**Acknowledgements**

These works were supported by the Research Grants Council and Innovation Technology Commission (ITC) of the Government of Hong Kong Special Administrative Region (HKSAR) with RGC/GRF Project No. 617812, 16205018, 618210, ITS/530/09, and ITS/162/16FP, and the International Science and Technology Project of Huangpu District of Guangzhou City (2019GH02). We acknowledge assistance from the Nanosystem Fabrication Facility (NFF) of HKUST for the device/system fabrication.

