Volker Beushausen

Detection of explosives based on surface-enhanced Raman spectroscopy

In this study we present a device based on surface-enhanced Raman scattering (SERS) for the detection of airborne explosives. The explosives are resublimated on a cooled nanostructured gold substrate. The explosives trinitrotoluene (TNT) and triacetone triperoxide (TATP) are used. The SERS spectrum of the explosives is analyzed. Thus, TNT is deposited from an acetonitrile solution on the gold substrate. In the case of TATP, first the bulk TATP Raman spectrum was recorded and compared with the SERS spectrum, generated by deposition out of the gas phase. The frequencies of the SERS spectrum are hardly shifted compared to the spectrum of bulk TATP. The influence of the nanostructured gold substrate temperature on the signals of TATP was studied. A decrease in temperature up to 200 K increased the intensities of the TATP bands in the SERS spectrum; below 200 K, the TATP fingerprint disappeared.

Fabrication and characterization of homogeneous surface-enhanced Raman scattering substrates by single pulse UV-laser treatment of gold and silver films.

The fabrication of SERS-active substrates, which offer high enhancement factors as well as spatially homogeneous distribution of the enhancement, plays an important role in the expansion of surface-enhanced Raman scattering (SERS) spectroscopy to a powerful, quantitative, and noninvasive measurement technique for analytical applications. In this paper, a novel method for the fabrication of SERS-active substrates by laser treatment of 20, 40, and 60 nm thick gold and of 40 nm thick silver films supported on quartz glass is presented. Single 308 nm UV-laser pulses were applied to melt the thin gold and silver films. During the cooling process of the noble metal, particles were formed. The particle size and density were imaged by atomic force microscopy. By varying the fluence, the size of the particles can be controlled. The enhancement factors of the nanostructures were determined by recording self-assembled monolayers of benzenethiol. The intensity of the SERS signal from benzenethiol is correlated to the mean particle size and thus to the fluence. Enhancement factors up to 10(6) with a high reproducibility were reached. Finally we have analyzed the temperature dependence of the SERS effect by recording the intensity of benzenethiol vibrations from 300 to 120 K. The temperature dependence of the SERS effect is discussed with regard to the metal properties.

Temperature- and pressure-dependent midinfrared absorption cross sections of gaseous hydrocarbons

Transmittance spectra of four gaseous hydrocarbons were measured by using a Fourier transform infrared spectrometer. The analyzed substances are propane, n-butane, ethanol, and iso-octane (2,2,4-trimethyl-pentane). Mixtures of hydrocarbons and nitrogen were prepared and analyzed in an optical cell between 298 and 473 K at pressures up to 1800 kPa. Molecule specific absorption cross sections were calculated for different temperatures and pressures that are relevant for technical absorption measurements. Dependences of the spectral absorption cross sections, as well as the integrated absorption cross sections on temperature and pressure, were investigated.

Crank Angle Resolved Determination of Fuel-Concentration and Air/Fuel Ratio in a SI-Production Engine by Using a Modified Optical Spark Plug

Local, crank angle resolved fuel density variations were detected with a fiber optical sensor system in the vicinity of the spark position in a cylinder of a four-stroke SI production engine. The infrared absorption sensor detects the attenuation of infrared radiation in the 3.4 μm wavelength region due to the infrared vibrational-rotational absorption band of hydrocarbons (HC). The absorption path was integrated in a modified spark plug and a tungsten halide lamp was used as an infrared light source. All investigations were carried out on a four-stroke spark ignition engine with fuel injection into the intake manifold. The engine operated with common gasoline (Euro Super) at different preset overall air/fuel-ratios. Fuel concentration variations and the mixing process before the combustion were investigated for single engine cycles. In order to derive air/fuel-ratios from the measured HC-concentrations a special approximation method was used.

Free-flow electrophoresis with electrode-less injection molded chips

In this work we present the first approach towards low-cost free-flow electrophoresis (FFE) devices utilizing injection molding as a microfabrication process which has the potential to manufacture FFE chips at a cost which make their use commercially viable. This is achieved by realizing a new straightforward micro free-flow electrophoresis (μFFE) design ensuring both, bubble free electrophoretic separation and effective electrical connection by implementing miniaturized partitioning bars. This creates a defined open gap of 20 μm in height and 500 μm in width between separation zone and electrode channels. The thermoplastic μFFE chips are ready to use, there is no need for a subsequent labor-intensive implementation of membranes or salt bridges to separate the electrode channels from the separation zone.

Faseroptischer Zündkerzensensor zur Optimierung motorischer Brennverfahren

Fur die Entwicklung und Optimierung aktueller motorischer Brennverfahren werden immer ausgefeiltere Analysewerkzeuge benotigt, die Messdaten direkt aus dem Brennraum von laufenden Motoren aufzeichnen konnen. Die im Bereich Lasermesstechnik etablierte Firma LaVision GmbH hat einen in eine Standardzundkerze integrierten optischen Sensor entwickelt, der dem Entwicklungsingenieur einen vollig neuen Zugang zu innermotorischen Kenngrosen eroffnet. Dieser faseroptische Sensor ermoglicht erstmals eine kurbelwinkelaufgeloste Messung der Kraftstoff- und Restgaskonzentration direkt im Brennraum von Verbrennungsmotoren. Die genaue Kenntnis des zeitlichen Verlaufs dieser Messgrosen ermoglicht eine wesentlich zielgerichtetere Optimierung umwelt- und ressourcenschonender Brennverfahren.