Tunable Electronic and Magnetic Properties of Transition Metal-Cyclopentadiene Sandwich Molecule Wires Functionalized Narrow Single Wall Carbon Nanotubes

The structural, electronic, and magnetic properties of 1D organometallic molecule wires functionalized narrow single wall carbon nanotube, [TMCp]_∞/SWCNTs (TM = Sc, V, Mn, Fe, Co, SWCNTs, (<i>n</i>, <i>m</i>) = (7,7), (10,0), (11,0)), are first studied by density functional theory calculations. In the case of the 1D [TMCp]_∞ wires encapsulated in SWCNTs, the reaction between 1D [TMCp]_∞ and SWCNTs are endothermic or exothermic depending on the diameters of SWCNTs, while the dimension confinement effect disappears through placing the organometallic molecular wires outside the SWCNTs. Moreover, obvious ionic bonding nature is identified in the systems by putting the 1D [TMCp]_∞ wire in or outside of the SWCNTs. In contrast, stronger covalent bonding nature is found for the derivatives by desorption of one raw of hydrogen atoms in the cyclopentadiene ligands. In particular, diverse electronic and magnetic properties are introduced by the choice of SWCNTs and the functionalized 1D [TMCp]_∞ wires, which allows the 1D [TMCp]_∞/SWCNTs wires to function as a basic building block for potential application in electronic- and spintronic-based devices

Ab Initio Study of Structural, Electronic, and Magnetic Properties of Transition Metal Atoms Intercalated AA-Stacked Bilayer Graphene

The structural, electronic, and magnetic properties of transition metal atoms intercalated bilayer graphene, [GTMG]_{<i>x</i>/<i>y</i>}, (<i>x</i>, <i>y</i> is integer, TM = Ti, Cr, Mn, Fe) with different TM/carbon hexagons ratios and insertion patterns, are systematically studied by density functional theory calculations. All the studied systems are thermodynamically stable and competitive ionic–covalent bonding characters are dominated in the TM–graphene interaction. Most studied systems are ferromagnetic; particularly, [GCrG]_1:18, [GCrG]_1:9, [GFeG]_1:6(1), and [GTMG]_1:6(2) (TM = Cr, Mn, Fe) exhibit large magnetic moment of 4.43, 5.60, 7.02, 10.85, 9.04, and 5.19 μ_B per unit cell, respectively. In contrast, [GCrG]_1:8 and [GFeG]_1:8 are ferrimagnetic, while eight other [GTMG]_{<i>x</i>/<i>y</i>} are nonmagnetic. Moreover, five intercalation nanostructures of [GTMG]_1:18 (TM = Ti, Mn), [GTMG]_1:9 (TM = Ti, Mn) and [GTiG]_1:6 are semiconductors with the gaps of 0.141/0.824 eV, 0.413/0.668 eV, and 0.087 eV, respectively. Comparison on different isomers with same TM/carbon hexagons ratios showed that the electronic and magnetic properties of these [GTMG]_{<i>x</i>/<i>y</i>} are largely dependent on the TM atoms arrangement. For thus, an effective way to control the electronic and magnetic properties of graphene based nanostructures is proposed

Tunable Electronic and Magnetic Properties of Boron/Nitrogen-Doped BzTMCp*TMBz/CpTMCp*TMCp Clusters and One-Dimensional Infinite Molecular Wires

We systematically studied the structural, electronic, and magnetic properties of B/N-doped BzTMCp*TMBz/CpTMCp*TMCp (Bz = C₆H₆; Cp = C₅H₅; Cp* = C_5–<i>x</i>D_<i>x</i>H₅; D = B, N; <i>x</i> = 1, 2; TM = V, Cr, Mn, Fe) sandwich clusters and their infinite molecular wires using first-principle calculations. It is found that the B/N-doped ligands do not degrade the linear stacked sandwich configurations compared with the pristine hydrocarbon ligand complexes. Different from the N-doped complexes, the B-doped ligands lead to more charge transfers from metal atoms, and such behavior allows for the enhanced structure stabilities and adds the advantage of electronic and magnetic properties manipulation. Moreover, the B-doped ligand makes the one-dimensional sandwich molecular wires conserve half metallic properties of the pristine molecular wires, undergo half metal–semiconductor transition, and vice versa. Thus, a novel strategy for efficient tailoring of the electronic and magnetic properties of metal–ligand sandwich complexes is presented

Role of Hydrogen in Graphene Chemical Vapor Deposition Growth on a Copper Surface

Synthesizing bilayer graphene (BLG), which has a band gap, is an important step in graphene application in microelectronics. Experimentally, it was broadly observed that hydrogen plays a crucial role in graphene chemical vapor deposition (CVD) growth on a copper surface. Here, by using <i>ab initio</i> calculations, we have revealed a crucial role of hydrogen in graphene CVD growth, terminating the graphene edges. Our study demonstrates the following. (i) At a low hydrogen pressure, the graphene edges are not passivated by H and thus tend to tightly attach to the catalyst surface. As a consequence, the diffusion of active C species into the area beneath the graphene top layer (GTL) is prohibited, and therefore, single-layer graphene growth is favored. (ii) At a high hydrogen pressure, the graphene edges tend to be terminated by H, and therefore, its detachment from the catalyst surface favors the diffusion of active C species into the area beneath the GTL to form the adlayer graphene below the GTL; as a result, the growth of BLG or few-layer graphene (FLG) is preferred. This insightful understanding reveals a crucial role of H in graphene CVD growth and paves a way for the controllable synthesis of BLG or FLG. Besides, this study also provides a reasonable explanation for the hydrogen pressure-dependent graphene CVD growth behaviors on a Cu surface

Formation and Healing of Vacancies in Graphene Chemical Vapor Deposition (CVD) Growth

The formation and kinetics of single and double vacancies in graphene chemical vapor deposition (CVD) growth on Cu(111), Ni(111), and Co(0001) surfaces are investigated by the first-principles calculation. It is found that the vacancies in graphene on the metal surfaces are dramatically different from those in free-standing graphene. The interaction between the vacancies and the metal surface and the involvement of a metal atom in the vacancy structure greatly reduce their formation energies and significantly change their diffusion barriers. Furthermore, the kinetic process of forming vacancies and the potential route of their healing during graphene CVD growth on Cu(111) and Ni(111) surfaces are explored. The results indicate that Cu is a better catalyst than Ni for the synthesis of high-quality graphene because the defects in graphene on Cu are formed in a lower concentration and can be more efficiently healed at the typical experimental temperature. This study leads to a deep insight into the atomic process of graphene growth, and the mechanism revealed in this study can be used for the experimental design of high-quality graphene synthesis

Structures and Stabilities of Two-Dimensional Boron Sheets with Point Defects

Borophene with diverse geometries and rich electronic properties has attracted great research interest over the past few years due to its multicenter bonding characteristics derived from the electron deficiency of boron. However, the members of borophene as well as their stability mechanism have not been fully explored yet. In this work, we explored the stabilities of various free-standing (β12-, α1-, β1-, α-, α4-, and α5-phase) borophenes with single/double vacancies (SVs/DVs) and adatom defects using density functional theory methods. Our results show that the most stable configurations of the single-vacant borophene favor the one with the A site vacancy and form the elongated hexagon in defected β12 borophene and hexagonal vacancies in other phase borophenes, respectively. The structures of borophene with DVs favor the ones with two fused hexagonal rings. All of the vacant borophenes are found to be experimentally feasible with low formation energies (Ef_vs) for the lowest-energy SVs/DVs around −1.11 to 1.49 eV. Among them, the Ef_vs of three single-vacant (α-, α4-, and α5-) phase borophenes and two double-vacant (α4- and α5-) phase borophenes are negative, showing that they are more stable than their pristine ones. Besides, the β12-phase borophene is energetically favorable to adsorb the B adatom. Detailed analysis shows that the stability of the defective borophene is sensitive to the ratio of hexagons in the systems. Moreover, the ultrahigh stability of the vacant α-, α4-, and α5-phase borophene can also be derived from the minimization of the imbalance ratio of the σ/π orbital occupation. This study is significant for evaluation of stability in defected borophene and very useful to understand the influence of defects in two-dimensional boron

Vacancy Engineering for High-Efficiency Nanofluidic Osmotic Energy Generation

Two-dimensional (2D) nanofluidic membranes have shown great promise in harvesting osmotic energy from the salinity difference between seawater and fresh water. However, the output power densities are strongly hampered by insufficient membrane permselectivity. Herein, we demonstrate that vacancy engineering is an effective strategy to enhance the permselectivity of 2D nanofluidic membranes to achieve high-efficiency osmotic energy generation. Phosphorus vacancies were facilely created on NbOPO4 (NbP) nanosheets, which remarkably enlarged their negative surface charge. As verified by both experimental and theoretical investigations, the vacancy-introduced NbP (V-NbP) exhibited fast transmembrane ion migration and high ionic selectivity originating from the improved electrostatic affinity of cations. When applied in a natural river water|seawater osmotic power generator, the macroscopic-scale V-NbP membrane delivered a record-high power density of 10.7 W m–2, far exceeding the commercial benchmark of 5.0 W m–2. This work endows the remarkable potential of vacancy engineering for 2D materials in nanofluidic energy devices