Electrical Generation of Light from Plasmonic Gold Nanoparticles
Résumé
Gold nanoparticles are used extensively in many aspects of science. In particular, their optical properties are exploited in diverse areas such as biosensing1, molecular rulers2, organic solar cells3 and photocatalysis,4 to name a few. In all these applications, light is used to excite the surface plasmon resonance and/or intra/interband transition in the gold nanoparticles5,6. However, the ability to use electrons rather than photons to induce light from gold nanoparticles opens up horizons which would otherwise be unattainable. Two main methods may be considered practically for obtaining light from the electrical excitation of gold nanoparticles: one can use low energy (~ 2 eV) tunnel electrons from a scanning tunneling microscope7,8 (STM) or high energy (~ 30 keV) electrons from a scanning electron microscope9,10. In both cases, the main advantage is the small size of the excitation when using electrons as compared to photons. Whereas the size of a photonic probe is limited by diffraction to a few hundred nanometers, the size of an electronic probe is truly nanoscale11,12. As will be shown in the following, such extremely high spatial selectivity enables completely new insights into the optical properties of gold nanoparticles. Indeed, excitation with a spatial selectivity on the order of 10 nm may not only be used to investigate single gold nanoparticles but moreover to provoke the emission of light by exciting specific locations inside a single gold nano-object. Low energy electrical excitation of a gold nanoparticle is of further interest for applications such as electron/photon transduction at the nanoscale. Using this technique, an electrical signal may be converted into a photonic one. This will lead to new applications in future optoelectronic devices. From an historical point of view, electron-to-photon energy conversion has played an emblematic role in physics over the last 150 years. The invention of the Crook’s tube in 1879, where the energy of an electrical discharge is converted into light, has led to a number of discoveries; the X-rays by W. Röntgen in 1895, the fluorescent tube by T. Edison in 1895, the discovery of the electron by J.J. Thomson in 1897…. More recently, the conversion of energy from high energy (keV) electrons to light via metallic films was first predicted by R.A. Ferrell13 in 1958 and experimentally observed by Steinmann14 and Brown et. al15 in 1960. Concerning low energy (~ 2 eV) tunnel electrons, the first observation of energy conversion into light dates back to 1976 when J. Lambe and S.L. McCarthy16 discovered this new method for the generation of light. This light emission method was extended to tunnel electrons from the STM in 1988 by J.K. Gimzewski et al.17,18 a few years after the invention of the STM by G. Binnig and H. Rohrer19. In this chapter, we review recent studies of electron-to-photon energy conversion in gold nanoparticles. In Section 1.2 we describe the fundamental mechanisms for the electrical generation of light from gold nanoparticles when using low energy (~ 2 eV) tunnel electrons from a scanning tunneling microscope or high energy (~ 30 keV) electrons from a scanning electron microscope. In Section 1.3 we report on examples of such electron/photon transduction experiments in various gold nanostructures.