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M.-H. Chien, S. Schmid:
"Nanomechanical 2D-scanning photothermal microscopy for analysis and imaging of single sub- 10 nm nanoparticles";
Talk: Nanophotonics and Micro/Nano Optics International Conference 2017, Barcelona; 2017-09-13 - 2017-09-15; in: "Nanophotonics and Micro/Nano Optics International Conference 2017 Book of Abstracts", (2017), 124.

Label-free optical detection and imaging of single nanoparticles and molecules are of
fundamental interests in great variety of fields due to its simpler detection scheme,
reduced limitations on samples and higher stability. For sub-100 nm nanoparticles,
absorption cross section exceeds scattering cross section by several orders of
magnitude, and the difference increases as the diameter of particles reduce, which has
made photothermal spectroscopy a powerful technique for the imaging of single Au
nanoparticles even under sub-10 nm regime. Instead of using polarization interference
and inhomogeneous refractive index [1,2] to create contrast, photothermal analysis and
imaging via the thermal frequency detuning of nanomechanical 1D string resonators of
single metal [3] and polymer [4] nanoparticles has been demonstrated alternatively. We
hereby introduce highly sensitive nanomechanical membrane resonator as a novel
methodology and optical platform for single nanoparticle detection and 2D imaging, as
shown in figure 1. The experiments were done with a rectangular silicon-rich silicon
nitride membrane with 500 μm in width, 50 nm in thickness and pre-stress of 250 MPa
and 30 MPa, and the results are shown in figure 2 and 3, respectively. When scanning a
heating laser over the membrane, the local photothermal heating of the nanoparticles
causes a heat influx into substrate and thus a measurable detuning of the membrane
resonance frequency, which was monitored with a phase-locked loop. With pumping
power of only 300 μW and spot size of 1 μm, we achieve the detection and imaging of
10 nm Au nanoparticles, as shown in figure 3, with a dissipated power of 300 fW and
integration time of 100 ms, which demonstrates even higher sensitivity than state-of-theart
photothermal microscopy [1,2], making this novel spectroscopic technique a potential
candidate toward single molecule detection and imaging.

Label-free optical detection and imaging of single nanoparticles and molecules are of
fundamental interests in great variety of fields due to its simpler detection scheme,
reduced limitations on samples and higher stability. For sub-100 nm nanoparticles,
absorption cross section exceeds scattering cross section by several orders of
magnitude, and the difference increases as the diameter of particles reduce, which has
made photothermal spectroscopy a powerful technique for the imaging of single Au
nanoparticles even under sub-10 nm regime. Instead of using polarization interference
and inhomogeneous refractive index [1,2] to create contrast, photothermal analysis and
imaging via the thermal frequency detuning of nanomechanical 1D string resonators of
single metal [3] and polymer [4] nanoparticles has been demonstrated alternatively. We
hereby introduce highly sensitive nanomechanical membrane resonator as a novel
methodology and optical platform for single nanoparticle detection and 2D imaging, as
shown in figure 1. The experiments were done with a rectangular silicon-rich silicon
nitride membrane with 500 μm in width, 50 nm in thickness and pre-stress of 250 MPa
and 30 MPa, and the results are shown in figure 2 and 3, respectively. When scanning a
heating laser over the membrane, the local photothermal heating of the nanoparticles
causes a heat influx into substrate and thus a measurable detuning of the membrane
resonance frequency, which was monitored with a phase-locked loop. With pumping
power of only 300 μW and spot size of 1 μm, we achieve the detection and imaging of
10 nm Au nanoparticles, as shown in figure 3, with a dissipated power of 300 fW and
integration time of 100 ms, which demonstrates even higher sensitivity than state-of-theart
photothermal microscopy [1,2], making this novel spectroscopic technique a potential
candidate toward single molecule detection and imaging.