3 research outputs found
Dispersant Effects in the Selective Reaction of Aryl Diazonium Salts with Single-Walled Carbon Nanotubes in Aqueous Solution
Current methods of synthesis for carbon nanotubes (CNTs) usually produce heterogeneous mixtures of different nanotube diameters and thus a mixture of electronic properties. Consequently, many techniques to sort nanotubes according to their electronic type have been devised. One such method involves the chemical reaction of CNTs with aryl diazonium salts. Here we examine the reactions of electric arc produced CNTs (dispersed by a variety of surfactants and polymers in aqueous solution) with 4-bromo-, 4-nitro-, and 4-carboxybenzenediazonium tetrafluoroborate salts in order to find conditions for maximum selectivity. Reactions were monitored through the semiconducting S<sub>22</sub> and metallic M<sub>11</sub> transitions in the UV–vis–NIR absorbance spectra of the nanotube dispersions. Selectivity was observed to depend heavily on the type of surfactant, the type of diazonium salt and its concentration, the reaction temperature, and the solution pH. Additionally, the surfactant concentration was found to exert a significant influence as the dediazoniation product yields are affected by this parameter. For certain combinations of surfactant and diazonium salt the selectivity is markedly improved, particularly in dispersions of nonionic surfactants Pluronic F-127 and Brij S-100, which are similar in structure. Smaller diameter HiPCO nanotubes were better functionalized in dispersions of Triton X-405. The greater selectivity afforded by these poly(ethylene oxide) containing polymers is postulated to arise from electron donation provided by their ether oxygens. The ionic surfactant sodium dodecyl sulfate was found to display unique behavior in that semiconducting nanotubes were preferentially functionalized at natural pH, likely due charge localization interactions with the surfactant
Surface and Near Surface Area Density of States for Magnetron-Sputtered ZnO and Al-ZnO: A MIES, UPS, and VBXPS Study Investigating Ultrahigh Vacuum Sputter Cleaning and UV Oxygen Plasma
The impact of nonsolvent-based cleaning
methods on zinc oxide and
aluminum-doped zinc oxide was investigated across a range of doping
concentrations up to 25% aluminum. A combination of electron spectroscopic
techniques was utilized in order to characterize the electronic states
present on the surface and to discern the differences between the
near surface area and outermost layer valence band states. Understanding
the differences between the near surface area and outermost layer
of an interface is crucial when optimizing devices for charge transfer.
The techniques were valence band X-ray photoelectron spectroscopy,
ultraviolet photoelectron spectroscopy, and metastable-induced electron
spectroscopy. The band gap was also measured via ultraviolet/visible
spectroscopy
Formation of N719 Dye Multilayers on Dye Sensitized Solar Cell Photoelectrode Surfaces Investigated by Direct Determination of Element Concentration Depth Profiles
The structure of the dye layer adsorbed on the titania
substrate
in a dye-sensitized solar cell is of fundamental importance for the
function of the cell, since it strongly influences the injection of
photoelectrons from the excited dye molecules into the titania substrate.
The adsorption isotherms of the N719 ruthenium-based dye were determined
both with a direct method using the depth profiling technique neutral
impact collision ion scattering spectroscopy (NICISS) and with the
standard indirect solution depletion method. It is found that the
dye layer adsorbed on the titania surface is laterally inhomogeneous
in thickness and there is a growth mechanism already from low coverage
levels involving a combination of monolayers and multilayers. It is
also found that the amount of N719 adsorbed on the substrate depends
on the titania structure. The present results show that dye molecules
in dye-sensitized solar cells are not necessarily, as presumed, adsorbed
as a self-assembled monolayer on the substrate