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51.
Ultrasonically assisted cathodic stripping voltammetry at a boron-doped diamond electrode was developed for the detection of manganese. Differential-pulse voltammetry was used to give the analytical signal from a cathodic strip of electrodeposited MnO2; linearity was observed from 10(-11) M to at least 3 x 10(-7) M, with 10(-11) M being the detection limit for a 2 min deposition. The procedure involves both ultrasonic-anodic deposition of MnO2 and ultrasonic-cathodic stripping. This novel analytical tool is robust, reproducible, mercury free, oxygen insensitive and highly specific towards manganese. The differential-pulse sono-cathodic stripping voltammetric technique was used to determine successfully the manganese content of two instant tea samples, giving excellent agreement with independent AAS analyses. 相似文献
52.
Widmann K Ao T Foord ME Price DF Ellis AD Springer PT Ng A 《Physical review letters》2004,92(12):125002
We report on a single-state measurement of electrical conductivity of warm dense gold in the solid to plasma transition regime. This is achieved using the idealized slab plasma approach of isochoric heating of ultrathin samples by a femtosecond laser, coupled with femtosecond probe measurements of reflectivity and transmission. The experiment also reveals the time scale associated with the disassembly of laser heated solid. 相似文献
53.
Bonalde I Yanoff BD Salamon MB Van Harlingen DJ Chia EM Mao ZQ Maeno Y 《Physical review letters》2000,85(22):4775-4778
We report measurements of the magnetic penetration depth in single crystals of Sr2RuO4 down to 0.04 K using a tunnel-diode based, self-inductive technique. We observe a power law temperature dependence below 0.8 K, with no sign of a second phase transition nor of a crossover predicted for a multiband superconductor. A power law dependence suggests that the gap function has nodes, inconsistent with candidate p-wave states. We argue that nonlocal effects, rather than impurity scattering, can explain the observed T2 dependence instead of the T-linear behavior expected for line nodes. 相似文献
54.
Ionization processes and charge-state distribution in a highly ionized high- Z laser-produced plasma
Foord ME Glenzer SH Thoe RS Wong KL Fournier KB Wilson BG Springer PT 《Physical review letters》2000,85(5):992-995
The charge-state distribution in a well-characterized highly ionized Au plasma was accurately determined using time-resolved x-ray spectroscopy. Simultaneous measurements of the electron temperature and density allow the first direct comparisons with nonlocal thermodynamic equilibrium model predictions for the charge-state distribution of a highly ionized high- Z plasma in a nonradiative environment. The importance of two-electron atomic processes is clearly demonstrated. 相似文献
55.
M.E. Foord P.K. Patel A.J. Mackinnon S.P. Hatchett M.H. Key B. Lasinski R.P.J. Town M. Tabak S.C. Wilks 《High Energy Density Physics》2007,3(3-4):365-370
The proton energy distribution generated from the interaction of an intense (Iλ2 ≈ 1020 W/cm2 μm2) short-pulse (100 fs) laser with a thin foil is investigated using energy resolved measurements and 2D collisional PIC-hybrid simulations. The measured absolute proton spectrum is well matched by a 1.7 MeV exponential function for energies <11 MeV. The proton conversion efficiency from hot electrons ≈6%. Simulations predict a strong radial dependence on the maximum proton energy and on the radial extent of 12 Å hydrocarbon depletion region. C and O ions in the hydrocarbon layer gain significant energies, limiting the efficiency to the protons. The efficiency scaling for ion mixtures is derived using a simple model, and is shown to strongly depend on the cooling rate of the hot electrons. Simulations using hydrogen-rich, layered targets predict much higher efficiencies. 相似文献
56.
DJ Smith KW Ledingham RP Singhal T McCanny P Graham HS Kilic P Tzallas C Kosmidis AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1366-1373
With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
57.
X Fang KW Ledingham P Graham DJ Smith T McCanny RP Singhal AJ Langley PF Taday 《Rapid communications in mass spectrometry : RCM》1999,13(14):1390-1397
The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
58.
59.
Frank Marken Richard G. Compton Christiaan H. Goeting John S. Foord Steven D. Bull Stephen G. Davies 《Journal of Solid State Electrochemistry》2001,5(2):88-93
Two important mechanisms for electron transfer processes at boron-doped diamond electrodes involving the oxidation of tetramethylphenylenediamine
(TMPD) dissolved in aqueous solution and the oxidation of tetrahexylphenylenediamine (THPD) deposited in the form of microdroplets
and immersed into aqueous eletrolyte solution are reported. For TMPD, the first oxidation step in aqueous solution follows
the equation:
Remarkably slow heterogeneous kinetics at a H-plasma-treated boron-doped diamond electrode are observed, consistent with a
process following a pathway more complex than outer-sphere electron transfer. At the same boron-doped diamond electrode surface
a deposit of THPD undergoes facile oxidation following the equation:
This oxidation and re-reduction of the deposited liquid material occurs at the triple interface organic droplet|diamond|aqueous
electrolyte and is therefore an example of a facile high-current-density process at boron-doped diamond electrodes due to
good electrical contact between the deposit and the diamond surface.
Received: 3 February 2000 / Accepted: 18 February 2000 相似文献
60.
Katherine Lawrence John D. Watkins Tony D. James James E. Taylor Steven D. Bull Geoffrey W. Nelson John S. Foord Yi‐Tao Long Frank Marken 《Electroanalysis》2012,24(5):1003-1010
Dioctylaminesulfonamide‐modified carbon nanoparticles are characterised and employed as high surface area substrate for (i) coenzyme Q10 and (ii) 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine (or DMPC) ‐ Q10 redox processes. The carbon nanoparticles provide a highly hydrophobic substrate with ca. 25 Fg?1 capacitance when bare. Q10 or DMPC‐Q10 immobilised onto the carbon nanoparticles lower the capacitance, but give rise to well‐defined pH‐dependent voltammetric responses. The DMPC‐Q10 deposit shows similar characteristics to those of Q10, but with better reproducibility and higher sensitivity. Both redox systems, Q10 and DMPC‐Q10, are sensitive to the Na+ concentration in the electrolyte and mechanistic implications are discussed. 相似文献