Improved Alcohol Oxidation through Combined Effects of Tensile Lattice Strain and Twin Defects in Core-Shell Electrocatalysts.

The direct alcohol fuel cells (DAFCs) rely on alcohol oxidation reactions (AORs) to produce electricity, which require catalysts with optimized electronic structure to accelerate the sluggish AORs. Herein, an epitaxial growth of Pd layer onto the pentatwinned Au@Ag core-shell nanorods (NRs) is reported to synthesize highly strained Au@AgPd core-shell NRs. The tensile strain in the AgPd shell of the Au@AgPd nanorods (NRs) arises not only from the core-shell lattice mismatch but also from twinning and lattice distortion occurring at the five twinned boundaries present in the structure. Theoretical simulations prove that the presence of tensile strains in the AgPd layer leads to a significant upward shift of the d-band center of the Pd site toward the Fermi level which remarkably changes the adsorption energy of alcohols on the surface. Highly strained Au@AgPd NRs show exceptional mass activities in electrochemical oxidation of biomass-derived alcohols (ethylene glycol, ethanol, and glycerol) reaching up to 18.66, 15.6, and 7.90 A mgpd -1, respectively. These values are 23.3, 23.6, and 23.2 times higher than commercial Pd/C catalysts. This strain engineering strategy set the platform for the design and synthesis of highly efficient and versatile catalysts for the construction of high-performance DAFCs.

Assembly of Gold Nanostar Cores Within Silica Shells and Its Impact on Solid-State SERS and Nonenzymatic Catalytic Sensing.

Metal core and dielectric shell nanoparticles (NPs) have garnered considerable attention for their multifaceted properties and extensive applications across diverse fields of nanoscience and nanotechnology. However, a literature gap exists regarding the impact of assembled metallic nanostar cores within a single shell, particularly concerning surface-enhanced Raman scattering (SERS) and electrochemical sensing. In this study, we have demonstrated the better performance of assemblies of gold nanostars (AuNSs) enclosed in single silica shell for SERS enhancement and electrocatalytic activity, particularly in the fields of ascorbic acid (AA) and glucose sensing. We have devised a method to isolate and passivate nanostar assemblies, ranging from 2 to 30 nanostars per assembly, with a functionalized silica (SiO2) shell, facilitating their preservation. The engineered thickness of the silica shell ensures unhindered optical measurements while elucidating the influence of multiple AuNS cores. Due to the formation of nanogaps and nanojunctions between AuNSs within assembly, we have achieved a maximum SERS enhancement factor (EF) of 1.416 × 1010 for the rhodamine 6G analyte. Utilizing assembled AuNS cores within a single silica shell, we have demonstrated AA (sensitivity of 5.278 × 10-5 µA µM-1 cm-2) and glucose (sensitivity of 7.519 × 10-4 µA µM-1 cm-2) sensing via a nonenzymatic electrochemical pathway.

Green to deep-red emissive carbon dot formation by C+ion implantation on nitrogen beam created self-masked nano-template.

We report the formation of green to red emissive arrays of carbon dot on silicon-nitride nano-templates by successive implantation of nitrogen and carbon broad ion beams. The patterned nano-templates are formed by 14 keV N2+ion-bombardment at grazing incident (70°) on Si. Subsequently, 5 keV C+ions are implanted at the selective sites of the pyramidal nano-template by taking advantage of the self-masking effect. The nano-pyramidal pattern and the implanted carbon dots at the specific sites are confirmed by atomic force microscopy and cross sectional transmission electron microscopy measurements. The developed carbon dots (CDs) are mostly amorphous and consists of SiC and graphitic nitrogen (CN). G-band and D-band carbons are identified by Raman spectroscopy, while the presence of SiC and CN are detected by XPS measurements. A change of band-gap is observed for C-implanted templates by the UV-vis spectroscopy. Excitation wavelength-dependent photoemission from the dots is found in the green to red region. Maximum intense PL is observed in the green-orange region for excitation wavelength of 425 nm and a redshift of PL with decreasing intensity is observed with the increase of excitation wavelength. The observed photoluminescence is described in terms of the combined effects of quantum confinement, graphitic nitrogen and defect induced additional states formation in the carbon dots. The potential applications of CDs are also addressed.

Effect of temperature on polaronic transport in CeO2 thin-film.

The outstanding catalytic property of cerium oxide (CeO2) strongly depends on the polaron formation due to the oxygen vacancy (V̈O) defect and Ce4+ to Ce3+ transformation. Temperature plays an important role in the case of polaron generation in CeO2 and highly influences its electrical transport properties. Therefore, a much needed attention is required for detailed understanding of the effect of temperature on polaron formation and oxygen vacancy migration to get an idea about the improvement in the redox property of ceria. In this work, we have probed the generation of polarons in CeO2 thin-film deposited on a silicon (Si) substrate using the resonance photoemission spectroscopy (RPES) study. The RPES data show an increase in polaron density at the substrate-film interface of the thermally annealed film, indicating the formation of an interfacial Ce2O3 layer, which is, indeed, a phase change from the cubic to hexagonal structure. This leads to a modified electronic band structure, which has an impact on the capacitance-voltage (C-V) characteristics. This result nicely correlates the microscopic property of polarons and the macroscopic transport property of ceria.

Magnetic-Proximity-Induced Efficient Charge-to-Spin Conversion in Large-Area PtSe2/Ni80Fe20 Heterostructures.

As a topological Dirac semimetal with controllable spin-orbit coupling and conductivity, PtSe2, a transition-metal dichalcogenide, is a promising material for several applications, from optoelectrics to sensors. However, its potential for spintronics applications has yet to be explored. In this work, we demonstrate that the PtSe2/Ni80Fe20 heterostructure can generate large damping-like current-induced spin-orbit torques (SOT), despite the absence of spin-splitting in bulk PtSe2. The efficiency of charge-to-spin conversion is found to be -0.1 ± 0.02 nm-1 in PtSe2/Ni80Fe20, which is 3 times that of the control sample, Ni80Fe20/Pt. Our band structure calculations show that the SOT due to PtSe2 arises from an unexpectedly large spin splitting in the interfacial region of PtSe2 introduced by the proximity magnetic field of the Ni80Fe20 layer. Our results open up the possibilities of using large-area PtSe2 for energy-efficient nanoscale devices by utilizing proximity-induced SOT.

Suberic Acid-Based Supramolecular Metallogels of Ni(II), Zn(II), and Cd(II) for Anti-Pathogenic Activity and Semiconducting Diode Fabrication.

The importance of three synthesized metallogels of suberic acid distinctly with nickel, zinc, and cadmium acetate salts has been uncovered. For the creation of these soft materials, N,N'-dimethyl formamide was utilized as a source of the trapped solvent. The synthesized metallogels display intriguing viscoelasticity, and the interpretation of experimental parameters obtained from rheological results advocates the gel behavior. Microstructural analysis combined with energy-dispersive X-ray confirms the occurrence of individual gel-developing constituents as observed in different hierarchical microstructural patterns. Significant variations in microstructural arrangements with diverse extent of supramolecular non-covalent patterns inside gel networks were perceived through field emission scanning electron microscopy, atomic force microscopy, and transmission electron microscopy analyses. Fourier transform infrared and electrospray ionization-mass spectral analyses and powder X-ray diffraction analysis of metallogel samples of different gel-establishing ingredients help to investigate the possible supramolecular interactions dictating the metallogel scaffolds. Thermogravimetric analysis of xerogel samples was collected from the synthesized metallogels to understand the thermal stability. These gel materials were characterized by their potential antibacterial efficiency. The potency of metallogels against selective Gram-positive and Gram-negative bacteria was visualized via a spectrophotometer. Human pathogens like Klebsiella pneumoniae (MTCC 109), Salmonella typhi (MTCC 733), Vibrio parahaemolyticus, Bacillus cereus (MTCC 1272), Lactobacillus fermentum (NCDO 955), and Staphylococcus aureus (MTCC 96) are employed in this study. Apart from the biological significance, our metallogels demonstrate as incredible diode performance of fabricated semiconducting systems, which exhibit a considerable amount of non-linearity demonstrating a non-ohmic conduction mechanism at room temperature in dark conditions. Device fabrication was achieved from these metallogels employing the sandwich model with indium tin oxide-coated glass substrates/metallogel/Al structure.

Charge-transfer-driven enhanced room-temperature ferromagnetism in BiFeO3/Ag nanocomposite.

We report observation of more than an order of magnitude jump in saturation magnetization in BiFeO3/Ag nanocomposite at room temperature compared to what is observed in bare BiFeO3nanoparticles. Using transmission electron microscopy together with energy dispersive x-ray spectra (which maps the element concentration across the BiFeO3/Ag interface) and x-ray photoelectron spectroscopy, we show that both the observed specific self-assembly pattern of BiFeO3and Ag nanoparticles and the charge transfer between Ag and O are responsible for such an enormous rise in room-temperature magnetization. The BiFeO3/Ag nanocomposites, therefore, could prove to be extremely useful for a variety of applications including biomedical.

A high-temperature ferromagnetic topological insulating phase by proximity coupling.

Topological insulators are insulating materials that display conducting surface states protected by time-reversal symmetry, wherein electron spins are locked to their momentum. This unique property opens up new opportunities for creating next-generation electronic, spintronic and quantum computation devices. Introducing ferromagnetic order into a topological insulator system without compromising its distinctive quantum coherent features could lead to the realization of several predicted physical phenomena. In particular, achieving robust long-range magnetic order at the surface of the topological insulator at specific locations without introducing spin-scattering centres could open up new possibilities for devices. Here we use spin-polarized neutron reflectivity experiments to demonstrate topologically enhanced interface magnetism by coupling a ferromagnetic insulator (EuS) to a topological insulator (Bi2Se3) in a bilayer system. This interfacial ferromagnetism persists up to room temperature, even though the ferromagnetic insulator is known to order ferromagnetically only at low temperatures (<17 K). The magnetism induced at the interface resulting from the large spin-orbit interaction and the spin-momentum locking of the topological insulator surface greatly enhances the magnetic ordering (Curie) temperature of this bilayer system. The ferromagnetism extends ~2 nm into the Bi2Se3 from the interface. Owing to the short-range nature of the ferromagnetic exchange interaction, the time-reversal symmetry is broken only near the surface of a topological insulator, while leaving its bulk states unaffected. The topological magneto-electric response originating in such an engineered topological insulator could allow efficient manipulation of the magnetization dynamics by an electric field, providing an energy-efficient topological control mechanism for future spin-based technologies.

Single Amino-Acid Based Self-Assembled Biomaterials with Potent Antimicrobial Activity.

The design and development of soft biomaterials based on amino acid and short-peptide have gained much attention due to their potent biomedical applications. A slight alteration in the side-chain of single amino acid in a peptide or protein sequence has a huge impact on the structure and function. Phenylalanine is one of the most studied amino acids, which contains an aromatic phenyl group connected through a flexible -CH2 - unit. In this work, we have examined whether flexibility and aromatic functionality of phenylalanine (Phe) are important in gel formation of model gelator Fmoc-Phe-OH or not. To examine this hypothesis, we synthesized Fmoc-derivatives of three analogues unnatural amino acids including cyclohexylalanine, phenylglycine, and homophenylalanine; which are slightly varied from Phe. Interestingly, all these three new analogues formed hydrogels in phosphate buffer at pH 7.0 having different gelation efficacy and kinetics. This study suggests that the presence of aromatic side-chain and flexibility are not mandatory for the gelation of this model gelator. Newly synthesized unnatural amino acid derivatives have also exhibited promising antimicrobial activity towards gram-positive bacteria by inhibiting cellular oxygen consumption. We further determined the biocompatibility of these amino acid derivatives by using a hemolysis assay on human blood cells. Overall studies described the development of single amino acid-based new injectable biomaterials with improved antimicrobial activity by the slight alteration in the side-chain of amino acid.

Enhanced exciton binding energy, Zeeman splitting and spin polarization in hybrid layered nanosheets comprised of (Cd, Mn)Se and nitrogen-doped graphene oxide: implication for semiconductor devices.

The exciton properties of (Cd,Mn)Se-NrGO (nitrogen doped reduced graphene oxide) hybrid layered nanosheets have been studied in a magnetic field up to 10 T and compared to those of (Cd,Mn)Se nanosheets. The temperature dependent photoluminescence reveals the hybridization of inter-band exciton and intra-center Mn transition with enhancement of the binding energy of exciton-Mn hybridized state (80 meV with respect to 60 meV in (Cd,Mn)Se nanosheets) and increase of exciton-phonon coupling strength to 90 meV (with respect to 55 meV in (Cd,Mn)Se nanosheets). The circularly polarized magneto-photoluminescence at 2 K provides evidence for magnetic field induced exciton spin polarization and the realization of excitonic giant Zeeman splitting withgeffas high as 165.4 ± 10.3, much larger than in the case of (Cd,Mn)Se nanosheets (63.9 ± 6.6), promising for implementation in spin active semiconductor devices.

Correction: Observation of ordered arrays of endotaxially grown nanostructures from size-selected Cu-nanoclusters deposited on patterned substrates of Si.

Correction for 'Observation of ordered arrays of endotaxially grown nanostructures from size-selected Cu-nanoclusters deposited on patterned substrates of Si' by Shyamal Mondal et al., Phys. Chem. Chem. Phys., 2021, 23, 6009-6016 DOI: 10.1039/D0CP06089E.

Observation of ordered arrays of endotaxially grown nanostructures from size-selected Cu-nanoclusters deposited on patterned substrates of Si.

We report the first time observation of endotaxial growth during thermal treatment of size-selected nanoclusters on a patterned substrate, when we fabricate highly ordered and partially embedded 3D crystalline Cu nanostructure arrays of controlled size in Si-substrates. For this purpose, we combine low energy cluster deposition on the ripple-patterned substrate with controlled annealing. We have investigated, in detail, the effect of the substrate pattern on the deposited size-selected clusters upon heat treatment. At the annealing temperature of 400 °C, nanosized islands are found to be organized into regular arrays, following the alignment of the substrate pattern exactly. The formed islands are trapped at the specific sites of the substrate where surface curvature is maximum and concave. It is also observed that the size of the produced nanoislands (or particles) in the direction of the ripple wave vector, i.e., across the ripples, are in congruence with the ripple wavelength. All the formed islands are partially buried in the substrate and the growth inside the substrate exhibits endotaxial growth. Such an embedded size-controlled nanoscale system can be very promising as sinter-resistant heterogenous catalyst with strong potential in clean energy technology and industrial chemical synthesis.

Large nonsaturating magnetoresistance and signature of nondegenerate Dirac nodes in ZrSiS.

Whereas the discovery of Dirac- and Weyl-type excitations in electronic systems is a major breakthrough in recent condensed matter physics, finding appropriate materials for fundamental physics and technological applications is an experimental challenge. In all of the reported materials, linear dispersion survives only up to a few hundred millielectronvolts from the Dirac or Weyl nodes. On the other hand, real materials are subject to uncontrolled doping during preparation and thermal effect near room temperature can hinder the rich physics. In ZrSiS, angle-resolved photoemission spectroscopy measurements have shown an unusually robust linear dispersion (up to [Formula: see text]2 eV) with multiple nondegenerate Dirac nodes. In this context, we present the magnetotransport study on ZrSiS crystal, which represents a large family of materials (WHM with W = Zr, Hf; H = Si, Ge, Sn; M = O, S, Se, Te) with identical band topology. Along with extremely large and nonsaturating magnetoresistance (MR), [Formula: see text]1.4 [Formula: see text] 105% at 2 K and 9 T, it shows strong anisotropy, depending on the direction of the magnetic field. Quantum oscillation and Hall effect measurements have revealed large hole and small electron Fermi pockets. A nontrivial [Formula: see text] Berry phase confirms the Dirac fermionic nature for both types of charge carriers. The long-sought relativistic phenomenon of massless Dirac fermions, known as the Adler-Bell-Jackiw chiral anomaly, has also been observed.

Tuning spinterface properties in iron/fullerene thin films.

In ferromagnetic (FM) metal/organic semiconductor (OSC) heterostructures charge transfer can occur which leads to induction of magnetism in the non-magnetic OSC. This phenomenon has been described by the change in the density of states in the OSC which leads to a finite magnetic moment at the OSC interface and it is called the 'spinterface'. One of the main motivations in this field of organic spintronics is how to control the magnetic moment in the spinterface. In this regard, there are several open questions such as (i) which combination of FM and OSC can lead to more moment at the spinterface? (ii) Is the thickness of OSC also important? (iii) How does the spinterface moment vary with the FM thickness? (iv) Does the crystalline quality of the FM matter? (v) What is the effect of spinterface on magnetization reversal, domain structure and anisotropy? In this context, we have tried to answer the last four issues in this paper by studying Fe/C60 bilayers of variable Fe thickness deposited on Si substrates. We find that both the induced moment and thickness of the spinterface vary proportionally with the Fe thickness. Such behavior is explained in terms of the growth quality of the Fe layer on the native oxide of the Si (100) substrate. The magnetization reversal, domain structure and anisotropy of these bilayer samples were studied and compared with their respective reference samples without the C60 layer. It is observed that the formation of spinterface leads to a reduction in uniaxial anisotropy in Fe/C60 on Si (100) in comparison to their reference samples.

Metal Nanoparticle-Decorated Silicon Nanowire Arrays on Silicon Substrate and their Applications.

Herein, we report an efficient method to produce silver (Ag) nanoparticle-decorated silicon (Si) nanowire (NW) arrays on a pyramidal Si (P-Si) substrate by using a pure chemical method and rapid thermal annealing in different atmospheres. A metal-assisted chemical etching technique was used to produce vertical Si NW arrays on pyramidal Si. The etching was observed to be heavily dependent on the substrate type. On planar Si (100), the etching was observed to occur in a uniform manner. However, the etching rate was observed to increase from the top to the base of the Si pyramid. The Si NWs produced from P-Si have zig-zag sidewalls as observed from high-resolution transmission electron microscopy images. However, for the same oxidant concentration, Si NWs produced from planar Si (100) consist of straight and amorphous sidewalls. Local variation of oxidant concentration is responsible for the formation of different sidewalls. The substrates are both surface-enhanced Raman scattering (SERS) active and hydrophobic. The hydrophobicity is due to the dual scale of roughness contributed to by both pyramidal and NW structures. Finite-difference time-domain simulation shows that the gap between two Ag spheres and also the gap between Si NWs and Ag spheres contributed to SERS enhancement.

Structural stability of coplanar 1T-2H superlattice MoS2 under high energy electron beam.

Coplanar heterojunctions composed of van der Waals layered materials with different structural polymorphs have drawn immense interest recently due to low contact resistance and high carrier injection rate owing to low Schottky barrier height. Present research has largely focused on efficient exfoliation of these layered materials and their restacking to achieve better performances. We present here a microwave assisted easy, fast and efficient route to induce high concentration of metallic 1T phase in the original 2H matrix of exfoliated MoS2 layers and thus facilitating the formation of a 1T-2H coplanar superlattice phase. High resolution transmission electron microscopy (HRTEM) investigations reveal formation of highly crystalline 1T-2H hybridized structure with sharp interface and disclose the evidence of surface ripplocations within the same exfoliated layer of MoS2. In this work, the structural stability of 1T-2H superlattice phase during HRTEM measurements under an electron beam of energy 300 keV is reported. This structural stability could be either associated to the change in electronic configuration due to induction of the restacked hybridized phase with 1T- and 2H-regions or to the formation of the surface ripplocations. Surface ripplocations can act as an additional source of scattering centers to the electron beam and also it is possible that a pulse train of propagating ripplocations can sweep out the defects via interaction from specific areas of MoS2 sheets.

Unidirectional endotaxial cobalt di-silicide nanowires on Si(110) substrates.

Self-organized growth of well-ordered endotaxial silicide nanowires (NWs) on clean Si(110) surfaces has been investigated by in situ scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). Co deposition on clean Si(110) reconstructed surfaces at ∼600 °C produces unidirectional CoSi2 NWs by reaction of cobalt with the hot silicon substrate. STM investigations reveal four major types of distinct NWs, all growing along the [-110] in-plane direction except one type growing along the in-plane [-113] direction. There are also some nanodots. The cross-sectional TEM measurements show that the unidirectional NWs are of two types-flat-top and ridged. The NWs grow not only on the substrate but also into the substrate. CoSi2 in flat top NWs are in the same crystallographic orientation as the substrate Si and the buried interfaces between CoSi2 and Si are A-type. In the ridged NWs CoSi2 and Si are in different crystallographic orientations and the interfaces are B-type. The ridged NWs are in general wider and grow deeper into the substrate.

Suppression of near band edge emission in specially engineered ZnO twin nanorods.

We report the synthesis of a unique zinc oxide nanorod structure in which an amorphous ZnO layer is sandwiched between two identical crystalline segments of ZnO. A simple hydrothermal reaction method was used for this purpose, which allowed us to tune the amorphous and crystalline sections of the nanorods via reaction temperature. A systematic study of the morphology and dimensions of the nanorods grown under various conditions was performed using a combination of scanning and transmission electron microscopy. Transmission electron microscopy (TEM) clearly showed an amorphous separation between the two crystalline segments. UV-vis absorption spectroscopy of the twin nanorods (TNRs) showed a redshift in the optical band gap as a function of the growth duration, indicating slightly stressed growth of the crystalline segments. For a longer growth duration, as the amorphous gap starts to get bridged by crystalline growth, redshift in optical band gap becomes constant. This confirms a true mechanical gap between the two crystalline segments of the nanorods. Temperature dependent photoluminescence (PL) spectra of the TNRs showed a variation in free exciton (FX) emission energy, which fitted very well to a model incorporating lattice dilation in addition to the standard electron-phonon interactions. At low temperatures (below ∼180 K) we observed the appearance of visible emission peaks due to localization of defect levels. A loss in the near band edge emission intensity was observed at low temperatures, commensurate with the appearance of defect emission in the visible range.

Gold-decorated highly ordered self-organized grating-like nanostructures on Ge surface: Kelvin probe force microscopy and conductive atomic force microscopy studies.

Nanoarchitecture by atomic manipulation is considered to be one of the emerging trends in advanced functional materials. It has a gamut of applications to offer in nanoelectronics, chemical sensing, and nanobiological science. In particular, highly ordered one-dimensional semiconductor nanostructures fabricated by self-organization methods are in high demand for their high aspect ratios and large number of applications. An efficient way of fabricating semiconductor nanostructures is by molecular beam epitaxy, where atoms are added to a crystalline surface at an elevated temperature during growth, yielding the desired structures in a self-assembled manner. In this article, we offer a room temperature process, in which atoms are sputtered away by ion impacts. Using gold ion implantation, the present study reports on the formation of highly ordered self-organized long grating-like nanostructures, with grooves between them, on a germanium surface. The ridges of the patterns are shown to have flower-like protruding nanostructures, which are mostly decorated by gold atoms. By employing local probe microscopic techniques like Kelvin probe force microscopy and conductive atomic force microscopy, we observe a spatial variation in the work function and different nanoscale electrical conductivity on the ridges of the patterns and the grooves between them, which can be attributed to gold atom decorated ridges. Thus, the architecture  presented offers the advantage of using the patterned germanium substrates as periodic arrays of conducting ridges and poorly conducting grooves between them.

Enhanced CO gas sensing properties of Cu doped SnO2 nanostructures prepared by a facile wet chemical method.

We report the synthesis of Cu doped SnO2 nanostructures with enhanced CO gas sensing properties by a facile wet chemical method. The effects of Cu doping on the structural and optical properties of SnO2 nanostructures were investigated using X-ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high resolution TEM (HRTEM) with energy dispersive X-ray spectroscopy, Raman spectroscopy and photoluminescence spectroscopy. FESEM studies revealed the presence of nanosheets and nanodisc-like structures in Cu doped SnO2 samples. Gas sensing studies showed that the sensor prepared using 1% Cu doped SnO2 nanostructures exhibits highly enhanced CO gas sensing properties as compared to pure SnO2 nanostructures and shows excellent selectivity for CO with negligible interference from CH4, CO2 and NO2. The possible mechanism for the enhanced CO gas sensing properties of Cu doped SnO2 nanostructures is proposed.