Fig. 1. Experimental setup and growth samples. (a) Schematic diagram of stove cavity; (b) schematic diagram of reverse airflow growth method; (c) schematic diagram of growth region; (d) structure diagram of 2H-phase WSe₂; (e) structure diagram of 3R-phase WSe₂; optical microscopy of growth sample of (f) region I, (g) region II, (h) region III, (i) region IV; local magnification of growth sample of (j) region I, (k) region II, (l) region III, (m) region IV

Fig. 2. Morphological and spectral characterization of monolayer, 2H-phase ,and 3R-phase WSe₂. Atomic force microscope characterizetion of (a) monolayer, (b) 2H-phase and (c) 3R-phase WSe₂; (d) Raman spectrogram of 2H-phase (AB-stacked) WSe₂ in monolayer region (lower panel) and bilayer region (upper panel); (e) Raman spectrogram of 3R-phase (AA-stacked) WSe₂ in monolayer region (lower panel) and bilayer region (upper panel); (f) PL spectra of monolayer, 2H-phase, and 3R-phase WSe₂; (g) PL imaging maps, (h) E¹_2g eigenpeak Raman spectroscopy, (i) B_2g eigenpeak Raman spectroscopy, and (j) SHG spectroscopy of 3R-phase WSe₂ at 760 nm; (k) PL imaging map, (l) E¹_2g eigenpeak Raman spectroscopy, (m) B_2g eigenpeak Raman spectroscopy, and (n) SHG spectroscopy of 2H-phase WSe₂ at 760 nm

Fig. 3. Morphological characterization of spiral structure WSe₂. （a） Schematic of furnace cavity used to grow spiral structure WSe₂； （b） schematic of growth and distribution of supersaturation； （c）（d） optical microscope images of epitaxial area of circled region in fig.3（b）； optical micrographs of （e） single-armed，（f） double-armed， and （g） triple-armed spiral structures， respectively； （h） scanning electron micrograph of double-armed spiral WSe₂； （i） atomic force microscopy characterization of double-armed spiral WSe₂

Fig. 4. Spectroscopic characterization of double-armed spiral structure WSe₂. (a) Raman mapping of E¹_2g mode; (b) PL spectrograms at axis along direction of armchair; (c)-(h) PL imaging maps of integral center from 750 nm to 800 nm, respectively; (i) contour line mapping of PL spectrum; (j) SHG mapping at axis along direction of armchair; (k) SHG imaging map; (l) rotating half wave plate λ/2 polarization SHG polar coordinate diagram