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Defects and reconstructions in two-dimensional (2D) moiré materials cause out-of-plane deformations that strongly modify their electronic properties but are difficult to experimentally access. Here, we solve the 3D atomic coordinates of twisted bilayer WSe₂with picometer-scale accuracy using multislice electron ptychography (MEP) acquired from a single orientation. The resulting atomic models individually visualize each of the six atomic planes, revealing the curvature of each WSe₂layer, variations in the interlayer spacing, and the 3D locations of individual vacancies, which lie exclusively in the outer Se planes. We also observe an unexpected type of structural disorder consisting of mixed bending- and breathing-type moiré-induced corrugations that should strongly affect the emergent electronic properties. Broadly, our methods generate 3D atom-by-atom models of a 2D heterointerface from data acquired in about 30 seconds, methods that should unlock routine access to 3D atomic information in 2D systems and catalyze design methods to control out-of-plane deformations. 

Balgacyclamide A−C are a family of cyanobactin natural products isolated from freshwater cyanobacteriaMicrocystis aeruginosa. These macrocyclic peptides are characterized by their oxazoline‐thiazole core, their 7 or 8 stereocenters, and their antiparasitic activities. Balgacyclamide B is known for its activity towardsPlasmodium falciparumchloroquine‐resistant strain K1,Trypanosoma brucei rhodesiense, andLeishmania donovani. In this report, the first total synthesis of Balgacyclamide B is described in a 17‐steps pathway and a 2 % overall yield. The synthetic pathway toward balgacyclamide B can be adapted for the future syntheses of balgacyclamide A and C. In addition, a brief history background of oxazolines syntheses is shown to emphasize the importance of the cyclization conditions used to interconvert or retain configuration of β‐hydroxy amides via dehydrative cyclization. 

Spatial and energy resolutions of state-of-the-art transmission electron microscopes (TEMs) have surpassed 50 pm and 5 meV. However, with respect to the time domain, even the fastest detectors combined with the brightest sources may only be able to reach the microsecond timescale. Thus, conventional methods are incapable of resolving myriad fundamental ultrafast ( i.e., attosecond to picosecond) atomic-scale dynamics. The successful demonstration of femtosecond (fs) laser-based (LB) ultrafast transmission electron microscopy (UEM) nearly 20 years ago provided a means to span this nearly 10-order-of-magnitude temporal gap. While nanometer-picosecond UEM studies of dynamics are now well established, ultrafast Å-scale imaging has gone largely unrealized. Further, while instrument development has rightly been an emphasis, and while new modalities and uses of pulsed-beam TEM continue to emerge, the overall chemical and materials application space has been only modestly explored to date. In this Perspectives article, we argue that these apparent shortfalls can be attributed to a simple lack of data and detail. We speculate that present work and continued growth of the field will ultimately lead to the realization that Å-scale fs dynamics can indeed be imaged with minimally modified UEM instrumentation and with repetition rates ( f rep ) below - and perhaps even well below - 1 MHz. We further argue that use of low f rep , whether for LB UEM or for chopped/bunched beams, significantly expands the accessible application space. This calls for systematically establishing modality-specific limits so that especially promising technologies can be pursued, thus ultimately facilitating broader adoption as individual instrument capabilities expand. 

We propose two mass and heat energy conservative, unconditionally stable, decoupled numerical algorithms for solving the Cahn–Hilliard–Navier–Stokes–Darcy–Boussinesq system that models thermal convection of two-phase flows in superposed free flow and porous media. The schemes totally decouple the computation of the Cahn–Hilliard equation, the Darcy equations, the heat equation, the Navier–Stokes equations at each time step, and thus significantly reducing the computational cost. We rigorously show that the schemes are conservative and energy-law preserving. Numerical results are presented to demonstrate the accuracy and stability of the algorithms. 

Twisted two-dimensional materials exhibit distinctive vibrational modes called moiré phonons, which arise from the moiré superlattice. Here, we demonstrate atom-by-atom imaging of phasons, an ultrasoft class of moiré phonons in twisted bilayer tungsten diselenide (WSe₂). Using ultrahigh-resolution (<15 picometers) electron ptychography, we imaged the size and shape of each atom to extract time-averaged vibrational amplitudes as a function of twist angle and position. We observed several signature properties of moiré phasons, such as increased vibrational amplitudes at solitons and AA-stacked regions. By correlating experiments with molecular dynamics simulations and lattice dynamics calculations, we show that phasons dominate the thermal vibrations in low-angle twisted bilayers. These results represent a powerful route to image thermal vibrations at atomic resolution, unlocking experimental studies of a thus far hidden branch of moiré phonon physics. 

Key properties of two-dimensional (2D) layered materials are highly strain tunable, arising from bond modulation and associated reconfiguration of the energy bands around the Fermi level. Approaches to locally controlling and patterning strain have included both active and passive elastic deformation via sustained loading and templating with nanostructures. Here, by float-capturing ultrathin flakes of single-crystal 2H-MoS₂ on amorphous holey silicon nitride substrates, we find that highly symmetric, high-fidelity strain patterns are formed. The hexagonally arranged holes and surface topography combine to generate highly conformal flake-substrate coverage creating patterns that match optimal centroidal Voronoi tessellation in 2D Euclidean space. Using TEM imaging and diffraction, as well as AFM topographic mapping, we determine that the substrate-driven 3D geometry of the flakes over the holes consists of symmetric, out-of-plane bowl-like deformation of up to 35 nm, with in-plane, isotropic tensile strains of up to 1.8% (measured with both selected-area diffraction and AFM). Atomistic and image simulations accurately predict spontaneous formation of the strain patterns, with van der Waals forces and substrate topography as the input parameters. These results show that predictable patterns and 3D topography can be spontaneously induced in 2D materials captured on bare, holey substrates. The method also enables electron scattering studies of precisely aligned, substrate-free strained regions in transmission mode.