15 Super-Resolution Imaging and Microscopy by Dielectric …
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resolution (for 400 nm wavelength) is estimated to be 215 nm in air [26], and 152 nm
when considering the solid-immersion effect of a particle. At peak wavelength of
600 nm, the limits are 333 nm in air and 228 nm with solid-immersion effect, respectively. Here, it is noted that the focal planes for the lines with and without particles
on top are different.
In another example (Fig. 15.1f, g), a fishnet 20-nmthick gold-coated anodic aluminium oxide (AAO) membrane fabricated by two-step anodizing in oxalic acid
(0.3 mol/l) under a constant voltage of 40 V is imaged with 4.7-μm-diameter microspheres. The pores are 50 nm in diameter, spaced 50 nm apart. The microsphere
nanoscope resolves these tiny pores clearly, obtaining an impressive resolution of
λ/8 in the visible. Note that the magnification in this case is around 8X—almost
two times that of the earlier grating example, implying that the performance of the
microsphere super lens is affected by the near-field interaction between the particle
and the substrate. The sample-dependent resolution brings in complexity in clarifying the physical mechanism of the technique, nevertheless the resolution range is
between 50 and 100 nm, far exceeding the classical limit of ~200 nm.
15.1.3 From Microsphere to Metamaterial Particle-Lens
The simplicity and high resolution of the microsphere imaging technique have
attracted considerable interests. The technique was validated and resolution levels
of ~λ/6–λ/8 was repeated by other groups [21, 27]. New microspheres including
Polystyrene [28, 68] and BaTiO 3 microspheres [29, 30, 69] (immersed in liquid or
solid encapsulated; mostly used particle now) were soon introduced and became
widely used in the field. Great efforts have since been devoted to the following
areas: (1) scanning functionality development and complete super-resolution image
construction. This is driven by the need of overcoming limitations of microsphere
lenses whose imaging window is too small for many applications. (2) Mechanism
exploration. Exact mechanisms have been debated in literature and considerable
efforts were devoted to developing a complete theoretical model for the technique.
(3) Development of next generation dielectric superlenses with improved resolution
and imaging quality, new physics and fabrication method were explored. This has
led to the development of all-dielectric metamaterial solid-immersion lens and nano
hybrid lens. Because these lenses are metamaterial-based whose working mechanisms are completely different from previous counterparts, we would classify them
as the ‘second-generation particle-lens’ and the previous microspheres the ‘firstgeneration particle-lens’. (4) Easier access of superlens. Efforts also went to developing simpler version of superlens which layman or general public can access. Biological superlens based on naturally occurring spider silks was developed for this
purpose. (5) New applications, including for example three-dimensional interferometry, endoscopy, and Lab-on-Chip (LoC) devices were developed.
375
resolution (for 400 nm wavelength) is estimated to be 215 nm in air [26], and 152 nm
when considering the solid-immersion effect of a particle. At peak wavelength of
600 nm, the limits are 333 nm in air and 228 nm with solid-immersion effect, respectively. Here, it is noted that the focal planes for the lines with and without particles
on top are different.
In another example (Fig. 15.1f, g), a fishnet 20-nmthick gold-coated anodic aluminium oxide (AAO) membrane fabricated by two-step anodizing in oxalic acid
(0.3 mol/l) under a constant voltage of 40 V is imaged with 4.7-μm-diameter microspheres. The pores are 50 nm in diameter, spaced 50 nm apart. The microsphere
nanoscope resolves these tiny pores clearly, obtaining an impressive resolution of
λ/8 in the visible. Note that the magnification in this case is around 8X—almost
two times that of the earlier grating example, implying that the performance of the
microsphere super lens is affected by the near-field interaction between the particle
and the substrate. The sample-dependent resolution brings in complexity in clarifying the physical mechanism of the technique, nevertheless the resolution range is
between 50 and 100 nm, far exceeding the classical limit of ~200 nm.
15.1.3 From Microsphere to Metamaterial Particle-Lens
The simplicity and high resolution of the microsphere imaging technique have
attracted considerable interests. The technique was validated and resolution levels
of ~λ/6–λ/8 was repeated by other groups [21, 27]. New microspheres including
Polystyrene [28, 68] and BaTiO 3 microspheres [29, 30, 69] (immersed in liquid or
solid encapsulated; mostly used particle now) were soon introduced and became
widely used in the field. Great efforts have since been devoted to the following
areas: (1) scanning functionality development and complete super-resolution image
construction. This is driven by the need of overcoming limitations of microsphere
lenses whose imaging window is too small for many applications. (2) Mechanism
exploration. Exact mechanisms have been debated in literature and considerable
efforts were devoted to developing a complete theoretical model for the technique.
(3) Development of next generation dielectric superlenses with improved resolution
and imaging quality, new physics and fabrication method were explored. This has
led to the development of all-dielectric metamaterial solid-immersion lens and nano
hybrid lens. Because these lenses are metamaterial-based whose working mechanisms are completely different from previous counterparts, we would classify them
as the ‘second-generation particle-lens’ and the previous microspheres the ‘firstgeneration particle-lens’. (4) Easier access of superlens. Efforts also went to developing simpler version of superlens which layman or general public can access. Biological superlens based on naturally occurring spider silks was developed for this
purpose. (5) New applications, including for example three-dimensional interferometry, endoscopy, and Lab-on-Chip (LoC) devices were developed.