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See detailMagnetic control of particle trapping in a hybrid plasmonic nanopore
Maccaferri, Nicolò UL; Vavassori, Paolo; Garoli, Denis

in Applied Physics Letters (2021), 118

Plasmonic nanopores are extensively investigated as single molecules detectors. The main limitations in plasmonic nanopore technology are the too fast translocation velocity of the molecule through the ... [more ▼]

Plasmonic nanopores are extensively investigated as single molecules detectors. The main limitations in plasmonic nanopore technology are the too fast translocation velocity of the molecule through the pore and the consequent very short analysis times, as well as the possible instabilities due to local heating. An interesting approach to enable longer acquisition times is represented by the ability to stably trap the nanoparticles used to tag molecules close to the nanopore. Here, we theoretically investigate the performance of a magneto-plasmonic nanopore prepared with a thin layer of cobalt sandwiched between two gold layers. A nanopore is then coupled with a bifunctional (magnetic and plasmonic) core–shell nanoparticle made of magnetite (core) covered with a thin layer of gold (shell). By setting the magnetic configuration of the cobalt layer around the pore by an external magnetic field, it is possible to generate a nanoscale magnetic tweezer to trap the nanoparticle at a specific point. Considering a ∼10 nm diameter magnetite nanoparticle, we calculate a trapping force up to 28 pN, an order of magnitude above the force that can be obtained with standard optical or plasmonic trapping approaches. Moreover, the magnetic force pulls the nanoparticle in close contact with the plasmonic nanopore's wall, thus enabling the formation of a nanocavity enclosing a sub-10 nm3 confined electromagnetic field with an average field intensity enhancement up to 230 at near-infrared wavelengths. The presented hybrid magneto-plasmonic system points toward a strategy to improve nanopore-based biosensors for single-molecule detection and potentially for the analysis of various biomolecules. [less ▲]

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See detailFormation of ultra-thin Ge1−xSnx/Ge1−x−ySixSny quantum heterostructures and their electrical properties for realizing resonant tunneling diode
Suwito, Galih Ramadana; Fukuda, Masahiro; Suprayoga, Edi et al

in Applied Physics Letters (2020), 117(23), 232104

Huge thermal noise owing to the narrow energy bandgap is one of the critical issues for group IV-based photonics in the mid-infrared regime. With this motivation, we examined to form Ge1−xSnx ... [more ▼]

Huge thermal noise owing to the narrow energy bandgap is one of the critical issues for group IV-based photonics in the mid-infrared regime. With this motivation, we examined to form Ge1−xSnx/Ge1−x−ySixSny quantum heterostructures (QHs) by molecular beam epitaxy for realizing resonant tunneling diodes composed of group-IV materials. We confirmed the formation of approximately 2 nm-thick Ge1−xSnx/Ge1−x−ySixSny QHs with atomically flat interfaces by x-ray diffraction and transmission electron microscopy methods. Moreover, by the current density–voltage (J–V) measurement at 10 K, we observed the occurrence of a non-linear distinct hump in the J–V characteristic, which is possibly originated from quantum transport of heavy holes. According to the tunneling transmission spectra simulation result, the hump property would be due to two possible scenarios: a resonant tunneling of heavy holes in the QH and/or a resonance phenomenon that heavy holes pass just above a potential barrier. [less ▲]

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See detailHigh-contrast imaging of 180 degrees ferroelectric domains by optical microscopy using ferroelectric liquid crystals
Nataf, Guillaume F.; Guennou, Mael UL; Scalia, Giusy UL et al

in APPLIED PHYSICS LETTERS (2020), 116(21),

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an ... [more ▼]

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an electric field gives rise to an immediate and lasting optical response when an appropriately aligned FLC is observed between crossed polarizers, with one field direction yielding a dark image and the opposite direction yielding a bright image. Here, this peculiar electro-optic response is used to image, with high optical contrast, 180 degrees ferroelectric domains in a crystalline substrate of magnesium-doped lithium niobate. The lithium niobate substrate contains a few domains with upward electric polarization surrounded by regions with downward electric polarization. In contrast to a reference non-chiral liquid crystal that is unable to show ferroelectric behavior due to its high symmetry, the FLC, which is used as a thin film confined between the lithium niobate substrate and an inert aligning substrate, reveals ferroelectric domains as well as their boundaries, with strong black and white contrast. The results show that FLCs can be used for non-destructive readout of domains in underlying ferroelectrics, with potential applications in, e.g., photonic devices and non-volatile ferroelectric memories. [less ▲]

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See detailAnisotropy-driven thermal conductivity switching and thermal hysteresis in a ferroelectric
Antonio Seijas-Bellido, Juan; Iñiguez, Jorge UL; Rurali, Riccardo

in APPLIED PHYSICS LETTERS (2019), 115(19),

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See detailSupraferromagnetic correlations in clusters of magnetic nanoflowers
Bender, Philipp Florian UL; Honecker, Dirk UL; Fernández Barquín, Luis

in Applied Physics Letters (2019), 115

Magnetic nanoflowers are densely packed aggregates of superferromagnetically coupled iron oxide nanocrystallites, which excel during magnetic hyperthermia experiments. Here, we investigate the nature of ... [more ▼]

Magnetic nanoflowers are densely packed aggregates of superferromagnetically coupled iron oxide nanocrystallites, which excel during magnetic hyperthermia experiments. Here, we investigate the nature of the moment coupling within a powder of such nanoflowers using spin-resolved small-angle neutron scattering. Within the powder, the nanoparticles are agglomerated to clusters, and we can show that the moments of neighboring nanoflowers tend to align parallel to each other. Thus, the whole system resembles a hierarchical magnetic nanostructure consisting of three distinct levels, i.e., (i) the ferrimagnetic nanocrystallites as building blocks, (ii) the superferromagnetic nanoflowers, and (iii) the supraferromagnetic clusters of nanoflowers. We surmise that such a supraferromagnetic coupling explains the enhanced magnetic hyperthermia performance in the case of interacting nanoflowers. [less ▲]

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See detailUltrafast carrier recombination in highly n-doped Ge-on-Si films
Allerbeck, J.; Herbst, A. J.; Yamamoto, Y. et al

in APPLIED PHYSICS LETTERS (2019), 114(24),

We study the femtosecond carrier dynamics of n-type doped and biaxially strained Ge-on-Si films which occurs upon impulsive photoexcitation by means of broadband near-IR transient absorption spectroscopy ... [more ▼]

We study the femtosecond carrier dynamics of n-type doped and biaxially strained Ge-on-Si films which occurs upon impulsive photoexcitation by means of broadband near-IR transient absorption spectroscopy. The modeling of the experimental data takes into account the static donor density in a modified rate equation for the description of the temporal recombination dynamics. The measurements confirm the negligible contribution at a high n-type doping concentration, in the 10(19)cm(-3) range, of Auger processes as compared to defect-related Shockley-Read-Hall recombination. Energy resolved dynamics reveal further insights into the doping-related band structure changes and suggest a reshaping of direct and indirect conduction band valleys to a single effective valley along with a significant spectral broadening of the optical transitions. [less ▲]

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See detail3D tomography of cells in micro-channels
Wagner, Christian UL; Quint, Serket; Guckenberger, A. et al

in Applied Physics Letters (2017)

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See detailSpace-charge-limited currents in CIS-based solar cells
Zelenina, Anastasiya UL; Werner, Florian UL; Elanzeery, Hossam UL et al

in Applied Physics Letters (2017), 111

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See detailMagnetoplasmonic control of plasmonic vortices
Maccaferri, Nicolò UL; Gorodetski, Yuri; Toma, Andrea et al

in Applied Physics Letters (2017), 111(20), 201104

We theoretically investigate the generation of far-field propagating optical beams with a desired orbital angular momentum by using an archetypical magnetoplasmonic tip surrounded by a gold spiral slit ... [more ▼]

We theoretically investigate the generation of far-field propagating optical beams with a desired orbital angular momentum by using an archetypical magnetoplasmonic tip surrounded by a gold spiral slit. The use of a magnetic material can lead to important implications once magneto-optical activity is activated through the application of an external magnetic field. The physical model and the numerical study presented here introduce the concept of magnetically tunable plasmonic vortex lens, namely a magnetoplasmonic vortex lens, which ensures a tunable selectivity in the polarization state of the generated nanostructured beam. The presented system provides a promising platform for a localized excitation of plasmonic vortices followed by their beaming in the far-field with an active modulation of both light's transmission and helicity. Published by AIP Publishing. [less ▲]

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See detailTime resolved photoluminescence on Cu(In, Ga)Se-2 absorbers: Distinguishing degradation and trap states
Redinger, Alex UL; Levcenko, Sergiu; Hages, Charles J. et al

in APPLIED PHYSICS LETTERS (2017), 110(12),

Recent reports have suggested that the long decay times in time resolved photoluminescence (TRPL), often measured in Cu(In, Ga)Se-2 absorbers may be a result of detrapping from sub-bandgap defects. In ... [more ▼]

Recent reports have suggested that the long decay times in time resolved photoluminescence (TRPL), often measured in Cu(In, Ga)Se-2 absorbers may be a result of detrapping from sub-bandgap defects. In this work, we show via temperature dependent measurements, that long lifetimes >50 ns can be observed that reflect the true minority carrier lifetime not related to deep trapping. Temperature dependent time resolved photoluminescence and steady state photoluminescence imaging measurements are used to analyze the effect of annealing in air and in a nitrogen atmosphere between 300K and 350K. We show that heating the Cu(In, Ga)Se-2 absorber in air can irreversibly decrease the TRPL decay time, likely due to a deterioration of the absorber surface. Annealing in an oxygen-free environment yields a temperature dependence of the TRPL decay times in accordance with Schockley Read Hall recombination kinetics and weakly varying capture cross sections according to T-0.6. Published by AIP Publishing. [less ▲]

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See detailNano-light-emitting-diodes based on InGaN mesoscopic structures for energy saving optoelectronics
Mikulics, Martin; Winden, Andreas; Marso, Michel UL et al

in Applied Physics Letters (2016), 109

Vertically integrated III-nitride based nano-LEDs (light emitting diodes) were designed and fabricated for operation in the telecommunication wavelength range in the (p-GaN/InGaN/n-GaN/sapphire) material ... [more ▼]

Vertically integrated III-nitride based nano-LEDs (light emitting diodes) were designed and fabricated for operation in the telecommunication wavelength range in the (p-GaN/InGaN/n-GaN/sapphire) material system. The band edge luminescence energy of the nano-LEDs could be engineered by tuning the composition and size of the InGaN mesoscopic structures. Narrow band edge photoluminescence and electroluminescence were observed. Our mesoscopic InGaN structures (depending on diameter) feature a very low power consumption in the range between 2 nWand 30 nW. The suitability of the technological process for the long-term operation of LEDs is demonstrated by reliability measurements. The optical and electrical characterization presented show strong potential for future low energy consumption optoelectronics. [less ▲]

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See detailQuasi Fermi level splitting of Cu-rich and Cu-poor Cu(In,Ga)Se2 absorber layers
Babbe, Finn UL; Choubrac, Léo UL; Siebentritt, Susanne UL

in Applied Physics Letters (2016), 109

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See detailOptical spectroscopy study on the photo-response in multiferroic BiFeO3
Burkert, F.; Kreisel, Jens UL; Kuntscher, C. A.

in APPLIED PHYSICS LETTERS (2016), 109(18),

We investigate the underlying mechanism of the photostriction effect in single-crystalline BiFeO3 by transmission measurements in the infrared and visible frequency range under continuous illumination ... [more ▼]

We investigate the underlying mechanism of the photostriction effect in single-crystalline BiFeO3 by transmission measurements in the infrared and visible frequency range under continuous illumination with a green 532 nm). The small photo-induced changes in the transmission spectrum reveal three well-defined absorption features at 1.22 eV, 1.66 eV, and 2.14 eV, which we assign to charge-transfer excitons and in-gap defect states probably related to oxygen vacancies. The intensity of the three absorption features follows a linear dependence on the illumination intensity for an irradiance above 90 W/m(2). Published by AIP Publishing. [less ▲]

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See detailDirect electro-optical pumping for hybrid CdSe nanocrystal/III-nitride based nano-light-emitting diodes
Mikulics, Martin; Arango, Y.C.; Winden, Andreas et al

in Applied Physics Letters (2016), 108

We propose a device concept for a hybrid nanocrystal/III-nitride based nano-LED. Our approach is based on the direct electro-optical pumping of nanocrystals (secondary excitation) by electrically driven ... [more ▼]

We propose a device concept for a hybrid nanocrystal/III-nitride based nano-LED. Our approach is based on the direct electro-optical pumping of nanocrystals (secondary excitation) by electrically driven InGaN/GaN nano-LEDs as the primary excitation source. To this end, a universal hybrid optoelectronic platform was developed for a large range of optically active nano- and mesoscopic structures. The advantage of the approach is that the emission of the nanocrystals can be electrically induced without the need of contacting them. The proof of principal was demonstrated for the electro-optical pumping of CdSe nanocrystals. The nano-LEDs with a diameter of 100 nm exhibit a very low current of 8 nA at 5V bias which is several orders of magnitude smaller than for those conventionally used. The leakage currents in the device layout were typically in the range of 8 pA to 20 pA/cm2 at 5V bias. The photon-photon down conversion efficiency was determined to be 27%. Microphotoluminescence and microelectroluminescence characterization demonstrate the potential for future optoelectronics and highly secure “green” information technology applications. [less ▲]

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See detailProbing electronic lifetimes and phonon anharmonicities in high-quality chemical vapor deposited graphene by magneto-Raman spectroscopy
Neumann, Christoph; Halpaap, Donatus; Reichardt, Sven UL et al

in Applied Physics Letters (2015), 107(23), 233105

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See detailDiffuse Electroreflectance of thin-film solar cells: Suppression of interference-related lineshape distortions
Krämmer, Christoph; Huber, Christian; Redinger, Alex UL et al

in Applied Physics Letters (2015), 107

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See detailDetection of Cu2Zn5SnSe8 and Cu2Zn6SnSe9 phases in co-evaporated Cu2ZnSnSe4 thin-films
Schwarz, Torsten; Marques, Miguel A.L.; Botti, Silvana et al

in Applied Physics Letters (2015), 107

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See detailReduction of skin effect losses in double-level-T-gate structure
Mikulics, Martin; Hardtdegen, Hilde; Arango, Y. C. et al

in Applied Physics Letters (2014), 105

We developed a T-gate technology based on selective wet etching yielding 200 nm wide T-gate structures used for fabrication of High Electron Mobility Transistors (HEMT). Major advantages of our process ... [more ▼]

We developed a T-gate technology based on selective wet etching yielding 200 nm wide T-gate structures used for fabrication of High Electron Mobility Transistors (HEMT). Major advantages of our process are the use of only standard photolithographic process and the ability to generate T-gate stacks. A HEMT fabricated on AlGaN/GaN/sapphire with gate length Lg=200 nm and double-stacked T-gates exhibits 60 GHz cutoff frequency showing ten-fold improvement compared to 6 GHz for the same device with 2 um gate length. HEMTs with a double-level-T-gate (DLTG) structure exhibit up to 35% improvement of fmax value compared to a single T-gate device. This indicates a significant reduction of skin effect losses in DLTG structure compared to its standard T-gate counterpart. These results agree with the theoretical predictions. [less ▲]

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See detailThe band gap of Cu2ZnSnSe4: Effect of order-disorder
Rey, Germain UL; Redinger, Alex UL; Sendler, Jan UL et al

in Applied Physics Letters (2014), 105

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