Crossover between Photochemical and Photothermal Oxidations of Atomically Thin Magnetic Semiconductor CrPS₄

Abstract

Many two-dimensional (2D) semiconductors represented by transition metal dichalcogenides have tunable optical bandgaps in the visible or near IR-range standing as a promising candidate for optoelectronic devices. Despite this potential, however, their photoreactions are not well understood or controversial in the mechanistic details. In this work, we report a unique thickness-dependent photoreaction sensitivity and a switchover between two competing reaction mechanisms in atomically thin chromium thiophosphate (CrPS4), a 2D antiferromagnetic semiconductor. CrPS4 showed a threshold power density two orders of magnitude smaller than that for MoS2 obeying a photothermal reaction route. In addition, reaction cross section quantified with Raman spectroscopy revealed distinctive power dependences in the low and high power regimes. Based on optical in-situ thermometric measurements and control experiments against O2, water, and photon energy, we proposed a photochemical oxidation mechanism involving singlet O2 in the low power regime with a photothermal route for the other. We also demonstrated a highly effective encapsulation with Al2O3 as a protection against the destructive photoinduced and ambient oxidations.

Recent Advances in 2D Layered Phosphorous Compounds

“…[ 69 ] CrPS 4 belongs to the monoclinic family with a = 10.87 Å, b = 7.25 Å, c = 6.14 Å, β = 91.88° and volume = 483.93 Å 3 , belonging to space group. [ 70,71 ] Each Cr atom exists in the form of a trivalent ion, and is coordinated by six strongly polarized S atoms in the middle of a distorted octahedron. The [CrS 6 ] octahedrons are arranged along b axis in edge‐sharing manner to form a chain, while the hexagonal‐close‐packed sulfur layers form a puckered structure.…”

“…The [CrS 6 ] octahedrons are arranged along b axis in edge‐sharing manner to form a chain, while the hexagonal‐close‐packed sulfur layers form a puckered structure. [ 69–71 ] Each P atom connects with four neighboring S atoms by strong covalent bond to compose a [PS 4 ] tetrahedron, which links [CrS 6 ] octahedra chains along the a axis (Figure 1d). [ 69 ] Since the [PS 4 ] tetrahedra are located between [CrS 6 ] octahedra chains, the discances of neighboring Cr atoms along b axis and a axis are unequal, which renders the structure in‐plane anisotropic.…”

“…In the case of CVT process, the precursors and transport agents are combined into the hot end of an evacuated and sealed quartz tube, and the precursors will be transported into the cold end for chemical reaction and then form bulk crystals at a certain temperature gradient (Figure 2b). [ 4 ] Through this method, bulk crystals of FePS 3 , [ 28 ] FePSe 3 , [ 66 ] NiPS 3 , [ 74 ] MnPS 3 , [ 75 ] CrPS 4 , [ 70 ] CuInP 2 S 6 [ 76 ] and b‐AsP [ 58 ] (Figure 2d–f) are successfully synthesized, which can be further used for the exfoliation of 2D flakes.…”

Band gap crossover and insulator–metal transition in the compressed layered CrPS4

“…Among the 2D vdW magnetic materials, CrPS 4 is currently enjoying a surge of interest [30][31][32][33][34][35] . CrPS 4 was first synthesized in the 1970s and found to possess a monoclinic symmetry (C2/m space group) 36 .…”

Probing the properties of lattice vibrations and surface electronic states in magnetic semiconductor CrPS4

“…1 Recently, a two-dimensional CrPS 4 single crystal was systematically investigated for their electronic, magnetic, and thermal transport properties and density functional theory computation. [2][3][4][5][6][7][8][9][10] In this work, the lattice vibration and surface electronic states of the (001) surface are systematically investigated by polarized Raman spectroscopy and ultraviolet photoelectron spectroscopy (UPS). Parallel and perpendicular Raman scattering technique is used to investigate the anisotropic optical response of the (001) crystal surface, combined with nuclear site group analysis; the Raman peaks can be assigned to A or B vibrational modes.…”