This PDF file contains the front matter associated with SPIE Proceedings Volume 10350, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Tip-Enhanced Raman Spectroscopy (TERS) affords the spatial resolution of traditional Scanning Probe Microscopy (SPM) while collecting the chemical information provided by RAMAN spectroscopy. This system, further aided by the benefits of Ultra-High Vacuum, is uniquely capable of obtaining surface data that would otherwise be unobtainable with less-specialized methods. Large polyatomic molecular adsorbates on various single crystal surface (Ag, Cu and Au) will be explored in this talk. By investigating substrate structures, superstructures, and the adsorption orientations obtained from vibrational modes, we extract novel surface-chemistry data at an unprecedented spatial (<1nm) and chemical resolution.

This review shows updated experimental cases of tip-enhanced Raman scattering (TERS) operated in solution/liquid systems. TERS in solution/liquid is still infancy, but very essential and challenging because crucial and complicated biological processes such as photosynthesis, biological electron transfer, and cellular respiration take place and undergo in water, electrolytes, or buffers. The measurements of dry samples do not reflect real activities in those kinds of systems. To deeply understand them, TERS in solution/liquid is needed to be developed. The first TERS experiment in solution/liquid is successfully performed in 2009. After that time, TERS in solution/liquid has gradually been developed. It shows a potential to study structural changes of biomembranes, opening the world of dynamic living cells. TERS is combined with electrochemical techniques, establishing electrochemical TERS (EC-TERS) in 2015. EC-TERS creates an interesting path to fulfil the knowledge about electrochemical-related reactions or processes. TERS tip can be functionalized with sensitive molecules to act as a “surface-enhanced Raman scattering (SERS) at tip” for investigating distinct properties of systems in solution/liquid e.g., pH and electron transfer mechanism. TERS setup is continuously under developing. Versatile geometry of the setup and a guideline of a systematic implementation for a setup of TERS in solution/liquid are proposed. New style of setup is also reported for TERS imaging in solution/liquid. From all of these, TERS in solution/liquid will expand a nano-scaled exploration into solution/liquid systems of various fields e.g., energy storages, catalysts, electronic devices, medicines, alternative energy sources, and build a next step of nanoscience and nanotechnology.

In this talk I will present our recent research on the design and preparation of three-dimensional (3D) hierarchical metamaterials and two-dimensional (2D) hierarchical metasurfaces as novel SERS substrates with ultrahigh sensitivity and reproducibility. The former substrate consists of close-packed arrays of nanoholes and uniformly distributed mesopores over the bulk and the second comprised of sub-wavelength-sized conical nanopores and sub-5-nm nanogrooves. Both substrates employ a cascaded field enhancement mechanism, leading to the ultrahigh sensitivity, and have a (quasi)periodic arrangement of plasmonic near-field hot-spots, ensuring excellent structural and signal reproducibility. In particular, the latter substrate is highly mechanically flexible, allowing for extreme adaptability to complex working conditions such as build-in real-time monitoring of trace level molecules. References: [1] X. Zhang, Y. Zheng, X. Liu, W. Lu, J. Dai, D. Y. Lei* & D. R. MacFarlane*, “Hierarchical porous plasmonic metamaterials for reproducible ultrasensitive surface-enhanced Raman Spectroscopy”, Advanced Materials 27, 1090-1096 (2015). [2] C. Xu, Y. Zhou, S. Lyu, Y.-L. Zhang, H. Yao, D. Mo, J. L. Duan* & D. Y. Lei*, “Highly flexible, hierarchical porous plasmonic metasurfaces for reproducible, ultrasensitive surface-enhanced Raman spectroscopy”, under preparation (2017). [3] K. Chen, X. Zhang, Y.-L. Zhang, D. Y. Lei, H. Li, T. Williams & D. R. MacFarlane, "Highly ordered Ag/Cu hybrid nanostructure arrays for ultrasensitive surface-enhanced Raman spectroscopy", Advanced Materials Interfaces 3, 1600115 (2016).

Tip-enhanced Raman scattering (TERS) can be observed highly sensitive spectral image with high spatial resolution. However, it shows low reproducibility due to difference and change in optical properties of the metallic tips. For surfaceenhanced Raman scattering (SERS), the spectra can be reproduced by the scattering spectra due to localized surface plasmon resonance (LSPR) of the individual metallic nanostructures, which observed with a dark field illumination, and the calculated electromagnetic field around the nanostructures. In the present study, we tried to relate TERS spectra with the LSPR spectra and the calculation, in a similar way of SERS. By conventional dark field illumination, LSPR scattering spectra at the apex of the tip were measured and were compared with the corresponding TERS spectra. By excitation using polarization parallel to the tip, the polarized LSPR peak was stronger than that by perpendicular polarization. Also in the case of TERS, the similar trend was observed. It was confirmed whether the vertical polarization to the sample plane (Z-polarization) is effective or not by the polarized LSPR and TERS spectra. By excitation at different wavelengths, moreover, TERS enhancement factors were compared. In the calculation for TERS, the nanostructure like a monopole antenna was adopted, because the EM field is enhanced not at both sides, but at only apex. The dependence on taper and curvature of the tip were compared with the calculated results for the nanostructure like a conventional dipole antenna.

Superresolution microscopy is rapidly becoming an essential tool in the biological sciences allowing imaging biological structure at length scales below 250 nm. Currently, superresolution microscopy has been applied successfully on single cells achieving resolutions of 100nm down to 20nm over a few microns of depth. When superresolution microscopy is applied in thicker samples the resolution rapidly degrades. Optical aberrations and scattering distort and reduce the point spread function causing different superresolution techniques to fail in different ways. I will discuss our work on combining structured illumination microscopy and stochastic optical reconstruction microscopy with adaptive optics to achieve sub-diffraction resolution in thick tissue.

We compare side lobe suppression methods for nonlinear superresolution optical microscopy using phase masked excitation beams. The excitation point spread function (PSF) can be engineered by introducing a phase mask for superresolution microscopy. By applying a single π phase step to the excitation the central spot can be narrowed and provide improved lateral resolution. However, the energy redistribution leads to side lobes with increased intensity that complicates imaging applications. Several methods have been implemented to suppress the strength of the side lobes including confocal detection and utilizing beams with different phase masks in multiphoton microscopy. Side lobe suppression methods using confocal detection and different phase masks for the excitation beams are compared theoretically and experimentally. These results demonstrate the additional flexibility for PSF engineering for nonlinear optical processes.

Raman scattering is a powerful probe of local bonding, strain, temperature, and other properties of materials via their influence on vibrational modes or optical phonons. Tip-enhanced Raman spectroscopy (TERS), in which plasmonic modes are excited at the apex of a metal-coated scanning probe tip, enables Raman scattering signals to be detected from nanoscale volumes with precise positional control. We discuss the application of TERS to characterize a variety of semiconductor nanostructures. In studies of Ge-SiGe core-shell nanowires, we measure spatially resolved Raman spectra along the length of a tapered nanowire to demonstrate the ability to measure local strain distributions with nanoscale spatial resolution. In tip-induced resonant Raman spectroscopy of monolayer and bilayer MoS₂, we observe large enhancements in Raman signal levels measured for MoS₂ associated with excitation of plasmonic gap modes between an Au-coated probe tip and Au substrate surface onto which MoS₂ has been transferred. Transitions in B exciton photoluminescence intensity between monolayer and bilayer regions of MoS₂ are observed and discussed. Significant differences in nanoscale Raman spectra between monolayer and bilayer MoS₂ are also observed. The origins of specific resonant Raman peaks, their dependence on Mo_S2 layer thickness, and spatial resolution associated with the transition in Raman spectra between monolayer and bilayer regions are described.

High-density localization of multiple fluorescent emitters is a common strategy to improve the temporal resolution of super-resolution localization microscopy. In recent years, various high-density localization algorithms have been developed. Despite their rigorous mathematical model and the subsequent improvement in image resolution, they still suffer from high computing complexity and the resulting extremely low computation speed, thus limiting the application to either small dataset or expensive computer clusters. It is still impractical as a routine tool for a large dataset. With the recent advance of high-throughput localization microscopy with sCMOS cameras that can produce a huge amount of data in a short period of time, fast processing now becomes even more important. Here, we present a simple algebraic algorithm based on our previously developed method, gradient fitting, for fast and precise high-density localization of multiple overlapping fluorescent emitters. Through numerical simulation and biological experiments, we showed that our algorithm can yield comparable localization precision and recall rate as DAOSTORM in various densities and signal levels, but with much simpler computation complexity. After being implemented on a GPU device (NVidia GTX1080) for parallel computing, it can run over three orders of magnitude faster than DAOSTORM implemented on a high-end workstation. Therefore, our method presents a possibility for online reconstruction of high-speed super-resolution imaging with high-density fluorescent emitters.

Plasmonically coupled electromagnetic field localization has generated a variety of new concepts and applications, and this has been one of the hottest topics in nanoscience, materials science, chemistry, physics and engineering and increasingly more important over the last decade. In particular, plasmonically coupled nanostructures with ultra-small gap (~1-nm or smaller) gap have been of special interest due to their ultra-strong optical properties that can be useful for a variety of signal enhancements such surface-enhanced Raman scattering (SERS) and nanoantenna. These promising nanostructures with extraordinarily strong optical signal, however, have rendered a limited success in widespread use and commercialization largely due to the lack of designing principles, high-yield synthetic strategies with nm-level structural controllability and reproducibility and lack of systematic single-molecule and single-particle level studies. All these are extremely important challenges because even small changes (~1 nm) of the coupled nanogap structures can significant affect plasmon mode and signal intensity and therefore structural and signal reproducibility and controllability can be in question. The plasmonic nanogap-enhanced Raman scattering (NERS) is defined as the plasmonic nanogap-based Raman signal enhancement within plasmonic nanogap particles with ~1 nm gap and a Raman dye positioned inside the gap.

We present our results in developing nanoscale photoacoustic tomography (nPAT) for label-free super-resolution imaging in 3D. We have made progress in the development of nPAT, and have acquired our first signal. We have also performed simulations that demonstrate that nPAT is a viable imaging modality for the visualization of malaria infected red blood cells (RBCs). Our results demonstrate that nPAT is both feasible and powerful for the high resolution labelfree imaging of RBCs.

We propose a new nano-imaging technique for intrinsic absorption properties of materials under a platform of conventional aperture-less near-field scanning optical microscopy (NSOM). In aperture-less NSOM, when a silicon nanotip is utilized and illuminated by the visible light instead of a metallic tip, Raman scattering of silicon from the tip apex can be obtained. Since the wavelength of this Raman scattered light is shifted to 520cm^-1 from the one of the excitation light, far-field background signal excited by the diffraction limited focus spot of the incident light, which is one of the major problems in aperture-less NSOM, can be avoided. When the silicon nano-tip is on the sample and illuminated, the Raman signal of silicon can be partially absorbed by the sample while passing through it, so that measuring the intensity of the Raman signal of silicon enables us to observe the absorption behavior of the sample at nano-scale. Because the absorbance of light is dependent on the absorption coefficient of the sample as well as its sample topography, it is needed to eliminate the effect of the sample topography from the absorption measurement to technically evaluate the absorption coefficient of the sample. For this purpose, we simultaneously employed two different incident lasers and utilized absorbance ratio between two wavelengths to monitor the absorption coefficient of the sample. As an example, we demonstrated that two types of carbon nanotubes, which have different absorption properties, could be clearly distinguished with nano-scale resolution by our technique.

A sharply focused azimuthally polarized beam (APB) presents a strong longitudinal magnetic field with a vanishing electric field at its beam axis, forming an effective magnetic dominant region at the vicinity. This magnetic dominance is extremely desirable in the proposed high-speed ultra-compact optical magnetic force manipulation and microscopy, where the interaction between matter and the magnetic field of light can be exclusively exploited. However, direct characterization of such beam is challenging due to its subwavelength features. Here we show for the first time a direct characterization on a sharply focused APB in nanoscale using the novel Photoinduced Force Microscopy (PIFM) technique, which simultaneously excites and detects incident beam in near-field. Comparing to the Scanning Near-field Optical Microscopy (SNOM) which has near-field excitation and far-field detection, PIFM boasts a much smaller background noise and a more robust system. Based on the measured force-map, we develop a theoretical model to retrieve the corresponding electric and magnetic field distribution, and correct the distortion caused by the imperfect probe-tip of the PIFM. This research pioneers the exploration in the experimental investigation on the sharply focused structured light, unveiling its potentials in a plethora of optoelectronics, chemical, or biomedical applications.

Super-resolution optical microscopy, commonly referred to as optical nanoscopy, has enabled imaging of biological samples with a resolution that was only achievable previously using electron microscopy. Optical nanoscopy is a rapidly growing field, with several different techniques and implementations that overcome the diffraction limit of light. However, the common nanoscope continues to be a rather complex, expensive and bulky instrument. Direct stochastic optical reconstruction microscopy (dSTORM) imaging was recently demonstrated using a waveguide platform for excitation in combination with a simple microscope for imaging. High refractive index waveguide materials have a high intensity evanescent field stretching around 100-200 nm outside the guiding material, which is ideally suited for total internal reflection fluorescence (TIRF) excitation over large areas. We demonstrate dSTORM imaging of the plasma membrane of liver sinusoidal endothelial cells (LSECs) and trophoblasts (HTR-8 cells) using waveguide excitation, with resolution down to around 70 nm. Additionally, we present TIRF imaging of LSEC micro-tubules over a 500 μm x 500 μm area, laying the foundation for large field of view (f-o-v) nanoscopy.

Similar to the other physical dimensions of light, such as time, space, polarization, wavelength, and intensity, optical angular momentum (AM) is another physically-orthogonal dimension of light. Owing to an unbounded set of orbital angular momentum (OAM) modes carried by helically-phased beams, the availability of using AM-carrying beams as information carrier to generate, transport and detect optical signals has recently been largely explored in both classical and quantum optical communications, suggesting that AM is indeed a promising candidate to dramatically boost the optical multiplexing capacity. However, the extrinsic nature of OAM modes restricts conventional OAM multiplexing to bulky phase sensitive elements, imposing a fundamental limit for realizing on-chip OAM multiplexing. Recently, we demonstrate an entirely-new concept of nanoplasmonic multiplexing of AM of light, which for the first time enables AM multiplexing to be carried out by an integrated device with six orders of magnitude reduced footprint as compared to the conventional OAM detectors. We show that nanoring slit waveguides exhibit a distinctive outcoupling efficiency on tightly-confined plasmonic AM modes coupled from AM-carrying beams. More intriguingly, unlike the linear momentum sensitivity with a typical sharp resonance, the discovered AM mode-sorting sensitivity is nonresonant in nature, leading to an ultra-broadband AM multiplexing ranging from visible to terahertz wavelengths. This nanoplasmonic manipulation of AM of ultra-broadband light offers exciting avenues for future on-chip AM applications in highly-sensitive bio-imaging and bio-sensing, ultrahigh-bandwidth optical communications, ultrahigh-definition displays, and ultrahigh-capacity data storage.

Practical application of optical vortex in a method of three-dimensional profilometry with nanoscale resolution was considered. It was shown that phase analysis of coherent light beam carrying axial optical vortex allow to retrieve information about sample surface relief. High spatial resolution caused by vortex helical phase sensitivity to disturbances in wave front after reflection or spreading through studying sample, which can be optically transparent or have a reflecting surface. This method applicable for non-destructive testing of live cells and biological tissues in real-time regime with exceeding optical diffraction limit. Computer processing of vortex interferograms allow to achieve a vertical resolution down to 1.75 nm. Specially designed optical scheme reduces an environment influence, in particular, vibration, misalignment of test sample and its local anisotropy and provides the possibility of investigating surfaces of large linear dimensions. The prospective tasks of automated systems creation for monitoring of surface quality were proposed, in particular those that will could be developed with methods based on singular optics and phase singularities.