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Photothermally activated motion of Al NPs with a single xenon flash pulse. (a) Photothermally activated motion of NPs observed by a fast camera at a frame rate of 10 kHz. Each frame size is 8.6 mm in height × 8.9 mm in width. (b) Height of photothermally activated motion is approximately quadratically dependent of flash power (enhanced online). [URL: http://dx.doi.org/10.1063/1.4776660.1]doi: 10.1063/1.4776660.1.
(a) Photothermally driven ignition of Al NPs by a single xenon flash pulse at a frame rate of 100 kHz, at incident power of 1.6 J/cm2. Ignition was identified in the second image, which was acquired ∼0.12 ms after the flash incidence. Ignition is spatially localized. Each frame size is 3.8 mm in height × 4.9 mm in width. (b) Flash power dependence for transition of ignition and motion only with and without the long pass filter cutoff at 540 nm. It shows that UV is more efficient for motion and ignition (enhanced online). [URL: http://dx.doi.org/10.1063/1.4776660.2]doi: 10.1063/1.4776660.2.
Electric-field distributions under the flash illumination for NPs with 2-nm alumina shell and aluminum core at their plasmon resonance. (a) Two contacting spheres with radii of 35 nm. The plasmon resonance is at 381 nm. (b) Three contacting spheres with radii of 20 nm. The plasmon resonance is at 354 nm. For both cases, the local electric-field enhancement can reach as much as 80 times, leading to local heat enhancement up to 6400 times as compared to the global heating.
Suggested positive feedback mechanism for the flash-induced photothermally activated motion and ignition of Al NPs.
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