Executive Summary : | This project envisages investigating the electron dynamics in van der Waals systems on their natural timescales – attoseconds – through state-of-the-art experimental techniques. This is made possible by various techniques including the emission of photons by high-harmonic generation where near-infrared (near-IR) femtosecond pulses interact nonlinearly with target systems and produce attosecond pulses with durations less than one-half the temporal cycle of incident exciting pulses. Alternate approaches such as time-resolved photoelectron spectroscopy using a combination of attosecond pulses in the XUV and soft x-ray in combination with parent near-IR pulses. While there is a considerable amount of work done on atomic and molecular systems in the gas phase addressing individual entities, quantum aggregates and van der Waals (vdW) systems are only beginning to be investigated. Unlike molecules, where structure, both physical and electronics, are well-known and remain robust, in vdW systems, inherent weak bonding leads to challenges for theoretical and computational methods. Nonetheless, vdW systems such as clusters of atoms and molecules produced in supersonic jets as well as few- and multiple-atomic layered structures such as graphene, MoS2, WS2, hBN and others are feasible to be produced in the lab. The experimental feasibility of generating attosecond pulses from thin films down to a few atomic layers has been demonstrated opening up a new technique to investigate the dynamics electrons in these systems on their natural timescale. Not only, is this technique time-resolved, angular resolution of the emitted high-order harmonics in the EUV and soft xray, rendered possible by polarization control of the incident IR or optical laser field. In contrast to static methods like x-ray diffraction which give information about the physical structure and photoelectron spectroscopy which provides static information about electronic structure. Angle-resolved high-harmonic generation is a game-changer which opens up a new dimension where spatio-temporal information of electron dynamics can be obtained. Further, this method is applicable with very little modification to a wide range of samples from individual atoms or molecules in the gas-phase to atomic layers and even bulk condensed matter, including liquid jets or films. In this project we will explore this intriguing region where atomic constituents aggregate to form vdW clusters with finite boundaries and thin atomic films in the form of few- and multi-layer films to study the attosecond quantum electronics of these systems. This is poised to provide new and potentially breakthrough information and insights. |