M. Grasserbauer

Development of crystallinity and morphology in hafnium dioxide thin films grown by atomic layer epitaxy

The structural development of HfO2 thin films grown from HfCl4 and water onto glass substrates by atomic layer epitaxy at 500 °C was studied with X-ray diffraction, atomic force microscopy and scanning electron microscopy. The films were found to contain two regions of different crystallinity: a thin amorphous starting layer and a subsequent preferentially oriented polycrystalline layer. The films were built up of densely packed grains. Substantial surface roughening occurred along with increasing film thickness. The films were chlorine free as analyzed by Rutherford backscattering spectrometry.

Phase imaging as an extension to tapping mode AFM for the identification of material properties on humidity-sensitive surfaces

A method for accessing information in addition to the topography primarily provided by tapping mode atomic force microscopy (TM-AFM) is presented. The phase difference between the driving signal of the piezo oscillating the cantilever in the TM-AFM and the resulting motion of the tip is exploited in order to access additional information about the tip sample interaction. Adhesive forces between the tip and the surface can be mapped simultaneously to the topographic data with the same lateral resolution. We found evidence that the phase signal is closely related to the nature of the water layer present on surfaces exposed to the ambient atmosphere by examining aerosol particles on polyester foil and the corrosion of potash-lime-silica glass with medieval composition. However, also the topography as well as operating parameters such as load force and scan speed contribute to the phase signal making quantitative comparisons difficult.

Surface roughness reduction in atomic layer epitaxy growth of titanium dioxide thin films

The surface smoothness of TiO2 films grown by atomic layer epitaxy was improved by incorporating thin intermediate Al2O3 layers into them. The elimination of light scattering from the film surface caused a marked increase in the specular transmittance. Optical measurements, atomic force microscopy, scanning electron microscopy and X-ray diffraction were used in examining the relationships between the amount of Al2O3 added and the optical, morphological and structural properties of the films. The mechanism of the surface roughness reduction is discussed.

Comparison of different sorbent materials for on-line solid-phase extraction with liquid chromatography-atmospheric pressure chemical ionization mass spectrometry of phenols.

On-line solid-phase extraction (SPE) was interfaced to liquid chromatography with atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS) for the determination of US Environmental Protection Agency (EPA) phenols. The system, allowing fully automated operation, was used to evaluate different SPE cartridge materials and dimensions. Six different SPE materials (C18 HD, Polymer Labs PLRP-s, Hamilton PRP-1, Hysphere GP, Hysphere SH and Waters Oasis) were tested. Criteria for their comparison were first the recovery for the different phenols and its reproducibility, but also chromatographically relevant items like peakshape in the on-line elution mode. High recoveries and good relative standard deviations were obtained particularly for the newer, strongly retaining SPE materials that have become commercially available recently (the Hysphere materials and Waters Oasis) compared to the well known silica-based and weaker polymeric adsorbents like PLRP-s and PRP-1. These advantages are, however, traded in for good chromatographic peakshape, since the stronger adsorbents give rise to notable peak broadening in on-line elution. This is particularly true when using APCI-MS detection which on the one hand offers excellent selectivity and sensitivity, but imposes additional restrictions on the mobile phase composition in order not to suppress the response significantly. The influence of these parameters on the on-line-SPE-HPLC-MS determination of EPA phenols is discussed and present limitations are pointed out.

Wavelet denoising of Gaussian peaks: A comparative study

Abstract In this paper we apply some recent results on non-linear wavelet analysis to simulated noisy signals of chemical interest. In particular, we compare the wavelet soft universal thresholding algorithm described by Donoho, to Fourier filters and to polynomial smoothers such as the Savitzky-Golay filters (SG). All reconstruction filters were evaluated on the basis of three different criteria: the mean squared error (MSE) both for the whole signal and for an interval centred around the peak, the signal-to-noise ratio (SNR) improvement and the change in the peak area. The simulated data consists of narrow Gaussian peaks with white noise. Signals with low SNR were investigated, since this is a challenging problem for each reconstruction filter. Four common wavelets (Haar, Daubechies, Symmlets and Coiflets) were selected for the wavelet denoising. Our results show that under the chosen conditions wavelet denoising (WD) gives in most cases superior performance over classical filter techniques.

Generalized Model for the Clustering of As Dopants in Si

A model for As clustering in single crystal silicon is presented that allows for the participation of arbitrary numbers of As ions, electrons, and arbitrarily charged vacancies. From this model the saturation behavior of the concentration of unclustered, electrically active As impurities is derived. It is shown that saturation (or electrical solubility) demands the participation of at least one negative charge in the formation of positively charged clusters, be it electron or negative vacancy. By analysis of our own experimental results and those by other authors, this general cluster model indicates that the participation of exactly one negative charge is the most likely case. In the course of this discussion the equilibrium saturation concentration of electrically active As is deduced from experiment as a function of temperature.

AFM studies on ZnS thin films grown by atomic layer epitaxy

Abstract Polycrystalline ZnS films were grown from ZnCl2 and H2S on glass and mica using the atomic layer epitaxy (ALE) technique. Morphological and crystalline changes during the ALE growth of ZnS were studied by AFM and XRD. AFM measurements revealed that substantial agglomeration took place in the beginning of the growth. On glass the nucleation density of ZnS was higher than on mica and consequently the films on glass remained smoother than those on mica. XRD measurements revealed that orientation of the films was stronger on mica than on glass.

High-performance liquid chromatography–atmospheric-pressure chemical ionization mass spectrometry as a new tool for the determination of the mycotoxin zearalenone in food and feed

A new method for the determination of the mycotoxin zearalenone (ZON) in food and feed, based on HPLC-MS with an atmospheric-pressure chemical ionization (APCI) interface after extraction from cereals and clean-up by either conventional solid-phase or immunoaffinity cartridge is presented. The APCI interface parameters are optimized to provide detection of ZON with maximum sensitivity after RP separation of ZON on a C18 column with acetonitrile-water (40:60, v/v) at 1 ml/min column flow without split. Using APCI-MS detection, the sensitivity of the method was improved by a factor of ca. 50 in comparison to HPLC with fluorescence detection, allowing determination of ZON down to 0.12 microgram/kg maize which is well below present threshold values. Due to the selectivity of MS detection, it also was possible to quantitatively determine ZON both in raw extracts without clean-up using a normal-size (100 mm) chromatographic column or using only a short (20 mm) chromatographic column, when a clean-up was done to minimize possible interferences.

Evaluation of solid-phase microextraction for sampling of volatile organic sulfur compounds in air for subsequent gas chromatographic analysis with atomic emission detection

Abstract The use of solid-phase microextraction (SPME) followed by GC–AED (atomic emission detection) for the analysis of volatile organic sulfur compounds (methanethiol, dimethyl sulfide, isopropanethiol and isobutanethiol) in spiked air samples was investigated. Gaseous standard mixtures were generated by means of a permeation apparatus with stopped flow facilities to permit sampling of the analytes with the SPME fiber. Detection limits between 4 ppt for dimethyl sulfide and isobutanethiol and 50 ppt (v/v) for methanethiol were achieved for extraction with the Carboxen–PDMS (polydimethylsiloxane) fiber followed by GC–AED analysis. The comparison of the performance of the 100 μm PDMS and the 75 μm Carboxen–PDMS fiber coating demonstrates the superiority of the latter in terms of sensitivity and repeatability. Despite the principal applicability of SPME to sampling of organosulfur compounds, artifacts are observed during analysis. Furthermore, the low storage stability, the dependence of the extraction efficiency on the relative humidity and the pronounced differences in sensitivity between fibers limit the usefulness of the method for quantitative on-site analysis.

Separation and identification of polar degradation products of benzo[a]pyrene with ozone by atmospheric pressure chemical ionization-mass spectrometry after optimized column chromatographic clean-up

The environmental relevance of oxidized degradation products of polycyclic aromatic hydrocarbons (PAHs) increases due to enhanced combustion of organic matter and fossil fuels. For PAHs consisting of more than three condensed aromatic rings, soot aerosols are the main carrier, on the surface of which they can react with trace gases like ozone. In this study the clean-up procedure and analysis of ozonized benzo[a]pyrene (B[a]P) was optimized. B[a]P and its degradation products were preseparated into three fractions. Different reversed-phase materials were evaluated for high-performance liquid chromatographic separation. Among these, a phenyl-modified silica material proved best-suited and the chromatographic separation was optimized on this material. For the detection of separated degradation products, liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) was used. With this method, 29 components could be characterized. Besides the three known main degradation products (B[a]P-1,6-dione, B[a]P-3,6-dione, B[a]P-6,12-dione, B[a]P-4,5-dione and 4-oxa-benzo[d,e,f]chrysene-5-one (B[def]C-lactone), were identified for the first time with the help of reference substances. B[def]C-lactone is known as a substance with a mutagenic potential similar to B[a]P. Several other compounds could be tentatively identified.