Surface-enhanced Raman Scattering Study on 1D-2D Graphene-based Structures

In order to explore novel functional nanomaterials, we have produced sp²-sp hybrid carbon structures composed of graphene layers (2D) and linear carbon chains (1D). A remarkable change of the graphene electronic and phononic behaviour is observed after the interaction with 1D carbon nanostructures. Raman and surface enhanced Raman spectroscopies together with a density functional theory approach are used to explain charge transfer phenomena as a function of linear molecule orientation in the produced 1D-2D carbon-based structures, inducing hole-doping in graphene layers.     

Supramolecular Materials from Inorganic Building Blocks

Inorganic materials of nanometric dimensions and controllable morphologies are now widely available permitting their use as building blocks in supramolecular structures. Incorporation of inorganic blocks into hybrid structures can yield unique materials that have no naturally occurring or organic synthetic analogues. In this short review, we describe the construction and functions of supramolecular materials prepared using inorganic building blocks, with emphasis on material-like components. Examples described in this review are categorized as (i) inorganic structures within organic assemblies (silica-supported Langmuir monolayers, organic–inorganic lipid bilayer vesicles etc.), (ii) organic components in inorganic nanospaces (mesoporous materials including biocomponents such as peptides and proteins), (iii) organic/inorganic nanohybrid blends (nanorod-liquid crystal blends and surfactant-guided gold nanostructures), and (iv) hierarchic structures (layer-by-layer assemblies of mesoporlous carbons and capsules).     

Evaluation of Graphene/WO<Subscript>3</Subscript> and Graphene/CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Structures as Electrodes for Supercapacitor Applications

The combination of graphene with transition metal oxides can result in very promising hybrid materials for use in energy storage applications thanks to its intriguing properties, i.e., highly tunable surface area, outstanding electrical conductivity, good chemical stability, and excellent mechanical behavior. In the present work, we evaluate the performance of graphene/metal oxide (WO₃ and CeO _x ) layered structures as potential electrodes in supercapacitor applications. Graphene layers were grown by chemical vapor deposition (CVD) on copper substrates. Single and layer-by-layer graphene stacks were fabricated combining graphene transfer techniques and metal oxides grown by magnetron sputtering. The electrochemical properties of the samples were analyzed and the results suggest an improvement in the performance of the device with the increase in the number of graphene layers. Furthermore, deposition of transition metal oxides within the stack of graphene layers further improves the areal capacitance of the device up to 4.55 mF/cm², for the case of a three-layer stack. Such high values are interpreted as a result of the copper oxide grown between the copper substrate and the graphene layer. The electrodes present good stability for the first 850 cycles before degradation.     

Self-assembled high aspect ratio gold nanostar/graphene oxide hybrid nanorolls

Owing to their unique properties and potential applications in nanoelectronics, graphene and its derivatives have received extensive attention over the last decade. Noble metal nanostructures, on the other hand, enable the confinement and manipulation of light at the nanoscale. Integration of nanocarbons and plasmonic nanostructures is expected to result in synergistic optoelectronic properties that can potentially revolutionize the design and fabrication of optoelectronic devices. In this letter, we demonstrate a simple self-assembly approach to achieve synergistic ensemble of plasmonic gold nanostars and graphene oxide. Gold nanostars are directly nucleated and grown on the surface of graphene oxide by in situ reduction method producing differential surface charged hybrid macroanionic sheets, which are then kinetically rolled and simultaneously assembled into high aspect ratio hybrid nanorolls by means of the interplay of kinetics and graphene–gold interactions.     

A surface-enhanced Raman spectroscopy study of thin graphene sheets functionalized with gold and silver nanostructures by seed-mediated growth

We describe a simple method for decorating graphene (1–5 layers) with Au and Ag nanostructures (nanoparticles, nanorods, and nanoplates). We deposit graphene electrostatically from highly-oriented pyrolytic graphite onto Si/SiO₂ surfaces functionalized with (aminopropyl)trimethoxysilane and grow the metal nanostructures by a seed-mediated growth method from hexanethiolate-coated Au monolayer-protected cluster “seeds” that are attached to graphene by hydrophobic interactions. Scanning electron microscopy reveals the selective growth of Au or Ag nanostructures on the graphene surface. In the case of Au, the low pH 2.8 growth solution causes etching of the graphene and formation of scroll-like structures. For Ag, the high pH 9.3 solution does not seem to affect the graphene. Raman spectroscopy is consistent with the graphene morphology and reveals that the presence of Au and Ag nanostructures increases the Raman scattering from the graphene by a factor of about 45 and 150, respectively. This work demonstrates a simple method for decorating graphene with noble metal nanostructures that may have interesting optical, electronic, and chemical properties for applications in nanoelectronics, sensing, and catalysis.     

Improving the field emission of graphene by depositing zinc oxide nanorods on its surface

Zinc oxide (ZnO) nanorods were vertically grown on the surface of graphene sheets by chemical vapor deposition, and their use in a field emission device was demonstrated. In comparison with pristine graphene, the graphene/ZnO nanorod hybrid structure exhibited efficient field emission with low turn-on field, low threshold field, high emission spot density, high field enhancement factor and excellent emitting stability. It is proposed that the introduction of mid-density ZnO nanorods on the surface of graphene sheets can increase the number of emitters, enhance tunneling probability, and lead to optimized field emission for the hybrid emitters. The results showed that the field emission properties of graphene can be tailored by growing various ZnO nanostructures on its surface.     

Assembly of Polyoxometalate-Based Composite Materials

This paper is a review the polyoxometalate-based composite materials, including polyoxometalate incorporated Langmuir and Langmuir–Blodgett, layer-by-layer multilayers and novel honeycomb films, self-assembly structures of modified polyoxometalate complexes (e.g., onion-like structures, new inorganic–organic–inorganic vesicles, thermotropic and lyotropic liquid crystalline structures, gels), and amino acid- and protein-polyoxometalate nanorods and nanoparticles. Polyoxometalate-embedded layer-by-layer multilayer films show electrocatalytic or photochemical activity; and, novel photoluminescent honeycomb films templated by microwater droplets are reviewed. Inorganic–organic–inorganic hybrid vesicles display the potential as nano-switches. In addition, amino acid- and protein-polyoxometalate composite nanostructures indicate potential antimicrobial applications. Therefore, the polyoxometalate-based composite materials have promising applications in electrochemistry, photochemistry and biomedicine.     

Catalytic chemical vapor deposition of methane on graphite to produce graphene structures

Graphene structures, obtained by catalytic chemical vapor deposition of methane on highly oriented pyrolitic graphite (HOPG), were examined using scanning tunneling microscopy. Depending on the Fe catalyst coverage and localization on the substrate steps and terraces, different graphene structures were obtained: curved graphene sheets at the edges of topmost stacked graphene bilayers, laterally grown terraces at the edges of individual graphene layers parallel to the HOPG basal plane and planar graphene islands on the terraces. A growth mechanism is proposed that takes into account the specific features of the spatial distribution of Fe catalytic nanoparticles on the substrate surface, driven by metal film-substrate interaction. The present synthesis approach is promising for the controlled growth and modification of graphene layers, as well as for engineering the edge characteristics of graphene systems at the atomic scales.     

Solid‐state dye‐sensitized and bulk heterojunction solar cells using TiO2 and ZnO nanostructures: recent progress and new concepts at the borderline

In the field of photovoltaic energy conversion, hybrid inorganic/organic devices represent promising alternatives to standard photovoltaic systems in terms of exploiting the specific features of both organic semiconductors and inorganic nanomaterials. Two main categories of hybrid solar cells coexist today, both of which make much use of metal oxide nanostructures based on titanium dioxide (TiO₂) and zinc oxide (ZnO) as electron transporters. These metal oxides are cheap to synthesise, are non‐toxic, are biocompatible and have suitable charge transport properties, all these features being necessary to demonstrate highly efficient solar cells at low cost. Historically, the first hybrid approach developed was the dye‐sensitized solar cell (DSSC) concept based on a nanostructured porous metal oxide electrode sensitized by a molecular dye. In particular, solid‐state hybrid DSSCs, which reduce the complexity of cell assembly, demonstrate very promising performance today. The second hybrid approach exploits the bulk heterojunction (BHJ) concept, where conjugated polymer/metal oxide interfaces are used to generate photocurrent. In this context, we review the recent progress and new concepts in the field of hybrid solid‐state DSSC and BHJ solar cells based on TiO₂ and ZnO nanostructures, incorporating dyes and conjugated polymers. We point out the specificities in common hybrid device structures and give an overview on new concepts, which couple and exploit the main advantages of both DSSC and BHJ approaches. In particular, we show that there is a trend of convergence between both DSSC and BHJ approaches into mixed concepts at the borderline which may allow in the near future the development of hybrid devices for competitive photovoltaic energy conversion. Copyright © 2011 Society of Chemical Industry     

Aggregate nanostructures of organic molecular materials

Conjugated organic molecules are interesting materials because of their structures and their electronic, electrical, magnetic, optical, biological, and chemical properties. However, researchers continue to face great challenges in the construction of well-defined organic compounds that aggregate into larger molecular materials such as nanowires, tubes, rods, particles, walls, films, and other structural arrays. Such nanoscale materials could serve as direct device components. In this Account, we describe our recent progress in the construction of nanostructures formed through the aggregation of organic conjugated molecules and in the investigation of the optical, electrical, and electronic properties that depend on the size or morphology of these nanostructures. We have designed and synthesized functional conjugated organic molecules with structural features that favor assembly into aggregate nanostructures via weak intermolecular interactions. These large-area ordered molecular aggregate nanostructures are based on a variety of simpler structures such as fullerenes, perylenes, anthracenes, porphyrins, polydiacetylenes, and their derivatives. We have developed new methods to construct these larger structures including organic vapor-solid phase reaction, natural growth, association via self-polymerization and self-organization, and a combination of self-assembly and electrochemical growth. These methods are both facile and reliable, allowing us to produce ordered and aligned aggregate nanostructures, such as large-area arrays of nanowires, nanorods, and nanotubes. In addition, we can synthesize nanoscale materials with controlled properties. Large-area ordered aggregate nanostructures exhibit interesting electrical, optical, and optoelectronic properties. We also describe the preparation of large-area aggregate nanostructures of charge transfer (CT) complexes using an organic solid-phase reaction technique. By this process, we can finely control the morphologies and sizes of the organic nanostructures on wires, tubes, and rods. Through field emission studies, we demonstrate that the films made from arrays of CT complexes are a new kind of cathode materials, and we systematically investigate the effects of size and morphology on electrical properties. Low-dimension organic/inorganic hybrid nanostructures can be used to produce new classes of organic/inorganic solid materials with properties that are not observed in either the individual nanosize components or the larger bulk materials. We developed the combined self-assembly and templating technique to construct various nanostructured arrays of organic and inorganic semiconductors. The combination of hybrid aggregate nanostructures displays distinct optical and electrical properties compared with their individual components. Such hybrid structures show promise for applications in electronics, optics, photovoltaic cells, and biology. In this Account, we aim to provide an intuition for understanding the structure-function relationships in organic molecular materials. Such principles could lead to new design concepts for the development of new nonhazardous, high-performance molecular materials on aggregate nanostructures.     

Ni/graphene/Ni nanostructures for spintronic applications

Here, we demonstrate chemical synthesis of graphene based nano-spin valve like structures using nickel layers as ferromagnetic contacts grown on both sides of graphene sheets. Magnetic measurements indicate that the spins on two opposite nickel layers are coupled through antiferromagnetic interaction up to room temperature. However, they switch into parallel configuration when a magnetic field of about 2000 Oe is applied resulting in a change in magnetoresistance of ~19%.     

One-dimensional organic-inorganic hybrid nanomaterials

This feature article presents the current research activities that concentrate on one-dimensional (1D) organic-inorganic hybrid nanostructures such as nanowires, nanorods, and nanotubes. The combination of organic and inorganic components in a 1D manner has been an increasingly expanding research field because the synergistic behavior of organic-inorganic materials is bound directly to the charming characteristics of 1D nanomaterials. These are responsible for the many novel optical and electrical properties, hierarchical superstructures, functions, and versatile applications that have been achieved. In this article, after justifying the interest in developing 1D organic-inorganic hybrid nanomaterials, we classify 1D hybrid nanostructures and review construction strategies that have been adopted, with a special focus on template-directed synthesis. In summary, we provide our personal perspectives on the future emphasis of the research on 1D organic-inorganic hybrid nanostructures.     

Nanofabrication of hybrid nanomaterials: Macroscopically aligned nanoparticles pattern via directed self-assembly of block copolymers

Periodic hybrid nanostructured materials based on aligned inorganic nanoparticles within self-assembled copolymer matrixes aimed to harness the collective properties of generated functional nanomaterials. The nanoparticles are desirable for their useful magnetic, optical, catalytic, and electronic properties owed to the quantum confinement effect. For instance, gold, palladium and platinum as nanoparticles, have shown significant change in the physiochemical properties in comparison to their bulk materials. If the nanoparticles are aligned into well-defined macroscopic periodic nanostructures in diverse of morphologies, the unique collective properties are significantly enhanced. These unique properties can be transformed to improve the performance of storage media, multi-contact tracks solar panels and optoelectronic devices. Within this review, the nanofabrication tools will be presented as an alternative route to conventional top-down methods for the fabrication of periodic nanostructured hybrid materials. A simple approach is reviewed to fabricate periodic nanostructured hybrid systems based on the directed assembly of inorganic nanoparticles into well-defined periodic three-dimensional nanostructures provided by the self-assembling ability of block copolymers. The fabrications of varieties morphologies and the formation mechanism at different dimensions will be discussed as well as the characterization techniques. Finally, several applications of the proposed hybrid nanostructures are highlighted for the next generation of miniaturized devices.     

Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0 0 0 1) layers

Quasi-free-standing monolayer and bilayer graphene is grown on homoepitaxial layers of 4H-SiC. The SiC epilayers themselves are grown on the Si-face of nominally on-axis semi-insulating substrates using a conventional SiC hot-wall chemical vapor deposition reactor. The epilayers were confirmed to consist entirely of the 4H polytype by low temperature photoluminescence. The doping of the SiC epilayers may be modified allowing for graphene to be grown on a conducing substrate. Graphene growth was performed via thermal decomposition of the surface of the SiC epilayers under Si background pressure in order to achieve control on thickness uniformity over large area. Monolayer and bilayer samples were prepared through the conversion of a carbon buffer layer and monolayer graphene respectively using hydrogen intercalation process. Micro-Raman and reflectance mappings confirmed predominantly quasi-free-standing monolayer and bilayer graphene on samples grown under optimized growth conditions. Measurements of the Hall properties of Van der Pauw structures fabricated on these layers show high charge carrier mobility (>2000 cm²/Vs) and low carrier density (<0.9 × 10¹³ cm⁻²) in quasi-free-standing bilayer samples relative to monolayer samples. Also, bilayers on homoepitaxial layers are found to be superior in quality compared to bilayers grown directly on SI substrates.     

Facile synthesis 3D flexible core-shell graphene/glass fiber via chemical vapor deposition

Direct deposition of graphene layers on the flexible glass fiber surface to form the three-dimensional (3D) core-shell structures is offered using a two-heating reactor chemical vapor deposition system. The two-heating reactor is utilized to offer sufficient, well-proportioned floating C atoms and provide a facile way for low-temperature deposition. Graphene layers, which are controlled by changing the growth time, can be grown on the surface of wire-type glass fiber with the diameter from 30 nm to 120 um. The core-shell graphene/glass fiber deposition mechanism is proposed, suggesting that the 3D graphene films can be deposited on any proper wire-type substrates. These results open a facile way for direct and high-efficiency deposition of the transfer-free graphene layers on the low-temperature dielectric wire-type substrates.

PACS

81.05.U-; 81.07.-b; 81.15.Gh     

One-dimensional hybrid nanostructures: synthesis via layer-by-layer assembly and applications

Assembly techniques are being intensely sought for preparing nanocomposites with tunable compositions and structures. Compared to other assembly techniques, the layer-by-layer (LBL) technique, which is based on the electrostatic attraction between oppositely charged species, provides a simple, versatile and powerful method to synthesize various types of one-dimensional (1D) hybrid nanostructures. In this review, we begin with the developments in the LBL synthesis of nanocomposites, with a focus on our recent results for synthesizing 1D hybrid nanostructures via LBL assembly. Compared to previous LBL processes, we conducted the in situ reaction on the surface of 1D nanostructures via electrostatic attraction between oppositely charged 1D nanostructures and ions in the solution in an attempt to produce 1D hybrid nanostructures. Moreover, these core-shell nanostructures can be transformed into nanotubes by the removal of the templates. The as-synthesized 1D hybrid nanostructures and nanotubes with tunable composition exhibited enhanced performance for various applications such as gas sensors, lithium-ion batteries and cellular imaging.     

Nano-engineering of high-performance PA6.6 nanocomposites by the integration of CVD-grown carbon fiber on graphene as a bicomponent reinforcement by melt-compounding

In this study, long carbon nanofibers (CNFs) were grown on graphene nanoplatelets (GNPs) by chemical vapor deposition (CVD) technique to develop three-dimensional (3D) bicomponent nanostructures. The structure and properties of graphene before and after CVD process were investigated in details. X-ray photoelectron analysis depicted the formation of Fe-C bonds by the deposition of carbon atoms on the catalyst surface of Fe₂O₃. This hybrid additive was firstly used as a reinforcing agent in melt compounding to fabricate PA6.6-based nanocomposites with enhanced mechanical and thermal properties. Both GNP and CNF-GNP have enough surface oxygen functional groups to improve the interfacial interactions with polyamide matrix and thus provide good wettability. Also, both neat GNP and its bicomponent additive with CNF also acted as a nucleating agent and allowed the crystal growth in nanocomposite structure. Homogeneous dispersion of nanoparticles was achieved by using thermokinetic mixer during compounding by applying high shear rates. Mechanical results showed that 23 and 34% improvement in flexural and tensile modulus values, respectively, was attained by the addition of 0.5 wt % CNF-GNP hybrid additive. The heat distortion temperature and Vicat softening temperature of the resulting PA6.6 nanocomposites were improved compared to neat PA6.6 material indicating performance enhancement at higher service temperature conditions. CNF was successfully grown on Fe-loaded GNP by CVD method and this hybrid additive was compounded with PA6.6 by melt-mixing process. Mechanical results showed that 34% improvement in tensile modulus value was attained by the addition of 0.5 wt % CNF-GNP hybrid additive because it acted as a nucleating agent and allowed the crystal growth in the nanocomposite structure. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48347.     

Microwave self-assembly of 3D graphene-carbon nanotube-nickel nanostructure for high capacity anode material in lithium ion battery

We report a microwave-assisted synthesis of a self-assembled three-dimensional graphene-carbon nanotube-nickel (3D G-CNT-Ni) nanostructure, which can be used as a high capacity anode material in lithium-ion batteries (LIBs). The unique 3D G-CNT-Ni nanostructure shows that CNTs are grown on graphene sheets through tip growth mechanism by Ni nano-particles. Bunches of CNTs and graphene sheets produce 3D network nanostructures with ultrahigh surface area, a large number of activation sites, and efficient ion pathways, all of which are crucial for high capacity anode materials in LIBs. The synthesized 3D nanostructure maintains a reversible specific capacity of 648.2 mA h/g after 50 cycles at a current density of 100 mA/g, as high capacity electrode structures in LIBs.     

Templating of inorganic nanomaterials by biomacromolecules and their assemblies

During the past decade biomacromolecules attracted tremendous attention as versatile materials for self-assembly, nanoconstruction, and templating. An increasing number of reports highlights creative applications of DNA, proteins, and their assemblies for construction of materials, which synthesis by traditional top-down techniques is not possible. This review summarizes various aspects of the application of biomacromolecules and their self-organized structures for building-up inorganic nanomaterials of different complicity by metallization or mineralization of natural templates. The central focus of the review is given to DNA-templated and DNA-directed synthesis of nanostructures, as the progress in the utilization of DNA for nanoconstruction is most considerable.     

An all-graphene based transparent and flexible field emission device

All-graphene based cathode and anode structures were fabricated and their application as a flexible and transparent field emission device is presented. The graphene film was grown on a Cu foil by thermal chemical vapor deposition and later transferred to a polymer substrate through a hot press lamination technique. Multiwall carbon nanotubes (MWCNTs) were spin-coated onto a graphene film on a transparent, flexible substrate to form the cathode of the field emission device. A green-phosphor coated graphene-PET film was used as the anode. The device showed good transparency and flexibility as well as giving an appreciable emission current. The simple processing techniques used can easily be upgraded to a larger scale and be tailored for any transparent and flexible substrate. The device offers exciting applications of carbon nanostructures in foldable electronics.