Heinz D. Wanzenböck

Surface-Enhanced Vibrational Spectroscopy: A New Tool in Chemical IR Sensing?

In order to further improve the sensitivity of chemical IR sensors, research into a significant change in the signal generation mechanism was carried out. This effort was realized by generating the surface-enhanced IR absorption and Raman-scattering effect at silver- and gold-island-covered Ge- and ZnSe ATR surfaces for surface-enhanced infrared absorption (SEIRA) and Ag-layer-covered brass plates for surface-enhanced Raman scattering (SERS), respectively, and linking the optimized tools to the IR sensor concept. By careful optimization of the generation of silver-island and gold-island films on Ge reflection elements, intensity gains by a factor of 50 were achieved. Chemical interactions between the silver-island layer and the various analytes investigated up to now (p-nitro benzoic acid, as a model compound, and selected aromatic and chlorinated pesticides) are likely, as indicated by significant IR spectral changes; the substances are, however, bound to the surfaces in a reversible manner. This property of the novel SEIRA sensor can be favorably exploited in flow-through systems. In a similar way, by a specially optimized treatment of anodically oxidized brass plates in a silver bath, repeatably usable SERS targets for the trace analysis of pesticide mixtures in aqueous systems could be developed. A signal enhancement factor of 1.4 million was obtained with pyridine as the standard sample. The data shown in this work suggest that both SEIRA and SERS can be coupled to a flow injection system in a reversible way for the molecular-specific trace analysis of organic compounds in aqueous solutions.

Fixed interface charges between AlGaN barrier and gate stack composed of in situ grown SiN and Al2O3 in AlGaN/GaN high electron mobility transistors with normally off capability

Using a generalized extraction method, the fixed charge density Nint at the interface between in situ deposited SiN and 5 nm thick AlGaN barrier is evaluated by measurements of threshold voltage Vth of an AlGaN/GaN metal insulator semiconductor high electron mobility transistor as a function of SiN thickness. The thickness of the originally deposited 50 nm thick SiN layer is reduced by dry etching. The extracted Nint is in the order of the AlGaN polarization charge density. The total removal of the in situ SiN cap leads to a complete depletion of the channel region resulting in Vth = +1 V. Fabrication of a gate stack with Al2O3 as a second cap layer, deposited on top of the in situ SiN, is not introducing additional fixed charges at the SiN/Al2O3 interface.

Multiple internal reflection in surface enhanced infrared absorption spectroscopy (SEIRA) and its significance for various analyte groups

Abstract The presence of rough metal surfaces is known to increase the infrared absorption of selected analytes. It could be shown that this surface enhancement effect applies to a wide range of chemical substrates with different molecular structure, although the observed enhancement is not equivalent for all absorption bands. For carboxyl groups, interactions with the metal surface were observed suggesting the formation of an adsorption complex. Furthermore, the potential of surface enhanced infrared absorption (SEIRA) as quantitative method is demonstrated.

Scanning Capacitance Microscopy Investigations of Focused Ion Beam Damage in Silicon

Abstract In this article we explore the application of scanning capacitance microscopy (SCM) for studying focused ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots and by comparison of topographical and SCM data. Further, we investigate the question how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analyzed by SCM in cross-sectional geometry.

Focussed ion beam induced damage in silicon studied by scanning capacitance microscopy

In this paper we explore the application of scanning capacitance microscopy (SCM) for studying focussed ion beam (FIB) induced damage in silicon. We qualitatively determine the technologically important beam shape by measuring the SCM image of FIB processed implantation spots, and by comparison of topographical and SCM data. Further, we investigate how deep impinging ions generate measurable damage below the silicon surface. For this purpose, trenches were manufactured using FIB and analysed by SCM in cross-sectional geometry.

Continuous surface enhanced Raman spectroscopy for the detection of trace organic pollutants in aqueous systems

Abstract In Raman spectroscopy, detection limits for organic pollutants in water can be lowered by several orders of magnitude when surface enhanced techniques are applied. In this work a continuous analytical device based on flow injection analysis using SERS detection is proposed. This system was tested with model analytes such as pyridine and nicotinic acid as well as several pesticides (carbendazim, metazachlorine).

Substituted triphenylamines as building blocks for star shaped organic electronic materials

A versatile synthetic protocol toward a series of various substituted triphenylamine derivatives serving as building blocks for organic electronic materials was developed. Key steps during synthesis were either Ullmann condensations or nucleophilic aromatic substitutions giving rise to structural modification of triphenylamines and their electronic nature. In turn, these scaffolds were exemplarily attached to a dendritic tris(2-thienyl)benzene core affording star shaped organic semiconducting materials which were characterized regarding their photo-physical, electro-chemical and thermal properties. A strong influence of the substituents nature on both photo-physical and morphological thin film characteristic of star shaped target compounds was observed. The applicability of these materials in organic electronic devices was demonstrated in an organic field effect transistor configuration yielding a hole mobility of nearly 10−3 cm2 V−1 s−1. The performance of the materials can be correlated to the substituents applied.

Surface enhanced infrared absorption (SEIRA) observed on different metal surface structures

Surface enhanced infrared absorption (SEIRA) spectroscopy is a novel method providing a significantly decreased limit of detection to conventional IR spectroscopy. The extent of spectral enhancement due to the presence of metal island layers is dependent on the surface morphology of the rough metal film. An improved two-staged deposition process is introduced enabling better control of the surface topology of the metal film. By modifying the angle of deposition a directional orientation of the growth process can be achieved approaching a needle-like shape of metal islands. With oblique metal deposition a significantly reduced background absorption of the metal film is obtained resulting in a decreased spectral noise. The strongest surface enhancement effect was obtained with metal layers deposited under a 18° angle.

Surface-enhanced Infrared Absorption Spectroscopy (SEIRA) Using Multireflection ATR-elements

This work shows the enhancement of spectral absorptions by noble metals (Ag, Au) deposited in nm-thick layers on the surface of ATR-crystals. By the surface-enhanced infrared absorption (SEIRA) technique, the absorption bands of p-nitrobenzoic acid can be enhanced by a factor of up to 40. This enables the detection of substance concentrations in the mM range. The structure of the metal deposit has been investigated by atomic force microscopy and correlated with the enhancement factor.