Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871, China;
Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871, China;
Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871, China;
Department of Physics and State Key Laboratory for Mesoscopic Physics, Peking University, Beijing 100871, China;
SNOM; probe-sample interaction; near-field scanning optical microscopy;