Imaging resonant dissipation from individual atomic defects in graphene

Conversion of electric current into heat involves microscopic processes that operate on nanometer length-scales and release minute amounts of power. While central to our understanding of the electrical properties of materials, individual mediators of energy dissipation have so far eluded direct observation. Using scanning nano-thermometry with sub-micro K sensitivity we visualize and control phonon emission from individual atomic defects in graphene. The inferred electron-phonon 'cooling power spectrum' exhibits sharp peaks when the Fermi level comes into resonance with electronic quasi-bound states at such defects, a hitherto uncharted process. Rare in the bulk but abundant at graphene's edges, switchable atomic-scale phonon emitters define the dominant dissipation mechanism. Our work offers new insights for addressing key materials challenges in modern electronics and engineering dissipation at the nanoscale

Why not use the thermal radiation for nanothermometry?

The measurement of temperature with nanoscale spatial resolution is an emerging new technology and it has important impact in various fields. An ideal nanothermometer should not only be accurate, but also applicable over a wide temperature range and under diverse conditions. Furthermore, the measurement time should be short enough to follow the evolution of the system. However, many of the existing techniques are limited by drawbacks such as low sensitivity and fluctuations of fluorescence. Therefore, Plank's law offers an appealing relation between the absolute temperature of the system under interrogation and the thermal spectrum. Despite this, thermal radiation spectroscopy is unsuitable for far-field nanothermometry, primarily because of the power loss in the near surroundings and a poor spatial resolution.Comment: 4 pages, 4 figure

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Enhancement of inherent Raman scattering in dielectric nanostructures with electric and magnetic Mie resonances

Resonantly enhanced Raman scattering in dielectric nanostructures has been recently proven to be an effcient tool for developing nanothermometry and experimental determination of their mode- composition. In this paper, we develop a rigorous analytical theory based on the Green's function approach to calculate the Raman emission from crystalline high-index dielectric nanoparticles. As an example, we consider silicon nanoparticles which have a strong Raman response due to active optical phonon modes. We relate enhancement of Raman signal emission to Purcell effect due to the excitation of Mie modes inside the nanoparticles. We also employ the numerical approach to the calculation of inelastic Raman emission in more sophisticated geometries, which do not allow a straightforward analytical form of the Green's function description. The Raman response from a silicon nanodisk has been analyzed within the proposed method, and the contribution of the various Mie modes has been revealed

Quantum-dot based nanothermometry in optical plasmonic recording media

We report on the direct experimental determination of the temperature increment caused by laser irradiation in a optical recording media constituted by a polymeric film in which gold nanorods have been incorporated. The incorporation of CdSe quantum dots in the recording media allowed for single beam thermal reading of the on-focus temperature from a simple analysis of the two-photon excited fluorescence of quantum dots. Experimental results have been compared with numerical simulations revealing an excellent agreement and opening a promising avenue for further understanding and optimization of optical writing processes and media

Optomagnetic Nanoplatforms for In Situ Controlled Hyperthermia

This is the peer reviewed version of the following article: Ortgies, Dirk H., Teran, Francisco J. Rocha, Uéslen, Cueva, Leonar de la, Salas, Gorka, cabrera, David, Vanetsev, Alexander S., Rähn, Mikhel, Väino,Sammelselg, Orlosvkii, Yurii V. and Jaque, Daneil "Optomagnetic nanoplatforms for in situ controlled hyperthermia" Advances Funtcional Materials 28.11 (2018) which has been published in final form at http://doi.org/10.1002/adfm.201704434. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."Magnetic nanoparticles (M:NPs) are unique agents for in vivo thermal therapies due to their multimodal capacity for efficient heat generation under optical and/or magnetic excitation. Nevertheless, their transfer from laboratory to the clinic is hampered by the absence of thermal feedback and by the influence that external conditions (e.g., agglomeration and biological matrix interactions) have on their heating efficiency. Overcoming these limitations requires, first, the implementation of strategies providing thermal sensing to M:NPs in order to obtain in situ thermal feedback during thermal therapies. At the same time, M:NPs should be modified so that their heating efficiency will be maintained independently of the environment and the added capability for thermometry. In this work, optomagnetic hybrid nanostructures (OMHSs) that simultaneously satisfy these two conditions are presented. Polymeric encapsulation of M:NPs with neodymium-doped nanoparticles results in a hybrid structure capable of subtissue thermal feedback while making the heating efficiency of M:NPs independent of the medium. The potential application of the OMHSs herein developed for fully controlled thermal therapies is demonstrated by an ex vivo endoscope-assisted controlled intracoronary heating experimentThis work was supported by the Spanish Ministry of Economy and Competitiveness under Projects # MAT2016-75362-C3-1-R, # MAT2015-71806-R and # MAT2013-47395-C4-3-R, the Comunidad de Madrid (NANOFRONTMAG-CM, S2013/MIT-2850), and through the Instituto de Salud Carlos III under Project # PI16/00812. This work has also received funding from European Union’s H2020 and FP7 programme (NOCANTHER, GA 685795). D.H.O. is grateful to the Spanish Ministry of Economy and Competitiveness for a Juan de la Cierva scholarship (FJCI-2014-21101) and F.J.T. for a Ramon y Cajal fellowship (RYC-2011-09617). COST Actions CM1403 and TD1402 (RADIOMAG) are also acknowledged. The synthesis and preliminary testing of the fluorescence properties of the LaF3:Nd(3%) NPs was supported by Project # 16-12-10077 of the Russian Science Foundation. Nonfluorescent characterization of the OMHSs was supported by projects IUT2-24 and IUT20-54 of the Estonian Ministry of Education and Researc

Heat in optical tweezers

Laser-induced thermal effects in optically trapped microspheres and single cells have been investigated by Luminescence Thermometry. Thermal spectroscopy has revealed a non-localized temperature distribution around the trap that extends over tens of microns, in agreement with previous theoretical models. Solvent absorption has been identified as the key parameter to determine laser-induced heating, which can be reduced by establishing a continuous fluid flow of the sample. Our experimental results of thermal loading at a variety of wavelengths reveal that an optimum trapping wavelength exists for biological applications close to 820 nm. This has been corroborated by a simultaneous analysis of the spectral dependence of cellular heating and damage in human lymphocytes during optical trapping. Minimum intracellular heating, well below the cytotoxic level (43 °C), has been demonstrated to occur for optical trapping with 820 nm laser radiation, thus avoiding cell damage