Electrochemical Modulation of the Fluorescence of Cyanine Dye Cy5

Organic fluorescent dyes are widely used in single molecule localization microscopy, where their performances are determined by the photophysical properties. Herein, we utilized a sensitive method to modulate the fluorescence of organic dyes by external potentials using a combination of electrochemical cell and super‐resolution fluorescent microscopy. Cy5 (cyanine dye) was chosen as a model molecule considering its wide application and commercial availability. We applied different potentials on the Au electrode to change the Coulombic charge microenvironment of Cy5. When the electrode potential was adjusted negatively, Cy5 displayed a better photostability. This method is proved effective in adjusting the fluorescence of organic dyes.     

Phase signatures in laser-assisted electron-atom collisions

We study electron-atom scattering in the presence of a laser field with elliptic polarization. We discuss the dependence of the differential cross sections for the cases of circular and linear polarizations as a function of scattering angle. Interesting typical signatures of the phase between the two components of the circular polarization of the laser field appear in the differential cross section.     

Are protons involved in the hydrogen-induced surface conductivity of diamond(001)?

We have investigated the mechanism underlying the surface conductivity observed for synthetic diamond(001) samples. It is found that (1) the surface conductivity depends on the pressure of the surrounding gas atmosphere, (2) the temperature dependence can be described as being due to a thermally activated process and (3) a chromogeneous WO₃ cathode turns color from transparent to blue and gas bubbles develop underneath the cathode if an electrical dc current is passed through such an arrangement. In contrast, the complementary WO₃ anode neither changed color nor were gas bubbles observed. One concludes that hydrogen develops at the negatively biased WO₃-diamond interface, recombining to gaseous H₂. However, most of the hydrogen invades the WO₃ cathode coloring it blue, thereby clearly indicating the involvement of protons. Though the conductivity crucially depends on temperature, time and history of a sample, the resistances of various and even differently prepared diamond specimens covering eleven orders of magnitude can be scaled onto one master curve reflecting a thermally activated behavior. Taken together, we propose that the mechanism of the diamond(001) surface conductivity as observed under ambient conditions is at least partly due to proton conduction. Received: 13 April 2000 / Accepted: 31 July 2000 / Published online: 22 November 2000     

Summing the derivative expansion of the effective action

The derivative expansion of the effective action is a perturbative development in derivatives of the fields. The expansion breaks down when some of the derivatives are too large. We show how to sum exactly the first and second derivatives and treat perturbatively derivatives higher than second.     

The orientation-selective growth of LaNiO3 films on Si(100) by pulsed laser deposition using a MgO buffer

Highly (100)-oriented, (110)-oriented and polycrystalline LaNiO₃ (LNO) films were successfully prepared on Si(100) using an oriented MgO film as a buffer. It was somewhat surprising to find that that the orientation relation between the LNO film and the corresponding MgO buffer was: LNO(100)\MgO(110), LNO(110)\MgO(111) and LNO(polycrystalline)\MgO(100). The crystalline quality of the LNO films was shown to be sensitive to the preparation conditions of the MgO buffer. The film surface was very smooth, without micrometer-sized droplets being observed. All LNO films were of metallic conductivity, with a room-temperature resistivities of approximately 250, 280 and 420 μΩ cm for the (110)-oriented, (100)-oriented and polycrystalline LNO, respectively. Received: 2 April 2001 / Accepted: 23 October 2001 / Published online: 3 June 2002     

Gauge-invariant sub-structures of tree-level double-emission exact QCD spin amplitudes

In this note we discuss possible separations of exact, massive, tree-level spin amplitudes into gauge-invariant parts. We concentrate our attention on processes involving two quarks entering a color-neutral current and, thanks to the QCD interactions, two extra external gluons. We will search for forms compatible with parton-shower languages, without applying approximations or restrictions on phase space regions. Special emphasis will be put on the isolation of parts necessary for the construction of evolution kernels for individual splittings and to some degree for the running coupling constant as well. Our aim is to better understand the environment necessary to optimally match hard matrix elements with parton-shower algorithms. To avoid complications and ambiguities related to regularization schemes, we ignore, at this point, virtual corrections. Our representation is quite universal: any color-neutral current can be used; in particular, our approach is not restricted to vector currents only. This work is partially supported by RTN European Programme, MRTN-CT-2006-035505 (HEPTOOLS, Tools and Precision Calculations for Physics Discoveries at Colliders).     

The second Born approximation in electron-helium scattering in a Nd-YAG laser field

The dynamics of laser-assisted elastic collisions in helium is studied using the second-order Born approximation. Detailed calculations of the scattering amplitudes are performed by using the Sturmian basis expansion. Differential cross sections for elastic scattering with the net absorption/emission of up to two photons are calculated for collision energies of 5 eV, 10 eV, and 20 eV. We discuss the influence of the low-energy electrons on the differential cross section (DCS) as a function of the scattering angle for selected choices of the laser frequency and the number of photons exchanged between the external field and electron-helium system.