Physikhttps://kops.uni-konstanz.de:443/handle/123456789/412019-07-18T14:08:43Z2019-07-18T14:08:43ZThe fabrication, characterization and simulation of inverted perovskite solar cellsHu, Haopop258246123456789/464472019-07-18T10:55:09Z2019The fabrication, characterization and simulation of inverted perovskite solar cells
Hu, Hao
2019Hu, Hao530DOCTORAL_THESISurn:nbn:de:bsz:352-2-wdi5qeq5e6w32eng2019-07-18T12:52:13+02:00123456789/412019-07-18T10:52:13ZEnergy scales and dynamics of electronic excitations in functionalized gold nanoparticles measured at the single particle levelBasu, Tuhin Shuvrapop253133Diesch, Simonpop210452Obergfell, Manuelpop169290Demsar, Jurepop169899Scheer, Elkepop23700123456789/464302019-07-17T11:48:02Z2019-07-07Energy scales and dynamics of electronic excitations in functionalized gold nanoparticles measured at the single particle level
Basu, Tuhin Shuvra; Diesch, Simon; Obergfell, Manuel; Demsar, Jure; Scheer, Elke
The knowledge of the electronic structure and dynamics of nanoparticles is a prerequisite to develop miniaturized single-electron devices based on nanoparticles. Low-temperature transport measurements of individual stable metallic nanoparticles enable unravelling the system specific electronic structure while ultrafast optical spectroscopy gives access to the electron dynamics. In this work, we investigate bare and thiol-functionalized gold nanoparticles. For the latter, we employ a fast and low-cost fabrication technique which yields nanoparticles with narrow size distribution. Using relatively long thiol-ended alkane chains for the functionalization modifies the electronic density of states of the nanoparticles. The study of decay dynamics of surface-plasmon-related hot electrons reveals the presence of electronic states at the interface which serve as a fast decay channel for electronic relaxation. By low-temperature scanning tunnelling microscopy we precisely investigate the energy scales and electronic interactions relevant for the tunnel charge transport through this system. We observe that the interaction between the functional ligand and the substrate on which the nanoparticles reside also influences the electronic transport. The procedure that we employ can be easily adapted to other metallic nanoparticles. Our findings are therefore important for incorporating them into single-electron devices.
2019-07-07Basu, Tuhin ShuvraDiesch, SimonObergfell, ManuelDemsar, JureScheer, Elke530The knowledge of the electronic structure and dynamics of nanoparticles is a prerequisite to develop miniaturized single-electron devices based on nanoparticles. Low-temperature transport measurements of individual stable metallic nanoparticles enable unravelling the system specific electronic structure while ultrafast optical spectroscopy gives access to the electron dynamics. In this work, we investigate bare and thiol-functionalized gold nanoparticles. For the latter, we employ a fast and low-cost fabrication technique which yields nanoparticles with narrow size distribution. Using relatively long thiol-ended alkane chains for the functionalization modifies the electronic density of states of the nanoparticles. The study of decay dynamics of surface-plasmon-related hot electrons reveals the presence of electronic states at the interface which serve as a fast decay channel for electronic relaxation. By low-temperature scanning tunnelling microscopy we precisely investigate the energy scales and electronic interactions relevant for the tunnel charge transport through this system. We observe that the interaction between the functional ligand and the substrate on which the nanoparticles reside also influences the electronic transport. The procedure that we employ can be easily adapted to other metallic nanoparticles. Our findings are therefore important for incorporating them into single-electron devices.JOURNAL_ARTICLEeng10.1039/c9cp02378j1463-90761463-908413446134522125Physical Chemistry Chemical Physics (PCCP)2019-07-17T13:48:01+02:00123456789/41Physical Chemistry Chemical Physics (PCCP) ; 21 (2019), 25. - S. 13446-13452. - ISSN 1463-9076. - eISSN 1463-9084true2019-07-17T11:48:01ZOrientation-dependent current-induced motion of skyrmions with various topologiesWeißenhofer, Markuspop518432Nowak, Ulrichpop209772123456789/464292019-07-17T11:44:07Z2019Orientation-dependent current-induced motion of skyrmions with various topologies
Weißenhofer, Markus; Nowak, Ulrich
We study the current-driven motion of metastable localized spin structures with various topological charges in a (Pt<sub>0.95</sub>Ir<sub>0.05</sub>)/Fe bilayer on a Pd(111) surface by combining atomistic spin model simulations with an approach based on the generalized Thiele equation. We demonstrate that besides a distinct dependence on the topological charge itself the dynamic response of skyrmionic structures with topological charges Q=−1 and Q=3 to a spin-polarized current exhibits an orientation dependence. We further show that such an orientation dependence can be induced by applying an in-plane external field, possibly opening up a different pathway to the manipulation of skyrmion dynamics.
2019Weißenhofer, MarkusNowak, Ulrich530We study the current-driven motion of metastable localized spin structures with various topological charges in a (Pt<sub>0.95</sub>Ir<sub>0.05</sub>)/Fe bilayer on a Pd(111) surface by combining atomistic spin model simulations with an approach based on the generalized Thiele equation. We demonstrate that besides a distinct dependence on the topological charge itself the dynamic response of skyrmionic structures with topological charges Q=−1 and Q=3 to a spin-polarized current exhibits an orientation dependence. We further show that such an orientation dependence can be induced by applying an in-plane external field, possibly opening up a different pathway to the manipulation of skyrmion dynamics.JOURNAL_ARTICLEeng10.1103/PhysRevB.99.2244302469-99502469-99699922Physical Review B2019-07-17T13:44:06+02:00123456789/41Physical Review B ; 99 (2019), 22. - 224430. - ISSN 2469-9950. - eISSN 2469-9969true2019-07-17T11:44:06ZAll optical control of comb-like coherent acoustic phonons in multiple quantum well structures through double-pump-pulse pump-probe experimentsLi, Changxiupop258243Gusev, VitalyDekorsy, Thomaspop102602Hettich, Mikepop205786123456789/464282019-07-18T01:04:16Z2019-06-24All optical control of comb-like coherent acoustic phonons in multiple quantum well structures through double-pump-pulse pump-probe experiments
Li, Changxiu; Gusev, Vitaly; Dekorsy, Thomas; Hettich, Mike
We present an advancement in applications of ultrafast optics in picosecond laser ultrasonics - laser-induced comb-like coherent acoustic phonons are optically controlled in a In0.27Ga0.73As/GaAs multiple quantum well (MQW) structure by a high-speed asynchronous optical sampling (ASOPS) system based on two GHz Yb:KYW lasers. Two successive pulses from the same pump laser are used to excite the MQW structure. The second pump light pulse has a tunable time delay with respect to the first one and can be also tuned in intensity, which enables the amplitude and phase modulation of acoustic phonons. This yields rich temporal acoustic patterns with suppressed or enhanced amplitudes, various wave-packet shapes, varied wave-packet widths, reduced wave-packet periods and varied phase shifts of single-period oscillations within a wave-packet. In the frequency domain, the amplitude and phase shift of the individual comb component present a second-pump-delay-dependent cosine-wave-like and sawtooth-wave-like variation, respectively, with a modulation frequency equal to the comb component frequency itself. The variations of the individual component amplitude and phase shift by tuning the second pump intensity exhibit an amplitude valley and an abrupt phase jump at the ratio around 1:1 of the two pump pulse intensities for certain time delays. A simplified model, where both generation and detection functions are assumed as a cosine stress wave enveloped by Gaussian or rectangular shapes in an infinite periodic MQW structure, is developed in order to interpret acoustic manipulation in the MQW sample. The modelling agrees well with the experiment in a wide range of time delays and intensity ratios. Moreover, by applying a heuristic-analytical approach and nonlinear corrections, the improved calculations reach an excellent agreement with experimental results and thus enable to predict and synthesize coherent acoustic wave patterns in MQW structures.
2019-06-24Li, ChangxiuGusev, VitalyDekorsy, ThomasHettich, Mike530We present an advancement in applications of ultrafast optics in picosecond laser ultrasonics - laser-induced comb-like coherent acoustic phonons are optically controlled in a In0.27Ga0.73As/GaAs multiple quantum well (MQW) structure by a high-speed asynchronous optical sampling (ASOPS) system based on two GHz Yb:KYW lasers. Two successive pulses from the same pump laser are used to excite the MQW structure. The second pump light pulse has a tunable time delay with respect to the first one and can be also tuned in intensity, which enables the amplitude and phase modulation of acoustic phonons. This yields rich temporal acoustic patterns with suppressed or enhanced amplitudes, various wave-packet shapes, varied wave-packet widths, reduced wave-packet periods and varied phase shifts of single-period oscillations within a wave-packet. In the frequency domain, the amplitude and phase shift of the individual comb component present a second-pump-delay-dependent cosine-wave-like and sawtooth-wave-like variation, respectively, with a modulation frequency equal to the comb component frequency itself. The variations of the individual component amplitude and phase shift by tuning the second pump intensity exhibit an amplitude valley and an abrupt phase jump at the ratio around 1:1 of the two pump pulse intensities for certain time delays. A simplified model, where both generation and detection functions are assumed as a cosine stress wave enveloped by Gaussian or rectangular shapes in an infinite periodic MQW structure, is developed in order to interpret acoustic manipulation in the MQW sample. The modelling agrees well with the experiment in a wide range of time delays and intensity ratios. Moreover, by applying a heuristic-analytical approach and nonlinear corrections, the improved calculations reach an excellent agreement with experimental results and thus enable to predict and synthesize coherent acoustic wave patterns in MQW structures.JOURNAL_ARTICLEurn:nbn:de:bsz:352-2-19ig1gmx9dd5q5eng10.1364/OE.27.0187061094-408718706187302713Optics Express2019-07-17T13:30:43+02:00123456789/41Optics Express ; 27 (2019), 13. - S. 18706-18730. - eISSN 1094-4087true2019-07-17T11:30:43Ztrue