Atomically thin films, like transition metal dichalcogenides, can now be synthesized at wafer scale while maintaining monolayer thickness. At such extreme aspect ratios, atomistic simulations and existing experimental techniques are unable to directly predict or measure the mechanical effects of intrinsic features like polycrystallinity without the interference of pinned boundaries or solid substrates. To address this challenge, here we introduce a versatile approach: we realize large scale free-floating membranes on water and measure their mechanical properties using atomic force microscopy (AFM) and Raman spectroscopy adapted to water’s surface. We reveal that free-standing polycrystalline membranes spontaneously form large athermal wrinkles. These wrinkles differ from those of extrinsic origin in that their size and shape depend on an intrinsic mesoscopic feature of the 2D material: the polycrystalline grain size. We rationalize the relationship between grain size and wrinkle shape using continuum theory and minimal mathematical models. Finally, we demonstrate experimentally that the wrinkles alter the mechanical properties of the sheet, introducing dramatic softening and spatial heterogeneity in response to a point probe. The present work illuminates the mechanics of polycrystalline nanomaterials at extreme aspect ratios and suggests principles for engineering strain-controlled nanomechanical responses.

The optical, electronic, and catalytic properties of nanocrystals (NCs) are often determined by their size, shape, and materials. Understanding the underlying mechanisms of shape-controlled synthesis and transformation is crucial for revealing fundamental reaction kinetics, enabling the design of more precisely controlled materials. Liquid cell transmission electron microscopy (LCTEM) enables the observation of individual NC growth and dissolution with millisecond time resolution and subnanometer space resolution. In this study, we harnessed the chemical environment to analyze the single-particle etching trajectories of well-faceted copper arsenide (Cu₃As) nanocubes. Distinct kinetically controlled dissolution trajectories are identified by adjusting the chemical reactions of Cu or As through pH, coordination, concentration, and oxidative species. These LCTEM observations illustrate how the nanoscale shape transformations in binary semiconductors can be controlled through manipulation of cationic and anionic reactivity within a highly reactive nonequilibrium radiolysis liquid environment.

Semiconductor quantum dots (QDs) are less stable than bulk materials due to their high surface-to-volume ratio, making them prone to degradation in water and oxygen. Understanding their structural transformation pathways during degradation is crucial for designing stable nanocrystals with robust photophysical properties. Among environmentally benign III–V materials, InP-based QDs remain less explored. In-situ liquid-phase transmission electron microscopy (TEM) enables real-time observation of nanocrystal degradation under native conditions, while four-dimensional scanning TEM (4D-STEM) provides nanoscale mapping of crystal structure, orientation, and disorder. However, performing 4D-STEM in liquids is challenging due to electron scattering and low signal-to-noise ratios under low-dose conditions.

Here, we introduce ultrathin carbon film liquid cells enabling multimodal imaging of InP nanocrystal degradation. Tris·HCl solution provides a controlled etching environment. Zinc-blende InP nanocrystals (~10 nm) and wurtzite InP nanoplates (~15 nm × 4 nm) both degrade under the beam. Bare InP nanoparticles shrink during etching, while InP/ZnSe/ZnS core–shell particles maintain size but become amorphous. 4D-STEM offers enhanced contrast and, combined with machine learning, distinguishes crystalline and amorphous regions. These findings highlight the potential of controlled environments for tuning nanocrystal degradation pathways and morphology.

Liquid-phase electron microscopy (LPEM) enables real-time imaging of nanoscale processes in liquids but traditional silicon nitride liquid cells (LCs) suffer from thick windows, excess liquid, and beam-induced radiolysis. Graphene liquid cells (GLCs) solved these issues by forming ultrathin, vacuum-stable pockets for high-resolution imaging, while boron nitride liquid cells (BNLCs) extended capabilities to low-energy spectroscopy. However, beam damage and bubble formation remain challenges.

Molybdenum disulfide (MoS₂) offers tunable properties and high chemical stability, making it a promising LC window material. We demonstrate monolayer MoS₂ liquid cells (MLCs) and hybrid MoS₂–graphene cells (MGLCs) fabricated via a polymer- and etching-free transfer, yielding clean, wrinkle-free MoS₂ membranes. Liquid pockets formed by drop-casting solutions and encapsulating with MoS₂ or graphene produced stable cells.

Ferritin-loaded MGLCs confirmed effective encapsulation, while imaging of CeO₂ aggregates in MLCs revealed Moiré patterns from stacked MoS₂ layers. EELS showed encapsulated CeO₂ maintained its Ce⁴⁺ oxidation state, while exposed particles reduced to Ce³⁺.

These results establish MoS₂ as a stable, contamination-free window for high-resolution liquid-phase TEM and a platform for in situ studies of electrochemical reactions.

Graphene liquid cells (GLCs) enable encapsulation of samples in 30–50 nm liquid layers for high-resolution imaging of beam-sensitive materials and in situ reactions. However, conventional fabrication often results in ruptured or wrinkled graphene, reducing encapsulation yield and reproducibility. To address this, we developed a modified method that incorporates a ~3 nm amorphous carbon layer onto the top graphene monolayer using pulsed carbon thread evaporation. This thin layer provides mechanical support during Cu etching, preventing graphene tearing while maintaining imaging quality.

After etching in ammonium persulfate and transferring onto graphene-coated TEM grids, stable encapsulation was achieved by lowering the amorphous carbon–graphene layer onto submerged grids containing Au nanorods or water droplets. HAADF imaging revealed massive GLCs (mGLCs) with channel networks spanning several micrometers. EELS confirmed the presence of water and radiolysis-induced H₂ (13.6 eV) throughout the encapsulated regions. Thickness analysis showed areas ranging from 50–150 nm, enabling both high-resolution and conventional imaging.

Low-loss EELS from encapsulated Au nanorods revealed distinct plasmon and water loss peaks, verifying successful encapsulation. Overall, the amorphous carbon-assisted method improved fabrication reproducibility by 60–80%, enabling large, stable GLCs for in situ nanoscale and catalytic studies in liquid environments.