We consider a new C₂H nanostructure based on bilayer graphene transformed under the covalent bond of hydrogen atoms adsorbed on its external surface, as well as compounds of carbon atoms located opposite each other in neighboring layers. They constitute a “film” of the 〈111〉 diamond with a thickness of less than 1 nm, which is called diamane. The energy characteristics and electron spectra of diamane, graphene, and diamond are calculated using the density functional theory and are compared with each other. The effective Young’s moduli and destruction thresholds of diamane and graphene membranes are determined by the molecular dynamics method. It is shown that C₂H diamane is more stable than CH graphane, its dielectric “gap” is narrower than the band gap of bulk diamond (by 0.8 eV) and graphane (by 0.3 eV), and is harder and more brittle than the latter.

Quantum conductivity of single-wall carbon nanotube Y-junctions is calculated. The current versus voltage characteristics of these junctions show asymmetry and rectification, in agreement with recent experimental results. Furthermore, rectification is found to be independent of the angle between the branches of these junctions, indicating this to be an intrinsic property of symmetric Y-junctions. The implications for the Y-junction to function as a nanoscale molecular electronic switch are investigated.

Magnetic properties of various ${\mathrm{C}}_{\mathrm{60}}$ polymers are calculated using tight-binding molecular-dynamics and ab initio methods. Our results suggest a mechanism involving an interplay between structural defects and $s{p}^3$ hybridization to be responsible for the origin of this magnetism. The onset of magnetism is found to occur much more readily for the $\mathrm{R}\mathrm{h}\mathrm{\text{−}}{\mathrm{C}}_{\mathrm{60}}$ polymeric phase with defects than for any of the other polymers, in agreement with the recent experiment. Our estimate of the magnetic moment is also in very good agreement with the value observed in experiment.

Quantum conductivity of a wide class of carbon nanotube Y junctions is calculated using an efficient Green’s function embedding scheme. Our results indicate that rectification and switching properties of these junctions depend strongly on the symmetry and to a lesser degree on chirality. We find that a zig-zag tube forming the stem of a symmetric Y junction is sufficient to cause perfect rectification across the junction, otherwise the $I-V$ characteristics remain asymmetric with some leakage current for positive bias voltages. For asymmetric Y junction, on the other hand, we find that no rectification at all is possible. We invoke a model calculation involving Y branching in molecules as well as in nanotubes to explain the dependence of rectification on the nature of the geometry at the branching.

The stability and elasto-mechanical properties of tetragonal and cagelike or clathrate nanowires of $\mathrm{Si}$ are investigated and compared using molecular dynamics simulations. Our results show that cagelike nanowires, while possessing lesser density, are able to maintain their structural integrity over a larger range of strain conditions than the tetrahedral nanowires, making them a better candidate for structural strength, chemical sensor, and electronics applications under strain conditions. This could have important technological implications.

Thermal conductivity of a $(10,10)$ carbon nanotube filled with ${\mathrm{C}}_{60}$ fullerenes (or a peapod) is computed using direct molecular-dynamics simulations with the Tersoff-Brenner potential for $\mathrm{C}\text{−}\mathrm{C}$ bonding interactions and the van der Waals potential for nonbonding interactions. The temperature-dependent thermal conductivity of the peapod, while showing qualitatively similar behavior to that of an unfilled carbon nanotube, is found to be higher than the nanotube at all temperatures. This is in agreement with recent experimental observations. The increase in thermal conductivity in the peapod is explained through (a) an energy transfer between fullerenes and nanotube due to low-frequency radial vibration coupling between fullerenes and nanotube, and (b) energy transfer along the peapod axis due to fullerene-fullerene collisions.