Abstract
The predicted strong piezoelectricity for monolayers of group IV monochalcogenides, together with their inherent flexibility, makes them likely candidates for developing flexible ...nanogenerators. Within this group, SnS is a potential choice for such nanogenerators due to its favourable semiconducting properties. To date, access to large-area and highly crystalline monolayer SnS has been challenging due to the presence of strong inter-layer interactions by the lone-pair electrons of S. Here we report single crystal across-the-plane and large-area monolayer SnS synthesis using a liquid metal-based technique. The characterisations confirm the formation of atomically thin SnS with a remarkable carrier mobility of ~35 cm
2
V
−1
s
−1
and piezoelectric coefficient of ~26 pm V
−1
. Piezoelectric nanogenerators fabricated using the SnS monolayers demonstrate a peak output voltage of ~150 mV at 0.7% strain. The stable and flexible monolayer SnS can be implemented into a variety of systems for efficient energy harvesting.
Colloidal liquid metal alloys of gallium, with melting points below room temperature, are potential candidates for creating electrically conductive and flexible composites. However, inclusion of ...liquid metal micro‐ and nanodroplets into soft polymeric matrices requires a harsh auxiliary mechanical pressing to rupture the droplets to establish continuous pathways for high electrical conductivity. However, such a destructive strategy reduces the integrity of the composites. Here, this problem is solved by incorporating small loading of nonfunctionalized graphene flakes into the composites. The flakes introduce cavities that are filled with liquid metal after only relatively mild press‐rolling (<0.1 MPa) to form electrically conductive continuous pathways within the polymeric matrix, while maintaining the integrity and flexibility of the composites. The composites are characterized to show that even very low graphene loadings (≈0.6 wt%) can achieve high electrical conductivity. The electrical conductance remains nearly constant, with changes less than 0.5%, even under a relatively high applied pressure of >30 kPa. The composites are used for forming flexible electrically‐conductive tracks in electronic circuits with a self‐healing property. The demonstrated application of co‐fillers, together with liquid metal droplets, can be used for establishing electrically‐conductive printable‐composite tracks for future large‐area flexible electronics.
An electrically conductive and flexible composite of eutectic gallium indium–graphene/polydimethylsiloxane is synthetized. High conductivity is achieved by creating microcavities around the graphene flakes that can be filled in with liquid metal after press‐rolling (<0.1 MPa). The cavities are formed due to the presence of nonwettable graphene flakes.
Surface patterning of liquid metals (LMs) is a key processing step for LM‐based functional systems. Current patterning methods are substrate specific and largely suffer from undesired ...imperfections—restricting their widespread applications. Inspired by the universal catechol adhesion chemistry observed in nature, LM inks stabilized by the assembly of a naturally abundant polyphenol, tannic acid, has been developed. The intrinsic adhesive properties of tannic acid containing multiple catechol/gallol groups, allow the inks to be applied to a variety of substrates ranging from flexible to rigid, metallic to plastics and flat to curved, even using a ballpoint pen. This method can be further extended from hand‐written texts to complex conductive patterns using an automated setup. In addition, capacitive touch and hazardous heavy metal ion sensors have been patterned, leveraging from the synergistic combination of polyphenols and LMs. Overall, this strategy provides a unique platform to manipulate LMs from hand‐written pattern to complex designs onto the substrate of choice, that has remained challenging to achieve otherwise.
Assembly of a ubiquitous natural polyphenol, tannic acid, allows the preparation of a new class of adhesive liquid metal inks and their utilization in the direct pen writing and patterning of liquid metals in a substrate‐independent manner—an important feature that has remained challenging using the current methods for liquid metal based conductive patterning.
Liquid metals offer unprecedented chemistry. Here it is shown that they can facilitate self‐limiting oxidation processes on their surfaces, which enables the growth of metal oxides that are ...atomically thin. This claim is exemplified by creating atomically thin hydrated MnO2 using a Galvanic replacement reaction between permanganate ions and a liquid gallium–indium alloy (EGaIn). The “liquid solution”–“liquid metal” process leads to the reduction of the permanganate ions, resulting in the formation of the oxide monolayer at the interface. It is presented that under mechanical agitation liquid metal droplets are established, and simultaneously, hydrated gallium oxides and manganese oxide sheets delaminate themselves from the interfacial boundaries. The produced nanosheets encapsulate a metallic core, which is found to consist of solid indium only, with the full migration of gallium out of the droplets. This process produces core/shell structures, where the shells are made of stacked atomically thin nanosheets. The obtained core/shell structures are found to be an efficient photocatalyst for the degradation of an organic dye under simulated solar irradiation. This study presents a new research direction toward the modification and functionalization of liquid metals through spontaneous interfacial redox reactions, which has implications for many applications beyond photocatalysis.
A “liquid metal”–“liquid solution” reaction to grow Cabrera–Mott like monolayers of hydrated MnO2 is introduced. These self‐limiting monolayers are formed on the surface of the eutectic EGaIn. A unique phenomenon of metal dealloying is observed as a result of mechanical agitation, leading to an extraordinary gallium migration out into oxidative dissolution, leaving an indium solid core behind, within a porous shell.
The nascent field of nanotechnology-enabled metallurgy has great potential. However, the role of eutectic alloys and the nature of alloy solidification in this field are still largely unknown. To ...demonstrate one of the promises of liquid metals in the field, we explore a model system of catalytically active Bi-Sn nano-alloys produced using a liquid-phase ultrasonication technique and investigate their phase separation, surface oxidation, and nucleation. The Bi-Sn ratio determines the grain boundary properties and the emergence of dislocations within the nano-alloys. The eutectic system gives rise to the smallest grain dimensions among all Bi-Sn ratios along with more pronounced dislocation formation within the nano-alloys. Using electrochemical CO
reduction and photocatalysis, we demonstrate that the structural peculiarity of the eutectic nano-alloys offers the highest catalytic activity in comparison with their non-eutectic counterparts. The fundamentals of nano-alloy formation revealed here may establish the groundwork for creating bimetallic and multimetallic nano-alloys.
Graphene‐based materials, primarily graphene oxide (GO), have shown excellent separation and purification characteristics. Precise molecular sieving is potentially possible using graphene oxide‐based ...membranes, if the porosity can be matched with the kinetic diameters of the gas molecules, which is possible via the tuning of graphene oxide interlayer spacing to take advantage of gas species interactions with graphene oxide channels. Here, highly effective separation of gases from their mixtures by using uniquely tailored porosity in mildly reduced graphene oxide (rGO) based membranes is reported. The gas permeation experiments, adsorption measurement, and density functional theory calculations show that this membrane preparation method allows tuning the selectivity for targeted molecules via the intercalation of specific transition metal ions. In particular, rGO membranes intercalated with Fe ions that offer ordered porosity, show excellent reproducible N2/CO2 selectivity of ≈97 at 110 mbar, which is an unprecedented value for graphene‐based membranes. By exploring the impact of Fe intercalated rGO membranes, it is revealed that the increasing transmembrane pressure leads to a transition of N2 diffusion mode from Maxwell–Stefan type to Knudsen type. This study will lead to new avenues for the applications of graphene for efficiently separating CO2 from N2 and other gases.
Membranes of reduced graphene oxide with interlaced transition metal ions offer effective separation of CO2 from N2 due to higher adsorption of N2 gas molecules within the Fe‐interacted nanochannels. Depending on the value of applied gas pressure, both Maxwell–Stefan and Knudsen diffusion contribute to the gas permeation process for these membranes.
A green carbon capture and conversion technology offering scalability and economic viability for mitigating CO2 emissions is reported. The technology uses suspensions of gallium liquid metal to ...reduce CO2 into carbonaceous solid products and O2 at near room temperature. The nonpolar nature of the liquid gallium interface allows the solid products to instantaneously exfoliate, hence keeping active sites accessible. The solid co‐contributor of silver–gallium rods ensures a cyclic sustainable process. The overall process relies on mechanical energy as the input, which drives nano‐dimensional triboelectrochemical reactions. When a gallium/silver fluoride mix at 7:1 mass ratio is employed to create the reaction material, 92% efficiency is obtained at a remarkably low input energy of 230 kWh (excluding the energy used for dissolving CO2) for the capture and conversion of a tonne of CO2. This green technology presents an economical solution for CO2 emissions.
With mechanical energy as the stimulus, CO2 is converted into solid carbon and O2 in a liquid‐metal‐based reaction system. Using the synergism of Ga nanodroplets and Ag–Ga nanorods, CO2 conversion proceeds through the triboelectrochemical reaction on Ga, while the Ag–Ga rods ensure the system's sustainability. This is achieved at a remarkably low energy consumption and high efficiency.
Phonon-polaritons (PhPs) in layered crystals, including hexagonal boron nitride (hBN), have been investigated by combined scattering-type scanning near-field optical microscopy (s-SNOM) and Fourier ...transform infrared (FTIR) spectroscopy. Nevertheless, many of such s-SNOM-based FTIR spectra features remain unexplored, especially those originated from the impact of boundaries. Here we observe real-space PhP propagations in thin-layer hBN sheets either supported or suspended by s-SNOM imaging. Then with a high-power broadband IR laser source, we identify two major peaks and multiple auxiliary peaks in the near-field amplitude spectra, obtained using scattering-type near-field FTIR spectroscopy, from both supported and suspended hBN. The major PhP propagation interference peak moves toward the major in-plane phonon peak when the IR illumination moves away from the hBN edge. Specific differences between the auxiliary peaks in the near-field amplitude spectra from supported and suspended hBN sheets are investigated regarding different boundary conditions, associated with edges and substrate interfaces. The outcomes may be explored in heterostructures for advanced nanophotonic applications.
Graphene is expected to bring substantial benefits for high-frequency applications, however, most of the studies in this area are based on theory. Here, the properties of epitaxial graphene grown on ...intrinsic silicon carbide on silicon substrates are investigated for potential radio frequency (RF) applications. Metal coplanar waveguides (CPWs) are fabricated that employ graphene as a shunt between the signal and ground planes. The CPWs are used for characterizing the frequency-dependent behavior of the sheet resistance of the graphene shunt from 10 MHz to 10 GHz. The process involves evaluating the CPW's RLCG transmission line parameters and comparing them to a reference un-shunted CPW to extract the sheet resistance. We find that the quality of the metal contact with graphene is one key parameter to observe adequate current injection in the 2D material in the RF spectrum. A mild argon plasma treatment was applied to reach an adequate contact quality. Furthermore, we observe a monotonic decrease of the sheet resistance of the epitaxial graphene for frequencies roughly above 100 MHz. We attribute this behavior to the progressively smaller influence of small-scale discontinuities, such as grain sizes, at those higher frequencies.
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