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Germanium sulfide (GeS) is an emerging layered material with high promise in its two-dimensional (2D) exfoliated form for energy storage applications. While liquid-phase exfoliation (LPE) has been utilized for the low-cost, scalable production of related 2D materials, it has not yet been demonstrated for GeS nanosheets due to its chemical instability in ambient conditions. Here, GeS LPE is achieved in anhydrous N-methyl-2-pyrrolidone using a customized sealed-tip sonication system, yielding sub-10 nm thick GeS nanosheets that are structurally pristine with minimal chemical degradation as revealed by atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. Lithium-ion battery anodes based on these high-quality GeS nanosheets possess superlative electrochemical performance including high cycling stability over 1000 cycles and high rate capability in excess of 10 A g-1. Overall, this work establishes a scalable LPE pathway for the production of pristine electrochemically active GeS nanosheets that are well-suited for high-power lithium-ion battery applications. [ABSTRACT FROM AUTHOR]

Efficient energy storage systems based on lithium-ion batteries represent a critical technology across many sectors including consumer electronics, electrified transportation, and a smart grid accommodating intermittent renewable energy sources. Nanostructured electrode materials present compelling opportunities for high-performance lithium-ion batteries, but inherent problems related to the high surface area to volume ratios at the nanometer-scale have impeded their adoption for commercial applications. Here, we demonstrate a materials and processing platform that realizes high-performance nanostructured lithium manganese oxide (nano-LMO) spinel cathodes with conformal graphene coatings as a conductive additive. The resulting nanostructured composite cathodes concurrently resolve multiple problems that have plagued nanoparticle-based lithium-ion battery electrodes including low packing density, high additive content, and poor cycling stability. Moreover, this strategy enhances the intrinsic advantages of nano-LMO, resulting in extraordinary rate capability and low temperature performance. With 75% capacity retention at a 20C cycling rate at room temperature and nearly full capacity retention at -20 °C, this work advances lithium-ion battery technology into unprecedented regimes of operation. [ABSTRACT FROM AUTHOR]

This paper describes how delamination-free, hierarchical patterning of graphene can be achieved on prestrained thermoplastic sheets by surface wrinkling. Conformal contact between graphene and the substrate during strain relief was maintained by the presence of a soft skin layer, resulting in the uniform patterning of three-dimensional wrinkles over large areas (>cm²). The graphene wrinkle wavelength was tuned from the microscale to the nanoscale by controlling the thickness of the skin layer with 1 nm accuracy to realize a degree of control not possible by crumpling, which relies on delamination. Hierarchical patterning of the skin layers with varying thicknesses enabled multiscale graphene wrinkles with predetermined orientations to be formed. Significantly, hierarchical graphene wrinkles exhibited tunable mechanical stiffness at the nanoscale without compromising the macroscale electrical conductivity. [ABSTRACT FROM AUTHOR]

The recent emergence of a wide variety of two-dimensional (2D) materials has created new opportunities for device concepts and applications. In particular, the availability of semiconducting transition metal dichalcogenides, in addition to semimetallic graphene and insulating boron nitride, has enabled the fabrication of "all 2D" van der Waals heterostructure devices. Furthermore, the concept of van der Waals heterostructures has the potential to be significantly broadened beyond layered solids. For example, molecular and polymeric organic solids, whose surface atoms possess saturated bonds, are also known to interact via van der Waals forces and thus offer an alternative for scalable integration with 2D materials. Here, we demonstrate the integration of an organic small molecule p-type semiconductor, pentacene, with a 2D n-type semiconductor, MoS2. The resulting p-n heterojunction is gate-tunable and shows asymmetric control over the antiambipolar transfer characteristic. In addition, the pentacene/MoS2 heterojunction exhibits a photovoltaic effect attributable to type II band alignment, which suggests that MoS2 can function as an acceptor in hybrid solar cells. [ABSTRACT FROM AUTHOR]

Sensing biological agents at the genomic level, while enhancing the response time for biodetection over commonly used, optics-based techniques such as nucleic acid microarrays or enzyme-linked immunosorbent assays (ELISAs), is an important criterion for new biosensors. Here, we describe the successful detection of a 35-base, single-strand nucleic acid target by Hall-based magnetic transduction as a mimic for pathogenic DNA target detection. The detection platform has low background, large signal amplification following target binding and can discriminate a single, 350nm superparamagnetic bead labeled with DNA. Detection of the target sequence was demonstrated at 364pM (<2 target DNA strands per bead) target DNA in the presence of 36 μM nontarget (noncomplementary) DNA (<10 ppm target DNA) using optical microscopy detection on a GaAs Hall mimic. The use of Hall magnetometers as magnetic transduction biosensors holds promise for multiplexing applications that can greatly improve point-of-care (POC) diagnostics and subsequent medical care. [ABSTRACT FROM AUTHOR]

Sensing biological agents at the genomic level, while enhancing the response time for biodetection over commonly used, optics-based techniques such as nucleic acid microarrays or enzyme-linked immunosorbent assays (ELISAs), is an important criterion for new biosensors. Here, we describe the successful detection of a 35-base, single-strand nucleic acid target by Hall-based magnetic transduction as a mimic for pathogenic DNA target detection. The detection platform has low background, large signal amplification following target binding and can discriminate a single, 350nm superparamagnetic bead labeled with DNA. Detection of the target sequence was demonstrated at 364pM (<2 target DNA strands per bead) target DNA in the presence of 36 μM nontarget (noncomplementary) DNA (<10 ppm target DNA) using optical microscopy detection on a GaAs Hall mimic. The use of Hall magnetometers as magnetic transduction biosensors holds promise for multiplexing applications that can greatly improve point-of-care (POC) diagnostics and subsequent medical care. [ABSTRACT FROM AUTHOR]

Gate dielectrics directly affectthe mobility, hysteresis, powerconsumption, and other critical device metrics in high-performancenanoelectronics. With atomically flat and dangling bond-free surfaces,hexagonal boron nitride (h-BN) has emerged as an ideal dielectricfor graphene and related two-dimensional semiconductors. While high-quality,atomically thin h-BN has been realized via micromechanical cleavageand chemical vapor deposition, existing liquid exfoliation methodslack sufficient control over h-BN thickness and large-area film quality,thus limiting its use in solution-processed electronics. Here, weemploy isopycnic density gradient ultracentrifugation for the preparationof monodisperse, thickness-sorted h-BN inks, which are subsequentlylayer-by-layer assembled into ultrathin dielectrics with low leakagecurrents of 3 × 10–9A/cm2at 2MV/cm and high capacitances of 245 nF/cm2. The resultingsolution-processed h-BN dielectric films enable the fabrication ofgraphene field-effect transistors with negligible hysteresis and highmobilities up to 7100 cm2V–1s–1at room temperature. These h-BN inks can also be used as coatingson conventional dielectrics to minimize the effects of underlyingtraps, resulting in improvements in overall device performance. Overall,this approach for producing and assembling h-BN dielectric inks holdssignificant promise for translating the superlative performance oftwo-dimensional heterostructure devices to large-area, solution-processednanoelectronics. [ABSTRACT FROM AUTHOR]

Thethickness-dependent band structure of MoS2implies thatdiscontinuities in energy bands exist at the interface of monolayer(1L) and multilayer (ML) thin films. The characteristics of such heterojunctionsare analyzed here using current versus voltage measurements, scanningphotocurrent microscopy, and finite element simulations of chargecarrier transport. Rectifying I–Vcurves are consistently observed between contacts on opposite sidesof 1L/ML junctions, and a strong bias-dependent photocurrent is observedat the junction. Finite element device simulations with varying carrierconcentrations and electron affinities show that a type II band alignmentat single layer/multilayer junctions reproduces both the rectifyingelectrical characteristics and the photocurrent response under bias.However, the zero-bias junction photocurrent and its energy dependenceare not explained by conventional photovoltaic and photothermoelectricmechanisms, indicating the contributions of hot carriers. [ABSTRACT FROM AUTHOR]