Robust_TIE_Solver.m

This function is utilized to robustly solve the transport-of-intensity equation (TIE) for retrieving the pseudo-phase of samples

Detecting 20 nm Wide Defects in Large Area Nanopatterns Using Optical Interferometric Microscopy

Due to the diffraction limited resolution and the presence of speckle noise, visible laser light is generally thought to be impractical for finding deep subwavelength defects in patterned semiconductor wafers. Here, we report on a nondestructive low-noise interferometric imaging method capable of detecting nanoscale defects within a wide field of view using visible light. The method uses a common-path laser interferometer and a combination of digital image processing techniques to produce 70 μm by 27 μm panoramic phase and amplitude images of the test nanopattern. Significant noise reduction and high sensitivity are achieved, which enables successful detection of several different types of sparse defects with sizes on the order of 20 nm wide by 100 nm long by 110 nm tall

Plasmonic Metal–Insulator–Metal Capped Polymer Nanopillars for SERS Analysis of Protein–Protein Interactions

The advancement of SERS as an analytical tool requires substrates that provide both sensitive and reproducible measurements. In this work, a gold–titanium dioxide–gold metal–insulator–metal capped polymer nanopillar array SERS substrate is presented and optimized for SERS-based biosensing applications. The optical properties of the multilayered nanoantenna array are investigated using a combination of simulation and experimental studies. It is found that hot spot engineering, the plasmon resonance of the array, and cavity structure optimization all contribute to fundamental SERS sensor properties such as enhancement factor and enhancement factor uniformity, which are critically studied using this highly tunable device. A spatially averaged enhancement factor of (2.4 ± 0.8) × 10⁷ with sufficient error for quantitative studies is demonstrated at an excitation wavelength of 633 nm. The label-free detection of protein–protein interactions on the metal–insulator–metal nanopillar array surface is then demonstrated including for the cancer biomarker cancer antigen 125 at a concentration of 100 ng/mL

Spectrometer-Free Plasmonic Biosensing with Metal–Insulator–Metal Nanocup Arrays

The development of high performing and accessible sensors is crucial to future point-of-care diagnostic sensing systems. Here, we report on a gold–titanium dioxide–gold metal–insulator–metal plasmonic nanocup array device for spectrometer-free refractometric sensing with a performance exceeding conventional surface plasmon resonance sensors. This device shows distinct spectral properties such that a superstrate refractive index increase causes a transmission intensity increase at the peak resonance wavelength. There is no spectral shift at this peak and there are spectral regions with no transmission intensity change, which can be used as internal device references. The sensing mechanism, plasmon–cavity coupling optimization, and material properties are studied using electromagnetic simulations. The optimal device structure is determined using simulation and experimental parameter sweeps to tune the cavity confinement and the resonance coupling. An experimental sensitivity of 800 Δ<i>T</i>%/RIU is demonstrated. Spectrometer-free, imaged-based detection is also carried out for the cancer biomarker carcinoembryonic antigen with a 10 ng/mL limit of detection. The high performance and distinct spectral features of this metal–insulator–metal plasmonic nanocup array make this device promising for future portable optical sensing systems with minimal instrumentation requirements

Measuring the Nonuniform Evaporation Dynamics of Sprayed Sessile Microdroplets with Quantitative Phase Imaging

We demonstrate real-time quantitative phase imaging as a new optical approach for measuring the evaporation dynamics of sessile microdroplets. Quantitative phase images of various droplets were captured during evaporation. The images enabled us to generate time-resolved three-dimensional topographic profiles of droplet shape with nanometer accuracy and, without any assumptions about droplet geometry, to directly measure important physical parameters that characterize surface wetting processes. Specifically, the time-dependent variation of the droplet height, volume, contact radius, contact angle distribution along the droplet’s perimeter, and mass flux density for two different surface preparations are reported. The studies clearly demonstrate three phases of evaporation reported previously: pinned, depinned, and drying modes; the studies also reveal instances of partial pinning. Finally, the apparatus is employed to investigate the cooperative evaporation of the sprayed droplets. We observe and explain the neighbor-induced reduction in evaporation rate, that is, as compared to predictions for isolated droplets. In the future, the new experimental methods should stimulate the exploration of colloidal particle dynamics on the gas–liquid–solid interface