Nanophotonics; walking beyond the classical limits of light

Nanophtonics has recently achieved new dimensions in several aspects of nanoscience, such as nano-imaging, nano-an alysis or even nano-manipulation of several kinds of samples ranging from semiconductors to biomolecules. The interaction volume between tight and sample is classically restricted by so-called diffraction limit of light: which is about half of the wavelength of the probing light. We have jumped over this classical limit in several nanophotonics technologies, such as in fabrication; in analysis and in imaging of samples at nanoscale, and have shown how light can interact will materials in a volume much smaller than the diffraction limis. Utilizing two-photon absorption we demonstrated the fabrication of micro sculpture [1]: which had finer structures of the order of 100 nm. in comparison with the probing wavelength of 780 nm. Later, some other structures with even smaller size were fabricated by this technique. 6y utilizing an array of metallic nanorods, we proposed nanolens [2] that can image a nano-light-object through the plasmon resonance of the nanorods. In our proposed model, a resolution of 40 nm could be achieved for the light sourcc of 532 nm. An improvcd design of such a metallic nanolens is capable of color and magnificd image of extremely subwavelength objects [3]. We also proposed the use of metallic nano-tip in near-field optical microscopy (NSOM). and demonstrated high-resolution microscopy beyond the diffraction limits [4]. Later, we combined NSOM technique with Raman microscopy and demonstrated how the use of a metallic nano-tip can confine and enhance the probing field, which results in high-resolution Raman microscopy [5-8]. In this technique. which is called the tip-enhanced Raman spectroscopy (TERS), interesting near-field effects could be observed which could be analyzed through Raman scattering process, as the tip molecules interacted with the sample molecules. We have utilized TESR to study several samples, such as carbon nanotubes, carbon-60 molecules and DNA-based adenine molecules, and were able to optically Image them with a resolution better than 25 nm in linear and 15 nm in nonlinear [5] TERS experiments, far beyond the diffraction limits of the probing tight. Also. a signal enhancement by a factor as nigh as one million was observed. In addition to this, if the tip is pressed against the sample molecules. the tip can also interact with the sample mechanically by applying a controlled pressure on the sample molecules. This effect shows up in interesting spectral changes, such as peak shitt, peak broadening and new peak rising, as the ATM-controlled tip-applied pressure is sequentially changed [0.7]. Further, inclusion of chemical effects in TERS can even indicates towards the possibility of single molecule detection [S] Due In extremely localized nature of the tip-applied pressure and chemical interaction, these techniques further advances the nano-imaging capabilities of TERS and takes it one step forward in super-resolved optical imaging far beyond the classical limits of diffraction.