This PDF file contains the front matter associated with SPIE Proceedings Volume 10726, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

skipped.

The rational design of electrochemical devices depends on the molecular understanding of the reaction processes under realistic working conditions. To gain insights into molecular adsorption/desorption on solid-liquid interfaces, highly sensitive in-situ molecular detection methods and the ability of controlling the Fermi level are required. In-operando surface-enhanced Raman scattering (EC-SERS) entails both requisites, but is diffraction limited. In contrast, electrochemical tip-enhanced Raman scattering (EC-TERS) offers unprecedented nanoscale chemical resolution of electrified solid-liquid interfaces. Here, we employ both tools, EC-SERS and EC-TERS, to study the Au oxidation/reduction, which represents a fundamental reaction for a wealth of electrochemical/electrocatalytic processes.

This talk will highlight underrated phenomena broadcasted through ultrasensitive surface-enhanced Raman scattering (SERS) and high resolution tip-enhanced Raman scattering (TERS). The ultimate goal of this presentation is to establish that these powerful techniques may be used for much more than mere ultrasensitive chemical detection and nanoscale chemical imaging. Achieving this goal nonetheless necessitates tackling fundamental challenges associated with SERS and TERS, particularly in scenarios where ensemble averaging is no longer appropriate. We identify some of these challenges and describe on-going works aimed at exploring and exploiting the full information content in SERS and TERS.

Plasmon nanofocusing, a phenomenon where plasmons propagate on a tapered metallic structure with compressing its energy into a nanometric volume of the apex to generate localized electric field, holds a great promise for near-field optical imaging techniques due to its background-free nature. Because it does not require to illuminate the tip apex with an incident laser, one can efficiently eliminate scattering background noise by the incident laser, which has been an issue in conventional near-field optical microscopies. To apply plasmon nanofocusing for near-field optical imaging, a tapered metallic tip plays an important role as a base material for plasmon propagation. It is therefore essential to establish an efficient and practical methods of the metallic tip fabrication for plasmon-nanofocusing-based optical imaging techniques. In this study, we propose an optimized tip fabrication for efficient plasmon nanofocusing, which achieved 100% reproducibility in plasmon nanofocusing. Through numerical analysis, we have optimized the tip structure, such as types of material, metal thickness, plasmon coupler structure, etc. Also, the fabrication conditions were well-optimized to obtain smooth metal surface down to 0.5 nm roughness to reduce energy loss of plasmon propagation. Through thorough optimizations, we observed plasmon nanofocusing with 100% reproducibility in more than 20 fabricated metallic tips. Such efficient, reliable and practical tip fabrication opens the doors for many potential scientists working in related fields.

During the last two decades, tip-enhanced Raman spectroscopy (TERS) has emerged as a promising tool for non-destructive and label-free surface chemical imaging at the nanoscale. TERS is increasingly being used for nanoscale chemical charaterisation in a wide range of applications. Furthermore, tip-enhanced plasmonic near-field can also enhance local photoluminescence (PL) and fluorescence signals to perform tip-enhanced PL (TEPL) and fluorescence (TEFL) microscopy. In this article, we demonstrate the application of TERS to map structural defects within single-layer graphene, application of TEPL microscopy to map defects or contaminants within single-layer MoS₂, combination of TERS, TEPL microscopy and photoconductive-atomic force microscopy for simultaneous topographical, chemical and electrical nanoscopy of organic photovoltaic devices and the application of TEFL microscopy to map catalytically active zeolite domains within industrially spent fluid cracking catalyst particles.

2D materials such as graphene and its derivatives and broad class of transition metal dichalcogenides attracted significant attention of the research community during last decade. Tip enhanced optical spectroscopy ( TEOS) that includes tip enhanced Raman spectroscopy (TERS) and tip enhanced photoluminescence (TEPL) allows characterization of defects and inhomogeneities in these materials at nanometer scale, something conventional confocal Raman or photoluminescence microscopy can not do. We observed that the gap mode TERS and TEPL reponse in grpahene, graphene oxide and TMDCs gets significantly enhanced over the wrinkles in 2D sheets. Despite similarity in behavior, the nature of this increased intensity is different for graphene and TMDCs. In case of 2D carbon, D,G,2D modes, all in-plain vibrations, got enhanced over wrinkles due to increased coupling of the optical electric field normal to the sample plain and the vertically aligned portions of 2D sheet in the wrinkles. In case of TMDCs such as WS2, or others, mechanical strain in wrinkles results in funneling of defects and excitons into those areas, which leads to increased concentration of defect bound excitons that demonstrate strongly enhanced and significantly red-shifted PL response, which should be expected taking into account that the binding energy of defect-bound excitons is lower compared to free excitons in 2D materials. Different nature of increased TEOS response in wrinkles of 2D sheets of carbon and TMDCs is further supported by the fact that TERS signal of flat graphene transferred to gold is negligible, since the in-plain modes do not couple to the electric field in the tip-substrate gap, while the TERS signal of flat sheets of TMDCs on gold or silver is very strong, specifically for the out-of-plain modes, which will be illustrated with examples of TERS maps of mono-to few-layer sheets of WS2, MoS2, and MoSe2.

Single-molecule detection provides ever-more powerful tools. Although technological advances have been made, smart image-processing and -analysis strategies are required for quantification, and to combat issues like unspecific background, limited signal, and optical aberrations. These techniques generally increase the usefulness of microscopy data, but the limits to which these results may be interpreted are often poorly quantified. Here, we suggest a meta-data standard for images obtained through fluorescence microscopy that aims to increasing data fidelity, ease future analysis and facilitate objective comparison of different datasets, experimental setups, and essays.

Hybrid lead halide perovskites APbX3 for 3D structures, and A2PbX4 for 2D structures, comprise fully corner-sharing (for 3D) and corner-sharing sheets of Pb-X octahedra for 2D structures. These organic semiconductors are great interests for applications in solar cells and LEDs, due to their high carrier mobility, tunable spectral absorption range and easy processing. In this presentation, the novel optical properties of 3D bulk CH3NH3PbBr3 under high pressure will be discussed. At ~2.3 GPa, photoluminescence intensity is enhanced by ~400 times, and broad emission appear at 4.2 GPa. All structural phases and physical properties are reversible after release. For the CH3NH3PbBr3 nanocrystals (NCs), pressure-induced sintering of 10 nm into nanoplate of 100 nm with different optical and electrical properties is reported. For 2D layered perovskite, the structure-property relationship is resolved and established via a comprehensive pressure study, where the decrease of < Pb-I-Pb> bond angle and Pb-I bond length exhibit an opposite influence on the band gap, i.e., smaller bond angle results a widened band gap, while smaller bond length results a narrowed band gap. In addition, the evolution of hydrogen-bonding and CH3NH3+ (MA) cation orientations in CH3NH3PbBr3 perovskite are investigated at temperature. The H atoms in NH3+ groups form H-bonds in all three polymorphs below room temperature, but with different Br atoms in different phases. However, the H atoms in CH3 groups form H-bonds with Br atoms only in the low-temperature orthorhombic phase. Extensive characterization techniques, including time-resolved spectroscopy, Raman micro-spectroscopy and imaging, photoluminescence and absorption spectroscopy, in-situ X-ray diffraction (XRD) and transmission electron microscopy (TEM) as well as ab initio calculations, are introduced to study the pressure-/temperature-induced structural evolution and physical properties change from hybrid perovskites.

The existence of sub-nm plasmonic hot-spots and its relevance in spectroscopy, microscopy, and photo-chemical applications remain elusive despite a few recent theoretical and experimental evidence. I will present new spectroscopic evidence that angstrom-sized hot-spots do exist on the surfaces of plasmon-excited nanostructures, and that these hot-spots enhance metal - molecule charge-transfer rates. Surface-enhanced Raman scattering (SERS) spectra of 4, 4’-biphenyl dithiols placed in metallic junctions reveal simultaneously blinking Stokes and anti-Stokes spectra, some of which exhibit only one prominent vibrational peak. The activated vibrational modes are found to vary widely between junction-sites. Such site-specific, single-peak spectra could be successfully modeled using single-molecule SERS induced by a hot-spot with a diameter no larger than 3.5 Å, located at specific molecular sites. The model, which assumes the stochastic creation of hot-spots on locally flat metallic surfaces, consistently reproduces the intensity distributions and occurrence statistics of the blinking SERS peaks. We also observe time-resolved Stokes and anti-Stokes SERS spectra of nitrobenzenethiols placed at plasmonic junctions strongly suggesting that such atomic-scale hotspots accelerate the hot-electron transfer between the metallic surface and the molecules, and thus promotes photo-reduction processes on metallic surfaces. This unusual photo-chemical activity of the hot-spots may provide new insight into “chemical” enhancement mechanism in SERS.

Aggregated gold nanoparticles are widely used in surface-enhanced Raman scattering (SERS), however, gold nanoparticles are excellent light absorbers and its local heating effect should be concerned. The optical properties of plasmonic nanoparticles are strongly dependent on interactions with other nanoparticles, which complicates analysis for systems larger than a few particles. In this work we examine heat dissipation in aggregated nanoparticles and its influence on surface-enhanced Raman scattering (SERS) through correlated photothermal heterodyne imaging (PHI). For dimers the per particle absorption cross sections show evidence of interparticle coupling; however, the effects are much smaller than those for the field enhancements that are important for SERS. For larger aggregates the total absorption was observed to be simply proportional to aggregate volume. This observation allows us to model light absorption and heating in the aggregates by assuming that the particles act as independent heating sources. To push the detection limits in PHI of our system, we use the home-built DC-10MHz low noise large area photodiode amplifier and obtain 7 nV/Hz^1/2 noise level which closed to the limitation of SR844 Lock-in amplifier itself. Our work aims to use local heating effects from molecules to improve the spatial resolution and chemical sensitivity of label-free microscopy.

In the paper new experimental techniques for nano-imaging and nano-spectroscopy operating with electromagnetic radiation in the nanometer wavelength range (soft X-rays - SXR and extreme ultraviolet – EUV) are presented. SXR and EUV radiation is generated using laser plasma sources in which a laser plasma is produced by irradiation of a gas puff target with nanosecond laser pulses at intensities of about 1011-1012 Wcm-2 in the interaction region. Commercially available Nd:YAG lasers (EXPLA) generating 4 ns pulses with energy up to 0.8 J at 10 Hz repetition rate are used to irradiate the targets that are formed by pulsed injection of working gas (Xe, Kr, Ar, N2) in an additional annular stream of He gas under high-pressure using a double-nozzle set up (a double-stream gas puff target approach [1]). Laboratory microscopy systems with the use of compact laser plasma sources of soft X-rays and EUV, operating in the ‘water window’ spectral range (wavelength: 2.3–4.4 nm; photon energy: 280–560 eV) or the EUV range at the wavelength of 13.8 nm have been developed [2]. Application of these microscopes for nano-imaging of hydrated and dry biological samples with spatial resolution from 50 nm to 100 nm and relatively short exposition time is presented. Moreover, a recently developed laboratory system for the near-edge X-ray absorption fine structure (NEXAFS) spectroscopy [3] is also presented. The new NEXAFS system has been used for elemental composition analysis of polymer samples. [1] H. Fiedorowicz et al. Appl. Phys. B 70 (2000) 305 [2] P. Wachulak et al. Appl. Sci. 7 (2017) 548 [3] P. Wachulak et al. (2018) - submitted

Our lab has shown that nanoparticles functionalized with short peptides can selectively bind to receptor proteins in vitro. Our results indicate that the Raman signals observed from purified receptors in surface enhanced Raman scattering (SERS) experiments match those observed with tip-enhanced Raman scattering (TERS) experiments performed on membrane receptors in intact cell membranes. Analysis of the observed Raman signals suggest the signals arise from the amino-acids in the protein receptor responsible for binding and recognition of the ligand attached to the nanoparticle probe. Further experiments show the variance in the data correlates with affinity of the nanoparticle probe with a specific receptor. This result illustrates a new approach to studying membrane receptors.

Plasmonically-induced optical heating is a crucial issue for field-enhanced spectroscopy of heat sensitive materials such as biomolecules. Here in this talk, we introduce efficient ways to spectroscopically evaluate the elevated temperature in the vicinity of metallic nanostructures and even to significantly suppress it. As an alternative to plasmonic nanostructures, we also introduce low-loss dielectric nanostructures to achieve complete suppression of the optical heating along with high field enhancement, enabling us to demonstrate field-enhanced spectroscopy of biomolecules without any thermal damages.

Two-dimensional layered materials, such as MoS2, have attracted a lot of research attention after the discovery of graphene. They are often used in optoelectronic devices in the form of a few layers, which are stacked through the weak interlayer van der Walls interactions. The orientations of different layers and their stacking configurations strongly affect the band structure and thus govern the electronic properties of the device. Shear mode and breathing mode vibrations of these layers that arise due to the in-plane and the out of plane vibrations of entire layers can characterize stacking configurations. Since these modes originate from the weak interlayer interactions, they have very low vibrational energies and appear in the extreme low-frequency range in Raman spectrum. Here in this research, we try to identify differences in stacking configurations of MoS2 layers using ultra-low-frequency Raman spectroscopy for small dimensions of the sample

Two-dimensional (2D) transition metal dichalcogenides (TMDs) play important role for optoelectronic applications such as photovoltaics, photodetectors, and field-effect transistors (FETs). However, there are still limited by several problems such as structural defects during the chemical vapor deposition (CVD) growth process, poor photoluminescence (PL) quantum yield (QY) and deeply understanding of exciton dynamics of TMDs. Recently, it was reported that treatment using the superacid bis (trifluoromethane) sulfonamide (TFSI) resulted in a PL QY near 100% in exfoliated 1L-MoS2 monolayers. One of main reason of improved PL QY is due to repair defects induced sulfur vacancies. however, the effects of these chemical treatments varied greatly depending on the synthesis method and the type of 1L-TMD; therefore, the exact origin of the emission enhancement is still challenge. Here, we perform detailed optical characterization of TFSI and 7,7,8,8-tetracyanoquinodimethane (TCNQ) treaded with CVD-grown 1L-MoS2 by using near-field scanning optical imaging and spectroscopy with nanoscale spatial resolution (~80nm). NSOM is optical imaging technique beyond the diffraction limit using narrow aperture that has aperture size much less than the wavelength of light. We found that 1L-MoS2 of systematic variation of the spectral weights among neutral excitons, trions indicated that p-doping by TFSI treatment. However, the PL enhancement was attributed mainly to the reduction of structural defects caused by TFSI treatment. Our results suggest that 1L-MoS2 helps to clarify the mechanism by which chemical treatment enhances the optical properties of 1L-TMDs.

Nitrogen vacancy (NV) quantum defects in diamond provide an unparalleled combination of magnetic field sensitivity and spatial resolution in a room-temperature solid, with wide-ranging applications in both the physical and life sciences.  NVs can be brought into few nanometer proximity of magnetic field sources of interest, such as single proton and electron spins while maintaining long NV spin coherence times, a large (~Bohr magneton) Zeeman shift of the NV spin states, and optical preparation and readout of the NV spin.  I will provide an overview of this nanoscale sensing technology and its diverse applications.

Absorbance modulation enables lateral superresolution in optical lithography and transmission microscopy by generating a dynamic aperture within a photochromic absorbance-modulation layer (AML) coated on a substrate or a specimen. The absorbance-modulation is the property of photochromic molecules modulated between two states. The process is therefore solely controlled by far-field radiation at different wavelengths. The applicability of this concept to reflection microscopy has not been addressed so far, although reflection imaging exhibits the important ability to image a wide range of samples, transparent or opaque, dielectric or metallic. We will present a simulation model for absorbance-modulation imaging (AMI) in confocal reflection microscopy and it is shown that imaging well beyond the diffraction limit is feasible. Our model includes the imaging properties of confocal microscopy, reflections at the boundaries, the photochromic process and diffraction due to propagation through a subwavelength aperture. We derive an analytical design equation which estimates the dependence of the achievable resolution on relevant parameters, such as the AML properties and the applied light powers. This equation is very similar to the corresponding equation for STED (Stimulated emission depletion) microscopy and it is helpful for a fast design of the arrangement of optical setup and AML. As rapid scanning is relevant for a short imaging duration, we further derived an estimation for the pixel dwell time. We prove the validity of these equations by comparing the estimations with the complex numerical simulations. In addition, we show that a resolution enhancement down to 1/5 of the diffraction limit is possible.

The toxicity of amyloids is a subject under intense scrutiny. Many studies link this toxicity to the existence of various intermediate structures prior to the fiber formation and/or their specific interaction with membranes. For the first time, natural Ab1–42 fibrils (WT) implicated in Alzheimers disease, as well as highly toxic oligomers (oG37C), are chemically characterized at the scale of a single structure by Tip-Enhanced Raman Spectroscopy and NanoIR. TERS is a powerful technique combining the high sensitivity of surface-enhanced Raman scattering (SERS) and the nanoscale lateral spatial resolution of atomic force microscopy (AFM). A careful examination of amide I and amide III bands allows us to clearly distinguish WT fibers organized in parallel b-sheets from the small and more toxic oG37C oligomers organized in anti-parallel b-sheets. The interaction between membrane models and Aβ1−42 peptides and variants were also investigated using various biophysical techniques and NanoIR spectroscopy. We established that toxic stable oligomeric form (oG37C) interacts strongly with membranes leading to its disruption.

Tip-enhanced Raman Scattering (TERS) can be used to image plasmon-enhanced local optical fields on the nanoscale. In the few molecule regime where the tensorial nature of Raman scattering is operative, this results in TERS images that directly reflect the local field characteristics. For a well-defined substrate, we can numerically simulate TERS spectral images to identify the effective molecular orientation on the tip that maps any experimentally encountered combination of local electric field components. For a corrugated surface where both the vector components of the local electric fields and the molecular orientation are unknown, we can simulate many spectral features.

Internal information such as mechanical properties and geometrical structures of non-transparent materials can be obtained non-destructively by means of a laser ultrasonic technique. The laser ultrasonic technique measures time of flight of an ultrasonic acoustic pulse generated at the surface of the materials by a pump pulse laser where the acoustic pulse is reflected from the internal structures of the material. The time of the flight of the acoustic pulse can be measured by the time-sequential modulation of the reflectance of a probe laser that is irradiated on the surface of the material. Assuming that the material has a structure of multilayer, each thickness of the multilayer can be reconstructed by fitting of numerical calculations of the time-sequential modulation of the reflectance to the experimental measurements with fitting parameters of the thicknesses. The numerical calculation, however, should solve the spatial distribution of the absorbed energy of the pump laser which determines the shape of the acoustic pulse, the strain tensor of the acoustic pulse, and the reflectance of the probe laser. It likely follows that the three different numerical calculation methods are necessary. Then, an efficient numerical calculation method for the reconstruction of the multi-layer structure using FDTD (Finite Difference Time Domain) algorithm where the method can be applied to the above-mentioned three different calculations in the same frame is proposed here.

A model of multilayer polycrystalline structure of films of biological fluids of human organs has been developed. Each layer is associated with a partial Jones-matrix operator of phase and amplitude anisotropy. A new principle for detecting polarization-inhomogeneous object fields using a coherent laser wave is proposed. Algorithms for digital holographic reconstruction of field distributions of complex amplitudes in the plane of a polycrystalline film of a biological fluid are found. A new optical technique is proposed: direct measurement of 3D distributions of elements of the Jones matrix. Maps of layer-by-layer distributions of elements of the Jones matrix of polycrystalline urine films are studied. Sensitivity, specificity and balanced accuracy of the 3D Jones-matrix tomography method of the polycrystalline structure of urine films of healthy donors and patients with albuminuria were determined. Within the framework of the statistical analysis of stratified maps of elements of the Jones matrix of polycrystalline urine films, objective criteria for the early diagnosis of the onset and course of albuminuria were found.

Novel methods aiming at understanding complex biophysical processes allow revealing the dynamics and behaviour in extreme detail down to a single protein. Developments of fluorescence-based super-resolution microscopy and nanoscopic tracking techniques helped to reach a spatial resolution in length scales below 10 nm. These advances rely on the efficient collection of fluorescence at single-molecule levels. However, complex photophysics and saturation of fluorescent labels limit the temporal resolution to milliseconds timescales. To overcome the spatiotemporal limitations of fluorescent-based techniques we are employing interferometric scattering microscopy (iSCAT). iSCAT is an optical microscopy technique which allows for the detection and localization of extremely low scattering signals. It is based on interference of light scattered on the particle with a reference wave, e.g. light partially reflected at a glass coverslip. The sensitivity of iSCAT was previously proven in detection experiments with small nanoparticles as well as unlabelled single proteins. Here, we show that scattering labels can be imaged and localized with a nanometer precision and a few microseconds temporal resolution. We investigate the limits of fast tracking of scattering labels and identify pitfalls of high-speed collection for which the tracking fidelity drops rapidly due to fluctuations in the label position.

Nanoparticle localization is an important tool for a wide range of applications from biomedical imaging to fluid mechanics and particle dynamics. We present a method for three-dimensional localization of micro- and nanoparticles based on a commonpath digital holographic microscope. In addition to amplitude images of conventional light microscopy, digital holography utilizes additional phase information, which allows three-dimensional representation of objects. While the lateral resolution is diffraction limited, quantitative phase measurement in combination with a novel depth-filtering technique enable an axial localization accuracy which exceeds the lateral resolution by far. This contributes to a more exact localization of particles and allows detailed characterization of structures. Our common-path interferometric setup offers high stability, which is a critical aspect in interferometry, as both reference beam and object beam follow the same optical path. Since it takes advantage of self-referencing it is also very insensitive for instabilities in the sample or sample path. The samples contain nanoparticles of varying size located in a transparent carrier material. They are placed in reflection geometry and illuminated by a diode laser at 760 nm. Their reflection is captured by a microscope objective, which provides the necessary magnification. A phase sensitive sCMOS-camera captures the image, which is then reconstructed using the angular spectrum method and a number of numerical correction methods.

Surface enhanced Raman scattering (SERS) is a powerful technique for food inspection because of its readiness, sensitivity, and minimum sample preparation requirements.¹ Milk is a vulnerable target for contamination. In this work, we demonstrate a reliable SERS method for detecting toxins in milk focusing on brodifacoum, an anticoagulant rodenticide and sodium fluoroacetate, also commonly known as 1080. Surface-enhanced Raman spectroscopy is an advanced Raman technique for ultrasensitive detection of chemical and biological species. Liquid milk presents further challenges due to the complex colloidal nature of milk itself; producing much weaker SERS. Therefore, we applied and omniphobic surface platform, which has the potential to deliver near 100% analyte concentration by constant contact angle drying (and therefore no contact line pinning). Such omniphobic SERS substrates, so-called Slippery liquid-infused porous surfaces (SLIPS) were recently reported.² SLIPSERS method coupled with the dilution of rodenticide spiked milk samples and then extraction with a mixed solvent of methanol: water (3:1) was performed for rodenticide detection.³ All the spectra were taken on an in-house Raman set up based on a Princeton Instruments FERGIE spectrometer using 532 nm excitation wavelength (with 2-3 mW laser power) focused onto the sample using a 40 × 0.65 NA objective. A series of diluted concentrations of each rodenticide ranging from 8- fold dilution to 1600-fold dilution were used to construct a calibration curve. There is a good linear relationship (R² =0.9897) in this concentration range. A critical challenge in detecting bioanalytes is to achieve high specificity, high throughput, and trace-level detection.4 The approach adopted in this work can be extended to detect various molecules in complex chemical and biological matrices.

Actoprobe team had developed custom Tip Enhancement Raman Spectroscopy System (TERS) with specially developed Ultra High Aspect Ratio probes for AFM and TERS measurements for small pixel infrared FPA sidewall characterization. Using this system, we report on stimulated Raman scattering observed in a standard tip-enhanced Raman spectroscopy (TERS) experiment on GaSb materials excited by 637-nm pump laser light. We explain our results by TERS-inherent mechanisms of enormous local field enhancement and by the special design and geometry of the ultrahigh-aspect-ratio tips that enabled conditions for stimulated Raman scattering in the sample with greatly enhanced resonance Raman gain when aided by a microcavity to provide feedback mechanism for the Raman emission. The approach has great potential for further, orders-of-magnitude, progress in TERS enhancement by significantly increasing its nonlinear component. We report development of novel class of probes for atomic force microscopy (AFM active optical probe - AAOP) by integrating a laser source and a photodetector monolithically into the AFM probe. The AAOPs are designed to be used in a conventional AFM and would enhance its functionality to include that of the instruments (NSOM, TERS, hybrid AFM).