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  1. Article ; Online: Probing the ultrafast dynamics of excitons in single semiconducting carbon nanotubes.

    Birkmeier, Konrad / Hertel, Tobias / Hartschuh, Achim

    Nature communications

    2022  Volume 13, Issue 1, Page(s) 6290

    Abstract: Excitonic states govern the optical spectra of low-dimensional semiconductor nanomaterials and their dynamics are key for a wide range of applications, such as in solar energy harvesting and lighting. Semiconducting single-walled carbon nanotubes emerged ...

    Abstract Excitonic states govern the optical spectra of low-dimensional semiconductor nanomaterials and their dynamics are key for a wide range of applications, such as in solar energy harvesting and lighting. Semiconducting single-walled carbon nanotubes emerged as particularly rich model systems for one-dimensional nanomaterials and as such have been investigated intensively in the past. The exciton decay dynamics in nanotubes has been studied mainly by transient absorption and time-resolved photoluminescence spectroscopy. Since different transitions are monitored with these two techniques, developing a comprehensive model to reconcile different data sets, however, turned out to be a challenge and remarkably, a uniform description seems to remain elusive. In this work, we investigate the exciton decay dynamics in single carbon nanotubes using transient interferometric scattering and time-resolved photoluminescence microscopy with few-exciton detection sensitivity and formulate a unified microscopic model by combining unimolecular exciton decay and ultrafast exciton-exciton annihilation on a time-scale down to 200 fs.
    Language English
    Publishing date 2022-10-21
    Publishing country England
    Document type Journal Article
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-022-33941-2
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Non-linear Raman scattering intensities in graphene.

    Giegold, Veit / Lange, Lucas / Ciesielski, Richard / Hartschuh, Achim

    Nanoscale

    2020  Volume 12, Issue 9, Page(s) 5612–5617

    Abstract: We show that the Raman scattering signals of the two dominant Raman bands G and 2D of graphene sensitively depend on the laser intensity in opposite ways. High electronic temperatures reached for pulsed laser excitation lead to an asymmetric Fermi-Dirac ... ...

    Abstract We show that the Raman scattering signals of the two dominant Raman bands G and 2D of graphene sensitively depend on the laser intensity in opposite ways. High electronic temperatures reached for pulsed laser excitation lead to an asymmetric Fermi-Dirac distribution at the different optically resonant states contributing to Raman scattering. This results in a partial Pauli blocking of destructively interfering quantum pathways for G band scattering, which is observed as a super-linear increase of the G band intensity with laser power. The 2D band, on the other hand, exhibits sub-linear intensity scaling due to the blocking of constructively interfering contributions. The opposite intensity dependencies of the two bands are found to reduce the observed 2D/G ratio, a key quantity used for characterizing graphene samples, by more than factor two for electronic temperatures around 3000 K.
    Language English
    Publishing date 2020-02-26
    Publishing country England
    Document type Journal Article
    ZDB-ID 2515664-0
    ISSN 2040-3372 ; 2040-3364
    ISSN (online) 2040-3372
    ISSN 2040-3364
    DOI 10.1039/c9nr10654e
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Tip-enhanced near-field optical microscopy.

    Hartschuh, Achim

    Angewandte Chemie (International ed. in English)

    2008  Volume 47, Issue 43, Page(s) 8178–8191

    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 ... ...

    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.
    MeSH term(s) Microscopy, Fluorescence/instrumentation ; Microscopy, Fluorescence/methods ; Microscopy, Scanning Probe/methods ; Nanotechnology/methods ; Optics and Photonics ; Spectrum Analysis, Raman/instrumentation ; Spectrum Analysis, Raman/methods
    Language English
    Publishing date 2008
    Publishing country Germany
    Document type Journal Article ; Research Support, Non-U.S. Gov't ; Review
    ZDB-ID 2011836-3
    ISSN 1521-3773 ; 1433-7851
    ISSN (online) 1521-3773
    ISSN 1433-7851
    DOI 10.1002/anie.200801605
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  4. Article ; Online: Controlling photon antibunching from 1D emitters using optical antennas.

    Lange, Lucas / Schäfer, Frank / Biewald, Alexander / Ciesielski, Richard / Hartschuh, Achim

    Nanoscale

    2019  Volume 11, Issue 31, Page(s) 14907–14911

    Abstract: Single-photon emission is a hallmark of atom-like 0D quantum emitters, such as luminescent semiconductor nanocrystals, nitrogen vacancies in diamond and organic dye molecules. In higher dimensional nanostructures, on the other hand, multiple spatially ... ...

    Abstract Single-photon emission is a hallmark of atom-like 0D quantum emitters, such as luminescent semiconductor nanocrystals, nitrogen vacancies in diamond and organic dye molecules. In higher dimensional nanostructures, on the other hand, multiple spatially separated electronic excitations may exist giving rise to more than one emitted photon at a time. We show that optical nanoantennas can be used to control the photon emission statistic of 1D nanostructures and to convert them into single-photon sources. Antenna-control exploits spatially confined near-field enhanced absorption and emission rates resulting in locally increased annihilation of mobile excitons and radiative recombination. As proof of concept, we experimentally demonstrate the improvement of the degree of antibunching in the photoluminescence of single carbon nanotubes using a metal tip at room temperature. Our results indicate that, in addition to improving the performance of single photon sources, optical antennas have the potential to open up a broad range of materials for quantum information technology.
    Language English
    Publishing date 2019-07-30
    Publishing country England
    Document type Journal Article
    ZDB-ID 2515664-0
    ISSN 2040-3372 ; 2040-3364
    ISSN (online) 2040-3372
    ISSN 2040-3364
    DOI 10.1039/c9nr03688a
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Ultrafast hot electron-hole plasma photoluminescence in two-dimensional semiconductors.

    Sousa, Frederico B / Perea-Causin, Raül / Hartmann, Sean / Lafetá, Lucas / Rosa, Bárbara / Brem, Samuel / Palekar, Chirag / Reitzenstein, Stephan / Hartschuh, Achim / Malic, Ermin / Malard, Leandro M

    Nanoscale

    2023  Volume 15, Issue 15, Page(s) 7154–7163

    Abstract: The transition metal dichalcogenide family of semiconducting two-dimensional materials has recently shown a prominent potential to be an ideal platform to study the exciton Mott transition into electron-hole plasma and liquid phases due to their strong ... ...

    Abstract The transition metal dichalcogenide family of semiconducting two-dimensional materials has recently shown a prominent potential to be an ideal platform to study the exciton Mott transition into electron-hole plasma and liquid phases due to their strong Coulomb interactions. Here, we show that pulsed laser excitation at high pump fluences can induce this exciton Mott transition to an electron-hole plasma in mono and few-layer transition metal dichalcogenides at room temperature. The formation of an electron-hole plasma leads to a broadband light emission spanning from the near infrared to the visible region. In agreement with our theoretical calculations, the photoluminescence emission at high energies displays an exponential decay that directly reflects the electronic temperature - a characteristic fingerprint of unbound electron-hole pair recombination. Furthermore, two-pulse excitation correlation measurements were performed to study the dynamics of electronic cooling, which shows two decay time components, one of less than 100 fs and a slower component of few ps associated with the electron-phonon and phonon-lattice bath thermalizations, respectively. Our work may shed light on further studies of the exciton Mott transition into other two-dimensional materials and their heterostructures and its applications in nanolasers and other optoelectronic devices.
    Language English
    Publishing date 2023-04-13
    Publishing country England
    Document type Journal Article
    ZDB-ID 2515664-0
    ISSN 2040-3372 ; 2040-3364
    ISSN (online) 2040-3372
    ISSN 2040-3364
    DOI 10.1039/d2nr06732c
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Article ; Online: Microfluidic mixing as platform technology for production of chitosan nanoparticles loaded with different macromolecules.

    Greco, Antonietta / Gabold, Bettina / Chen, Siyu / Wang, Xiaoxuan / Xu, Zehua / Hartschuh, Achim / Chiesa, Enrica / Genta, Ida / Ried, Christian L / Merdan, Thomas / Merkel, Olivia M

    European journal of pharmaceutics and biopharmaceutics : official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V

    2023  Volume 188, Page(s) 170–181

    Abstract: In recent decades, biotechnological drugs have emerged as relevant therapeutic tools. However, therapeutic molecules can exert their activity only if properly formulated and delivered into the body. In this regard, nano-sized drug delivery systems have ... ...

    Abstract In recent decades, biotechnological drugs have emerged as relevant therapeutic tools. However, therapeutic molecules can exert their activity only if properly formulated and delivered into the body. In this regard, nano-sized drug delivery systems have been shown to provide protection, stability, and controlled release of payloads, increasing their therapeutic efficacy. In this work, a microfluidic mixing technique for the preparation of chitosan-based nanoparticles was established with the capability of easily exchanging macromolecular biological cargos such as the model protein β-Galactosidase, mRNA, and siRNA. The nanoparticles obtained showed hydrodynamic diameters ranging from 75 nm to 105 nm, low polydispersity of 0.15 to 0.22 and positive zeta potentials of 6 mV to 17 mV. All payloads were efficiently encapsulated (>80 %) and the well-known cytocompatibility of chitosan-based nanoparticles was confirmed. Cell culture studies demonstrated increased cellular internalization of loaded nano-formulations compared to free molecules as well as successful gene silencing with nano-formulated siRNA, suggesting the ability of these nanoparticles to escape the endosome.
    MeSH term(s) Chitosan ; Microfluidics ; Nanoparticles ; Macromolecular Substances ; RNA, Small Interfering/genetics ; Particle Size
    Chemical Substances Chitosan (9012-76-4) ; Macromolecular Substances ; RNA, Small Interfering
    Language English
    Publishing date 2023-05-22
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 1065368-5
    ISSN 1873-3441 ; 0939-6411
    ISSN (online) 1873-3441
    ISSN 0939-6411
    DOI 10.1016/j.ejpb.2023.05.010
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article ; Online: Tip-enhanced near-field optical microscopy.

    Mauser, Nina / Hartschuh, Achim

    Chemical Society reviews

    2013  Volume 43, Issue 4, Page(s) 1248–1262

    Abstract: Tip-enhanced near-field optical microscopy (TENOM) is a scanning probe technique capable of providing a broad range of spectroscopic information on single objects and structured surfaces at nanometer spatial resolution and with highest detection ... ...

    Abstract Tip-enhanced near-field optical microscopy (TENOM) is a scanning probe technique capable of providing a broad range of spectroscopic information on single objects and structured surfaces at nanometer spatial resolution and with highest detection sensitivity. In this review, we first illustrate the physical principle of TENOM that utilizes the antenna function of a sharp probe to efficiently couple light to excitations on nanometer length scales. We then discuss the antenna-induced enhancement of different optical sample responses including Raman scattering, fluorescence, generation of photocurrent and electroluminescence. Different experimental realizations are presented and several recent examples that demonstrate the capabilities of the technique are reviewed.
    Language English
    Publishing date 2013-10-07
    Publishing country England
    Document type Journal Article
    ZDB-ID 1472875-8
    ISSN 1460-4744 ; 0306-0012
    ISSN (online) 1460-4744
    ISSN 0306-0012
    DOI 10.1039/c3cs60258c
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  8. Article ; Online: Freely Suspended, van der Waals Bound Organic Nanometer-Thin Functional Films: Mechanical and Electronic Characterization.

    Schaffroth, Lilian S / Lenz, Jakob / Giegold, Veit / Kögl, Maximilian / Hartschuh, Achim / Weitz, R Thomas

    Advanced materials (Deerfield Beach, Fla.)

    2019  Volume 31, Issue 16, Page(s) e1808309

    Abstract: Determining the electronic properties of nanoscopic, low-dimensional materials free of external influences is key to the discovery and understanding of new physical phenomena. An example is the suspension of graphene, which has allowed access to their ... ...

    Abstract Determining the electronic properties of nanoscopic, low-dimensional materials free of external influences is key to the discovery and understanding of new physical phenomena. An example is the suspension of graphene, which has allowed access to their intrinsic charge transport properties. Furthermore, suspending thin films enables their application as membranes, sensors, or resonators, as has been explored extensively. While the suspension of covalently bound, electronically active thin films is well established, semiconducting thin films composed of functional molecules only held together by van der Waals interactions could only be studied supported by a substrate. In the present work, it is shown that by utilizing a surface-crystallization method, electron conductive films with thicknesses of down to 6 nm and planar chiral optical activity can be freely suspended across several hundreds of nanometers. The suspended membranes exhibit a Young's modulus of 2-13 GPa and are electronically decoupled from the environment, as established by temperature-dependent field-effect transistor measurements.
    Language English
    Publishing date 2019-03-04
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 1474949-X
    ISSN 1521-4095 ; 0935-9648
    ISSN (online) 1521-4095
    ISSN 0935-9648
    DOI 10.1002/adma.201808309
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  9. Article ; Online: Temperature-Dependent Ambipolar Charge Carrier Mobility in Large-Crystal Hybrid Halide Perovskite Thin Films.

    Biewald, Alexander / Giesbrecht, Nadja / Bein, Thomas / Docampo, Pablo / Hartschuh, Achim / Ciesielski, Richard

    ACS applied materials & interfaces

    2019  Volume 11, Issue 23, Page(s) 20838–20844

    Abstract: Perovskite-based thin-film solar cells today reach power conversion efficiencies of more than 22%. Methylammonium lead iodide (MAPI) is prototypical for this material class of hybrid halide perovskite semiconductors and at the focal point of interest for ...

    Abstract Perovskite-based thin-film solar cells today reach power conversion efficiencies of more than 22%. Methylammonium lead iodide (MAPI) is prototypical for this material class of hybrid halide perovskite semiconductors and at the focal point of interest for a growing community in research and engineering. Here, a detailed understanding of the charge carrier transport and its limitations by underlying scattering mechanisms is of great interest to the material's optimization and development. In this article, we present an all-optical study of the charge carrier diffusion properties in large-crystal MAPI thin films in the tetragonal crystal phase from 170 K to room temperature. We probe the local material properties of individual crystal grains within a MAPI thin film and find a steady decrease of the charge carrier diffusion constant with increasing temperature. From the resulting charge carrier mobility, we find a power law dependence of μ ∝ T
    Language English
    Publishing date 2019-05-28
    Publishing country United States
    Document type Journal Article
    ISSN 1944-8252
    ISSN (online) 1944-8252
    DOI 10.1021/acsami.9b04592
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  10. Article ; Online: Tip-enhanced near-field optical microscopy of quasi-1 D nanostructures.

    Böhmler, Miriam / Hartschuh, Achim

    Chemphyschem : a European journal of chemical physics and physical chemistry

    2012  Volume 13, Issue 4, Page(s) 927–929

    Abstract: High-resolution imaging and spectroscopy of single CdSe nanowires and carbon nanotubes using tip-enhanced near-field optical microscopy increases the optical excitation and emission rates within a nanoscale sample volume. The resulting signal enhancement ...

    Abstract High-resolution imaging and spectroscopy of single CdSe nanowires and carbon nanotubes using tip-enhanced near-field optical microscopy increases the optical excitation and emission rates within a nanoscale sample volume. The resulting signal enhancement for Raman scattering and photoluminescence as well as the tip-sample-distance dependence are investigated.
    Language English
    Publishing date 2012-03
    Publishing country Germany
    Document type Journal Article
    ISSN 1439-7641
    ISSN (online) 1439-7641
    DOI 10.1002/cphc.201100670
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