that is pre-requisite for ideal dressing materials.

Sensing behaviors of lipophilic calix[4]arene phosphonate based Langmuir-Blodgett thin films for detection of volatile organic vapors

This study concentrates on the lower rim effect of calix[4]arenes based lipophilic phosphonate (CTPO4 and CPO4) with and without tert-butyl group Langmuir-Blodgett (LB) thin films in the volatile organic vapors (VOCs) sensing applications. Surface plasmon resonance (SPR) technique was employed to determine optical parameters and to investigate VOCs sensor properties of thin films. The thicknesses of 3 layered CTPO4 and CPO4 thin films were estimated as 1.9 ± 0.02 and 2.6 ± 0.02 nm. Atomic force microscope (AFM) and contact angle (CA) analysis were taken for the morphological study. Both thin film surfaces showed a uniform distribution, the surface roughness of CTPO4 thin film (23.04 nm) was found to be higher than the CPO4 thin film (10.53 nm). The equilibrium contact angle values of 58.96° ± 0.43° for CTPO4 and 44.23° ± 2.25° for the CPO4 thin film surface were determined. CTPO4 and CPO4 LB thin films were exposed to various VOCs gas in real time. Ficks’ second law of diffusion was adopted to explain the sorption process of VOCs into the thin films, and the diffusion is interpreted as a two-region interaction. The diffusion coefficients were determined between 2.7 × 10−22–63.19 × 10−22 cm2 s−1 and 2.7 × 10−24–63.19 × 10−24 cm2 s−1 for the first and second region of the interaction respectively. The responses of CTPO4 are higher than CPO4 due to the upper rim tert-butyl groups onto CTPO4 molecule. Both films were highly affiliated by the chlorinated VOCs compared with the aromatic compounds. The presence of tert-butyl group has improved sensing properties and these new calix[4]arenes are good candidates for sensor applications.

The influence of calcium chloride concentration on the mechanical and barrier properties of high amylose corn starch film

In this study, high amylose corn starch (HACS) films were prepared using CaCl2 as cosolvent. The interaction between CaCl2 and HACS during the preparation was investigated. Differences in physicochemical properties between HACS films with and without CaCl2 were characterized using wide-angle X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), water vapor permeability (WVP), thermogravimetric analysis (TG) and atomic force microscopy (AFM). The tensile strength and elongation at break increased to 27.01 ± 1.13 MPa and 17.4 ± 1.9%, respectively, CaCl2 had plasticizing effect and provided mechanical reinforcement to the formed HACS films. The reinforcement was mainly due to (ⅰ) CaCl2 increased the content of free amylose chains in the aqueous phase, and (ⅱ) chelation between Ca2+ and starch chains enhanced the entanglement between HACS chains. The results of XRD and FTIR indicated the crystalline region and shot-range orderliness of films decreased, CaCl2 significantly increased the dispersion of starch chains and made the HACS films more homogeneous. CaCl2 improved the barrier properties and surface morphology. The surface roughness of the HACS films decreased fromRa = 189 nm, Rq = 242 nm toRa = 103 nm, Rq = 152 nm as the concentration of CaCl2 increased. However, high concentration of CaCl2 destroyed the inner and surface structure of the film to some extent.

Overcoming the Outcoupling Limit of Perovskite Light-Emitting Diodes with Artificially Formed Nanostructures.

The external quantum efficiency (EQE) of state-of-the-art planar-structure perovskite light-emitting diodes (PeLEDs) is mainly limited by the outcoupling efficiency, which is around 20% and decreases significantly with the perovskite thickness. Here, an approach to artificially form textured perovskite films to boost the outcoupling limit of the PeLEDs is reported. By manipulating the dwell time of antisolvents, the perovskite phase precipitation mechanism, film-forming process, and surface texture can be finely controlled. The film surface roughness can be tuned from 15.3 to 241 nm, with haze increasing accordingly from 6% to >90% for films with an average thickness of 1.5 µm. The light outcoupling limit increases accordingly from 11.7% for the flat PeLEDs to 26.5% for the textured PeLEDs due to photon scattering at the interface. Consequently, the EQE is boosted significantly from around 10% to 20.5% with an extraordinarily thick emissive layer of 1.5 µm. This study provides a novel way of forming light-extraction nanostructures for perovskite optoelectronic devices.

Tissue Engineering Scaffold Material with Enhanced Cell Adhesion and Angiogenesis from Soy Protein Isolate Loaded with Bio Modulated Micro-TiO2 Prepared via Prolonged Sonication for Wound Healing Applications.

Tissue engineering is a technique that promotes healing by creating an ideal environment for endogenous cells to migrate and grow into the site of injury via a scaffold, improving regeneration and reducing the time required for in vitro cell culture. In this work, the effect of the addition of sonicated TiO2 in the soy protein isolate (SPI) matrix for tissue engineering applications was studied. In comparison to adding expensive nano TiO2, this method of incorporating sonicated TiO2 into the SPI matrix will aid in achieving improved properties at a lower cost. The effect of the addition of sonicated TiO2 on the morphological, UV transmittance, mechanical, thermal, surface energy, and hydrophilicity of SPI films was investigated. The result shows that the uniformly distributed TiO2 particles successfully blocked 95% of UV light. Scanning electron microscopy revealed a significant reduction in the TiO2 agglomerate size and homogeneous distribution of the same when sonication was applied instead of mechanical dispersion. A simultaneous increase of tensile strength (from 3.16 to 4.58 MPa) and elongation at break values (from 24.25% to 95.31%) with 0.5% TiO2 was observed. The addition of 0.25% TiO2 was found to significantly enhance the elongation at break value to 120.83%. Incorporation of micro-TiO2 particles could improve the surface roughness, surface energy, and wettability of SPI films. In vitro cell adhesion studies and in vivo subcutaneous implantation studies were performed to assess the cell growth and angiogenesis of the developed film membranes. An MTT assay showed that SPI-1%TiO2 film favored cell viability up to 118%, and in vivo subcutaneous implantation studies showed enhanced cell growth and angiogenesis for SPI-1% TiO2 films. This SPI-TiO2 film with enhanced surface properties can be used as an ideal candidate for tissue engineering applications.

Influence mechanism of RF bias on microstructure and superconducting properties of sputtered niobium thin films

In this study, radio frequency (RF) biased direct current (DC) magnetron sputtering was used to simultaneously improve the surface roughness and superconducting properties of Nb thin films for Josephson circuits application. The surface roughness of the Nb films decreased with an increase in RF powers, whereas the transition temperature, transition width, and residual resistance ratio of the Nb film were optimum at an RF power of 20 W but will deteriorate at higher RF powers. The film resistivities at 10 K obviously increased when the RF power was increased to 40 W and 60 W, which indicates that electron-impurity scattering and scattering on lattice defects are severer in these Nb films. The microstructures, impurities (mainly Ar) and dislocation states were correlated with the electrical and superconducting properties of Nb films. In summary, an optimal process for depositing Nb films with simultaneously improved surface roughness and superconducting properties was found, the Nb film deposited at a DC power of 500 W and an RF bias power of 20 W with a substrate bias voltage of approximately −100 V had the best overall quality. The method is prospective to be applicated in multilayer superconducting electronic devices fabrication based on Nb and other superconductors.

Suppressing the Hofmeister Anion Effect by Thermal Annealing of Thin-Film Multilayers Made of Weak Polyelectrolytes.

Thin films made of weak polyelectrolytes poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) have been fabricated on silicon wafers using the layer-by-layer (LbL) method. To study the influence of counteranion type on the growth and properties of PAH/PAA multilayers, the nature of the supporting sodium salt was varied from cosmotropic to chaotropic anions (F-, Cl-, and ClO4 -). Results of ellipsometry and AFM measurements indicate that the film thickness and surface roughness systematically increase on the order F- < Cl- < ClO4 -. Furthermore, we found that the hydrophobicity of the PAH/PAA multilayer also follows the described trend when a polycation is the terminating layer. However, the heating of PAH/PAA multilayers to 60 °C during the LbL assembly suppressed the influence of background anions on the multilayer formation and properties. On the basis of the obtained results, it could be concluded that thermal annealing induces changes at the polymer-air interface in the sense of reorientation and migration of polymer chains.

Evaluation of the influence of thermal annealing on the performance of vertical topological insulator p-n heterojunction broadband photodetector

The rapid progress and continuum search for new broadband photodetectors generation with ultrafast response synchronizes with the conductive surface electronic structure and the strong broadband absorption properties of 3D topological insulators. Here, we introduce the fabrication of a vertical p-n heterojunction based on thermally evaporated thin films of Sb2Te3/Bi2Te3 on Si substrate for broadband photodetection. The realization of these characteristics dictated us to study the structural, optical absorption, and morphological properties of each layer in the fabricated device as a function of annealing temperature using XRD, spectrophotometric measurements, and FE-SEM techniques, respectively. The annealing process up to T = 423 K enhanced the film’s crystallinity, and grain growth process besides improving the film quality and surface roughness. Furthermore, the optoelectronic characterizations showed that all fabricated photodetectors exhibit a good response to halogen light illumination in the wavelength range (310–1100) nm with different intensities (10–50) mW/cm2. Whilst the 423 K annealed photodetector showed the highest photosensitivity with a conspicuous stable and fast response. The main device parameters, including spectral responsivity, specific detectivity, and response times were determined in addition to explaining the forward and reverse bias conduction mechanisms. The estimated spectral responsivity of the fabricated devices was about 0.247, 0.397, and 0.148 A/W for the as fabricated and 423 K and 573 K, respectively. This significant improvement of the device’s performance rather than other topological insulator devices may be due to the strong built-in field at the topological insulators’ interfaces. Moreover, the fabricated photodetectors showed improved and repeatable ON/OFF transient switching behavior with 85.23 ms and 84.66 ms as a rise and fall time, respectively. According to the prominent results in addition to the simple architecture of the fabricated photodetectors, this topological insulator photosensor can be considered a potential candidate in prospective high-performance optoelectronics.

Boosting Energy Storage of Poly(vinylidene difluoride) Nanocomposite Based Flexible Self-Standing Film with Low Amount of Hydroxylated V2O5

Polymer-ceramic based nanocomposite dielectric materials have become an attraction for researchers due to their lightweight and high dielectric breakdown strength as well as good dielectric properties. We have synthesized poly(vinylidene difluoride) (PVDF)/hydroxylated-V2O5 (Hy-V2O5) ferroelectric polymer nanocomposite self-standing film, with an average thickness of 0.07 ± 0.005 mm. The phase identification, surface analysis, and structural analysis were performed using differential scanning calorimetry, X-ray photoelectron spectroscopy analysis, and X-ray diffraction, respectively. The analysis of atomic force micrographs reveals lower surface roughness of the nanocomposite films and confirms that the film is suitable for energy storage rather than charge transport with the help of the isotropic power spectral density (PSD) profile. The loading of a low amount of Hy-V2O5 filler in PVDF significantly enhances the ferroelectric polarization, making it highly suitable for high energy storage applications. Enhancement of the dielectric constant (from ∼9 to 29.86) and polarization (Pmax for PVDF = 0.86 μC/cm2 to Pmax for PVDF/Hy-V2O5 = 2.7 μC/cm2 at the 1000 kV/cm field) is obtained. The energy density for the nanocomposite increased to 220% of that of the pure PVDF. Due to the low amount of filler, there is no substantial reduction in the dielectric breakdown strength of the nanocomposite, which is maintained at 1766.93 kV/cm.

Unveiling the growth mode and structure relaxation of Polytetrafluoroethylene film by radio-frequency magnetron sputtering

Relying on radio-frequency (RF) magnetron sputtering, Polytetrafluoroethylene (PTFE) films with a series of thicknesses in the range from 80 to 2000 nm were prepared on silicon substrates. The surface morphology and roughness of the PTFE films were measured by atomic force microscope (AFM) technology at microscale. Results indicated that the PTFE film grew in an island pattern during sputtering, while the surface roughness of PTFE films was almost invariable throughout the sputtering process. Then the structure relaxation of PTFE film annealed at 100 °C for 15–480 min was investigated. Annealing treatment induced columnar protrusions on the PTFE surface, which was due to the flow and rearrangement of molecules. During annealing duration, the columnar structures could continuously rearrange and decompose, and therefore lowering film thickness from 2000 to 1110 nm with increasing annealing time. Due to molecule flow and redistribution of the annealed film, the columnar structures were formed on the surface, which resulted in the higher roughness. Finally, the effects of film thickness and annealing time on the hydrophobicity were also studied.

Evaluation of a surface roughness-dependent trimodal switchable mirror using a dry deposition method

We used a nanoparticle deposition system (NPDS) to fabricate surface roughness-dependent trimodal switchable mirrors using a non-electrochromic antimony-doped tin oxide (ATO) film with dry-deposited micro- and nano-sized ATO particles. The devices switched among transparent, mirror and black states. Reversible Ag electrodeposition onto flat ITO glass and the rough surface of the ATO film obviated the need for an electrochromic material. NPDS creates very rough films by supersonically spraying powder onto a substrate. The roughness of the micro-sized ATO film was greater than that of the nano-sized ATO film. As both films were sufficiently rough, a completely black state could be achieved by both devices (0% transmittance over the entire visible wavelength), attributable to light scattering. In contrast, the electrochemical properties of devices with the micro-sized ATO film were superior to those of devices using the nano-sized ATO film because the greater roughness increased the active surface. The charge transfer resistance of devices with the micro-sized film (38 Ω) was lower than that of devices with the nano-sized film (44 Ω). The charge capacity of devices with the micro-sized film (109.87 mC/cm2) was much higher than that of devices with the nano-sized (95.59 mC/cm2). The cyclic transmittance of the device using the micro-sized ATO film was evaluated over 500 cycles with 0% diminution for its durability. Therefore, a trimodal switchable mirror was demonstrated by controlling the surface roughness of a non-electrochromic film. • Dry deposition of particles can control surface roughness of the film. • Trimodal switchable mirror was achieved successfully without electrochromic film. • The electrode with rough surface forms complete black state by light scattering. • Performance of switchable mirror device was compared depending on surface roughness.

Effect of Temperature on Crystal Structure of W Films Electrodeposited from Molten CsF–CsCl–WO3

The electrodeposition of W was studied in detail using CsF–CsCl–WO3. Prior to electrodeposition, the WO3 solubility was confirmed to be 1.0 mol% at 773 K and increase with temperature. To investigate the effect of temperature on the crystal structure, electrodeposition was conducted at 6–25 mA cm−2 between 773 and 923 K with a unified charge density of 90 C cm−2. X-ray diffraction analysis confirmed that the crystal structures of the electrodeposited W films were β-W at 773 and 823 K, a mixed phase (α-W and β-W) at 873 K, and α-W at 923 K. The shape of the crystal grains varied with temperature: grains of β-W obtained at 773 and 823 K were spherical, while those of α-W obtained at 923 K were angular. Scanning electron microscopy observations showed that W films with smoother surfaces were obtained at lower current densities at all temperatures. In particular, a dense and smooth W film (surface roughness: 0.66 μm, thickness: 10 μm) was obtained at 6 mA cm−2 and 773 K. When the charge density was increased to 210 C cm−2 at 6 mA cm−2 and 773 K, a W film with a smooth surface and thickness of 30 μm was obtained.

Electrostatic layer-by-layer deposition of diamond nanoparticles onto substrate surfaces

Diamond nanoparticles (DNPs) are expected as splendid coating materials to give, e.g. corrosion resistance, anti-bacterial properties, and antireflection function. In this paper, we demonstrate a technique of electrostatic layer-by-layer deposition of DNPs onto substrate surfaces using DNP colloidal suspensions with different signs of zeta potentials alternately. The formed DNP layers are investigated in terms of film thickness, surface roughness, and homogeneity. Plus, those morphologies of DNP layers are theoretically correlated with the colloidal properties of DNP suspensions based on the electrostatic interaction potential energy between colloidal DNPs and substrate surfaces. Consequently, it turns out that the demonstrated technique enables formation of DNP thin layers with desired thickness, particle density, and surface roughness on substrate surfaces by controlling the ionic strength of colloidal DNPs.

Functional enhancement of hydroxypropyl cellulose‐based bionanocomposite films incorporating chitosan nanoparticles

SummaryThe aims of the present study were to investigate the effect of the incorporation of chitosan nanoparticles (ChiNPs) on the physicochemical properties and antifungal activity of hydroxypropyl cellulose (HPC) bionanocomposite films. The films of 4% HPC and ChiNP at various dosages (0%, 0.1%, 0.5%, 1%, 1.5%, 3% w/w of HPC) were prepared. Atomic force microscopy (AFM) verified the dispersion of spherical‐shaped ChiNP in a nanoscale size range (14.75–56.74 nm). Incorporation of nanofiller affected the functional properties by increasing the film–water contact angle to &gt;53°, improving the optical properties, and reducing water vapour permeability by 5.73–12.54%. These results were influenced by surface roughness and microstructure characteristics of a bionanocomposite film, which were confirmed using AFM and scanning electron microscopy (SEM). Tensile assays of the films showed slight increases in tensile strength from 8.87 to 11.08 MPa and Young's modulus from 0.10 to 0.15 GPa with increasing proportions of ChiNP (1.5%). An effective concentration of ChiNP of 1.5% (w/w of HPC) was able to improve the performance of HPC and offered antifungal activity against Botrytis cinerea, as confirmed through mycelial growth inhibition assays and by membrane integrity changes. The HPC/ChiNP bionanocomposite films may have potential applications for active packaging, particularly for fresh fruit commodities.

Atomic force microscopic investigations of MoS2 thin films produced by low pressure sulfurization

Molybdenum disulfide (MoS2) thin films were produced on Si/SiO2 substrate by low pressure sulfurization of molybdenum (Mo) film. Mo films are treated with sulfur vapor at different temperatures to investigate the effect of growth temperature on the structural and morphological features of MoS2 films. Raman measurements confirmed the existence of multilayer MoS2. Atomic force microscopy (AFM) measures film thickness and examines surface topography. The statistical analysis of variance (ANOVA) technique is applied to assess temperature effects and validate AFM findings. The growth temperature affects film thickness, surface roughness and grain size. Thickness increases with an increase in temperature while the roughness decreases. The least roughness is obtained when MoS2 is produced at 800 °C. Interestingly, the grain size initially increases with increasing temperature and then drops. The largest grain size is found for sulfurization at 750 °C. These findings will help adjust MoS2 thin film morphology and crystalline quality.

One-Step Exfoliation Method for Plasmonic Activation of Large-Area 2D Crystals.

Advanced exfoliation techniques are crucial for exploring the intrinsic properties and applications of 2D materials. Though the recently discovered Au-enhanced exfoliation technique provides an effective strategy for the preparation of large-scale 2D crystals, the high cost of gold hinders this method from being widely adopted in industrial applications. In addition, direct Au contact could significantly quench photoluminescence (PL) emission in 2D semiconductors. It is therefore crucial to find alternative metals that can replace gold to achieve efficient exfoliation of 2D materials. Here, the authors present a one-step Ag-assisted method that can efficiently exfoliate many large-area 2D monolayers, where the yield ratio is comparable to Au-enhanced exfoliation method. Differing from Au film, however, the surface roughness of as-prepared Ag films on SiO2 /Si substrate is much higher, which facilitates the generation of surface plasmons resulting from the nanostructures formed on the rough Ag surface. More interestingly, the strong coupling between 2D semiconductor crystals (e.g., MoS2 , MoSe2 ) and Ag film leads to a unique PL enhancement that has not been observed in other mechanical exfoliation techniques, which can be mainly attributed to enhanced light-matter interaction as a result of extended propagation of surface plasmonic polariton (SPP). This work provides a lower-cost and universal Ag-assisted exfoliation method, while at the same time offering enhanced SPP-matter interactions.