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This paper explores the evolution mechanisms of metastable phases during the nanoindentation on monocrystalline silicon. Both the molecular dynamics (MD) and the in situ scanning spreading resistance microscopy (SSRM) analyses were carried out on Si(100) orientation, and for the first time, experimental verification was achieved quantitatively at the same nanoscopic scale. It was found that under equivalent indentation loads, the MD prediction agrees extremely well with the result experimentally measured using SSRM, in terms of the depth of the residual indentation marks and the onset, evolution and dimension variation of the metastable phases, such as beta-Sn. A new six-coordinated silicon phase, Si-XIII, transformed directly from Si-I was discovered. The investigation showed that there is a critical size of contact between the indenter and silicon, beyond which a crystal particle of distorted diamond structure will emerge in between the indenter and the amorphous phase upon unloading.

The C-H activation of methane catalyzed by cis-and trans-platin in aqueous solution has been studied by density functional based computational methods. By analogy with the Shilov reaction, the initial step is the replacement of an ammonia ligand by methane, followed by the formation of a methyl complex and the elimination of a proton. The computations utilize the B3LYP hybrid functionals, effective core potentials, and double-ζ to polarized double-ζ basis sets and include solvation effects by a dielectric continuum method. In contrast with the Shilov reaction studied by Siegbahn and Crabtree (J. Am. Chem. Soc. 1996, 118, 4442), in the platins the replacement of an ammonia ligand by methane is found to be effectively rate determining, in that the energy barriers to C-H activation are comparable with those of the initial substitution reaction, viz. ∼ 34 and 44 kcal/mol for cis-and trans-platin, respectively. Several reaction pathways for C-H activation and subsequent proton elimination were identified. For cis-platin the energy barriers associated with the oxidative addition and σ-bond metathesis type mechanisms were found to be comparable, while for trans-platin oxidative addition is predicted to be strongly preferred over σ-bond metathesis, which, interestingly, also proceeds through a Pt(IV) methyl hydrido complex as reaction intermediate. In line with accepted ideas on trans influence, the methyl and hydride ligands in the Pt(IV) complexes that arise in the oxidative addition reactions were always found to be cis to each other. On the basis of the population analyses on the Pt(IV) complexes it is suggested that the Pt-H and Pt-CH 3 bonds are best described as covalent bonds and, further, that the preference of the hydride and methyl anions to be cis to each other is a consequence of such covalent bonding. In light of these findings, the energies of several methyl Pt(IV) hydrido bisulfate complexes were also recalculated, with CH 3 and H placed cis to each other. The revised results provide evidence for the thermodynamic feasibility of oxidative addition of methane to catalysts such as [Pt(NH 3 ) 2 (OSO 3 H) 2 ] or [Pt(NH 3 ) 2 (OSO 3 H)(H 2 SO 4 )] + .

To make full use of the strength of carbon nanotubes in a composite, it is important to have a high-stress transfer at the matrix−nanotube interface via strong chemical bonding. This paper investigates the possible polyethylene−nanotube bonding with the aid of a quantum mechanics analysis. The polyethylene chains were represented by alkyl segments, and the nanotubes were modeled by nanotube segments with H atoms added to the dangling bonds of the perimeter carbons. The study predicts that covalent bonding between an alkyl radical and a nanotube is energetically favorable, and that the tubes of smaller diameters have higher binding energies. Hence, a high-stress transfer can be realized in polyethylene-based carbon nanotube composites in the presence of free-radical generators.

Wrinkling was observed for a circular monolayer graphene sheet in nanoindentation based on moleculardynamics simulations. The mechanics fundamentals of this phenomenon were then explored using a twodimensional plate model. It was found that the graphene wrinkles when the indentation depth reaches a critical value, the wrinkling is induced by the circumferential compression in the graphene, and the bending stiffness of the graphene sheet plays an essential role in stabilizing its one-atom layer nanostructures. It was shown that bending stiffness and in-plane stiffness are key indicators that signify the intrinsic mechanical properties of a graphene.