School of Science Department of Physics 64 Scanning Tunneling Probe Experiments on Materials with Novel Electronic Properties Supervisor: LORTZ Rolf Walter / PHYS Student: LAW Chak Nam / SSCI Course: UROP1100, Summer This project aims to test a new home-made scanning tunnelling spectroscopy (STS) probe on a superconductor. We begin with explaining the principles of Andreev reflection point contact spectroscopy and tunnelling spectroscopy. Then, the principle of the probe is detailed, and the sample preparation process is explained. We explain the procedures of performing point contact spectroscopy at cryogenic temperature and finally analyse the experimental data. We will discuss the experimental problems and limitation we encountered and point out ways to improve the experiment. Investigation of CP Symmetry in Neutrino Oscillation Supervisor: LUK Kam Biu / PHYS Student: CHAN Chung Yuen / PHYS FONG Shing Hei / PHYS Course: UROP1000, Summer This project is to determine the charge-parity(CP) violating phase in the process that a muon neutrino turns into an electron neutrino. In weak interaction, CP symmetry can break, which means that the particle and anti-particle do not behave the same way. In this measurement, muon neutrino and anti-neutrino beams are generated through pion decay. When the muon neutrinos travel, some of them change to electron neutrinos. A 20000-ton detector filled with liquid scintillator placed at 100 km from the neutrino source is used to capture the neutrinos. The expected number of neutrino interactions is the product of neutrino interaction cross-section, appearance probability, number of muon neutrinos that are generated and number of atoms in the detector. The CP-violating phase can be determined by counting the number of detected electron-neutrino events and their energy distribution. Charge Generation and Carrier Diffusion in Organic Solar Cells Supervisor: WONG Kam Sing / PHYS Student: CHANG Fan Ut / SUSEE Course: UROP1100, Fall Non-fullerene acceptors (NFAs) are a popular research topic in the organic solar cells (OSCs) recently since they have shown several advantages including higher tunabilities and better spectral absorption in certain region over traditional fullerene acceptors (FAs). In this study, three different NFA-OSC devices, PM6:Y6, PM6:m-BTP-phC6 and PM6:m-BTP-phC6:Y6 are tested by measuring their transient photocurrent and transient photovoltage lifetimes. The results showed that PM6:m-BTP-phC6 has the longest TPV lifetime, indicating the slowest recombination of charge carriers; while PM6:m-BTP-phC6:Y6 has the shortest TPC lifetime, indicating the fastest charge extraction. Overall, PM6:m-BTP-phC6:Y6 shows the highest external quantum efficiency and the highest power conversion efficiency of 18.2%, showing that the ternary strategy of tuning the morphology of the NFA-OSCs has a great potential for further studies in the future.
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