Co-reporter:Richard Ciesielski, Alberto Comin, Matthias Handloser, Kevin Donkers, Giovanni Piredda, Antonio Lombardo, Andrea C. Ferrari, and Achim Hartschuh
Nano Letters 2015 Volume 15(Issue 8) pp:4968-4972
Publication Date(Web):June 29, 2015
DOI:10.1021/acs.nanolett.5b00893
We investigate near-degenerate four-wave mixing in graphene using femtosecond laser pulse shaping microscopy. Intense near-degenerate four-wave mixing signals on either side of the exciting laser spectrum are controlled by amplitude and phase shaping. Quantitative signal modeling for the input pulse parameters shows a spectrally flat phase response of the near-degenerate four-wave mixing due to the linear dispersion of the massless Dirac Fermions in graphene. Exploiting these properties we demonstrate that graphene is uniquely suited for the intrafocus phase characterization and compression of broadband laser pulses, circumventing disadvantages of common methods utilizing second or third harmonic light.
Co-reporter:Nina Mauser, Dawid Piatkowski, Tobia Mancabelli, Marcin Nyk, Sebastian Mackowski, and Achim Hartschuh
ACS Nano 2015 Volume 9(Issue 4) pp:3617
Publication Date(Web):March 15, 2015
DOI:10.1021/nn504993e
We present tip-enhanced upconversion photoluminescence (PL) images of Er3+- and Yb3+-doped NaYF4 nanocrystals on glass substrates with subdiffraction spatial resolution. Tip–sample distance dependent measurements clearly demonstrate the near-field origin of the image contrast. Time-resolved PL measurements show that the tip increases the spontaneous emission rate of the two emission channels of Er3+ in the visible region. Very efficient enhancement of upconversion PL is discussed in the context of the two-photon nature of the excitation process and homoenergy transfer between the ions within the nanocrystals. Comparison between different nanocrystals and tips shows a strong influence of the tip shape on the image contrast that becomes particularly relevant for the larger dimensions of the investigated nanocrystals.Keywords: optical antenna; rare earth ion doped crystals; tip-enhanced near-field optical microscopy; upconverted luminescence;
Co-reporter:Nina Mauser, Nicolai Hartmann, Matthias S. Hofmann, Julia Janik, Alexander Högele, and Achim Hartschuh
Nano Letters 2014 Volume 14(Issue 7) pp:3773-3778
Publication Date(Web):May 30, 2014
DOI:10.1021/nl5006959
We report on the first antenna-enhanced optoelectronic microscopy studies on nanoscale devices. By coupling the emission and excitation to a scanning optical antenna, we are able to locally enhance the electroluminescence and photocurrent along a carbon nanotube device. We show that the emission source of the electroluminescence can be pointlike with a spatial extension below 20 nm. Topographic and antenna-enhanced photocurrent measurements reveal that the emission takes place at the location of highest local electric field indicating that the mechanism behind the emission is the radiative decay of excitons created via impact excitation.
Co-reporter:M.E. Regler, H.J. Krenner, A.A. Green, M.C. Hersam, A. Wixforth, A. Hartschuh
Chemical Physics 2013 Volume 413() pp:39-44
Publication Date(Web):21 February 2013
DOI:10.1016/j.chemphys.2012.10.014
Abstract
We show that the photoluminescence intensity and decay dynamics of semiconducting single-walled carbon nanotube films can be remotely controlled by surface acoustic waves (SAW) launched on the piezoelectric substrate LiNbO3. Time-resolved measurements in the picosecond regime reveal that photoluminescence quenching results from a decrease of the radiative recombination rate by up to 25% for the accessible SAW amplitudes. The SAW-induced piezoelectric field acts as a quasi-static perturbation that polarizes the luminescent exciton state reducing the oscillator strength of the radiative transition following a quadratic field dependence. Surface acoustic waves could be used for the remote and contact-free electrical control of high-speed electronic and optoelectronic nanotube-based devices.
Co-reporter:Nicolai Hartmann, Dawid Piatkowski, Richard Ciesielski, Sebastian Mackowski, and Achim Hartschuh
ACS Nano 2013 Volume 7(Issue 11) pp:10257
Publication Date(Web):October 12, 2013
DOI:10.1021/nn404611q
We investigated the angular radiation patterns, a key characteristic of an emitting system, from individual silver nanowires decorated with rare earth ion-doped nanocrystals. Back focal plane radiation patterns of the nanocrystal photoluminescence after local two-photon excitation can be described by two emission channels: excitation of propagating surface plasmons in the nanowire followed by leakage radiation and direct dipolar emission observed also in the absence of the nanowire. Theoretical modeling reproduces the observed radiation patterns which strongly depend on the position of excitation along the nanowire. Our analysis allows us to estimate the branching ratio into both emission channels and to determine the diameter-dependent surface plasmon quasi-momentum, important parameters of emitter-plasmon structures.Keywords: back focal plane imaging; metallic nanowires; plasmonics; rare earth ions; upconversion
Co-reporter:Nicolai Hartmann, Giovanni Piredda, Johann Berthelot, Gérard Colas des Francs, Alexandre Bouhelier, and Achim Hartschuh
Nano Letters 2012 Volume 12(Issue 1) pp:177-181
Publication Date(Web):December 16, 2011
DOI:10.1021/nl203270b
We report on the excitation of propagating surface plasmon polaritons in thin metal films by a single emitter. Upon excitation in the visible regime, individual semiconducting single-walled carbon nanotubes are shown to act as directional near-infrared point dipole sources launching propagating surface plasmons mainly along the direction of the nanotube axis. Plasmon excitation and propagation is monitored in Fourier and real space by leakage radiation microscopy and is modeled by rigorous theoretical calculations. Coupling to plasmons almost completely reshapes the emission of nanotubes both spatially and with respect to polarization as compared to photoluminescence on a dielectric substrate.
Co-reporter:Nina Rauhut, Michael Engel, Mathias Steiner, Ralph Krupke, Phaedon Avouris, and Achim Hartschuh
ACS Nano 2012 Volume 6(Issue 7) pp:6416
Publication Date(Web):May 28, 2012
DOI:10.1021/nn301979c
We present the first photocurrent measurements along single carbon nanotube (CNT) devices with 30 nm resolution. Our technique is based on tip-enhanced near-field optical microscopy, exploiting the plasmonically enhanced absorption controlled by an optical nanoantenna. This allows for imaging of the zero-bias photocurrent caused by charge separation in local built-in electric fields at the contacts and close to charged particles that cannot be resolved using confocal microscopy. Simultaneously recorded Raman scattering images reveal the structural properties and the defect densities of the CNTs. Antenna-enhanced scanning photocurrent microscopy extends the available set of scanning-probe techniques by combining high-resolution photovoltaic and optical probing and could become a valuable tool for the characterization of nanoelectronic devices.Keywords: nanoscale devices; optical antennas; scanning photocurrent microscopy; single-walled carbon nanotubes; tip-enhanced near-field optical microscopy
Co-reporter:Carsten Georgi, Alexander A. Green, Mark C. Hersam, and Achim Hartschuh
ACS Nano 2010 Volume 4(Issue 10) pp:5914
Publication Date(Web):September 21, 2010
DOI:10.1021/nn101443d
We observe localization of excitons in semiconducting single-walled carbon nanotubes at room temperature using high-resolution near-field photoluminescence (PL) microscopy. Localization is the result of spatially confined exciton energy minima with depths of more than 15 meV connected to lateral energy gradients exceeding 2 meV/nm as evidenced by energy-resolved PL imaging. Simulations of exciton diffusion in the presence of energy variations support this interpretation predicting strongly enhanced PL at local energy minima.Keywords: excitons; localization; near-field microscopy; photoluminescence; single-walled carbon nanotubes
Co-reporter:Hayk Harutyunyan, Tobias Gokus, Alexander A. Green, Mark C. Hersam, Maria Allegrini and Achim Hartschuh
Nano Letters 2009 Volume 9(Issue 5) pp:2010-2014
Publication Date(Web):March 30, 2009
DOI:10.1021/nl9002798
We show that new low-energy photoluminescence (PL) bands can be created in the spectra of semiconducting single-walled carbon nanotubes by intense pulsed excitation. The new bands are attributed to PL from different nominally dark excitons that are “brightened” because of a defect-induced mixing of states with different parity and/or spin. Time-resolved PL studies on single nanotubes reveal a significant reduction of the bright exciton lifetime upon brightening of the dark excitons. The lowest-energy dark state has longer lifetimes and is not in thermal equilibrium with the bright state.
Co-reporter:A. Hartschuh;H. Qian;C. Georgi;M. Böhmler
Analytical and Bioanalytical Chemistry 2009 Volume 394( Issue 7) pp:1787-1795
Publication Date(Web):2009 August
DOI:10.1007/s00216-009-2827-4
We review recent experimental studies on single-walled carbon nanotubes on substrates using tip-enhanced near-field optical microscopy (TENOM). High-resolution optical and topographic imaging with sub 15 nm spatial resolution is shown to provide novel insights into the spectroscopic properties of these nanoscale materials. In the case of semiconducting nanotubes, the simultaneous observation of Raman scattering and photoluminescence (PL) is possible, enabling a direct correlation between vibrational and electronic properties on the nanoscale. So far, applications of TENOM have focused on the spectroscopy of localized phonon modes, local band energy renormalizations induced by charge carrier doping, the environmental sensitivity of nanotube PL, and inter-nanotube energy transfer. At the end of this review we discuss the remaining limitations and challenges in this field.
Co-reporter:Huihong Qian, Paulo T. Araujo, Carsten Georgi, Tobias Gokus, Nicolai Hartmann, Alexander A. Green, Ado Jorio, Mark C. Hersam, Lukas Novotny and Achim Hartschuh
Nano Letters 2008 Volume 8(Issue 9) pp:2706-2711
Publication Date(Web):August 1, 2008
DOI:10.1021/nl801038t
We studied the local optical response of semiconducting single-walled carbon nanotubes to wrapping by DNA segments using high resolution tip-enhanced near-field microscopy. Photoluminescence (PL) near-field images of single nanotubes reveal large DNA-wrapping-induced red shifts of the exciton energy that are two times higher than indicated by spatially averaging confocal microscopy. Near-field PL spectra taken along nanotubes feature two distinct PL bands resulting from DNA-wrapped and unwrapped nanotube segments. The transition between the two energy levels occurs on a length scale smaller than our spatial resolution of about 15 nm.
Co-reporter:Achim Hartschuh Dr.
Angewandte Chemie International Edition 2008 Volume 47( Issue 43) pp:8178-8191
Publication Date(Web):
DOI:10.1002/anie.200801605
Abstract
Spectroscopic methods with high spatial resolution are essential for understanding the physical and chemical properties of nanoscale materials, including quantum structures and biological surfaces. An optical technique is reviewed that relies on the enhanced electric fields in the proximity of a sharp, laser-irradiated metal tip. These fields are utilized for spatially confined probing of various optical signals, thus allowing for a detailed sample characterization far below the diffraction limit. In addition, tip-enhanced fields also provide the sensitivity crucial for the detection of nanoscale volumes. After outlining the principles of near-field optics, the mechanisms contributing to local field enhancement and how it can be used to enhance optical signals are discussed. Different experimental methods are presented and several recent examples of Raman and fluorescence microscopy with 10 nm spatial resolution of single molecules are reviewed.
Co-reporter:Achim Hartschuh Dr.
Angewandte Chemie 2008 Volume 120( Issue 43) pp:8298-8312
Publication Date(Web):
DOI:10.1002/ange.200801605
Abstract
Spektroskopiemethoden mit höchster Ortsauflösung sind von grundlegender Bedeutung für die Untersuchung der physikalischen und chemischen Eigenschaften von nanostrukturierten Materialien einschließlich Quantenstrukturen und biologischen Oberflächen. Wir stellen ein optisches Verfahren vor, das auf den stark überhöhten elektrischen Feldern in der Nähe einer laserbeleuchteten Metallspitze basiert. Diese Felder ermöglichen die Messung verschiedener optischer Signale in räumlich stark begrenzten Bereichen und ermöglichen so eine detaillierte Probencharakterisierung weit jenseits der Beugungsgrenze. Darüber hinaus liefern die verstärkten Felder auch die notwendige Nachweisempfindlichkeit für die Messung kleinster Probenvolumina. Zunächst werden die Grundlagen der Nahfeldoptik erläutert, im Anschluss behandeln wir die verschiedenen Mechanismen, die zur lokalen Feldverstärkung beitragen, und zeigen, wie sich damit optische Signale verstärken lassen. Verschiedene experimentelle Umsetzungen und einige aktuelle Ergebnisse zu Raman- und Fluoreszenzmikroskopie mit bis zu 10 nm Ortsauflösung an einzelnen Molekülen werden vorgestellt.
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![[(1s,3r)-3-hydroxy-4-[(3e,5e,7e,9e,11z)-11-[4-[(e)-2-[(1r,3s,6s)-3-hydroxy-1,5,5-trimethyl-7-oxabicyclo[4.1.0]heptan-6-yl]ethenyl]-5-oxofuran-2-ylidene]-3,10-dimethylundeca-1,3,5,7,9-pentaenylidene]-3,5,5-trimethylcyclohexyl] Acetate](http://img.cochemist.com/ccimg/33300/33281-81-1_b.png)
