This article reviews the novel technology named nanophotonics, which is an innovative technology utilizing the local energy transfer between nanometric materials induced by optical near fields. As an introduction to other review articles in this issue, history of this technology, theoretical picture of optical near fields, and examples of technical developments are surveyed. Among a variety of applications, progresses in developing devices, fabrications, system applications, and energy conversions are introduced. Recent status of research and development in US and EU, cooperation between industry and academia, and future outlook are also described.
This article explains unique photochemical reaction named nonadiabatic photochemical process. First, the experimental results of the deposition of Zn nano-dots using the nonadiabatic optical chemical vapor deposition are reviewed. Their deposition rate dependences on the incident optical power are explained by the excitation of the molecular vibrational state by the dressed photon. Second application of the nonadiabatic photochemical reaction to the photolithography is reviewed using fabrication of Fresnel zone plates as an experimental example.
This article reviews the recent development of optical nanofabrication with self-assemble manner based on the non-adiabatic chemical reaction. In the first part of this article, we propose a new polishing method that uses near-field etching based on a non-adiabatic process, with which we obtained ultra-flat silica surface that had a minimum roughness of 1.37 Å. We believe our technique can be applied not only to flat substrates but also to three-dimensional substrates that have convex or concave surfaces. In the second part, we demonstrate the selective photochemical etching of Si in a self-organized manner, which strongly depends on the distribution of the optical near-field. This dependence was described by the virtual exciton-phonon-polariton model. The photoluminescence (PL) spectra from the etched Si exhibited a blueshifted PL peak at 1.8 eV, corresponding to Si nanocrystals of 2.8 nm diameter. Since, both method are based on the photochemical reaction they are compatible with mass-production and can be applicable to other materials.
Nanophotonics allows the design of optical devices and systems at densities beyond those conventionally limited by the diffraction of light. Such higher integration density, however, is only one of the benefits of optical near-fields over conventional optics and electronics. In this article, architectural approaches are presented to exploit the unique physical principles enabled by optical near-field interactions for information and communications technologies (ICT). Sample demonstrations are based on optical excitation transfer via optical near-field interactions and hierarchical properties associated with optical near-fields.
We observed visible light emission in the wavelength range (λ = 600-690 nm) from aggregated 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM) dye molecule microcrystals pumped by infrared light (λ = 805 nm). This visible light emission occurs through the nonadiabatic transition processes induced by the optical near field at the microcrystal surface. From an observation of the dependence of the emitted light intensity on the excitation intensity, we found that the visible light emission is originated both from the nonadiabatic one-step and two-steps transition processes. The frequency up-conversion efficiency for our DCM microcrystals was experimentally estimated to be higher than that of the second harmonic generation from a potassium dihydrogen phosphate (KDP) crystal.
Currently, near-field scanning optical microscopy offers a spatial resolution down to 10−30 nm. High resolution imaging spectroscopy enables us to visualize the exciton wavefunctions confined in semiconductor quantum structures. In this article, the principle of near-field optical wavefunction mapping is described. Then as an application, we performed mapping out of exciton and biexciton wavefunctions in single GaAs quantum dots. Significant displacement of the center of emission profiles was found, in contrast to the usual difference in the emission profiles of an exciton and a biexciton. By conducting a numerical calculation, such a displacement could be reproduced by introducing a shallow potential dip, which causes a significant difference in the penetration of the wavefunctions into the barrier. Precise mapping of exciton and biexciton wavefunctions of quantum-confined structures will provide a good probe for weakly localized states due to local strain and disorder.
Near-field optical phenomena at the nanoscale are outlined, on the basis of the fact that they are, in essence, a photon-matter interacting system. They indicate that material systems and optical near fields, cannot be treated independently nor separately. The linear dimension of dressing nature or virtual clouds is simply estimated by the Heisenberg uncertainty principle, which shows approximately 100 nm for a visible light, which indicates that dressing effects might be prominent on the nanoscale. As an approach to such a system, a picture of photons dressed by material excitations is proposed and discussed, where a finite material system, not an infinite bulk system, is emphasized, and dressed photon operators are explicitly derived. The applicability is mentioned, and it is pointed out that the related developments in future are expected, for opening up a new area of research and development.