Near-field thermal transport in a nanotip under laser irradiation

Abstract

We report on a systematic study of highly enhanced optical field and its induced thermal transport in nanotips under laser irradiation. The effects on electric field distribution caused by curvature radius, tip aspect ratio, and polarization angle of the incident laser are studied. Our Poynting vectors' study clearly shows that when a laser interacts with a metal tip, it is bent around the tip and concentrated under the apex, where extremely high field enhancement appears. This phenomenon is more like a liquid flow being forced/squeezed to go through a narrow channel. As the tip-substrate distance increases, the peak field enhancement decreases exponentially. A shift of field peak position away from the tip axis is observed. For the incident light, only its component along the tip axis direction has a contribution to the electric field enhancement under the tip apex. The optimum tip apex radius for field enhancement is about 9 nm when the half taper angle is 10°. For a tip with a fixed radius of 30 nm, field enhancement increases with the half taper angle when it is less than 25°. The thermal transport inside the nanoscale tungsten tips due to absorption of incident laser light is explored using the finite element method. A small fraction of light penetrates into the tip. As the polarization angle or apex radius increases, the peak apex temperature decreases. The peak apex temperature goes down as the half taper angle increases, even though the mean laser intensity inside the tip increases, revealing a very strong effect of the taper angle on thermal transport.

Magnonic topological insulators in antiferromagnets

“…[114] reported the observation of magnon Hall-like effect 8 . Therefore, we can expect that the observations of the magnonic WF law in the topologically trivial bulk AF and the magnonic QSHE (helical edge magnons) in the topological AF are now within experimental reach 80,82,83,[115][116][117] via measurement schemes proposed in Ref. [46].…”

“…Using such a periodically extended fields only over a distance that can be much smaller than the sample dimensions or even the electric length l E , we 46 have seen that the requirement of strong field gradients E needed for creating a quantum Hall effect of magnons in FMs (e.g., Landau levels and the resultant level spacing) can be substantially softened, while still producing welldefined chiral edge magnon states 46 , since the magnitude of E for each period remains the same. Periodic fields may be realized by periodically arranging STM tips 46,82,83 . Such periodic potentials are easily implemented in our approach by assuming in Eq.…”

“…[46]. The considered electric field with the constant gradient can be realized by an electric skewharmonic potential 46 and, while being challenging, it may be realized by STM tips 82,83 . The resulting magnetization gradient from the applied thermal gradient plays a role of an effective magnetic field gradient and works as a nonequilibrium magnonic spin chemical potential [71][72][73]78,79 that has been established experimentally in Ref.…”

Solid-to-super-critical phase change and resulting stress wave during internal laser ablation

“…The stress wave in the target is very clear. Our previous work has presented detailed analysis and discussion of the stress wave in a solid [31,35] under laser ablation. The stress wave forms at 10 ps and propagates in the x and z directions.…”

Silver patterning using an atomic force microscope tip and laser-induced chemical deposition from liquids

“…This enhancement is higher at the apex of the tip, and hence, the field at the apex of the tip can be up to two orders of magnitude higher than the incident field. [19][20][21] If the photoreduction due to the irradiation of the liquid precursor depends on the local electromagnetic intensity, then deposition will be accelerated in an area with a diameter approximately the radius of curvature of the tip. 22 If a higher deposition rate is obtained just below the tip's apex, the deterministic movement of the tip should generate patterns narrower than the radius of the tip.…”