Fig. 1. (Color online) Crystal structures of two-dimensional anisotropic materials, including (a) orthorhombic black-arsenic. Reproduced with permission^[35]. Copyright 2018, John Wiley and Sons. (b) Orthorhombic black-phosphorus. Reproduced with permission^[46]. Copyright 2014, Springer Nature. (c) Monoclinic GeAs. Reproduced with permission^[47]. Copyright 2018, John Wiley and Sons. (d) Orthorhombic GeSe. Reproduced with permission^[41]. Copyright 2017, American Chemical Society. (e) Triclinic KP₁₅. Reproduced with permission^[45]. Copyright 2018, American Chemical Society. (f) Monoclinic TiS₃. Reproduced with permission^[48]. Copyright 2018, Wiley-VCH. (g) Triclinic ReSe₂. Reproduced with permission^[49]. Copyright 2016, American Chemical Society.

Fig. 2. (Color online) Raman spectroscopy. (a)–(c) the schematic diagram of three typical polarized-Raman configurations. Reproduced with permission^[62]. Copyright 2017, CPB. (d) The left is the Raman spectra of ReSe₂ grown on hBN and SiO₂ respectively. The right is the angular-dependent Raman intensity of 238 cm^–1 shown in polar plot under different polarized-Raman configurations. Reproduced with permission^[44]. Copyright 2018, American Chemical Society. (e) the angular-dependent Raman intensity of 212 and 406 cm^–1 in ReS_2(1–x)Se_2x. Reproduced with permission^[49]. Copyright 2016, American Chemical Society. (f) Angle-resolved polarized Raman spectra of KP₁₅. The right picture is the intensity of peak 9. (g) Polarization-resolved PL intensity of KP₁₅. The polar plots show the PL intensity of KP₁₅ as the function of the detection angle and excitation angle respectively. Reproduced with permission^[45]. Copyright 2018, American Chemical Society.

Fig. 3. (Color online) (a) The angle-dependent Raman spectrum of GeSe and the corresponding contour color map in the parallel-polarization configuration (left) and cross-polarization configuration (right). Reproduced with permission^[41]. Copyright 2017, American Chemical Society. (b) The Raman spectrum of B-As with laser polarized along different directions (up). The angle-resolved intensity of A_g¹ and B_2g-mode are extracted and shown in polar plot (down). Reproduced with permission^[35]. Copyright 2018, John Wiley and Sons. (c) The Raman spectrum of GeAs in the non-polarized, parallel-polarized and cross-polarized configuration (left). The angle-dependent Raman spectrum of GeAs under traditional configuration (right). (d) The intensities of angle-dependent Raman peak are extracted and shown in the polar plot. Reproduced with permission^[40]. Copyright 2018, American Chemical Society.

Fig. 4. (Color online) (a) Schematic of the optical measurement under visible light (left-picture) and infrared light (right-picture). (b) Light absorption of B-P flake with different polarized light. (c) B-P photodetector with broadband response and polarization sensitivity. (1) The optical image of B-P photodetector with ring-electrode. (2) Polarization dependence of photoresponsivity from 400 to 1700 nm with polarization along x crystal axis (0°) and y crystal axis (90°). (3) The spatial mapping of photocurrent under polarization angle of 0 and 90 degree. Reproduced with permission^[38]. Copyright 2015, Springer Nature. (d) The angle-dependent electrical conductance of B-As. The optical image of device for the anisotropic electrical measurements is inserted in it. (e) Temperature dependent resistance based on B-As Hall device shown in the inset(left). The magnetic field -dependent conductively and , corresponding with the direction of armchair and zigzag (right). Reproduced with permission^[35]. Copyright 2018, John Wiley and Sons. (f) The I_ds–V_ds curves of As_0.83P_0.17 with illumination and dark environment along x axis and y axis. (g) The laser polarization-sensitive photocurrents of As_0.83P_0.17 in polar plot at V_ds = 0 V (left). Photocurrent mapping of As_0.83P_0.17 at V_ds = 0 V (right) when polarization direction parallels (0°) and perpendicular (90°) to the contact edge of the metal. Reproduced with permission^[39]. Copyright 2017, American Association for the Advancement of Science.

Fig. 5. (Color online) The properties of electricity and photoelectricity. (a) The optical image of GeAs for angle-dependent transporting measurement. (b) The anisotropic field-effect mobility in polar plot. Reproduced with permission^[47]. Copyright 2018, John Wiley and Sons. (c) Angle-resolved absorption spectra of GeAs from 400 to 2000 nm. (d) The schematic diagram of polarized photodetection devices. (e) The polarization-sensitive photocurrents in polar plot under 520 and 830 nm laser. (f) The mapping of polarization-dependent photocurrent under 520 and 830 nm laser. Reproduced with permission^[40]. Copyright 2018, American Chemical Society. (g) Polarization-resolved experimental absorption spectra of GeSe from 400 to 950 nm. (h) The colormap of anisotropic photo response under the 808 nm laser. x-axis represents the voltage of source and drain, y-axis represents the polarized angle, and I_ph is denoted by the color bar. (i) The data of polarized I_ph are extracted and shown in polar plot. Reproduced with permission^[41]. Copyright 2017, American Chemical Society.

Fig. 6. (Color online) (a) The polarization sensitive transmission spectra of ReSe₂ nanoflake. (b) Polarization dependent photocurrent mapping based on ReSe₂ FET. The thickness of the ReSe₂ channel is 12 nm. Reproduced with permission^[44]. Copyright 2016, American Chemical Society. (c) Angle-dependent mobility of ReSe₂, ReS_0.38Se_1.62 and ReS_1.02Se_0.98 alloys. Reproduced with permission^[48]. Copyright 2017, John Wiley and Sons. (d) The polarization-sensitive transmittance spectra of a TiS₃ crystal from 400 to 1000 nm (up-picture). Polar plot of the transmittance at 500, 600, 700, 800 nm wavelengths (down-picture). (e) I–V curves of the TiS₃/Si-based device under the illumination of linearly polarized laser (660 nm). (f) Two polar plots of polarization-sensitive light currents under the bias voltage of –2 V (left-picture) and 0 V (right-picture). Reproduced with permission^[48]. Copyright 2018, Wiley-VCH.

Table 1. 2D anisotropic materials and reported crystal system, space group, bandgap, responsivity and anisotropic dichroic ratio.