Emerging two-dimensional bismuth oxychalcogenides for electronics and optoelectronics

Atomically thin two-dimensional(2D)bismuth oxychalcogenides(Bi_(2)O_(2)X,X=S,Se,Te)have recently attracted extensive attention in the material research community due to their unique structure,outstanding long-term ambient stability,and high carrier mobility,which enable them as promising candidates for high-performance electronic and optoelectronic applications.Herein,we present a comprehensive review on the recent advances of 2D bismuth oxychalcogenides research.We start with an introduction of their fundamental properties including crystal structure and electronic band structure.Next,we summarize the common techniques for synthesizing these 2D structures with high crystallinity and large lateral size.Furthermore,we elaborate on their device applications including transistors,artificial synapses,optical switch and photodetectors.The last but not the least,we summarize the existing challenges and prospects for this emerging 2D bismuth oxychalcogenides field.

Bandgap narrowing in the layered oxysulfide semiconductor Ba_3Fe_2O_5Cu_2S_2: Role of FeO_2 layer

A new layered Cu-based oxychalcogenide Ba_3Fe_2O_5Cu_2S_2 has been synthesized and its magnetic and electronic properties were revealed. Ba_3Fe_2O_5Cu_2S_2 is built up by alternatively stacking [Cu_2S_2]^（2-） layers and iron perovskite oxide[（FeO_2）（BaO）（FeO_2）]^（2-）layers along the c axis that are separated by barium ions with Fe^（3＋） fivefold coordinated by a square-pyramidal arrangement of oxygen. From the bond valence arguments, we inferred that in layered CuC h-based（Ch =S, Se, Te） compounds the ＋3 cation in perovskite oxide sheet prefers a square pyramidal site, while the lower valence cation prefers the square planar sites. The studies on susceptibility, transport, and optical reflectivity indicate that Ba_3Fe_2O_5Cu_2S_2 is an antiferromagnetic semiconductor with a Ne′el temperature of 121 K and an optical bandgap of 1.03 eV. The measurement of heat capacity from 10 K to room temperature shows no anomaly at 121 K. The Debye temperature is determined to be 113 K. Theoretical calculations indicate that the conduction band minimum is predominantly contributed by O 2p and 3 d states of Fe ions that antiferromagnetically arranged in FeO_2 layers. The Fe 3d states are located at lower energy and result in a narrow bandgap in comparison with that of the isostructural Sr_3Sc_2O_5Cu_2S_2.