Ultrastable tip-enhanced hyperspectral optical nanoimaging for defect analysis of large-sized WS ₂ layers

Abstract

Optical nanoimaging techniques, such as tip-enhanced Raman spectroscopy (TERS), are nowadays indispensable for chemical and optical characterization in the entire field of nanotechnology and have been extensively used for various applications, such as visualization of nanoscale defects in two-dimensional (2D) materials. However, it is still challenging to investigate micrometer-sized sample with nanoscale spatial resolution because of severe limitation of measurement time due to drift of the experimental system. Here, we achieved long-duration TERS imaging of a micrometer-sized WS 2 sample for 6 hours in a reproducible manner. Our ultrastable TERS system enabled to reveal the defect density on the surface of tungsten disulfide layers in large area equivalent to the device scale. It also helped us to detect rare defect-related optical signals from the sample. The present study paves ways to evaluate nanoscale defects of 2D materials in large area and to unveil remarkable optical and chemical properties of large-sized nanostructured materials.

Nanoscale chemical analysis of 2D molecular materials using tip-enhanced Raman spectroscopy

“…Furthermore, the instrument/sample drift is a significant issue in hyperspectral TERS imaging, as highlighted in recent works. 32,57 Therefore, the step size of TERS imaging should be selected carefully depending on the size of the region of interest. For TERS measurements of homogeneous samples such as uniform supported lipid monolayers or bilayers, a large step size (up to 50 nm) can be an effective method to obtain an overview of the sample.…”

Noise Learning of Instruments for High-contrast, High-resolution and Fast Hyperspectral Microscopy and Nanoscopy

“…Similar distortion can be seen in the center Au hole region. The second effect is the signal weakening due to the drift of the plasmon nanocavity (formed between the tip and the sample) with respect to the focus of the objective lens, thus reducing the signal collection e ciency 47 . This is re ected by the gradual weakening of the peak intensity of the ν CC band along the black dashed line (Fig.…”

Tip-enhanced nanoscopy of two-dimensional transition metal dichalcogenides: progress and perspectives

“…The defect density was estimated to be 5.2%. 59 Wrinkles might be formed in 2D TMD thin layers prepared by mechanical exfoliation or transferring. The strain field may change the elastic properties of the surrounding area, inducing Raman signal variation in the nanoscale spatial width around the wrinkles.…”