The work performed in the 2DCHEX project was centred around the following key aspects:
- Fabrication of TMD monolayers and characterization of their photoluminescence properties. During my secondment at DTU I learned the state-of-the-art techniques of monolayer fabrication and used these skills for fabrication of my own samples at the host institution (mechanical exfoliation, dry transfer, assembly of van-der-Waals heterostructures). I designed and built experimental setups for laser excitation of samples and characterization of generated photoluminescence (spectral properties, polarization response, time dynamics). While testing my setups with a system I am familiar with – a colloidal quantum dot (0D system) – I developed a spectral filtering technique to purify single photon emission at room temperature (I published my results as a first-author paper in Nanoscale (DOI: 10.1039/D2NR04744F).
- Development of electrochemical electron-doping technique to manipulate the exciton charging and its optical response. I designed a custom-built electrochemical cell which could control the formation of charged excitons in various monolayers (WS2, WSe2, MoSe2) and described its operational principle (I discovered that the ionization dynamics of the neutral exciton follows the temperature-dependent Fermi-Dirac distribution, which interestingly allowed me to quantify the position of Fermi level and electron doping densities). I demonstrated that the electrochemical doping provides the highest doping densities among all the doping techniques available for TMD monolayers, which unlocks the remarkable properties of charged excitons at room temperature. Based on my research I published a first-author manuscript in Advanced Optical Materials (DOI: 10.1002/adom.202101305).
- Inducing robust valley polarization of charged excitons. I utilized the developed electrochemical doping technique to control the charged excitons and demonstrated the highest observable to date valley polarization at room temperature. I explained my results via enhancing the recombination rate under exciton charging and charge-screening effects in K and -K valleys (first-author manuscript under preparation).
- Development of a novel type of antenna for enhancing the electron interaction with TMD monolayers. As monolayers are atomically thin, the exposed volume to electron beam at normal incidence is extremely small, which severely limits the electron-monolayer interaction. Therefore, I developed an antenna – a gold crystalline nanodisk, which redirects incoming electrons along the monolayer plane, allowing for in-plane excitations. Remarkably, under such an excitation I achieved the highest observable to date photon bunching. I published these results as an equal-contribution author in 2D Materials (DOI: 10.1088/2053-1583/acbf66).
2DCHEX project generated high quality scientific results on understanding and exploitation of charged exciton properties in 0D and 2D systems for quantum information and valleytronic applications. My results were disseminated through publications in scientific journals, conferences, educational seminars at SDU, CNO, POLIMA, and DTU, 2DCHEX website, social media (ResearchGate, LinkedIn, Twitter). For communication with the broader public and industry, I prepared infographics and teasing video material. My results on the induced valley polarization at room temperature could be directly exploited by industry for an implementation of opto-valleytronic devices operating at room temperature.
