Modulation of supramolecular structure by stepwise removal of tert-butyl groups from tetraazaperopyrene derivatives on Ag(111).

Tert-butyl functional groups can modulate the self-assembly behavior of organic molecules on surfaces. However, the precise construction of supramolecular architectures through their controlled thermal removal remains a challenge. Herein, we precisely controlled the removal amount of tert-butyl groups in tetraazaperopyrene derivatives by stepwise annealing on Ag(111). The evolution of 4tBu-TAPP supramolecular self-assembly from the grid-like structure composed of 3tBu-TAPP through the honeycomb network formed by 2tBu-TAPP to the one-dimensional chain co-assembled by tBu-TAPP and TAPP was successfully realized. This series of supramolecular nanostructures were directly visualized by high resolution scanning tunneling microscopy. Tip manipulation and density functional theory calculations show that the formation of honeycomb network structure can be attributed to the van der Waals interactions, N-Ag-N coordination bonds, and weak C-H⋯N hydrogen bonds. Further addition of two tert-butyl groups (6tBu-TAPP) leads to a completely different assembly evolution, due to the fact that the additional tert-butyl groups affect the molecular adsorption behavior and ultimately induce desorption. This work can possibly be exploited in constructing stable and long-range ordered nanostructures in surface-assisted systems, which can also promote the development of nanostructures in functional molecular devices.

Two-dimensional semiconductor materials with high stability and electron mobility in group-11 chalcogenide compounds: MNX (M = Cu, Ag, Au; N = Cu, Ag, Au; X = S, Se, Te; M ≠ N).

It is still an urgent task to find new two-dimensional (2D) semiconductor materials with a suitable band gap, high stability and high mobility for the applications of next generation electronic devices. Based on first-principles calculations, we report a new class of 2D group-11-chalcogenide trielement monolayers (MNX, where M = Cu, Ag, Au; N = Cu, Ag, Au; X = S, Se, Te; M ≠ N) with a wide band gap, excellent stability (dynamic stability, thermodynamic stability and environmental stability) and high mobility. At the mixed density functional level, the energy band gap extends from 0.61 eV to 2.65 eV, covering the ultraviolet-A and visible light regions, which is critical for a broadband optical response. For δ-MNX monolayers, the carrier mobility is as high as 104 cm2 V-1 s-1 at room temperature. In particular, the mobility of δ-AgAuS is as high as 6.94 × 104 cm2 V-1 s-1, which is of great research significance for the application of electronic devices in the future. Based on the above advantages, group-11 chalcogenide MNX monomolecular films have broad prospects in the field of nanoelectronics and optoelectronics in the future.