ToF-SIMS study of 1-dodecanethiol adsorption on Au, Ag, Cu and Pt surfaces

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has been used to perform a chemical analysis of long-chain thiol (CH3(CH2)(11)SH)-treated gold, silver, copper and platinum surfaces. All the mass peaks from positive and negative ion spectra within the range m/z = 0-2000 u are studied. ToF-SIMS data revealed that on gold, silver and copper substrates 1-dodecanethiol form dense standing-up phases, but on platinum being a catalytically active substrate, we were able to identify also surface-aligned parallel lying molecules in addition to a standing thiolate layer. Our study shows that when ToF-SIMS spectra are analyzed, not only the existence of oligomers but also metal + hydrocarbon fragments give information about the order of SAM. Copyright (c) 2008 John Wiley & Sons, Ltd

Recent results in Euclidean dynamical triangulations

We study a formulation of lattice gravity defined via Euclidean dynamical triangulations (EDT). After fine-tuning a non-trivial local measure term we find evidence that four-dimensional, semi-classical geometries are recovered at long distance scales in the continuum limit. Furthermore, we find that the spectral dimension at short distance scales is consistent with 3/2, a value that is also observed in the causal dynamical triangulation (CDT) approach to quantum gravity.Comment: 7 pages, 3 figures. Proceedings for the 3rd conference of the Polish society on relativit

Influence of initial oxygen on the formation of thiol layers

In this study, X-ray photoelectron spectroscopy (XPS) has been used to study thin organic films. For comparison, monolayers were formed on clean and air-exposed metal substrates. Obtained results show that thiols remove contamination oxygen from gold, silver, platinum and copper surfaces. The tightly packed thiolate layers can be formed. In addition, oxygen does not take part in the final bonding of molecules to the surfaces. (c) 2005 Elsevier B.V. All rights reserved

Lattice Quantum Gravity and Asymptotic Safety

We study the nonperturbative formulation of quantum gravity defined via Euclidean dynamical triangulations (EDT) in an attempt to make contact with Weinberg's asymptotic safety scenario. We find that a fine-tuning is necessary in order to recover semiclassical behavior. Such a fine-tuning is generally associated with the breaking of a target symmetry by the lattice regulator; in this case we argue that the target symmetry is the general coordinate invariance of the theory. After introducing and fine-tuning a nontrivial local measure term, we find no barrier to taking a continuum limit, and we find evidence that four-dimensional, semiclassical geometries are recovered at long distance scales in the continuum limit. We also find that the spectral dimension at short distance scales is consistent with 3/2, a value that could resolve the tension between asymptotic safety and the holographic entropy scaling of black holes. We argue that the number of relevant couplings in the continuum theory is one, once symmetry breaking by the lattice regulator is accounted for. Such a theory is maximally predictive, with no adjustable parameters. The cosmological constant in Planck units is the only relevant parameter, which serves to set the lattice scale. The cosmological constant in Planck units is of order 1 in the ultraviolet and undergoes renormalization group running to small values in the infrared. If these findings hold up under further scrutiny, the lattice may provide a nonperturbative definition of a renormalizable quantum field theory of general relativity with no adjustable parameters and a cosmological constant that is naturally small in the infrared.Comment: 69 pages, 25 figures. Revised discussion of target symmetry throughout paper. Numerical results unchanged and main conclusions largely unchanged. Added references and corrected typos. Conforms with version published in Phys. Rev.

Counteranion-controlled properties of polyelectrolyte multilayers

Polyelectrolyte multilayers consisting of poly(diallyldimethylammonium chloride) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) were studied on a quartz crystal microbalance (QCM) utilizing a novel method to determine the elastic properties of the films. Since the multilayer was found to consist of a hard core and soft outer layer, as can be realized on the basis of the multilayer zone model, the multilayer films were made thick enough to reveal the elastic properties of the bulk material of the film. Several hundreds of layers were deposited using a fully automated multilayer deposition machine. We found out that, in addition to the increase in the bilayer mass, a remarkable increase of stiffness of the polyelectrolyte multilayer was observed while changing the counteranion used in the deposition process. The increase of stiffness was found to be comparable to the glass transition of common polymers. The increase is attributed to the counteranions that take part in polyelectrolyte charge compensation. The correlation of storage shear modulus and mass density to the hydration entropy of the anion could be clearly observed

Modally Resolved Fabry-Perot Experiment with Semiconductor Waveguides

Based on the interaction between different spatial modes, semiconductor Bragg-reflection waveguides provide a highly functional platform for non-linear optics. Therefore, the control and engineering of the properties of each spatial mode is essential. Despite the multimodeness of our waveguide, the well-established Fabry-Perot technique for recording fringes in the optical transmission spectrum can successfully be employed for a detailed linear optical characterization when combined with Fourier analysis. A prerequisite for the modal sensitivity is a finely resolved transmission spectrum that is recorded over a broad frequency band. Our results highlight how the features of different spatial modes, such as their loss characteristics and dispersion properties, can be separated from each other allowing their comparison. The mode-resolved measurements are important for optimizing the performance of such multimode waveguides by tailoring the properties of their spatial modes.Comment: 8 pages, 7 figure

XPS and FTIR study of the influence of electrode potential on activation of pyrite by copper or lead

Activation of pyrite by either copper or lead ions and subsequent xanthate adsorption on activated surfaces were studied in aqueous solutions of pH 5, 6.5 and 9 under different electrochemical conditions using X-ray Photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). At pH 5, the copper concentration on the surface of pyrite increased strongly when the electrode potential was changed towards cathodic direction. At low activation potentials (E-h less than or equal to + 100 mV), a change in the chemical state of sulfur on the surface was observed by XPS proposing formation of a copper-containing surface sulfide phase. In electrochemically-controlled xanthate adsorption, the behavior of copper-activated pyrite resembled that of chalcopyrite (CuFeS2). The results indicate that activation of pyrite by copper at pH 5 can be controlled by the potential of the mineral. At pH 9. the copper content on the surface was independent of the potential of pyrite and no changes were observed in chemical state of sulfur if compared to unactivated pyrite in the potential region - 100 to + 400 mV (SHE). In the case of pyrite activation by lead, no changes were observed in sulfur spectra at either pH 5 or 9 at different electrode potentials. The concentration of lead on the surface increased at pH 5 when potential was changed towards cathodic direction. All lead present at the surface of pyrite was concluded to be in the form of lead(II)-oxygen species and no evidence of exchange between lead and iron was found. Both adsorbed xanthate and dixanthogen were observed on the surface of Cu-activated pyrite after activation at cathodic potentials (- 100 to + 50 mV) and subsequent treatment in either ethyl or amyl xanthate solution of pH 5 or 6.5 at potential region + 350 to 550 mV (standard hydrogen electrode, SHE). In a similar experiments with Pb-activated pyrite, only a faint indication of the adsorbed collector species was found proposing that lead rather depresses than activates pyrite. (C) 1999 Elsevier Science B.V. All rights reserved

Core-level XPS spectra of fullerene, highly oriented pyrolitic graphite, and glassy carbon

The C 1s spectra of fullerene C-60, highly oriented pyrolitic graphite (HOPG) and amorphous carbon (a-C) have been measured using X-ray photoemission. The assumed background due to the inelastic scattering of electrons of these spectra has been subtracted by the Tougaard's method. The relative intensities and the energy positions for the core-level satellites have been determined. For C-60, a comparison of the low energy pi type shake-up satellites gives good agreement between theory and experiment. Also, the energies of these features for fullerene and glassy carbon are very similar, whereas the corresponding energies for HOPG are somewhat larger, presumably, because of the higher density of the latter. Moreover, the atomic force microscopy (AFM) study indicates that the C-60 samples consist of a thick layer of large clusters on the Si(111) surface, which is in line with the molecular character of the XPS spectrum. Furthermore, the broad high energy satellite does not consist of a single plasmon but of many components due to collective excitations characteristic of molecules and solids. These features are discussed in the light of theoretical excitation energies. (C) 2002 Elsevier Science B.V. All rights reserved