In situ observations of freestanding single-atom-thick gold nanoribbons suspended in graphene

Bulk gold's attributes of relative chemical inertness, rarity, relatively low melting point and its beautiful sheen make it a prized material for humans. Recordings suggest it was the first metal employed by humans dating as far back to the late Paleolithic period approximate to 40 000 BC. However, at the nanoscale gold is expected to present new and exciting properties, not least in catalysis. Moreover, recent studies suggest a new family of single-atom-thick two-dimensional (2D) metals exist. This work shows single-atom-thick freestanding gold membranes and nanoribbons can form as suspended structures in graphene pores. Electron irradiation is shown to lead to changes to the graphene pores which lead to dynamic changes of the gold membranes which transition to a nanoribbon. The freestanding single-atom-thick 2D gold structures are relatively stable to electron irradiation for extended periods. The work should advance the development of 2D gold monolayers significantly.Web of Scienceart. no. 200043

Large-Area Single-Crystal Graphene via Self-Organization at the Macroscale

In 1665 Christiaan Huygens first noticed how two pendulums, regardless of their initial state, would synchronize. It is now known that the universe is full of complex self-organizing systems, from neural networks to correlated materials. Here, graphene flakes, nucleated over a polycrystalline graphene film, synchronize during growth so as to ultimately yield a common crystal orientation at the macroscale. Strain and diffusion gradients are argued as the probable causes for the long-range cross-talk between flakes and the formation of a single-grain graphene layer. The work demonstrates that graphene synthesis can be advanced to control the nucleated crystal shape, registry, and relative alignment between graphene crystals for large area, that is, a single-crystal bilayer, and (AB-stacked) few-layer graphene can been grown at the wafer scale. © 2020 The Authors. Published by Wiley-VCH Gmb

In situ N-doped graphene and Mo nanoribbon formation from Mo2Ti2C3 MXene monolayers

Since the advent of monolayered 2D transition metal carbide and nitrides (MXenes) in 2011, the number of different monolayer systems and the study thereof have been on the rise. Mo2Ti2C3 is one of the least studied MXenes and new insights to this material are of value to the field. Here, the stability of Mo2Ti2C3 under electron irradiation is investigated. A transmission electron microscope (TEM) is used to study the structural and elemental changes in situ. It is found that Mo2Ti2C3 is reasonably stable for the first 2 min of irradiation. However, structural changes occur thereafter, which trigger increasingly rapid and significant rearrangement. This results in the formation of pores and two new nanomaterials, namely, N-doped graphene membranes and Mo nanoribbons. The study provides insight into the stability of Mo2Ti2C3 monolayers against electron irradiation, which will allow for reliable future study of the material using TEM. Furthermore, these findings will facilitate further research in the rapidly growing field of electron beam driven chemistry and engineering of nanomaterials.Web of Scienceart. no. 190711

Facile production of ultra-fine silicon nanoparticles

A facile procedure for the synthesis of ultra-fine silicon nanoparticles without the need for a Schlenk vacuum line is presented. The process consists of the production of a (HSiO1.5)n sol–gel precursor based on the polycondensation of low-cost trichlorosilane (HSiCl3), followed by its annealing and etching. The obtained materials were thoroughly characterized after each preparation step by electron microscopy, Fourier transform and Raman spectroscopy, X-ray dispersion spectroscopy, diffraction methods and photoluminescence spectroscopy. The data confirm the formation of ultra-fine silicon nanoparticles with controllable average diameters between 1 and 5 nm depending on the etching time

Strain regulating and kinetics accelerating of micro-sized silicon anodes via dual-size hollow graphitic carbons conductive additives

Micro-sized silicon (mu Si) anode features fewer interfacial side reactions and lower costs compared to nanosized silicon, and has higher commercial value when applied as a lithium-ion battery (LIB) anode. However, the high localized stress generated during (de)lithiation causes electrode breakdown and performance deterioration of the mu Si anode. In this work, hollow graphitic carbons with tailored dual sizes are employed as conductive additives for the mu Si anode to overcome electrode failure. The dual-size hollow graphitic carbons (HGC) additives consist of particles with micrometer size similar to the mu Si particles; these additives are used for strain regulation. Additionally, nanometer-size particles similar to commercial carbon black Spheron (SP) are used mainly for kinetics acceleration. In addition to building an efficient conductive network, the dual-size hollow graphitic carbon conductive additive prevents the fracture of the electrode by reducing local stress and alleviating volume expansion. The mu Si anode with dual-size hollow graphitic carbons as conductive additives achieves an impressive capacity of 651.4 mAh g(-1) after 500 cycles at a high current density of 2 A g(-1). These findings suggest that dual-size hollow graphitic carbons are expected to be superior conductive additives for micro-sized alloy anodes similar to mu Si.Web of Scienc

Chemical vapor deposition of twisted bilayer and few-layer MoSe2 over SiOx substrates

The chemical vapor deposition of monolayer and few-layer transition metal dichalcogenides is a rapidly developing area of materials science due to the exciting electrical, optical, thermal and mechanical properties of transition metal dichalcogenides in their layered form. These properties make these innovative materials potentially relevant to wide-ranging commercial applications. One of these promising materials is MoSe2; however, just recently, a few research groups have been able to demonstrate its synthesis via chemical vapor deposition. Moreover, only oriented few-layer MoSe2 has been exhibited by synthetically formed material using chemical vapor deposition thus far. Here, we confirm twisted-layer MoSe2 can also form during chemical vapor deposition. Twisted-layer transition metal dichalcogenides alter their properties as compared to their oriented counterparts. Therefore, twisted-layer structures are of interest because they can tune their properties.1891sciescopu

Quasistatic equilibrium chemical vapor deposition of graphene

This study reviews the majorly used chemical vapor deposition (CVD) with a focus on confined reaction configurations in which quasistatic equilibrium conditions are obtained for the fabrication of graphene with large size and high quality through controlled nucleation density, feedstock flux, and growth rates. The confinement configurations can also be used to tune the thickness, domain size and shape, and stacking order of the synthetic graphene. The confined CVD reaction configurations discussed include enclosure systems, inner-tube setups, sandwiched substrates, as well as other types of configurations. The advantages and limitations of the different confinement configurations are presented, along ways to optimize the operational parameters for them.Web of Scienceart. no. 210150

A review of recent developments in Si/C composite materials for Li-ion batteries

Rechargeable lithium batteries play an increasingly significant role in our daily lives. Hence, the development of high capacity secondary lithium batteries has become a research hotspot. In the past decade, silicon has been extensively studied as anode material for Li-ion batteries because of its extremely high specific capacity. However, the dramatic volume change and troublesome SEI (solid electrolyte interface) issues during lithiation and delithiation hinder the commercialisation of Si anode materials. To circumvent these issues, carbon materials have been widely utilized in composites with Si materials due to their excellent electrochemical and physical properties. Established preparation methods of Si/C composite materials facilitate the design of novel Si/C composites. Different forms of carbon can improve the electrochemical performance of silicon materials in different ways. Advanced characterisation techniques further verify and explain the contribution of carbon materials to the performance improvement of Si. Si/C composite materials are anticipated to be the anode material for the next generation of commercial lithium batteries.Web of Science3475473

Adsorption-free growth of ultra-thin molybdenum membranes with a low-symmetry rectangular lattice structure

Although low-symmetry lattice structure of 2D transition metals is highly anticipated for both fundamental research and potentially distinctive application, it still has not been experimentally realized, which greatly hinders the exploration of the unique properties. Here, ultra-thin body-centered-cubic (bcc) phase molybdenum (Mo) membranes are successfully synthesized with a low-symmetry rectangular (110) crystal face via an adsorption-free reaction. Through experimental and density functional theory studies, no foreign atoms being adsorbed is shown to be a key factor for the successful preparation of the bcc phase 2D transition metal with (110) faces. The realization of 2D Mo(110) with a low-symmetric rectangular lattice structure extends the scope of 2D structures and is also beneficial for the exploration and development of low-symmetry rectangular lattice-structured materials with unique properties.Web of Scienceart. no. 200132