Reaction of gold substrates with diazonium salts in acidic solution at open-circuit potential

The reaction of gold substrates with p-nitrobenzene diazonium tetrafluoroborate (NBD) in 0.1 M H2SO4 at open-circuit potential (OCP) is demonstrated to proceed by electron transfer from gold to the NBD cation. Electrochemical, atomic force microscopy, and X-ray photoelectron spectroscopy analyses reveal the formation of multilayer films with the same composition as electrografted films. The film growth characteristics (surface concentration and film thickness vs time) also follow those observed during electrografting, consistent with electron transfer from the substrate to the diazonium cation. The OCP of the gold substrate increases during the period of film growth (∼60 min) and then decreases to close to its initial value. The increase corresponds to accumulation of positive charge as electrons are transferred to NBD; the discharge process is tentatively attributed to slow oxidation of adventitious impurities in the reaction solution. Films formed at OCP or by electrografting from aqueous acid solution are markedly less stable to sonication in acetonitrile than are those electrografted from acetonitrile. Increased amounts of physisorbed material in films prepared in aqueous media or bonding of aryl groups to different gold sites in the two media are tentatively proposed to account for the different stabilities

Endohedral Filling Effects in Sorted and Polymer-Wrapped Single-Wall Carbon Nanotubes

Widespread use of the polymer extraction method for single-wall carbon nanotubes (SWCNTs) and the ability of endohedral functionalization to alter their material properties make it important to examine the effect of filling on the separation result. Rate-zonal centrifugation is used to obtain empty, water-filled and perfluorooctane-filled large (∼1.45 nm), and single-chirality small (∼0.78 nm) diameter SWCNTs. These are transferred from water to toluene by dispersion with poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6′-(2,2′-bipyridine))] (PFO-BPy), and absorption and Raman spectroscopy are used to follow the extent of endohedral filling at each step. Measurements are made before and after centrifugation (supernatant) but also in the pellet. PFO-BPy is found to stabilize endohedral-functionalized SWCNTs in the supernatant, but a clear preference for less-filled or empty species is shown. Molecular dynamics simulations are used to model the absorption spectrum of encapsulated water molecules in the PFO-BPy/SWCNT/toluene system and explain why partial water filling is difficult to directly measure. These findings are then used to interpret separation results obtained for raw soot (without intentional filling) and with a view to the low yield of polymer-based SWCNT extraction

Patterning of metal, carbon, and semiconductor substrates with thin organic films by microcontact printing with aryldiazonium salt inks

Surface modification through reduction of aryldiazonium salts to give covalently attached layers is a widely investigated procedure. However, realization of potential applications of the layers requires development of patterning methods. Here, we demonstrate that microcontact printing with poly(dimethylsiloxane) stamps inked with aqueous acid solutions of aryldiazonium salts gives stable organic layers on gold, copper, silicon, and graphitic carbon surfaces. Depending on the substrate−diazonium salt combination, the layers range from relatively irregular multilayers to smooth films with close to monolayer thickness. After printing, surface attached aminophenyl and carboxyphenyl groups retain their usual reactivity toward amide bond formation with solution species, and hence, the method is a simple route to patterned, covalently attached, reactive tether layers. Multicomponent patterned films can be prepared by printing a second modifier onto a film-coated surface. Microcontact printing using aryldiazonium salt inks is experimentally very simple and is applicable to the broad range of substrates capable of spontaneously reducing aryldiazonium salts

Fully integrated quantum photonic circuit with an electrically driven light source

Photonic quantum technologies allow quantum phenomena to be exploited in applications such as quantum cryptography, quantum simulation and quantum computation. A key requirement for practical devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Nanophotonic circuits enable the realization of complex linear optical systems, while non-classical light can be measured with waveguide-integrated detectors. However, reproducible single-photon sources with high brightness and compatibility with photonic devices remain elusive for fully integrated systems. Here, we report the observation of antibunching in the light emitted from an electrically driven carbon nanotube embedded within a photonic quantum circuit. Non-classical light generated on chip is recorded under cryogenic conditions with waveguide-integrated superconducting single-photon detectors, without requiring optical filtering. Because exclusively scalable fabrication and deposition methods are used, our results establish carbon nanotubes as promising nanoscale single-photon emitters for hybrid quantum photonic devices