RSC Applied Interfaces最新文献

The deposition behavior of two state-of-the-art electrolytes, magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)₄]₂) in dimethoxyethane (DME) and magnesium bis(hexamethyldisilazide) with two equivalents of aluminum chloride (Mg(HMDS)₂–2AlCl₃) in tetrahydrofuran (THF) was investigated. Using symmetric flooded magnesium–magnesium cells with different electrolyte concentrations and current densities the deposition process was monitored optically in situ by a video microscope. The deposits were also investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy and compared to deposition from methylmagnesium chloride (MeMgCl) in THF, known for its dendritic growth. Furthermore, the chemical composition of the surfaces after deposition was tested by X-ray photoelectron spectroscopy (XPS). In this work, MeMgCl showed unidirectional growth and for the harshest applied conditions, mossy deposition, but no branching dendrites as previously reported in the literature. Mg[B(hfip)₄]₂ and Mg(HMDS)₂–2AlCl₃ did not show the formation of dendrites or a dendrite preform but also did not result in the desired smooth layer but in spherical deposits. For the Mg[B(hfip)₄]₂ electrolyte, the influence of magnesium borohydride (Mg(BH₄)₂) as an additive was additionally tested, resulting in a more planar growth.

Sulfide solid electrolytes, known for their high ionic conductivity and formability, are key materials for the practical use of all-solid-state sodium batteries. In this study, new sulfide solid electrolyte materials, Na_3−xZn_1−xAl_1+xS₄ (x ≤ 0.2), were prepared via a self flux synthesis route, using reagents such as Na₂S, Zn, Al, and S. The new materials were characterized using X-ray powder diffraction, Raman spectroscopy, and electrochemical impedance spectroscopy. Na_3−xZn_1−xAl_1+xS₄ formed a solid solution up to x = 0.2 and crystallized with a β-Ca₃Ga₂N₄-type structure. As the Al content increased, the number of sodium vacancies also increased, resulting in improved ionic conductivity. Among Na_3−xZn_1−xAl_1+xS₄ samples, Na_2.9Zn_0.9Al_1.1S₄ exhibited the highest ionic conductivity of 4.5 × 10⁻⁶ S cm⁻¹ at 25 °C and lowest activation energy of 32 kJ mol⁻¹. Furthermore, the Na_2.9Zn_0.9Al_1.1S₄ phase was relatively stable when exposed to humid air, which facilitated its practical use in all-solid-state sodium batteries.

Gallium oxide (Ga₂O₃), which is one among the ultra-wide band gap materials, is promising for the next generation of electronic and optoelectronic devices due to its fascinating material properties for utilization in extreme environments. In this work, Ga₂O₃ films containing refractory tungsten (W) (GWO or Ga–W–O) were fabricated via pulsed laser deposition (PLD) by varying the oxygen partial pressure (pO₂), which is the most important thermodynamic parameter that governs the growth, structure and properties of the resulting multi-component oxide films. The effect of variable pO₂ on the structure, surface chemistry, chemical bonding, optical properties and photodetector device performance of the resulting Ga–W–O films was studied using X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, UV-vis spectroscopy, and photoluminescence spectroscopy measurements. The films containing Ga₂O₃ combined with W exhibited no secondary phase development. The impact of W on the chemical and optical characteristics of Ga₂O₃ films was found to be substantial. W⁵⁺ formation is prevalent when the adatom mobility is high at lower working pressure, whereas lower migration energy favors W⁶⁺ at higher working pressure. In contrast, the valance band maxima (VBM) of the films have a minor shift to higher energies with increasing pO₂, confirming the dominance of O 2p states on VBM in PLD GWO films. Additionally, there is not much change in the optical band gap, but it shows a slight blue shift of the luminescence peak, directing a selective W incorporation into the Ga₂O₃ matrix. The processing conditions were optimized to demonstrate the excellent performance UV-photodetectors based on PLD GWO films. The structure–property correlation established will be useful in the production of W-alloyed β-Ga₂O₃ films with superior structural and optical properties for integration into optoelectronic and photonic device applications.

While quantum plasmonic behaviors benefit many applications in quantum optics and nanophotonics, they can have detrimental effects in optical processes such as surface-enhanced Raman spectroscopy (SERS). Here, we measure the SERS intensity for a colloidal metasurface composed of Ag nanocubes coupled to an ultra-flat Au backplane to characterize the classical, crossover, and quantum regimes of the metasurface as a function of gap distance. Gap distance is controlled via chemical modification of the nanocube and backplane surface with self-assembled monolayers composed of alkanethiols with varying chain lengths. Electrodynamic simulations employing a quantum-corrected model are used to characterize the hybrid plasmon modes and charge transfer plasmon modes of the metasurface with respect to gap distance. These results indicate the importance of charge transfer effects in dictating SERS intensities for even relatively large optical gap distances due to the presence of molecular analytes.

We propose a facile and fast control method to obtain perpendicularly oriented microphase-separated structures in block copolymer (BCP) thin films for nanopatterning with a BCP lithography technique. By synthesizing a derivative of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) with precisely introduced two hydroxy groups at the junction (PS-(OH)₂-PMMA) and by applying it onto silicon substrates, we investigated the lamellar orientations in PS-(OH)₂-PMMA thin films with respect to the annealing time of neutral layers (NLs) for modifying silicon substrates to neutralize the interfacial free energies between the substrate and each block component in the BCP thin films. Various NLs, including PS-(OH)₂-PMMA itself, were applied onto silicon substrates, and PS-(OH)₂-PMMA has turned out to take a dual role of BCP thin films for nanopatterning and NLs, which shows its supremacy over other methods. PS-(OH)₂-PMMA needs only 20 minutes of annealing to form NLs that sufficiently neutralize the substrates and induce perpendicular lamellae, which is a significant improvement over non-functionalized PS-b-PMMA. This result highlights the enhanced adsorbability of BCP neutral layers by the introduction of only a small amount of hydroxy groups.

Electrochromic devices (ECDs), which combine optical modulation and energy storage, have sparked widespread interest in window/façade applications and are becoming increasingly popular for energy conservation. It is established that by adjusting the electrochromic (EC) layer surface, the charge–discharge profile and the optical output can be individually regulated. Here, EC bilayers were created by overcoating MnO₂ on both amorphous and crystalline WO₃ thin films. The heterojunction considerably improved the cyclic stability and charge storage capacity of the WO₃ electrode, without affecting the EC functions. The presence of the MnO₂ layer has significantly enhanced both the areal capacitance and volumetric capacitance of the electrodes. The crystalline WO₃ electrodes have a peak volumetric capacitance of 341 F cm⁻³ at 0.1 mA cm⁻² discharge current, associated with an impressive retention rate of 50% even when charging at a higher rate of 1.0 mA cm⁻². The ECDs exhibited outstanding visible and IR blocking capability of around 98% beyond 600 nm. A comprehensive study employing spectroscopy and electrochemistry was performed to examine the chemical and electrochemical effects of MnO₂ overcoating. The results showed that these bilayers may be effectively employed to create EC energy storage devices (EESD) that are both highly stable and superior in performance.

Development of durable nanoscale electrocatalysts is an important step towards improving the affordability and sustainability of fuel cell technology. Nanostructured platinum catalysts are used to facilitate the two half reactions for hydrogen fuel cells. The sluggish kinetics of the cathodic oxygen reduction reaction and the less than optimal stability of cathode catalysts provide motivation for additional efforts to improve the catalytic performance of platinum. Metal oxide coatings on electrocatalysts have been found to increase durability of nanostructured catalysts and to impart additional properties such as increased activity and resistance to poisoning by contaminants. Niobium oxides have been studied as supporting materials for platinum fuel cell catalysts and shown to have a relatively high stability. It has also been suggested that niobium oxides can impart an increased activity due to strong metal support interactions. However, the lack of electrical conductivity of niobium pentoxide limits its viability as a support. Herein, coatings of niobium oxide were applied to nanotextured platinum catalysts prepared by electrodeposition against self-assembled templates to explore the impact of the coatings on the durability and electrocatalytic activity of the catalyst both during and after an accelerated stress test. The catalysts were characterized via scanning electron microscopy, X-ray photoelectron spectroscopy, conductive atomic force microscopy, and electrochemical techniques. Increasing the thickness of the coating from ∼0.5 nm to ∼4.5 nm was found to preserve the initial nanostructured morphology of the electrodeposited platinum catalyst. The thicker coatings did, however, result in larger charge transfer resistances towards the oxygen reduction reaction. These studies provide further evidence of the utility of ultrathin coatings to improve the properties of nanostructured electrocatalysts.

Microporous solid acid catalysts offer a vast amount of control over chemical processes. However, their coveted smaller pores also have several drawbacks, including a limited substrate scope, faster deactivation, and pore blockage. As such, there are significant advantages to introducing mesopores alongside the microporous framework, to create hierarchically porous frameworks. This work explores the influence of adapting our microporous synthetic procedure for silicoaluminophosphate (SAPO-5) to include different shaped carbon nanotemplates. The differing size of the mesopores formed is explored using nitrogen physisorption, transmission electron microscopy and small angle neutron scattering. In this work, we uniquely use small angle neutron scattering for probing hierarchical silicoaluminophosphates synthesised with hard templating methods. Here small angle neutron scattering was able to probe the shape and size of the mesopores and link their accessibility to their catalytic performance.

Using van der Waals heterostructures (VDWHs) to engineer novel electronic properties of two-dimensional (2D) material systems has proven to be a viable strategy in recent years. Given the excellent mechanical and electronic properties of air-stable MoSi₂N₄ and the high electron mobility of air-sensitive wide band gap 2D monolayers of GaSe and InSe, we investigate the interaction of these materials using first-principles calculations. We find that the VDWHs have narrow type-II direct band gaps. We apply either vertical electric field, vertical strain or biaxial strain to MoSi₂N₄/GaSe and MoSi₂N₄/InSe for band gap modulation. We find that the band structure of MoSi₂N₄/GaSe and MoSi₂N₄/InSe is highly tunable, exhibiting a variety of behaviours such as type-II-to-type-H band alignment, large band gap changes and direct-to-indirect band gap transitions. Interestingly, we also find that both heterostructures have a large band gap modulation of 1.4 to 2.3 eV under 8% biaxial strain. We also find that we can reverse the direction of the electron transfer between the monolayers under external stimuli. These findings therefore reveal another viable path towards InSe and GaSe based electronics and optoelectronics by using MoSi₂N₄-based VDWHs.

The Al₂O₃/TiO₂ nanolaminates (ATA NLs), with the dominant Maxwell–Wagner interfacial polarization, have been extensively explored in last decade due to their potential for new-generation energy storage applications. Here, we report the fabrication of device-grade sub-nanometric (<1 nm) ATA NLs using an optimized pulsed laser deposition technique, where the interface-confined carrier relaxation and sublayer conductivity contrast-induced Maxwell–Wagner interfacial polarization mechanism was engineered by precisely tailoring the individual Al₂O₃ and TiO₂ sublayer thickness along with the top-bottom capping layer thickness. The formation of oxygen vacancy-generated carriers in reduced titania sublayers across Al₂O₃/TiO₂ heterointerfaces and their relative response towards the applied field were responsible for both charge storage and leakage. An NL with a TiO₂ and Al₂O₃ sublayer thickness of ∼1 and 0.6 nm, respectively, sandwiched between ∼3 nm Al₂O₃ barrier layers, has demonstrated an improved capacitance density of ∼33.1 fF μm⁻² and a high cut-off frequency up to ∼0.5 MHz, along with a low dielectric loss of ∼0.032 and a reduced leakage current density of ∼3.08 × 10⁻⁷ A cm⁻² at 1 V. The calculated energy density value of ∼4.6 J cm⁻³ achieved with this optimized subnanometric Al₂O₃/TiO₂ laminate is comparable to those of state-of-the-art capacitive devices. These superior electrical properties and controllable dielectric relaxation make this laminate a promising high-k and low-loss dielectric material for next-generation nano-electronics and high-density energy storage capacitors.