Interlayer vacancy defects in AA-stacked bilayer graphene: Density functional theory predictions

© 2017 IOP Publishing Ltd.AA-stacked graphite and closely related structures, where carbon atoms are located in registry in adjacent graphene layers, are a feature of graphitic systems including twisted and folded bilayer graphene, and turbostratic graphite. We present the results of ab initio density functional theory calculations performed to investigate the complexes that are formed from the binding of vacancy defects across neighbouring layers in AA-stacked bilayers. As with AB stacking, the carbon atoms surrounding lattice vacancies can form interlayer structures with sp 2 bonding that are lower in energy than in-plane reconstructions. The sp 2 interlayer bonding of adjacent multivacancy defects in registry creates a type of stable sp 2 bonded 'wormhole' or tunnel defect between the layers. We also identify a new class of 'mezzanine' structure characterised by sp 3 interlayer bonding, resembling a prismatic vacancy loop. The V 6 hexavacancy variant, where six sp 3 carbon atoms sit midway between two carbon layers and bond to both, is substantially more stable than any other vacancy aggregate in AA-stacked layers. Our focus is on vacancy generation and aggregation in the absence of extreme temperatures or intense beams

Anion sensing with cobalt corrinoid grafted quartz crystal microbalances

Corrin macrocycles are well known for their interesting and multifaceted coordination chemistry at the axial positions of the cobalt center. In this work, the use of such cobalt corrinoids as sensitive elements for sorption based chemical sensors like the quartz crystal microbalance (QCM) is described for the first time. This approach of fast and reversible ion detection extends the versatility and applicability of this class of metal-containing ionophores and colorimetric indicators. QCMs were grafted with aquacyano and dicyano cobalt corrinoids and assessed in their sensing characteristics during exposure to cyanide, thiocyanate, and other ionic species as well as selected organic compounds. The liquid sensing characteristics of the corronoids were found to be excellent. Sensors reach equilibrium in <3 s from the stable baseline after analyte exposure and the responses are fully reversible. Sensors of high sensitivity and selectivity for cyanide have been obtained with detection limits at 1 μM. At the same time, the sensitivities to common organic compounds are negligible. The results demonstrate that corrin grafted QCMs exhibit enormous potential as chemical sensors for the detection of anions, especially cyanide, in aqueous samples

Cyclotetrahalo-p-phenylenes: simulations of halogen substituted cycloparaphenylenes and their interaction with C 60

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The role of charge distribution on the friction coefficients of epitaxial graphene grown on the Si-terminated and C-terminated faces of SiC

The friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients. © 2021 Elsevier LtdBAP059 117F476 Türkiye Bilimsel ve Teknolojik Araştirma Kurumu, TÜBITAKThis work was supported by the Scientific and Technological Research Council of Turkey (TÜBİTAK) under project Grant No. TÜBİTAK 117F476 and by Yaşar University Project Evaluation Commission (PEC) as part of the Project No. BAP059. The calculations were performed at the High Performance and Grid Computing Center (TRUBA Resources) of TÜBİTAK ULAKBİM. We would like to acknowledge Prof. Savas Berber and Dr. Chris Ewels for useful discussions

Prismatic edge dislocations in graphite

Dislocations are a central concept in materials science, which dictate the plastic deformation and damage evolution in materials. Layered materials such as graphite admit two general types of interlayer dislocations: basal and prismatic dislocations, of which prismatic dislocations have been relatively less studied. Using density functional theory (DFT) calculations, we have examined different prismatic core structures in graphite and evaluated their structure, energetics and mobility. We find close energetic interplay between bonded and “free-standing” core structures in both zigzag and armchair directions, with a reconstructed stable zigzag core identified. We explore grain boundaries and prismatic dislocation pile-up, identifying metastable structures which may be important in energy storage. The role of interlayer stacking in core structure, dislocation glide and climb is also considered in-depth. Our calculations suggest that the prismatic dislocation core is stable up to high temperatures of approximately 1500 K in bulk graphite. Above this temperature, the breaking of bonds in the dislocation core can facilitate climb, grain-boundary motion, and the annealing of damage through prismatic dislocation glide. © 2021 Elsevier LtdANR-20-CE08-0026, TUBITAK-2219; Engineering and Physical Sciences Research Council, EPSRC: EP/P020232/1, EP/R005745/1This work was supported by the United Kingdom EPSRC grant EP/R005745/1 , Mechanisms of Retention and Transport of Fission Products in Virgin and Irradiated Nuclear Graphite. Kenny Jolley and Pavlos Mouratidis also gratefully acknowledge funds from EDF energy generation 2016–2021 . The authors gratefully acknowledge the use of Athena at HPC Midlands+, which was funded by the EPSRC grant EP/P020232/1 as part of the HPC Midlands + consortium. CE and AI acknowledge ANR-16-CE24-0008-01 “EdgeFiller” and ANR-20-CE08-0026 “OPIFCat” for funding. DE acknowledges support from the TUBITAK-2219 post-doctoral research abroad fund.This work was supported by the United Kingdom EPSRC grant EP/R005745/1, Mechanisms of Retention and Transport of Fission Products in Virgin and Irradiated Nuclear Graphite. Kenny Jolley and Pavlos Mouratidis also gratefully acknowledge funds from EDF energy generation 2016?2021. The authors gratefully acknowledge the use of Athena at HPC Midlands+, which was funded by the EPSRC grant EP/P020232/1 as part of the HPC Midlands + consortium. CE and AI acknowledge ANR-16-CE24-0008-01 ?EdgeFiller? and ANR-20-CE08-0026 ?OPIFCat? for funding. DE acknowledges support from the TUBITAK-2219 post-doctoral research abroad fund

Poly(2-n-propyl-2-oxazoline) surface modified quartz crystal microbalance sensor for highly sensitive detection of alkali cyanides, alkali chlorides, and other ionic species in water

Poly(2-oxazoline)s are a class of organic polymers having tertiary amide groups in their chemical structure. They are currently under intense study for potential applications in many different fields due to the tunability of their physical and chemical properties. In this work, poly(2-oxazoline)s are demonstrated for the first time as the sensing elements for chemical sensors. More specifically, a poly(2-n-propyl-2-oxazoline) (PnPropOx) with a xanthate end-group is synthesized and used to modify a quartz crystal microbalance (QCM) transducer. The general liquid sensing properties and sensor responses of the resulting PnPropOx-QCM sensor to a variety of ionic compounds in aqueous solutions have been evaluated revealing excellent liquid sensing properties showing a strong response to alkali chlorides and cyanides, especially. The sensor response is fast and fully reversible and the selectivity for alkali chlorides and cyanides is remarkably high. The observed sensitivity using 5 MHz PnPropOx-QCMs reaches approximate to 8 Hz mu M-1 at 30 degrees C, enabling analyte detection down to a limit of detection of 0.2 mu M concentration. According to these results, it can be concluded that PnPropOx, and possibly poly(2-oxazoline)s in general, is very promising as a sensing material for chemical sensors in liquids to selectively detect a variety of ionic species

Nitrogen segregation in nanocarbons

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