Exploring Favorable Supramolecular Interactions of Multifluorinated Aromatics in Dendronized Push-Pull Chromophores for Electro-Optics.

Multifluorinated aromatics serve as supramolecular synthons in the research of organic electro-optic (EO) materials by exploiting π-π stacking interaction between the aromatic hydrocarbon and multifluorinated aromatic groups for performance improvement. However, non-classical hydrogen bonding remains largely unexplored in fluorinated EO dendrimers. In this study, three Fréchet-type generation 1 benzyl ether co-dendrons were synthesized by replacing one benzyl group with 2,3,5,6-tetrafluorobenzyl (p-HFBz), pentafluorobenzyl (CFBz), and 2,3,4,5-tetrafluorobenzyl (o-HFBz) groups, to afford the benzoic acid derivatives D1, D2, and D3, which were further bonded to the donor and π-bridge moieties to afford three co-dendronized push-pull phenyltetraene chromophores EOD1, EOD2, and EOD3, respectively.

Ultrahigh Lubricity between Two-Dimensional Ice and Two-Dimensional Atomic Layers.

Low temperature and high humidity conditions significantly degrade the performance of solid-state lubricants consisting of van der Waals (vdW) atomic layers, owing to the liquid water layer attached/intercalated to the vdW layers, which greatly enhances the interlayer friction. However, using low temperature atomic force microscopy (AFM) and friction force microscopy (FFM), we unveil the unexpected ultralow friction between two-dimensional (2D) ice, a solid phase of water confined to the 2D space, and the 2D molybdenum disulfides (MoS). The friction of MoS and 2D ice is reduced by more than 30% as compared to bare MoS and the rigid surface.

Controlled Adhesion of Ice-Toward Ultraclean 2D Materials.

The scalable 2D device fabrication and integration demand either the large-area synthesis or the post-synthesis transfer of 2D layers. While the direct synthesis of 2D materials on most targeted surfaces remains challenging, the transfer approach from the growth substrate onto the targeted surfaces offers an alternative pathway for applications and integrations. However, the current transfer techniques for 2D materials predominantly involve polymers and organic solvents, which are liable to contaminate or deform the ultrasensitive atomic layers.

In Situ Scanning Transmission Electron Microscopy Observations of Fracture at the Atomic Scale.

The formation, propagation, and structure of nanoscale cracks determine the failure mechanics of engineered materials. Herein, we have captured, with atomic resolution and in real time, unit cell-by-unit cell lattice-trapped cracking in two-dimensional (2D) rhenium disulfide (ReS_{2}) using in situ aberration corrected scanning transmission electron microscopy (STEM). Our real time observations of atomic configurations and corresponding strain fields in propagating cracks directly reveal the atomistic fracture mechanisms.

Anomalous fracture in two-dimensional rhenium disulfide.

Low-dimensional materials usually exhibit mechanical properties from those of their bulk counterparts. Here, we show in two-dimensional (2D) rhenium disulfide (ReS) that the fracture processes are dominated by a variety of previously unidentified phenomena, which are not present in bulk materials. Through direct transmission electron microscopy observations at the atomic scale, the structures close to the brittle crack tip zones are clearly revealed.

Spontaneously Ordered Hierarchical Two-Dimensional Wrinkle Patterns in Two-Dimensional Materials.

Achieving two-dimensionally (2D) ordered surface wrinkle patterns is still challenging not only for the atomic-thick 2D materials but also in general for all soft surfaces. Normally disordered 2D wrinkle patterns on isotropic surfaces can be rendered via biaxial straining. Here, we report that the 1D and 2D ordered wrinkle patterns in 2D materials can be produced by sequential wrinkling controlled by thermal straining and vertical spatial confinement.

Site-specific electrical contacts with the two-dimensional materials.

Electrical contact is an essential issue for all devices. Although the contacts of the emergent two-dimensional materials have been extensively investigated, it is still challenging to produce excellent contacts. The face and edge type contacts have been applied previously, however a comparative study on the site-specific contact performances is lacking.

Catalyzed Kinetic Growth in Two-Dimensional MoS.

It remains difficult to control the morphology of two-dimensional (2D) materials via direct chemical vapor deposition (CVD) growth. In particular, off-equilibrium (kinetic) growth may produce flakes with non-Wulff shapes (e.g.

Critical Stable Length in Wrinkles of Two-Dimensional Materials.

The emergent two-dimensional (2D) materials are atomically thin and ultraflexible, promising for a variety of miniaturized, high-performance, and flexible devices in applications. On one hand, the ultrahigh flexibility causes problems: the prevalent wrinkles in 2D materials may undermine the ideal properties and create barriers in fabrication, processing, and quality control of materials. On the other hand, in some cases the wrinkles are used for the architecturing of surface texture and the modulation of physical/chemical properties.

Superior Dielectric Screening in Two-Dimensional MoS Spirals.

Metals have the best dielectric screening capability among all materials; however, it is usually difficult to fabricate continuous and uniform ultrathin (few-atomic-layer thickness) metal films. Conversely, high-quality atomic-thick semiconductor or semimetal materials (so called two-dimensional materials) such as graphene or MoS can be readily obtained and robust in ambient conditions; however, their dielectric screening capabilities are greatly reduced by their reduced dimensionality. Particularly, in the vertical direction, the dielectric screening of two-dimensional materials is insufficient; thus, the performances of devices by two-dimensional materials were easily affected by the coulomb-scattering or other kind of sources.

Edge Delamination of Monolayer Transition Metal Dichalcogenides.

Delamination of thin films from the supportive substrates is a critical issue within the thin film industry. The emergent two-dimensional, atomic layered materials, including transition metal dichalcogenides, are highly flexible; thus buckles and wrinkles can be easily generated and play vital roles in the corresponding physical properties. Here we introduce one kind of patterned buckling behavior caused by the delamination from a substrate initiated at the edges of the chemical vapor deposition synthesized monolayer transition metal dichalcogenides, led by thermal expansion mismatch.