Size Of Nanoclusters Research Articles

Creation and Magnetic Study of Ferrites with Magnetoplumbite Structure Multisubstituted by Al3+, Cr3+, Ga3+, and In3+ Cations.

Multisubstituted barium ferrites with a magnetoplumbite structure were obtained by the method of solid-phase reactions with ferritization and pre-firing. Three-charged, mainly diamagnetic cations Al3+, Cr3+, Ga3+, and In3+ were chosen as substituents for the Fe3+ iron cations, the proportion of which in solid solutions did not exceed 50%. The values of the configurational mixing entropy were calculated for all the compositions. A slight deviation of the chemical composition of the obtained solid solutions from the nominal value was established by the energy-dispersive X-ray spectroscopy method. The phase purity and values of the unit cell parameters were refined from X-ray scattering data using full-profile analysis in the Rietveld method. A non-monotonic behavior of the unit cell parameters as a function of the B-sub-lattice average ionic radius of the magnetoplumbite structure was found. A minimum unit cell volume of ~667.15 Å3 was found for the composition BaFe6.11Al1.56Cr2.17Ga2.16O19 with a B-sub-lattice average ionic radius of ~7.449 Å. The average crystallite size varied within 5.5–6.5 μm. The temperature and field dependencies of the magnetization have been measured. The values of the saturation magnetization, residual magnetization, hysteresis loop squareness, and coercivity at 50 K and 300 K were extracted from the experimental data. Using the Law of Approach to Saturation, the magnetic crystallographic anisotropy coefficient and anisotropy field were calculated. Multisubstitution leads to a significant decrease in such magnetic parameters as the magnetic ordering temperature and spontaneous magnetization at both temperatures. The maximum magnetic ordering temperature of ~297.7 K was found for the composition BaFe5.84Ga6.19O19 with a B-sub-lattice average ionic radius of ~7.586 Å in a field of 500 Oe. A maximum saturation magnetization of ~24.7 emu/g was found for the composition BaFe5.84Ga6.19O19 with a B-sub-lattice average ionic radius of ~7.586 Å at 50 K. A maximum hysteresis loop squareness of ~0.72 was found for the composition BaFe6.11Al1.56Cr2.17Ga2.16O19 with an average ionic radius of ~7.449 Å at 50 K. A maximum magnetic crystallographic anisotropy coefficient of ~2.09 × 105 Erg/g was found for the composition BaFe6.19Al1.25Cr1.57Ga1.74In1.26O19 with a B-sub-lattice average ionic radius of ~7.706 Å at 50 K. The frustrated magnetic state including the nano-sized clusters with an average diameter in the range of 50–200 nm was established from the results of measuring the ZFC and FC temperature magnetizations. The interpretation of the obtained experimental data is carried out taking into account the increased stability of high-entropy phases and regular changes in the intensity of the Fe3+(Al3+, Cr3+, Ga3+, In3+)–O2−–Fe3+(Al3+, Cr3+, Ga3+, In3+) indirect superexchange interactions as a result of magnetic dilution of the iron sub-lattice in the magnetoplumbite structure.

Magnetization changes with surface decorated in different ferrimagnetic nanoclusters

Based on the effective field theory with correlations, the magnetic characteristics of two sizes of surface-decorated nanoclusters were investigated. The magnetic phenomena of the two systems were observed. The size, exchange coupling, anisotropy, and transverse magnetic field have critical effects on the phase diagram. The reentrant behavior, namely, the two-phase transition temperatures, was observed in the phase diagram. In particular, the possibility of depressed saturation magnetization in the system was analyzed.

Molecular modelling and computational studies of peptide diphenylalanine nanotubes, containing waters: structural and interactions analysis.

The work is devoted to computer studies of the structural and physical properties of such self-organizing structures as peptide nanotubes (PNT) based on diphenylalanine (FF) dipeptide with different initial isomers of the left (L-FF) and right (D-FF) chiralities of these dipeptides. The structures under study are considered both with empty anhydrous and with internal cavities filled with water molecules. Molecular models of both chiralities are investigated using quantum-chemical DFT and semi-empirical methods, which are in consistent with the known experimental data. To study the effect of nano-sized clusters of water molecules embedded in the inner hydrophilic cavity on the properties of nanotubes (including the changes in their dipole moments and polarizations), as well as the changes in the structure and properties of water clusters themselves (their own dipole moments and polarizations), the surfaces of internal cavities of nanotubes and outer surfaces of water cluster structures for both types of chirality are analyzed. A specially developed method of visual differential analysis of structural features of (bio)macromolecular structures is applied for these studies. The results obtained of a number of physical properties (interacting energies, dipole moments, polarization values) are given for various cases and analyzed in comparison with the known data. These data are necessary for analyzing the interactions of water molecules with hydrophilic parts of nanotube molecules based on FF, such as COO- and NH3 + , since they determine many properties of the structures under study. The data obtained are useful for further analysis of the possible adhesion and capture of medical molecular components by active layers of FF-based PNT, which can be designed for creating capsules for targeted delivery of pharmaceuticals and drugs on their basis.

Electro-physical properties of GaAs nanoscopic clusters

The electric current through the Cu-GaAs-Cu nanoclusters and their quasi-bandgap widths (HOMO-LUMO differences) are calculated. The ab initio electron propagator theory (Green-Keldysh functions formalism) is implemented for the calculations (that has been never done before for Cu-As-Cu nanoclusters). The calculated current-voltage characteristics exhibit non-linear character with magnitudes of current reaching several pAs. The calculated quasi-bandgap width (HOMO-LUMO difference) of nanocluster exhibits solid-like behavior with the increase of nanocluster's size. The obtained dependencies and characteristics will be useful for semiconductor quantum-dots manufactures and practitioners in the field of semiconductor nanoelectronics and optoelectronics, in particular, for developers of EM radiation sources and detectors with frequency-tuning ability.

Ligand Induced Double-Chair Conformation Ln12 Nanoclusters Showing Multifunctional Magnetic and Proton Conductive Properties.

Many methods have been utilized to adjust the size of superatomic metal nanoclusters, while tuning the geometric conformations of specific nanoclusters is rare. Here, we demonstrate that conformation variation can be realized by slightly modifying the ligand under maintaining the nuclei number of metal atoms. A series of novel "double-chair" conformation Ln12 (Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)) clusters were generated by replacing 3-formylsalicylic acid with 2,3-dihydroxybenzoic acid in the Ln12 nanocluster. Intriguingly, Dy12 displays slow magnetic relaxation at low temperatures, while Gd12 shows a large magnetocaloric effect (MCE) of 35.63 J kg-1 K-1 at 2 K for ΔH = 7 T. Additionally, the introduction of numerous coordination water molecules in these clusters enables Dy12 and Gd12 with high proton conductivity, namely, 2.13 × 10-4 and 3.62 × 10-4 S cm-1 under 358 K and 95% RH humidity conditions.

Facile fabrication of size-controlled Pd nanoclusters supported on Al2O3 as excellent catalyst for solvent-free aerobic oxidation of benzyl alcohol

Selective oxidation of benzyl alcohol (BzOH) to benzaldehyde is one of the most important organic transformations. It is vital to explore a stable, economic and highly efficient catalyst. Here, Pd/R-Al2O3 (R = Al(NO3)3/urea molar ratio) was prepared by hydrothermal process followed by cation-assisted polyol method, and utilized for solvent-free aerobic oxidation of BzOH without any additives. Characterization results from TEM, NH3/CO2/O2-TPD and XPS showed that the size of Pd nanoclusters on Pd/R-Al2O3 was controlled by base number on R-Al2O3, and the order of oxygen mobility was Pd/1:6-Al2O3 > Pd/1:7-Al2O3 > Pd/1:8-Al2O3 > Pd/1:9-Al2O3. In the BzOH oxidation, R-Al2O3 as a basic additive could improve the benzaldehyde selectivity, and all surface atoms of Pd nanoclusters displayed the same catalytic activity. Excellent oxygen mobility indicated a high catalytic performance since it accelerated oxygen transfer from gaseous molecular oxygen to the surface of Pd nanoclusters to rapidly regenerate active Pd0 species. Among Pd/R-Al2O3 catalysts, Pd/1:6-Al2O3 exhibited a turnover frequency of 70381 h−1 due to the smallest Pd size and the best oxygen mobility, and good stability after five recycles owing to the strong interaction between Pd0 species and R-Al2O3. Therefore, Pd/R-Al2O3 may be great potential as a promising candidate for numerous catalytic reactions.

Processing and properties of yttria and lanthana dispersed ODS duplex stainless steels

In the present study, yttria (alloy B) and lanthana (alloy C) based oxide dispersion strengthened (ODS) duplex stainless steels (Fe–21Cr–8Ni–1Ti) have been synthesized using mechanical alloying followed by spark plasma sintering (SPS). For comparison, duplex steel without dispersion (alloy A) has also been synthesized. The variation of sintering temperature (900, 1000 and 1050 °C) on the density, microstructure, and mechanical properties of the steels have been reported. The austenite phase fraction increased with the sintering temperature as well as by the addition of oxides. TEM analysis confirmed the presence of nano-clusters (size in the range of 2–8 nm) of Y–Ti–Cr–O and La–Ti–Cr–O in the alloy B and alloy C, respectively. Alloy C, sintered at 1000 °C, exhibited the highest micro-hardness and compressive strength of 739 ± 9.1 HV and 2835 ± 87 MPa, respectively. At all sintering temperatures, the lower hardness values of the alloy B as compared to alloy A were ascribed to the significantly higher austenite phase fraction in the former, which resulted in overcoming the dispersion strengthening effect. Overall, La2O3-based ODS duplex stainless steels exhibited the better room temperature mechanical properties than Y2O3-based ODS steels.

Experimentally probing ionic solutions in single-digit nanoconfinement

Understanding ionic solutions in single-digit nanoconfinement is crucial to explain the behavioral transition of confined solutions. This is particularly the case when the system length scale crosses the classical key length scales describing energetics and equilibrium of ionic solutions next to surfaces. Experimentally probing nanoconfinement would open large perspectives to test modelling or theory predictions. Here, using a new test vehicle that consists in 3 and 5 nm-height silica nanochannels associated with an original characterization technique based on the interface hard X-ray reflectivity analysis, we directly probed the transport of solutions containing cations having increasing kosmotropic properties (XCl2 with X: Ba < Ca < Mg) and obtained their distributions inside the nanochannels. We observed that cation adsorption decreases with the size of the confinement and that small cation adsorption is favored. In addition, nanochannel clogging occurs when ions tend to form ion pairs. These ion pairs may play the role of nano-sized prenucleation clusters leading to phase precipitation. These results evidence the specific ion effect in single-digit nanoconfinement that may result in dramatic changes of solution properties. In this line, our new method opens new perspectives for the characterization of ionic solutions and of interfaces in single-digit nanoconfinement.

Influence of the Electronic Properties of the Ligand on the Photoelectrochemical Behavior of Au25 Nanocluster-Sensitized TiO2 Photoanode

Atomically precise metal nanoclusters (NCs) have recently emerged as a new class of bifunctional (photoactive and catalytically active) photosensitizers in light energy conversion applications. Despite the size and alloy effects of NCs, no effort has been made to elucidate how the protecting ligand affects the photoelectrochemistry of the NC-sensitized photoelectrodes. With a nanoporous TiO2 array as model support, Au25 NCs protected by various thiol-bearing ligands have been used to prepare four different photoanodes. It is revealed that a subtle change of the ligand from an alkanethiol to an aromatic thiol facilitates the charge transfer between the NC and TiO2, which in turn improves the photoelectrochemical performance of the corresponding photoanode by at least 6 times. This new insight highlights the importance of the electronic properties of the ligand on the design of more efficient NC-sensitized photoelectrodes.

Formation mechanism of nano-sized η and ω structures in β phase in ECP treated Cu-40Zn alloy

Two nano-scaled hexagonal distortions in high temperature BCC phase during cooling is commonly observed in many alloys systems. Although efforts have been made on studying the lattice softening of the BCC structure during cooling, the distortion mechanisms are less addressed. Thus, the formation of two hexagonal structures in the β precipitates in a Cu-40Zn alloy treated by ECP was thoroughly investigated. Results show that the β precipitates contain two kinds of nano-sized and diffuse atomic clusters one with a η structure obeying the Burgers OR and the other a ω structure obeying the Blackburn OR. They were each formed through a two-stepped atomic displacement. For the η structure, the first step is the atomic shuffle of each second 110β plane in the <11¯0>β direction and the second is a structure change mainly by a {1 1¯ 2} < 1¯11>β shear. For the ω structure, the first is an atomic shuffle on each second and third {112¯}β plane in the ± [111]β directions and then normal strains in three mutually perpendicular directions. The concomitant formation of the two structures minimizes the lattice distortion of single formation. The present results provide new information on the formation mechanism of the two hexagonal structures in a BCC matrix.

High-frequency sonication for the synthesis of nanocluster-decorated titania nanorods: Making a better photocatalyst for the selective oxidation of monoaromatic alcohol

The designing and synthesis of novel photocatalysts are the most important parts, with TiO2-based materials to be consider as prosperous candidates for the selective photo-oxidation of aromatic alcohol. Herein, we established an ultrasound-assisted (500 kHz) precipitation synthetic protocol which led to titanate nanorods of 30 nm maximum length, decorated with nanoclusters of size 1–3 nm. The physicochemical features of the synthesized catalysts were characterized by various techniques. The 1-D nanomaterial obtained at low ultrasound power revealed highest yield towards selective photo-oxidation of benzyl alcohol to benzaldehyde comparing to the material synthesized at higher ultrasound power, in silent, and the commercial TiO2-P25.

Coupling surfactant-free Ru nanoclusters with defect carbon for efficient pH-universal hydrogen evolution

A novel strategy was adopted to fabricate pH-universal Ru-based electrocatalysts. Due to the synergistic effect of the ultra-small size of Ru nanoclusters and defective CNTs with oxygen-containing groups, the Ru nanoclusters directly grown on defective carbon (O-Ru NCs/CNTs) catalysts exhibited superior hydrogen evolution activity in the whole pH window. An overpotential of only 37, 13, and 50 mV was needed to reach 10 mA cm−2 in 0.5 M H2SO4, 1.0 M KOH and 1.0 M PBS, respectively. Moreover, this catalyst has shown higher stability. This work is important for the potential application of Ru-based electrocatalysts for hydrogen production.

Insights into mechanisms of diphosphine-mediated controlled surface construction on Au nanoclusters.

Unraveling the rules governing the size regulation of nanoclusters is of great importance not only in fundamental research, but also in practical applications because of the high structure-property correlation in nanoclusters. Diphosphine-mediated size tailoring is recognized as a powerful method for modulating the size, configuration, and properties of nanoclusters, but the role of diphosphines in these size-controlled processes is still poorly understood due to a lack of systematic studies. Herein, using Au23(SR)16- as the template for modification, the factors influencing the size-modulation of nanoclusters by diphosphines were systematically investigated. It is revealed that by controlling the length of the diphosphines (from shorter to longer), Au21(SR)12L2+ (L = diphosphine) and Au22(SR)14L can be produced. Moreover, introducing a rigid group into the diphosphines can twist the structural framework or lead to the formation of a new surface motif configuration in the nanoclusters, forming twisted Au22(SR)14L and Au25(SR)16L2+. The size regulation of these nanoclusters enables fine-tuning of the optical properties, including the absorption wavelengths and photoluminescence emission intensity, affording an avenue for precise control of the physicochemical properties of nanoclusters for practical applications.

A highly efficient and transparent luminescent solar concentrator based on a nanosized metal cluster luminophore anchored on polymers

Organic–inorganic nano-sized hexanuclear complexes were copolymerized with PMMA to generate a LSC device with a high efficiency up to 1.24% and a transparency &gt;85%. Our LSC suggests a practical future direction for smart windows.

Surface Engineering Assisted Size and Structure Modulation of Gold Nanoclusters by Ionic Liquid Cations

AbstractSurface modification induced core size/structure change is a recent discovery in inorganic nanoparticles research, and has rarely been revealed at the molecular level. Here, we exemplify with atomically precise Au nanoclusters (NCs) that proper surface modification can selectively stabilize the desired Au0 core, conducive to the formation of size/structure‐controlled Au NCs. Leveraging π–π enhanced ion‐pairing interactions, ionic liquid (IL) cations are bonded to AuI‐thiolate complexes. The hydrophobic–hydrophobic interactions between IL cations subsequently provide a good mechanism to prolong the size of the AuI‐thiolate complexes, selectively producing small‐sized Au NCs upon reduction. Through combined control over the structure and concentration of IL cations, pH and solvent polarity, we are able to produce atomically precise Au NCs with customizable size, atomic packing structure, and surface chemistry. This work also provides a facile means to integrate/synergize the materials functionalities of Au NCs and ILs, increasing their acceptance in diverse fields.

Surface Engineering Assisted Size and Structure Modulation of Gold Nanoclusters by Ionic Liquid Cations.

Surface modification induced core size/structure change is a recent discovery in inorganic nanoparticles research, and has rarely been revealed at the molecular level. Here, we exemplify with atomically precise Au nanoclusters (NCs) that proper surface modification can selectively stabilize the desired Au0 core, conducive to the formation of size/structure-controlled Au NCs. Leveraging π-π enhanced ion-pairing interactions, ionic liquid (IL) cations are bonded to AuI -thiolate complexes. The hydrophobic-hydrophobic interactions between IL cations subsequently provide a good mechanism to prolong the size of the AuI -thiolate complexes, selectively producing small-sized Au NCs upon reduction. Through combined control over the structure and concentration of IL cations, pH and solvent polarity, we are able to produce atomically precise Au NCs with customizable size, atomic packing structure, and surface chemistry. This work also provides a facile means to integrate/synergize the materials functionalities of Au NCs and ILs, increasing their acceptance in diverse fields.

Study of stabilization of self-assembly processes in fullerene C60 solution

The dynamics of changes in the values of the refractive index of solutions of C60 in xylene at various concentrations has been studied by the refractometric method. It was found that the deviation from the linear form of the dependence of the refractive index on the C60 concentration occurs at a C60 concentration of 1.8 mg/ml. The deviation is associated with the largest number of molecular interactions between C60−C60 and the formation of large nanoclusters on their basis in solution. It was found by the dynamic light scattering (DLS) that the final size of C60 nanoclusters in solution depends on the initial concentration of the solute. A higher initial concentration of C60 leads to the synthesis of nanoclusters with a larger diameter. Using the method of optical spectroscopy, the processes of self-organization of fullerene C60 molecules in a xylene solution in time are studied. The character of stability of synthesized fullerene nanoclusters in solution is discussed. The results obtained are of particular importance for numerous applications of nanotechnology for understanding self-assembly processes and the development of new nanomaterials.

Nucleation mechanisms in a SiO2-Li2O-P2O5-ZrO2 biomedical glass-ceramic: Insights on crystallisation, residual glasses and Zr4+ structural environment

In manufacturing reliable glass-ceramics, bulk chemistry and appropriate thermal treatments are critical points. To better understand the influence of nucleation parameters on the crystallisation behaviour and mechanical properties of multicomponent glass-ceramics, we studied the effects of time and temperature on phase stabilisation, the evolution of the crystal phases and physical properties of a Zr-rich lithium-silicate having a SiO2/Li2O molar ratio < 2. Here, we also provide insights into the structural environment of Zr4+ at the early stage of nucleation by Anomalous X-ray Scattering (AXS). By reverse-engineering a commercial material through remelting and sequential thermal treatments, we observed the strong effect of the nucleation temperature on the final mineral assemblage and of the volume fractions of the lithium-disilicate phase on the fracture toughness (KIc). Indeed, the KIc value was increased from ∼0.8 MPa.m½ in the pristine glass up to ∼ 2 MPa.m½, if compared to the original commercial material exhibiting a KIc value of 1.6 MPa.m½. Furthermore, the synthesis of residual glasses at different stages of the thermal treatments allowed us to observe the changes in the glass network structure and properties. AXS was used to extract the contribution exclusively coming from Zr for different nucleation steps. The differential pair distribution functions ΔZrg(r) show two distinct peaks at ∼2.10 Å and 3.44 Å, respectively associated with Zr-O and Zr-Zr/Zr-Si correlations with the formation of edge sharing in addition to corner sharing polyhedra. It was discerned the occurrence of (sub)nano-sized clusters enriched in Zr. These local clusters do not show changes during the different thermal treatments, either for higher temperatures or longer times. No Zr phases are stabilised in the crystallised materials, suggesting that these clusters do not evolve above the critical nucleus size. All evidence points to a highly heterogeneous environment and the coexistence of three structural regions i) (sub)nano Zr-clusters, ii) P enriched μ-areas, iii) residual silicate glass. The evolution and spatial distribution of these units influence the final properties.

Evolution of nanosized Cu-rich clusters in a Fe–15Cu–15Ni alloy produced by laser powder bed fusion

Designing a metastable microstructure with a coherent nano-sized precipitation phase in the matrix is an effective strategy in improving the strength of materials. Recently, the rapid fusion and solidification cycle associated with laser-based additive manufacturing (AM) has emerged as a promising strategy to design unique microstructures with lattice distortion, solute segregation, and nano-sized precipitations. In this study, the evolution of nano-sized Cu-rich clusters in an AM-processed Fe–15Cu–15Ni alloy (wt.%) was investigated by conducting multiscale microstructural characterization. The results reveal that nano-sized Cu-rich clusters were generated inside the matrix due to a phase decomposition induced by the intrinsic heat treatment during the AM process. The heat energy generated by the laser beam not only initiated Cu-rich cluster formation, but also induced precipitation growth. Therefore, the average Cu-rich cluster size increased with an increase in the volumetric energy density. The hardness of the AM-processed Fe–15Cu–15Ni alloy at first increased with an increase in the energy density until a medium energy density level (140 J/mm3), due to formation of Cu-rich clusters. The hardness decreased with further increase in energy density (185 J/mm3), due to the Cu-rich cluster growth and retained austenite. The results reveal that laser-based AM successfully induces nano-cluster without the need for post-treatment and that the mechanical properties of materials can be optimized by adjusting the processing parameters in a way to enable nano-sized cluster and phase formation.

Photo-assisted sequential assembling of uniform metal nanoclusters on semiconductor support

SummaryDispersing metal nanoclusters on the oxide supports is attracting close attention in heterogeneous catalysis, but great challenges still lie in controlling the size and dispersion of nanoclusters due to the inevitable agglomeration. Here, we propose a sequential photochemical deposition strategy named “first store, and then release” to uniformly fabricate the size-controlling noble metal nanoclusters on semiconductor oxides. Using the typical semiconductor TiO2, the photoexcited electrons can be first stored as reduced species (e.g. Ti3+) under irradiation and the Ti3+ species can optimize both the nucleation and growth processes in dark reaction, resulting in a uniform dispersing of various noble metals (Au, Pt, Ag etc.) with size diameters of ∼1 nm. The nanoclusters catalysts exhibited superior performance in catalytic oxidation of HCHO compared with that of nanoparticles. This work brings a new and useful strategy to construct size-controlling noble metals on the oxide supports for heterogeneous catalysis and the related fields.