Liquid phase exfoliation of GeS nanosheets in ambient conditions for lithium ion battery applications
John B. BolandRuiyuan TianAndrew HarveyVíctor Vega‐MayoralAideen GriffinDominik HorváthCian GabbettMadeleine BreshearsJoshua PepperYanguang LiJonathan N. Coleman
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The propensity of many 2D materials to oxidize in ambient conditions can complicate production and limit applications potential. Here we describe ambient liquid phase exfoliation of GeS, a layered material known for its chemical instability. Ambient exfoliation in organic solvents such as N-methyl-pyrrolidone yields good quality multi-layer GeS nanosheets. Although oxidation appears to occur with a time constant of ∼10 d, the data suggests it to be limited to nanosheet edges leaving the basal plane intact. The rate of oxidation is slow enough to allow processing of the dispersions. For example, it was possible to size-select GeS nanosheets and characterize the size-dependence of nanosheet optical properties, leading to the observation of significant changes in bandgap with nanosheet thickness. Additionally, we were able to fabricate the nanosheets into lithium ion battery anodes using carbon nanotubes as both binder and conductive additive. These electrodes were relatively stable, showing ∼0.2% capacity decay per cycle, and displayed low-rate capacity of 1523 mAh g−1 which is within 93% of the theoretical value. However, detailed analysis showed relatively poor rate performance, possibly due to nanosheet alignment.Keywords:
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Abstract Nanosheet transistors are poised to become the preferred choice for the next generation of smaller-sized devices in the future. To address the future demand for high-performance and low-power computing applications, this study proposes a nanosheet structure with a vertically stacked design, featuring a high I ON / I OFF ratio. This Nanosheet design is combined with an induced tunnel field-effect transistor. By utilizing SiGe with a carrier mobility three times that of Si and employing a line tunneling mechanism, the research successfully achieves superior Band to Band characteristics, resulting in improved switching behavior and a lower Subthreshold Swing ( SS ). Comparative studies were conducted on three TFET types: Nanosheet PIN TFET, Nanosheet Schottky iTFET, and Fin iTFET. Results show that the Nanosheet PIN TFET has a higher I ON / I OFF ratio but poorer SSavg values at 47.63 mV/dec compared to the others. However, with a SiGe Body thickness of 3 nm, both Nanosheet iTFET and Fin iTFET exhibit higher I ON / I OFF ratios and superior SSavg values at 17.64 mV/dec. These findings suggest the potential of Nanosheet iTFET and Fin iTFET for low-power, lower thermal budgets, and fast-switching applications.
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Layer-by-layer (LbL) assembly of oppositely charged materials has been widely used as an approach to make two-dimensional (2D) nanosheet-based membranes, which often involves 2D nanosheets being alternately deposited with polymer-based polyelectrolytes to obtain an electrostabilized nanosheet-polymer structure. In this study, we hypothesized that using 2D nanosheets with matching physical properties as both polyanions and polycations may result in a more ordered nanostructure with better stability than a nanosheet-polymer structure. To compare the differences between nanosheet–nanosheet vs nanosheet-polymer structures, we assembled negatively charged molybdenum disulfide nanosheets (MoS2) with either positively charged graphene oxide (PrGO) nanosheets or positively charged polymer (PDDA). Using combined measurements by ellipsometer and quartz crystal microbalance with dissipation, we discovered that the swelling of MoS2–PrGO in ionic solutions was 60% lower than that of MoS2–PDDA membranes. Meanwhile, the MoS2–PrGO membrane retained its permeability upon drying, whereas the permeability of MoS2–PDDA decreased by 40% due to the restacking of MoS2. Overall, the MoS2–PrGO membrane demonstrated a better filtration performance. Additionally, our X-ray photoelectron spectroscopy results and analysis on layer density revealed a clearer transition in material composition during the LbL synthesis of MoS2–PrGO membranes, and the X-ray diffraction pattern suggested its resemblance to an ordered, layer-stacked structure. In conclusion, the MoS2–PrGO membrane made with nanosheets with matching size, shape, and charge density exhibited a much more aligned stacking structure, resulting in reduced membrane swelling under high salinity solutions, controlled restacking, and improved separation performance.
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Two-dimensional nanosheets have attracted tremendous attention because of their promising practical application and theoretical values. The atomic-thick nanosheets are able to not only enhance the intrinsic properties of their bulk counterparts but also give birth to new promising properties. Herein, we highlight an available pathway to prepare the ultrathin graphitic-phase C3N4 (g-C3N4) nanosheets by a "green" liquid exfoliation route from bulk g-C3N4 in water for the first time. The as-obtained ultrathin g-C3N4 nanosheet solution is very stable in both the acidic and alkaline environment and shows pH-dependent photoluminenscence (PL). Compared to the bulk g-C3N4, ultrathin g-C3N4 nanosheets show enhanced intrinsic photoabsorption and photoresponse, which induce their extremely high PL quantum yield up to 19.6%. Thus, benefiting from the inherent blue light PL with high quantum yields and high stability, good biocompatibility, and nontoxicity, the water-soluble ultrathin g-C3N4 nanosheet is a brand-new but promising candidate for bioimaging application.
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The propensity of many 2D materials to oxidize in ambient conditions can complicate production and limit applications potential. Here we describe ambient liquid phase exfoliation of GeS, a layered material known for its chemical instability. Ambient exfoliation in organic solvents such as N-methyl-pyrrolidone yields good quality multi-layer GeS nanosheets. Although oxidation appears to occur with a time constant of ∼10 d, the data suggests it to be limited to nanosheet edges leaving the basal plane intact. The rate of oxidation is slow enough to allow processing of the dispersions. For example, it was possible to size-select GeS nanosheets and characterize the size-dependence of nanosheet optical properties, leading to the observation of significant changes in bandgap with nanosheet thickness. Additionally, we were able to fabricate the nanosheets into lithium ion battery anodes using carbon nanotubes as both binder and conductive additive. These electrodes were relatively stable, showing ∼0.2% capacity decay per cycle, and displayed low-rate capacity of 1523 mAh g−1 which is within 93% of the theoretical value. However, detailed analysis showed relatively poor rate performance, possibly due to nanosheet alignment.
Nanosheet
Exfoliation joint
Nanometre
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Citations (27)