Flake Size Research Articles

Synthesis, Toxicity Assessment, Environmental and Biomedical Applications of MXenes: A Review.

MXenes are a family of two-dimensional (2D) composite materials based on transition metal carbides, nitrides and carbonitrides that have been attracting attention since 2011. Combination of electrical and mechanical properties with hydrophilicity makes them promising materials for biomedical applications. This review briefly discusses methods for the synthesis of MXenes, their potential applications in medicine, ranging from sensors and antibacterial agents to targeted drug delivery, cancer photo/chemotherapy, tissue engineering, bioimaging, and environmental applications such as sensors and adsorbents. We focus on in vitro and in vivo toxicity and possible mechanisms. We discuss the toxicity analogies of MXenes and other 2D materials such as graphene, mentioning the greater biocompatibility of MXenes. We identify existing barriers that hinder the formation of objective knowledge about the toxicity of MXenes. The most important of these barriers are the differences in the methods of synthesis of MXenes, their composition and structure, including the level of oxidation, the number of layers and flake size; functionalization, test concentrations, duration of exposure, and individual characteristics of biological test objects Finally, we discuss key areas for further research that need to involve new methods of nanotoxicology, including predictive computational methods. Such studies will bring closer the prospect of widespread industrial production and safe use of MXene-based products.

Phase-controlled synthesis of SnS2 and SnS flakes and photodetection properties

Two-dimensional (2D) layered tin sulfide compounds including SnS2 and SnS have attracted increasing attention due to their great potential application in the fields of optoelectronics and energy storage. However, device development has been delayed by the lack of capabilities to synthesize large-scale and high-quality 2D tin sulfide. Here, a phase-controlled synthesis of SnS2 and SnS flakes with lateral size over 100 μm was successfully realized via a facile chemical vapor deposition method. The lateral size of flakes and phase transformation of SnS2 to SnS can be tuned via changing the synthesis temperature. Compared to the formation of the SnS2 phase at relative low temperature (<750 °C), the SnS phase is favorable at higher temperature. The phototransistor based on the as-prepared SnS2 and SnS exhibits excellent photoresponse to 405 nm laser, including a high responsivity (1.7 × 106 mA W−1), fast response rates (rise/decay time of 13/51 ms), an outstanding external quantum efficiency (5.3 × 105%), and a remarkable detectivity (6.24 × 1012 Jones) for SnS2-based phototransistor, and these values are superior to the most reported SnS2 based photodetectors. Although the responsivity (3390 mA W−1) and detectivity (1.1 × 1010 Jones) of SnS-based device is lower than that of the SnS2 phototransistor, it has a faster rise/decay time of 3.10/1.59 ms. This work provides a means of tuning the size and phase of 2D layered tin sulfide, and promotes the application of SnS2 in high-performance optoelectronic devices.

Surface Functionalities of Graphene Oxide with Varying Flake Size

Surface Functionalities of Graphene Oxide with Varying Flake Size

Assessment of kernel characteristics to predict popping performance in grain sorghum

AbstractGrowth in the niche market of popped grain sorghum [Sorghum bicolor (L.) Moench] has increased the demand for grain sorghum lines or hybrids with improved popping quality. While there is a clear morphological difference in kernel morphology between popcorn [Zea mays L. everta] and most other types of corn, most grain sorghum genotypes have kernels with generally similar morphological structure. The absence of a specific kernel morphology for sorghum makes it impossible to eliminate types of grain sorghum that will not pop based solely on that morphology. Consequently, screening of any sorghum genotype requires the actual popping of grain from that genotype. As such, the identification of traits or combinations thereof that effectively screen grain sorghum genotypes for popping efficiency (PE), expansion ratio (ER), flake size (FS), and popped density (PD) is necessary. Herein, grain from 78 diverse genotypes grown in two environments were characterized for physical (i.e., diameter, thousand kernel weight, kernel hardness index, test weight, and visual hardness rating), compositional (i.e., starch, fiber, fat, ash, and protein), and popping characteristics (i.e., PE, ER, FS, and PD). No single physical or compositional trait was sufficiently correlated to prediction of popping performance. Multi‐trait models better predicted popping performance than the single trait correlations. Further, multi‐trait models using compositional predictors increased prediction accuracies by 10.1% for PE, 42.9% for ER, 24.4% for FS, and 40.6% for PD compared with physical predictors. Among subgroups of genotypes, prediction accuracies varied considerably based on the criteria used to subdivide the genotypes. In conclusion, indirect selection for popping performance is possible by leveraging specific multi‐trait models.

Dynamic growth/etching model for the synthesis of two-dimensional transition metal dichalcogenides via chemical vapour deposition

The preparation of two-dimensional transition metal dichalcogenides on an industrially relevant scale will rely heavily on bottom-up methods such as chemical vapour deposition. In order to obtain sufficiently large quantities of high-quality material, a knowledge-based optimization strategy for the synthesis process must be developed. A major problem that has not yet been considered is the degradation of materials by etching during synthesis due to the high growth temperatures. To address this problem, we introduce a mathematical model that accounts for both growth and, for the first time, etching to describe the synthesis of two-dimensional transition metal dichalcogenides. We consider several experimental observations that lead to a differential equation based on several terms corresponding to different supply mechanisms, describing the time-dependent change in flake size. By solving this equation and fitting two independently obtained experimental data sets, we find that the flake area is the leading term in our model. We show that the differential equation can be solved analytically when only this term is considered, and that this solution provides a general description of complex growth and shrinkage phenomena. Physically, the dominance suggests that the supply of material via the flake itself contributes most to its net growth. This finding also implies a predominant interplay between insertion and release of atoms and their motion in the form of a highly dynamic process within the flake. In contrast to previous assumptions, we show that the flake edges do not play an important role in the actual size change of the two-dimensional transition metal dichalcogenide flakes during chemical vapour deposition.

Stone toolmaking difficulty and the evolution of hominin technological skills

Stone tools are a manifestation of the complex cognitive and dexterous skills of our hominin ancestors. As such, much research has been devoted to understanding the skill requirements of individual lithic technologies. Yet, comparing skill across different technologies, and thus across the vast timespan of the Palaeolithic, is an elusive goal. We seek to quantify a series of commensurable metrics of knapping skill across four different lithic technologies (discoids, handaxes, Levallois, and prismatic blades). To compare the requisite dexterity, coordination, and care involved in each technology, we analysed video footage and lithic material from a series of replicative knapping experiments to quantify deliberation (strike time), precision (platform area), intricacy (flake size relative to core size), and success (relative blank length). According to these four metrics, discoidal knapping appears to be easiest among the sample. Levallois knapping involved an intricate reduction sequence, but did not require as much motor control as handaxes and especially prismatic blades. Compared with the other Palaeolithic technologies, we conclude that prismatic blade knapping is set apart by being a skill intensive means of producing numerous standardised elongate end-products.

Insight into chelating agent stimulated in-situ growth of MgAl-LDH films on magnesium alloy AZ31: The effect of initial cationic concentrations

A strategy based on chelating agent addition was used to assist the in-situ growth of MgAl-layered double hydroxides (LDHs) films on magnesium alloy AZ31 in a relatively mild condition. The growth behavior of MgAl-LDH films was studied on the magnesium alloy AZ31 substrate as the sole source of Al3+ and/or adding aluminum compounds as a supplementary source of respective ions. The composition, structure, corrosion resistance, and formation mechanism of LDH films were investigated and discussed. Results showed that the LDH-coated samples could effectively retard the corrosion of magnesium alloy. A thicker Mg (OH)2/MgAl-LDH composite film with larger flake size was formed without additional aluminum source. MgAl-LDH film fabricated with moderate additional Al3+ concentrations showed better corrosion resistance and an interesting stable network structure on a flat surface both covered/consisting of very fine LDH flakes.

Direct synthesis of graphene on silicon by reactive magnetron sputtering deposition

In the present research, the graphene was grown directly on the Si (100) substrate by a high-power impulse reactive magnetron sputtering the copper target. The samples' structure, morphology, and composition were investigated by Raman scattering spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy. The synthesis temperature, time, sample position in relation to the magnetron, and grid bias effects were studied. The graphene layer number decreased with growth temperature and distance between the sample and magnetron. The defects density in graphene decreased, and graphene crystallite size increased with synthesis temperature. These parameters were changed with lateral movement of the sample's position. The graphene layer number and defects density non-monotonically depended on the grid bias voltage. We revealed that the synthesis time, the distance between the substrate and the magnetron cathode target surface, and the grid bias voltage determine the graphene surface morphology and the shape and size of the graphene flakes. It was explained by competition between the graphene growth from the CHx species, growth activation by hydrogen, etching by hydrogen and argon ions, radiative defects creation, hydrogen atoms adsorption. The changes of the electrons, argon ions and copper atoms concentration and energy, and methane dissociation products density were taken into account. The temperature gradient and ion bombardment induced stress and their release were considered.

ТЕОРЕТИЧЕСКАЯ ОЦЕНКА ПАРАМЕТРОВ РАБОТЫ ФРЕЗЫ СНЕГООЧИСТИТЕЛЯ ОТБРАСЫВАЮЩЕГО ДЕЙСТВИЯ ВЗАВИСИМОСТИ ОТ УГЛА ЗАХОДА ЛЕНТЫ ФРЕЗЫ И РАЗМЕРОВ ЧАСТИЦ

The work objective is to assess the effect of cutter band angle on the power required for transporting the snow by the cutter feeder of the rotary snowplow and its performance, taking into account the interaction of snowflakes with each other.&#x0D; The problem to which the paper is devoted is to find out the influence of the angle, the size of the transported particles on the productivity of the feeder cutter and the power spent on moving the snow as a group of interacting flakes of finite size.&#x0D; Research methods: theoretical studies and simulation of the feeder cutter operation during transportation of snow as a group of interacting flakes of finite size. &#x0D; The novelty of the work lies in the fact that simulation, for the first time, gives theoretical description of changes in the productivity of a cutter and rotary snowplow feeder of and the power costs for transporting snow depending on the cutter band angle and the typical size of snowflakes in conditions of their interaction with each other, and also approximating equations of changes in productivity and power costs depending on the cutter band angle and typical size of snowflakes. &#x0D; The study results show that an increase in the cutter band angle leads to a nonlinear increase in power costs for transporting snowflakes, described by a fourth degree polynomial. An increase in the typical flake size of the transported snow in the cutter feeder of the rotary snowplow also causes a nonlinear increase in the power costs for transporting snow, which is described by a second degree polynomial. The increase in productivity with an increase in the cutter band angle is described by a fourth degree polynomial, and with an increase in the typical flake size by the third degree one. The areas of maximum power consumption and maximum productivity have an offset relative to each other in the coordinates of the typical flake size and the cutter band angle. &#x0D; Conclusions: the influence of the cutter band angle and the size of transported snowflakes on the main parameters of the cutter feeder operation are defined. The results of theoretical studies correlate with the results of practical studies, which indicates the feasibility of using a mathematical model that takes into account the interaction of transported snowflakes in further studies aimed at improving the efficiency of feeder of the rotary snowplows.

Atomistic insights into highly active reconstructed edges of monolayer 2H-WSe2 photocatalyst.

Ascertaining the function of in-plane intrinsic defects and edge atoms is necessary for developing efficient low-dimensional photocatalysts. We report the wireless photocatalytic CO2 reduction to CH4 over reconstructed edge atoms of monolayer 2H-WSe2 artificial leaves. Our first-principles calculations demonstrate that reconstructed and imperfect edge configurations enable CO2 binding to form linear and bent molecules. Experimental results show that the solar-to-fuel quantum efficiency is a reciprocal function of the flake size. It also indicates that the consumed electron rate per edge atom is two orders of magnitude larger than the in-plane intrinsic defects. Further, nanoscale redox mapping at the monolayer WSe2–liquid interface confirms that the edge is the most preferred region for charge transfer. Our results pave the way for designing a new class of monolayer transition metal dichalcogenides with reconstructed edges as a non-precious co-catalyst for wired or wireless hydrogen evolution or CO2 reduction reactions.

Structural and Morphological Studies of Bi2O3/MWCNTs Doped Reduced Graphene Oxide for Energy Storage Applications

Bismuth oxide (Bi2O3), multi-wall carbon nanotubes (MWCNTs), reduced graphene oxide (rGO) and its composite were synthesized by modified Hummers method followed by chemical and thermal reduction processes. During synthesis, graphene oxide (GO) was reduced to rGO and decorated evenly with Bi2O3 and CNTs. Average crystallite size of graphite flakes (GF), GO, rGO, rGO/Bi2O3, rGO/CNTs and rGO/Bi2O3/CNTs is calculated from XRD profiles using the Scherer equation are 77.75, 11.91, 1.79, 18.1, 21.05 and 18.05 nm, respectively. In XRD, deconvolution of rGO/Bi2O3/CNTs, C60 and C70 diffraction peaks were observed. The morphology of rGO/Bi2O3/CNTs have smoother surface similar to GO, rGO, rGO/Bi2O3 and rGO/CNTs except GF, was revealed in SEM images. HR-TEM analysis revealed carbon (002) in rGO with d-spacing of 0.34 nm, Bi (102) with d-spacing of 0.31 nm and MWCNTs on 2 nm scale. Bonding of Bi2O3 and CNTs with graphene layers led to the formation of novel functionalized nanocomposite which enhances electrical conductivity of rGO. Using AFM images of rGO/CNTs films thicknesses, arithmetic mean and RMS roughness were estimated as 6 nm at 14.91 nm and 19.27 nm, respectively. Results of rGO/Bi2O3/CNTs revealed that with the small crystallite size, functionalization and nanoscale roughness could be promising for energy storage applications.

Effect of pre-treatment and oil popping conditions on quinoa popping quality

Abstract Quinoa is a pseudocereal having outstanding nutritional profile and health-promoting biofunctional compounds. It is able to pop into an affordable, crispy, and flavourful ready-to-eat snack by conventional oil-popping method. Oil-popping is the process of frying grains in hot oil for a short time to induce vapour-driven expansion of grains. The effects of process variables on oil-popping quality of quinoa were evaluated. The conditions of processing were optimised using Response Surface Methodology. The grains (10 g) were hydrated by adding 0.1–0.3 mL of water containing a varying salt concentration of 0–1%, w/w and popped in coconut oil maintained at a popping temperature of 200–240 °C for a popping time of 10–30 s. The developed popped quinoa was analysed for popping quality indices. It was found that the increase in popping temperature, popping time, and salt concentration, and decrease in moisture level significantly decreased bulk density but increased popping yield (% popped grains), expansion ratio (degree of volume expansion), and flake size (average kernel size) of popped quinoa. Overall acceptability of popped quinoa in terms of sensory attributes was positively correlated with popping temperature and popping time. The optimised variables generated a popping yield of 75.56%, expansion ratio of 3.07, flake size of 11.58 mm3, bulk density of 0.29 g mL−1, and overall acceptability score of 8.40. A threefold expansion and a fair popping yield obtained from oil-popped quinoa offer a significant potential to generate profit for manufacturers.

Deformation of and Interfacial Stress Transfer in Ti3C2 MXene-Polymer Composites.

Transitional metal carbides and nitrides (MXenes) have promise for incorporation into multifunctional composites due to their high electrical conductivity and excellent mechanical and tribological properties. It is unclear, however, to what extent MXenes are also able to improve the mechanical properties of the composites and, if so, what would be the optimal flake size and morphology. Herein, Ti3C2Tx MXene is demonstrated to be indeed a good candidate for mechanical reinforcement in polymer matrices. In the present work, the strain-induced Raman band shifts of mono-/few-/multilayer MXenes flakes have been used to study the mechanical properties of MXene and the interlayer/interfacial stress transfer on a polymer substrate. The mechanical performance of MXene was found to be less dependent upon flake thickness compared to that of graphene. This enables Ti3C2Tx MXene to offer an efficient mechanical reinforcement to a polymer matrix with a flake length of >10 μm and a thickness of 10s of nanometers. Therefore, the degree of exfoliation of MXenes is not as demanding as other two-dimensional (2D) materials for the purpose of mechanical enhancement in polymers. In addition, the active surface chemistry of MXene facilitates possible functionalization to enable a stronger interface with polymers for applications, such as strain engineering and mechanical enhancement, and in materials including membranes, coatings, and textiles.

A Novel Method for the Determination of the Lateral Dimensions of 2D Rectangular Flakes.

We present a novel method for the determination of the lateral dimensions of thin rectangular flakes, as they exist randomly dispersed in flake composites. Knowledge of flake size and shape is essential for the correct prediction of the mechanical, electrical, thermal and barrier properties of flake composites. The required information is the distribution function of lengths of the lines representing the intersection of flakes with a sectioning plane, as seen in cross-sections of composite samples used in optical or electron microscopy or obtained using tomographic imaging techniques. The key observation is that the major peak of the distribution function coincides with the short dimension S of the flake while a secondary peak corresponds to its long dimension W. These observations are explained using Monte-Carlo simulations, as well as deterministic, geometry-based modeling and probability analysis. Since the strength of the secondary peak diminishes with increasing flake aspect ratio , we develop two additional methods for the determination of W. The first finds W from the maximum intersection length; this procedure is justified by computing the relevant probability fields through Monte-Carlo simulations. The second method finds r from the average intersection length and is valid in the range . The performance of these techniques is tested and found to be very good using blind experiments in numerically sectioned specimens.

The mediating effect of platform width on the size and shape of stone flakes.

To understand the ways in which past stone knappers controlled the morphology of the flakes they produced, archaeologists have focused on examining the effects of striking platform attributes on flake size and shape. Among the variables commonly considered, platform width has routinely been noted to correlate with flake size and hence used to explain past knapping behaviors. Yet, the influence of platform width on flake variation remains equivocal due to the fact that the attribute is not under the direct control of the knapper. Instead, platform width tends to be treated as a by-product of other independent knapping parameters, such as platform depth. In this study, we hypothesize that platform width acts as an intermediary that intervenes the effect of other independent variables on flake attributes. By analyzing experimental flakes produced under both controlled and replicative settings, the results support the hypothesis that platform width mediates the effect of platform depth on flake width, such that flakes with relatively larger platform widths are generally wider but no longer. This finding provides a way to incorporate platform width into discussions of the interrelationships among knapping variables, and highlights the importance of platform width for investigating how past knappers controlled flake production through platform manipulation.

Quartz Crystal Microbalance Humidity Sensors Based on Structured Graphene Oxide Membranes with Magnesium Ions: Design, Mechanism and Performance.

The application of graphene oxide (GO)-based membranes combined with a quartz crystal microbalance (QCM) as a humidity sensor has attracted great interest over the past few years. Understanding the influence of the structure of the GO membrane (GOM) on the adsorption/desorption of water molecules and the transport mechanism of water molecules in the membrane is crucial for development of applications using GOM-based humidity sensors. In this paper, by investigating the effects of oxygen-containing groups, flake size and interlayer spacing on the performance of humidity sensing, it was found that humidity-sensing performance could be improved by rational membrane-structure design and the introduction of magnesium ions, which can expand the interlayer spacing. Therefore, a novel HGO&GO&Mg2+ structure prepared by uniformly doping magnesium ions into GO&HGO thin composite membranes was designed for humidity sensing from 11.3% RH to 97.3% RH. The corresponding sensor exhibits a greatly improved humidity sensitivity (~34.3 Hz/%RH) compared with the original pure GO-based QCM sensor (~4.0 Hz/%RH). In addition, the sensor exhibits rapid response/recovery times (7 s/6 s), low hysteresis (~3.2%), excellent repeatability and good stability. This research is conducive to understanding the mechanism of GOM-based humidity sensors. Owing to its good humidity-sensing properties, the HGO&GO&Mg2+ membrane-based QCM humidity sensor is a good candidate for humidity sensing.

Influence of the coffee-ring effect and size of flakes of graphene oxide films on their electrochemical reduction.

Electrodes for electrochemical reduction of graphene oxide (GO) are coated with thin films using drop-casting and evaporation-assisted self-assembly. The influence of loading, the size of the flakes of GO, and the macroscopic coffee-ring effect occurring during drying are investigated. The effective transfer of protons and electrons in the electrochemical reduction of GO is decisive.

Surface Functionalities of Graphene Oxide with Varying Flake Size

Surface Functionalities of Graphene Oxide with Varying Flake Size

Direct graphene synthesis on Si(1 0 0) by inductively coupled plasma beam source

The graphene was synthesized directly on the Si(100) substrate by an Inductively Coupled Plasma Beam Source without any catalyst. Plasma power, methane gas flow, hydrogen gas flow, temperature and time effects on graphene layers number and flake size, defects density, and surface morphology were studied. Prevailing defects type was considered. Boundary defects dominated in most samples due to the polycrystalline nature of the directly synthesized graphene. However, high methane gas flows, low synthesis times, and low synthesis temperatures were beneficial for the hydrogenation of the growing graphene. On-site defects prevailed in these samples. It was found that synthesis power, temperature, and time should be optimized to avoid out-of-plane graphene growth. An additional hydrogen gas flow effectively controlled graphene layers number. D + D‘ and D + D“ peaks were explored. It was supposed that the D + D‘ peak is mainly related to the on-site defects associated with a hydrogen atom bonded to the carbon atom in the graphene sheet. The line-of-sight graphene deposition was demonstrated. The main graphene growth-related physical and chemical processes were considered. The observed results were explained by a competition between graphene growth, hydrogen etching, hydrogenation, and thermal stress release.

Role of the A-Element in the Structural, Mechanical, and Electronic Properties of Ti3AC2 MAX Phases.

Combining metallic and ceramic properties, and as precursors for MXenes, MAX phases have attracted extensive attention. In recent years, A-element substitution has been demonstrated as an effective scheme to enrich the MAX family. To explore more possible MAX members, the structural, mechanical, and electronic properties and stabilities of 31 Ti3AC2 (A = Al, Si, P, S, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, Os, Ir, Pt, Au, Hg, TI, Pb, Bi, and Po) configurations are investigated in this work. Moreover, the interfacial strength implicating the possibility of exfoliating MAX into MXenes is examined. The A-element plays a crucial role in the lattice parameters and mechanical strength of Ti3AC2, and their variations are well explained by the synergistic effects of d-d and p-d hybridizations between the valence orbitals of Ti and A. Ti3SC2 presents the largest Young's modulus of 360 GPa, which is 6.82% higher than that in the well-studied Ti3SiC2. Ti3SbC2 is a mechanical quasi-isotropic configuration. After checking the mechanical, dynamical, and thermodynamic stability, Ti3AC2 (A = Al, Si, P, S, Ga, Ge, As, Cd, In, Sn, Sb, Au, Hg, Pb, TI, and Po) are stable, while Ti3AC2 (A = Fe, Co, Zn, Se, Ru, Rh, Pd, Ag, Te, Ir, Pt, and Bi) are metastable. Compared to Ti3AlC2, Ti3AC2 (A = Ag, Sb, Te, Bi, and Po) exhibit much lower interfacial strength in Ti-A interfaces and larger ratios between the interfacial strengths of neighboring Ti-C and Ti-A interfaces. This implies that these configurations are promising precursors for the synthesis of Ti3C2Tx (Tx denotes surface groups) with a large flake size. All of the configurations are metallic, and Ti3AC2 (A = Fe and Co) are magnetic. Based on the phonon dispersion and electronic structure, these Ti3AC2 configurations might have potential applications in phononic crystals and topological materials.