Doping of magic nanoclusters in the submonolayer In/Si(100) system

Si(100)4 x 3-In reconstruction is essentially a superlattice of magic (identical-size) Si7In6 nanoclusters. Using scanning tunneling microscopy (STM) observations, we have found that under appropriate growth conditions up to 35% of these clusters can be modified; namely, two Si atoms in the cluster can be replaced by two In atoms, thus forming a Si5In8 cluster. This modification can be considered as a doping of the magic cluster, as it changes the electronic properties of the cluster from semiconducting towards metallic. The doped cluster is less rigid than the ordinary one and swings in the electrical field of the STM tip. The atomic structure and stability of the doped magic cluster have been examined using first-principles total-energy calculations.     

Sidelobe contrast reduction for optical vortex beams using a helical axicon

We present a new approach for generating an optical vortex pattern with reduced sidelobes without increasing the radius of the vortex and without excessive energy loss. Our technique combines the spiral phase plate with a weak axicon to form a helical axicon. Experimental results using a liquid crystal display agree with theory.     

Kinetics and Energetics of Intramolecular Electron Transfer in Single-Point Labeled TUPS-Cytochrome c Derivatives

Electron transfer within and between proteins is a fundamental biological phenomenon, in which efficiency depends on several physical parameters. We have engineered a number of horse heart cytochrome c single-point mutants with cysteine substitutions at various positions of the protein surface. To these cysteines, as well as to several native lysine side chains, the photoinduced redox label 8-thiouredopyrene-1,3,6-trisulfonate (TUPS) was covalently attached. The long-lived, low potential triplet excited state of TUPS, generated with high quantum efficiency, serves as an electron donor to the oxidized heme c. The rates of the forward (from the label to the heme) and the reverse (from the reduced heme back to the oxidized label) electron transfer reactions were obtained from multichannel and single wavelength flash photolysis absorption kinetic experiments. The electronic coupling term and the reorganization energy for electron transfer in this system were estimated from temperature-dependent experiments and compared with calculated parameters using the crystal and the solution NMR structure of the protein. These results together with the observation of multiexponential kinetics strongly support earlier conclusions that the flexible arm connecting TUPS to the protein allows several shortcut routes for the electron involving through space jumps between the label and the protein surface.     

Properties of 8-hydroxyquinoline immobilized on a silica surface

The ionization constants of benzeneazo-8-hydroxyquinoline grafted to a silica surface were determined by potentiometric titration. The spectrophotometric measurements showed that with increase in pH, deprotonation of the grafted 8-hydroxyquinoline nitrogen takes place. The dynamic capacity of the sorbent obtained with respect to the Cu²⁺, Co²⁺, and Ni²⁺ ions at various pH was determined. The immobilized benzeneazo-8-hydroxyquinoline is suitable for removing trace amounts of metal ions from solutions and for their chromatographic separation. It was found that the metal complexes of Cu²⁺ and Co²⁺ with grafted benzeneazo-8-hydroxyquinoline exhibit catalytic activity in the oxidation of hydrazine by molecular oxygen in aqueous solutions.Translated from Teoreticheskaya i Ékperimental'naya Khimiya, Vol. 25, No. 1, pp. 108–112, January–February, 1989.     

Surface phases and nanostructures on silicon surface

The paper gives definitions of conventional terms related to silicon surface science, such as surface, surfaced phase, adatoms, “in phase” and “on phase” atoms. The formation methods of surface phases are illustrated as well as their role in physical processes on the surface. The influence of surface phases on diffusion, desorption, adsorption, and phase interface formation at the silicon surface is described.     

The different behavior of rutile and anatase nanoparticles in forming oxy radicals upon illumination with visible light: an EPR study

Photoexcited TiO(2) has been found to generate reactive oxygen species, yet the precise mechanism and chemical nature of the generated oxy species especially regarding the different crystal phases remain to be elucidated. Visible light-induced reactions of a suspension of titanium dioxide (TiO(2)) in water were investigated using electron paramagnetic resonance (EPR) coupled with the spin-trapping technique. Increased levels of both hydroxyl (˙OH) and superoxide anion (˙O(2)(-)) radicals were detected in TiO(2) rutile and anatase nanoparticles (50 nm). The intensity of signals assigned to the ˙OH and ˙O(2)(-) radicals was larger for the anatase phase than that originating from rutile. Moreover, illumination with visible (nonUV) light enhanced ˙O(2)(-) formation in the rutile phase. Singlet oxygen was not detected in water suspension of TiO(2) neither in rutile nor in anatase nanoparticles, but irradiation of the rutile phase with visible light revealed a signal, which could be attributed to singlet oxygen formation. The blue part of visible spectrum (400-500 nm) was found to be responsible for the light-induced ROS in TiO(2) nanoparticles. The characterization of the mechanism of visible light-induced oxy radicals formation by TiO(2) nanoparticles could contribute to its use as a sterilization agent.     

High-speed analysis of multiplexed short tandem repeats with an electrophoretic microdevice

We report the development of a robust and effective method for multiplexed short tandem repeat (STR) analysis within a chip-based microdevice. The method uses a laser-induced fluorescence detection system and simultaneously detects three- and four-color multiplexed polymerase chain reaction (PCR) samples. Analyses of the eight combined DNA index system (CODIS) STR loci were performed in 20 min with single-base-pair resolution ranging from 0.75 to 1. A simultaneous analysis of fifteen loci-ladders and a gender marker Amelogenin based on the PowerPlexTM 16 System was achieved in less than 35 min. The system is capable of repetitive operation and may be extended to high-throughput multilane devices that could be readily interfaced to an automated sample loading system.     

High-resolution STM imaging of novel single G4-DNA molecules

The molecular morphology of long G4-DNA wires made by a novel synthetic method was, for the first time, characterized by high-resolution scanning tunneling microscopy (STM). The STM images reveal a periodic structure seen as repeating "bulbs" along the molecules. These bulbs reflect the helix morphology of the wires. The STM measurements were supported by a statistical morphology analysis of the DNA pitch length and apparent height relative to the surface. In the absence of X-ray and NMR data for these wires, the STM measurements provide a unique alternative to characterize the helix morphology.     

Diffraction of a plane, finite-radius wave by a spiral phase plate

We derive analytical expressions containing a hypergeometric function to describe the Fresnel and Fraunhofer diffraction of a plane wave of circular and ringlike cross section by a spiral phase plate (SPP) of an arbitrary integer order. Experimental diffraction patterns generated by an SPP fabricated in resist through direct e-beam writing are in good agreement with the theoretical intensity distribution.     

X-ray absorption spectra of cobalt in ferromagnetic borides

The K x-ray absorption spectra of cobalt in the borides, the oxide, and in the pure metal are compared with the magnetic properties. The intensity of the initial absorption region decreases essentially linearly with the transition to higher borides, because of the progressive filling of d-like vacancies in the valence band of the metal by valence sp electrons of boron.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 1, pp. 24–28, January, 1970.