Search

The electronic structures and transition properties of three types of triangle MoS 2 clusters, A (Mo edge passivated with two S atoms), B (Mo edge passivated with one S atom), and C (S edge) have been explored using quantum chemistry methods. The highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap of B and C is larger than that of A, due to the absence of the dangling of edge S atoms. The frontier orbitals (FMOs) of A can be divided into two categories, edge states from S 3 p at the edge and hybrid states of Mo 4 d and S 3 p covering the whole cluster. Due to edge/corner states appearing in the FMOs of triangle MoS 2 clusters, their absorption spectra show unique characteristics along with the edge structure and size.

Encouraged by the successful fabrication of C60‐GNR (GNR=graphene nanoribbon) single‐molecule transistors in experiments, four Fe‐containing derived double‐layered devices of Fe@C60‐GNR are designed by employing different electrode linkages and their transport properties are investigated by using density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods. Regardless of electrode connection, all these devices give rise to a smaller negative differential resistance (NDR) peak at V=0.2 and a higher peak at 1.2 V, suggesting their stable maneuverability as molecular devices and good candidates for developing on(off)‐off(on)‐on(off) current switches. The macroscopic NDR performance depends on the delocalization character and the crossing mechanism of the frontier orbitals. The peak‐to‐valley current ratios (Rmax) range from 454 to 2737, determined by the electrode linkage. Such a large Rmax‐value is necessary for developing dynamic random‐access memory (DRAM) cells. Encapsulating the Fe atom inside C60 not only improves the conductivity but also introduces the spin‐polarized transport property. The spin‐filtering efficiency (SFE) of almost all devices oscillates up and down in response to the bias voltage, indicating the possibility of designing on(off)‐off(on)‐on(off) spin switches and up‐down spin switches. All these fascinating properties provide an important clue for designing similar molecular devices with multiple functions by trapping magnetic transition metal atoms inside fullerenes. [ABSTRACT FROM AUTHOR]

Encouraged by the promising performance of C60-graphene single-molecule transistors observed in experiments, two types of Fen/C60-GNR (n = 2 and 4 and GNR = graphene nanoribbon) molecules with Fe atoms sandwiched between the upper and lower GNR layers were designed and their electronic and transport properties were investigated by employing density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods. Adding the Fe atoms induces high spin magnetism in the systems. Within the considered bias, almost all Fe2/C60-GNR devices generate double NDR peaks, and some of the Fen/C60-GNR devices (n = 2 and 4) possess a large peak-to-valley current ratio R = Ipeak/Ivalley (>400), implying potential applications in developing on–off–on/off–on–off current switches. The NDR character originates from the crossing of the frontier molecular orbitals. In addition, these systems show distinct spin-polarized transport characteristics, with up-spin channels displaying higher conductivity than down-spin pathways. The spin filter efficiency (SFE) oscillates up and down as bias is scanned for almost all devices, suggesting the possibility of designing on–off–on/off–on–off current switches as well as up–down spin switches. All these findings provide guidance for exploring single molecular devices with promising properties combined with graphene, fullerenes, and transition metals. [ABSTRACT FROM AUTHOR]

A series of four-terminal V7(Bz)8-WGNR devices were established with wrinkled graphene nanoribbon (WGNR) and vanadium-benzene nanowire (V7(Bz)8). The spin-polarized V7(Bz)8 as the gate channel was placed crossing the plane, the concave (endo-positioned) and the convex (endo-positioned) surface of WGNR with different curvatures via Van der Waals interaction. The density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods were adopted to calculate the transport properties of these devices at various bias voltages (VS) and gate voltages (VG), such as the conductance, spin-polarized currents, transmission spectra (TS), local density of states (LDOS), and scattering states. The results indicate that the position of V7(Bz)8 and the bending curvature of WGNR play important roles in tuning the transport properties of these four-terminal devices. A spin-polarized transport property is induced for these four-terminal devices by the spin-polarized nature of V7(Bz)8. Particularly, the down-spin channel disturbs strongly on the source-to-drain conductance of WGNR when V7(Bz)8 is endo-positioned crossing the WGNR. Our findings on the novel property of four-terminal V7(Bz)8-WGNR devices provide useful guidelines for achieving flexible graphene-based electronic nanodevices by attaching other similar multidecker metal-arene nanowires. [ABSTRACT FROM AUTHOR]

We have investigated the electronic and transport properties of a series of 2D Fc(X)n–MoS2 (Fc=Fe(Cp)2; X=SiH2, CH2, CH=CH, or C≡C; n = 1 or 2) systems by using ferrocene derivatives Fc(X)n to be grafted onto a MoS2 surface. Calculations have been carried out by density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods. All these Fc(X)n–MoS2 give type-II heterostructures, and the grafted Fc(X)n behaves as a quantum dot-like group. No matter which Fc(X)n group is introduced, the conductivity is improved. The current magnitudes at a certain bias voltage follow the sequence of Fc(C≡C)-MoS2 ≈ Fc(CH=CH)-MoS2 > Fc(SiH2)2-MoS2 ≈ Fc(SiH2)-MoS2 > Fc(CH2)2-MoS2 ≈ Fc(CH2)-MoS2, corresponding well to the abilities of supplying electrons from the (X)n group to MoS2. The armchair direction exhibits a larger current by about 4 times compared to the zigzag direction. A distinct NDR behavior is found for the Fc(C≡C)-MoS2, meaning that the transport channel can be electrically switched from the off state to the on state, and again turned to the off state. [ABSTRACT FROM AUTHOR]

The photogalvanic effect of monolayer SnS was investigated at a small bias voltage under perpendicular irradiation using density functional theory combined with the non-equilibrium Green's function method. The photocurrent was generated over the entire visible light range, and it was saturated at a small bias voltage for photon energies of 2.4, 2.6, 3.2 and 3.4 eV. The photocurrent shows cosine dependence of the polarization angle, which is attributed to the second-order response to the photoelectric field. These results provide a deeper understanding of the photogalvanic properties of the 2D SnS nanosheet based devices. [ABSTRACT FROM AUTHOR]

Theoretical studies are carried out on a "wheel-and-axle" architecture, (NDGY)k-Vm(Bz)n, by using density functional theory, nonequilibrium Green's function (NEGF), and Keldysh nonequilibrium Green's function (KNEGF) methods. Here, (NDGY)k and Vm(Bz)n denote the wheels formed by nitrogen-doped graphynes and the axle formed by a one-dimensional (1D) vanadium benzene nanowire, respectively. The electronic structure, transport property, and linear photoresponse of (NDGY)k-Vm(Bz)n are investigated. Within the range of 0.0 ~ 1.0 V except at 0.5 V and 0.6 V bias voltages, (NDGY)k-Vm(Bz)n shows a spin polarized transport character as the minority spin state serving as the primary transport path. The spin filter efficiency (SFE) of (NDGY)k-Vm(Bz)n can reach 100%, suggesting a good candidate for spin filter. Interestingly, a nonpolarized transport character is found at 0.5 V and 0.6 V bias voltages owing to the opening of the majority spin channel and leading to a negative differential resistance behavior entailing it for making electronic oscillators, electronic switches, and spin switches. When applied light irradiation, the minority spin state gives rise to stronger photoresponse than the majority spin state. Moreover, the magnitude of photoresponse can be tuned by the photon energy. All of these fascinating properties of (NDGY)k-Vm(Bz)n give a clue toward exploring new wheel-and-axle architectures with potential applications in electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

The electronic and transport properties of a series of covalently functionalized graphene sheets m (FeBz) n -G (m , n = 1, 2) are calculated by density functional theory (DFT) and the nonequilibrium Green's function (NEGF) methods. All the studied systems are chemically stable due to the d – π interaction between Fe and graphene. Addition of (FeBz) n (n = 1, 2) introduces a half-metallic behavior: the up-spin state degradates into a semiconductor channel while the down-spin state behaves as a metallic channel. Particularly, two-fold anisotropy magnetism could be obtained, with the ferromagnetic ordering extending either parallel to the graphene plane originated from the Fe- d up-spin state or perpendicular due to the d -electron coupling along the Fe-Bz-Fe-Bz chain in the down-spin state. Because of the trapping effect, attaching (FeBz) n decreases the conductivity. Anisotropy inherited from graphene after functionalized with (FeBz) n (n = 1, 2): zigzag direction has higher conductivity than armchair direction. The number and alignment style of (FeBz) n (n = 1, 2), and the spin-polarized character, all have impacts on the transport property. Our findings provide useful guidelines for achieving graphene-based electronic and spintronic nanodevices by attaching other similar long multi-decker metal-arene systems. [Display omitted] • Electronic and transport properties of functionalized graphene m (FeBz) n -G (m , n = 1, 2) are calculated theoretically. • Addition of (FeBz) n (n = 1, 2) introduces half-metallic behavior. • Ferromagnetic ordering extends not only parallel to the graphene plane but perpendicular to it. • Conductivity is determined by anisotropy inherited from graphene, number and alignment of (FeBz) n , and spin polarization. [ABSTRACT FROM AUTHOR]

Curved π bowl compounds represent another class of the completely conjugated materials with quantum dot nature. Non-equivalent hybridisation type from rim to hub carbon atoms in curved π bowl compound triggers anisotropic physical properties. With density functional method (CAM-B3LYP) and response theory calculations, curved π bowl compounds exhibit large radial and axial component ratio for its polarisability and the second hyperpolarisability. More importantly, they possess larger effective mass second hyperpolarisability (γmass) and nondiagonal components (γxxyy) compared to C60. Except the static properties, the dispersion characters of dynamic cubic response of curved π bowl compounds have been analysed in large frequency range. [ABSTRACT FROM AUTHOR]

We present a theoretical study on a novel one-dimensional nanomaterial (FeCpVCp) n @MoS 2 NT which are constructed with encapsulating organometallic sandwich molecular wires (FeCpVCp) n into armchair (8, 8) MoS 2 NT, using density functional theory (DFT) and nonequilibrium Green's function (NEGF) techniques. It is found that ferromagnetic (FeCpVCp) n @MoS 2 NT is thermally stable with a high Curie or Neél temperature of 722.8 K. Transport property of (FeCpVCp) n @MoS 2 NT is in good agreement with the electronic structure. (FeCpVCp) n offers a notable transport pathway along the axial direction, electron hopping may happen from (FeCpVCp) n to MoS 2 NT sheath, which plays a significant role in electron transporting. Conductivity of (FeCpVCp) n @MoS 2 NT is dependent on the spin states: spin-down state gives a higher conductivity than the spin-up state, opening out a spin-polarized transport property. These novel properties of (FeCpVCp) n @MoS 2 NT render their potential applications in nanoscale spintronic and molecular electronics. [ABSTRACT FROM AUTHOR]