Monolayer Sheets Research Articles

Axial tunable plasmonic talbot effect based on monolayer graphene

In this paper, the axial plasmonic Talbot effect is investigated with a graphene monolayer sheet with different chemical potential distribution. The Talbot distance of axial self-imaging effect is discussed by controlling the chemical potential of graphene and the frequency. The Talbot distance is in inverse proportion to the frequency, and decreases when the chemical potential of graphene increases. Moreover, the full width at half maximum (FWHM) of Talbot image is also studied by varying the frequency and the chemical potential of graphene. The result shows that the FWHM follows an upward curve with the increase of chemical potential and frequency. The proposed structure might find applications in the fields of deep sub-wavelength imaging and nano-lithography.

Multilayered Cell Sheets of Cardiac Reprogrammed Cells for the Evaluation of Drug Cytotoxicity.

Various cell-culture systems have been used to evaluate drug toxicity in vitro. However, factors that affect cytotoxicity outcomes in drug toxicity evaluation systems remain elusive. In this study, we used multilayered sheets of cardiac-mimetic cells, which were reprogrammed from human fibroblasts, to investigate the effects of the layer number on drug cytotoxicity outcomes. Cell sheets of cardiac-mimetic cells were fabricated by reprogramming of human fibroblasts into cardiac-mimetic cells via coculture with cardiac cells and electric stimulation, as previously described. Double-layered cell sheets were prepared by stacking the cell sheets. The mono- and double-layered cell sheets were treated with 5-fluorouracil (5-FU), an anticancer drug, in vitro. Subsequently, apoptosis and lipid peroxidation were analyzed. Furthermore, effects of cardiac-mimetic cell density on cytotoxicity outcomes were evaluated by culturing cells in monolayer at various cell densities. The double-layered cell sheets exhibited lower cytotoxicity in terms of apoptosis and lipid peroxidation than the mono-layered sheets at the same 5-FU dose. In addition, the double-layered cell sheets showed better preservation of mitochondrial function and plasma membrane integrity than the monolayer sheets. The lower cytotoxicity outcomes in the double-layered cell sheets may be due to the higher intercellular interactions, as the cytotoxicity of 5-FU decreased with cell density in monolayer cultures of cardiac-mimetic cells. The layer number of cardiac-mimetic cell sheets affects drug cytotoxicity outcomes in drug toxicity tests. The in vitro cellular configuration that more closely mimics the in vivo configuration in the evaluation systems seems to exhibit lower cytotoxicity in response to drug.

Reduced Drift of CMOS ISFET pH Sensors Using Graphene Sheets

Reduction of drift in Complementary Metal Oxide-Semiconductor (CMOS) Ion-Sensitive Field-Effect Transistor (ISFET) pH sensors is demonstrated using monolayer and multilayer graphene sheets. Graphene blocks the ion penetration in the CMOS passivation layers and provides the physisorption sites needed for electrical double layer formation allowing sensing. With an in-house polymer-assisted graphene transfer (PAGT) process, monolayer and multilayer graphene sheets were manually transferred on top of the sensing membrane of CMOS ISFET sensors on a 2 by 4 mm chip. Experiments with pH buffers on five different chips were performed to extract the average performance parameters of capacitive attenuation, trapped charge, sensitivity, drift and noise. The stretched exponential function, that describes dispersion processes in amorphous solids such as silicon dioxide and silicon nitride, was modified to model the dynamic drift behaviour and analyse the effect of graphene on the performance of the sensors. The results show that on average the graphene coated ISFET sensors experience about 50% reduction in drift amplitude, up to 3 times slower surface modification and perform overall better compared to the plain unmodified devices.

Lone pair Halogen (X2)…π Interactions Stabilizes Molecular Halogens (X2=I2, Br2, Cl2, and F2) on Reduced Graphene Oxide surface: Structural, Solvent Effect and optical properties

In this work, we investigate the lone pair (lp)…π interaction for the halogens (X2=I2, Br2, Cl2, and F2) binding to the rGO surface. Electronic and optical properties of rGO significantly tuned upon adsorption of halogen molecules, although the weak nature of (lp)…π forces. The structure and optical properties of rGO, rGOI2, rGOBr2, rGOCl2 and rGOF2 adducts were investigated by density functional theory (DFT) and time-dependent DFT (TD-DFT) method. Halogen molecules (X2) stable structures were planer on rGO surface and stabilized by the lone pair X2(lp)…π(C) interactions. The surface oxygen atoms contributed to the stability by the O(lp)… π(X2) charge transfer process. Bader analysis reveals significant charge transfer and bond length elongation for X2 on rGO monolayer sheet in the order I2 > Br2 > Cl2 > F2. Surface adsorption of X2 molecules on rGO surface tunes both band gap energy and optical properties. The TDOS and PDOS reveal that X2 adsorption on rGO surface forms an intermediate states in band gap region, which decrease the energy values. These results are beneficial for photocatalysis and light harvesting applications.

Graphene edge method for three‐dimensional probing of Raman microscopes focal volumes

AbstractIn this work, a layer of graphene was used as a standard material for the measurement of the dimensions of Raman microscopes focal volumes of different confocal Raman spectrometers equipped with different objectives and excitation laser wavelengths. This method consists in probing the volume near the focal point of the system by using a flat graphene monolayer sheet with a straight edge. Graphene was selected because of its high Raman cross section and mechanically and chemically stability, allowing fast measurements and easy manipulation. In this paper, a method to employ graphene to accurately and precisely measure the three dimensions of the focal volume of a Raman microscope is presented; scanning along the axial and lateral directions, it is possible to reconstruct the three dimensions of the focal volume. Furthermore, these operations can be combined in a single procedure which allows the measurement of projections of the volume on planes parallel to the optical axis. Knowledge of these parameters enable absolute quantification of Raman‐active molecules and support high‐resolution Raman imaging.

Croatia’s First Experiences in Cytological Diagnosis of High-Grade Ductal Carcinoma in Situ of the Breast: Case Reports and a Review of Literature

Cases here presented are also first Croatia’s experiences in the cytological diagnosis of breast ductal carcinoma in situ (DCIS). The first patient was a 64-year-old woman, by imaging methods with a wide area of suspect microcalcifications in the left breast lower medial quadrant and abundant, dense, yellow-greyish discharge of the same mammilla and second was a 65-year-old woman with an equivocal lesion in left breast lower lateral quadrant. Morphological findings of both aspirates and nipple discharge from the first patient were practically the same - moderately to highly cellular, with 3D solid aggregates, monolayer sheets and many scattered single clearly malignant cells of large - mainly >5x the diameter of an erythrocyte, round-to-ovaloid, manifestly irregular nuclei, dark blue, polymorphous, often multiple (macro)nucleoli, irregular nuclear outlines and dense, more basophilic, mostly scant cytoplasms arranged in syncytium–like structures. “Dirty” background was overfull of comedo necrosis and dark grayish, sharp, irregular microcalcifications. Cytological diagnosis in both cases was DCIS, high-grade, comedo type. Histopathologically first tumor was big, 6 cm large, estimated as comedo carcinoma with microinvasion focuses not bigger than 1 mm, but without signs of angioinvasion, while the second tumor was smaller, 0.6 cm with wide ducts fully with large polymorphic malignant epithelial cells, central comedo necrosis, cancerisation of some lobules but with the intact basement membrane. It was pure high-grade DCIS, comedo type. Presented cases completely reflect to date knowledge about cytological diagnostic of high-grade DCIS; include necessary morphological criteria - highgrade nuclear atypia, an abundance of comedo necrosis and microcalcifications, confirm our limitation in the presumption of invasion status with large lesion extent, but also prove that cytology is the unquestionably reliable in breast morphological diagnostic, even in such sophisticated and demanding pathological issue like DCIS.

Enhancement of Endothelialization by Topographical Features Is Mediated by PTP1B-Dependent Endothelial Adherens Junctions Remodeling.

Endothelial Cells (ECs) form cohesive cellular lining of the vasculature and play essential roles in both developmental processes and pathological conditions. Collective migration and proliferation of endothelial cells (ECs) are key processes underlying endothelialization of vessels as well as vascular graft, but the complex interplay of mechanical and biochemical signals regulating these processes are still not fully elucidated. While surface topography and biochemical modifications have been used to enhance endothelialization in vitro, thus far such single-modality modifications have met with limited success. As combination therapy that utilizes multiple modalities has shown improvement in addressing various intractable and complex biomedical conditions, here, we explore a combined strategy that utilizes topographical features in conjunction with pharmacological perturbations. We characterized EC behaviors in response to micrometer-scale grating topography in concert with pharmacological perturbations of endothelial adherens junctions (EAJ) regulators. We found that the protein tyrosine phosphatase, PTP1B, serves as a potent regulator of EAJ stability, with PTP1B inhibition synergizing with grating topographies to modulate EAJ rearrangement, thereby augmenting global EC monolayer sheet orientation, proliferation, connectivity, and collective cell migration. Our data delineates the crosstalk between cell-ECM topography sensing and cell-cell junction integrity maintenance and suggests that the combined use of grating topography and PTP1B inhibitor could be a promising strategy for promoting collective EC migration and proliferation.

Fracture Analysis of Vacancy Defected Nitrogen Doped Graphene Sheets Via MD Simulations

The novel hexagonal monolayer sheet of carbon atoms, graphene, has attracted great attention due to their exceptional electrical and mechanical properties. Their phenomenally high strength and elastic strain, nevertheless, can be altered by structural defects due to stress concentration. In this paper, the fracture behaviour of graphene sheets and nitrogen doped graphene sheets with vacancies were investigated using molecular dynamics (MD) simulations at the different temperatures of 300K, 500K, and 900K. The results reveal a significant strength loss caused by both the defects and vacancies and doped nitrogen in graphene. The deformation process of graphene at various strain rate levels, with regard to the failure behaviour, is discussed. The validity of the proposed MD simulations is verified by comparing the simulation results with the available predictions from the quantized fracture mechanics.

Self-Assembly of MoS2 Monolayer Sheets by Desulfurization.

Self-assembled structures of two-dimensional (2D) materials exhibit novel physical properties distinct from those of their parent materials. Herein, the critical role of desulfurization on the self-assembled structural morphologies of molybdenum disulfide (MoS2) monolayer sheets is explored using molecular dynamics (MD) simulations. MD results show that there are differences in the atomic energetics of MoS2 monolayer sheets with different desulfurization contents. Both free-standing and substrate-hosted MoS2 monolayer sheets show diversity in structural morphologies, for example, flat plane structures, wrinkles, nanotubes, and folds, depending on the desulfurization contents, planar dimensions, and ratios of length to width of MoS2 sheets. Particularly, at the critical desulfurization content, they can roll up into nanotubes, which is in good agreement with previous experimental observations. Importantly, these observed differences in the molecular structural morphologies between free-standing and substrate-hosted MoS2 monolayer sheets can be attributed to interatomic interactions and interlayer van der Waals interactions. Furthermore, MD results have demonstrated that the surface-driven stability of MoS2 structures can be indicated by the desulfurization contents on one surface of MoS2 monolayer sheets, and the self-assembly of MoS2 monolayer sheets by desulfurization can emerge to adjust their surface-driven stability. The study provides important atomic insights into tuning the self-assembling structural morphologies of 2D materials through defect engineering in the future science and engineering applications.

Tuning structure, electronic, and catalytic properties of non-metal atom doped Janus transition metal dichalcogenides for hydrogen evolution

The doping of hetero-non-metal atoms into the conventional Transition Metal Dichalcogenide (TMD) monolayer sheets is reported to tune their structural, electronic, magnetic, and catalytic properties. Herein, the physicochemical properties of Janus MoSSe monolayer with the doping of atoms viz. B, C, N, and P are systematically studied using density functional theory. The high binding energies for the doping of non-metal atoms into TMD sheets show energetic stability of the doped Janus sheets. The doping reduces the band gaps as compared to pristine sheet because of the introduction of the bands near the Fermi region. The doping of non-metal atoms also tunes the magnetic properties of Janus nanosheets and broaden up their applications in spintronics. The catalytic activity of the Janus TMDs for Hydrogen Evolution Reaction (HER) is explored which possess inherent strain due to asymmetry. The density functional theoretical studies of the pristine and non-metal atom doped Janus TMDs as HER catalysts are reported in terms of Gibbs free energy which depends on the electronegativity of dopants. The Gibbs free energy of adsorption is tuned to ~0 eV with heteroatom doping. Overall results indicate that the boron doped Janus sheet possesses reduced band gap and tunable work function which contributes to the superior catalytic performance for HER even in the absence of external strain and large basal plane vacancies.

Tsg101 Is Necessary for the Establishment and Maintenance of Mouse Retinal Pigment Epithelial Cell Polarity

The retinal pigment epithelium (RPE) forms a monolayer sheet separating the retina and choroid in vertebrate eyes. The polarized nature of RPE is maintained by distributing membrane proteins differentially along apico-basal axis. We found the distributions of these proteins differ in embryonic, post-natal, and mature mouse RPE, suggesting developmental regulation of protein trafficking. Thus, we deleted tumor susceptibility gene 101 (Tsg101), a key component of endosomal sorting complexes required for transport (ESCRT), in embryonic and mature RPE to determine whether ESCRT-mediated endocytic protein trafficking correlated with the establishment and maintenance of RPE polarity. Loss of Tsg101 severely disturbed the polarity of RPE, which forms irregular aggregates exhibiting non-polarized distribution of cell adhesion proteins and activation of epidermal growth factor receptor signaling. These findings suggest that ESCRT-mediated protein trafficking is essential for the development and maintenance of RPE cell polarity.

Strong Self-Trapped Exciton Emissions in Two-Dimensional Na-In Halide Perovskites Triggered by Antimony Doping.

Soft lattice and strong exciton-phonon coupling have been demonstrated in layered double perovskites (LDPs) recently; therefore, LDPs represents a promising class of compounds as excellent self-trapped exciton (STE) emitters for applications in solid-state lighting. However, few LDPs with outstanding STE emissions have been discovered, and their optoelectronic properties are still unclear. Based on the three-dimensional (3D) Cs2 NaInCl6 , we synthesized two 2D derivatives (PEA)4 NaInCl8 :Sb (PEA=phenethylamine) and (PEA)2 CsNaInCl7 :Sb with monolayer and bilayer inorganic sheets by a combination of dimensional reduction and Sb-doping. Bright broadband emissions were obtained for the first time under ambient temperature and pressure, with photoluminescence quantum efficiency (PLQE) of 48.7 % (monolayer) and 29.3 % (bilayer), superior to current known LDPs. Spectroscopic characterizations and first-principles calculations of excited state indicate the broadband emissions originate from STEs trapped at the introduced [SbCl6 ]3- octahedron.

Strong Self‐Trapped Exciton Emissions in Two‐Dimensional Na‐In Halide Perovskites Triggered by Antimony Doping

AbstractSoft lattice and strong exciton–phonon coupling have been demonstrated in layered double perovskites (LDPs) recently; therefore, LDPs represents a promising class of compounds as excellent self‐trapped exciton (STE) emitters for applications in solid‐state lighting. However, few LDPs with outstanding STE emissions have been discovered, and their optoelectronic properties are still unclear. Based on the three‐dimensional (3D) Cs2NaInCl6, we synthesized two 2D derivatives (PEA)4NaInCl8:Sb (PEA=phenethylamine) and (PEA)2CsNaInCl7:Sb with monolayer and bilayer inorganic sheets by a combination of dimensional reduction and Sb‐doping. Bright broadband emissions were obtained for the first time under ambient temperature and pressure, with photoluminescence quantum efficiency (PLQE) of 48.7 % (monolayer) and 29.3 % (bilayer), superior to current known LDPs. Spectroscopic characterizations and first‐principles calculations of excited state indicate the broadband emissions originate from STEs trapped at the introduced [SbCl6]3− octahedron.

Features that make macromolecules 2D polymers

The article compares two-dimensional (2D) polymers with their congeners, the abundantly available linear polymers (1D) to show that both kinds of macromolecules are in fact polymer molecules. Repeat units and end (or edge) groups fully describe both kinds of structures. Both structures are obtainable as individual entities. Growth mechanisms well known for 1D polymers have now also been either elucidated or postulated for the first few 2D polymers. 2D copolymers are accessible by reacting different monomers in different feed ratios. Molar masses and molar mass distributions are obtainable when analysing 2D polymers in monolayer sheet form.The author therefore concludes that 2D polymers are in fact polymer molecules, very much as their linear 1D counterparts and that both kinds of structures therefore belong in this very subcategory of macromolecules. Dimensionality differences come with significant property differences and may therefore justify dividing the subcategory ‘polymer molecules’ further into 1D, 2D and – in the near future - 3D polymer molecules. In terms of materials, 2D polymers establish a subclass of organic 2D materials with the unique characteristic of meeting the conditions for polymer molecules.

Papillary lesions of the breast: A systematic evaluation of cytologic parameters.

The cytologic diagnosis of papillary lesions of the breast is challenging because of the diverse morphology, including epithelial hyperplasia, atypia, low-grade malignancy, and neuroendocrine differentiation; also, traditional malignant features such as necrosis and myoepithelial cell loss can be lacking. Thus, the diagnostic criteria for papillary lesions may differ from those for other breast lesions. This study evaluated various cytologic parameters in a large cohort to identify useful diagnostic features. Cytologic preparations of papillary lesions with histologic follow-up were reviewed for features related to cellularity, epithelial cohesiveness, cellular and stromal architecture, cytomorphology, and background. Corresponding histologic slides were also reviewed. In all, 153 cases were included. Epithelial discohesion, solid and cribriform patterns, atypical nuclear features, and mitoses (P ≤ .001 to P = .017) were associated with malignancy. Cell balls, monolayer sheets, and features of cystic change (P < .001 to P = .016) were associated with benign lesions. Complex (P = .031) and slender (P = .026) papillae and neuroendocrine features (P < .001) were associated with malignancy. Hemorrhage, background, and infiltrating neutrophils (P < .001 to P = .025) were associated with malignancy; fibrotic broad papillary stromal fragments (naked papillary fronds [NPFs]; P = .043) were associated with benignity. The presence of any single parameter, including the absence of myoepithelial cells within epithelial structure, the presence of cytoplasmic granules, an increased amount of cytoplasm, and a nuclear to cytoplasmic (N/C) ratio greater than 0.7, which were identified by principal component analysis, yielded a sensitivity of 95.1% and a specificity of 100.0% in predicting malignancy. Methodological assessment of multiple features is recommended. Myoepithelial cells, cytoplasmic granules, the amount of cytoplasm, and the N/C ratio are key features for diagnosis.

Outstanding Performance of Transition-Metal-Decorated Single-Layer Graphene-like BC6N Nanosheets for Disease Biomarker Detection in Human Breath.

In the present work, we report highly sensitive and selective nanosensors constructed with metal-decorated graphene-like BC6N employing nonequilibrium Green’s function (NEGF) formalism combined by density functional theory (DFT) toward multiple inorganic and sulfur-containing gas molecules (NO, NO2, NH3, CO, CO2, H2S, and SO2) as disease biomarkers from human breath. Monolayer sheets of pristine BC6N and Pd-decorated BC6N were evaluated for their gas adsorption properties, electronic property changes, sensitivity, and selectivity toward disease biomarkers. The pristine BC6N nanosheets exhibited sharp drops in the bandgap when interacted with gases such as NO2 while barely affected by other gases. However, the nanosecond recovery time and low adsorption energies limit the gas sensing applications of the pristine BC6N sheet. On the other hand, the Pd-decorated BC6N-based sensor underwent a semiconductor to metal transition upon the adsorption of NOx gas molecules. The conductance change of the sensor’s material in terms of I–V characteristics revealed that the Pd-decorated BC6N sensor is highly sensitive (98.6–134%) and selective (12.3–74.4 times) toward NOx gas molecules with a recovery time of 270 s under UV radiation at 498 K while weakly interacting with interfering gases in exhaled breath such as CO2 and H2O. The gas adsorption behavior suggests that metal-decorated BC6N sensors are excellent candidates for analyzing pulmonary disease and cardiovascular biomarkers, among other ailments of the stomach, kidney, and intestine.

Ultrathin Porous Hydrocarbon Membranes Templated by Nanoparticle Assemblies.

Porous polymer membranes are widely desired as catalyst supports, sensors, and active layers for separation membranes. We demonstrate that electron beam irradiation of freely suspended gold or Fe3O4 nanoparticle (NP) monolayer sheets followed by wet chemical etching is a high-fidelity strategy to template two-dimensional (2D) porous cross-linked hydrocarbon membranes. This approach, which relies on secondary electrons generated by the NP cores, can further be used to transform three-dimensional (3D) terraced gold NP supercrystals into 3D porous hydrocarbon membranes. We utilize electron tomography to show how the number of NP layers (monolayer to pentalayer) controls attenuation and scattering of the primary e-beam, which in turn determines ligand cross-link density and 3D pore structure. Electron tomography also reveals that many nanopores are vertically continuous because of preferential sintering of NPs. This work demonstrates new routes for the construction of functional nanoporous media.

An atomistic model for predicting charge distribution in hexagonal boron nitride

We propose an atomistic charge-dipole model for predicting the distribution of doping charge in hexagonal boron nitride (h-BN), based on parameterization using density functional theory calculations. Using this model, we predict the charge distribution in h-BN nanosheets of different geometries. A significant nanometer-size effect is revealed: The charge enhancement effect on the zigzag edge is more significant than that on the armchair one, while the charge enhancement factor increases sublinearly with the dimension of rectangular monolayer sheets or the number of layers for multilayer nanoribbons. This model is also parameterized for predicting the effect of the external electric field on the distribution of intrinsic charge. It can be integrated into molecular simulations in combination with classical force fields for predicting electrostatic effects such as electrostriction, electrodeflection, piezoelectricity and flexoelectricity in finite-size two-dimensional nanostructures.

Exploring the Optoelectronic Properties of Solution Processed 2D TMD Nanoflakes Exfoliated Via Large Molecule Electrointercalation

The remarkable semiconducting properties of 2D transition metal dicalcogenides (TMDs) are of great interest to researchers hoping to harness such traits for optoelectronic and photoelectrochemical (PEC) applications. 2D MoS2, WSe2, and related materials have been incorporated in ultrathin devices including transistors1, LEDs2, solar cells3, and photoelectrodes4,5. While typical approaches like chemical vapor deposition produce pristine monolayer or few-layer 2D TMD sheets and flakes, these methods are expensive and energy intensive making them unsuitable for large scale implementation. Thus, developing scalable solution processable methods to prepare high-quality 2D TMD materials is crucial.Typical solution-based production approaches have historically yielded TMDs with poor semiconducting behavior. Recently a novel electrointercalation technique was reported by Lin et al. wherein large organic cations are inserted in between MoS2 layers in a bulk single crystal thereby exfoliating it to thin nanoflakes while maintaining benchmark semiconducting performance. Despite this advance, there remains a lack of information concerning the optoelectronic properties of these flakes and their ability to be used in solar energy conversion devices.Herein we use the electrointercalation of large cation tetraheptylammonium bromide (THAB) to exfoliate a variety of bulk TMDs, investigate their optoelectronic properties, and process them into photoelectrodes for solar-to-chemical energy conversion. When compared to alternative solution processing methods such as ultrasonication and shear-mixing exfoliation, these THAB-assisted exfoliated flakes show increased photocurrents, photovoltages, and internal quantum efficiencies. We show that this is, in part, a result of thinner 2D flakes with larger lateral dimensions. Raman, photoluminescence, and X-ray spectroscopy suggest that this technique results in a lower defect density when compared to traditional methods. These results suggest that THAB-intercalated 2D TMDs are promising for scalable solar energy applications.

Efecto de sorbato de potasio como agente de interfase en bicapas a base de polímeros biodegradables

Studies that are focused on the design and development of biodegradable materials with promising physicochemical properties for industrial use have been of great importance. In this research, bilayer materials were developed using TPS monolayers assembled with monolayers sheets of amorphous polylactic acid (PLAa) and polycaprolactone (PCL). Potassium sorbate was evaluated as an interfacial adhesion material. Structural properties of the laminated materials (FTIR and SEM), behaviour with water (rate of water vapour transmission, solubility in water and moisture content) and biodegradation of the materials were evaluated. Physical and chemical interactions between the studied monolayers by the addition of potassium sorbate were found. The use of monolayer sheets of PLAa and PCL overcomes the disadvantages of the materials obtained from starch. A practical alternative was developed to obtain materials with better properties. Besides, the degradation time of TPS was evaluated and compared with other polymers. These laminated materials are a great alternative to the decrease in the use of conventional plastics and are applicable as packaging in the food industry.