Macroscopic Uniformity Research Articles

(Invited) Engineering Nanocomposite Substrates for Metal Deposition

Reversible metal plating is at the heart of aqueous based energy storage. Since virtually all metal anodes, e.g., Fe, and Zn, operate outside the stability window of water, it is thus essential to minimize their surface area by controlling the nucleation and growth during deposition and the pit formation during stripping.While epitaxial growth has shown promise as exemplified by the horizontal zinc deposition on graphene, an approximate heteroepitaxy, we will focus our effort in developing a nanocomposite substrate that promotes uniform nucleation sites and fast surface transport. The strategy is potentially highly scalable to address the need for large scale storage. Recently, we have shown that a nanocomposite substrate can induce single crystalline Li growth. By reacting FeF3 with Li, a nanocomposite of Fe and LiF is formed which features Fe nanoparticles of < 2 nm in size uniformly distributed in a matrix of LiF. Despite the global lithiophobility of the substrate, nano Fe domains provide energetically uniform nucleation sites for Li deposition while LiF enables rapid surface transport. Corporative merging of neighboring seeds lead to the formation of single crystalline Li. Unlike single crystal substrates, the nanocomposite features uniformly distributed, energetically equivalent sites for nucleation.We have adopted a similar strategy for Fe and Zn deposition. Preliminary results show that significantly improved macroscopic uniformity is achieved with the nanocomposite substrate. We will discuss materials requirements for operation in an aqueous environment and the general applicability of the approach for other materials.

Current Status and Future Prospects of Kesterite Cu2ZnSn(S,Se)4(CZTSSe) Thin Film Solar Cells Prepared via Electrochemical Deposition

AbstractThe fabrication of kesterite Cu2ZnSn(S,Se)4(CZTSSe) thin‐film solar cells using the electrochemical deposition (ED), which is valued for its industrial feasibility, offers a cost‐effective and environmentally friendly approach to the carbon‐free and clean energy production. However, the reported power conversion efficiency of approximately 10 % for electrodeposited CZTSSe thin‐film solar cells is lower compared to the alternative methods like sputtering and spin‐coating, which is mainly attributed to the phase inhomogeneity and the rough morphology generated during the ED process. Ensuring the microscopic and macroscopic uniformity of the electrodeposited films is crucial for the improvement of the film quality and the device performances. In this review, strategies to address these challenges including the intrinsic film control such as the deposition mode, pH, concentration of metal ions, and complexing agents, as well as the extrinsic approaches such as doping, substitution of metal elements, and the introduction of interfacial layers. In addition, the prospects for the electrochemically deposited CZTSSe solar cells were presented, focusing on the promising applications in tandem, flexible, and solar water‐splitting devices. Finally, this review will provide technical insights into the ED process for preparing CZTSSe solar cells, outlining a perspective for the future development of highly efficient CZTSSe thin film solar cells.

Combined influence of airflows and a parallel magnetic field on the discharge characteristics of AC dielectric barrier discharge

The combined influence of airflows and a parallel magnetic field on an AC-driven dielectric barrier discharge plasma is experimentally investigated through image analyses, electrical measurements, and optical diagnoses. After applying a parallel magnetic field, more discharge filaments are generated during one discharge cycle. Besides, the electrical and optical diagnoses show that the magnetic field can increase the plasma parameters, such as the electron temperature and electron density. When airflows and a parallel magnetic field are applied in combination, the discharge uniformity presented in the long-exposure images is significantly enhanced by the airflows and slightly improved by the magnetic field. With increasing airflow velocity, the distribution of discharge filaments goes through four phases, namely, spot-like distribution, line-like distribution, cotton-like distribution, and stripe-like distribution, among which the stripe-like distribution exhibits the highest discharge uniformity. High-speed video analyses reveal that the improved discharge uniformity can be attributed to the changed breakdown positions and the increased number of filaments. Although airflow can significantly improve the macroscopic uniformity of the discharge, it leads to a decrease in the maximum current pulse amplitude, electron temperature, electron density, and gas temperature. Applying a magnetic field in flowing air can not only improve the discharge uniformity but also ensure that the discharge has high maximum current pulse amplitude intensity, electron temperature, and electron density. Based on the analyses of the electron trajectory and the estimation of the force condition of the micro-discharge remnants, the modulated charged particles, reduced electric field, and pre-ionization degree are responsible for the changed discharge uniformity and plasma parameters in the parallel magnetic field and flowing air.

Influence of the Solvent on the Assembly of Ni3(hexaiminotriphenylene)2 Metal–Organic Framework Nanosheets at the Air/Liquid Interface

Abstract Nanosheets of metal–organic frameworks (MOFs)—porous crystalline materials consisting of metal ions and organic ligands—are actively studied for their intrinsic chemical/physical properties attributed to the reduced dimensionality and for their potential to function as ideal components of nanodevices, especially when electrical conduction is present. Air/liquid interfacial synthesis is a promising technique to obtain highly oriented MOF nanosheets. However, rational control of size and shape combined with the aimed functionality remains an important issue to address making it necessary to research the critical factors governing nanosheet characteristics in the interfacial synthesis. Here, we investigate the influence of the solvent—methanol (MeOH) versus N,N-dimethylformamide (DMF)—used to prepare a ligand spread solution on an assembly of MOF nanosheets composed of Ni2+ and 2,3,6,7,10,11-hexaiminotriphenylene (HITP) (HITP-Ni-NS). We find that the macroscopic morphological uniformity in the micrometer scale is higher when DMF is used as the solvent. Regarding the microscopic crystalline domain, molecules of DMF with relatively high polarity and boiling point are involved in HITP-Ni-NS formation, hindering its growth and resulting in nanosheets with slightly smaller lateral size than that grown when MeOH is used. These findings provide crucial guidelines towards establishing a judicious strategy for creating desired MOF nanosheets at the air/liquid interface, thereby driving forward research on both fundamental and applied aspects of this field.

PDMS/PVDF Electrospinning Membranes for Water-in-Oil Emulsion Separation and UV Protection.

With industry development, the separation of oily wastewater is becoming more critical. Inspired by organisms such as lotus leaves, biomimetic superhydrophobic surfaces with micro-nano structures have shown great potential in this regard. In this work, PDMS/PVDF oil-water separation membranes with designed microstructures were prepared by electrospinning technology. The membrane-forming effect of electrospinning with different ratios of PDMS and PVDF was studied. The study found that membranes with high PDMS content were more likely to form microspheres, and PDMS tended to concentrate on the microspheres. The results also showed that the microspheres would bring better hydrophobicity to the membrane. When the ratio of PDMS to PVDF is 1:2, the membrane has a water contact angle of up to 150° and an oil contact angle of 0°. At this ratio, the separation efficiency of the membrane for the water-in-oil emulsion is 98.7%, and it can still maintain more than 98% after ten separation cycles, which is a good candidate for oil-water separation. Furthermore, microspheres enable the membrane to achieve macroscopic uniformity and microscopic phase separation so that the membranes have both good elongation and fracture strength. In addition, the PDMS/PVDF membranes also exhibit excellent UV resistance, and their UV protection factor is greater than 185, making them a potential UV protective material.

Corrosion of Laser Cladding High-Entropy Alloy Coatings: A Review

Material corrosion is a common phenomenon. Severe corrosion not only causes material failure, but may also lead to unexpected catastrophic accidents. Therefore, reducing the loss caused by corrosion has become a problem faced by countries around the world. As a surface modification technology, laser cladding (LC) can be used to prepare coatings that can achieve metallurgical bonding with the substrate. High-entropy alloys (HEAs) are a new material with superior anti-corrosion ability. Therefore, HEA coatings prepared by LC have become a research hotspot to improve the anti-corrosive ability of material surfaces. In this work, the effects of LC process parameters, post-processing, and the HEA material system on the anti-corrosion ability of HEA coatings and their mechanisms are reviewed. Among them, the LC process parameters influence the anti-corrosion ability by affecting the macroscopic quality, dilution rate, and uniformity of the coatings. The post-processing enhances the anti-corrosion ability of the coatings by improving the internal defects and refining the grain structure. The anti-corrosion ability of the coatings can be improved by appropriately adding transition metal elements such as Ni, Cr, Co, and rare earth elements such as Ce and Y. However, the lattice distortion, diversification of phase composition, and uneven distribution caused by excess elements will weaken the corrosion protection of the coatings. We reviewed the impact of corrosion medium on the anti-corrosion ability of coatings, in which the temperature and pH value of the corrosion medium affect the quality of the passive film on the surface of the coatings, thereby affecting the anti-corrosion ability of the coatings. Finally, to provide references for future research, the development trend of preparing HEA coatings by LC technology is prospected.

A novel method for generation of particle packing model used in numerical simulation for the mechanical behavior of multi-component material

This study presents a novel algorithm to establish a numerical model for the study of mechanical behavior of multi-component material such as particle reinforced metal matrix composites, concrete, particle filled polymers, etc. The algorithm consists of two steps, one is to divide the given region into sub-regions of a specified size distribution, and the other is to fill each sub-region with particles of specified shapes. During the filling process, the contact states between particles can be controlled by the number and positions of reference points. Taking the quasi-static uniaxial tensile simulation of concrete as a verification example, two concrete models with the same particle size distribution but different shapes have been established. Through the comparison of elastoplastic responses of different aggregate shape models in different tensile directions, it is concluded that the models meet the requirements of macroscopic uniformity, meso-scale randomness and statistical rationality. This verifies the feasibility of modeling method and its advantages in precise control of particle shape, distribution and other parameters.

Jejunal diverticulitis secondary to a gastrointestinal stromal tumor: A case report.

IntroductionThe common manifestations of gastrointestinal stromal tumors (GIST) are well established. However, jejunal diverticulosis is an uncommon phenomenon to be associated with this lesion, with its rarity compounded by the relative difficulty associated with its diagnosis. Limited literature is available on this topic. This article examines one such case of jejunal diverticulitis as a result of a GIST, and the intervention of said disease.Case presentationA 69 year old lady presented with abdominal pain, vomiting, and low grade fevers, on a background of ulcerative colitis. She was peritonitic, raising concerns of an acute abdomen. Her imaging identified an intra-abdominal contained perforation, prompting a transfer to theatres overnight for a laparotomy, which identified a jejunal diverticulum, which resembled a contained perforation. This was resected, and sent for histopathological analysis, identifying the lesion as a GIST.DiscussionUnlike other forms of jejunal diverticular disease, those arising from GISTs tend to present perforated, necessitating resection. This disease displays a tendency towards formation on the anti-mesenteric border of the small bowel. Additionally, this particular form of GIST shows macroscopic and histopathological uniformity across reported cases to date despite significant geographical disparity.ConclusionA scant number of case reports worldwide have identified jejunal diverticulitis from GISTs. We suggest diverticula be excised if perforation is suspected, while incidental findings of such be left untouched. However, overall management should be undertaken at the discretion of the operating surgeon.

Solvent Effect to the Uniformity of Surfactant-Free Salmon-DNA Thin Films.

Fabrication of surfactant-modified DNA thin films with high uniformity, specifically DNA–CTMA, has been well considered via drop-casting and spin-coating techniques. However, the fabrication of thin films with pure DNA has not been sufficiently studied. We characterize the uniformity of thin films from aqueous salmon DNA solutions mixed with ethanol, methanol, isopropanol, and acetone. Measurements of thickness and macroscopic uniformity are made via a focused-beam ellipsometer. We discuss important parameters for optimum uniformity and note what the effects of solvent modifications are. We find that methanol- and ethanol-added solutions provide optimal fabrication methods, which more consistently produce high degrees of uniformity with film thickness ranging from 20 to 200 nm adjusted by DNA concentration and the physical parameters of spin-coating methods.

Direct growth of graphene films without catalyst on flexible glass substrates by PECVD* *Project supported by the National Natural Science Foundation of China (Grant No. 51302215), the Joint Research Funds of Department of Science & Technology of Shaanxi Province and Northwestern Polytechnical University, China (Grant No. 2020GXLH-Z-029), and the Natural Science Basic Research Program of Shaanxi Province, China (Grant Nos.

A hydrogen-plasma-etching-based plasma-enhanced chemical vapor deposition (PECVD) synthesis route without metal catalyst for preparing the graphene films on flexible glass is developed. The quality of the prepared graphene films is evaluated by scanning electron microscopy, x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, and electrochemical measurements. In a radio frequency (RF) power range of 50 W–300 W, the graphene growth rate increases with RF power increasing, while the intensity ratio of D- to G-Raman peak (I D/I G) decreases. When the RF power is higher than 300 W, the I D/I G rises again. By optimizing experimental parameters of hydrogen plasma etching and RF power, the properties of as-prepared flexible graphene on glass are modulated to be able to achieve the graphene’s transparency, good electrical conductivity, and better macroscopic uniformity. Direct growth of graphene film without any metal catalyst on flexible glass can be a promising candidate for applications in flexible transparent optoelectronics.

Study on the morphology and microstructure of 5A06 alloy by high-pulse-frequency pulsed laser micro polishing

The surface quality of aluminum alloy seriously affects its service life and following processing quality. The innovative high-pulse-frequency pulsed laser micro-polished 5A06 alloy provides defect-free high-precision micro-domain modified surfaces. The effects of surface morphology and microstructure under processing speed and spot distance were investigated. As the processing speed and spot distance decreased, the macroscopic uniformity increased. The minimum surface roughness was 0.53 μm. The processing speed causes the difference in line energy to affect the spread of the molten pool. Spot distance distinguishes the size of the remelted area. Both affect the surface roughness. After laser micro polishing, the remelting layer and HAZ were observed in the cross-section. The EBSD results show the remelting layer is a single grain but has more small angle grain boundaries, i.e. higher dislocation density. The second phase of HAZ was significantly refined, and the grain size was reduced by 11.36% compared to base material. Mg evaporation in the remelting layer was researched using saturated vapor pressure.

A study on the nucleation and MPCVD growth of thin, dense, and contiguous nanocrystalline diamond films on bare and Si3N4-coated N-polar GaN

We report upon the microwave plasma chemical vapor deposition (MPCVD) growth of polycrystalline diamond on varying crystallographic orientations of GaN (Ga-polar and N-polar), as well as on Si3N4-coated N-polar GaN, as applied to top-side heat spreading layers for III-N-based high electron mobility transistors. Integration of diamond with GaN in this configuration is subject to differing process constraints from previous research focusing on backside heat sinks. A critical requirement is to prevent hydrogen-related etching of the III-N surface in the H+ plasma ambient, as well as to avoid plasma damage to the GaN crystal or HEMT channel region near the surface. Thus we developed the seeding and MPCVD techniques under a low power density plasma with low sample temperatures during deposition. We systematically investigated samples seeded via polymer-assisted dip seeding in a nanoparticle suspension, which were then subjected to MPCVD growth under identical conditions. We evaluated the quality of the films via scanning electron microscopy and Raman spectroscopy to understand the relationship between grain size, interface abruptness, propensity for surface etching, as well as film uniformity. Finally, we were able to identify a process window for both N-polar GaN and Si3N4-coated N-polar GaN which yields thin, fully coalesced, nanocrystalline diamond films with an abrupt interface to the underlying substrate. These diamond films exhibit microscopic uniformity in crystal grain size, and macroscopic uniformity in thickness and interface abruptness via a process which is scalable to large wafer sizes.

Fabrication of polymer colloidal/Au composite nanofilms for stable and reusable SERS-active substrates with highly-dense hotspots

Two-dimensional (2D) nanostructured arrays are regarded as attractive materials for surface-enhanced Raman scattering (SERS)-active substrates because of their excellent stability and signal reproducibility. We present a novel approach for fabricating stable and reusable 2D polymer colloidal monolayer on a SERS-active nanostructured Au substrate with high-density hotspots. Poly(styrene-co-N-isopropylacrylamide)@polyacrylic acid (PSN@PAA) polymer particles with core@shell structure were synthesized by a two-step polymerization. Using the soft microgel polymer particles as building blocks, a 2D close-packed PSN@PAA colloid nanofilm was fabricated at air–water interface. An ultra-thin Au nanofilm was sputtered onto the 2D PSN@PAA colloidal monolayer by a simple and efficient sputter-deposition technique. The aggregation structure of Au nanoparticles on the surface of the 2D microgel nanolayer could be regulated by shrinking the polymer microgels in methanol. Furthermore, the electrostatic interaction of sodium citrate on nanoparticles and the ripening process to Au nanoclusters could facilitate the formation of crevices. The region of Au nano-islands and nanocaps formed on the surface of the soft 2D polymer monolayer could generate very dense enhanced electromagnetic field hotspots, which can greatly enhance the Raman signals of R6G adsorbed on the substrate. The excellent reusability of the PSN@PAA/Au composite nanofilm was mainly due to the preferable adsorption of probe molecules on the 2D soft microgel particles. Moreover, the shrinkage of polymer microgel particles in the ethanol solvent made it easy to desorb the probe molecules from the substrate surface. Therefore, the macroscopic uniformity of the nanofilms ensured the reproducibility of SERS signals, providing an ideal candidate for SERS applications.

Paper swab based SERS detection of non-permitted colourants from dals and vegetables using a portable spectrometer

Rising concern about the use of non-permitted colourants, in common food items such as dals and green vegetables sold in Indian markets, have led to a demand for low-cost point-of-use chemical analysis tools. Conventional food-analysis techniques involving tedious sample preparation protocols are not suited for in-field applications. Surface Enhanced Raman Spectroscopy (SERS) is an analytical technique that is well-suited for point-of-use chemical analysis with molecular level detection capability, which can also serve as a quality assurance tool for businesses. Effective and rapid signal collection from a large-area sample within a field-setting using disposable, low-cost SERS substrates is a key challenge in implementing such a solution.Herein, we demonstrate the use of inkjet-printed thin films comprising of robust nanostructured-silver as flexible, paper-based SERS (P-SERS) swabs for the direct detection of Metanil Yellow (MY) from toor dal (yellow split pigeon peas) samples and Malachite Green (MG) from green peas and green chillies. The macroscopic uniformity of these thin-films in combination with a portable Raman spectrometer equipped with orbital raster scanning (ORS™) technology for signal collection results in an unprecedented precision (RSD ∼ 1.6%) upon characterizing samples saturated with Rhodamine-6G (R6G), a standard Raman probe. As several food-cleansing products have appeared in the marketplace, the adulterant removal efficacy of some commercially available ‘washes’ as well as products such as ‘ozoniser’, which was determined by SERS characterization of swabs before and after use, is also reported.

Direct synthesis of flexible graphene glass with macroscopic uniformity enabled by copper-foam-assisted PECVD

The copper-foam-assisted PECVD approach harnesses the direct production of flexible graphene glass at relatively low temperatures, which readily serve in flexible and wearable electronic and energy applications.

The spatial inhomogeneity and X-ray absorption spectroscopy of superconducting nanocrystalline boron doped diamond films

The local electrical conductivity and impurity band evolution in superconducting nanocrystalline boron doped diamond (BNCD) film are investigated using conducting atomic force microscopy (C-AFM) and X-ray absorption spectroscopy (XAS). C-AFM has been employed to investigate the local conductivity of superconducting BNCD with Tc = 4.3 K and upper critical field Hc2(0) = 5.2 T. A high local electrical heterogeneity of the BNCD film as evidenced from the C-AFM profile points to the uneven boron uptake during the process of doping. C-AFM also revealed that grain boundaries are the highly conducting regions, possibly, due to the presence of p-type trans-polyacetylene along with the CC and CH bonds in the grain boundaries. From the in-depth XPS profiling of the B 1s spectra we confirmed the macroscopic uniformity of the boron concentration across the depth of BNCD layers. X-ray absorption spectroscopy (XAS) measurements near B K-edge and C K-edge showed formation of in-gap states as a result of heavy boron doping. Near C K-edge, bandgap states at 282.8 eV and 284.1 eV are found which are responsible for superconductivity in the BNCD film. This work explores the non-uniform boron doping and its effect on the conduction band structure of a superconducting BNCD film.

Potential energy surface of monatomic liquids

In the last decade, significant progress has been made in the many-body Hamiltonian formulation of liquid dynamics theory. Earlier analysis of experimental data for a wide variety of elemental liquids had provided the reliable but qualitative description of the atomic motion: vibrations in a representative $3N$-dimensional potential energy valley, plus transits, in which atoms cross the intersections between these valleys. Recent comparisons of first-principles theory with experiment for several elemental liquids at melt revealed a highly accurate and versatile theory. In the present work, we report on an extensive quench study of the entire condensed-matter structure-energy distribution for a metallic Na MD system. With these results, all that was learned from experimental data is confirmed, refined in detail, and made more accurate. We show the entire structure-energy distribution, composed of widespread symmetrics and higher lying randoms, we show the increasing dominance of the randoms as $N$ increases, until the symmetrics vanish completely, and we show the random distribution continue its spectacular narrowing as $N$ continues to increase. This behavior certifies our early assignment of the random distribution to the liquid phase and our prediction of macroscopic uniformity of the random structures. Procedures are discussed to identify and calibrate a single random structure to represent the liquid, and the role of the structure energy in liquid thermodynamics is described. A comparison with other liquid dynamics theories is observed in the Introduction, and the relation to the equation-of-state program is noted in the Conclusion.

Surface-floating gold nanorod super-aggregates with macroscopic uniformity

We present a simple method for obtaining high-density two- and threedimensional assemblies of gold nanorods (AuNRs) on polymer brush, referred to as “surface-floating super-aggregates”, with uniform distribution spanning macroscopic distances. This was achieved via the single-step immersion of a poly(oligo ethylene glycol methacrylate) brush-containing substrate in a AuNR solution without any form of functionalization. Owing to extensive macroscale plasmonic coupling, we observed for the first time the gradual evolution of a unique sharp peak in addition to the transverse and longitudinal peaks, in this case, in the near-infrared (NIR) region. We also highlight the dynamic nature of these surface-floating super-aggregates, in which the AuNRs spread out when immersed in solution and collapse when dried to facilitate the access of probe molecules for biosensing applications. As a proof of concept, the surface-floating super-aggregates were used for surface-enhanced Raman spectroscopy, with which we detected rhodamine 6G at as low as sub-femtomolar concentrations. Owing to the excellent large-area uniform coverage and extreme simplicity of the fabrication method, such AuNR assemblies can easily be mass-produced and incorporated into cheap biosensors suitable for consumer use in the near future.

Switching Vertical to Horizontal Graphene Growth Using Faraday Cage-Assisted PECVD Approach for High-Performance Transparent Heating Device.

Plasma-enhanced chemical vapor deposition (PECVD) is an applicable route to achieve low-temperature growth of graphene, typically shaped like vertical nanowalls. However, for transparent electronic applications, the rich exposed edges and high specific surface area of vertical graphene (VG) nanowalls can enhance the carrier scattering and light absorption, resulting in high sheet resistance and low transmittance. Thus, the synthesis of laid-down graphene (LG) is imperative. Here, a Faraday cage is designed to switch graphene growth in PECVD from the vertical to the horizontal direction by weakening ion bombardment and shielding electric field. Consequently, laid-down graphene is synthesized on low-softening-point soda-lime glass (6 cm × 10 cm) at ≈580 °C. This is hardly realized through the conventional PECVD or the thermal chemical vapor deposition methods with the necessity of high growth temperature (1000 °C-1600 °C). Laid-down graphene glass has higher transparency, lower sheet resistance, and much improved macroscopic uniformity when compare to its vertical graphene counterpart and it performs better in transparent heating devices. This will inspire the next-generation applications in low-cost transparent electronics.

Gold Nanoparticles Sliding on Recyclable Nanohoodoos—Engineered for Surface‐Enhanced Raman Spectroscopy

AbstractRobust, macroscopically uniform, and highly sensitive substrates for surface‐enhanced Raman spectroscopy (SERS) are fabricated using wafer‐scale block copolymer lithography. The substrate consists of gold nanoparticles that can slide and aggregate on dense and recyclable alumina/silicon nanohoodoos. Hot‐spot engineering is conducted to maximize the SERS performance of the substrate. The substrate demonstrates remarkably large surface‐averaged SERS enhancements, greater than 107 (&gt;108 in hot spots), with unrivalled macroscopic signal uniformity as characterized by a coefficient of variation of only 6% across 4 cm. After SERS analyses, the nanohoodoos can be recycled by complete removal of gold via a one‐step, simple, and robust wet etching process without compromising performance. After eight times of recycling, the substrate still exhibits identical SERS performance in comparison to a new substrate. The macroscopic uniformity combined with recyclability at conserved high performance is expected to contribute significantly on the overall competitivity of the substrates. These findings show that the gold nanoparticles sliding on recyclable nanohoodoo substrate is a very strong candidate for obtaining cost‐effective, high‐quality, and reliable SERS spectra, facilitating a wide and simple use of SERS for both laboratorial and commercial applications.