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Surface-enhanced infrared absorption (SEIRA) and surface-enhanced Raman scattering (SERS) represent very effective techniques to detect molecular vibrational fingerprints. These techniques can be improved thanks to the use of plasmonic antennas that produce strong resonant near-fields in their vicinity, enhancing the signal of vibrational samples. Here we study the role of plasmonic absorption and scattering of the hosting antennas in the resulting SEIRA signal. Using numerical simulations of the antenna–sample infrared response, we show that the optimal SEIRA signal measured in transmittance (as extinction) is achieved when the spectral maxima of absorption and scattering of the antennas are of similar magnitude. Paradoxically, when the optimal condition for SEIRA is fulfilled, the decomposition of the signal into the contribution from scattering and from absorption show that the vibrational fingerprint is exclusively a result of the scattering, with no contribution from absorption. Using a simple analytical model for the description of the fundamental resonance of linear nanoantennas made of a Drude-type metal, we provide guidelines for controlling the plasmonic light scattering and light absorption properties, thus showing how the optimal condition for SEIRA can be achieved in practical situations., J.V. and C.H. acknowledge financial support by the Heidelberg Graduate School of Fundamental Physics. C.H. acknowledges financial support by the Helmholtz Graduate School for Hadron and Ion Research. J.A. and T.N. acknowledge the project FIS2013-14481-P from the Spanish Ministry of Economy and Competitiveness (MINECO), and ETORTEK project nanoGUNE’14 from the Department of Industry of the Basque Country Government. F.N. acknowledges financial support by the Baden-Wü rttemberg-Stiftung (PROTEINSENS).

Near-field optical microscopy techniques provide information on the amplitude and phase of local fields in samples of interest in nanooptics. However, the information on the near field is typically obtained by converting it into propagating far fields where the signal is detected. This is the case, for instance, in polarization-resolved scattering-type scanning near-field optical microscopy (s-SNOM), where a sharp dielectric tip scatters the local near field off the antenna to the far field. Up to now, basic models have interpreted S- and P-polarized maps obtained in s-SNOM as directly proportional to the in-plane (Ex or Ey) and out-of-plane (Ez) near-field components of the antenna, respectively, at the position of the probing tip. Here, a novel model that includes the multiple-scattering process of the probing tip and the nanoantenna is developed, with use of the reciprocity theorem of electromagnetism. This novel theoretical framework provides new insights into the interpretation of s-SNOM near-field maps: the model reveals that the fields detected by polarization-resolved interferometric s-SNOM do not correlate with a single component of the local near field, but rather with a complex combination of the different local near-field components at each point (Ex, Ey and Ez). Furthermore, depending on the detection scheme (S- or P-polarization), a different scaling of the scattered fields as a function of the local near-field enhancement is obtained. The theoretical findings are corroborated by s-SNOM experiments which map the near field of linear and gap plasmonic antennas. This new interpretation of nanoantenna s-SNOM maps as a complex-valued combination of vectorial local near fields is crucial to correctly understand scattering-type near-field microscopy measurements as well as to interpret the signals obtained in field-enhanced spectroscopy.

Time-domain interferometry and near-field scanning microscopy are used to investigate infrared phonon polaritons exhibiting hyperbolic dispersion. Negative phase velocity and group velocity as small as 0.002c are confirmed. Polaritons with hyperbolic dispersion are key to many emerging photonic technologies, including subdiffraction imaging, sensing and spontaneous emission engineering1,2,3,4,5,6,7,8. Fundamental to their effective application are the lifetimes of the polaritons, as well as their phase and group velocities7,9. Here, we combine time-domain interferometry10 and scattering-type near-field microscopy11 to visualize the propagation of hyperbolic polaritons in space and time, allowing the first direct measurement of all these quantities. In particular, we study infrared phonon polaritons in a thin hexagonal boron nitride8,12,13 waveguide exhibiting hyperbolic dispersion and deep subwavelength-scale field confinement. Our results reveal—in a natural material—negative phase velocity paired with a remarkably slow group velocity of 0.002c and lifetimes in the picosecond range. While these findings show the polariton's potential for mediating strong light–matter interactions and negative refraction, our imaging technique paves the way to explicit nanoimaging of polariton propagation characteristics in other two-dimensional materials, metamaterials and waveguides.

Grimmelshausen’s language satire on one hand turns patriotic against the foreign word addiction of his time, but mainly criticizes from a Catholic point of view the purism of the Protestant dominated Opitz school. He refers in religious and linguistic respects both to the old use, as it was taught to the Germans by the Latin Rome, and rejects any form of reformation that pretends to restore artificially a supposedly old state, but actually applying arbitrary own inventions and thus putting man’s salvation at risk.

Grimmelshausen’s language satire on one hand turns patriotic against the foreign word addiction of his time, but mainly criticizes from a Catholic point of view the purism of the Protestant dominated Opitz school. He refers in religious and linguistic respects both to the old use, as it was taught to the Germans by the Latin Rome, and rejects any form of reformation that pretends to restore artificially a supposedly old state, but actually applying arbitrary own inventions and thus putting man’s salvation at risk.

We numerically study the local field enhancement of mid-infrared light beating the diffraction limit in an integrated photonic-plasmonic structure. The light is locally transferred from a photonic crystal waveguide to a metallic transmission line on top of it. The transmission line connects the two sections of the photonic crystal waveguide in a passage configuration. The field intensity is locally enhanced in the transmission line passage by a factor larger than 50, with a power transfer efficiency of 33%. This passage structure holds the promise of enabling highly sensitive miniaturized sensing schemes and mid-infrared spectroscopy equipment.

Materials of reduced dimensionality (graphene, thin BN layers, etc.) open new pathways to control electromagnetic fields at the nanoscale by the excitation of tunable and highly confined propagating surface plasmon-polaritons. However, compressing and channeling of plasmons along 2D ribbons suffer from scattering at edges. The concept of using edgeless 2D rolled-up sheets, in particular carbon nanotubes (CNTs), for potential integration into plasmonic nanocircuits has not been explored yet. Apart from supporting plasmons with extremely short wavelengths (providing thus a strong light compression), the optical properties of CNTs are highly sensitive to the environment and external fields. Here, we study the launching and propagation of CNT plasmons in different key plasmonic structures, which include both coupled CNT waveguides and coupled CNT–graphene resonators. We also show an efficient way of launching and phase control of propagating graphene plasmons with the help of a CNT antenna. Combining CNTs wit...

As a two-dimensional semimetal, graphene offers clear advantages for plasmonic applications over conventional metals, such as stronger optical field confinement, in situ tunability, and relatively low intrinsic losses. However, the operational frequencies at which plasmons can be excited in graphene are limited by the Fermi energy E

Metallic split ring resonators have achieved broad interest in the field of metamaterials and light matter interaction in general. We present split ring resonators fabricated from the van-der Waals material Boron Nitride and designed to operate in the reststrahlen band arround 1400 cm−1. We observe two distinct modes in far field transmission spectra exhibiting high quality factors of 55 and 88. Simulations allow to identify the lowest mode as an LC-mode for which the displacement current is provided by the phononinc material instead of electrons as in metallic counterparts.

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, the Mineco grants Ramón y Cajal (RYC-2012-12281) and Plan Nacional (FIS2013-47161-P and FIS2014-59639-JIN), and support from the Government of Catalonia trough the SGR grant (2014-SGR-1535). Furthermore, the research leading to these results has received funding from the European Union Seventh Framework Programme under grant agreement no.696656 Graphene Flagship, and the ERC starting grant (307806, CarbonLight). Y.G. and J.H. acknowledge support from the US Office of Naval Research N00014-13-1-0662. P.A.-G. acknowledges funding from the Spanish Ministry of Economy and Competitiveness through the national projects FIS2014-60195-JIN., Woessner, A.; Parret, R.; Davydovskaya, D.; Gao, Y.; Wu, JS.; Lundeberg, M. B.; Nanot, S.; Alonso González, P.; Watanabe, K.; Taniguchi, T.; Hillenbrand, R.; Fogler, M. M.; Hone, J.; Koppens, F. H. L.

Infrared nanospectroscopy enables novel possibilities for chemical and structural analysis of nanocomposites, biomaterials or optoelectronic devices. Here we introduce hyperspectral infrared nanoimaging based on Fourier transform infrared nanospectroscopy with a tunable bandwidth-limited laser continuum. We describe the technical implementations and present hyperspectral infrared near-field images of about 5,000 pixel, each one covering the spectral range from 1,000 to 1,900 cm−1. To verify the technique and to demonstrate its application potential, we imaged a three-component polymer blend and a melanin granule in a human hair cross-section, and demonstrate that multivariate data analysis can be applied for extracting spatially resolved chemical information. Particularly, we demonstrate that distribution and chemical interaction between the polymer components can be mapped with a spatial resolution of about 30 nm. We foresee wide application potential of hyperspectral infrared nanoimaging for valuable chemical materials characterization and quality control in various fields ranging from materials sciences to biomedicine., In hyperspectral imaging a broadband spectrum is recorded at each pixel, which creates information-rich images. Here, the authors combine this concept with Fourier transform infrared nanospectroscopy to achieve 5,000-pixel, nanoscale-resolution images at wavelengths between 5 and 10 micrometres.

Background. Treatment with omalizumab, a humanized recombinant monoclonal anti-IgE antibody, results in clinical efficacy in patients with Chronic Spontaneous Urticaria (CSU). The mechanism of action of omalizumab in CSU has not been elucidated in detail. Objectives. To determine the effects of omalizumab on levels of high affinity IgE receptor-positive (FceRI+) and IgE-positive (IgE+) dermal cells and blood basophils. Treatment efficacy and safety were also assessed. Study design. In a double-blind study, CSU patients aged 18‑75 years were randomized to receive 300 mg omalizumab (n=20) or placebo (n=10) subcutaneously every 4 weeks for 12 weeks. Changes in disease activity were assessed by use of the weekly Urticaria Activity Score (UAS7). Circulating IgE levels, basophil numbers and levels of expression of FceRI+ and IgE+ cells in the skin and in blood basophils were determined. Results. Patients receiving omalizumab showed a significantly greater decrease in UAS7 compared with patients receiving placebo. At Week 12 the mean difference in UAS7 between treatment groups was -14.82 (p=0.0027), consistent with previous studies. Total IgE levels in serum were increased after omalizumab treatment and remained elevated up to Week 12. Free IgE levels decreased after omalizumab treatment. Mean levels of FceRI+ skin cells in patients treated with omalizumab 300 mg were decreased at Week 12 compared with baseline in the dermis of both non-lesional and lesional skin, reaching levels comparable with those seen in healthy volunteers (HVs). There were no statistically significant changes in mean FcɛRI+ cell levels in the placebo group. Similar results were seen for changes in IgE+ cells, although the changes were not statistically significant. The level of peripheral blood basophils increased immediately after treatment start and returned to Baseline values after the follow-up period. The levels of FceRI and IgE expression on peripheral blood basophils were rapidly reduced by omalizumab treatment up to Week 12. Conclusions. Treatment with omalizumab resulted in rapid clinical benefits in patients with CSU. Treatment with omalizumab was associated with reduction in FcɛRI+ and IgE+ basophils and intradermal cells.

Resumen del póster presentado a la International Conference on Nanoscience + Technology (ICN+T), celebrada en Brno (Czech Republic) del 22 al 27 de julio de 2018., Graphene plasmons (GPs) have shown strong potentials for many interesting applications, such as tunable metamaterials, optical modulators, molecular sensors, among others. When a graphene sheet is placed above a metallic substrate separated from graphene by a dielectric spacer, it can support a particularly interesting GP mode – acoustic graphene plasmons (AGPs). AGPs can provide strong electromagnetic field confinement and enhancement in the dielectric spacer, thus being promising candidates for field enhanced infrared molecular spectroscopy, particularly for probing small amounts of molecules. Here we propose and demonstrate numerically an AGP nanoresonator for sensing, consisting of a GP nanodisk separated from a metallic film by a nanometric spacer. Compared to conventional GPs, AGPs exhibit a much higher spontaneous emission rate, higher sensitivity to the dielectric permittivity inside the AGP nanoresonator and remarkable capability to enhance molecular vibrational fingerprints of nanoscale analyte samples. Our work opens novel avenues for sensing of ultra-small volume of molecules, as well as for studying enhanced light-matter interaction, e.g. strong coupling applications.

Enhanced light-matter interactions are the basis of surface-enhanced infrared absorption (SEIRA) spectroscopy, and conventionally rely on plasmonic materials and their capability to focus light to nanoscale spot sizes. Phonon polariton nanoresonators made of polar crystals could represent an interesting alternative, since they exhibit large quality factors, which go far beyond those of their plasmonic counterparts. The recent emergence of van der Waals crystals enables the fabrication of high-quality nanophotonic resonators based on phonon polaritons, as reported for the prototypical infrared-phononic material hexagonal boron nitride (h-BN). In this work we use, for the first time, phonon-polariton-resonant h-BN ribbons for SEIRA spectroscopy of small amounts of organic molecules in Fourier transform infrared spectroscopy. Strikingly, the interaction between phonon polaritons and molecular vibrations reaches experimentally the onset of the strong coupling regime, while numerical simulations predict that vibrational strong coupling can be fully achieved. Phonon polariton nanoresonators thus could become a viable platform for sensing, local control of chemical reactivity and infrared quantum cavity optics experiments., We also acknowledge support from the European Commission under the Graphene Flagship (GrapheneCore1, Grant no. 696656), the Marie SklodowskaCurie individual fellowship (SGPCM-705960), the Spanish Ministry of Economy and Competitiveness (Maria de Maetzu Units of Excellence Programme MDM-2016-0618 and national projects FIS2014-60195-JIN, MAT2014-53432- C5-4-R, MAT2015-65525-R, MAT2015-65159-R, FIS2016-80174-P, MAT2017- 88358-C3-3-R), the Basque government (PhD fellowship PRE-2016-1-0150, PRE-2016-2-0025), the Department of Industry of the Basque Government (ELKARTEK project MICRO4FA), the Regional Council of Gipuzkoa (project no. 100/16) and the ERC starting grant 715496, 2DNANOPTICA.

Polaritons in layered materials—including van der Waals materials—exhibit hyperbolic dispersion and strong field confinement, which makes them highly attractive for applications including optical nanofocusing, sensing and control of spontaneous emission. Here we report a near-field study of polaritonic Fabry–Perot resonances in linear antennas made of a hyperbolic material. Specifically, we study hyperbolic phonon–polaritons in rectangular waveguide antennas made of hexagonal boron nitride (h-BN, a prototypical van der Waals crystal). Infrared nanospectroscopy and nanoimaging experiments reveal sharp resonances with large quality factors around 100, exhibiting atypical modal near-field patterns that have no analogue in conventional linear antennas. By performing a detailed mode analysis, we can assign the antenna resonances to a single waveguide mode originating from the hybridization of hyperbolic surface phonon–polaritons (Dyakonov polaritons) that propagate along the edges of the h-BN waveguide. Our work establishes the basis for the understanding and design of linear waveguides, resonators, sensors and metasurface elements based on hyperbolic materials and metamaterials., Here, the authors report a near-field study of hyperbolic phonon polaritons in linear antennas made of hexagonal boron nitride. Infrared nanospectroscopy and nanoimaging experiments reveal sharp Fabry-Perot resonances with large quality factors, exhibiting atypical modal behaviour.

The response of an electron system to electromagnetic fields with sharp spatial variations is strongly dependent on quantum electronic properties, even in ambient conditions, but difficult to access experimentally. We use propagating graphene plasmons, together with an engineered dielectric-metallic environment, to probe the graphene electron liquid and unveil its detailed electronic response at short wavelengths.The near-field imaging experiments reveal a parameter-free match with the full theoretical quantum description of the massless Dirac electron gas, in which we identify three types of quantum effects as keys to understanding the experimental response of graphene to short-ranged terahertz electric fields. The first type is of single-particle nature and is related to shape deformations of the Fermi surface during a plasmon oscillations. The second and third types are a many-body effect controlled by the inertia and compressibility of the interacting electron liquid in graphene. We demonstrate how, in principle, our experimental approach can determine the full spatiotemporal response of an electron system., Comment: 8 pages, 4 figures

Terahertz (THz) fields are widely used for sensing, communication and quality control. In future applications, they could be efficiently confined, enhanced and manipulated well below the classical diffraction limit through the excitation of graphene plasmons (GPs). These possibilities emerge from the strongly reduced GP wavelength, λ

Modulating the amplitude and phase of light is at the heart of many applications such as wavefront shaping, transformation optics, phased arrays, modulators and sensors. Performing this task with high efficiency and small footprint is a formidable challenge. Metasurfaces and plasmonics are promising , but metals exhibit weak electro-optic effects. Two-dimensional materials, such as graphene, have shown great performance as modulators with small drive voltages. Here we show a graphene plasmonic phase modulator which is capable of tuning the phase between 0 and 2{\pi} in situ. With a footprint of 350nm it is more than 30 times smaller than the 10.6$\mu$m free space wavelength. The modulation is achieved by spatially controlling the plasmon phase velocity in a device where the spatial carrier density profile is tunable. We provide a scattering theory for plasmons propagating through spatial density profiles. This work constitutes a first step towards two-dimensional transformation optics for ultra-compact modulators and biosensing.

We demonstrate that functional infrared transmission lines (TLs) with gap widths of 25 and 5 nm can be fabricated by gallium and helium ion beam milling of gold films thermally evaporated on insulating substrates. Interferometric and polarization-resolved scattering-type scanning near-field microscopy at λ0 = 9.3 μm is applied to image in real space the propagation and confinement of the TL modes. Mapping the p-polarized scattered field, we obtain the distribution of the out-of-plane near-field component of the mode. When s-polarized scattered field is detected, we map the strongly confined in-plane fields propagating inside the gap. With decreasing gap width, we experimentally confirm the predicted reduction of mode diameter Dm, wavelength λm, and propagation length Lm. For TLs with 25 nm gap width we experimentally verify λm = 5.1 μm mode wavelength and Dm = 42 nm mode diameter (λ0/220). The propagation length is about Lm = 8.3 μm, which is more than 2 orders of magnitude larger than the mode diameter; ...

Trabajo presentado al Microscopy & Microanalysis Meeting, celebrado en Baltimore (USA) del 5 al 9 de agosto de 2018., AK acknowledges Thermo Fisher Scientific and the Czechoslovak Microscopic Society scholarship for young researchers.

The images of a church service with animal figures — in Strasbourg cathedral —, later destroyed, are characteristically interpreted by the Protestant Fischart and the Catholic Nas in favour of their own denomination, although they agree in their misunderstanding of the actual meaning of the images. The view of Nas that heretical dissenters are criticized through the animals, is more convincing than the attempt by Fischart to see the medieval sculptors as critics of the church and thus as precursors of Protestantism.

Scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier transform infrared nanospectroscopy (nano-FTIR) are emerging tools for nanoscale chemical material identification. Here, we push s-SNOM and nano-FTIR one important step further by enabling them to quantitatively measure local dielectric constants and infrared absorption. Our technique is based on an analytical model, which allows for a simple inversion of the near-field scattering problem. It yields the dielectric permittivity and absorption of samples with 2 orders of magnitude improved spatial resolution compared to far-field measurements and is applicable to a large class of samples including polymers and biological matter. We verify the capabilities by determining the local dielectric permittivity of a PMMA film from nano-FTIR measurements, which is in excellent agreement with far-field ellipsometric data. We further obtain local infrared absorption spectra with unprecedented accuracy in peak position and shape, which is the key to quantitative chemometrics on the nanometer scale.

We perform far-field spectroscopy of infrared metal antennas on silicon oxide layers of different thickness, where we find a splitting of the plasmonic resonance. This splitting can result in a transparency window, corresponding to suppression of antenna scattering, respectively "cloaking" of the antenna. Backed up by theory, we show that this effect is caused by strong coupling between the metal antenna plasmons and the surface phonon polaritons in the oxide layer. The effect is a kind of induced transparency in which the strength of the phonon-polariton field plays the crucial role. It represents a further tuning possibility for the optical performance of infrared devices.

Optical activity and circular dichroism are fascinating physical phenomena originating from the interaction of light with chiral molecules or other nano objects lacking mirror symmetries in three-dimensional (3D) space. While chiral optical properties are weak in most of naturally occurring materials, they can be engineered and significantly enhanced in synthetic optical media known as chiral metamaterials, where the spatial symmetry of their building blocks is broken on a nanoscale. Although originally discovered in 3D structures, circular dichroism can also emerge in a two-dimensional (2D) metasurface. The origin of the resulting circular dichroism is rather subtle, and is related to non-radiative (Ohmic) dissipation of the constituent metamolecules. Because such dissipation occurs on a nanoscale, this effect has never been experimentally probed and visualized. Using a suite of recently developed nanoscale-measurement tools, we establish that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating., The effect of Ohmic dissipation in two-dimensional chiral materials has never been experimentally verified. Here, Khanikaev et al. demonstrate that the circular dichroism in a nanostructured metasurface occurs due to handedness-dependent Ohmic heating.

Controlling, detecting and generating propagating plasmons by all-electrical means is at the heart of on-chip nano-optical processing. Graphene carries long-lived plasmons that are extremely confined and controllable by electrostatic fields; however, electrical detection of propagating plasmons in graphene has not yet been realized. Here, we present an all-graphene mid-infrared plasmon detector operating at room temperature, where a single graphene sheet serves simultaneously as the plasmonic medium and detector. Rather than achieving detection via added optoelectronic materials, as is typically done in other plasmonic systems, our device converts the natural decay product of the plasmon-electronic heat-directly into a voltage through the thermoelectric effect. We employ two local gates to fully tune the thermoelectric and plasmonic behaviour of the graphene. High-resolution real-space photocurrent maps are used to investigate the plasmon propagation and interference, decay, thermal diffusion, and thermoelectric generation.

Recently, so-called "superlenses", made from metamaterials that are structured on a length scale much less than an optical wavelength, have shown impressive diffraction-beating image resolution, but they use materials with negative dielectric responses, and they absorb much of the light in a way that seriously degrades both the resolution and brightness of the image. Here we demonstrate an alternative "quantum metamaterials" (QM) approach that uses materials structured at the nanoscale, i.e., comparable to an electron wavelength. This allows us to use quantum mechanical design principles to generate structures with a highly elliptical isofrequency dispersion characteristic that circumvents this loss problem. The physics of the loss improvement is analyzed analytically and the QM superlens subdiffraction imaging is modeled numerically, with a finite-element method. Finally, we demonstrate a working QM superlens device, utilizing intersubband transitions between the confined electron states in a III-V semiconductor multiquantum-well. It images down to a resolution of better than ∼ λ/10 and has loss figures improved by roughly a decade over previous "classical" designs. This QM approach is an alternative paradigm for designing radiation-manipulating devices and offers the prospect of practical super-resolving devices at new wavelengths and geometries.

Chiral antennas and metasurfaces can be designed to react differently to left- and right-handed circularly polarized light, which enables novel optical properties such as giant optical activity and negative refraction. Here, we demonstrate that the underlying chiral near-field distributions can be directly mapped with scattering-type scanning near-field optical microscopy employing circularly polarized illumination. We apply our technique to visualize, for the first time, the circular-polarization selective nanofocusing of infrared light in Archimedean spiral antennas, and explain this chiral optical effect by directional launching of traveling waves in analogy to antenna theory. Moreover, we near-field image single-layer rosette and asymmetric dipole–monopole metasurfaces and find negligible and strong chiral optical near-field contrast, respectively. Our technique paves the way for near-field characterization of optical chirality in metal nanostructures, which will be essential for the future development of chiral antennas and metasurfaces and their applications., The authors acknowledge support by the European Union through ERC starting grants (TERATOMO Grant 258461); the Spanish Ministry of Economy and Competitiveness (National Projects MAT2012-36580, MAT2012-37638, and FIS2013-41184P) and from the Basque Government (Project PI2011-1 and project ETORTEK nanogune’14). G.S. acknowledges support by the Office of Naval Research (Grant N00014-13-1-0837).

yperbolic polaritons in van der Waals materials recently attract a lot of attention, owing to their strong electromagnetic field confinement, ultraslow group velocities and long lifetimes. Typically, volume confined hyperbolic polaritons (HPs) are studied. Here we show the first near-field optical images of hyperbolic surface polarities, HSPs, which are confined and guided at the edges of thin flakes of a vdW material. To that end, we applied scattering-type scanning near-field optical microscopy (s-SNOM) for launching and real-space nanoimaging of hyperbolic surface phonon polariton modes on a hexagonal boron nitride, h-BN, flake. Our imaging data reveal that the fundamental HSP mode exhibits stronger field confinement, smaller group velocities and nearly identical lifetimes, as compared to the fundamental HP mode of the same h-BN flake. Our experimental data, corroborated by theory, establish a solid basis for future studies and applications of HPs and HSPs in vdW materials., This document is the Accepted Manuscript version of a Published Work that appeared in final form in Nano Letters, copyright \c{opyright} American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see: https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.6b03920

We present and demonstrate scattering-type near-field microscopy (s-SNOM) with circularly polarized illumination to map the chiral near-field distributions in metal nanostructures. We apply our technique to Archimedean spiral antennas and resolve circular polarization resolved nanofocusing of infrared light. Moreover, we near-field image single-layer chiral metasurfaces and connect the observed near-field response with circular dichroism in the far field. Our technique opens new ways of characterizing optical chirality in the near field of metal nanostructures which will be essential in the future development of chiral antennas and metasurfaces.

Research and development of nanomaterials, especially those made of organic molecules, has rapidly increased in the last couple of years. Novel nanomaterials exhibit extraordinary material properties and will have a huge impact on chemical, pharmaceutical, and microelectronic products of the near future.

We study the propagation of mid-infrared surface plasmons on non-tapered and tapered two-wire transmission lines on Si and CaF2 substrates, the two materials representing substrates with large and small refractive index, respectively. A comparative numerical study predicts a larger effective wavelength and an increased propagation length (i.e. weaker damping) for the CaF2 substrate. By near-field microscopy we image the near-field distribution along the transmission lines and experimentally verify surface plasmon propagation. Amplitude- and phase-resolved near-field images of a non-tapered transmission line on CaF2 reveal a standing wave pattern caused by back-reflection of the surface plasmons at the open-ended transmission line. Calculated and experimental near-field images of tapered transmission lines on Si and CaF2 demonstrate that for both substrates the mid-IR surface plasmons are compressed when propagating along the taper. Importantly, the nanofocus at the taper apex yields a stronger local field enhancement for the low-refractive index substrate CaF2. We assign the more efficient nanofocusing on CaF2 to the weaker damping of the surface plasmons.

Background: Activation of somatostatin receptors (sstr1–5) by somatostatin and its analogues exerts an inhibitory effect on hormone secretion and provides the basis for the treatment of a range of endocrine diseases such as acromegaly, Cushing’s disease and neuroendocrine tumors (NET). The lack of well-characterized commercially available sstr subtype-specific antibodies prevents routine identification of the sstr expression profile in patients. Methods: We generated and characterized new mouse monoclonal antibodies (mAbs) targeting the five human sstr subtypes using ELISA and immunohistochemistry, and tested their suitability in formalin-fixed and paraffin-embedded (FFPE) human tissues and archival samples of normal pancreatic tissue and NET. Results: All mAbs were highly specific with no cross-reactivity. The sstr1–5 immunoreactivity in gastrointestinal NET (n = 67) was correlated with clinicopathologic data. With the exception of sstr3, NET were highly positive for all receptor subtypes (42, 63, 6, 32 and 65% of tumors were positive for sstr1, sstr2a, sstr3, sstr4 and sstr5, respectively). sstr1, sstr2a and sstr5 were present at the plasma membrane and in the cytoplasm of tumor cells, whereas sstr3 and sstr4 were almost exclusively cytoplasmic. Immunoreactivity of sstr1, sstr2a and sstr4 tended to decrease as tumor aggressiveness increased. sstr5 showed an opposite pattern, with higher staining in well-differentiated carcinomas compared with well-differentiated tumors. sstr5 immunoreactivity was correlated with the presence of metastases and angioinvasion, suggesting a possible association with more aggressive behavior. Conclusion: Determination of the sstr1–5 by immunohistochemistry using subtype-specific mAbs is feasible in FFPE tissue and may provide a tool for routine clinical practice.

We introduce a new perspective on magnetoplasmonics in nickel nanoferromagnets by exploiting the phase tunability of the optical polarizability due to localized surface plasmons and simultaneous magneto-optical activity. We demonstrate how the concerted action of nanoplasmonics and magnetization can manipulate the sign of rotation of the reflected light’s polarization (i.e., to produce Kerr rotation reversal) in ferromagnetic nanomaterials and, further, how this effect can be dynamically controlled and employed to devise conceptually new schemes for biochemosensing. © 2011 American Chemical Society., A.D. and Z.P. acknowledge support from the Swedish Research Council and Swedish Foundation for Strategic Research (Framework program Functional Electromagnetic Metamaterials, project RMA08). J.Å. acknowledges support from the Swedish Research Council, the Swedish Foundation for Strategic Research (Future Research Leader Programme), and the G€oran Gustafsson Foundation. J.Å. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. V.B. acknowledges the G€oran Gustafsson Foundation and the Blanceflor Boncompagni-Ludovisi Foundation. P.V. acknowledges funding from the Basque Government through the ETORGAI Program, Project No. ER- 2010/00032 and Program No. PI2009-17, the Spanish Ministry of Science and Education under Projects No. CSD2006-53 and No. MAT2009-07980. J.N. acknowledges funding for the Generalitat de Catalunya and the Spanish Ministry of Science and Education through No. 2009-SGR-1292 and No. MAT2010-20616-C02 projects.

Infrared absorption spectroscopy is a powerful and widely used tool for analyzing the chemical composition and structure of materials. Because of the diffraction limit, however, it cannot be applied for studying individual nanostructures. Here we demonstrate that the phase contrast in substrate-enhanced scattering-type scanning near-field optical microscopy (s-SNOM) provides a map of the infrared absorption spectrum of individual nanoparticles with nanometer-scale spatial resolution. We succeeded in the chemical identification of silicon nitride nanoislands with heights well below 10 nm, by infrared near-field fingerprint spectroscopy of the Si-N stretching bond. Employing a novel theoretical model, we show that the near-field phase spectra of small particles correlate well with their far-field absorption spectra. On the other hand, the spectral near-field contrast does not scale with the volume of the particles. We find a nearly linear scaling law, which we can attribute to the near-field coupling between the near-field probe and the substrate. Our results provide fundamental insights into the spectral near-field contrast of nanoparticles and clearly demonstrate the capability of s-SNOM for nanoscale chemical mapping based on local infrared absorption.

Using a tapered two-wire transmission line, researchers experimentally focus mid-infrared energy to a nanoscale confined spot with a diameter of 60 nm at the taper apex.

An unprecedented control of the spectral response of plasmonic nanoantennas has recently been achieved by designing structures that exhibit Fano resonances. This new insight is paving the way for a variety of applications, such as biochemical sensing and surface-enhanced Raman spectroscopy. Here we use scattering-type near-field optical microscopy to map the spatial field distribution of Fano modes in infrared plasmonic systems. We observe in real space the interference of narrow (dark) and broad (bright) plasmonic resonances, yielding intensity and phase toggling between different portions of the plasmonic metamolecules when either their geometric sizes or the illumination wavelength is varied. © 2011 American Chemical Society., P.A.-G, M.S., P.S., P.A., and R.H. acknowledge support from the European FP7 project “Nanoantenna” (FP7-HEALTH-F5-2009-241818-NANOANTENNA) and the National Project MAT2009-08393 from the Spanish Ministerio de Ciencia e Innovacion. M.S. and P.S. acknowledges financial support from “Programa de Formación de Personal Investigador” promoted by the Department of Education, Universities and Research of the Basque Government. P.N. and H.S. acknowledge support from the Robert A. Welch foundation (C-1222), the US Department of Defense NSEFF program (N00244-09-1-0067), and the Office of Naval Research (N00244-09-1-0989). C.W., N.A., A. K., and G.S. acknowledge support from the Office of Naval Research (N00014-10-1-0929) and the Air Force Research Laboratory.

7 páginas, 6 figuras.-- El pdf del artículo es la versión post-print.-- et al., The fundamental optical properties of pure nickel nanostructures are studied by far-field extinction spectroscopy and optical near-field microscopy, providing direct experimental evidence of the existence of particle plasmon resonances predicted by theory. Experimental and calculated near-field maps allow for unambiguous identification of dipolar plasmon modes. By comparing calculated near-field and far-field spectra, dramatic shifts are found between the near-field and far-field plasmon resonances, which are much stronger than in gold nanoantennas. Based on a simple damped harmonic oscillator model to describe plasmonic resonances, it is possible to explain these shifts as due to plasmon damping., Supported by the European FP7 project ‘Nanoantenna’ (FP7-HEALTH-F5-2009-241818-NANOANTENNA) and the National Project MAT2009 –08398 from the Spanish Ministerio de Ciencia e Innovacion. J.A. acknowledges fi nancial help by the Department of Industry of the Basque Government through the ETORTEK program NANOPHOT. P.V. acknowledges funding from the Basque Government under Programs No. PI2009–17 as well as the Spanish Ministry of Science and Education under Project No. MAT2009–07980. Z. P. acknowledges support from Swedish Foundation for Strategic Research through RMA08–0109 “Functional Electromagnetic Metamaterials” program. J. N. acknowledges funding from the Generalitat de Catalunya and the Spanish Ministry of Science and Education through No. 2009-SGR-1292 and No. MAT2010–20616-C02 projects. A.D. acknowledges support from the Swedish Research Council.

4 páginas, 3 figuras.-- SpringerOpen., The electromagnetic interaction of light with polar materials shows a sharp and well defined electromagnetic response in the infrared (IR) region that consists mainly of excitation of optical phonons. Similar to surface plasmons in the visible region, surface phonons can couple efficiently to infrared light in micron-sized antennas made of polar materials. We applied the boundary element method to calculating the infrared electromagnetic response of single SiC disks acting as effective infrared antennas as a function of different parameters such as disk size and thickness. We also analyzed the effect of locating a probing metallic tip near the SiC disk to scatter light in the proximity of the SiC disk, thereby obtaining new spectral peaks connected with localized modes between the tip and the SiC disk. We then further investigated their application in IR scanning probe microscopy. A near-field map of the phononic resonances enhances the understanding of the nature of the IR extinction peaks.

Grimmelshausen gestaltet mit Springinsfelds Erzählung seines eigenen Lebens die unvollkommene Erzählperspektive eines zwar bekehrbaren, aber noch nicht bekehrten Sünders, der die nötige Selbsterkenntnis nicht erreicht hat und sich daher zur eigenständigen Autorschaft nicht qualifiziert. Die Aufgabe, das von Simplicius korrigierte Erzählen des Titelhelden poetisch zu vermitteln, wird an Philarchus Grossus übertragen, weil er im Gegensatz zu Springinsfeld nicht nur die Fehler der Mitmenschen, sondern auch seine eigenen einzusehen gelernt hat. Durch die Erzählerschachtelung können nicht nur Parallelen im Verhalten der drei Helden, sondern auch Differenzen in ihrer Reaktion auf das Gehörte programmatisch aufgezeigt werden. Der Bekehrungsversuch an Springinsfeld durch simplicianische Erzählanleitung beweist in Verbindung mit der Gaukeltaschenallegorie den engen Zusammenhang von Grimmelshausens moralisch-religiösen und poetologisch-ästhetischen Grundsätzen.

Probing conductivity in a contactless way with nanoscale resolution is a pressing demand in such active fields as quantum materials, superconductivity, and molecular electronics. Here, we demonstrate a laser- and cryogen-free microwave-technology-based scattering-type scanning near-field optical microscope powered by an easily aligned free-space beam with a tunable frequency up to 0.75 THz. It uses Schottky diode components to record background-free amplitude and phase nano-images, for the first time in the terahertz range, which is uniquely sensitive for assessing conduction phenomena. Images of Si with doped nanostructures prove a conductance sensitivity corresponding to 1016 cm−3 mobile carriers, at 50 nm spatial resolution.

5 páginas, 4 figuras.-- El pdf del artículo es la versión pre-print.-- et al., We describe transmission-mode scattering-type near-field optical microscopy (s-SNOM) with interferometric detection. Using this technique, we map the near-field modes of infrared antennas in both amplitude and phase. The use of dielectric probing tips, higher-harmonic demodulation, and a complex-valued subtraction of residual background yields accurate near-field images of the antenna modes. We map metallic nanorods, disks, and triangles, designed for antenna resonance at mid-infrared frequencies, in good agreement with numerical calculations of the modal field distribution. Furthermore, we show that transmission-mode s-SNOM can map the z-component of the antenna near fields. Our results establish a basis for future near-field characterization of complex antenna structures for molecular sensing and spectroscopy., Supported by the Etortek program of the Department of Industry of the Basque Government and the European FP7 project “Nanoantenna” (Health-F5-2009- 241818).

The control of optical fields on the nanometer scale is a central theme of plasmonics and nanophotonics. Methods for characterizing localized optical field distributions are necessary to validate theoretical predictions, to test nanofabrication procedures, and to provide feedback for design improvements. Typical methods of probing near fields (e.g., single molecule fluorescence and near-field microscopy) cannot probe both the complex-valued and vectorial nature of the field distributions. We demonstrate that a nanoparticle probe with isotropic polarizability in combination with polarization control of excitation and detection beams provides access to this information through the interaction tensor. For a sample consisting of a single nanoparticle we show that the recorded images correspond to maps of the local Green's function tensor elements that couple the probe and sample. The tensorial mapping of interacting nanoparticles is of interest for optical sensing, optical antennas, surface-enhanced Raman scattering, nonlinear optics, and molecular rulers.

Silicon carbide (SiC) is often used for electronic devices operating at elevated temperatures. Spectroscopic temperature measurements are of high interest for device monitoring because confocal Raman microscopy provides a very high spatial resolution. To this end, calibration data are needed that relate Raman line-shift and temperature. The shift of the phonon wavenumbers of single crystal SiC was investigated by Raman spectroscopy in the temperature range from 3 to 112°C. Spectra were obtained in undoped 6HSiC as well as in undoped and nitrogen-doped 4HSiC. All spectra were acquired with the incident laser beam oriented parallel as well as perpendicular to the c-axis to account for the anisotropy of the phonon dispersion. Nearly all individual peak centers were shifting linearly towards smaller wavenumbers with increasing temperature. Only the peak of the longitudinal optical phonon A1(LO) in nitrogen-doped 4HSiC was shifting to larger wavenumbers. For all phonons, a linear dependence of the Raman peaks on both parameters, temperature and phonon frequency, was found in the given temperature range. The linearity of the temperature shift allows for precise spectroscopic temperature measurements. Temperature correction of Raman line-shifts also provides the ability to separate thermal shifts from mechanically induced ones. Copyright © 2009 John Wiley & Sons, Ltd.

Optical and infrared antennas enable a variety of cutting-edge applications ranging from nanoscale photodetectors to highly sensitive biosensors. All these applications critically rely on the optical near-field interaction between the antenna and its ‘load’ (biomolecules or semiconductors). However, it is largely unexplored how antenna loading affects the near-field response. Here, we use scattering-type near-field microscopy to monitor the evolution of the near-field oscillations of infrared gap antennas progressively loaded with metallic bridges of varying size. Our results provide direct experimental evidence that the local near-field amplitude and phase can be controlled by antenna loading, in excellent agreement with numerical calculations. By modelling the antenna loads as nanocapacitors and nanoinductors, we show that the change of near-field patterns induced by the load can be understood within the framework of circuit theory. Targeted antenna loading provides an excellent means of engineering complex antenna configurations in coherent control applications, adaptive nano-optics and metamaterials., This research was supported by the Etortek program of the Department of Industry of the Basque Government and the Basque Foundation for Science (Ikerbasque). J.A. acknowledges CSIC special intramural project PIE 2008601039.

Knowledge about strain at the nanometre scale is essential for tailoring the mechanical and electronic properties of materials. Flaws, cracks and their local strain fields can be detrimental to the structural integrity of many solids1,2. Conversely, the controlled straining of silicon can be used to improve the performance of electronic devices3,4,5. Here, we demonstrate that infrared near-field microscopy6 allows direct, non-invasive mapping and a semiquantitative analysis of residual strain fields in polar semiconductor crystals with nanometre-scale resolution. Our experiments with silicon carbide crystals yield optical images of nanoindents showing strain features as small as 50 nm and the evolution of nanocracks. In addition, by imaging nanoindents in doped silicon, we provide experimental evidence for plasmon-assisted near-field imaging of free-carrier properties in nanoscale strain fields. Near-field infrared strain mapping provides possibilities for nanoscale material and device characterization, and could become a tool for nanoscale mapping of the local free-carrier mobility in strain-engineered semiconductors. Knowledge about strain at the nanoscale is essential for tailoring the mechanical and electronic properties of materials. It has now been shown that infrared near-field microscopy can provide direct, non-invasive mapping of residual strain fields, with nanoscale resolution. In addition, plasmon-assisted near-field imaging of free-carrier properties in nanoscale strain fields has been demonstrated.

We demonstrate that mid-infrared surface phonon polariton excitation, propagation and interference can be studied by scattering-type near-field optical microscopy (s-SNOM). In our experiments we image surface phonon polaritons (SPPs) propagating on flat SiC crystals. They are excited by weakly focused illumination of single or closely spaced metal disks we fabricated on the SiC surface by conventional photolithography. SPP imaging is performed by pseudo-heterodyne interferometric detection of infrared light scattered by the metal tip of our s-SNOM. The pseudo-heterodyne technique simultaneously yields optical amplitude and phase images which allows us to measure the SPP wave vector--including its sign--and the propagation length and further to study SPP interference. High resolution imaging of SPPs could be applied to investigate for example SPP focusing or heat transfer by SPPs in low dimensional nanostructures.

Nanostructures are at the heart of ever-shrinking electronic and photonic devices. The engineering of nanocomposite materials, building blocks, and conduction properties necessitate advanced microscopy tools to assess critical dimensional, compositional, structural, and conduction properties for analysis and quality control. Here we demonstrate with industrial bipolar and metal-oxide-semiconductor (MOS) devices that mid-IR scattering-type near-field optical microscopy (s-SNOM) has the potential to probe all of these parameters, and thereby excels electron and other scanning-probe microscopies. Within a single IR image, all relevant components such as Al, Ti, TiN, Si, Si3N4, and SiO2 are positively identified by material-specific amplitude and phase contrasts in addition to local conductivity in the form of mobile-carrier concentration, here over the range 10–10 cm. We image cross sections of the devices routinely prepared for failure analysis at 30 nm resolution, and this limit could be pushed below 10 nm in the course of future development. Resolution combined with high specificity to material and conductivity properties makes IR s-SNOM a promising tool beyond the microelectronics field for chemical nanotechnology, molecular electronics, photonics, and bioanalytics. IR spectroscopy has tremendous merit in the chemical and structural analyses of materials and in conduction assessment, but until now the limited spatial resolution has prevented its application in industrial failure analysis and quality control. Instead, scanning electron microscopy (SEM) is employed, which offers nanoscale resolution and sensitivity to materials, particularly when combined with Auger, energy-dispersive X-ray (EDX), or wavelength-dispersive X-ray (WDX) spectroscopies. However, only qualitative doping information with decoration-etched samples can be obtained. Transmission electron microscopy (TEM) offers elemental sensitivity in combination with EDX or electron energy loss spectroscopy (EELS), but it suffers from complicated and time-consuming sample preparation. Moreover, the feature sizes of semiconductor structures have already been reduced below the minimum thickness of TEM samples so that details can no longer be imaged. Scanning probe microscopy (SPM) provides topography, and in the extended versions of scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM), also doping but poor material sensitivity. We introduce IR s-SNOM as a method of choice, as SNOM generally extends SPM by the optical near-field interaction between tip and sample, and it thus enables the power of optical spectroscopies, such as fluorescence, Raman, or IR, to be exploited with nanoscale spatial resolution. In particular, IR s-SNOM has a demonstrated specificity to chemical composition, material category, structural variation, and electrical conduction. Our IR s-SNOM technique is based on atomic force microscopy (AFM) as described previously; imaging relies on a commercial, Pt-coated, cantilevered tip operating in tapping mode (frequency X ≈ 30 kHz) with a 20–30 nm radius of curvature. The tip is illuminated by a focused CO2 laser beam at a wavelength k = 10.7 lm. The backscattered light is analyzed interferometrically to record both amplitude and phase. Pure near-field image contrast is attained by pseudoheterodyne interferometric detection at a harmonic frequency nX, with n>1, yielding amplitude sn and phase!n signals simultaneously. According to a point-dipole model, these parameters relate to the complex dielectric value of the sample, e= e1 + ie2. Thus, s-SNOM enables us to distinguish the different materials and doping levels that can be described by a point-dipole model. In this model the field E scattered by the tip is approximated by a dipolar near-field interaction between the tip apex and the sample surface, yielding