Zinc Chalcogenides Research Articles

Intrinsic Chiroptical Activity and Excitonic Properties of Group II-VI Magic-Size Clusters.

Semiconductor magic-size clusters (MSCs), lying in the local minima of the potential landscape, are important intermediates that emerge during the synthesis of colloidal quantum dots. They have definite geometrical and electronic structures, thus serving as atomically precise building blocks for assembling supramolecular structures and devices with unprecedented functionalities. Here we report the intrinsic chiroptical activity in the magic-size cadmium and zinc chalcogenide clusters with magic numbers of 13, 33, and 34 possessing unique core-shell structures. They are responsive to circularly polarized light from the ultraviolet to visible region, with size-tunable energy gap, absorption wavelength, and excitonic characteristics. The origin of the chiroptical activity and the evolution of excitonic states with magic size are disclosed by time-dependent density functional theory calculations within a correlated electron-hole picture. This molecular-level understanding of the photophysical properties of group II-VI MSCs provides essential guidelines for utilizing them for chiral optoelectronics and photonics.

Multishell Silver Indium Selenide-Based Quantum Dots and Their Poly(methyl methacrylate) Composites for Application in Red-Light-Emitting Diodes.

In this work, the production of novel multishell silver indium selenide quantum dots (QDs) shelled with zinc selenide and zinc sulfide through a multistep synthesis precisely designed to develop high-quality red-emitting QDs is explored. The formation of the multishell nanoheterostructure significantly improves the photoluminescence quantum yield of the nanocrystals from 3% observed for the silver indium selenide core to 27 and 46% after the deposition of the zinc selenide and zinc sulfide layers, respectively. Moreover, the incorporation of the multishelled QDs in a poly(methyl methacrylate) (PMMA) matrix via in situ radical polymerization is investigated, and the role of thiol ligand passivation is proven to be fundamental for the stabilization of the QDs during the polymerization step, preventing their decomposition and the relative luminescence quenching. In particular, the role of interface chemistry is investigated by considering both surface passivation by inorganic zinc chalcogenide layers, which allows us to improve the optical properties, and organic thiol ligand passivation, which is fundamental to ensuring the chemical stability of the nanocrystals during in situ radical polymerization. In this way, it is possible to produce silver-indium selenide QD-PMMA composites that exhibit bright red luminescence and high transparency, making them promising for potential applications in photonics. Finally, it is demonstrated that the new silver indium selenide QD-PMMA composites can serve as an efficient color conversion layer for the production of red light-emitting diodes.

Armchair zinc chalcogenide nanoribbons for high-performance photodetectors: A computational study

In this study, we employ density functional theory and non-equilibrium Green's function methods to investigate the electronic and photoelectric response properties of one-dimensional hexagonal ZnX (X = S, Se) nanoribbons (NRs). Remarkably, armchair (ARM) NRs demonstrate superior photoelectric response in the visible and near-ultraviolet regions. It is worth noting that for all considered photon energies, the photocurrent exhibits a cosine dependence on the polarization angle, which is consistent with the photogalvanic effect. when the width of NR is eight atoms, the zinc blende ZnSe/ARM NR-based device achieves a maximum extinction ratio of 63.9 at the photon energy of 3.0 eV. The significant photocurrent and high polarization sensitivity suggest the potential of ZnX NRs for applications in optoelectronic devices, particularly in visible and near-ultraviolet light detection.

Вивчення взаємодії інфрачервонопрозорих матеріалів ZnSe, ZnS, Si, Ge з розплавами металів

Wetting of infrared-transparent materials — selenide and sulfide zinc, germanium, and silicon by metal melts in a vacuum in a wide temperature range was studied by the sessile drop method using the method of capillary purification of the drop melt during the experiment. Pure metals In, Sn, Pb, Al, Fe, Ni, binary Al—Si, Ge—Si, In—Cu and multicomponent In—Sn—Cu—Ti alloys were used. When zinc chalcogenides are wetted with In—Sn—Cu—Ti melts, zinc selenide is wetted better than zinc sulfide. This is due to the lower thermodynamic stability of selenide. In systems where copper is present in melts, wetting is affected not only by the interaction of selenium or sulfur with titanium, but also by the interaction of copper and zinc (in the copper-zinc system, solid solutions of copper and zinc are formed and copper dissolves in solid zinc). This conclusion also confirms the wetting of the substrate by the In—Cu melt. The values of the contact angle at 650 C are equal to 32, which is less than for the In—Sn—Ti melt at the same temperature. It can be said that for such a system, the interaction of zinc with copper is very important, which is not inferior to the wetting effect of the interaction of chalcogens with titanium. The wetting of single crystals of germanium and silicon by metal melts improves with increasing temperature. Iron and nickel wet silicon (contact angles close to zero) at temperatures lower than their melting point. Contact melting also occurs when silicon substrates are wetted with aluminum melts (the eutectic in the Al—Si system has a temperature of 577 °C). Germanium is better wetted by tin than by indium and lead. Technological processes of soldering infrared transparent materials with metals were developed and soldered joints were obtained. Keywords: infrared transparent materials, polycrystalline zinc selenide and sulfide, single crystals of germanium and silicon, wetting, soldering.

Elastic, Optical, and Thermoelectric Properties of 2D Square Lattice and Hexagonal Zinc Chalcogenides under First‐Principles Calculations

Herein, elastic, optical, and thermoelectric properties of zinc chalcogenides with 2D square lattice and hexagonal phases [s‐ and h‐ZnX (X = GrVI)] are reported. The s‐ZnX and h‐ZnX structures are achieved to be dynamically stable, according to the phonon dispersion studies. All s‐ and h‐ZnX compounds are found to be semiconductor, with direct and indirect bandgaps ranging from 0.81 to 2.77 eV under PBE and 1.70 to 4.15 eV by HSE06 calculations. The effective mass, mobility, and relaxation time of electron and hole carriers in the band structures of s‐ and h‐ZnX are investigated to gain a better insight of these materials. In addition to the phonon dispersion analysis, their mechanical stability in terms of elastic properties is evaluated, and the resulting elastic parameters validate their mechanical stability. The optical properties of s‐ and h‐ZnX are inspected in the occurrence of field polarizations across parallel and perpendicular directions. At room temperature, s‐ZnTe compound has an optimum figure of merit (ZT) value, indicating it as the superlative thermoelectric material in the entire series. These compounds may also be explored in ultraviolet lasers, solar cells, electronic image displays, high‐density optical memory, photodetectors, and solid‐state laser devices.

A Review of Cr2+ or Fe2+ Ion-Doped Zinc Sulfide and Zinc Selenide Ceramics as IR Laser Active Media

Zinc chalcogenides doped with Cr2+ or Fe2+ ions are of considerable interest as active media for IR lasers operating in the 2–5 µm wavelength range. Such lasers are in demand in various fields of medicine, remote sensing and atmospheric monitoring, ranging, optical communication systems, and military applications. In recent years, however, the rate of improvement in the characteristics of zinc chalcogenide laser sources has slowed considerably. Unwanted thermally induced effects, parasitic oscillations, and laser-induced damage of the active element have hindered the scaling of output power and efficiency. However, the physical and chemical properties of the materials leave ample room for further improvements. In particular, the control of the dopant concentration profile in the active element is of great importance. Zero concentration of Cr2+ or Fe2+ ions on the radiation input/output surfaces can significantly increase the laser-induced damage threshold; the designed concentration distribution in the element volume allows regulation of heat dissipation and reduction of parasitic oscillations. The zinc chalcogenide ceramic technology seems to be the most suitable to solve this challenge. This review presents and discusses the state of the art in ZnS and ZnSe optical and laser ceramics and the directions for further development of their technology.

Comprehensive studies of dielectric behavior, resistive switching, and a.c. conduction in zinc-containing quaternary glasses of Se-Te-Sn

The dielectric behavior, thermally activated a.c. conduction and resistive switching form the basis for revealing new information about the conduction mechanics of glassy chalcogenide materials. Zinc has been chosen as a modifier to control different electrical properties in a parent ternary glass Se78Te20Sn2 of Se-Te-Sn system in the present work keeping in mind the exceptional physical properties of zinc chalcogenides. The detailed analysis indicates that dielectric constant (ε′), dielectric loss (ε″), and a.c. conductivity (σac) is changed appreciably with varying concentrations of zinc atoms in the parent glass. The a.c. conduction follows the correlated barrier hopping (CBH) with bi-polaron hopping as the leading conduction mechanism. We have also determined the density of localized states by using the CBH model. Further, the resistive switching is modified significantly after zinc incorporation. The results have been explained using the chemically ordered network (CON) model and heavy cross-linking of glass-matrix due to isomers of SeyZny nanoclusters.

Nonequilibrium quantum transport properties of tetragonal zinc chalcogenide monolayers

Tetragonal zinc chalcogenide monolayers (TZCM) are emerging as interesting electronic materials with a direct band gap and relatively high carrier mobility. In this work, we report a theoretical investigation of electronic transport properties and photoelectric response properties of TZCM with gold contacts by density functional theory (DFT) and non-equilibrium Green's function (NEGF) methods. When there is no gate voltage applied, the current increases nonlinearly as bias voltage increases. Among the four proposed devices, the Au(100)/ZnS/Au(100) device has the best electronic transport performance and is most sensitive to the adjustment of bias voltage and gate voltage. The photocurrent calculation results indicate that the low-frequency oscillatory photocurrent of the Au(100)/ZnSe/Au(100) device in the high photon energy region may have potential applications in ultraviolet light-emitting diodes. The Au(100)/Zn2SeS/Au(100) device has more stable photoelectric response and polarization sensitivity than the Au(100)/Zn2SSe/Au(100) device. The Au(100)/TZCM/Au(100) devices exhibit considerable photocurrent and good extinction ratios. This work could pave the way for the future application of TZCM in the field of optoelectronics and so on.

A Heteroanionic Zinc Ion Conductor for Dendrite-Free Zn Metal Anodes.

Although zinc-based batteries are promising candidates for eco-friendly and cost-effective energy storage devices, their performance is severely retarded by dendrite formation. As the simplest zinc compounds, zinc chalcogenides, and halides are individually applied as a Zn protection layer due to high zinc ion conductivity. However, the mixed-anion compounds are not studied, which constrains the Zn2+ diffusion in single-anion lattices to their own limits. A heteroanionic zinc ion conductor (Zny O1- x Fx ) coating layer is designed by in situ growth method with tunable F content and thickness. Strengthened by F aliovalent doping, the Zn2+ conductivity is enhanced within the wurtzite motif for rapid lattice Zn migration. Zny O1- x Fx also affords zincophilic sites for oriented superficial Zn plating to suppress dendrite growth. Therefore, Zny O1- x Fx -coated anode exhibits a low overpotential of 20.4mV for 1000h cycle life at a plating capacity of 1.0mAhcm-2 during symmetrical cell test. The MnO2 //Zn full battery further proves high stability of 169.7 mAhg-1 for 1000 cycles. This work may enlighten the mixed-anion tuning for high-performance Zn-based energy storage devices.

Generalized Einstein relation in disordered organic semiconductors: Influence of the acoustic phonons–charge carriers scattering

In this work, we analyze the generalized Einstein relation for disordered organic semiconductors with a non-equilibrium Druyvesteyn-type distribution function. The Druyvesteyn behavior of hot electrons in a solid state is associated with the acoustic phonons–charge carriers scattering. Such a case has been experimentally demonstrated in electroluminescent inorganic rare–earth–doped zinc chalcogenides. Therefore, we can assume that, in a part of organic materials used in organic light-emitting diodes (OLEDs), we can also find the Druyvesteyn-type distribution of charge carriers under external electric fields. It looks that the electric-field-dependent diffusion coefficient, which is observed in the phonon-induced hopping electron transport, plays a key role here. The theoretical analysis of the Einstein relation shows that for lower concentrations of charge carriers, the diffusivity–mobility ratio (D/μ) reaches a value lower than 1 (in kT/q units). The temperature dependencies of D/μ are similar to the tendencies reported for the equilibrium conditions. The obtained satisfactory agreement between experimental results and calculations based on the Druyvesteyn-type distribution function confirms the usefulness of the presented model.

2D II-VI Semiconductor Nanoplatelets: From Material Synthesis to Optoelectronic Integration.

The field of colloidal synthesis of semiconductors emerged 40 years ago and has reached a certain level of maturity thanks to the use of nanocrystals as phosphors in commercial displays. In particular, II-VI semiconductors based on cadmium, zinc, or mercury chalcogenides can now be synthesized with tailored shapes, composition by alloying, and even as nanocrystal heterostructures. Fifteen years ago, II-VI semiconductor nanoplatelets injected new ideas into this field. Indeed, despite the emergence of other promising semiconductors such as halide perovskites or 2D transition metal dichalcogenides, colloidal II-VI semiconductor nanoplatelets remain among the narrowest room-temperature emitters that can be synthesized over a wide spectral range, and they exhibit good material stability over time. Such nanoplatelets are scientifically and technologically interesting because they exhibit optical features and production advantages at the intersection of those expected from colloidal quantum dots and epitaxial quantum wells. In organic solvents, gram-scale syntheses can produce nanoparticles with the same thicknesses and optical properties without inhomogeneous broadening. In such nanoplatelets, quantum confinement is limited to one dimension, defined at the atomic scale, which allows them to be treated as quantum wells. In this review, we discuss the synthetic developments, spectroscopic properties, and applications of such nanoplatelets. Covering growth mechanisms, we explain how a thorough understanding of nanoplatelet growth has enabled the development of nanoplatelets and heterostructured nanoplatelets with multiple emission colors, spatially localized excitations, narrow emission, and high quantum yields over a wide spectral range. Moreover, nanoplatelets, with their large lateral extension and their thin short axis and low dielectric surroundings, can support one or several electron-hole pairs with large exciton binding energies. Thus, we also discuss how the relaxation processes and lifetime of the carriers and excitons are modified in nanoplatelets compared to both spherical quantum dots and epitaxial quantum wells. Finally, we explore how nanoplatelets, with their strong and narrow emission, can be considered as ideal candidates for pure-color light emitting diodes (LEDs), strong gain media for lasers, or for use in luminescent light concentrators.

A zinc-conducting chalcogenide electrolyte

A solid-state zinc-ion battery can fundamentally eliminate dendrite formation and hydrogen evolution on the zinc anode from aqueous systems. However, enabling fast zinc ion + conduction in solid crystals is thought to be impossible. Here, we demonstrated a fluorine-doping approach to achieving fast Zn2+ transport in mesoporous ZnyS1-xFx. The substitutional doping of fluoride ion with sulfide substantially reduces Zn2+ migration barrier in a crystalline phase, while mesopore channels with bounded dimethylformamide enable nondestructive Zn2+ conduction along inner pore surface. This mesoporous conductor features a high room-temperature Zn2+ conductivity (0.66 millisiemens per centimeter, compared with 0.01 to 1 millisiemens per centimeter for lithium solid-state electrolyte) with a superior cycling performance (89.5% capacity retention over 5000 cycles) in a solid zinc-ion battery and energy density (0.04watt-hour per cubic centimeter) in a solid zinc-ion capacitor. The universality of this crystal engineering approach was also verified in other mesoporous zinc chalcogenide materials, which implies various types of potential Zn2+-conducting solid electrolytes.

Efficient H2O2 dissociation and formation on zinc chalcogenides: A density functional theory study

Establishing the structure–activity relationship is very important for the design of new catalysts for advanced oxidation process with low energy consumption and high efficiency. In this work, the atomic mechanism of hydrogen peroxide (H2O2) dissociation and formation on zinc chalcogenides (ZnX, where X denotes O, S, Se, and Te) was investigated. It was found that the catalytic activity of H2O2 dissociation and formation on ZnX was determined by the surface micro-engineering construction including surface orientation and heteroatomic doping. H2O2 can dissociate to easily form hydroxyl radicals on ZnO (110), ZnSe (100), ZnTe (110) and ZnTe (100) surfaces, while only the ZnO (110) surface can catalyze water oxidation to form H2O2. Furthermore, the H2O2 selectivity of water oxidation on the ZnO (110) surface can be enhanced by the doping with silver atoms due to the weak adsorption strength of OH*, while introducing copper atom into the ZnO (110) surface can promote H2O2 dissociation. These results not only unveil the mechanism of H2O2 dissociation and formation on ZnX, but also can provide helpful guidance for the development of new catalytic oxidation systems.

Heteroepitaxial chemistry of zinc chalcogenides on InP nanocrystals for defect-free interfaces with atomic uniformity

Heteroepitaxy on colloidal semiconductor nanocrystals is an essential strategy for manipulating their optoelectronic functionalities. However, their practical synthesis typically leads to scattered and unexpected outcomes due to the intervention of multiple reaction pathways associated with complicated side products of reactants. Here, the heteroepitaxy mechanism of zinc chalcogenide initiated on indium phosphide (InP) colloidal nanocrystals is elucidated using the precursors, zinc carboxylate and trialkylphosphine selenide. The high magnetic receptivity of 77Se and the characteristic longitudinal optical phonon mode of ZnSe allowed for monitoring the sequence of epilayer formation at the molecular level. The investigation revealed the sterically hindered acyloxytrialkylphosphonium and diacyloxytrialkylphosphorane to be main intermediates in the surface reaction, which retards the metal ion adsorption by a large steric hindrance. The transformation of adsorbates to the crystalline epilayer was disturbed by surface oxides. Raman scattering disclosed the pathway of secondary surface oxidation triggered by carboxylate ligands migrated from zinc carboxylate. The surface-initiated heteroepitaxy protocol is proposed to fabricate core/shell heterostructured nanocrystals with atomic-scale uniformity of epilayers. Despite the large lattice mismatch of ZnS to InP, we realised a uniform and interface defect-free ZnS epilayer (~0.3 nm thickness) on InP nanocrystals, as evidenced by a high photoluminescence quantum yield of 97.3%.

Exfoliable and self-healable two-dimensional materials from wurtzite zinc chalcogenides as building blocks of nanodevices.

With the advent of graphene, two-dimensional (2D) materials have emerged as promising candidates for next-generation electronic and optoelectronic applications. The most anticipated 2D materials have been synthesized and exploited for novel applications. Multilayered zinc chalcogenides (ZnX) are the best precursors for obtaining atomic layer two-dimensional materials by exfoliation. Therefore, we carry out a detailed density functional theory-based study to achieve an exfoliation process of ZnX non-van der Waals sheets by straining and provide a microscopic understanding of the ferroelectric, optic, and spin behaviors of ZnX systems and the corresponding self-healable two-dimensional ZnX devices. The results revealed that 2D ZnX sheets can be obtained when strain is 14% for ZnS and ZnSe, and the peak values of exfoliation energy have a similar order of magnitude to those of traditional 2D materials, indicating the possibility of obtaining 2D ZnX monolayers. For intrinsic 2D ferroelectric materials with in-plane electric polarization, the direction of ZnX sheets can be reversed using an electric field with an energy barrier of ∼0.175 eV per atom for ZnSe, offering a promising functional basis for their application in ferroelectric nanodevices. The first absorption of photons for polarization perpendicular to the monolayer plane occurs in a high energy range of photons, facilitating their application in LEDs. The spin splitting in non-centrosymmetric ZnX crystals exhibits a Rashba spin-texture according to first-principles calculations. The self-healable two-dimensional nanodevices have a smooth curve from -0.5 to 0.5 eV. This work indicates the potential value of non-van der Waals ZnX 2D materials for their application in photoelectric and spintronic nanodevices.

Computational evaluation of novel barium zinc chalcogenides Ba2ZnCh3 (Ch = S, Se, Te) for advanced optoelectronic applications.

Due to their outstanding optoelectronic characteristics, ternary chalcogenides are considered an attractive choice for absorbers of visible light. Here, a novel family of ternary chalcogenides, Ba2ZnCh3 (Ch = S, Se, Te), is examined in the context of density functional theory calculations. The atomic locations in these materials are determined before the bulk modulus, cohesive energy, and lattice constant predictions. Our examined materials are semiconductors by nature, as indicated by the electronic band profiles with both the WC-GGA potential and TB-mBJ potential revealing an energy gap between the valence and conduction bands. Using full geometrical optimization and the force minimization technique based on Broyden's scheme, the interior atomic positions and the relaxed structures were obtained. The formation energies are likely more consistent with a convex hull near the configuration of interest. The cohesive energies confirmed that Ba2ZnS3 has the most cohesive nature as compared to the other two materials. Likewise, the calculated components of the dielectric function of the individual materials were anisotropic having dissimilar values along different dimensions. The computed sharp peaks of the absorption coefficient for Ba2ZnS3, Ba2ZnSe3, and Ba2ZnTe3 confirm their improved absorption behavior in the UV range. Moreover, the thermoelectric characteristics were computed, and the findings are detailed, indicating that all of these materials are efficient for thermoelectric device applications.

Fabrication of a dye-based random laser using ZnS:Mn quantum dots and investigating the effects of their concentration

Zinc chalcogenide quantum dots (QDs) doped with paramagnetic transition metal ions (particularly ZnS:Mn QDs) are new attractive but rarely examined semiconductor nanocrystals that have excellent optical properties and enhanced thermal and environmental stability compared to Cd-based QDs. In this paper, we demonstrate a dye-based random laser (RL) with nonresonant feedback using ZnS:Mn QDs as the scattering medium that are dispersed in a Rhodamine B (RhB) dye solution. The nonlinear variation of the emission spectrum as a function of the excitation energy implies a random lasing threshold. Moreover, we observe a blue-shift of the emission wavelength by 10.3 nm and a 5.3 times decrease in the RL threshold by increasing the scatterer concentration. We also provide a theoretical discussion based on the diffusion theory for explaining the observed experimental results.

Determination of stoichiometry deviation in wide-band II-VI semiconductors on the basis of equilibrium vapor phase composition

A method of determining stoichiometry deviation in cadmium and zinc chalcogenides that is based on the temperature dependence of the ratio of components partial pressures during evaporation of solid compounds in a limited volume has been suggested. The new method differs from methods implying the collection of excessive component during evaporation in large volumes. The method includes measuring vapor phase components partial pressures during material heating to above 800 K, solving a set of material balance equations and the electric neutrality equation, and calculating the stoichiometry deviation in the initial compound at room temperature. Intrinsic point defect concentrations are calculated using the method of quasichemical reactions. The independent variables in the set of equations are the sought stoichiometry deviation, the partial pressure of the metal and the concentration of free electrons. We show that the parameter of the material balance equation which determines the method’s sensitivity to stoichiometry deviation, i.e., the volume ratio of vapor and solid phases, can be considered constant during heating and evaporation unless this parameter exceeds 50. If the partial pressure is measured based on the optical density of the vapors, then the sensitivity of the method can be increased to not worse than 10-6 at.%.

Determination of stoichiometry deviation in wide-band II–VI semiconductors on the basis of equilibrium vapor phase composition

A method has been suggested for determining stoichiometry deviation in cadmium and zinc chalcogenides based on the temperature dependence of the ratio of components partial pressures during evaporation of solid compounds in a limited volume. The new method differs from methods implying the collection of excessive component during evaporation in large volumes. The method includes measuring the partial pressures of vapor phase components during material heating to above 800 K, solving a set of material balance equations and the electric neutrality equation, and calculating the stoichiometry deviation in the initial compound at room temperature. Intrinsic point defect concentrations are calculated using the method of quasichemical reactions. The independent variables in the set of material balance equations are the sought stoichiometry deviation, the partial pressure of the metal and the concentration of free electrons. We show that the parameter of the material balance equation which determines the method’s sensitivity to stoichiometry deviation, i.e., the volume ratio of vapor and solid phases, can be considered constant during heating and evaporation if this parameter does not exceed 50. If the partial pressure is measured based on the optical density of the vapors, then the sensitivity of the method can be increased to not worse than 10–6 at.%.

Single-layer honeycomb sheets of zinc selenide and beyond with superior electronic and optical properties

The freestanding four-atom-thick double-layer honeycomb sheets of zinc chalcogenides which were synthesized recently are outstanding two-dimensional (2D) materials for next-generation ultrathin optoelectronic nanodevice. In this work, we report a theoretical study on two different single-layer honeycomb sheets of MX (M = Zn, Cd; X = Se, S). The two kinds of single-layer sheets of MX would be thought by cutting along the zinc blende (ZB) bulk as well as wurtzite (WZ) bulk. By using state-of-the-art calculations based upon quasiparticle GW and Bethe–Salpeter equation (BSE), the single-layer sheets of MX possess wide band gaps and are capable of being used as photocatalysts for solar water splitting. The optical absorbance demonstrates that the single-layer sheets of CdSe and CdS have substantial absorption within the visible light region, and the optical absorption of the single-layer sheets of ZnSe can be easily modulated via strains. Furthermore, the electronic transport properties of the single-layer sheets of MX are investigated through the nonequilibrium Green’s function (NEGF) method combined with density functional theory (DFT). It is anticipated that these novel freestanding single-layer honeycomb sheets of MX would be great candidates for abundant potential applications in energy storage and conversion.