Pseudoheterodyne detection for background-free near-field spectroscopy

Ocelic, N.; Huber, Andreas; Hillenbrand, Rainer

doi:10.1063/1.2348781

Cited by 480 publications

(519 citation statements)

References 28 publications

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“…It is based on an atomic force microscope (AFM), where the tip is illuminated with monochromatic infrared radiation of frequency ω. Recording of the tipscattered infrared field with a pseutoheterodyne interferometer yields infrared amplitude and phase images simultaneously with topography [45]. Strong phase contrast reveals areas of strong molecular vibrational absorption [46,47].…”

Section: Membrane Characterizationmentioning

confidence: 99%

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

Etxeberría-Benavides

David

Johnson

et al. 2018

Journal of Membrane Science

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103

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A R T I C L E I N F O Keywords:Metal organic frameworks ZIF-94 Mixed matrix membrane CO 2 capture A B S T R A C T Carbon capture and storage (CCS) using membranes for the separation of CO 2 holds great promise for the reduction of atmospheric CO 2 emissions from fuel combustion and industrial processes. Among the different process outlines, post-combustion CO 2 capture could be easily implemented in existing power plants. However, for this technology to become viable, new membrane materials have to be developed. In this article we present the development of high performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer matrix. The CO 2 /N 2 separation performance was evaluated by mixed gas tests (15CO 2 :85N 2 ) at 25°C and 1-4 bar transmembrane pressure difference. The CO 2 membrane permeability was increased by the addition of the ZIF-94 particles, maintaining a constant CO 2 /N 2 selectivity of~22. The largest increase in CO 2 permeability of~200% was observed for 40 wt% ZIF-94 loading, reaching the highest permeability (2310 Barrer) at similar selectivity among 6FDA-DAM MMMs reported in literature. For the first time, the ZIF-94 metal organic framework crystals with particle size smaller than 500 nm were synthesized using nonhazardous solvent (tetrahydrofuran and methanol) instead of dimethylformamide (DMF) in a scalable process. Membranes were characterized by three non-invasive image techniques, i.e. SEM, AFM and nanoscale infrared imaging by scattering-type scanning near-field optical microscopy (s-SNOM). The combination of these techniques demonstrates a very good dispersion and interaction of the filler in the polymer layer, even at very high loadings.

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Section: Membrane Characterizationmentioning

confidence: 99%

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

Etxeberría-Benavides

David

Johnson

et al. 2018

Journal of Membrane Science

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103

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“…[20][21][22][23] However, the notorious interference and electromagnetic coupling of the probe tip especially to metallic samples continues to be a troublesome limiting factor. Often it prevents even qualitative interpretation of aSNOM images.…”

mentioning

confidence: 99%

“…The photoelectric signal is therefore not proportional to scattered intensity but the electric field itself. [20][21][22][23] Recording it twice with a relative phase shift of 90°in the reference yields optical amplitude and phase information. Figure 2 (and Figure 4) show representative measurement results for small and large nanodisks.…”

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confidence: 99%

Direct Near-Field Optical Imaging of Higher Order Plasmonic Resonances

et al. 2008

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We map in real space and by purely optical means near-field optical information of localized surface plasmon polariton (LSPP) resonances excited in nanoscopic particles. We demonstrate that careful polarization control enables apertureless scanning near-field optical microscopy (aSNOM) to image dipolar and quadrupolar LSPPs of the bare sample with high fidelity in both amplitude and phase. This establishes a routine method for in situ optical microscopy of plasmonic and other resonant structures under ambient conditions.When nanoscopic metallic structures are illuminated at adequate frequencies, the incoming radiation can couple to charge density oscillations and excite so-called localized surface plasmon polaritons (LSPPs). Recently, the nearfield enhancing qualities of LSPPs have been realized to hold promise for a bounty of novel applications in optics and photonics. 1 These applications often rely on the fine details of LSPPs and their interactions with nanostructures. For example, in the fields of ultra sensitive bio(chemo)detectors 2,3 or plasmonic metamaterials, 4-6 direct near-field optical microscopy of LSPPs would be of great benefit. While spectroscopic far-field properties of LSPP resonances are routinely accessible, real-space near-field information is difficult to obtain.To assess LSPPs of real nanostructures, microscopy techniques are required that are capable of spatially resolving the relevant structure sizes. One approach is the subsequent investigation by means of atomic force microscopy (AFM) of chemical or mechanical changes induced in suitable substrates by the excitation of optical eigenmodes. 7,8 A second approach uses electron energy loss or induced cathode-luminescence scanning electron microscopy to map LSPPs with nanometer resolution. 9,10 This technique requires vacuum compatible samples.For many applications in plasmonics, an all-optical detection of LSPPs with ultimate spatial resolution is called for. Characterizing local optical fields under ambient conditions has been achieved with AFM by carrying nanoscopic optical probes to the immediate vicinity of the nanostructures. [11][12][13][14][15][16] However, such an optical probe has to perform contradicting tasks: as an "optical nano-antenna", its reception/emission efficiency improves with larger size, 17 and as a near-field detector, the achievable spatial resolution improves with smaller size, which can also reduce parasitic interference and coupling effects between probe and sample. 14 In this communication, we demonstrate that these competing demands can be concerted by polarization control of the exciting and scattered radiation, even with off-the-shelf AFM tips as optical probes. We are able to clearly map dipolar and quadrupolar LSPPs, both in phase and in amplitude.In apertureless scanning near field optical microscopy (aSNOM), parasitic background signal from bulk scattering in the sample and tip is often suppressed by anharmonic lockin detection techniques, 18,19 and homodyne, heterodyne, or pseudoheterodyne inte...

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“…1 Sketch of s-SNOM. The basic AFM is operated with its tip-sample separation z modulated at frequency Ω. Backscattering of an applied laser beam is detected interferometrically, in the sketched example using a Michelson configuration and a phase modulation at frequency M for electronic sideband filtering (pseudoheterodyne detection) [6].…”

Section: Experimental Techniquementioning

confidence: 99%

“…5 Mid-infrared near-field microscopy of highly-doped semiconductors Much of the advancement of s-SNOM has been attained using the CO 2 and CO lasers, in the 9-11µm and 5-6µm wavelength regions, respectively [5,6,8,10,11,20,21,24,[27][28][29][30][31][32][33][34][35][36][37]. This came first of all because mid-infrared can be used to exploit chemical fingerprints for recognizing chemical composition, now at nanometric resolution [8,31,33,37,38], but furthermore for technical reasons.…”

Section: Apertureless Near-field Microscopy Development From Microwavmentioning

confidence: 99%

Nanoscale Conductivity Contrast by Scattering-Type Near-Field Optical Microscopy in the Visible, Infrared and THz Domains

Keilmann

Huber

Hillenbrand

2009

J Infrared Milli Terahz Waves

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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 lightscattering channel, wherein a standard cantilevered tip suffices to accomodate the full spectral range from visible to THz frequencies. The optical maps appear in amplitude and phase contrast, simultaneously with the topography map, at a spatial resolution of typically 20 nm. Visible and near-infrared operation is best suited for distinguishing metals, while a sensitive response to semiconductors is ideally provided with infrared and THz operation. Various types of conductivity spectral features can be explored in specific regions, corresponding to the elementary excitation linked to e.g. superconductivity, electron correlation, or low-dimensional conduction.

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Pseudoheterodyne detection for background-free near-field spectroscopy

Cited by 480 publications

References 28 publications

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

Direct Near-Field Optical Imaging of Higher Order Plasmonic Resonances

Nanoscale Conductivity Contrast by Scattering-Type Near-Field Optical Microscopy in the Visible, Infrared and THz Domains

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