Nanometer Thickness Research Articles

2D Ti3AlC2 and Ti3C2 nanosheets: Excellent optical limiting materials for laser protection

MXenes have important research value in the field of photonics. In this work, Ti3C2 MXene was obtained by etching the Ti3AlC2 MAX phase with hydrofluoric acid, Ti3AlC2 and Ti3C2 nanosheets with a thickness of several nanometers were prepared by ultrasound-assisted liquid-phase exfoliation using anhydrous ethanol as the exfoliation solvent. The nonlinear absorption properties of the two nanosheets at 1064, 532 and 355 nm excitation wavelengths (infrared to ultraviolet band), especially the optical limiting behavior, were systematically investigated with the help of open aperture Z-scan technique. Interestingly, Ti3C2 MXene, obtained from Ti3AlC2 MAX by a simple hydrofluoric acid etching operation only, exhibits different nonlinear optical properties from Ti3AlC2 MAX under the same experimental conditions. Ti3AlC2 nanosheets exhibited excellent two-photon absorption behavior in the visible light band, while the two-photon absorption behavior of Ti3C2 nanosheets is better in the ultraviolet band. The excellent nonlinear absorption properties exhibited by Ti3AlC2 and Ti3C2 nanosheets demonstrate their advantages as OL materials with great potential for applications in laser protection.

Генерация и детектирование спинового тока в гетероструктурах иридат/манганит

Kotel'nikov Institute of Radioengineering and Electronics of Russian Academy of Sciences The results of experimental studies on spin current at the interface of iridate/manganite heterostructure SrIrO3/La0.7Sr0.3MnO3 consisted of oxide epitaxial films with nanometer thickness are presented. A pure spin current was induced by microwave irradiation in GHz frequency band under conditions of ferromagnetic resonance. The spin current was detected due to inverse spin-Hall effect measuring the spectral characteristics of charge current arising on electrically conductive SrIrO3 film with strong spin-orbit interaction. The spin-Hall angle, which characterizes the efficiency of spin current conversion to the charge current, was determined by measurements of the angular dependences of spin magnetoresistance of the iridate/manganite interface.

π-Sticked Metal‒Organic Monolayers for Single-Metal-Site Dependent CO2 Photoreduction and Hydrogen Evolution Reaction.

Hierarchical self-assembly of 2D metal‒organic layers (MOLs) for the construction of advanced functional materials have witnessed considerable interest, due to the increasing atomic utilizations and well-defined atom‒property relationship. However, the construction of atomically precise MOLs with mono-/few-layered thickness through hierarchical self-assembly process remains a challenge, mostly because the elaborate long-range order is difficult to control via conventional noncovalent interaction. Herein, a quadruple π-sticked metal‒organic layer (πMOL) is reported with checkerboard-like lattice in ≈1.0 nanometre thickness, on which the catalytic selectivity can be manipulated for highly efficient CO2 reduction reaction (CO2RR) and hydrogen evolution reaction (HER) over a single metal site. In saturated CO2 aqueous acetonitrile, Fe-πMOL achieves a highly effective CO2RR with the yield of ≈3.98mmolg‒1h‒1 and 91.7% selectivity. In contrast, the isostructural Co-πMOL as well as mixed metallic FeCo-πMOL exhibits a high activity toward HER under similar conditions. DFT calculations reveal that single metal site exhibits the significant difference in CO2 adsorption energy and activation barrier, which triggers highly selective CO2RR for Fe site and HER for Co site, respectively. This work highlights the potential of supramolecular π…π interaction for constructing monolayer MOL materials to uniformly distribute the single metal sites for artificial photosynthesis.

Monodispersed semiconducting SWNTs significantly enhanced the thermoelectric performance of regioregular poly(3-dodecylthiophene) films

The improved thermoelectric (TE) properties of conducting polymers are generally achieved through the use of single-walled carbon nanotubes (SWNTs) as additives. However, their aggregation and aggregation-induced over-loading of SWNTs generally result in high thermal and low electrical conductivity. Herein, sc-SWNTs were selectively captured by regioregular poly(3-dodecylthiophene)(rr-P3DDT) in a toluene solution containing a semiconducting and metallic carbon nanotubes mixture (mix-SWNTs) to achieve rr-P3DDT films with monodispersed semiconducting SWNTs (rr-P3DDT/sc-SWNT). The single sc-SWNTs were tightly wrapped by a rr-P3DDT layer with a thickness of several nanometers, which was orderly aligned at the micrometer scale. The large number of rr-P3DDT/sc-SWNT nanointerfaces present in composite films contributed to increasing carrier mobility through π–π conjugation while reducing the thermal conductivity via phonon scattering. Thus, the rr-P3DDT/sc-SWNT films had significantly higher electrical conductivity and lower thermal than the rr-P3DDT/mix-SWNT composite films. Both the electrical conductivity and Seebeck coefficient of the rr-P3DDT/sc-SWNT composite films were much greater than the calculated values using the parallel connected mixture model. The maximum ZT value of the rr-P3DDT/sc-SWNT composite film was 0.1, approximately 18 times greater compared to the rr-P3DDT/mix-SWNT films and among the highest for the polymer/carbon nanotube composites. This work provides a convenient but efficient method to maximize the TE properties of conducting polymers.

Amorphous high-entropy IrRuCrFeCoNiOx as efficient water splitting oxygen evolution reaction electrocatalysts

The process of oxygen evolution reaction (OER) for water splitting is intricate and demands a substantial amount of energy. It necessitates the utilization of catalysts that are both highly efficient and durable in order to overcome the slow reaction kinetics. Amorphous, high-entropy oxide nanoparticles were prepared using simple one-step coprecipitation in this work. Due to highly disordered atomic arrangement in the amorphous structure of these catalysts and their high specific surface area, they compete to form active sites in the OER. Among them, IrRuCrFeCoNiOx demonstrated the optimal OER catalytic activity, requiring just a low overpotential (190 mV) with minimal Tafel slope (51.1 mV dec−1) to achieve the current density of 10 mA cm−2 in 1 M KOH. Through surface self-reconstruction in the OER, a crystalline active layer with a thickness of several nanometers formed on the catalyst’s surface. The stable core-shell nanoarchitectures composed of crystalline and amorphous regions substantially improved the stability of the catalyst. This work verified the effectiveness of high-entropy design and the significant improvement of noble metal doping on OER performance. It develops a new OER catalyst for water splitting with great activity and stability.

Lamellar particle self-assembling of graphene oxide into continuous thin and thick films by automated atmospheric pressure plasma jet deposition

This work shows the achievement of obtaining graphene oxide coatings deposited under ambient conditions using the plasma jet technique at atmospheric pressure in an automated system with robotic arms. Graphene oxide nanoparticles in an aqueous solution were sonicated to obtain a colloidal solution. This was projected in an ultrasonic mist perpendicularly through an air plasma of about 260 °C. The primary process parameters were deposition time, speed, concentration, and distance to obtain coating thickness from about 100 nm to microns. These were homogeneous and adherent coatings on aluminum, steel, glass, and polymers (PMMA and polycarbonate), showing similar characteristics on all these substrates. The highlight of this contribution is transforming nanometric thickness flakes into continuous layers with chemical bonding to surfaces with contrasting characteristics such as those mentioned. The GO obtained layer differs from those obtained by spin-coating, dipping, drop-casting, or electrophoretic deposition. We propose that APPJ eliminates OH radicals around the particles, allowing them to self-assemble by connecting them through bonds. This work probes the feasibility of depositing horizontally/vertically self-assembled GO on polymers and aluminum in a modular industrial facility. This achievement opens the possibility of transferring the characteristics of graphene oxide to surfaces for industrial use, making nanotechnology accessible for social benefit.

Concerted Mechanism of Carrier Dynamics in Laser‐Excited Fen/(MgO)m(001) Heterostructures from Real‐Time Time‐Dependent DFT

AbstractUsing real‐time time‐dependent density functional theory (RT‐TDDFT), the electronic response of a Fen/(MgO)m(001) (n=1,3,5 and m=3,5,7) metal/insulator heterostructure to an optical excitation is calculated, considering laser frequencies below, near, and above the bandgap of the insulator and two directions of polarization. The spatial redistribution of electronic charge after illumination shows a strong dependence on the frequency and polarization direction of the laser pulse with a similar pattern for all thicknesses. The comparison of the layer‐resolved changes in occupation of the ground‐state orbitals after optical excitation obtained for Fen/(MgO)m(001) and bulk Fe reveals the origin of excited carriers in the heterostructures: In the central and interface Fe layers carriers are excited from states in the vicinity of the Fermi‐level to the conduction band of MgO. Simultaneously, excitations take place from the valence band of MgO to Fe states above the Fermi‐level. This concerted mechanism allows for an effective bidirectional relocation of excited carriers between the metallic and insulating subsystems in heterostructures with a thickness of several nanometers, providing an effective accumulation of hot carriers in the insulating layers, even at photon energies in the vicinity and below the bandgap of bulk MgO.

Facile Synthesis of Ru Nanoboxes with a Hexagonal Close-Packed Structure by Templating with Ag Nanocubes and Their Catalytic Properties.

Noble-metal nanoboxes offer an attractive form of nanomaterials for catalytic applications owing to their open structure and highly efficient use of atoms. Herein, we report the facile synthesis of Ag-Ru core-shell nanocubes and then Ru nanoboxes with a hexagonal close-packed (hcp) structure, as well as evaluation of their catalytic activity toward a model hydrogenation reaction. By adding a solution of Ru(acac)3 in ethylene glycol (EG) dropwise to a suspension of silver nanocubes in EG at 170 °C, Ru atoms are generated and deposited onto the entire surface of a nanocube. As the volume of the RuIII precursor is increased, Ru atoms are also produced through a galvanic replacement reaction, generating Ag-Ru nanocubes with a hollow interior. The released Ag+ ions are then reduced by EG and deposited back onto the nanocubes. By selectively etching away the remaining Ag with aqueous HNO3 , the as-obtained Ag-Ru nanocubes are transformed into Ru nanoboxes, whose walls are characterized by an hcp structure and an ultrathin thickness of a few nanometers. Finally, we evaluated the catalytic properties of the Ru nanoboxes with two different wall thicknesses by using a model hydrogenation reaction; both samples showed excellent performance.

Ferroelectric Schottky diodes of CuInP2S6 nanosheet

Ferroelectricity in van der Waals (vdW) layered material has attracted a great deal of interest recently. CuInP2S6 (CIPS), the only vdW layered material whose ferroelectricity in the bulk was demonstrated by direct polarization measurements, was shown to remain ferroelectric down to a thickness of a few nanometers. However, its ferroelectric properties have just started to be explored in the context of potential device applications. We report here the preparation and measurements of metal-ferroelectric semiconductor-metal heterostructures using nanosheets of CIPS obtained by mechanical exfoliation. Four bias voltage and polarization dependent resistive states were observed in the current–voltage characteristics, which we attribute to the formation of ferroelectric Schottky diode, along with switching behavior.

Gentle ions for cryo-FIB milling

Cryo-EM imaging of vitreous samples is limited to a few hundred nanometers in thickness. Focused ion beams can mill windows into cells and tissues for imaging, but they damage biological samples. In this issue of Structure, Yang etal. (2023) quantitatively describe this damage and suggest ways to minimize it.

Novel Strategy Toward Light Absorption Enhancement of Organic Solar Cells Using M13 Bacteriophage

In organic photovoltaics (OPVs), the development of efficient light‐harvesting organic donor and acceptor materials and the design of a device structure with appropriate visible light transmittance play an important role in increasing their power conversion efficiency. Light manipulation strategies in OPV are widely used to improve photovoltaic performance. One of the most popular technologies is antireflective coating (ARC), which enhances light utilization in devices. However, ARC has been investigated less in OPV cells than in organic silicon solar cells. Herein, a novel approach that employs the natural biomaterial M13 bacteriophage (M13) as an intermediate layer with a thickness of a few nanometers between the hole transport layer (HTL) and indium tin oxide is investigated. The functional surface hydrophilicity, obtained by genetic manipulation of M13, improves the light transmittance by more than 84% over the visible wavelength range of the OPV cells. Furthermore, it enhances the coherence between the HTL and the photoactive layer. Therefore, the photocurrent density and power conversion efficiency significantly increase, producing a high photovoltaic performance. The proposed approach of using natural biomaterials is the basis for a novel, low‐cost, and eco‐friendly design for light manipulation in solar cells.

Dual S-scheme CuSe-Cu3Se2/Ag-PANI heterostructures for the impressive degradation of dye pollutants

A dual S-scheme structure for the photocatalytic activity of copper selenide (CuxSey)/Ag-polyaniline (CuxSey/Ag-PANI) nanocomposites to degrade dye pollutants under visible light illumination conditions has been proposed. In the first step, PANI composites have been decorated by Ag nanoparticles (NPs) with different concentrations of Ag NPs. Then, a cost-effective and straightforward co-precipitation method has synthesized the CuxSey/Ag-PANI nanocomposites with different Ag NPs concentrations. Additions of the CuxSey/Ag-PANI nanocomposites, pristine CuxSey nanostructures, and CuxSey/PANI nanocomposites have also been synthesized with the same conditions. X-ray diffraction patterns (XRD) and high-resolution transmission electron microscopy (HRTEM) images indicated the CuxSey nanostructures in the nanocomposites included two phases that were CuSe nanodisks with a few nanometers in thickness and Cu3Se2 NPs with average diameters of 10±2 nm. In contrast, the pristine CuxSey nanostructures have included several extra phases. These microscopy images showed the Cu3Se2 NPs have decorated the CuSe nanodisks. According to the UV–vis results, the Ag NPs in the CuSe-Cu3Se2/Ag-PANI nanocomposites showed surface plasmon resonance (SPR) effects, and this factor became one of the most critical factors for the better photocatalytic performance of the CuSe-Cu3Se2/Ag-PANI nanocomposites. By comparing the Fermi level (Ef) of the structures that make up the CuSe-Cu3Se2/Ag-PANI heterostructures, these structures had the conditions for forming the dual S-scheme structure. Based on this structure and also the synergistic effect of the plasmonic properties of the Ag NPs, the reason for the better photocatalytic performance of the CuxSey/Ag-PANI nanocomposites compared to the pristine CuxSey nanostructures and CuxSey/PANI nanocomposites has been explained.

Significant efficiency increment of spintronic terahertz emitters by oxygen engineering

Spintronic terahertz (THz) emitters have been intensively explored as next-generation sources of THz waves due to their low-cost, nanometer thickness, and broadband spectra. Growing research works are focusing on how to improve the THz emission efficiency, mainly by using a larger spin-Hall angle heavy metal. Currently, the highest intensity spintronic THz emission was based on a CoFeB/Pt heterostructure. Here, we significantly improve the THz emission intensity of CoFeB/Pt by a factor up to 270% through simply incorporating oxygen atoms into the Pt layer. The oxidation of a Pt layer generates a large extrinsic spin Hall angle, which promotes the spin-to-charge conversion of PtOx. Furthermore, the oxygen incorporation also causes a finite oxidation of CoFeB near the interface. We revealed that the significantly enhanced THz emission of CoFeB/PtOx is contributed by both the bulk inverse spin Hall effect of PtOx and the interface effect. Finally, we demonstrated that the oxygen engineering procedure to improve the THz emission of spintronic THz emitters is a common phenomenon as verified in examples, including Co/PtOx, NiFe/PtOx, CoFeB/WOx, and CoFeB/TaOx heterostructures. These findings show that an oxidized heavy metal is a simple, low-cost, and effective route to enhance the spin-to-charge conversion and achieve intense THz pulses, which is promising especially for on-chip THz devices.

Alkali metal ion-mediated ice nucleation

Understanding the effects of ion specificities on ice nucleation is essential for atmospheric science and biology. Although valence and concentration changes of ions can regulate ice nucleation, it is unclear if alkali metal ions of different species with the same valence can regulate ice nucleation. This study investigated the behavior of ice nucleation on alkali metal ion-modified surfaces with atomic-scale roughness and (sub)nanometer thickness to decouple the effect of alkali metal ions on ice nucleation. The results showed that modulating the type of alkali metal ion could regulate ice nucleation. Additionally, it was found that different hydration shells of alkali metal ions may influence the structure of interfacial water and the thermodynamic phase transition to play a key role in regulating ice nucleation. This study shed light on a long-standing problem of the mechanism of alkali metal ions in ice nucleation and provided a strategy for effectively regulating ice nucleation .

Kinetics and TD-DFT calculations of base-catalyzed oxidation of acriflavine hydrochloride: Removal of dyes colors from wastewater

The oxidation kinetics of acriflavine hydrochloride (AFH) to nitro-acriflavine (N-AFH) by KMnO4 as oxidizing agent in sodium hydroxide medium at a constant ionic strength of 0.5 moldm−3 was studied using spectrophotometric methods. It was found that the reaction went through two distinct steps that could be monitored. In the first stage, coordination species including transient blue pentavalent manganese and/or green hexavalent manganese species may be made quite quickly followed by the decomposition of intermediates in the second slow stage to produce soluble Mn (IV) and the nitroacriflavine as resulting products of oxidation. It has been investigated how several variables such as pH, ionic strength, permanganate ion concentration, and AFH substrate concentration affect oxidation rates. The experimental results demonstrated a first-order dependence in [MnO4−] and fractional first-order kinetics in each of [AFH] and alkali concentration under pseudo-first-order reaction conditions of [MnO4−] >>10 [AFH]. Sodium hydroxide concentrations accelerated the oxidation reaction, and as the alkali concentration rose, so the type of catalyzed is base-catalyzed. Evidence for the creation of a 1:1 intermediate complex was discovered using spectrophotometry and kinetics. In accordance with the kinetic findings, an efficient oxidation process that is compatible with the kinetic data obtained in terms of the activation parameters evaluated was analyzed, proposed, and debated. There are several techniques used to study the nanostructure thin films (AFH)TF and (N- AFH)TF, with using FT-IR, kinetic, isotherms of liquid-phase adsorption, and optical characteristics. A low deposition rate and a chamber pressure of 5 × 105 mbar are used in the PVD method to create (AFH)TF and (N-AFH)TF thin coatings with a 95 nanometer thickness. The isolated molecules (AFH)Iso and (N-AFH)Iso were additionally optimized using time-dependent density functional theory (TD-DFT) using TD-DFTD/Mol3 and Cambridge Serial Total Energy Bundle (TD-FDT/CASTEP). The optimized geometries, vibrational wavenumbers, intensity of vibrational bands, and various atomic charges of 9VC have all been investigated using DFT-B3LYP system using a 6-31G (d,p) basis set.

Flexoelectricity-stabilized ferroelectric phase with enhanced reliability in ultrathin La:HfO2 films

Doped HfO2 thin films exhibit robust ferroelectric properties even for nanometric thicknesses, are compatible with current Si technology, and thus have great potential for the revival of integrated ferroelectrics. Phase control and reliability are core issues for their applications. Here, we show that, in (111)-oriented 5%La:HfO2 (HLO) epitaxial thin films deposited on (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates, the flexoelectric effect, arising from the strain gradient along the film's normal, induces a rhombohedral distortion in the otherwise Pca21 orthorhombic structure. Density functional calculations reveal that the distorted structure is indeed more stable than the pure Pca21 structure, when applying an electric field mimicking the flexoelectric field. This rhombohedral distortion greatly improves the fatigue endurance of HLO thin films by further stabilizing the metastable ferroelectric phase against the transition to the thermodynamically stable non-polar monoclinic phase during repetitive cycling. Our results demonstrate that the flexoelectric effect, though negligibly weak in bulk, is crucial to optimize the structure and properties of doped HfO2 thin films with nanometric thicknesses for integrated ferroelectric applications.

Precise Control of Broadband Light Absorption and Density of Ti3+ States in Sputtered Black TiO2 Thin Films

Defect‐rich black titanium dioxide (B‐TiO2) has been extensively studied over the past decade due to its enhanced photoelectrochemical efficiency compared to titanium dioxide (TiO2), which is known for its outstanding photocatalytic stability. So far, most of the B‐TiO2 material is obtained by hydrogenation of crystalline TiO2, resulting in a disordered outer layer of a few nanometers thickness. Recently, a new sputtering process has been introduced to produce B‐TiO2 thin films without the usage of hydrogen. Herein, the influence of the sputtering process on the creation of Ti3+ defect states within the films is discussed. Comprehensive optical, structural, and electronic studies of the thin film suggest that increasing the density of Ti3+ states enhances the conductivity of the films and results in increased and broadband light absorption. In addition, the new sputtering method can also be used to alter the density of the defect states in the film in a controlled manner, allowing the optical and electronical properties of the thin film to be changed in a precise and controllable way.

Pompom 3D flower like carbon-based Mn3O4 thin film electrodes for high performance supercapacitors

Manganese oxides have received a lot of attention as positive electrode materials for supercapacitors, but they still present challenges due to their weak electrical conductivity, lack of electroactive sites, and slow charge transfer kinetics. Herein, utilizing the electron beam evaporation technique, we effectively create pompom 3D flower-like C/Mn3O4 particles on Au/Ti/SiO2/(textured) Silicon (ATS) substrates with a few nanometers thickness. High accessibility to active species is provided by the linked carbon with Mn3O4 and the flower-shaped particles with multiple petals, which further enhance charge transfer kinetics. As a result, C/Mn3O4 thin film electrodes showed outstanding cycling stability of 89% even after 10,000 cycles and a reversible capacity of 1452 Fg−1 at 1 mVs−1 scan rate. The C/Mn3O4 thin film-based electrodes improved electrochemical performance is attributable to their unique surface topology.

Visualization of invisible cell-death sign by electric-double-layer modulation

Leakage and self-spreading of a cytoplasmic lipid droplet in association with cell death, which was totally invisible in a conventional optical microscope, was discovered by using the recently developed electric-double-layer modulation imaging (EDLMI). The method allowed real-time imaging of the leaked lipid droplet with the thickness of a few nanometers. We demonstrate that the discovered phenomenon is useful as a new cellular sign for diagnosis of cell death.

Thin Cationic Polymer Coatings against Foodborne Infections

Biocidal coatings are known to minimize or terminate development of bacterial and fungicidal infections. In this paper, biocidal activity of seven cationic (co)polymers with amino groups—polyethyleneimine, polyallylamine, polydiallyldimethylammonium chloride/polyhexamethylene guanidine copolymer, diallyldimethylammonium chloride/SO2 copolymer, linear and hyperbranched epichlorohydrin/dimethylamine copolymers, polydiallyldimethylammonium chloride—were tested toward Gram-positive and Gram-negative cells. The polymers showed a significant biocidal effect in both aqueous solution and after formation of polymer films on the hydrophilic glass plates. Polymer films were almost completely removed by water during 10 wash-off cycles, that finally resulted in the ultrathin monolayers with a thickness of several nanometers. A polyethyleneimine film showed the most resistance to water with a 50% loss after three wash-off cycles and 75% loss after six wash-off cycles. Binding and subsequent deactivation of pathogenic microorganisms occurs on the outer surface of cationic polymer films. It is expected that a gradual polymer wash-off will allow renewal of the outer film surface and thereby restore the biocidal properties of the polycationic coatings, including those with a nanoscale thickness.