Atomic carbon adsorption on Ni nanoclusters: a DFT study

Atomic carbon is a key intermediate interacting with transition metal clusters during the growth of carbon nanotube (CNT). Present density functional calculations studied the initial carbon adsorption on four Ni nanoclusters (N₁₃, N₁₅, N₃₈, and N₅₅). Our results show that carbon atoms preferentially adsorb on high-coordination sites, and carbon adsorption energies are larger on smaller Ni clusters. Ni cluster reconstruction plays an important role in creating more stable subsurface adsorption sites. The migration of adsorbed carbon atom on the surface threefold hollow site into the underlying interstitial subsurface positions is thermodynamically and kinetically feasible. The results indicate that the investigation of CNT growth mechanism should include both surface and subsurface carbon atoms, coupled with surface reconstruction of Ni nanoclusters.     

Synthesis and light‐emitting properties of platinum‐containing oligoynes and polyynes derived from oligo(fluorenyleneethynylenesilylene)s

A series of blue‐light‐emitting oligo(fluorenyleneethynylenesilylene)s (OFESs) of the general formula HC?CRC?C(EC?CRC?C)_mEC?CRC?CH (E = SiPh₂, SiMe₂, or SiMe₂? SiMe₂; m = 0–2; R = 9,9‐dihexylfluorene‐2,7‐diyl) and their phosphorescent platinum‐containing oligoynes and polyynes were synthesized and characterized. The solution properties and regiochemical structures of this new structural class of organosilicon‐based polyplatinayne polymers {trans‐[? Pt(PBu₃)₂C ?CRC?C(EC?CRC?C)_mEC?CRC?C? ]_n} were studied with IR and NMR (¹H, ¹³C, ²⁹Si, and ³¹P) spectroscopy. The optical absorption and photoluminescence spectra of these metallopolymers were examined and compared with their discrete oligomeric model complexes. Our studies led to a novel approach of using the sp³‐silyl moiety as a conjugation interrupter to limit the effective conjugation length in metal polyynes, which could boost the phosphorescence decay rates essential for light‐energy harvesting from the triplet excited state. The influence of the heavy platinum atom and the group 14 silyl unit possessing different side‐group substituents on the thermal and phosphorescence properties was investigated in detail. We also established the goal of studying the evolution of the lowest singlet and triplet excited states with chain length m of OFESs and the nature of E in these metallopolymers. This work indicated that the phosphorescence emission efficiency harnessed through the heavy‐atom effect of platinum in the main chain did not change very much with oligomer chain length m but generally decreased with the E group in the order SiMe₂ > SiMe₂? SiMe₂ > SiPh₂. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4804–4824, 2006     

Generalized crichton-like ambiguities

We extend the treatment of two-fold ambiguities in elastic scattering (a) by considering only even or only odd waves, and (b) by allowing non-zero inelasticities. We consider physical applications of these results toππ and toαα scattering.     

Theory of shear magnetostriction in amorphous and crystalline ferromagnetic metals

The theory of shear magnetostriction (SMS) in ferromagnetic metallic systems is formulated in terms of Green functions in real space for a tight binding model. This is general enough to include amorphous (“glassy”) alloys, as well as crystalline materials. It is shown that the SMS coefficient λ_s(E_F) must have at least four zeros as a function of band filling E_F through the d-band, which explains the change in sign between Fe alloys and Co, Ni alloys. A method is presented for computing the indefinite integral of the imaginary part of the product of two Green functions expressed as continued fractions, not necessarily over the same band width, and some preliminary calculations explore the importance of various terms.     

Collision and rotation of solitons in three space-time dimensions

We investigate properties of soliton solutions in two space and one time dimension of two confining field theories, in particular rotation and Regge trajectories. Numerically we study the collision process in a two-soliton collision.