We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne's mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5 × 10(7) N·m/kg, requiring a force of ∼10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be "switched on" by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic semiconductor state by mechanical twisting. We reconstruct the equivalent continuum elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g., a nominal Young's modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 2.6 to 4.7 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne-carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).

Semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDCs) are promising gas-sensing materials due to their large surface-to-volume ratio. However, their poor gas-sensing performance resulting from the low response, incomplete recovery, and insufficient selectivity hinders the realization of high-performance 2D TMDC gas sensors. Here, we demonstrate the improvement of gas-sensing performance of large-area tungsten disulfide (WS) nanosheets through surface functionalization using Ag nanowires (NWs). Large-area WS nanosheets were synthesized through atomic layer deposition of WO followed by sulfurization. The pristine WS gas sensors exhibited a significant response to acetone and NO but an incomplete recovery in the case of NO sensing. After AgNW functionalization, the WS gas sensor showed dramatically improved response (667%) and recovery upon NO exposure. Our results establish that the proposed method is a promising strategy to improve 2D TMDC gas sensors.

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We report a first-principles study of hydrogen storage media consisting of calcium atoms and graphene-based nanostructures. We find that Ca atoms prefer to be individually adsorbed on the zigzag edge of graphene with a Ca-Ca distance of 10 A without clustering of the Ca atoms, and up to six H(2) molecules can bind to a Ca atom with a binding energy of approximately 0.2 eV/H(2). A Ca-decorated zigzag graphene nanoribbon (ZGNR) can reach the gravimetric capacity of approximately 5 wt % hydrogen. We also consider various edge geometries of the graphene for Ca dispersion.

We perform an extensive combinatorial search for optimal nanostructured hydrogen storage materials among various metal-decorated polymers using first-principles density-functional calculations. We take into account the zero-point vibration as well as the pressure-and temperature-dependent adsorption-desorption probability of hydrogen molecules. An optimal material we identify is Tidecorated cis-polyacetylene with reversibly usable gravimetric and volumetric density of 7.6 weight percent and 63 kg/m 3 respectively near ambient conditions. We also propose "thermodynamically usable hydrogen capacity" as a criterion for comparing different storage materials.PACS numbers: 68.43. Bc, 71.15.Nc Hydrogen storage is a crucial technology to the development of the hydrogen fuel-cell powered vehicles [1,2]. Recently, nanostructured materials receive special attention because of potentially large storage capacity (high gravimetric and volumetric density), safety (solidstate storage), and fast filling and delivering from the fuel tank (short molecular adsorption and desorption time) [3,4,5]. However, when the thermodynamic behavior of the gas under realistic environments is taken into account, the usable amount of hydrogen with these nanomaterials falls far short of the desired capacity for practical applications and search for novel storage materials continues worldwide [6,7,8,9]. It is to be emphasized that hydrogen storage in nanostructured materials utilizes the adsorption of hydrogen molecules on the host materials and its thermodynamic analysis is distinct from that of metal or chemical hydrides. Each adsorption site on the nanomaterial behaves more or less independently and the probability of the hydrogen adsorption follows the equilibrium statistics which is a smooth function of the pressure and temperature. There is no sharp thermodynamic phase transition between the gas and the adsorbed state of H 2 , in contrast to the case of metal or chemical hydrides where an abrupt phase transition occurs at well-defined pressure at a given temperature [10].With this caveat, a general formalism applicable to the hydrogen adsorption on nanomaterials was derived in the present study from the grand partition function with the chemical potential determined by that of the surrounding H 2 gas acting as a thermal reservoir. As each site can adsorb more than one H 2 molecule, information on the multiple adsorption energy is necessary. (The situation is analogous to the O 2 adsorption and desorption on hemoglobin which can bind up to 4 O 2 molecules.) In equilibrium of the H 2 molecules between the adsorbed and desorbed (gas) states, the occupation (adsorption) number f is obtained from f=kT ∂lnZ/∂µ, where Z is the grand partition function, µ is the chemical potential of H 2 in the gas phase at given pressure p and temperature T, and k is the Boltzmann constant. Here, f per site is reduced towhere ε l is the adsorption energy per H 2 molecule when the number of adsorbed molecules is l and g l is the multiplicity (degeneracy) of the co...

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Precise three-dimensional (3D) atomic structure determination of individual nanocrystals is a prerequisite for understanding and predicting their physical properties. Nanocrystals from the same synthesis batch display what are often presumed to be small but possibly important differences in size, lattice distortions, and defects, which can only be understood by structural characterization with high spatial 3D resolution. We solved the structures of individual colloidal platinum nanocrystals by developing atomic-resolution 3D liquid-cell electron microscopy to reveal critical intrinsic heterogeneity of ligand-protected platinum nanocrystals in solution, including structural degeneracies, lattice parameter deviations, internal defects, and strain. These differences in structure lead to substantial contributions to free energies, consequential enough that they must be considered in any discussion of fundamental nanocrystal properties or applications.

Graphynes, two-dimensional layers of sp-and sp 2 -bonded carbon atoms, have recently received considerable attention because of their potential as new Dirac materials.Here, focusing on their large surface area, we explore the applicability of graphynes as lithium ion battery anodes through the first-principles density functional calculations.We have found that Li potential energies are in the range suitable to be used as anodes. Furthermore, the maximum composite of Li-intercalated multilayer αand γ-graphynes is found to be C 6 Li 3 , which corresponds to a specific capacity of 1117 mAh g −1 , twice as large as the previous theoretical prediction for graphynes. The volumetric capacity of Liintercalated multilayer αand γ-graphynes is 1364 and 1589 mAh cm −3 , respectively. Both specific and volumetric capacities of Li-intercalated graphynes are significantly larger than the corresponding value of graphite, from which we conclude that multilayer graphynes can serve as high-capacity lithium ion battery anodes.