We propose new carbon nanoribbons with Dirac bands. Hydrogen edge passivation triggers RTD behavior in molecular electronic devices.

In this work, we investigate the electronic transport properties of a graphene allotrope composed of 5–6-7 carbon aromatic rings called phagraphene and compare with the results of the transition-voltage spectroscopy (TVS) and propose the behavior at low voltage characteristic of a topological insulator. Phagraphene properties were compared to those of graphene in a zigzag nanoribbon configuration, zigzag graphene vs zigzag phagraphene nanoribbon (zzGNR and zzPGNR). The molecular geometry and the electronic properties were calculated by density functional theory (DFT) without spin, and the electronic transport and TVS were obtained by means of DFT combined with non-equilibrium Green´s function when we couple the optimized geometry of zzGNR and zzPGNR to the leads (left and right), forming the molecular junction that will be subjected to the action of an external bias voltage (V_e) to generate the molecular device. The results exhibit (i) a metal-insulator transition when V_e is increased until V_e = 1.4 V which corresponds to the nonlinear region (resonance), showing the field effect transistor behaviour for zzGNR junctions; and (ii) two nonlinear regions (two negative differential resistances), showing a resonant tunnel diode behaviour with two operation windows (V_e = 0.5 V and V_e = 1.7 V) for the zzPGNR junction. In addition, the zzPGNR junction exhibits topological insulator characteristics upon introducing topological defects such as pentagons and heptagons in the hexagonal lattice of graphene, and when V_e = 1.7 V, there occurs a topological insulator-metal transition that can be seen in the behaviour of the density of states, transmittance, and frontier molecular orbitals with V_e.

In this work, we theoretically investigated the effect of width on the energetic stability, and structural, electronic and transport properties of five carbon nanoribbons (three zigzag and two armchair) with 5-8-5 carbon ring symmetry based on 2D POPGraphene, to understand how the width can tune their features and to suggest possible applications in nanoelectronics. Our study was conducted via Density Functional Theory (DFT) implemented in the SIESTA package, to compute the energetic, structural, and electronic properties, and DFT combined with the non-equilibrium Green's function, to compute the transport properties. The results show that all the nanoribbons are stable, with cohesive energy values in the range of those of several carbon allotropes. Furthermore, we see that the stability increases with the width, strongly depends on edge terminations (penta-rings improve stability), and reaches values similar to those of 2D POPGraphene. The structural properties show that the width effect associated with edge shape acts like a uniaxial tensile strain application in most of the nanoribbons. The electronic properties show that most of the nanoribbons are metallic, except for the two armchair cases, which have a tiny indirect bandgap. We see that the armchair cases have several sub-bandgap regions that trigger negative differential resistance in devices, and this possibly suggests applications in optoelectronic devices. These regions decrease with increasing width. The transport properties show that the zigzag devices in general have Field Effect Transistor (FET) or Resonant Tunneling Diode (RTD) behaviour, and the armchair ones show FET, RTD and Zener diode behaviour. Therefore, the width of a carbon nanoribbon can be used to adjust its features, which consequently suggests several applications of this kind of material in nanoelectronics.

In the present work we propose a novel treatment to investigate ballistic electron transport under mechanical strain in a 1-D molecular bridge composed of alternating simple and triple bonds (polyyne) connected between two Single-Wall Carbon Nanotube (SWCNT) electrodes. Calculations with the DFT-NEGF methodology were performed in order to analyze this system at low values of mechanical strain (compression and distension) and at equilibrium length in the presence of bias voltages applied along the longitudinal direction. The results show that, while the mechanical strain displaces the energy levels and changes the band gap in the nanotube caps, the applied bias breaks the degeneracy in the nanotube cap states and defines the electrical conductance along the system. The analysis of the PDOS suggests that the main contribution to the electrical current comes from the superposition of the nanotube cap states, which is in agreement with the transmission calculation, and this device can be employed as a transistor observed in the I–V curve.

The increasing use of petroleum plastics has caused environmental damage due to the degradation time of these materials. An alternative to petroleum plastics could be thermoplastic starch (TPS). However, thermoplastic starch does not exhibit satisfactory tensile properties. The mechanical properties of thermoplastic starch can be improved by adding sisal microfibers. Thus, the objective of this study was to evaluate the influence of different levels of glycerol and sisal microfibers on the thermal and tensile properties of thermoplastic corn starch composites. The microfibers were obtained via mechanical treatment followed by chemical treatment (alkaline treatment and bleaching). The films were obtained by the casting method using commercial corn starch and glycerol as a plasticizing agent, reinforced with sisal microfibers. Fourier transform infrared spectroscopy (FTIR) results revealed that the addition of microfibers did not change the chemical structure of the TPS matrix. The films from the samples with 18% glycerol and 10% microfibers had the highest value for the maximum tension, equal to 4.78 MPa. The thermal decomposition profile of TPS was not altered by the addition of microfibers. Our findings demonstrated the profound influence of glycerol and microfiber contents on the tensile properties of thermoplastic starch composites.