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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]

Based on the successful achievement of graphene-C60 single-molecule transistors in experiments, a series of double-layered GNR-C60, X/GNR-C60 (GNR = graphene nanoribbon; X = H, O, S, passivated edge atoms) devices were designed and their transport properties investigated by means of density functional theory (DFT) and nonequilibrium Green's function (NEGF) methods. The overall conductivity followed the sequence: H/GNR-C60 > S/GNR-C60 > O/GNR-C60, exactly opposite to the electronegativity order of O > S > H. All the X/GNR-C60 (X = H, O, S) devices presented a multiple negative differential resistance (NDR) feature within the considered bias range of 0.0–1.4 V. The magnitude, position, and number of NDR peaks were remarkably influenced by the passivated edges, electrode linkages, interactions between the upper and lower GNRs, and applied voltage. C60, as a medium, had a blocking action at low bias for all H/GNR-C60 devices, and the NDR character originated from the crossing of the frontier molecular orbitals (FMOs), while it behaved as a conductor at high bias, and the NDR behavior was still derived from the change in FMO distributions along the scatter region. C60 always acted as a blocking body in both O/GNR-C60 and S/GNR-C60 devices at any applied voltage, and their NDR peaks also stemmed from the crossing of the FMOs. In addition, which channel to be mainly used depended on the synergistic effect of the applied bias and connecting positions of the electrodes. All these fascinating properties suggest the materials potential applications in the field of nano-electronic devices. [ABSTRACT FROM AUTHOR]

We examine the transport properties of multi-channels of a porphyrin phenylacetylene (PPA) molecule by changing gate and source voltages at its two terminals. Density functional theory (DFT) within the non-equilibrium Green's function framework (NEGF) is employed to calculate the four probe PPA device by connecting with four Au electrodes using S linkages. Two gate voltages are chosen as 0.6 V (denoted as PPA-0.6) and 1.0 V (denoted as PPA-1.0), respectively. At each certain gate voltage, source voltages are applied in the range of 0.0 V to 1.0 V at a step of 0.2 V. It is found that the magnitude of the gate voltage plays a significant role in the whole transport property. No matter in PPA-0.6 or in PPA-1.0, evident NDR behavior is observed for lead currents. Moreover, a smaller gate voltage could induce a more prominent NDR effect. On the other hand, the relative magnitude of the gate voltage and the source voltage determines the current directions of the gate and source leads. Furthermore, input/output current switches can be achieved for the gate lead at the critical voltage of Vgate = Vsource. These interesting transport characteristics are further analyzed from the transmission spectra and the local density of states (LDOS). This presentation provides a clue for exploring novel functional nano-electronic molecular devices based on PPA by tuning gate voltages and source voltages as well as changing lead-to-lead channels. [ABSTRACT FROM AUTHOR]

The electronic structures and transport properties of the heterojunctions (X/BP) (X = BN, MoS2, or graphene) formed by vdW interactions of black phosphorus (BP) with insulative BN, semi-conductive MoS2, conductive graphene (G), and their corresponding intercalation composites X/Pt/BP and X/PtCl2/BP constructed by encapsulating Pt and PtCl2 into the heterojunction layers have been explored using density functional theory (DFT) and the nonequilibrium Green's function (NEGF). The linear photogalvanic effects of Pt and PtCl2 on the intercalation composites have been further studied by employing Keldysh nonequilibrium Green's function (KNEGF) methods. The BP and X layers are packed in a zigzag–zigzag (also an armchair–armchair) orientation. The band edges of BN/BP are mainly contributed by BP with a type-I alignment. The valence band of MoS2/BP is controlled by BP while the conduction band is dominated by MoS2, leading to a type-II alignment. Both BP and G contribute to the valence band and the conduction band; moreover, the Dirac-cone band ribbon of G and the direct band gap of BP are preserved in G/BP. For BN/BP-based systems, intercalating PtCl2 could largely improve the conductivity compared to inserting Pt. However, the case is exactly opposite in the G/BP-based species, where the conductivity of G/Pt/BP is much larger than those of G/PtCl2/BP and G/BP. While for MoS2/BP-based systems, Pt and PtCl2 exert similar effects on conductivity. Evident anisotropic transport property is found for BN/BP-based and G/BP-based systems, while no obvious anisotropic feature is observed for MoS2/BP-based systems. Under linear illumination, encapsulating PtCl2 shows a much stronger photoresponse than Pt. The strength of the photoresponse in PtCl2-doped systems can be tuned by the irradiation angle, the photon energy, and the type of X. All these fascinating properties can be interpreted from multiple factors such as band structures, Pt(PtCl2)–BP(X) interactions and BP–X interactions. These new 2D materials are especially attractive for electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

A series of 2D transition metal dichalcogenide (TMD) intercalation compounds, PdCl2/PtCl2@MX2 (M = Mo, W; X = S, Se), formed by covalently intercalating PdCl2/PtCl2 into the bilayer space of MX2, have been designed and investigated using density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. The intercalation compounds adopt a planar quadridentate coordination structure of PdCl2X2/PtCl2X2. The possibility of electron–hole recombination is enhanced because of the introduction of the PdCl2/PtCl2 groups, and on the other hand, the PdCl2/PtCl2-derived HOMO and LUMO are shielded well by the MX2 band gap, both of which are beneficial for improving the fluorescence quantum yield. The conductivity of the intercalation compounds is slightly lowered owing to the trap effect of PdCl2/PtCl2. In addition, electron transportation is easier along the zigzag direction than along the armchair direction. Contrary to the conductivity, a robust photogalvanic effect (PGE) can be observed when linearly polarized light is applied onto the PdCl2/PtCl2 groups, and the armchair direction exhibits a much higher photoresponse compared with the zigzag direction. The largest photocurrent could reach up to 1.83 × 10−2 a02 per photon. For a given MX2, the PdCl2 groups induce a higher maximum photocurrent than the PtCl2. Significantly, the photocurrent is highly dependent on the polarization angle ϑ and the applied photon energy, making the intercalation compounds appealing for designing photoresponse on/off switches by tuning ϑ or photon energy. Our simulation frameworks as well as the results offer guidelines for novel 2D functional device design and fabrication. [ABSTRACT FROM AUTHOR]

Covalent functionalization is an efficient approach to modulate the nanoelectronic properties, advance the charge separation efficiency, and thus optimize the optoelectronic applications of nanomaterials. Here, the electronic structures, transport properties, and linear photogalvanic effects of two dimensional (2D) monolayer black phosphorus (MLBP) functionalized by PtCl2 groups, (PtCl2)n-MLBP (n = 1, 2, and 4) have been theoretically investigated using density functional theory (DFT), nonequilibrium Green's function (NEGF), and the Keldysh nonequilibrium Green's functions (KNEGF) methods. In the functionalized systems, the valence band maximum comes from the PtCl2 groups while the conduction band minimum originates from the MLBP. Such spatial charge separation hinders electron–hole recombination, suggesting MLBP-based 2D materials as promising candidates for solar cells. The MLBP-based device exhibits opposite responses for the transport properties and linear photogalvanic effects. The transport properties of MLBP along both the armchair and zigzag directions decrease after being grafted with PtCl2 groups. Moreover, the larger the grafting density n, the lower the conductivity. In comparison, the linear photogalvanic effects augment after functionalization, and this phenomenon is more significant with large n. Further, the photoresponse in the zigzag direction is larger by an order of magnitude than that in the armchair direction. [ABSTRACT FROM AUTHOR]

Single-molecule junctions provide the additional flexibility of tuning the on/off conductance states through molecular design. Here, we focus on a family of organometallic complexes with a conjugated curved buckybowl as the ligand. Using first-principles calculations, a multi-mode reversible spin switching based on the CpFe·corannulene complex is predicted by the temperature control of the CpFe+ coordination position in corannulene. The different spin conductance states for three coordinated modes are ascribed to the different electronic spin states of the organometallic complex due to crystal field effects. The predicted relative stabilities of isomers and the energy barriers of isomerization reactions can ensure that the conversion among the three isomers can occur quickly and, at a specific temperature, a dominant isomer has a higher proportion than the other two isomers. This provides a new framework for understanding transport in organometallic complexes with localized d states. This presents an exciting opportunity for exploiting junctions involving molecular spin switching. [ABSTRACT FROM AUTHOR]

The structures, circular dichroism (CD) spectra and nonlinear optical (NLO) responses of a series of inorganic double-helix chains, PnLin (n = 6–12), have been investigated using the quantum chemistry method. P–P and P–Li interactions play a major role in stabilizing double-helix chains. The distinctive CD spectra of the double-helix frameworks (namely, a sharp negative CD band at short-wavelength region and a positive CD band at long-wavelength region) become obvious with increasing number of PLi units. The NLO response augments with the length of the double-helix chains, and the contribution of the axial component along the chain direction gradually becomes crucial simultaneously. Synergistic effects, a decrease of crucial electronic transition energies and charge transfer excitation give rise to enhanced NLO responses. In particular, the electronic transitions from the highest occupied molecular orbital to the lowest unoccupied molecular orbital make significant contributions not only to the positive CD bands in the long-wavelength region, but also to the NLO responses of the double-helix PnLin (n = 6–12) chains. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) hybrid nanobud-array structures, (C24)n/MoS2 and (C24V)n/MoS2, are designed by grafting (C24)n or (C24V)n fullerene arrays onto the surface of 2D monolayer MoS2 (ML-MoS2). Our density functional theory (DFT) computations show that the attachment of the (C24)n array onto the ML-MoS2 surface turns the 2D semiconductor (ML-MoS2) into a half metal, while the attachment of the (C24V)n array onto the ML-MoS2 surface turns the 2D semiconductor into a ferromagnetic (FM) metal. Our non-equilibrium Green's function (NEGF) computation indicates that the zigzag direction of the hybrid nanobud-array structures is more preferential for electron transport than the armchair direction. For the (C24)n/MoS2 system, the grafted (C24)n array not only can markedly increase the electron conductivity of ML-MoS2 but can also induce spin-polarized transport, that is, the spin-up state exhibits higher conductivity than the spin-down state. After placing a V atom between every two-neighboring C24 fullerenes along the zigzag direction, the conductivity is further enhanced. In contrast to (C24)n/MoS2, for (C24V)n/MoS2, the spin-down state exhibits higher conductivity than the spin-up state due to the strong contribution of the V 3d state to the spin-down state. The FM metal (C24V)n/MoS2 entails a magnetic moment of 2.3 μB per V atom. These results suggest that the 2D hybrid nanobud-array structures can be tailored as nanoelectronic parts with different electronic and transport properties by design. [ABSTRACT FROM AUTHOR]

The goal is to search for more efficient as well as more practical nonlinear optical (NLO) chromophores. Two series of three-dimensional NLO chromophores with five substituted branches and curved conjugated frameworks as the central coupling unit were investigated in the present work. Curvature of the central core plays an important role in determining the electronic structure and physical properties of multibranched conjugated π bowl derivatives. Compared to dipolar and octupolar NLO chromophores, multibranched conjugated π bowl derivatives have a different origin of the NLO response and exhibit considerable β values in both hyper-Rayleigh scattering and electric field-induced second harmonic generation processes due to effective dipolar and octupolar contributions. Additionally, multibranched conjugated π bowl derivatives can be easily assembled in a highly ordered manner due to their permanent dipole moments. A cooperative effect in the crystal will significantly enhance the macroscopic NLO response of the molecular crystal due to intermolecular dipole interactions among monomers. [ABSTRACT FROM AUTHOR]

The structure and electronic properties of puckered GeS nanotubes have been investigated using first-principles density functional theory calculation. Our results show that both the armchair and zigzag GeS nanotubes are semiconductor materials with an adjustable band gap. The band gap increases gradually with increasing the tube diameter, and slowly converges to the monolayer limit. On the application of strain, the GeS nanotubes provide interesting strain-induced band gap variation. When the compressive strain reached 20%, zigzag GeS nanotubes are completely transformed into armchair GeS nanotubes. In addition, the elastic properties of the relatively stable armchair GeS nanotubes have been studied, the Young's modulus of the armchair (11, 11), (13, 13) and (15, 15) nanotubes were calculated to be 227.488 GPa, 211.888 GPa and 213.920 GPa, respectively. Our work confirms that compared with carbon nanotubes, two-dimensional materials with a puckered structure are easier to realize phase transition by stress., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The electronic, transport, and optoelectronic properties of monolayer black phosphorus (MLBP) are much influenced by grafting PdCl 2 groups, demonstrated here by using density functional theory (DFT) and non-equilibrium Green's function (NEGF) as well as the Keldysh Nonequilibrium Green's Functions (KNEGF) methods. We find that the PdCl 2 groups prefer to locate over the furrow site of MLBP and form a planar quadridentate structure of . The PdCl 2 groups serve as quantum dots by introducing discrete flat levels between the MLBP valence band and the Fermi level ( E f ). The conductivity is much lowered after attaching PdCl 2 quantum dots, due to the fact that the scattering effect of PdCl 2 plays a major role in the process of electron transporting. A threshold voltage is found for the functionalized system with a large density of PdCl 2 quantum dots, a valuable clue for exploring current switches. However, no evident threshold voltage is found for the pure MLBP. Electrons permeate easier through the armchair direction compared with the zigzag either in the pure MLBP or in the functionalized composites. More importantly, grafting PdCl 2 quantum dots is very beneficial for enhancing photoresponse. The values of photoresponse for the modified species are about 20 times higher than the free MLBP. A significant photoresponse anisotropy is observed for both MLBP and n PdCl 2 -BP ( n = 1, 2, and 4), contrary to the conductivity, the zigzag direction shows much stronger photoresponse than the armchair. All of the aforementioned unique properties make these new two-dimensional (2D) MLBP based materials especially attractive for both electronic and optoelectronic devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The structures, circular dichroism (CD) spectra and nonlinear optical (NLO) responses of a series of inorganic double-helix chains, PnLin (n = 6-12), have been investigated using the quantum chemistry method. P-P and P-Li interactions play a major role in stabilizing double-helix chains. The distinctive CD spectra of the double-helix frameworks (namely, a sharp negative CD band at short-wavelength region and a positive CD band at long-wavelength region) become obvious with increasing number of PLi units. The NLO response augments with the length of the double-helix chains, and the contribution of the axial component along the chain direction gradually becomes crucial simultaneously. Synergistic effects, a decrease of crucial electronic transition energies and charge transfer excitation give rise to enhanced NLO responses. In particular, the electronic transitions from the highest occupied molecular orbital to the lowest unoccupied molecular orbital make significant contributions not only to the positive CD bands in the long-wavelength region, but also to the NLO responses of the double-helix PnLin (n = 6-12) chains.