New trlfs laboratory at the CTU in Prague

Early in 2006, construction and equipment of a new TRLFS (Time-Resolved Laser-induced Fluorescence Spectroscopy) laboratory was accomplished at the Czech Technical University in Prague, Czech Republic. In this contribution, the system is described in detail, the results of the first measurements obtained in the new laboratory for a standard UO ₂ ²⁺ - SO ₄ ²⁻ system are presented, and the future research plans are outlined.     

Metastable precursor for oxygen dissociation on Si(0 0 1) 2 × 1 resolved by high lateral resolution work function measurements

The development of contact potential difference (CPD) inhomogeneities on oxide-covered silicon samples was investigated by monitoring the CPD of a clean Si(0 0 1) 2 × 1 surface during exposure to molecular oxygen with Kelvin Probe Force Microscopy. A steady fluctuation level is reached within the completion of a monolayer of oxide. Non-continuous oxygen exposure at room temperature and at lower temperatures unequivocally demonstrates the coexistence of two oxidation processes. One of these processes involves a metastable precursor to oxygen dissociation.     

Chemically patterned flat stamps for microcontact printing

Locally oxidized patterns on flat poly(dimethylsiloxane) stamps for microcontact printing were used as a platform for the transfer of a hydrophilic fluorescent ink to a glass substrate. The contrast was found to be limited. These locally oxidized patterns were conversely used as barriers for the transfer of hydrophobic n-octadecanethiol. In this case a good contrast was obtained, but the pattern was found to be susceptible to defects (cracks) in the barrier layer. Local stamp surface oxidation and subsequent modification with 1H,1H,2H,2H-perfluorodecyltrichlorosilane, for use as a barrier in the transfer of n-octadecanethiol, 16-mercaptohexadecanoic acid, and octanethiol, resulted in remarkably good contrast and stable patterns. The improved ink transfer control is ascribed to the reduction of undesired surface spreading and a superior mechanical stability of the stamp pattern. This new approach substantially expands the applicability of microcontact printing and provides a tool for the faithful reproduction of even extremely low filling ratio patterns.     

Thermal properties and crystallization of BaO–MoO3–P2O5 glasses

Journal of Thermal Analysis and Calorimetry - The thermal behavior and crystallization of barium molybdate-phosphate glasses were studied in two compositional series, namely A:...     

Does the A.T or G.C base-pair possess enhanced stability? Quantifying the effects of CH...O interactions and secondary interactions on base-pair stability using a phenomenological analysis and ab initio calculations

An empirically based relationship between overall complex stability (-DeltaG degrees ) and various possible component interactions is developed to probe the question of whether the A.T/U and G.C base-pairs exhibit enhanced stability relative to similarly hydrogen-bonded complexes. This phenomenological approach suggests ca. 2-2.5 kcal mol-1 in additional stability for A.T owing to a group interaction containing a CH...O contact. Pairing geometry and the role of the CH...O interaction in the A.T base-pair were also probed using MP2/6-31+G(d,p) calculations and a double mutant cycle. The ab initio studies indicated that Hoogsteen geometry is preferred over Watson-Crick geometry in A.T by ca. 1 kcal mol-1. Factors that might contribute to the preference for Hoogsteen geometry are a shorter CH...O contact, a favorable alignment of dipoles, and greater distances between secondary repulsive sites. The CH...O interaction was also investigated in model complexes of adenine with ketene and isocyanic acid. The ab initio calculations support the result of the phenomenological approach that the A.T base-pair does have enhanced stability relative to hydrogen-bonded complexes with just N-H...N and N-H...O hydrogen bonds.     

Dynamics or Stochastic Conductance Switching of Phenylene–Ethynylene Oligomers?

Scanning tunneling microscopy (STM) studies of phenylene-ethynylene oligomers inserted in alkanethiolate self assembled monolayers (SAMs) are presented. Spontaneous changes in appearance of bundles of inserted molecules during imaging are observed. The results indicate that the appearance changes are caused by fluctuations of the number of molecules in the bundles, by diffusion and exchange of molecules, in contrast to previous reports which attribute the changes to stochastic conductance switching. The packing density of the SAM around the bundles of inserted molecules influence the fluctuations, as the fluctuations observed at 77 K all take place in bundles inserted at locally less-densely packed SAM areas. At room temperature fluctuations of bundles inserted in well-ordered areas are also observed.     

Thermodynamically consistent mesoscopic model of the ferro/paramagnetic transition

A continuum evolutionary model for micromagnetics is presented that, beside the standard magnetic balance laws, includes thermomagnetic coupling. To allow conceptually efficient computer implementation, inspired by relaxation method of static minimization problems, our model is mesoscopic in the sense that possible fine spatial oscillations of the magnetization are modeled by means of Young measures. Existence of weak solutions is proved by backward Euler time discretization.     

Investigation of the 2νEC/EC Decay of 106Cd

Search for the β⁺β⁺, β⁺ EC, and EC/EC modes of the ¹⁰⁶Cd decay was carried out with the TGV-2 (Telescope Germanium Vertical) low-background multidetector spectrometer installed at the Modane underground laboratory (4800 m w.e.). The measured foil samples ～50 μm thick and 52 mm in diameter were placed between the entrance windows of the neighboring detectors inside the cryostat. The total measurement time for 10 g of ¹⁰⁶Cd enriched to 75% was 8687 h. New limits (at the 90% confidence level, CL) were obtained for the ¹⁰⁶Cd half-lives against various branches of the decay to the ground state 0⁺ and excited states 2⁺ of the ¹⁰⁶Pd daughter nucleus. They are T _1/2(2νβ⁺β⁺) ≥ 6.0 × 10¹⁹ y, and T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 3.0 × 10²⁰ y for the transitions to the 0⁺ ground state of ¹⁰⁶Pd; T _1/2(2νβ⁺β⁺) ≥ 5.7 × 10¹⁹ y, T _1/2(2νβ⁺ EC) ≥ 5.9 × 10¹⁹ y, and T _1/2(2νEC/EC) ≥ 4.2 × 10¹⁹ y for the transitions to the 2⁺, 512-keV excited state of ¹⁰⁶Pd; and T _1/2(2νEC/EC) ≥ 3.1 × 10¹⁹ y for the transition to the 0 ₁ ⁺ , 1334-keV excited state of ¹⁰⁶Pd.