A paper in Science Advances (12 August) provides proof of a new concept, using new solid 3D superlenses to break through the scale of things previously visible through a microscope.
Illustrating the strength of the new superlens, the scientists describe seeing for the first time, the actual information on the surface of a Blue Ray DVD. That shiny surface is not as smooth as we think. Current microscopes cannot see the grooves containing the data- but now even the data itself is revealed.
Super-resolution optical imaging through the TiO2 mSIL. (A to P) SEM images of a Blu-ray disk containing 100-nm-wide grooves (A) and the wafer patterns with 60-nm (E), 50-nm (I), and 45-nm pitches (M) after gold coating of sample (I). (B) and (C), (G), and (K) are the bottom surfaces of the mSIL detached from the surface of samples (A), (E), and (I), respectively. AFM images of the wafer pattern with 60-nm (F) and 50-nm pitches (J). Optical microscopy images of the TiO2 mSIL focused on the surface of a Blu-ray disk (D) and wafer patterns with 60-nm (H), 50-nm (L), and 45-nm pitches (N to P), with magnification factors of 1.8, 3.1, 3.0, and 3.1, respectively. The last mSIL was illuminated under white light (N), green light (λ ~ 540 nm) (O), or blue light (λ ~ 470 nm) (P). The mSIL had widths of about 20 μm.
Schematic illustration of the assembly of the all-dielectric TiO2 mSIL.
Led by Dr Zengbo Wang at Bangor University, UK and Prof Limin Wu at Fudan University, China, the team created minute droplet-like lens structures on the surface to be examined. These act as an additional lens to magnify the surface features previously invisible to a normal lens.
Made of millions of nanobeads, the spheres break up the light beam. Each bead refracts the light, acting as individual torch-like minute beam. It is the very small size of each beam of light which illuminate the surface, extending the resolving ability of the microscope to record-breaking levels. The new superlens adds 5x magnification on top of existing microscopes.
Extending the limit of the classical microscope’s resolution has been the ‘El Dorado’ or ‘Holy Grail’ of microscopy for over a century. Physical laws of light make it impossible to view objects smaller than 200 nm – the smallest size of bacteria, using a normal microscope alone. However, superlenses have been the new goal since the turn of the millennium, with various labs and teams researching different models and materials.
“We’ve used high-index titanium dioxide (TiO2) nanoparticles as the building element of the lens. These nanoparticles are able to bend light to a higher degree than water. To explain, when putting a spoon into a cup of this material, if it were possible, you’d see a larger bend where you spoon enters the material than you would looking at the same spoon in a glass of water,” Dr Wang says.
“Each sphere bends the light to a high magnitude and splits the light beam, creating millions of individual beams of light. It is these tiny light beams which enable us to view previously unseen detail.”
Wang believes that the results will be easily replicable and that other labs will soon be adopting the technology and using it for themselves.
The advantages of the technology is that the material, titanium dioxide, is cheap and readily available, and rather than buying a new microscope, the lenses are applied to the material to be viewed, rather than to the microscope.
“We have already viewed details to a far greater level than was previously possible. The next challenge is to adapt the technology for use in biology and medicine. This would not require the current use of a combination of dyes and stains and laser light- which change the samples being viewed. The new lens will be used to see germs and viruses not previously visible.”
Although all-dielectric metamaterials offer a low-loss alternative to current metal-based metamaterials to manipulate light at the nanoscale and may have important applications, very few have been reported to date owing to the current nanofabrication technologies. We develop a new “nano–solid-fluid assembly” method using 15-nm TiO2 nanoparticles as building blocks to fabricate the first three-dimensional (3D) all-dielectric metamaterial at visible frequencies. Because of its optical transparency, high refractive index, and deep-subwavelength structures, this 3D all-dielectric metamaterial-based solid immersion lens (mSIL) can produce a sharp image with a super-resolution of at least 45 nm under a white-light optical microscope, significantly exceeding the classical diffraction limit and previous near-field imaging techniques. Theoretical analysis reveals that electric field enhancement can be formed between contacting TiO2 nanoparticles, which causes effective confinement and propagation of visible light at the deep-subwavelength scale. This endows the mSIL with unusual abilities to illuminate object surfaces with large-area nanoscale near-field evanescent spots and to collect and convert the evanescent information into propagating waves. Our all-dielectric metamaterial design strategy demonstrates the potential to develop low-loss nanophotonic devices at visible frequencies.
SOURCES- Eurekalert, Science Advances