Nanoscale Horizons最新文献

MoS₂ and related transition metal dichalcogenides (TMDs) have recently been reported as having extensive applications in nanoelectronics and catalysis because of their unique physical and chemical properties. However, one practical challenge for MoS₂-based applications arises from the easiness of oxygen contamination, which is likely to degrade performance. To this end, understanding the states and related energetics of adsorbed oxygen is critical. Herein, we identify various states of oxygen species adsorbed on the MoS₂ surface with first-principles calculations. We reveal a “dissociative” mechanism through which a physisorbed oxygen molecule trapped at a sulfur vacancy can split into two chemisorbed oxygen atoms, namely a top-anchoring oxygen and a substituting oxygen, both of which show no adsorbate induced states in the bandgap. The electron and hole masses show an asymmetric effect in response to oxygen species with the hole mass being more sensitive to oxygen content due to a strong hybridization of oxygen states in the valence band edge of MoS₂. Alteration of oxygen content allows modulation of the work function up to 0.5 eV, enabling reduced Schottky barriers in MoS₂/metal contact. These results show that oxygen doping on MoS₂ is a promising method for sulfur vacancy healing, carrier mass controlling, contact resistance reduction, and anchoring of surface electron dopants. Our study suggests that tuning the chemical composition of oxygen is viable for modulating the electronic properties of MoS₂ and likely other chalcogen-incorporated TMDs, which offers promise for new optoelectronic applications.

M–N₄–C single-atom catalysts (MN₄) have gained attention for their efficient use at the atomic level and adjustable properties in electrocatalytic reactions like the ORR, OER, and HER. Yet, understanding MN₄'s activity origin and enhancing its performance remains challenging. Edge-doped substituents profoundly affect MN₄'s activity, explored in this study by investigating their interaction with MN₄ metal centers in ORR/OER/HER catalysis (Sub@MN₄, Sub = B, N, O, S, CH₃, NO₂, NH₂, OCH₃, SO₄; M = Fe, Co, Ni, Cu). The results show overpotential variations (0 V to 1.82 V) based on Sub and metal centers. S and SO₄ groups optimize FeN₄ for peak ORR activity (overpotential at 0.48 V) and reduce OER overpotentials for NiN₄ (0.48 V and 0.44 V). N significantly reduces FeN₄'s HER overpotential (0.09 V). Correlation analysis highlights the metal center's key role, with ΔG_*H and ΔG_*OOH showing mutual predictability (R² = 0.92). E_g proves a reliable predictor for Sub@CoN₄ (ΔG_*OOH/ΔG_*H, R² = 0.96 and 0.72). Machine learning with the KNN model aids catalyst performance prediction (R² = 0.955 and 0.943 for ΔG_*OOH/ΔG_*H), emphasizing M–O/M–H and the d band center as crucial factors. This study elucidates edge-doped substituents' pivotal role in MN₄ activity modulation, offering insights for electrocatalyst design and optimization.

VO₂ possesses a unique property of solid-state phase transition near room temperature wherein it transforms from monoclinic (M1) to tetragonal phase (R) that alters its physical properties, such as resistivity, mechanical modulus, and lattice strain, at an ultrafast time scale known as MIT. Such a phenomenon offers a distinct advantage to use VO₂ in switching applications using heat flux as a stimulus. However, such alteration in properties can also be triggered under an electric field (E), which is known as E-MIT. A nanomechanical resonator coated with VO₂ recently received traction where the resonance behavior can be modulated by taking advantage of its phase transition. Herein, we demonstrate that by fabricating a microstring of 400 μm (L) × 5 μm (W) × 240 nm (t) of suspended SiN_x coated with VO₂, the frequency (f_r) of the resonator can be modulated by applying an electric field. We show that at room temperature, the f_r of the microstring can be either reduced (by 0.5% at 15 V mm^-1) or enhanced (by 2.2% at 25 V mm^-1) or can be varied in a cycle under E-field. Using theoretical models, we establish the simulated results and explain the processes behind it, which demonstrate excellent mechanical tuning properties of the VO₂-based microstring resonator, making it an attractive and alternative option for highly efficient MEMS-based switches and neuromorphic devices.

Peptide-based biofluorescents are of great interest due to their controllability and biocompatibility, as well as their potential applications in biomedical imaging and biosensing. Here, we present a simple approach to synthesizing full-color fluorescent nanomaterials with broad-spectrum fluorescence emissions, high optical stability, and long fluorescence lifetimes. By doping amino acids during the enzyme-catalyzed oxidative self-assembly of tyrosine-based peptides, we can precisely control the intermolecular interactions to obtain nanoparticles with fluorescence emission at different wavelengths. The synthesized peptide-based fluorescent nanomaterials with excellent biocompatibility and stable near-infrared fluorescence emission were shown to have potential for bioimaging applications. This research provides new ideas for the development of new bioluminescent materials that are cost-effective, environmentally friendly, and safe for biomedical use.

In this work, we explore focused electron beam induced etching (FEBIE) of niobium thin films with the XeF₂ precursor as a route to edit, on-the-fly, superconducting devices. We report the effect of XeF₂ pressure, electron beam current, beam energy, and dwell time on the Nb etch rate. To understand the mass transport and reaction rate limiting mechanisms, we compare the relative electron and XeF₂ gas flux and reveal the process is reaction rate limited at low current/short dwell times, but shifts to mass transport limited regimes as both are increased. The electron stimulated etching yield is surprisingly high, up to 3 Nb atoms/electron, and for the range studied has a maximum at 1 keV. It was revealed that spontaneous etching accompanies the electron stimulated process, which was confirmed by varying the etched box size. An optimized etch resolution of 17 nm was achieved. Given that the Nb superconducting coherence length is 38 nm and scales with thickness, this work opens the possibility to direct write Nb superconducting devices via low-damage FEBIE.

The unique features of metal–organic frameworks (MOFs) such as biodegradability, reduced toxicity and high surface area offer the possibility of developing smart nanosystems for biomedical applications through the simultaneous functionalization of their structure with biologically relevant ligands and the loading of biologically active cargos, ranging from small drugs to large biomacromolecules, into their pores. Aiming to develop efficient, naturally inspired biocompatible systems, recent research has combined organic and materials chemistry to design innovative composites that exploit carbohydrate chemistry for the functionalization and structural modification of MOFs. Scientific investigation in the field has seen a significant rise in the past five years, and it is becoming crucial to acknowledge both the limits and benefits of this approach for future investigation. In this review, the latest research results merging carbohydrates and MOFs are discussed, with a particular emphasis on the advances in the field and the remaining challenges, including addressing sustainability and real-case applicability.

The interaction between nanoparticles on mirror (NPoM) nanostructures and molecules is of great significance for the development of plasmon-enhanced spectroscopy (PES) techniques. However, the coupling mechanism between resonantly excited molecules and plasmonics has not been fully understood. In this work, we took viologen molecules within an Au plasmonic nanocavity (AuNC) as an example to illustrate how resonant molecules influence the near-field distributions. We found that the near-fields are highly enhanced and the near-field distributions are altered when the monocationic viologen (V⁺˙) is in resonance. In the AuNC, the near-field enhancement of a molecule is significantly enhanced by the adjacent molecules. However, the average near-field enhancements experienced by each molecule decrease with the increasing coverage of the molecular monolayer. Furthermore, the contributions of molecules to the near-field enhancement initially increase and then decrease as coverage increases. The interactions between the molecules and the nanocavity exhibit negative contributions to near-field enhancement. Overall, this work offers valuable insights into the impact of resonantly excited molecules on near-field enhancements in nanocavities and offers guidance for tuning excitation wavelength. We propose that the resonance state and coverage of molecules are critical to improving the sensitivity and specificity of PES techniques.

The development and understanding of alternative plasmonic materials are crucial steps for leveraging new plasmonic technologies. Although gold and silver nanostructures have been intensively studied, the promising plasmonic, chemical and physical attributes of rhodium remain poorly investigated. Here, we report the synthesis and plasmonic response of spherical Rh nanoparticles (NPs) with sizes in the 20–40 nm range. Due to the high cohesive energy of this metal, synthesis and experimental investigations of Rh nanospheres in this size range have not been reported; yet, it becomes possible here using a green and one-step laser ablation in liquid method. The localized surface plasmon (LSP) of Rh NPs falls in the ultraviolet spectral range (195–255 nm), but the absorption tail in the visible region increases significantly upon clustering of the nanospheres. The surface binding ability of Rh NPs towards thiolated molecules is equivalent to that of Au and Ag NPs, while their chemical and physical stability at high temperatures and in the presence of strong acids such as aqua regia is superior to those of Au and Ag NPs. The plasmonic features are well described by classical electrodynamics, and the results are comparable to Au and Ag NPs in terms of extinction cross-section and local field enhancement, although blue shifted. This allowed, for instance, their use as an optical nanosensor for the detection of ions of toxic metals in aqueous solution and for the surface enhanced Raman scattering of various compounds under blue light excitation. This study explores the prospects of Rh NPs in the realms of UV and visible plasmonics, while also envisaging a multitude of opportunities for other underexplored applications related to plasmon-enhanced catalysis and chiroplasmonics.

Biomimetic-based drug delivery systems (DDS) attempt to recreate the complex interactions that occur naturally between cells. Cell membrane-coated nanoparticles (CMCNPs) have been one of the main strategies in this area to prevent opsonization and clearance. Moreover, coating nanoparticles with cell membranes allows them to acquire functions and properties inherent to the mother cells. In particular, cells from bloodstream show to have specific advantages depending on the cell type to be used for that application, specifically in cases of chronic inflammation. Thus, this review focuses on the biomimetic strategies that use membranes from blood cells to target and treat inflammatory conditions.

Aqueous batteries and supercapacitors are promising electrochemical energy storage systems (EESSs) due to their low cost, environmental friendliness, and high safety. However, aqueous EESS development faces challenges like narrow electrochemical windows, irreversible dendrite growth, corrosion, and low energy density. Recently, two-dimensional (2D) transition metal carbide and nitride (MXene) have attracted more attention due to their excellent physicochemical properties and potential applications in aqueous EESSs. Understanding the atomic-level working mechanism of MXene in energy storage through theoretical calculations is necessary to advance aqueous EESS development. This review comprehensively summarizes the theoretical insights into MXene in aqueous batteries and supercapacitors. First, the basic properties of MXene, including structural composition, experimental and theoretical synthesis, and advantages in EESSs are introduced. Then, the energy storage mechanism of MXene in aqueous batteries and supercapacitors is summarized from a theoretical calculation perspective. Additionally, the theoretical insights into the side reactions and stability issues of MXene in aqueous EESSs are emphasized. Finally, the prospects of designing MXene for aqueous EESSs through computational methods are given.