Micro-Machining by Nearfield Optics

这种扫描近场光学显微镜（SNOM）的探针是在透明基底上的直径为500 nm的介质球。用波长为632.8nm的He-Ne激光在全内反射条件下入射形成的倏逝波照射探测球。来自探针的光由常规显微镜通过基板收集。当样品被带入探针周围的近场时，检测到的光强度显著变化。近场探测光强的变化与样品的复折射率有关，折射率的真实的部分越小，探测光强的增加越明显。这一结果是通过使用电偶极子模型的探针和样品之间的电磁相互作用解释。用真空蒸镀法制备的标准样品，其纵向和横向分辨率分别为1 nm和10 nm左右。我们研制了一种不受衍射极限影响的高分辨率的SNOM，它采用直径为500 nm的聚苯乙烯乳胶球作为探针。为了研究SNOM的空间分辨率，我们制备了标准样品并测量了其表面的形状。实验结果表明，SNOM的纵向分辨率约为1 nm，横向分辨率约为10 nm。因此，SNOM的空间分辨率比传统的光学显微镜高得多。虽然SNOM的空间分辨率的极限尚未在理论上确定，但它将取决于生产探针的技术。未来空间分辨率的提高将需要可靠和可重复的制造技术，以生产具有较小尖端曲率半径的探针。

The probe of this scanning nearfield optical microscope (SNOM) is a dielectric sphere 500nm in diameter on a transparent substrate. The probe sphere is illuminated by evanescent waves which are formed by the incidence of a He-Ne laser with the wavelength of 632.8nm under the condition of total internal reflection. The light from the probe is collected by a conventional microscope through the substrate. The detected light intensity varies markedly when a sample is brought into the near-field around the probe. The variation of detected light intensity in the near-field depends on the complex index of refraction of samples ; the smaller the real part of the refractive index, the more marked the increase of detected light intensity. This result is explained through use of an electric dipole model for the electromagnetic interaction betweem probe and sample. The vertical and lateral resolutions of about 1nm and 10nm, respectively, are obtained for a standard sample which is prepared by vacuum evaporation of metal.We develop an SNOM that achieves high resolution which is not affected by a diffraction limit and that uses a polystirene latex sphere 500nm in diameter located on a quartz substrate as a probe. To investigate the spatial resolution of the SNOM,we prepared a standard sample and measured the shape of its surface. As a result, the vertical resolution of SNOM was found to be about 1nm and the lateral resolution about 10nm. Therefore the spatial resolution of the SNOM is much higher than that of a conventional optical microscope.Although the limit of the spatial resolution of the SNOM has not been theoretically determined, it will depend on the technique by which the probe is produced. Future improvement of the spatial resolution will require reliable and reproducible fabrication technology in order to produce a probe with a smaller tip curvature radius.