4 research outputs found
Confocal nonlinear optical imaging on hexagonal boron nitride nanosheets
Optical microscopy with optimal axial resolution is critical for precise visualization of two-dimensional flat-top structures. Here, we present sub-diffraction-limited ultrafast imaging of hexagonal boron nitride (hBN) nanosheets using a confocal focus-engineered coherent anti-Stokes Raman scattering (cFE-CARS) microscopic system. By incorporating a pinhole with a diameter of approximately 30μm, we effectively minimized the intensity of side lobes induced by circular partial pi-phase shift in the wavefront (diameter, d0) of the probe beam, as well as nonresonant background CARS intensities. Using axial-resolution-improved cFE-CARS (acFE-CARS), the achieved axial resolution is 350nm, exhibiting a 4.3-folded increase in the signal-to-noise ratio compared to the previous case with 0.58 d0 phase mask. This improvement can be accomplished by using a phase mask of 0.24 d0. Additionally, we employed nondegenerate phase matching with three temporally separable incident beams, which facilitated cross-sectional visualization of highly-sample-specific and vibration-sensitive signals in a pump-probe fashion with subpicosecond time resolution. Our observations reveal time-dependent CARS dephasing in hBN nanosheets, induced by Raman-free induction decay (0.66ps) in the 1373cm−1 mode. © 2023, Chinese Society for Optical Engineering.TRU
Sub 100 nm resolution confocal focus-engineered coherent anti-Stokes Raman scattering microscopy under non-degenerate pumping condition
For the development of microscopic tools that can resolve non-fluorescent samples beyond the diffraction limit, we propose focus-engineered non-degenerate pumped coherent anti-Stokes Raman scattering (CARS) using spa-tial light modulator (SLM)-based phase shaping, liquid lens focus control, and confocal detection. Non-degenerate pumped CARS (ND-CARS) with frequency-doubled probe pulses resulted in approximately 75% improvement in resolution compared to that of degenerate CARS. Focal adjustment using the liquid lens facilitated the accurate overlapping of three beams. The circular pi-phase modulation at the center of the probe-beam wavefront demar-cated the net CARS focal volume into a sub 100 nm-scale core and surrounding side lobes. The confocal geometry detection setup successfully removed the side lobes, allowing optical imaging of 81 nm-sized zinc oxide particles at 87 nm, and edge-to-edge resolution was determined to be 103 nm.FALS
Gold-Nanoparticle Layer Substrate Assisted Transmission-Mode Laser Desorption for Atmospheric Pressure Mass Spectrometry Imaging
We demonstrate continuous-wave laser-based ambient mass spectrometry imaging with the use of a gold-nanoparticle layer substrate. When a fresh tissue slice is placed on a gold-nanoparticle layer substrate and irradiated with a 532-nm continuous-wave laser, the transmission-mode laser configuration provides precise desorption performance to facilitate mass spectrometry imaging. The subsequent ionization process with non-thermal atmospheric pressure plasma jets generates sufficient amounts of molecular ions. By using this method, micrometer-spatial-resolution mass spectrometry imaging of humid tissues can be obtained. The gold-nanoparticle layer substrates can be prepared and stored in advance of the experiment, resulting in simplified specimen preparation and an advantage in faster preparing of fresh tissue specimen for analysis.1
Nonconventional Strain Engineering for Uniform Biaxial Tensile Strain in MoS<sub>2</sub> Thin Film Transistors
Strain engineering has been employed
as a crucial technique
to
enhance the electrical properties of semiconductors, especially in
Si transistor technologies. Recent theoretical investigations have
suggested that strain engineering can also markedly enhance the carrier
mobility of two-dimensional (2D) transition-metal dichalcogenides
(TMDs). The conventional methods used in strain engineering for Si
and other bulk semiconductors are difficult to adapt to ultrathin
2D TMDs. Here, we report a strain engineering approach to apply the
biaxial
tensile strain to MoS2. Metal-organic chemical vapour deposition
(MOCVD)-grown large-area MoS2 films were transferred onto
SiO2/Si substrate, followed by the selective removal of
the underneath Si. The release of compressive residual stress in the
oxide layer induces strain in MoS2 on top of the SiO2 layer. The amount of strain can be precisely controlled by
the thickness of oxide stressors. After the transistors were fabricated
with strained MoS2 films, the array of strained transistors
was transferred onto plastic substrates. This process ensured that
the MoS2 channels maintained a consistent tensile strain
value across a large area