No abstract

Diamond is the hardest natural material, but its practical strength is low and its elastic deformability extremely limited. While recent experiments have demonstrated that diamond nanoneedles can sustain exceptionally large elastic tensile strains with high tensile strengths, the size- and orientation-dependence of these properties remains unknown. Here we report maximum achievable tensile strain and strength of diamond nanoneedles with various diameters, oriented in <100>, <110> and <111> -directions, using in situ transmission electron microscopy. We show that reversible elastic deformation depends both on nanoneedle diameter and orientation. <100> -oriented nanoneedles with a diameter of 60 nm exhibit highest elastic tensile strain (13.4%) and tensile strength (125 GPa). These values are comparable with the theoretical elasticity and Griffith strength limits of diamond, respectively. Our experimental data, together with first principles simulations, indicate that maximum achievable elastic strain and strength are primarily determined by surface conditions of the nanoneedles.

Two-dimensional (2D) van der Waals (vdW) heterostructures, known as layer by layer stacked 2D materials in a precisely chosen sequence, have received more and more attention in spintronics for the...

Helicene-based emitters with unique inherent circularly polarized luminescence (CPL) are promising yet remain a formidable challenge for highly efficient circularly polarized organic light emitting diodes (CP-OLEDs), ascribed to their tough synthesis, low emission efficiency, and easy racemization in thermal deposition process. Herein, a pair of helicene-based enantiomers, namely (P)-helicene-BN and (M)-helicene-BN, were developed, which merge helical chirality and the B/N/S inserted polycyclic aromatic framework to concurrently feature CPL and narrow thermally activated delayed fluorescence (TADF) characteristics. Benefiting from the excellent thermal/photophysical/chiroptical properties, the narrowband green CP-OLEDs based on the enantiomers achieved maximum external quantum efficiencies (EQE max ) of up to 31.5%, and dissymmetry factor (|g EL |) of 2.2 × 10 -3 . This work reveals the great potential of helicene-based emitters in CP-OLEDs.