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Beyreuther E, Grafström S, Eng LM. Designing a Robust Kelvin Probe Setup Optimized for Long-Term Surface Photovoltage Acquisition. Sensors (Basel) 2018; 18:s18114068. [PMID: 30469394 PMCID: PMC6264026 DOI: 10.3390/s18114068] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 11/16/2018] [Accepted: 11/17/2018] [Indexed: 11/16/2022]
Abstract
We introduce a robust low-budget Kelvin probe design that is optimized for the long-term acquisition of surface photovoltage (SPV) data, especially developed for highly resistive systems, which exhibit-in contrast to conventional semiconductors-very slow photoinduced charge relaxation processes in the range of hours and days. The device provides convenient optical access to the sample, as well as high mechanical and electrical stability due to off-resonance operation, showing a noise band as narrow as 1 mV. Furthermore, the acquisition of temperature-dependent SPV transients necessary for SPV-based deep-level transient spectroscopy becomes easily possible. The performance of the instrument is demonstrated by recording long-term SPV transients of the ultra-slowly relaxing model oxide strontium titanate (SrTiO 3 ) over 20 h.
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Affiliation(s)
- Elke Beyreuther
- Institut für Angewandte Physik, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
| | - Stefan Grafström
- Fakultät Physik, Technische Universität Dresden, Haeckelstr. 3, 01069 Dresden, Germany.
| | - Lukas M Eng
- Institut für Angewandte Physik, Technische Universität Dresden, Nöthnitzer Str. 61, 01187 Dresden, Germany.
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Thiessen A, Beyreuther E, Grafström S, Dörr K, Werner R, Kleiner R, Koelle D, Eng LM. The Mn(2+)/Mn(3+) state of La0.7Ce0.3MnO3 by oxygen reduction and photodoping. J Phys Condens Matter 2014; 26:045502. [PMID: 24389924 DOI: 10.1088/0953-8984/26/4/045502] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Films of cerium-doped LaMnO3, which has been intensively discussed as an electron-doped counterpart to hole-doped mixed-valence lanthanum manganites during the past decade, were analyzed by x-ray photoemission spectroscopy with respect to their manganese valence under photoexcitation. The comparative analysis of the Mn 3s exchange splitting of La0.7Ce0.3MnO3 (LCeMO) films in the dark and under illumination clearly shows that both oxygen reduction and illumination are able to decrease the Mn valence towards a mixed 2+/3+ state, independently of the film thickness and the degree of CeO2 segregation. Charge-injection from the photoconductive SrTiO3 substrate into the Mn eg band with carrier lifetimes in the range of tens of seconds and intrinsic generation of electron-hole pairs within the films are discussed as two possible sources of the Mn valence shift and the subsequent electron doping.
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Affiliation(s)
- A Thiessen
- Institut für Angewandte Photophysik, Technische Universität Dresden, D-01062 Dresden, Germany
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Kullock R, Hille A, Haussmann A, Grafström S, Eng LM. SHG simulations of plasmonic nanoparticles using curved elements. Opt Express 2011; 19:14426-14436. [PMID: 21934805 DOI: 10.1364/oe.19.014426] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We demonstrate that simulating plasmonic nanostructures by means of curved elements (CEs) significantly increases the accuracy and computation speed not only in the linear but also in the nonlinear regime. We implemented CEs within the discontinuous Galerkin (DG) method and, as an example of a nonlinear effect, investigated second-harmonic generation (SHG) at a silver nanoparticle. The second-harmonic response of the material is simulated by an extended Lorentz model (ELM). In the linear regime the CEs are ≈ 9 times faster than ordinary elements for the same accuracy, provide a much better convergence and show fewer unphysical field artifacts. For DG-SHG calculations CEs are almost indispensable to obtain physically reasonable results at all. Additionally, their boundary approximation has to be of the same order as their polynomial degree to achieve artifact-free field distributions. In return, the use of such CEs with the DG method pays off more than evidently, since the additional computation time is only 1%.
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Affiliation(s)
- René Kullock
- Institute of Applied Photophysics, Technische Universität Dresden, 01062 Dresden, Germany
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Hille A, Kullock R, Grafström S, Eng LM. Improving Nano-Optical Simulations Through Curved Elements Implemented within the Discontinuous Galerkin Method Computational. ACTA ACUST UNITED AC 2010. [DOI: 10.1166/jctn.2010.1522] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Beyreuther E, Thiessen A, Grafström S, Dörr K, Eng LM. Large photoconductivity of oxygen-deficient La(0.7)Ca(0.3)MnO(3)/SrTiO(3) heterostructures. J Phys Condens Matter 2010; 22:175506. [PMID: 21393673 DOI: 10.1088/0953-8984/22/17/175506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The electrical resistance of stoichiometric and oxygen-deficient epitaxial 10 nm thick La(0.7)Ca(0.3)MnO(3) thin films on SrTiO(3) under photoexcitation covering the visible to the ultraviolet range has been investigated systematically as a function of illumination intensity, wavelength and temperature. In contrast to as-prepared films, the oxygen-deficient samples exhibit large photoconductivity of several orders of magnitude at low temperatures. By our detailed comparative analysis of the electrical conductivity of the film/substrate heterostructure and the bare substrate we are able to elucidate contributions of both carrier generation in the film and carrier injection from the substrate to the observed effect.
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Affiliation(s)
- E Beyreuther
- Institute of Applied Photophysics, Technische Universität Dresden, D-01062 Dresden, Germany.
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Kullock R, Hendren WR, Hille A, Grafström S, Evans PR, Pollard RJ, Atkinson R, Eng LM. Polarization conversion through collective surface plasmons in metallic nanorod arrays. Opt Express 2008; 16:21671-21681. [PMID: 19104599 DOI: 10.1364/oe.16.021671] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
For two-dimensional (2D) arrays of metallic nanorods arranged perpendicular to a substrate several methods have been proposed to determine the electromagnetic near-field distribution and the surface plasmon resonances, but an analytical approach to explain all optical features on the nanometer length scale has been missing to date. To fill this gap, we demonstrate here that the field distribution in such arrays can be understood on the basis of surface plasmon polaritons (SPPs) that propagate along the nanorods and form standing waves. Notably, SPPs couple laterally through their optical near fields, giving rise to collective surface plasmon (CSP) effects. Using the dispersion relation of such CSPs, we deduce the condition of standing-wave formation, which enables us to successfully predict several features, such as eigenmodes and resonances. As one such property and potential application, we show both theoretically and in an experiment that CSP propagation allows for polarization conversion and optical filtering in 2D nanorod arrays. Hence, these arrays are promising candidates for manipulating the light polarization on the nanometer length scale.
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Affiliation(s)
- René Kullock
- Institute of Applied Photophysics, Technische Universität Dresden, 01062 Dresden, Germany
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Wenzel MT, Härtling T, Olk P, Kehr SC, Grafström S, Winnerl S, Helm M, Eng LM. Gold nanoparticle tips for optical field confinement in infrared scattering near-field optical microscopy. Opt Express 2008; 16:12302-12312. [PMID: 18679508 DOI: 10.1364/oe.16.012302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
We report on the implementation of metal nanoparticles as probes for scattering and apertureless near-field optical investigations in the mid-infrared (mid-IR) spectral regime. At these wavelengths, an efficient electric-field confinement is necessary and achieved here through a gold metal nanoparticle of 80 nm in diameter (Au80-MNP) acting as the optical antenna. The Au80-MNP is attached to a standard AFM cantilever used as the spatial manipulator. When approached to a sample surface while being illuminated with an infrared beam, the Au80-MNP produces a considerably improved spatial confinement of the electric field compared to an ordinary scattering AFM tip. We demonstrate here the confinement normal to the sample surface by making use of a sample-induced phonon polariton resonance in a ferroelectric lithium niobate sample. Our experimental findings are in very good agreement with the quasistatic dipole model and show improved optical resolution via well-selected antenna particles.
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Affiliation(s)
- Marc Tobias Wenzel
- Institute of Applied Photophysics, Technische Universität Dresden, 01062 Dresden, Germany.
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Kehr SC, Cebula M, Mieth O, Härtling T, Seidel J, Grafström S, Eng LM, Winnerl S, Stehr D, Helm M. Anisotropy contrast in phonon-enhanced apertureless near-field microscopy using a free-electron laser. Phys Rev Lett 2008; 100:256403. [PMID: 18643683 DOI: 10.1103/physrevlett.100.256403] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/20/2007] [Revised: 05/14/2008] [Indexed: 05/26/2023]
Abstract
We demonstrate the imaging of ferroelectric domains in BaTiO3, using an infrared-emitting free-electron laser as a tunable optical source for scattering scanning near-field optical microscopy and spectroscopy. When the laser is tuned into the spectral vicinity of a phonon resonance, ferroelectric domains can be resolved due to the anisotropy of the dielectric properties of the material. Slight detuning of the wavelength gives rise to a contrast reversal clearly evidencing the resonant character of the excitation. The near-field domain contrast shows that the orientation of the dielectric tensor with respect to the sample surface has a clear influence on the near-field signal.
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Affiliation(s)
- S C Kehr
- Institute of Applied Photophysics, Technische Universität Dresden, D-01062 Dresden, Germany
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Seidel J, Grafström S, Eng L. Stimulated emission of surface plasmons at the interface between a silver film and an optically pumped dye solution. Phys Rev Lett 2005; 94:177401. [PMID: 15904333 DOI: 10.1103/physrevlett.94.177401] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2004] [Indexed: 05/02/2023]
Abstract
Surface plasmons (SPs) are surface-bound electromagnetic waves supported by metals, offering the possibility of strong spatial confinement of electromagnetic fields on the micro- and nanoscales. They suffer, however, from strong damping caused by internal absorption and radiation losses. Here we demonstrate amplification of SPs by stimulated emission, which marks a possible solution to this problem. We use an attenuated-total-reflection setup to detect stimulated emission of SPs at the interface between a silver film and an optically pumped dye solution acting as the amplifying medium. Clear evidence of stimulated emission is provided by an excellent agreement of the experimental observations with a theoretical analysis. Amplification of SPs can be considered analogous to photon amplification in a laser, thereby suggesting novel approaches in the field of nano-optics.
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Affiliation(s)
- J Seidel
- Institute of Applied Photophysics, Dresden University of Technology, D-01062 Dresden, Germany
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Renger J, Grafström S, Eng LM, Deckert V. Evanescent wave scattering and local electric field enhancement at ellipsoidal silver particles in the vicinity of a glass surface. J Opt Soc Am A Opt Image Sci Vis 2004; 21:1362-1367. [PMID: 15260267 DOI: 10.1364/josaa.21.001362] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We report on the numerical analysis of the local electric field enhancement of nanosized silver ellipsoids placed in the evanescent field near a glass surface. Across the visible spectrum the enhancement factor for silver particles varies by more than one order of magnitude because of surface-plasmon resonance. Because of the spatially inhomogeneous excitation, higher-order modes additionally contribute and modify the spectral dependence of the electric field compared with plane-wave excitation. Moving the metal particle toward the glass surface increases the field enhancement and shifts the plasmon resonance, which in addition splits between both ends of the particle. Besides the near-field properties of such a probe we also discuss to what extent these local properties can be measured in the far field.
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Affiliation(s)
- Jan Renger
- Institute of Applied Photophysics, University of Technology Dresden, D-01062 Dresden, Germany.
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Loppacher C, Trogisch S, Braun F, Zherebov A, Grafström S, Eng LM, Voit B. Metal Salt Complexation of Spin-Coated Ultrathin Diazosulfonate Terpolymer Films. Macromolecules 2002. [DOI: 10.1021/ma0114335] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ch. Loppacher
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
| | - S. Trogisch
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
| | - F. Braun
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
| | - A. Zherebov
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
| | - S. Grafström
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
| | - L. M. Eng
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
| | - B. Voit
- Institute of Applied Photophysics, George-Bähr-Strasse 1, 01069 Dresden, Germany, and Institute of Polymer Research, Hohe Strasse 6, 01069 Dresden, Germany
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Grafström S, Suter D. Interaction of spin-polarized atoms with a surface studied by optical-reflection spectroscopy. Phys Rev A 1996; 54:2169-2179. [PMID: 9913709 DOI: 10.1103/physreva.54.2169] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Abstract
Using reflection spectroscopy of optically pumped sodium vapor, we have performed what is to our knowledge the first direct measurement of the spatially inhomogeneous spin polarization near a glass surface. On the basis of a theoretical description of the reflection at an inhomogeneous, anisotropic medium, we deduce the magnitude of the small residual magnetization at the surface from an analysis of the optical line shape. This allows us to specify the depolarizing properties of the surface.
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Kemmer H, Grafström S, Neitzert M, Wörtge M, Neumann R, Trautmann C, Vetter J, Angert N. Scanning tunneling microscopy of surface modifications induced by UNILAC heavy-ion irradiation. Ultramicroscopy 1992. [DOI: 10.1016/0304-3991(92)90446-q] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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