TY - JOUR A1 - Stete, Felix A1 - Koopman, Wouter-Willem Adriaan A1 - Bargheer, Matias T1 - Signatures of strong coupling on nanoparticles BT - revealing absorption anticrossing by tuning the dielectric environment JF - ACS Photonics N2 - In the strong coupling regime, exciton and plasmon excitations are hybridized into combined system excitations. The correct identification of the coupling regime in these systems is currently debated, from both experimental and theoretical perspectives. In this article we show that the extinction spectra may show a large peak splitting, although the energy loss encoded in the absorption spectra clearly rules out the strong coupling regime. We investigate the coupling of J-aggregate excitons to the localized surface plasmon polaritons on gold nanospheres and nanorods by fine-tuning the plasmon resonance via layer-by-layer deposition of polyelectrolytes. While both structures show a characteristic anticrossing in extinction and scattering experiments, the careful assessment of the systems’ light absorption reveals that strong coupling of the plasmon to the exciton is not present in the nanosphere system. In a phenomenological model of two classical coupled oscillators, a Fano-like regime causes only the resonance of the light-driven oscillator to split up, while the other one still dissipates energy at its original frequency. Only in the strong-coupling limit do both oscillators split up the frequencies at which they dissipate energy, qualitatively explaining our experimental finding. KW - hybrid nanoparticles KW - exciton plasmon coupling KW - layer-by-layer deposition KW - strong coupling KW - absorption measurements Y1 - 2017 U6 - https://doi.org/10.1021/acsphotonics.7b00113 SN - 2330-4022 VL - 4 SP - 1669 EP - 1676 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Stete, Felix A1 - Schossau, Phillip A1 - Bargheer, Matias A1 - Koopman, Wouter-Willem Adriaan T1 - Size-Dependent coupling of Hybrid Core-Shell Nanorods BT - Toward Single-Emitter Strong-Coupling JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Owing to their ability of concentrating electromagnetic fields to subwavelength mode volumes, plasmonic nanoparticles foster extremely high light-matter coupling strengths reaching far into the strong-coupling regime of light matter interaction. In this article, we present an experimental investigation on the dependence of coupling strength on the geometrical size of the nanoparticle. The coupling strength for differently sized hybrid plasmon-core exciton-shell nanorods was extracted from the typical resonance anticrossing of these systems, obtained by controlled modification of the environment permittivity using layer-by-layer deposition of polyelectrolytes. The observed size dependence of the coupling strength can be explained by a simple model approximating the electromagnetic mode volume by the geometrical volume of the particle. On the basis of this model, the coupling strength for particles of arbitrary size can be predicted, including the particle size necessary to support single-emitter strong coupling. Y1 - 2018 U6 - https://doi.org/10.1021/acs.jpcc.8b04204 SN - 1932-7447 VL - 122 IS - 31 SP - 17976 EP - 17982 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sarhan, Radwan Mohamed A1 - Koopman, Wouter-Willem Adriaan A1 - Pudell, Jan-Etienne A1 - Stete, Felix A1 - Rössle, Matthias A1 - Herzog, Marc A1 - Schmitt, Clemens Nikolaus Zeno A1 - Liebig, Ferenc A1 - Koetz, Joachim A1 - Bargheer, Matias T1 - Scaling up nanoplasmon catalysis BT - the role of heat dissipation JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - Nanoscale heating by optical excitation of plasmonic nanoparticles offers a new perspective of controlling chemical reactions, where heat is not spatially uniform as in conventional macroscopic heating but strong temperature gradients exist around microscopic hot spots. In nanoplasmonics, metal particles act as a nanosource of light, heat, and energetic electrons driven by resonant excitation of their localized surface plasmon resonance. As an example of the coupling reaction of 4-nitrothiophenol into 4,4′-dimercaptoazobenzene, we show that besides the nanoscopic heat distribution at hot spots, the microscopic distribution of heat dictated by the spot size of the light focus also plays a crucial role in the design of plasmonic nanoreactors. Small sizes of laser spots enable high intensities to drive plasmon-assisted catalysis. This facilitates the observation of such reactions by surface-enhanced Raman scattering, but it challenges attempts to scale nanoplasmonic chemistry up to large areas, where the excess heat must be dissipated by one-dimensional heat transport. KW - Gold KW - Raman spectroscopy KW - Silicon KW - Irradiation KW - Lasers Y1 - 2019 U6 - https://doi.org/10.1021/acs.jpcc.8b12574 SN - 1932-7447 VL - 123 IS - 14 SP - 9352 EP - 9357 PB - American Chemical Society CY - Washington ER - TY - GEN A1 - Stete, Felix A1 - Schossau, Phillip Gerald A1 - Koopman, Wouter-Willem Adriaan A1 - Bargheer, Matias T1 - Size Dependence of the Coupling Strength in Plasmon-Exciton Nanoparticles T2 - Quantum Nano-Photonics N2 - The coupling between molecular excitations and nanoparticles leads to promising applications. It is for example used to enhance the optical cross-section of molecules in surface enhanced Raman scattering, Purcell enhancement or plasmon enhanced dye lasers. In a coupled system new resonances emerge resulting from the original plasmon (ωpl) and exciton (ωex) resonances as ω±=12(ωpl+ωex)±14(ωpl−ωex)2+g2−−−−−−−−−−−−−−−√, (1) where g is the coupling parameter. Hence, the new resonances show a separation of Δ = ω+ − ω− from which the coupling strength can be deduced from the minimum distance between the two resonances, Ω = Δ(ω+ = ω−). Y1 - 2018 SN - 978-94-024-1546-9 SN - 978-94-024-1544-5 SN - 978-94-024-1543-8 U6 - https://doi.org/10.1007/978-94-024-1544-5_26 SN - 1871-465X SP - 381 EP - 383 PB - Springer CY - Dordrecht ER - TY - GEN A1 - Stete, Felix A1 - Koopman, Wouter-Willem Adriaan A1 - Bargheer, Matias T1 - Signatures of strong coupling on nanoparticles BT - revealing absorption anticrossing by tuning the dielectric environment T2 - Quantum Nano-Photonics N2 - The electromagnetic coupling of molecular excitations to plasmonic nanoparticles offers a promising method to manipulate the light-matter interaction at the nanoscale. Plasmonic nanoparticles foster exceptionally high coupling strengths, due to their capacity to strongly concentrate the light-field to sub-wavelength mode volumes. A particularly interesting coupling regime occurs, if the coupling increases to a level such that the coupling strength surpasses all damping rates in the system. In this so-called strong-coupling regime hybrid light-matter states emerge, which can no more be divided into separate light and matter components. These hybrids unite the features of the original components and possess new resonances whose positions are separated by the Rabi splitting energy h Omega. Detuning the resonance of one of the components leads to an anticrossing of the two arising branches of the new resonances omega(+) and omega(-) with a minimal separation of Omega = omega(+) - omega(-). Y1 - 2018 SN - 978-94-024-1546-9 SN - 978-94-024-1544-5 SN - 978-94-024-1543-8 U6 - https://doi.org/10.1007/978-94-024-1544-5_53 SN - 1871-465X SP - 445 EP - 447 PB - Springer CY - Dordrecht ER - 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 - THES A1 - Stete, Felix T1 - Gold at the nanoscale BT - plasmon-exciton coupling and optical heating N2 - In this cumulative dissertation, I want to present my contributions to the field of plasmonic nanoparticle science. Plasmonic nanoparticles are characterised by resonances of the free electron gas around the spectral range of visible light. In recent years, they have evolved as promising components for light based nanocircuits, light harvesting, nanosensors, cancer therapies, and many more. This work exhibits the articles I authored or co-authored in my time as PhD student at the University of Potsdam. The main focus lies on the coupling between localised plasmons and excitons in organic dyes. Plasmon–exciton coupling brings light–matter coupling to the nanoscale. This size reduction is accompanied by strong enhancements of the light field which can, among others, be utilised to enhance the spectroscopic footprint of molecules down to single molecule detection, improve the efficiency of solar cells, or establish lasing on the nanoscale. When the coupling exceeds all decay channels, the system enters the strong coupling regime. In this case, hybrid light–matter modes emerge utilisable as optical switches, in quantum networks, or as thresholdless lasers. The present work investigates plasmon–exciton coupling in gold–dye core–shell geometries and contains both fundamental insights and technical novelties. It presents a technique which reveals the anticrossing in coupled systems without manipulating the particles themselves. The method is used to investigate the relation between coupling strength and particle size. Additionally, the work demonstrates that pure extinction measurements can be insufficient when trying to assess the coupling regime. Moreover, the fundamental quantum electrodynamic effect of vacuum induced saturation is introduced. This effect causes the vacuum fluctuations to diminish the polarisability of molecules and has not yet been considered in the plasmonic context. The work additionally discusses the reaction of gold nanoparticles to optical heating. Such knowledge is of great importance for all potential optical applications utilising plasmonic nanoparticles since optical excitation always generates heat. This heat can induce a change in the optical properties, but also mechanical changes up to melting can occur. Here, the change of spectra in coupled plasmon–exciton particles is discussed and explained with a precise model. Moreover, the work discusses the behaviour of gold nanotriangles exposed to optical heating. In a pump–probe measurement, X-ray probe pulses directly monitored the particles’ breathing modes. In another experiment, the triangles were exposed to cw laser radiation with varying intensities and illumination areas. X-ray diffraction directly measured the particles’ temperature. Particle melting was investigated with surface enhanced Raman spectroscopy and SEM imaging demonstrating that larger illumination areas can cause melting at lower intensities. An elaborate methodological and theoretical introduction precedes the articles. This way, also readers without specialist’s knowledge get a concise and detailed overview of the theory and methods used in the articles. I introduce localised plasmons in metal nanoparticles of different shapes. For this work, the plasmons were mostly coupled to excitons in J-aggregates. Therefore, I discuss these aggregates of organic dyes with sharp and intense resonances and establish an understanding of the coupling between the two systems. For ab initio simulations of the coupled systems, models for the systems’ permittivites are presented, too. Moreover, the route to the sample fabrication – the dye coating of gold nanoparticles, their subsequent deposition on substrates, and the covering with polyelectrolytes – is presented together with the measurement methods that were used for the articles. N2 - In der vorliegenden publikationsbasierten Dissertation möchte ich meinen Beitrag aus meiner Zeit als Doktorand an der Universität Potsdam zum Forschungsgebiet plasmonischer Nanopartikel vorstellen. Letztere zeichnen sich durch Resonanzen des freien Elektronengases im Spektralbereich sichtbaren Lichts aus mit vielversprechenden Anwenungsgebieten, unter anderem in Bereichen der Nanosensorik, lichtbasierter Nanoschaltkreise oder auch der Krebstherapie. Die Arbeit beinhaltet die von mir mitverfassten wissenschaftlichen Artikel, mit dem Hauptaugenmerk auf der Kopplung zwischen lokalisierten Plasmonen in Gold-Nanopartikeln und Exzitonen in organischen Farbstoffen. Plasmonen konzentrieren Lichtfelder auf kleinstem Raum. Dadurch verstärkt sich die Licht–Materie-Wechselwirkung, welche es etwa ermöglicht, die Effizienz von Solarzellen zu erhöhen, die Spektren weniger bis einzelner Moleküle aufzunehmen oder auch Laser auf der Nanoskala zu entwickeln. Überschreitet die Wechselwirkung zwischen Plasmonen und Exzitonen alle anderen Dissipationskanäle, spricht man vom Regime der starken Kopplung. In diesem Regime entstehen neue untrennbare Licht–Materie-Hybridzustände aus denen ultraschnelle optische Schalter, Quantennetzwerke oder pumpschwellenfreie Laser konstruiert werden können. Die Artikel bieten dabei sowohl Erkenntnisse der Grundlageforschung als auch neue technische Verfahren. So wird unter anderem eine Methode zur Sichtbarmachung der vermiedenen Kreuzung gekoppelter Resonanzen vorgestellt, in der die Partikel selber nicht verändert werden. Die Technik wird hier beispielsweise verwendet, um den Zusammenhang zwischen Kopplungsstärke und Partikelgröße zu untersuchen. Zusätzlich zeigt die Arbeit, dass das alleinige Betrachten von Extinktionsspektren unzureichend für die Beurteilung des Kopplungsregimes sein kann. Desweiteren wird die Sättigung durch Vakuumfelder vorgestellt, ein Effekt der Quantenelektrodynamik, der im Zusammenhang mit Plasmonen bisher unbekannt war. Die Reaktion von Gold-Nanopartikeln auf optische Erwärmung stellt den zweiten Themenbereich der Arbeit dar. Da durch optische Anregung grundsätzlich auch Wärme entsteht, ist die Kenntnis über diese Reaktion für alle Anwendungen plasmonischer Nanopartikel von Bedeutung. Zum einen wird hier die spektrale Änderung nach der Anregung gekoppelter Gold–Farbstoff-Partikel untersucht und quantitativ modelliert, zum anderen betrachtet die Arbeit Gold-Nanodreiecke bei optischer Anregung. In zeitaufgelösten Messungen wurde die Ausdehnung des Kristallgitters direkt mit Röntgen-Pulsen aufgenommen. Mit Hilfe von kontinuierlicher Röntgenstrahlung wurde außerdem die Temperatur der Teilchen bei konstanter Beleuchtung von Laserlicht gemessen, wobei die Größe der beleuchteten Fläche und die Lichtintensität variierten. Durch oberflächenverstärkte Raman-Spektren und REM-Bilder ließ sich indes das Schmelzen der Teilchen beobachten. Den Artikeln steht eine ausführliche Einleitung voran, die eine detaillierte Übersicht sowohl über die theoretischen Grundlagen als auch über die experimentelle Methodik bietet. Sie führt lokalisierte Plasmonen auf unterschiedlich geformten Teilchen ein. Für diese Arbeit wurden die Teilchen mit J-Aggregaten ummantelt. Folglich werden diese speziellen Aggregate organischer Farbstoffe mit ihren intensiven und scharfen Resonanzen vorgestellt und die Kopplung ihrer Anregungen mit Plasmonen diskutiert. Für Ab-initio-Simulationen der gekoppelten Spektren werden Modelle für Permittivität der beiden Komponenten besprochen. Abschließend werden die Herstellung der Proben sowie alle in den Artikeln verwendeten Messmethoden eingeführt. KW - Nanoparticles KW - Plasmons KW - Light-Matter Coupling KW - Licht-Materie-Wechselwirkung KW - Nanopartikel KW - Plasmonen Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-496055 ER -