Nanophotonics involves the study of light at the nanometer scale and its interaction with nanometer-scale objects. Generally, nanophotonics is associated with plasmonic materials and structures made of noble metals such as gold or silver. However, conventional plasmonic materials have several disadvantages restricting their applications. For instance, plasmonic materials like gold and silver suffer from high optical loss at optical frequencies, they are rare and not feasible for large scale production and lastly, nanoparticles only hold electric dipole-like resonance which cannot tailor and direct the optical field as we want. Consequently, there has been an intense search for all-dielectric materials (ADMs) which could offer unique opportunities for reduced dissipative losses and large resonant enhancement of both electric and magnetic near-fields beyond plasmonic materials. There are usually three types of ADMs, i.e., firstly high-index ADMs such as silicon, germanium and gallium arsenide, secondly mid-index ADMs such as titanium dioxide, silicon carbide and boron and thirdly low-index ADMs such as silicon dioxide and polymer. ADMs with different refractive indexes bring a lot of freedom to design nanostructures with different optical properties.
Overall, although many efforts have been devoted to prepare ADMs and study the related nanophotonic applications, researchers still face fundamental challenges: i.e. how to control phase, size and shape of building blocks in the synthesis of ADMs, how to fabricate functional nanostructures by using these building blocks, and further how to achieve the transformation from simple nanoparticles synthesis to functional nanostructures fabrication. To this note, Dr. Jiahao Yan and Dr. Churong Ma at the Jinan University in China together with researchers from the Sun Yat-sen University: Dr. Xinyue Liu, Dr. Yingcong Huang and Professor Guowei Yang introduced the latest progresses of ADMs preparation via top-down and bottom-up methods and related applications in nanophotonics. Their work is currently published in the research journal, Materials Science & Engineering R.
In their review, they first presented the basic optical properties of ADMs. They then introduced various approaches for the fabrication of AMD-based nanostructures and their merits and demerits. The researchers then summarized the nanophotonic applications of ADMs, including the utilization of unique resonant modes in silicon nanoparticles, enhancement of both linear and nonlinear optical signals, biosensing, light trapping and harvesting, and light matter interaction enhancement.
The researchers discussed several strategies for improvement of nanophotonic performances of ADMs. For example, through designing specific ADM nanostructures, they showed that one could obtain higher Q factor and better near-field feature. Further, the review presented recent progresses on active tuning of ADM-based nanodevices which make contributions to the practical use of ADMs.
In summary, the review was able to summarize the current deficiencies of ADM-based nanostructures in the various application areas of nanophotonics and deliver an outlook for the follow-up research work, which aims to provide guidelines on the future progress of this fast-developing area. Overall, the authors established that ADMs have actually opened a window toward building highly efficient nanophotonic devices from their unique attributes, namely: ADMs containing a group of materials which have varied optical properties. This diversity provides us freedom and possibilities of functional structural design. Secondly, most of ADMs are compatible with mature semiconductor processing technology and have much lower cost compared with plasmonic materials of noble metals. Lastly, ADM-based nanostructures can generate intriguing resonant modes, such as magnetic dipole, toroidal, anapole modes and others.
Jiahao Yan, Xinyue Liu, Churong Ma, Yingcong Huang, Guowei Yang. All-dielectric materials and related nanophotonic applications. Materials Science & Engineering R 141 (2020) 100563