Theoretical and experimental investigations of various exfoliated samples taken from layered In4Se3crystals are performed. In spite of the ionic character of interlayer interactions in In4Se3and hence much higher calculated cleavage energies compared to graphite, it is possible to produce few‐nanometer‐thick flakes of In4Se3by mechanical exfoliation of its bulk crystals. The In4Se3flakes exfoliated on Si/SiO2have anisotropic electronic properties and exhibit field‐effect electron mobilities of about 50 cm2 V−1 s−1at room temperature, which are comparable with other popular transition metal chalcogenide (TMC) electronic materials, such as MoS2and TiS3. In4Se3devices exhibit a visible range photoresponse on a timescale of less than 30 ms. The photoresponse depends on the polarization of the excitation light consistent with symmetry‐dependent band structure calculations for the most expected
2D spin glass MnIn 2 Se 4 : application of liquid-phase exfoliation to a layered structure with seven-atom-thick layers
We report liquid-phase exfoliation (LPE) of bulk layered-structure semiconductor, MnIn 2 Se 4 , to nanoscale thick sheets by ultrasonication followed by sequential centrifugation at 2000, 5000, and 7500 rpm. The nanosheets exfoliated by LPE in isopropyl alcohol show an average thickness of 50, 40, and 14 nm, respectively. The smallest of these values corresponds approximately to ten 7-atom thick [Se–In–Se–Mn–Se–In–Se] layers that compose the bulk structure of MnIn 2 Se 4 . Both the bulk material and the exfoliated samples show photoluminescence, but the weak shoulder observed from the indirect band gap emission is obviously suppressed in the nanosheet samples as compared to the bulk sample. Similar to the bulk, the nanosheets isolated at 2000 and 5000 rpm exhibit spin-glass behavior with a freezing temperature of ∼3 K. In contrast, the nanosheets isolated at 7500 rpm do not exhibit any anomalies in their low-temperature magnetic behavior. These results demonstrate the possibility to extend the LPE technique to van-der-Waals materials with several-atom-thick layers.
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- Award ID(s):
- 1905499
- NSF-PAR ID:
- 10424546
- Date Published:
- Journal Name:
- Journal of Materials Chemistry C
- Volume:
- 11
- Issue:
- 2
- ISSN:
- 2050-7526
- Page Range / eLocation ID:
- 609 to 615
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract ac cleavage plane. These results demonstrate that mechanical exfoliation of layered ionic In4Se3crystals is possible, while the fast anisotropic photoresponse makes In4Se3a competitive electronic material, in the TMC family, for emerging optoelectronic device applications. -
Liquid phase exfoliation (LPE) is a method that can be used to produce bulk quantities of two-dimensional (2D) nanosheets from layered van der Waals (vdW) materials. In recent years, LPE has been applied to several non-vdW materials with anisotropic bonding to produce nanosheets and platelets, but it has not been demonstrated for materials with strong isotropic bonding. In this paper, we demonstrate the exfoliation of boron carbide (B 4 C), the third hardest known material, into ultrathin nanosheets. B 4 C has a structure consisting of strongly bonded boron icosahedra and carbon chains, but does not have anisotropic cleavage energies to suggest that it can be readily cleaved into nanosheets. B 4 C has been widely studied for its very high melting point, high mechanical strength, and chemical stability, as well as its zero- and one-dimensional nanostructured forms. Herein, ultrathin nanosheets are successfully prepared by sonication of B 4 C powder in organic solvents and are characterized by microscopy and spectroscopy. Density functional theory (DFT) simulations reveal that B 4 C can be cleaved along several different crystallographic planes with similar energetic favourability, facilititated by an unexpected mechanism of breaking boron icosahedra and forming new boron-rich cage structures at the surface. Atomic force microscopy (AFM) shows that the nanosheets produced by LPE are as thin as 5 nm, with an average thickness of 31.4 nm and average area of 16 000 nm 2 . Raman spectroscopy shows that many of the nanosheets exhibit additional carbon-rich peaks that change with laser irradiation, which are attributed to atomic rearrangements and amorphization at the nanosheet surfaces, consistent with the diverse cleavage planes. High-resolution transmission electron microscopy (HRTEM) demonstrates that many different cleavage planes exist among the exfoliated nanosheets, in agreement with DFT simulations. This work elucidates the exfoliation mechanism of 2D B 4 C and suggests that LPE can be applied to generate nanosheets from a variety of non-layered and non-vdW materials.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2TC03776A
