The work focuses on lanthanum cerium copper oxide, one of the materials produced by introducing additional electrons into a parent copper-oxide compound. Substitution of lanthanum with cerium is the electron-doping strategy used in the experiment. This differs from the other principal approach, in which chemical substitutions remove electrons and create mobile charge carriers called holes.

The distinction matters because the highest critical temperatures are found among hole-doped cuprates, whereas the new measurements establish the link between spin fluctuations and superconductivity on the electron-doped side. Superconductivity permits electrical current to flow without energy loss, and the researchers sought to determine which microscopic process is responsible for the transition in the electron-doped material. In conventional, lower-temperature superconductors, the relevant process involves vibrations of the ions forming the crystal lattice.

For many years, researchers have searched for a different mechanism in high-temperature copper oxides, with fluctuating electronic spin and charge considered important possibilities. Electrons possess both a charge, which can fluctuate in space and time, and a spin, which produces a magnetic field and can likewise fluctuate. The new experiment concentrates on how conduction electrons interact with these spin fluctuations.

Although spin and charge fluctuations had previously been mapped in considerable detail in copper oxides, the supplied research describes a missing connection: evidence tying the strength of the interaction between conduction electrons and those fluctuations to the critical temperature, or Tc. The central idea was that this information might be encoded in the material’s electrical resistance. If resistance could be measured across finely spaced values of Tc while other experimental variables remained controlled, the researchers could test whether the strength of the electron–spin interaction varied with the superconducting transition temperature.

To create such a range of transition temperatures within one specimen, the team prepared a special lanthanum cerium copper oxide thin film. They deposited the material layer by atomic layer on a substrate, producing a smooth gradient in Tc along the film’s length. The gradient extended from the maximum value in the sample to zero.

Because the transition temperature changed gradually across the device, the specimen supplied many closely spaced superconducting states that could be investigated using the same film. The researchers used lithography to pattern a series of electrical contacts along the film. This arrangement allowed them to measure resistance at many values of Tc while keeping the level of disorder constant across the sample.

The experiments were performed at the high magnetic-field facility of the European Magnetic Field Laboratory in the Netherlands. During magnetotransport measurements, the team recorded changes in resistance as a function of temperature, applied magnetic-field strength and local Tc. The thin-film samples were loaded into a cryostat, cooled to temperatures close to absolute zero and inserted into the bore of the magnet for these measurements.

Analysis of the high-field resistance data allowed the team to identify the dominant source of scattering in the material. The resulting interpretation was that conduction electrons scatter from fluctuating spins, and the strength of this interaction correlated with Tc. In other words, the quantity associated with the electron–spin interaction changed systematically as the point of the superconducting transition changed across the film.

The investigators regard this correlation as confirmation that the superconductivity observed in this material originates from the interaction between conduction electrons and spin fluctuations. The paper reports this result as evidence for spin-fluctuation-mediated pairing in electron-doped cuprates. The findings are significant because they connect a measurable transport property with a proposed microscopic pairing process in a material known for high-temperature superconductivity.

The specially engineered gradient film made it possible to examine the relationship over a broad range of critical temperatures without changing the underlying film, and the high-field measurements supplied the resistance data used for the analysis. The result does not establish that spin fluctuations are the only relevant process in all copper oxides. Rather, it identifies the dominant interaction and its relationship to Tc in the electron-doped compound examined here, narrowing the explanation of superconductivity for this particular part of the cuprate family.

The study nevertheless leaves a second ingredient unresolved. The researchers note that electron- and hole-doped cuprates are made from the same broad family of materials but behave differently, particularly in the values of Tc they attain. The highest Tc values occur only on the hole-doped side.

It may appear that simply increasing the strength of coupling to fluctuating spins, or increasing the frequency of those fluctuations, would extend the electron-doped result to the higher transition temperatures of hole-doped materials. Their earlier high-field studies of the hole-doped counterparts, however, indicate that this simple explanation is insufficient and that another ingredient is responsible for their higher Tc values. That limitation is central to the study’s interpretation.

The team has found what it describes as the first key ingredient in one side of the superconductivity puzzle, but says that theorists will need a complete account of both electron- and hole-doped behavior before the full mechanism of high-temperature superconductivity can be assembled. Its narrower finding is experimentally specific: in the specially prepared electron-doped film, the dominant resistance was attributed to scattering from fluctuating spins, and the strength of that interaction tracked Tc. Identifying this first component gives researchers a concrete foundation for investigating the missing factor associated with the higher transition temperatures of hole-doped cuprates.

Subject of Research: Experimental evidence for spin-fluctuation-mediated pairing in electron-doped copper-oxide superconductors

Article Title: Researchers discover ‘smoking gun’ to help solve mystery of high-temperature superconductivity

Article References: Researchers discover ‘smoking gun’ to help solve mystery of high-temperature superconductivity. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: high-temperature superconductivity, electron-doped cuprates, spin fluctuations, critical temperature, magnetotransport, electrical resistance, lanthanum cerium copper oxide, thin films, Nature Physics, Researchers, discover, smoking

Scanning probe microscopy measurements gave root-mean-square surface roughness values, expressed as Rq, of 80.91 nm for CBD, 78.18 nm for SILAR and 42.29 nm for FTCD. Thus, the FTCD coating had a markedly lower measured roughness than the two conventionally deposited films. Its Rq value was about 52% of the CBD value and slightly more than half the SILAR value. The authors described the continuous-flow reactor approach as producing a coating with lower surface roughness and better wetting behavior than the conventional coating methods, while the reported contact-angle data provide a more specific picture of the difference in water repellency.

All three coatings were hydrophobic according to their water contact angles. The measured values were 145.26° ± 3.04° for CBD, 141.09° ± 3.50° for SILAR and 130.63° ± 3.78° for FTCD. The CBD and SILAR films therefore had higher water contact angles than the FTCD film, with the FTCD value lower by about 15 degrees than CBD and 10 degrees than SILAR when the reported means are compared. Within this set of three films, the rougher CBD and SILAR surfaces were associated with greater measured water repellency, whereas the smoother FTCD surface had a lower contact angle. The results establish a relationship between surface roughness and wettability for the tested coatings, but they do not isolate roughness as the sole cause of the differences or show that the same relationship applies to other compositions or substrates.

The researchers characterized the nanocomposite films with X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet–visible spectroscopy, Fourier transform infrared spectroscopy and scanning probe microscopy. These methods were used to examine structural, optical, chemical and morphological properties. Water contact angle measurements assessed the hydrophobic character of the ZnO coatings. The study’s evidence supports a comparison of the fabrication methods through the reported roughness and contact-angle values, together with the broader characterization of film structure and composition; the available summary does not specify individual values for every characterization technique or the full preparation parameters used for each method.

The findings identify a measurable trade-off between surface smoothness and water repellency in ZnO/stearic acid nanocomposite thin films. FTCD produced the lowest roughness, but CBD and SILAR produced the highest contact angles. The results may help inform the design of hydrophobic nanostructured coatings for applications including self-cleaning surfaces and corrosion inhibition, which the authors identified as potential uses for hydrophobic ZnO coatings. Because the reported comparison concerns laboratory thin films deposited on glass, the results describe fabrication-dependent differences in this material system rather than performance across different applications or operating conditions.

Subject of Research: Comparison of fabrication methods for hydrophobic ZnO/stearic acid nanocomposite thin films

Article Title: Effect of the fabrication method on the hydrophobicity of ZnO/stearic acid nanocomposite thin films: comparison of flow-through chemical deposition (FTCD) with SILAR and CBD methods

Article References: Yücel, Y., & Yücel, E. (2026). Effect of the fabrication method on the hydrophobicity of ZnO/stearic acid nanocomposite thin films: comparison of flow-through chemical deposition (FTCD) with SILAR and CBD methods. Journal of Nanoparticle Research, 28(11), Article 274. https://doi.org/10.1007/s11051-026-06794-9

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06794-9

Keywords: ZnO nanocomposites, flow-through chemical deposition, chemical bath deposition, SILAR, surface roughness, water contact angle, hydrophobic coatings, wettability, thin films, Effect, fabrication, method

Perovskite solar cells owe their appeal to a rare combination of traits: power conversion efficiencies that now rival established silicon technology, and a manufacturing route based on low-cost solution processing that can be printed, coated, or spin-cast at temperatures far below those needed for silicon wafer fabrication. Yet the technology remains haunted by stubborn bottlenecks. Devices degrade under sustained illumination, heat, and humidity; non-radiative recombination losses drain voltage; energy levels at interfaces misalign in ways that waste charge carriers; and producing large, uniform films across square meters of module area remains notoriously difficult. These problems, the review argues, share a common root in the delicate chemistry of the perovskite layer itself.

Ionic liquids, salts that remain liquid at or near room temperature, have emerged as one of the most versatile tools for addressing these weaknesses. Composed of bulky organic cations paired with organic or inorganic anions, they are essentially non-volatile, thermally robust, and electrically conductive. Crucially for perovskite researchers, both halves of the molecule can be tuned independently. The review emphasizes that this structural modularity is the key to their effectiveness: the cation backbone, the length of alkyl side chains, the type of functional substituents, and the coordination behavior of the anion collectively determine how, and how strongly, an ionic liquid interacts with the perovskite components.

The first major mechanism the authors dissect is crystallization control. Perovskite films form from solution, and the speed and orderliness of crystal growth determine whether the final film is riddled with grain boundaries and voids or dense and well-oriented. Ionic liquids can coordinate with lead ions and intermediate phases during deposition, slowing nucleation and guiding the formation of larger, more uniform grains. The review highlights work showing that ionic liquid additives enable high-quality crystallization even in air atmosphere, a significant practical advantage since perovskite processing has traditionally demanded inert-glovebox conditions. Viscosity effects, noted in earlier studies of ionic-liquid-assisted growth, also modulate how nanoparticles assemble into the final film.

Defect passivation is the second pillar. The surfaces and grain boundaries of perovskite crystals are littered with undercoordinated lead atoms and halide vacancies that act as traps for charge carriers, sapping efficiency through non-radiative recombination. Ionic liquids attack this problem from both ends of the molecule: the anion, whether a halide, pseudohalide, acetate, or fluorinated species, can bond to exposed lead sites, while cations such as imidazolium, pyrrolidinium, and pyridinium derivatives interact with the halide-rich side of the lattice. The review catalogs studies in which such dual-action passivation pushed fill factors above 83 percent in cesium-based cells and lifted efficiencies beyond 23 and even 25 percent, including air-fabricated devices reaching 25.11 percent efficiency.

Interfacial energetics form the third mechanism. A solar cell is a stack of dissimilar materials, and every junction between the perovskite and its transport layers can either help or hinder the flow of electrons and holes. Ionic liquids, with their permanent dipoles and tunable work functions, can realign energy levels at these buried interfaces, reducing voltage losses. The review describes strategies ranging from ionic liquid optimization of the interface between spray-coated nickel oxide and the perovskite, to hybrids of self-assembled monolayers and ionic liquids for buried interface modulation in tandem devices, to ionic liquid engineering that strengthens the perovskite/self-assembled-monolayer heterointerface itself.

Moisture resistance and long-term stability round out the picture. Water ingress is a primary degradation pathway for perovskites, and the hygroscopic character of ionic liquids is a double-edged sword that the review examines carefully. Some ionic liquids form protective encapsulating layers or stabilize one-dimensional perovskite phases at the surface that shield the underlying three-dimensional absorber. A landmark study cited in the review demonstrated that ionic liquids can dramatically improve the long-term operational stability of perovskite solar cells, and related work showed modules stabilized with ionic liquids exceeding 20 percent power conversion efficiency. The review also notes that in situ oligomerization of ionic liquids has produced robust encapsulation even in perovskite single crystals for X-ray detection, hinting that the same chemistry could harden photovoltaic devices.

The review’s most distinctive contribution is its insistence on structure-property relationships. Rather than treating ionic liquids as interchangeable additives, it categorizes them by chemical family, imidazolium, pyrrolidinium, ammonium, pyridinium, and protic variants among them, and links each family’s behavior to its molecular features. Alkyl chain length governs hydrophobicity and how deeply the cation inserts into the lattice; functional groups such as sulfonates, fluorine atoms, and Lewis base sites dictate coordination strength and passivation mode; and anion identity determines whether the additive manages iodine, moderates strain, or forms low-dimensional surface phases. This framework explains why, for example, a piperidinium salt famously stabilized high-efficiency perovskite cells in work published in Science, and why acetate-based ionic liquids excel at crystallization regulation in inorganic compositions.

The implications extend well beyond the laboratory. Ionic liquids have enabled printable mesoscopic cells exceeding 20 percent efficiency, improved the humidity tolerance of vacuum-deposited large-area modules, and even accelerated the oxidation of the widely used hole transport material Spiro-OMeTAD for more reproducible devices. They are also opening a greener processing route: protic ionic liquids have allowed researchers to formulate perovskite inks from water and alcohols for slot-die coating, moving the field away from toxic solvents. Machine learning is now being deployed to accelerate the search for optimal ionic liquid formulations, a development the review flags as a coming inflection point for the field.

Challenges remain before ionic liquid engineering becomes standard practice. The review acknowledges that the sheer diversity of possible cation-anion combinations makes systematic optimization difficult, that the long-term behavior of some additives under real-world operating conditions needs further scrutiny, and that the green credentials of ionic liquids themselves deserve honest reassessment rather than assumption. Still, the authors argue that the correlations they have mapped between molecular design and device performance provide the theoretical foundation needed to move from empirical discovery to deliberate engineering. If perovskite solar cells are to graduate from record-breaking lab curiosities to durable, bankable products on rooftops and solar farms, the humble ionic liquid, they suggest, may be one of the decisive ingredients.

Subject of Research: The role of ionic liquid molecular design in improving the efficiency and stability of perovskite solar cells

Article Title: Ionic liquids for perovskite solar cells: from molecular design to device performance

Article References: Sun, Z., Yang, L., Du, F., Wang, H., & Li, Z. (2026). Ionic liquids for perovskite solar cells: from molecular design to device performance. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13946-8

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13946-8

Keywords: perovskite solar cells, ionic liquids, defect passivation, crystallization, photovoltaics, interface engineering, device stability, molecular design, thin films, renewable energy, Ionic, liquids

Outer membrane vesicles, or OMVs, are roughly 50 to 150 nanometers in diameter, cannot replicate, and carry multiple pathogen-associated molecular patterns that make them potent adjuvants. They have already been engineered to display influenza antigens, including the Matrix two protein extracellular domain, and recombinant OMV vaccines have protected mice against lethal influenza A challenge. Their weakness is thermal: OMVs are unstable above 37 degrees Celsius and are normally stored frozen or freeze-dried long term. The authors report their own observations that OMVs precipitate from solution within hours at room temperature and overnight at 4 degrees Celsius, underscoring how fragile these vesicles are in liquid form.

The team, led by Stephanie M. Curley in the Electrical, Computer, and Biomedical Engineering Department, generated OMVs from engineered ClearColi cells displaying four heterologous M2e epitope sequences fused to the bacterial protein ClyA with a C-terminal histidine tag. Vesicles were purified by vacuum filtration and ultracentrifugation, quantified by total protein content, and characterized by dynamic light scattering to confirm particle size distribution and concentration. Films were then prepared by drop casting 750 microliters of formulation into 12-well plates and drying for at least 24 hours at room temperature.

Formulation engineering was a central part of the study. The researchers screened solvents including water, phosphate-buffered saline, sodium chloride, and Tris buffers, finding that 20 millimolar Tris at pH 8.8 produced the most consistent film formation across excipients. Two molecular weights of hydroxypropyl methylcellulose, or HPMC, were tested, but only the 10 kilodalton version dissolved fully at the concentrations needed; the 86 kilodalton polymer failed to dissolve, and 1 percent HPMC yielded thin, brittle films while 5 percent and above proved unwieldy. The final films used 2.5 percent HPMC, combined with poly(vinyl) alcohol, poly(ethylene) glycol, sorbitol, glycerol, or the amphiphilic compound PMAL, and OMVs were loaded to a reconstituted total protein concentration of 0.03 milligrams per milliliter.

Physical characterization revealed how the vesicles integrate into the film matrix. Fourier transform infrared spectroscopy showed broader and more intense peaks in the approximately 3500 per centimeter region, which the authors attribute to enhanced hydrogen bonding between hydroxyl groups of the HPMC matrix and functional groups on OMV surface proteins and lipopolysaccharides. Hydrophilic, hydroxyl-dense additives such as PVA, sorbitol, and glycerol further strengthened these interactions. Scanning electron microscopy showed spherical protrusions on the surface of OMV-containing films that were absent from control films, and cross-sectional imaging established a film thickness of approximately 50 to 100 micrometers, thin enough for rapid dissolution.

Long-term stability testing produced the study’s most consequential findings. Four film types were stored at room temperature for up to eight weeks, then reconstituted in phosphate-buffered saline and assessed by particle count and protein analysis. Films containing PMAL, an amphiphilic compound often used to stabilize biomolecules, degraded the OMV structure completely within four weeks, an outcome the authors link to its detergent-like nature, since surfactants are routinely used to degrade OMVs in laboratory assays. In contrast, films containing PVA with sorbitol or PVA with glycerol maintained consistent particle counts over the full eight weeks, with only a slight reduction in the PEG-containing film at the final time point.

Protein stability told a more nuanced story. Dot blots probing the histidine-tagged ClyA-M2e antigen on intact vesicles showed that PMAL-containing films lost detectable antigen by two weeks, earlier than the four-week point at which particle degradation became apparent, suggesting that surface proteins interact directly with film components and degrade before the vesicle structure collapses. SDS-PAGE analysis indicated protein degradation in PMAL films as early as one week after film formation, although the low antigen concentration of approximately 0.03 milligrams per milliliter limited the resolution of the expected 50 kilodalton ClyA-M2e band. Western blotting, which captures antigen both within and on the surface of vesicles, showed that ClyA-M2e content remained relatively consistent across eight weeks in sorbitol-containing films and, to a large extent, in PEG-containing films, with PEG formulations providing the most protein stability overall and some reduction visible in glycerol-containing films at eight weeks.

Dissolution testing addressed the platform’s intended route of administration. Because only the first two formulations, HPMC-PVA-sorbitol and HPMC-PVA-glycerol, were mechanically stable enough to be removed intact from the casting molds, these films were tested in solutions mimicking the salivary environment, containing alpha-amylase, lipase, and lysozyme alone and in combination in cell culture medium at 37 degrees Celsius. All dissolution times fell below roughly 400 seconds, with most films dissolving in under five minutes, and alpha-amylase produced the fastest dissolution of the three single enzymes. The authors note this is unexpected, since cellulose compounds inhibit alpha-amylase activity, and suggest instead that amylase binding to the cellulose surface may physically disrupt the film structure and accelerate dissolution.

The implications reach beyond the laboratory bench. Lower respiratory infections are currently the fourth leading cause of death worldwide, and influenza alone causes an estimated 389,000 deaths annually. Systemic injection often fails to promote immunity at the oral and nasal mucosa, the primary site of infection for respiratory pathogens, whereas mucosal vaccines can induce both local and systemic responses and eliminate needles entirely. Prior modeling work cited in the study predicts that improving the thermostability of a single pentavalent vaccine would make it available in almost every part of developing countries, and thin film platforms have previously achieved up to 100 percent recovery of infectious and immunogenic agents while preserving active and inactive viruses, bacteria, and proteins without refrigeration.

The authors are candid about limitations. Background scattering from reconstituted HPMC particles complicated dynamic light scattering analysis, and they suggest nanoparticle tracking analysis with an instrument such as the NanoSight300, which counts individual particles, may be better suited to future work. Formulations three and four frequently tore during removal from the casting molds, and the team is investigating silicone molds, which have provided a greater success rate in film removal and could yield films with fewer defects and more uniformity. The next step is animal testing to determine whether OMV immunogenicity remains consistent after long-term room temperature storage. If it does, a thin film that dissolves on the cheek within minutes and survives eight weeks on a shelf could bring mucosal nanovaccines to populations that ultra-cold freezers have left behind.

Subject of Research: Biomaterials Science

Article Title: Outer membrane vesicle loaded thin films as a stable room temperature vaccine platform

Article References: Randall, N. M., Squissato, J., Numanoglu, C., Dubois, W., Lee, H., & Curley, S. M. (2026). Outer membrane vesicle loaded thin films as a stable room temperature vaccine platform. Frontiers in Biomaterials Science, 5, Article 1913356. https://doi.org/10.3389/fbiom.2026.1913356

Image Credits: AI Generated

DOI: 10.3389/fbiom.2026.1913356

Keywords: outer membrane vesicles, thin films, vaccine thermostability, cold chain, mucosal vaccination, biomaterials, Outer, membrane, vesicle, loaded, thin, films

The team, led by A. A. Mancharkar, J. H. Kim, and Habib M. Pathan, grew thin films of Zn(OH)2 on stainless steel substrates using two low-cost, low-temperature techniques: chemical bath deposition (CBD) and successive ionic layer adsorption and reaction (SILAR). Both methods draw from the same precursor chemistry—zinc acetate and aqueous ammonia—yet they produce films with dramatically different architectures, crystallinities, and, ultimately, electrochemical behavior. When tested as supercapacitor electrodes in a 2 M KOH electrolyte, the CBD-grown needles delivered a specific capacitance of 329 F/g at a current density of 1 A/g, while the SILAR-grown microflowers managed 179 F/g under identical conditions. The needles also retained 78 percent of their original capacitance after 3,000 charge–discharge cycles at a scan rate of 100 mV/s, compared with 74 percent for the microflowers.

To understand why one morphology outperforms the other, it helps to look at how each method builds the film at the molecular level. In the CBD process, zinc acetate and ammonium hydroxide are combined in a single aqueous bath held at 50 °C for two hours. Ammonia acts as a complexing agent, binding Zn2+ ions into soluble zinc–ammonia complexes such as [Zn(NH3)4]2+. This controlled complexation suppresses rapid homogeneous precipitation and instead releases Zn2+ ions gradually as the equilibrium shifts, maintaining a low supersaturation level that favors heterogeneous nucleation directly on the stainless steel surface. Because the entire bath stays warm throughout, nucleation and crystal growth proceed continuously, allowing the nuclei to develop into well-defined needle-like Zn(OH)2 nanostructures with improved crystallinity, high porosity, and strong adhesion to the substrate.

The SILAR method, by contrast, is a stepwise affair. The substrate is dipped sequentially into three beakers: first a 0.1 M zinc acetate solution for 5 seconds to adsorb Zn2+ ions, then double-distilled water for 5 seconds to rinse away loosely bound species, and finally a 2 M ammonia solution held at 50 °C for 10 seconds, where the adsorbed zinc ions react with hydroxide ions to form Zn(OH)2. This sequence constitutes a single cycle, and 50 cycles were carried out to achieve uniform film growth. Crucially, only the alkaline solution is heated; the adsorption and rinsing steps occur at room temperature. Each cycle initiates nucleation afresh rather than sustaining it, resulting in discontinuous crystal growth with comparatively slower kinetics. The outcome is a microflower-like architecture with lower crystallinity and a smaller specific surface area.

X-ray diffraction confirmed that both films crystallized in the orthorhombic phase of Zn(OH)2, matching standard reference data (JCPDS No. 00-048-1066), with prominent reflections from the (100), (002), (101), (102), (110), and (103) crystallographic planes. But the CBD-derived film showed stronger diffraction intensities, indicating higher crystallinity—a direct consequence of its continuous growth process. Applying the Scherrer equation to the diffraction peaks, the team estimated average crystallite sizes of 34 nm for the CBD film and 27 nm for the SILAR film. The SILAR route also produced a wider optical bandgap: 3.34 eV versus 3.19 eV for the CBD film, as determined from Tauc plots of UV–visible absorption data. FTIR spectroscopy verified the hydroxide nature of both films through characteristic Zn–OH bending modes near 1,033, 896, and 856 cm−1, alongside O–H stretching vibrations in the 3,806–3,793 cm−1 region.

Scanning electron microscopy revealed the morphological divide in vivid detail. The CBD film consists of densely packed, vertically aligned needle-like structures uniformly distributed across the substrate, with an average width of approximately 0.5 μm. This architecture offers a larger surface area and a greater number of electrochemically active sites, facilitating efficient charge storage. The SILAR film, in contrast, displays a microflower-like texture composed of uniformly dispersed flower-shaped assemblies with lateral dimensions ranging from 300 to 600 nm, forming a porous network with abundant accessible surface sites. Energy-dispersive X-ray spectroscopy confirmed zinc and oxygen as the major constituents in both samples, with atomic ratios consistent with Zn(OH)2 formation.

Brunauer–Emmett–Teller (BET) analysis quantified the textural differences. The N2 adsorption–desorption isotherms of both samples displayed typical type-IV behavior with H3 hysteresis loops, indicating mesoporous structures. The CBD film achieved a specific surface area of 17.63 m²/g, roughly double the 8.59 m²/g of the SILAR film. Pore-size distribution analysis using the Barrett–Joyner–Halenda model yielded average pore diameters of 16.34 nm for the CBD film and 17.89 nm for the SILAR film. The enhanced surface area of the CBD sample is likely associated with its highly crystalline nature and distinctive needle-like architecture, which expose a greater number of surface sites to the electrolyte.

Electrochemical testing in a three-electrode configuration—using the Zn(OH)2 films as the working electrode, a platinum wire counter electrode, and a Hg/HgO reference electrode—confirmed the pseudocapacitive charge-storage mechanism. Cyclic voltammetry showed well-defined redox peaks, indicating that charge storage is governed predominantly by reversible Faradaic reactions at the electrode–electrolyte interface. During charging, Zn(OH)2 is oxidized to ZnOOH with the release of an electron; during discharge, the reverse reduction regenerates Zn(OH)2. From CV data at a scan rate of 5 mV/s, the specific capacitances were calculated to be 402 F/g for the CBD film and 238 F/g for the SILAR film. The team also fabricated five independent electrodes under identical conditions to verify reproducibility: the CBD electrodes ranged from 392 to 410 F/g, while the SILAR electrodes fell between 230 and 242 F/g, demonstrating excellent electrode-to-electrode consistency for both methods.

Kinetic analysis using a power-law model revealed b-values of 0.66 for the CBD electrode and 0.73 for the SILAR electrode, both between 0.5 and 1.0, indicating a combination of diffusion-limited ion transport and surface-controlled capacitive effects. At a scan rate of 5 mV/s, the diffusion-controlled contribution accounted for nearly 78 percent of the total current in the CBD electrode and approximately 71 percent in the SILAR electrode. As the scan rate increased to 100 mV/s, the surface-controlled capacitive processes became more pronounced, with the SILAR electrode exhibiting a larger capacitive contribution of 64 percent compared to 56 percent for the CBD electrode. Electrochemical impedance spectroscopy showed comparable equivalent series resistance values of 0.72 and 0.78 Ω/cm² for the CBD and SILAR electrodes, respectively, but the charge-transfer resistance was 25.36 Ω/cm² for the CBD film versus 31.98 Ω/cm² for the SILAR film, and the Warburg impedance was 0.0015 Ω/cm² versus 0.0082 Ω/cm², indicating faster ion diffusion in the needle-like film.

The superior performance of the CBD-grown electrode traces back to its distinct growth mechanism. The gradual release of Zn2+ ions from zinc–ammonia complexes promotes controlled nucleation and crystal growth, resulting in a highly porous needle-like structure with improved crystallinity and larger specific surface area. These characteristics enhance electrolyte penetration, increase the number of electroactive sites, and facilitate rapid ion diffusion. The SILAR process, with its successive adsorption and reaction cycles, produces microflower-like structures with comparatively lower crystallinity and surface area, leading to reduced electrolyte accessibility and electrochemical activity. Both electrodes demonstrated satisfactory cycling durability, retaining 78 and 74 percent of their original capacitance after 3,000 cycles, indicating suitability for prolonged energy-storage operation. The findings underscore that precise control over synthesis methodology is essential for improving the electrochemical performance of Zn(OH)2-based electrodes and advancing their application in high-performance supercapacitor systems.

Subject of Research: Comparative electrochemical study of CBD and SILAR grown Zn(OH)2 thin films for supercapacitor electrodes

Article Title: A comparative study of electrochemical properties of CBD and SILAR grown Zn(OH)2 thin films

Article References: Mancharkar, A. A., Bodke, M. R., Malavekar, D. B., Bachankar, S. S., Choi, H., Kim, J. H., & Pathan, H. M. (2026). A comparative study of electrochemical properties of CBD and SILAR grown Zn(OH)2 thin films. Frontiers in Batteries and Electrochemistry, 5, Article 1905059. https://doi.org/10.3389/fbael.2026.1905059

Image Credits: AI Generated

DOI: 10.3389/fbael.2026.1905059

Keywords: zinc hydroxide, supercapacitor, chemical bath deposition, SILAR, thin films, pseudocapacitor, specific capacitance, electrochemistry, nanostructures, energy storage, crystallite size, bandgap

MXenes are a family of two-dimensional transition-metal carbides, nitrides, and carbonitrides first discovered in 2011, made by chemically stripping away the A-layers of a layered ceramic precursor called a MAX phase. The most studied member, Ti3C2Tx, is produced by etching aluminum out of Ti3AlC2 with hydrofluoric acid, leaving behind sheets of titanium carbide decorated with surface terminations such as hydroxyl, oxygen, and fluorine groups. Those terminations are the secret to the material’s compatibility with polymers: they form hydrogen bonds with the hydroxyl-rich backbones of PVA, anchoring the nanosheets into the matrix. Ti3C2Tx is also a superb electrical conductor, with reported conductivities between 2.0 and 2.4 times ten to the fourth siemens per centimeter, making it one of the most attractive fillers available for turning insulating plastics into functional electronic materials.

In the new work, the researchers began by making their own MXene. They slowly added 1.5 grams of Ti3AlC2 MAX phase powder to a 30 weight percent hydrofluoric acid solution, stirred the mixture at 50 degrees Celsius for twelve hours, and then filtered and washed the product until the supernatant reached a neutral pH of roughly seven. To split the resulting multilayered stacks into single and few-layer nanosheets, they intercalated dimethyl sulfoxide into the galleries between layers for a full day, washed out the solvent, and bath-sonicated the sediment in deionized water. The synthesis was verified by X-ray diffraction: the characteristic MAX phase peak near 39 degrees disappeared entirely, while the basal (002) reflection shifted from 9.59 degrees down to 7.19 degrees and broadened, the classic signature of successful etching.

The structural data also revealed a striking expansion of the MXene’s internal architecture. The interlayer spacing increased from 0.922 nanometers in the parent MAX phase to 1.228 nanometers in the MXene, an expansion of about 33 percent that the authors attribute to the removal of the aluminum layers and the attachment of oxygen, hydroxyl, and fluorine surface groups. The average crystallite size dropped slightly from 39.11 to 36.38 nanometers. Electron microscopy showed the transformation vividly: the dense, close-packed plate-like structure of the MAX phase gave way to an accordion-like arrangement of loosely stacked thin nanosheets. Energy-dispersive X-ray spectroscopy confirmed that aluminum content plunged from 9.39 to 1.52 weight percent, while oxygen at 29.76 percent and fluorine at 9.17 percent emerged, evidence of the new surface chemistry.

X-ray photoelectron spectroscopy provided an even finer-grained view of the surface. The team deconvoluted the core-level spectra into their constituent chemical states, identifying carbon-titanium-fluorine terminations, titanium fluoride species, and minor residual fluorinated byproducts in the fluorine 1s region. The carbon 1s spectrum contained the carbide carbon peak at 281.78 electron-volts that defines the intact MXene lattice, alongside adventitious carbon, ether-type carbon, and carboxyl groups. The titanium 2p envelope resolved into three spin-orbit doublet pairs corresponding to the carbide framework, partially oxidized titanium species, and titanium dioxide at the surface, with the expected spin-orbit splitting of about 5.7 electron-volts. Together these results map a complex but chemically coherent surface, rich in the functional groups that bond polymers.

The films themselves were made by a method simple enough to run in any laboratory. PVA and PEG were dissolved together in deionized water at a fixed 80:20 weight ratio, chosen because prior studies show this composition offers optimal miscibility and a good balance between crystallinity and chain mobility. Separately dispersed MXene was added at loadings of 0.5, 1.0, and 1.5 weight percent, the mixture was stirred, ultrasonicated, and drop-cast onto glass, then vacuum-dried. Infrared spectroscopy of the finished films showed the hydroxyl stretching band near 3,420 reciprocal centimeters broadening and shifting to lower wavenumbers as MXene content rose, a sign that hydrogen bonds between the polymer chains and the nanosheets’ surface groups were strengthening. Crucially, no new chemical bands appeared, indicating the composite is held together by physical hydrogen bonding rather than new covalent chemistry.

Perhaps the most subtle result concerns crystallinity. At the lowest loading of 0.5 weight percent, the crystallinity index of the polymer blend jumped from 34.60 to 48.01 percent as measured by X-ray diffraction, and from 42.45 to 49.87 percent by infrared analysis. The well-dispersed nanosheets act as heterogeneous nucleation sites, giving polymer chains additional surfaces on which to organize into ordered crystalline domains. But the effect is non-monotonic. At 1.0 and 1.5 weight percent, the crystallinity index fell back to 42.94 and 33.60 percent respectively, because the two-dimensional sheets begin to confine chain motion and, at higher loadings, partially aggregate, disrupting the regular packing needed for crystal growth. Microstrain and dislocation density rose in parallel, confirming that MXene introduces genuine structural disorder into the lattice even as it nucleates order at low doses.

The optical consequences were the study’s headline. Using ultraviolet-visible absorption spectroscopy and the Tauc method, the team extracted both direct and indirect band gap energies for each film. The pristine PVA/PEG blend, with its saturated, non-conjugated backbone, was a wide-gap insulator with direct and indirect gaps of 5.49 and 5.17 electron-volts. As MXene content increased, the absorption edge red-shifted steadily and the gaps fell monotonically: to 5.42 and 4.93 electron-volts at 0.5 weight percent, 5.17 and 3.88 at 1.0 weight percent, and finally 4.98 and 3.28 electron-volts at 1.5 weight percent. Remarkably, the indirect gap narrowed far more than the direct one, a 36.6 percent reduction versus 9.3 percent. The authors suggest this asymmetry arises because indirect transitions involve phonon-assisted excitation and therefore respond more sensitively to the localized electronic states and structural disorder that MXene introduces into the polymer’s electronic environment.

All the while, the films kept a useful optical property: they remained moderately transparent in the visible region even as their ultraviolet absorption intensified. That combination of enhanced ultraviolet shielding and preserved transparency is exactly what is sought for protective coatings, and the systematic gap tuning opens routes toward flexible optoelectronics, chemical sensors, and energy-related devices built from nothing more exotic than water-soluble polymers and a fraction of a percent of nanosheets. The study demonstrates that in the world of polymer nanocomposites, dosage is destiny: the same nanofiller can nucleate order at one concentration and disrupt it at another, while continuously rewriting the electronic band structure. As MXene research moves from laboratory curiosity toward practical devices, this work offers a clear, quantitative map of how to dial in the properties of a flexible plastic film with nothing more than careful control of filler loading.

Subject of Research: Tuning the structural properties and optical band gap of PVA/PEG polymer nanocomposite thin films with Ti3C2Tx MXene nanosheet loading

Article Title: Effect of Ti3C2Tx MXene content on the structural properties and optical band gap of PVA/PEG nanocomposite thin films

Article References: Sonowal, J., Tanti, A., & Kalita, P. C. (2026). Effect of Ti3C2Tx MXene content on the structural properties and optical band gap of PVA/PEG nanocomposite thin films. Frontiers in Materials, 13, Article 1934242. https://doi.org/10.3389/fmats.2026.1934242

Image Credits: AI Generated

DOI: 10.3389/fmats.2026.1934242

Keywords: MXene, Ti3C2Tx, polymer nanocomposites, PVA, PEG, optical band gap, crystallinity index, thin films, X-ray diffraction, UV-Vis spectroscopy, XPS, flexible optoelectronics

In a study published in Frontiers in Chemistry, Mahdi Hesari and Marysa Colvin describe a one-pot synthesis in which Au25 nanoclusters are locked into a silica network through a sol-gel process, producing either chunky particles or ultrathin films depending only on how the material is purified. The choice matters enormously: when tested as catalysts for the hydrogenation of 4-nitrophenol, a benchmark reaction in nanoscience, the film version ran roughly 2.5 times faster than the particle version, while both could be recovered and reused with 96 percent recovery over ten cycles. The finding suggests that for nanocluster catalysts, architecture is not a cosmetic detail—it is a performance dial.

The key to the whole scheme is a remarkably clever molecule called 3-mercaptopropyl trimethoxysilane, or MPTS. It is a dual-functional ligand: on one end sits a thiol group that bonds covalently to gold atoms, exactly like the thiols traditionally used to stabilize gold nanoclusters; on the other end sits a trimethoxysilane group, the workhorse of sol-gel chemistry. Once the silane ends are exposed to traces of water, they hydrolyze and condense, knitting together a network of Si-O-Si bonds—essentially glass—that physically connects every nanocluster to its neighbors. In other words, the same ligand that stabilizes each cluster individually also serves as the molecular glue that assembles them collectively.

The synthesis itself follows a modified one-pot route. Tetrachloroaurate is dissolved in tetrahydrofuran with tetra-n-octylammonium bromide, chilled in an ice bath, and treated with MPTS, which displaces the chloride ligands and forms Au-S bonds. A rapid injection of ice-cold sodium borohydride then reduces the gold, turning the solution a dark brown—the telltale sign of nanocluster formation. After 24 hours of stirring, gravity filtration removes unreacted gold-thiolate polymer intermediates, leaving a bright brown solution ready for the sol-gel stage. From there, the two purification pathways diverge, and it is that divergence that decides the final shape of the material.

In procedure A, the crude product is rotary-evaporated to an oily residue and washed with ethanol, the conventional purification for these clusters. In the presence of residual water in the THF solution and added methanol, the silane groups condense into a solid sol-gel network, yielding the Au25-SiO2 particle form—dark brownish chunks whose individual particles average roughly 62 by 49 micrometers. Procedure B takes a gentler route: size exclusion chromatography on a Sephadex LH-20 column separates the clusters from excess thiol based on molecular weight, and the solvent is removed by rotary evaporation at room temperature. Because the excess thiol is stripped away, no ethanol or methanol is introduced, and the water content stays low, the clusters instead condense into a continuous film just 12.76 nanometers thick—roughly a thousand times thinner than the particles are wide.

Confirming that the delicate Au25 clusters survive both the gelation and the solidification required a battery of analytical techniques. Solid-state UV-visible spectroscopy revealed the cluster’s signature features, including absorption maxima and valleys matching those reported for Au25(SR)18 species in solution, in both the particle and the film. Mass spectrometry of the soluble precursor detected multiply charged fragments of the intact cluster, along with telltale losses of methyl groups from the ligand shells—51 such losses observed against a theoretical count of about 54. X-ray photoelectron spectroscopy mapped the elemental landscape of the solids, detecting gold, silicon, sulfur, carbon, nitrogen, and oxygen, with the nitrogen 1s signal at 401.96 electron-volts confirming the tetra-octylammonium counterion and thus the negative charge state of the embedded clusters. Scanning electron microscopy with energy-dispersive X-ray analysis showed gold, silicon, and sulfur distributed homogeneously across both forms, and X-ray diffraction revealed broad peaks consistent with compact face-centered-cubic gold domains and the amorphous silica texture of the gel.

Perhaps the most reassuring result came from photoluminescence. When the film was excited with a 532-nanometer laser, it emitted near-infrared light with a peak near 940 nanometers and a shoulder at 765 nanometers—essentially the same emission spectrum reported for purified Au25 clusters in solution. Those emissions arise from intraband transitions between the cluster’s quantized electronic states, so their persistence in the solid state is strong evidence that the gold cores remain intact and electronically unperturbed inside the silica matrix. The team even observed a partial enhancement of the luminescence, which they attribute to energy transfer between neighboring embedded clusters—a hint that the assembled superstructure is more than the sum of its parts, precisely as the superstructure concept predicts.

The catalytic test case was the reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride, a fast, well-studied reaction that serves as a standard yardstick for metal nanocatalysts. Monitoring the decay of the 4-nitrophenol absorption at 400 nanometers, the researchers found that after 15 minutes the film had converted 92 percent of the substrate while the particle had managed 81 percent. The extracted rate constants were 2.44 × 10⁻³ per second for the film and 9.83 × 10⁻⁴ per second for the particle—a 2.5-fold advantage for the film. The explanation is structural: the film’s silica layer is far thinner, giving reactants more effective access to the gold surfaces, whereas the thicker silica coating of the particles imposes a longer diffusion path. The results also demonstrate that the silica content is calibrated just right—enough to weld the clusters into a robust network, but not so much that it buries the active sites.

For practical catalysis, the silica shell delivers a crucial bonus: recyclability. Bare Au25 clusters in solution are fast catalysts—some reported systems run considerably faster than the silica-embedded versions—but they are difficult to recover and can degrade at the elevated temperatures and harsh chemical conditions that heterogeneous catalysis often demands. The Au25-SiO2 solids, by contrast, can simply be filtered out of the reaction mixture and used again, retaining their activity over at least ten cycles with 96 percent recovery. The authors note that the measured rates sit close to published values for other silica-coated and water-soluble gold and silver-copper nanocluster catalysts, placing this material squarely within the competitive landscape of modern nanocatalysis while adding the durability that industrial applications require.

Beyond the immediate catalytic numbers, the study opens a general recipe: any atomically precise metal nanocluster protected with a silane-functionalized thiol could, in principle, be fused into particle, film, or potentially other morphologies simply by tuning the purification conditions. The authors suggest that synchrotron spectroscopy could further illuminate how structure and performance are linked in these morphologies, and that the same assembly strategy might extend across the rich family of Au, Ag, and alloy nanoclusters now being synthesized worldwide. What began as a routine purification step has turned into a design principle—proof that when it comes to atomically precise catalysts, how you wash your chemistry can determine how it works.

Subject of Research: Sol-gel assembly of Au25 gold nanoclusters into silica particles and films for enhanced catalysis

Article Title: Controlled sol-gel nanoassembly of Au25(SR)18 nanoclusters for structural and functional integration

Article References: Hesari, M., & Colvin, M. (2026). Controlled sol-gel nanoassembly of Au25(SR)18 nanoclusters for structural and functional integration. Frontiers in Chemistry, 14, Article 1982602. https://doi.org/10.3389/fchem.2026.1982602

Image Credits: AI Generated

DOI: 10.3389/fchem.2026.1982602

Keywords: gold nanoclusters, Au25, sol-gel, nanoassembly, silica, catalysis, nitrophenol hydrogenation, MPTS, thin films, heterogeneous catalysis, photoluminescence, XPS

The work, published in Frontiers in Batteries and Electrochemistry, centers on a family of materials called nickel cobalt tungstates, written chemically as Ni_xCo_1-xWO₄. Tungstates have attracted growing attention in the supercapacitor community because tungsten can adopt multiple oxidation states and the W-O framework offers relatively high conductivity. But pristine nickel tungstate and cobalt tungstate suffer from compact morphologies, limited surface area, and non-porous structures that hinder electrolyte penetration. The new study tackles these limitations through composition engineering: rather than choosing one metal or the other, the team tuned the cationic ratio to optimize the structural, morphological, and electronic properties of the resulting thin film.

What makes the approach particularly striking is its simplicity. The researchers used a technique called successive ionic layer adsorption and reaction, or SILAR, in which a polished stainless steel substrate is dipped sequentially into a cationic precursor solution containing nickel and cobalt chlorides, rinsed in deionized water, dipped into an anionic precursor containing sodium tungstate, and rinsed again. Each cycle deposits a thin layer of the mixed metal tungstate. After 100 cycles, a uniform, adherent film forms directly on the substrate, with no binder, no conductive additive, and no post-deposition processing. The films changed color from light apple green to purple depending on the nickel-cobalt ratio, a visible sign of the compositional shift.

Direct growth on the conductive substrate is more than a convenience. Because the active material is self-supported, electrons travel efficiently from the substrate into the electroactive film, and strong interfacial adhesion reduces charge-transfer resistance. The absence of a polymeric binder eliminates an extra source of internal resistance that plagues conventional powder electrodes. Meanwhile, the amorphous structure of the films, confirmed by X-ray diffraction showing no distinct diffraction peaks, provides a high density of unsaturated electrochemically active sites, abundant structural defects, and shortened ion diffusion pathways that facilitate rapid redox kinetics.

Microscopy revealed how dramatically the nickel-cobalt ratio reshapes the film morphology. Pristine nickel tungstate formed agglomerated nano-pebbles averaging 340 nanometers. As cobalt content increased, the particles shrank and became more porous, reaching a minimum of 105 nanometers at the 50:50 composition. But the standout electrode, labeled NCW4 with a 25:75 nickel-to-cobalt ratio, formed interconnected nanospherical particles averaging 160 nanometers with a highly porous structure. Pristine cobalt tungstate reverted to compact 320-nanometer particles. The porous nanospherical morphology of NCW4 enables effective electrolyte penetration into the electrode matrix, a critical factor for high-rate charge storage.

Electrochemical testing in a three-electrode configuration using 1 M potassium hydroxide electrolyte confirmed the superiority of the cobalt-rich composition. The NCW4 electrode delivered a specific capacity of 785.72 C g−1 at a current density of 1.1 A g−1, nearly three times higher than pristine nickel tungstate (247.24 C g−1) or cobalt tungstate (186.88 C g−1). Cyclic voltammetry showed distinct redox peaks associated with the Co2+/Co3+, Co3+/Co4+, and Ni2+/Ni3+ couples, and the NCW4 electrode exhibited the largest enclosed voltammetric area and highest current response of the series.

Perhaps the most intriguing finding concerns the charge storage mechanism. Using the Trasatti method and power-law analysis of cyclic voltammetry data, the researchers calculated a b-value for each electrode that reveals whether charge storage is diffusion-controlled (b ≈ 0.5) or surface-controlled (b ≈ 1). The b-values climbed from 0.50 for pristine nickel tungstate to 0.95 for pristine cobalt tungstate, with NCW4 at 0.82. This means increasing cobalt content shifts the charge storage from bulk diffusion toward rapid surface redox reactions. For NCW4, the surface-controlled contribution rose from about 50% at 2 mV s−1 to 69% at 10 mV s−1, explaining its excellent rate capability even at high scan rates.

Impedance spectroscopy added further insight. All electrodes showed comparable series resistance around 0.3 to 0.45 Ω cm−2, but NCW4 exhibited the lowest charge-transfer resistance at 25.72 Ω cm−2, compared to 73.70 Ω cm−2 for pristine nickel tungstate. Double-layer capacitance measurements in a non-faradaic potential window confirmed that NCW4 possesses the highest density of accessible electroactive sites. The combination of optimized composition, favorable morphology, and fast interfacial kinetics explains why this particular ratio outperforms the rest of the series.

Cycling stability is where many pseudocapacitive materials falter, but NCW4 held up remarkably well. After 5,000 charge-discharge cycles at 4.1 A g−1, the electrode retained 77% of its initial capacity with 95% coulombic efficiency. Post-cycling X-ray diffraction, microscopy, and Raman spectroscopy showed that the fundamental tungstate framework remained largely intact, though surface cracks and slight particle agglomeration appeared, consistent with repeated volume changes during faradaic reactions. The capacity fade likely stems from gradual structural relaxation of the amorphous framework, partial loss of active sites, and slight dissolution of transition metal species rather than catastrophic breakdown.

To demonstrate practical viability, the team assembled a two-electrode aqueous hybrid supercapacitor pairing the NCW4 positive electrode with reduced graphene oxide as the negative electrode. The device operated stably at 1.6 V in 1 M KOH, delivering a maximum specific energy of 50.41 Wh kg−1 at a specific power of 1.74 kW kg−1, and retaining 37.03 Wh kg−1 at 4.30 kW kg−1. After 5,000 cycles at 5.6 A g−1, the full cell retained 95.1% of its capacitance with 90% coulombic efficiency. These figures compare favorably with previously reported cobalt tungstate and nickel tungstate devices, suggesting that composition-engineered amorphous nickel cobalt tungstate thin films, grown by a cost-effective binder-free method, could become a serious contender for next-generation supercapacitor electrodes.

Subject of Research: Nickel cobalt tungstate thin film electrodes for high-performance asymmetric supercapacitors

Article Title: Facile synthesis of self-supported amorphous cobalt-nickel tungstate thin films for high performance asymmetric supercapacitor: role of Co and Ni variation

Article References: Mohite, R., Jadhav, G., Jadhav, S., Magdum, V., Pujari, S., Malavekar, D., Patil, U., Kim, J. H., & Pavaskar, P. (2026). Facile synthesis of self-supported amorphous cobalt-nickel tungstate thin films for high performance asymmetric supercapacitor: role of Co and Ni variation. Frontiers in Batteries and Electrochemistry, 5, Article 1903174. https://doi.org/10.3389/fbael.2026.1903174

Image Credits: AI Generated

DOI: 10.3389/fbael.2026.1903174

Keywords: supercapacitor, nickel cobalt tungstate, SILAR, pseudocapacitor, reduced graphene oxide, energy storage, thin films, specific energy, Facile, synthesis, self-supported, amorphous

The work, published in the Journal of Materials Science, sits at the intersection of supramolecular chemistry and solid-state sensing. Calixarenes are bowl-shaped macrocyclic molecules whose cavities can be chemically tuned to capture specific guest molecules, much like a molecular lock accepting only certain keys. By incorporating sulfur atoms into the calixarene framework, the researchers created a family of thiacalixarene analogs whose electronic and host-guest properties differ meaningfully from their oxygen-rich cousins. When deposited as thin films, these compounds behave as organic semiconductors, and their electrical response changes measurably when chloroform molecules lodge themselves within the molecular cavities and between the polymer-like chains of the film.

The optical characterization of the films revealed a combination of properties that is highly desirable for sensing platforms. Using UV-Vis-NIR spectroscopy across the 300 to 2500 nanometer range, the team found that the films absorb strongly in the ultraviolet region while transmitting more than 90 percent of visible light. This transparency matters: it means the films could be integrated into optoelectronic devices or optical sensor architectures without interfering with light passing through them. The researchers then applied Tauc plot analysis, a standard technique for extracting optical band gaps from absorption spectra of amorphous semiconductors, and found band gap values ranging from 3.29 to 3.53 electronvolts across the compound series.

Those band gap numbers place the materials firmly in the wide-band-gap organic semiconductor regime, but the variation within the series tells a more interesting story. The lowest value, 3.29 electronvolts, belonged to the compound labeled 3b, which the authors attribute to improved conjugation within its molecular structure. Greater conjugation means the pi-electron systems of the molecule are more delocalized, which lowers the energy required to promote an electron across the gap. In practical sensing terms, a smaller band gap generally makes the film’s conductivity more sensitive to perturbations such as the adsorption of polarizable vapor molecules, and this expectation played out in the subsequent gas sensing experiments.

When the films were exposed to chloroform vapor, all of the tested compounds produced measurable responses, but compound 3b stood out decisively. It achieved a maximum response value of approximately 0.83, with a response time of just 3 seconds and a recovery time of 6 seconds. For context, many commercial gas sensors based on heated metal oxides require operating temperatures of several hundred degrees Celsius and exhibit response and recovery times measured in tens of seconds or minutes. A room-temperature organic sensor that completes a full detection cycle in under 10 seconds represents a meaningful advance in speed and energy efficiency, and it hints at applications in portable, battery-powered monitoring devices.

Selectivity is where many promising sensor materials stumble. A sensor that reacts equally to acetone, ethanol, benzene, and chloroform is of limited use in real environments, where gas mixtures are the norm rather than the exception. The sulfur-containing calixarene films, however, showed a strong preference for chloroform over other tested gases, with a selectivity value of roughly 83 toward chloroform. The researchers connect this selectivity to the host-guest chemistry inherent to the calixarene scaffold: the size, polarity, and polarizability of the chloroform molecule appear to match the cavity environment created by the sulfur-containing macrocycle particularly well, producing a stronger perturbation of the film’s electronic properties than other vapors can achieve.

Equally important for any practical sensor is a predictable, quantitative response to concentration. A detector that merely signals the presence of a gas without indicating how much of it is present offers only half the picture. The calixarene films delivered a linear response across chloroform concentrations from 50 to 200 parts per million, with a coefficient of determination, or R-squared value, of 0.998. That near-perfect linearity means the sensor output can be converted directly into a concentration reading with simple calibration, satisfying a key requirement for regulatory monitoring applications, where occupational exposure limits and water quality standards are defined in precise numerical terms.

Durability is the third pillar of sensor performance, and here too the results were encouraging. After 30 days of storage, the compound 3b sensor retained a response of 0.836, essentially indistinguishable from its initial performance. Organic semiconductor films are often vulnerable to oxidation, humidity, and structural degradation over time, so demonstrating month-scale stability suggests that the sulfur-containing calixarene chemistry is robust enough for real-world deployment rather than being a laboratory curiosity. The combination of speed, selectivity, linearity, and stability in a single material is rare, and it is what distinguishes this work from many earlier demonstrations of organic vapor sensors.

The broader context makes the achievement more compelling. Chloroform detection has previously been pursued with metal oxide composites such as zinc oxide and copper oxide structures, conductive polymer fibers, plasmonic nanostructures, graphene field-effect transistors, and even carbon dot-modified photonic crystals. Calixarenes themselves have a long history in sensing, having been incorporated into quartz crystal microbalances, surface acoustic wave devices, and Langmuir-Blodgett films for detecting a range of volatile organic compounds. What the new study adds is the demonstration that sulfur-containing calixarene analogs, used directly as semiconducting thin films, can deliver chloroform selectivity with exceptional kinetics, potentially simplifying device architectures by removing the need for separate transduction layers.

Looking ahead, the research opens several avenues. The tunability of the calixarene platform means that the cavity chemistry could, in principle, be re-engineered to target other hazardous VOCs, from industrial solvents to clinical breath biomarkers, an area of growing interest for noninvasive disease diagnostics. The high visible transparency and semiconducting behavior of the films also suggest dual use in optoelectronic circuits where sensing and signal processing could be integrated on the same substrate. For now, the immediate significance is clear: a molecularly engineered, room-temperature film that catches one of the world’s most common chlorinated pollutants in 3 seconds flat, holds its performance for a month, and tells you exactly how much of it is in the air. In the quiet race to make chemical sensing faster, cheaper, and more selective, a humble bowl-shaped molecule with a few sulfur atoms may have just taken a significant lead.

Subject of Research: Sulfur-containing calixarene thin films for selective chloroform vapor sensing

Article Title: Optoelectronic and gas sensing properties of sulfur-containing calixarene thin films: selective detection of chloroform vapor

Article References: Hajjar, D., Makki, A. A., Omran, O. A., Kamel, M. S., & Mohery, M. (2026). Optoelectronic and gas sensing properties of sulfur-containing calixarene thin films: selective detection of chloroform vapor. Journal of Materials Science, 61(43), 33626-33649. https://doi.org/10.1007/s10853-026-13797-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13797-3

Keywords: calixarene, thiacalixarene, chloroform, gas sensor, volatile organic compounds, organic semiconductor, thin films, optical band gap, Tauc plot, VOC detection, room-temperature sensing, selectivity

The material at the heart of the study is (TiZrVCrAl)N, a nitride of a high-entropy alloy containing five metallic elements: titanium, zirconium, vanadium, chromium, and aluminum. High-entropy alloys, first articulated as a class in landmark reviews by Brian Cantor and by Daniel Miracle and Oleg Senkov, abandon the traditional idea of one dominant base metal. Instead, five or more elements are mixed in near-equal proportions, producing extreme configurational entropy that stabilizes unexpected crystalline phases. When such alloys are reacted with nitrogen, the resulting nitride films inherit this chemical complexity, and with it a combination of high hardness, thermal stability, and wear resistance that conventional binary nitrides such as TiN struggle to match.

High-entropy nitride coatings of the TiZrVCrAl family have already shown promise in demanding applications. Earlier work published in the Journal of Vacuum Science and Technology A reported that a TiZrVCrAl coating on aerospace bearings reduced the friction coefficient in oil-liquid mixed media, while magnetron-sputtered TiVZrCrAl nitride films have achieved super-hard behavior. The new study adds a critical piece to this picture by examining how these coatings form on the workhorse titanium alloy Ti-6Al-4V, the material that carries much of the structural load in modern aircraft, and by asking whether the way that alloy is processed changes the coating that grows on it.

To explore this question, the team prepared two versions of the Ti-6Al-4V substrate. One had a conventional coarse-grained structure. The other was converted to an ultrafine-grained state using severe plastic deformation, a family of processing techniques, including equal-channel angular pressing, that refines grains to sub-micrometer dimensions by imposing enormous strain without changing the shape of the part. Ultrafine-grained titanium alloys are prized for their enhanced strength, fatigue resistance, and creep performance, and previous studies by the same research groups had already shown that such substrates can improve the scratch resistance and adhesive strength of protective coatings. The new work investigates what happens at the finest structural level when a high-entropy nitride is deposited on each substrate type.

The coatings themselves were produced by vacuum arc physical vapor deposition, or arc-PVD, a technique in which an electric arc vaporizes a metallic cathode, ionizes the vapor, and accelerates the ions toward a negatively biased substrate. Arc-PVD is prized industrially because it produces dense, strongly adherent films at reasonable deposition rates. The researchers deposited two architectures on both substrate types: a monolayer coating of (TiZrVCrAl)N and a multilayer coating in which (TiZrVCrAl)N layers alternate with layers of conventional TiN. Multilayer designs are widely used to toughen hard coatings, because interfaces between layers can block dislocation motion and deflect cracks.

The first major result concerns the internal structure of the monolayer coating. Using X-ray diffraction and transmission electron microscopy, the team found that the monolayer (TiZrVCrAl)N film is not structurally uniform through its thickness. Instead, it exhibits a pronounced phase gradient. At the interface where the coating meets the titanium alloy, the film is largely amorphous, lacking long-range crystalline order. Moving toward the outer surface, the structure progressively crystallizes into a face-centered cubic lattice, the same rock-salt-type structure adopted by classical transition-metal nitrides. This gradient makes physical sense: the earliest atoms to arrive on the substrate condense onto a chemically different surface with imperfect lattice matching, so the first atomic layers cannot easily find a crystalline template. As the film thickens, however, newly arriving atoms nucleate on the already-formed crystalline material beneath them, and the face-centered cubic phase establishes itself and grows toward the surface.

The multilayer (TiZrVCrAl)N/TiN coating told a different story. Rather than a single smooth gradient, it displayed pronounced structural and chemical periodicity, with alternating regions of varying degrees of crystallinity repeating through the film thickness. This periodicity mirrors the alternating layer architecture imposed by the deposition sequence, confirming that the multilayer design is faithfully reproduced at the nanometer scale and that each layer transition resets, at least in part, the structural state of the growing film. Such periodic interfaces are precisely what multilayer coating designers intend, and their clear observation in a five-element high-entropy system is an encouraging sign that sophisticated architectures can be engineered in these chemically complex nitrides.

The most striking discovery, however, is the influence of the substrate itself. When the coating was deposited on the ultrafine-grained Ti-6Al-4V rather than the coarse-grained alloy, the coherent scattering region in the coating, the size of the domains over which the crystal lattice remains perfectly aligned, dropped from 14.0 plus or minus 0.3 nanometers to 8.2 plus or minus 0.6 nanometers. In other words, the crystalline domains in the film became roughly forty percent smaller simply because the metal underneath had a finer grain structure. The effect extended to grain morphology as well: near the substrate-coating interface, the ultrafine-grained substrate produced more equiaxed grains, meaning grains with roughly equal dimensions in all directions rather than elongated columnar shapes, and their average size was about twenty percent smaller than the corresponding grains grown on the coarse-grained substrate.

Why should the substrate grain size matter so much? The interface between a coating and its substrate is a zone of intense atomic activity during deposition. Nucleation of the first crystalline layers depends on the topography, chemistry, and defect structure of the surface, all of which differ between coarse-grained and ultrafine-grained titanium. An ultrafine-grained surface presents a far higher density of grain boundaries, which can act as preferential nucleation sites and disrupt the lateral growth of columnar grains. The result is a finer, more equiaxed initial grain structure in the coating, and that initial structure propagates its influence through the film as growth continues, reflected in the reduced coherent scattering domain size measured by diffraction. The study thus demonstrates that substrate microstructure is not a passive backdrop but an active participant in coating formation.

The practical implications are considerable. The authors connect these microstructural differences to the mechanical properties of the coatings, discussing how composition, architecture, and now substrate grain structure jointly determine performance. Smaller crystalline domains and more equiaxed grains near the interface are generally associated with higher hardness and better load-bearing capacity, following the well-established Hall-Petch-type reasoning that grain boundaries impede dislocation motion. Combined with earlier findings that ultrafine-grained titanium substrates enhance coating adhesion and scratch resistance, the new results support a coherent design strategy: process the titanium alloy into an ultrafine-grained state first, then deposit the high-entropy nitride coating, and obtain a component whose surface layer is finer, more defect-controlled, and potentially longer-lasting than anything achievable by coating alone. For aerospace components such as bearings, shafts, and fasteners, where Ti-6Al-4V must resist wear, corrosion, and fatigue simultaneously, that strategy could translate directly into longer service intervals and lighter, more efficient machines. The work also fits into a broader vision, championed by proponents of severe plastic deformation, of so-called superfunctional materials in which bulk nanostructuring and surface engineering are combined deliberately rather than by accident. As high-entropy coatings mature from laboratory curiosities into industrial workhorses, studies like this one make clear that the full performance of these remarkable films can only be unlocked by treating the substrate and the coating as a single engineered system, designed together from the grain boundaries of the metal to the outermost atomic layers of the film.

Subject of Research: Microstructure of high-entropy (TiZrVCrAl)N nitride coatings deposited on coarse-grained and ultrafine-grained Ti-6Al-4V titanium alloy

Article Title: Microstructure of high-entropy (TiZrVCrAl)N coatings deposited on Ti–6Al–4V alloy with different grain structures

Article References: Valiev, R. R., Ovchinnikov, S. V., Savina, Y. N., Belyakov, A. N., Modina, I. M., Nikolaev, A. A., Nazarov, A. Y., Ramazanov, K. N., Caron, A., & Valiev, R. Z. (2026). Microstructure of high-entropy (TiZrVCrAl)N coatings deposited on Ti–6Al–4V alloy with different grain structures. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13813-6

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13813-6

Keywords: high-entropy alloys, thin films, arc-PVD, Ti-6Al-4V, ultrafine-grained titanium, severe plastic deformation, nitride coatings, transmission electron microscopy, X-ray diffraction, coating microstructure, aerospace materials, nanocrystalline materials