@misc{BueckerHoffmannAcker, author = {B{\"u}cker, Stefan and Hoffmann, Volker and Acker, J{\"o}rg}, title = {Determination of Fluorine by Molecular Absorption Spectrometry of AlF Using a High-Resolution Continuum Source Spectrometer and a C2H2/N2O Flame}, series = {Current Analytical Chemistry}, volume = {10}, journal = {Current Analytical Chemistry}, number = {3}, issn = {1573-4110}, pages = {426 -- 434}, abstract = {The molecular absorption of the diatomic AlF molecule in the C2H2/N2O flame was studied using a highresolution continuum source flame atomic absorption spectrometer. AlF has a structured absorption spectrum in the range of 227.30 nm and 227.80 nm. From this band system, the remarkably narrow absorption band at 227.66 nm proved to be the optimum for analytical purposes. The signal intensity was studied as a function of the C2H2 : N2O ratio, the aspiration flow, and the aluminum concentration added to the analytical solution to generate the AlF molecules in the flame. The AlF molecule formation is significantly affected by the bonding state of the fluorine source used. Compared to ionic bound fluorine, organic bound fluorine leads to a markedly less sensitive molecular absorbance of AlF. Furthermore, several ions, such as Na+, K+ and NH4+, and acids, such as HCl, CH3COOH, and HNO3, affect the AlF signal intensity severely. It has to be concluded that the determination of fluorine by AlF F MAS only leads to reliable analytical results in simple matrices.}, language = {en} } @misc{AckerBueckerHoffmann, author = {Acker, J{\"o}rg and B{\"u}cker, Stefan and Hoffmann, Volker}, title = {The Formation of AlF Molecules and Al Atoms in a C2H2/N2O Flame Studied by Absorption and Emission Spectrometry of Molecules and Atoms}, series = {Current Analytical Chemistry}, volume = {10}, journal = {Current Analytical Chemistry}, number = {3}, issn = {1875-6727}, pages = {418 -- 425}, abstract = {The absorption of the diatomic molecule AlF in the C2H2/N2O flame at 227.66 nm reveals an interesting feature. The calibration curve of the AlF absorption plotted against a rising concentration of hydrofluoric acid in solutions of constant aluminum content consists of two subsequent linear sections of different slopes. The bend position is reproducibly found at a molar fluorine-to-aluminum ratio of 3, calculated from the composition of the studied solutions. To explain this behavior, the most prominent aluminum flame species Al, AlF, and AlO were recorded as a function of the burner gas composition and flame observation height, using a high-resolution continuum source flame absorption spectrometer. As a result, the two-sectioned calibration curve is explained by two different pathways of AlF molecule formation: At a molar fluorine-to-aluminum ratio of below 3, aluminum is transported into the flame by two parallel pathways. One is the common pathway in absence of fluorine via the reduction of oxidic and/or carbidic species by the flame gases. The second pathway comprises the formation of gaseous AlF3 and its decomposition into AlF molecules and, subsequently, Al atoms. The fractionation of AlF3 releases Al atoms much faster than through the reduction of the oxidic and/or carbidic species. At molar fluorine-to-aluminum ratios of above 3, all aluminum is introduced to the flame via gaseous AlF3. A further increase of the hydrofluoric acid concentration increases the fluorine atom concentration in the flame, so that the AlF formation is determined by the recombination of aluminum and fluorine atoms.}, language = {en} } @misc{BrachmannSeifertNeumannetal., author = {Brachmann, Erik and Seifert, Marietta and Neumann, Niels and Alshwawreh, Nidal and Uhlemann, Margitta and Menzel, Siegfried and Acker, J{\"o}rg and Herold, Steven and Hoffmann, Volker and Gemming, Thomas}, title = {Electroless-Deposited Platinum Antennas for Wireless Surface Acoustic Wave Sensors}, series = {Materials}, volume = {12}, journal = {Materials}, number = {7}, issn = {1996-1944}, doi = {10.3390/ma12071002}, pages = {1002 -- 1014}, abstract = {In an effort to develop a cost-efficient technology for wireless high-temperature surface acoustic wave sensors, this study presents an evaluation of a combined method that integrates physical vapor deposition with electroless deposition for the fabrication of platinum-based planar antennas. The proposed manufacturing process becomes attractive for narrow, thick, and sparse metallizations for antennas in the MHz to GHz frequency range. In detail, narrow platinum-based lines of a width down to 40 μm were electroless-deposited on γ-Al2O3 substrates using different seed layers. At first, the electrolyte chemistry was optimized to obtain the highest deposition rate. Films with various thickness were prepared and the electrical resistivity, microstructure, and chemical composition in the as-prepared state and after annealing at temperatures up to 1100 ∘C were evaluated. Using these material parameters, the antenna was simulated with an electromagnetic full-wave simulation tool and then fabricated. The electrical parameters, including the S-parameters of the antenna, were measured. The agreement between the simulated and the realized antenna is then discussed.}, language = {en} } @misc{AckerBueckerHoffmann, author = {Acker, J{\"o}rg and B{\"u}cker, Stefan and Hoffmann, Volker}, title = {Impact of the chemical form of different fluorine sources on the formation of AlF molecules in a C2H2/N2O flame}, series = {Journal of Analytical Atomic Spectrometry}, volume = {31}, journal = {Journal of Analytical Atomic Spectrometry}, issn = {0267-9477}, doi = {10.1039/C5JA00470E}, pages = {902 -- 911}, abstract = {The formation of diatomic AlF molecules was studied in a C2H2/N2O flame by means of a high-resolution continuum source flame absorption spectrometer using different fluorine containing compounds HF, H2SiF6, HBF4 and CF3COOH as fluorine sources. The fragmentation of these fluorine sources, as well the resulting impact on the AlF molecule formation, was derived from flame height distribution studies of the atomic and molecular species Al, AlO, Si, SiO, SiF, B and BF as a function of the fluorine concentration, the molar Al : F ratio and the burner gas composition. As a consequence, the used fluorine sources HF, H2SiF6, HBF4 and CF3COOH have been divided into two major groups. The first group of fluorine sources, covering HF, H2SiF6 and HBF4, decomposes during the drying of the aerosol under the formation of AlF3, which is the dominating species for the transport of aluminium into the flame. Its decomposition into AlF results in a high sensitivity of AlF molecular absorption at low flame observation heights. The second group of fluorine sources is exemplarily given by CF3COOH. In the upper parts of the flame the cleavage of the very stable C-F bond proceeds incompletely so that the sensitivity of the AlF molecular absorption is considerably lower than that for the other fluorine sources. In consequence, the AlF molecules are formed by the reaction between the fluorine atoms and the aluminium atoms, which are transported into the flame without the aid of fluorine, presumably via oxidic and/or carbidic species. The present investigations show that the sensitivity of the AlF molecular absorption and the pathway of AlF formation depend on the chemical form of the fluorine in the studied samples.}, language = {en} } @misc{DavinRechidBreiletal., author = {Davin, Edouard and Rechid, Diana and Breil, Marcus and Cardoso, Rita M. and Coppola, Erika and Hoffmann, Peter and Jach, Lisa L. and Katragkou, Eleni and Noblet-Ducoudr{\´e}, Nathalie de and Radtke, Kai and Raffa, Mario and Soares, Pedro and Sofiadis, Giannis and Strada, Susanna and Strandberg, Gustav and T{\"o}lle, Merja H. and Warrach-Sagi, Kirsten and Wulfmeyer, Volker}, title = {Biogeophysical impacts of deforestation in Europe First results from the LUCAS Regional Climate Mode intercomparison}, series = {Earth System Dynamics}, volume = {11}, journal = {Earth System Dynamics}, number = {1}, issn = {2190-4995}, doi = {10.5194/esd-11-183-2020}, pages = {183 -- 200}, abstract = {The Land Use and Climate Across Scales Flagship Pilot Study (LUCAS FPS) is a coordinated community effort to improve the integration of land use change (LUC) in regional climate models (RCMs) and to quantify the biogeophysical effects of LUC on local to regional climate in Europe. In the first phase of LUCAS, nine RCMs are used to explore the biogeophysical impacts of re-/afforestation over Europe: two idealized experiments representing respectively a non-forested and a maximally forested Europe are compared in order to quantify spatial and temporal variations in the regional climate sensitivity to forestation. We find some robust features in the simulated response to forestation. In particular, all models indicate a year-round decrease in surface albedo, which is most pronounced in winter and spring at high latitudes. This results in a winter warming effect, with values ranging from +0.2 to +1 K on average over Scandinavia depending on models. However, there are also a number of strongly diverging responses. For instance, there is no agreement on the sign of temperature changes in summer with some RCMs predicting a widespread cooling from forestation (well below -2 K in most regions), a widespread warming (around +2 K or above in most regions) or a mixed response. A large part of the inter-model spread is attributed to the representation of land processes. In particular, differences in the partitioning of sensible and latent heat are identified as a key source of uncertainty in summer. Atmospheric processes, such as changes in incoming radiation due to cloud cover feedbacks, also influence the simulated response in most seasons. In conclusion, the multi-model approach we use here has the potential to deliver more robust and reliable information to stakeholders involved in land use planning, as compared to results based on single models. However, given the contradictory responses identified, our results also show that there are still fundamental uncertainties that need to be tackled to better anticipate the possible intended or unintended consequences of LUC on regional climates.}, language = {en} }