@article{LoehmannsroebenLau2005, author = {L{\"o}hmannsr{\"o}ben, Hans-Gerd and Lau, Steffen}, title = {Isotope selectivity in environmental monitoring : NIR diode laser spectroscopy for isotope-selective sensing of soil-respired carbon dioxide}, year = {2005}, language = {en} } @article{HornerLauKantoretal.2004, author = {Horner, G. and Lau, Steffen and Kantor, Z. and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Isotope selective analysis of CO2 with tunable diode laser (TDL) spectroscopy in the NIR}, issn = {0003-2654}, year = {2004}, abstract = {The performance of a home-built tunable diode laser (TDL) spectrometer, aimed at multi-line detection of carbon dioxide, has been evaluated and optimized. In the regime of the (3001)(III) <-- (000) band of (CO2)-C-12 around 1.6 mum, the dominating isotope species (CO2)-C-12, (CO2)-C-13, and (COO)-C-12-O-18-O-16 were detected simultaneously without interference by water vapor. Detection limits in the range of few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. High sensitivity in conjunction with high precision-typically +/-1\% and +/-6\% for 3\% and 0.7\% of CO2, respectively-renders this experimental approach a promising analytical concept for isotope-ratio determination of carbon dioxide in soil and breath gas. For a moderate (CO2)-C-12 line, the pressure dependence of the line profile was characterized in detail, to account for pressure effects on sensitive measurements}, language = {en} } @misc{LauSalffnerLoehmannsroeben2006, author = {Lau, Steffen and Salffner, Katharina and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Isotopic resolution of carbon monoxide and carbon dioxide by NIR diode laser spectroscopy}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10135}, year = {2006}, abstract = {Near-infrared (NIR) absorption spectroscopy with tunable diode lasers allows the simultaneous detection of the three most important isotopologues of carbon dioxide (¹²CO₂, ¹³CO₂, ¹²C¹⁸O¹⁶O) and carbon monoxide (¹²CO, ¹³CO, ¹²C¹⁸O). The flexible and compact fiber-optic tunable diode laser absorption spectrometer (TDLAS) allows selective measurements of CO₂ and CO with high isotopic resolution without sample preparation since there is no interference with water vapour. For each species, linear calibration plots with a dynamic range of four orders of magnitude and detection limits (LOD) in the range of a few ppm were obtained utilizing wavelength modulation spectroscopy (WMS) with balanced detection in a Herriott-type multipass cell. The high performance of the apparatus is illustrated by fill-evacuation-refill cycles.}, subject = {Isotop}, language = {en} } @misc{HoernerLauLoehmannsroeben2004, author = {H{\"o}rner, Gerald and Lau, Steffen and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {NIR-diode laser spectroscopy for isotope-selective sensing of soil-respired carbon dioxide}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10148}, year = {2004}, abstract = {The performance of a home-built tunable diode laser (TDL) spectrometer has been optimized regarding multi-line detection of carbon dioxide in natural gases. In the regime of the (30⁰1)_III ← (000) band of ¹²CO₂ around 1.6 μm, the dominating isotope species ¹²CO₂, ¹³CO₂, and ¹²C¹⁸O¹⁶O were detected simultaneously. In contrast to most established techniques, selective measurements are performed without any sample preparation. This is possible since the CO₂ detection is free of interference from water, ubiquitous in natural gases. Detection limits in the range of a few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. Linear calibration plots cover a dynamic range of four orders of magnitude, allowing for quantitative CO₂ detection in various samples, like soil and breath gas. High isotopic resolution enables the excellent selectivity, sensitivity, and stability of the chosen analytical concept. The obtained isotopic resolution of typically ± 1.0 per mille and ± 1.5 per mille (for 3 vol. \% and 0.7 vol. \% of CO₂, respectively) offers a promising analytical tool for isotope-ratio determination of carbon dioxide in soil gas. Preliminary experiments on soil respiration for the first time combine the on-line quantification of the overall carbon dioxide content with an optode sensor and isotopic determination (TDL system) of natural gas species.}, subject = {Kohlendioxid}, language = {en} } @misc{HoernerLauKantoretal.2004, author = {H{\"o}rner, Gerald and Lau, Steffen and Kantor, Zoltan and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Isotope selective analysis of CO2 with tunable diode laser (TDL) spectroscopy in the NIR}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-10167}, year = {2004}, abstract = {The performance of a home-built tunable diode laser (TDL) spectrometer, aimed at multi-line detection of carbon dioxide, has been evaluated and optimized. In the regime of the (30⁰1)_III / (000) band of ¹²CO₂ around 1.6 μm, the dominating isotope species ¹²CO₂, ¹³CO₂, and ¹²C¹⁸O¹⁶O were detected simultaneously without interference by water vapor. Detection limits in the range of few ppmv were obtained for each species utilizing wavelength modulation (WM) spectroscopy with balanced detection in a long-path absorption cell set-up. High sensitivity in conjunction with high precision —typically ±1 per mille and ±6 per mille for 3\% and 0.7\% of CO₂, respectively— renders this experimental approach a promising analytical concept for isotope-ratio determination of carbon dioxide in soil and breath gas. For a moderate ¹²CO₂ line, the pressure dependence of the line profile was characterized in detail, to account for pressure effects on sensitive measurements.}, subject = {Isotopenverh{\"a}ltnis}, language = {en} } @misc{EngelbrechtLauSalffneretal.2006, author = {Engelbrecht, Rainer and Lau, Steffen and Salffner, Katharina and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Fasergekoppelte NIR-Diodenlaser-Spektrometer zur simultanen und isotopen-aufgel{\"o}sten Messung von CO und CO2 : Anwendungen in Plasma-Diagnostik und Bodengasanalyse}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12348}, year = {2006}, abstract = {Die Anwendung zweier {\"a}hnlicher fasergekoppelte Diodenlaser-Spektrometer-Systeme werden vorgestellt. Basis sind handels{\"u}bliche DFB-Laserdioden der optischen Kommunikationstechnik. Der faseroptische Aufbau, das Detektionsverfahren (2f Wellenl{\"a}ngenmodulations-Spektroskopie mit Balanced Receiver), Rauschverhalten und Detektionslimit werden diskutiert. Zur in-situ Plasma-Diagnostik von CO- und CO2-Konzentrationen in industriellen CO2-Lasern der Materialbearbeitung wurde eine Wellenl{\"a}nge von 1582 nm verwendet. Bei einem Gasdruck von 100 hPa und einer Absorptionswegl{\"a}nge von 14,9 cm wurden mit einer Laserdiode simultan CO- und CO2-Konzentrationen von 0\% bis 11\% im Gasgef{\"a}ß bei laufender Hochfrequenzgasentladung des CO2-Lasers zeitaufgel{\"o}st gemessen. Vorgestellt und diskutiert werden Aufbau und Eigenschaften des Spektrometers sowie die Ergebnisse der dynamischen Gasanalysen, die zu einer Verbesserung der Katalysator-Technik im CO2-Laser beigetragen haben.Mit isotopenaufgel{\"o}ster CO- und CO2-Spektroskopie k{\"o}nnen biologische Gasaustauschprozesse, z.B. in Gasen aus dem Erdboden untersucht werden. Hierzu wurde ein fasergekoppeltes feldtaugliches Diodenlaser-Spektrometer bei Wellenl{\"a}ngen um 1605 nm zur Messungder Isotopologe 12C16O, 13C16O, 12C18O und 12C16O2, 13C16O2, 12C18O16O aufgebaut. Die Messung erfolgt extraktiv in Langwegzellen mit unterschiedlichen Absorptionswegl{\"a}ngen von 100.9 m und 29.9 m. Es werden Kalibrationsmessungen zur Linearit{\"a}t und zur Pr{\"a}zision der Bestimmung der Isotopenverh{\"a}ltnisse sowie Wiederholungsmessungen zur Stabilit{\"a}t vorgestellt. Nachweisgrenzen von wenigen ppm konnten f{\"u}r die CO- und CO2-Isotopologen erhalten werden.}, language = {de} } @article{SchwarzeSchellhammerOrtsteinetal.2019, author = {Schwarze, Martin and Schellhammer, Karl Sebastian and Ortstein, Katrin and Benduhn, Johannes and Gaul, Christopher and Hinderhofer, Alexander and Toro, Lorena Perdigon and Scholz, Reinhard and Kublitski, Jonas and Roland, Steffen and Lau, Matthias and Poelking, Carl and Andrienko, Denis and Cuniberti, Gianaurelio and Schreiber, Frank and Neher, Dieter and Vandewal, Koen and Ortmann, Frank and Leo, Karl}, title = {Impact of molecular quadrupole moments on the energy levels at organic heterojunctions}, series = {Nature Communications}, volume = {10}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/s41467-019-10435-2}, pages = {9}, year = {2019}, abstract = {The functionality of organic semiconductor devices crucially depends on molecular energies, namely the ionisation energy and the electron affinity. Ionisation energy and electron affinity values of thin films are, however, sensitive to film morphology and composition, making their prediction challenging. In a combined experimental and simulation study on zinc-phthalocyanine and its fluorinated derivatives, we show that changes in ionisation energy as a function of molecular orientation in neat films or mixing ratio in blends are proportional to the molecular quadrupole component along the p-p-stacking direction. We apply these findings to organic solar cells and demonstrate how the electrostatic interactions can be tuned to optimise the energy of the charge-transfer state at the donor-acceptor interface and the dissociation barrier for free charge carrier generation. The confirmation of the correlation between interfacial energies and quadrupole moments for other materials indicates its relevance for small molecules and polymers.}, language = {en} } @phdthesis{Lau2009, author = {Lau, Steffen}, title = {Djodenlaser-Absorptionsspektroskopie (DLAS) zur isotopenselektiven Gasanalye von Kohlenmonoxid, Kohlendioxide und Methan}, address = {Potsdam}, pages = {110 S. : graph. Darst.}, year = {2009}, language = {de} } @article{LauMaierBrauneetal.2021, author = {Lau, Skadi and Maier, Anna and Braune, Steffen and Gossen, Manfred and Lendlein, Andreas}, title = {Effect of endothelial culture medium composition on platelet responses to polymeric biomaterials}, series = {International journal of molecular sciences}, volume = {22}, journal = {International journal of molecular sciences}, number = {13}, publisher = {Molecular Diversity Preservation International}, address = {Basel}, issn = {1422-0067}, doi = {10.3390/ijms22137006}, pages = {13}, year = {2021}, abstract = {Near-physiological in vitro thrombogenicity test systems for the evaluation of blood-contacting endothelialized biomaterials requires co-cultivation with platelets (PLT). However, the addition of PLT has led to unphysiological endothelial cell (EC) detachment in such in vitro systems. A possible cause for this phenomenon may be PLT activation triggered by the applied endothelial cell medium, which typically consists of basal medium (BM) and nine different supplements. To verify this hypothesis, the influence of BM and its supplements was systematically analyzed regarding PLT responses. For this, human platelet rich plasma (PRP) was mixed with BM, BM containing one of nine supplements, or with BM containing all supplements together. PLT adherence analysis was carried out in six-channel slides with plasma-treated cyclic olefin copolymer (COC) and poly(tetrafluoro ethylene) (PTFE, as a positive control) substrates as part of the six-channel slides in the absence of EC and under static conditions. PLT activation and aggregation were analyzed using light transmission aggregometry and flow cytometry (CD62P). Medium supplements had no effect on PLT activation and aggregation. In contrast, supplements differentially affected PLT adherence, however, in a polymer- and donor-dependent manner. Thus, the use of standard endothelial growth medium (BM + all supplements) maintains functionality of PLT under EC compatible conditions without masking the differences of PLT adherence on different polymeric substrates. These findings are important prerequisites for the establishment of a near-physiological in vitro thrombogenicity test system assessing polymer-based cardiovascular implant materials in contact with EC and PLT.}, language = {en} }