Properties Of Nanoribbons Research Articles

Universal Zigzag Edge Reconstruction of an α-Phase Puckered Monolayer and Its Resulting Robust Spatial Charge Separation.

Edges are important, because they dictate the stability and properties of nanoribbons. Here, we reveal a universal reconstruction of the ZZ edge into a (2 × 1) tubed [ZZ(Tube)] edge, enabling an ultimate narrow nanotube to terminate nanoribbons for α-puckered group-V elemental and compound monolayers (GeS/Se and SnS/Se). The reconstructed edge formations are confirmed by CALYPSO. The ZZ(Tube) edge forms easily, is highly stable, and is semiconducting. Remarkably, the ZZ(Tube) edge always exhibits a type-II band structure and robust spatial charge separation. For a compound monolayer monochalcogenide, mild (2 × 1) ZZ(S-R) occurs at the chalcogenide-terminated edge. TDDFT simulations indicate that charge separation occurs only at 672 fs, while the lifetime is over 5 ns, thus facilitating robust spatial charge accumulation. These remarkable features of ZZ(Tube) edge-terminated α-puckered nanoribbons are ideal for optoelectronic and photocatalytic applications.

Structure, electronic and optical properties of bilayer anatase nanoribbons

The highest surface area anatase TiO2 containing two layers of titanium atoms and exposing facets (0 0 1) is investigated. The material has maximal theoretical surface area of 1080 m2/g, but its stability has been questionable so far. Nanoribbons of this material were considered with the lateral size of 0.4–4.6 nm with varied length of the hydroxylated and non-hydroxylated edges. All the nanoribbons were stable and had flat (0 0 1) surface according to both computational methods used PM6 and SCC-DFTB. The nanoribbons had electronic band gap of around 3.4–3.6 eV and optical band gap of 3.7 eV. They possessed XRD patterns different from those of anatase nanoparticles showing different peaks. Distribution of top orbitals of valence band and bottom orbitals of conduction band as representation for locations of photogenerated holes and electrons showed that orbitals are localized differently depending on the width of nanoribbons, but HOMO and LUMO always occupied different space. Hence, the bilayer nanoribbons are expected to be excellent photocatalysts and sensor materials with good separation of charges. The effect of different conformations of hydroxyl groups on properties of nanoribbons was studied. Interestingly, alignment of all hydroxyl groups in each edge to form hydrogen bonds changes the HOMO, LUMO positions and electronic band gap by up to 0.5 eV, while the optical band gap remained unchanged. It was demonstrated that nanoribbons with even number of layers of Ti atoms had flat structure, while odd-layer nanoribbons showed curvature radius equal to or larger than 3 nm and they can form nanotubes. Given the unique adsorptive and photocatalytic properties of the bilayer nanosheets they are expected to be of great importance in sensors, photocatalysts and adsorbents.

Mechanical properties of graphene nanoribbons with disordered edges

Using density functional theory (DFT), we investigate mechanical properties and failure characteristics of chiral and achiral graphene nanoribbons. Specifically, we study the dependence of maximum strength, Young’s modulus and failure pattern of nanoribbons on their widths, edge chirality and passivation. Besides investigating nanoribbons with perfect edges, nanoribbons with defective edges are considered and the impacts of the presence of Klein or edge pentagonal defects on the properties of nanoribbons are studied. Our DFT results show that as the width of achiral ribbons are reduced, their strength increases. Moreover, significant size effects on the Poisson’s ratio of armchair ribbons and Young’s modulus of zigzag ribbons are observed. The DFT modeling predicts that the presence of defects reduce the strength of chiral nanoribbons while defects might counter intuitively increase the Young’s modulus of chiral nanoribbons. The first-principle simulations show that achiral nanoribbons always fail along a zigzag surface, however the failure pattern of chiral nanoribbons can be more complicated and be accompanied by the nucleation of other kind of defects such as pentagonal–heptagonal rings prior to failure.

Tailoring the Electronic Structure of Zigzag Graphene Nanoribbons via Cu Impurities

We employed density functional theory based spin polarised calculations to explore the structural stability and electronic properties of ZGNR using Cu as a terminating element as well as a substitutional dopant at various sites. In both the cases (termination and doping) Cu impurities affect the electronic properties of nanoribbons in a different way. The calculated formation energy indicates that all the structures are energetically feasible except the both edges Cu-doped ribbons. Binding energy analysis confirms that Cu impurities are strongly bound to ZGNR in all considered configurations. Moreover, ribbon edge is regarded as the most feasible site for substitutional Cu atoms in ZGNR. The electronic properties of ZGNR are sensitive to the position of Cu atoms and the ribbon width. It is revealed that ZGNR can be made semiconducting, semi-metallic, half metallic or purely metallic in nature merely by changing the ribbon width or the position of Cu atoms. The predicted half metallicity for one edge Cu-terminated ZGNR is robust against the choice of exchange correlation potential.