A- CityU101/20
Quantum tunnelling enhanced optical harmonic generation in single plasmonic junctions
Hong Kong Principal Investigator: Dr Dangyuan LEI (City University of Hong Kong)
French Principal Investigator: Dr Yannick De Wilde (Institut LANGEVIN ESPCI Paris-CNRS)

Sophisticated control over the size and geometry of strongly coupled metallic nanostructures makes their linear and nonlinear optical properties sensitive to quantum mechanical size effects, such as the spill out of conduction electrons and the electron tunneling across nanoscale gap junctions. Recent theories have predicted that the electron tunnelling across the plasmonic nano-junctions can significantly enhance the effective optical nonlinearities of metal that in turn benefits the generation of optical harmonics. This also brings about new physical mechanisms for producing huge nonlinear emission enhancements compared to traditional near-field enhancement based effects.

This project will investigate both experimentally and theoretically quantum tunneling enhanced optical harmonic generation in rationally designed plasmonic nano-junctions. In experiment, we plan to employ molecular self-assembly to achieve subnanometer-level control over the widths of Au-Ag core-shell heterojunctions and Ag-Ag nanocube homojunctions. To probe the electron tunneling induced nonlinear emissions in those nano-junctions, we will develop a multifunctional dark-field microspectroscope and imaging system to characterize their plasmon resonance bands, measure the second- and third-harmonic emissions, and map the harmonic radiation patterns all as functions of tunneling barrier, incident power and incident/detection polarization at the single-particle level. These far-field spectroscipic and mapping measurements will be complemented by the French team’s near-field measurements, including three-dimensional spatial mapping of the amplitude and phase of electromagnetic fields generated at the fundamental and harmonic frequencies and hyper-spectral near-field mapping of the electromagnetic local density of states. Together with comprehensive theoretical calculations based on quantum-corrected and nonlocal hydrodynamic nonlinear models, the two teams aim to distinguish the respective roles of classical field enhancement and quantum tunneling effects in the optical harmonic generation of quantum-sized plasmonic systems. Our study could open up new avenues for nonlinear nano-opics and nanoplasmonics, and also shed light on such research fields as quantum transport and molecular electronics.

 

A-HKUST604/20
Casimir forces in two dimensional materials
Hong Kong Principal Investigator: Prof Ho Bun Chan (The Hong Kong University of Science and Technology)
French Principal Investigator: Prof Mauro Antezza (Laboratoire Charles Coulomb, University of Montpellier)

The collaborative project aims to investigate Casimir forces in two-dimensional (2D) materials with thickness as small as one atom layer, by combining the theory (France) and experimental (Hong Kong) expertise of the two teams. Casimir forces refer to the interactions between neutral conductors that arise when the presence of boundaries leads to changes in the quantum zero-point energy. These forces are practically negligible for large separations but they increase rapidly with decreasing distance and become the dominant interaction between electrically neutral bodies at submicron separations. With continual miniaturization of micromechanical devices, a better understanding of the fundamental interactions between their movable parts will be crucial for the successful fabrication and operation of these systems in the future.

This project will leverage recent advances in the understanding of the novel electronic and optical properties in the 2D material system of graphene, as well as progress in semiconductor nanofabrication technologies, to study Casimir effects in regimes not yet explored. For example, the dispersion of the quasiparticles in graphene leads to strong thermal effects on the Casimir force occurring at separations significantly smaller compared to metals. At these short distances, the Casimir force on graphene is expected to be strong enough to be experimentally detected. A number of different ways to modify the Casimir force in graphene will be investigated, including changing the Femi level, suspending the graphene under tensile stress and placing the graphene on a nanoscale grating to achieve strong interplay between geometry, material properties and thermal effects. Successful implementation of the proposed project will bring about new ways of controlling the Casimir interaction through engineering the properties of 2D materials. 

The HK and French teams are experts in the experiments and theory of Casimir forces respectively. For the HK team, the PI pioneered the use of micromechanical torsional resonators in the study of Casimir forces. Recently, he developed a monolithic platform for measuring Casimir forces between silicon components of complex, non-conventional shapes. The PI on the French team developed the first theory of Casimir forces for systems out of thermal equilibrium and a general theory for calculating the Casimir force between bodies of arbitrary shapes and materials. Ongoing collaboration between the two teams, as evidenced by a joint publication in 2020 and a working paper, will be further strengthened through this proposed project.

 

A-EdUHK801/20
Role of distraction on children's math performance
Hong Kong Principal Investigator: Professor Kerry Lee (The Education University of Hong Kong)
French Principal Investigator: Professor Patrick Lemaire (Aix-Marseille University & CNRS)

Math is a key subject that paves the way for success in higher education and in many professional areas. Indeed, early math performance is closely and linearly related to future earnings. Research on math development and math learning has documented the main determiners of children’s math performance. Children’s performance in math is influenced by a variety of parameters, including participants’ characteristics (e.g., their age, school level, working-memory and executive control skills), stimulus features (e.g., problem size, side of larger operand), strategies (e.g., retrieval, counting), as well as situational or task environment (e.g., speed-accuracy pressures, culture). In addition to determining which factors influence children’s math performance and learning, research has focused on determining the key underlying mechanisms, as knowing these mechanisms is important for developing intervention to improve math education and math development. This project will contribute to this endeavour by examining how distraction influences children’s performance in math, by determining how its influence changes with children’s age, and by establishing which key individual characteristics are crucial in children’s sensitivity to distraction. By comparing children from Hong Kong and from France, this project will also further document cultural differences in math learning.