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The transport properties of a series of double-layered GNR-C60 devices are investigated, revealing deep insights into experimental discoveries, and provides theoretical guidance for optimizing the transport properties of GNR-C60 devices.

The recently synthesized triangulenes with non-bonding edge states could have broad potential applications in magnetics, spintronics and electro-optics if they have appropriate electronic structure modulation. In the present work, strategies based on molecular orbital theory through heteroatom doping are proposed to redistribute, reduce or eliminate the spin of triangulenes for novel functional materials design, and the role of B, N, NBN, and BNB in such intended electronic structure manipulation is scrutinized. π-Extended triangulenes with tunable electronic properties could be potential nonlinear optical (NLO) materials with appropriate inhibition of their polyradical nature. The elimination of spin is achieved by B, N, NBN, and BNB doping with the intended geometric arrangement for enhanced polarity. Intended doping of BNB results in an optimal structure with large static first hyperpolarizability (〈

Novel carbon based “X-type” graphene nanoribbons (GNRs) with azulenes were designed for applications in nonlinear optics in the present work, and the second order nonlinear optical (NLO) properties of those X-type GNRs were predicted using the sum-over-states (SOS) model. The GNRs with edge states are feasibly polarized. The effects of zigzag edges on the NLO properties of GNRs are scrutinized by passivation, and the electronic structures of GNRs are modulated with heteroatoms at the zigzag edges for improved stability and NLO properties. Those nanomaterials were further functionalized with electron-donating and electron-withdrawing groups (NH2/NO2) to enhance the NLO responses, and the connection of those functional groups at the azulene ends play a determinant role in the enhancement of the NLO properties of those X-type nanoribbons, e.g., the static first hyperpolarizability (〈β0〉) changes from −783.23 × 10−30 esu to −1421.98 × 10−30 esu. The mechanism of such an enhancement has been investigated. Through two-dimensional second order NLO spectra simulations, particularly besides the strong electro-optical Pockels effect and optical rectification responses, strong electronic sum frequency generations and difference frequency generations are observed in those GNRs. The strong second order NLO responses of those GNRs in the visible light region bring about potential applications of these carbon nanomaterials in nonlinear nanophotonic devices and biological nonlinear optics.

The high stability, feasible modification, and good π-conjugation of porphyrin derivatives render these porphyrin-based nanomaterials suitable as potential third order nonlinear optical (NLO) materials. Introducing an azulene in pristine porphyrins can significantly improve the second order NLO properties of the system, and this is studied in the present work using density functional theory based methods and the sum-over-states model. The relative orientation of azulene plays a determinant role in the enhancement of the static first hyperpolarizability (〈

The current study has obtained excellent potential nonlinear optical(NLO) materials by combining density functional theory methods with sum-over-states model to predict the second order NLO properties of helical graphene nanoribbons(HGNs) through introducing azulene defects or/and BN units. The introduction of these functional groups deforms the pristine HGN (compression or tension) and enhances obviously the static first hyperpolarizability(〈β0〉) of system by up to two orders of magnitude. The tensor components along the helical axis of HGNs play a dominant role in the total 〈β0〉. The azulene defects and the BN units polarize the pristine HGN to different degrees, and the azulenes and contiguous benzenes are involved in the major electron excitations with significant contributions to 〈β0〉 but the BN units are not. The BN-doped chiral HGNs have good kinetic stability and strong second order NLO properties(6.84 × 105 × 10−30 esu), and can be a potential candidate of high-performance second order NLO materials. The predicted two-dimensional second order NLO spectra provide useful information for further exploration of those helicenes for electro-optic applications.

Optical nonlinearity of two-dimensional (2D) materials with a permanent dipole is a subject of intense research in the fields ranging from all-optical signal processing to laser nanotechnology due to the potential outstanding performance of 2D materials in nonlinear optical processes, and the feasibility for extensive integration into optoelectronic devices. In the present work, the group-VA binary monolayers are predicted to have giant and broadband second harmonic generation (SHG) properties superior to some of the most popular NLO materials by first-principles calculations. The SHG susceptibility of the α-PAs reaches up to 8.0 × 106 pm2 V−1, which is nearly 1–2 orders of magnitude higher than that of honeycomb monolayer MoS2 and h-BN, and twice larger than the record-high SHG susceptibility of a 2D ferroelectric GeSe monolayer. This intriguing peak is formed by intraband two photon transition ascribed to the relatively small bandgap and large transition matrix elements between valence and conduction band edges. A high-performance nonlinear optical device can be developed using those 2D group-VA monolayer materials with puckled structure and in-plane polarizabilities for multifunctional and integrated optoelectronic applications.

For materials lacking inversion symmetries, an interband transition induced by a photon may result in excited electrons (holes) experiencing a spatial shift leading to generation of directional photocurrents. This phenomenon known as bulk photovoltaic effect (BPVE) shift photocurrent (SPC) has recently attracted immense attention owing to its potential in generating photovoltages that are not restricted by Shockley-Queisser limitations imposed by materials' electronic band gaps. The BPVE was recently reformulated in a quantum mechanics viewpoint as the change in the geometrical phase upon photoexcitation and can now be promptly calculated from Bloch wave functions generated by first-principles calculations. The SPC of an electron (hole) is robust against crystal defects and impurities both in the interior and the surface and can be less dissipative and ultrafast. Herein, an emergence of colossal SPC in a pristine two-dimensional (2D) single-layer α-SbP crystal is predicted from first-principles calculations. An external electric field is further applied on the 2D crystal, and a large SPC enhancement is achieved. The locations of the SPC peaks due to both in-plane and out-of-plane responses suggest that α-SbP can generate a large photocurrent both in visible-light and ultraviolet regions. Single-layer 2D α-SbP is thus an excellent material for strong SPC. This finding is thus expected to open a pathway to exploring efficient photovoltaic devices based on monolayer α-SbP and similar materials.

Two-dimensional (2D) V–V binary materials are gaining extensive attention because of high carrier mobility, largely tunable optical exciton properties, and high sensitivity to optical excitation. H...

The third order static and dynamic nonlinear optical (NLO) responses of Ih symmetry fullerenes (C60, C240, and C540) and fullerene onions (C60@C240 and C60@C240@C540) are predicted using the ZINDO method and the sum-over-states model. The static second hyperpolarizability of Ih symmetry fullerenes increases exponentially with fullerene size [from 10.00 × 10−34 esu in C60 to 3266.74 × 10−34 esu ≈ γ0(C60) × 92.63 in C540]. The external fields of strong third order NLO responses of Ih symmetry fullerenes change from ultra-violet (C60) to the visible region (C540) as the fullerene size increases. The outer layer fullerene in the fullerene onions has dominant contributions to the third order NLO properties of the fullerene onions, and the inter-shell charge-transfer excitations have conspicuous contributions to the third order NLO properties. The two-dimensional two-photon absorption spectra of C60 and C240 show that those fullerenes have strong two-photon absorptions in the visible region with short wavelength and in the ultra-violet region.

Inducing new nonlinear optical (NLO) properties while maintaining the thermal stability of carbon based nanomaterials broadens the application of carbon nanomaterials in opto-electronics. In the present work, polar azulene defects are introduced in Y-type carbon based molecules to induce polarity thus enhancing the second order NLO properties (for example, the static first hyperpolarizability of Y-type carbon based molecules with azulene defects reaches 4.18 × 10−30 esu per heavy atom while that of p-nitroaniline is 2.97 × 10−30 esu per heavy atom). The addition of an electron acceptor at the heptagon end modifies the π electron distribution of Y-type carbon based molecules and significantly enhances the static first hyperpolarizability from 1.73 × 10−30 esu per heavy atom to 8.87 × 10−30 esu per heavy atom, much larger than that of similarly synthesized NLO compounds. The cause of such enhancement by introduction of electron acceptors has been scrutinized.

Defect-engineering of few-layer graphene, by modulating local electronic structure and forming highly-active reaction sites, benefits the charge storage and electrochemical reactions. To control defect morphology of graphene, herein, we devise a CH4- chemical vapor deposition (CVD) approach to directly synthesize graphene film with extremely high defect density of 5.9 × 1011 cm−2 and relatively high crystallinity at a low temperature of 700 °C. The C atoms involved in Cu bulk are induced to segregate onto the Cu surface to establish synergetic C–Cu complex catalyst. Theoretical evidence verifies that the interaction between the Cu and C atoms in form of C cluster atop the Cu plane lowers energy barriers for stepwise decomposition of CH4. The 13CH4 isotope data demonstrate that the C clusters are integrated sequentially into the graphene lattice, unraveling the dual roles of carbon impurities. The defective graphene film exhibits a specific capacitance of 10.6 μF/cm2 and excellent electro-catalytic performance. Such a self-induced synergetic catalyst can innovate the methodology of catalysis engineering for controllable synthesis of graphene and other 2D materials.

This work presents a theoretical investigation on the electronic properties of double atomic carbon chains bridging graphene electrodes with density functional theory in combination with non-equilibrium Green's function. The influence of strain on the conductance of atomic carbon chains is significant. However, the coupling effect between adjacent chains dominates the intrinsic transport of double atomic carbon chains. For the coupled double atomic chains, the electron conductance of even-numbered atomic chains is significantly enhanced, while the electron conductance of odd-numbered atomic chains decreases to a certain degree, and the dependence of the conductance of double atomic chains on electrode configuration is stronger than the corresponding single atomic chain. More intriguingly, the coupled double atomic chains exhibit excellent spin-filtering properties with antiparallel spins on two electrodes. The current spin polarization stems from the coupling-induced changes of electron density and band offset reaches 100%. The coupled double atomic carbon chains have great potential application in spintronic devices and carbon-based field-effect transistors.

In this work, a systematical investigation on the transformation of tetrachloro-p-benzoquinone (TCBQ) under UV irradiation (at 253.7 nm) in aqueous solution has been conducted through quantum chemical calculations. The UV irradiation at 253.7 nm could induce the excitation of TCBQ to its first excited singlet state, followed by the intersystem crossing to its first triplet state. In aqueous solution, the first triplet state of TCBQ was thermodynamically and kinetically feasible to react with H2O via 1,4-addition, where the addition of OH− to the α–β conjugated system was the dominant step. Interestingly, with the addition of hydroxyl to TCBQ, the dechlorination of TCBQ occurred with the formation of the monohydroxylated product of TCBQ (OH-TriCBQ). The UV photolysis pathway of OH-TriCBQ was similar to that of TCBQ, and the 1,4-addition of OH− to the ortho-position of the hydroxyl was the most efficient pathway. The dechlorination by 1,4-addition of OH− was also observed for OH-TriCBQ. With much larger forward energy barriers, the nucleophilic addition of carbonyl by OH− (i.e., 1,2-addition) might be less important for the UV photolysis of TCBQ and OH-TriCBQ. The findings in the present study may help to understand the transformation of TCBQ in aqueous solution.

High efficient catalysts for hydrogen evolution reaction are crucial for hydrogen production. As potential catalysts for hydrogen evolution reaction, NimMon (m + n = 5) clusters have been studied i...

Inducing new nonlinear optical (NLO) properties while keeping the thermal stability of carbon-based nanomaterials paves a new path for the application of carbon nanomaterials in optoelectronics. In...

Structural analogue between pure carbonic nanostructures and their boron nitride counterparts provides possibilities for the fabrication of BCN hetero-nanomaterials, which have attracted widespread interest and been synthesized with stacked-layer, monolayer and tubular morphologies. In this work, the arrangement-dominated chiral interface states and conductivities of BCN heteronanotubes are investigated in detail by first principles calculations. The π-conjugated states can be driven by the high potential barrier of insulating BN domains to form chiral transport states along the interfaces. The emerging antiparallel and parallel chiral interface states play a dominant role for resonant transport and provide possibilities for the formation of chiral currents. Moreover, the unidirectional chiral currents have advantages to induce a magnetic field which can reach over 0.1 T. In contrast to the parallel-arranged chiral heteronanotubes, the antiparallel-arranged chiral heteronanotubes with the same stoichiometry have narrower band-gaps and stronger chiral conductivities. Such arrangement-dominated chiral transport interface states endow CHNTs with potential application in magneto-electronics.

The hydrogen adsorption capacity of dual-Ti-doped (7, 7) single-walled carbon nanotube (Ti-SWCNTs) has been studied by the first principles calculations. Ti atoms show different characters at different locations due to local doping environment and patterns. The dual-Ti-doped SWCNTs can stably adsorb up to six H2 molecules through Kubas interaction at the Ti2 active center. The intrinsic curvature and the different doping pattern of Ti-SWCNTs induce charge discrepancy between these two Ti atoms, and result in different hydrogen adsorption capacity. Particularly, eight H2 molecules can be adsorbed on both sides of the dual-Ti decorated SWCNT with ideal adsorption energy of 0.198 eV/H2, and the physisorption H2 on the inside Ti atom has desirable adsorption energy of 0.107 eV/H2, ideal for efficient reversible storage of hydrogen. The synergistic effect of Ti atoms with different doping patterns enhances the hydrogen adsorption capacity 4.5H2s/Ti of the Ti-doped SWCNT (VIII), and this awaits experimental trial.

The third order static and dynamic nonlinear optical (NLO) responses of Ih symmetry fullerenes (C60, C240, and C540) and fullerene onions (C60@C240 and C60@C240@C540) are predicted using the ZINDO method and the sum-over-states model. The static second hyperpolarizability of Ih symmetry fullerenes increases exponentially with fullerene size [from 10.00 × 10-34 esu in C60 to 3266.74 × 10-34 esu ≈ γ0(C60) × 92.63 in C540]. The external fields of strong third order NLO responses of Ih symmetry fullerenes change from ultra-violet (C60) to the visible region (C540) as the fullerene size increases. The outer layer fullerene in the fullerene onions has dominant contributions to the third order NLO properties of the fullerene onions, and the inter-shell charge-transfer excitations have conspicuous contributions to the third order NLO properties. The two-dimensional two-photon absorption spectra of C60 and C240 show that those fullerenes have strong two-photon absorptions in the visible region with short wavelength and in the ultra-violet region.

Recent successful syntheses of azulene-defect graphene nanosheets (GNSs) pave a path for the applications of those GNSs in nonlinear optics , since azulene-defect GNSs maintains the thermal stability of carbon-based nanomaterials and possesses potential large nonlinear optical (NLO) responses. In the present work, azulene-defect GNSs with different relative position and orientation are designed for applications in optoelectronics and nonlinear optics. The all-carbon azulene-defect GNS Paral-2 with parallel orientated azulenes has good electronic kinetic stability as well as a large static first hyperpolarizability ( 0>) of 1032.28 × 10−30 esu (18.43 × 10−30 esu per heavy atom). The Paral-0-4N, formed by replacing four edge C atoms with N atoms in the GNS Paral-0, has the largest (1247.68 × 10−30 esu, 22.28 × 10−30 esu per heavy atom) due to the charge transfer based electron excitations and the polar structure while with enhanced electronic kinetic stability. The two-dimensional second order NLO spectra of those azulene-defect GNSs provide vital information for further experimental exploration and applications. The introduction of polar azulene in GNSs to improve the NLO responses and doping of nitrogen atoms to enhance the electronic kinetic stability of GNSs provide a practical strategy and useful information for future NLO materials design.

Metallo-β-lactamase (MβL) is a eubacterial zinc metallo-hydrolase superfamily. Despite their well-known lactamase activities, MβL family members also have the ability to catalyze phosphotriester hydrolysis with different phosphotriesterase activities. In the present study, based on crystal structure comparisons of the related MβL members, a series of models was constructed and calculated using the density functional theory (DFT) method to explore the relationship between active-site changes and phosphotriesterase activities. These calculations show that the energetic barriers for phosphotriesterase activity are considerably reduced due to active-site differences, which describes an evolutionary trend for the development of phosphotriesterase activity in the MβL superfamily. The key event is the appearance of a specialized and negatively charged residue bridging both zinc ions, which plays the two important roles of maintaining charge balance and stabilizing the binuclear active-site structure. This pathway is also consistent with the evolutionary relationships determined by phylogenetic tree analysis using complete residue sequences. Our studies provide the first methodology to explore the development of a new enzyme activity within a superfamily, and to shed new light on understanding the catalytic mechanism from an evolutionary perspective.

In this work, the effect of alcohols as hydrogen donors on hydrated electron (e aq − ) generation from p -benzoquinone ( p -BQ) photolysis was investigated by quantum chemical calculations and experiments to further understand the underlying mechanisms associated within the p -BQ/UV process. Theoretically, the UV photolysis of p -BQ at 253.7 nm in the presence of H 2 O could induce the formation of p -HOC 6 H 4 OH and hydroxy- p -benzoquinone, which was almost independent of the addition of CH 3 OH. While, the first triplet state of hydroxy- p -benzoquinone preferred to react with CH 3 OH (rather than H 2 O) to release the corresponding semiquinone radical and hydroxymethyl radical ( CH 2 OH). These two radicals could induce the reduction of p -BQ to p -benzosemiquinone radical and thus enhanced the formation of p -HOC 6 H 4 OH as the precursor of e aq − . Experimentally, the detection of e aq − generated in the process was accomplished by the degradation of monochloroacetic acid (MCAA) (the probe of e aq − ). With the addition of CH 3 OH, the degradation of MCAA was accelerated in the p -BQ/UV process. A similar acceleration was also observed by the addition of ethanol or 2-propanol with the α-H. However, tert -butanol, which is without the α-H in the structure, didn’t induce the acceleration. Since the quinone-like and alcoholic groups are widely distributed in the environment, these findings may improve the understanding of the photochemistry of quinones in the presence of alcohols with the α-H.

Phase-change memory (PCM) material is the promising material system for nonvolatile-memory technology. Performance optimization of PCM device urgently requires the deeper clarification of its material “Gene”. In this study, through first-principles calculations, p-orbital-aligned atom chains are identified to play important roles in governing optoelectronic reflectivity in amorphous Ge2Sb2Te5. These atom chains make the electronic state of the amorphous Ge2Sb2Te5 hold strong electron-polarized components, thereby governing the optical property. The present study offers a new understanding of “Gene” for PCM materials which benefit the material design and the performance improvement of PCM devices.

Ge–Sb–Te superlattice (GST-SL) is a newly emerging electronic material for nonvolatile phase-change memory with ultralow energy cost. However, its switching mechanism is still unclear with intensive debates. In this work, by first-principles calculations and an electron counting model study, we study the possible mechanism of phase change and the accompanying property transition of GST-SL. GST-SL are separated into individual layers by van der Waals gaps. We demonstrate that both the global chemical stoichiometry of the material and the local chemical stoichiometry of individual layer block are required to have an insulating band gap according to an electron counting model analysis. The electrical property can be adjusted by changing the local stoichiometry, such as producing defects around van der Waals gaps. Inspired by a previous experiment, we propose that a stacking-fault motion can spontaneously alter the band gap and results in a metal–insulator transition. This transition may provide a significant change of carrier concentration and indicate an ultralow energy-consumption process with a low energy barrier. The present investigations reveal a picture of electrical transition in GST-SL and may guide us to improve its device performances.

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.

Two-dimensional (2D) semiconductors have attracted considerable attentions from electronic-engineering community due to their unique electronic properties. Especially, the inherent advantage of scaling semiconductor into atomic thickness has raised the prospect of possible extension of the Moore’s law. To achieve 2D electronics, a full comprehension of semiconductor defect physics and chemistry is indispensable due to its controlling electrical performance of 2D materials and functionalizing their devices. In this review, first we explain why 2D semiconductors is important for nanoelectronics and optoelectronics. Second, we elucidate how native defects or intentional impurities affect and control electrical characteristic in 2D semiconductors, such as carrier concentration and their conductive type. In this section, experimental pictures of defects and several updated theoretical methods to evaluate carrier ionization energies of defects and their conductive type are introduced in detail. Third, typical device experiments are shown to demonstrate a direct role of defects to functionalize 2D electronic device. Furthermore, a database of popular defects and their electrical properties in current popular 2D semiconductors is summarized for references. Last, we discuss the challenges and potential prospects of defect engineering for 2D devices. The present paper offers important viewpoints from semiconductor defects to design the emerging 2D electronics.

A p -benzoquinone ( p -BQ)/UV process to induce hydrated electron (e aq − ) generation was predicted by quantum chemical calculations and validated by experiment in this work. Theoretically, the photolysis of p -BQ under UV irradiation at 253.7 nm could induce water to generate e aq − with a molar ratio of 1:2 via the direct triplet mechanism, in which 1,4-addition reaction of the first triplet state of p -BQ with water was the key step. Experimentally, monochloroacetic acid (MCAA) (the probe of e aq − ) was used to detect e aq − generated in the p -BQ/UV process. The generation efficiency showed a positive linear dependence on the p -BQ concentration, which illustrated the crucial role of p -BQ on the generation of e aq − . During the photolysis, p -hydroquinone was the primary intermediate for the generation of e aq − . Kinetically, the energy barriers of the e aq − generation from p -HOC 6 H 4 OH, p -HOC 6 H 4 O − and p - − OC 6 H 4 O − were 100.8 kcal mol −1 , 46.5 kcal mol −1 and 5.6 kcal mol −1 , respectively. Both the experimental and theoretical results show that the generation of e aq − was much more efficient from the anions than that from p -HOC 6 H 4 OH. The findings in the present study may help to understand the mechanism of e aq − generation from natural organic matters (NOM), since quinone-like groups are usually contained in NOM.

A new carbon-based morphology, graphene spirals (GSs), possesses interesting electronic features with inter-layer interaction and intra-layer interaction, ascribed to its unique intra-system electronic coupling states. The spin-polarization and the tunneling patterns of GSs manipulated by the periphery structural modification were investigated in detail with first principle calculations. The spin-polarized edge-states and transport properties can be enhanced and modulated by the constructed trigonal corners efficiently. Governed by the position and the number of the introduced carbon-hexagons, diverse spin-polarized tunneling states and various edge-state couplings between central spiral structure and electrodes can be achieved. More significantly, the contribution of inter-layer tunneling and intra-layer tunneling can be dominated by the topological signatures of GSs. For all spiral conformations, inter-layer tunneling always contributes to the net spin-dependent current. Remarkably, when carbon-hexagons are introduced at some typical positions, the complete spiral current along spiral construction is induced by intra-layer tunneling. Those features provide a good tunability of spin-polarized couplings and tunneling patterns in GSs for spintronic applications.

A phenol/UV (253.7 nm) process to generate hydrated electron (eaq−) was experimentally and theoretically studied in the present work, where monochloroacetic acid (MCAA) was selected as the probe of eaq−. It was demonstrated that the eaq− generation efficiency was dependent on the phenol concentration and pH. To interpret the dependence, a mechanism for the generation of eaq− from phenol was proposed and confirmed by the quantum chemical calculations. Theoretically, phenol could eject eaq− and phenoxyl radical (C6H5O ), followed by the addition of hydroxyl ion (OH−) to C6H5O , and the simultaneous formation of phenol and p-hydroquinone was accomplished by hydrogen abstraction of the adduct with C6H5O as hydrogen acceptor (period I). The generated p-hydroquinone could also release eaq− with p-benzoquinone as the product (period II). Totally, one mole of phenol could generate four moles of eaq− via two periods, and two moles were generated in period I and two moles were in period II. Experimentally, eaq− could be ejected from phenol and phenolate, and the molar ratios of the species were determined by pH. Kinetically, the energy barriers of the electron release from phenol and phenolate were 63.7 kcal mol−1 and 62.3 kcal mol−1, respectively, which confirmed that the generation of eaq− from phenolate was much more efficient than that from phenol. These results may promote the development of novel eaq− reduction processes based on the phenolic compounds, since they are abundant in the environment.

The ionization of dopants is a crucial process for electronics, yet it can be unexpectedly difficult in two-dimensional materials due to reduced screening and dimensionality. Using first-principles calculations, here we propose a dopant ionization process for two-dimensional semiconductors where charge carriers are only excited to a set of defect-bound band edge states, rather than to the true band edge states, as is the case in three-dimensions. These defect-bound states have small enough ionization energies but large enough spatial delocalization. With a modest defect density, carriers can transport through band by such states.

Because of the remarkable semi-metallicity and edge states, graphene-based nanoelectronics has become an intense arena in low-dimensional atomic device science and technology. Nowadays, various single atomic chains have been successfully fabricated, which can serve as multi-functional interconnects to bridge atomic devices. Using first principles approach, the spintronic applications of graphene-based carbon atomic chains and boron nitride atomic chains MTJs (magnetic tunnelling junctions) are systematically investigated in this work. The results show that the half-metallicity is only contact-dominated (sp and sp2 contacts), which cannot be switched by gate voltages, strain, the length of atomic chains, or the width of zigzag graphene nanoribbon leads. The intrinsic physics is that the electronic coupling in sp junctions provides partial transmission states for both spin currents, while one spin state is completely blocked by the electronic coupling in sp2 junctions. Therefore, the sp2 junctions present half-metallicity and remarkable tunnelling magneto-resistance (105%–106%), demonstrating the potential applications as spin-valve.

The development of carbon-based catalysts with excellent activity for hydrogen evolution reaction (HER) is highly desirable but still remains a significant challenge. Chemical doping and morphology engineering are paramount to enhance their catalytic performance toward HER. Herein, we present a novel and effective strategy to synthesize heteroatoms-doped three-dimensional (3D) carbon nanotubes/graphene hierarchical architecture (N,S-CNTs/N,S-G) on layered double oxide substrates, in which the N,S-doped CNTs are in-situ grown on both sides of N,S-doped graphene, by two differentiated chemical vapor deposition (CVD) processes. The high concentrations of N and S dopants (up to 6.5 at.%) provide sufficient catalytic active sites for HER, while the CNTs seamlessly grafted on graphene ensure the excellent electric conductivity of N,S-CNTs/N,S-G hybrids. Consequently, the 3D N,S-CNTs/N,S-G composites display superior electrocatalytic activity for HER with an onset potential of 62 mV vs. RHE (achieve current density of 1 mA cm−2) and a small overpotential of 126 mV at 10 mA cm−2, which outperforms most of reported chemical doped carbon-based composites. The synthetic strategy facilitates the fabrication of other heteroatoms-doped 3D electrochemical catalysts.

The electronic properties and second-order nonlinear optical (NLO) responses of B/N-doped zigzag graphene nanoribbon (ZGNR) have been investigated using quantum chemistry methods. The electron-deficient B atoms prefer to form π-conjugation with the C atoms nearby along the B-doped zigzag edge. On the other hand, the electron-rich N atoms with radical characteristics weaken the conjugated bonding effects in the N-doped ZGNR. The NLO response of the ZGNR is enhanced by doping only one zigzag edge with B or N atoms. The conjugated B-doped zigzag edge takes the role of electron donor, while the N-doped zigzag edge serves as electron acceptor, giving rise to the discordant impact on the second-order NLO response of the BN-doped ZGNR.

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.

From the same piece of finite size graphene (F-graphene) sheet through different directions (zigzag edge or armchair edge), (4, 4) and (8, 0) carbon nanotube clips form. The electronic properties of the intermediate structures in the two rolling processes 44 (zigzag) and 80 (armchair) have been investigated using quantum chemistry method. The magnetism of the F-graphene sheet disappears with the rolling operation in 44, while it is maintained throughout the whole rolling operation in 80. Furthermore, the highest occupied molecular orbital (HOMO) α and HOMO β gradually extend to the whole framework from the zigzag edges with the rolling operation in 44, and they gradually localize to the lower and upper half of the framework in 80. Oxygen passivation along the opening of the intermediate structures effectively improves the nonlinear optical (NLO) response of the intermediate structures in both the zigzag and the armchair processes. Oxygen passivation along the armchair opening in 80 enhances the βtot value, yet does not bring essential changes to the electron transitions contributed to the NLO response. Oxygen passivation along the zigzag opening in 44 is able not only to enhance the βtot value but also to change the transition nature of electron excitations with a major contribution to the NLO response.

Hierarchical networks, constructed by non-covalent bond stabilized cross-junctions of covalent one-dimensional molecular wires, are synergistically formed at the liquid/solid interface through in situ on-surface condensation of aromatic amines and aldehydes. Our investigation demonstrates the significant impact of the concentration and structure of monomers on the hierarchical construction of these nanoarchitectures at the interface.

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.

Organic single-crystalline semiconductors with long-range periodic order have attracted much attention for potential applications in electronic and optoelectronic devices due to their high carrier mobility, highly thermal stability, and low impurity content. Molecular doping has been proposed as a valuable strategy for improving the performance of organic semiconductors and semiconductor-based devices. However, a fundamental understanding of the inherent doping mechanism is still a key challenge impeding its practical application. In this study, solid evidence for the "perfect" substitutional doping mechanism of the stacking mode between the guest and host molecules in organic single-crystalline semiconductors using polarized photoluminescence spectrum measurements and first-principles calculations is provided. The molecular host-guest doping is further exploited for efficient color-tunable and even white organic single-crystal-based light-emitting devices by controlling the doping concentration. The clarification of the molecular doping mechanism in organic single-crystalline semiconductor host-guest system paves the way for their practical application in high-performance electronic and optoelectronic devices.

Possible isomers of buckybowl with various N contents (5–15%) were systematically searched with density functional theory (DFT) calculations. N doped buckybowls are predicted to be more stable than the well-known C48N12 azafullerene. The N-doping pattern in buckybowl presents different character from that of fullerenes. Vibrational properties of the heterobuckybowls vary with the relative positions of substituted atoms in buckybowl. The modified electronic properties of buckybowl by N doping lead to enhancement of the second hyperpolarizabilities, which implies that heterobuckybowls could be potential nonlinear optical materials and possible building blocks for molecular electronics and photonic devices. © 2015 Wiley Periodicals, Inc.

From the same piece of graphene sheet, (3, 3) and (6, 0) carbon nanotube clips were obtained on the basis of the different manners of rolling. The nature of the electronic state varies differently with different manners of rolling and is significantly affected by zigzag edges. The intermediate structures formed during the rolling process were functionalized with fluorine and oxygen atoms to investigate the electronic states and nonlinear optical (NLO) responses. Passivation of the intermediate structures with fluorine neither changes the nature of electronic states and nor improves the NLO responses. In constrast, passivation with oxygen enhances the NLO properties and changes the electronic states of the structures upon passivating at the open zigzag edges.

Electronic spectra, and the nonlinear optical (NLO) properties of five isomers of C96 were investigated using density functional theory and semi-empirical methods. The simulated electronic spectra of C2:181, C1:144, C1:145, and C2:176 have strong absorptions above 500 nm. The electronic spectra of C1:144, C1:145, and C2:176 are similar. The third-order NLO properties of the isomers were analyzed under an external field. Small structural differences between C1:144 and C1:145 result in NLO responses that occur at different external fields. Entropy effects on the NLO properties are significant. The NLO responses of the five most stable isomers differ in the concentration averaged sample.

The lowest-lying 10 isomers of C106 satisfying the isolated-pentagon rule (IPR) were predicted from 1233 IPR isomers with semiempirical and density functional theory based methods. The structures, stabilities, IR and UV spectroscopic, and the third-order nonlinear optical (NLO) properties of those low-lying isomers were explored in detail. Cs:331, C2:1194, and C1:534 are the three lowest-energy isomers with almost identical energies and could be observed in experiment. When the entropy effects in the isomeric fullerene system are taken into account, isomer C2:1194 prevails up to 3000 °C. In the high temperature region, the concentrations of those ten low-lying isomers are very similar, indicating that the isomers at high temperatures will be hard to isolate. The third-order NLO properties under external fields (0.0–3.0 eV) of the five lowest-lying isomers were analyzed, and the average NLO properties of those isomers were predicted at room temperature for experimental exploration.

Single-crystalline anatase TiO2 nanobelts with a dominant surface of the {101} facet were hydrogenated and used as substrates of platinum for methanol oxidation reaction (MOR). The hydrogenated TiO2 anatase{101} supporting Pt exhibits a 228% increase of current density for methanol oxidation compared with the same system without hydrogenation under dark conditions. The synergetic interactions of hydrogenated anatase{101} with the Pt cluster were investigated through first principles calculations, and found that the hydrogenation shifts the conduction band minimum to the Fermi level of pristine TiO2, and reduces the activation barrier for methanol dissociation considerably. Thus, this work provides an experimental and theoretical basis for developing non-carbon substrates with high electro-catalytic activity toward MOR.

Based on first-principles calculations, we designed for the first time a boron-kagome-based two-dimensional MgB6 crystal, in which two boron kagome layers sandwich a triangular magnesium layer. The two-dimensional lattice is metallic with several bands across the Fermi level, and among them a Dirac point appears at the K point of the first Brillouin zone. This metal-stabilized boron kagome system displays electron-phonon coupling, with a superconductivity critical transition temperature of 4.7 K, and thus it is another possible superconducting Mg-B compound besides MgB2. Furthermore, the proposed 2D MgB6 can also be used for hydrogen storage after decoration with Ca. Up to five H2 molecules can be attracted by one Ca with an average binding energy of 0.225 eV. The unique properties of 2D MgB6 will spur broad interest in nanoscience and technology.

The landscape of second-order nonlinear optical (2nd NLO) responses of a system can be depicted as two-dimensional second-order nonlinear optical spectra in a range of external fields, and this is difficult to be realized in experiment for a wide range of external fields. In the present study, an efficient method for application of sum-over-states model to simulate electronic two-dimensional NLO (2DNLO) spectra has been developed, and techniques to analyze NLO response-structure correlation have been proposed. This 2DNLO method has been applied to simulate the 2DNLO spectra of a series of typical electron push-pull chromophores under external fields of up to 5.00 eV. The correlation between the NLO properties and structure has been disclosed, and a further strategy to enhance the NLO properties of push-pull chromophores has been proposed.