TY - JOUR A1 - von Reppert, Alexander A1 - Sarhan, Radwan Mohamed A1 - Stete, Felix A1 - Pudell, Jan-Etienne A1 - Del Fatti, N. A1 - Crut, A. A1 - Koetz, Joachim A1 - Liebig, Ferenc A1 - Prietzel, Claudia Christina A1 - Bargheer, Matias T1 - Watching the Vibration and Cooling of Ultrathin Gold Nanotriangles by Ultrafast X-ray Diffraction JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - We study the vibrations of ultrathin gold nanotriangles upon optical excitation of the electron gas by ultrafast X-ray diffraction. We quantitatively measure the strain evolution in these highly asymmetric nano-objects, providing a direct estimation of the amplitude and phase of the excited vibrational motion. The maximal strain value is well reproduced by calculations addressing pump absorption by the nanotriangles and their resulting thermal expansion. The amplitude and phase of the out-of-plane vibration mode with 3.6 ps period dominating the observed oscillations are related to two distinct excitation mechanisms. Electronic and phonon pressures impose stresses with different time dependences. The nanosecond relaxation of the expansion yields a direct temperature sensing of the nano-object. The presence of a thin organic molecular layer at the nanotriangle/substrate interfaces drastically reduces the thermal conductance to the substrate. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpcc.6b11651 SN - 1932-7447 VL - 120 SP - 28894 EP - 28899 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Reinecke, Antje A1 - Koetz, Joachim T1 - "Green" gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering JF - RSC Advances N2 - The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering. Y1 - 2016 U6 - https://doi.org/10.1039/c6ra04808k SN - 2046-2069 VL - 6 SP - 33561 EP - 33568 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Reinecke, Antje A1 - Koetz, Joachim T1 - “Green” gold nanotriangles: synthesis, purification by polyelectrolyte/micelle depletion flocculation and performance in surface-enhanced Raman scattering N2 - The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 317 KW - morphological transformation KW - halide-ions KW - nanoparticles KW - shape KW - size KW - nanoprisms KW - vesicles KW - nanorods KW - silver KW - poly(ethyleneimine) Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394430 SP - 33561 EP - 33568 ER - TY - JOUR A1 - El-Nagar, Gumaa A. A1 - Sarhan, Radwan Mohamed A1 - Abouserie, Ahed A1 - Maticiuc, Natalia A1 - Bargheer, Matias A1 - Lauermann, Iver A1 - Roth, Christina T1 - Efficient 3D-Silver Flower-like Microstructures for Non-Enzymatic Hydrogen Peroxide (H2O2) Amperometric Detection JF - Scientific reports Y1 - 2017 U6 - https://doi.org/10.1038/s41598-017-11965-9 SN - 2045-2322 VL - 7 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Sander, Mathias A1 - Koopman, Wouter-Willem Adriaan A1 - Schuetz, Roman A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Deposition of Gold Nanotriangles in Large Scale Close-Packed Monolayers for X-ray-Based Temperature Calibration and SERS Monitoring of Plasmon-Driven Catalytic Reactions JF - ACS applied materials & interfaces KW - gold nanotriangles KW - monolayer formation KW - SERS KW - dimerization KW - heat measurement Y1 - 2017 U6 - https://doi.org/10.1021/acsami.7b07231 SN - 1944-8244 VL - 9 SP - 20247 EP - 20253 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - El-Nagar, Gumaa A. A1 - Lauermann, Iver A1 - Sarhan, Radwan Mohamed A1 - Roth, Christina T1 - Hierarchically structured iron-doped silver (Ag-Fe) lotus flowers for an efficient oxygen reduction reaction JF - Nanoscale N2 - The development of cheap and efficient electrocatalysts for the oxygen reduction reaction (ORR) is vital for the immediate commercialization of fuel cells which are still limited by the high cost and low performance of the utilized commercial Pt-based electrodes. As a promising alternative, this study reports on the synthesis of hierarchical iron-doped silver lotus flowers (AgFelotus) by a facile chemical procedure as robust and efficient ORR electrocatalysts. Succinic acid was used as a structure directing agent to tune the morphology of undoped and iron-doped silver particles. In the absence of succinic acid, ball-like silver particles were obtained, while using 2 mM succinic acid led to peony-like flower structures. The doping of silver peony-flowers with iron resulted in lotus-like flower structures with high electrocatalytic activity for ORR together with outstanding tolerance against poisoning with various hydrocarbon (HC) impurities, in situ generated during fuel cell operation, as well as different fuels from anodic crossover. AgFelotus exhibited a superior ORR activity with more than 40 times higher stability than the commercial Pt/C catalyst in alkaline media. This substantial performance enhancement is attributed to the unique lotus-like flower structures providing more electroactive surface sites, in addition to the iron dopants which facilitate ORR charge transfer. Y1 - 2018 U6 - https://doi.org/10.1039/c8nr00020d SN - 2040-3364 SN - 2040-3372 VL - 10 IS - 15 SP - 7304 EP - 7310 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Thünemann, Andreas F. A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Undulated Gold Nanoplatelet Superstructures BT - In Situ Growth of Hemispherical Gold Nanoparticles onto the Surface of Gold Nanotriangles JF - Langmuir N2 - Negatively charged flat gold nanotriangles, formed in a vesicular template phase and separated by an AOT-micelle-based depletion flocculation, were reloaded by adding a cationic polyelectrolyte, that is, a hyperbranched polyethylenimine (PEI). Heating the system to 100 degrees C in the presence of a gold chloride solution, the reduction process leads to the formation of gold nanoparticles inside the polymer shell surrounding the nanoplatelets. The gold nanoparticle formation is investigated by UV-vis spectroscopy, small-angle X-ray scattering, and dynamic light scattering measurements in combination with transmission electron microscopy. Spontaneously formed gold clusters in the hyperbranched PEI shell with an absorption maximum at 350 nm grow on the surface of the nanotriangles as hemispherical particles with diameters of similar to 6 nm. High-resolution micrographs show that the hemispherical gold particles are crystallized onto the {111} facets on the bottom and top of the platelet as well as on the edges without a grain boundary. Undulated gold nanoplatelet superstructures with special properties become available, which show a significantly modified performance in SERS-detected photocatalysis regarding both reactivity and enhancement factor. Y1 - 2018 U6 - https://doi.org/10.1021/acs.langmuir.7b02898 SN - 0743-7463 VL - 34 IS - 15 SP - 4584 EP - 4594 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Liebig, Ferenc A1 - Henning, Ricky A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - A new route to gold nanoflowers JF - Nanotechnology N2 - Catanionic vesicles spontaneously formed by mixing the anionic surfactant bis(2-ethylhexyl)sulfosuccinate sodium salt with the cationic surfactant cetyltrimethylammonium bromide were used as a reducing medium to produce gold clusters, which are embedded and well-ordered into the template phase. The gold clusters can be used as seeds in the growth process that follows by adding ascorbic acid as a mild reducing component. When the ascorbic acid was added very slowly in an ice bath round-edged gold nanoflowers were produced. When the same experiments were performed at room temperature in the presence of Ag+ ions, sharp-edged nanoflowers could be synthesized. The mechanism of nanoparticle formation can be understood to be a non-diffusion-limited Ostwald ripening process of preordered gold nanoparticles embedded in catanionic vesicle fragments. Surface-enhanced Raman scattering experiments show an excellent enhancement factor of 1.7 . 10(5) for the nanoflowers deposited on a silicon wafer. KW - catanionic vesicles KW - gold cluster KW - gold nanoflowers KW - crystal growth KW - HRTEM KW - SEM Y1 - 2018 U6 - https://doi.org/10.1088/1361-6528/aaaffd SN - 0957-4484 SN - 1361-6528 VL - 29 IS - 18 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Liebig, Ferenc A1 - Sarhan, Radwan Mohamed A1 - Prietzel, Claudia Christina A1 - Schmitt, Clemens Nikolaus Zeno A1 - Bargheer, Matias A1 - Koetz, Joachim T1 - Tuned Surface-Enhanced raman scattering performance of undulated Au@Ag triangles JF - ACS applied nano materials N2 - Negatively charged ultraflat gold nanotriangles (AuNTs) stabilized by the anionic surfactant dioctyl sodium sulfosuccinate (AOT) were reloaded with the cationic surfactant benzylhexadecyldimethylammonium chloride (BDAC). Because of the spontaneous formation of a catanionic AOT micelle/BDAC bilayer onto the surface of the reloaded AuNTs, a reduction of Ag+ ions leads to the formation of spherical silver nanoparticles (AgNPs). With increasing concentration of AgNPs on the AuNTs, the localized surface plasmon resonance (LSPR) is shifted stepwise from 1300 to 800 nm. The tunable LSPR enables to shift the extinction maximum to the wavelength of the excitation laser of the Raman microscope at 785 nm. Surface-enhanced Raman scattering (SERS) experiments performed under resonance conditions show an SERS enhancement factor of the analyte molecule rhodamine RG6 of 5.1 X 10(5), which can be related to the silver hot spots at the periphery of the undulated gold nanoplatelets. KW - gold nanotriangles KW - catanionic surfactant bilayer KW - undulated nanoplatelets KW - SERS KW - LSPR Y1 - 2018 U6 - https://doi.org/10.1021/acsanm.8b00570 SN - 2574-0970 VL - 1 IS - 4 SP - 1995 EP - 2003 PB - American Chemical Society CY - Washington ER - TY - GEN A1 - Sarhan, Radwan Mohamed A1 - Koopman, Wouter-Willem Adriaan A1 - Schuetz, Roman A1 - Schmid, Thomas A1 - Liebig, Ferenc A1 - Koetz, Joachim A1 - Bargheer, Matias T1 - The importance of plasmonic heating for the plasmondriven photodimerization of 4-nitrothiophenol T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - Metal nanoparticles form potent nanoreactors, driven by the optical generation of energetic electrons and nanoscale heat. The relative influence of these two factors on nanoscale chemistry is strongly debated. This article discusses the temperature dependence of the dimerization of 4-nitrothiophenol (4-NTP) into 4,4′-dimercaptoazobenzene (DMAB) adsorbed on gold nanoflowers by Surface-Enhanced Raman Scattering (SERS). Raman thermometry shows a significant optical heating of the particles. The ratio of the Stokes and the anti-Stokes Raman signal moreover demonstrates that the molecular temperature during the reaction rises beyond the average crystal lattice temperature of the plasmonic particles. The product bands have an even higher temperature than reactant bands, which suggests that the reaction proceeds preferentially at thermal hot spots. In addition, kinetic measurements of the reaction during external heating of the reaction environment yield a considerable rise of the reaction rate with temperature. Despite this significant heating effects, a comparison of SERS spectra recorded after heating the sample by an external heater to spectra recorded after prolonged illumination shows that the reaction is strictly photo-driven. While in both cases the temperature increase is comparable, the dimerization occurs only in the presence of light. Intensity dependent measurements at fixed temperatures confirm this finding. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 698 KW - enhanced raman-scattering KW - charge-transfer KW - metal KW - nanoparticles KW - catalysis KW - AU KW - 4-nitrobenzenethiol KW - aminothiophenol KW - photocatalysis KW - wavelength Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-427197 SN - 1866-8372 IS - 698 ER -