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  - JOUR
A1  - Liebig, Ferenc
A1  - Thünemann, Andreas F.
A1  - Koetz, Joachim
T1  - Ostwald Ripening Growth Mechanism of Gold Nanotriangles in Vesicular Template Phases
JF  - Langmuir
N2  - The mechanism of nanotriangle formation in multivesicular vesicles (MMV) is investigated by using time-dependent SAXS measurements in combination with UV-vis spectroscopy, light, and transmission electron microscopy. In the first time period 6.5 nm sized spherical gold nanoparticles are formed inside of the vesicles, which build up soft nanoparticle aggregates. a) In situ SAXS experiments show a linear increase of the volume and molar mass of nanotriangles in the second time period. The volume growth rate of the triangles is 16.1 nm(3)/min, and the growth rate in the vertical direction is only 0.02 nm/min. Therefore, flat nanotriangles with a thickness of 7 nm and a diameter of 23 nm are formed. This process can be described by a diffusion limited Ostwald ripening growth mechanism. TEM micrographs visualize soft coral-like structures with thin nanoplatelets at the periphery of the aggregates, which disaggregate in the third time period into nanotriangles and spherical particles. The 16 times faster growth of nanotriangles in the lateral than that in the vertical direction is related to the adsorption of symmetry breaking components, i.e., AOT and the polyampholyte PalPhBisCarb, on the {111} facets of the gold nanoplatelets in combination with confinement effects of the vesicular template phase.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.langmuir.6b02662
SN  - 0743-7463
VL  - 32
SP  - 10928
EP  - 10935
PB  - American Chemical Society
CY  - Washington
ER  -