Non-universal gauge bosons Z′Z^{\prime} and rare top decays

We study a new method for detecting non-universal gauge bosons $Z'$ via considering their effects on rare top decays. We calculate the contributions of the non-universal gauge bosons $Z'$ predicted by topcolor-assisted technicolor (TC2) models and flavor-universal TC2 models on the rare top decays $t\longrightarrow cV(V=g,\gamma,Z)$ and $t\longrightarrow cl_{i}l_{j}(l_{i}, l_{j}=\tau, \mu$, or $e)$. We show that the branching ratios of these processes can be significantly enhanced. Over a sizable region of the parameter space, we have $Br(t\longrightarrow cg)\sim10^{-5}$ and $Br(t\longrightarrow c\tau\tau)\sim10^{-7}$, which may approach the observable threshold of near future experiments. Non-universal gauge bosons $Z'$ may be detected via the rare top decay processes at the top-quark factories such as the CERN LHC.Comment: references adde

Aligned Graphene Nanoribbons and Crossbars from Unzipped Carbon Nanotubes

Aligned graphene nanoribbon (GNR) arrays were made by unzipping of aligned single-walled and few-walled carbon nanotube (CNT) arrays. Nanotube unzipping was achieved by a polymer-protected Ar plasma etching method, and the resulting nanoribbon array was transferred onto any substrates. Atomic force microscope (AFM) imaging and Raman mapping on the same CNTs before and after unzipping confirmed that ~80% of CNTs were opened up to form single layer sub-10 nm GNRs. Electrical devices made from the GNRs (after annealing in H2 at high temperature) showed on/off current (Ion/Ioff) ratios up to 103 at room temperature, suggesting semiconducting nature of the narrow GNRs. Novel GNR-GNR and GNR-CNT crossbars were fabricated by transferring GNR arrays across GNR and CNT arrays, respectively. The production of ordered graphene nanoribbon architectures may allow for large scale integration of GNRs into nanoelectronics or optoelectronics.Comment: published in Nano Researc