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We demonstrate numerical refocusing in coherent confocal laser scanning microscopy based on synthetic optical holography. This physics-based approach implements a computational propagation on the complex signal recovered in synthetic holography consistent with the wave physics and the parameters of the microscope. An experimental demonstration is shown to restore an in-focus image of a test object from data acquired at several focal plane off-sets. Numerical refocusing can provide focused views on samples with large height variation with a potential application in confocal optical surface profiling.

Optical anapoles are intriguing charge-current distributions characterized by a strong suppression of electromagnetic radiation. They originate from the destructive interference of the radiation produced by electric and toroidal multipoles. Although anapoles in dielectric structures have been probed and mapped with a combination of near- and far-field optical techniques, their excitation using fast electron beams has not been explored so far. Here, we theoretically and experimentally analyze the excitation of optical anapoles in tungsten disulfide (WS$_2$) nanodisks using Electron Energy Loss Spectroscopy (EELS) in Scanning Transmission Electron Microscopy (STEM). We observe prominent dips in the electron energy loss spectra and associate them with the excitation of optical anapoles and anapole-exciton hybrids. We are able to map the anapoles excited in the WS$_2$ nanodisks with subnanometer resolution and find that their excitation can be controlled by placing the electron beam at different positions on the nanodisk. Considering current research on the anapole phenomenon, we envision EELS in STEM to become a useful tool for accessing optical anapoles appearing in a variety of dielectric nanoresonators., 4 figures

Strain is an effective strategy to modulate the optoelectronic properties of 2D materials, but it has been almost unexplored in layered hybrid organic–inorganic metal halide perovskites (HOIPs) due to their complex band structure and mechanical properties. Here, we investigate the temperature-dependent microphotoluminescence (PL) of 2D (C6H5CH2CH2NH3)2Cs3Pb4Br13 HOIP subject to biaxial strain induced by a SiO2 ring platform on which flakes are placed by viscoelastic stamping. At 80 K, we found that a strain of, This work is supported by the Spanish MICINN under Project PID2019-108153GA-I00 and under the María de Maeztu Units of Excellence Programme (MDM-2016-0618). B.M-G. thanks Gipuzkoa Council (Spain) in the frame of Gipuzkoa Fellows Program and to Prof. A. Mateo-Alonso (Molecular and Supramolecular Materials Group - POLYMAT) for the access to the Chemistry Lab to grow the crystals. M.G. acknowledges support from la Caixa Foundation (ID 0010434) for a Junior Leader fellowship (Grant No. LCF/BQ/PI19/11690017).

Scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared nanospectroscopy (nano-FTIR) are emerging tools for physical and chemical nanocharacterization of organic and inorganic composite materials. Being based on (i) diffraction-limited illumination of a scanning probe tip for nanofocusing of light and (ii) recording of the tip-scattered radiation, the efficient suppression of background scattering has been critical for their success. Here, we show that indirect tip illumination via far-field reflection and scattering at the sample can produce s-SNOM and nano-FTIR signals of materials that are not present at the tip position – despite full background suppression. Although these artefacts occur primarily on or near large sample structures, their understanding and recognition are of utmost importance to ensure correct interpretation of images and spectra. Detailed experimental and theoretical results show how such artefacts can be identified and eliminated by a simple signal normalization step, thus critically strengthening the analytical capabilities of s-SNOM and nano-FTIR spectroscopy.

Polaritons are hybrid excitations of matter and photons. In recent years, polaritons in van der Waals nanomaterials—known as van der Waals polaritons—have shown great promise to guide the flow of light at the nanoscale over spectral regions ranging from the visible to the terahertz. A vibrant research field based on manipulating strong light–matter interactions in the form of polaritons, supported by these atomically thin van der Waals nanomaterials, is emerging for advanced nanophotonic and opto-electronic applications. Here we provide an overview of the state of the art of exploiting interface optics—such as refractive optics, meta-optics and moire engineering—for the control of van der Waals polaritons. This enhanced control over van der Waals polaritons at the nanoscale has not only unveiled many new phenomena, but has also inspired valuable applications—including new avenues for nano-imaging, sensing, on-chip optical circuitry, and potentially many others in the years to come. This Review discusses the state of the art of interface optics—including refractive optics, meta-optics and moire engineering—for the control of van der Waals polaritons.

Phonon polaritons (PhPs) in van der Waals (vdW) crystal slabs enable nanoscale infrared light manipulation. Specifically, periodically structured vdW slabs behave as polaritonic crystals (vdW-PCs), where the polaritons form Bloch modes. Because the polariton wavelengths are smaller than that of light, conventional far-field spectroscopy does not allow for a complete characterization of vdW-PCs or for revealing their band structure. Here, we perform hyperspectral infrared nanoimaging and analysis of PhPs in a vdW-PC slab made of h-BN. We demonstrate that infrared spectra recorded at individual spatial positions within the unit cell of the vdW-PC can be associated with its band structure and local density of photonic states (LDOS). We thus introduce hyperspectral infrared nanoimaging as a tool for the comprehensive analysis of polaritonic crystals, which could find applications in the reconstruction of complex polaritonic dispersion surfaces in momentum-frequency space or for exploring exotic electromagnetic modes in topological photonic structures., A.Y.N., L.M.-M., and S.G.R. acknowledge the Spanish Ministry of Science, Innovation and Universities (grant MAT201788358-C3.) A.Y.N. acknowledges the Basque Department of Education (grant PIBA-2020-1-0014). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA and from the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-111156GB-I00). R.H., F.C., and L.E.H. acknowledge the Spanish Ministry of Science, Innovation and Universities (national projects MAT2017-88358-C3, RTI2018-094830-B-100, RTI2018-094861-B-100, and the project MDM-2016-0618 of the Maria de Maeztu Units of Excellence Program). A.Y.N. and R.H. acknowledge funding from the Basque Government (grant no. IT1164-19).

Terahertz radiation has become an important diagnostic tool in the development of new technologies. However, the diffraction limit prevents terahertz radiation (λ ≈ 0.01–3 mm) from being focused to the nanometre length scale of modern devices. In response to this challenge, terahertz scanning probe microscopy techniques based on coupling terahertz radiation to subwavelength probes such as sharp tips have been developed. These probes enhance and confine the light, improving the spatial resolution of terahertz experiments by up to six orders of magnitude. In this Review, we survey terahertz scanning probe microscopy techniques that achieve spatial resolution on the scale of micrometres to angstroms, with particular emphasis on their overarching approaches and underlying probing mechanisms. Finally, we forecast the next steps in the field. Recent progress in terahertz scanning probe microscopy is reviewed with an emphasis on techniques that access length scales below 100 nm relevant to material science. An outlook on the future of nanoscale terahertz scanning probe microscopy is also provided.

Advanced control over the excitation of ultraconfined polaritons—hybrid light and matter waves—empowers unique opportunities for many nanophotonic functionalities, e.g., on-chip circuits, quantum information processing, and controlling thermal radiation. Recent work has shown that highly asymmetric polaritons are directly governed by asymmetries in crystal structures. Here, we experimentally demonstrate extremely asymmetric and unidirectional phonon polariton (PhP) excitation via directly patterning high-symmetry orthorhombic van der Waals (vdW) crystal α-MoO 3 . This phenomenon results from symmetry breaking of momentum matching in polaritonic diffraction in vdW materials. We show that the propagation of PhPs can be versatile and robustly tailored via structural engineering, while PhPs in low-symmetry (e.g., monoclinic and triclinic) crystals are largely restricted by their naturally occurring permittivities. Our work synergizes grating diffraction phenomena with the extreme anisotropy of high-symmetry vdW materials, enabling unexpected control of infrared polaritons along different pathways and opening opportunities for applications ranging from on-chip photonics to directional heat dissipation.

7 pags., 4 figs., Negative reflection occurs when light is reflected toward the same side of the normal to the boundary from which it is incident. This exotic optical phenomenon is not only yet to be visualized in real space but also remains unexplored, both at the nanoscale and in natural media. Here, we directly visualize nanoscale-confined polaritons negatively reflecting on subwavelength mirrors fabricated in a low-loss van der Waals crystal. Our near-field nanoimaging results unveil an unconventional and broad tunability of both the polaritonic wavelength and direction of propagation upon negative reflection. On the basis of these findings, we introduce a device in nano-optics: a hyperbolic nanoresonator, in which hyperbolic polaritons with different momenta reflect back to a common point source, enhancing the intensity. These results pave way to realize nanophotonics in low-loss natural media, providing an efficient route to control nanolight, a key for future on-chip optical nanotechnologies., G.Á.-P. and J.T.-G. acknowledge support through the Severo Ochoa Program from the Government of the Principality of Asturias (grant numbers PA-20-PF-BP19-053 and PA-18-PF-BP17-126, respectively). Q.O. acknowledges support from the Australian Research Council (ARC; CE170100039 and DE220100154). This work was performed in part at the Melbourne Centre for Nanofabrication (MCN) in the Victorian Node of the Australian National Fabrication Facility (ANFF). hBN crystal growth was supported by the National Science Foundation award number CMMI 1538127. V.G. acknowledges the Ministerio de Ciencia, Innovación y Universidades through the grant MELODIA (PGC2018-095777-B-C21). V.G. thanks the “ENSEMBLE 3–Centre of Excellence for nanophotonics, advanced materials and novel crystal growth-based technologies” project (GA no. MAB/2020/14) carried out within the International Research Agendas program of the Foundation for Polish Science cofinanced by the European Union under the European Regional Development Fund and the European Union’s Horizon 2020 research and innovation programme Teaming for Excellence (GA no. 857543) for support of this work. R.H. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (national project RTI2018-094830-B-100 and the project MDM-2016-0618 of the María de Maeztu Units of Excellence Program) and the Basque Government (grant no. IT1164-19). J.M.-S. acknowledges financial support from the Ramón y Cajal Program of the Government of Spain and FSE (RYC2018-026196-I) and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-110308GA-I00). A.Y.N. acknowledges the Spanish Ministry of Science and Innovation (grants MAT201788358-C3-3-R and PID2020-115221GB-C42) and the Basque Department of Education (grant PIBA-2020-1-0014). P.A.-G. acknowledges support from the European Research Council under starting grant no. 715496, 2DNANOPTICA and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation grant number PID2019-111156GB-I00). Q.B. acknowledges the support from Shenzhen Nanshan District Pilotage Team Program (LHTD20170006).

EnglishTrakl confronts a materialistic and an idealistic concept of reality in order to criticize everyday life as deficient and to poetically gain a spiritual counter-reality of orphic inwardness. He uses, based on antique and christian models, a traditional imagery, according to which death appears as a world of shadows, life as a dream or play, and a coherent symbolism. Ultimately, however, this purely subjective search for meaning through the memory of better times fails because of the incurable senselessness of the social and cultural present. DeutschTrakl konfrontiert ein materialistisches und ein idealistisches Wirklichkeitskonzept, um die Alltagsrealitat als defizient zu kritisieren und auf poetische Weise eine geistige Gegenwirklichkeit orphischer Innerlichkeit zu gewinnen. Er benutzt dazu in Anlehnung an antike und christliche Vorbilder eine traditionelle Bildlichkeit, wonach der Tod als Schattenwelt, das Leben als Traum oder Theaterspiel erscheint, und eine in sich stimmige Symbolik. Zuletzt aber scheitert auch diese rein subjektive Sinnsuche der Erinnerung an bessere Zeiten an der unheilbaren Sinnlosigkeit der sozialen und kulturellen Gegenwart.

Polaritons allow for strong light-matter coupling and for highly sensitive analysis of (bio)chemical substances and processes. Nanoimaging of the polaritons' evanescent fields is critically important for experimental mode identification and field confinement studies. Here we describe two setups for polariton nanoimaging and spectroscopy in liquid. We first demonstrate the mapping of localized plasmon polaritons in metal antennas with a transflection infrared scattering-type scanning near-field optical microscope (s-SNOM), where the tip acts as a near-field scattering probe. We then demonstrate a total internal reflection (TIR)-based setup, where the tip is both launching and probing ultraconfined polaritons in van der Waals materials (here phonon polaritons in hexagonal boron nitride flakes), laying the foundation for s-SNOM-based polariton interferometry in liquid. Our results promise manifold applications, for example, in situ studies of strong coupling between polaritons and molecular vibrations or chemical reactions at the bare or functionalized surfaces of polaritonic materials.

Nanoscale Fourier transform infrared spectroscopy (nano-FTIR) is an emerging technique that allows for label-free chemical nanoimaging. Here, we introduce its application to studying multicomponent...

The modeling of the near-field interaction in the scattering-type scanning near-field optical microscope (s-SNOM) is rapidly advancing, although an accurate yet versatile modeling framework that can be easily adapted to various complex situations is still lacking. In this work, we propose a time-efficient numerical scheme in the quasi-electrostatic limit to capture the tip-sample interaction in the near field. This method considers an extended tip geometry, which is a significant advantage compared to the previously reported method based on the point-dipole approximation. Using this formalism, we investigate, among others, nontrivial questions such as uniaxial and biaxial anisotropy in the near-field interaction, the relationship between various experimental parameters (e.g. tip radius, tapping amplitude, etc.), and the tip-dependent spatial resolution. The demonstrated method further sheds light on the understanding of the contrast mechanism in s-SNOM imaging and spectroscopy, while also representing a valuable platform for future quantitative analysis of the experimental observations.

Scattering-type scanning near-field optical microscopy (s-SNOM), and its derivate, Fourier transform infrared nanospectroscopy (nano-FTIR) are emerging techniques for infrared (IR) nanoimaging and spectroscopy with applications in diverse fields ranging from nanophotonics, chemical imaging and materials science. However, spectroscopic nanoimaging is still challenged by the limited acquisition rate of current nano-FTIR technology. Here we combine s-SNOM, nano-FTIR and synthetic optical holographic (SOH) to achieve infrared spectroscopic nanoimaging at unprecedented speed (8 spectroscopically resolved images in 20 min), which we demonstrate with a polymer composite sample. Beyond being fast, our method promises to enable nanoimaging in the long IR spectral range, which is covered by IR supercontinuum and synchrotron sources, but not by current quantum cascade laser technology., 17 pages, 4 figures, plus supplementary information

Integrating and manipulating the nano-optoelectronic properties of Van der Waals heterostructures can enable unprecedented platforms for photodetection and sensing. The main challenge of infrared photodetectors is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. Here, we overcome all of those challenges in one device, by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hexagonal-BN to highly concentrate mid-infrared light into a graphene pn-junction. We balance the interplay of the absorption, electrical and thermal conductivity of graphene via the device geometry. This approach yields remarkable device performance featuring room temperature high sensitivity (NEP of 82 pW/Hz−−−√) and fast rise time of 17 nanoseconds (setup-limited), among others, hence achieving a combination currently not present in the state-of-the-art graphene and commercial mid-infrared detectors. We also develop a multiphysics model that shows very good quantitative agreement with our experimental results and reveals the different contributions to our photoresponse, thus paving the way for further improvement of these types of photodetectors even beyond mid-infrared range., F.H.L.K. acknowledges financial support from the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centres of Excellence in R& D (SEV-2015-0522), support by Fundacio Cellex Barcelona, Generalitat de Catalunya through the CERCA program, and the Agency for Management of University and Research Grants (AGAUR) 2017 SGR 1656. Furthermore, the research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement no. 785219 and no. 881603 Graphene Flagship for Core2 and Core3. ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). K.J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 804349. R.H. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (national project RTI2018-094830-B-100 and the project MDM-2016-0618 of the Marie de Maeztu Units of Excellence Program) and the Basque Government (grant No. IT1164-19). S.C. acknowledges financial support from the Barcelona Institute of Science and Technology (BIST), the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya and the European Social Fund (L’FSE inverteix en el teu futur)—FEDER. D.E. acknowledges partial support from the Army Research Office MURI “Ab-Initio Solid-State Quantum Materials” Grant No. W911NF18-1-0431. J.G. was supported by the ARL-MIT Institute for Soldier Nanotechnologies (ISN). T.S. and L.M.M. acknowledge support by Spain’s MINECO under Grant No. MAT2017-88358-C3-1-R and the Aragon Government through project Q-MAD.

Improving the efficiency of enzymes towards decomposing substrates has been one of the central goals in the biotechnology industry. However, the modification of enzymes for upgrading natural materials to high-value performant materials is largely unexplored. Here, we demonstrate that the ancestral form of a Cel5A bacterial endoglucanase, unlike its modern descendant from Bacillus subtilis, was able to generate cellulose nanocrystals (EnCNC) chemically pure, maintaining native cellulose structure and displaying higher thermal stability and crystallinity than standard CNC obtained by acidic treatment. We demonstrate that EnCNC alone is a suitable matrix to grow cells in 2D and 3D cultures. Importantly, EnCNC accepts well graphene derivatives to fabricate conductive hybrids inks forming a stable flat surface where cells also attach and proliferate. Our results demonstrate that EnCNC has physicochemical properties unattainable with standard CNC, making it a unique material ideal as a matrix for the design of biocompatible advanced materials for tissue engineering and other applications. Enzymes are effective at upgrading natural materials to high-performance biomaterials. Here, an ancestral endoglucanase is used to obtain highly crystalline cellulose nanocrystals, which can act as a matrix for cell growth and be combined with graphene for conducting inks.

Phonon polaritons in polar van der Waals materials enable strong electromagnetic-field confinement and enhancement for deeply subwavelength scale light-matter interactions. Here we propose and theo...

Modern scattering-type scanning near-field optical microscopy (s-SNOM) has become an indispensable tool in material research. However, as the s-SNOM technique marches into the far-infrared (IR) and terahertz (THz) regimes, emerging experiments sometimes produce puzzling results. For example, "anomalies" in the near-field optical contrast have been widely reported. In this Letter, we systematically investigate a series of extreme subwavelength metallic nanostructures via s-SNOM near-field imaging in the GHz to THz frequency range. We find that the near-field material contrast is greatly impacted by the lateral size of the nanostructure, while the spatial resolution is practically independent of it. The contrast is also strongly affected by the connectivity of the metallic structures to a larger metallic "ground plane". The observed effect can be largely explained by a quasi-electrostatic analysis. We also compare the THz s-SNOM results to those of the mid-IR regime, where the size-dependence becomes significant only for smaller structures. Our results reveal that the quantitative analysis of the near-field optical material contrasts in the long-wavelength regime requires a careful assessment of the size and configuration of metallic (optically conductive) structures.

Hexagonal boron nitride (hBN) hosts long-lived phonon polaritons, yielding a strong mid-infrared (mid-IR) electric field enhancement and concentration on the nanometer scale. It is thus a promising material for highly sensitive mid-IR sensing and spectroscopy. In addition, hBN possesses high chemical and thermal stability as well as mechanical durability, making it suitable for operation in demanding environments. In this work, we demonstrate a mid-IR CO2 gas sensor exploiting phonon polariton (PhP) modes in hBN nanoresonators functionalized by a thin CO2-adsorbing polyethylenimine (PEI) layer. We find that the PhP resonance shifts to lower frequency, weakens, and broadens for increasing CO2 concentrations, which are related to the change of the permittivity of PEI upon CO2 adsorption. Moreover, the PhP resonance exhibits a high signal-to-noise ratio even for small ribbon arrays of 30 × 30 μm2. Our results show the potential of hBN nanoresonators to become a novel platform for miniaturized phonon-enhanced SEIRA gas sensors., The research leading to these results has received funding from the H2020 Programme under Grant Agreement No. 881603 (Graphene Flagship). This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 754510. This project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 665884. This work was partially funded by CEX2019-000910-S [MICINN/AEI/10.13039/501100011033] and Project TUNA-SURF (PID2019-106892RB-I00), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya through CERCA. We acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities (RTI2018-094830-B-100 and the Project MDM-2016-0618 of the Maria de Maeztu Units of Excellence Program) and the Basque Government (Grant Number IT1164-19). We acknowledge the Ministry of Science, Innovation and Universities through the ‘Maria de Maezt’ Programme for Units of Excellence in R&D (CEX2018-000805-M). Further, support from the Materials Engineering and Processing program of the National Science Foundation, Award Number CMMI 1538127 for h-BN crystal growth is greatly appreciated. The hBN crystals growth is also supported by an Office of Naval Research Award No. N00014-20-1-2474. I.D. acknowledges the Basque Government (Grant No. PRE_2019_2_0164). We acknowledge Project PID2020-115221GB-C41 financed by MCIN/AEI/10.13039/501100011033 and Aragon Government through Project Q-MAD.

Optical nanoantennas are of great importance for photonic devices and spectroscopy due to their capability of squeezing light at the nanoscale and enhancing light–matter interactions. Among them, nanoantennas made of polar crystals supporting phonon polaritons (phononic nanoantennas) exhibit the highest quality factors. This is due to the low optical losses inherent in these materials, which, however, hinder the spectral tuning of the nanoantennas due to their dielectric nature. Here, active and passive tuning of ultranarrow resonances in phononic nanoantennas is realized over a wide spectral range (≈35 cm−1, being the resonance linewidth ≈9 cm−1), monitored by near-field nanoscopy. To do that, the local environment of a single nanoantenna made of hexagonal boron nitride is modified by placing it on different polar substrates, such as quartz and 4H-silicon carbide, or covering it with layers of a high-refractive-index van der Waals crystal (WSe2). Importantly, active tuning of the nanoantenna polaritonic resonances is demonstrated by placing it on top of a gated graphene monolayer in which the Fermi energy is varied. This work presents the realization of tunable polaritonic nanoantennas with ultranarrow resonances, which can find applications in active nanooptics and (bio)sensing., J.M.-S. acknowledges financial support from the Ramón y Cajal Program of the Government of Spain and FSE (Grant No. RYC2018-026196-I) and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation Grant Number PID2019-110308GA-I00). P.A.-G. acknowledges support from the European Research Council under starting Grant No. 715496, 2DNANOPTICA, and the Spanish Ministry of Science and Innovation (State Plan for Scientific and Technical Research and Innovation Grant Number PID2019-111156GB-I00). G.Á.-P. and J.T.-G. acknowledge support through the Severo Ochoa Program from the Government of the Principality of Asturias (Grant nos. PA20-PF-BP19-053 and PA-18-PF-BP17-126, respectively). A.Y.N. acknowledges the Spanish Ministry of Science and Innovation (Grant Nos. MAT201788358-C3-3-R and PID2020-115221GB-C42) and the Basque Department of Education (Grant No. PIBA-2020-1-0014) J.H.E. acknowledges support for h-BN crystal growth from the National Science Foundation, Award Number CMMI-1538127. R.H. acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities (National Project Grant No. RTI2018-094830-B-100 and the Project Grant No. MDM-2016-0618 of the Marie de Maeztu Units of Excellence Program), the Basque Government (Grant No. IT1164-19), and the European Union's Horizon 2020 research and innovation programme under the Graphene Flagship (Grant Agreement Numbers 785219 and 881603, GrapheneCore2 and GrapheneCore3). I.D. acknowledges the Basque Government (Grant No. PRE_2019_2_0164). Work at MIT was partly supported through AFOSR Grant No. FA9550-16-1-0382, through the NSF QII-TAQS program (Grant No. 1936263), and the Gordon and Betty Moore Foundation EPiQS Initiative through Grant No. GBMF9643 to P.J.-H.

We present the preparation of nanostructured conducting PEDOT:PSS thin films by solvent vapor annealing (SVA), using the low boiling point solvent tetrahydrofuran (THF). An Atomic Force Microscopy (AFM) study allowed the observation of distinct nanostructure development as a function of solvent exposure time. Moreover, the nanostructures’ physical properties were evaluated by nanomechanical, nanoelectrical, and nanoinfrared (nano-FTIR) measurements. In this way, we were able to differentiate the local response of the developed phases and to identify their chemical nature. The combination of these techniques allowed to demonstrate that exposure to THF is a facile method to effectively and selectively modify the surface nanostructure of PEDOT:PSS, and thereafter its final properties. Moreover, our nanoscale studies provided evidence about the molecular rearrangements that PEDOT:PSS suffers during nanostructure fabrication, a fundamental fact in order to expand the potential applications of this polymer in thermoelectric and optoelectronic devices., M. S., A. A. and D. E. M-T, acknowledge funding from the Basque Government (projects codes: IT-1175-19 and IT-1566-22) and the Spanish Ministry of Science and Innovation (MCIU/AEI/FEDER; EU. Code: PID2019-104650GB-C21). R. H. and L. M., acknowledge funding from the Spanish Ministry of Science and Innovation (projects codes: RTI2018-094830-B-100 and MDM-2016-0618 of the Maria de Maeztu Units of Excellence Program) and from the Basque Government (projects codes: IT1164-19).

Scattering-type scanning near-field optical microscopy (s-SNOM) allows for nanoscale optical mapping of manifold material properties. It is based on interferometric recording of the light scattered at a scanning probe tip. For dielectric samples such as biological materials or polymers, the near-field amplitude and phase signals of the scattered field reveal the local reflectivity and absorption, respectively. Importantly, absorption in s-SNOM imaging corresponds to a positive phase contrast relative to a non-absorbing reference sample. Here, we describe that in certain conditions (weakly or non- absorbing material placed on a highly reflective substrate), a slight negative phase contrast may be observed, which can hinder the recognition of materials exhibiting a weak infrared absorption. We first document this effect and explore its origin using representative test samples. We then demonstrate straightforward simple correction methods that remove the negative phase contrast and that allow for the identification of weak absorption contrasts.

The scattering-type scanning near-field optical microscope (s-SNOM) has emerged as a powerful tool for resolving nanoscale inhomogeneities in laterally heterogeneous samples. However, most analytical models used to predict the scattering near-field signals are assuming homogenous landscapes (bulk materials), resulting in inconsistencies when applied to samples with more complex configurations. In this work, we combine the point-dipole model (PDM) to the finite-element method (FEM) to account for the lateral and vertical heterogeneities while keeping the computation time manageable. Full images, spectra, or hyperspectral line profiles can be simulated by calculating the self-consistent dipole radiation demodulated at higher harmonics of the tip oscillation, mimicking real experimental procedures. Using this formalism, we clarify several important yet puzzling experimental observations in near-field images on samples with rich typography and complex material compositions, heterostructures of two-dimensional material flakes, and plasmonic antennas. The developed method serves as a basis for future investigations of nano-systems with nontrivial topography.

Peer reviewed: True, BACKGROUND: Inclusion of cerebrospinal fluid (CSF) oligoclonal IgG bands (OCGB) in the revised McDonald criteria increases the sensitivity of diagnosis when dissemination in time (DIT) cannot be proven. While OCGB negative patients are unlikely to develop clinically definite (CD) MS, OCGB positivity may lead to an erroneous diagnosis in conditions that present similarly, such as neuromyelitis optica spectrum disorders (NMOSD) or neurosarcoidosis. OBJECTIVE: To identify specific, OCGB-complementary, biomarkers to improve diagnostic accuracy in OCGB positive patients. METHODS: We analysed the CSF metabolome and proteome of CDMS (n=41) and confirmed non-MS patients (n=64) comprising a range of CNS conditions routinely encountered in neurology clinics. RESULTS: OCGB discriminated between CDMS and non-MS with high sensitivity (85%), but low specificity (67%), as previously described. Machine learning methods revealed CCN5 levels provide greater accuracy, sensitivity, and specificity than OCGB (79%, +5%; 90%, +5%; and 72%, +5% respectively) while glial fibrillary acidic protein (GFAP) identified CDMS with 100% specificity (+33%). A multiomics approach improved accuracy further to 90% (+16%). CONCLUSION: The measurement of a few additional CSF biomarkers could be used to complement OCGB and improve the specificity of MS diagnosis when clinical and radiological evidence of DIT is absent.