Fritz Keilmann

• Senior Researcher at Ludwig-Maximilians-Universität in Munich

We present combined experimental and numerical work on light-matter interactions at nanometer length scales. We report novel numerical simulations of near-field infrared nanospectroscopy that consider, for the first time, detailed tip geometry and have no free parameters. Our results match published spectral shapes of amplitude and phase measuremen...

We present combined experimental and numerical work on light-matter interactions at nanometer length scales. We report numerical simulations of near-field infrared nanospectroscopy that consider detailed tip geometry and have no free parameters. Our results match published spectral shapes of amplitude and phase measurements even for strongly resona...

We report on the first implementation of ultrafast near field measurements carried out with the transient pseudoheterodyne detection method (Tr-pHD). This method is well suited for efficient and artifact free pump-probe scattering-type near-field optical microscopy with nanometer scale resolution. The Tr-pHD technique is critically compared to othe...

We investigated phonon-polaritons in hexagonal boron nitride − a naturally hyperbolic van der Waals material − by means of the scattering-type scanning near-field optical microscopy. Real-space nano-images we have obtained detail how the polaritons are launched when the light incident on a thin hexagonal boron nitride slab is scattered by various i...

We report on the first implementation of ultrafast transient near field nanoscopy carried out with the psuedoheterodyne detection method (Tr-pHD). This method is well suited for efficient and artifact free pump-probe scattering-type near-field optical microscopy with nanometer scale resolution. The Tr-pHD technique is critically compared to other d...

A method has been developed to stabilize and transfer nanofilms of functional organic semiconductors. The method is based on crosslinking of their topmost layers by low energy electron irradiation. The films can then be detached from their original substrates and subsequently deposited onto new solid or holey substrates retaining their structural i...

We investigated emission and propagation of polaritons in a two dimensional van der Waals material hexagonal boron nitride (hBN). Our specific emphasis in this work is on hyperbolic phonon polariton emission that we investigated by means of scattering-type scanning near-field optical microscopy. Real-space nano-images detail how the polaritons are...

Self-detection is demonstrated as a simplifying new operation mode of scattering-type near-field optical microscopy (s-SNOM) in the mid infrared (6.2 μm wavelength). The back-scattered light from a tapping AFM tip is fed back into the quantum cascade laser used as illumination source such that recording of the laser voltage, at harmonics of the tap...

The success of metal-based plasmonics for manipulating light at the nanoscale has been empowered by imaginative designs and advanced nano-fabrication. However, the fundamental optical and electronic properties of elemental metals, the prevailing plasmonic media, are difficult to alter using external stimuli. This limitation is particularly restrict...

Moiré patterns are periodic superlattice structures that appear when two crystals with a minor lattice mismatch are superimposed. A prominent recent example is that of monolayer graphene placed on a crystal of hexagonal boron nitride. As a result of the moiré pattern superlattice created by this stacking, the electronic band structure of graphene i...

We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At sub-nanometer separation, such layers can form either a strongly coupled bilayer graphene with a Bernal stacking or a weakly coupled double-layer graphene with a random stacking order. Effects due to interlayer tunneling dominate in...

Near-field optical microscopy (by scattering from an AFM tip, s-SNOM) returns local absorbance from a tiny volume of only (20 nm) 3 under the tip apex, thus enabling VIS-to-IR-to-THz mapping at exciting 20 nm resolution. The mid-infrared is ideal for nanoscale chemical recognition by vibrational and phonon contrasts. Highlights will be presented of...

div class="title">Infrared Pump-Probe Spectroscopy of Plasmons in Graphene and Semiconductors - Volume 21 Issue S3 - M. Wagner, Z. Fei, A. S. McLeod, S. J. Maddox, A. S. Rodin, W. Bao, E. G. Iwinski, Z. Zhao, M. Goldflam, M. Liu, G. Dominguez, M. Thiemens, M. M. Fogler, A. H. Castro-Neto, C. N. Lau, S. Amarie, F. Keilmann, S. R. Bank, R. D. Averitt...

Scattering scanning near-field optical microscopy (s-SNOM) has emerged as a powerful nano-scale spectroscopic tool capable of characterizing individual biomolecules and molecular materials. However, applications of scattering-based near-field techniques in the infrared (IR) to native biosystems still await a solution of how to implement the require...

We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At sub-nanometer separation, such layers can form either a strongly coupled bilayer graphene with a Bernal stacking or a weakly coupled double-layer graphene with a random stacking order. Effects due to interlayer tunneling dominate in...

Hexagonal boron nitride (h-BN) is a natural hyperbolic material 1 , in which the dielectric constants are the same in the basal plane (ε t ≡ ε x = ε y) but have opposite signs (ε t ε z < 0) in the normal plane (ε z) 1–4. Owing to this property, finite-thickness slabs of h-BN act as multimode waveguides for the propagation of hyperbolic phonon polar...

Uniaxial materials whose axial and tangential permittivities have opposite signs are referred to as indefinite or hyperbolic media. In such materials light propagation is unusual, leading to novel and often non-intuitive optical phenomena. Here we report infrared nano-imaging experiments demonstrating that crystals of hexagonal boron nitride (hBN),...

We have implemented and investigated the tunable hyperbolic response in heterostructures comprised of a monolayer graphene deposited on hexagonal boron nitride (G-hBN) slabs. Electrostatic gating of the graphene layer enables electronic tunability of phonon polaritonic properties of hBN: a layered material with well-documented hyperbolic response i...

Advances in the spatial resolution of modern analytical techniques have tremendously augmented the scientific insight gained from the analysis of natural samples. Yet, while techniques for the elemental and structural characterization of samples have achieved sub-nanometre spatial resolution, infrared spectral mapping of geochemical samples at vibr...

Advances in the spatial resolution of modern analytical techniques have tremendously augmented the scientific insight gained from the analysis of natural samples. Yet, while techniques for the elemental and structural characterization of samples have achieved sub-nanometre spatial resolution, infrared spectral mapping of geochemical samples at vibr...

Controlling the domain size and degree of crystallization in organic films is highly important for electronic applications such as organic photovoltaics, but suitable nanoscale mapping is very difficult. Here we apply infrared-spectroscopic nano-imaging to directly determine the local crystallinity of organic thin films with 20-nm resolution. We fi...

The microwave influence on the growth of yeast cells is studied in a novel experimental set-up designed to observe individual cells growing for several division cycles. The results are in accordance with resonant microwave-induced growth stimulation as observed in our earlier set-up where the turbidity of a stirred suspension of cells was used as t...

Recent observations of nonthermal, resonant biological responses to weak millimeter microwave irradiation have led us to investigate whether similar influences exist on enzymatic functions in vitro. We chose (i) the reduction of ethanol in the presence of alcohol dehydrogenase and (ii) the cooperative binding of oxygen on hemoglobin. Using an irrad...

Weak microwave irradiation of aqueous yeast cultures was found to affect their growth rate in a frequency-selective manner. Depending on frequency (near 42 GHz), both increases and decreases of the growth rate were observed. The resonance bandwidths are of the order of 0.01 GHz. Simple thermal effects can be excluded. These findings support theoret...

A hypothesis is proposed to explain resonant biological effects of microwaves. The interaction is thought to occur with low-frequency electronic transitions of transient triplet (or quartet etc.) molecules. As the transient molecules’ substate populations can be assumed to be far from thermal equilibrium the effect of resonant microwaves would be t...

A recently developed ultra-resolving near-field infrared nanoscope is applied to investigate methyl methacrylate embedded, un-decalcified human bone sections. Results show detail at a resolution of 30 nm. Specific contrasting of mineral components is enabled by choosing an appropriate infrared wavelength, here 9.47 μm, in the phosphate vibrational...

Nanoimaged Polaritons Engineered heterostructures consisting of thin, weakly bound layers can exhibit many attractive electronic properties. Dai et al. (p. 1125 ) used infrared nanoimaging on the surface of hexagonal boron nitride crystals to detect phonon polaritons, collective modes that originate in the coupling of photons to optical phonons. Th...

Pump-probe spectroscopy is central for exploring ultrafast dynamics of fundamental excitations, collective modes, and energy transfer processes. Typically carried out using conventional diffraction-limited optics, pump-probe experiments inherently average over local chemical, compositional, and electronic inhomogeneities. Here, we circumvent this d...

We introduce pump−probe sub-diffraction infrared imaging and spectroscopy with 100fs temporal and 10nm spatial resolution. On graphene single-layers, we demonstrate time-resolved access to local optical conductivity at technologically relevant mid-infrared frequencies

We introduce pump-probe sub-diffraction infrared imaging and spectroscopy with 100fs temporal and 10nm spatial resolution. On graphene single-layers, we demonstrate timeresolved access to local optical conductivity at technologically relevant mid-infrared frequencies.

Graphene, a two-dimensional honeycomb lattice of carbon atoms of great interest in (opto)electronics and plasmonics, can be obtained by means of diverse fabrication techniques, among which chemical vapour deposition (CVD) is one of the most promising for technological applications. The electronic and mechanical properties of CVD-grown graphene depe...

Identification of chemical compounds and their mapping at a 20 ns scale are enabled, by combining FTIR with near-field microscopy. A first application is demonstrated with biominerals and human bone sections. Generally, nano-FTIR yields broad quantitative fingerprint spectra which can directly rely on common IR databases for chemical recognition.

form only given. Fourier-transform infrared (FTIR) spectroscopy is an established technique for characterization and recognition of inorganic, organic and biological materials by their far-field absorption spectra in the infrared fingerprint region. However, due to the diffraction limit conventional FTIR spectroscopy is unsuitable for measurements...

Line defects that are omnipresent in graphene films fabricated with chemical vapor deposition method (CVD) were studied with scanning plasmon interferometry (SPI)---a technique capable of convenient nano-characterization of graphene devices in ambient conditions. The characteristic SPI patterns of line defects are plasmonic twin fringes, which are...

Recently, impressive progress in nanoplasmonics of graphene using near-field spectroscopy and imaging has been reported [Z. Fei et al., Nano Lett. 11, 4701 (2011); Z. Fei et al., Nature 487, 82 (2012)]. However, these studies of the interaction of the graphene plasmon with the SiO2 substrate surface phonon were time-independent. Here we combine ima...

NanoFTIR is a new technique to probe infrared modes below the diffraction limit of FTIR. We apply it here to examine an amorphous Stardust silicate.

We present the application of scanning near-field microscopy and nanoscale broadband infrared spectroscopy to the study of chondrites and presolar grains.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 - August 2, 2012.

Surface plasmons are collective oscillations of electrons in metals or semiconductors that enable confinement and control of electromagnetic energy at subwavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One su...

We demonstrate Fourier transform infrared nanospectroscopy (nano-FTIR) based on a scattering-type scanning near-field optical microscope (s-SNOM) equipped with a coherent-continuum infrared light source. We show that the method can straightforwardly determine the infrared absorption spectrum of organic samples with a spatial resolution of 20 nm, co...

Methods for imaging of nanocomposites based on X-ray, electron, tunneling or force microscopy provide information about the shapes of nanoparticles; however, all of these methods fail on chemical recognition. Neither do they allow local identification of mineral type. We demonstrate that infrared near-field microscopy solves these requirements at 2...

We describe a coherent mid-infrared continuum source with 700 cm-1 usable bandwidth, readily tuned within 600 - 2500 cm-1 (4 - 17 \mum) and thus covering much of the infrared "fingerprint" molecular vibration region. It is based on nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed Er fiber laser system providing two am...

Surface plasmons are collective oscillations of electrons in metals or semiconductors enabling confinement and control of electromagnetic energy at subwavelength scales. Rapid progress in plasmonics has largely relied on advances in device nano-fabrication, whereas less attention has been paid to the tunable properties of plasmonic media. One such...

Near-field infrared spectroscopy has recently been demonstrated with the capability to resolve optical properties of sub-wavelength sample areas across a broad range of infrared frequencies. This method holds promise for the direct identification of sub-wavelength chemical composition in nanostructured and heterogeneous samples. We apply this techn...

We employed near-field infrared (IR) nanoscopy and nanoimaging to study mid-IR nanoplasmonic effects of both single-layer graphene (SLG) and bilayer graphene (BLG) on SiO2/Si substrate. In our previous study, we found that SLG enhanced and blueshifted the surface phonon resonance of SiO2 due to plasmon-phonon coupling [Z. Fei et al. Nano. Lett. 201...

We report on infrared (IR) nanoscopy of 2D plasmon excitations of Dirac fermions in graphene. This is achieved by confining mid-IR radiation at the apex of a nanoscale tip: an approach yielding 2 orders of magnitude increase in the value of in-plane component of incident wavevector q compared to free space propagation. At these high wavevectors, th...

DOI:https://doi.org/10.1103/PhysRevB.84.199904

We apply mid-infrared near-field microscopy with broad-band spectroscopic operation to problems in biomineralization. Inspecting tooth material we find vibrational resonances of phosphate nanocrystals distinctly shifted from bulk phosphates. This is enabled by the extraordinary spectral narrowing promoted by the near-field interaction over far-fiel...

Terahertz time-domain magneto-optics using pulsed magnetic fields is demonstrated with two different approaches. The first uses a fiber coupled high-speed delay line in combination with a long duration pulsed magnet. The second uses a table-top short duration pulsed magnet scanned repetitively and a step-scan readout of the THz electric field.

We use ultra-resolving terahertz (THz) near-field microscopy based on THz scattering at atomic force microscope tips to analyze 65-nm technology node transistors. Nanoscale resolution is achieved by THz field confinement at the very tip apex to within 30 nm. Images of semiconductor transistors provide evidence of 40 nm (λ/3000) spatial resolution a...

We investigate the electronic and structural changes at the nanoscale in vanadium dioxide (VO2) in the vicinity of its thermally driven phase transition. Both electronic and structural changes exhibit phase coexistence leading to percolation. In addition, we observe a dichotomy between the local electronic and structural transitions. Nanoscale x-ra...

We have performed near-field spectroscopic studies of both monolayer suspended graphene (SG) and graphene on SiO2/Si substrate (GOS) using scattering-type scanning near-field optical microscope (s-SNOM). Our data show that SG produces reliable near-field signal in mid-infrared frequencies. Images taken with high spatial resolution (˜20nm) show nano...

Infrared Spectroscopy is a powerful tool for characterizing materials by their vibrational mode fingerprint and/or electron conductivity. Its application to nanoscale resolved studies is highly desirable but remained challenging mainly for two reasons: a suitable source of intense, broadband infrared illumination was not widely available and the sp...

The phonon-enhanced near-field response of polar materials is studied in theory and with a broadband midinfrared near-field microscope that generates spectra in real time. Absolute magnitude and phase spectra are determined for SiC, SiO2, and a-SiO2 at several demodulation orders. The data set is compared with results from two theoretical models of...

We present time-resolved cyclotron resonance spectra of holes in p-Ge measured during single magnetic field pulses by using a rapid-scanning, fiber-coupled terahertz time-domain spectroscopy system. The key component of the system is a rotating monolithic delay line featuring four helicoid mirror surfaces. It allows measurements of THz spectra at u...

We use ultra-resolving terahertz (THz) near-field microscopy based on THz scattering at atomic force microscope tips to analyze 65-nm technology node transistors. Nanoscale resolution is achieved by THz field confinement at the very tip apex to within 30 nm. Images of semiconductor transistors provide evidence of 40 nm (λ/3000) spatial resolution a...

We present time-resolved cyclotron resonance spectra of holes in p-germanium measured during a single magnetic field pulse by using a rapid-scanning, fiber-coupled THz time-domain spectroscopy system.

We demonstrate 300 cm-1 wide spectra in the 800-1400 cm-1 range taken from single pixels of about 20 nm size. Technical issues of coupling a fiber-laser-powered coherent spectrometer with a standard near-field microscope will be discussed, together with results on the phonon-resonant response of numerous crystals. Quantitative amplitude and phase s...

We demonstrate continuous infrared spectra from 20 nm sample spots, by combining dispersive Fourier-transform infrared spectroscopy (FTIR) with scattering near-field microscopy (s-SNOM). With the “apertureless” tip of a standard AFM cantilever in one arm of a Michelson interferometer the spectra arise simultaneously in amplitude and phase. The effe...

Near-field techniques have overcome the diffraction limit that plagues classical light microscopy. Liberated from this century-long constraint the power of infrared/THz spectroscopy can now be unleashed for material inspection at virtually unlimited spatial resolution. In the competition with electron and atomic-force microscopes infrared/THz nanos...

We investigate the percolative insulator-to-metal transition (IMT) in films of the correlated material vanadium dioxide (VO2). Scattering-type scanning near-field infrared microscopy and atomic force microscopy were used to explore the relationship between the nucleation of metallic regions and the topography in insulating VO2. We demonstrate that...

Ultrahigh-resolution (40 nm) near-field microscopy is demonstrated using a 2.5 THz illumination at 118 mum wavelength. In the experiment, this technique is applied to transistors of the 65-nm technology for THz inspection of semiconductor conductivity and carrier mobility. This is made possible by the extreme THz field concentration at the metallic...

We demonstrate the wide application potential of optical near-field microscopy for mapping samples with locally varying conductivity. The apertureless, scattering-type optical near-field microscope (s-SNOM) operates on an AFM basis with an added light-scattering channel, wherein a standard cantilevered tip suffices to accomodate the full spectral r...

We present a detailed infrared study of the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) thin films. Conventional infrared spectroscopy was employed to investigate the IMT in the far-field. Scanning near-field infrared microscopy directly revealed the percolative IMT with increasing temperature. We confirmed that the phase transiti...

We present a detailed infrared study of the insulator-to-metal transition (IMT) in vanadium dioxide (VO2) thin films. Conventional infrared spectroscopy was employed to investigate the IMT in the far field. Scanning near-field infrared microscopy directly revealed the percolative IMT with increasing temperature. We confirmed that the phase transiti...

We determine infrared transmission amplitude and phase spectra of metamaterial samples at well-defined incidence and polarization with a vector ('asymmetric') frequency-comb Fourier-transform spectrometer (c-FTS) that uses no moving elements. The metamaterials are free-standing metallic hole arrays; we study their resonances in the 7–13 μm and 100–...

We introduce ultraresolving terahertz (THz) near-field microscopy based on THz scattering at atomic force microscope tips. Nanoscale resolution is achieved by THz field confinement at the very tip apex to within 30 nm, which is in good agreement with full electro-dynamic calculations. Imaging semiconductor transistors, we provide first evidence of...

A Fourier-transform spectrometer has been developed that can simultaneously determine the amplitude and the phase spectrum. It is based on the interference of two coherent frequency-comb beams and uses no moving part. As its first application, the complex transmission of free-standing metal wire materials is measured at varying, precise incidence s...

Near-field microscopy of scattering type (s-SNOM) has well-known merits in chemical recognition at 20-nm spatial resolution, using infrared vibrational-fingerprint resonances of molecules or crystal lattices. Here we report on s-SNOM application in semiconductor technology and correlated-metal physics, performed both at 10 mum and 118 mum wavelengt...

We demonstrate a metamaterial device whose far-infrared resonance frequency can be dynamically tuned. Dynamic tuning should alleviate many bandwidth-related roadblocks to metamaterial application by granting a wide matrix of selectable electromagnetic properties. This tuning effect is achieved via a hybrid-metamaterial architecture; intertwining sp...

We evaluate the efficiency of back-scattering, η B , from a standard cantilevered AFM probe contacting a flat sample, and also the back-scattering phase. Both quantities are spectroscopically determined over a broad 9-12 μm wavelength range by coherent frequency-comb Fourier-transform spectroscopy (c-FTIR). While Fresnel reflectivity contributes a...

We demonstrate a Fourier-transform infrared (FTIR) spectrometer without moving parts based on frequency-combs where the interference of two coherent frequency-comb beams occurs via wavefront combination, thereby eliminating the need of a dielectric combiner. This enables dispersionless operation over eventually the complete THz-to-visible spectrum...

We investigate the changes in the infrared response due to charge carriers introduced by electrostatic doping of the correlated insulator vanadium dioxide (VO2) integrated in the architecture of the field effect transistor. Accumulation of holes at the VO2 interface with the gate dielectric leads to an increase in infrared absorption. This phenomen...

We report optical imaging at ultrahigh resolution < 30 nm of cross-sectional preparations of state-of-the-art transistors. Our technique employs a scanning optical near-field microscope of scattering type (s-SNOM). It is based on a tapping-mode AFM with a standard, metallized tip, and an interferometric receiver. This detects a pseudo-heterodyne si...

Advances in the field of metamaterials have created many new and exciting devices, but the performance and applicability of these devices to date have been hindered by the reliance on a dispersive resonance. In this talk we present a metamaterial device with the ability to dynamically tune the center frequency of its far-infrared resonance in real-...

The driving mechanism for the temperature-induced insulator-to- metal transition (IMT) in vanadium dioxide (VO2) has been debated for the past five decades. Central to this debate is the relative importance of electron-electron correlations and charge-ordering to the IMT. We report near-field infrared images of VO2 films that directly show the perc...

We demonstrate a scattering-type scanning near-field optical microscope (s-SNOM) with broadband THz illumination. A cantilevered W tip is used in tapping AFM mode. The direct scattering spectrum is obtained and optimized by asynchronous optical sampling (ASOPS), while near-field scattering is observed by using a space-domain delay stage and harmoni...

Electrons in correlated insulators are prevented from conducting by Coulomb repulsion between them. When an insulator-to-metal transition is induced in a correlated insulator by doping or heating, the resulting conducting state can be radically different from that characterized by free electrons in conventional metals. We report on the electronic p...

Electrons in correlated insulators are prevented from conducting by Coulomb repulsion between them. When an insulator-to-metal transition is induced in a correlated insulator by doping or heating, the resulting conducting state can be radically different from that characterized by free electrons in conventional metals. We report on the electronic p...

My contribution is to highlight a recent advance in the area of microscopy: infrared near-field microscopy of the scattering type (infrared s-SNOM). This ultra-resolving infrared microscopy has come quite as a surprise because the >3 mum wavelengths seemed to prohibit - from Abbe's rule - any sub-micrometer resolution. The realization of a 10-nm re...

The nanoscale Infrared scattering-type near-field optical microscopy (IR s-SNOM) method was introduced for IR material recognition and conductivity mapping. The IR s-SNOM technique was based on atomic force microscopy (AFM), and the nanoscale spatial resolution relied on a commercial, Pt-coated, cantilevered tip operating in tapping mode with a 20-...

Third-harmonic generation of high-power millimeter-wave radiation is obtained in bulk semiconductors with low doping. The underlying mechanism is based on the nonlinear response of single mobile electrons. This is in contrast to previously studied centimeter-wave frequency tripling which rests on heating of the carrier gas as a whole at high doping...

In this paper we demonstrate that infrared scattering-type scanning near-field optical microscopy (s-SNOM) allows mapping of different materials and electron concentrations in cross-sectional samples of industrial integrated circuit device structures at nanoscale spatial resolution.

One implementation of coherent frequency-comb spectroscopy (c-FTIR) uses GaSe for the mid-infrared wavelength range 9-11 mum. Here we use direct interference of sample and reference beams on a power detector, the output of which is online-Fourier transformed in a digital scope. This paper illustrate this setup and the achievement of 3000 spectra of...

We report on the nanoscale infrared response of a prototypical ferromagnetic semiconductor Ga1-xMnxAs at Mn doping fractions in the range of x=1.8-7.75 %. These studies have been carried out using an apertureless scattering Scanning Near field Infrared Microscope (s-SNIM) with a pseudoheterodyne detection scheme operating at the wavelength near 10...

We demonstrate real-time recording of chemical vapor fluctuations from 22 m away with a fast Fourier-transform infrared (FTIR) spectrometer that uses a laser-like infrared probing beam generated from two 10-fs Ti:sapphire lasers. The spectrometer's broad 9-12 μm spectrum in the "molecular fingerprint" region is dispersed by fast heterodyne self-sca...

We introduce a new concept of spectroscopic near-field optical microscopy that records broad infrared spectra at each pixel during scanning. Two coherent beams with harmonic frequency-comb spectra are employed, one for illuminating the scanning tip, the other as reference for multi-heterodyne detection of the scattered light. Our implementation yie...

The usefulness of scattering-type near-field optical microscopy for mapping the material and doping in microelectronic devices at nanoscale resolution is demonstrated. Both amplitude and phase of infrared (λ = 10.7 μm) laser light scattered by a metallised, vibrating AFM tip scanned a few nanometers above the sample are detected and transformed int...

We report the application of a new type of Fourier-transform spectroscopy called coherent frequency-comb FTIR. This new spectrometer is used to illuminate and read out a scanning mid-infared near-field microscope. The latter is based on an AFM with commercial, cantilevered tips and works on the principle of light scattering; thus it is named scatte...

We demonstrate that scattering near-field microscopy (s-SNOM) can determine infrared "fingerprint" spectra of individual poly(methyl methacrylate) nanobeads and viruses as small as 18 nm. Amplitude and phase spectra are found surprisingly strong, even at a probed volume of only 10(-20) l, and robust in regard to particle size and substrate. This ma...

The usefulness of scattering-type near-field optical microscopy for mapping the material and doping in microelectronic devices at nanoscale resolution is demonstrated. Both amplitude and phase of infrared (λ = 10.7 μm) laser light scattered by a metallised, vibrating AFM tip scanned a few nanometers above the sample are detected and transformed int...

We demonstrate that scattering-type scanning near-field optical microscopy (s-SNOM) allows nanoscale-resolved imaging of objects below transparent surface layers at both visible and mid-infrared wavelengths. We show topography-free subsurface imaging at λ=633 nm. At λ=10.7 μm, gold islands buried 50 nm below a polymer surface are imaged with a late...