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Nanogaps between Au nanoparticles and Au substrates are the simplest systems that generate extremely high electric fields at hotspots for surface-enhanced Raman spectroscopy (SERS). However, the electric field cancellation at the hotspots in the systems can cause the reduction of Raman signal when two metallic materials are physically contacted due to the low concentration of analytes. Here, we propose an atomically thin hexagonal boron nitride (h-BN) shielding layer for Au substrates, which can be used as an insulating spacer to prevent electrical shorts at nanogaps. Experimental investigation of the SERS effect combined with theoretical studies by finite-difference time-domain simulations demonstrate that the Au NP/h-BN/Au substrate structure has excellent performance in electrical short prevention, thus facilitating ultrasensitive Raman detection. The outstanding chemical and thermal stability of h-BN allow the efficient recycling of the SERS substrate by protecting the Au surface during the removal of Au NPs and molecular analytes by chemical and thermal processes.

A graphene nanowrinkle (GNW) formed on a Ni substrate, with a width below 5 nm, exhibits a unique feature (van Hove singularities (vHS)) in its electronic structure, owing to the one-dimensional (1D) electron confinement in GNWs. Considering that the 1D electron confinement effect normally appears when the electron motion is isolated in a 1D structure with the insulator-surrounding environment, the experimental observation of vHS in the electronic structure of GNW wedged between metallic graphene sheets has been regarded as extraordinary. Density functional theory calculations were systematically performed and revealed the origin of the 1D quantum confinement in GNW on the Ni substrate, which originated from the crucial role of chemisorption-like interaction between the graphene sheet and Ni surface in spatially separating the π-conjugated state of GNW from that of the graphene sheet. A series of standing waves corresponding to “the 1D particle-in-a-box model” was confirmed by computationally obtained charge densities of GNW. These results demonstrated that the graphene–GNW–graphene on the Ni substrate served a sufficient potential to lead to 1D-electron confinement. Our investigations provide a deeper understanding of the electronic structure in pseudo-1D materials and suggest a novel approach for modulating the electronic structure without chemical modification or complicated etching to break the C–C bond to produce graphene-based 1D nanomaterials, e.g., graphene nanoribbon.

We report facile growth methods for high-quality monolayer and multilayer MoS2 films using MoOCl4 as the vapor-phase molecular Mo precursor. Compared to the conventional covalent solid-type Mo precursors, the growth pressure of MoOCl4 can be precisely controlled. This enables the selection of growth mode by adjusting growth pressure, which facilitates the control of the growth behavior as the growth termination at a monolayer or as the continuous growth to a multilayer. In addition, the use of carbon-free precursors eliminates concerns about carbon contamination in the produced MoS2 films. Systematic studies for unveiling the growth mechanism proved two growth modes, which are predominantly the physisorption and chemisorption of MoOCl4. Consequently, the thickness of MoS2 can be controlled by our method as the application demands.

Although surface engineering has been regarded to be a great approach to modulate the optical and electrical properties of nanomaterials, the spontaneous covalent functionalization on semiconductin...

We report a chemical route to synthesize centimeter-scale stoichiometric "graphenol (C6OH1)", a 2D crystalline alcohol, via vapor phase hydroxylation of epitaxial graphene on Cu(111). Atomic resolution scanning tunneling microscopy revealed this highly-ordered configuration of graphenol and low energy electron diffraction studies on a large-area single crystal graphene film demonstrated the feasibility of the same superstructure being achieved at the centimeter length scale. Periodic density functional theory (DFT) calculations about the formation of C6(OH)1 and its electronic structure are also reported.

A supra-quantum dot (SQD) is a three-dimensionally assembled QD structure composed of several hundreds to thousands of QDs connected through oriented attachments. Owing to their three-dimensional interconnected structures and relatively large volumes, impurity atoms are thermodynamically more stable in SQDs than in conventional QDs. Herein, we report the facile in-situ synthesis of colloidal Ag-doped CdSe SQDs. Ag dopants were efficiently incorporated into CdSe SQDs through the three-dimensional interconnection of Ag-doped primary CdSe QDs, as confirmed by elemental analysis combined with chemical etching. Photoelectron spectroscopic studies revealed that the Ag-doped CdSe SQDs exhibit n-type doping behavior, since the valence electrons from the interstitial Ag atoms are directly donated to the lattice.

We report facile growth methods for high-quality monolayer and multilayer MoS

Photoexcited electron extraction from semiconductors can be useful for converting solar energy into useful forms of energy. Although InP quantum dots (QDs) are considered alternative materials for solar energy conversion, the inherent instability of bare InP QDs demands the use of passivation layers such as ZnS for practical applications, which impedes carrier extraction from the QDs. Here, we demonstrate that Cu-doped InP/ZnS (InP/Cu:ZnS) QDs improve the electron transfer ability due to hole capture by Cu dopants. Steady-state and time-resolved photoluminescence studies confirmed that electrons were effectively transferred from the InP/Cu:ZnS QDs to a benzoquinone acceptor by retarding the electron-hole recombination within the QD. We evaluated the photocatalytic H

Although surface engineering has been regarded to be a great approach to modulate the optical and electrical properties of nanomaterials, the spontaneous covalent functionalization on semiconducting 2H-MoS

Nickel(II) dichloride complexes with a pyridine-chelated imidazo[1,5-a]pyridin-3-ylidene py-ImPy ligand were developed as novel catalyst precursors for acrylate synthesis reaction from ethylene and carbon dioxide (CO2), a highly promising sustainable process in terms of carbon capture and utilization (CCU). Two types of ImPy salts were prepared as new C,N-bidentate ligand precursors, py-ImPy salts (3, 4a&ndash, 4e) having a pyridine group at C(5) on ImPy and a N-picolyl-ImPy salt (10) having a picolyl group at N atom on ImPy. Nickel(II) complexes such as py-ImPyNi(II)Cl2 (7, 8a&ndash, 8e) and N-picolyl-ImPyNi(II)Cl2 (12) were synthesized via transmetalation protocol from silver(I) complexes, py-ImPyAgCl (5, 6a&ndash, 6e) and N-picolyl-ImPyAgCl (11). X-ray diffraction analysis of nickel(II) complexes (7, 8b, 12) showed a monomeric distorted tetrahedral geometry and a six-membered chelate ring structure. py-ImPy ligands formed a more planar six-membered chelate with the nickel center than did N-picolyl-ImPy ligand. py-ImPyNi(II)Cl2 complexes (8a&ndash, 8e) with tert-butyl substituents exhibited noticeable catalytic activity in acrylate synthesis from ethylene and CO2 (up to 108% acrylate). Interestingly, the use of additional additives including monodentate phosphines increased catalytic activity up to 845% acrylate (TON 8).

An atomically thin two-dimensional (2D) covalent organic framework (COF) was successfully synthesized via the photon-assisted imine condensation reaction within 1 h from the highly uniform and homogeneous precursor solution layer floating on the water surface. The polarity optimization of the precursor solution was the key step for the successful formation of the high-quality 2D COF because only the precursor solution consisting of polarity-controlled solvents allows ideal floating on the water surface. The polarity-controlled solution not only prohibits the agglomeration of the organic precursors on the water surface but also facilitates the wafer scale and layer number-controllable synthesis of the 2D COF. The resulting 2D COF has a uniform porous structure and highly oriented layered structure along the out-of-plane direction as observed by microscopy analysis and X-ray diffraction, respectively. In addition, we successfully fabricated field effect transistor type polyimine-based COF (pi-COF) electronic devices to demonstrate the prompt electrical responses to photo-exposure and water vapor exposure, suggesting the potential applications of the pi-COF in electrical photodetector or moisture-detector devices.

Fast-growth of single crystal monolayer graphene by CVD using methane and hydrogen has been achieved on “homemade” single crystal Cu/Ni(111) alloy foils over large area. Full coverage was achieved in 5 min or less for a particular range of composition (1.3 at.% to 8.6 at.% Ni), as compared to 60 min for a pure Cu(111) foil under identical growth conditions. These are the bulk atomic percentages of Ni, as a superstructure at the surface of these foils with stoichiometry Cu6Ni1 (for 1.3 to 7.8 bulk at.% Ni in the Cu/Ni(111) foil) was discovered by low energy electron diffraction (LEED). Complete large area monolayer graphene films are either single crystal or close to single crystal, and include folded regions that are essentially parallel and that were likely wrinkles that “fell over” to bind to the surface; these folds are separated by large, wrinkle-free regions. The folds occur due to the buildup of interfacial compressive stress (and its release) during cooling of the foils from 1075 °C to room tempera...

We investigated the temperature-dependent photoluminescence (PL) properties of colloidal CsPbX3 (X = Br, I, and mixed Br/I) quantum dot (QD) samples in the 30–290 K temperature range. Temperature-dependent PL experiments reveal thermal quenching of PL, blue shifting of optical band gaps, and line width broadening for all CsPbX3 QD samples with increasing temperature. Interestingly, side-peak emissions that are spectrally separated from the excitonic PL peaks were observed for both CsPbBr3 and CsPb(Br/I)3 QD samples at temperatures below ∼250 K. The side-peak emission for the CsPbBr3 QD sample is located at a lower energy compared to the band-edge peak, whereas that of the Br-rich CsPb(Br/I)3 alloy QD sample is located at a higher energy than that of the band-edge peak. We found that the CsPbBr3 QDs have two emissive states, a band-edge state, and one involving shallow defects, which can be spectrally separated by narrowing the emission line widths at low temperature. In the case of the Br-rich CsPb(Br/I)3...

Interlayer excitons were observed at the heterojunctions in van der Waals heterostructures (vdW HSs). However, it is not known how the excitonic phenomena are affected by the stacking order. Here, we report twist-angle-dependent interlayer excitons in MoSe2/WSe2 vdW HSs based on photoluminescence (PL) and vdW-corrected density functional theory calculations. The PL intensity of the interlayer excitons depends primarily on the twist angle: It is enhanced at coherently stacked angles of 0° and 60° (owing to strong interlayer coupling) but disappears at incoherent intermediate angles. The calculations confirm twist-angle-dependent interlayer coupling: The states at the edges of the valence band exhibit a long tail that stretches over the other layer for coherently stacked angles; however, the states are largely confined in the respective layers for intermediate angles. This interlayer hybridization of the band edge states also correlates with the interlayer separation between MoSe2 and WSe2 layers. Furthermo...

We report a chemical route to synthesize centimeter-scale stoichiometric "graphenol (C

Folded graphene in which two layers are stacked with a twist angle between them has been predicted to exhibit unique electronic, thermal, and magnetic properties. We report the folding of a single crystal monolayer graphene film grown on a Cu(111) substrate by using a tailored substrate having a hydrophobic region and a hydrophilic region. Controlled film delamination from the hydrophilic region was used to prepare macroscopic folded graphene with good uniformity on the millimeter scale. This process was used to create many folded sheets each with a defined twist angle between the two sheets. By identifying the original lattice orientation of the monolayer graphene on Cu foil, or establishing the relation between the fold angle and twist angle, this folding technique allows for the preparation of twisted bilayer graphene films with defined stacking orientations and may also be extended to create folded structures of other two-dimensional nanomaterials.

Transition metal dichalcogenides (TMDs) have recently received increasing attention because of their potential applications in semiconducting and optoelectronic devices exhibiting large optical absorptions in the visible range. However, some studies have reported that the grain boundaries of TMDs can be easily degraded by the presence of oxygen in water and by UV irradiation, ozone, and heating under ambient conditions. We herein demonstrate the photodegradation of WSe2 and MoSe2 by laser exposure (532 nm) and the subsequent prevention of this photodegradation by encapsulation with hexagonal boron nitride (h-BN) layers. The photodegradation was monitored by variation in peak intensities in the Raman and photoluminescence spectra. The rapid photodegradation of WSe2 under air occurred at a laser power of ≥0.5 mW and was not observed to any extent at ≤0.1 mW. However, in the presence of a water droplet, the photodegradation of WSe2 was accelerated and took place even at 0.1 mW. We examined the encapsulation of WSe2 with h-BN and found that this prevented photodegradation. However, a single layer of h-BN was not sufficient to fully prevent this photodegradation, and so a triple layer of h-BN was employed. We also demonstrated that the photodegradation of MoSe2 was prevented by encapsulation with h-BN layers. On the basis of X-ray photoelectron spectroscopy and scanning photoemission microscopy data, we determined that this degradation was caused by the photoinduced oxidation of TMDs. These results can be used to develop a general strategy for improving the stability of 2D materials in practical applications.

Demonstration of graphene growth on metal substrates using chemical vapor deposition method (CVD) facilitated the large-area synthesis of graphene, which extended the graphene research from the fundamental investigation with a small graphene flake to the various practical applications. Spectroscopic studies using 13C-labeled carbon precursor first suggested two different growth mechanisms of graphene on Ni and Cu substrates during the conventional CVD process, ‘segregation growth’ and ‘surface growth’ for Ni and Cu substrates, respectively. However, the growth mechanism of graphene is not simply understood. For example, the surface science studies have suggested the Ni2C conversion mechanism or the direct surface growth even on Ni surface. Herein, the conformational changes of underlying metal substrate during graphene growth on Ni(111) and Cu(111) are presented, which are highly affected by the different types of growth mechanisms. We believe that our results may widen the knowledge to understand the graphene growth mechanisms on Ni and Cu. Also, the influence of graphene-metal interaction on the electronic structures has been elucidated for graphene grown on Ni and Cu substrates by scanning tunneling spectroscopic studies combined with the theoretical calculation.

Heterostructures of hexagonal boron nitride (h-BN) and graphene have attracted a great deal of attention for potential applications in 2D materials. Although several methods have been developed to produce this material through the partial substitution reaction of graphene, the reverse reaction has not been reported. Though the endothermic nature of this reaction might account for the difficulty and previous absence of such a process, we report herein a new chemical route in which the Pt substrate plays a catalytic role. We propose that this reaction proceeds through h-BN hydrogenation; subsequent graphene growth quickly replaces the initially etched region. Importantly, this conversion reaction enables the controlled formation of patterned in-plane graphene/h-BN heterostructures, without needing the commonly employed protecting mask, simply by using a patterned Pt substrate.

Interlayer excitons were observed at the heterojunctions in van der Waals heterostructures (vdW HSs). However, it is not known how the excitonic phenomena are affected by the stacking order. Here, we report twist-angle-dependent interlayer excitons in MoSe

Along with the explosive interest in graphene research, much attention has been paid to other two-dimensional (2D) materials such as transition metal dichalcogenides (TMDs) and hexagonal boron nitride (h-BN). In particular, the stacking of various 2D materials in the vertical and lateral directions has been studied recently, as novel physicochemical properties are expected that could result in new applications for electronic devices. In this Perspective, recent advances in the stacking of 2D materials are discussed from the point of view of materials chemistry. In particular, methods for stacking of 2D materials (h-BN/graphene, graphene/WS2 (or MoS2)/graphene, etc.), the properties of vertically and laterally stacked 2D materials, and possible applications are discussed. Finally, we discuss important emerging issues to be studied in future.

Synthesis of morphologically well-defined crystals of metalloporphyrin by direct crystallization based on conventional anti-solvent crystallization method without using any additives has been rarely reported. Herein, we demonstrate an unconventional and additive-free synthetic method named reverse anti-solvent crystallization method to achieve well-defined zinc-porphyrin cube crystals by reversing the order of the addition of solvents. The extended first solvation shell effect mechanism is therefore suggested to support the synthetic process by providing a novel kinetic route for reaching the local supersaturation environment depending on the order of addition of solvents, which turned out to be critical to achieve clean cube morphology of the crystal. We believe that our work not only extends fundamental knowledge about the kinetic process in binary solvent systems, but also enables great opportunities for shape-directing crystallization of various organic and organometallic compounds.

Because the direct formation of large, patterned graphene layers on active electronic devices without any physical transfer process is an ultimate important research goal for practical applications, we first developed a cost-effective, scalable, and sustainable process to form graphene films from solution-processed common polymers directly on a SiO2/Si substrate. We obtained few-layer graphene by heating the thin polymer films covered with a metal capping layer in a high-temperature furnace under low vacuum in an Ar/H2 atmosphere. We find that the metal capping layer appears to have two functions: prevention of vaporization of dissociated molecules and catalysis of graphene formation. We suggest that polymer-derived graphene growth directly on inert substrates in active electronic devices will have great advantages because of its simple, inexpensive, and safer process.

The site-dependent and spontaneous functionalization of 4-bromobenzene diazonium tetrafluoroborate (4-BBDT) and its doping effect on a mechanically exfoliated graphene (MEG) were investigated. The spatially resolved Raman spectra obtained from both edge and basal region of MEG revealed that 4-BBDT molecules were noncovalently functionalized on the basal region of MEG, while they were covalently bonded to the edge of MEG. The chemical doping effect induced by noncovalently functionalized 4-BBDT molecules on a basal plane region of MEG was successfully explicated by Raman spectroscopy. The position of Fermi level of MEG and the type of doping charge carrier induced by the noncovalently adsorbed 4-BBDT molecules were determined from systematic G band and 2D band changes. The successful spectroscopic elucidation of the different bonding characters of 4-BBDT depending on the site of graphene is beneficial for the fundamental studies about the charge transfer phenomena of graphene as well as for the potential applications, such as electronic devices, hybridized composite structures, etc.

Noncovalent approaches havebeen considered appropriate to softly modify the surfaceproperties of carbon nanotubes sufficient for chemical andbiological applications. However, the importance of thedevelopment of covalent bond-forming chemical reactionshas recently been refocused on, since the strategically drivencovalent bonds are known to promptly alter the electricalproperties of carbon nanotubes to secure a high population ofsemiconducting carbon nanotubes from mixtures.

We synthesized single-phase CoS2 on a large scale by adding graphene oxide of sufficient quantity via the hydrothermal method using cobalt acetate and thioacetamide as precursors; this produced the hybrid of CoS2 with reduced graphene oxide which exhibited high electrocatalytic activity in the hydrogen evolution reaction. Electronic supplementary material The online version of this article (doi:10.1186/s40580-016-0066-x) contains supplementary material, which is available to authorized users.

Additional file 1: Figure S1. XRD patterns of CoS /rGO samples synthesized at different temperatures: 200 (black), 240 (red),and 265 C (blue). Figure S2. TEM image of cobalt sulfides without GO: (a) low magnification and (b) high-magnificationimages. The inset in (b) indicates the (111) diffraction pattern of Co S in the white square. Figure S3. EDS elemental mapping of Co and S for CoS /rGO (2.3 mg/mL of GO), EDX spectrum and tableshowing elemental composition. The atomic ratio of S and Co is 2, confirming the stoichiometry of CoS . Figure S4. TEM image of CoS /rGO (1 mg/mL of GO). (a) Bright field TEM image in low magnification (b)High resolution TEM image of CoS particle. (c) High resolution TEM image of a CoS particle which is not covered by rGO. Inset of (b) shows planes of CoS including (311) plane and inset of (c) shows planes of CoS including (100) plane. Figure S5. XRD patterns of the CoS /rGO hybrids with various GO concentrations. Figure S6. (a) Plots for the extraction of the double-layer capacitance (C ) for CoS /rGO electrodes. CV cycles of CoS /rGO samples with 1 mg/mL of GO (b) and 2.3 mg/mL of GO (c) at different scan rates. Figure S7. Polarization curves of CoS /rGO depending on the concentration of GO at (a) higher and (b) lower applied oveportentials show the HER performance. (c) Tafel analysis of the data shown in Figure S5a. (d) Summary of the electrochemical performance for CoS /rGO samples with various GO concentrations. Figure S8. Electrochemical impedance spectroscopy (EIS) for CoS /rGO samples. Figure S9. (a) SEM image of CoS /rGO (2.3 mg/mL of GO) after the cycling test for 14 hours. (b) High resolution TEM image of a CoS particle after the cycling test. Inset of (b) shows planes of CoS including (102) plane. Table S1. Comparison of growth condition for CoS /rGO with other reported cobalt sulfide/rGO materials. Table S2. The weight percentage of rGO in products by elemental analysis. Table S3. Comparison of HER activity measured for our CoS2/rGO with other reported CoS materials as HER catalyst.

Graphene-based carbon materials such as fullerenes, carbon nanotubes, and graphenes have distinct and unique electronic properties that depend on their dimensionality and geometric structures. Graphene wrinkles with pseudo one-dimensional structures have been observed in a graphene sheet. However, their one-dimensional electronic properties have never been observed because of their large widths. Here we report the unique electronic structure of graphene nanowrinkles in a graphene sheet grown on Ni(111), the width of which was small enough to cause one-dimensional electron confinement. Use of spatially resolved, scanning tunnelling spectroscopy revealed bandgap opening and a one-dimensional van Hove singularity in the graphene nanowrinkles, as well as the chemical potential distribution across the graphene nanowrinkles. This observation allows us to realize a metallic-semiconducting-metallic junction in a single graphene sheet. Our demonstration of one-dimensional electron confinement in graphene provides the novel possibility of controlling its electronic properties not by chemical modification but by ‘mechanical structuring'., Wrinkles in graphene can restrict the motion of electrons to one dimension. Here, the authors observe a one-dimensional van Hove singularity and bandgap opening in a five nanometre wide wrinkle, which enables them to create a metallic-semiconducting-metallic junction in a single graphene sheet.

Understanding of electrochemical process in rechargeable Li–O2 battery has suffered from lack of proper analytical tool, especially related to the identification of chemical species and number of electrons involved in the discharge/recharge process. Here we present a simple and straightforward analytical method for simultaneously attaining chemical and quantified information of Li2O2 (discharge product) and byproducts using in situ XRD measurement. By real-time monitoring of solid-state Li2O2 peak area, the accurate efficiency of Li2O2 formation and the number of electrons can be evaluated during full discharge. Furthermore, by observation of sequential area change of Li2O2 peak during recharge, we found nonlinearity of Li2O2 decomposition rate for the first time in ether-based electrolyte.

A novel type of action spectrum representing multiple overtone excitations of the $v(M\text{\ensuremath{-}}\mathrm{C})$ mode was observed for lateral hopping of a CO molecule on Ag(110) induced by inelastically tunneled electrons from the tip of a scanning tunneling microscope. The yield of CO hopping shows sharp increases at $261\ifmmode\pm\else\textpm\fi{}4\text{ }\text{ }\mathrm{mV}$, corresponding to the C-O internal stretching mode, and at $61\ifmmode\pm\else\textpm\fi{}2$, $90\ifmmode\pm\else\textpm\fi{}2$, and $148\ifmmode\pm\else\textpm\fi{}7\text{ }\text{ }\mathrm{mV}$, even in the absence of corresponding fundamental vibrational modes. The mechanism of lateral CO hopping on Ag(110) was explained by the multistep excitation of overtone modes of $v(M\text{\ensuremath{-}}\mathrm{C})$ based on the numerical fitting of the action spectra, the nonlinear dependence of the hopping rate on the tunneling current, and the hopping barrier obtained from thermal diffusion experiments.

Citation: Walen, H., Liu, D. J., Oh, J., Lim, H., Evans, J. W., Aikens, C. M., . . . Thiel, P. A. (2015). Cu2S3 complex on Cu(111) as a candidate for mass transport enhancement. Physical Review B, 91(4), 7. doi:10.1103/PhysRevB.91.045426

Despite potential advantages of covalent organic frameworks (COFs) in wide area applications, several limitations in conventional solvothermal synthesis, such as long reaction time and high reaction temperature, reduce reaction efficiency and prohibit technical processes for practical applications. Therefore, the development of a novel synthesis method that provides better reaction efficiency and spatial controllability has become a critical challenge. Herein, a photochemical synthesis of C9H4BO2 (COF-5) is demonstrated for the first time, by which “sea urchin-shaped” COF-5 (UV-COF-5) with uniform size is synthesized with a highly enhanced growth rate, ≈48 times faster than that of the solvothermal method for 75% yield. In addition, an enlarged surface area is measured from UV-COF-5, which originates from its hierarchical morphology. The selectively increased growth rate of UV-COF-5 in the [001] direction observed by microscopic analysis results in the local 1D morphology of the hierarchical structure. Density functional theory calculations determine that the enhanced growth rate along the [001] direction can be understood by the characteristic of the interlayer orbital coupling at the frontier energy region. In addition, this study successfully demonstrates the preparation of COF-5 patterns without any complicated postsynthesis lithography process, but simply by utilizing optical masks during the photochemical method.

Graphene functionalization is of great importance in applying graphene as a component in functional devices or in activating it for use as a catalyst. Here we reveal that atomic oxidation of epitaxial graphene grown on a metal substrate results in the formation of enolate, i.e., adsorption of atomic oxygen at the on-top position, on the basal plane of a graphene, using periodic density functional theory calculations. This is striking because the enolate corresponds to the transition state between the epoxides on free-standing graphene and on graphite. Improved interfacial interaction between graphene and the metal substrate during atomic oxidation makes the graphene enolate a local minimum and further highly stabilizes it over the graphene epoxide. Our results provide not only a novel perspective for a chemical route to functionalizing graphene but also a new opportunity to utilize graphene enolate for graphene-based applications.

Various solid carbon sources, particularly poly(methyl methacrylate), have been used as precursors to graphene. The corresponding growth process generally involves the decomposition of the solids to hydrocarbon gases followed by their adsorption on metallic substrates (e.g., Cu). We report a different approach that uses a thermally-resistant polyimide (PI) as a carbon precursor. Langmuir–Blodgett films of poly(amic acid) (PAA) were transferred to copper foils and then converted to graphene via a PI intermediate. The Cu foil substrate was also discovered to facilitate the orientation of aromatic moieties upon carbonization process of the PI. As approximately 50% of the initial quantity of the PAA was found to remain at 1000 °C, thermally-stable polymers may reduce the quantity of starting material required to prepare high quality films of graphene. Graphene grown using this method featured a relatively large domain size and an absence of adventitious adlayers.

Metal catalyst-free growth of large scale single layer graphene film on a sapphire substrate by a chemical vapor deposition (CVD) process at 950 °C is demonstrated. A top-gated graphene field effect transistor (FET) device is successfully fabricated without any transfer process. The detailed growth process is investigated by the atomic force microscopy (AFM) studies.

A direct and metal layer-free growth of flat graphene pads on exfoliated hexagonal boron nitride substrate (h-BN) are demonstrated by atmospheric chemical vapour deposition (CVD) process. Round shape with high flatness graphene pads are grown in high yield (∼95%) with a pad thickness of ∼0.5 nm and homogenous diameter.

A Au-coated C(60) wire device showed wavelength-selective silencing of photocurrent on illumination with 532 nm light.

We have developed a process to convert C(60) nanostructures into graphitic nanostructures. Disk-shaped and wire-shaped C(60) nanostructures synthesized by the liquid-liquid interfacial precipitation method, the vapor-solid process, and solvent evaporation were successfully converted into graphitic structures by thermal annealing in hydrogen at 900 degrees C. Scanning electron and tunneling electron microscopic studies confirmed that the converted nanostructures were composed of multi-graphitic structures such as multi-walled carbon nanotubes, carbon nanofibers, and carbon onions. Fourier transform Raman spectroscopy and conductance measurements were carried out to further confirm the successful formation of graphitic layers. In the Raman spectra, the nanostructures converted from C(60) disks showed signature D, G, and G(') bands of graphitic structures, while the A(g) mode (1469 cm(-1)) of the original C(60) molecule disappeared. C(60) nanowire devices fabricated for the conductance measurements of the converted structures showed dramatically decreased resistance (R approximately 100 kOmega) compared to the pristine C(60) wire (R>100 MOmega). Further manipulation of the reaction environment, including the gas and the annealing temperature, may reveal a new way to attain diverse graphitic nanostructures economically.