Enhancement of Exciton-Phonon Scattering from Monolayer to Bilayer WS2.

Layered transition metal dichalcogenides exhibit the emergence of a direct bandgap at the monolayer limit along with pronounced excitonic effects. In these materials, interaction with phonons is the dominant mechanism that limits the exciton coherence lifetime. Exciton-phonon interaction also facilitates energy and momentum relaxation, and influences exciton diffusion under most experimental conditions. However, the fundamental changes in the exciton-phonon interaction are not well understood as the material undergoes the transition from a direct to an indirect bandgap semiconductor. Here, we address this question through optical spectroscopy and microscopic theory. In the experiment, we study room-temperature statistics of the exciton line width for a large number of mono- and bilayer WS2 samples. We observe a systematic increase in the room-temperature line width of the bilayer compared to the monolayer of 50 meV, corresponding to an additional scattering rate of ∼0.1 fs-1. We further address both phonon emission and absorption processes by examining the temperature dependence of the width of the exciton resonances. Using a theoretical approach based on many-body formalism, we are able to explain the experimental results and establish a microscopic framework for exciton-phonon interactions that can be applied to naturally occurring and artificially prepared multilayer structures.

Patterning Superatom Dopants on Transition Metal Dichalcogenides.

This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS2 samples from moderately to heavily electron-doped states. The same approach applied on WSe2 films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p-n junction by selectively doping only a portion of the channel in a WSe2 device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment.

Single-Molecule Reaction Chemistry in Patterned Nanowells.

A new approach to synthetic chemistry is performed in ultraminiaturized, nanofabricated reaction chambers. Using lithographically defined nanowells, we achieve single-point covalent chemistry on hundreds of individual carbon nanotube transistors, providing robust statistics and unprecedented spatial resolution in adduct position. Each device acts as a sensor to detect, in real-time and through quantized changes in conductance, single-point functionalization of the nanotube as well as consecutive chemical reactions, molecular interactions, and molecular conformational changes occurring on the resulting single-molecule probe. In particular, we use a set of sequential bioconjugation reactions to tether a single-strand of DNA to the device and record its repeated, reversible folding into a G-quadruplex structure. The stable covalent tether allows us to measure the same molecule in different solutions, revealing the characteristic increased stability of the G-quadruplex structure in the presence of potassium ions (K(+)) versus sodium ions (Na(+)). Nanowell-confined reaction chemistry on carbon nanotube devices offers a versatile method to isolate and monitor individual molecules during successive chemical reactions over an extended period of time.

van der Waals Solids from Self-Assembled Nanoscale Building Blocks.

Traditional atomic van der Waals materials such as graphene, hexagonal boron-nitride, and transition metal dichalcogenides have received widespread attention due to the wealth of unusual physical and chemical behaviors that arise when charges, spins, and vibrations are confined to a plane. Though not as widespread as their atomic counterparts, molecule-based two-dimensional (2D) layered solids offer significant benefits; their structural flexibility will enable the development of materials with tunable properties. Here we describe a layered van der Waals solid self-assembled from a structure-directing building block and C60 fullerene. The resulting crystalline solid contains a corrugated monolayer of neutral fullerenes and can be mechanically exfoliated. The absorption spectrum of the bulk solid shows an optical gap of 390 ± 40 meV that is consistent with thermal activation energy obtained from electrical transport measurement. We find that the dimensional confinement of fullerenes significantly modulates the optical and electronic properties compared to the bulk solid.

Trouble-makers in cytologic interpretation of the uterine cervix.

The development and standardization of cytologic screening of the uterine cervix has dramatically decreased the prevalence of squamous cell carcinoma of the uterine cervix. Advances in the understanding of biology of human papillomavirus have contributed to upgrading the histologic diagnosis of the uterine cervix; however, cytologic screening that should triage those that need further management still poses several difficulties in interpretation. Cytologic features of high grade intraepithelial squamous lesion (HSIL) mimics including atrophy, immature metaplasia, and transitional metaplasia, and glandular lesion masquerades including tubal metaplasia and HSIL with glandular involvement are described with accentuation mainly on the differential points. When the cytologic features lie in a gray zone between the differentials, the most important key to the more accurate interpretation is sticking to the very basics of cytology; screening the background and cellular architecture, and then scrutinizing the nuclear and cytoplasmic details.

Ulcerative Colitis Diagnosed through Evaluation of Underlying Diseases in a Pyoderma Gangrenosum Adolescent without Gastrointestinal Symptoms.

Pyoderma gangrenosum (PG) is a rare, non-infectious, neutrophilic dermatosis characterized by painful ulcers with indistinct borders and peripheral erythema. The diagnosis of PG requires the exclusion of other causes of similar appearing skin manifestations, including vasculitis and infections. The pathogenesis of PG is not clear; however, dysregulation of the immune system has been suggested in previous studies. More than half of the PG patients have underlying diseases; the most common being inflammatory bowel disease (IBD). The progression of PG in IBD patients is seen after the onset of IBD, usually during its exacerbation. On the other hand, PG may follow a course independent of the intestinal disease. We present a case of an 18-year-old young male with PG that presented before being diagnosed with ulcerative colitis as an associated condition. He had a painful ulcerative lesion on his right shin with no previous gastrointestinal symptoms. This case suggests that investigating for underlying disorders is essential in PG patients despite the lack of symptoms other than the skin lesions.

Sucrose-induced abiotic stress improves the phytochemical profiles and bioactivities of mung bean sprouts.

This study aimed to examine the impact of sucrose treatment on the growth conditions, dietary nutritional quality, and biological activities of mung bean sprouts. Mung bean seeds were sprouted with solutions containing different sucrose concentrations (10, 20, and 30 g/L). The application of exogenous sucrose significantly decreased the height and fresh weight of mung bean sprouts. However, the sucrose-treated sprouts contained more polyphenols, flavonoids, γ-aminobutyric acid, phytosterols, and vitamins. The antioxidant capacities were also significantly higher in the sucrose-treated sprouts than in the control sprouts. The sprouts treated with 2-3 % sucrose showed markedly improved FFA-induced insulin resistance and alcohol-induced oxidative injury in HepG2 cells. Taken together, the elicitor application of sucrose at 3 % during mung bean sprouting could be an effective strategy to improve the dietary phytochemical composition and provide potential health benefits.

Photographic Assessment of Intermittent Exotropia Using a Translucent Cover.

PURPOSE: To evaluate the validity of the photographic assessment with a translucent cover that is clinically available for the evaluation of intermittent exotropia. METHODS: Photographs of 270 patients who cooperated for the prism and alternate cover test (PACT) were reviewed. Full-face images were obtained with a digital camera while a translucent cover was placed in front of either eye. The change in distance from the medial canthus to the nasal limbus with occlusion was measured and the photographic angle was estimated by three independent ophthalmologists based on representative photographs. These two measurements were correlated with the angle measured using the PACT, and clinical features related to the discrepancy between the photographic angle and the angle measured with the PACT were determined. RESULTS: Patients with intermittent exotropia of 27.0 ± 6.1 prism diopters (PD) showed a 4.5 ± 3.3 mm exodrift and an estimated angle of 29.0 ± 4.3 PD on the photographs with occlusion. The exodrift distance and photographic angle were positively correlated with the angle of PACT (r = 0.256, P < .001 and r = 0.546, P < .001, respectively). Of the 47 patients with a discrepancy of greater than 8 PD, 38 patients (80.9%) were regarded as having a photographic angle that was larger than the angle of PACT, which was more common in older patients, in those with a small distance angle, and when taking off the spectacles. CONCLUSIONS: Photographs with a translucent cover can reveal the latent components of intermittent exotropia. However, the photographic angle might differ from the real angle, particularly in older patients with a small angle and with the spectacles off. [J Pediatr Ophthalmol Strabismus. 2021;58(5):331-338.].

Mechanical capping of silica nanotubes for encapsulation of molecules.

Multifunctional silica nanotubes (SNTs) are being widely used for many biomedical applications due to their structural benefits. Controlling the structure of the open end of an SNT is a crucial step for drug/gene delivery and for fabrication of multifunctional SNTs. We developed a mechanical capsulation method to fabricate caps at the ends of SNTs. A thin layer of malleable capping materials (Au, Ag, PLGA) was deposited onto the surface of an SNT-grown AAO template. Capped SNTs were then obtained by hammering with alumina microbeads. For a proof-of-concept experiment, we demonstrated dye-encapsulated SNTs without any chemical functionalizations. Since a mechanical approach is free of the issue of chemical compatibility between cargo molecules and capping materials, the method can provide an effective platform for the preparation of smart multifunctional nanotubes for biomedical applications.

Two-Dimensional Nanosheets from Redox-Active Superatoms.

We describe a new approach to synthesize two-dimensional (2D) nanosheets from the bottom-up. We functionalize redox-active superatoms with groups that can direct their assembly into multidimensional solids. We synthesized Co6Se8[PEt2(4-C6H4COOH)]6 and found that it forms a crystalline assembly. The solid-state structure is a three-dimensional (3D) network in which the carboxylic acids form intercluster hydrogen bonds. We modify the self-assembly by replacing the reversible hydrogen bonds that hold the superatoms together with zinc carboxylate bonds via the solvothermal reaction of Co6Se8[PEt2(4-C6H4COOH)]6 with Zn(NO3)2. We obtain two types of crystalline materials using this approach: one is a 3D solid and the other consists of stacked layers of 2D sheets. The dimensionality is controlled by subtle changes in reaction conditions. These 2D sheets can be chemically exfoliated, and the exfoliated, ultrathin 2D layers are soluble. After they are deposited on a substrate, they can be imaged. We cast them onto an electrode surface and show that they retain the redox activity of the superatom building blocks due to the porosity in the sheets.

Coulomb engineering of the bandgap and excitons in two-dimensional materials.

The ability to control the size of the electronic bandgap is an integral part of solid-state technology. Atomically thin two-dimensional crystals offer a new approach for tuning the energies of the electronic states based on the unusual strength of the Coulomb interaction in these materials and its environmental sensitivity. Here, we show that by engineering the surrounding dielectric environment, one can tune the electronic bandgap and the exciton binding energy in monolayers of WS2 and WSe2 by hundreds of meV. We exploit this behaviour to present an in-plane dielectric heterostructure with a spatially dependent bandgap, as an initial step towards the creation of diverse lateral junctions with nanoscale resolution.

A solid dielectric gated graphene nanosensor in electrolyte solutions.

This letter presents a graphene field effect transistor (GFET) nanosensor that, with a solid gate provided by a high-κ dielectric, allows analyte detection in liquid media at low gate voltages. The gate is embedded within the sensor and thus is isolated from a sample solution, offering a high level of integration and miniaturization and eliminating errors caused by the liquid disturbance, desirable for both in vitro and in vivo applications. We demonstrate that the GFET nanosensor can be used to measure pH changes in a range of 5.3-9.3. Based on the experimental observations and quantitative analysis, the charging of an electrical double layer capacitor is found to be the major mechanism of pH sensing.

An aptameric graphene nanosensor for label-free detection of small-molecule biomarkers.

This paper presents an aptameric graphene nanosensor for detection of small-molecule biomarkers. To address difficulties in direct detection of small molecules associated with their low molecular weight and electrical charge, we incorporate an aptamer-based competitive affinity assay in a graphene field effect transistor (FET), and demonstrate the utility of the nanosensor with dehydroepiandrosterone sulfate (DHEA-S), a small-molecule steroid hormone, as the target analyte. In the competitive affinity assay, DHEA-S specifically binds to aptamer molecules pre-hybridized to their complementary DNA anchor molecules immobilized on the graphene surface. This results in the competitive release of the strongly charged aptamer from the DNA anchor and hence a change in electrical properties of the graphene, which can be measured to achieve the detection of DHEA-S. We present experimental data on the label-free, specific and quantitative detection of DHEA-S at clinically appropriate concentrations with an estimated detection limit of 44.7 nM, and analyze the trend observed in the experiments using molecular binding kinetics theory. These results demonstrate the potential of our nanosensor in the detection of DHEA-S and other small molecules in biomedical applications.

Epitaxial growth of molecular crystals on van der waals substrates for high-performance organic electronics.

Epitaxial van der Waals (vdW) heterostructures of organic and layered materials are demonstrated to create high-performance organic electronic devices. High-quality rubrene films with large single-crystalline domains are grown on h-BN dielectric layers via vdW epitaxy. In addition, high carrier mobility comparable to free-standing single-crystal counterparts is achieved by forming interfacial electrical contacts with graphene electrodes.

Signal enhancement in a protein chip array using a 3-D nanosurface.

A silica based 3-D nanosurface was developed to enhance the signal intensity of a protein chip by increasing the surface density and reducing the aggregation of captured proteins immobilized on the nanosurface. The 3-D nanosurface was composed of silica nanopillar bundles formed from a nanoporous alumina template using the sol-gel method. The signal intensity of a protein spot increased exponentially when the capture probe was immobilized on a nanosurface with higher roughness and the amount of protein immobilized on the surface was proportional to the roughness of the nanosurface. To further investigate this nanosurface effect, changes in the nanosurface roughness before and after protein immobilization were investigated by AFM. The surface roughness was shown to increase after protein immobilization when the nanosurface initially had a relatively low surface roughness (Rq: 30-40nm); however, the surface roughness decreased after protein immobilization when it initially had a high roughness (Rq: 60-130nm). These results imply that a high nanosurface roughness decreases the overall aggregation of proteins on the surface. These findings were also confirmed by comparing the level of protein aggregation on nanosurfaces with high roughness and low roughness using AFM.