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• Light-driven microdrones Wu, Xiaofei; Ehehalt, Raphael; Razinskas, Gary; Feichtner, Thorsten; Qin, Jin; Hecht, Bert in Nature Nanotechnology (2022).

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  further coverage:
  Nature Research Highlight, Nature Community blog post
  • [ Abstract ]
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  When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.

  @article{wu2022lightdriven, abstract = {When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.}, author = {Wu, Xiaofei and Ehehalt, Raphael and Razinskas, Gary and Feichtner, Thorsten and Qin, Jin and Hecht, Bert}, journal = {Nature Nanotechnology}, keywords = {myown}, month = {April}, note = {<i style="font-style: normal;"><a href="https://rdcu.be/cLP6O">Shared Link</a><br><br><b>further coverage:</b><br> <a href="https://www.nature.com/articles/d41586-022-01132-0">Nature Research Highlight</a>, <a href="https://engineeringcommunity.nature.com/posts/light-driven-microdrones-a-new-level-of-optical-manipulation">Nature Community blog post</a></i>}, title = {Light-driven microdrones}, year = 2022 }

  %0 Journal Article %1 wu2022lightdriven %A Wu, Xiaofei %A Ehehalt, Raphael %A Razinskas, Gary %A Feichtner, Thorsten %A Qin, Jin %A Hecht, Bert %D 2022 %J Nature Nanotechnology %R https://doi.org/10.1038/s41565-022-01099-z %T Light-driven microdrones %U https://www.nature.com/articles/s41565-022-01099-z %X When photons interact with matter, forces and torques occur due to the transfer of linear and angular momentum, respectively. The resulting accelerations are small for macroscopic objects but become substantial for microscopic objects with small masses and moments of inertia, rendering photon recoil very attractive to propel micro- and nano-objects. However, until now, using light to control object motion in two or three dimensions in all three or six degrees of freedom has remained an unsolved challenge. Here we demonstrate light-driven microdrones (size roughly 2 μm and mass roughly 2 pg) in an aqueous environment that can be manoeuvred in two dimensions in all three independent degrees of freedom (two translational and one rotational) using two overlapping unfocused light fields of 830 and 980 nm wavelength. To actuate the microdrones independent of their orientation, we use up to four individually addressable chiral plasmonic nanoantennas acting as nanomotors that resonantly scatter the circular polarization components of the driving light into well-defined directions. The microdrones are manoeuvred by only adjusting the optical power for each motor (the power of each circular polarization component of each wavelength). The actuation concept is therefore similar to that of macroscopic multirotor drones. As a result, we demonstrate manual steering of the microdrones along complex paths. Since all degrees of freedom can be addressed independently and directly, feedback control loops may be used to counteract Brownian motion. We posit that the microdrones can find applications in transport and release of cargos, nanomanipulation, and local probing and sensing of nano and mesoscale objects.

• Topological Defect Engineering and $\mathcal{P}\mathcal{T}$ Symmetry in Non-Hermitian Electrical Circuits Stegmaier, Alexander; Imhof, Stefan; Helbig, Tobias; Hofmann, Tobias; Lee, Ching Hua; Kremer, Mark; Fritzsche, Alexander; Feichtner, Thorsten; Klembt, Sebastian; H\"ofling, Sven; Boettcher, Igor; Fulga, Ion Cosma; Ma, Libo; Schmidt, Oliver G.; Greiter, Martin; Kiessling, Tobias; Szameit, Alexander; Thomale, Ronny in Phys. Rev. Lett. (2021). 126(21) 215302.
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  We employ electric circuit networks to study topological states of matter in non-Hermitian systems enriched by parity-time symmetry PT and chiral symmetry anti-PT (APT). The topological structure manifests itself in the complex admittance bands which yields excellent measurability and signal to noise ratio. We analyze the impact of PT-symmetric gain and loss on localized edge and defect states in a non-Hermitian Su-Schrieffer-Heeger (SSH) circuit. We realize all three symmetry phases of the system, including the APT-symmetric regime that occurs at large gain and loss. We measure the admittance spectrum and eigenstates for arbitrary boundary conditions, which allows us to resolve not only topological edge states, but also a novel PT-symmetric Z2 invariant of the bulk. We discover the distinct properties of topological edge states and defect states in the phase diagram. In the regime that is not PT symmetric, the topological defect state disappears and only reemerges when APT symmetry is reached, while the topological edge states always prevail and only experience a shift in eigenvalue. Our findings unveil a future route for topological defect engineering and tuning in non-Hermitian systems of arbitrary dimension.

  @article{PhysRevLett.126.215302, abstract = {We employ electric circuit networks to study topological states of matter in non-Hermitian systems enriched by parity-time symmetry PT and chiral symmetry anti-PT (APT). The topological structure manifests itself in the complex admittance bands which yields excellent measurability and signal to noise ratio. We analyze the impact of PT-symmetric gain and loss on localized edge and defect states in a non-Hermitian Su-Schrieffer-Heeger (SSH) circuit. We realize all three symmetry phases of the system, including the APT-symmetric regime that occurs at large gain and loss. We measure the admittance spectrum and eigenstates for arbitrary boundary conditions, which allows us to resolve not only topological edge states, but also a novel PT-symmetric Z2 invariant of the bulk. We discover the distinct properties of topological edge states and defect states in the phase diagram. In the regime that is not PT symmetric, the topological defect state disappears and only reemerges when APT symmetry is reached, while the topological edge states always prevail and only experience a shift in eigenvalue. Our findings unveil a future route for topological defect engineering and tuning in non-Hermitian systems of arbitrary dimension.}, author = {Stegmaier, Alexander and Imhof, Stefan and Helbig, Tobias and Hofmann, Tobias and Lee, Ching Hua and Kremer, Mark and Fritzsche, Alexander and Feichtner, Thorsten and Klembt, Sebastian and H\"ofling, Sven and Boettcher, Igor and Fulga, Ion Cosma and Ma, Libo and Schmidt, Oliver G. and Greiter, Martin and Kiessling, Tobias and Szameit, Alexander and Thomale, Ronny}, journal = {Phys. Rev. Lett.}, keywords = {myown}, month = {05}, number = 21, pages = 215302, publisher = {American Physical Society}, title = {Topological Defect Engineering and $\mathcal{P}\mathcal{T}$ Symmetry in Non-Hermitian Electrical Circuits}, volume = 126, year = 2021 }

  %0 Journal Article %1 PhysRevLett.126.215302 %A Stegmaier, Alexander %A Imhof, Stefan %A Helbig, Tobias %A Hofmann, Tobias %A Lee, Ching Hua %A Kremer, Mark %A Fritzsche, Alexander %A Feichtner, Thorsten %A Klembt, Sebastian %A H\"ofling, Sven %A Boettcher, Igor %A Fulga, Ion Cosma %A Ma, Libo %A Schmidt, Oliver G. %A Greiter, Martin %A Kiessling, Tobias %A Szameit, Alexander %A Thomale, Ronny %D 2021 %I American Physical Society %J Phys. Rev. Lett. %N 21 %P 215302 %R 10.1103/PhysRevLett.126.215302 %T Topological Defect Engineering and $\mathcal{P}\mathcal{T}$ Symmetry in Non-Hermitian Electrical Circuits %U https://link.aps.org/doi/10.1103/PhysRevLett.126.215302 %V 126 %X We employ electric circuit networks to study topological states of matter in non-Hermitian systems enriched by parity-time symmetry PT and chiral symmetry anti-PT (APT). The topological structure manifests itself in the complex admittance bands which yields excellent measurability and signal to noise ratio. We analyze the impact of PT-symmetric gain and loss on localized edge and defect states in a non-Hermitian Su-Schrieffer-Heeger (SSH) circuit. We realize all three symmetry phases of the system, including the APT-symmetric regime that occurs at large gain and loss. We measure the admittance spectrum and eigenstates for arbitrary boundary conditions, which allows us to resolve not only topological edge states, but also a novel PT-symmetric Z2 invariant of the bulk. We discover the distinct properties of topological edge states and defect states in the phase diagram. In the regime that is not PT symmetric, the topological defect state disappears and only reemerges when APT symmetry is reached, while the topological edge states always prevail and only experience a shift in eigenvalue. Our findings unveil a future route for topological defect engineering and tuning in non-Hermitian systems of arbitrary dimension.
• The patterning toolbox {FIB}-o-mat: Exploiting the full potential of focused helium ions for nanofabrication Deinhart, Victor; Kern, Lisa-Marie; Kirchhof, Jan N; Juergensen, Sabrina; Sturm, Joris; Krauss, Enno; Feichtner, Thorsten; Kovalchuk, Sviatoslav; Schneider, Michael; Engel, Dieter; Pfau, Bastian; Hecht, Bert; Bolotin, Kirill I; Reich, Stephanie; Höflich, Katja in Beilstein Journal of Nanotechnology (2021). 12 304–318.
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  Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.

  @article{Deinhart_2021, abstract = {Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.}, author = {Deinhart, Victor and Kern, Lisa-Marie and Kirchhof, Jan N and Juergensen, Sabrina and Sturm, Joris and Krauss, Enno and Feichtner, Thorsten and Kovalchuk, Sviatoslav and Schneider, Michael and Engel, Dieter and Pfau, Bastian and Hecht, Bert and Bolotin, Kirill I and Reich, Stephanie and Höflich, Katja}, journal = {Beilstein Journal of Nanotechnology}, keywords = {myown}, month = {apr}, pages = {304–318}, publisher = {Beilstein Institut}, title = {The patterning toolbox {FIB}-o-mat: Exploiting the full potential of focused helium ions for nanofabrication}, volume = 12, year = 2021 }

  %0 Journal Article %1 Deinhart_2021 %A Deinhart, Victor %A Kern, Lisa-Marie %A Kirchhof, Jan N %A Juergensen, Sabrina %A Sturm, Joris %A Krauss, Enno %A Feichtner, Thorsten %A Kovalchuk, Sviatoslav %A Schneider, Michael %A Engel, Dieter %A Pfau, Bastian %A Hecht, Bert %A Bolotin, Kirill I %A Reich, Stephanie %A Höflich, Katja %D 2021 %I Beilstein Institut %J Beilstein Journal of Nanotechnology %P 304--318 %R 10.3762/bjnano.12.25 %T The patterning toolbox {FIB}-o-mat: Exploiting the full potential of focused helium ions for nanofabrication %U https://doi.org/10.3762%2Fbjnano.12.25 %V 12 %X Focused beams of helium ions are a powerful tool for high-fidelity machining with spatial precision below 5 nm. Achieving such a high patterning precision over large areas and for different materials in a reproducible manner, however, is not trivial. Here, we introduce the Python toolbox FIB-o-mat for automated pattern creation and optimization, providing full flexibility to accomplish demanding patterning tasks. FIB-o-mat offers high-level pattern creation, enabling high-fidelity large-area patterning and systematic variations in geometry and raster settings. It also offers low-level beam path creation, providing full control over the beam movement and including sophisticated optimization tools. Three applications showcasing the potential of He ion beam nanofabrication for two-dimensional material systems and devices using FIB-o-mat are presented.

• Resonant behavior of a single plasmonic helix H\"{o}flich, Katja; Feichtner, Thorsten; Hansj\"{u}rgen, Enno; Haverkamp, Caspar; Kollmann, Heiko; Lienau, Christoph; Silies, Martin in Optica (2019). 6(9) 1098–1105.
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  Chiral plasmonic nanostructures will be of increasing importance for future applications in the field of nano optics and metamaterials. Their sensitivity to incident circularly polarized light in combination with the ability of extreme electromagnetic field localization renders them ideal candidates for chiral sensing and for all-optical information processing. Here, the resonant modes of single plasmonic helices are investigated. We find that a single plasmonic helix can be efficiently excited with circularly polarized light of both equal and opposite handedness relative to that of the helix. An analytic model provides resonance conditions matching the results of full-field modeling. The underlying geometric considerations explain the mechanism of excitation and deliver quantitative design rules for plasmonic helices being resonant in a desired wavelength range. Based on the developed analytical design tool, single silver helices were fabricated and optically characterized. They show the expected strong chiroptical response to both handednesses in the targeted visible range. With a value of 0.45, the experimentally realized dissymmetry factor is the largest obtained for single plasmonic helices in the visible range up to now.

  @article{Hoflich:19, abstract = {Chiral plasmonic nanostructures will be of increasing importance for future applications in the field of nano optics and metamaterials. Their sensitivity to incident circularly polarized light in combination with the ability of extreme electromagnetic field localization renders them ideal candidates for chiral sensing and for all-optical information processing. Here, the resonant modes of single plasmonic helices are investigated. We find that a single plasmonic helix can be efficiently excited with circularly polarized light of both equal and opposite handedness relative to that of the helix. An analytic model provides resonance conditions matching the results of full-field modeling. The underlying geometric considerations explain the mechanism of excitation and deliver quantitative design rules for plasmonic helices being resonant in a desired wavelength range. Based on the developed analytical design tool, single silver helices were fabricated and optically characterized. They show the expected strong chiroptical response to both handednesses in the targeted visible range. With a value of 0.45, the experimentally realized dissymmetry factor is the largest obtained for single plasmonic helices in the visible range up to now.}, author = {H\"{o}flich, Katja and Feichtner, Thorsten and Hansj\"{u}rgen, Enno and Haverkamp, Caspar and Kollmann, Heiko and Lienau, Christoph and Silies, Martin}, journal = {Optica}, keywords = {spin_orbital_momentum}, month = {sep}, number = 9, pages = {1098–1105}, publisher = {OSA}, title = {Resonant behavior of a single plasmonic helix}, volume = 6, year = 2019 }

  %0 Journal Article %1 Hoflich:19 %A H\"{o}flich, Katja %A Feichtner, Thorsten %A Hansj\"{u}rgen, Enno %A Haverkamp, Caspar %A Kollmann, Heiko %A Lienau, Christoph %A Silies, Martin %D 2019 %I OSA %J Optica %N 9 %P 1098--1105 %R 10.1364/OPTICA.6.001098 %T Resonant behavior of a single plasmonic helix %U http://www.osapublishing.org/optica/abstract.cfm?URI=optica-6-9-1098 %V 6 %X Chiral plasmonic nanostructures will be of increasing importance for future applications in the field of nano optics and metamaterials. Their sensitivity to incident circularly polarized light in combination with the ability of extreme electromagnetic field localization renders them ideal candidates for chiral sensing and for all-optical information processing. Here, the resonant modes of single plasmonic helices are investigated. We find that a single plasmonic helix can be efficiently excited with circularly polarized light of both equal and opposite handedness relative to that of the helix. An analytic model provides resonance conditions matching the results of full-field modeling. The underlying geometric considerations explain the mechanism of excitation and deliver quantitative design rules for plasmonic helices being resonant in a desired wavelength range. Based on the developed analytical design tool, single silver helices were fabricated and optically characterized. They show the expected strong chiroptical response to both handednesses in the targeted visible range. With a value of 0.45, the experimentally realized dissymmetry factor is the largest obtained for single plasmonic helices in the visible range up to now.

• {Plasmonic nanoantenna design and fabrication based on evolutionary optimization} Feichtner, Thorsten; Selig, Oleg; Hecht, Bert in Optics Express (2017). 25(10) 10828.
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  @article{Feichtner2015, author = {Feichtner, Thorsten and Selig, Oleg and Hecht, Bert}, journal = {Optics Express}, keywords = {imported}, month = {may}, number = 10, pages = 10828, title = {{Plasmonic nanoantenna design and fabrication based on evolutionary optimization}}, volume = 25, year = 2017 }

  %0 Journal Article %1 Feichtner2015 %A Feichtner, Thorsten %A Selig, Oleg %A Hecht, Bert %D 2017 %J Optics Express %N 10 %P 10828 %R 10.1364/OE.25.010828 %T {Plasmonic nanoantenna design and fabrication based on evolutionary optimization} %U https://www.osapublishing.org/abstract.cfm?URI=oe-25-10-10828 %V 25
• {Mode Matching for Optical Antennas} Feichtner, Thorsten; Christiansen, Silke; Hecht, Bert in Physical Review Letters (2017). 119(21) 217401.
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  @article{Feichtner2017, author = {Feichtner, Thorsten and Christiansen, Silke and Hecht, Bert}, journal = {Physical Review Letters}, keywords = {imported}, month = {nov}, number = 21, pages = 217401, title = {{Mode Matching for Optical Antennas}}, volume = 119, year = 2017 }

  %0 Journal Article %1 Feichtner2017 %A Feichtner, Thorsten %A Christiansen, Silke %A Hecht, Bert %D 2017 %J Physical Review Letters %N 21 %P 217401 %R 10.1103/PhysRevLett.119.217401 %T {Mode Matching for Optical Antennas} %U https://link.aps.org/doi/10.1103/PhysRevLett.119.217401 %V 119

• {Self-Catalyzed Growth of Vertically Aligned InN Nanorods by Metal-Organic Vapor Phase Epitaxy} Tessarek, C.; Fladischer, S.; Dieker, C.; Sarau, G.; Hoffmann, B.; Bashouti, M.; G{\"{o}}belt, M.; Heilmann, M.; Latzel, M.; Butzen, E.; Figge, S.; Gust, A.; H{\"{o}}flich, K.; Feichtner, T.; B{\"{u}}chele, M.; Schwarzburg, K.; Spiecker, E.; Christiansen, S. in Nano Letters (2016). 16(6) 3415–3425.
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  Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal-organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorods indicate a self-catalytic vapor-liquid-solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, is necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.

  @article{Tessarek2016, abstract = {Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal-organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorods indicate a self-catalytic vapor-liquid-solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, is necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.}, author = {Tessarek, C. and Fladischer, S. and Dieker, C. and Sarau, G. and Hoffmann, B. and Bashouti, M. and G{\"{o}}belt, M. and Heilmann, M. and Latzel, M. and Butzen, E. and Figge, S. and Gust, A. and H{\"{o}}flich, K. and Feichtner, T. and B{\"{u}}chele, M. and Schwarzburg, K. and Spiecker, E. and Christiansen, S.}, journal = {Nano Letters}, keywords = {well,as}, month = {jun}, number = 6, pages = {3415–3425}, publisher = {American Chemical Society}, title = {{Self-Catalyzed Growth of Vertically Aligned InN Nanorods by Metal-Organic Vapor Phase Epitaxy}}, volume = 16, year = 2016 }

  %0 Journal Article %1 Tessarek2016 %A Tessarek, C. %A Fladischer, S. %A Dieker, C. %A Sarau, G. %A Hoffmann, B. %A Bashouti, M. %A G{\"{o}}belt, M. %A Heilmann, M. %A Latzel, M. %A Butzen, E. %A Figge, S. %A Gust, A. %A H{\"{o}}flich, K. %A Feichtner, T. %A B{\"{u}}chele, M. %A Schwarzburg, K. %A Spiecker, E. %A Christiansen, S. %D 2016 %I American Chemical Society %J Nano Letters %N 6 %P 3415--3425 %R 10.1021/acs.nanolett.5b03889 %T {Self-Catalyzed Growth of Vertically Aligned InN Nanorods by Metal-Organic Vapor Phase Epitaxy} %U http://pubs.acs.org/doi/abs/10.1021/acs.nanolett.5b03889 %V 16 %X Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal-organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorods indicate a self-catalytic vapor-liquid-solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, is necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.
• {New insights into colloidal gold flakes: structural investigation, micro-ellipsometry and thinning procedure towards ultrathin monocrystalline layers} Hoffmann, B.; Bashouti, M. Y.; Feichtner, T.; Ma{\v{c}}kovi{\’{c}}, M.; Dieker, C.; Salaheldin, A. M.; Richter, P.; Gordan, O. D.; Zahn, D. R. T.; Spiecker, E.; Christiansen, S. in Nanoscale (2016). 8(8) 4529–4536.
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  High-quality fabrication of plasmonic devices often relies on wet-chemically grown ultraflat, presumably single-crystalline gold flakes due to their superior materials properties. However, important details about their intrinsic structure and their optical properties are not well understood yet. In this study, we present a synthesis routine for large flakes with diameters of up to 70 $\mu$m and an in-depth investigation of their structural and optical properties. The flakes are precisely analyzed by transmission electron microscopy, electron backscatter diffraction and micro-ellipsometry. We found new evidence for the existence of twins extending parallel to the Au flake {\{}111{\}} surfaces which have been found to not interfere with the presented nanopatterning. Micro-Ellipsometry was carried out to determine the complex dielectric function and to compare it to previous measurements of bulk single crystalline gold. Finally, we used focused ion beam milling to prepare smooth crystalline layers and high-quality nanostructures with desired thickness down to 10 nm to demonstrate the outstanding properties of the flakes. Our findings support the plasmonics and nano optics community with a better understanding of this material which is ideally suited for superior plasmonic nanostructures.

  @article{Hoffmann2016, abstract = {High-quality fabrication of plasmonic devices often relies on wet-chemically grown ultraflat, presumably single-crystalline gold flakes due to their superior materials properties. However, important details about their intrinsic structure and their optical properties are not well understood yet. In this study, we present a synthesis routine for large flakes with diameters of up to 70 $\mu$m and an in-depth investigation of their structural and optical properties. The flakes are precisely analyzed by transmission electron microscopy, electron backscatter diffraction and micro-ellipsometry. We found new evidence for the existence of twins extending parallel to the Au flake {\{}111{\}} surfaces which have been found to not interfere with the presented nanopatterning. Micro-Ellipsometry was carried out to determine the complex dielectric function and to compare it to previous measurements of bulk single crystalline gold. Finally, we used focused ion beam milling to prepare smooth crystalline layers and high-quality nanostructures with desired thickness down to 10 nm to demonstrate the outstanding properties of the flakes. Our findings support the plasmonics and nano optics community with a better understanding of this material which is ideally suited for superior plasmonic nanostructures.}, author = {Hoffmann, B. and Bashouti, M. Y. and Feichtner, T. and Ma{\v{c}}kovi{\'{c}}, M. and Dieker, C. and Salaheldin, A. M. and Richter, P. and Gordan, O. D. and Zahn, D. R. T. and Spiecker, E. and Christiansen, S.}, journal = {Nanoscale}, keywords = {imported}, number = 8, pages = {4529–4536}, publisher = {The Royal Society of Chemistry}, title = {{New insights into colloidal gold flakes: structural investigation, micro-ellipsometry and thinning procedure towards ultrathin monocrystalline layers}}, volume = 8, year = 2016 }

  %0 Journal Article %1 Hoffmann2016 %A Hoffmann, B. %A Bashouti, M. Y. %A Feichtner, T. %A Ma{\v{c}}kovi{\'{c}}, M. %A Dieker, C. %A Salaheldin, A. M. %A Richter, P. %A Gordan, O. D. %A Zahn, D. R. T. %A Spiecker, E. %A Christiansen, S. %D 2016 %I The Royal Society of Chemistry %J Nanoscale %N 8 %P 4529--4536 %R 10.1039/C5NR04439A %T {New insights into colloidal gold flakes: structural investigation, micro-ellipsometry and thinning procedure towards ultrathin monocrystalline layers} %U http://xlink.rsc.org/?DOI=C5NR04439A %V 8 %X High-quality fabrication of plasmonic devices often relies on wet-chemically grown ultraflat, presumably single-crystalline gold flakes due to their superior materials properties. However, important details about their intrinsic structure and their optical properties are not well understood yet. In this study, we present a synthesis routine for large flakes with diameters of up to 70 $\mu$m and an in-depth investigation of their structural and optical properties. The flakes are precisely analyzed by transmission electron microscopy, electron backscatter diffraction and micro-ellipsometry. We found new evidence for the existence of twins extending parallel to the Au flake {\{}111{\}} surfaces which have been found to not interfere with the presented nanopatterning. Micro-Ellipsometry was carried out to determine the complex dielectric function and to compare it to previous measurements of bulk single crystalline gold. Finally, we used focused ion beam milling to prepare smooth crystalline layers and high-quality nanostructures with desired thickness down to 10 nm to demonstrate the outstanding properties of the flakes. Our findings support the plasmonics and nano optics community with a better understanding of this material which is ideally suited for superior plasmonic nanostructures.
• {Gold platelets for high-quality plasmonics} Hoffmann, Bj{\"{o}}rn; Feichtner, Thorsten; Christiansen, Silke in Materials Today (2016). 19(4) 240–241.
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  @article{Hoffmann2016a, author = {Hoffmann, Bj{\"{o}}rn and Feichtner, Thorsten and Christiansen, Silke}, journal = {Materials Today}, keywords = {imported}, month = {apr}, number = 4, pages = {240–241}, title = {{Gold platelets for high-quality plasmonics}}, volume = 19, year = 2016 }

  %0 Journal Article %1 Hoffmann2016a %A Hoffmann, Bj{\"{o}}rn %A Feichtner, Thorsten %A Christiansen, Silke %D 2016 %J Materials Today %N 4 %P 240--241 %R 10.1016/j.mattod.2016.03.017 %T {Gold platelets for high-quality plasmonics} %U http://www.sciencedirect.com/science/article/pii/S1369702116300025 %V 19
• {Electromechanically Tunable Suspended Optical Nanoantenna.} Chen, Kai; Razinskas, Gary; Feichtner, Thorsten; Grossmann, Swen; Christiansen, Silke; Hecht, Bert in Nano letters (2016). 16(4) 2680–5.
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  Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nanoantenna acting like a nanoelectrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonance wavelength and the field enhancement of the suspended optical nanoantenna can be reversibly tuned. Our experiments highlight the potential to realize large bandwidth optical nanoelectromechanical systems.

  @article{Chen2016, abstract = {Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nanoantenna acting like a nanoelectrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonance wavelength and the field enhancement of the suspended optical nanoantenna can be reversibly tuned. Our experiments highlight the potential to realize large bandwidth optical nanoelectromechanical systems.}, author = {Chen, Kai and Razinskas, Gary and Feichtner, Thorsten and Grossmann, Swen and Christiansen, Silke and Hecht, Bert}, journal = {Nano letters}, keywords = {imported}, month = {apr}, number = 4, pages = {2680–5}, publisher = {American Chemical Society}, title = {{Electromechanically Tunable Suspended Optical Nanoantenna.}}, volume = 16, year = 2016 }

  %0 Journal Article %1 Chen2016 %A Chen, Kai %A Razinskas, Gary %A Feichtner, Thorsten %A Grossmann, Swen %A Christiansen, Silke %A Hecht, Bert %D 2016 %I American Chemical Society %J Nano letters %N 4 %P 2680--5 %R 10.1021/acs.nanolett.6b00323 %T {Electromechanically Tunable Suspended Optical Nanoantenna.} %U http://dx.doi.org/10.1021/acs.nanolett.6b00323 %V 16 %X Coupling mechanical degrees of freedom with plasmonic resonances has potential applications in optomechanics, sensing, and active plasmonics. Here we demonstrate a suspended two-wire plasmonic nanoantenna acting like a nanoelectrometer. The antenna wires are supported and electrically connected via thin leads without disturbing the antenna resonance. As a voltage is applied, equal charges are induced on both antenna wires. The resulting equilibrium between the repulsive Coulomb force and the restoring elastic bending force enables us to precisely control the gap size. As a result the resonance wavelength and the field enhancement of the suspended optical nanoantenna can be reversibly tuned. Our experiments highlight the potential to realize large bandwidth optical nanoelectromechanical systems.

• {Remote detection of single emitters via optical waveguides} Then, Patrick; Razinskas, Gary; Feichtner, Thorsten; Haas, Philippe; Wild, Andreas; Bellini, Nicola; Osellame, Roberto; Cerullo, Giulio; Hecht, Bert in Physical Review A (2014). 89(5) 053801.
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  @article{Then2014, author = {Then, Patrick and Razinskas, Gary and Feichtner, Thorsten and Haas, Philippe and Wild, Andreas and Bellini, Nicola and Osellame, Roberto and Cerullo, Giulio and Hecht, Bert}, journal = {Physical Review A}, keywords = {imported}, month = {may}, number = 5, pages = {053801}, title = {{Remote detection of single emitters via optical waveguides}}, volume = 89, year = 2014 }

  %0 Journal Article %1 Then2014 %A Then, Patrick %A Razinskas, Gary %A Feichtner, Thorsten %A Haas, Philippe %A Wild, Andreas %A Bellini, Nicola %A Osellame, Roberto %A Cerullo, Giulio %A Hecht, Bert %D 2014 %J Physical Review A %N 5 %P 053801 %R 10.1103/PhysRevA.89.053801 %T {Remote detection of single emitters via optical waveguides} %U http://link.aps.org/doi/10.1103/PhysRevA.89.053801 %V 89

• {Evolutionary Optimization of Optical Antennas} Feichtner, Thorsten; Selig, Oleg; Kiunke, Markus; Hecht, Bert in Physical Review Letters (2012). 109(12) 127701.
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  The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.

  @article{Feichtner2012, abstract = {The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime.}, annote = {From Duplicate 9 ( Evolutionary Optimization of Optical Antennas - Feichtner, Thorsten; Selig, Oleg; Kiunke, Markus; Hecht, Bert )}, author = {Feichtner, Thorsten and Selig, Oleg and Kiunke, Markus and Hecht, Bert}, journal = {Physical Review Letters}, keywords = {imported}, month = {sep}, number = 12, pages = 127701, title = {{Evolutionary Optimization of Optical Antennas}}, volume = 109, year = 2012 }

  %0 Journal Article %1 Feichtner2012 %A Feichtner, Thorsten %A Selig, Oleg %A Kiunke, Markus %A Hecht, Bert %D 2012 %J Physical Review Letters %N 12 %P 127701 %R 10.1103/PhysRevLett.109.127701 %T {Evolutionary Optimization of Optical Antennas} %U http://link.aps.org/doi/10.1103/PhysRevLett.109.127701 http://prl.aps.org/abstract/PRL/v109/i12/e127701 %V 109 %X The design of nanoantennas has so far been mainly inspired by radio-frequency technology. However, the material properties and experimental settings need to be reconsidered at optical frequencies, which would entail the need for alternative optimal antenna designs. Here we subject a checkerboard-type, initially random array of gold cubes to evolutionary optimization. To illustrate the power of the approach, we demonstrate that by optimizing the near-field intensity enhancement, the evolutionary algorithm finds a new antenna geometry, essentially a split-ring–two-wire antenna hybrid that surpasses by far the performance of a conventional gap antenna by shifting the n=1 split-ring resonance into the optical regime. %Z From Duplicate 9 ( Evolutionary Optimization of Optical Antennas - Feichtner, Thorsten; Selig, Oleg; Kiunke, Markus; Hecht, Bert )

• {Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry} Huang, Jer-Shing; Callegari, Victor; Geisler, Peter; Br{\"{u}}ning, Christoph; Kern, Johannes; Prangsma, Jord C; Wu, Xiaofei; Feichtner, Thorsten; Ziegler, Johannes; Weinmann, Pia; Kamp, Martin; Forchel, Alfred; Biagioni, Paolo; Sennhauser, Urs; Hecht, Bert in Nature communications (2010). 1(9) 150--.
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  Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large ({\textgreater}100 $\mu$m(2)) but thin ({\textless}80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.

  @article{Huang2010, abstract = {Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large ({\textgreater}100 $\mu$m(2)) but thin ({\textless}80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.}, author = {Huang, Jer-Shing and Callegari, Victor and Geisler, Peter and Br{\"{u}}ning, Christoph and Kern, Johannes and Prangsma, Jord C and Wu, Xiaofei and Feichtner, Thorsten and Ziegler, Johannes and Weinmann, Pia and Kamp, Martin and Forchel, Alfred and Biagioni, Paolo and Sennhauser, Urs and Hecht, Bert}, journal = {Nature communications}, keywords = {TVF}, month = {jan}, number = 9, pages = {150—-}, publisher = {Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.}, title = {{Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry}}, volume = 1, year = 2010 }

  %0 Journal Article %1 Huang2010 %A Huang, Jer-Shing %A Callegari, Victor %A Geisler, Peter %A Br{\"{u}}ning, Christoph %A Kern, Johannes %A Prangsma, Jord C %A Wu, Xiaofei %A Feichtner, Thorsten %A Ziegler, Johannes %A Weinmann, Pia %A Kamp, Martin %A Forchel, Alfred %A Biagioni, Paolo %A Sennhauser, Urs %A Hecht, Bert %D 2010 %I Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved. %J Nature communications %N 9 %P 150---- %R 10.1038/ncomms1143 %T {Atomically flat single-crystalline gold nanostructures for plasmonic nanocircuitry} %U http://www.ncbi.nlm.nih.gov/pubmed/21267000 %V 1 %X Deep subwavelength integration of high-definition plasmonic nanostructures is of key importance in the development of future optical nanocircuitry for high-speed communication, quantum computation and lab-on-a-chip applications. To date, the experimental realization of proposed extended plasmonic networks consisting of multiple functional elements remains challenging, mainly because of the multi-crystallinity of commonly used thermally evaporated gold layers. This can produce structural imperfections in individual circuit elements that drastically reduce the yield of functional integrated nanocircuits. In this paper we demonstrate the use of large ({\textgreater}100 $\mu$m(2)) but thin ({\textless}80 nm) chemically grown single-crystalline gold flakes that, after immobilization, serve as an ideal basis for focused ion beam milling and other top-down nanofabrication techniques on any desired substrate. Using this methodology we obtain high-definition ultrasmooth gold nanostructures with superior optical properties and reproducible nano-sized features over micrometre-length scales. Our approach provides a possible solution to overcome the current fabrication bottleneck and realize high-definition plasmonic nanocircuitry.

• {Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit} Huang, Jer-Shing; Feichtner, Thorsten; Biagioni, Paolo; Hecht, Bert in Nano Letters (2009). 9(5) 1897–1902.
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  An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.

  @article{Huang2009, abstract = {An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.}, author = {Huang, Jer-Shing and Feichtner, Thorsten and Biagioni, Paolo and Hecht, Bert}, institution = {Nano-Optics {\&} Biophotonics Group, Department of Experimental Physics 5, Rontgen Research Center for Complex Material Research, Physics Institute, University of W{\"{u}}rzburg, Am Hubland, D-97074 W{\"{u}}rzburg, Germany.}, journal = {Nano Letters}, keywords = {TVF}, number = 5, pages = {1897–1902}, publisher = {ACS Publications}, title = {{Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit}}, volume = 9, year = 2009 }

  %0 Journal Article %1 Huang2009 %A Huang, Jer-Shing %A Feichtner, Thorsten %A Biagioni, Paolo %A Hecht, Bert %D 2009 %I ACS Publications %J Nano Letters %N 5 %P 1897--1902 %R 10.1021/nl803902t %T {Impedance Matching and Emission Properties of Nanoantennas in an Optical Nanocircuit} %U http://pubs.acs.org/doi/abs/10.1021/nl803902t %V 9 %X An experimentally realizable prototype optical nanocircuit consisting of a receiving and an emitting nanoantenna connected by a two-wire optical transmission line is studied using finite-difference time- and frequency-domain simulations. To optimize the coupling between optical nanocircuit elements we apply impedance matching concepts in analogy to radio frequency technology. We show that the degree of impedance matching, and in particular the impedance of the emitting nanoantenna, can be inferred from the experimentally accessible standing wave pattern on the transmission line. We demonstrate the possibility of matching the nanoantenna impedance to the transmission line by variations of the antenna length and width realizable by modern microfabrication techniques. The radiation efficiency of the emitting antenna also depends on its geometry but is independent of the degree of impedance matching. The case study presented here provides the basis for experimental realizations of general optical nanocircuits based on readily available gold nanostructures and a large variety of derived novel devices.