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Estrada-Vargas A.,Ruhr University Bochum | Bandarenka A.,Nanosystems Initiative Munich NIM | Bandarenka A.,TU Munich | Kuznetsov V.,Ruhr University Bochum | And 2 more authors.
Analytical Chemistry | Year: 2016

Control over the properties of ultrathin films plays a crucial role in many fields of science and technology. Although nondestructive optical and electrical methods have multiple advantages for local surface characterization, their applicability is very limited if the surface is in contact with an electrolyte solution. Local electrochemical methods, e.g., scanning electrochemical microscopy (SECM), cannot be used as a robust alternative yet because their methodological aspects are not sufficiently developed with respect to these systems. The recently proposed scanning electrochemical impedance microscopy (SEIM) can efficiently elucidate many key properties of the solid/liquid interface such as charge transfer resistance or interfacial capacitance. However, many fundamental aspects related to SEIM application still remain unclear. In this work, a methodology for the interpretation of SEIM data of "charge blocking systems" has been elaborated with the help of finite element simulations in combination with experimental results. As a proof of concept, the local film thickness has been visualized using model systems at various tip-to-sample separations. Namely, anodized aluminum oxide (Al2O3, 2-20 nm) and self-assembled monolayers based on 11-mercapto-1-undecanol and 16-mercapto-1-hexadecanethiol (2.1 and 2.9 nm, respectively) were used as model systems. (Figure Presented). © 2016 American Chemical Society. Source


Blanch A.J.,Ludwig Maximilians University of Munich | Doblinger M.,Nanosystems Initiative Munich NIM | Doblinger M.,Ludwig Maximilians University of Munich | Rodriguez-Fernandez J.,Ludwig Maximilians University of Munich
Small | Year: 2015

Branched gold nanoparticles with sharp tips are considered excellent candidates for sensing and field enhancement applications. Here, a rapid and simple synthesis strategy is presented that generates highly branched gold nanoparticles with hollow cores and a ca.100% yield through a simple one-pot seedless reaction at room temperature in the presence of Triton X-100. It is shown that multibranched hollow gold nanoparticles of tunable dimensions, branch density and branch length can be obtained by adjusting the concentrations of the reactants. Insights into the formation mechanism point toward an aggregative type of growth involving hollow core formation first, and branching thereafter. The pronounced near-infrared (NIR) plasmon band of the nanoparticles is due to the combined contribution from hollowness and branching, and can be tuned over a wide range (≈700-2000 nm). It is also demonstrated that the high environmental sensitivity of colloidal dispersions based on multibranched hollow gold nanoparticles can be boosted even further by separating the nanoparticles into fractions of given sizes and improved monodispersity by means of a glycerol density gradient. The possibility to obtain highly monodisperse multibranched hollow gold nanoparticles with predictable dimensions (50-300 nm) and branching and, therefore, tailored NIR plasmonic properties, highlights their potential for theranostic applications. Gold nanoparticles with multiple branches and hollow cores are synthesized in high yield in a simple one-pot seedless process. The plasmon resonance of the nanoparticles is tunable across the NIR, and its NIR character stems from the combined contribution of hollowness and branching. It is also shown how the high environmental sensitivity of the nanoparticles can be significantly boosted through centrifugal size sorting. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source


Ardelt P.-L.,TU Munich | Gawarecki K.,Wroclaw University of Technology | Muller K.,TU Munich | Muller K.,Stanford University | And 11 more authors.
Physical Review Letters | Year: 2016

We report Coulomb mediated hybridization of excitonic states in optically active InGaAs quantum dot molecules. By probing the optical response of an individual quantum dot molecule as a function of the static electric field applied along the molecular axis, we observe unexpected avoided level crossings that do not arise from the dominant single-particle tunnel coupling. We identify a new few-particle coupling mechanism stemming from Coulomb interactions between different neutral exciton states. Such Coulomb resonances hybridize the exciton wave function over four different electron and hole single-particle orbitals. Comparisons of experimental observations with microscopic eight-band k·p calculations taking into account a realistic quantum dot geometry show good agreement and reveal that the Coulomb resonances arise from broken symmetry in the artificial semiconductor molecule. © 2016 American Physical Society. Source


Berkes B.B.,Eotvos Lorand University | Berkes B.B.,Karlsruhe Institute of Technology | Bandarenka A.S.,Nanosystems Initiative Munich NIM | Bandarenka A.S.,TU Munich | Inzelt G.,Eotvos Lorand University
Journal of Physical Chemistry C | Year: 2014

Electropolymerization is a promising route to design new functional surfaces. In this work, we investigate electropolymerization of indole at polycrystalline Pt electrode surfaces in acidic sulfuric media using in situ nanogravimetry, electrochemical impedance spectroscopy, and direct current (dc) measurements applied simultaneously to elucidate the physical model of the electrified interface during this process. Monitoring the electrode mass change with a quartz crystal nanobalance allows quantification of the overall electropolymerization kinetics and, together with the dc-response, provides further insight into the dynamics of the film formation. Complementary electrochemical impedance spectroscopy measurements quantify specific parameters characterizing the processes which involve the interfacial charge transfer during the film growth. Importantly for various applications, it has been also demonstrated that the growth of polyindole thin films can be controlled using just molecular oxygen dissolved in the electrolytes. © 2015 American Chemical Society. Source


Brenneis A.,TU Munich | Gaudreau L.,ICFO - Institute of Photonic Sciences | Seifert M.,TU Munich | Karl H.,University of Augsburg | And 6 more authors.
Nature Nanotechnology | Year: 2015

Non-radiative transfer processes are often regarded as loss channels for an optical emitter because they are inherently difficult to access experimentally. Recently, it has been shown that emitters, such as fluorophores and nitrogen-vacancy centres in diamond, can exhibit a strong non-radiative energy transfer to graphene. So far, the energy of the transferred electronic excitations has been considered to be lost within the electron bath of the graphene. Here we demonstrate that the transferred excitations can be read out by detecting corresponding currents with a picosecond time resolution. We detect electronically the spin of nitrogen-vacancy centres in diamond and control the non-radiative transfer to graphene by electron spin resonance. Our results open the avenue for incorporating nitrogen-vacancy centres into ultrafast electronic circuits and for harvesting non-radiative transfer processes electronically. © 2015 Macmillan Publishers Limited. Source

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