Stability Of Graphene Nanoribbons Research Articles

Impacts of graphene nanoribbon dispersion and stability on the mechanical and hydration properties of cement paste: Insights from surfactant-assisted ultrasonication

In this study, we aim to evaluate the different dispersion methods that affect the dispersion behavior of graphene nanoribbons (GNRs) and to conduct a contrastive analysis of the different surfactants that influence the dispersion and stability of GNRs in deionized (DI) water and alkaline solution. Moreover, we studied uniformly dispersed GNRs with respect to the hydration, mechanical properties, and microstructure of the cement paste. Owing to the surface defects of the GNRs, electrostatic repulsion was sufficient to overcome the van der Waals force and provide a long-term period of high stability. The results show that by using SPs and 60 min of ultrasonication, the dispersibility of GNRs improved by 8.5 % and 25.7 % in DI water and alkaline solution, respectively. Uniformly dispersed GNRs accelerate the hydration and C-S-H polymerization, resulting in significant increases in compressive strength and splitting tensile strength by 17 % and 33 %, respectively, and reduced porosity by 14.6 % after 28 days of curing.

Highly efficient sers performance from the silver nanoparticles/graphene nanoribbons/ cellulose paper

Introduction: Metal/graphene heterojunction structure has been one of the most crucial tools in the growth of high-performance Surface-enhanced Raman spectroscopy (SERS) platform, which is appropriate for sensing applications. In this research, we developed a SERS platform, graphene nanoribbons (GNRs) decorated silver nanoparticles (AgNPs) on cellulose paper substrate, in which GNRs was synthesized by wet chemical based on unzipping process of Multi-walled carbon nanotubes (MWCNTs), then GNRs hybridized with AgNPs through magnetron sputtering method.
 Methods: The morphology of graphene nanoribbons coated-Ag (AgNPs@GNRs) was analyzed by field emission scanning electronic microscopy (FESEM) and transmission electron microscopy (TEM). The quality and thermal stability of GNRs were characterized using thermogravimetric analysis. Besides, its structure and quality were also characterized by Raman spectroscope.
 Results: The results show that the unzipping process of MWCNTs to form GNRs was strongly affected by dispersing time and stirring temperature. The suitable condition creating the Graphene Nanoribbons using MWCNTs was the dispersing time of 10 mins in an acid environment, stirring in 30 mins at room temperature and in 45 min at 100°C. Moreover, SERS platform of AgNPs@GNRs exhibit the outstanding SERS signal enhancement with rhodamine 6G (R6G) low concentration of 10-5 M compared with pristine graphene and silver thin film. This could be attributed to the synergistic effect between AgNPs, GNRs and analyze molecules based on the enhancement of electromagnetic mechanism (EM) and chemical mechanism (CM), which plays a vital role in promoting the improvement SERS behavior.
 Conclusion: Ag NPs assembled onto graphene nanoribbons/ cellulose paper substrate could also serve as SERS active substrates for practical applications in various fields at trace levels.

Oxidization stability of atomically precise graphene nanoribbons

The stability of graphene nanoribbons (GNRs) against oxidation is critical for their practical applications. Here we study both the thermal stability and the oxidation process of the ambient-exposed armchair GNRs with a width of seven carbon atoms (7-aGNR), grown on an Au(111) surface. The atomic scale evolution of the armchair edges and the zigzag ends of the aGNRs after annealing at different temperatures are revealed by using scanning tunneling microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and first-principles calculations. We observe evidence that the zigzag ends start to be oxidized and decomposed at 180 \ifmmode^\circ\else\textdegree\fi{}C, while the armchair edges are intact at 430 \ifmmode^\circ\else\textdegree\fi{}C but become oxidized at 520 \ifmmode^\circ\else\textdegree\fi{}C. Two different oxygen species are identified at the armchair edges, namely the hydroxyl pair and the epoxy bonding motif with one oxygen bonded to two edge carbons. These oxidization species modify the electronic properties of the pristine 7-aGNRs, with a band-gap reduction from 2.6 to 2.3 eV and 1.9 eV for the hydroxyl pair- and epoxy-terminated edges, respectively. These findings demonstrate the oxidation stability of both the zigzag and armchair edges of GNRs, and they provide an opportunity to harness the high density of edge atoms in applications such as GNR-based high-temperature oxygen sensors.

High vacuum synthesis and ambient stability of bottom-up graphene nanoribbons.

Carbon-based nanomaterials such as graphene are at a crucial point in application development, and their promising potential, which has been demonstrated at the laboratory scale, must be translated to an industrial setting for commercialization. Graphene nanoribbons in particular overcome one limitation of graphene in some electronic applications because they exhibit a sizeable bandgap. However, synthesis of bottom-up graphene nanoribbons is most commonly performed under ultra-high vacuum conditions, which are costly and difficult to maintain in a manufacturing environment. Additionally, little is known about the stability of graphene nanoribbons under ambient conditions or during transfer to technologically relevant substrates and subsequent device processing. This work addresses some of these challenges, first by synthesizing bottom-up graphene nanoribbons under easily obtained high vacuum conditions and identifying water and oxygen as the residual gases responsible for interfering with proper coupling during the polymerization step. And second, by using Raman spectroscopy to probe the stability of nanoribbons during storage under ambient conditions, after transfer to arbitrary substrates, and after fabrication of field-effect transistor devices, which shows structurally intact nanoribbons even several months after synthesis. These findings demonstrate the potential of graphene nanoribbon technologies by addressing some limitations which might arise in their commercialization.

Super flexibility and stability of graphene nanoribbons under severe twist.

The structure and properties of nanostructured materials formed upon deformation are determined to a great extent by the states of stress and strain and the regimes of deformation. The nanostructures and properties of the graphene nanoribbons (GNRs) subjected to severe twist deformation were studied using molecular dynamics (MD) simulations. The GNRs show superflexibility and withstanding severe twisting, which leads to GNR nanostructures transforming from flat to twisted and then getting thoroughly coiled and fail. The appearance of a decreasing Young's moduli of the GNRs was observed with increasing rotation in general. The chirality has little effect on the Young's moduli of flat GNRs, whereas the degree of the GNR aspect ratio does. The severely twisted GNRs follow a similar rule but with slightly decreased Young's moduli (∼0.1 TPa), which demonstrates that the twisted GNRs maintain their stiff nature. The electronic properties of the GNRs under severely twisted conditions also show slight changes studied by density-functional theory (DFT) simulations. The stable mechanical properties and structure changes of GNRs under severely twisted conditions makes them a good candidate in some polymers, enhancing the load transfer and interfacial bonding by adding the twisted GNRs.

Influence of Stone–Wales defects orientations on stability of graphene nanoribbons under a uniaxial compression strain

Abstract In this study, the buckling of graphene nanoribbons (GNRs) containing Stone–Wales (SW) defects is investigated by using molecular dynamics (MD) simulation. The orientation and concentration of SW defects are taken into account to evaluate buckling onset strain of GNRs. It is shown that the SW defect orientation has an influence on stability of GNRs under compression. Furthermore, it is explored that the shape of the deformed GNRs depends on the SW defect concentrations, and their orientations.

Bending mode fluctuations and structural stability of graphene nanoribbons

We analyze the thermal fluctuations of a narrow graphene nanoribbon. Using a continuum membranelike model in the harmonic approximation, we study the height-height correlation functions and the destabilization modes corresponding to two different boundary conditions: fixed and free edges. For the first case, the thermal spectrum has a gap and the correlations along the ribbon decay exponentially. Thermal fluctuations produce only local perturbations of the flat situation. However, the long range crystalline order is not distorted. For free edges the situation changes as thermal excitations are gapless. The low energy spectrum decouples into a bulk and an edge excitation. The bulk excitation tends to destabilize the crystalline order producing a homogeneous rippling. Furthermore, we can relate the edge mode to a precluding perturbation leading to scrolled edges, as seen in suspended graphene samples. We also analyze the implications of our results in the thermal conductivity of graphene nanoribbons.

First-principles calculations of graphene nanoribbons in gaseous environments: Structural and electronic properties

The stability of graphene nanoribbons in the presence of typical atmospheric molecules is systematically investigated by means of density functional theory. We calculate the edge formation free energy of five different edge configurations passivated by H, H$_2$, O, O$_2$, N$_2$, CO, CO$_2$, and H$_2$O, respectively. In addition to the well known hydrogen passivated armchair and zig-zag edges, we find the zig-zag edge saturated by oxygen atoms to be particularly stable under atmospheric conditions. Saturation by oxygen leads to the formation of metallic states strictly localized on the oxygen atoms. Finally, the vibrational spectrum of the hydrogen and oxygen passivated ribbons are calculated and compared.

Structure and stability of graphene nanoribbons in oxygen, carbon dioxide, water, and ammonia

We determine, by means of density functional theory, the stability and the structure of graphene nanoribbon (GNR) edges in presence of molecules such as oxygen, water, ammonia, and carbon dioxide. As in the case of hydrogen-terminated nanoribbons, we find that the most stable armchair and zigzag configurations are characterized by a non-metallic/non-magnetic nature, and are compatible with Clar's sextet rules, well known in organic chemistry. In particular, we predict that, at thermodynamic equilibrium, neutral GNRs in oxygen-rich atmosphere should preferentially be along the armchair direction, while water-saturated GNRs should present zigzag edges. Our results promise to be particularly useful to GNRs synthesis, since the most recent and advanced experimental routes are most effective in water and/or ammonia-containing solutions.

Electronic properties and stability of graphene nanoribbons: An interpretation based on Clar sextet theory

The electronic structure and the stability of hydrogen-terminated graphene nanoribbons (GNRs) are evaluated by means of gradient-corrected density functional theory calculations and rationalized by application of Clar’s theory of the aromatic sextet. Our results show that the electronic properties of GNRs are deeply related to the description of the bonding pattern provided from the valence bond picture obtained by application of Clar’s theory. This finding applies either to zigzag-, armchair- and chiral-terminated GNRs and can be expected to have strong impact in the interpretation of experiments and on the design of devices based on nanostructured graphene materials.

Stability analysis of graphene nanoribbons by molecular dynamics simulations

AbstractIn this work, stability of graphene nanoribbons are investigated using molecular dynamics. Simulations include heating armchair and zigzag‐edged nanoribbons of widths varying between one and nine hexagonal rings until the bonds between carbon atoms start to break. Breaking temperatures and binding energies per atom for different widths are presented for both armchair and zigzag‐edged cases. A nontrivial relation between stability and width is observed and discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)