Department of Physics and Materials Science

The highly temperature sensitive delayed luminescence from the well-known phosphor Gd2O2S:Eu (1%) was characterized for excitation at 365 nm of 1 second duration. The main component of the luminescence decay time ranged from 1.87 to 0.07 s from 24.5 °C to 55.1 C, exhibiting a sensitivity of 11% /°C. The amplitude also showed a marked temperature dependence increase of 7% /°C. A parameter Q(T), defined as the ratio of the decay constant to amplitude, has a sensitivity determined as 18%°C. Four measurements of a shorter component also showed pronounced temperature dependence, ranging from 0.14 s at 24.5 to 0.02 s at 43.5 °C.

The present study aims to improve the magnetic properties with tunable coercivity of SrM hexaferrite by substituted Co and Zn ions instead of Fe and to elucidate in detail the changes in their structural, morphological, and site occupancy characteristics. Sr$${\text{Co}}_x {\text{Zn}}_x {\text{Fe}}_{12 - 2x} {\text{O}}_{19}$$(Co, Zn; x=0.4, 0.8, 1.2, 1.6 and 2.0) powders were synthesized by the autocombustion sol--gel method. Substitution of Co--Zn ions caused the formation of magnetoplumbite and a secondary phase (CoFe2O4) in the structure. Increasing the Co--Zn content ratio led to a nonlinear increment in crystallite size ranging from 41.9 to 49.8 nm. SEM micrographs depicted platelet-shaped hexagonal particles that were nano-scale in thickness and micro-scale in diameter. Mössbauer spectra revealed that the substituent tends to occupy both spin-up sites 12k-2a-2b and spin-down sites 4f1 and 4f2 of crystal lattice from x=0.4 to x=2.0, which elucidate meagre change observed in magnetization, as per literature. The saturation magnetization (Ms) and remanent magnetization (Mr) were higher than the initial values of Ms=75.26 emu/g and Mr=26.95 emu/g. The highest coercivity and saturation magnetization was observed as, 4159 Oe and 80 emu/g, respectively, for x=2.0. The squareness ratio (Mr/Ms) of x=1.6 and x=2.0 samples, was observed to be greater than 0.5, elucidating the existence of single-domain particles. The magnetic parameters Ms with tunable Hc, Mr/Ms, and magnetic susceptibility (dM/dH) results make the synthesized sample considerable for recording applications.

Due to their redox features, Fe/Ni-phosphides and phosphates could be utilized as multi-functional electrode materials for hydrogen and oxygen evolution processes (HER and OER) and supercapacitors, however, regulation in their geometry and electrical structure for further performance improvement is still challenging. Herein, we developed a solvent-assisted approach to modify the NiP material's phase, growing Ni2P, Ni12P5, and Ni(PO3)2 cross-linked nanosheets on Ni-foam using the same precursor and different solvents. When compared to Ni2P and Ni12P5, the Ni(PO3)2 sample showed outstanding activity and endurance towards HER (134 mV overpotential@10 mA/cm2 and 112 mV/dec Tafel value) and OER (342 mV overpotential@10 mA/cm2 and 78 mV/dec Tafel value), respectively. Moreover, the specific capacitance of the Ni(PO3)2 electrode was found to be 4366 (at 10 mV/s) and 7582 mF/cm2 (at 1 mA/cm2). Theoretical calculations showed that the density of states and its distribution across the Fermi level increased in the order of Ni2P < Ni12P5 < Ni(PO3)2 which improved their conductivity and electronic properties, benefiting electrocatalytic HER and OER activity and the charge-storing capacity of Ni(PO3)2.

Keywords: Transition metal phosphate, Electrocatalysts, Water splitting, OER, HER, Supercapacitor

Electrochemical energy conversion (via water splitting) and storage (via supercapacitors) are emerging strategies for developing the renewable energy sector; nevertheless, the hunt for low-cost and effective electrode material is a bottleneck issue. Herein, a bimetallic manganese nickel hydroxide was electrodeposited on Ni-foam without polymeric binder, followed by calcination to reveal its oxide configuration. As prepared, manganese nickel hydroxide (MnNi-hydroxide) displayed low Oxygen evolution reaction (OER) and Hydrogen evolution reaction (HER) overpotentials of 231 mV and 327 mV at 10 mA/cm2 during electrochemical water splitting, along with a superior turnover frequency of 0.12 sec−1 and 0.056 sec−1, respectively. Theoretical investigations revealed an increase in MnNi-hydroxide activity due to synergistic electronic interaction between Mn and Ni. Further, the MnNi-hydroxide, having high specific capacitances of 1174 mF/cm2 at 2 mV/s and 308 mF/cm2 at 1 mA/cm2, demonstrated a retention capacity of 98.9% over 5000 cycles.

Keywords: Transition metal hydroxides, Bimetallic catalysts, Water splitting, Supercapacitors

Aluminum-doped ErCr1-xAlxO3 orthochromites prepared via autocombustion technique were investigated for their magnetic and magnetocaloric properties. X-ray diffraction confirmed that samples were orthorhombic phases with the Pbnm space group without a trace of any impurity. As analyzed via Rietveld refinement of XRD data, structural parameters such as lattice parameters, volume, bond angle, and bond lengths were affected by doping nonmagnetic Al3+ in the compound. ErCrO3 possesses the long-range antiferromagnetic ordering with a weak display ferromagnetism at TN =133 K. Low-temperature high-field magnetic study shows a decrease in Neel temperature (TN ∼ 114 K for x = 0.5), suggesting magnetic ordering suppression due to Al3+ doping. The asymptotic paramagnetic Curie temperature Tcw = −25 K suggests the predominance of antiferromagnetic interactions in ErCrO3 orthochromites, which was observed to increase with Al3+ doping. Isothermal magnetization data show changes in magnetic entropy (−ΔSMmax) and relative cooling power (RCP). The magnetic entropy change, −ΔSMmax, for ErCrO3 estimated from magnetization measurements show 11.60 J kg−1 K−1 at 11 K and a relative cooling power (RCP) of 209.4 J kg−1 at 5 T applied field. While ErCr0.75Al0.25O3 show a maximum magnetic entropy of 11.52 J kg−1 K−1 at 11 K with a 5 T applied field and RCP of 186.66 J kg−1, whereas ErCr0.5Al0.5O3 displayed −ΔSMmax of 11.63 J kg−1 K−1 at 5 K with a 5 T applied field and RCP value of 160.78 J kg−1. The results show that nonmagnetic doping, such as Al3+, could maintain the compound’s magnetocaloric property to an extent.

This study reports the magnetic and magnetocaloric properties of different concentrations of alkaline earth metal, such as Ca-doped La0.97−xCaxHo0.03MnO3 (x=0.3, 0.33, and 0.37) composites, which were synthesized via autocombustion technique. The second-order paramagnetic-to-ferromagnetic phase transition temperature appeared at the temperature-dependent field-cooled magnetization curve. The result shows an increase in the Curie temperature of the compound with Ca2+ doping. In addition, increasing the Ca2+ doping concentration further increased the change in magnetic entropy, − ∆SM, up to 0.206 J kg−1 K−1, resulting in a higher RCP value up to 30 J kg−1 at x=0.37. This work's key aspect is demonstrating the potentiality of enhancing the magnetocaloric effect in the framework via the spin coupling mechanism of Ca2+-doped rare-earth perovskite compounds.

Manganese oxide has emerged as a promising material for use as a charge storage electrode material. In this work, we demonstrate the low-pressure chemical vapour deposition (CVD) growth of manganese oxide conformal coatings on Ni-foams utilising an MnCl2 solid source precursor, utilising an oxide formed on the surface of the Ni-foam as an oxygen reservoir for the synthesis of a predominantly MnO x layer. The resulting MnO x layer is highly dependent on sample pre-treatment, owing to modifications in the Ni oxide layer. The phase structure, electronic states, morphology, and electrochemical analysis were determined by x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning-electron microscopy (FE-SEM), and capacitance–voltage (CV) measurements. The importance of the oxide layer is demonstrated by modifying the thickness of the NiO layer over the Ni foam, with clear changes in the resultant structure, morphology, and areal capacitance, with the highest performance MnO x coating found to be obtained without any oxide removal from the Ni foam substrate.

The few intuitive challenges are the high clean energy demand, the dire need for sustainable development, and low carbon footprints. Thereby, the wastewater rich in urea from sanitary units, and industries are subjected to produce green energy as a source for hydrogen through waste water-splitting. Thus, anodic reaction in electrochemical hydrogen production is the most widely promoted towards oxygen evolution reaction (OER) and urea oxidation reaction (UOR). However, both possess sluggish kinetics which need to be improved. Therefore, the development of novel materials that can meet the demands of both reaction mechanisms is highly required. Herein, Fe2P2O7-based composite grown on the conductive substrate can effectively enhance the electrical transportation of ions during electrocatalytic activity. The experimental and theoretical investigations are adopted to get a comprehensive insight and understanding of the catalytic nature of the as-prepared samples. Compared with other as-synthesized materials, Fe2P2O7 exhibits splendid performance with a low onset potential of 1.482 and 1.317 V (vs RHE) to obtain a current density of 10 mA/cm2 towards the OER and UOR process, respectively. The low Tafel slope and high turnover frequency offer low resistance during charge transfer. Additionally, greater ECSA and roughness factors enrich the attributes of Fe2P2O7 and offer more active sites for reaction to be held, producing a higher amount of gas bubbles. Hence, improved electrical conductivity, low charge transfer resistance, more electrochemical active surface area, and impressive durability reconfirm the Fe2P2O7 as an effective catalyst.

Keywords: Nickel pyrophosphate, Cobalt pyrophosphate, Iron pyrophosphate, Oxygen evolution reaction, Urea oxidation reaction

The slow kinetics of electrochemical urea and water oxidation processes at electrode surfaces, which can be recognised as promising resources for pollution-free hydrogen energy production, motivate the scientific community to design and fabricate low-cost, high-efficiency electrocatalysts. Because the performance of electrocatalysts is dependent on their structural, morphological, and electronic properties, herein, the tuning of these properties of Fe3O4@Ni-Foam via phosphorylation and sulfurization, yielding iron phosphide (FeP@Ni-Foam) and iron sulphide (FeS@Ni-Foam), with nanoneedles (along with microstructures) and nanoflower-like morphologies, respectively, is investigated. Among all the prepared samples, FeP is found to be the most effective electrocatalyst for the oxygen evolution process (OER), the urea oxidation reaction (UOR), and seawater electrolysis. The overpotentials observed for OER, UOR, and seawater splitting are significantly reduced when using FeP as compared to other materials, with values of 207 mV, 133 mV, and 287.1 mV, respectively, at a current density of 10 mA/cm2. The enhanced catalytic activity of FeP over FeS and Fe3O4 is attributed to morphological changes, improved electronic conductivity, and exceptional endurance. The theoretical studies reveal that FeP has a better density of states over the fermi level than FeS and Fe3O4, lowering the energy barriers for the OER and UOR processes and demonstrating significant catalytic activity towards these processes. This work demonstrates that phosphorylation and sulfurization treatments can alter morphologies and electrical characteristics, hence improving the catalytic activity of the materials.

Keywords: Electrocatalysts, Iron phosphide, Oxygen evolution reaction, Urea oxidation reaction, And seawater splitting

In this work, carbonization and subsequent activation procedures were adopted to synthesize waste shea butter shells into oxygen-rich interconnected porous activated carbon (SAC_x, x is the mass ratio of KOH used for activation). The SAC_1.5 electrode material showed outstanding electrochemical performance with high specific capacitance (286.6 F/g) and improved rate capability, owing to various synergistic effects originating from a high specific surface area (1233.5 m2/g) and O-rich content. The SAC_1.5-based symmetric device delivered an impressive specific capacitance of 91.6 F/g with a high energy density of 12.7 Wh/kg at 0.5 A/g. The device recorded 99.9 % capacitance retention after 10,000 charge-discharge cycles. The symmetric supercapacitor device successfully lit an LED bulb for more than 1 h, signifying the potential of bio-waste as an efficient carbon precursor for electrode material in practical supercapacitors. This work offers an efficient, affordable, and environmentally friendly strategy for potential renewable energy storage devices.

Keywords: Shea butter shells, Hierarchical porous carbon, High- energy density, Energy storage

Abstract Developing high-performance materials for electrochemical energy storage devices such as batteries, and supercapacitors is a significant topic in material chemistry-based research. The high consumption and limited availability of numerous materials used in energy devices lead to the development of alternative, effective, and cost-effective materials exhibiting superior electrochemical chemical performance. A porous activated carbon, derived from polyaniline (PANI) synthesized through chemical oxidative polymerization, can be considered a viable solution in this context. In this study, the electrochemical window of the nitrogen-doped porous activated carbon was enhanced through a combined synthesis process involving the carbonization and activation of PANI nanotubes with KOH. Moreover, alternations in surface area and porosity were evaluated using BET analysis for the samples having PANI to KOH ratios 1:0.5, 1:1, and 1:2. The results revealed a significant improvement in surface area and pore volume, increasing from 18 to 3535 m2/g from pure PANI to chemically treated samples. Among those materials, the PANI to KOH ratio of 1:1 exhibited the highest surface area of 3535 m2/g and the highest pore volume of 0.7131 cm3/g. Subsequently, the electrochemical performance of all materials was evaluated using a three-electrode cell system and a symmetrical coin-cell device. Electrodes fabricated with PANI to KOH ratio of 1:1 by weight showed better electrochemical performance in an aqueous electrolyte (6 M KOH) in both systems. This material exhibited the highest capacitance of 378 F/g (at 0.5 A/g) in the three-electrode system and 143 F/g (at 0.5 A/g) in the SCCD. The SCCD achieved a maximum energy density of 23 Wh/kg with a power density of 544 W/kg. Additionally, these supercapacitors provided a good Coulombic efficiency of about 99% with capacitance retention of 97% at 7 A/g current density after 10 000 charge–discharge cycles. Further, this study expanded by investigating variations of electrochemical performance across various electrolytes, including aqueous, organic, and ionic liquids in coin-cell supercapacitors. The findings reveal promising results, suggesting potential commercial applications for this facile approach to synthesize nitrogen-doped activated carbon, especially for supercapacitors with aqueous electrolytes.

Keywords: activated porous carbon, polyaniline nanotubes, symmetrical coin-cell supercapacitor

This study synthesizes cuboidal-shaped hierarchical Mn2O3 (MNO) particles using a simple hydrothermal technique with Good's buffer piperazine and examines their electrochemical performance. The research explores how varying piperazine concentrations (piperazine concentration x in MNO-x) affect the structure and electrochemical properties of the MNO particles. X-ray diffraction (XRD) confirms the crystalline nature of MNO while scanning electron microscopy reveals that piperazine concentration influences the particles’ shape, size, and morphology. The MNO synthesized with 6 mmole piperazine (MNO-6) has the highest surface area of 8.67 m²/g. Electrochemical tests in 1 M and 6 M KOH electrolytes show that MNO-6 achieves the highest specific capacitance, with 440 F/g in 1 M and 952 F/g in 6 M KOH at a 1 mV/s scan rate. At a 1 A g-1 current density, MNO-6 exhibits a specific capacitance of ∼545.8 F/g in 1 M KOH and 809.0 F/g in 6 M KOH, with corresponding energy densities of 27.3 Wh/kg and 40.4 Wh/kg, and power densities of 315.7 W/kg and 365 W/kg, respectively. The superior electrochemical performance is attributed to the high surface area and porous structure of MNO synthesized with piperazine, highlighting its potential for advanced energy storage applications.

Keywords: MnO, Piperazine, Urea, X-ray diffraction, Electrochemical analysis, Supercapacitor, Hydrothermal synthesis

In this study, Gd3Fe5O12 nanoparticles were synthesized using the sol–gel autocombustion method and subsequently coated with polyvinylpyrrolidone (PVP) polymer. The study focuses on understanding the influence of PVP coating on garnet particles’ magnetic and magnetocaloric properties. The crystallite size upon PVP-coating remained unaltered, but the grain size and surface area of coated particles increased. The magnetization of PVP-coated particles decreased by around 11% as compared to the uncoated particles at 5 K. Mössbauer and photoelectron spectroscopy confirmed the presence of a paramagnetic phase Fe3+ in the PVP-coated nanoparticles responsible for the reduction in magnetization value. The maximum value of magnetic entropy change (−ΔS m ) for uncoated Gd3Fe5O12 was 3.78 Jkg−1 K−1 at 37.5 K with a 5T applied field, accompanied by a relative cooling power (RCP) of 382 Jkg−1. On the other hand, for PVP-coated Gd3Fe5O12, the maximum −ΔS m was 3.38 Jkg−1 K−1 at 57.5 K with a 5T applied field, and the RCP was 308 Jkg−1. The observed maximum magnetic entropy changes at higher temperatures for the PVP-coated Gd3Fe5O12 sample are noteworthy. This characteristic indicates that the PVP-coated garnet may have an advantage in terms of usability over a wider temperature range compared to the uncoated counterpart, which can potentially be a promising material for applications in cryogenic temperature magnetic refrigeration.

Due to its unique electronic and optical properties, tungsten disulfide (WS₂) is a promising material for various device applications. However, achieving an efficient and cost-effective method for synthesizing large-area uniform WS2 is still challenging. In this work, we demonstrate the synthesis of few-layer WS2 crystallites by NaCl-assisted low-pressure chemical vapor deposition and study the effect of temperature and the carrier gas flow rate on the morphology, structure, and optical properties of the as-grown WS2 films. We observe transitions between regular triangular to strongly disordered structures with sizes up to 50 µm through temperature and carrier gas flow rate tuning. As-grown samples were characterized by Raman spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The result of this work provides a path toward the optimization of growth conditions for obtaining WS2 with desired morphologies for various applications.

The study reports the synthesis and magnetocaloric properties of the rare-earth element as Eu3+ doped La1.4Ca1.6Mn2O7-Mn3O4 composites prepared by the one-pot autocombustion technique. Eu3+ co-doping enhanced the Curie temperatures from 181 K for La1.4Ca1.6Mn2O7 (LCMO) to 186 K for La1.3Ca1.6Eu0.1Mn2O7 perovskites, which consequently enhanced the relative cooling power value of the compound. Moreover, these composites were also prepared in the presence of 10 wt% of Mn3O4 nanoparticles. The presence of Mn3O4 at the intervening grain boundaries between La1.4Ca1.6Mn2O7 (A) and La1.3Ca1.6Eu0.1Mn2O7 (B) phases altered the double exchange interaction between Mn3+ and Mn4+ ions. The temperature-dependent field-cooled magnetization curves showed that these nanocomposites’ interfacial magnetic interactions significantly expanded the second-order ferromagnetic-to-paramagnetic phase transition temperature. This further enhanced the magnetic entropy magnitudes |ΔSMax| up to 0.521 J kg−1 k−1 and the associated relative cooling power value to 43.67 J kg−1 under a 5T applied magnetic field. The temperature-averaged entropy change (TEC) values of composites outperformed the individual values of samples A and B between the temperature range of 80–240 K. The fundamental key of this work is to demonstrate the potentiality of enhancing the magnetic phase transition temperature and magnetocaloric effect in the framework of interfacial coupling between LCMO and the Mn3O4 phases of the nanocomposites.

Keywords: Nanocomposites, Perovskite manganites, Magnetocaloric, Phase transition, Entropy change

Metal oxides have been a focus of research for energy storage devices. Herein, xLaMnO3 – (100-x) Mn3O4 (LMO-MO) composites (xwt%: 100, 90, 70, and 50) were prepared via one-pot synthesis to elucidate the synergistic effect of the composite constituents on composite’s electrochemical performance. The X-ray diffraction analysis confirmed the presence of individual compounds in the desired ratio and phase. The X-ray photoelectron spectroscopy confirmed the presence of Mn2+ and Mn3+ oxidation states, indicating the presence of both LaMnO3 (LMO) and Mn3O4 (MO) in the composite. The electrochemical performance of composite electrodes prepared using nickel foam was assessed in 1 and 6 M KOH solutions. High specific capacitance measured via cyclic voltammetry of ∼ 770 Fg−1 at a scan rate of 1 mVs−1 was recorded for the composite of LMO-MO (70 %: 30 %) in 6 M KOH. At the same time, charge-discharge curves revealed a maximum specific capacitance of around 405 Fg−1 for an x =70 % sample at a current density of 0.5 Ag−1. The EIS studies show a reduction in the internal resistance of the composite due to the interconnected structure and reversible faradic process at the interface with a high degree of Coulombic efficiency. A higher overall electrochemical performance of the electrode was recorded in a 6 M KOH electrolyte. The enhanced electrochemical performance of the composite is attributed to efficient charge transfer kinetics through the electrode-electrolyte interface via easy electron hopping pathways between LMO and MO in the composite. These findings suggest that the studied LMO-MO composites could be a potential material for pseudocapacitor energy devices.

Keywords: LaMnO MnO composite, XRD, Autocombustion, Electrochemical characterizations, Pseudocapacitors

The plasmonic coupling between silver (Ag) and gold (Au) nanoparticles (NPs) under four polarization modes was examined: a longitudinal mode (L-mode), where the electric field of a linearly polarized incident light parallels the dimer axis, and three transverse modes (T-modes), where the electric field of the light is perpendicular to the dimer axis. The coupling was studied using the discrete dipole approximation followed by an in-house postprocessing code that determines the extinction (Qext), absorption (Qabs), and near-field (Qnf) spectra from the individual NPs as well as the whole system. In agreement with the literature results, the extinction/absorption spectra of the whole dimer have two peaks, one near the Ag localized surface plasmon resonance (LSPR) region and the other at the Au LSPR region, with the peak at Ag LSPR being reduced in all modes and the peak at Au LSPR being red-shifted and increased in the L-mode but not in the T-modes. It is further shown that the scattering at the Ag LSPR region is reduced and becomes less than the isolated Ag NPs, but the absorption at the Ag LSPR is increased and becomes greater than the isolated Ag NPs for the 50 nm Ag–Au heterodimer. This suggests that the scattering from Ag NPs is being reabsorbed by the neighboring Au NPs due to the interband electronic transition in Au at that wavelength range. The Qext from the individual NP in the heterodimer shows the presence of the Fano profile on the Au NP but not on the Ag NP. This phenomenon was further investigated by using a dielectric particle (DP) placed near the Ag or Au NPs. The Fano profile appears in the absorbing DP spectra placed near either Ag or Au NPs. However, the Fano profile is masked upon further increases in the refractive index value of the DP particle. This explains the absence of a Fano profile on the Ag NPs in the Ag–Au heterodimer. The large near-field enhancement on both Ag and Au NPs at the Au plasmonic wavelength in the L-mode for large NPs was investigated through a DP-Au system. The large enhancement was shown to arise from a large imaginary component of the DP refractive index and a small real component. Through examination of both the near- and far-field properties of the individual NPs as well as the whole system and examinations of DP-Ag and DP-Au systems, our study provides a new understanding of the couplings between Ag and Au NPs.

In recent years, there has been a heightened interest in the self-assembly of nanoparticles (NPs) that is mediated by their adsorption onto lipid membranes. The interplay between the adhesive energy of NPs on a lipid membrane and the membrane's curvature energy causes it to wrap around the NPs. This results in an interesting membrane curvature-mediated interaction, which can lead to the self-assembly of NPs on lipid membranes. Recent studies have demonstrated that Janus spherical NPs, which adhere to lipid vesicles, can self-assemble into well-ordered nanoclusters with various geometries, including a few Platonic solids. The present study explores the additional effect of geometric anisotropy on the self-assembly of Janus NPs on lipid vesicles. Specifically, the current study utilized extensive molecular dynamics simulations to investigate the arrangement of Janus spherocylindrical NPs on lipid vesicles. We found that the additional geometric anisotropy significantly expands the range of NPs' self-assemblies on lipid vesicles. The specific geometries of the resulting nanoclusters depend on several factors, including the number of Janus spherocylindrical NPs adhering to the vesicle and their aspect ratio. The lipid membrane-mediated self-assembly of NPs, demonstrated by this work, provides an alternative cost-effective route for fabricating highly engineered nanoclusters in three dimensions. Such structures, with the current wide range of material choices, have great potential for advanced applications, including biosensing, bioimaging, drug delivery, nanomechanics, and nanophotonics.

Tungsten disulfide (WS2) is a promising two-dimensional material owing to its remarkable optical, electronic, and electrocatalytic behavior. However, morphology of this material varies significantly with growth conditions. In this work, we use salt-assisted low-pressure chemical vapor deposition (LP-CVD) to grow WS2 crystals of a few layers reaching over 50 μm in size on SiO2/Si substrates. We observe a transition from large, dendritic to triangular growth by systematically varying the amount of the NaCl promotor material as well as the presence of intermediate Wx+ states for low NaCl amounts. The transition from dendritic to triangular growth is discussed in the context of diffusion limited aggregation, with the transformation likely being the result of reduced formation energy, owing to increasing concentrations of transition metal oxyhalides for given precursor quantities. These results help to clarify the role of effects of the NaCl precursor in salt-assisted LP-CVD of WS2 and provide a new means to tune the morphology of this material.

Abstract While many studies are performed on the effect of ligands on the adhesion and endocytosis of NPs, the effects of ligand length and surface density on the NPs' interaction with lipid membranes are poorly investigated. Here, a computational investigation is presented, based on molecular dynamics of a coarse-grained implicit-solvent model, of the interaction between ligand-decorated spherical NPs and lipid membranes. Specifically,the case is considered where the ligands interact attractively with lipid membranes only through their ends. In particular, the effects of ligand grafting density, ligand length, and strength of ligand-lipid interaction is investigated on the degree of wrapping of the NP by the membrane and on the morphology of the membrane close to the NP. Whereas the degree of wrapping is found to increase with increasing the grafting density for a given interaction strength and ligand length, it decreases with ligand length for a given grafting density and interaction strength. For moderate values of the adhesion strength and long ligands, it is found that the end ligands form long linear clusters, which lead to an anisotropic conformation of the membrane around the NP. For short ligands, the wrapping of the membrane around the NP is almost complete, with the wrapped NP showing a regular faceted structure for high adhesion strength.

Keywords: coarse grained models, lipid membranes, molecular dynamics, nano particle adhesion

Molecular dynamics simulations are conducted to systematically investigate the insertion of spherical nanoparticles (NPs) in polymer brushes as a function of their size, strength of their interaction with the polymers, polymer grafting density, and polymer chain length. For attractive interactions between the NPs and the polymers, the depth of NPs’ penetration in the brush results from a competition between the enthalpic gain due to the favorable polymer–NP interaction and the effect of osmotic pressure resulting from displaced polymers by the NP’s volume. A large number of simulations show that the average depth of the NPs increases by increasing the strength of the interaction strength. However, it decreases by increasing the NPs’ diameter or increasing the polymer grafting density. While the NPs’ effect on the polymer density is local, their effect on their conformations is long-ranged and extends laterally over length scales larger than the NP’s size. This effect is manifested by the emergence of laterally damped oscillations in the normal component of the chains’ radius of gyration. Interestingly, we found that for high enough interaction strength, two NPs dimerize in the polymer brush. The dimer is parallel to the substrate if the NPs’ depth in the brush is shallow. However, the dimer is perpendicular to the substrate if the NPs’ are deep in the brush. These results imply that polymer brushes can be used as a tool to localize and self-assemble NPs in polymer brushes.

The stability and resonance spectra associated with a domain wall skyrmion embedded within a Néel skyrmion, forming a 1-kink skyrmion, has been studied using micromagnetic simulations. We show that the 1-kink skyrmion is stable over a wide range of fields at moderate strengths of the Dzyaloshinskii-Moriya interaction. By exciting these structures with a broadband magnetic field excitation, we find complex resonance behavior deviating from that of a pure Néel skyrmion. For out-of-plane excitations, the 1-kink skyrmion demonstrates an additional mode relative to that of the Néel skyrmion at reduced amplitude. These consist of low frequency and high frequency modes associated with both a breathing mode and an oscillation of the embedded domain wall skyrmion. Following an in-plane excitation, both Néel and 1-kink skyrmions exhibit a counterclockwise rotational mode with similar frequencies, as well as a higher frequency mode associated with the interaction of the structure with the ferromagnetic background state. These results may help pave the way for exploration of more complex spin structures for magnetic-based microwave devices.

Ferroelectric (FE) metals have been attracting attention as they possess both metallicity and ferroelectricity, the two seemingly incompatible physical properties. An important problem for both fundamental research and potential applications is how to realize a strong FE metal. One strategy is to dope a strong FE insulator and turn it into an FE metal, provided that the induced free electrons do not destroy FE distortion. Strained EuTiO3 is a strong FE ferromagnet and a promising candidate for such a strategy. Here, we calculate the structural, electronic, and polarization properties of Nb-doped strained EuTiO3 using the hybrid density-functional theory. The results show that the strained EuTi0.875Nb0.125O3 is a strong FE metal as the Nb doping induces metallicity without weakening the FE distortion. The underlying atomistic mechanism of the coexistence of metallicity and strong ferroelectricity is discussed. The findings show that combining doping and strain engineering is a promising way to realize new EuTiO3-based strong FE metals and may be used in other materials as well.

Understanding what shapes the cold gas component of galaxies, which both provides the fuel for star formation and is strongly affected by the subsequent stellar feedback, is a crucial step towards a better understanding of galaxy evolution. Here, we analyse the H i properties of a sample of 46 Milky Way halo-mass galaxies, drawn from cosmological simulations (EMP-Pathfinder and Firebox). This set of simulations comprises galaxies evolved self-consistently across cosmic time with different baryonic sub-grid physics: three different star formation models [constant star formation efficiency (SFE) with different star formation eligibility criteria, and an environmentally dependent, turbulence-based SFE] and two different feedback prescriptions, where only one sub-sample includes early stellar feedback. We use these simulations to assess the impact of different baryonic physics on the H i content of galaxies. We find that the galaxy-wide H i properties agree with each other and with observations. However, differences appear for small-scale properties. The thin H i discs observed in the local universe are only reproduced with a turbulence-dependent SFE and/or early stellar feedback. Furthermore, we find that the morphology of H i discs is particularly sensitive to the different physics models: galaxies simulated with a turbulence-based SFE have discs that are smoother and more rotationally symmetric, compared to those simulated with a constant SFE; galaxies simulated with early stellar feedback have more regular discs than supernova-feedback-only galaxies. We find that the rotational asymmetry of the H i discs depends most strongly on the underlying physics model, making this a promising observable for understanding the physics responsible for shaping the interstellar medium of galaxies.