Low-dimensional Carbon Nanostructures Research Articles

Revealing the Influence of Molecular Chemisorption Direction on the Reaction Selectivity of Dehalogenative Coupling on Au(111): Polymerization versus Cyclization.

The control of reaction selectivity is of great interest in chemistry and depends crucially on the revelation of key influencing factors. Based on well-defined molecule-substrate model systems, various influencing factors have been elucidated, focusing primarily on the molecular precursors and the underlying substrates themselves, while interfacial properties have recently been shown to be essential as well. However, the influence of molecular chemisorption direction on reaction selectivity, as a subtle interplay between molecules and underlying substrates, remains elusive. In this work, by a combination of scanning tunneling microscopy imaging and density functional theory calculations, we report the influence of molecular chemisorption direction on the reaction selectivity of two types of dehalogenative coupling on Au(111), i.e., polymerization and cyclization, at the atomic level. The diffusion step of a reactive dehalogenated intermediate in two different chemisorption directions was theoretically revealed to be the key to determining the corresponding reaction selectivity. Our results highlight the important role of molecular chemisorption directions in regulating the on-surface dehalogenative coupling reaction pathways and products, which provides fundamental insights into the control of reaction selectivity by exploiting some subtle interfacial parameters in on-surface reactions for the fabrication of target low-dimensional carbon nanostructures.

Separation of Halogen Atoms by Sodium from Dehalogenative Reactions on a Au(111) Surface.

On-surface dehalogenative reactions have been promising in the construction of nanostructures with diverse morphologies and intriguing electronic properties, while halogen (X), as the main byproduct, often impedes the formation of extended nanostructures and property characterization, and the reaction usually requires high C-X activation temperatures, especially on relatively inert Au(111). Enormous efforts in precursor design, halogen-to-halide conversion, and the introduction of extrinsic metal atoms have been devoted to either eliminating dissociated halogens or reducing reaction barriers. However, it is still challenging to separate halogens from molecular systems while facilitating C-X activation under mild conditions. Herein, a versatile halogen separation strategy has been developed based on the introduction of extrinsic sodium (Na) into dehalogenative reactions on Au(111) as model systems that both isolates the dissociated halogens and facilitates the C-Br activation under mild conditions. Moreover, the combination of scanning tunneling microscopy imaging and density functional theory calculations reveals the formation of sodium halides (NaX) from halogens in these separation processes as well as the reduction in reaction temperatures and barriers, demonstrating the versatility of extrinsic sodium as an effective "cleaner" and "dehalogenator" of surface halogens. Our study demonstrates a valuable strategy to facilitate the on-surface dehalogenative reactions, which will assist in the precise fabrication of low-dimensional carbon nanostructures.

Passively Q-Switched Thulium-Holmium Doped Fibre Laser with Electrochemical Exfoliation Graphene in Chitin Based Passive Saturable Absorber

Recent years saw low-dimensional carbon nanostructures like graphene as excellent saturable absorber (SA) for its unique electric and optical properties. Graphene exhibits ultrafast recovery times and high damage thresholds and can be manufactured by relatively simple methods. In this work, Graphene was synthesized using the electrochemical exfoliation (ECE) method. Chitin biopolymer was used to develop graphene-based SA as a more environmentally friendly alternative to conventional synthetic polymers. The fabricated passive SA was then integrated into Thulium-Holmium-doped fibre laser (THDFL) in ring cavity for pulsed laser generation via Q-switching. The optical and physical properties of the graphene-based SA were characterized using Raman spectroscopy, field emission scanning electron microscopy (FESEM) and energy-dispersive x-ray spectroscopy (EDS). Q-switched pulse was successfully demonstrated using the fabricated graphene SAs. ECE graphene-chitin SA generated a Q-switched pulse region at 2 micro-metre with the repetition rate and shortest pulse width of 67.78 kHZ and 10.03 micro-second, respectively. The signal-to-noise ratio (SNR) values obtained was 40 dB indicating high stability of the pulse laser-generated. This study demonstrated the potential of graphene embedded in chitin biopolymer as a sustainable and environmentally friendly SA for a wide range of applications, particularly for pulsed fibre lasers.

Size effect on transverse free vibrations of ultrafine nanothreads

Due to their unique properties and appealing applications, low dimensional sp3 carbon nanostructures have attracted increasing attention recently. Based on the beam theory and atomistic studies, this work carries out a comprehensive investigation on the vibrational properties of the ultrathin carbon nanothreads (NTH). Size effect is observed in transverse free vibrations of NTHs. To quantify such effects, the modified couple stress theory (MCST) is utilized to modify the Timoshenko beam theory. According to the first four order frequencies of NTHs from atomistic simulations, the critical length scale parameter of MCST is calibrated as 0.1 nm. It is shown that MCST has minor effect on the first four order modal shapes, except for the clamped boundary. MCST makes the modal shapes at the clamped boundary closer to those observed in atomistic simulations. This study suggests that to some extent the MCST-based Timoshenko beam theory can well describe the transverse vibration characteristics of the ultrafine NTHs, which are helpful for designing and fabricating the NTH-based nanoscale mechanical resonators.

Tensile properties of functionalized carbon nanothreads

Low dimensional sp3 carbon nanostructures have attracted increasing attention recently, due to their unique properties and appealing applications. Based on in silico studies, this work exploits the impacts from functional groups on the tensile properties of carbon nanothreads (NTH) – a new sp3 carbon nanostructure. It is found that functional groups will alter the local bond configuration and induce initial stress concentration, which significantly reduces the fracture strain/strength of NTH. Different functional types lead to different local bond re-configurations, and introduce different impacts on NTH. Further studies reveal that the tensile properties decreases generally when the content of functional groups increases. However, some NTHs with higher content of functional groups exhibit higher fracture strain/strength than their counterparts with lower percentage. Such observations are attributed to the synergetic effects from the sample length, self-oscillation, and distribution of functional groups. Simulations show that the tensile behaviour of NTH with the same functional percentage differs when the distribution pattern varies. Overall, ethyl groups are found to induce larger degradation on the tensile properties of NTH than methyl and phenyl groups. This study provides a comprehensive understanding of the influence from functional groups, which should be beneficial to the engineering applications of NTH.

Structural effect of Low-dimensional carbon nanostructures on Long-term stability of dye sensitized solar cells

A major challenge in upscaling and commercializing dye-sensitized solar cells (DSSC) is to simultaneously rely on a robust photoconversion efficiency (PCE) along with long-term device stability. Two-dimensional (2D) nanocarbon materials are known to improve the PCE and stability of devices made of hybrid nanocomposite photoanodes. However, there is inadequate knowledge on how the morphology of 2D nanocarbon materials plays an important role in improving photovoltaic (PV) performance and stability. Here we report the comparative effect on the PV performance and the long-term stability of DSSCs made of optimal loadings of few-layer graphene (FLG) flakes and graphene nanoribbons (GNR) into the mesoporous TiO2 active layer. DSSCs were fabricated by using standard nanocrystalline TiO2, GNR-TiO2 and FLG-TiO2 hybrid mesoporous films as anodes and subjected to continuous visible light irradiation to monitor their long-term stability. Results show that the optimized incorporation of GNR (0.005 wt%) and FLG (0.010 wt%) in the mesoporous TiO2 active layer enhances the PCE by 34% and 21% compared to pristine TiO2, respectively. Moreover, the operational stability of hybrid devices shows a 51.6% (for GNR-TiO2) and a 10% (for FLG-TiO2) sustained higher PCE than the device based on bare TiO2, after 273 h of continuous one sunlight soaking. The electrochemical impedance spectroscopy (EIS) and transient photovoltage decay were studied to investigate how GNR strikingly reduces degradation of device performance as compared to its counterpart FLG-TiO2 and TiO2 based cells. This significant enhancement can be attributed to the structural modifications induced by GNR within the TiO2 photoanode, which improves the electron lifetime and reduces non-radiative carrier recombination.

Role of low-dimensional carbon nanostructures in hybrid material as anticorrosive coating

In this work, different low-dimensional carbon nanostructures (graphite oxide, graphene oxide and amino-functionalized graphene oxide and graphite oxide) integrated into a hybrid, organic-inorganic matrix, were developed, obtaining different nanocomposite coatings. The hybrid matrix was obtained from an inorganic component, tetraethyl orthosilicate, and an organic composition resin, diglycidyl ether bisphenol-A. Each of the different coatings were separately applied on AISI 1018 carbon steel surfaces. The corrosion test was carried out by Electrochemical Impedance Spectroscopy on the coated metal in two different media, saline and acidic. The resistance to charge transfer was higher for coating containing graphene oxide in both electrolytes. A comparison between the coating's performance containing graphite oxide and graphene oxide showed that the exfoliation of graphite oxide is important to have a greater distribution and intercalation of the low dimensionality sheets inside the hybrid matrix up to form a uniform protective barrier. Wear test were carried out and structural stability of the coatings after 100 cycles was demonstrated, showing the persistent SiOSi groups produce a protection against corrosion to AISI 1018 carbon steel.

On-Surface Synthesis of sp-Carbon Nanostructures.

The on-surface synthesis of carbon nanostructures has attracted tremendous attention owing to their unique properties and numerous applications in various fields. With the extensive development of scanning tunneling microscope (STM) and noncontact atomic force microscope (nc-AFM), the on-surface fabricated nanostructures so far can be characterized on atomic and even single-bond level. Therefore, various novel low-dimensional carbon nanostructures, challenging to traditional solution chemistry, have been widely studied on surfaces, such as polycyclic aromatic hydrocarbons, graphene nanoribbons, nanoporous graphene, and graphyne/graphdiyne-like nanostructures. In particular, nanostructures containing sp-hybridized carbons are of great advantage for their structural linearity and small steric demands as well as intriguing electronic and mechanical properties. Herein, the recent developments of low-dimensional sp-carbon nanostructures fabricated on surfaces will be summarized and discussed.

Chemical Identification and Bond Control of π-Skeletons in a Coupling Reaction.

Highly unsaturated π-rich carbon skeletons afford versatile tuning of structural and optoelectronic properties of low-dimensional carbon nanostructures. However, methods allowing more precise chemical identification and controllable integration of target sp-/sp2-carbon skeletons during synthesis are required. Here, using the coupling of terminal alkynes as a model system, we demonstrate a methodology to visualize and identify the generated π-skeletons at the single-chemical-bond level on the surface, thus enabling further precise bond control. The characteristic electronic features together with localized vibrational modes of the carbon skeletons are resolved in real space by a combination of scanning tunneling microscopy/spectroscopy (STM/STS) and tip-enhanced Raman spectroscopy (TERS). Our approach allows single-chemical-bond understanding of unsaturated carbon skeletons, which is crucial for generating low-dimensional carbon nanostructures and nanomaterials with atomic precision.

Effects of geometric variations on buckling properties of carbon nanostructures: A finite element analysis

Critical Bucking Load (CBL) is one of the essential parameters to describe the mechanic stabilities of materials, e.g. the low-dimensional carbon nanostructures. While the CBL of pristine carbon nanotubes have been previously investigated using the quantum mechanics-based calculations, the effect of geometrical variation on the CBL of carbon nanomaterials is rarely reported since it need considerably large atomic models, which needs high computational cost. In this study, both the analytical and Finite Element (FE) methods were employed to systematically explore the impact of atomic vacancies, shapes and heterostructures on the CBLs of carbon nanomaterials with the acceptable computational cost. Our studies on the pristine CNTs first demonstrate the validity of the method we used. After that, the systems with mono-/bi-/tri-/pinole-vacancies either on nanocones, nanotube, linearly-joined nanotubes or angle-adjoined were simulated and analyzed. Our results reveal that the CBL values decrease with the increase of the aspect ratio of all considered nanomaterials. Based on the obtained results, the CBL of nanocone with the aspect ratio of 1, reduces significantly, from 50 nN to 10 nN when the aspect ratio is 3. The CBL of homogeneous, capped, and joint CNTs reduces to below 2 nN when the aspect ratio is above 14. The introduction of geometric variations can greatly affect the CBL values. The larger atomic vacancy has more serious impact on the CBLs. The most highlighted impact is for the pinhole vacancy where the CBL reduces to up to 70% of the original value. Our studies on linearly-joint and angle-joint carbon hybrids further demonstrate that the CBL can also be affected by the boundary conditions and joint structures of the hybrids.

Thermoelectric Applications of Low-Dimensional Carbon Nanostructures with Acoustically Mismatched Boundaries

Thermoelectric applications of low-dimensional carbon nanostructures offer new ways to manipulate the electron and phonon properties of a given material. High-resolution Raman spectroscopy of ultra-thin silicon-on-insulator structures reveals multiple peaks in the spectral range from 50 cm−1 to 160 cm−1. The peak positions are consistent with the theoretical predictions and indicate the confined nature of phonon-transport in thin films and superlattices with a finite acoustic mismatch between layers. This opens up a novel turning capability for optimization of the thermoelectric properties of low-dimensional structures.

(Invited) Fundamental Understanding of Faradaic and Non-Faradaic Processes in Carbon-Based Supercapacitors

Nanostructured carbon materials, such as graphene and nanoporous carbon, have become increasingly prominent for use as electrodes in supercapacitors, owing to their high specific and volumetric surface area and good electrical conductivity. A conventional understanding of supercapacitors relates the high power to fast ion accumulation at the polarized electrode interface, forming the so-called electric double layer, and the low energy to limited electrode surface area (SA). As such, low-dimensional carbon nanostructures have been extensively explored. However, anomalous and nonlinear relationships between observed capacitances and SAs have prompted a need to revise our mechanistic understanding of charge storage. In this talk, we present our recent findings regarding charge storage mechanisms, along with possible faradaic reactions, in carbon-based supercapacitors from combined quantum mechanical and classical molecular dynamics simulations. Our first-principles studies suggest that the total interfacial capacitance (CT ) of graphene-based supercapacitors is determined from both electrode (CQ ) and electric double layer (CD ) capacitances which are in series. It has also been demonstrated that the CQ , and thereby CT , can be significantly enhanced as a result of changes to the electronic structure through chemical functionalization, doping, and/or structural deformation. Furthermore, our voltammetric molecular dynamics simulations have revealed the complex non-equilibrium processes associated with extreme confinement of ionic liquid electrolytes within subnanometer pores. Based on these results, we will also discuss a mechanistic perspective centered around ion reorganization kinetics, particularly the dependence of ion migration efficiency, and relatedly, the capacitance, on pore morphology. This talk will also briefly touch on possible faradaic reactions that may cause self-discharge.

(Invited) Fundamental Understanding and Optimal Design of Low-Dimensional Carbon Nanomaterials for Supercapacitors

Nanostructured carbon materials, such as graphene and nanoporous carbon, have become increasingly prominent for use as electrodes in supercapacitors, owing to their high specific and volumetric surface area and good electrical conductivity. A conventional understanding of supercapacitors relates the high power to fast ion accumulation at the polarized electrode interface, forming the so-called electric double layer, and the low energy to limited electrode surface area (SA). As such, low-dimensional carbon nanostructures have been extensively explored. However, anomalous and nonlinear relationships between observed capacitances and SAs have prompted a need to revise our mechanistic understanding of charge storage. In this talk, we present our recent findings regarding charge storage mechanisms in carbon-based supercapacitors from combined quantum mechanical and classical molecular dynamics simulations. Our first-principles studies suggest that the total interfacial capacitance (CT ) of graphene-based supercapacitors is determined from both electrode (CQ ) and electric double layer (CD ) capacitances which are in series. It has also been demonstrated that the CQ , and thereby CT , can be significantly enhanced as a result of changes to the electronic structure through chemical functionalization, doping, and/or structural deformation. Furthermore, our voltammetric molecular dynamics simulations have revealed the complex non-equilibrium processes associated with extreme confinement of ionic liquid electrolytes within subnanometer pores. Based on these results, we will also discuss a mechanistic perspective centered around ion reorganization kinetics, particularly the dependence of ion migration efficiency, and relatedly, the capacitance, on pore morphology.

On-Surface Synthesis of Carbon Nanostructures.

Novel carbon nanomaterials have aroused significant interest owing to their prospects in various technological applications. The recently developed on-surface synthesis strategy provides a route toward atomically precise fabrication of nanostructures, which paves the way to functional molecular nanostructures in a controlled fashion. A plethora of low-dimensional nanostructures, challenging to traditional solution chemistry, have been recently fabricated. Within the last few decades, an increasing interest and flourishing studies on the fabrication of novel low-dimensional carbon nanostructures using on-surface synthesis strategies have been witnessed. In particular, carbon materials, including fullerene, carbon nanotubes, and graphene nanoribbons, are synthesized with atomic precision by such bottom-up methods. Herein, starting from the basic concepts and progress made in the field of on-surface synthesis, the recent developments of atomically precise fabrication of low-dimensional carbon nanostructures are reviewed.

Simulation of mechanical parameters of graphene using the DREIDING force field

Molecular mechanics/molecular dynamics (MM/MD) methods are widely used in computer simulations of deformation (including buckling, vibration, and fracture) of low-dimensional carbon nanostructures (single-layer graphene sheets (SLGSs), single-walled nanotubes, fullerenes, etc). In MM/MD simulations, the interactions between carbon atoms in these nanostructures are modeled using force fields (e.g., AIREBO, DREIDING, MM3/MM4). The objective of the present study is to fit the DREIDING force field parameters (see Mayo et al. J Phys Chem 94:8897–8909, 1990) to most closely reproduce the mechanical parameters of graphene (Young’s modulus, Poisson’s ratio, bending rigidity modulus, and intrinsic strength) known from experimental studies and quantum mechanics simulations since the standard set of the DREIDING force field parameters (see Mayo et al. 1990) leads to unsatisfactory values of the mechanical parameters of graphene. The values of these parameters are fitted using primitive unit cells of graphene acted upon by forces that reproduce the homogeneous deformation of this material in tension/compression, bending, and fracture. (Different sets of primitive unit cells are used for different types of deformation, taking into account the anisotropic properties of graphene in states close to failure.) The MM method is used to determine the dependence of the mechanical moduli of graphene (Young’s modulus, Poisson’s ratio, and bending rigidity modulus) on the scale factor. Computer simulation has shown that for large linear dimensions of SLGSs, the mechanical parameters of these sheets are close to those of graphene. In addition, computer simulation has shown that accounting for in-layer van der Waals forces has a small effect on the value of the mechanical moduli of graphene.

Special Issue Dedicated to Prof. Daoben Zhu's 75th Birthday

First of all, I, together with my colleagues and friends, would like to send our best wishes to Professor Daoben Zhu on the occasion of his 75th birthday. Professor Zhu began his chemistry studies at East China University of Science and Technology (ECUST) in 1965 and graduated in 1968. He then joined the Institute of Chemistry, Chinese Academy of Sciences as an assistant professor, and was promoted to associate professor in 1985 and professor at 1987. He was a visiting scholar at the Max-Planck Institute for Medical Research in Heidelberg, Germany, from 1977 to 1979. He again worked as a visiting scientist at the same Max-Planck Institute in 1985 and 1986. Professor Zhu is one of the pioneers in the area of molecular materials and devices in China. He has been the director of the CAS Key Laboratory of Organic Solids since its establishment. He and his co-workers have made remarkable contributions to interdisciplinary cutting-edge research areas including organic conductors and superconductors, functional Langmuir–Blodgett films, fullerene chemistry and physics, light-emitting materials and devices, organic semiconductors and devices, and organic thermoelectronic materials and devices. These research achievements have provided in-depth understanding of the electronic processes and related phenomena in organic solids, thus boosting research into molecular materials and devices. Professor Zhu has published two books and more than 1000 papers in scientific journals, which have received more than 24 000 citations, and has an H-index of 90. His research accomplishments have been well recognized by the scientific community. He has received National Natural Sciences of China second-class prizes five times, in 1988, 2002, 2004, 2007 and 2014. He was the winner of the Chinese Chemical Society—the China Petroleum and Chemical Corporation Chemical Contribution Award in 2008, and he won the Tan Kah Kee Science Award in chemistry in 2012. Professor Zhu was elected as a Chinese Academy of Sciences Academician in 1997 and a member of the World Academy of Sciences for the advancement of science in developing countries in 2009. In 2014 and 2015, Professor Zhu was selected by Thomson Reuters as one of the world's most influential scientific minds both in chemistry and materials science. Apart from doing scientific research, Professor Zhu has made great contributions to the administration and management of scientific research in China. Among the administration positions he has held, he was the director of the Institute of Chemistry, Chinese Academy of Sciences from 1992 to 2000, vice president of the National Natural Science Foundation of China from 2000 to 2007, president of the Chinese Chemical Society from 1994 to 1997, and vice president of the Chinese Materials Society from 2001 to 2005. He was the vice chairman of the second, fourth and fifth advisory committees of the National Basic Research Program of China (973 Program). He is now the vice chairman of the Academic Committee of Chinese Academy of Sciences (CAS) and the committee chair of the Academic Division of Chemistry, CAS. Professor Zhu has continuously supported and actively promoted scientific exchanges and collaborations between Chinese scientists and leading scientists across the world. We publish this special issue to celebrate the 75th birthday of Professor Zhu and express sincere thanks to him for his continuous support over many years. This special issue collects research communications, full research papers, and reviews that cover the following topics: organic semiconductors, doping of organic semiconductors and field-effect transistors, graphdiyne and carbon ene-yne nanoribbon, photovoltaic cells and photodetectors, bioelectronics, and organic nonlinear optical materials. We would like to take this opportunity to thank the distinguished authors who contributed to this special issue, and the editorial staff of Advanced Electronic Materials for enabling its publication. Professor Yuliang Li has worked at the Institute of Chemistry, Chinese Academy of Sciences since 1975. He was a visiting scholar in the Department of Chemistry at University of Amsterdam (The Netherlands) from 1987 to 1989, was a visiting professor at the Radiation Lab at University of Notre Dame (USA) from August 1998 to March 1999, and worked in the Department of Chemistry at the University of Hong Kong from September 1999 to February 2000. His research interests include the growth of low-dimensional and two-dimensional carbon nanostructures, covalently and non-covalently assembled molecular materials, and supramolecular chemistry.

Thermal Diffusivity of a Single Carbon Nanocoil: Uncovering the Correlation with Temperature and Domain Size

The helical geometries and polycrystalline-amorphous structure of carbon nanocoils (CNCs), an exotic class of low-dimensional carbon nanostructures, distinguish them from carbon nanotubes and graphene. These distinct structures result in very different energy transport from that in carbon nanotubes and graphene, leading to important roles in applications as wave absorbers, near-infrared sensors, and nanoelectromechanical sensors. Here we report a systematic study of the thermal diffusivity (α) and conductivity (κ) of CNCs from 290 to 10 K and uncover their property-structure aspects. Our room-temperature α study reveals a correlation between α and the line diameter (d): α = (5.43 × 104 × e-d/37.7 + 9.5) × 10-7 m2/s. Combined with the Raman-based grain size (La) characterization, α and La are correlated as α = [81.2 × (La - 3.32)1.5 + 9.5] × 10-7 m2/s. With temperature decreasing from 290 K to 10 K, α has a 1-1.6-fold increase, and κ shows a peak around 75 K. To best understand the defect level and polycrystalline-amorphous structure of CNCs, the thermal reffusivity (Θ = α-1) of CNCs is studied and compared with that of graphite and graphene foam from 290 K down to 10 K. Very interestingly, CNC's Θ linearly decreases with decreased temperature, while Θ of graphite and graphene foam have an exponential decrease. The extrapolated 0 K-limit Θ is determined by low-momentum phonon scattering and gives a structure domain size of CNC samples (d = 455, 353, and 334 nm) of 1.28, 2.03 and 3.24 nm. These sizes are coherent with the X-ray diffraction results (3.5 nm) and the Raman spectroscopy study and confirm the correlation among d, La, and α.

π-Plasmon model for carbon nano structures: Application to porphyrin

In traditional concept, the optical properties of semiconductors and semimetals near their fundamental optical band gaps are attributed to single excitations (such electron-hole pairs, excitons...). In our earlier article, we proposed the collective mechanism of π-plasmons for optical properties of low dimensional carbon nano structures. A simple way to calculate the peak positions of UV-vis absorption spectra was pointed out and gave a good agreement with experimental data. In this work we analyze different schemas to calculate the UV-vis absorption peaks. A new parameter k which characterizes the dependence of schema on geometry and number of carbon sites is defined. As an example, the case of porphyrin was investigated.

Physical properties of low-dimensionalsp2-based carbon nanostructures

This review focuses on the fundamental physical properties of low-dimensional carbon nanostructures (graphene, graphene nanoribbons, and carbon nanotubes), with an emphasis on understanding and utilizing the unique physical properties that make this class of materials ideal building blocks for future nanoscience and nanotechnology development. In depth discussions of the structural, electronic, vibrational, and transport properties of these carbon nanostructures from both theoretical and experimental standpoints provide a coherent and foundational overview for researchers interested in broader areas of carbon science and related noncarbon systems.

The Analytical Transmission Electron Microscopy: A Powerful Tool for the Investigation of Low-Dimensional Carbon Nanomaterials

Chemical and physical characterization of nanomaterials is essential to improve synthesis processes, for new technological and commercial applications, and to assess their toxicity through <i>in vitro</i> and <i>in vivo</i> studies. New nanomaterials and new synthesis processes are continuously tested and updated to exploit their innovative properties. In this paper, low-dimensional carbon nanostructure characterization was performed using analytical transmission electron microscopy. Conventional and advanced microscopy techniques, such as acquisition of high resolution images, nanobeam electron diffraction patterns, X-ray energy dispersion, and electron energy loss spectra, were used to determine the main physical and chemical properties of single wall and multiwall carbon nanotubes, graphene flakes, and amorphous carbon films. Through the resulting micrographs, diffraction patterns, and spectra, the main low-dimensional carbon nanostructures properties were determined in terms of structural defects and/or the presence of metallic or heavy elements, such as those used as catalyst or to decorate nanotubes. The obtained information is of crucial importance to investigate low-dimension nanomaterial biological activity.