TY - JOUR A1 - El Malah, T. A1 - Ciesielski, A. A1 - Piot, L. A1 - Troyanov, S.I. A1 - Mueller, U. A1 - Weidner, Steffen A1 - Samorì, P. A1 - Hecht, S. T1 - Conformationally pre-organized and pH-responsive flat dendrons: synthesis and self-assembly at the liquid-solid interface N2 - Efficient Cu-catalyzed 1,3-dipolar cycloaddition reactions have been used to prepare two series of three regioisomers of G-1 and G-2 poly(triazole-pyridine) dendrons. The G-1 and G-2 dendrons consist of branched yet conformationally pre-organized 2,6-bis(phenyl/pyridyl-1,2,3-triazol-4-yl)pyridine (BPTP) monomeric and trimeric cores, respectively, carrying one focal and either two or four peripheral alkyl side chains. In the solid state, the conformation and supramolecular organization were studied by means of a single crystal X-ray structure analysis of one derivative. At the liquid–solid interface, the self-assembly behavior was investigated by scanning tunneling microscopy (STM) on graphite surfaces. Based on the observed supramolecular organization, it appears that the subtle balance between conformational preferences inherent in the dendritic backbone on the one side and the adsorption and packing of the alkyl side chains on the graphite substrate on the other side dictate the overall structure formation in 2D. KW - Dendrons KW - MALDI Massenspektrometrie PY - 2012 DO - https://doi.org/10.1039/c1nr11434d SN - 2040-3364 SN - 2040-3372 VL - 4 SP - 467 EP - 472 PB - RSC Publ. CY - Cambridge AN - OPUS4-25378 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mielke, Johannes A1 - Martınez-Blanco, J. A1 - Peters, M. V. A1 - Hecht, S. A1 - Grill, L. T1 - Observing single-atom diffusion at a molecule-metal interface N2 - The dynamics at the interface between a close-packed porphyrin monolayer and Au(111) is investigated by time-dependent scanning tunneling microscopy, detecting the motion of single-interface adatoms in real space. Imaging sequences reveal predominant switching of the molecular appearance in adjacent molecules, pointing to a spatial correlation that is consistent with adatom diffusion from one molecule to the next. In some cases, the number of switching molecules is drastically increased, indicating collective switching events. In addition to the thermally induced motion of adatoms at the interface, also voltage pulses from the microscope tip can induce the process—revealing different yields in agreement with the model of adatom hopping. KW - STM KW - molecular switch KW - single molecule KW - switching dynamics KW - porphyrin KW - Au(111) PY - 2016 UR - http://journals.aps.org/prb/abstract/10.1103/PhysRevB.94.035416 DO - https://doi.org/10.1103/PhysRevB.94.035416 VL - 94 IS - 3 SP - 035416-1 EP - 035416-7 PB - American Physical Society AN - OPUS4-37177 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gauert, C. A1 - Schannor, M. A1 - Hecht, L. A1 - Radtke, Martin A1 - Reinholz, Uwe T1 - A comparison of in situ analytical methods for trace element measurement in gold samples from various South African gold deposits N2 - Trace element concentrations in gold grains from various geological units in South Africa were measured in situ by field emission-electron probe microanalysis (FE-EPMA), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and synchrotron micro X-ray fluorescence spectroscopy (SR-µ-XRF). This study assesses the accuracy, precision and detection limits of these mostly non-destructive analytical methods using certified reference materials and discusses their application in natural sample measurement. FE-EPMA point analyses yielded reproducible and discernible concentrations for Au and trace concentrations of S, Cu, Ti, Hg, Fe and Ni, with detection limits well below the actual concentrations in the gold. LA-ICP-MS analyses required larger gold particles (> 60 µm) to avoid contamination during measurement. Elements that measured above detection limits included Ag, Cu, Ti, Fe, Pt, Pd, Mn, Cr, Ni, Sn, Hg, Pb, As and Te, which can be used for geochemical characterisation and gold fingerprinting. Although LA-ICP-MS measurements had lower detection limits, precision was lower than FE-EPMA and SR-µ-XRF. The higher variability in absolute values measured by LA-ICP-MS, possibly due to micro-inclusions, had to be critically assessed. Non-destructive point analyses of gold alloys by SR-µ-XRF revealed Ag, Fe, Cu, Ni, Pb, Ti, Sb, U, Cr, Co, As, Y and Zr in the various gold samples. Detection limits were mostly lower than those for elements measured by FE-EPMA, but higher than those for elements measured by LA-ICP-MS. N2 - Les concentrations en éléments traces de grains d'or provenant de différentes unités géologiques d'Afrique du Sud ont été mesurées in situ par microsonde électronique à émission de champ (FE-EPMA), spectrométrie de masse couplée à une source plasma et un système d'ablation laser (LA-ICP-MS) et micro spectroscopie de fluorescence des rayons X au Synchrotron (SR-µ-XRF). Cette étude évalue l'exactitude, la précision et les limites de détection de ces méthodes d'analyse pour la plupart non-destructives en utilisant des matériaux de référence certifiés, et discute de leur application dans les mesures sur échantillon naturel. Les points d'analyses FE-EPMA ont fournis des concentrations reproductibles et discernables pour l'Au et des concentrations en traces de S, Cu, Ti, Hg, Fe et Ni, avec des limites de détection bien inférieures aux concentrations réelles dans l'or. Les analyses LA-ICP-MS ont nécessitées des particules d'or de plus grande taille (> 60 µm) pour éviter toute contamination pendant la mesure. Les éléments mesurés au-dessus des limites de détection inclus Ag, Cu, Ti, Fe, Pt, Pd, Mn, Cr, Ni, Sn, Hg, Pb, A et Te, qui peuvent être utilisés pour les caractérisations géochimique et le «fingerprinting» de l'or. Bien que les mesures LA-ICP-MS aient des limites de détection plus basses, la précision est inférieure par rapport à celles de la microsonde FE et de la SR-µ-XRF. La plus grande variabilité des valeurs absolues mesurées par LA-ICP-MS, probablement reliée à la présence de micro-inclusions, a du être évaluée de manière critique. Les points d'analyse non-destructifs des alliages d'or par SR-µ-XRF ont révélés la présence de Ag, Fe, Cu, Ni, Pb, Ti, Sb, U, Cr, Co, As, Y et Zr dans les différents échantillons. Les limites de détection ont été pour la plupart inférieures à celles des éléments mesurés par FE-EPMA, mais supérieures à celles des éléments mesurés par LA-ICP-MS. KW - Trace elements KW - Gold KW - FE-EPMA KW - LA-ICP-MS KW - SR-µ-XRF KW - Precision KW - Précision KW - Comparison of techniques KW - Éléments traces PY - 2016 DO - https://doi.org/10.1111/j.1751-908X.2015.00362.x SN - 1639-4488 SN - 1751-908X VL - 40 IS - 2 SP - 267 EP - 289 PB - Blackwell CY - Oxford AN - OPUS4-34882 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mielke, Johannes A1 - Hanke, F. A1 - Peters, M.V. A1 - Hecht, S. A1 - Persson, M. A1 - Grill, L. T1 - Adatoms underneath single porphyrin molecules on Au(111) N2 - The adsorption of porphyrin derivatives on a Au(111) surface was studied by scanning tunneling microscopy and spectroscopy at low temperatures in combination with density functional theory calculations. Different molecular appearances were found and could be assigned to the presence of single gold adatoms bonded by a coordination bond underneath the molecular monolayer, causing a characteristic change of the electronic structure of the molecules. Moreover, this interpretation could be confirmed by manipulation experiments of individual molecules on and off a single gold atom. This study provides a detailed understanding of the role of metal adatoms in surface–molecule bonding and anchoring and of the appearance of single molecules, and it should prove relevant for the imaging of related molecule–metal systems. PY - 2015 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-324144 UR - http://pubs.acs.org/doi/pdf/10.1021/ja510528x DO - https://doi.org/10.1021/ja510528x SN - 0002-7863 SN - 1520-5126 VL - 137 IS - 5 SP - 1844 EP - 1849 PB - American Chemical Society CY - Washington, DC AN - OPUS4-32414 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Calero, P. A1 - Hecht, Mandy A1 - Martínez-Mánez, Ramon A1 - Sancenón, F. A1 - Soto, J. A1 - Vivancos, J.L. A1 - Rurack, Knut T1 - Silica nanoparticles functionalised with cation coordination sites and fluorophores for the differential sensing of anions in a quencher displacement assay (QDA) N2 - In conjunction with quenching metal ions, silica nanoparticles carrying terpyridine coordination sites and sulforhodamine B signalling units were employed for the differential fluorometric recognition of anions. KW - Hybridmaterial KW - Silica-Nanopartikel KW - Fluoreszenz KW - Anionen KW - Verdrängungsassay PY - 2011 DO - https://doi.org/10.1039/c1cc13039k SN - 0022-4936 SN - 0009-241x SN - 1359-7345 SN - 1364-548x VL - 47 IS - 38 SP - 10599 EP - 10601 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-24489 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -