Zigzag-Shaped Superlattices on the Basis of Graphene Nanoribbons: Structure and Electronic Properties

This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record.The paper focuses on superlattices consisting of two coplanar fragments of one-layer graphene nanoribbons that have different width and are connected at an angle. Classification of such superlattices was carried out; their electronic properties were studied using the tight-binding method. It was demonstrated that in superlattices consisting of two fragments of graphene nanoribbons with armchair edges connected at an angle of 60°, the band gap can be regulated by the number of dimeric carbon atom chains of one of the fragments. In that case one can observe a periodic dependence of the band gap on the number of chains with a characteristic period equal to three dimeric chains. The number of dimeric chains of the second superlattice fragment regulates the average band gap value near which the periodic oscillations occur, as well as the amplitude of those oscillations. Therefore, one can accomplish a sufficiently precise band gap tuning for such structures. Such tuning can find its wide application in the booming carbon nanoelectronics industry when creating generators, amplifiers and sensors in the nanochains.This research was supported by projects FP7 ITN NOTEDEV(FP7-607521), CACOMEL(FP7-247007), FAEMCAR (FP7-318617) and CANTOR (FP7-612285); project H2020-MSCA-RISE-2014 CoExAN (SEP-210156718); European Graphene Flagship project (604391), as well as by the Belarusian Ministry of Education (grant 20140773), Belarusian State University (grant 11, 2014), and the international grant AFOSR “Nanosized CherenkovType Terahertz Light Emitter Based on Double-Walled Carbon Nanotubes and Bi-graphene Nanoribbons”

Optical selection rules of zigzag graphene nanoribbons

PublishedThis is the final version of the article. Available from American Physical Society via the DOI in this record.We present an analytical tight-binding theory of the optical properties of graphene nanoribbons with zigzag edges. Applying the transfer matrix technique to the nearest-neighbor tight-binding Hamiltonian, we derive analytical expressions for electron wave functions and optical transition matrix elements for incident light polarized along the structure axis. It follows from the obtained results that optical selection rules result from the wave function parity factor (−1)J, where J is the band number. These selection rules are that ΔJ is odd for transitions between valence and conduction subbands and that ΔJ is even for transitions between only valence (conduction) subbands. Although these selection rules are different from those in armchair carbon nanotubes, there is a hidden correlation between absorption spectra of the two structures that should allow one to use them interchangeably in some applications. The correlation originates from the fact that van Hove singularities in the tubes are centered between those in the ribbons if the ribbon width is about a half of the tubes circumference. The analysis of the matrix elements dependence on the electron wave vector for narrow ribbons shows a smooth nonsingular behavior at the Dirac points and the points where the bulk states meet the edge states.This work was supported by the EU FP7 ITN NOTEDEV (Grant No. FP7-607521), EU H2020 RISE project CoExAN (Grant No. H2020-644076), FP7 IRSES projects CANTOR (Grant No. FP7-612285), QOCaN (Grant No. FP7-316432), InterNoM (Grant No. FP7-612624), and Graphene Flagship (Grant No. 604391). The authors are very thankful to R. Keens and C. A. Downing for a careful reading of the manuscript and to A. Shytov and K. G. Batrakov for useful advice and fruitful discussions

Band gaps in jagged and straight graphene nanoribbons tunable by an external electric field.

PublishedJournal ArticleResearch Support, Non-U.S. Gov'tThis is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this record.Band gap control by an external field is useful in various optical, infrared and THz applications. However, widely tunable band gaps are still not practical due to a variety of reasons. Using the orthogonal tight-binding method for π-electrons, we have investigated the effect of the external electric field on a subclass of monolayer chevron-type graphene nanoribbons that can be referred to as jagged graphene nanoribbons. A classification of these ribbons was proposed and band gaps for applied fields up to the SiO2 breakdown strength (1 V nm(-1)) were calculated. According to the tight-binding model, band gap opening (or closing) takes place for some types of jagged graphene nanoribbons in the external electric field that lies on the plane of the structure and perpendicular to its longitudinal axis. Tunability of the band gap up to 0.6 eV is attainable for narrow ribbons. In the case of jagged ribbons with armchair edges larger jags forming a chevron pattern of the ribbon enhance the controllability of the band gap. For jagged ribbons with zigzag and armchair edges regions of linear and quadratic dependence of the band gap on the external electric field can be found that are useful in devices with controllable modulation of the band gap.Thisworkwas supported by EU FP7 ITNNOTEDEV (through Grant No. FP7-607521); IRSES projects CACOMEL (Grant No. FP7-247007), FAEMCAR (Grant No. FP7-318617) and CANTOR (Grant No. FP7-612285); Graphene Flagship (Grant No. 604391) and the Ministry of Education of the Republic of Belarus (Grant No. 20140773). The authors are very grateful to Prof P Lambin and Prof M Portnoi for their useful advice and Charles Downing for his careful reading of the manuscript

Hidden correlation between absorption peaks in achiral carbon nanotubes and nanoribbons

This is the final version. Available on open access from Elsevier via the DOI in this recordIn this paper we study the effect of absorption peak correlation in finite length carbon nanotubes and graphene nanoribbons. It is shown, in the orthogonal {\pi}-orbital tight-binding model with the nearest neighbor approximation, that if the ribbon width is a half of the tube circumference the effect takes place for all achiral ribbons (zigzag, armchair and bearded), and corresponding tubes, starting from lengths of about 30 nm. This correlation should be useful in designing nanoribbon-based optoelectronics devices fully integrated into a single layer of graphene.This work was supported by the EU FP7 ITN NOTEDEV (Grant No. FP7-607521), EU H2020 RISE project CoExAN (Grant No. H2020-644076), FP7 IRSES projects CANTOR (Grant No. FP7-612285), QOCaN (Grant No. FP7-316432), InterNoM (Grant No. FP7-612624); Graphene Flagship (Grant No. 604391) and partially by the Belarus state program of scientific investigations “Convergence-2020”

Erratum: Optical selection rules of zigzag graphene nanoribbons [Phys. Rev. B 95, 155438 (2017)]

This is the final version of the article. Available from American Physical Society via the DOI in this record

Att leva med skammen, En kvalitativ studie om upplevelser av sexuella övergrepp

Denna uppsats belyser upplevelser av sexuella övergrepp i uppväxten ur ett retroperspektiv. Studiens syfte är att lyfta upplevelser av sexuella övergrepp och bidra till att tabut kring ämnet minskar. Vårt urval har bestått av flickor som utsatts för sexuella övergrepp under sin uppväxt av sin far, styvfar eller adoptivfar, som har skrivit om sina upplevelser i en självbiografi. Den metod vi använt oss av är en kvalitativ tematisk analys som baserats på självbiografierna. Studiens resultat är främst att upplevelser av att utsättas för sexuella övergrepp är komplexa och unika. Vår analys visar på att ha blivit utsatt för sexuella övergrepp kan präglas av mångbottnade känslor, samt att omgivningens inverkan både kan fungera positivt och negativt. Kvinnornas handlingsstrategier har vi sett ligger nära sammankopplade med konsekvenserna de fått som en följd av de sexuella övergrepp de utsatts för

How to live without BRCA1

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this record.Interband dipole transitions are calculated in quasi-metallic single-walled carbon nan-otubes and armchair graphene nanoribbons. It is shown that the curvature effects for tubes and the edge effects for ribbons result not only in a small band gap opening, corresponding to THz frequencies, but also in a significant enhancement of the transition probability rate across the band gap. This makes these nanostructures perspective canditates for sources and detectors of THz radiation.This work was supported by the EU FP7 ITN NOTEDEV (Grant No. FP7-607521); FP7 IRSES projects QOCaN (Grant No. FP7-316432), INTERNOM (Grant No. FP7-612624), CANTOR (Grant No. FP7-612285), H2020 RISE project CoExAN (Grant No. H2020-644076) and the British Council

Multilayer phosphorene quantum dots in an electric field: Energy levels and optical absorption

This is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this recordTriangular and hexagonal multilayer phosphorene quantum dots with armchair and zigzag terminations are investigated with the orthogonal tight-binding model. The effect of increasing the number of layers is revealed. The obtained results show that in a small size multilayer quantum dot, the edge states are as sensitive to the out-of-plane external electric fields as the edge states in a single layer dot to the in-plane external electric fields. The investigated optical absorption cross sections show that armchair phosphorene quantum dots have a regular behavior which should be useful for infrared detectors. In particular, it was found that in hexagonal armchair phosphorene dots, absorption peaks can be increased, decreased, or totally removed from the low-energy region depending on the orientation of the applied electric field. The effect of spurious doping can suppress the transitions < 0.4 eV, while the effect of the finite temperature is almost negligible.This work was supported by the EU FP7 ITN NOTEDEV (FP7-607521), EU H2020 RISE project CoExAN (H2020-644076), and FP7 IRSES projects CANTOR (FP7-612285). The work of M.E.P. was financially supported by the Government of the Russian Federation through the ITMO Fellowship and Professorship Program