Two-dimensional atomic crystals are extensively studied in recent years due to their exciting physics and device applications. However, a molecular counterpart, with scalable processability and competitive device performance, is still challenging. Here, we demonstrate that high-quality few-layer dioctylbenzothienobenzothiophene molecular crystals can be grown on graphene or boron nitride substrate via van der Waals epitaxy, with precisely controlled thickness down to monolayer, large-area single crystal, low process temperature and patterning capability. The crystalline layers are atomically smooth and effectively decoupled from the substrate due to weak van der Waals interactions, affording a pristine interface for high-performance organic transistors. As a result, monolayer dioctylbenzothienobenzothiophene molecular crystal field-effect transistors on boron nitride show record-high carrier mobility up to 10 cm 2 V À 1 s À 1 and aggressively scaled saturation voltage B1 V. Our work unveils an exciting new class of two-dimensional molecular materials for electronic and optoelectronic applications.

While solid-state batteries are tantalizing for achieving improved safety and higher energy density, solid ion conductors currently available fail to satisfy the rigorous requirements for battery electrolytes and electrodes. Inorganic ion conductors allow fast ion transport, but their rigid and brittle nature prevents good interfacial contact and impedes device integration and stability.Conversely, flexible polymeric ion conductors provide better interfacial compatibility and mechanical tolerance, but suffer from inferior ionic conductivity (< 10 −5 S cm −1 at room temperature) due to the coupling of ion transport with the polymer chain motion 1-3 . In this work, we report a general design strategy for achieving one-dimensional (1D), high-performance polymer solid-state ion conductors through molecular channel engineering, which we demonstrate via Cu 2+ -coordination of cellulose nanofibrils. The cellulose nanofibrils by themselves are not ionic conductive; however, by opening the molecular channels between the cellulose chains through Cu 2+ coordination we are able to achieve a Li-ion conductivity as high as 1.5×10 −3 S cm −1 at room temperature-a record among all known polymer ion conductors. This improved conductivity is enabled by a unique Li + hopping mechanism that is decoupled from the polymer segmental motion. Also benefitted from such decoupling, the cellulose-based ion conductor demonstrates multiple advantages, including a high transference number (0.78 vs. 0.2-0.5 in other polymers 2 ), low activation energy (0.19 eV), and a wide electrochemical stability window (4.5 V) that accommodate both Li metal anode and high-voltage cathodes. Furthermore, we demonstrate this 1D ion conductor not only as a thin, high-conductivity solid-state electrolyte but also as an effective ion-conducting additive for the solid cathode, providing continuous ion transport pathways with a low percolation threshold, which allowed us to utilize the thickest LiFePO4 solidstate cathode ever reported for high energy density. This approach has been validated with other 3 polymers and cations (e.g., Na + and Zn 2+ ) with record-high conductivities, offering a universal strategy for fast single-ion transport in polymer matrices, with significance that could go far beyond safe, high-performance solid-state batteries.

MnX (X = P, As) monolayers: room-temperature ferromagnetic half-metallicity and sizable magnetic anisotropy.

Two-dimensional (2D) ferromagnetic materials with intrinsic half-metallicity are highly desirable for nanoscale spintronic applications. Here, we predict a new and stable family of 2D transition-metal dihydride (MH; M = Sc, Ti, V, Cr, Fe, Co, Ni) monolayers with novel properties. Our density functional theory computation shows that CoH and ScH monolayers are ferromagnetic metals, while the others are antiferromagnetic semiconductors. In particular, the CoH monolayer is a perfect half-metal with a wide spin gap of 3.48 eV. The ScH monolayer can also possess half-metallicity through hole doping. Most importantly, our Monte Carlo simulations show that the CoH monolayer possesses an above-room-temperature Curie point (339 K), while that of the ScH monolayer can also reach 160 K. A synthetic approach is proposed to realize CoH and ScH monolayers in the laboratory. Notably, their half-metallicity can be well maintained on substrates. The new family of MH monolayers are promising functional materials for spintronic applications due to their novel magnetic properties.

Localized surface plasmon resonances (LSPRs) have attracted much recent attention for their potential in promoting chemical reactions with light. However, the mechanism of LSPR-induced chemical reactions is still not clear, even for H2 dissociation on metal nanoparticles. In this work, we investigate the mechanism for photoinduced H2 dissociation using a simple H2@Au6 model. Our time-dependent density functional theory calculations indicate that the initial excitation is largely restricted to the metal cluster, involving intraband excitation that produces hot electrons (HEs). However, diabatization via overlapping orbitals reveals two types of nested electronic states, one involving excitations of the metallic electrons, namely, the HE states, and the other concerned with charge transfer (CT) to the adsorbate antibonding σ* orbital. Dissociation of H2 thus takes place by transitions from the former to the latter. Quantum dynamics simulations on the diabatic CT states suggest rapid dissociation of H2, while no such dissociation occurs on diabatic HE states. Our research provides a clear physical picture of photoinduced H2 dissociation on Au clusters, which has important implications in plasmonic facilitated photocatalysis.

Auxetic materials, known with negative Poisson's ratio, are highly desirable for many advanced applications, but the candidates are rather scarce, especially at low dimension. Motivated by the re-entrant structure that often exposes negative Poisson's ratio, we predict a two-dimensional (2D) planar B 4 N monolayer as a promising auxetic material with unusual in-plane negative Poisson's ratio within the framework of density functional theory calculations. B 4 N monolayer also exhibits a highly emerged mechanical anisotropy, characterized by Young's modulus and Poisson's ratio. In addition, this monolayer shows superior mechanical flexibility in ideal tensile strength and critical strain values. The phonon dispersion calculations and ab initio molecular dynamics simulations further demonstrate that this monolayer also owns excellent dynamical and thermal stabilities. The fantastic mechanical properties coupled with robust structural stability render the auxetic B 4 N monolayer promising for future nanomechanical devices.

van der Waals (vdW) epitaxy of ultrathin organic films on two-dimensional (2D) atomic crystals has become a sovereign area because of their unique advantages in organic electronic devices. However, the dynamic mechanism of the self-assembly remains elusive. Here, we visualize the nanoscale self-assembly of organic molecules on graphene and boron nitride monolayer from a disordered state to a 2D lattice via molecular dynamics simulation for the first time. It is revealed that the assembly toward 2D ordered structures is essentially the minimization of the molecule-molecule interaction, that is, the vdW interaction in nonpolar systems and the vdW and Coulomb interactions in polar systems that are the decisive factors for the formation of the 2D ordering. The role of the substrate is mainly governing the array orientation of the adsorbates. The mechanisms unveiled here are generally applicable to a broad class of organic thin films via vdW epitaxy.

Crystals of organic semiconductors are excellent candidates for flexible and array-based electronics. Large-scale synthesis of organic crystals in a controllable way while maintaining homogeneous single-crystal property has been a great challenge. The existence of grain boundaries and small crystal domains, however, restrict the device performance and limit the access to commercially viable organic electronics in the industry. Herein, we report the inch-scale synthesis of highly oriented 2,7-dioctyl[1]­benzothieno­[3,2-b]­[1]­benzothiophene (C8-BTBT) organic single crystal by nucleation seed-controlled shearing method. The organic field-effect transistors developed from such single crystal have excellent carrier mobility as high as 14.9 cm2 V–1 s–1 and uniformity (standard deviation is 1.3 cm2 V–1 s–1) of 225 devices. We also found that the rotation of the principal axis in the crystal is governed by the orientations of seeds and the possible mechanism behind this phenomenon is proposed based on the density functional theory calculations. We anticipate that this proposed approach will have great potential to be developed as a platform for the growth of organic crystals with high crystallinity on a large scale.