Publications

2024

[61] A. Ungeheuer, N. Bach, M. T. Mir, A. S. Hassanien, L. Nöding, T. Baumert, S. Schäfer, A. Senftleben. Coherent acoustic phonons in coupled hexagonal boron nitride-graphite heterostructure. Struct. Dyn. 11, 014501 (2024).

[60] A. Schröder, Chr. Rathje, L. van Velzen, M. Kelder, S. Schäfer, Improving the temporal resolution of event-based electron detectors using neural network cluster analysis. Ultramicroscopy 256, 113881 (2023).

2023

[59] J. T. Weber, S. Schäfer, Electron imaging of nanoscale charge distributions induced by femtosecond light pulses. arXiv: 2308.10272 (2023).

[58] Chr. Rathje, R. von Seggern, L. A. Gräper, J. Kredl, J. Walowski, M. Münzenberg, S. Schäfer. Coupling broadband terahertz dipoles to microscale resonators. ACS Photonics 10, 3467 (2023).

[57] N. Müller, S. Schäfer. Of Electrons and Photons, News and Views: Of electrons and photons. Nature Physics 19, 1239 (2023).

2022

[56] N. Bach, A. Feist, M. Möller, C. Ropers, S. Schäfer, Tailored nanophononic wavefield in a patterned bilayer system probed by ultrafast convergent beam electron diffraction. Structural Dynamics 9, 034301 (2022).

[55] D. Pareek, M. A. Gonzalez, N. Grewo, M. L. Janßen, K. Arunakiri, K. Luqman Alimi, M. Silies, J. Parisi, L. Gütay, S. Schäfer. Large-Area Growth of MoS2/WS2 Heterostructures by a sequential atomic layer deposition and spin-coating approach. Adv. Mater. Interfaces 9, 2200816 (2022).

[54] C. Lattyak, M. Vehse, M. A. Gonzalez, D. Pareek, L. Gütay, S. Schäfer, C. Agert. Optoelectronic properties of MoS2 in proximity to carrier selective metal oxides. Adv. Opt. Mater. 10, 2102226 (2022).

2021

[53] A. Hariharan, S. Schäfer, S. J. Heise. Decay of excess carriers in a two-defect model semiconductor: A time-resolved photoluminescence study. J. Appl. Phys. 130, 235702 (2021).

[52] H. Ahmed, V. Solovyeva, M. A. Gonzalez, M. Elshabasi, M. Richter, D. Pareek, S. J. Heise, M. Stölzel, A. Weber, Th. Dalibor, S. Schäfer, J. Parisi. Impact of the buffer/absorber interface on the metastability of fill factor temperature coefficients in CIGSSe solar cells. Adv. Mat. Interfaces. 18, 2100778 (2021).

[51] N. Bach, S. Schäfer. Ultrafast strain propagation and acoustic resonances in nanoscale bilayer systems. Structural Dynamics 8, 035101 (2021).

[50] D. Pareek, K. G. Roach, M. A. Gonzalez, L. Büsing, J. Parisi, L. Gütay, S. Schäfer, Micro-patterned deposition of MoS2 ultrathin-films by a controlled droplet dragging approach. Scientific Reports, 11, 13993 (2021). 

[49] T. Harvey, N. Rubiano, J. H. Gaida, M. Möller, A. Feist, S. Schäfer, C. Ropers, Ultrafast electron microscopy for probing magnetic dynamics. MRS Bulletin 46, 711 (2021).

[48] M. A. Gonzalez, D. Pareek, L. Büsing, M. Beer, J. Parisi, S. Schäfer, L. Gütay, Rapid formation of large area MoS2 monolayers by a parameter resilient atomic layer deposition approach, APL Materials 9, 051122 (2021).

[47] H. Ahmed, M. Elshabasi, J. Ohland, M. Stölzel, A. Weber, R. Lechner, Th. Dalibor, J. Parisi, S. Schäfer, S. J. Heise, Temperature coefficient characterization of CIGSSe solar cells with layer modifications. Solar Energy Materials and Solar Cells, 225, 111059 (2021).

[46] N. Müller, V. Hock, C. Rathje, H. Koch, S. Schäfer, Broadband coupling of fast electrons to high-Q whispering gallery mode resonators. ACS Photonics 8 1569-1575 (2021).

2020

[45] A. Feist, S.V. Yalunin, S. Schäfer, C. Ropers, High-purity free-electron momentum states prepared by three-dimensional optical phase modulation. Phys. Rev. Research 2, 043227 (2020).

[44] P. Dombi, Z. Pápa, J. Vogelsang, S. V. Yalunin, M. Sivis, G. Herink, S. Schäfer, P. Gross, C. Ropers, Ch. Lienau. Strong-field nano-optics. Rev. Mod. Phys. 92, 025003 (2020).

[43] M. Möller, J.H. Gaida, S. Schäfer, C. Ropers. Few-nm tracking of current-driven magnetic vortex orbits using ultrafast Lorentz microscopy. Communications Physics 3, 1-7 (2020).

[42] K. Eickhoff, Chr. Rathje, D. Köhnke, S. Kerbstadt, L. Englert, T. Bayer, S. Schäfer and M. Wollenhaupt. Orbital angular momentum superposition states in transmission electron microscopy and bichromatic multiphoton ionization. New. J. Phys. 22, 103045 (2020).

2019

[41] N. Bach, T. Domröse, A. Feist, T. Rittmann, S. Strauch, C. Ropers, S. Schäfer. Coulomb interactions in high-coherence femtosecond electron pulses from tip emitters. Struct. Dyn. 6, 014301 (2019).

[40] D. Pareek, M. A. Gonzalez, J. Zohrabian, M. H. Sayed, V. Steenhoff, C. Lattyak,  M. Vehse,  C. Agert, J. Parisi   S. Schäfer, L. Gütay. A vapor-phase-assisted growth route for large-scale uniform deposition of MoS2 monolayer films. RSC Advances 9, 107-113 (2019).

2018

[39] N. Rubiano da Silva, M. Möller, A. Feist, H. Ulrichs, C. Ropers, S. Schäfer. Nanoscale mapping of ultrafast magnetization dynamics with femtosecond Lorentz microscopy. Phys. Rev. X 8, 031052 (2018).

[38] A. Feist, G. Storeck, S. Schäfer, C. Ropers. Structural dynamics probed by high-coherence electron pulses. MRS Bulletin 43, 505 (2018).

[37] A. Feist, N. Rubiano da Silva, W. Liang, C. Ropers, S. Schäfer. Nanoscale diffractive probing of strain dynamics in ultrafast transmission electron microscopy. Struct. Dyn. 5, 014302 (2018).

[36] S. Vogelgesang, G. Storeck, S. Schramm, K. Rossnagel, S. Schäfer, C. Ropers. Phase ordering of charge density waves traced by ultrafast low-energy electron diffraction. Nature Physics 14, 184 (2018).

2017

[35] O. Kfir, S. Zayko, C. Nolte, M. Sivis, M. Möller, B. Hebler, S. S. P. K. Arekapudi, D. Steil, S. Schäfer, M. Albrecht, O. Cohen, S. Mathias, C. Ropers. Tabletop Nanoscale Magnetic Imaging using High-Harmonic Radiation. Science Advances, 3, eaao4641 (2017).

[34] K. E. Priebe, C. Rathje, S. V. Yalunin, Th. Hohage, A. Feist, S. Schäfer, C. Ropers. Attosecond electron pulse trains and quantum state reconstruction in ultrafast transmission electron microscopy. Nature Photonics 11, 793 (2017).

[33] G. Storeck, S. Vogelgesang, M. Sivis, S. Schäfer, C. Ropers. Nanotip-based photoelectron microgun for ultrafast LEED. Struct. Dyn. 4, 044024 (2017).

[32] Th. Danz, A. Neff, J. H. Gaida, R. Bormann, C. Ropers, S. Schäfer. Ultrafast sublattice pseudospin relaxation in graphene probed by polarization-resolved photoluminescence. Phys. Rev. B 95, 241412(R) (2017).

[31] A. Feist, N. Bach, N. Rubiano da Silva, Th. Danz, M. Möller, K. E. Priebe, T. Domröse, J. G. Gatzmann, S. Rost, J. Schauss, S. Strauch, R. Bormann, M. Sivis, S. Schäfer, C. Ropers. Ultrafast transmission electron microscopy using a laser-driven field emitter: femtosecond resolution with a high coherence electron beam. Ultramicroscopy 176, 63-73 (2017).

[30] T. Eggebrecht, M. Möller, J. G. Gatzmann, N. Rubiano da Silva, A. Feist, U. Martens, H. Ulrichs, M. Münzenberg, C. Ropers, S. Schäfer. Light induced metastable magnetic texture uncovered by in-situ Lorentz microscopy. Phys. Rev. Lett. 118, 097203 (2017).
Featured in: Research Highlights, Nature Nanotech. 12, 286 (2017).

2016

[29] M. Gulde, A. Rissanou, V. Harmandaris, M. Müller, S. Schäfer, C. Ropers. Structure and dynamics of monolayer polymer crystallites on graphene. Nano Lett. 16, 6994–7000 (2016).

[28] K. E. Echternkamp, A. Feist, S. Schäfer, C. Ropers. Ramsey-type phase control of free electron beams. Nature Phys. 12, 1000-1004 (2016).

[27] S. Zayko, M. Sivis, S. Schäfer, C. Ropers. Polarization contrast of nanoscale waveguides in high-harmonic imaging. Optica 3, 239 (2016).

[26] K. E. Echternkamp, G. Herink, S. V. Yalunin, K. Rademann, S. Schäfer, C. Ropers. Strong-field photoemission in nanotip near-fields: from quiver to sub-cycle electron dynamics. Appl. Phys. B 122, 1­–10 (2016).

2015

[25] B. Schröder, M. Sivis, R. Bormann, S. Schäfer, C. Ropers. An ultrafast nanotip electron gun triggered by grating-coupled surface plasmons. Appl. Phys. Lett. 107, 231105 (2015).

[24] R. Bormann, S. Strauch, S. Schäfer, C. Ropers. An ultrafast electron microscope gun driven by two-photon photoemission from a nanotip cathode. J. Appl. Phys. 118, 173105 (2015).

[23] B. Schröder, T. Weber, S. V. Yalunin, C. Matyssek, T. Kiel, M. Sivis, S. Schäfer, F. von Cube, S. Irsen, K. Busch, C. Ropers, S. Linden. Real space imaging of nanotip plasmons using electron energy-loss spectroscopy. Phys. Rev. B 92, 085411 (2015).

[22] S. Zayko, E. Mönnich, M. Sivis, D. Mai, T. Salditt, S. Schäfer, C. Ropers. Coherent diffractive imaging beyond the projection approximation: Waveguiding at extreme ultraviolet wavelengths. Opt. Exp. 23, 19911 (2015).

[21] A. Feist, K. Echternkamp, J. Schauss, S. V. Yalunin, S. Schäfer, C. Ropers. Quantum coherent optical phase modulation in an ultrafast transmission electron microscope. Nature 521, 200–203 (2015).
Featured in: Mathieu Kociak. Microscopy: Quantum control of free electrons, Nature 521, 166-167 (2015), and R. Vogelgesang, J. Vogelsang, C. Lienau. Elektronen steuern mit Licht. Physik Journal, 06/2015.

2014

[20] M. Gulde, S. Schweda, G. Storeck, M. Maiti, H. K. Yu, A. M. Wodtke, S. Schäfer, C. Ropers. Ultrafast low-energy electron diffraction in transmission resolves polymer/graphene superstructure dynamics. Science 345, 200–204 (2014).
Featured in: Erik T. J. Nibbering. Low-energy electron diffraction at ultrafast speeds. Science 345, 137–138 (2014).

2012

[19] A. Paarmann, M. Gulde, M. Müller, S. Schäfer, S. Schweda, M. Maiti, C. Xu, T. Hohage, F. Schenk, C. Ropers, R. Ernstorfer. Coherent femtosecond low-energy single-electron pulses for time-resolved diffraction and imaging: a numerical study. J. Appl. Phys. 112, 113109 (2012).

[18] W. Liang, S. Schäfer, A. H. Zewail. Ultrafast electron crystallography of heterogeneous structures: gold-graphene bilayer and ligand-encapsulated nanogold on graphene. Chem. Phys. Lett. 542, 8–12 (2012).

[17] W. Liang, S. Schäfer, A. H. Zewail. Ultrafast electron crystallography of monolayer adsorbates on clean surfaces: structural dynamics. Chem. Phys. Lett. 542, 1–7 (2012).

[16] A. Yurtsever, S. Schäfer, A. H. Zewail. Ultrafast Kikuchi diffraction: nanoscale stress–strain dynamics of wave-guiding structures. Nano Lett. 12, 3772–3777 (2012).

[15] S. M. Kast, S. Schäfer, R. Schäfer. Thermally induced polarizabilities and dipole moments of small tin clusters. J. Chem. Phys. 136, 134320 (2012).

2011

[14] S. Schäfer, W. Liang, A. H. Zewail. Structural dynamics of surfaces by ultrafast electron crystallography: Experimental and multiple scattering theory. J. Chem. Phys., 135, 214201 (2011).

[13] S. Schäfer, W. Liang, A. H. Zewail. Structural dynamics of nanoscale gold by ultrafast electron crystallography. Chem. Phys. Lett. 515, 278–282 (2011).

[12] S. Heiles, S. Schäfer, R. Schäfer. On the rotational temperature and structure dependence of electric field deflection experiments: A case study of germanium clusters. J. Chem. Phys. 135, 034303 (2011).

[11] S. Schäfer, W. Liang, A. H. Zewail. Primary structural dynamics in graphite. New J. Phys. 13, 063030 (2011).

2010

[10] S. Schäfer, W. Liang, A. H. Zewail. Structural dynamics and transient electric-field effects in ultrafast electron diffraction from surfaces. Chem. Phys. Lett. 493, 11–18 (2010).

[9] B. Assadollahzadeh, S. Schäfer, P. Schwerdtfeger. Electronic properties for small tin clusters Snn (n≤ 20) from density functional theory and the convergence toward the solid state. J. Comp. Chem. 31, 929–937 (2010).

[8] S. Heiles, S. Schäfer, R. Schäfer. Mass spectrometry and beam deflection studies of tin–lead nanoalloy clusters. Phys. Chem. Chem. Phys. 12, 247–253 (2010).

2009

[7] U. Rohrmann, S. Schäfer, R. Schäfer. Size-and temperature-dependent magnetic response of molecular cage clusters: manganese-doped tin clusters. J. Phys. Chem. A 113, 12115–12121 (2009).

2008

[6] C. Thierfelder, B. Assadollahzadeh, P. Schwerdtfeger, S. Schäfer. R. Schäfer, Relativistic and electron correlation effects in static dipole polarizabilities for the group-14 elements from carbon to element Z= 114: Theory and experiment. Phys. Rev. A 78, 052506 (2008).

[5] S. Schäfer, B. Assadollahzadeh, M. Mehring, P. Schwerdtfeger, R. Schäfer. Structure and Electric Properties of SnN Clusters (N= 6− 20) from Combined Electric Deflection Experiments and Quantum Theoretical Studies. J. Phys. Chem. A 112, 12312–12319 (2008).

[4] S. Schäfer, R. Schäfer. New Molecular Cage Clusters of Pb by Encapsulation of Mg. ChemPhysChem 9, 1925–1929 (2008).

[3] S. Schäfer, S. Heiles, J. A. Becker, R. Schäfer. Electric deflection studies on lead clusters. J. Chem. Phys. 129, 44304–44304 (2008).

[2] S. Schäfer, R. Schäfer. Dielectric response of germanium clusters. Phys. Rev. B 77, 205211 (2008).

[1] S. Schäfer, M. Mehring, R. Schäfer, P. Schwerdtfeger. Polarizabilities of Ba and Ba2: Comparison of molecular beam experiments with relativistic quantum chemistry. Phys. Rev. A 76, 052515 (2008).

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