Probing induced defects in individual carbon nanotubes using electrostatic force microscopy

Structural defects greatly affect the electronic properties of single wall carbon nanotubes (CNT’s), for instance by increasing the sensitivity to their environment; an effect which can be utilized for better performance of CNT based chemical sensors. Here we show that electrostatic force microscopy (EFM) can be used as a non-invasive technique for probing defects in individual CNT’s supported on insulating substrates. The technique is demonstrated by monitoring the change in EFM signal upon intentionally inducing defect by an oxygen plasma etch, and is applied to assess the quality of as-grown CNT samples and to study the effect of exposing CNT’s to the low energy electron irradiation of a scanning electron microscope (SEM). PACS 68.37.-d; 68.37.Ps; 61.46.Fg; 68.35.Dv     

Direct titration of glycerol by constant current potentiometry

A direct, constant-current potentiometric titration method allows quantitative determination of 0.50-5.00 mg samples of glycerol in aqueous solution with errors ranging from 0.2% for the large samples to 2.0% for the smaller samples. Perchloratocerate is used as the standard oxidant and pyrolytic graphite as the electrode material. A direct determination is made possible by elevated temperatures, high acidity, and a relatively large constant current. Sources of error and possible interferences are discussed.     

Standoff alpha radiation detection for hot cell imaging and crime scene investigation

Optical Review - This paper presents the remote detection of alpha contamination in a nuclear facility. Alpha-active material in a shielded nuclear radiation containment chamber has been localized...     

Probing the sub-microsecond photodissociation dynamics in gas-phase retinal chromophores

The photoinduced fragmentation of a retinal model chromophore (all-trans-n-butyl protonated Schiff-base retinal) was studied in vacuo using a new experimental technique. The apparatus is able to record the photodissociation yield of gas-phase biomolecular ions in the first microseconds after absorption. Together with the existing ion storage ring ELISA, which operates on the millisecond to second time scale, the complete decay dynamics of such molecules can now be followed. In the case of retinal, the time-dependent fragmentation yield observed after irradiation with a 410 nm laser pulse exhibits contributions from one- and two-photon absorption, which decay non-exponentially with lifetimes on the order of 1 ms and 1 micros, respectively. The decay can be simulated using a statistical model, yielding good agreement with the experimental findings on both the millisecond and the microsecond time scales. No indication for nonstatistical processes is found for this molecule, the upper limit for a possible direct rate being a factor of 10(4) below the observed statistical dissociation rate.     

A Triptycene‐Based Approach to Solubilising Carbon Nanotubes and C60

We describe herein the synthesis of a triptycene‐based surfactant designed with the ability to solubilise single‐walled carbon nanotubes (SWNTs) and C₆₀ in water through non‐covalent interactions. Furthermore, an amphiphilic naphthalene‐based surfactant with the same ability to solubilise SWNTs and C₆₀ has also been prepared. The compounds synthesised were designed with either two ionic or non‐ionic tails to ensure a large number of supramolecular interactions with the solvent, thereby promoting strong solubilisation. The surfactants produced stable suspensions in which the SWNTs are dispersed and the surfactant/SWNT complexes formed are stable for more than one year. UV/Vis/NIR absorption spectroscopy, TEM and AFM were employed to probe the solubilisation properties of the dispersion of surfactants and SWNTs in water.     

über die Sorption von basischen Farbstoffen im Polyacrylnitril

Zusammenfassung Die Vorstellung von der Sorption von Ionen in Polymersubstraten lä\t für die Aufnahme basischer Farbstoffe in Polyacrylnitril den Mechanismus einer aktivierten Diffusion erwarten. Sorptionsmessungen mit einem basischen Farbstoff in^®Orlon 42-Garn erweisen eine deutliche Konzentrationsabhängigkeit des scheinbaren Diffusionskoeffizienten, im Gegensatz zu einer in der Literatur vertretenen Auffassung.Die Interpretation der Ergebnisse mit einem Potentialgradientansatz erscheint sinnvoll.     

Determination of environmentally important metal ions by fluorescence quenching in anionic micellar solution

This work describes the effect of a variety of metal ions as quenchers of the fluorescence of naphthalene, in aqueous micellar solutions of sodium dodecyl sulfate (SDS). The quenching by the metal ions can be adequately described by the Stern-Volmer equation and the best signal to noise ratios are obtained with low micellized detergent concentrations. Apparent Stern-Volmer constants decrease in the order: Fe3+ > Cu2+ > Pb2+ > Cr3+ > Ni2+ and directly reflect the relative sensitivity of the method for these ions. Detection limits (defined as three times the standard deviation of the blank for n= 10) for the fluorescence quenching of naphthalene by the metal ions in aqueous micellar SDS are in the range of 1.0 x 10(-6) to 1.0 x 10(-5) mol dm(-3). The proposed fluorescence quenching method shows good repeatibility for a variety of added quencher metal ions, indicating that anionic micelle-enhanced fluorescence quenching by metal ions constitutes an analytical method of rather general application.