Single-, two-, and multi-photon driven molecular motion and nanopatterning in azo-polymer films
Single-, two-, and multi-photon driven molecular motion and nanopatterning in azo-polymer films
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偶氮聚合物薄膜中的单光子、双光子和多光子驱动的分子运动和纳米图案
DOI：
10.1117/12.890511
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
and S. Kawata
中科院分区：
文献类型：
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作者：
Z. Sekkat;H. Ishitobi;M. Tanabe;T. Hiramatsu;and S. Kawata
我们回顾了我们在固体本体聚合物中通过单光子、双光子和多光子驱动的分子运动在偶氮聚合物薄膜中进行纳米图案化的工作。现在已知，光诱导的分子运动发生在低于聚合物玻璃化转变温度时，通过线性或非线性吸收的发色团光异构化，在本文中，我们将证明纳米级聚合物运动是由偶氮聚合物薄膜中紧密聚焦的激光束在光的衍射极限处诱导的。偶氮染料的光异构化产生的变形图案强烈依赖于入射激光偏振和激光束沿光轴的纵向焦点位置。聚合物薄膜的各向异性纳米流动性和光学梯度力在光诱导聚合物运动中发挥着重要作用。我们探索了光致变形大小的极限，发现变形取决于激光强度和曝光时间。实现的最小变形尺寸为半峰全宽200 nm；该值几乎等于衍射极限激光光斑的尺寸。此外，通过金属尖端增强的近场照明，在薄膜表面上光学诱导出纳米突起，超出了光衍射的极限。镀银尖端位于聚焦激光束 (460 nm) 的衍射极限光斑内，由于局部表面等离激元，在尖端附近产生了具有 30 nm 光斑的增强近场。仔细调节入射光强度，以通过这种近场光斑诱导表面纳米变形。诱导出半高宽为 47 nm、高度为 7 nm 的纳米突起。出现突出是因为在照射过程中薄膜被吸引向尖端。在突起的顶部，聚合物的各向异性纳米运动发生在几乎平行于入射光偏振的方向上，这表明在尖端处不仅存在纵向分量，即沿着尖端长轴，而且还存在光电场的横向分量。偶氮聚合物薄膜有助于绘制尖端附近的电场图。我们还报告了薄膜的双光子图案。在可见光范围（λmax = 480 nm）吸收的偶氮聚合物薄膜暴露在强烈的 920 nm 照射下会导致偏振依赖性图案化，这与光选择性双光子顺式↔反式异构化引起的聚合物纳米运动相关，而 780 nm 的照射会引起偶氮发色团的多光子漂白。这些波长分别影响发色团中的漂白和异构化途径。
We review our work on nanopatterning in azo-polymer films by single, two- and multi-phopton driven molecular motion in solid bulk polymer. It is now known that light induced molecular movement occurs below the polymer glass transition temperature by chromophores photoisomerization via either linear or nonlinear absorption, and in this paper we will show that nanoscale polymer movement is induced by a tightly focused laser beam in an azo-polymer film just at the diffraction limit of light. The deformation pattern which is produced by photoisomerization of the azo dye is strongly dependent on the incident laser polarization and the longitudinal focus position of the laser beam along the optical axis. The anisotropic nanofluidity of the polymer film and the optical gradient force played important roles in the light induced polymer movement. We explored the limits of the size of the photo-induced deformation, and we found that the deformation depends on the laser intensity and the exposure time. The smallest deformation size achieved was 200 nm in full width of half maximum; a value which is nearly equal to the size of the diffraction limited laser spot. Furthermore, a nano protrusion was optically induced on the surface of the films, beyond the limit of light diffraction, by metal tip enhanced near-filed illumination. A silver coated tip was located inside the diffraction limited spot of a focused laser beam (460 nm), and an enhanced near-field, with 30 nm light spot, was generated in the vicinity of the tip due to localized surface plasmons. The incident light intensity was carefully regulated to induce surface nanodeformation by such a near-field spot. A nano protrusion with 47 nm full width of half maximum and 7 nm height was induced. The protrusion occurs because the film is attracted towards the tip end during irradiation. At the top of the protrusion, an anisotropic nanomovement of the polymer occurs in a direction nearly parallel to the polarization of the incident light, and suggests the existence at the tip end of not only a longitudinal, i.e., along the tip long axis, but also a lateral component of the electric field of light. The azo-polymer film helps map the electric field in the close vicinity of the tip. We also report on two-photon patterning of the films. Exposure of azo polymer films, which absorb in the visible range (λmax= 480 nm), to intense 920 nm irradiation leads to polarization dependent patterning which are associated with polymer nanomovement caused by photoselective two-photon cis ↔ trans isomerization, while irradiation at 780 nm induces multi-photon bleaching of the azo chromophore. These wavelengths hit bleaching and isomerization pathways in the chromophore, respectively.