TY - GEN A1 - Liebig, Ferenc A1 - Henning, Ricky A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Schmitt, Clemens Nikolaus Zeno A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - A simple one-step procedure to synthesise gold nanostars in concentrated aqueous surfactant solutions T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Due to the enhanced electromagnetic field at the tips of metal nanoparticles, the spiked structure of gold nanostars (AuNSs) is promising for surface-enhanced Raman scattering (SERS). Therefore, the challenge is the synthesis of well designed particles with sharp tips. The influence of different surfactants, i.e., dioctyl sodium sulfosuccinate (AOT), sodium dodecyl sulfate (SDS), and benzylhexadecyldimethylammonium chloride (BDAC), as well as the combination of surfactant mixtures on the formation of nanostars in the presence of Ag⁺ ions and ascorbic acid was investigated. By varying the amount of BDAC in mixed micelles the core/spike-shell morphology of the resulting AuNSs can be tuned from small cores to large ones with sharp and large spikes. The concomitant red-shift in the absorption toward the NIR region without losing the SERS enhancement enables their use for biological applications and for time-resolved spectroscopic studies of chemical reactions, which require a permanent supply with a fresh and homogeneous solution. HRTEM micrographs and energy-dispersive X-ray (EDX) experiments allow us to verify the mechanism of nanostar formation according to the silver underpotential deposition on the spike surface in combination with micelle adsorption. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 769 KW - optical-properties KW - nanoparticles KW - sers KW - ultrafast KW - size KW - nanotriangles KW - nanoflowers KW - wavelength Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-438743 SN - 1866-8372 IS - 769 SP - 23633 EP - 23641 ER - TY - THES A1 - Sarhan, Radwan Mohamed T1 - Plasmon-driven photocatalytic reactions monitored by surface-enhanced Raman spectroscopy T1 - Plasmonen-getriebene photokatalytische Reaktionen, gemessen mittels oberflächenverstärkter Raman-Spektroskopie N2 - Plasmonic metal nanostructures can be tuned to efficiently interact with light, converting the photons into energetic charge carriers and heat. Therefore, the plasmonic nanoparticles such as gold and silver nanoparticles act as nano-reactors, where the molecules attached to their surfaces benefit from the enhanced electromagnetic field along with the generated energetic charge carriers and heat for possible chemical transformations. Hence, plasmonic chemistry presents metal nanoparticles as a unique playground for chemical reactions on the nanoscale remotely controlled by light. However, defining the elementary concepts behind these reactions represents the main challenge for understanding their mechanism in the context of the plasmonically assisted chemistry. Surface-enhanced Raman scattering (SERS) is a powerful technique employing the plasmon-enhanced electromagnetic field, which can be used for probing the vibrational modes of molecules adsorbed on plasmonic nanoparticles. In this cumulative dissertation, I use SERS to probe the dimerization reaction of 4-nitrothiophenol (4-NTP) as a model example of plasmonic chemistry. I first demonstrate that plasmonic nanostructures such as gold nanotriangles and nanoflowers have a high SERS efficiency, as evidenced by probing the vibrations of the rhodamine dye R6G and the 4-nitrothiophenol 4-NTP. The high signal enhancement enabled the measurements of SERS spectra with a short acquisition time, which allows monitoring the kinetics of chemical reactions in real time. To get insight into the reaction mechanism, several time-dependent SERS measurements of the 4-NTP have been performed under different laser and temperature conditions. Analysis of the results within a mechanistic framework has shown that the plasmonic heating significantly enhances the reaction rate, while the reaction is probably initiated by the energetic electrons. The reaction was shown to be intensity-dependent, where a certain light intensity is required to drive the reaction. Finally, first attempts to scale up the plasmonic catalysis have been performed showing the necessity to achieve the reaction threshold intensity. Meanwhile, the induced heat needs to quickly dissipate from the reaction substrate, since otherwise the reactants and the reaction platform melt. This study might open the way for further work seeking the possibilities to quickly dissipate the plasmonic heat generated during the reaction and therefore, scaling up the plasmonic catalysis. N2 - Plasmonische Metallnanostrukturen können so eingestellt werden, dass sie effizient mit Licht interagieren, Photonen in energetische Ladungsträger und wärmeenergie umwandeln. Aus diesem Grund wirken plasmonische Nanopartikel wie Gold und Silbernanopartikel als Nanoreaktoren, wenn Moleküle mit deren Oberfläche verbunden sind. Durch das verstärkte elektromagnetische Feld und den somit erzeugten energetischen Ladungsträgern und der wärmeenergie können chemische Umwandlungen entstehen. Das bedeutet, in der plasmonischen Chemie sind Metallnanopartikel ein einzigartiges system um chemische Reaktionen auf der Nanoebene unter der Kontrolle von Licht verfolgen zu können. Die Herausforderung liegt darin, grundlegende Konzepte hinter den Reaktionen für das mechanistische Verständnis in Bezug auf die plasmonisch unterstützte Chemie zu definieren. Oberflächenverstärkte Raman Streuung (SERS) ist eine leistungsfähige Technik, die sich mit plasmonverstärkten, elektromagnetischen Feldern beschäftigt, um die Vibrationsmoden von den auf den Nanopartikeln absorbierten Molekülen zu analysieren. In dieser kumulativen Dissertation wurde die Dimerisierung von 4-Nitrothiophenol (4-NTP) mittels SERS als Beispielreaktion für die plasmonische Chemie untersucht. Aufgrund der hohen SERS Signalverstärkung konnten die SERS Spektren mit einer kurzen Erfassungszeit aufgenommen werden, was die Untersuchung der Kinetik und des Reaktionsmechanismus in Echtzeit ermöglichte. KW - plasmonic chemistry KW - plasmonische Chemie KW - heiße Elektronen KW - SERS KW - SERS Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-433304 ER -