Jiuxiang Dai

Amorphous red phosphorus (a-P) can be described on the atomic scale by combining emerging machine-learning-based and dispersion-corrected DFT approaches. The a-P models reported here complete the first-principles stability range of the phosphorus allotropes, and they allow for new insight into chemical bonding and electronic states.

Abstract

Amorphous red phosphorus (a-P) is one of the remaining puzzling cases in the structural chemistry of the elements. Here, we elucidate the structure, stability, and chemical bonding in a-P from first principles, combining machine-learning and density-functional theory (DFT) methods. We show that a-P structures exist with a range of energies slightly higher than those of phosphorus nanorods, to which they are closely related, and that the stability of a-P is linked to the degree of structural relaxation and medium-range order. We thus complete the stability range of phosphorus allotropes [Angew. Chem. Int. Ed. 2014, 53, 11629] by now including the previously poorly understood amorphous phase, and we quantify the covalent and van der Waals interactions in all main phases of phosphorus. We also study the electronic densities of states, including those of hydrogenated a-P. Beyond the present study, our structural models are expected to enable wider-ranging first-principles investigations—for example, of a-P-based battery materials.

The current conduction mechanisms of hexagonal boron nitride-based threshold memristors with nickel electrodes in high and low resistance states are investigated by temperature-dependent current-voltage measurements . Transmission electron microscopy images (TEM) confirm that the method is a valuable addition to analyzing resistive switching mechanisms with specialized TEM and conductive atomic force microscopy.

Abstract

The 2D insulating material hexagonal boron nitride (h-BN) has attracted much attention as the active medium in memristive devices due to its favorable physical properties, among others, a wide bandgap that enables a large switching window. Metal filament formation is frequently suggested for h-BN devices as the resistive switching (RS) mechanism, usually supported by highly specialized methods like conductive atomic force microscopy (C-AFM) or transmission electron microscopy (TEM). Here, the switching of multilayer hexagonal boron nitride (h-BN) threshold memristors with two nickel (Ni) electrodes is investigated through their current conduction mechanisms. Both the high and the low resistance states are analyzed through temperature-dependent current–voltage measurements. The formation and retraction of nickel filaments along boron defects in the h-BN film as the resistive switching mechanism is proposed. The electrical data are corroborated with TEM analyses to establish temperature-dependent current–voltage measurements as a valuable tool for the analysis of resistive switching phenomena in memristors made of 2D materials. The memristors exhibit a wide and tunable current operation range and low stand-by currents, in line with the state of the art in h-BN-based threshold switches, a low cycle-to-cycle variability of 5%, and a large On/Off ratio of 10⁷.

Nature Communications, Published online: 05 May 2023; doi:10.1038/s41467-023-37866-2

Nature Electronics, Published online: 04 May 2023; doi:10.1038/s41928-023-00959-3

Nature Nanotechnology, Published online: 04 May 2023; doi:10.1038/s41565-023-01391-6

Nature Communications, Published online: 04 May 2023; doi:10.1038/s41467-023-38344-5

Abstract

Owing to stable spatial framework and large electrochemical interface, self-supported transition metal chalcogenides have been actively explored in renewable energy fields, especially in oxygen evolution reaction (OER). Here, we review the research progress of self-supported transition metal chalcogenides (including sulfides, selenides, and tellurides) for the OER in recent years. The basic principle and evaluation parameters of OER are first introduced, and then the preparation methods of transition metal chalcogenides on various self-supporting substrates (including Ni foam (NF), carbon cloth (CC), carbon fiber paper (CFP), metal mesh/plate, etc.) are systematically summarized. Subsequently, advanced optimization strategies (including interface and defect engineering, heteroatom doping, edge engineering, surface morphology engineering, and construction of heterostructure) are introduced in detail to improve the inherent catalytic activity of self-supported electrocatalysts. Finally, the challenges and prospects of developing more promising self-supported chalcogenide electrocatalysts are proposed.

Nature, Published online: 03 May 2023; doi:10.1038/s41586-023-05853-8

Dip Pen Nanolithography

In article number 2208069, Bart Jan Ravoo and co-workers report the surface patterning of nanoparticles using dip pen nanolithography. Metal and metal oxide nanoparticles functionalized with various organic ligands can be patterned in nanosized clusters. Depending on the polarity of the ligand shell, water or toluene is used as ink solvent. No modification of atomic force microscope (AFM) tip or substrate surface is required.

Quantum well states (QWS) and two-dimensional electron gas (2DEG) coexist in few-layer GaSe. The QWS are located in the valence bands and exhibit a peak feature, with the number of quantum wells being equal to the number of atomic layers. Meanwhile, the 2DEG is located in the conduction bands and exhibits a standing-wave feature.

Abstract

Conventional two-dimensional electron gas (2DEG) typically occurs at the interface of semiconductor heterostructures and noble metal surfaces, but it is scarcely observed in individual 2D semiconductors. In this study, few-layer gallium selenide (GaSe) grown on highly ordered pyrolytic graphite (HOPG) is demonstrated using scanning tunneling microscopy and spectroscopy (STM/STS), revealing that the coexistence of quantum well states (QWS) and 2DEG. The QWS are located in the valence bands and exhibit a peak feature, with the number of quantum wells being equal to the number of atomic layers. Meanwhile, the 2DEG is located in the conduction bands and exhibits a standing-wave feature. Additionally, monolayer GaSe/HOPG heterostructures with different stacking angles (0°, 33°, 8°) form distinct moiré patterns that arise from lattice mismatch and angular rotation between adjacent atomic layers in 2D materials, which effectively modulate the electron effective mass, charge redistribution, and band gap of GaSe. Overall, this work reveals a paradigm of band engineering based on layer numbers and moiré patterns that can modulate the electronic properties of 2D materials.

Nature Communications, Published online: 02 May 2023; doi:10.1038/s41467-023-38172-7