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van der Waals solids have been recognized as highly photosensitive materials that compete conventional Si and compound semiconductor based devices. While 2-dimensional nanosheets of single and multiple layers and 1-dimensional nanowires of molybdenum and tungsten chalcogenides have been studied, their nanostructured derivatives with complex morphologies are not explored yet. Here, we report on the electrical and photosensitive properties of WS2 nanowire-nanoflake hybrid materials we developed lately. We probe individual hybrid nanostructured particles along the structure using focused ion beam deposited Pt contacts. Further, we use conductive atomic force microscopy to analyze electrical behavior across the nanostructure in the transverse direction. The electrical measurements are complemented by in situ laser beam illumination to explore the photoresponse of the nanohybrids in the visible optical spectrum. Photodetectors with responsivity up to ∼0.4 AW−1 are demonstrated outperforming graphene as well as most of the other transition metal dichalcogenide based devices. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) field effect transistors (FET) were fabricated on atomically smooth large-area single layers grown by chemical vapor deposition. The layer qualities and physical properties were characterized using high-resolution Raman and photoluminescence spectroscopy, scanning electron microscopy, and atomic force microscopy. Electronic performance of the FET devices was measured using field effect mobility measurements as a function of temperature. The back-gated devices had mobilities of 6.0 cm2/V s at 300 K without a high-κ dielectric overcoat and increased to 16.1 cm2/V s with a high-κ dielectric overcoat. In addition the devices show on/off ratios ranging from 105 to 109. [ABSTRACT FROM AUTHOR]

Resonant tunneling structures [M. Bockrath, W. Liang, D. Bozovic, J. H. Hafner, C. B. Lieber, M. Tinkham, and H. Park, Science 291, 283 (2001)], formed between the junction of two single walled nanotubes and the conductive atomic force microscopy tip contact were investigated using current sensing atomic force microscopy. Oscillations in the current voltage characteristics were measured at several positions of the investigated nanotube. The oscillatory behavior is shown to follow a simple quantum mechanical model, dependent on the energy separation in the quantum well formed within the two junctions. Our model shows that these observations seen over several hundreds of nanometers, are possible only if the scattering cross section at defects is small resulting in long phase coherence length, and if the effective mass of the carrier electrons is small. We have calculated the approximate mass of the conduction electrons to be 0.003 me. [ABSTRACT FROM AUTHOR]

[Display omitted] Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., transition metal dichalcogenides (TMDCs) and MXenes, from one substrate to another has been a necessity for successful device fabrication. With both mechanical exfoliation and chemical vapor deposition (CVD) widely used, a versatile, clean, deterministic, and yet simple transfer technique is highly needed. To address such need, we developed a transfer method that takes advantage of wettability contrast between interfaces without the use of sacrificial layers or chemical processes. More importantly, a setup was developed to carry out this transfer method with high sample selectivity and fine control of the position and orientation of transferred TMDC crystals, a feature required for fabrication of the devices based on vertical 2D heterostructures. Using both exfoliated and CVD grown materials and subsequent atomic force microscopy (AFM), photoluminescence (PL), confocal Raman and tip enhanced Raman spectroscopy (TERS) characterization, we ascertained the quality of interfaces resulting from the transfer process while preserving excellent 2D material integrity. PL and TERS maps revealed nanometer-scale heterogeneities in the interfaces of fabricated heterostructures, which should enable further perfection of the transfer technique. TERS/TEPL information were employed to identify areas suitable for nanodevice fabrication, making the reported transfer and characterization methods ideal for making high quality assembly of 2D heterostructure more accessible, which should facilitate exploration of vertical 2D heterostructures for applications in electronics, batteries, solar cells, and twistronics. [ABSTRACT FROM AUTHOR]

Investigation of few layer 2D materials is fundamentally important to bridge the gap between monolayer and bulk properties, and practically meaningful for applications as reinforcement nanofillers and layered electronic devices. Few layer introduces differences from intrinsic properties of monolayers due to the complexity of structural heterogeneities, such as lattice stacking orientation and local thickness variation. In this work, few layer graphene oxide (GO) with different structural heterogeneities were studied using atomic force microscopy-based deflection measurements and transmission electron microscopy (TEM). Direct TEM evidence of fracture surfaces and molecular dynamics (MD) simulations revealed decoupled and dissimilar layer crack patterns for misaligned bilayer. In contrast, aligned bilayer GO generally fractured with a larger portion of common cracks shared by both layers, indicating stronger interlayer interaction. MD results also revealed insignificant effect of lattice alignment on the strength and toughness of GO bilayers. Scaling up even to ∼5 layers and above revealed significant local thickness heterogeneity and consequently a ∼60% reduction of the normalized fracture force and toughness. MD simulations on partially intercalated few layer GO revealed anisotropic and heterogeneous stress distributions, as well as stress concentration near the inner edges, which may account for the significant reduction of strength and toughness. [ABSTRACT FROM AUTHOR]