pinpoint mode UnivCollegeLondon ring shape AdhesionForce single_layer HexagonalBN lithography Sapphire PinPointMode Hair Monisha molecules Tapping PDMS PetruPoni neodymium_magnets OpticalWaveguides EvatecAG Singapore Patterns SiliconeOxide Switching HanyangUniv Neodymium TCS Fluoride Fendb NUS_Physics PetruPoni_Institute OpticalElement C60H122 SRAM HiVacuum flakes Yttria_stabilized_Zirconia