Abstract : A simple and facile solution phase synthesis of two-dimensional (2D) layered BiOI single-crystalline square sheets at tunable reaction conditions yielded dominant exposed (001) facets. The bismuth oxyiodide (BiOI) structures analyzed by scanning electron microscopy and atomic force microscopy (AFM) reveal screw-dislocation-driven growth of spiral pyramid-like layer-by-layer (LBL) stacking of ultrathin BiOI sheet of about 2.5 nm. Vertically aligned, oriented Au nanotriangles (Au NTs) allow more analyte molecules to access their sharp tips to form hot-spots thereby enabling development of ultrasensitive plasmonic sensors. Injection of plasmonic hot carriers into the semiconductor at the plasmonic metal-semiconductor interface (Au-BiOI) fabricated under optimal conditions with Au NTs form tunable surface enhanced Raman scattering substrate with maximum enhancement factor on the order of 106 and 27 nanomol as a limit of detection. Electrical transport measurements on BiOI and Au-BiOI LBL 2D square sheet materials under applied pressure using conducting-AFM established the use of these nanosheets as a nanoscale pressure sensor. Photodetector studies show good photoresposnsivity, reproducibility, and fast photoresponse time indicating that the materials is a promising candidate for visible light-photodetector using 454 and 535 nm led lights. © 2019 American Chemical Society.