Yue-Wen Mu

Observation of an all-boron fullerene

After the discovery of fullerene-C60, it took almost two decades for the possibility of boron-based fullerene structures to be considered. So far, there has been no experimental evidence for these nanostructures, in spite of the progress made in theoretical investigations of their structure and bonding. Here we report the observation, by photoelectron spectroscopy, of an all-boron fullerene-like cage cluster at B40(-) with an extremely low electron-binding energy. Theoretical calculations show that this arises from a cage structure with a large energy gap, but that a quasi-planar isomer of B40(-) with two adjacent hexagonal holes is slightly more stable than the fullerene structure. In contrast, for neutral B40 the fullerene-like cage is calculated to be the most stable structure. The surface of the all-boron fullerene, bonded uniformly via delocalized σ and π bonds, is not perfectly smooth and exhibits unusual heptagonal faces, in contrast to C60 fullerene.

Cage-Like B41+ and B422+: New Chiral Members of the Borospherene Family†

The newly discovered borospherenes B40 (-/0) and B39 (-) mark the onset of a new class of boron nanostructures. Based on extensive first-principles calculations, we introduce herein two new chiral members to the borospherene family: the cage-like C1 B41 (+) (1) and C2 B42 (2+) (2), both of which are the global minima of the systems with degenerate enantiomers. These chiral borospherene cations are composed of twelve interwoven boron double chains with six hexagonal and heptagonal faces and may be viewed as the cuborenes analogous to cubane (C8 H8 ). Chemical bonding analyses show that there exists a three-center two-electron σ bond on each B3 triangle and twelve multicenter two-electron π bonds over the σ skeleton. Molecular dynamics simulations indicate that C1 B41 (+) (1) fluctuates above 300 K, whereas C2 B42 (2+) (2) remains dynamically stable. The infrared and Raman spectra of these borospherene cations are predicted to facilitate their experimental characterizations.

Binary nature of monolayer boron sheets from ab initio global searches

Boron could be the next element after carbon to form two-dimensional monolayer structures. Using the ab initio global searches, we found all low-lying monolayer boron sheets with 1-4 hexagonal holes in each unit cell. The two most stable boron sheets are composed of two kinds of elementary units with isolated-hexagon and twin-hexagon holes, respectively, so that the boron sheets are binary structures in nature. Detailed structural analyses indicate that there exist two types of close-lying stable monolayer boron sheets, revealing the polymorphism of boron sheet. These binary monolayer boron sheets are expected to serve as precursors to build various boron nanotubes, boron fullerenes, and other boron-based low-dimensional nanomaterials.

Structures and magnetic properties of SinMn(n=1–15) clusters

The structure, electronic, magnetic properties of Si(n)Mn clusters up to n=15 are systematically investigated using the density functional theory within the generalized gradient approximation. In the most stable configurations of Si(n)Mn clusters, the equilibrium site of Mn atom gradually moves from convex, to a surface, and to a concave site as the number of Si atoms varying from 1 to 15. Starting from n=11, the Mn atom completely falls into the center of the Si outer frame, forming Mn-encapsulated Si cages. Maximum peaks of second-order energy difference are found at n=6, 8, 10, and 12, indicating that these clusters possess relatively higher stability. The electronic structures and magnetic properties of Si(n)Mn clusters are discussed. The magnetic moment of Si(n)Mn clusters mainly is located on Mn atom. The 3d electrons in Mn atom play a dominant role in the determination of the magnetism of Mn atom in Si(n)Mn clusters. Furthermore, the moment of Mn atom in Si(n)Mn clusters exhibits oscillatory behavior and are quenched at n>7 except for n=12, mainly due to the charge transfer, strong hybridization between Mn 4s, 3d, 4p and Si 3s, 3p states.

Two-dimensional gradient Ag nanoparticle assemblies: multiscale fabrication and SERS applications.

We report a novel method for fabricating silver nanoparticle assemblies with a featured gradient of spatial organizations. The unique step is to generate a gradient of deposit mass by dynamical deposition on a mask-covered substrate with a collimated cluster beam in oblique incidence. Then such gradient can be translated to the gradients of sizes or number densities of the nanoparticles separately, depending on the nature of the substrate surface. Multiscale gradients are implemented from mesoscopic to macroscopic. One-chip rapid detection of the optimal structure for surface enhanced Raman scattering (SERS) is achieved on the gradient assembly with particle number densities.

Lithium-Decorated Borospherene B40: A Promising Hydrogen Storage Medium

The recent discovery of borospherene B40 marks the onset of a new kind of boron-based nanostructures akin to the C60 buckyball, offering opportunities to explore materials applications of nanoboron. Here we report on the feasibility of Li-decorated B40 for hydrogen storage using the DFT calculations. The B40 cluster has an overall shape of cube-like cage with six hexagonal and heptagonal holes and eight close-packing B6 triangles. Our computational data show that Lim&B40(1–3) complexes bound up to three H2 molecules per Li site with an adsorption energy (AE) of 0.11–0.25 eV/H2, ideal for reversible hydrogen storage and release. The bonding features charge transfer from Li to B40. The first 18 H2 in Li6&B40(3) possess an AE of 0.11–0.18 eV, corresponding to a gravimetric density of 7.1 wt%. The eight triangular B6 corners are shown as well to be good sites for Li-decoration and H2 adsorption. In a desirable case of Li14&B40-42 H2(8), a total of 42 H2 molecules are adsorbed with an AE of 0.32 eV/H2 for the first 14 H2 and 0.12 eV/H2 for the third 14 H2. A maximum gravimetric density of 13.8 wt% is achieved in 8. The Li-B40-nH2 system differs markedly from the previous Li-C60-nH2 and Ti-B40-nH2 complexes.

“W-X-M” transformations in isomerization of B39− borospherenes

The Stone-Wales transformation plays an important role in the isomerization of fullerenes and graphenic systems. The continuous conversions between neighboring six- and seven-membered rings in the borospherene (all-boron fullerene) B40 had been discovered (Martinez-Guajardo et al. Sci. Rep. 5, 11287 (2015)). In the first axially chiral borospherenes C3 B39− and C2 B39−, we identify three active boron atoms which are located at the center of three alternative sites involving five boron atoms denoted as “W”, “X”, and “M”, respectively. The concerted movements of these active boron atoms and their close neighbors between neighboring six- and seven-membered rings define the “W-X-M” transformation of borospherenes. Extensive first-principles molecular dynamics simulations and quadratic synchronous transit transition-state searches indicate that, via three transition states (TS1, TS2, and TS3) and two intermediate species (M1 and M2), the three-step “W-X-M” transformations convert the C3 B39− global minimum int...

Strain-induced Metal-Semimetal Transition of BeB2 Monolayer

The Dirac point and cones make some two-dimensional materials (e.g., graphene, silicone and graphyne) exhibit ballistic charge transport and enormously high carrier mobilities. Here, we present a novel semimetal with triangular lattice. Metallic BeB2 monolayer could transform to a semimetal with a Dirac point at the Fermi level when the lattice parameters are isotropically compressed by about 5%, while it becomes metallic again under larger compression. The Fermi velocity of semimetallic BeB2 monolayer is 0.857 × 106 m s−1, just a little smaller than that of graphene. Furthermore, it is found that uniaxial compressive strain opens a band gap in the BeB2 monolayer, while uniaxial tensile strain keeps it metallic. Our study expands the Dirac systems and provides new insight to explore novel semimetallic materials.

Zigzag double-chain C–Be nanoribbon featuring planar pentacoordinate carbons and ribbon aromaticity

Low-dimensional materials (LDMs) involving planar hypercoordinate carbon bonding were predicted to have applications in electronic devices, energy materials, and optical materials, etc. The majority of carbon atoms in such LDMs adopt a tetracoordinate structure, while examples with a higher coordination number are extremely rare and the bonding geometries of those carbons are not perfectly planar. In this work, we designed ribbon-like clusters CnBe3n+2H2n+22+ with planar pentacoordinate carbons (ppCs) and extended the corresponding structural model under 1D periodic boundary conditions (PBCs), leading to a zigzag double-chain C–Be nanoribbon. The beryllium atoms in such a nanoribbon arrange in a cosine shape around the perfect ppCs, which are unprecedented in LDMs. Detailed analyses revealed that the perfect ppC structure in the nanoribbon was geometrically achieved by opening a Be–Be edge of small Be5 rings, thereby making the intra-ring space adjustable to fit the size of the carbons. Electronically, the structure is stabilized by a favourable sandwich type charge distribution and satisfaction of the octet rule for ppCs. Note that all the valence electrons in the nanoribbon are locally delocalized within each ppC moiety, representing a new type of ribbon aromaticity, which should be useful in nanoelectronics. The nanoribbon and its cluster precursor C2Be8H62+ are thermodynamically stable, and are promising targets for experimental realization. The nanoribbon was predicted to be an indirect band gap semiconductor; thus it has potential applications in designing light-weight electronic devices.

From Quasi-Planar B56 to Penta-Ring Tubular Ca©B56: Prediction of Metal-Stabilized Ca©B56 as the Embryo of Metal-Doped Boron α-Nanotubes.

Motifs of planar metalloborophenes, cage-like metalloborospherenes, and metal-centered double-ring tubular boron species have been reported. Based on extensive first-principles theory calculations, we present herein the possibility of doping the quasi-planar C2v B56 (A-1) with an alkaline-earth metal to produce the penta-ring tubular Ca©B56 (B-1) which is the most stable isomer of the system obtained and can be viewed as the embryo of metal-doped (4,0) boron α-nanotube Ca©BNT(4,0) (C-1). Ca©BNT(4,0) (C-1) can be constructed by rolling up the most stable boron α-sheet and is predicted to be metallic in nature. Detailed bonding analyses show that the highly stable planar C2v B56 (A-1) is the boron analog of circumbiphenyl (C38H16) in π-bonding, while the 3D aromatic C4v Ca©B56 (B-1) possesses a perfect delocalized π system over the σ-skeleton on the tube surface. The IR and Raman spectra of C4v Ca©B56 (B-1) and photoelectron spectrum of its monoanion C4v Ca©B56− are computationally simulated to facilitate their spectroscopic characterizations.