In situ monitoring of atomic layer deposition in nanoporous thin films using ellipsometric porosimetry

Ellipsometric porosimetry (EP) is a handy technique to characterize the porosity and pore size distribution of porous thin films with pore diameters in the range from below 1 nm up to 50 nm and for the characterization of porous low-k films especially. Atomic layer deposition (ALD) can be used to functionalize porous films and membranes, e.g., for the development of filtration and sensor devices and catalytic surfaces. In this work we report on the implementation of the EP technique onto an ALD reactor. This combination allowed us to employ EP for monitoring the modification of a porous thin film through ALD without removing the sample from the deposition setup. The potential of in situ EP for providing information about the effect of ALD coating on the accessible porosity, the pore radius distribution, the thickness, and mechanical properties of a porous film is demonstrated in the ALD of TiO(2) in a mesoporous silica film.     

X-ray photoelectron diffraction study of ultrathin PbTiO3 films

Full hemispherical X-ray photoelectron diffraction (XPD) experiments have been performed to investigate at the atomic level ultrathin epitaxial c-axis oriented PbTiO₃ (PTO) films grown on Nb-doped SrTiO₃ substrates. Comparison between experiment and theory allows us to identify a preferential ferroelectric polarization state in a 60 ? -thick PTO film. Multiple scattering theory based on a cluster-model [ Phys. Rev. B , 075404 (2001)] is used to simulate the experiments.     

Satellite transitions in natural abundance solid-state (33)S MAS NMR of alums--sign change with zero-crossing of C(Q) in a variable temperature study

Experiences obtained from recent improvements in the performance of solid-state (14)N MAS NMR spectroscopy have been used in a natural abundance (33)S MAS NMR investigation of the satellite transitions for this interesting spin I=3/2 isotope. This study reports the first observation of manifolds of spinning sidebands for these transitions in (33)S MAS NMR as observed for the two alums XAl(SO(4))(2) x 12H(2)O with X=NH(4) and K. For the NH(4)-alum a variable temperature (33)S MAS NMR study, employing the satellite transitions, shows that the (33)S quadrupole coupling constant (C(Q)) exhibits a linear temperature dependence (in the range -35 degrees C to 70 degrees C) with a temperature gradient of 3.1 kHz/ degrees C and undergoes a sign change with zero-crossing for C(Q) at 4 degrees C (277 K). For the isostructural K-alum a quite similar increase in the magnitude of C(Q) with increasing temperature is observed, and with a temperature gradient of 2.3 kHz/ degrees C. Finally, for optimization purposes, a study on the effect of the applied pulse widths at constant rf field strength on the intensity and variation in second-order quadrupolar lineshape for the central (1/2<-->-1/2) transition of the K-alum has been performed.     

A new model for CO ordering at high coverages on low index metal surfaces: A correlation between LEED,HREELS and IRS: I. CO adsorbed on fcc (100) surfaces

In this paper, we reexamine the surface structures of CO on (100) surfaces of copper, palladium, nickel and platinum. We use the types of site determined by High Resolution Energy Electron Loss Spectroscopy (HREELS), or Infra Red Spectroscopy (IRS), to propose new models for the arrangement of CO molecules at coverages exceeding $\text{1}\text{2}$, i.e. at coverages higher than those corresponding to simple structures c(2 × 2) and $\text{p}\text{(2}\text{2}\text{×}\text{2}\text{)}\text{R}\text{45°}$. Laser simulations allow us to decide the validity of the proposed models. The consequences of these models are the existence of at most two adsorption sites at all coverages, and the existence of antiphase domains separated by walls to form the complex structures. The transition between two consecutive structures due to an increase of coverage is a unidirectional compression, generating more wall regions.     

Geometry of hydrogen chemisorption on Ni(111) analyzed by low energy electron diffraction

A LEED analysis predicts that hydrogen chemisorbed in a half monolayer on Ni(111) arranges in an overlayer with graphite-layer geometry of (2×2) unit cell, adsorbing in both types of threefold hollow sites with indistinguishable Ni-H bond lengths of 1.84+-0.06 Å, corresponding to an overlayer-substrate spacing of 1.15+-0.1 Å.     

The role of valence quarks in proton fragmentation

Following earlier theoretical and experimental work (Kalinowski et al. [6], Bourquin et al. [7]), baryon production by fragmentation of incident protons in high energy hadron collisions is re-investigated in terms of a fragmentation-recombination mechanism similar to a model proposed by Fukuda and Iso [4]. The multiplicitiesn _f (B) for the various types of baryonsB produced in proton fragmentation are expressed in terms of the probabilitiesa _i fori=0, ..., 3 valence quarks of the incident proton to emerge in the baryonB and 3?i to emerge in mesons (following [7] we suppose that antibaryon production is mostly due to baryon-antibaryon pair production by a mechanism of non-fragmentation type, and this is taken into account in deducingn _f (B) from baryon and antibaryon multiplicity data). The positivity of thea _i is found to impose remarkably narrow constraints on then _f (B) for (meta)stableB, and we find the data to satisfy these constraints. We show furthermore that the data are compatible with uncorrelated behaviour of the valence quarks of the incident proton, each of them having a probability ? 0.6 to emerge in the fragmentation baryonB, and a probability ? 0.4 to emerge in a meson. We also briefly discuss the relation of our analysis to previous work on the recombination model of proton fragmentation and its possible extension to meson fragmentation.     

Two problems concerning hot hadronic matter and high energy collisions (Equilibrium formation,plasma deflagration)

This paper addresses two questions concerning the hydrodynamical approach to high energy collisions producing large multiplicities of hadrons. The first one concerns the difficulty of understanding in terms of successive parton interactions the formation of local thermal equilibrium for the small and short-lived blobs of excited hadronic matter created in such collisions. We argue that the number of successive parton interactions is not the only relevant factor for equilibrium formation, another factor being the early randomization present in all experiments which observe a subsystem of the complete final state and average over many unobserved degrees of freedom. This conjecture helps to understand the high degree of universality of hadronic jets and the fact that quite different dynamical models manage to describe the same data. The second problem concerns the hadronization of a blob of quark-gluon plasma as could be produced in a very high energy collision. Assuming the transition of plasma to hadron gas to have high latent heat, we show for small chemical potential that the plasma can deflagrate and convert a fraction of its latent heat into collective flow of the hadron gas. In such deflagrations very little entropy is produced, but the flow velocity of the hadron gas with respect to the plasma can be more than half of the velocity of light.     

LEED study of the Pt(110)-(1 × 2) surface

The results of a quantitative LEED study of the clean, reconstructed Pt(110)-(1 × 2) surface are described, in which experimental intensity-energy spectra for ten diffracted beams have been compared, by an γ-factor analysis, to intensity spectra calculated using a dynamic theory for various structural models. Despite considerable effort in ensuring the reliability of the experimental and calculated intensities, a satisfactory level of agreement has not been achieved for any of the model structures considered although a “missing-row” model leads to the closest agreement between experimental and calculated intensities.