Albert Lauwers

Influence of Ge substrate crystallinity on Co germanide formation in solid-state reactions

A strong influence of substrate crystallinity is observed for thin-film Co∕Ge reactions. For the detected phases (CoGe, Co5Ge7, and CoGe2), the formation temperatures on amorphous Ge (a-Ge) are found to be the lowest, while the highest are on single-crystalline Ge(100). Moreover, while the phase sequence on Ge(100) and polycrystalline Ge (poly-Ge) was unaltered, the formation of intermediate Co5Ge7 was not observed on a-Ge. It is likely that this is due to a promoted CoGe2 formation on a-Ge, resulting in a ∼200°C decrease in formation temperature (depending on the ramp rate). These observations suggest a strong competition among the formation of these Ge-rich phases.

Kinetic investigation of the degradation of hyaluronan by hyaluronidase using gel permeation chromatography.

A gel permeation chromatography (GPC) system for the analysis of hyaluronan was set up and calibrated by means of the universal calibration method. Using GPC, a kinetic assay of the action of hyaluronidase on hyaluronan has been developed. Applying Michaelis-Menten theory and the direct linear plot we have estimated the kinetic constants of the enzyme. By evaluating the decrease of the various molecular mass averages during the enzymatic reactions, we have given a demonstration of the at random degradation of hyaluronan by hyaluronidase in the initial stage of the reaction.

Kinetics of Ni3Si2 formation in the Ni2Si–NiSi thin film reaction from in situ measurements

The kinetics of Ni3Si2 formation in the Ni2Si–NiSi thin film reaction were determined from simultaneous in situ x-ray diffraction (XRD) measurements, performed using a synchrotron source, and sheet resistance measurements. Samples consisted of 90nm Ni∕100nm polycrystalline-Si∕SiO2 stacks, of interest for fully silicided gate applications, on (100) Si. After initial formation of a Ni2Si∕NiSi bilayer, these films reacted to form Ni3Si2. The evolution of sheet resistance and of the intensity of XRD peaks were used to extract the fraction of Ni3Si2 formed during ramp and isothermal annealings. A Kissinger analysis was performed for ramp annealing with ramp rates of 1, 3, 5, 9, and 27°C∕s, obtaining the activation energy of Ni3Si2 formation, Ea=1.92±0.15eV. A Kolmogorov-Johnson-Mehl-Avrami analysis was performed for isothermal anneals, finding an Avrami exponent of 2.1±0.2, suggesting two-dimensional growth. This is consistent with a nucleation controlled process for Ni3Si2 formation, with nucleation sites at ...

Fractionation and purification of the thiol proteinases from papaya latex

Three cysteine proteinases, i.e. chymopapain, papaya proteinase IV and proteinase III, were purified to homogeneity from papaya latex using a combination of ion-exchange chromatography and hydrophobic interaction chromatography. During the purification procedure, the thiol-groups of the active center were reversibly blocked as mixed disulfides with 2-thiopyridone. Homogeneity was proved electrophoretically by native polyacrylamide gel electrophoresis (PAGE), sodium dodecyl sulfate (SDS)-PAGE and rechromatography on a Mono S 5/5 column at pH 5.0.

Kinetic constants for the hydrolysis of aggrecan by the papaya proteinases and their relevance for chemonucleolysis

The four known proteinases from papaya latex, namely papain (EC 3.4.22.2), chymopapain (EC 3.4.22.6), caricain (EC 3.4.22.30), and glycyl endopeptidase (EC 3.4.22.25), were purified to homogeneity and fully characterized by single radial immunodiffusion and active-site titration. A modified HPLC gel permeation assay was used to determine the kinetic constants for aggrecan hydrolysis by the papaya proteinases. The disappearance of intact aggrecan monomer was first-order, indicating that for the four enzymes studied the Km was much larger than 0.5 microM and that kcat/Km = 1.2 +/- 0.1 x 10(6) M-1 s-1 for chymopapain, 1.20 +/- 0.08 x 10(6) M-1 s-1 for caricain, 0.90 +/- 0.02 x 10(6) M-1 s-1 for papain, and 0.120 +/- 0.005 x 10(6) M-1 s-1 for glycyl endopeptidase. Chymodiactin, the chymopapain preparation used for chemonucleolysis, consists of a mixture of chymopapain (70%), caricain (20%), and glycyl endopeptidase (4%). The rate constant for the aggrecan hydrolysis by such a mixture was not significantly different from the rate constant for pure chymopapain. As a result of these observations, we predict that pure chymopapain could replace partially purified chymopapain preparations for chemonucleolysis.

In situ transmission electron microscopy study of the silicidation process in Co thin films on patterned (001) Si substrates

The results of an in situ transmission electron microscopy study of the formation of Co-silicides on patterned (001) Si substrates are discussed. It is shown that the results of the in situ heating experiments agreed very well with the data based on standard rapid thermal annealing experiments. Fast heating rates resulted in better definition of the silicide lines. Also, better lines were obtained for samples that received already a low-temperature ex situ anneal. A Ti cap layer gave rise to a higher degree of epitaxy in the CoSi 2 silicide.

High-performance size-exclusion chromatography of proteoglycans extracted from bovine articular cartilage

Abstract The applicability of high-performance size-exclusion chromatography for determining the relative molecular weight of proteoglycans was tested with a new type of column. The method is extremely reproducible, precise and rapid and allows molecular weight determinations up to 3 millions, even done in the presence of considerable impurities of low molecular weight. This technique offers important advantages over the traditional techniques, such as light scattering, sedementation velocity and equilibrium ultracentrifugation and viscosity. The peak position method was used to calibrate our system using pullulan standards. For the pullulan standards in the molecular weight range between 1.0 × 10 4 and 8.5 × 10 5 , an almost linear relationship between log M p and the ratio between the retention time of the standard and that of the excluded salt was found. For the lower molecular weight standards, even at the lowest measured concentration, the curve deviated sharply for ratios above 0.80. The influence of the flow-rate on this ratio was negligible. We were able to separate the proteoglycan aggregates from the proteoglycan monomers in the KCl extracts. In the CaCl 2 extract however, we could not separate the monomers from the aggregates, since these were present in a much higher concentration than in the KCl extract. After the addition of hyaluronidase from bovine testes, the proteoglycan aggregates were broken down by lysis of the hyaluronic acid molecules, who are essential for the formation of these aggregates.