Measuring the Au(1 1 1) surface state at the solid–liquid interface

We present the first direct observation of an occupied noble metal surface state at the metal/liquid interface. The Au(1 1 1) Shockley-like surface state was measured by scanning tunneling spectroscopy (STS) at the Au(1 1 1)/n-tetradecane interface. These results show that the surface state of gold survives in a liquid environment, and can be probed by STS. More generally it indicates that STS can be used to study electronic properties of surfaces at the solid/liquid interface, and that spectra can be directly compared to measurements and calculations of a surface’s electronic structure in ultra-high vacuum.     

Interfacial adhesion mechanisms in incompatible semicrystalline polymer systems

The mechanism of adhesion at semicrystalline polymer interfaces between isotactic polypropylene (iPP) and linear low‐density polyethylene (PE) was studied with transmission electron microscopy (TEM) and an asymmetric‐double‐cantilever‐beam test. From the TEM images, both the interfacial width and the lamellar thickness of the polymers were extracted. During annealing, the interfacial width increased with the annealing temperature, and this indicated the accumulation of amorphous polymers at the interface. The interfacial strength, determined from the critical fracture energy (G_c), also increased with the annealing temperature and reached a maximum above the melting temperatures of iPP and PE, whereas the smallest G_c value was obtained below the melting temperatures of the two materials. A mechanism of interfacial strengthening was proposed accounting for the competition between the interdiffusion of PE and crystallization of iPP. As the annealing temperature increased, the rates of PE diffusion and iPP crystallization increased. Although the crystallization of iPP hindered the interdiffusion of PE, both the interfacial width and the fracture energy increased with the temperature, and this indicated that PE interdiffusion dominated iPP crystallization. Below the critical temperature, the fracture surfaces of both iPP and PE were smooth, and chain pullout dominated the fracture mechanism. Above the critical temperature, iPP crystallization still hindered the interdiffusion, and crazes could be seen on the iPP side. Above the melting temperatures of the two materials, ruptured surfaces could also be seen on the PE side, and crazing was the fracture mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2667–2679, 2004     

The epitaxial growth of Pd electrodeposition on Au(1 0 0) studied by LEED and RHEED

The epitaxial growth of Pd adlayers electrochemically deposited onto Au(1 0 0) has been studied by LEED, RHEED and AES. For the first 6 ML, the Pd deposits grow pseudomorphically on Au(1 0 0) with a lateral expansion of 4.5% with respect to bulk Pd. The strain in the expanded commensurate (1 × 1) Pd layers on Au(1 0 0) begins to be relieved at the Pd coverage between 6 and 9 ML range by formation of a compressed Pd film with respect to Au(1 0 0) surface and the compression increases continuously with thickness. At ca. 20 ML Pd the lattice constant of the film approaches to the bulk Pd and three-dimensional Pd islands develop since around 30 ML coverage. No superstructure due to the Pd-Au surface alloy can be found for coverages from monolayer up to 30 ML Pd on Au(1 0 0). A c(2 × 2) phase has been observed on the Pd-deposited Au(1 0 0) electrodes, which is ascribed to an ordered Cl adlayers adsorbed on Pd adlayers rather than a Pd-Au surface alloy.     

Mn-doped GaN/AlN heterojunction for spintronic devices

We present first principles calculations of Mn-doped GaN/AlN(0001) heterostructures obtained within the framework of density functional theory by using plane wave pseudopotential techniques. We found that for diluted Mn concentration this system present an integer magnetization that is a fingerprint of half-metallic property; this suggests the possibility to use this junction as a spin injector.     

Determination of the heterogeneous association constants of metal ions to omega-mercaptoalkanoic acids by using double-layer capacity measurements.

The binding of metal ions to ligands in homogeneous solutions and that to the same ligands anchored to metallic surfaces through self-assembled monolayers (SAMs) are expected to differ primarily due to the difference in the degree of freedom of the ligands and the surface potential. We studied the heterogeneous binding of CdII ions to omega-mercaptoalkanoic-acid SAMs on Au. This was accomplished by adding metal ions at a constant pH and following the changes in the double-layer capacity. A mathematical treatment, which is based on calculating the electrochemical-potential differences at the double layer-solution interface, has been developed. Our approach follows that proposed by White et al. and Kakiuchi, who used the acid-base equilibrium at the monolayer-electrolyte interface as a means of calculating the pK of ionizable SAMs. Experimentally, SAMs of omega-mercaptoalkanoic acids, HS(CH2)nCO2H, with different chain lengths (i.e., n=2, 5, and 10) in 0.1 M sodium perchlorate were assembled on Au surfaces and studied. The capacity was measured first in the absence of CdII at different pH values, and then at a constant pH while increasing the concentration of CdII in the solution. We found that the interfacial capacity decreased as the concentration (of either protons or CdII) increased. The results matched the model fairly well, which allowed the extraction of the thermodynamic equilibrium constant that is established at the monolayer-electrolyte interface. The suggested mathematical treatment of this model system is simple and yet very useful for estimating the heterogeneous association constants of metal ions by SAMs.     

Twin photons entangled in polarization and angular momentum

Quantum states of twin photons entangled in angular momentum and polarization provide new degrees of freedom to researchers in quantum information and imaging. This work discuss these states and also emphasizes differences between two proposed models for twin photons entangled in angular momentum. Answers to the presented questions would contribute to a better understanding of this nonlinear process. Received 30 August 2002 / Received in final form 10 October 2002 Published online 21 January 2003     

Comparative study of silanisation reactions for the biofunctionalisation of Ti-surfaces

In the present work, we report on the biofunctionalisation of silanised Ti-surfaces with gelatin. In recent years, a large number of papers have been published about the silanisation of different substrates including Ti-surfaces for biomedical applications. However, a comparative study evaluating the effects of different pre-treatment methods (cleaning and/or oxidation) and the efficiency of different silanisation reactions has to our information not yet been published. Since a clean and reproducible surface is required for studying structure-property relations, all Ti-surfaces were subjected to a three step procedure including a cleaning step, an oxidation step and a silanisation step. XPS analysis and contact angle measurements revealed that the pre-treatment of the Ti samples (cleaning + oxidation) had a drastic effect both on the surface composition and its wettability. A detailed study on the effect of different silanisation parameters indicated that the siloxane concentration, the siloxane type, the solvent and a catalyst affect the coupling efficiency of siloxanes to Ti-surfaces. Stability studies revealed a dependency between the siloxane type and the stability of the siloxane coating against hydrolytic cleavage from a Ti-surface. Since Ti-surfaces modified with a methacrylate containing silane possessed the highest hydrolytic stability, these surfaces were selected for the subsequent immobilisation of methacrylamide-modified gelatin via high energy irradiation induced cross-linking. The present work clearly demonstrates the need of a proper reaction strategy for immobilising ligands on Ti-surfaces.     

Formation of sharp metal-organic semiconductor interfaces: Ag and Sn on CuPc

A detailed investigation of the chemistry and electronic structure during the formation of the interfaces between thin films of the archetypal organic molecular semiconductor copper phthalocyanine (CuPc) and Ag or Sn deposited on it was performed using photoemission and near-edge X-ray absorption spectroscopies with synchrotron light. Our study demonstrates the formation of sharp, abrupt interfaces, a behavior which is of particular importance for applications in organic devices. Moreover, for Ag on CuPc we demonstrate that this interface is free from any reaction, whereas there is slight interface reaction for Sn/CuPc.     

Role of interfacial interactions on the anomalous swelling of polymer thin films in supercritical carbon dioxide

It has recently been shown that thin polymer films in the nanometer thickness range exhibit anomalous swelling maxima in supercritical CO₂ (Sc‐Co₂) in the vicinity of the critical point of CO₂. The adsorption isotherm of CO₂ on carbon black, silica surfaces, porous zeolites, and other surfaces, is known to exhibit anomalous maxima under similar CO₂ conditions. It is believed that because CO₂ possesses a low cohesive energy density, there would be an excess amount of CO₂ at the surfaces of these materials and hence the CO₂/polymer interface. This might cause excess CO₂ in the polymer films near the free surface, and hence the swelling anomaly. In addition, an excess of CO₂ would reside at the polymer/substrate and polymer/CO₂ interfaces for entropic reasons. These interfacial effects, as have been suggested, should account for an overall excess of CO₂ in a thin polymer film compared to the bulk, and would be responsible for the anomalous swelling. In this study, we use in situ spectroscopic ellipsometry to investigate the role of interfaces on the anomalous swelling of polymer thin films of varying initial thicknesses, h₀, exposed to Sc‐CO₂. We examined three homopolymers, poly(1,1′‐dihydroperflurooctyl methacrylate) (PFOMA), polystyrene (PS), poly(ethylene oxide) (PEO), that exhibit very different interactions with Sc‐CO₂, and the diblock copolymer of PS‐b‐PFOMA. We show that the anomalous swelling cannot be solely explained by the excess adsorption of CO₂ at interfaces. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1313–1324, 2007