We consider a new C 2 H 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 C 2 H 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.

We explore how a few-layer graphene can undergo phase transformation into thin diamond film under reduced or no pressure, if the process is facilitated by hydrogenation of the surfaces. Such a "chemically induced phase transition" is inherently nanoscale phenomenon, when the surface conditions directly affect thermodynamics, and the transition pressure depends greatly on film thickness. For the first time we obtain, by ab initio computations of the Gibbs free energy, a phase diagram (P, T, h) of quasi-two-dimensional carbon-diamond film versus multilayered graphene. It describes accurately the role of film thickness h and shows the feasibility of creating novel quasi-two-dimensional materials. Further, the role of finite diameter of graphene flakes and possible formation of the diamond films with the (110) surface are described as well.

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1The atomic structure and physical properties of few-layered 111 oriented diamond nanocrystals (diamanes), covered by hydrogen atoms from both sides are studied using electronic band structure calculations. It was shown that energy stability linear increases upon increasing of the thickness of proposed structures. All 2D carbon films display direct dielectric band gaps with nonlinear quantum confinement response upon the thickness. Elastic properties of diamanes reveal complex dependence upon increasing of the number of 111 layers. All theoretical results were compared with available experimental data.

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.