Size Confinement Research Articles

Structural, Magnetic and Photocatalytic Properties of BiFeO3 Nanoparticles

Single phase BiFeO3 nanoparticles as a visible light photocatalyst were successfully synthesized by thermal decomposition of the glyoxylate precursor. The glyoxylate precursors were formed by the redox reaction between ethylene glycol and nitrate ions. The phase evolution, structure and optical properties of BiFeO3 nanoparticles were characterized by X-ray diffraction, electron microscopy and UV–Vis spectroscopy methods. The BiFeO3 nanoparticles showed the quasi spherical shape. The BiFeO3 nanoparticles synthesized at 500 °C showed the weak ferromagnetism behavior, due to the size confinement effect, in spite of the antiferromagnetic behavior of the BiFeO3 nanoparticles synthesized at 600 °C. The BiFeO3 nanoparticles exhibited strong absorption in the visible region with the optical band gap calculated from Tauc’s plot. The optical band gap decreased from 2.10 to 2.08 eV by the increasing of thermal decomposition temperature. Moreover, the BiFeO3 nanoparticles were used for the degradation of methylene blue as a typical dye pollutant under direct sunlight irradiation.

Structural, Magnetic and Photocatalytic Properties of BiFeO3 Nanoparticles

Single phase BiFeO3 (BFO) nanoparticles as a visible light photocatalyst were successfully synthesized by thermal decomposition of the glyoxylate precursor. The glyoxylate precursors were formed by the redox reaction between ethylene glycol and nitrate ions. The phase evolution, structure and optical properties of BFO nanoparticles were characterized by X-ray diffraction, electron microscopy and UV–Vis spectroscopy methods. The BFO nanoparticles showed the quasi spherical shape. The BFO nanoparticles synthesized at 500 °C showed the weak ferromagnetism behavior, due to the size confinement effect, in spite of the antiferromagnetic behavior of the BFO nanoparticles synthesized at 600 °C. The BFO nanoparticles exhibited strong absorption in the visible region with the optical band gap calculated from Tauc’s plot. The optical band gap decreased from 2.10 to 2.08 eV by the increasing of thermal decomposition temperature. Moreover, the BFO nanoparticles were used for the degradation of methylene blue (MB) as a typical dye pollutant under direct sunlight irradiation.

Effect of notch depth on the mechanical behavior of Cu50Zr50 metallic glasses revealed by molecular dynamics simulations

Metallic glasses (MGs) with various geometrical notches have been one of the most attractive research topics because of their interesting mechanical behavior. In this work, molecular dynamics simulations were employed to examine the effect of internal notch depth on the mechanical behavior of Cu50Zr50 MGs. It is shown that both the strength and the deformation mode are sensitive to the notch depth, and in particular to the inter-void ligament distance. With increasing the notch depth, the notch intensification gets enhanced, while the deformation mode is seen to change from shear banding dominated to mixed mode and then to necking governed. Detailed stress distribution analysis reveals that the notch intensification and the deformation mode transition result from the stress state change induced by the presence of notches. The critical effective shear stress corresponding to local/atomic yielding in the MGs is identified to be around 1.9 GPa. In addition, the intrinsic size confinement effect also influences the deformation process. The findings are expected to provide useful guidance for materials design and investigation of yielding in MGs based on atomistic simulations.

Solidification loops in the phase diagram of nanoscale alloy particles: from a specific example towards a general vision

Interface contributions as well as size confinement effects need to be taken into account into the description of phase equilibria and phase transformations in nanoscale systems. Here, a modified Gibbsian thermodynamic approach has been suggested to describe the solidification of a nano-sized liquid alloy droplet and the equilibrium states in the two-phase region of the phase diagram. Cu–Ni has been chosen as a model system due to the availability of thermodynamic data. This description shows for the first time the occurrence of solidification loops at the size-dependent temperature–composition phase diagram for the isolated Cu–Ni nano-droplet, showing two-phase equilibrium states for droplet radii of 25 and 40 nm, i.e. well within the size domain of nanoparticles that are, for example, used for applications in additive manufacturing. Furthermore, the current results show quantitatively that these equilibrium loops that are specific for the nano-sized systems do not coincide with the solubility curve. It leads to the new “solidification loop” concept concerning the phase diagram introduced in the paper. The isolated liquid Cu–Ni nanoscale droplet can actually crystallize along different trajectories, whereas the dominant transition type is comparable to homogeneous nucleation that proceeds from the inner part of the droplet towards the surface: the newly formed phase after initial nucleation is a Ni-rich crystal with a Cu-rich liquid shell. The decrease in the nanoparticle size causes the decrease in the solidification temperature and the temperature width of the phase transition, the increase in the solubility limit and the concentration width of the solidification loop as well as a change in the shape and slope of the equilibrium curves of the two-phase region of the phase diagram. For larger droplets, the size-dependent phase diagram approaches the well-known bulk phase diagram.

Origin of charge storage in cobalt oxide - Anchored graphene nanocomposites

Prospects of transition metal oxide (TMO) anodes in practical Li-ion batteries are limited despite their high capacity, owing to conversion reaction-driven inefficiencies and poor cycle life. Size confinement of TMOs and compositing them with carbon architectures is an established approach to realize high-performance electrodes. Here, we report cobalt oxide nanoparticles anchored on graphene (CoG) nanocomposite for Li-ion batteries; the anode exhibits a reversible capacity of 1270 mA h g−1 at 2 C rate and delivers 770 mA h g−1 even at a high rate of 50 C (44.5 Ag-1) of which >99% is retained at the end of 1000 cycles. Although many papers have reported exorbitant high capacity and rate performance for graphene–3d metal oxide composites, the nature of charge storage in these nanocomposites remains unidentified particularly in the voltage region of conversion reaction. By using cobalt oxide-anchored graphene as a model system, we reveal that the charge storage is a collective response from conversion/intercalation and pseudocapacitive processes. In addition, the CoG composite anode reported here provides excellent chemical stability and high durability as witnessed in terms of high capacity, impressive rate performance, and long cycle life. This study illustrates the benefits of nanoarchitecturing toward designing high-performance electrodes.

Ionogels for Safer Energy Storage: The Determining Effect of the Interface

Ionogels represent a route to biphasic materials, for the use of ionic liquids (ILs) for all-solid devices. Confining ILs within host networks enhances their averaged dynamics, resulting in improved charge transport. Fragility, short relaxation times, low viscosity, and good ionic conductivity, all them appear to be related to the IL / host network interface. The presence of ILs at interface neighborhood leads to the breakdown of aggregated, structured regions that are systematically found in bulk ILs. This “destructuration”,[1] as well as segregative interactions at interface,[2,3] coupled with percolation of the bicontinuous solid/liquid interface,[4] make these materials very competitive among the existing solid electrolytes. Such approach could provide (i) a route to lower locally the viscosity of ILs, and (ii) an easier pathway for diffusion of charged species. Several types of ionogels demonstrate this effect, taking into account of fully inorganic, hybrid, polymeric or organic-inorganic host networks . This “all-solid” approach can be applied to several electrochemical energy storage sources, including lithium batteries (Fig 1)[3,5] and supercapacitors (Fig. 2)[6,7]. Strikingly, high performance were shown on these devices, thanks to interfacial effects of confined ILs, with sometimes heightened properties of the chosen ILs as referred to their bulk properties[3,4,7,8]. Such solid electrolytes are particularly well suited for microdevices that we have been or are being developed (Fig. 3)[6,9]. Herein we will emphasize the results of a systematic study of the effect of size of confinement.

Experimental and numerical investigations of slot jet impingement with and without a semi-circular bottom confinement

In this paper, the details of experimental and numerical investigations of slot air jet impingement cooling of a circular heated cylinder have been presented. To improve heat transfer rate behind the cylinder, a semi-circular confinement is also considered. In the parametric study, the Reynolds number ReD, defined based on the cylinder diameter D, is varied from 6000 to 20,000. The ratio of the spacing between the nozzle exit and the heated cylinder H to the width S of the nozzle, H/S is varied from 2 to 12 and the non-dimensional parameter, the diameter of the target to the slot width, D/S=5.5, 8.5 and 17 are considered. To understand the effect of the bottom flow confinement, the ratio of the confinement radius Rc to the radius R, of the heated cylinder, Rc/R was varied from 1.7 to 3.7 and the ratio of the width of the bottom opening W of the confinement to the radius of the heated cylinder, W/R is varied from 0 to 1.2. Numerical simulations are carried out using the v′2‾-f model to obtain the flow pattern and temperature distribution over the cylinder and in the fluid region. In the case of jet impingement flow with a semi-circular confinement wall behind the target cylinder, after the flow separation from the cylinder, the heated fluid is diverted towards the inner wall of the confinement. The major part of the diverted hot fluid leaves through the opening provided at the bottom of the flow confinement without a direct contact with the bottom surface of the heated cylinder. In the case of smaller size semi-circular confinement walls, Rc/R=1.7 and 2.6, the strength of recirculation is higher than that of the unconfined flow and the flow with a larger size confinement. Hence, the local Nusselt number values are higher at the bottom surface of the heated cylinder when smaller size semi-circular confinement walls are used behind the cylinder.

Tunable properties of cadmium substituted ZnS nanocrystals

Tailored Zn1−xCdxS (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles, synthesized by co-precipitation method under ultrasonic irradiation, were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV–Vis and photoluminescence (PL) spectroscopy measurements. According to the XRD results, substitution of Zn2+ by Cd2+ ion leads to an increase in the lattice parameters and the average size of zinc blended nanoparticles are in the range of 3–4nm. Transmission electron microscopy image revealed the formation of nano-sized particles with dimension of 5nm confirming that the samples are quantum dots. The shift observed in the absorption edges by increasing Cd2+ ion substitution is ascribed by the alloying effect but the enhancement of band gap energy compared to that of the corresponding bulk value is attributed to the nanometric grain size and quantum confinement effects. The position and intensity of PL emission peaks are tuned with Cd2+/Zn2+ ion content.

Epitaxially stabilized thin films of \u03b5-Fe2O3 (001) grown on YSZ (100)

Epsilon ferrite (ε-Fe2O3) is a metastable phase of iron(III) oxide, intermediate between maghemite and hematite. It has recently attracted interest because of its magnetocrystalline anisotropy, which distinguishes it from the other polymorphs, and results in a gigantic coercive field and a natural ferromagnetic resonance frequency in the THz range. Moreover, it possesses a polar crystal structure, making it a potential ferroelectric, hence a potential multiferroic. Due to the need of size confinement to stabilize the metastable phase, ε-Fe2O3 has been synthesized mainly as nanoparticles. However, to favor integration in devices, and take advantage of its unique functional properties, synthesis as epitaxial thin films is desirable. In this paper, we report the growth of ε-Fe2O3 as epitaxial thin films on (100)-oriented yttrium-stabilized zirconia substrates. Structural characterization outlined the formation of multiple in-plane twins, with two different epitaxial relations to the substrate. Transmission electron microscopy showed how such twins develop in a pillar-like structure from the interface to the surface. Magnetic characterization confirmed the high magnetocrystalline anisotropy of our film and revealed the presence of a secondary phase which was identified as the well-known magnetite. Finally, angular analysis of the magnetic properties revealed how the presence of twins impacts their azimuthal dependence.

Frustrated crystallization of a monolayer of magnetized beads under geometrical confinement.

We present a systematic experimental study of the confinement effect on the crystallization of a monolayer of magnetized beads. The particles are millimeter-scale grains interacting through the short range magnetic dipole-dipole potential induced by an external magnetic field. The grains are confined by repulsing walls and are homogeneously distributed inside the cell. A two-dimensional (2d) Brownian motion is induced by horizontal mechanical vibrations. Therefore, the balance between magnetic interaction and agitation allows investigating 2d phases through direct visualization. The effect of both confinement size and shape on the grains' organization in the low-energy state has been investigated. Concerning the confinement shape, triangular, square, pentagonal, hexagonal, heptagonal, and circular geometries have been considered. The grain organization was analyzed after a slow cooling process. Through the measurement of the averaged bond order parameter for the different confinement geometries, it has been shown that cell geometry strongly affects the ordering of the system. Moreover, many kinds of defects, whose observation rate is linked to the geometry, have been observed: disclinations, dislocations, defects chain, and also more exotic defects such as a rosette. Finally, the influence of confinement size has been investigated and we point out that no finite-size effect occurs for a hexagonal cell, but the finite-size effect changes from one geometry to another.

Lattice discrete particle modeling of plain concrete perforation responses

This paper numerically investigates the large-caliber hard projectile perforation of plain concrete slab with steel culvert confinement by using the recently developed Lattice Discrete Particles Model (LDPM). With mesoscale constitutive laws governing the interaction between adjacent particles, LDPM simulates concrete features like cohesive fracture, strain hardening in compression and compaction due to pore collapse. The perforation simulation model is established with LDPM for concrete, elastoplastic model for steel culvert and penalty contact for projectile-concrete interaction. Simulation of 5 shots concrete perforation tests are carried out to validate the numerical model, and the numerical results are in good agreement with the experimental data in terms of residual velocities as well as target damage mode. Extensive simulations are further performed to investigate the effects of aggregate discretization, steel culvert confinement and diameter size on perforation responses. Comparative numerical study indicates that with culvert confinement, the projectile residual velocity is significantly reduced except for perforation case with 0.3 m thickness target. Meanwhile, crack fills the 0.6 m diameter target which poses less resistance to projectile impact.

Doping-Concentration-Induced Ferromagnetism and Antiferromagnetism in In2S3:Dy3+ Quantum Dots

Diluted magnetic semiconductor (DMS) quantum dots have been researched extensively due to their potential applications in next-generation spin-based devices. Herein, the cubic In2S3:Dy3+ DMS quantum dots (3–5 nm) with different doping concentrations were synthesized via a gas–liquid phase chemical deposition method. The effect of Dy3+ content on the photoluminescence (PL) and ferromagnetism was investigated. The PL emission spectra exhibit a blue-shift compared with those reported previously due to the increased quantum size confinement and enhanced intensity attributed to the Dy3+ doping. The distinct and stronger room-temperature ferromagnetism is observed from vibrating sample magnetometer (VSM) measurement. The coexistence of ferromagnetic (FM) and antiferromagnetic (AFM) phases and antiferromagnetic interation plays a dominant position after a certain doping concentration value can be further confirmed according to the zero field cooling/field cooling (ZFC/FC) curves. As revealed in the magnetic origin study from first-principles calculations, the ferromagnetism obtained arises not only from the Dy atoms but also from the In vacancies. In addition, we also proposed a spontaneous mechanism based on the bound magnetic polaron theory to explain the change of saturation magnetizations along with Dy3+ doping concentration. This work provides experimental and theoretical guidance for designing and synthesizing unique spintronic materials, which can promote development of spintronic applications.

Synthesis and characterization of nano-scale and submicro-scale silicon carbide whiskers on C/C composites

In this paper, a novel synthesis route of nano-scale and submicro-scale silicon carbide (SiC) whiskers on C/C composites was reported. H-PSO-DVB as the organic precursor was used to fabricate the SiC whiskers. The phase, chemical bonds and microstructure of the synthesized whiskers were analyzed in detail. It was shown that C/C composites were packed with a porous network consisting of random-oriented β-SiC whiskers when the preparation temperature is 1500–1600 °C. In view of that most of the SiC whiskers are tip flat or tapering, a vapor-vapor mechanism was used to explain the growth process of the whiskers. The differences of attenuated total reflection (ATR) and Raman spectra between the nano-scale SiC whiskers and bulk SiC were analyzed, which could be reasonably interpreted with the size confinement effect of nanomaterials.

Electrochemical Lithiation-Delithiation of Sulfur in Single-Walled Carbon Nanotubes

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage technologies because of the high theoretical capacity of sulfur as cathode. However, the high electrical resistivity of sulfur and the dissolution of lithium polysulfides into electrolytes are greatly limiting the performance of Li-S batteries. Interestingly, when the sulfur confinement size is smaller than 1 nm, different electrochemical behaviors and excellent cycle stabilities have been observed. However, the mechanism of sub-nano confinement of sulfur has not been investigated in details. Single-walled carbon nanotubes (SWCNTs) with their various pore size, uniform pore size distribution, and excellent electron conductivity are ideal hosts for studying the effect of different sulfur confinement sizes. In this study, we investigate the effect of sulfur confinement size by incorporating sulfur into both EA- (electric arc) and HiPco- (high-pressure carbon monoxide) SWCNTs with diameter of 1.55 ± 0.1 and 1.0 ± 0.2 nm, respectively. Interestingly, when sulfur is incorporated into HiPco-SWCNTs, the polymerized long chain sulfur molecules inside the tubes largely changes the Raman spectra. The giant Raman response from the sulfur provides an ideal opportunity to perform in situ studies on the lithiation-delithiation reactions of the confined sulfur. High-resolution TEM images confirm the chain structure of sulfur in EA- and HiPco-SWCNTs. Cyclic voltammetry and galvanostatic charge–discharge are performed by using different electrolytes, and sulfur in EA- and HiPco-SWCNTs show distinctively different electrochemical behaviors. In situ Raman spectra and ex situ XPS are measured during galvanostatic charge–discharge to investigate the lithiation-delithiation mechanism. A solid-state reaction mechanism was proposed when sulfur is in sub-nano confinement.

Ultrahigh Thermoelectric Performance in SrNb0.2Ti0.8O3 Oxide Films at a Submicrometer-Scale Thickness

Localized refrigeration and power generation via thermoelectric technology rely on efficient thermoelectric materials with high performance at room temperature. Although the two-dimensional electron gas (2DEG)-related materials exhibit ultrahigh thermoelectric performance near room temperature, such performance is only preserved at thicknesses within subnanometer scales, limited by the requirement of two-dimensional size confinements. Here we report ultrahigh thermoelectric performance similar to 2DEG-related materials but achieved in SrNb0.2Ti0.8O3 oxide films with a submicrometer-scale thickness by regulating strain-induced lattice polarizations and interfacial polarizations. A large figure of merit, zT, and power factor (∼102–103 μW cm–1 K–2) were achieved near room temperature, and the maximum zT is estimated to be ∼1.6 for a 49 nm thick film. These performances exceed those of the existing n-type thermoelectric materials for room-temperature uses and the reported best oxide materials beyond subnanome...

Benchmark values of Shannon entropy for spherically confined hydrogen atom

AbstractThe information‐theoretic measure of confined hydrogen atom has been investigated extensively in the literature. However, most of them were focused on the ground state and accurate values of information entropies, such as Shannon entropy, for confined hydrogen are still not determined. In this work, we establish the benchmark results of the Shannon entropy for confined hydrogen atom in a spherical impenetrable sphere, in both position and momentum spaces. This is done by examining the bound state energies, the normalization of wave functions, and the scaling property with respect to isoelectronic hydrogenic ions. The angular and radial parts of Shannon entropy in two conjugate spaces are provided in detail for both free and confined hydrogen atom in ground and several excited states. The entropies in position space decrease logarithmically with decreasing the size of confinement, while those in momentum space increase logarithmically. The Shannon entropy sum, however, approaches to finite values when the confinement radius closes to zero. It is also found that the Shannon entropy sum shares same trend for states with similar density distributions. Variations of entropy for nodeless bound states are significantly distinct form those owning nodes when changing the confinement radius.

Soft Confinement-Induced Morphologies of the Blends of AB Diblock Copolymers and C Homopolymers.

Self-assembly behavior of the blends of AB diblock copolymers and C homopolymers in soft confinement is studied by using a simulated annealing method. Polymer solution droplets in a poor solvent environment realize the soft confinement. Several sequences of soft confinement-induced copolymer aggregates with different shapes and internal structures are predicted as functions of the size of confinement, the number ratio of AB diblock copolymers to C homopolymers, the volume fraction of blocks, the selectivity of confinement's surface, the incompatibility between blocks, and the competition between two block-homopolymer interactions. Simulation results demonstrate that those factors are able to tune the morphology of the aggregates precisely. We anticipate the rules achieved here is helpful to fabrication of polymeric particle with predesigned morphology.

NO2 sensing properties of a borazine doped nanographene: A DFT study

Nanographenes are definite segments of graphene whose end atoms are saturated with hydrogens and their properties are different from those of the graphene because of size confinement. Herein, we investigated the structural properties, reactivity and electronic sensitivity of a newly synthesized borazine-like ring doped nanographene (BNG) to NO2 gas by means of density functional theory. We found that the central and peripheral rings of BNG are aromatic, while the middle ones are non-aromatic, revealing that this pattern follows the Clar’s sextet rule of aromaticity. Different thermodynamically stable NO2/BNG complexes are predicted, but most of them cannot be formed at room temperature because of the high transition barrier energies. The most favorable complex is that in which one oxygen atom of NO2 molecule is located above the center of B3N3 doped ring with adsorption energy of about −5.1kcal/mol. It was found that the electronic properties of BNG are highly sensitive to the presence of NO2 molecules so that after the NO2 adsorption, the BNG is converted from a semiconductor to a semimetal compound. Thus, it was concluded that the BNG may be used in the NO2 sensor devices. Also, a short recovery time is predicted for the NO2 desorption process.

Effect of High Substrate Temperature on Morphology, Structural and Optical Properties of CdZnS Nanostructures

One-dimensional CdZnS nanostructures have been synthesized through the sublimation. Effect of high substrate temperature on morphology, structural and optical properties of these nanostructures has been studied. X-Ray diffraction peak intensity, lattice parameters, crystallite size decreased with an increase in substrate temperature. The morphology changed with the increase in the substrate temperature. Raman Spectroscopy confirmed the existence of constituent elements in CdZnS solid solution and an increase of Zn concentration with the rise in substrate temperature. The nanostructures exhibited strong photoluminescence emission in the green light region with a substrate temperature-dependent blue shift of 53 meV in emission energy. The Stoke’s shift energy raised from 45 meV to 302 meV as the substrate temperature increased from 510 °C to 550 °C. The stoichiometric deviancies, crystallite size, and quantum confinement effects resulted into an increase in the optical band gap from 2.4 eV to 2.71 eV. The results showed that CdZnS nanostructures could be potential candidates for nanostructure based optoelectronics and photovoltaic devices.

Properties of Surface Plasmon Polaritons Excited by Radially Polarized Sinh Gaussian Beams

Properties of surface plasmon polaritons (SPPs) excited by radially polarized sinh Gaussian beams with high-numerical-aperture system is investigated theoretically based on vector diffraction theory. It is observed that by properly tuning the beam waist size (w 0 ) and beam order (m) of the incident sinh Gaussian beam, one can achieve higher confinement in axial and lateral size of the generated plasmonic focal spot. We observed that sinh Gaussian beam of larger w 0 and m results in generation of highly confined plasmonic focal spot.