Ultrathin Free-Standing Nanosheets of Bi₂O₂Se: Room Temperature Ferroelectricity in Self-Assembled Charged Layered Heterostructure

Abstract

S2 MethodsReagents. Bismuth nitrate (Bi(NO3)35H2O, Alfa Aesar, 99.9%), selenourea (SeC(NH2)2, Alfa Aesar, 99.9%), potassium hydroxide (KOH, S D Fine-Chem Limited (SDFCL)), sodium hydroxide (NaOH, SDFCL), Disodium EDTA (C10H14O8Na2N2H2O, SDFCL) and ethanol were used without any further purification.Synthesis procedure. 100 mg (0.206 mmol) of Bi(NO3)35H2O, 12.7 mg (0.103 mmol) of SeC(NH2)2 and 306.8 mg (0.824 mmol) of disodium EDTA were sequentially added at a 5 minutes interval into 20 ml water in a glass beaker. The solution was stirred continuously. The addition of Bi(NO3)35H2O into water results in a milky white color solution which turns into an orange color solution after the addition of SeC(NH2)2. The solution becomes clear after the addition of disodium EDTA. Finally, 120 mg (2.14 mmol) of KOH and 320 mg (8 mmol) of NaOH were added into the solution which turns the solution color black. After 10 minutes of stirring, the solution was put to rest which results in precipitation of the dark brown color nanosheets. We observed that nanosheets of similar morphology and thickness can also be obtained without using disodium EDTA, however, in that case, the required amount of water solvent is much higher, 200 ml. These were then washed with alcohol and water and centrifuged to remove disodium EDTA. The purified product was then dried in a vacuum oven at 150 C.Step I: In water, Bi(NO3)3 undergoes hydrolysis to produce BiONO3 and the process of hydrolysis is expedites in alkaline medium:Step II: Selenourea SeC(NH2)2 undergoes decomposition in alkaline medium to generate selenide ions (Se 2-) along with cyanamide (H2NCN): SeC(NH2)2 + OH -→ Se 2-+ H2NCN + H2O

Gate‐Tunable Polar Optical Phonon to Piezoelectric Scattering in Few‐Layer Bi2O2Se for High‐Performance Thermoelectrics

“…Whereas in the low temperature piezoelectric scattering regime, the carrier mobility follows a gentle temperature dependence of μ ~ T −0.47 [26][27][28][29][30] and reveals the intrinsically high mobility. [21,[31][32][33] Consequently, a persistently high PF above 400 µW m −1 K −2 over a wide temperature range (80-200 K) is obtained, which corresponds to high carrier mobility in the piezoelectric scattering regime. The high PF over such a wide temperature range is unusual since the PF for most material has the peak value at a very narrow temperature range corresponding to the materials bandgap.…”

“…www.advmat.de www.advancedsciencenews.com associated with POP scattering due to the polar nature of ferroelectric Bi 2 O 2 Se flake. [21,32,33] The in-plane (x direction) polarizations of 2D Bi 2 O 2 Se originated from the asymmetric charge transfer in the top Bi-O parallelogram channel. And the strong dipole polarization in the cross-plane (z direction) duo to the high electronegativity of O atom.…”

2D Polarized Materials: Ferromagnetic, Ferrovalley, Ferroelectric Materials, and Related Heterostructures

“…For instance, 2D ferroelectricity has been demonstrated in CIPS, WTe 2 , In 2 Se 3 , SnS, SnTe, Bi 2 O 2 Se, and 1T‐MoTe 2 . [ 14,54,74,78,82,83,100,162–165 ] Notably, traditional ferroelectric materials are insulator, but researchers proved that 2D ferroelectric materials could be insulators, semiconductors, and metals, which endows them with wider applications in electronic and optoelectronic devices. In this section, the intrinsic ferroelectricity in 2D layered materials is summarized.…”

Microscopic Manipulation of Ferroelectric Domains in SnSe Monolayers at Room Temperature

“… 21 Microscopic imaging and controlled manipulation of the out-of-plane polarization in 2D ferroelectric materials via PFM have been demonstrated in MoTe 2 MLs, 2 freestanding perovskite thin films, 22 as well as several-layer thick van der Waals ferroelectrics. 5 , 11 , 13 , 15 − 17 However, although PFM studies of in-plane ferroelectricity have been reported in several nanometer thick layered materials, 13 − 15 , 18 − 20 to the best of our knowledge none of the current PFM studies of in-plane polarized ferroelectrics has reached the thickness limit of a single van der Waals ML.…”