Tran Minh Duc

The chemistry of deposits formed from acrylic acid plasmas

SIMS and XPS were used to characterise the chemistry of thin plasma polymerised acrylic acid films (ppAAc), and to determine how this was influenced by plasma power. Quartz microbalance weight measurements were used to monitor the effect of power on the deposition rate and identify the uptake of water vapour by the films upon exposure to the atmosphere. Functional group derivatisation and XPS were used to quantify the proportion of carboxylic acid and ester functionalities. Derivatisation revealed that the level of retention in the deposit could be controlled by the plasma deposition power (P) up to a maximum of 66% at P=2 W. TOF SIMS analysis identified the presence of linear structures with up to five monomer units in the high retention deposit. The role of such structures in functional retention is discussed with reference to mass spectrometry data in the literature.

X-ray photoelectron spectroscopy of thermally grown silicon dioxide films on silicon

Abstract At various stages of in situ thermal oxidation of Si(111) monocrystals, X-ray photoelectron spectroscopy (XPS or ESCA) reveals a shift in the silicon core-level binding energies which varies continuously from 2.4 to 4.2 eV. From the oxygen and silicon ESCA peak intensities, these films can be said to have the silicon dioxide composition with an excess in oxygen concentration. By correlating the silicon 2p or 2s binding-energy shifts with oxygen KLL Auger energy and oxygen 1s binding-energy shifts, it is shown that a Fermi level shift and differential extra-atomic relaxation energy in the interfacial region must be invoked, in addition to chemical structure considerations, to interpret these data.

Quantitative determination of Young's modulus on a biphase polymer system using atomic force microscopy

Atomic force microscopy (AFM) is currently used to investigate polymer surface morphology, to obtain roughness parameters or to map the qualitative differences of surface properties. Some previous studies have attempted to determine quantitatively the elastic surface properties, but the difficulty with AFM is that the contact geometry is not very well known, due to the complexity of the mechanical system composed of the cantilever-tip set and the solid surface. We propose here a relative method for measuring the Youngs modulus E of a polymer surface by AFM indentation, involving a calibration step obtained from a set of standards constituted by pure polymers with known modulus. Contact stiffness, indentation at peak load and shape of unloading curve are obtained for each reference polymer, leading to a linear relationship between E and a function of these parameters. This calibration curve allows the unknown Youngs modulus values of the different phases at the surface of a biphase polymer system to be determined. The force volume mode was used to record force curves. Compared to classical indentation techniques, the force volume mode gives the advantage of imaging surface domains exhibiting elasticity differences. Thus, the elastic modulus can be quantified with a spatial resolution on a nanometric scale.

Interfacial interactions of plasma‐polymerized acrylic acid and an oxidized aluminium surface investigated using XPS, FTIR and poly(acrylic acid) as a model compound

X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) are used to characterize the interface between poly(acrylic acid) (PAA) and an aluminium oxyhydroxide (AlOOH) surface. Reaction of the PAA carboxylic acid functionality with hydroxyl groups at the surface of the oxide to form a monodentate carboxylate complex C(O)OAl was identified by FTIR. The degree of conversion of the acid to the salt at the interface was estimated to be 40% from the XPS analysis of PAA overlayers of varying thickness. An equivalent reaction was identified at the interface between AlOOH and a monolayer of strongly bonded plasma-polymerized acrylic acid (ppAAc) that remained after solvent washing. The resistance of the monolayer of ppAAc to solvent washing was attributed to the formation of interfacial carboxylate complexes with the AlOOH surface.

Effect of heat treatment on chemical and electronic structure of solid SiO : An electron spectroscopy study

Abstract Photoelectron spectroscopy (XPS and UPS) and X-ray excited Auger electron spectroscopy (XAES) measurements for commercial SiO powder and for SiO thin films show direct evidence for the evolution of the chemical structure of SiO from a characteristic metastable phase to a microscopic mixture of Si and SiO 2 when the temperature increases.

Pt10Ni90(111) single crystal alloy: Determination of the surface composition by AES, XPS and ISS

Abstract The surface composition of the Pt 10 Ni 90 (111) single crystal alloy has been determined from AES, XPS and ISS experiments. The clean surface is largely enriched with platinum: 30–40% in the top layer instead of 10% in the bulk. This enrichment concerns mainly the ultimate surface layer and appears to be only slightly dependent on the sample temperature.

Characterization of lacrymal component accumulation on worn soft contact lens surfaces by atomic force microscopy

The purpose of this study was to investigate lacrymal component accumulation on a soft contact lens (SCL) surface after various periods of continuous wear, using the recently developed atomic force microscopy (AFM). AFM allowed high resolution images of unworn and worn SCL, and presented two main advantages. 1. The SCL are analysed under nearly physiological conditions without being dried or destroyed. So the same SCL was analysed at various times during a long wearing period. To identify the deposited tear proteins, a qualitative analysis of solubilized deposit by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) on 4-15% gradient minigels was performed as well. We present typical images which emphasize the importance of the coating by lacrymal components. AFM analysis of worn SCL showed the deposition on the surface of a uniform lacrymal component coating (named deposit type I) with a progressive accumulation of numerous discrete granules (named deposit type II). SDS-PAGE of extracted deposits revealed the main tear proteins as: IgA, lactoferrin, tear lipocalin and lysozyme and the unknown protein of molecular weight 30,000. There is no clear difference in the protein patterns of the two types of deposits. Furthermore, a particular mode of use of AFM is described to illustrate the potential of this technique as a local tool for measuring protein coating thickness. Thus, for analysis of protein deposits on SCL surfaces, SDS-PAGE on minigels and AFM were easy and rapid to perform. When associated, these two techniques could find use in a wide range of worn SCL evaluation and most generally in biocompatibility evaluation studies.

Protein encapsulation in biodegradable amphiphilic microspheres

MPOE-PLA microspheres containing bovine serum albumin (BSA) were prepared by the double emulsion method with high encapsulation efficiency ( approximately 93%). Confocal scanning microscopic analysis using MPOE-PLA labelled with 1-pyrenemethanol showed the MPOE coating of the microsphere surface. This coating improves the performance of the release system compared with PLA microspheres; the hydrophilic chains reduce the BSA adsorption onto the microspheres and increase the amount of BSA released in the supernatant. Microsphere analysis using atomic force microscopy showed that the presence of the MPOE chains also leads to surface roughness. Studies of the diffusion of 1% rhodamine aqueous solution into the microspheres by means of confocal microscopy showed a fast diffusion of water through the matrices containing high molecular weight MPOE chains (?10 000 g mol-1) and could explain the fast release of BSA from these microspheres.

Surface modification of polytetrafluoroethylene by microwave plasma downstream treatment

Abstract The surface modification of polytetrafluoroethylene (PTFE) by microwave plasma treatment was investigated by means of contact angle measurement and e.s.c.a. studies. Various gases (e.g. O 2 , O 2 N 2 , NH 3 ) were used. The influence of the various plasma parameters, such as power, gas flow, distance between the sample and the centre of the discharge, treatment time, etc., has been evaluated. No modification was induced by O 2 and O 2 N 2 treatment, whatever the treatment conditions. NH 3 plasma irradiation, however, rendered the PTFE surfaces more hydrophilic, leading to an increase of the polar component of the surface energy from 4.5 to ∼ 57 mJ m −2 under optimized treatment conditions. NH 3 treatment led to defluorination, crosslinking, hydrocarbon (CC,CH) bond formation, and incorporation of nitrogen-containing groups, as confirmed by e.s.c.a. Oxygen was also detected at the surface of treated PTFE. Correlations between the contact angle, defluorination rate, and surface nitrogen and oxygen contents, have been established. Optimization of operational NH 3 plasma parameters, leading to the best wettability of the treated samples, is also reported.

ESCA study of molecular GeS3-x Tex As2 glasses

Abstract X-ray, photoelectron spectroscopy associated with thermodynamical and electrical measurements is used in order to demonstrate a molecular structure for