Nanoscale transition-metal dichalcogenide (TMDC) materials, such as MoS, exhibit promising behavior in next-generation electronics and energy-storage devices. TMDCs have a highly anisotropic crystal structure, with edge sites and basal planes exhibiting different structural, chemical, and electronic properties. In virtually all applications, two-dimensional or bulk TMDCs must be interfaced with other materials (such as electrical contacts in a transistor). The presence of edge sites vs basal planes (i.e., the crystallographic orientation of the TMDC) could influence the chemical and electronic properties of these solid-state interfaces, but such effects are not well understood. Here, we use in situ X-ray photoelectron spectroscopy (XPS) to investigate how the crystallography and structure of MoS influence chemical transformations at solid-state interfaces with various other materials. MoS materials with controllably aligned crystal structures (horizontal vs vertical orientation of basal planes) were fabricated, and in situ XPS was carried out by sputter-depositing three different materials (Li, Ge, and Ag) onto MoS within an XPS instrument while periodically collecting photoelectron spectra; these deposited materials are of interest due to their application in electronic devices or energy storage. The results showed that Li reacts readily with both crystallographic orientations of MoS to form metallic Mo and LiS, while Ag showed very little chemical or electronic interaction with either type of MoS. In contrast, Ge showed significant chemical interactions with MoS basal planes, but only minor chemical changes were observed when Ge contacted MoS edge sites. These findings have implications for electronic transport and band alignment at these interfaces, which is of significant interest for a variety of applications.

In this Letter, we report, to the best of our knowledge, the first demonstration of high-quality integrated microdisk resonators (MDRs) on a 3C-silicon carbide-on-insulator (SiCOI) platform, working over a wide bandwidth from visible to near-infrared wavelengths. We show record-high quality factors for 3C-silicon carbide (SiC) MDRs of 242,000, 112,000, and 83,000 at the wavelengths of 1550 nm, 770 nm, and 650 nm, respectively, based on high-quality 3C-SiC films with the surface roughness as low as 1.4 Å, achieved by sample-transfer bonding, and precise chemical-mechanical polishing of the SiC film, to remove growth defects. Our study of 3C-SiC films grown on Si using transmission electron microscopy shows that even considerably higher-quality single-crystalline SiCOI can be achieved by flipping and thinning down an ultra-thick ( ∼ 5 − 10 µ m ) 3C-SiC film grown on Si. The SiCOI platform can be used to realize ultra-wideband high-quality SiC devices that are desirable for applications in nonlinear and quantum photonics.

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Composition modulation of two-dimensional transition-metal dichalcogenides (TMDs) has introduced an enticing prospect for the synthesis of Van der Waals alloys and lateral heterostructures with tunable optoelectronic properties. Phenomenologically, the optoelectronic properties of alloys are entangled to a strain that is intrinsic to synthesis processes. Here, we report an unprecedented biaxial strain that stems from the composition modulation of monolayer TMD alloys (e.g., MoS 2x Se 2(1 -x) ) and inflicts fracture on the crystals. We find that the starting crystal (MoSe 2 ) fails to adjust its lattice constant as the atoms of the host crystal (selenium) are replaced by foreign atoms (sulfur) during the alloying process. Thus, the resulting alloy forms a stretched lattice and experiences a large biaxial tensile strain. Our experiments show that the biaxial strain relaxes via formation of cracks in interior crystal domains or through less constraint bounds at the edge of the monolayer alloys. Griffith's criterion suggests that defects combined with a sulfur-rich environment have the potential to significantly reduce the critical strain at which cracking occurs. Our calculations demonstrate a substantial reduction in fracture-inducing critical strain from 11% (in standard TMD crystals) to a range below 4% in as-synthesized alloys.

Spatially resolved RNA and protein molecular analyses have revealed unexpected heterogeneity of cells. Metabolic analysis of individual cells complements these single-cell studies. Here, we present a three-dimensional spatially resolved metabolomic profiling framework (3D-SMF) to map out the spatial organization of metabolic fragments and protein signatures in immune cells of human tonsils. In this method, 3D metabolic profiles were acquired by time-of-flight secondary ion mass spectrometry to profile up to 189 compounds. Ion beams were used to measure sub–5-nanometer layers of tissue across 150 sections of a tonsil. To incorporate cell specificity, tonsil tissues were labeled by an isotope-tagged antibody library. To explore relations of metabolic and cellular features, we carried out data reduction, 3D spatial correlations and classifications, unsupervised K-means clustering, and network analyses. Immune cells exhibited spatially distinct lipidomic fragment distributions in lymphatic tissue. The 3D-SMF pipeline affects studying the immune cells in health and disease.